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The document provides an English/metric conversion chart that lists common units of measurement for distance, mass, volume, temperature, pressure, energy and power, viscosity, bending moment/torque, density, and impact strength. It provides the conversion factors to convert between English and metric units by multiplying the English value by the listed factor. The chart contains over 20 different types of measurements and their corresponding conversion factors between unit systems.

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English/Metric Conversion Chart To Convert To Multiply English System Metric System . English Value by... DISTANCE inches millimeters 25.38 feet meters 0.30478 MASS ounce (avdp) gram 28.3495 pound gram 453.5925 pound kilogram 0.4536 U.S. ton metric ton 0.9072 VOLUME inch3 centimeter 3 16.3871 inch3 liter 0.016387 fluid ounce centimeter3 29.5735 quart (liquid) decimeter 3 (liter) 0.9464 gallon (U.S.) decimeter 3 (liter) 3.7854 TEMPERATURE degree F degree C (°F- 32)/1.8 =°C PRESSURE psi bar 0.0689 psi kPa 6.8948 ksi MN/m2 6.8948 psi MPa 0.00689 ENERGY AND POWER in lbf Joules 0.113 ft lbf Joules 1.3558 kW metric horsepower 1.3596 U.S. horsepower kW 0.7457 Btu Joules 1055.1 Btu in/(hr ft2 °F) W/m °K 0.1442 VISCOSITY poise Pa s 0.1 BENDING MOMENT OR TORQUE ft lb Nm 1.356 DENSITY lb/in3 g/cm3 27.68 lb/ft3 kg/m3 16.0185 NOTCHED IZOD ft lb/in J/m 53.4
Table of Contents Chapter Part/Page 1. Introduction General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Homopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Impact Modified Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Reinforced Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Processing Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Personal Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Material Safety Data Sheets (MSDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. General Part Design Section Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Undercuts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Recommended Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Draft Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Standards & Practices of Plastics Molders . . . . . . . . . . . . . . . . . . . . . . 12 4. The Injection Molding Machine Machine Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw and Barrel Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Symptoms of Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Barrel Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Nozzle Tip Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Check Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Clamp Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Force and Cavity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Vented Barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5. Mold & Tooling Considerations Tool Steel Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Texturing and Surface Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Sprue Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Sprue Puller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Cold Slug Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Cold Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Hot Runner Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Chapter Page 5. Mold & Tooling Considerations (continued) Gate Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 6. Auxiliary Equipment Dryer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Mold Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Granulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7. Processing Ultramid Nylon Processing Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Drying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Melt Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Hot Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Residence Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Mold Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Holding Pressure and Pack Pressure . . . . . . . . . . . . . . . . . . . . . . . . 42 Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Injection Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Decompression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Purging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Regrind. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Pre-Colored Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Processing Cadmium-Free vs. Cadmium Colors . . . . . . . . . . . . . . . 44 8. Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Brittleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Bubbles, Voids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Cracking, Crazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Dimensional Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Discoloration, Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Excessive Cycle Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Flow Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Lamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Nozzle Drooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Part Sticking in Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Splay (Silver Streaking) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Sprue Sticking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Surface Imperfections (Glass On Surface, Mineral Bloom) . . . . . . . . 56 Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 1 Introduction General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Ultramid Homopolymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Impact Modified Ultramid Nylon. . . . . . . . . . . . . . . . . . . . . . . . . 2 Reinforced Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Introduction Chapter 1: Introduction General Information Ultramid Homopolymers Ultramid resin is available as uniform pellets predried to a Ultramid homopolymers are used in a wide variety of very low moisture content. Depending upon the extrusion and injection molding applications. Major particular grade, it is available in 55 lb. (25 kg) bags, or attributes include strength, toughness, and excellent 1500 lb. (680 kg) corrugated boxes. Each of the two chemical and abrasion resistance. containers includes a moisture barrier liner to maintain a low moisture level in the Ultramid nylon. Open containers Standard Grades should be resealed to maintain low moisture levels. Most Standard products include 8200 a medium viscosity grades are available in heat stabilized (HS), black (BK- injection molding grade; 8202 , a low viscosity injection 102), and UV stabilized black (BK-106) formulations. molding grade; 8270, a modified, ultra high viscosity Standard and custom colors are also available upon grade for extrusion and blow molding applications; 5202, request. a low viscosity injection molding grade based on nylon 6,6. Ultramid Nylon Alpha Grades Alpha grades differ in crystalline structure compared to The majority of the Ultramid family is based on nylon standard Ultramid grades. This results in increased polyamide) 6. BASF is a fully integrated supplier of strength, stiffness, and heat distortion temperature nylon 6. This includes full responsibility for production of combined with faster set up time. Grades include feedstocks to the compounding, manufacturing, and 8202C , a low viscosity, highly crystalline injection distributing o hundreds of grades of resin. f molding grade; 8202CQ , a low viscosity, improved Ultramid nylon 6 is one of the most versatile and productivity injection molding grade; 8203C , an performance-proven engineering thermoplastics. Impact intermediate viscosity, highly crystalline tubing and cable modification of Ultramid nylon results in an extremely liner extrusion grade; and 5202CQ , a low viscosity, flexible and impact-resistant product, while reinforcement improved productivity injection molding grade based on produces high strength, stiffness, and dimensional nylon 6,6. stability. Rotational Molding Grades Another attribute of Ultramid nylon is ease of processability. Ultramid 8280 nylon and 8281 nylon are specifically tailored It is known for its wide processing window in both for rotational molding. 8280 exhibits excellent strength extrusion and injection molding processes and for its ability and toughness. 8281 is a plasticized rotomolding resin to achieve a resin-rich, uniform surface appearance, even that offers increased flexibility. with high levels of reinforcement. Impact Modified Ultramid Nylon The Ultramidproduct line also includes nylon 6, 6/6 for film extrusion products and nylon 6,6 for injection Impact modification of Ultramid nylon results in a series of molding products. polymers containing various levels of enhanced toughness and flexibility combined with excellent chemical and thermal resistance. Impact-modified injection molding grades include 8253, which exhibits improved dry-as-molded toughness over conventional nylon 6 while maintaining excellent strength and stiffness characteristics; 8255, which offers a high degree of flexibility combined with toughness; 8351, a high impact, faster cycling grade; and Ultratough Nylon BU50I, offering high impact strength and ductility to -40° C (-40° F). 2
Introduction Reinforced Ultramid Nylon Fiberglass or a combination of fiberglass and mineral reinforcement enhances the performance characteristics of Ultramid nylon molding compounds. Fiberglass Reinforced Grades Fiberglass reinforcement improves Ultramid nylon’s strength, stiffness, dimensional stability, and performance at elevated temperatures. Glass reinforced grades include HMG10, 50% glass, high modulus; HMG13, 63% glass, high modulus; SEG7, 35% glass; 8230G, 6% glass reinforcement; 8231G, 14% glass; 8232G, 25% glass; 8233G, 33% glass; 8234G, 44% glass; 8235G, 50% glass; HPN 9233G, 33% glass TM reinforced, improved productivity; and 5233G, 33% fiberglass based on nylon 6,6. Fiberglass Reinforced, Impact Modified Grades Combining fiberglass reinforcement along with impact modification produces compounds that offer increased dry-as-molded impact while maintaining excellent strength and stiffness properties. Products include TG3S, 15% glass, impact modified; TG7S, 34% glass, impact modified; 8331G, 14% glass, impact modified; 8332G, 25% glass, impact modified; 8333G HI, 33% glass, high impact, improved productivity and surface appearance; 8334G, 40% glass reinforced, impact modified; and HPN 9333G, 33% glass reinforced, impact modified, improved productivity. Mineral Reinforced Grades Mineral reinforcement enhances strength and stiffness properties while maintaining typical chemical resistance associated with Ultramid nylon. Mineral reinforced products include 8260, 40% mineral, chrome plateable; 8360, 34% mineral; and 8362, 34% mineral, impact modified; and HPN 9362, 40% mineral reinforced, impact modified, improved productivity. Mineral/Glass Reinforced Grades Mineral and glass reinforcement leads to products with an excellent balance of mechanical properties combined with warpage resistance. Mineral/Glass reinforced grades include SEGM35 H1, 40% glass/mineral reinforced; 8262G, 20% mineral/glass reinforced; 8266G, 40% mineral/glass reinforced; and 8267G, 40% mineral/glass reinforced. 3
Chapter 2 Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Processing Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Personal Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 7 Material Safety Data Sheets (MSDS) . . . . . . . . . . . . . . . . . . . . . 7
Health, Safety, and Environmental Considerations Chapter 2: Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Safety is an important consideration during the processing Thermal Processing Hazards of any thermoplastic resin. While the molding of Ultramid resins is generally considered safe, failure to take Thermal processing of thermoplastic materials is always adequate precautions in the following areas may lead to accompanied by the release of fumes and vapors. At personal injury. recommended processing temperatures, these fumes and vapors will generally be low boiling volatiles. In the Housekeeping case of Ultramid products, the fumes will be principally caprolactam monomer. Caprolactam vapor can cause Slips and Falls irritation of the eyes, nose, throat, and skin at sufficiently Ultramid nylon resin comes in cylindrical-shaped pellets. high concentrations. Proper ventilation should be When spilled on a floor, they can be dangerous. To provided at all possible emission points on the injection avoid falls from pellet spills or leaks, sweep up or vacuum molding machine to minimize exposure of volatiles to material and place it in a container for possible reuse or equipment operators. disposal. Thermal Decomposition Material Handling The recommended processing temperatures for Ultramid Cuts resins have been optimized to provide excellent process- The product may be packaged in drums, bags or ability and performance characteristics. Normal gaylords. Gloves are recommended when handling processing temperatures may range from 450° F to 590° drums to avoid cuts during manual movements and when F (230° C to 310° C). Please reference Chapter 7: removing the ring seals, releasing the locking rings, and Processing Ultramid Nylon for further specific information. removing the drum lids. The rigid paper used in bags or Excessively high processing temperatures can lead to the corrugated construction of the gaylords may also cut thermal decomposition. Thermal breakdown may create the skin. Cutting tools should have a protected cutting a complex mixture of organic and inorganic compounds edge to guard against lacerations. (Please see section on which may be flammable, toxic, and/or irritating. The Personal Protective Equipment, page 7). components generated can vary depending on colorants, specific temperature, exposure time, and other Thermal Hazards environmental factors. Proper ventilation should be Burns provided at all possible emission points on the injection Due to the temperatures necessary to process nylon molding machine to minimize exposure of volatiles to resins, injection molding machine parts and equipment equipment operators. Injection molding machinery may be hot and cause burns on contact with the skin. In suppliers also provide purge guards containing limit addition, contact with molten resin from normal operation switches that prevent operation of the press while in the or unexpected occurrences may result in burns involving open position. This helps to minimize exposure to any any exposed areas of the body. Operators should wear volatiles emitted by the molten extrudate, in addition to personal protective equipment. Injection molding protecting the operator from burns from spattering machinery suppliers also provide purge guards which molten polymer. Under no circumstances help to protect the operator from burns from spattering should the protective circuitry provided on processing molten polymer. (Please see section on Personal equipment be altered to allow operation while guards are Protective Equipment, page 7). in the open position. 6
Health, Safety, and Environmental Considerations Personal Protective Equipment Material Safety Data Sheets (MSDS) Proper personal protective equipment should be worn MSDS are supplied by BASF for all Ultramid products. depending upon conditions that exist in the molding The MSDS provide health, safety, and environmental facility. data specific to Ultramid nylon grades or resin families. The MSDS include information concerning first aid Eye and Face Protection measures, hazards information, precautions/procedures, Safety glasses containing side shields should be worn as personal protective equipment, physical and reactivity a minimum when working in a plastics processing facility. data, hazardous ingredients, and environmental data. A face shield should be considered for additional Also included on the MSDS is a Product Safety protection when purging or working near molten material. Department contact where additional information can be Contact lenses should not be worn when processing obtained. MSDS can be found on our website at materials for extended time periods since their permeable www.plasticsportal.com/usa structure may absorb vapors which can cause eye irritations. Hands, Arms, and Body Gloves are recommended when handling or opening drums to avoid abrasion hazards from sharp surfaces. When handling molten polymer or hot parts, insulated gloves should be worn. Arm protection should be considered for additional protection against hot surfaces, such as machine barrels and tooling, and when handling hot parts. Respiratory Protection In dusty conditions, a mechanical filter respirator should be worn. If exposed to thermal processing fumes or vapors in excess of permissible exposure levels, an organic vapor respirator is suggested. Respiratory protection for the conditions listed above should be approved by NIOSH. Foot Protection Safety shoes should be worn when working in areas where heavy objects are being moved, such as transporting or setting molds. 7
Chapter 3 General Part Design Section Thickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Undercuts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Recommended Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Draft Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Ribs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Standards & Practices of Plastics Molders . . . . . . . . . . . . . . . 12
;; General Part Design ; ;; Chapter 3: General Part Design Section Thickness Undercuts Uniformity in wall thickness is critical when designing When necessary, undercuts producing 2% strain are parts to minimize warpage, distortion, internal stresses allowable for reinforced Ultramid nylon grades. If properly and cycle times. Figure 3A shows several examples of designed, undercuts producing up to 8% strain are proper design. When non-uniform section thickness is possible with unreinforced grades. However, wall unavoidable, gradual blending should be used between thickness, part design and mold temperature are factors which can influence ease of part ejection from the mold. ;; the sections as shown in Figure 3B. In general, using the ; thinnest wall allowable, based on the expected function Parts with undercuts should be thoroughly inspected of the part, will help to reduce cycle time and material after molding for unwanted damage or aesthetic flaws in costs. Typical wall thickness for Ultramid resin parts range the undercut area. from .040 inch (1mm) to .200 inch (5mm). Recommended Radii Sharp corners act as stress concentrators and often contribute to part failure. In addition, sharp corners prevent smooth flow when filling. For these reasons, good poor parts should be designed with generous radii and fillets ; wherever possible. A minimum radius of .020" (0.5mm) is recommended at all sharp corners and larger radii are generally beneficial when possible. However, making the ;; radius too large will cause a sink mark on the opposite good poor surface due to the greater mass of material. Figure 3C shows the relationship between stress concentration and fillet radius. As the stress concentration factor (K) increases, the part becomes more prone to failure. The preferred value of R/T is 0.6 for most parts designed with Ultramid resin. good poor Stress-Concentration Factor [K] P good 3.0 poor R 2.5 Figure 3A T 2.0 1.5 1.0 best 0 .2 .4 .6 .8 .10 .12 .14 R/T Ratio Figure 3C good poor Figure 3B 10
General Part Design Draft Angles Tolerances For most parts molded from Ultramid resin, a draft angle Figure 3E shows the SPI tolerance standards for nylon of 1° per side is required for facilitating part ejection. resins, including Ultramid nylon. This is a general guide for However, draft angles as low as 0.5° (requires highly design, based on typical parts produced by several polished surfaces) and as high as 1.5° per side are not different molders and resin suppliers. The numbers uncommon depending on part design and complexity. shown should not be interpreted as final design In general, larger draft angles make it easier to eject the specifications for all applications, but rather as a part from the mold, especially parts with deep pockets, reference for nylon parts similar to the example shown, tall ribs, or heavy textures. molded under normal conditions. Parts with non- standard designs or complex geometry should be Ribs evaluated on an individual basis. Ribs are effective design features which add strength and Many factors must be considered when maintaining often facilitate flow during filling. However, proper design tolerances in molded parts, such as processing is important as ribs sometimes cause sink marks or conditions, mold/part design, and end-use environment. aesthetic irregularities. Ribs should only be used when In general, parts with many close tolerance requirements needed for stiffness and strength. In structural parts will be more difficult to produce consistently than parts where sink marks are of no concern, rib base thickness (t) with fewer or less critical requirements. can be between 75% - 85% of the adjoining wall thickness (T). For appearance parts, where sink marks Effect of Processing on Tolerances are objectionable, rib base thickness (t) should not Control of tolerances will be influenced by molding exceed 50% of the adjoining wall thickness (T) if the conditions. Since shrinkage can directly affect outside surface is textured and 30% if not textured. In dimensional change, it is important to provide adequate addition, ribs should include proper draft and a base pressure during the filling and packing stages. In radius of at least .020" (0.5mm) as shown in Figure 3D. addition, machine consistency, temperature control, and cycle time must be carefully maintained to prevent dimensional shift. Process conditions typically have more effect on the shrinkage of unreinforced and impact modified grades of Ultramid nylon than on reinforced grades. Effect of Mold Design on Tolerances The complexity of the mold has a direct influence on control of part tolerance. Family or multi-cavity molds with non-uniform runner systems and/or slides and cams Rib Design should be given special consideration since tolerances will be harder to maintain under such circumstances. Figure 3D Gates and runners must be large enough to provide good packing pressure and thereby minimize shrinkage. After many cycles, mold wear can also contribute to dimensional shift, especially with mineral and/or glass fiber reinforced grades. Proper tooling selection should be considered when high volume production is expected. (Please see Tooling Considerations, Chapter 5.) 11
General Part Design Material Standards & Practices Polyamide (Nylon) of Plastics Molders (PA) Note: The Commercial values shown below represent common production tolerances at the most economical level. The Fine values represent closer tolerances that can be held but at a greater cost. Addition of reinforcements will alter both physical properties and dimensional stability. Please consult the manufacturer. Drawing Code A=Diameter (See note #1) B=Depth (See note #3) C=Height (See note #3) Comm. ± Fine ± 0.003 0.002 D=Bottom Wall (See note #3) 0.004 0.003 E= Side Wall (See note #4) 0.005 0.003 F=Hole Size 0.000 to 0.125 0.002 0.001 Diameter 0.126 to 0.250 0.003 0.002 (See note #1) 0.251 to 0.500 0.003 0.002 0.501 and over 0.005 0.003 G=Hole Size 0.000 to 0.250 0.004 0.002 Depth 0.251 to 0.500 0.004 0.003 Reference Notes (See note #5) 0.501 to 1.000 0.005 0.004 1. These tolerances do not include allowance for H=Corners, aging characteristics of material. Ribs, Fillets (See note #6) 0.021 0.013 2. Tolerances are based on 0.125" (3.175mm) wall section. Flatness 0.000 to 3.000 0.010 0.004 3. Parting line must be taken into consideration. (See note #4) 3.001 to 6.000 0.015 0.007 4. Part design should maintain a wall thickness as nearly constant as possible. Complete Thread Size Internal 1 2 uniformity in this dimension is sometimes impossible to achieve. Walls of non-uniform (Class) External 1 2 thickness should be gradually blended from Concentricity (See note #4)(F.I.M.) 0.005 0.003 thick to thin. 5. Care must be taken that the ratio of the depth Draft Allowance of a cored hole to its diameter does not reach per side 1.5° 0.5° a point that will result in excessive pin damage. Surface Finish (See note #7) 6. These values should be increased whenever Color Stability (See note #7) compatible with desired design and good molding techniques. 7. Customer-Molder understanding is necessary prior to tooling. Figure 3E Table reprinted from S.P.I.’s Standards & Practices of Plastics Molders. Guidelines For Molders and Their Customers. Material reproduced with the permission of S.P.I. 12
Chapter 4 The Injection Molding Machine Machine Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw and Barrel Selection . . . . . . . . . . . . . . . . . . . . . . . 14 Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Symptoms of Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Barrel Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Nozzle Tip Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Check Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Clamp Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Force and Cavity Pressure . . . . . . . . . . . . . . . . . . 19 Vented Barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
The Injection Molding Machine Chapter 4: The Injection Molding Machine Machine Selection Screw and Barrel Selection Selecting an injection molding machine with proper Screw Design design is critical to molding a quality part and ensuring The screw performs the following functions in the economic success. injection molding process. 1. Conveys the material through the barrel. 2. Mixes the material to the proper molten state. 3. Compresses the material to maximum density. 4. Forces the material into the mold. Adjustments to the injection process often involve the screw to some degree. The screw, when performing its function, provides important contributions to the overall process. Below are several process parameters that are affected by screw design. Figure 4A 1. Material melting profile 2. Melt temperature Below are four important molding machine points to 3. Material mixing consider when molding Ultramid nylon. These issues are 4. Shearing of the resin discussed in detail in this chapter. Therefore, it is important to be aware of the type of screw • Proper Screw and Barrel Selection that is being used for each application. As mentioned • Proper Nozzle Tip Type above, in most cases Ultramid products can be processed • Condition and Type of Check Valve with general purpose screws that are supplied by the • Clamp Requirements machine manufacturer. However, when molding Ultramid products for extended periods of time in a production environment, specific barrel and screw designs are recommended for maximum machine wear resistance and proper material plastication. Depending on the level of reinforcement in the material, different barrel and screw combinations are recommended by BASF. Refer to Figure 4B for recommended screw and barrel composition. Ultramid Wear Screw Barrel Base Material Root Material Type Environment Flight O.D. Liner Homopolymers and ANSI 4140 or Standard Nickel alloy Chrome plated Bimetallic A unfilled polymers Nitrided steel Filled material Tungsten carbide Abrasive Nitrided steel Nitrided steel Bimetallic B < 20% loading + Nickel alloy Highly filled material Highly Tungsten carbide Tungsten carbide Bimetallic screw Bimetallic B >20% loading Abrasive composites composites Bimetallic A Chromium-modified boron-iron alloy containing 5 to 7% nickel Bimetallic B Tungsten Carbide Composite Figure 4B. Barrel and Screw Recommendations for Ultramid Products. 14
The Injection Molding Machine Screw design is critical to ensure that proper melt quality Symptoms of Wear is achieved. The two critical parameters to be aware of when moldingUltramid nylon products are the L/D ratio There are several symptoms of cylinder, screw, and and the compression ratio. These are defined in Figure valve wear which can be observed in the molding 4C and shown in Figure 4D. process. 1. Significant amount of screw rotation during injection indicates a worn barrel and/or check valve. This allows a backflow of melt over the ring, causing the screw flights to counter rotate. 2. Inability of screw to hold a cushion usually indicates a worn cylinder or valve. Figure 4C 3. Excessive recovery time required. Shank 4. Defective, streaked, splayed, or non-uniform parts Length Flight Length L due to poor melt quality resulting from worn Df Dm components. 5. Difficulty in achieving consistent color change from D plastic hanging up in worn areas of cylinders and Feed Transition Metering Check screws. Section Section Section Valve 60% 20% 20% 6. Front and center barrel heats may override settings. Typical Screw Configuration 7. Inconsistent shot size. Figure 4D The recommended L/D ratio and compression ratio for molding Ultramid nylon are listed in Figure 4E. When possible, it is recommended that the minimum L/D be 20:1. This will ensure proper melt dispersion. Ideal Ultramid Nylon Compression Material Type L/D Ratio Unreinforced min. 20:1 3:1 homopolymers Reinforced min. 20:1 2.5:1 material Figure 4E 15
The Injection Molding Machine Barrel Sizing When choosing a press in which to run a mold, it is important to check the shot size as a percentage of the total barrel capacity. Most barrels are rated in ounces of general-purpose styrene (GPPS). To know the shot capacity for any material other than GPPS, the GPPS ounce rating must be converted to the density of the other material. For Ultramid resins, one must insert the specific gravity (S.G. – a measure of density) of the Ultramid resin grade into the formula shown in Figure 4F. The specific gravity is easily obtained from the data sheet for the given Ultramid nylon grade. Barrel Size S.G. Ultramid Barrel Size X = (oz GPPS) S.G. GPPS (oz Ultramid) Figure 4F For example, if you have a molding machine with a 64-ounce barrel and you want to know the barrel capacity using Ultramid 8233 nylon, the barrel capacity would be calculated as follows: 64 1.38 83.2 X = (oz GPPS) 1.06 (oz Ultramid) Figure 4G The total shot weight, in ounces (all parts, including runners), is then divided by the Ultramid nylon ounces found in figure 4G. This will yield the percentage of shot size. When injection molding Ultramid products, it is recommended that the shot size not exceed 75% of barrel capacity. Shots larger than 75% may not allow the material to thoroughly melt and mix. On the other hand, a shot size of less than 30% of the barrel capacity is not recommended. This may lead to extended material residence time in the barrel which can, in turn, lead to material degradation, part brittleness and discoloration. This is especially true in products using cadmium-free pigment systems. On occasions when a mold is already being run in a press, this ratio can be observed by comparing the linear shot size being used to the maximum shot size available and calculating the percent comparison.
