Ttqc (1)

Ttqc (1)

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  1 Department Of TextileEngineering Assignment on Cotton Fibre Length Measurement By Using Fibrograph. Course Code: Tex-2031 Course Title: Textile Testing & Quality Control-1 Submitted To: Mr. S.M. Masum Alam Lecturer, Southeast University. Submitted By: Name : Sagor Saha Id : 2015100400006 Batch : 29th Section : A Submission Date: 19.04.2017
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  2 Introduction: Fiber length isone of the most important quality of cotton contributing to higher yarn strength, spin ability and reduced end breakages in spinning. Short fibre content has pronounced effect on waste, yarn irregularity, appearance and end breakages Conventional and HVI instruments used for testing fibre length parameters of cottons are briefly reviewed here. The determination of fibre length is of a greater importance both for the trader and technician. Several instruments are available for determining the fibre length characteristics of cotton. However, each instrument is based on a different principle. The fibrograph is an optical instrument employing photovoltaic cells for scanning samples of parallel fibers and tracing a type of length- frequency curve. The theory is developed for a sample of parallel fibers in which the fibers are positioned at random. Due to the method of holding the sample in the comb, the instrument does not include in its measurement those fibers of approximately ¼ inch and shorter. Therefore, the use of the instrument for determining the length of machine waste results in entirely erroneous and misleading measurements, inasmuch as a large proportion of the fibers in waste is made up of very short fibers. Objects: 1.To know about different length of fibres. 2. To know about the Fibrograph m/c and its different parts. 3. To find out the fibre length by using Fibrograph. Principle: It is an optical instrument with light sensitive cells for scanning cotton fibres and simultaneously drawing a length- frequency curve. The height of the vertical axis of the fibro gram is equal to the total fibre length if it is assumed that the fibres have the same linear density, it can be state that the height of the fibrograph is proportional to the weight of the fibre. The horizontal axis of the fibrograph: The horizontal axis of the fibrograph is expressed in percentages of amount of fibres. A span length is that length which a certain percentage of fibres from the original fibre population would spam when caught at random along their length. i.e, span length is a distance from a line where the fibres are caught randomly to a point where only a certain percentage of fibre extend. Thus, 2.5%span length is that length which 1/40th of the fibres would span when randomly caught along their lengths. The figure represents a state of fibres caught by a clamp all loose fibres to the right of the clamp are removed. The clamp moves from this position
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  3 to the righttill only 225 fibres, i.e, 2.5% of 9000. The distance D is the 2.5% span length. In this way 50%SL, and 67.7%s.l can all be determined. This method of measuring fibre length is more realistic than can sorter technique, since it is a measure derived from the fibre oriented in a similar fashion to fibre in process. i.e, randomly arranged rather than the fibre ends co-terminus along base line. Difference between Fibre length and Span length: Span length is the fibre extension distance and it is not the fibre length. The staple diagram is universally accepted as the ultimate in expression of the end- to- end length of fibre. The sorter test is the laboratory method of expressing fibre length in staple diagram configuration. Fibre arrangements of the staple diagram relate to end-to-end fibre length but not so easy to yarn spinning. Fibre arrangements of the fibrogram relate to spinning but not so easy to end-to-end fibre length. Actual fibre extension in yarn manufacture cannot be easily determined from the staple diagram. Similarly span length cannot be used to determine the end- to-end fibre length. The staple diagram represents fibres as observed in the laboratory the fibrogram represents the same fibre as they would appear in spinning. Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to total length of all fibres in the sample and that the point of catch for a fibre is at random along its length.
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  4 Fig. Fibrograph.
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  5 Apparatus: B- Photocell, L-LightSource, C- Fibre length, p- Pen, D-Card, H- Card Holder, E- Comb, G- Galvanometer, S1- Scanning slit, S2- Glass Screen, W1- LH Hand Wheel, W2- RH Hand Wheel. Preparation of test samples: Select small tufts of fibres at random from the lab sample. The weight of the test sample is around 400 milligram. The small tufts are placed one above the other and entire bundle is pulled apart into two parts with thumb and fore finger. The two parts of the sample are superimposed over each other with the broken edges of two parts in one line. Using one comb, comb all the broken edges until the fibre sample is uniformly distributed over the full length of the comb. Then holding this comb with its teeth pointing upwards, comb the fibre gently with other comb, increasing the depth of penetration of the teeth for each stroke. The hold both the combs with their teeth pointing upwards, place one comb in a position such that its teeth almost touch the base or the teeth of the other comb. Deposit the fibre on the teeth of the bottom comb by pushing straight down the top Comb. Repeat this combing and transferring three times. At the last transfer, the fibres will be distributed evenly over the length of the combs, with an equal amount being on each comb. Combing Strokes for cotton 20 for initial combing, 10 after first transfer and 10 after second transfer.
