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Bearings PPT

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The document provides a comprehensive overview of bearings, covering their introduction, history, types, structure, installation, and maintenance. It details classification into rolling and sliding contact bearings, their materials, lubrication methods, and failure types. Additionally, it discusses bearing designations, specifications, and practical applications in various machines and structures.

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BEARINGS •Kanan Sadigzada •k.sadiqzade@stp.az •Kheyrulla Amirov •xeyrullamirov@gmail.com 19/07/2019
BEARINGS • Introduction • History • Classification of Bearing • Bearing Types • Bearing Structure • Bearing Mounting and Dismounting • Bearing Lubrication • Bearing Selection • Bearing Failure 19/07/2019
Bearings 19/07/2019 Any machine or structure that has relative movement requires the use of bearings. Bearings are the most common component feature used in machines and structures The range of bearing types and associated applications is huge and without bearings the all motion would grind to a halt. Bearings are used in everyday items ranging from the more obvious applications such as washing machines, cars, the watches on our wrists but also super structures such as building supported on bearings to allow relative movements during earthquakes
• Bearing provides relative rotational freedom and transmits a load between two structures. Inner Ring Cage Rolling Elements Outer Ring Wind Turbine Gearbox Construction of a bearing Bearings Bearings inside Gas Turbine Engine Induction Motor Bearing 4 19/07/2019
What is Friction ? Friction is resistance to movement  it opposes sliding  it assists rotation 19/07/2019
WHAT IS FRICTION? Plain bearings sliding friction Rolling bearings rolling friction   19/07/2019
HISTORY 19/07/2019
How did a bearing evolve ? Bearing history - a never-ending story 1100 B.C. 3500 B.C. 1995 1794 40 A.D. 1869 19/07/2019
How did a bearing evolve ? * Invention of wheel * Wheel rotates on axle * Wear Plate + Rollers * Inner ring + Outer ring + Rollers * With introduction of cage Rolling Bearing was created 19/07/2019
• BASED ON NATURE OF CONTACT • 1. Rolling Contact Bearings Balls or rollers introduced between moving and fixed elements and it is also known as anti-friction bearings • 2. Sliding Contact Bearing Sliding takes place between the fixed and moving element of bearing and its also known as plain bearing CLASIFICATION OF BEARING 1 19/07/2019
Rolling Element Bearings They are also called antifriction bearings/rolling contact bearings/rolling bearings. Load is transferred through elements in rolling contact. These bearings locate the shaft in axial and radial direction. Starting friction is twice as the running friction. REB is an assembly rather than single element. There bearings are manufactured to take loads: - Pure radial - Pure axial (thrust) - Combined (radial and thrust) They are designed taking into consideration below points: - Space limitations - Load characteristics - Life fatigue - Friction, heat - Corrosion resistance - Material properties - Lubrication - Tolerances - Cost and etc 19/07/2019
BEARING TYPES: Can be classified according to shape of element and load type. According to the type of element: - Ball bearings - Roller Bearings According to the type of the load Some bearings can carry both axial and radial loads - Radial bearings (ring bearings radial loads) - Thrust bearings (axial loads 19/07/2019
The components of a bearing Seal Rolling elements Inner ring Outer ring SealCage 19/07/2019
Pg. 7 Bearing Installation and Maintenance Guide Bearing Basics 19/07/2019
BALL POINT CONTACT SPHERICAL LINE CONTACT TAPERED LINE CONTACT Bearing Basics 19/07/2019
Characteristics Deep groove Angular ball bearing contact ball bearing Self-aligning ball bearing Ball bearings Point Contact : Cylindrical roller bearing Taper Needle roller roller bearing bearing Spherical roller bearing * Less area of contact * Less friction * More speed * Less load Roller bearings Line Contact : * More area of contact * More friction * Less speed * More load 19/07/2019
Rolling elements name the bearing Spherical roller (symmetrical) Ball Spherical roller (asymmetrical) Needle roller Cylindrical roller Taper roller 19/07/2019
Bearing loads Radial load Fr Axial load Fa C o m b in e d load 19/07/2019
Radial rolling bearings Deep groove ball bearing Angular contact ball bearing Self-aligning ball bearing Cylindrical roller bearing Taper roller Needle roller bearing bearing Spherical roller bearing Ball bearings Roller bearings Radial rolling bearings 19/07/2019
Thrust ball bearing Ball bearings Roller bearings Thrust bearings Angular Contact Ball Thrust bearing Taper Roller Thrust bearing Spherical Roller Thrust bearing Cylindrical / Needle Roller Thrust bearing 19/07/2019
Bearings with shields and seals Shields Low-friction seals Seals -Z and -2Z -RZ and -2RZ -RS1 and -2RS1 Contaminant exclusion Silent running Grease retention Speed capability 19/07/2019
BALL BEARINGS Rolling elements are balls and are used in simple bearing applications. They have smaller load carrying capacity when compared to similar size roller bearings. Radial bearings: 1) Deep Groove Ball bearings (rigid, non-separable, both axial and radial loads, highest speed limits). Both rings contain grooves and due to this they can support high radial loads as well as some axial loads. Most widely used ball bearings. They are not self- aligning therefore accurate alignment between shaft and housing is required. There is a cage to position the rolling elements Single row deep groove ball bearings Have continuous deep raceways. Designed for radial loads. Can take some axial thrust as well 19/07/2019
STANDARDIZATION OF BEARINGS 19/07/2019
Ball bearing properties Deep groove ball bearing Angular contact Self-aligning ball bearing ball bearing radial load carrying capacity axial load carrying capacity speed capability can accommodate misalignment 19/07/2019
Self-aligning bearings They have 2 rows of balls with common raceway in the outer ring. This enables relative positioning of inner ring with respect to the outer ring and gives the bearing its self-aligning property. Accommodate misalignment due to mounting and shaft deflection. 19/07/2019
Angular contact ball bearings: Can support thrust loads combined with moderate radial loads. The axial difference between inner and outer rings provides the contact angles. There are: - Single row angular contact ball bearings (1 directional thrust) - Double row angular contact ball bearings (2 directional thrust) - Four-point (duplex) ball bearings (2 directional thrust) 19/07/2019
Thrust ball bearing a) Single direction thrust ball bearings: Carry thrust loads in one direction. They can locate shaft in 1 direction. b) Double direction thrust ball bearing Separable, only thrust capacity, not suitable for high speeds. Can carry thrust loads in both directions and can locate shaft in both directions. 19/07/2019