The Injection Molding Machine Nozzle Tip Type 1. Lack of ability to maintain a cushion, resulting in forward screw slippage. Reverse taper nylon tip nozzles are recommended when moldingUltramidproducts. The reverse taper will 2. Inconsistent shot size. minimize material drool and stringing which can be encountered when molding crystalline resins. The 3. Dimensional inconsistency in parts. reverse taper design is suggested when molding unreinforced nylon, and may be used with reinforced 4. Sink marks due to lack of pack pressure. grades. However, nozzle bore diameters are recommended to be approximately 25% larger for 5. Surface imperfections from splay, whitening, or reinforced Ultramidproducts than for unreinforced Ultramid mineral bloom. nylon due to the higher material viscosities encountered. Typically, general purpose nozzles are recommended 6. Potential to degrade material. when using reinforced grades. Temperature control on the nozzle should be controlled separately from other 7. Screw rotation upon injection. barrel zones. Extended nozzles may require two or more zones of control. Reference Chapter 7: Processing 8. Possible override of barrel temperature settings. Ultramid Nylon for proper barrel temperature settings. Below are acceptable types of check ring design that have Below are examples of a reverse taper nozzle design. been used successfully when processing Ultramid resin. Figure 4H shows a one-piece nozzle. Figure 4I shows a removable nozzle tip that may be used on general purpose nozzle bodies. For ease of sprue removal, attempt where possible to design the sprue bushing diameter 0.005"–0.030" (.125mm– .75mm) larger than the nozzle tip orifice diameter. Tip Seat Check Ring Standard Valve Figure 4J Figure 4H Tip Check Ring Seat Free-Flow Valve Figure 4K Figure 4I Retainer/Tip Check Valve Wrench BASF recommends that the non-return check valve be of Flats Rear the “Free-Flowing” ring design type. This design, while Front Seal Check Seat ensuring a consistent shot size, tends to wear the best Ring while running materials containing higher filler content. Four-Piece Valve Maintaining the check valve in a proper working condition is critical to ensuring quality and consistent moldings. Figure 4L There are several issues that may result if the check valve is not functioning properly. 17
The Injection Molding Machine Clamp Requirements Clamp Sizing It is important to have adequate clamp force to maintain a fully closed tool during the injection process. High injection pressure, which is often required to fill a cavity, must be offset by pressure exerted by the clamp on the parting line of the tool. If sufficient clamp pressure is not present, the following may result: 1. Flash at parting line. 2. Peened over parting line resulting from repeated flash. 3. Inability to mold a part that is fully packed out. Often, larger machines are equipped with proportionally Toggle Clamp sized injection barrels and clamping systems. However, injection molding machines can be equipped with Figure 4N oversized platens. This will allow larger molds with a relatively small shot size to be processed in a smaller, more economical molding machine. Traditional clamping systems for injection molding machines fall into two main categories. These include the following types of clamps: 1. Hydraulic Clamp 2. Toggle Clamp The two main clamping mechanisms and the advantages and limitations of each are shown in Figures 4M and 4N, respectively. Hydraulic Clamp Figure 4M 18
The Injection Molding Machine Clamp Style Advantages Limitations Hydraulic Fast mold set up. Requires large volume of hydraulic oil. Easily read clamp pressure. Energy Inefficient. Low maintenance. Must overcompensate due to compressibility of oil. Not Low platen deflection. floorspace efficient. Force concentrated at center of platen. Toggle Less expensive. Requires more maintenance. Fast clamp motion. Clamping force may not be concentrated at center of platen. Energy efficient. Difficult to adjust. Auto decelerated clamping. Figure 4P Clamp Force and Cavity Pressure It is important to verify that the clamp pressure of the molding machine is capable of maintaining a tightly closed mold during the injection process. In other words, the total clamp force exerted must exceed the opposing total force generated during injection. Since the clamping force is usually known, it is important to determine what the injection pressure exerted in the cavity of the tool may be and multiplying this by the projected area of the part and runner. The same equation may also be used to determine if clamp force is sufficient. This is a function of two components; the projected area parallel with the line of draw in the tool and the type of material used to mold the part. The projected area may be calculated by measuring the part. Below is a table of cavity pressure estimates for Ultramid products using the equation provided. The value obtained is the minimum value recommended for clamp tonnage in the injection molding machine. Ultramid Nylon Type Cavity Pressure Estimate Unreinforced Polymers 2 – 3 tons/in2 Reinforced Materials 3 – 5 tons/in2 Minimum Part Cavity Clamp Force (tons) = Projected (in ) X Area 2 Pressure (tons/in2) Estimate Required (measured) (see above) Figure 4Q 19
The Injection Molding Machine Vented Barrels Vented barrels are commonly used as a method of If a vented barrel is selected, BASF recommends the use removing gases (mainly moisture from hygroscopic of a longer screw. Recommended L/D ratio for this materials). The basic concept involves melting the application ranges from 26:1 to 32:1. The longer screw material through the first transition and metering section will facilitate producing a homogeneous melt. In addition, of the screw and then depositing the material into a a hood placed above the vent is recommended to decompression zone. At this point, most of the moisture remove the volatiles from the molding facility. in the material is released from the barrel through a vent. The resin is then processed through a second transition and metering section prior to passing through the check ring assembly. Below is a sketch of a typical vented barrel configuration. Material Hopper Hood Vent Non-return valve 2nd 2nd Decompression 1st 1st Feed Metering Transition or volatile Metering Transition section section section zone section section Typical Vented Barrel Configuration Figure 4R Many molders prefer vented barrels when processing Ultramid products as a way of removing the moisture from the material. However, in cases where the material Temperature Control contains a very high level of moisture, the vented barrel process is not capable of removing all of the volatiles. Heaters surrounding the barrel heat the material in the Below are advantages and disadvantages of using a screw channel by means of electricity, and in some vented barrel. instances hot oil or steam. In addition to this conducted heat, it is important to note that the material is also Advantages subjected to shear heat developed by the mechanical 1. Possibly eliminate pre-drying of the material. working of the material in the barrel by the screw. 2. Assists in reducing gas entrapment in the tool cavity. 3. Possibly avoid the cost of drying equipment for most A minimum of three heater control zones for the barrel Ultramid products, but may require a starve feeder. corresponding to the three functional zones of the screw 4. Easier and quicker material changes. is recommended. However, in most cases additional heater zones are likely when using a larger barrel. Disadvantages Thermocouples are often used and recommended as a 1. Potentially greater variation in part quality due to temperature feedback to the controller. Maintaining inconsistent levels of moisture in the material. accurate temperature control together with a feedback 2. Risk of partially clogged vent ports resulting in poor system will assist in maximum processing potential. part quality. Such a feedback system has also been used in data 3. Vented barrels may result in longer cycle times and recording for statistical process control purposes. inability to operate successfully at full injection stroke. 4. Longer residence time in barrel possibly leading to resin degradation in smaller shot sizes. 20
Chapter 5 Mold & Tooling Considerations Tool Steel Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Texturing and Surface Finish . . . . . . . . . . . . . . . . . . . . . . 22 Sprue Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Sprue Puller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Cold Slug Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Cold Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Hot Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Gate Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Gate Location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Mold & Tooling Considerations Chapter 5: Mold & Tooling Considerations Tool Steel Materials Below is a table of information regarding more commonly used textures and the recommended draft angle. The careful selection of the tool steel for the construction of an injection mold designed for Ultramid resins is important to ensure the long-term durability of the tool. TEXTURING: Draft Angle Requirements Many of the Ultramid materials contain high levels of filler Grain Type: Grain Depth: Min. Draft Angle: reinforcement which tend to wear on the surface of the inch (mm) tool. High wear is most effectively countered with high Turf 0.004" (0.0875) 1 + 6 = 7 surface hardness. Selecting the right tool steel can 0.003" (0.075) 1 + 4.5 = 5.5 increase the useful service life of the tool as well as 0.002" (0.05) 1 + 3 = 4 greatly improve the maintenance of any texturing or Naples 0.0033" (0.083) 1 + 5 = 6 graining of the mold surface. The following tool steels are 0.0026" (0.067) 1 + 4 = 5 recommended when constructing cavity and core 0.002" (0.05) 1 + 3 = 4 sections. Figure 5B Typical Recommended Hardness AISI-SAE as In addition (as shown in figure 5C), where possible Steel Tool Steel Finished Material Designation Characteristics (Rockwell C) maintain an area around the parting line perimeter of P20 Medium alloy mold steel 30 – 36 Rc .010" (0.25mm) without the textured pattern. This will Unfilled protect the shut off region at the parting line. Polymers ------------------------------------------------------------------------------------- Reinforced S7 Shock resisting tool steel 54 - 56 Rc 0.010" (.25mm) Materials H13 Hot work tool steel (Cr based)50 - 52 Rc 420 Stainless steel 50 - 52 Rc Figure 5A Texture For increased wear resistance, the tools may be pattern hardened, plated, or surface treated. If the tool is to be grained and surface treated to improve Cavity block wear resistance, it is recommended that any surface or hardness treatment be performed after the texture Typical Textured Cavity process. Figure 5C Texturing and Surface Finish Ultramid products, when molded in tooling containing a Below are several suggestions for tool design when textured, grained, or polished surface, will reproduce the specifying a texture or grain. surface of the tool. All of the tool steels that are recommended for use with Ultramid products can be 1. Prior to texturing, heat treating the tool is chemically etched or textured. However, prior to recommended. texturing, the mold should be heat treated. This will result 2. To ensure a consistent texture, the depth of the heat in a finer grain structure of the steel which will result in a treat into the steel should exceed that of the texture. smoother surface to etch into. Typical texture depths range between .0004" (0.01mm) and .005" (.125mm). 3. In order to ensure proper release of the part from textured side walls, do not exceed a depth of etching To ensure ease of part ejection and reduce the chance of .001 inches (.025mm) per 1.5° draft. for streaks and scuff marks, the following rule is recommended for incorporating draft into part walls 4. Texturing of the core half of the mold is not containing a texture. recommended based on potential part release problems. 1° draft + 1.5° draft for each 0.001" (0.025mm) grain depth 22
Mold & Tooling Considerations Sprue Bushing The sprue bushing is the material entry port into the The figure below presents recommendations for sprue mold. The injection molding machine nozzle interfaces design. with the sprue bushing. For ease of part and runner system ejection from the tool, a minimum taper of 1.5°–3.5° is recommended over the length of the sprue bushing. It is also recommended that the sprue be polished in the draw direction. When molding Ultramid products, it is also suggested that the minimum diameter of the opening of the sprue bushing at the nozzle interface be at least 0.118" (3.0mm). For best results, ensure that the machine nozzle orifice diameter be less than the sprue bushing inner diameter by .005" – .030" (.125mm – .75mm). This condition will ensure that a smooth transition occurs as the material enters the tool, thereby not creating a shear condition or a pressure drop which can lead to improper packing of the part and surface appearance problems. The sprue diameter at the intersection of the primary Tmax = Maximum runner thickness runner should be at least equal to or greater than the Dia. A = Diameter of opening at end of diameter or depth of the runner. machine nozzle Dia. B = Diameter of sprue at machine The overall dimensions of the sprue depend primarily on the nozzle interface dimensions of the component to be molded and especially Dia. C = Diameter of sprue bushing at its wall thickness. Following are general guidelines to be part intersection considered. L = Overall length of sprue A. The sprue must not freeze before any part cross Figure 5D section in order to permit sufficient transmission of holding pressure. It is important that the sprue bushing bore be properly B. The sprue should demold easily and consistently. draw polished for ease of demolding and ensuring that the part will run on an automatic cycle consistently C. It is very important that the radius on the machine without the sprue sticking. Grinding and polishing in a nozzle match that of the sprue bushing. pattern perpendicular to the direction of ejection results in undercuts, which may detrimentally affect the ejection of the sprue. 23
Mold & Tooling Considerations Sprue Puller Typically, the sprue and the molded part are removed from the cavity at the same time, with both remaining on the moveable (or core) half of the mold. In multi-cavity molds, where a cold runner system is employed, a sprue puller on the moveable half of the mold is recommended. This will ensure that the sprue remains on the moveable half of the tool when the mold opens. A sprue puller is designed with an intentional undercut of various types depending on design, as shown in figures 5E through 5H. The reverse taper sprue puller is recommended, as it typically functions best and will also act as a cold slug Reverse Taper Sprue Puller Design (Best) well. Figure 5E “Z Puller” Sprue Design (Good) Figure 5F Undercut Ring Sprue Puller Design (Not Recommended) Figure 5G Ball Sprue Puller Design (Not Recommended) Figure 5H 24
Mold & Tooling Considerations Cold Slug Well Use of cold slug wells is always recommended in cold runner systems. A cold well is designed to catch any material in the tip of the machine nozzle that may have cooled below the melting point and begun to solidify. If injected into the part, this cold slug can lead to surface imperfections, such as jetting and gate blush, and also result in a potentially weakened part. Examples of typical cold slug well placement and design are included in Figures 5I and 5J. Figure 5I Figure 5J 25
Mold & Tooling Considerations Runner Systems The runner design is a very important phase of tooling design. There are several objectives which the runner must perform to ensure the quality requirements of most parts. Both cold runner and hot runner manifold systems can be used when molding Ultramid products. Insulated runners are NOT recommended. Suggested criteria for runner design are listed below: Full Round Modified Trapezoid Runner Trapezoid 1. Minimize restrictions to flow in the runner system, such as inconsistent cross section. Da = Tmax + 0.060” Wb = 1.25 Db B = 5° to 10° (1.5mm) Db = Tmax + 0.060” Wc = 1.25 Dc 2. Design for ease of part ejection. (1.5mm) Dc = Tmax + 0.060” (1.5mm) 3. Overall length should be as short as possible to reduce losses in material pressure and temperature Tmax = Maximum Cross Section of Part and excessive regrind generation. Recommended Runner Designs 4. Make runner cross section large enough whereby runner freeze-off time exceeds that of the gate. This Figure 5K ensures that proper hold pressure is applied. 5. The runner system should not be the limiting factor when reducing cycle time. 6. Minimize rate of runner weight to part weight without conflicting with other guidelines. Box Section Half Round Unfavorable Runner Designs Figure 5L Runner Style Advantages Disadvantages Full Round 1. Smallest surface to cross section ratio. Matching into cavity/core difficult. 2. Slowest cooling rate. 3. Low heat and frictional loss. 4. Center of channel freezes last; maintains hold pressure. Modified 1. Easier to machine; usually in one half of More heat loss and scrap compared Trapezoid tool only. to full round. 2. Offers similar advantages of full round. Trapezoid Easy to machine. More heat loss than modified trapezoid. Box Section Easy to machine. 1. Reduced cross section efficiency. 2. Reduced ability to transfer pressure. 3. Difficult to eject. Half Round Easy to machine. 1. Smallest cross-sectional area. 2. Most inefficient runner design. 3. Poor pressure transmission into cavity. 4. Generates more regrind. Figure 5M 26
Mold & Tooling Considerations Cold Runner Design Hot Runner Design The full round runner is recommended. This type allows Both hot runner and cold runner systems can be utilized for the most efficient material flow and tends to induce when molding Ultramid products. When using a hot the least chilling effect on the material. Trapezoid and runner system, the resin is injected from the machine modified trapezoid runners are also feasible. However, barrel into a heated manifold network within the tool. resin flow to the part is less efficient with these designs. An externally heated hot manifold system is recommended They also tend to induce more of a chilling effect on the for Ultramid resins. This manifold commonly directs the material in the runner and generate more regrind. The material through a series of heated channels to the half round runner is not suggested because it does not location of the gate in order to fill out the part. provide for optimum flow and it causes the greatest chilling effect on the resin. If the material in the runner freezes prematurely, the material in the cavity will not be adequately packed, which may lead to excessive shrinkage or other problems. In addition, to ensure part to part consistency, the runner length from the sprue to each cavity should be of the same diameter and length. By balancing the cavities in this fashion, you will ensure that each cavity receives equal flow and pressure simultaneously. The table below shows suggested runner diameters and corresponding runner lengths and part thicknesses. Primary Maximum Maximum Runner Diameter Length Part Thickness Hot Runner and Nozzle System 0.125" – 0.187" 6.0" 0.187" Figure 5N (3.18mm – 4.75mm) (152mm) (4.75mm) Suggestions for designing hot runner systems for 0.25" – 0.312" 12.0" 0.50" optimum performance: (6.35mm – 7.94mm) (304.8mm) (12.7mm) 1. When machining the melt passage in the manifold, 0.375" 15.0" 0.75" take care not to create any dead spots where material (9.53mm) (381mm) (19.05mm) may hang up. Over time, this material may degrade and contaminate the material flowing through the Table 1A system. 2. Placement of heaters in the manifold design is critical to ensuring uniform heat transfer in the melt, thereby avoiding a cold spot in the system which may lead to freeze-off or uneven fill patterns. 3. Reduce contact areas between the hot runner manifold system and the tool steel. Heat transfer to the mold from the manifold should be minimized. 4. Where possible, attempt to locate cooling lines away from the manifold system. This can also lead to undesirable heat transfer out of the manifold. 5. The use of a temperature insulator is recommended between the mold base and the machine platens to reduce heat loss (especially on the stationary half). 6. To eliminate the chance for electrical interference, which may lead to false thermocouple readings, try to locate the heater wire leads away from the thermocouple wires. 7. Proper water cooling around the gate orifice is key to control. Also critical is a separate zone of temperature control for the gate area of the hot manifold tip. 27
Mold & Tooling Considerations Gate Design The gate connects the part to the runner. It is usually the smallest cross section in the entire system. Designing the gating concept for a part is highly dependent on both tool design and part geometry. Often, the most desirable gating scenario is not feasible due to tooling or part design limitations. Equally important to molding a successful part is the location of the gate on this part. As a guide, the following gating configurations are presented: Figure 5Q Sub gating, Figure 5Q, can be designed to provide automatic degating of the part from the runner system during ejection. Sub gate size is highly dependent on both part size and tooling limitations. Each application should be thoroughly reviewed. Figure 5P Tab or film gating, Figure 5P, is often used where flatness is critical or in large surface areas where warpage may be a concern. Due to the nature of this type of gate, a post molding operation is typically required to properly remove the gate vestige. Figure 5R 28
Mold & Tooling Considerations The fan gate or the edge gate, shown in Figures 5R and 5S, is often used to feed flat, thin sections which will tend to allow the material to flow across the cavity in a uniform fashion. It also has proven successful in reducing warpage. The gate cross-sectional area should always be less than the cross-sectional area of the runner. The edge gate is the most common gate type used and generally presents a good compromise between ease of part filling and gate removal. Figure 5S The diaphragm gate, shown in Figure 5T, is used when molding cylindrical parts requiring a high level of concentricity and weld-line strength. However, due to the nature of this type of gate, a post mold degating operation is typically required. Figure 5U Figure 5T Cashew gating can be highly effective when using more flexible materials. Due to the required degree of bending of the runner, as shown in sketches 3 and 4 of Figure 5U, filled or stiffer materials are not recommended for use with this type of gate as they often break during ejection. This could lead to broken ---pieces of plastic becoming lodged in the tool, plugging the gate on the next shot. Therefore, it is recommended that only unfilled materials be used with this type of gating. 29
Mold & Tooling Considerations Gate Sizing The placement and quantity of gates required will have an effect on the overall flow length and orientation of the Figure 5V shows the recommended gate thicknesses for material. Typically, the maximum flow length from each both filled and unfilled grades of Ultramid resins for typical gate for Ultramid nylon in an injection mold is 15 inches part thickness cross sections. These values can be (381mm). This value is highly dependent on runner applied when using all types of gates. diameter, runner length, part geometry, and part thickness. Recommended Gate Thicknesses The following suggestions may be used when proposing Typical Unfilled Filled gating location concepts for Ultramid products: Part Thickness Ultramid Nylon Ultramid Nylon Up to 0.060" 0.040" 0.040" – 0.060" 1. Direct incoming flow against the cavity wall or core to (1.5mm) (1.0mm) (1.0 – 1.5mm) minimize gate blush and jetting. Up to 0.125" 0.060" – 0.090" 0.060" – 0.125" 2. Avoid gating that will cause melt fronts to converge (3.2mm) (1.5 – 2.3mm) (1.5 – 3.2mm) such that air is entrapped. Where possible, attempt to Up to 0.187" 0.090" - 0.125" 0.125" – 0.187" direct flow fronts and air toward vents. (4.7mm) (2.3 – 3.2mm) (3.2 – 4.7mm) 3. If possible, position the gate location at the thickest Up to 0.250" 0.125" – 0.187" 0.187" – 0.250" (low pressure) section of the part. Always try to flow (6.4mm) (3.2 – 4.7mm) (4.7 – 6.4mm) from thick to thin sections. Figure 5V 4. Select gate location to obtain the best strength relative to loading. Tensile and impact strength are highest in If the gate is to be enlarged for increased material flow direction of flow, especially with filled or reinforced and pressure transfer, focus on increasing gate Ultramid nylon. thickness rather than the width. Keeping the gate to a square (or round) cross section will be the most efficient. 5. The gate should be positioned away from any area of the part that will be subject to impact or bending Gate Location stress. The gate area tends to contain high residual stresses from the filling process may become a Gate location is critical because it ultimately determines likely site for fracture initiation. the direction of the material flow within the cavity. In many cases, this has an effect on the following factors: 6. Minimize weld lines especially in impact or highly • Shrinkage stressed areas. Locate weld lines to thicker areas on • Physical properties the part. • Distortion or warpage • Part appearance 7. In multiple cavity tooling applications, it is imperative that each gate among the various cavities be of the The above factors are a result of the orientation of the same size (diameter, thickness, etc.). This will ensure molecular structure of the material or any fillers that equal pressure and flow to each cavity. may be present. Note that: 8. If possible, locate the gate in an inconspicuous area of 1. The amount of orientation is higher in thin walled the part where finishing will not be required. moldings. 2. Higher strength and impact resistance values are observed in the direction of flow while sections in the perpendicular direction may exhibit reduced toughness. Therefore, prior to designing the injection mold and gate location(s), the mode of stress loading that the part will experience should be determined. 30