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  6 Description and working: Thecombs are placed in the instrument as shown in fig. so that the fibres can be scanned. A narrow slit is provided in which the photo electric cell A is placed. Over the slit, the combed fibres are placed. Above the fibres, a fluorescent tubular light is provided. Another light from an incandescent lamp through a glass screen falls onto a second photo cell B. The intensity of this light can be varied by rotating the right hand-hand wheel. If the current passing through the photo cell A is matched by the current passing through the photo cell B then the system is in balance and the galvanometer will show null deflection. The fibre fringe is so positioned that the centre line of the scanning slit coincides with a line ¼ inch away from the comb teeth. In this condition, the right hand- hand wheel is turned to give an optical balance. The fringes are now traversed upwards by the left hand – hand wheel which imparts corresponding movement to a pen. The vertical displacement of the pen thus registers the fibre length. As the fibres are going up, the obstruction to the light by the fibres becomes less and the amounts of light through the photo cell a increases. The extent of increase is measured by rotating the right hand –hand wheel, which not only adjust the current through the cell B but also traverses the card horizontally. The horizontal displacement of the pen relative to the card is thus taken to represent the changes in relative number of fibres during scanning. By rotating both LH and RH wheels simultaneously, we get a smooth length – frequency curve which is called as Fibrogram. Time taken for one test is 10 minutes. Analysis of the Fibrogram: The fibrogram obtained from fibrograph is shown in fig. From the point X which is either the starting point of the pen ¼ inch above the base line, a tangent is drawn to the curve, which meets OX at the point N and OY at the point A. Measure OA which is the mean length. Measure ON, take a point S which is half of ON . Draw another tangent from S to the curve meeting the like OY at T. Measure OT ie, Upper Half Mean length. The upper Half Mean length is the mean length of the longer 50% of the fibres in the sample from which the clamped fibre test specimen was prepared. Getting the two values, mean length and upper half mean length, uniformity ratio of the sample can be measured which is the ratio between mean length and upper half mean length expressed as a percentage. 2.5% Span length: It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial
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  7 starting point ofthe scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH". 50% Span length: It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH". For the span lengths measured, average the results for all specimens in inches to two decimal places or in millimeters to one decimal place. Calculate the Uniformity ratio by dividing the average of the shorter span lengths by the average of the longer span lengths. Multiply the ratio by 100 to convert it to a percentage and round it off to a whole number I.e., Uniformity Ratio = 50% span length /2.5% span length*100
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  8 Classification of cottonaccording to Staple Length and Span Length Values: At present five staple length categories are used for classification of cotton as follows: No category Staple length range in mm 01 Short 19 and below 02 Medium 20 to 21.5 03 Superior Medium 22 to 24 04 Long 24.5 to 26 05 Superior Long 27 and above According to 2.5% span length values cotton is classified into the staple length categories as follows: No Category 2.5% span length in inch 01 Short Below 1 02 Medium 1 to 1.14 03 Long 1.15 to 1.29 04 Extra long Above 1.29 Merits: 1. Simulates beard formed by fibres held by back or front roller nip of a drafting system 2. Very rapid (about 1 - 4 min per sample) 3. Does not depend much upon operator skill. 4. Effective length is close to graders staple length 5. Provides accurate estimate of short fibre content Limitations: Fibrograph: Beard of fibres is prepared by picking the fibres randomly from the sample by a comb and loose fibres brushed aside. The beard is optically scanned from the base to tip from which a fibrogram is drawn. The comb has 28 needles/inch. Since long fibres have a proportionally higher probability to be caught by comb this results in a length biased sample. The instrument based on this principle was developed by Hertel. Upper half mean length, mean length and Uniformity index are determined from the fibrogram by drawing tangents to the curve. ASTM D1447 - 07(2012)e1 gives the Standard Test Method for Length and Length Uniformity of Cotton Fibers by instruments like Fibrograph. Mechanisation of measurement of length in the instrument resulted in servo fibrograph.
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  9 Conclusion: Fibrograph measurements providea relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner. Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors. Fibrograph tests are more objective than commercial staple length classifications and also provide additional information on fibre length uniformity of cotoon fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes. THE END