Angular Contact Thrust Ball Bearing Uses same principle as its radial counterpart in terms of raceway geometry. Capable of operating at higher speeds due to ability to support centrifugal loads on the balls by virtue of the inclined contact angle. Reasonable axial load capacity and offers high precision, typically assembled with pre-load or as preloaded pair Some features of ball bearings: - shields provide partial protection against dirt - seals provide better protection against dirt - if the bearing has seals on both sides’ leakage is prevented and the bearing may be factory oiled for life - single row bearings can withstand small amount of shaft misalignment and deflection - if there is severe misalignment or deflection, self- aligning bearings should be used. - Double row bearings can carry higher radial and thrust loads. They are better than two single row bearings because they require fewer parts and less space 19/07/2019
Roller Bearings In general, these bearings have greater load carrying capacity due to increased contact surface. They require closer tolerance on raceways and rollers. Heavier retainers are used. Some straight roller bearings can carry NO thrust load, some can carry thrust to a limited extend and some can carry great amount. Radial Roller Bearings 1. Cylindrical roller bearings: Separable, higher load carrying capacity, relatively high rotational speeds, those with lips on inner and outer rings can carry some thrust. Can accommodate LESS misalignment and deflection (very sensitive to misalignment). Construction differs for different types where locating lips are either present on one of the races or both. If both rings have location lips, then axial loads can be taken. When used with only location lips on one race relative axial movements possible 19/07/2019
Cylindrical roller bearings More and larger rollers Logarithmic contact profile plus optimised surface finish Improved roller end/flange contact geometry 3 cage variants: steel, polyamide, brass NU NUPNJ N NJ+HJNU+HJ 19/07/2019
2. Needle roller bearings Takes less radial space, they are long and thin (diameter to length ratio 2.5-10), high load carrying capacity. Should not be used where misalignment exist. 19/07/2019
3. Spherical roller bearings Have two rows of rollers with a common raceway in the outer ring. The two inner raceways are inclined to an angle to the bearing axis. Insensitive to misalignment. They can carry thrust loads in both directions in addition to radial loads. Allowable angular misalignment is between 1.50-30 Radial load capacity is high and high axial loads can be accommodated with appropriate ratio of radial load, axial load only capacity is poor and not recommended 19/07/2019
Spherical roller bearings Symmetrical rollers for maximum life under any conditions Floating guide ring gives minimum friction and ensures reliable operation Window-type steel cages strong and tolerant to high temperatures 19/07/2019
4. Taper roller bearings Have tapered inner and outer raceways Suitable for combined radial and axial loading They can carry axial loads in 1 direction only (single tapered) They should be used in pairs. Can support high loads. 19/07/2019
Spherical roller bearings Symmetrical rollers for maximum life under any conditions Floating guide ring gives minimum friction and ensures reliable operation Window-type steel cages strong and tolerant to high temperatures 19/07/2019
Thrust Roller Bearings 1. Cylindrical roller thrust bearing Carry only thrust loads in 1 direction Locate shaft in 1 direction Used mainly if capacity of thrust ball bearing is inadequate. No radial loads, speed is limited Sensitive to misalignment 2. Needle roller thrust bearing Suitable for axial space limited application 3. Spherical roller thrust bearings Carry radial loads in addition to thrust loads. Locate shaft in 1 direction Self-aligning can accommodate misalignment very high loads and moderate radial loads 19/07/2019
ROLLER BEARINGS 19/07/2019
4. Tapered roller thrust bearings Suitable for extremely high axial loads- no radial loads. Sensitive to face misalignment but can compensate for radial misalignment. Limited operating speeds, help to reduce sliding 19/07/2019
Single row and paired single row taper roller bearings Single row Face-to-face arrangement suffix DF Back-to-back arrangement suffix DB 19/07/2019
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Compact Aligning Roller Bearings CARB TM Safer, more optimized design Increased service life Lower running temperature Lower vibration and noise level Extended maintenance interval Higher axial clearence No internal Friction force Longer life Higher speed Downsizing possibility 19/07/2019
CARBTM - Bearing Compact Aligning Roller Bearing  Self-aligning as spherical roller bearing  Permits axial displacements like a cylindrical roller bearing  Compact as a needle roller bearing 19/07/2019
Advantages and disadvantages of rolling bearings compared to journal bearings: Advantages: - Low starting friction/torque - Ease of lubrication - Less axial space - Thrust and radial load support - Early warning against failure - Standard close tolerances - Preloading is possible - Freedom of shaft positioning - Special housing is available Disadvantages: - Greater radial space - Higher initial cost - More noise - Possibility of early failure - Finite life - Lower shock resistance Failure types of Rolling Element bearings: Failure is happening due to inadequate shaft guidance, excessive noise and vibration 1. Fatigue due to high fluctuating stresses (indications are pitting, spalling) 2. Failure due to misalignment, unsuitable loading, lack of lubrication, dirt/contamination 3. Outer raceway breakage due to overload 4. Cage (separator, retainer) failure- due to high centrifugal forces at high speeds 19/07/2019
Bearings are precision products Example: Tolerances for bore diameter 75 mm Precision High precision bearing bearing Normal Tolerance classes Standard P6 P5 SP P4A UP PA9A PA9B 0/-7 m 0/-2,5 m 0/-15 m 0/-12 m 0/-9 m How much is a m 1 0,06 mm A human hair 19/07/2019
Materials for rolling bearings Bearing rings and rolling elements 1. Through-hardening steels Carbon chromium steel containing approximately 1 %carbon and 1,5 % chromium 2. Case-hardening steels – Chromium-nickel alloyed steel – Manganese-chromium alloyed steel appr. 0,20 % carbon bearing steels have very high cleanliness – the content of macroand microinclusions is extremely low. 19/07/2019
Cages keep the rolling elements separated Prevent immediate contact between rolling elements to minimise friction and heat generation Guide the rolling elements Provide space for lubricant Serve to retain the rolling elements when bearings of separable design are mounted or dismounted 19/07/2019
Cage variants Polyamide cage + lightweight + high elasticity + good sliding properties + good marginal lubrication properties - operating temperature limit +120°C Window-type steel cage + lightweight + high strength + no operating temperature limit + high vibration and acceleration resistance - sensitive to poor lubrication Window-type brass cage + very high strength + very high vibration and acceleration resistance + suitable for very high speeds in connection with circulating oil lubrication - relatively expensive 19/07/2019
• Based on Nature ofContact 1. Sliding Contact Bearing Sliding takes place between the fixed and moving element of bearing and its also known as plain bearing 19/07/2019