Mold & Tooling Considerations Venting During the filling of the cavity with Ultramid resins, the melt Suggested concepts which may be used for has to displace the air which is contained in the cavity. If incorporating vents: there is nowhere for this air to go, it may compress, forming a pressure head that will resist the flow of plastic. 1. Parting line vents. As the air compresses, it will also heat. In some cases 2. Ejector pins (flats ground on pins). the air can reach temperatures that exceed the ignition temperature of the plastic and volatiles that are present. 3. Add venting pins. This results in a burn line where the trapped air contacts the plastic, which can produce an undesirable charred 4. Incorporating inserts at sections that trap air. blemish on the surface of the part and may even oxidize 5. Add an overflow well. and erode the mold. 6. Sintered metal inserts. Part geometry, position in the mold, and gating location all have a big impact on the venting. Figure 5W shows a sketch of a typical parting line vent and the corresponding dimensions are shown in Figure 5X. Suggestions for locating and designing vents into tools designed for Ultramid nylon: 1. Tooling inserts may be incorporated at ribs or part sections that tend to trap air. The mere existence of the insert may alleviate a trapped air problem. 2. When molding thin walled parts <.125" ( 3.0mm) with a high injection rate, the cavity should be vented close to the gate as well as at the extremity of flow. Air removal from the tool reduces the chance of a L = Land of Vent significant pressure build-up. W = Width of Vent 3. Avoid venting to internal pockets in the tool. Vent to D1 = Depth of Vent atmosphere. D2 = Depth of Relief 4. Thick walled > .125" (3.0mm) parts with high surface Typical Parting Line Vent Design appearance requirements may require extra venting. Figure 5W Vent Dimensions Material Type L W D1 D2 Unfilled 0.03" – .06" .375" – .5" .0005" – .001" 0.01" 0.75 – 1.5mm 9.5 – 12.5mm .013 – .025mm 0.25mm Mineral 0.03" .375" – .5" .001" – .002" 0.01" Filled 0.75mm 9.5 – 12.5mm .05 – .05mm 0.25mm Glass 0.03" .375" – .5" .001" – .002" 0.01" Filled 0.75mm 9.5 – 12.5mm .03 – .05mm 0.25mm Figure 5X 31
Mold & Tooling Considerations The figures below show two venting schemes that are Cooling commonly used when relieving vents to atmosphere. Figure 5Y shows the use of vent channels from the To ensure optimum molding cycles while maintaining part parting line to the edge of the tool. The venting scheme surface requirements and mold filling capability, a stable in Figure 5Z ensures a positive shut off area outside the mold temperature should be determined and maintained. parting line area and then relieving the entire parting line. This is accomplished by incorporating cooling lines This latter design is referred to as continuous venting. throughout both the cavity and core of the mold. It is important that the temperature variation throughout both halves of the part cavity be kept to a minimum. When designing the tool, take into account potential hot spots such as hot runner manifolds and gate locations as well as cold areas such as the area last to fill. Hot spots and cool spots often require extra water channels to maintain temperature consistency throughout the tool. Inconsistent mold temperatures may lead to the following problems: 1. Non-uniform part surface finish. 2. Non-uniform part shrinkage and warpage. Independent Venting Channels 3. Lack of part dimensional control. Figure 5Y 4. Potential binding of tightly fitting cavity and core sections. In general, it is advisable to maintain less than a 20° F (11° C) differential in tool steel temperatures over the molding surface of a large mold and 5° F (3° C) with smaller tools. Designing for a tighter tool temperature range will assist in providing a greater processing window. Figure 5AA shows a typical design of a cooling channel layout arranged around the part surface. To maintain a stable process, tool temperature can be best controlled by incorporating a sufficient amount of water channels and placing them approximately .5 inch (13mm) Continuous Venting Channels from the part surface. Also, where the design permits, place the lines no more than 2 inches (51mm) apart for maximum control. Figure 5Z Water Channel Configuration Figure 5AA 32
Mold & Tooling Considerations Often, part designs make the installation of adequate Shrinkage cooling lines difficult. In those cases, techniques other than a typical cooling line can be utilized, such as: Shrinkage is the difference between the dimensions of the cooled part and the tool. Ultramid nylon 6 products 1. Heat pipes are considered semi-crystalline products. Having this inherent characteristic, Ultramid products tend to exhibit 2. Air pipes shrinkage resulting from a decrease in part volume as 3. Bubblers material crystal-lization occurs. Resins with higher filler content will have less shrinkage. When designing the 4. Baffles injection mold, it is important to specify the proper material shrinkage in order to achieve a part that meets In addition, alloy materials such as beryllium copper offer your dimensional requirements. thermal conductivity values upwards of 10 times that of standard P-20 steel. These materials can be inserted in Below are several factors which may affect the shrinkage areas of the tool where water lines may be difficult to of an injection molded component: install, while maintaining tool durability. For best efficiency, water lines should always go through a portion of the 1. Location and size of the gate(s). Shrinkage is usually beryllium copper insert. greater in the cross flow direction. The following suggestions are recommended when 2. Part designs that contain large variations in cross designing and maintaining cooling systems of the section thickness can lead to unequal stresses injection mold: throughout the part and tend to cause differential shrinkage and warpage to become more pronounced. 1. Use a pyrometer to check that the cavity surfaces of 3. Increased glass content as a filler reinforcement will the tool are at the desired temperature. tend to lower the shrinkage of the material. 2. Minimize looping of hoses to maximize cooling 4. Random glass orientation, which can result from tool efficiency. design scenarios containing multiple gates, can be effective in leading to a more uniform part shrinkage 3. Blow out water lines with compressed air to remove condition. any foreign matter that may have collected. 5. Thicker areas shrink more than thinner areas. 4. Attempt to flow opposite directions (horizontal to vertical) between cavity and core. 5. Prior to mold start up, check all waterlines to ensure coolant flow is occurring. 6. Ensure that the flow pattern through the tool meets requirements for turbulent flow. Cooling simulation packages can be used to evaluate this. 7. To ensure operator safety, allow hot molds to cool prior to removing the mold from the molding machine. 8. Maintain and frequently check for wear or weakening of cooling hoses. With conventional rubber hoses, do not exceed 200°F (95°C) water temperature to ensure operator safety and the long-term integrity of hoses. Temperatures in excess of 200° F (95°C) require steel- braided hose. 33
Mold & Tooling Considerations Refer to Figure 5BB which suggests the typical material shrinkage values for the Ultramid products. Nonetheless, there are many conditions, including part design and material processing, that can affect part shrinkage. As an accurate prediction mechanism, prototyping is often the most valuable tool for determining precise part shrinkage. Please contact a BASF Technical Development Engineer for assistance in determining material shrinkage. Category Product Ultramid Shrinkage General 8200 HS 0.012 Purpose 8202 HS 0.012 Homopolymers Flexible 8253 HS 0.012 and Impact 8254 HS 0.013 Resistant 8350 HS 0.014 8351 HS 0.014 BU50I 0.018 Reinforced 8230G HS 0.008 for High 8231G HS 0.005 Stiffness and 8232G HS 0.004 Strength 8233G HS 0.003 8234G HS 0.002 8235G HS 0.002 8262G HS 0.008 8266G HS 0.004 8267G HS 0.004 8331G HS 0.005 8332G HS 0.004 8333G HS 0.003 8334G HS 0.002 HMG10 0.002 HMG13 0.002 SEG7 0.003 SEGM35 0.004 TG3S 0.004 TG7S 0.003 Mineral 8260 HS 0.009 Reinforced 8360 HS 0.010 8362 HS 0.010 Tested samples were 5.0" x 0.5" x 0.125" (127mm x 12.7mm x 3.2mm) molded bars. These values are presented as a guide. Shrinkage values may be different depending on the actual application, including part design, mold design, and processing variables. Figure 5BB 34
Chapter 6 Auxiliary Equipment Material Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Mold Temperature Control . . . . . . . . . . . . . . . . . . . . . . . 36 Granulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Auxiliary Equipment Chapter 6: Auxiliary Equipment Material Drying Mold Temperature Control Since Ultramid resins are hygroscopic materials, they must Mold (water) heaters are commonly used to maintain a be in a dry condition prior to injection molding. (Reference consistent temperature throughout the injection mold. Chapter 7: Processing Ultramid Nylon for drying recommen- In most cases, water is used as the heat transfer media, dations). Therefore, the dryer is an important piece of however, ethylene glycol mixtures as well as oil are equipment. For optimum drying conditions, BASF commonly used. Occasionally, two heaters are required recommends a closed loop desiccant dryer. A typical per mold to allow different mold temperatures between dessicant drying system is depicted in figure 6A. the cavity and the core. Selecting the proper heater to use for a particular mold is very important to ensure an efficient process. An undersized heater may be less of an upfront cost but the operating costs may outweigh the original savings. This is due to the fact that in many undersized cases, the heater will be required to run at 100% capacity for extended periods of time. Mold heaters are commonly rated in tons. One ton equals the ability to transfer 12,000 BTU/hr. To calculate the appropriate size thermolator for each mold, the formula in Figure 6B can be used. A x (B - C) Required = 12,000 Tonnage Figure 6A A = Actual material used in lbs/hr B = Temperature of melt (°F) Dryers should provide uniform and even distribution of air C = Temperature of part when it through the hopper. The critical temperature when comes out of the mold measuring the heated air is the temperature at the entrance to the hopper. Recommended air flow into Figure 6B the hopper is one cubic foot of air per minute for every pound per hour of use. If 200 lbs of material are consumed per hour, the airflow to the hopper should be 200 cubic feet of air per minute. Below are several guidelines for using and maintaining dryer systems: • Clean the filters on the dryers on a regular basis to ensure that the specified airflow is maintained. • Avoid loading regrind with high levels of fines or small dust- like particles into the dryer. • Using a dewpoint meter, check the dewpoint of the air entering the hopper. The recommended dewpoint should range between -20° F and -40° F (-30° C and - 40° C). • Change and maintain the desiccant in the dryer per the manufacturers recommendations. 36
Auxiliary Equipment Sufficient water flow through the tool is also critical to Granulators ensure that an efficient heat transfer process is occurring. This is demonstrated in Figure 6C. As the gallons per Many molding applications allow the use of regrind back minute of flow (GPM) through the tool decreases, the into the process. This will require the use of material difference between the tool inlet and outlet temperatures grinders. Many styles of granulators have been used (Delta T) must increase dramatically. Therefore, to run at successfully with Ultramid resins. To ensure a consistent a lower flow rate through the tool and still achieve the regrind blend, granulator maintenance is often critical. In results of running with a higher flow, the inlet coolant addition to maintenance, proper safety should be observed in temperature must be set significantly lower. This results accordance with the manufacturer’s recommendations. in lower mold heater settings, which may be costly to operate. The following are suggestions to maintain a consistent regrind blend while maintaining the equipment in proper working order: 1. Following material changes, the granulator should be cleaned and vacuumed to remove any foreign material that may contaminate the blend. 2. Blades should be sharpened and screens cleaned regularly to ensure a consistent regrind pellet size. 3. When grinding filled materials, for prolonged periods, components, such as blades, rotors and screens, should be made of hardened materials to resist the Figure 6C erosive effects of these more abrasive plastic compounds. Following are several other suggestions that may be helpful when designing the coolant system for a specific 4. In many instances, ear protection is recommended tool: when operating a granulator. 1. Typical temperature losses through the coolant handling system is 20%. This includes the coolant lines, mold base, and platens. 2. Antifreeze does not transfer heat as well as water. 3. If antifreeze is needed, use only inhibited ethylene glycol with high corrosion resistance. A straight ethylene glycol can become acidic and corrosive with use and may form a gel within two years in open air systems. 4. Where equal heat transfer is desired, ensure that equal coolant flow is occurring between the coolant channels. This may be accomplished by the use of adjustable flow regulators. 37
Chapter 7 Processing U ltramid Nylon Processing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Melt Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Hot Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Residence Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Mold Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Holding Pressure and Pack Pressure . . . . . . . . . . . . . . . 42 Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Injection Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Rotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Decompression. . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Regrind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Pre-Colored Ultramid Nylon. . . . . . . . . . . . . . . . . . . . . . . .44 Processing Cadmium-Free vs. Cadmium Colors . . . . . . 44
Processing Ulramid Nylon Chapter 7: Processing Ultramid Nylon Processing Conditions Recommended Dryer Settings Ultramid resin has very good molding characteristics due Dryer Inlet Air Dryer Drying to its excellent ability to flow. Since Ultramid products Temperature Dewpoint Time have a wide processing window, the following conditions Ultramid Nylon 6 180°F (82°C) <-20°F (-30°C) 4 hours are typical recommended settings that can be used at machine set up. Included in this chapter are the key NOTE: Not to exceed 25 0°F (121°C) for two hours. processing variables that may be manipulated in order to control the molding process. Figure 7B Drying Moisture absorption and moisture loss is a function of pellet surface area. In other words, the smaller the pellet, Ultramid resins are hygroscopic materials and are supplied the more surface area per weight, and therefore, the more dry. Therefore, care should be taken to ensure that the moisture that it will absorb or lose in a given period of material remains in an enclosed container prior to time. Therefore, when molding regrind, which may molding as nylon will tend to absorb moisture from the contain larger sized pellets, additional drying time at 180° atmosphere over time. As supplied from BASF in sealed F (82°C) may be required. boxes and bags , Ultramid resin is usually dry enough for injection molding. However, a moisture analysis of the To ensure that the material is dried for the recommended material is always a good idea to ensure that the material time, the equation in Figure 7C may be used to calculate is within the recommended moisture range. Figure 7A the residence time of the material in the dryer for a shows the moisture content recommendations for continuously running process. To perform this injection moldingUltramid resins. calculation, the following variables are needed: 1. Total shot weight (including sprue and runner) Ultramid Recommended 2. Total cycle time Produc t Moisture Content (by weight) 3. Total dryer capacity Unreinforced homopolymers 0.10 – 0.20% These values are then entered in the appropriate position in the equations below: <20% Reinforced 0.10 – 0.16% >20% A Reinforced 0.06 – 0.12% Figure 7A B In order to ensure proper material properties the , moisture content should not be dried to moisture levels below 0.02%. Figure 7C If the material contains higher levels of moisture than listed on the chart, drying may be required to ensure Below are key recommendations for maintaining an proper processing and desired part quality. A dryer (as acceptable moisture level for injection moldingUltramid discussed in Chapter 6) containing a desiccant system is products: highly recommended for best results. Figure 7B gives the drying recommendations for Ultramid products. These 1. Prior to molding, store the material in a container that values are for 100% virgin products. is sealed from the atmosphere. 2. Minimize the distance from the dryer to the machine The data presented are general guidelines for moisture hopper and/or dryer hopper in an effort to minimize content. Refer to the particular resin’s property data heat loss through the connecting hoses. sheet for more specific recommendations. 3. Check the drying equipment for crimped or cracked hoses which may reduce the heat transfer to the hopper. 40
Processing Ultramid Nylon Melt Temperature The actual melt temperature is influenced by barrel temperature settings, screw design, screw RPM, back pressure, material residence time and shear heat through the nozzle. Since it is difficult to estimate the effect that each variable has on the process, the actual melt temperature should be measured with a pyrometer. Actual measurement of the melt temperature will ensure process repeatability. The barrel temperature profiles in Figures 7D through 7I are representative for processing of the various categories of resins. Figure 7D Figure 7G Figure 7E Figure 7H Figure 7F 41
Processing Ultramid Nylon Hot Runner Systems The ability to control mold temperature is often highly dependent on tool design. If possible, all surfaces of the The purpose of a hot runner system is to maintain heat in tool should be maintained at a consistent temperature. the material and not add, nor remove, heat. When This will ensure consistent properties throughout the part. molding Ultramid resins through a hot runner system, use Below are additional suggestions for setting mold standard injection molding processing guidelines. temperature: Recommended manifold temperature settings should be similar to the front or center zones of the machine barrel. 1. When possible, use a pyrometer to verify that the mold temperature is at the desired temperature and Residence Time consistent throughout both halves of the tool. Residence time of Ultramid resin in the barrel at 2. Avoid a temperature differential between the halves processing temperatures should be minimized to 3 –5 of the tool greater than 75° F (24° C). This will reduce minutes. Residence time may be calculated by using the the risk of tool steel interference or binding from equation in Figure 7J. temperature-induced expansion in the mold. Calculating Residence Time 3. A temperature differential between the mold halves may induce the part to warp toward the hotter side of the tool. Total Shots Cycle Time (sec) Barrel X 60 = Residence Time (minutes) Injection Pressure Figure 7J The actual required injection pressure will depend on many variables, such as melt and mold temperatures, This calculation (7J) will be a rough estimate only, as at part thick-ness, geometry, and flow length. Generally, any given time there is significantly more material in the low to medium pressures are desirable to maintain barrel than 100% of the maximum shot size. material properties, appearance criteria, and cycle time. Mold Temperature Holding Pressure and Pack Pressure Ultramid nylon 6 should always be molded in temperature- Holding pressure is the pressure transferred through the controlled molds. Recommended mold temperatures melt into the part cavity following the filling of the mold. range from 50° F to 200° F (10° C to 93° C). For best The change from injection pressure to holding pressure is properties and cycle time, a mold temperature of 180° F commonly called the transfer point. Holding pressures (82° C) is recommended. When molding parts that are normally 1/2 to 2/3 of the maximum injection pressure require good aesthetics, a mold temperature between and should take effect after the cavity is filled. 180° F to 200° F (82° C to 93° C) is suggested. Holding pressure should be maintained until the gate Ultramid nylon 6,6 resins should also be molded in a freezes off. Applying pressure beyond this point will not temperature-controlled mold. Recommended mold affect the part. To estimate when the gate is freezing off, temperatures range from 110° F to 220° F (43° C to 104° C). adjust the process to mold a full consistent shot. Begin by molding without a hold time and incrementally with Mold temperature will influence cycle time, part each successive shot increase hold time by one second. dimensions, warpage and mechanical properties. The Weigh each part and plot the weight on a curve of part effects of varying mold temperature when molding weight vs. hold time. When the curve begins to level off, Ultramid resins are listed in Figure 7K. In some cases, it showing a consistent part weight, the gate freeze off time may be required to elevate or reduce the mold can be noted. The first point at which the curve becomes temperature to attain the desired results. horizontal is the freeze off temperature. Mold Temperature General Holding Pressure Guidelines Lower Higher Increasing Decreasing Minimal shrink Maximum material shrink Reduces shrinkage Reduces part sticking Reduced cool (cycle) time Increased flow Reduces sink marks Increases shrinkage Higher molded-in stress Improved knit line strength Reduces warpage Reduces sprue sticking Less than optimum surface Reduced molded-in stresses Potential to flash parting line Induces surface gloss Improved impact properties Improved surface appearance Reduces gloss on grained parts Possibly reduces part strength Figure 7K Figure 7L 42
Processing Ultramid Nylon Back Pressure Cushion Back pressure on a screw results when its backward The use of a cushion of material at the end of the screw movement (screw recovery) is restricted. Back pressure stroke is highly recommended when moldingUltramid is always recommended to ensure a consistent shot size products. Typically, a small cushion is acceptable for and homogeneous melt. Higher pressures may be any Ultramid resin to promote shot to shot consistency. required for more intensive mixing but may induce higher A cushion of 0.100"–0.25" (2.5mm–6.35mm) is recom- melt temperature, glass breakage (reinforced materials), mended. The inability to hold a consistent cushion is and increased cycle time due to hotter melt temperatures usually indicative of a worn non-return valve. On injection and slower screw recovery. Typical back pressure molding machines with process controllers, the cushion settings for Ultramid products are 25 to 100 psi. can often be maintained automatically since the process Increasing back pressure as a substitute for a proper controller will monitor screw location and can heat profile or an inadequate screw design is not compensate for any deviation in cushion. recommended. Maintaining a cushion as suggested will assist in the Injection Speed processing of the material in the following ways: Generally speaking, reinforced Ultramid resins should be 1. Helps to maintain consistent physical properties injected with high velocity rates because of the inherent throughout the molded part. crystalline nature. A greater range of injection speeds can be utilized with reinforcedUltramid nylon grades. 2. Aids in ensuring dimensional reproducibility, weld line integrity and control of sink marks. Fast injection provides for longer flow improved pack , condition, and better surface aesthetics when molding 3. Assists maintaining a consistent surface quality. reinforced grades. Filling the cavity at a faster rate will allow the material to crystallize at a uniform rate in the Screw Rotation tool which tends to result in lower molded-in stress. Screw recovery speeds that will permit screw rotation Slower fill speeds may be required when filling through during 75–90% of the cooling time are recommended. gate designs where jetting or gate blush is occurring. This will prevent excessive melt temperature increases Slow fill is also used in tools with poor venting to and maintain a homogeneous melt temperature. eliminate part burning and in parts with thick cross sections to reduce sink marks and voids. Screw Decompression Programmed or profiled injection has been proven Decompression or “suck back ” is the intentional pulling successful when molding parts with non-uniform wall back of the screw and polymer from the nozzle area to stock to reduce voids and gas entrapment burning. It prevent drool. It is usually accomplished by time or has also proved to be an advantage when molding screw position settings. The result is introducing air to through subgates and pinpoint gates. the molten plastic, which cools and may oxidize the plastic. Therefore, it is recommended to minimize the Slow injection speeds at the start of injection can be use of decompression. used to eliminate/reduce gate blush, jetting and burning of the material. The nylon reverse taper machine nozzle has been used successfully to minimize drool and stringing. Please refer to Chapter 4 of this guide for more information on nozzle tips. Purging The barrel should be purged if the process will be shut down or idled for any length of time. For short interruptions, one need only purge several shots, but longer shut downs require a complete purging or emptying of the barrel. It is always a good idea to purge the first several shots at start up to reduce the chance of contamination from previous processing. 43