SLIDING CONTACT BEARING • 1. Based on type of load carried • 2. Based on type of lubrication • 3. Based on lubrication mechanism Sliding contact bearings are classified in three ways. 19/07/2019
SLIDING CONTACT BEARING • Working surfaces separated by some medium or force • Working medium can be solids, fluids, gas or magnetic forces (or combination) • Reduced local friction but can have high drag losses • Life can become theoretically infinite due to lack of fatigue loads and wear • Often dependent on presence of other equipment to provide working media 19/07/2019
BASED ON TYPE OF LOAD CARRIED a. Radial bearings (These bearings carry only radial loads.) b. Thrust bearings or axial bearings ( These bearings carry only axial loads) c. Radial – thrust bearings (These bearings carry both radial and thrust loads. ) 19/07/2019
BASED ON TYPE OF LUBRICATION • The type of lubrication means the extent to which the contacting surfaces are separated in a shaft bearing combination. This classification includes (a) Thick film lubrication (b) Thin film lubrication (c) Boundary lubrication 19/07/2019
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JOURNAL BEARING Hydrodynamic Bearing Hydrostatic Bearing 19/07/2019
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Journal (Sleeve) Bearings Load is transferred through a lubricant in sliding contact 19/07/2019
JOURNAL (SLEEVE) BEARINGSThick-film lubrication (hydrodynamic), pressure distribution, and film thickness. hmin = minimum film thickness, c = radial clearance, e = eccentricity 19/07/2019
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PREVENTION OF ROTATION OF BRASSES 19/07/2019
DESIGNATION OF BEARINGS: Rolling contact bearings and necessary parts used for mounting and sealing of them have been all standardized by ISO. Bearings are designated by numbers and letters. 1. Bearing type 2. Dimension series 3. Borenumber 4. Specialshape 5. Special accuracy and clearance Bearing type: Numeric or alphanumeric designations areused 6- single row deep groove ball bearings 2- spherical roller bearings 3- taper roller bearings N-cylindrical roller bearings ….. etc Dimension series For each bearings size, there are standard series of outside diameter and width designations. - The first number in the dimension series indicates the shape of the cross section of the bearings, which is the ratio of the width to the outside diameter and called as width number. - The second number indicates the ratio of the outside diameter to the bore diameter and called as diameter number Width number- 0, 1, 2, 3, 4, 5, 6 Diameter number- 8, 9, 0, 1, 2, 3, 4 19/07/2019
EXAMPLE: 6314-ZN-C2 6- deep groove ball bearing 3- dimension series (03, 0 width is not written) 14- bore number 14x5=70mm Z- shield (non-rubbing seal) at one side N- snap ring groove at the surface of the outer ring C2- internal clearance is less than standard 6305-ZNR-P62 P6+C2 closer tolerance Bore Number Indicates the bore diameter of the bearing Bore number Bore diameter (mm) 00 10 01 12 02 15 03 17 n (n≥4) 5n Special Shape Numeric or alphanumeric designations are used Z : shield (non-rubbing seal) at one side of bearing 2Z: Z shields at both sides N : snap ring groove in outside cylindrical surface of outer ring NR: N with snap ring F : machined cage made of steel or iron 19/07/2019
PREPARATION FOR MOUNTING AND DIMOUNTING. Before mounting, all the necessary parts, tool, equipment and data need to be at hand. It is also recommended that any drawings or instruction be studied to determine the correct order in which to assemble the various components. Housing, shafts, seals and other components of the bearing arrangement need to be checked to see that they are clean, particularly any threaded holes, leads or grooves where remnants of previous machining operation might have collected. 19/07/2019
MOUNTING METHOD Depending on the bearing type, and size, mechanical, thermal and hydraulic methods are used for mounting. 1. Cold Mounting Method. 2. Hot Mounting Method 19/07/2019
COLD MOUNTING If the fit is not too tight, small bearings may be driven into position by applying light hammer blows to a sleeve placed against the bearing ring face. The blows should be evenly distributed around the ring to prevent the bearing from tilting or skewing. The use of the mounting dolly instead of a sleeve allows the mounting force to be applied centrally. 19/07/2019
HOT MOUNTING It is generally not possible to mount larger bearing in the cold state, as the force required to mount a bearing increases very considerably with increasing bearing size . The inner rings or the housings are there fore heated prior to mounting. Bearing should not be heated to more than 125c as otherwise dimensional changes caused by alterations in the structure of the bearing material may occur. Bearing fitted with shields or seals should not be heated above 80c because of their grease fill or seal material. 19/07/2019
POSITIONS OF BEARING 19/07/2019
DISMOUNTING METHOD If the bearings are to be used again after removal, the force used to dismount them must never be applied through the rolling elements. With separable bearings, the ring with the rolling element and cage assembly can be removed independently of the other ring. To dismount a bearing having an interference fit, the tools described in the following section may be used, the choice of tools will depend on bearing type, size and fit. 1. Cold dismounting. 2. Hot dismounting. 19/07/2019
COLD DISMOUNTING Small bearing maybe removed from their settings by applying light hammer blows via a suitable drift to the ring face, or preferably by using a puller The claws of the puller should be placed around the side face of the ring to be removed or an adjacent component. 19/07/2019
HOT DISMOUNTING Special induction heaters have been developed to dismount the inner ring of cylindrical roller bearing having no flanges or only one flange. They heat the inner ring rapidly without heating the shaft to any degree, so that the expanded ring can easily be removed. 19/07/2019
BEARING CLEARANCE Radial clearance Axial clearance 19/07/2019
Clearance Normal clearance Increased clearance because of temperature Reduced clearance because of tight fit Example: 6210/C3 = Deep groove ball bearing with clearance greater than Normal CN does not normally appear in the bearing designation Suffix clearance /C1 less than C2 /C2 less than Normal /CN Normal /C3 greater than Normal /C4 greater than C3 /C5 greater than C4 19/07/2019
SPECIALIZED BEARINGS: There are, of course, several kinds of bearings that are manufactured for specific applications, such as magnetic bearings and giant roller bearings.  Magnetic Bearings: Magnetic bearings are found in high-speed devices because it has no moving parts this stability enables it to support devices that move unconscionably fast.  Giant Roller Bearings: Giant roller bearings are used to move extremely large and heavy loads, such as buildings and large structural components. 19/07/2019
BEARING LUBRICATION 19/07/2019 Lubrication reduces friction. It also prevents wear and corrosion, and guards against solid and liquid contamination. Theoretically, a properly lubricated bearing operating under ideal conditions will last forever. This is not possible in reality, of course. But a properly lubricated bearing has the best chance of achieving its maximum service life.
LUBRICANT SUPLLY SYSTEM Oil and grease require different types of supply systems. Several oil and grease supply systems exist that meet the needs of various bearing applications. Oil supply systems include: oil baths, circulating oil systems, spray or mist systems, and the wick feed method. Grease supply systems include: housings (with or without grease fittings), grease chamber lubrication, and the grease quantity regulator. 19/07/2019
WHYLUBRICATION?? • Formation of protective film to        Reduce friction Prevent corrosion Remove wear particles and debris Provide efficient cooling Reduce wear Shock absorption Overall life improvement
LUBRICATION THEORY • Full film ● ● Static Hydrodynamic • Elastohydrodynamic ● ● Application of pressure / load Depends upon speeds, loads, lubricant viscosity • Boundary layer ● ● Layer separation not complete Results from insufficient lube, incorrect lube
GREASE Vs OILWhen greases?  Normal speed and temp conditions  Simpler / cheaper installation  Better adhesion  Protection against impurities  Less frequent application required When Oils?  High Speed and temp  Excellent cleaning and flushing characteristics  Can be used in recirculative systems  Can serve better in excessive dirt environment  More stable than greases
Bearing Life Failure mode - Spalling 19/07/2019
BEARING LIFE Bearing life is defined as the Number of revolutions that a bearing undergoes under a constant load ( Equivalent Dynamic Bearing Load ) before the first sign of fatigue failure occurs.
Calculating Dynamic Bearing Load G Kr Ka G1 Kr1 I II l a1 FrII FrI l a1 a2 Kr Ka III FrI FrII Kr1 Stationary Electrical Machine a2 19/07/2019
Bearing Selection Bearings are selected based on:  Load  Speed  Temperature  Environment  Life expectancy 19/07/2019
Selection of bearings Some aspects to be considered Available space Misalignment Speed Life Load/Direction Operating conditions L10 P = (C)p 19/07/2019
Load carrying capacity is expressed as the basic dynamic load rating Load carrying capacity of different bearing types having the same bore and outside diameters 19/07/2019
0 r/min Oil lubrication speed rating Grease lubrication speed rating Bearingspeed limit Speed ratings = speed limit 19/07/2019
Factors influencing speed capability Increases speed  Low loads  High accuracy  Good sliding properties of cage guiding surface  Correct clearance  Optimised lubrication  Effective cooling Reduces speed  High loads  Poor accuracy  Excess of lubricant  Lack of lubricant  Excessive lubricant viscosity  Poor cooling 19/07/2019
Basic Terminologies : 1. Static Load 1. Dynamic Load 1. Life Requirement 19/07/2019
BASIC DYNAMIC LOAD RATING ISO dynamicload rating C= Load that gives a basic rating life of 1 000 000 revolutions C 19/07/2019
BEARING LIFE CONSIDERATIONS VARY DEPENDING ON : Type of Rolling Element 1. Ball 2. Roller a. Cylindrical b. Needle c. Tapered d. Spherical I. Symmetrical II. Asymmetrical 19/07/2019
Load carrying capacity L10 = basic rating life, millions of revolutions C = basic dynamic load rating, N P = equivalent dynamic bearing load, N p = exponent of the life equation With the load P = C the L10 life will be 1 million revolutions 0Basic dynamic load rating C Basic static load rating C P P0 P P0 The ISO life equation s0 P0 C0 = static safety factor = equivalent static bearing load, N = basic static load rating, N With the load P = C0 the static safety factor s0 will be 1 The static safety factor s =0 C0 P0 ( )L =10 C P p 19/07/2019
Basic rating life equation: 19/07/2019
Adjusted Rating Life Equations: In the basic life equation effect of bearing load on the life is considered. However, by using adjusted bearing life equation effects of other factors can be considered. Index i (sometimes n) above represents difference between 100% and the required reliability (probability of a bearing to achieve a specified life). For instance, for 95% reliability, adjusted bearing rating life is denoted as L5a. If bearing is operating at constant speed, it may more convenient to express the rated life in terms of hours. The factors a2 and a3 are independent from each other and can be combined as a23. It is life adjustment factor for material and operating conditions. Lna=a1a23L10 Lna=a1a23(C/P)p Reliability factor a1 – This factor modifies the calculated life down to account for the extra level of reliability required above 90% and is based the fatigue probability principles already applied. Material adjustment factor a2 – For standard bearings the factor is equal to 1. The factor addresses the potential performance gains that can be achieved by material processing and principally cleanliness control. For specialist steel factors of 6 or more are quoted. Operating condition factor a3 – This factor takes into consideration the impact of operating conditions within the bearing. In particular is considers the effects of the lubrication conditions and material lubricant/environment cleanliness 19/07/2019
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Example: Solutions; a1=1 (80+40)/2=60=dm From fig.2 (with n=1500rpm) V1=15mm2/s From fig.3 (with T=60C, v40=220) V=60 mm2/s X=V/V1=60/15=4 a23=3 (from fig.4) L=a1*a23*(C/P)^p=1*3*(32.5/24)^3=1058= =8 million revolutions Lh=8*10^6/(1500*60)=89 hours 6208 DEEP Groove Ball bearing is to be used in application T=60 deg C, n=1500 rpm, ν40=220mm2/s. P=24000N. What is the adjusted rating life? 19/07/2019
Equivalent bearing load (Fe or P) Equivalent dynamic bearing load  Used for combination of radial and axial load. It is stationary radial load or axial if thrust bearing, if applied to a bearing, it will give same life as actual loading and rotating conditions.  A fictitious radial load is calculated to be compared with basic static and/or dynamic load rating.  P is supposed to have the same effect on bearing life as the actual loading consisting of Fa and Fr.  Thrust ball bearings Pa=Fa No radial load carrying capacity  Radial bearings P=Fr  Combined loading P=VXFr+YFa o P: equivalent dynamic load N o Fr: actual bearing radial load o Fa: actual bearing axial load o X: radial load factor o Y: axial load factor o The damaged bearing fit on the shaft o V: rotation factor  V=1 for rotating inner ring  V=1.2 for rotating outer ring (V=1 for self-aligning bearings) X and Y depends on the bearing type and its geometry. Plotting 19/07/2019
Basic static load rating ISO basic load rating Co corresponds to a stress that gives permanent deformation of 0,0001 of the rolling element diameter 19/07/2019
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BEARING LIFE P10 L = (C ) p Lnaa= a1 a SKF P (C)p ISO Load P Finite life Life The SKF New Life Theory Service life: This is the actual life achieved by the bearing before it fails. Load P Infinite life PU Life 19/07/2019
Friction Under certain conditions the frictional moment can be calculated with sufficient accuracy M = 0,5 . µ . F . d M = frictional moment (Nmm) µ = coefficient of friction F = bearing load (N) d = bearing bore diameter (mm) 19/07/2019
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Bearings PPT