Processing Ultramid Nylon Regrind Processing Cadmium-Free vs. Cadmium Colors Ultramid nylon, like many thermoplastic materials, may be BASF has established itself as a leader in “cad-free” color used with its own regrind. Typical levels of regrind range technology for nylon 6. At present, cad-free pigments, from 25–30% if the initial molding did not cause thermal especially bright reds, bright oranges, and bright yellows degradation or severe glass breakage (in filled materials) do not have as high a melt stability as cadmium to the Ultramid product. pigments. For this reason, care should be taken when molding cad-free color Ultramid resins, especially when Below are several suggestions when using regrind: melt temperatures of greater than 570° F (299° C) are required. We recommend the following for good color 1. Mix regrind back into the virgin material type from repeatability in cad-free colors: which it was originally molded. 1. Do not dry the bright cad-free colors above 180° F 2. It is important that the material to be reground be free (82° C) and do not dry for an extended period of time from oil, grease or dirt, and show no signs of (over 10 hours). If needs require longer drying, degradation. reduce dryer set-point to 130° F (55° C) after 8 hours. 3. Regrind that contains excessive quantities of fines or 2. Minimize residence time in the barrel. A shot size of dust-like particles may result in molding problems 50% to 60% of barrel capacity is ideal. If the shot such as burning or splay. Try to select grinder screens size is less than 50% of barrel capacity, profile barrel that will minimize fines. temperatures with lower settings in the middle and rear zones. 4. It is advantageous to try to make the particle size of the regrind as close to the initial pellet size as possible. 3. Establish the molding process with the lowest melt This will allow for ease of blending and for consistent temperature that yields a good part. drying of the material. 4. Ensure that the check valve is holding a cushion. A 5. Prior to processing the regrind, ensure that the free- flow check ring is recommended. Ball check moisture level is similar to that of the virgin material. valves tend to have dead spots where material may This will help in processing. hang-up for several shots and lead to discolored streaks in molded parts. 6. If the regrind material does become wet it is usually better to dry the material off line in a separate dryer. 5. Ensure that the clearance between the screw and barrel inner diameter is not excessive. Any leakage 7. Some color shift may occur when using regrind. It is around the check valve will excessively shear heat ° important to dry the regrind at 180 F (82° C) the material. maximum to reduce the amount of color shift. 6. Attempt to design-out or remove all instances where 8. To maintain a consistent regrind blend, it is shear may be induced in the melt (i.e. thick to thin recommended to use your regrind back into the wall transitions and sharp corners). process as it is generated. 7. Acceptable regrind levels may be lower than those 9. If regrind is to be stored for future use, store it in a typically used for non-cadmium-free pigment container with a moisture barrier. systems. This is due to the inherently lower thermal stability of cad-free pigments. Pre-Colored Ultramid Nylon 8. Adjust screw RPM so that screw rotation lasts for a Ultramid nylon resins can be supplied in numerous custom minimum of 80% to 90% of the cooling time. This and standard compounded colors. Ultramid resins can will reduce thermal history on the material. also be easily colored by dry-blending natural resin with commercially available color concentrates. Please call 9. Nozzle bore, sprue bushing bore, gate thickness, and BASF for a list of commercial sources. diameter should all be as large as possible to minimize shear heating during injection. 10. Avoid the use of a reverse taper nozzle if possible. This will also reduce shear during injection. 44
Chapter 8 Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Brittleness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Bubbles, Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Cracking, Crazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Dimensional Variations . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Discoloration, Contamination. . . . . . . . . . . . . . . . . . . . . . 50 Excessive Cycle Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Flow Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Lamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Nozzle Drooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Part Sticking in Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Splay (Silver Streaking) . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Sprue Sticking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Surface Imperfections (Glass On Surface, Mineral Bloom) . . . . . . . . . . . . . . . . 56 Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Ultramid Nylon Troubleshooting Guide for Injection Molding Chapter 8 : Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction Ultramid nylon molding compounds are formulated to perform well in both the end-product and in the The purpose of the tables that constitute the major part of fabrication process. BASF provides a generous array of this chapter are to identify the broad categories of Ultramid engineering plastics from which to choose. molded-part deficiencies and molding problems that can Assistance with the selection of the most appropriate arise in injection molding. Under each category, possible Ultramid nylon molding polymer for your needs is always causes are identified and remedies suggested. While the available from BASF. You will find our address and phone suggestions are specifically made for parts molded from number at the end of this guide. Ultramid nylon resins, many of them have more general applicability. With its resident expertise and comprehensive resources and equipment, the BASF customer support staff has Responsibility for the proper molding of a part lies with built a strong base of technical experience and data on the molder, who applies knowledge and skill to achieve a injection molding. We continue to perform studies on satis-factory result from a complex interplay of factors injection molding and investigations into the performance including: properties of our nylon resins. Our technical personnel are always ready to share their knowledge with you. • Choice of Material • Mold Design Calling for Technical Assistance • Melt Stability When it is necessary to call the technical service staff for • Moisture Sensitivity help, please have the following information available: • Material Stress Behavior • Throughput Rate 1. Type of problem, i.e. molding defect, part failure. • Machine Characteristics 2. Material type, color number, and lot number. • Aesthetics 3. Material handling procedures, regrind percent used, • Dimensions drying times and temperatures. 4. Injection molding parameters. Actual melt and mold temperatures, actual fill time injection pressures and , times, back pressure , screw RPMs , cooling time, clamp tonnage, shot size versus barrel size. 5. Miscellaneous: Nominal wall thickness, gate size, number of cavities, balance of flow to each cavity, etc. 46
Ultramid Nylon Troubleshooting Guide for Injection Molding Brittleness Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature (weak weld lines). 2. Material overheated, resulting in a. Decrease melt temperature. molecular breakdown. b. Residence time in cylinder excessive– use smaller barrel. c. Decrease overall cycle. d. Reduce back pressure. 3. Contamination by foreign material or a. Inspect resin for contamination (replace if contaminated). excessive pigment usage. b. Purge injection cylinder thoroughly. c. Keep hopper covered. d. Review material handling procedures for regrind usage. e. Reduce filler or pigment loading. 4. Excessive amounts of regrind. a. Reduce regrind % mixed with virgin. b. Regrind level dependent upon application: general rule – 25–30%. c. Keep hopper covered. d. Review material handling procedures for regrind usage. e. Reduce filler or pigment loading. 5. Injection rate too slow. a. Increase injection or first stage pressure. b. Increase boost time. 6. Improper gate location or size. a. Relocate gate away from potential stress area. b. Increase gate size to obtain optimum filling. 7. Moisture in material during processing. a. Review material handling to eliminate moisture pick up. b. Dry material prior to molding. c. Utilize hopper dryers. 8. Dry-as-molded properties. Moisture condition parts to increase toughness. 47
Ultramid Nylon Troubleshooting Guide for Injection Molding Bubbles, Voids Possible Cause Suggested Remedy 1. Excessive internal shrinkage. a. Increase packing pressure. b. Increase injection forward time. c. Increase gate thickness. d. Minimize, or core out, heavy sections in part design. e. Increase feed, ensure cushion. f. Replace check valve if cushion cannot be held. 2. Melt temperature too high. a. Decrease melt temperature. b. Lower back pressure. c. Lower screw RPM. 3. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Utilize hopper dryers. d. Review percent of regrind. 4. Air entrapment. a. Add mold venting. b. Relocate gate. c. Reduce clamp pressure to allow parting line vents to work. 5. Condensation on mold surface. a. Wipe mold surface thoroughly with solvent. b. Increase mold temperature. Burn Marks Possible Cause Suggested Remedy 1. Melt temperature too high. a. Decrease melt temperature. b. Lower back pressure. c. Lower screw RPM. 2. Air entrapped in mold. a. Vent cavity at final point of fill. b. Decrease first stage pressure or injection speed. c. Relocate gate. d. Clean vents and/or enlarge vents. e. Reduce clamp pressure to allow parting line vents to work. 3. Injec tion rate too fas t. a. Dec reas e injec tion rate. b. Decrease first stage pressure. c. Decrease boost time. d. Enlarge gates. 4. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Utilize hopper dryers. 48
Ultramid Nylon Troubleshooting Guide for Injection Molding Cracking, Crazing Possible Cause Suggested Remedy 1. Packing excessive material into the mold. a. Decrease packing pressure. b. Decrease shot size. c. Increase transfer position (to lower injection peak pressure). d. Decrease injection time. 2. Non-uniform or too cold a a. Increase mold temperature. mold temperature. b. S upply uniform c ooling to the c avity. 3. Knockout system poorly designed. Redesign knockout system for balanced ejection forces. 4. Inadequate draft angles or Rework mold. excessive undercuts. Dimensional Variations Possible Cause Suggested Remedy 1 Non-uniform feeding of material. a. Adjust temperature profile for optimum feeding. b. Increase shot size to maintain uniform cushion. c. Replace check valve if cushion cannot be held. 2. Large variation in cylinder temperature Replace or calibrate controllers. due to inadequate or defective controllers. 3. Unbalanced runner system, resulting in a. Increase holding pressure to maximum. non-uniform cavity pressure. b. Increase injection rate. c. Balance/increase runner and gate sizes to provide uniform filling. 4. Insufficient packing of part. Increase injection forward time and/or pressure to ensure gate freeze off. 5. Regrind not uniformly mixed with virgin. a. Review regrind blending procedure. b. Decrease percentage of regrind. 6. Molding conditions varied from a. Check molding records to ensure duplication of previous run. process conditions. 7. Part distortion upon ejection. See Part Sticking in Mold, page 53 . 49
Ultramid Nylon Troubleshooting Guide for Injection Molding Discoloration, Contamination Possible Cause Suggested Remedy 1. Material overheated in injection cylinder. a. Decrease melt temperature. b. Decrease overall cycle. c. Residence time in cylinder excessive for shot size – use smaller barrel. d. Decrease nozzle temperature. e. Decrease screw RPM. f. Decrease back pressure. g. Check calibration of cylinder controllers. h. Check barrel and nozzle heater bands and thermocouples. 2. Burned material hanging up in cylinder, a. Purge injection cylinder. nozzle (black specks), or check ring. b. Remove and clean nozzle. c. Remove and inspect non-return valve for wear. d. Inspect barrel for cracks or gouges. e. Decrease injection rate. 3. Material oxidized by drying at too high Reduce drying temperature to 180 F (82 o C). o temperature. 4. Contamination by foreign material. a. Keep hopper covered. b. Review material handling procedures for virgin and regrind. c. Purge injection cylinder. Excessive Cycle Time Possible Cause Suggested Remedy 1. Poor mold cooling design. a. Increase mold cooling in hot spots. b. Ensure fast turbulent flow of water through cooling channels. 2. Platen speeds excessively slow. a. Adjust clamp speeds to safely open and close quickly. b. Low pressure close time excessive, adjust clamp positions and pressures to safely and efficiently open and close mold. 3. Melt temperature too high. Decrease melt temperature. 4. Mold temperature too high. Decrease mold temperature. 5. Screw recovery time excessive. a. Check machine throat and hopper for blockage or bridging. b. Check for worn screw and barrel, especially in the feed zone. 50
Ultramid Nylon Troubleshooting Guide for Injection Molding Flashing Possible Cause Suggested Remedy 1. Material too hot. a. Dec reas e melt temperature. b. Decrease mold temperature. c. Lengthen cycle time. 2. Injection pressure too high. a. Decrease injection pressure. b. Decrease boost time. c. Decrease injection rate. d. Increase transfer position (to lower injection peak pressure). 3. Excessive packing of material Decrease packing pressure. in cavities. 4. Projected area too large for available Use larger tonnage machine. clamping force. 5. Mold clamping pressure not a. Increase clamping pressure. properly adjus ted. b. C hec k mold parting line for obs truc tion. c. Check platen parallelism. 6. Uneven or poor parting line and a. Remove mold, carefully inspect and repair parting lines, cavities and cores which do not have positive shut off. b. Add support for mold cores and cavities. 7. Non-uniform cavity pressure due to a. Balance/increase runner and gate sizes to obtain unbalanc ed filling. uniform filling. b. Properly balance cavity layout for maintaining uniform cavity pressure. Flow Lines Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Gate size too restrictive, causing jetting. a. Increase gate size. b. Decrease injection rate. 4. Material impinging on cavity wall or core. a. Decrease injection rate. b. Relocate gate. 5. Non-uniform wall thickness. Redesign part to obtain a more uniform wall thickness to provide for optimum filling. 6. Insufficient mold venting. Improve mold venting. 51
Ultramid Nylon Troubleshooting Guide for Injection Molding Lamination Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Injection rate too low. a. Increase first stage pressure. b. Increase boost time. 4. Holding pressure too low. Increase packing pressure. 5. G ate s ize too s mall. Inc reas e gate s ize for improved filling. 6. C ontamination. S ee Discoloration, Contamination, page 50 . Nozzle Drooling Possible Cause Suggested Remedy 1. Nozzle temperature too hot. a. Reduce nozzle temperature. b. Decrease melt temperature. c. Reduce back pressure. d. Increase screw decompression. e. Use enough screw RPM’s to allow screw to recover using approximately 90% of the cooling time. 2. Wrong nozzle design. Use reverse taper nozzle. 3. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Use hopper dryers. 52
Ultramid Nylon Troubleshooting Guide for Injection Molding Part Sticking in Mold Possible Cause Suggested Remedy 1. Overpacking material in mold. a. Decrease first stage injection pressure. b. Decrease boost time. c. Decrease injection forward time. d. Decrease packing pressure. e. Increase injection transfer position (to lower injection peak pressure). 2. Improper finish on mold. Draw polish mold to proper finish. 3. Insufficient draft on cavities and sprue. Polish and provide maximum allowable draft. 4. Knockout system poorly designed. a. Redesign knockout system for balanced ejection forces. b. Review operation of knockout system, plates not opening in proper sequence. 5. Core shifting and cavity misalignment. a. Realign cavities and cores. b. Add interlocks to mold halves. 6. Undercuts in mold and possible a. Repair and polish. surface imperfections. b. If undercut is intentional, redesign or reduce. 7. Non-uniform cavity pressure in Redesign runners and gates for balanced filling of cavities. multi-cavity mold. 8. Molded parts too hot for ejection. a. Increase cooling time. b. Decrease melt temperature. c. Decrease mold temperature. 9. Molded parts sticking to stationary a. Redesign sprue puller. half of mold. b. Apply mold releas e. c. Increase nozzle temperature. d. If parts remain on wrong side of mold, undercut other side or try differential mold temperatures. 53
Ultramid Nylon Troubleshooting Guide for Injection Molding Short Shots Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Injection pressure too low. a. Increase first stage pressure. b. Increase boost time. c. Increase injection speed. 4. Ins uffic ient feed. a. Inc reas e s hot s ize to maintain a c ons tant c us hion. b. Inspect non-return valve for wear. 5. Insufficient injection forward time. a. Increase injection forward time. b. Increase injection rate. 6. Entrapped air causing resistance to fill. a. Provide proper venting. b. Increase number and size of vents. 7. Restricted flow of material to cavity. a. Increase gate size. b. Increase runner size. c. Use nozzle with larger orifice. 8. Unbalanced flow to cavity in a. Increase gate size. multi- c avity mold. b. R edes ign runner to provide balanc ed flow. Splay (Silver Streaking) Possible Cause Suggested Remedy 1. Excess moisture in material during processing. a. Review material handling to eliminate moisture pick up. b. Dry material prior to molding. c. Utilize hopper dryers. 2. Melt temperature too high . a. Decrease barrel temperature. b. Decrease nozzle temperature. 3. Excessive shear heat from injection. a. Decrease injection rate. b. Reduce screw RPM. c. Increase runner size and/or gates. d. Check for nozzle obstruction. 4. Air entrapment. a. R educ e s c rew dec ompres s ion. b. Improve mold venting. 5. Condensation and/or excessive lubricant a. Increase mold temperature. on mold s urfac e. b. C lean mold s urfac e with s olvent. c. Use mold release sparingly. 6. Moisture condensing in feed a. Decrease throat cooling. s ec tion of barrel. b. Inc reas e rear zone temperature s etting. 54
Ultramid Nylon Troubleshooting Guide for Injection Molding Sprue Sticking Possible Cause Suggested Remedy 1. Improper fit between nozzle and sprue bushing. Nozzle orifice should be smaller than sprue bushing orifice. 2. Insufficient taper on sprue bushing. Increase taper. 3. Rough surface of sprue bushing. Eliminate imperfections and draw polish surface. 4. Sprue puller design inadequate. a. Redesign sprue puller and increase undercut. b. Increase sprue diameter if too small for strength. c. Decrease sprue diameter if too large for cooling. 5. Overpacking material in sprue. a. Decrease packing pressure. b. Decrease injection forward time. c. Use machine sprue break. 6. Nozzle temperature too low to provide a. Increase nozzle temperature. c lean break. b. Us e revers e taper nozzle. 55
Ultramid Nylon Troubleshooting Guide for Injection Molding Surface Imperfections (Glass On Surface, Mineral Bloom) Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Insufficient packing pressure. Increase packing pressure. 4. Injection rate too slow. a. Increase first stage pressure. b. Increase boost time. c. Increase injection speed. 5. Insufficient material in mold. a. Increase shot size and maintain constant cushion. b. Inspect non-return valve for wear. c. Decrease injection transfer position (thereby increasing the peak pressure). 6. Water on mold surface. a. Increase mold temperature. b. Repair any water leaks. 7. Excessive lubricant on mold surface. a. Clean mold surface with solvent. b. Use mold release sparingly. 8. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Use hopper dryers. 9. Ins uffic ient venting. P rovide adequate vents . Warpage Possible Cause Suggested Remedy 1. Molded part ejected too hot. a. Decrease melt temperature. b. Decrease mold temperature. c. Increase cooling time. d. Cool part in warm water after ejection. e. Utilize shrink fixture. 2. Differential shrinkage due to a. Increase injection rate. non- uniform filling. b. Inc reas e pac king pres s ure. c. Balance gates and runners. d. Increase/decrease injection time. e. Increase runner and gate size. 3. Differential shrinkage due to non-uniform a. Provide increased cooling to thicker sections. wall thic knes s . b. Inc reas e c ooling time. c. Operate mold halves at different temperatures. d. Redesign part with uniform wall sections. 4. Knockout system poorly designed. Redesign knockout system for balanced ejection forces. 5. Melt temperature too low. Increase melt temperature to pack out part better. 6. Glass fiber orientation. Relocate gate. 56
Ultramid Nylon Troubleshooting Guide for Injection Molding Weld Lines (Knit Lines) Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Insufficient pressure at the weld. a. Increase first stage injection pressure. b. Increase boost time. c. Increase packing pressure. d. Increase pack time. e. Increase injection speed. 4. Entrapped air unable to escape from a. Increase or provide adequate vents at the weld area. mold fas t enough. b. Dec reas e injec tion rate. 5. Excessive lubricant on mold surface a. Clean mold surface with solvent. plugging vents . b. Us e mold releas e s paringly. 6. Distance from gate to weld line too far. a. Relocate or use multiple balanced gates. b. Cut overflow tab in mold to improve weld line strength. 7. Injection rate too slow. a. Increase injection speed. b. Increase first stage injection pressure. c. Increase boost time. DISCLAIMER: Although all statements and information in this publication are believed to be accurate and reliable, they are presented withou t guarantee or warranty of any kind, express or implied, and risks and liability for results obtained by use of the products or application of the suggestions described are assumed by the user. Statements or suggestions concerning possible use of the products are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe any patent. The user should not assume that toxicity data and safety measures are indicated or that other measures may not be required. 57
Processing Quality Checklist
IMPORTANT: WHILE THE DESCRIPTIONS, DESIGNS, DATA AND INFORMATION CONTAINED HEREIN ARE PRESENTED IN GOOD FAITH AND BELIEVED TO BE ACCURATE, IT IS PROVIDED FOR YOUR GUIDANCE ONLY. BECAUSE MANY FACTORS MAY AFFECT PROCESSING OR APPLICATION/USE, WE RECOMMEND THAT YOU MAKE TESTS TO DETERMINE THE SUITABILITY OF A PRODUCT FOR YOUR PARTICULAR PURPOSE PRIOR TO USE. NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE MADE REGARDING PRODUCTS DESCRIBED OR DESIGNS, DATA OR INFORMATION SET FORTH, OR THAT THE PRODUCTS, DESIGNS, DATA OR INFORMATION MAY BE USED WITHOUT INFRINGING THE INTELLECTUAL PROPERTY RIGHTS OF OTHERS. IN NO CASE SHALL THE DESCRIPTIONS, INFORMATION, DATA OR DESIGNS PROVIDED BE CONSIDERED A PART OF OUR TERMS AND CONDITIONS OF SALE. FURTHER, YOU EXPRESSLY UNDERSTAND AND AGREE THAT THE DESCRIPTIONS, DESIGNS, DATA, AND INFORMATION FURNISHED BY BASF HEREUNDER ARE GIVEN GRATIS AND BASF ASSUMES NO OBLIGATION OR LIABILITY FOR THE DESCRIPTION, DESIGNS, DATA AND INFORMATION GIVEN OR RESULTS OBTAINED, ALL SUCH BEING GIVEN AND ACCEPTED AT YOUR RISK. Ultramid®, Petra® and Ultratough® are registered trademarks of BASF Corporation www.plasticsportal.com/usa

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Displayanyfile

  • 2. English/Metric Conversion Chart To Convert To Multiply English System Metric System . English Value by... DISTANCE inches millimeters 25.38 feet meters 0.30478 MASS ounce (avdp) gram 28.3495 pound gram 453.5925 pound kilogram 0.4536 U.S. ton metric ton 0.9072 VOLUME inch3 centimeter 3 16.3871 inch3 liter 0.016387 fluid ounce centimeter3 29.5735 quart (liquid) decimeter 3 (liter) 0.9464 gallon (U.S.) decimeter 3 (liter) 3.7854 TEMPERATURE degree F degree C (°F- 32)/1.8 =°C PRESSURE psi bar 0.0689 psi kPa 6.8948 ksi MN/m2 6.8948 psi MPa 0.00689 ENERGY AND POWER in lbf Joules 0.113 ft lbf Joules 1.3558 kW metric horsepower 1.3596 U.S. horsepower kW 0.7457 Btu Joules 1055.1 Btu in/(hr ft2 °F) W/m °K 0.1442 VISCOSITY poise Pa s 0.1 BENDING MOMENT OR TORQUE ft lb Nm 1.356 DENSITY lb/in3 g/cm3 27.68 lb/ft3 kg/m3 16.0185 NOTCHED IZOD ft lb/in J/m 53.4
  • 3. Table of Contents Chapter Part/Page 1. Introduction General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Homopolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Impact Modified Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Reinforced Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Processing Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Personal Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Material Safety Data Sheets (MSDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. General Part Design Section Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Undercuts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Recommended Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Draft Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Standards & Practices of Plastics Molders . . . . . . . . . . . . . . . . . . . . . . 12 4. The Injection Molding Machine Machine Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw and Barrel Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Symptoms of Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Barrel Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Nozzle Tip Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Check Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Clamp Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Force and Cavity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Vented Barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5. Mold & Tooling Considerations Tool Steel Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Texturing and Surface Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Sprue Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Sprue Puller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Cold Slug Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Cold Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Hot Runner Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
  • 4. Chapter Page 5. Mold & Tooling Considerations (continued) Gate Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Gate Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 6. Auxiliary Equipment Dryer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Mold Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Granulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7. Processing Ultramid Nylon Processing Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Drying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Melt Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Hot Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Residence Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Mold Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Holding Pressure and Pack Pressure . . . . . . . . . . . . . . . . . . . . . . . . 42 Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Injection Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Decompression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Purging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Regrind. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Pre-Colored Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Processing Cadmium-Free vs. Cadmium Colors . . . . . . . . . . . . . . . 44 8. Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Brittleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Bubbles, Voids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Cracking, Crazing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Dimensional Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Discoloration, Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Excessive Cycle Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Flow Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Lamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Nozzle Drooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Part Sticking in Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Splay (Silver Streaking) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Sprue Sticking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Surface Imperfections (Glass On Surface, Mineral Bloom) . . . . . . . . 56 Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