  • 2. BEARINGS • Introduction • History • Classification of Bearing • Bearing Types • Bearing Structure • Bearing Mounting and Dismounting • Bearing Lubrication • Bearing Selection • Bearing Failure 19/07/2019
  • 3. Bearings 19/07/2019 Any machine or structure that has relative movement requires the use of bearings. Bearings are the most common component feature used in machines and structures The range of bearing types and associated applications is huge and without bearings the all motion would grind to a halt. Bearings are used in everyday items ranging from the more obvious applications such as washing machines, cars, the watches on our wrists but also super structures such as building supported on bearings to allow relative movements during earthquakes
  • 4. • Bearing provides relative rotational freedom and transmits a load between two structures. Inner Ring Cage Rolling Elements Outer Ring Wind Turbine Gearbox Construction of a bearing Bearings Bearings inside Gas Turbine Engine Induction Motor Bearing 4 19/07/2019
  • 5. What is Friction ? Friction is resistance to movement  it opposes sliding  it assists rotation 19/07/2019
  • 6. WHAT IS FRICTION? Plain bearings sliding friction Rolling bearings rolling friction   19/07/2019
  • 8. How did a bearing evolve ? Bearing history - a never-ending story 1100 B.C. 3500 B.C. 1995 1794 40 A.D. 1869 19/07/2019
  • 9. How did a bearing evolve ? * Invention of wheel * Wheel rotates on axle * Wear Plate + Rollers * Inner ring + Outer ring + Rollers * With introduction of cage Rolling Bearing was created 19/07/2019
  • 10. • BASED ON NATURE OF CONTACT • 1. Rolling Contact Bearings Balls or rollers introduced between moving and fixed elements and it is also known as anti-friction bearings • 2. Sliding Contact Bearing Sliding takes place between the fixed and moving element of bearing and its also known as plain bearing CLASIFICATION OF BEARING 1 19/07/2019
  • 11. Rolling Element Bearings They are also called antifriction bearings/rolling contact bearings/rolling bearings. Load is transferred through elements in rolling contact. These bearings locate the shaft in axial and radial direction. Starting friction is twice as the running friction. REB is an assembly rather than single element. There bearings are manufactured to take loads: - Pure radial - Pure axial (thrust) - Combined (radial and thrust) They are designed taking into consideration below points: - Space limitations - Load characteristics - Life fatigue - Friction, heat - Corrosion resistance - Material properties - Lubrication - Tolerances - Cost and etc 19/07/2019
  • 12. BEARING TYPES: Can be classified according to shape of element and load type. According to the type of element: - Ball bearings - Roller Bearings According to the type of the load Some bearings can carry both axial and radial loads - Radial bearings (ring bearings radial loads) - Thrust bearings (axial loads 19/07/2019
  • 13. The components of a bearing Seal Rolling elements Inner ring Outer ring SealCage 19/07/2019
  • 14. Pg. 7 Bearing Installation and Maintenance Guide Bearing Basics 19/07/2019
  • 16. Characteristics Deep groove Angular ball bearing contact ball bearing Self-aligning ball bearing Ball bearings Point Contact : Cylindrical roller bearing Taper Needle roller roller bearing bearing Spherical roller bearing * Less area of contact * Less friction * More speed * Less load Roller bearings Line Contact : * More area of contact * More friction * Less speed * More load 19/07/2019
  • 17. Rolling elements name the bearing Spherical roller (symmetrical) Ball Spherical roller (asymmetrical) Needle roller Cylindrical roller Taper roller 19/07/2019
  • 18. Bearing loads Radial load Fr Axial load Fa C o m b in e d load 19/07/2019
  • 19. Radial rolling bearings Deep groove ball bearing Angular contact ball bearing Self-aligning ball bearing Cylindrical roller bearing Taper roller Needle roller bearing bearing Spherical roller bearing Ball bearings Roller bearings Radial rolling bearings 19/07/2019
  • 20. Thrust ball bearing Ball bearings Roller bearings Thrust bearings Angular Contact Ball Thrust bearing Taper Roller Thrust bearing Spherical Roller Thrust bearing Cylindrical / Needle Roller Thrust bearing 19/07/2019
  • 21. Bearings with shields and seals Shields Low-friction seals Seals -Z and -2Z -RZ and -2RZ -RS1 and -2RS1 Contaminant exclusion Silent running Grease retention Speed capability 19/07/2019
  • 22. BALL BEARINGS Rolling elements are balls and are used in simple bearing applications. They have smaller load carrying capacity when compared to similar size roller bearings. Radial bearings: 1) Deep Groove Ball bearings (rigid, non-separable, both axial and radial loads, highest speed limits). Both rings contain grooves and due to this they can support high radial loads as well as some axial loads. Most widely used ball bearings. They are not self- aligning therefore accurate alignment between shaft and housing is required. There is a cage to position the rolling elements Single row deep groove ball bearings Have continuous deep raceways. Designed for radial loads. Can take some axial thrust as well 19/07/2019
  • 24. Ball bearing properties Deep groove ball bearing Angular contact Self-aligning ball bearing ball bearing radial load carrying capacity axial load carrying capacity speed capability can accommodate misalignment 19/07/2019
  • 25. Self-aligning bearings They have 2 rows of balls with common raceway in the outer ring. This enables relative positioning of inner ring with respect to the outer ring and gives the bearing its self-aligning property. Accommodate misalignment due to mounting and shaft deflection. 19/07/2019
  • 26. Angular contact ball bearings: Can support thrust loads combined with moderate radial loads. The axial difference between inner and outer rings provides the contact angles. There are: - Single row angular contact ball bearings (1 directional thrust) - Double row angular contact ball bearings (2 directional thrust) - Four-point (duplex) ball bearings (2 directional thrust) 19/07/2019
  • 27. Thrust ball bearing a) Single direction thrust ball bearings: Carry thrust loads in one direction. They can locate shaft in 1 direction. b) Double direction thrust ball bearing Separable, only thrust capacity, not suitable for high speeds. Can carry thrust loads in both directions and can locate shaft in both directions. 19/07/2019
  • 28. Angular Contact Thrust Ball Bearing Uses same principle as its radial counterpart in terms of raceway geometry. Capable of operating at higher speeds due to ability to support centrifugal loads on the balls by virtue of the inclined contact angle. Reasonable axial load capacity and offers high precision, typically assembled with pre-load or as preloaded pair Some features of ball bearings: - shields provide partial protection against dirt - seals provide better protection against dirt - if the bearing has seals on both sides’ leakage is prevented and the bearing may be factory oiled for life - single row bearings can withstand small amount of shaft misalignment and deflection - if there is severe misalignment or deflection, self- aligning bearings should be used. - Double row bearings can carry higher radial and thrust loads. They are better than two single row bearings because they require fewer parts and less space 19/07/2019