  • 5. Chapter 1 Introduction General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Ultramid Homopolymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Impact Modified Ultramid Nylon. . . . . . . . . . . . . . . . . . . . . . . . . 2 Reinforced Ultramid Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
  • 6. Introduction Chapter 1: Introduction General Information Ultramid Homopolymers Ultramid resin is available as uniform pellets predried to a Ultramid homopolymers are used in a wide variety of very low moisture content. Depending upon the extrusion and injection molding applications. Major particular grade, it is available in 55 lb. (25 kg) bags, or attributes include strength, toughness, and excellent 1500 lb. (680 kg) corrugated boxes. Each of the two chemical and abrasion resistance. containers includes a moisture barrier liner to maintain a low moisture level in the Ultramid nylon. Open containers Standard Grades should be resealed to maintain low moisture levels. Most Standard products include 8200 a medium viscosity grades are available in heat stabilized (HS), black (BK- injection molding grade; 8202 , a low viscosity injection 102), and UV stabilized black (BK-106) formulations. molding grade; 8270, a modified, ultra high viscosity Standard and custom colors are also available upon grade for extrusion and blow molding applications; 5202, request. a low viscosity injection molding grade based on nylon 6,6. Ultramid Nylon Alpha Grades Alpha grades differ in crystalline structure compared to The majority of the Ultramid family is based on nylon standard Ultramid grades. This results in increased polyamide) 6. BASF is a fully integrated supplier of strength, stiffness, and heat distortion temperature nylon 6. This includes full responsibility for production of combined with faster set up time. Grades include feedstocks to the compounding, manufacturing, and 8202C , a low viscosity, highly crystalline injection distributing o hundreds of grades of resin. f molding grade; 8202CQ , a low viscosity, improved Ultramid nylon 6 is one of the most versatile and productivity injection molding grade; 8203C , an performance-proven engineering thermoplastics. Impact intermediate viscosity, highly crystalline tubing and cable modification of Ultramid nylon results in an extremely liner extrusion grade; and 5202CQ , a low viscosity, flexible and impact-resistant product, while reinforcement improved productivity injection molding grade based on produces high strength, stiffness, and dimensional nylon 6,6. stability. Rotational Molding Grades Another attribute of Ultramid nylon is ease of processability. Ultramid 8280 nylon and 8281 nylon are specifically tailored It is known for its wide processing window in both for rotational molding. 8280 exhibits excellent strength extrusion and injection molding processes and for its ability and toughness. 8281 is a plasticized rotomolding resin to achieve a resin-rich, uniform surface appearance, even that offers increased flexibility. with high levels of reinforcement. Impact Modified Ultramid Nylon The Ultramidproduct line also includes nylon 6, 6/6 for film extrusion products and nylon 6,6 for injection Impact modification of Ultramid nylon results in a series of molding products. polymers containing various levels of enhanced toughness and flexibility combined with excellent chemical and thermal resistance. Impact-modified injection molding grades include 8253, which exhibits improved dry-as-molded toughness over conventional nylon 6 while maintaining excellent strength and stiffness characteristics; 8255, which offers a high degree of flexibility combined with toughness; 8351, a high impact, faster cycling grade; and Ultratough Nylon BU50I, offering high impact strength and ductility to -40° C (-40° F). 2
  • 7. Introduction Reinforced Ultramid Nylon Fiberglass or a combination of fiberglass and mineral reinforcement enhances the performance characteristics of Ultramid nylon molding compounds. Fiberglass Reinforced Grades Fiberglass reinforcement improves Ultramid nylon’s strength, stiffness, dimensional stability, and performance at elevated temperatures. Glass reinforced grades include HMG10, 50% glass, high modulus; HMG13, 63% glass, high modulus; SEG7, 35% glass; 8230G, 6% glass reinforcement; 8231G, 14% glass; 8232G, 25% glass; 8233G, 33% glass; 8234G, 44% glass; 8235G, 50% glass; HPN 9233G, 33% glass TM reinforced, improved productivity; and 5233G, 33% fiberglass based on nylon 6,6. Fiberglass Reinforced, Impact Modified Grades Combining fiberglass reinforcement along with impact modification produces compounds that offer increased dry-as-molded impact while maintaining excellent strength and stiffness properties. Products include TG3S, 15% glass, impact modified; TG7S, 34% glass, impact modified; 8331G, 14% glass, impact modified; 8332G, 25% glass, impact modified; 8333G HI, 33% glass, high impact, improved productivity and surface appearance; 8334G, 40% glass reinforced, impact modified; and HPN 9333G, 33% glass reinforced, impact modified, improved productivity. Mineral Reinforced Grades Mineral reinforcement enhances strength and stiffness properties while maintaining typical chemical resistance associated with Ultramid nylon. Mineral reinforced products include 8260, 40% mineral, chrome plateable; 8360, 34% mineral; and 8362, 34% mineral, impact modified; and HPN 9362, 40% mineral reinforced, impact modified, improved productivity. Mineral/Glass Reinforced Grades Mineral and glass reinforcement leads to products with an excellent balance of mechanical properties combined with warpage resistance. Mineral/Glass reinforced grades include SEGM35 H1, 40% glass/mineral reinforced; 8262G, 20% mineral/glass reinforced; 8266G, 40% mineral/glass reinforced; and 8267G, 40% mineral/glass reinforced. 3
  • 8. Chapter 2 Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Processing Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Thermal Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Personal Protective Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 7 Material Safety Data Sheets (MSDS) . . . . . . . . . . . . . . . . . . . . . 7
  • 9. Health, Safety, and Environmental Considerations Chapter 2: Health, Safety, and Environmental Considerations for Processing Ultramid Nylon Safety is an important consideration during the processing Thermal Processing Hazards of any thermoplastic resin. While the molding of Ultramid resins is generally considered safe, failure to take Thermal processing of thermoplastic materials is always adequate precautions in the following areas may lead to accompanied by the release of fumes and vapors. At personal injury. recommended processing temperatures, these fumes and vapors will generally be low boiling volatiles. In the Housekeeping case of Ultramid products, the fumes will be principally caprolactam monomer. Caprolactam vapor can cause Slips and Falls irritation of the eyes, nose, throat, and skin at sufficiently Ultramid nylon resin comes in cylindrical-shaped pellets. high concentrations. Proper ventilation should be When spilled on a floor, they can be dangerous. To provided at all possible emission points on the injection avoid falls from pellet spills or leaks, sweep up or vacuum molding machine to minimize exposure of volatiles to material and place it in a container for possible reuse or equipment operators. disposal. Thermal Decomposition Material Handling The recommended processing temperatures for Ultramid Cuts resins have been optimized to provide excellent process- The product may be packaged in drums, bags or ability and performance characteristics. Normal gaylords. Gloves are recommended when handling processing temperatures may range from 450° F to 590° drums to avoid cuts during manual movements and when F (230° C to 310° C). Please reference Chapter 7: removing the ring seals, releasing the locking rings, and Processing Ultramid Nylon for further specific information. removing the drum lids. The rigid paper used in bags or Excessively high processing temperatures can lead to the corrugated construction of the gaylords may also cut thermal decomposition. Thermal breakdown may create the skin. Cutting tools should have a protected cutting a complex mixture of organic and inorganic compounds edge to guard against lacerations. (Please see section on which may be flammable, toxic, and/or irritating. The Personal Protective Equipment, page 7). components generated can vary depending on colorants, specific temperature, exposure time, and other Thermal Hazards environmental factors. Proper ventilation should be Burns provided at all possible emission points on the injection Due to the temperatures necessary to process nylon molding machine to minimize exposure of volatiles to resins, injection molding machine parts and equipment equipment operators. Injection molding machinery may be hot and cause burns on contact with the skin. In suppliers also provide purge guards containing limit addition, contact with molten resin from normal operation switches that prevent operation of the press while in the or unexpected occurrences may result in burns involving open position. This helps to minimize exposure to any any exposed areas of the body. Operators should wear volatiles emitted by the molten extrudate, in addition to personal protective equipment. Injection molding protecting the operator from burns from spattering machinery suppliers also provide purge guards which molten polymer. Under no circumstances help to protect the operator from burns from spattering should the protective circuitry provided on processing molten polymer. (Please see section on Personal equipment be altered to allow operation while guards are Protective Equipment, page 7). in the open position. 6
  • 10. Health, Safety, and Environmental Considerations Personal Protective Equipment Material Safety Data Sheets (MSDS) Proper personal protective equipment should be worn MSDS are supplied by BASF for all Ultramid products. depending upon conditions that exist in the molding The MSDS provide health, safety, and environmental facility. data specific to Ultramid nylon grades or resin families. The MSDS include information concerning first aid Eye and Face Protection measures, hazards information, precautions/procedures, Safety glasses containing side shields should be worn as personal protective equipment, physical and reactivity a minimum when working in a plastics processing facility. data, hazardous ingredients, and environmental data. A face shield should be considered for additional Also included on the MSDS is a Product Safety protection when purging or working near molten material. Department contact where additional information can be Contact lenses should not be worn when processing obtained. MSDS can be found on our website at materials for extended time periods since their permeable www.plasticsportal.com/usa structure may absorb vapors which can cause eye irritations. Hands, Arms, and Body Gloves are recommended when handling or opening drums to avoid abrasion hazards from sharp surfaces. When handling molten polymer or hot parts, insulated gloves should be worn. Arm protection should be considered for additional protection against hot surfaces, such as machine barrels and tooling, and when handling hot parts. Respiratory Protection In dusty conditions, a mechanical filter respirator should be worn. If exposed to thermal processing fumes or vapors in excess of permissible exposure levels, an organic vapor respirator is suggested. Respiratory protection for the conditions listed above should be approved by NIOSH. Foot Protection Safety shoes should be worn when working in areas where heavy objects are being moved, such as transporting or setting molds. 7
  • 11. Chapter 3 General Part Design Section Thickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Undercuts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Recommended Radii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Draft Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Ribs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Standards & Practices of Plastics Molders . . . . . . . . . . . . . . . 12
  • 12. ;; General Part Design ; ;; Chapter 3: General Part Design Section Thickness Undercuts Uniformity in wall thickness is critical when designing When necessary, undercuts producing 2% strain are parts to minimize warpage, distortion, internal stresses allowable for reinforced Ultramid nylon grades. If properly and cycle times. Figure 3A shows several examples of designed, undercuts producing up to 8% strain are proper design. When non-uniform section thickness is possible with unreinforced grades. However, wall unavoidable, gradual blending should be used between thickness, part design and mold temperature are factors which can influence ease of part ejection from the mold. ;; the sections as shown in Figure 3B. In general, using the ; thinnest wall allowable, based on the expected function Parts with undercuts should be thoroughly inspected of the part, will help to reduce cycle time and material after molding for unwanted damage or aesthetic flaws in costs. Typical wall thickness for Ultramid resin parts range the undercut area. from .040 inch (1mm) to .200 inch (5mm). Recommended Radii Sharp corners act as stress concentrators and often contribute to part failure. In addition, sharp corners prevent smooth flow when filling. For these reasons, good poor parts should be designed with generous radii and fillets ; wherever possible. A minimum radius of .020" (0.5mm) is recommended at all sharp corners and larger radii are generally beneficial when possible. However, making the ;; radius too large will cause a sink mark on the opposite good poor surface due to the greater mass of material. Figure 3C shows the relationship between stress concentration and fillet radius. As the stress concentration factor (K) increases, the part becomes more prone to failure. The preferred value of R/T is 0.6 for most parts designed with Ultramid resin. good poor Stress-Concentration Factor [K] P good 3.0 poor R 2.5 Figure 3A T 2.0 1.5 1.0 best 0 .2 .4 .6 .8 .10 .12 .14 R/T Ratio Figure 3C good poor Figure 3B 10
  • 13. General Part Design Draft Angles Tolerances For most parts molded from Ultramid resin, a draft angle Figure 3E shows the SPI tolerance standards for nylon of 1° per side is required for facilitating part ejection. resins, including Ultramid nylon. This is a general guide for However, draft angles as low as 0.5° (requires highly design, based on typical parts produced by several polished surfaces) and as high as 1.5° per side are not different molders and resin suppliers. The numbers uncommon depending on part design and complexity. shown should not be interpreted as final design In general, larger draft angles make it easier to eject the specifications for all applications, but rather as a part from the mold, especially parts with deep pockets, reference for nylon parts similar to the example shown, tall ribs, or heavy textures. molded under normal conditions. Parts with non- standard designs or complex geometry should be Ribs evaluated on an individual basis. Ribs are effective design features which add strength and Many factors must be considered when maintaining often facilitate flow during filling. However, proper design tolerances in molded parts, such as processing is important as ribs sometimes cause sink marks or conditions, mold/part design, and end-use environment. aesthetic irregularities. Ribs should only be used when In general, parts with many close tolerance requirements needed for stiffness and strength. In structural parts will be more difficult to produce consistently than parts where sink marks are of no concern, rib base thickness (t) with fewer or less critical requirements. can be between 75% - 85% of the adjoining wall thickness (T). For appearance parts, where sink marks Effect of Processing on Tolerances are objectionable, rib base thickness (t) should not Control of tolerances will be influenced by molding exceed 50% of the adjoining wall thickness (T) if the conditions. Since shrinkage can directly affect outside surface is textured and 30% if not textured. In dimensional change, it is important to provide adequate addition, ribs should include proper draft and a base pressure during the filling and packing stages. In radius of at least .020" (0.5mm) as shown in Figure 3D. addition, machine consistency, temperature control, and cycle time must be carefully maintained to prevent dimensional shift. Process conditions typically have more effect on the shrinkage of unreinforced and impact modified grades of Ultramid nylon than on reinforced grades. Effect of Mold Design on Tolerances The complexity of the mold has a direct influence on control of part tolerance. Family or multi-cavity molds with non-uniform runner systems and/or slides and cams Rib Design should be given special consideration since tolerances will be harder to maintain under such circumstances. Figure 3D Gates and runners must be large enough to provide good packing pressure and thereby minimize shrinkage. After many cycles, mold wear can also contribute to dimensional shift, especially with mineral and/or glass fiber reinforced grades. Proper tooling selection should be considered when high volume production is expected. (Please see Tooling Considerations, Chapter 5.) 11
  • 14. General Part Design Material Standards & Practices Polyamide (Nylon) of Plastics Molders (PA) Note: The Commercial values shown below represent common production tolerances at the most economical level. The Fine values represent closer tolerances that can be held but at a greater cost. Addition of reinforcements will alter both physical properties and dimensional stability. Please consult the manufacturer. Drawing Code A=Diameter (See note #1) B=Depth (See note #3) C=Height (See note #3) Comm. ± Fine ± 0.003 0.002 D=Bottom Wall (See note #3) 0.004 0.003 E= Side Wall (See note #4) 0.005 0.003 F=Hole Size 0.000 to 0.125 0.002 0.001 Diameter 0.126 to 0.250 0.003 0.002 (See note #1) 0.251 to 0.500 0.003 0.002 0.501 and over 0.005 0.003 G=Hole Size 0.000 to 0.250 0.004 0.002 Depth 0.251 to 0.500 0.004 0.003 Reference Notes (See note #5) 0.501 to 1.000 0.005 0.004 1. These tolerances do not include allowance for H=Corners, aging characteristics of material. Ribs, Fillets (See note #6) 0.021 0.013 2. Tolerances are based on 0.125" (3.175mm) wall section. Flatness 0.000 to 3.000 0.010 0.004 3. Parting line must be taken into consideration. (See note #4) 3.001 to 6.000 0.015 0.007 4. Part design should maintain a wall thickness as nearly constant as possible. Complete Thread Size Internal 1 2 uniformity in this dimension is sometimes impossible to achieve. Walls of non-uniform (Class) External 1 2 thickness should be gradually blended from Concentricity (See note #4)(F.I.M.) 0.005 0.003 thick to thin. 5. Care must be taken that the ratio of the depth Draft Allowance of a cored hole to its diameter does not reach per side 1.5° 0.5° a point that will result in excessive pin damage. Surface Finish (See note #7) 6. These values should be increased whenever Color Stability (See note #7) compatible with desired design and good molding techniques. 7. Customer-Molder understanding is necessary prior to tooling. Figure 3E Table reprinted from S.P.I.’s Standards & Practices of Plastics Molders. Guidelines For Molders and Their Customers. Material reproduced with the permission of S.P.I. 12
  • 15. Chapter 4 The Injection Molding Machine Machine Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Screw and Barrel Selection . . . . . . . . . . . . . . . . . . . . . . . 14 Screw Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Symptoms of Wear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Barrel Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Nozzle Tip Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Check Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Clamp Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Clamp Force and Cavity Pressure . . . . . . . . . . . . . . . . . . 19 Vented Barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
  • 16. The Injection Molding Machine Chapter 4: The Injection Molding Machine Machine Selection Screw and Barrel Selection Selecting an injection molding machine with proper Screw Design design is critical to molding a quality part and ensuring The screw performs the following functions in the economic success. injection molding process. 1. Conveys the material through the barrel. 2. Mixes the material to the proper molten state. 3. Compresses the material to maximum density. 4. Forces the material into the mold. Adjustments to the injection process often involve the screw to some degree. The screw, when performing its function, provides important contributions to the overall process. Below are several process parameters that are affected by screw design. Figure 4A 1. Material melting profile 2. Melt temperature Below are four important molding machine points to 3. Material mixing consider when molding Ultramid nylon. These issues are 4. Shearing of the resin discussed in detail in this chapter. Therefore, it is important to be aware of the type of screw • Proper Screw and Barrel Selection that is being used for each application. As mentioned • Proper Nozzle Tip Type above, in most cases Ultramid products can be processed • Condition and Type of Check Valve with general purpose screws that are supplied by the • Clamp Requirements machine manufacturer. However, when molding Ultramid products for extended periods of time in a production environment, specific barrel and screw designs are recommended for maximum machine wear resistance and proper material plastication. Depending on the level of reinforcement in the material, different barrel and screw combinations are recommended by BASF. Refer to Figure 4B for recommended screw and barrel composition. Ultramid Wear Screw Barrel Base Material Root Material Type Environment Flight O.D. Liner Homopolymers and ANSI 4140 or Standard Nickel alloy Chrome plated Bimetallic A unfilled polymers Nitrided steel Filled material Tungsten carbide Abrasive Nitrided steel Nitrided steel Bimetallic B < 20% loading + Nickel alloy Highly filled material Highly Tungsten carbide Tungsten carbide Bimetallic screw Bimetallic B >20% loading Abrasive composites composites Bimetallic A Chromium-modified boron-iron alloy containing 5 to 7% nickel Bimetallic B Tungsten Carbide Composite Figure 4B. Barrel and Screw Recommendations for Ultramid Products. 14
  • 17. The Injection Molding Machine Screw design is critical to ensure that proper melt quality Symptoms of Wear is achieved. The two critical parameters to be aware of when moldingUltramid nylon products are the L/D ratio There are several symptoms of cylinder, screw, and and the compression ratio. These are defined in Figure valve wear which can be observed in the molding 4C and shown in Figure 4D. process. 1. Significant amount of screw rotation during injection indicates a worn barrel and/or check valve. This allows a backflow of melt over the ring, causing the screw flights to counter rotate. 2. Inability of screw to hold a cushion usually indicates a worn cylinder or valve. Figure 4C 3. Excessive recovery time required. Shank 4. Defective, streaked, splayed, or non-uniform parts Length Flight Length L due to poor melt quality resulting from worn Df Dm components. 5. Difficulty in achieving consistent color change from D plastic hanging up in worn areas of cylinders and Feed Transition Metering Check screws. Section Section Section Valve 60% 20% 20% 6. Front and center barrel heats may override settings. Typical Screw Configuration 7. Inconsistent shot size. Figure 4D The recommended L/D ratio and compression ratio for molding Ultramid nylon are listed in Figure 4E. When possible, it is recommended that the minimum L/D be 20:1. This will ensure proper melt dispersion. Ideal Ultramid Nylon Compression Material Type L/D Ratio Unreinforced min. 20:1 3:1 homopolymers Reinforced min. 20:1 2.5:1 material Figure 4E 15
  • 18. The Injection Molding Machine Barrel Sizing When choosing a press in which to run a mold, it is important to check the shot size as a percentage of the total barrel capacity. Most barrels are rated in ounces of general-purpose styrene (GPPS). To know the shot capacity for any material other than GPPS, the GPPS ounce rating must be converted to the density of the other material. For Ultramid resins, one must insert the specific gravity (S.G. – a measure of density) of the Ultramid resin grade into the formula shown in Figure 4F. The specific gravity is easily obtained from the data sheet for the given Ultramid nylon grade. Barrel Size S.G. Ultramid Barrel Size X = (oz GPPS) S.G. GPPS (oz Ultramid) Figure 4F For example, if you have a molding machine with a 64-ounce barrel and you want to know the barrel capacity using Ultramid 8233 nylon, the barrel capacity would be calculated as follows: 64 1.38 83.2 X = (oz GPPS) 1.06 (oz Ultramid) Figure 4G The total shot weight, in ounces (all parts, including runners), is then divided by the Ultramid nylon ounces found in figure 4G. This will yield the percentage of shot size. When injection molding Ultramid products, it is recommended that the shot size not exceed 75% of barrel capacity. Shots larger than 75% may not allow the material to thoroughly melt and mix. On the other hand, a shot size of less than 30% of the barrel capacity is not recommended. This may lead to extended material residence time in the barrel which can, in turn, lead to material degradation, part brittleness and discoloration. This is especially true in products using cadmium-free pigment systems. On occasions when a mold is already being run in a press, this ratio can be observed by comparing the linear shot size being used to the maximum shot size available and calculating the percent comparison.