  • 29. Roller Bearings In general, these bearings have greater load carrying capacity due to increased contact surface. They require closer tolerance on raceways and rollers. Heavier retainers are used. Some straight roller bearings can carry NO thrust load, some can carry thrust to a limited extend and some can carry great amount. Radial Roller Bearings 1. Cylindrical roller bearings: Separable, higher load carrying capacity, relatively high rotational speeds, those with lips on inner and outer rings can carry some thrust. Can accommodate LESS misalignment and deflection (very sensitive to misalignment). Construction differs for different types where locating lips are either present on one of the races or both. If both rings have location lips, then axial loads can be taken. When used with only location lips on one race relative axial movements possible 19/07/2019
  • 30. Cylindrical roller bearings More and larger rollers Logarithmic contact profile plus optimised surface finish Improved roller end/flange contact geometry 3 cage variants: steel, polyamide, brass NU NUPNJ N NJ+HJNU+HJ 19/07/2019
  • 31. 2. Needle roller bearings Takes less radial space, they are long and thin (diameter to length ratio 2.5-10), high load carrying capacity. Should not be used where misalignment exist. 19/07/2019
  • 32. 3. Spherical roller bearings Have two rows of rollers with a common raceway in the outer ring. The two inner raceways are inclined to an angle to the bearing axis. Insensitive to misalignment. They can carry thrust loads in both directions in addition to radial loads. Allowable angular misalignment is between 1.50-30 Radial load capacity is high and high axial loads can be accommodated with appropriate ratio of radial load, axial load only capacity is poor and not recommended 19/07/2019
  • 33. Spherical roller bearings Symmetrical rollers for maximum life under any conditions Floating guide ring gives minimum friction and ensures reliable operation Window-type steel cages strong and tolerant to high temperatures 19/07/2019
  • 34. 4. Taper roller bearings Have tapered inner and outer raceways Suitable for combined radial and axial loading They can carry axial loads in 1 direction only (single tapered) They should be used in pairs. Can support high loads. 19/07/2019
  • 35. Spherical roller bearings Symmetrical rollers for maximum life under any conditions Floating guide ring gives minimum friction and ensures reliable operation Window-type steel cages strong and tolerant to high temperatures 19/07/2019
  • 36. Thrust Roller Bearings 1. Cylindrical roller thrust bearing Carry only thrust loads in 1 direction Locate shaft in 1 direction Used mainly if capacity of thrust ball bearing is inadequate. No radial loads, speed is limited Sensitive to misalignment 2. Needle roller thrust bearing Suitable for axial space limited application 3. Spherical roller thrust bearings Carry radial loads in addition to thrust loads. Locate shaft in 1 direction Self-aligning can accommodate misalignment very high loads and moderate radial loads 19/07/2019
  • 38. 4. Tapered roller thrust bearings Suitable for extremely high axial loads- no radial loads. Sensitive to face misalignment but can compensate for radial misalignment. Limited operating speeds, help to reduce sliding 19/07/2019
  • 39. Single row and paired single row taper roller bearings Single row Face-to-face arrangement suffix DF Back-to-back arrangement suffix DB 19/07/2019
  • 41. Compact Aligning Roller Bearings CARB TM Safer, more optimized design Increased service life Lower running temperature Lower vibration and noise level Extended maintenance interval Higher axial clearence No internal Friction force Longer life Higher speed Downsizing possibility 19/07/2019
  • 42. CARBTM - Bearing Compact Aligning Roller Bearing  Self-aligning as spherical roller bearing  Permits axial displacements like a cylindrical roller bearing  Compact as a needle roller bearing 19/07/2019
  • 43. Advantages and disadvantages of rolling bearings compared to journal bearings: Advantages: - Low starting friction/torque - Ease of lubrication - Less axial space - Thrust and radial load support - Early warning against failure - Standard close tolerances - Preloading is possible - Freedom of shaft positioning - Special housing is available Disadvantages: - Greater radial space - Higher initial cost - More noise - Possibility of early failure - Finite life - Lower shock resistance Failure types of Rolling Element bearings: Failure is happening due to inadequate shaft guidance, excessive noise and vibration 1. Fatigue due to high fluctuating stresses (indications are pitting, spalling) 2. Failure due to misalignment, unsuitable loading, lack of lubrication, dirt/contamination 3. Outer raceway breakage due to overload 4. Cage (separator, retainer) failure- due to high centrifugal forces at high speeds 19/07/2019
  • 44. Bearings are precision products Example: Tolerances for bore diameter 75 mm Precision High precision bearing bearing Normal Tolerance classes Standard P6 P5 SP P4A UP PA9A PA9B 0/-7 m 0/-2,5 m 0/-15 m 0/-12 m 0/-9 m How much is a m 1 0,06 mm A human hair 19/07/2019
  • 45. Materials for rolling bearings Bearing rings and rolling elements 1. Through-hardening steels Carbon chromium steel containing approximately 1 %carbon and 1,5 % chromium 2. Case-hardening steels – Chromium-nickel alloyed steel – Manganese-chromium alloyed steel appr. 0,20 % carbon bearing steels have very high cleanliness – the content of macroand microinclusions is extremely low. 19/07/2019
  • 46. Cages keep the rolling elements separated Prevent immediate contact between rolling elements to minimise friction and heat generation Guide the rolling elements Provide space for lubricant Serve to retain the rolling elements when bearings of separable design are mounted or dismounted 19/07/2019
  • 47. Cage variants Polyamide cage + lightweight + high elasticity + good sliding properties + good marginal lubrication properties - operating temperature limit +120°C Window-type steel cage + lightweight + high strength + no operating temperature limit + high vibration and acceleration resistance - sensitive to poor lubrication Window-type brass cage + very high strength + very high vibration and acceleration resistance + suitable for very high speeds in connection with circulating oil lubrication - relatively expensive 19/07/2019
  • 48. • Based on Nature ofContact 1. Sliding Contact Bearing Sliding takes place between the fixed and moving element of bearing and its also known as plain bearing 19/07/2019
  • 49. SLIDING CONTACT BEARING • 1. Based on type of load carried • 2. Based on type of lubrication • 3. Based on lubrication mechanism Sliding contact bearings are classified in three ways. 19/07/2019
  • 50. SLIDING CONTACT BEARING • Working surfaces separated by some medium or force • Working medium can be solids, fluids, gas or magnetic forces (or combination) • Reduced local friction but can have high drag losses • Life can become theoretically infinite due to lack of fatigue loads and wear • Often dependent on presence of other equipment to provide working media 19/07/2019
  • 51. BASED ON TYPE OF LOAD CARRIED a. Radial bearings (These bearings carry only radial loads.) b. Thrust bearings or axial bearings ( These bearings carry only axial loads) c. Radial – thrust bearings (These bearings carry both radial and thrust loads. ) 19/07/2019
  • 52. BASED ON TYPE OF LUBRICATION • The type of lubrication means the extent to which the contacting surfaces are separated in a shaft bearing combination. This classification includes (a) Thick film lubrication (b) Thin film lubrication (c) Boundary lubrication 19/07/2019
  • 56. Journal (Sleeve) Bearings Load is transferred through a lubricant in sliding contact 19/07/2019
  • 57. JOURNAL (SLEEVE) BEARINGSThick-film lubrication (hydrodynamic), pressure distribution, and film thickness. hmin = minimum film thickness, c = radial clearance, e = eccentricity 19/07/2019
  • 59. PREVENTION OF ROTATION OF BRASSES 19/07/2019
  • 60. DESIGNATION OF BEARINGS: Rolling contact bearings and necessary parts used for mounting and sealing of them have been all standardized by ISO. Bearings are designated by numbers and letters. 1. Bearing type 2. Dimension series 3. Borenumber 4. Specialshape 5. Special accuracy and clearance Bearing type: Numeric or alphanumeric designations areused 6- single row deep groove ball bearings 2- spherical roller bearings 3- taper roller bearings N-cylindrical roller bearings ….. etc Dimension series For each bearings size, there are standard series of outside diameter and width designations. - The first number in the dimension series indicates the shape of the cross section of the bearings, which is the ratio of the width to the outside diameter and called as width number. - The second number indicates the ratio of the outside diameter to the bore diameter and called as diameter number Width number- 0, 1, 2, 3, 4, 5, 6 Diameter number- 8, 9, 0, 1, 2, 3, 4 19/07/2019
  • 61. EXAMPLE: 6314-ZN-C2 6- deep groove ball bearing 3- dimension series (03, 0 width is not written) 14- bore number 14x5=70mm Z- shield (non-rubbing seal) at one side N- snap ring groove at the surface of the outer ring C2- internal clearance is less than standard 6305-ZNR-P62 P6+C2 closer tolerance Bore Number Indicates the bore diameter of the bearing Bore number Bore diameter (mm) 00 10 01 12 02 15 03 17 n (n≥4) 5n Special Shape Numeric or alphanumeric designations are used Z : shield (non-rubbing seal) at one side of bearing 2Z: Z shields at both sides N : snap ring groove in outside cylindrical surface of outer ring NR: N with snap ring F : machined cage made of steel or iron 19/07/2019
  • 62. PREPARATION FOR MOUNTING AND DIMOUNTING. Before mounting, all the necessary parts, tool, equipment and data need to be at hand. It is also recommended that any drawings or instruction be studied to determine the correct order in which to assemble the various components. Housing, shafts, seals and other components of the bearing arrangement need to be checked to see that they are clean, particularly any threaded holes, leads or grooves where remnants of previous machining operation might have collected. 19/07/2019
  • 63. MOUNTING METHOD Depending on the bearing type, and size, mechanical, thermal and hydraulic methods are used for mounting. 1. Cold Mounting Method. 2. Hot Mounting Method 19/07/2019
  • 64. COLD MOUNTING If the fit is not too tight, small bearings may be driven into position by applying light hammer blows to a sleeve placed against the bearing ring face. The blows should be evenly distributed around the ring to prevent the bearing from tilting or skewing. The use of the mounting dolly instead of a sleeve allows the mounting force to be applied centrally. 19/07/2019
  • 65. HOT MOUNTING It is generally not possible to mount larger bearing in the cold state, as the force required to mount a bearing increases very considerably with increasing bearing size . The inner rings or the housings are there fore heated prior to mounting. Bearing should not be heated to more than 125c as otherwise dimensional changes caused by alterations in the structure of the bearing material may occur. Bearing fitted with shields or seals should not be heated above 80c because of their grease fill or seal material. 19/07/2019
  • 67. DISMOUNTING METHOD If the bearings are to be used again after removal, the force used to dismount them must never be applied through the rolling elements. With separable bearings, the ring with the rolling element and cage assembly can be removed independently of the other ring. To dismount a bearing having an interference fit, the tools described in the following section may be used, the choice of tools will depend on bearing type, size and fit. 1. Cold dismounting. 2. Hot dismounting. 19/07/2019
  • 68. COLD DISMOUNTING Small bearing maybe removed from their settings by applying light hammer blows via a suitable drift to the ring face, or preferably by using a puller The claws of the puller should be placed around the side face of the ring to be removed or an adjacent component. 19/07/2019
  • 69. HOT DISMOUNTING Special induction heaters have been developed to dismount the inner ring of cylindrical roller bearing having no flanges or only one flange. They heat the inner ring rapidly without heating the shaft to any degree, so that the expanded ring can easily be removed. 19/07/2019
  • 71. Clearance Normal clearance Increased clearance because of temperature Reduced clearance because of tight fit Example: 6210/C3 = Deep groove ball bearing with clearance greater than Normal CN does not normally appear in the bearing designation Suffix clearance /C1 less than C2 /C2 less than Normal /CN Normal /C3 greater than Normal /C4 greater than C3 /C5 greater than C4 19/07/2019
  • 72. SPECIALIZED BEARINGS: There are, of course, several kinds of bearings that are manufactured for specific applications, such as magnetic bearings and giant roller bearings.  Magnetic Bearings: Magnetic bearings are found in high-speed devices because it has no moving parts this stability enables it to support devices that move unconscionably fast.  Giant Roller Bearings: Giant roller bearings are used to move extremely large and heavy loads, such as buildings and large structural components. 19/07/2019
  • 73. BEARING LUBRICATION 19/07/2019 Lubrication reduces friction. It also prevents wear and corrosion, and guards against solid and liquid contamination. Theoretically, a properly lubricated bearing operating under ideal conditions will last forever. This is not possible in reality, of course. But a properly lubricated bearing has the best chance of achieving its maximum service life.