  • 19. The Injection Molding Machine Nozzle Tip Type 1. Lack of ability to maintain a cushion, resulting in forward screw slippage. Reverse taper nylon tip nozzles are recommended when moldingUltramidproducts. The reverse taper will 2. Inconsistent shot size. minimize material drool and stringing which can be encountered when molding crystalline resins. The 3. Dimensional inconsistency in parts. reverse taper design is suggested when molding unreinforced nylon, and may be used with reinforced 4. Sink marks due to lack of pack pressure. grades. However, nozzle bore diameters are recommended to be approximately 25% larger for 5. Surface imperfections from splay, whitening, or reinforced Ultramidproducts than for unreinforced Ultramid mineral bloom. nylon due to the higher material viscosities encountered. Typically, general purpose nozzles are recommended 6. Potential to degrade material. when using reinforced grades. Temperature control on the nozzle should be controlled separately from other 7. Screw rotation upon injection. barrel zones. Extended nozzles may require two or more zones of control. Reference Chapter 7: Processing 8. Possible override of barrel temperature settings. Ultramid Nylon for proper barrel temperature settings. Below are acceptable types of check ring design that have Below are examples of a reverse taper nozzle design. been used successfully when processing Ultramid resin. Figure 4H shows a one-piece nozzle. Figure 4I shows a removable nozzle tip that may be used on general purpose nozzle bodies. For ease of sprue removal, attempt where possible to design the sprue bushing diameter 0.005"–0.030" (.125mm– .75mm) larger than the nozzle tip orifice diameter. Tip Seat Check Ring Standard Valve Figure 4J Figure 4H Tip Check Ring Seat Free-Flow Valve Figure 4K Figure 4I Retainer/Tip Check Valve Wrench BASF recommends that the non-return check valve be of Flats Rear the “Free-Flowing” ring design type. This design, while Front Seal Check Seat ensuring a consistent shot size, tends to wear the best Ring while running materials containing higher filler content. Four-Piece Valve Maintaining the check valve in a proper working condition is critical to ensuring quality and consistent moldings. Figure 4L There are several issues that may result if the check valve is not functioning properly. 17
  • 20. The Injection Molding Machine Clamp Requirements Clamp Sizing It is important to have adequate clamp force to maintain a fully closed tool during the injection process. High injection pressure, which is often required to fill a cavity, must be offset by pressure exerted by the clamp on the parting line of the tool. If sufficient clamp pressure is not present, the following may result: 1. Flash at parting line. 2. Peened over parting line resulting from repeated flash. 3. Inability to mold a part that is fully packed out. Often, larger machines are equipped with proportionally Toggle Clamp sized injection barrels and clamping systems. However, injection molding machines can be equipped with Figure 4N oversized platens. This will allow larger molds with a relatively small shot size to be processed in a smaller, more economical molding machine. Traditional clamping systems for injection molding machines fall into two main categories. These include the following types of clamps: 1. Hydraulic Clamp 2. Toggle Clamp The two main clamping mechanisms and the advantages and limitations of each are shown in Figures 4M and 4N, respectively. Hydraulic Clamp Figure 4M 18
  • 21. The Injection Molding Machine Clamp Style Advantages Limitations Hydraulic Fast mold set up. Requires large volume of hydraulic oil. Easily read clamp pressure. Energy Inefficient. Low maintenance. Must overcompensate due to compressibility of oil. Not Low platen deflection. floorspace efficient. Force concentrated at center of platen. Toggle Less expensive. Requires more maintenance. Fast clamp motion. Clamping force may not be concentrated at center of platen. Energy efficient. Difficult to adjust. Auto decelerated clamping. Figure 4P Clamp Force and Cavity Pressure It is important to verify that the clamp pressure of the molding machine is capable of maintaining a tightly closed mold during the injection process. In other words, the total clamp force exerted must exceed the opposing total force generated during injection. Since the clamping force is usually known, it is important to determine what the injection pressure exerted in the cavity of the tool may be and multiplying this by the projected area of the part and runner. The same equation may also be used to determine if clamp force is sufficient. This is a function of two components; the projected area parallel with the line of draw in the tool and the type of material used to mold the part. The projected area may be calculated by measuring the part. Below is a table of cavity pressure estimates for Ultramid products using the equation provided. The value obtained is the minimum value recommended for clamp tonnage in the injection molding machine. Ultramid Nylon Type Cavity Pressure Estimate Unreinforced Polymers 2 – 3 tons/in2 Reinforced Materials 3 – 5 tons/in2 Minimum Part Cavity Clamp Force (tons) = Projected (in ) X Area 2 Pressure (tons/in2) Estimate Required (measured) (see above) Figure 4Q 19
  • 22. The Injection Molding Machine Vented Barrels Vented barrels are commonly used as a method of If a vented barrel is selected, BASF recommends the use removing gases (mainly moisture from hygroscopic of a longer screw. Recommended L/D ratio for this materials). The basic concept involves melting the application ranges from 26:1 to 32:1. The longer screw material through the first transition and metering section will facilitate producing a homogeneous melt. In addition, of the screw and then depositing the material into a a hood placed above the vent is recommended to decompression zone. At this point, most of the moisture remove the volatiles from the molding facility. in the material is released from the barrel through a vent. The resin is then processed through a second transition and metering section prior to passing through the check ring assembly. Below is a sketch of a typical vented barrel configuration. Material Hopper Hood Vent Non-return valve 2nd 2nd Decompression 1st 1st Feed Metering Transition or volatile Metering Transition section section section zone section section Typical Vented Barrel Configuration Figure 4R Many molders prefer vented barrels when processing Ultramid products as a way of removing the moisture from the material. However, in cases where the material Temperature Control contains a very high level of moisture, the vented barrel process is not capable of removing all of the volatiles. Heaters surrounding the barrel heat the material in the Below are advantages and disadvantages of using a screw channel by means of electricity, and in some vented barrel. instances hot oil or steam. In addition to this conducted heat, it is important to note that the material is also Advantages subjected to shear heat developed by the mechanical 1. Possibly eliminate pre-drying of the material. working of the material in the barrel by the screw. 2. Assists in reducing gas entrapment in the tool cavity. 3. Possibly avoid the cost of drying equipment for most A minimum of three heater control zones for the barrel Ultramid products, but may require a starve feeder. corresponding to the three functional zones of the screw 4. Easier and quicker material changes. is recommended. However, in most cases additional heater zones are likely when using a larger barrel. Disadvantages Thermocouples are often used and recommended as a 1. Potentially greater variation in part quality due to temperature feedback to the controller. Maintaining inconsistent levels of moisture in the material. accurate temperature control together with a feedback 2. Risk of partially clogged vent ports resulting in poor system will assist in maximum processing potential. part quality. Such a feedback system has also been used in data 3. Vented barrels may result in longer cycle times and recording for statistical process control purposes. inability to operate successfully at full injection stroke. 4. Longer residence time in barrel possibly leading to resin degradation in smaller shot sizes. 20
  • 23. Chapter 5 Mold & Tooling Considerations Tool Steel Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Texturing and Surface Finish . . . . . . . . . . . . . . . . . . . . . . 22 Sprue Bushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Sprue Puller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Cold Slug Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Cold Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Hot Runner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Gate Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Gate Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Gate Location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
  • 24. Mold & Tooling Considerations Chapter 5: Mold & Tooling Considerations Tool Steel Materials Below is a table of information regarding more commonly used textures and the recommended draft angle. The careful selection of the tool steel for the construction of an injection mold designed for Ultramid resins is important to ensure the long-term durability of the tool. TEXTURING: Draft Angle Requirements Many of the Ultramid materials contain high levels of filler Grain Type: Grain Depth: Min. Draft Angle: reinforcement which tend to wear on the surface of the inch (mm) tool. High wear is most effectively countered with high Turf 0.004" (0.0875) 1 + 6 = 7 surface hardness. Selecting the right tool steel can 0.003" (0.075) 1 + 4.5 = 5.5 increase the useful service life of the tool as well as 0.002" (0.05) 1 + 3 = 4 greatly improve the maintenance of any texturing or Naples 0.0033" (0.083) 1 + 5 = 6 graining of the mold surface. The following tool steels are 0.0026" (0.067) 1 + 4 = 5 recommended when constructing cavity and core 0.002" (0.05) 1 + 3 = 4 sections. Figure 5B Typical Recommended Hardness AISI-SAE as In addition (as shown in figure 5C), where possible Steel Tool Steel Finished Material Designation Characteristics (Rockwell C) maintain an area around the parting line perimeter of P20 Medium alloy mold steel 30 – 36 Rc .010" (0.25mm) without the textured pattern. This will Unfilled protect the shut off region at the parting line. Polymers ------------------------------------------------------------------------------------- Reinforced S7 Shock resisting tool steel 54 - 56 Rc 0.010" (.25mm) Materials H13 Hot work tool steel (Cr based)50 - 52 Rc 420 Stainless steel 50 - 52 Rc Figure 5A Texture For increased wear resistance, the tools may be pattern hardened, plated, or surface treated. If the tool is to be grained and surface treated to improve Cavity block wear resistance, it is recommended that any surface or hardness treatment be performed after the texture Typical Textured Cavity process. Figure 5C Texturing and Surface Finish Ultramid products, when molded in tooling containing a Below are several suggestions for tool design when textured, grained, or polished surface, will reproduce the specifying a texture or grain. surface of the tool. All of the tool steels that are recommended for use with Ultramid products can be 1. Prior to texturing, heat treating the tool is chemically etched or textured. However, prior to recommended. texturing, the mold should be heat treated. This will result 2. To ensure a consistent texture, the depth of the heat in a finer grain structure of the steel which will result in a treat into the steel should exceed that of the texture. smoother surface to etch into. Typical texture depths range between .0004" (0.01mm) and .005" (.125mm). 3. In order to ensure proper release of the part from textured side walls, do not exceed a depth of etching To ensure ease of part ejection and reduce the chance of .001 inches (.025mm) per 1.5° draft. for streaks and scuff marks, the following rule is recommended for incorporating draft into part walls 4. Texturing of the core half of the mold is not containing a texture. recommended based on potential part release problems. 1° draft + 1.5° draft for each 0.001" (0.025mm) grain depth 22
  • 25. Mold & Tooling Considerations Sprue Bushing The sprue bushing is the material entry port into the The figure below presents recommendations for sprue mold. The injection molding machine nozzle interfaces design. with the sprue bushing. For ease of part and runner system ejection from the tool, a minimum taper of 1.5°–3.5° is recommended over the length of the sprue bushing. It is also recommended that the sprue be polished in the draw direction. When molding Ultramid products, it is also suggested that the minimum diameter of the opening of the sprue bushing at the nozzle interface be at least 0.118" (3.0mm). For best results, ensure that the machine nozzle orifice diameter be less than the sprue bushing inner diameter by .005" – .030" (.125mm – .75mm). This condition will ensure that a smooth transition occurs as the material enters the tool, thereby not creating a shear condition or a pressure drop which can lead to improper packing of the part and surface appearance problems. The sprue diameter at the intersection of the primary Tmax = Maximum runner thickness runner should be at least equal to or greater than the Dia. A = Diameter of opening at end of diameter or depth of the runner. machine nozzle Dia. B = Diameter of sprue at machine The overall dimensions of the sprue depend primarily on the nozzle interface dimensions of the component to be molded and especially Dia. C = Diameter of sprue bushing at its wall thickness. Following are general guidelines to be part intersection considered. L = Overall length of sprue A. The sprue must not freeze before any part cross Figure 5D section in order to permit sufficient transmission of holding pressure. It is important that the sprue bushing bore be properly B. The sprue should demold easily and consistently. draw polished for ease of demolding and ensuring that the part will run on an automatic cycle consistently C. It is very important that the radius on the machine without the sprue sticking. Grinding and polishing in a nozzle match that of the sprue bushing. pattern perpendicular to the direction of ejection results in undercuts, which may detrimentally affect the ejection of the sprue. 23
  • 26. Mold & Tooling Considerations Sprue Puller Typically, the sprue and the molded part are removed from the cavity at the same time, with both remaining on the moveable (or core) half of the mold. In multi-cavity molds, where a cold runner system is employed, a sprue puller on the moveable half of the mold is recommended. This will ensure that the sprue remains on the moveable half of the tool when the mold opens. A sprue puller is designed with an intentional undercut of various types depending on design, as shown in figures 5E through 5H. The reverse taper sprue puller is recommended, as it typically functions best and will also act as a cold slug Reverse Taper Sprue Puller Design (Best) well. Figure 5E “Z Puller” Sprue Design (Good) Figure 5F Undercut Ring Sprue Puller Design (Not Recommended) Figure 5G Ball Sprue Puller Design (Not Recommended) Figure 5H 24
  • 27. Mold & Tooling Considerations Cold Slug Well Use of cold slug wells is always recommended in cold runner systems. A cold well is designed to catch any material in the tip of the machine nozzle that may have cooled below the melting point and begun to solidify. If injected into the part, this cold slug can lead to surface imperfections, such as jetting and gate blush, and also result in a potentially weakened part. Examples of typical cold slug well placement and design are included in Figures 5I and 5J. Figure 5I Figure 5J 25
  • 28. Mold & Tooling Considerations Runner Systems The runner design is a very important phase of tooling design. There are several objectives which the runner must perform to ensure the quality requirements of most parts. Both cold runner and hot runner manifold systems can be used when molding Ultramid products. Insulated runners are NOT recommended. Suggested criteria for runner design are listed below: Full Round Modified Trapezoid Runner Trapezoid 1. Minimize restrictions to flow in the runner system, such as inconsistent cross section. Da = Tmax + 0.060” Wb = 1.25 Db B = 5° to 10° (1.5mm) Db = Tmax + 0.060” Wc = 1.25 Dc 2. Design for ease of part ejection. (1.5mm) Dc = Tmax + 0.060” (1.5mm) 3. Overall length should be as short as possible to reduce losses in material pressure and temperature Tmax = Maximum Cross Section of Part and excessive regrind generation. Recommended Runner Designs 4. Make runner cross section large enough whereby runner freeze-off time exceeds that of the gate. This Figure 5K ensures that proper hold pressure is applied. 5. The runner system should not be the limiting factor when reducing cycle time. 6. Minimize rate of runner weight to part weight without conflicting with other guidelines. Box Section Half Round Unfavorable Runner Designs Figure 5L Runner Style Advantages Disadvantages Full Round 1. Smallest surface to cross section ratio. Matching into cavity/core difficult. 2. Slowest cooling rate. 3. Low heat and frictional loss. 4. Center of channel freezes last; maintains hold pressure. Modified 1. Easier to machine; usually in one half of More heat loss and scrap compared Trapezoid tool only. to full round. 2. Offers similar advantages of full round. Trapezoid Easy to machine. More heat loss than modified trapezoid. Box Section Easy to machine. 1. Reduced cross section efficiency. 2. Reduced ability to transfer pressure. 3. Difficult to eject. Half Round Easy to machine. 1. Smallest cross-sectional area. 2. Most inefficient runner design. 3. Poor pressure transmission into cavity. 4. Generates more regrind. Figure 5M 26
  • 29. Mold & Tooling Considerations Cold Runner Design Hot Runner Design The full round runner is recommended. This type allows Both hot runner and cold runner systems can be utilized for the most efficient material flow and tends to induce when molding Ultramid products. When using a hot the least chilling effect on the material. Trapezoid and runner system, the resin is injected from the machine modified trapezoid runners are also feasible. However, barrel into a heated manifold network within the tool. resin flow to the part is less efficient with these designs. An externally heated hot manifold system is recommended They also tend to induce more of a chilling effect on the for Ultramid resins. This manifold commonly directs the material in the runner and generate more regrind. The material through a series of heated channels to the half round runner is not suggested because it does not location of the gate in order to fill out the part. provide for optimum flow and it causes the greatest chilling effect on the resin. If the material in the runner freezes prematurely, the material in the cavity will not be adequately packed, which may lead to excessive shrinkage or other problems. In addition, to ensure part to part consistency, the runner length from the sprue to each cavity should be of the same diameter and length. By balancing the cavities in this fashion, you will ensure that each cavity receives equal flow and pressure simultaneously. The table below shows suggested runner diameters and corresponding runner lengths and part thicknesses. Primary Maximum Maximum Runner Diameter Length Part Thickness Hot Runner and Nozzle System 0.125" – 0.187" 6.0" 0.187" Figure 5N (3.18mm – 4.75mm) (152mm) (4.75mm) Suggestions for designing hot runner systems for 0.25" – 0.312" 12.0" 0.50" optimum performance: (6.35mm – 7.94mm) (304.8mm) (12.7mm) 1. When machining the melt passage in the manifold, 0.375" 15.0" 0.75" take care not to create any dead spots where material (9.53mm) (381mm) (19.05mm) may hang up. Over time, this material may degrade and contaminate the material flowing through the Table 1A system. 2. Placement of heaters in the manifold design is critical to ensuring uniform heat transfer in the melt, thereby avoiding a cold spot in the system which may lead to freeze-off or uneven fill patterns. 3. Reduce contact areas between the hot runner manifold system and the tool steel. Heat transfer to the mold from the manifold should be minimized. 4. Where possible, attempt to locate cooling lines away from the manifold system. This can also lead to undesirable heat transfer out of the manifold. 5. The use of a temperature insulator is recommended between the mold base and the machine platens to reduce heat loss (especially on the stationary half). 6. To eliminate the chance for electrical interference, which may lead to false thermocouple readings, try to locate the heater wire leads away from the thermocouple wires. 7. Proper water cooling around the gate orifice is key to control. Also critical is a separate zone of temperature control for the gate area of the hot manifold tip. 27
  • 30. Mold & Tooling Considerations Gate Design The gate connects the part to the runner. It is usually the smallest cross section in the entire system. Designing the gating concept for a part is highly dependent on both tool design and part geometry. Often, the most desirable gating scenario is not feasible due to tooling or part design limitations. Equally important to molding a successful part is the location of the gate on this part. As a guide, the following gating configurations are presented: Figure 5Q Sub gating, Figure 5Q, can be designed to provide automatic degating of the part from the runner system during ejection. Sub gate size is highly dependent on both part size and tooling limitations. Each application should be thoroughly reviewed. Figure 5P Tab or film gating, Figure 5P, is often used where flatness is critical or in large surface areas where warpage may be a concern. Due to the nature of this type of gate, a post molding operation is typically required to properly remove the gate vestige. Figure 5R 28
  • 31. Mold & Tooling Considerations The fan gate or the edge gate, shown in Figures 5R and 5S, is often used to feed flat, thin sections which will tend to allow the material to flow across the cavity in a uniform fashion. It also has proven successful in reducing warpage. The gate cross-sectional area should always be less than the cross-sectional area of the runner. The edge gate is the most common gate type used and generally presents a good compromise between ease of part filling and gate removal. Figure 5S The diaphragm gate, shown in Figure 5T, is used when molding cylindrical parts requiring a high level of concentricity and weld-line strength. However, due to the nature of this type of gate, a post mold degating operation is typically required. Figure 5U Figure 5T Cashew gating can be highly effective when using more flexible materials. Due to the required degree of bending of the runner, as shown in sketches 3 and 4 of Figure 5U, filled or stiffer materials are not recommended for use with this type of gate as they often break during ejection. This could lead to broken ---pieces of plastic becoming lodged in the tool, plugging the gate on the next shot. Therefore, it is recommended that only unfilled materials be used with this type of gating. 29
  • 32. Mold & Tooling Considerations Gate Sizing The placement and quantity of gates required will have an effect on the overall flow length and orientation of the Figure 5V shows the recommended gate thicknesses for material. Typically, the maximum flow length from each both filled and unfilled grades of Ultramid resins for typical gate for Ultramid nylon in an injection mold is 15 inches part thickness cross sections. These values can be (381mm). This value is highly dependent on runner applied when using all types of gates. diameter, runner length, part geometry, and part thickness. Recommended Gate Thicknesses The following suggestions may be used when proposing Typical Unfilled Filled gating location concepts for Ultramid products: Part Thickness Ultramid Nylon Ultramid Nylon Up to 0.060" 0.040" 0.040" – 0.060" 1. Direct incoming flow against the cavity wall or core to (1.5mm) (1.0mm) (1.0 – 1.5mm) minimize gate blush and jetting. Up to 0.125" 0.060" – 0.090" 0.060" – 0.125" 2. Avoid gating that will cause melt fronts to converge (3.2mm) (1.5 – 2.3mm) (1.5 – 3.2mm) such that air is entrapped. Where possible, attempt to Up to 0.187" 0.090" - 0.125" 0.125" – 0.187" direct flow fronts and air toward vents. (4.7mm) (2.3 – 3.2mm) (3.2 – 4.7mm) 3. If possible, position the gate location at the thickest Up to 0.250" 0.125" – 0.187" 0.187" – 0.250" (low pressure) section of the part. Always try to flow (6.4mm) (3.2 – 4.7mm) (4.7 – 6.4mm) from thick to thin sections. Figure 5V 4. Select gate location to obtain the best strength relative to loading. Tensile and impact strength are highest in If the gate is to be enlarged for increased material flow direction of flow, especially with filled or reinforced and pressure transfer, focus on increasing gate Ultramid nylon. thickness rather than the width. Keeping the gate to a square (or round) cross section will be the most efficient. 5. The gate should be positioned away from any area of the part that will be subject to impact or bending Gate Location stress. The gate area tends to contain high residual stresses from the filling process may become a Gate location is critical because it ultimately determines likely site for fracture initiation. the direction of the material flow within the cavity. In many cases, this has an effect on the following factors: 6. Minimize weld lines especially in impact or highly • Shrinkage stressed areas. Locate weld lines to thicker areas on • Physical properties the part. • Distortion or warpage • Part appearance 7. In multiple cavity tooling applications, it is imperative that each gate among the various cavities be of the The above factors are a result of the orientation of the same size (diameter, thickness, etc.). This will ensure molecular structure of the material or any fillers that equal pressure and flow to each cavity. may be present. Note that: 8. If possible, locate the gate in an inconspicuous area of 1. The amount of orientation is higher in thin walled the part where finishing will not be required. moldings. 2. Higher strength and impact resistance values are observed in the direction of flow while sections in the perpendicular direction may exhibit reduced toughness. Therefore, prior to designing the injection mold and gate location(s), the mode of stress loading that the part will experience should be determined. 30