  • 74. LUBRICANT SUPLLY SYSTEM Oil and grease require different types of supply systems. Several oil and grease supply systems exist that meet the needs of various bearing applications. Oil supply systems include: oil baths, circulating oil systems, spray or mist systems, and the wick feed method. Grease supply systems include: housings (with or without grease fittings), grease chamber lubrication, and the grease quantity regulator. 19/07/2019
  • 75. WHYLUBRICATION?? • Formation of protective film to        Reduce friction Prevent corrosion Remove wear particles and debris Provide efficient cooling Reduce wear Shock absorption Overall life improvement
  • 76. LUBRICATION THEORY • Full film ● ● Static Hydrodynamic • Elastohydrodynamic ● ● Application of pressure / load Depends upon speeds, loads, lubricant viscosity • Boundary layer ● ● Layer separation not complete Results from insufficient lube, incorrect lube
  • 77. GREASE Vs OILWhen greases?  Normal speed and temp conditions  Simpler / cheaper installation  Better adhesion  Protection against impurities  Less frequent application required When Oils?  High Speed and temp  Excellent cleaning and flushing characteristics  Can be used in recirculative systems  Can serve better in excessive dirt environment  More stable than greases
  • 78. Bearing Life Failure mode - Spalling 19/07/2019
  • 79. BEARING LIFE Bearing life is defined as the Number of revolutions that a bearing undergoes under a constant load ( Equivalent Dynamic Bearing Load ) before the first sign of fatigue failure occurs.
  • 80. Calculating Dynamic Bearing Load G Kr Ka G1 Kr1 I II l a1 FrII FrI l a1 a2 Kr Ka III FrI FrII Kr1 Stationary Electrical Machine a2 19/07/2019
  • 81. Bearing Selection Bearings are selected based on:  Load  Speed  Temperature  Environment  Life expectancy 19/07/2019
  • 82. Selection of bearings Some aspects to be considered Available space Misalignment Speed Life Load/Direction Operating conditions L10 P = (C)p 19/07/2019
  • 83. Load carrying capacity is expressed as the basic dynamic load rating Load carrying capacity of different bearing types having the same bore and outside diameters 19/07/2019
  • 84. 0 r/min Oil lubrication speed rating Grease lubrication speed rating Bearingspeed limit Speed ratings = speed limit 19/07/2019
  • 85. Factors influencing speed capability Increases speed  Low loads  High accuracy  Good sliding properties of cage guiding surface  Correct clearance  Optimised lubrication  Effective cooling Reduces speed  High loads  Poor accuracy  Excess of lubricant  Lack of lubricant  Excessive lubricant viscosity  Poor cooling 19/07/2019
  • 86. Basic Terminologies : 1. Static Load 1. Dynamic Load 1. Life Requirement 19/07/2019
  • 87. BASIC DYNAMIC LOAD RATING ISO dynamicload rating C= Load that gives a basic rating life of 1 000 000 revolutions C 19/07/2019
  • 88. BEARING LIFE CONSIDERATIONS VARY DEPENDING ON : Type of Rolling Element 1. Ball 2. Roller a. Cylindrical b. Needle c. Tapered d. Spherical I. Symmetrical II. Asymmetrical 19/07/2019
  • 89. Load carrying capacity L10 = basic rating life, millions of revolutions C = basic dynamic load rating, N P = equivalent dynamic bearing load, N p = exponent of the life equation With the load P = C the L10 life will be 1 million revolutions 0Basic dynamic load rating C Basic static load rating C P P0 P P0 The ISO life equation s0 P0 C0 = static safety factor = equivalent static bearing load, N = basic static load rating, N With the load P = C0 the static safety factor s0 will be 1 The static safety factor s =0 C0 P0 ( )L =10 C P p 19/07/2019
  • 90. Basic rating life equation: 19/07/2019
  • 91. Adjusted Rating Life Equations: In the basic life equation effect of bearing load on the life is considered. However, by using adjusted bearing life equation effects of other factors can be considered. Index i (sometimes n) above represents difference between 100% and the required reliability (probability of a bearing to achieve a specified life). For instance, for 95% reliability, adjusted bearing rating life is denoted as L5a. If bearing is operating at constant speed, it may more convenient to express the rated life in terms of hours. The factors a2 and a3 are independent from each other and can be combined as a23. It is life adjustment factor for material and operating conditions. Lna=a1a23L10 Lna=a1a23(C/P)p Reliability factor a1 – This factor modifies the calculated life down to account for the extra level of reliability required above 90% and is based the fatigue probability principles already applied. Material adjustment factor a2 – For standard bearings the factor is equal to 1. The factor addresses the potential performance gains that can be achieved by material processing and principally cleanliness control. For specialist steel factors of 6 or more are quoted. Operating condition factor a3 – This factor takes into consideration the impact of operating conditions within the bearing. In particular is considers the effects of the lubrication conditions and material lubricant/environment cleanliness 19/07/2019
  • 95. Example: Solutions; a1=1 (80+40)/2=60=dm From fig.2 (with n=1500rpm) V1=15mm2/s From fig.3 (with T=60C, v40=220) V=60 mm2/s X=V/V1=60/15=4 a23=3 (from fig.4) L=a1*a23*(C/P)^p=1*3*(32.5/24)^3=1058= =8 million revolutions Lh=8*10^6/(1500*60)=89 hours 6208 DEEP Groove Ball bearing is to be used in application T=60 deg C, n=1500 rpm, ν40=220mm2/s. P=24000N. What is the adjusted rating life? 19/07/2019
  • 96. Equivalent bearing load (Fe or P) Equivalent dynamic bearing load  Used for combination of radial and axial load. It is stationary radial load or axial if thrust bearing, if applied to a bearing, it will give same life as actual loading and rotating conditions.  A fictitious radial load is calculated to be compared with basic static and/or dynamic load rating.  P is supposed to have the same effect on bearing life as the actual loading consisting of Fa and Fr.  Thrust ball bearings Pa=Fa No radial load carrying capacity  Radial bearings P=Fr  Combined loading P=VXFr+YFa o P: equivalent dynamic load N o Fr: actual bearing radial load o Fa: actual bearing axial load o X: radial load factor o Y: axial load factor o The damaged bearing fit on the shaft o V: rotation factor  V=1 for rotating inner ring  V=1.2 for rotating outer ring (V=1 for self-aligning bearings) X and Y depends on the bearing type and its geometry. Plotting 19/07/2019
  • 97. Basic static load rating ISO basic load rating Co corresponds to a stress that gives permanent deformation of 0,0001 of the rolling element diameter 19/07/2019
  • 100. BEARING LIFE P10 L = (C ) p Lnaa= a1 a SKF P (C)p ISO Load P Finite life Life The SKF New Life Theory Service life: This is the actual life achieved by the bearing before it fails. Load P Infinite life PU Life 19/07/2019
  • 101. Friction Under certain conditions the frictional moment can be calculated with sufficient accuracy M = 0,5 . µ . F . d M = frictional moment (Nmm) µ = coefficient of friction F = bearing load (N) d = bearing bore diameter (mm) 19/07/2019

Editor's Notes