  • 33. Mold & Tooling Considerations Venting During the filling of the cavity with Ultramid resins, the melt Suggested concepts which may be used for has to displace the air which is contained in the cavity. If incorporating vents: there is nowhere for this air to go, it may compress, forming a pressure head that will resist the flow of plastic. 1. Parting line vents. As the air compresses, it will also heat. In some cases 2. Ejector pins (flats ground on pins). the air can reach temperatures that exceed the ignition temperature of the plastic and volatiles that are present. 3. Add venting pins. This results in a burn line where the trapped air contacts the plastic, which can produce an undesirable charred 4. Incorporating inserts at sections that trap air. blemish on the surface of the part and may even oxidize 5. Add an overflow well. and erode the mold. 6. Sintered metal inserts. Part geometry, position in the mold, and gating location all have a big impact on the venting. Figure 5W shows a sketch of a typical parting line vent and the corresponding dimensions are shown in Figure 5X. Suggestions for locating and designing vents into tools designed for Ultramid nylon: 1. Tooling inserts may be incorporated at ribs or part sections that tend to trap air. The mere existence of the insert may alleviate a trapped air problem. 2. When molding thin walled parts <.125" ( 3.0mm) with a high injection rate, the cavity should be vented close to the gate as well as at the extremity of flow. Air removal from the tool reduces the chance of a L = Land of Vent significant pressure build-up. W = Width of Vent 3. Avoid venting to internal pockets in the tool. Vent to D1 = Depth of Vent atmosphere. D2 = Depth of Relief 4. Thick walled > .125" (3.0mm) parts with high surface Typical Parting Line Vent Design appearance requirements may require extra venting. Figure 5W Vent Dimensions Material Type L W D1 D2 Unfilled 0.03" – .06" .375" – .5" .0005" – .001" 0.01" 0.75 – 1.5mm 9.5 – 12.5mm .013 – .025mm 0.25mm Mineral 0.03" .375" – .5" .001" – .002" 0.01" Filled 0.75mm 9.5 – 12.5mm .05 – .05mm 0.25mm Glass 0.03" .375" – .5" .001" – .002" 0.01" Filled 0.75mm 9.5 – 12.5mm .03 – .05mm 0.25mm Figure 5X 31
  • 34. Mold & Tooling Considerations The figures below show two venting schemes that are Cooling commonly used when relieving vents to atmosphere. Figure 5Y shows the use of vent channels from the To ensure optimum molding cycles while maintaining part parting line to the edge of the tool. The venting scheme surface requirements and mold filling capability, a stable in Figure 5Z ensures a positive shut off area outside the mold temperature should be determined and maintained. parting line area and then relieving the entire parting line. This is accomplished by incorporating cooling lines This latter design is referred to as continuous venting. throughout both the cavity and core of the mold. It is important that the temperature variation throughout both halves of the part cavity be kept to a minimum. When designing the tool, take into account potential hot spots such as hot runner manifolds and gate locations as well as cold areas such as the area last to fill. Hot spots and cool spots often require extra water channels to maintain temperature consistency throughout the tool. Inconsistent mold temperatures may lead to the following problems: 1. Non-uniform part surface finish. 2. Non-uniform part shrinkage and warpage. Independent Venting Channels 3. Lack of part dimensional control. Figure 5Y 4. Potential binding of tightly fitting cavity and core sections. In general, it is advisable to maintain less than a 20° F (11° C) differential in tool steel temperatures over the molding surface of a large mold and 5° F (3° C) with smaller tools. Designing for a tighter tool temperature range will assist in providing a greater processing window. Figure 5AA shows a typical design of a cooling channel layout arranged around the part surface. To maintain a stable process, tool temperature can be best controlled by incorporating a sufficient amount of water channels and placing them approximately .5 inch (13mm) Continuous Venting Channels from the part surface. Also, where the design permits, place the lines no more than 2 inches (51mm) apart for maximum control. Figure 5Z Water Channel Configuration Figure 5AA 32
  • 35. Mold & Tooling Considerations Often, part designs make the installation of adequate Shrinkage cooling lines difficult. In those cases, techniques other than a typical cooling line can be utilized, such as: Shrinkage is the difference between the dimensions of the cooled part and the tool. Ultramid nylon 6 products 1. Heat pipes are considered semi-crystalline products. Having this inherent characteristic, Ultramid products tend to exhibit 2. Air pipes shrinkage resulting from a decrease in part volume as 3. Bubblers material crystal-lization occurs. Resins with higher filler content will have less shrinkage. When designing the 4. Baffles injection mold, it is important to specify the proper material shrinkage in order to achieve a part that meets In addition, alloy materials such as beryllium copper offer your dimensional requirements. thermal conductivity values upwards of 10 times that of standard P-20 steel. These materials can be inserted in Below are several factors which may affect the shrinkage areas of the tool where water lines may be difficult to of an injection molded component: install, while maintaining tool durability. For best efficiency, water lines should always go through a portion of the 1. Location and size of the gate(s). Shrinkage is usually beryllium copper insert. greater in the cross flow direction. The following suggestions are recommended when 2. Part designs that contain large variations in cross designing and maintaining cooling systems of the section thickness can lead to unequal stresses injection mold: throughout the part and tend to cause differential shrinkage and warpage to become more pronounced. 1. Use a pyrometer to check that the cavity surfaces of 3. Increased glass content as a filler reinforcement will the tool are at the desired temperature. tend to lower the shrinkage of the material. 2. Minimize looping of hoses to maximize cooling 4. Random glass orientation, which can result from tool efficiency. design scenarios containing multiple gates, can be effective in leading to a more uniform part shrinkage 3. Blow out water lines with compressed air to remove condition. any foreign matter that may have collected. 5. Thicker areas shrink more than thinner areas. 4. Attempt to flow opposite directions (horizontal to vertical) between cavity and core. 5. Prior to mold start up, check all waterlines to ensure coolant flow is occurring. 6. Ensure that the flow pattern through the tool meets requirements for turbulent flow. Cooling simulation packages can be used to evaluate this. 7. To ensure operator safety, allow hot molds to cool prior to removing the mold from the molding machine. 8. Maintain and frequently check for wear or weakening of cooling hoses. With conventional rubber hoses, do not exceed 200°F (95°C) water temperature to ensure operator safety and the long-term integrity of hoses. Temperatures in excess of 200° F (95°C) require steel- braided hose. 33
  • 36. Mold & Tooling Considerations Refer to Figure 5BB which suggests the typical material shrinkage values for the Ultramid products. Nonetheless, there are many conditions, including part design and material processing, that can affect part shrinkage. As an accurate prediction mechanism, prototyping is often the most valuable tool for determining precise part shrinkage. Please contact a BASF Technical Development Engineer for assistance in determining material shrinkage. Category Product Ultramid Shrinkage General 8200 HS 0.012 Purpose 8202 HS 0.012 Homopolymers Flexible 8253 HS 0.012 and Impact 8254 HS 0.013 Resistant 8350 HS 0.014 8351 HS 0.014 BU50I 0.018 Reinforced 8230G HS 0.008 for High 8231G HS 0.005 Stiffness and 8232G HS 0.004 Strength 8233G HS 0.003 8234G HS 0.002 8235G HS 0.002 8262G HS 0.008 8266G HS 0.004 8267G HS 0.004 8331G HS 0.005 8332G HS 0.004 8333G HS 0.003 8334G HS 0.002 HMG10 0.002 HMG13 0.002 SEG7 0.003 SEGM35 0.004 TG3S 0.004 TG7S 0.003 Mineral 8260 HS 0.009 Reinforced 8360 HS 0.010 8362 HS 0.010 Tested samples were 5.0" x 0.5" x 0.125" (127mm x 12.7mm x 3.2mm) molded bars. These values are presented as a guide. Shrinkage values may be different depending on the actual application, including part design, mold design, and processing variables. Figure 5BB 34
  • 37. Chapter 6 Auxiliary Equipment Material Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Mold Temperature Control . . . . . . . . . . . . . . . . . . . . . . . 36 Granulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
  • 38. Auxiliary Equipment Chapter 6: Auxiliary Equipment Material Drying Mold Temperature Control Since Ultramid resins are hygroscopic materials, they must Mold (water) heaters are commonly used to maintain a be in a dry condition prior to injection molding. (Reference consistent temperature throughout the injection mold. Chapter 7: Processing Ultramid Nylon for drying recommen- In most cases, water is used as the heat transfer media, dations). Therefore, the dryer is an important piece of however, ethylene glycol mixtures as well as oil are equipment. For optimum drying conditions, BASF commonly used. Occasionally, two heaters are required recommends a closed loop desiccant dryer. A typical per mold to allow different mold temperatures between dessicant drying system is depicted in figure 6A. the cavity and the core. Selecting the proper heater to use for a particular mold is very important to ensure an efficient process. An undersized heater may be less of an upfront cost but the operating costs may outweigh the original savings. This is due to the fact that in many undersized cases, the heater will be required to run at 100% capacity for extended periods of time. Mold heaters are commonly rated in tons. One ton equals the ability to transfer 12,000 BTU/hr. To calculate the appropriate size thermolator for each mold, the formula in Figure 6B can be used. A x (B - C) Required = 12,000 Tonnage Figure 6A A = Actual material used in lbs/hr B = Temperature of melt (°F) Dryers should provide uniform and even distribution of air C = Temperature of part when it through the hopper. The critical temperature when comes out of the mold measuring the heated air is the temperature at the entrance to the hopper. Recommended air flow into Figure 6B the hopper is one cubic foot of air per minute for every pound per hour of use. If 200 lbs of material are consumed per hour, the airflow to the hopper should be 200 cubic feet of air per minute. Below are several guidelines for using and maintaining dryer systems: • Clean the filters on the dryers on a regular basis to ensure that the specified airflow is maintained. • Avoid loading regrind with high levels of fines or small dust- like particles into the dryer. • Using a dewpoint meter, check the dewpoint of the air entering the hopper. The recommended dewpoint should range between -20° F and -40° F (-30° C and - 40° C). • Change and maintain the desiccant in the dryer per the manufacturers recommendations. 36
  • 39. Auxiliary Equipment Sufficient water flow through the tool is also critical to Granulators ensure that an efficient heat transfer process is occurring. This is demonstrated in Figure 6C. As the gallons per Many molding applications allow the use of regrind back minute of flow (GPM) through the tool decreases, the into the process. This will require the use of material difference between the tool inlet and outlet temperatures grinders. Many styles of granulators have been used (Delta T) must increase dramatically. Therefore, to run at successfully with Ultramid resins. To ensure a consistent a lower flow rate through the tool and still achieve the regrind blend, granulator maintenance is often critical. In results of running with a higher flow, the inlet coolant addition to maintenance, proper safety should be observed in temperature must be set significantly lower. This results accordance with the manufacturer’s recommendations. in lower mold heater settings, which may be costly to operate. The following are suggestions to maintain a consistent regrind blend while maintaining the equipment in proper working order: 1. Following material changes, the granulator should be cleaned and vacuumed to remove any foreign material that may contaminate the blend. 2. Blades should be sharpened and screens cleaned regularly to ensure a consistent regrind pellet size. 3. When grinding filled materials, for prolonged periods, components, such as blades, rotors and screens, should be made of hardened materials to resist the Figure 6C erosive effects of these more abrasive plastic compounds. Following are several other suggestions that may be helpful when designing the coolant system for a specific 4. In many instances, ear protection is recommended tool: when operating a granulator. 1. Typical temperature losses through the coolant handling system is 20%. This includes the coolant lines, mold base, and platens. 2. Antifreeze does not transfer heat as well as water. 3. If antifreeze is needed, use only inhibited ethylene glycol with high corrosion resistance. A straight ethylene glycol can become acidic and corrosive with use and may form a gel within two years in open air systems. 4. Where equal heat transfer is desired, ensure that equal coolant flow is occurring between the coolant channels. This may be accomplished by the use of adjustable flow regulators. 37
  • 40. Chapter 7 Processing U ltramid Nylon Processing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Melt Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Hot Runner Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Residence Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Mold Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Injection Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Holding Pressure and Pack Pressure . . . . . . . . . . . . . . . 42 Back Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Injection Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Cushion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Rotation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Screw Decompression. . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Regrind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Pre-Colored Ultramid Nylon. . . . . . . . . . . . . . . . . . . . . . . .44 Processing Cadmium-Free vs. Cadmium Colors . . . . . . 44
  • 41. Processing Ulramid Nylon Chapter 7: Processing Ultramid Nylon Processing Conditions Recommended Dryer Settings Ultramid resin has very good molding characteristics due Dryer Inlet Air Dryer Drying to its excellent ability to flow. Since Ultramid products Temperature Dewpoint Time have a wide processing window, the following conditions Ultramid Nylon 6 180°F (82°C) <-20°F (-30°C) 4 hours are typical recommended settings that can be used at machine set up. Included in this chapter are the key NOTE: Not to exceed 25 0°F (121°C) for two hours. processing variables that may be manipulated in order to control the molding process. Figure 7B Drying Moisture absorption and moisture loss is a function of pellet surface area. In other words, the smaller the pellet, Ultramid resins are hygroscopic materials and are supplied the more surface area per weight, and therefore, the more dry. Therefore, care should be taken to ensure that the moisture that it will absorb or lose in a given period of material remains in an enclosed container prior to time. Therefore, when molding regrind, which may molding as nylon will tend to absorb moisture from the contain larger sized pellets, additional drying time at 180° atmosphere over time. As supplied from BASF in sealed F (82°C) may be required. boxes and bags , Ultramid resin is usually dry enough for injection molding. However, a moisture analysis of the To ensure that the material is dried for the recommended material is always a good idea to ensure that the material time, the equation in Figure 7C may be used to calculate is within the recommended moisture range. Figure 7A the residence time of the material in the dryer for a shows the moisture content recommendations for continuously running process. To perform this injection moldingUltramid resins. calculation, the following variables are needed: 1. Total shot weight (including sprue and runner) Ultramid Recommended 2. Total cycle time Produc t Moisture Content (by weight) 3. Total dryer capacity Unreinforced homopolymers 0.10 – 0.20% These values are then entered in the appropriate position in the equations below: <20% Reinforced 0.10 – 0.16% >20% A Reinforced 0.06 – 0.12% Figure 7A B In order to ensure proper material properties the , moisture content should not be dried to moisture levels below 0.02%. Figure 7C If the material contains higher levels of moisture than listed on the chart, drying may be required to ensure Below are key recommendations for maintaining an proper processing and desired part quality. A dryer (as acceptable moisture level for injection moldingUltramid discussed in Chapter 6) containing a desiccant system is products: highly recommended for best results. Figure 7B gives the drying recommendations for Ultramid products. These 1. Prior to molding, store the material in a container that values are for 100% virgin products. is sealed from the atmosphere. 2. Minimize the distance from the dryer to the machine The data presented are general guidelines for moisture hopper and/or dryer hopper in an effort to minimize content. Refer to the particular resin’s property data heat loss through the connecting hoses. sheet for more specific recommendations. 3. Check the drying equipment for crimped or cracked hoses which may reduce the heat transfer to the hopper. 40
  • 42. Processing Ultramid Nylon Melt Temperature The actual melt temperature is influenced by barrel temperature settings, screw design, screw RPM, back pressure, material residence time and shear heat through the nozzle. Since it is difficult to estimate the effect that each variable has on the process, the actual melt temperature should be measured with a pyrometer. Actual measurement of the melt temperature will ensure process repeatability. The barrel temperature profiles in Figures 7D through 7I are representative for processing of the various categories of resins. Figure 7D Figure 7G Figure 7E Figure 7H Figure 7F 41
  • 43. Processing Ultramid Nylon Hot Runner Systems The ability to control mold temperature is often highly dependent on tool design. If possible, all surfaces of the The purpose of a hot runner system is to maintain heat in tool should be maintained at a consistent temperature. the material and not add, nor remove, heat. When This will ensure consistent properties throughout the part. molding Ultramid resins through a hot runner system, use Below are additional suggestions for setting mold standard injection molding processing guidelines. temperature: Recommended manifold temperature settings should be similar to the front or center zones of the machine barrel. 1. When possible, use a pyrometer to verify that the mold temperature is at the desired temperature and Residence Time consistent throughout both halves of the tool. Residence time of Ultramid resin in the barrel at 2. Avoid a temperature differential between the halves processing temperatures should be minimized to 3 –5 of the tool greater than 75° F (24° C). This will reduce minutes. Residence time may be calculated by using the the risk of tool steel interference or binding from equation in Figure 7J. temperature-induced expansion in the mold. Calculating Residence Time 3. A temperature differential between the mold halves may induce the part to warp toward the hotter side of the tool. Total Shots Cycle Time (sec) Barrel X 60 = Residence Time (minutes) Injection Pressure Figure 7J The actual required injection pressure will depend on many variables, such as melt and mold temperatures, This calculation (7J) will be a rough estimate only, as at part thick-ness, geometry, and flow length. Generally, any given time there is significantly more material in the low to medium pressures are desirable to maintain barrel than 100% of the maximum shot size. material properties, appearance criteria, and cycle time. Mold Temperature Holding Pressure and Pack Pressure Ultramid nylon 6 should always be molded in temperature- Holding pressure is the pressure transferred through the controlled molds. Recommended mold temperatures melt into the part cavity following the filling of the mold. range from 50° F to 200° F (10° C to 93° C). For best The change from injection pressure to holding pressure is properties and cycle time, a mold temperature of 180° F commonly called the transfer point. Holding pressures (82° C) is recommended. When molding parts that are normally 1/2 to 2/3 of the maximum injection pressure require good aesthetics, a mold temperature between and should take effect after the cavity is filled. 180° F to 200° F (82° C to 93° C) is suggested. Holding pressure should be maintained until the gate Ultramid nylon 6,6 resins should also be molded in a freezes off. Applying pressure beyond this point will not temperature-controlled mold. Recommended mold affect the part. To estimate when the gate is freezing off, temperatures range from 110° F to 220° F (43° C to 104° C). adjust the process to mold a full consistent shot. Begin by molding without a hold time and incrementally with Mold temperature will influence cycle time, part each successive shot increase hold time by one second. dimensions, warpage and mechanical properties. The Weigh each part and plot the weight on a curve of part effects of varying mold temperature when molding weight vs. hold time. When the curve begins to level off, Ultramid resins are listed in Figure 7K. In some cases, it showing a consistent part weight, the gate freeze off time may be required to elevate or reduce the mold can be noted. The first point at which the curve becomes temperature to attain the desired results. horizontal is the freeze off temperature. Mold Temperature General Holding Pressure Guidelines Lower Higher Increasing Decreasing Minimal shrink Maximum material shrink Reduces shrinkage Reduces part sticking Reduced cool (cycle) time Increased flow Reduces sink marks Increases shrinkage Higher molded-in stress Improved knit line strength Reduces warpage Reduces sprue sticking Less than optimum surface Reduced molded-in stresses Potential to flash parting line Induces surface gloss Improved impact properties Improved surface appearance Reduces gloss on grained parts Possibly reduces part strength Figure 7K Figure 7L 42
  • 44. Processing Ultramid Nylon Back Pressure Cushion Back pressure on a screw results when its backward The use of a cushion of material at the end of the screw movement (screw recovery) is restricted. Back pressure stroke is highly recommended when moldingUltramid is always recommended to ensure a consistent shot size products. Typically, a small cushion is acceptable for and homogeneous melt. Higher pressures may be any Ultramid resin to promote shot to shot consistency. required for more intensive mixing but may induce higher A cushion of 0.100"–0.25" (2.5mm–6.35mm) is recom- melt temperature, glass breakage (reinforced materials), mended. The inability to hold a consistent cushion is and increased cycle time due to hotter melt temperatures usually indicative of a worn non-return valve. On injection and slower screw recovery. Typical back pressure molding machines with process controllers, the cushion settings for Ultramid products are 25 to 100 psi. can often be maintained automatically since the process Increasing back pressure as a substitute for a proper controller will monitor screw location and can heat profile or an inadequate screw design is not compensate for any deviation in cushion. recommended. Maintaining a cushion as suggested will assist in the Injection Speed processing of the material in the following ways: Generally speaking, reinforced Ultramid resins should be 1. Helps to maintain consistent physical properties injected with high velocity rates because of the inherent throughout the molded part. crystalline nature. A greater range of injection speeds can be utilized with reinforcedUltramid nylon grades. 2. Aids in ensuring dimensional reproducibility, weld line integrity and control of sink marks. Fast injection provides for longer flow improved pack , condition, and better surface aesthetics when molding 3. Assists maintaining a consistent surface quality. reinforced grades. Filling the cavity at a faster rate will allow the material to crystallize at a uniform rate in the Screw Rotation tool which tends to result in lower molded-in stress. Screw recovery speeds that will permit screw rotation Slower fill speeds may be required when filling through during 75–90% of the cooling time are recommended. gate designs where jetting or gate blush is occurring. This will prevent excessive melt temperature increases Slow fill is also used in tools with poor venting to and maintain a homogeneous melt temperature. eliminate part burning and in parts with thick cross sections to reduce sink marks and voids. Screw Decompression Programmed or profiled injection has been proven Decompression or “suck back ” is the intentional pulling successful when molding parts with non-uniform wall back of the screw and polymer from the nozzle area to stock to reduce voids and gas entrapment burning. It prevent drool. It is usually accomplished by time or has also proved to be an advantage when molding screw position settings. The result is introducing air to through subgates and pinpoint gates. the molten plastic, which cools and may oxidize the plastic. Therefore, it is recommended to minimize the Slow injection speeds at the start of injection can be use of decompression. used to eliminate/reduce gate blush, jetting and burning of the material. The nylon reverse taper machine nozzle has been used successfully to minimize drool and stringing. Please refer to Chapter 4 of this guide for more information on nozzle tips. Purging The barrel should be purged if the process will be shut down or idled for any length of time. For short interruptions, one need only purge several shots, but longer shut downs require a complete purging or emptying of the barrel. It is always a good idea to purge the first several shots at start up to reduce the chance of contamination from previous processing. 43
  • 45. Processing Ultramid Nylon Regrind Processing Cadmium-Free vs. Cadmium Colors Ultramid nylon, like many thermoplastic materials, may be BASF has established itself as a leader in “cad-free” color used with its own regrind. Typical levels of regrind range technology for nylon 6. At present, cad-free pigments, from 25–30% if the initial molding did not cause thermal especially bright reds, bright oranges, and bright yellows degradation or severe glass breakage (in filled materials) do not have as high a melt stability as cadmium to the Ultramid product. pigments. For this reason, care should be taken when molding cad-free color Ultramid resins, especially when Below are several suggestions when using regrind: melt temperatures of greater than 570° F (299° C) are required. We recommend the following for good color 1. Mix regrind back into the virgin material type from repeatability in cad-free colors: which it was originally molded. 1. Do not dry the bright cad-free colors above 180° F 2. It is important that the material to be reground be free (82° C) and do not dry for an extended period of time from oil, grease or dirt, and show no signs of (over 10 hours). If needs require longer drying, degradation. reduce dryer set-point to 130° F (55° C) after 8 hours. 3. Regrind that contains excessive quantities of fines or 2. Minimize residence time in the barrel. A shot size of dust-like particles may result in molding problems 50% to 60% of barrel capacity is ideal. If the shot such as burning or splay. Try to select grinder screens size is less than 50% of barrel capacity, profile barrel that will minimize fines. temperatures with lower settings in the middle and rear zones. 4. It is advantageous to try to make the particle size of the regrind as close to the initial pellet size as possible. 3. Establish the molding process with the lowest melt This will allow for ease of blending and for consistent temperature that yields a good part. drying of the material. 4. Ensure that the check valve is holding a cushion. A 5. Prior to processing the regrind, ensure that the free- flow check ring is recommended. Ball check moisture level is similar to that of the virgin material. valves tend to have dead spots where material may This will help in processing. hang-up for several shots and lead to discolored streaks in molded parts. 6. If the regrind material does become wet it is usually better to dry the material off line in a separate dryer. 5. Ensure that the clearance between the screw and barrel inner diameter is not excessive. Any leakage 7. Some color shift may occur when using regrind. It is around the check valve will excessively shear heat ° important to dry the regrind at 180 F (82° C) the material. maximum to reduce the amount of color shift. 6. Attempt to design-out or remove all instances where 8. To maintain a consistent regrind blend, it is shear may be induced in the melt (i.e. thick to thin recommended to use your regrind back into the wall transitions and sharp corners). process as it is generated. 7. Acceptable regrind levels may be lower than those 9. If regrind is to be stored for future use, store it in a typically used for non-cadmium-free pigment container with a moisture barrier. systems. This is due to the inherently lower thermal stability of cad-free pigments. Pre-Colored Ultramid Nylon 8. Adjust screw RPM so that screw rotation lasts for a Ultramid nylon resins can be supplied in numerous custom minimum of 80% to 90% of the cooling time. This and standard compounded colors. Ultramid resins can will reduce thermal history on the material. also be easily colored by dry-blending natural resin with commercially available color concentrates. Please call 9. Nozzle bore, sprue bushing bore, gate thickness, and BASF for a list of commercial sources. diameter should all be as large as possible to minimize shear heating during injection. 10. Avoid the use of a reverse taper nozzle if possible. This will also reduce shear during injection. 44
  • 46. Chapter 8 Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Brittleness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Bubbles, Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Burn Marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Cracking, Crazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Dimensional Variations . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Discoloration, Contamination. . . . . . . . . . . . . . . . . . . . . . 50 Excessive Cycle Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Flashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Flow Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Lamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Nozzle Drooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Part Sticking in Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Short Shots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Splay (Silver Streaking) . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Sprue Sticking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Surface Imperfections (Glass On Surface, Mineral Bloom) . . . . . . . . . . . . . . . . 56 Warpage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Weld Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
  • 47. Ultramid Nylon Troubleshooting Guide for Injection Molding Chapter 8 : Ultramid Nylon Troubleshooting Guide for Injection Molding Introduction Ultramid nylon molding compounds are formulated to perform well in both the end-product and in the The purpose of the tables that constitute the major part of fabrication process. BASF provides a generous array of this chapter are to identify the broad categories of Ultramid engineering plastics from which to choose. molded-part deficiencies and molding problems that can Assistance with the selection of the most appropriate arise in injection molding. Under each category, possible Ultramid nylon molding polymer for your needs is always causes are identified and remedies suggested. While the available from BASF. You will find our address and phone suggestions are specifically made for parts molded from number at the end of this guide. Ultramid nylon resins, many of them have more general applicability. With its resident expertise and comprehensive resources and equipment, the BASF customer support staff has Responsibility for the proper molding of a part lies with built a strong base of technical experience and data on the molder, who applies knowledge and skill to achieve a injection molding. We continue to perform studies on satis-factory result from a complex interplay of factors injection molding and investigations into the performance including: properties of our nylon resins. Our technical personnel are always ready to share their knowledge with you. • Choice of Material • Mold Design Calling for Technical Assistance • Melt Stability When it is necessary to call the technical service staff for • Moisture Sensitivity help, please have the following information available: • Material Stress Behavior • Throughput Rate 1. Type of problem, i.e. molding defect, part failure. • Machine Characteristics 2. Material type, color number, and lot number. • Aesthetics 3. Material handling procedures, regrind percent used, • Dimensions drying times and temperatures. 4. Injection molding parameters. Actual melt and mold temperatures, actual fill time injection pressures and , times, back pressure , screw RPMs , cooling time, clamp tonnage, shot size versus barrel size. 5. Miscellaneous: Nominal wall thickness, gate size, number of cavities, balance of flow to each cavity, etc. 46
  • 48. Ultramid Nylon Troubleshooting Guide for Injection Molding Brittleness Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature (weak weld lines). 2. Material overheated, resulting in a. Decrease melt temperature. molecular breakdown. b. Residence time in cylinder excessive– use smaller barrel. c. Decrease overall cycle. d. Reduce back pressure. 3. Contamination by foreign material or a. Inspect resin for contamination (replace if contaminated). excessive pigment usage. b. Purge injection cylinder thoroughly. c. Keep hopper covered. d. Review material handling procedures for regrind usage. e. Reduce filler or pigment loading. 4. Excessive amounts of regrind. a. Reduce regrind % mixed with virgin. b. Regrind level dependent upon application: general rule – 25–30%. c. Keep hopper covered. d. Review material handling procedures for regrind usage. e. Reduce filler or pigment loading. 5. Injection rate too slow. a. Increase injection or first stage pressure. b. Increase boost time. 6. Improper gate location or size. a. Relocate gate away from potential stress area. b. Increase gate size to obtain optimum filling. 7. Moisture in material during processing. a. Review material handling to eliminate moisture pick up. b. Dry material prior to molding. c. Utilize hopper dryers. 8. Dry-as-molded properties. Moisture condition parts to increase toughness. 47
  • 49. Ultramid Nylon Troubleshooting Guide for Injection Molding Bubbles, Voids Possible Cause Suggested Remedy 1. Excessive internal shrinkage. a. Increase packing pressure. b. Increase injection forward time. c. Increase gate thickness. d. Minimize, or core out, heavy sections in part design. e. Increase feed, ensure cushion. f. Replace check valve if cushion cannot be held. 2. Melt temperature too high. a. Decrease melt temperature. b. Lower back pressure. c. Lower screw RPM. 3. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Utilize hopper dryers. d. Review percent of regrind. 4. Air entrapment. a. Add mold venting. b. Relocate gate. c. Reduce clamp pressure to allow parting line vents to work. 5. Condensation on mold surface. a. Wipe mold surface thoroughly with solvent. b. Increase mold temperature. Burn Marks Possible Cause Suggested Remedy 1. Melt temperature too high. a. Decrease melt temperature. b. Lower back pressure. c. Lower screw RPM. 2. Air entrapped in mold. a. Vent cavity at final point of fill. b. Decrease first stage pressure or injection speed. c. Relocate gate. d. Clean vents and/or enlarge vents. e. Reduce clamp pressure to allow parting line vents to work. 3. Injec tion rate too fas t. a. Dec reas e injec tion rate. b. Decrease first stage pressure. c. Decrease boost time. d. Enlarge gates. 4. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Utilize hopper dryers. 48
  • 50. Ultramid Nylon Troubleshooting Guide for Injection Molding Cracking, Crazing Possible Cause Suggested Remedy 1. Packing excessive material into the mold. a. Decrease packing pressure. b. Decrease shot size. c. Increase transfer position (to lower injection peak pressure). d. Decrease injection time. 2. Non-uniform or too cold a a. Increase mold temperature. mold temperature. b. S upply uniform c ooling to the c avity. 3. Knockout system poorly designed. Redesign knockout system for balanced ejection forces. 4. Inadequate draft angles or Rework mold. excessive undercuts. Dimensional Variations Possible Cause Suggested Remedy 1 Non-uniform feeding of material. a. Adjust temperature profile for optimum feeding. b. Increase shot size to maintain uniform cushion. c. Replace check valve if cushion cannot be held. 2. Large variation in cylinder temperature Replace or calibrate controllers. due to inadequate or defective controllers. 3. Unbalanced runner system, resulting in a. Increase holding pressure to maximum. non-uniform cavity pressure. b. Increase injection rate. c. Balance/increase runner and gate sizes to provide uniform filling. 4. Insufficient packing of part. Increase injection forward time and/or pressure to ensure gate freeze off. 5. Regrind not uniformly mixed with virgin. a. Review regrind blending procedure. b. Decrease percentage of regrind. 6. Molding conditions varied from a. Check molding records to ensure duplication of previous run. process conditions. 7. Part distortion upon ejection. See Part Sticking in Mold, page 53 . 49
  • 51. Ultramid Nylon Troubleshooting Guide for Injection Molding Discoloration, Contamination Possible Cause Suggested Remedy 1. Material overheated in injection cylinder. a. Decrease melt temperature. b. Decrease overall cycle. c. Residence time in cylinder excessive for shot size – use smaller barrel. d. Decrease nozzle temperature. e. Decrease screw RPM. f. Decrease back pressure. g. Check calibration of cylinder controllers. h. Check barrel and nozzle heater bands and thermocouples. 2. Burned material hanging up in cylinder, a. Purge injection cylinder. nozzle (black specks), or check ring. b. Remove and clean nozzle. c. Remove and inspect non-return valve for wear. d. Inspect barrel for cracks or gouges. e. Decrease injection rate. 3. Material oxidized by drying at too high Reduce drying temperature to 180 F (82 o C). o temperature. 4. Contamination by foreign material. a. Keep hopper covered. b. Review material handling procedures for virgin and regrind. c. Purge injection cylinder. Excessive Cycle Time Possible Cause Suggested Remedy 1. Poor mold cooling design. a. Increase mold cooling in hot spots. b. Ensure fast turbulent flow of water through cooling channels. 2. Platen speeds excessively slow. a. Adjust clamp speeds to safely open and close quickly. b. Low pressure close time excessive, adjust clamp positions and pressures to safely and efficiently open and close mold. 3. Melt temperature too high. Decrease melt temperature. 4. Mold temperature too high. Decrease mold temperature. 5. Screw recovery time excessive. a. Check machine throat and hopper for blockage or bridging. b. Check for worn screw and barrel, especially in the feed zone. 50
  • 52. Ultramid Nylon Troubleshooting Guide for Injection Molding Flashing Possible Cause Suggested Remedy 1. Material too hot. a. Dec reas e melt temperature. b. Decrease mold temperature. c. Lengthen cycle time. 2. Injection pressure too high. a. Decrease injection pressure. b. Decrease boost time. c. Decrease injection rate. d. Increase transfer position (to lower injection peak pressure). 3. Excessive packing of material Decrease packing pressure. in cavities. 4. Projected area too large for available Use larger tonnage machine. clamping force. 5. Mold clamping pressure not a. Increase clamping pressure. properly adjus ted. b. C hec k mold parting line for obs truc tion. c. Check platen parallelism. 6. Uneven or poor parting line and a. Remove mold, carefully inspect and repair parting lines, cavities and cores which do not have positive shut off. b. Add support for mold cores and cavities. 7. Non-uniform cavity pressure due to a. Balance/increase runner and gate sizes to obtain unbalanc ed filling. uniform filling. b. Properly balance cavity layout for maintaining uniform cavity pressure. Flow Lines Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Gate size too restrictive, causing jetting. a. Increase gate size. b. Decrease injection rate. 4. Material impinging on cavity wall or core. a. Decrease injection rate. b. Relocate gate. 5. Non-uniform wall thickness. Redesign part to obtain a more uniform wall thickness to provide for optimum filling. 6. Insufficient mold venting. Improve mold venting. 51
  • 53. Ultramid Nylon Troubleshooting Guide for Injection Molding Lamination Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Injection rate too low. a. Increase first stage pressure. b. Increase boost time. 4. Holding pressure too low. Increase packing pressure. 5. G ate s ize too s mall. Inc reas e gate s ize for improved filling. 6. C ontamination. S ee Discoloration, Contamination, page 50 . Nozzle Drooling Possible Cause Suggested Remedy 1. Nozzle temperature too hot. a. Reduce nozzle temperature. b. Decrease melt temperature. c. Reduce back pressure. d. Increase screw decompression. e. Use enough screw RPM’s to allow screw to recover using approximately 90% of the cooling time. 2. Wrong nozzle design. Use reverse taper nozzle. 3. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Use hopper dryers. 52
  • 54. Ultramid Nylon Troubleshooting Guide for Injection Molding Part Sticking in Mold Possible Cause Suggested Remedy 1. Overpacking material in mold. a. Decrease first stage injection pressure. b. Decrease boost time. c. Decrease injection forward time. d. Decrease packing pressure. e. Increase injection transfer position (to lower injection peak pressure). 2. Improper finish on mold. Draw polish mold to proper finish. 3. Insufficient draft on cavities and sprue. Polish and provide maximum allowable draft. 4. Knockout system poorly designed. a. Redesign knockout system for balanced ejection forces. b. Review operation of knockout system, plates not opening in proper sequence. 5. Core shifting and cavity misalignment. a. Realign cavities and cores. b. Add interlocks to mold halves. 6. Undercuts in mold and possible a. Repair and polish. surface imperfections. b. If undercut is intentional, redesign or reduce. 7. Non-uniform cavity pressure in Redesign runners and gates for balanced filling of cavities. multi-cavity mold. 8. Molded parts too hot for ejection. a. Increase cooling time. b. Decrease melt temperature. c. Decrease mold temperature. 9. Molded parts sticking to stationary a. Redesign sprue puller. half of mold. b. Apply mold releas e. c. Increase nozzle temperature. d. If parts remain on wrong side of mold, undercut other side or try differential mold temperatures. 53
  • 55. Ultramid Nylon Troubleshooting Guide for Injection Molding Short Shots Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Injection pressure too low. a. Increase first stage pressure. b. Increase boost time. c. Increase injection speed. 4. Ins uffic ient feed. a. Inc reas e s hot s ize to maintain a c ons tant c us hion. b. Inspect non-return valve for wear. 5. Insufficient injection forward time. a. Increase injection forward time. b. Increase injection rate. 6. Entrapped air causing resistance to fill. a. Provide proper venting. b. Increase number and size of vents. 7. Restricted flow of material to cavity. a. Increase gate size. b. Increase runner size. c. Use nozzle with larger orifice. 8. Unbalanced flow to cavity in a. Increase gate size. multi- c avity mold. b. R edes ign runner to provide balanc ed flow. Splay (Silver Streaking) Possible Cause Suggested Remedy 1. Excess moisture in material during processing. a. Review material handling to eliminate moisture pick up. b. Dry material prior to molding. c. Utilize hopper dryers. 2. Melt temperature too high . a. Decrease barrel temperature. b. Decrease nozzle temperature. 3. Excessive shear heat from injection. a. Decrease injection rate. b. Reduce screw RPM. c. Increase runner size and/or gates. d. Check for nozzle obstruction. 4. Air entrapment. a. R educ e s c rew dec ompres s ion. b. Improve mold venting. 5. Condensation and/or excessive lubricant a. Increase mold temperature. on mold s urfac e. b. C lean mold s urfac e with s olvent. c. Use mold release sparingly. 6. Moisture condensing in feed a. Decrease throat cooling. s ec tion of barrel. b. Inc reas e rear zone temperature s etting. 54
  • 56. Ultramid Nylon Troubleshooting Guide for Injection Molding Sprue Sticking Possible Cause Suggested Remedy 1. Improper fit between nozzle and sprue bushing. Nozzle orifice should be smaller than sprue bushing orifice. 2. Insufficient taper on sprue bushing. Increase taper. 3. Rough surface of sprue bushing. Eliminate imperfections and draw polish surface. 4. Sprue puller design inadequate. a. Redesign sprue puller and increase undercut. b. Increase sprue diameter if too small for strength. c. Decrease sprue diameter if too large for cooling. 5. Overpacking material in sprue. a. Decrease packing pressure. b. Decrease injection forward time. c. Use machine sprue break. 6. Nozzle temperature too low to provide a. Increase nozzle temperature. c lean break. b. Us e revers e taper nozzle. 55
  • 57. Ultramid Nylon Troubleshooting Guide for Injection Molding Surface Imperfections (Glass On Surface, Mineral Bloom) Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Insufficient packing pressure. Increase packing pressure. 4. Injection rate too slow. a. Increase first stage pressure. b. Increase boost time. c. Increase injection speed. 5. Insufficient material in mold. a. Increase shot size and maintain constant cushion. b. Inspect non-return valve for wear. c. Decrease injection transfer position (thereby increasing the peak pressure). 6. Water on mold surface. a. Increase mold temperature. b. Repair any water leaks. 7. Excessive lubricant on mold surface. a. Clean mold surface with solvent. b. Use mold release sparingly. 8. Mois ture in material. a. R eview material handling to eliminate mois ture pic k up. b. Dry material prior to molding. c. Use hopper dryers. 9. Ins uffic ient venting. P rovide adequate vents . Warpage Possible Cause Suggested Remedy 1. Molded part ejected too hot. a. Decrease melt temperature. b. Decrease mold temperature. c. Increase cooling time. d. Cool part in warm water after ejection. e. Utilize shrink fixture. 2. Differential shrinkage due to a. Increase injection rate. non- uniform filling. b. Inc reas e pac king pres s ure. c. Balance gates and runners. d. Increase/decrease injection time. e. Increase runner and gate size. 3. Differential shrinkage due to non-uniform a. Provide increased cooling to thicker sections. wall thic knes s . b. Inc reas e c ooling time. c. Operate mold halves at different temperatures. d. Redesign part with uniform wall sections. 4. Knockout system poorly designed. Redesign knockout system for balanced ejection forces. 5. Melt temperature too low. Increase melt temperature to pack out part better. 6. Glass fiber orientation. Relocate gate. 56
  • 58. Ultramid Nylon Troubleshooting Guide for Injection Molding Weld Lines (Knit Lines) Possible Cause Suggested Remedy 1. Melt temperature too low. Increase melt temperature. 2. Mold temperature too cold. Increase mold temperature. 3. Insufficient pressure at the weld. a. Increase first stage injection pressure. b. Increase boost time. c. Increase packing pressure. d. Increase pack time. e. Increase injection speed. 4. Entrapped air unable to escape from a. Increase or provide adequate vents at the weld area. mold fas t enough. b. Dec reas e injec tion rate. 5. Excessive lubricant on mold surface a. Clean mold surface with solvent. plugging vents . b. Us e mold releas e s paringly. 6. Distance from gate to weld line too far. a. Relocate or use multiple balanced gates. b. Cut overflow tab in mold to improve weld line strength. 7. Injection rate too slow. a. Increase injection speed. b. Increase first stage injection pressure. c. Increase boost time. DISCLAIMER: Although all statements and information in this publication are believed to be accurate and reliable, they are presented withou t guarantee or warranty of any kind, express or implied, and risks and liability for results obtained by use of the products or application of the suggestions described are assumed by the user. Statements or suggestions concerning possible use of the products are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe any patent. The user should not assume that toxicity data and safety measures are indicated or that other measures may not be required. 57
  • 60. IMPORTANT: WHILE THE DESCRIPTIONS, DESIGNS, DATA AND INFORMATION CONTAINED HEREIN ARE PRESENTED IN GOOD FAITH AND BELIEVED TO BE ACCURATE, IT IS PROVIDED FOR YOUR GUIDANCE ONLY. BECAUSE MANY FACTORS MAY AFFECT PROCESSING OR APPLICATION/USE, WE RECOMMEND THAT YOU MAKE TESTS TO DETERMINE THE SUITABILITY OF A PRODUCT FOR YOUR PARTICULAR PURPOSE PRIOR TO USE. NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE MADE REGARDING PRODUCTS DESCRIBED OR DESIGNS, DATA OR INFORMATION SET FORTH, OR THAT THE PRODUCTS, DESIGNS, DATA OR INFORMATION MAY BE USED WITHOUT INFRINGING THE INTELLECTUAL PROPERTY RIGHTS OF OTHERS. IN NO CASE SHALL THE DESCRIPTIONS, INFORMATION, DATA OR DESIGNS PROVIDED BE CONSIDERED A PART OF OUR TERMS AND CONDITIONS OF SALE. FURTHER, YOU EXPRESSLY UNDERSTAND AND AGREE THAT THE DESCRIPTIONS, DESIGNS, DATA, AND INFORMATION FURNISHED BY BASF HEREUNDER ARE GIVEN GRATIS AND BASF ASSUMES NO OBLIGATION OR LIABILITY FOR THE DESCRIPTION, DESIGNS, DATA AND INFORMATION GIVEN OR RESULTS OBTAINED, ALL SUCH BEING GIVEN AND ACCEPTED AT YOUR RISK. Ultramid®, Petra® and Ultratough® are registered trademarks of BASF Corporation www.plasticsportal.com/usa