Baer’s Comb Sorter

Baer’s Comb Sorter Diagram Fibre Length: The â€Å"length† of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries Mean length:It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight. Upper quartile length: It is that value of length for which 75% of all the observed values are lower, and 25% higher. Effective length: It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a numerical length distribution liminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length. Modal length: It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the follwing way.(Mode-Mean) = 3(Median-Mean) where, Median is the particular value of length above and below which exactly 50% of the fibres lie. 2. 5% Span length: It is defined as the distance spanned by 2. % 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 â€Å"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 te st is considered 100%. This length is measured using â€Å"DIGITAL FIBROGRAPH†.The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths. Effective length = 1. 013 x 2. 5% Span length + 4. 39 Mean length = 1. 242 x 50% Span length + 9. 78 Baer’s Comb sorter Method: For the determination of the length and of the length distribution of cotton fibers in purified cotton the Baer’s Comb Sorter method: These directions describe the mode of procedure that is well adapted to the sorter* most extensively used in the United States at the present time.Apparatus— The sorter Duplex Cotton Fiber Sorter consists of two banks of combs rigidly mounted side by side on a common base. Each bank of combs consists of at least 12 individual combs spaced 3. 2 mm apart, one behind the other, and mounted in grooves so that as they are approached during the fractionating pr ocess and no longer needed, they may be dropped below the working plane. Each individual comb has a single row of accurately aligned and sharply pointed teeth, 12 mm long, consisting of needles 0. 38 mm in diameter. The teeth are spaced 62 to 25 mm over an extent of approximately 50 mm.Accessory equipment consists of fiber-sorter forceps, fiber-depressing grid, fiber-depressing smooth plate, and velvet-covered plates. The sorter forceps consist of two brass pieces approximately 75 mm long, hinged on one end and slightly curved to present a beaked aspect at the gripping end for gripping the protruding fibers close to the surfaces of the combs. Usually, one of the gripping edges has a leather or other fibrous padding. The gripping edge is approximately 19 mm wide. The fiber-depressing grid consists of a series of brass rods spaced 3. mm apart so that they may be placed between the combs to press the fibers down between the teeth. The fiber-depressing smooth plate consists of a polishe d brass plate approximately 25 ? 50 mm, with a knob or handle on the upper surface whereby the plate may be smoothed over the fibers as they are laid on the velvet surface of the array plates. The velvet-covered plates, upon which the fibers may be arrayed, are aluminum sheets approximately 100 mm ? 225 mm ? 2. 4 mm thick, covered on both sides with high-grade velvet, preferably black.Standard Atmosphere For Testing: The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2 ° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2 ° C, may be used. Procedure With the fiber-depressing grid carefully insert the weighed test portion into one bank of combs of the cotton sorter, so that it extends across the combs at approximately right angles.With the sorter forceps, grip by the free ends a small portion of the fibers extending through the teeth of the comb nearest to the operator; gently and smoothly draw them forward out of the combs, and transfer them to the tips of the teeth in the second bank of combs, laying them parallel to themselves, straight, and approximately at right angles to the faces of the combs, releasing the gripped ends as near to the face of the front comb as possible. With the depressor grid carefully press the transferred fibers down into the teeth of the combs.Continue the operation until all of the fibers are transferred to the second bank of combs. During this transfer of the fibers, drop the combs of the first bank in succession when and as all of the protruding fibers have been removed. Turn the machine through 180, and transfer the cotton fibers back to the first bank of combs in the manner described in the preceding paragraph. Take great care in evening up the ends of the fibers during both of the above transfers, arranging them as closel y as possible to the front surface of the proximal comb.Such evening out of the ends of the protruding fibers may involve drawing out straggling fibers from both the front and rear aspects of the banks of combs, and re-depositing them into and over the main bundle in the combs. Turn the machine again through 180. Drop successive combs if necessary to expose the ends of the longest fibers. It may be necessary to re-deposit some straggling fibers. With the forceps withdraw the few most protuberant fibers. In this way continue to withdraw successively the remaining protuberant fibers back to the front face of the proximal comb.Drop this comb and repeat the series of operations in the same manner until all of the fibers have been drawn out. In order not to disturb seriously the portion being tested, and thereby vitiate the length fractionation into length groups, make several pulls (as many as 8 to 10) between each pair of combs. Lay the pulls on the velvet-covered plates alongside each other, as straight as possible, with the ends as clearly defined as possible, and with the distal ends arranged in a straight line, pressing them down gently and smoothly with the fiber-depressing smooth plate before releasing the pull from the forceps.Employ not fewer than 50 and not more than 100 pulls to fractionate the test portion. Group together all of the fibers measuring 12. 5 mm (about 1/2 inch) or more in length, and weigh the group to the nearest 0. 3 mg. In the same manner, group together all fibers 6. 25 mm (about 1/4 inch) or less in length, and weigh in the same manner. Finally, group the remaining fibers of intermediate lengths together and weigh. The sum of the three weights does not differ from the initial weight of the test portion by more than 3 mg.Divide the weight of each of the first two groups by the weight of the test portion to obtain the percentage by weight of fiber in the two ranges of length. Geometrical Construction of Comb Sorter Diagram Figure . Geo metrical analysis of comb sorter diagram 1. Q is the mid-point of OA, i. e OQ = ? OA. 2. From Q draw QP? parallel to OB to cut the curve at P?. 3. Drop the perpendicular P? P. 4. Mark off OK equal to ? OP and erect the perpendicular K? K. This is a first a approximation to the effective length. 5. S is the mid-point of K? K 6. From S draw SR? parallel to OB to cut the curve at R?. 7.Drop the perpendicular R? R. 8. Mark off OL equal to ? OR. 9. Erect the perpendicular L? L. This is the effective length. Fibre Length Variation: Even though, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by any one of the following attributes Co-efficient of variation of length (by weight or number) irregularity percentage Dispersion percentage and percentage of short fibres Uniformity ratio Uniformity ratio is defined as the ratio of 50% span length to 2. 5% span length expressed as a percentage. uniformity ration = (50% span length / 2. 5% span length) x 100 uniformity index = (mean length / upper half mean length) x 100 Short Fibres:The negative effects of the presence of a high proportion of short fibres is well known. A high percentage of short fibres is usually associated with, – Increased yarn irregularity and ends dddown which reduce quality and increase processing costs – Increased number of neps and slubs whiiich is detrimental to the yarn appearance – Higher fly liberation and mach ine contttamination in spinning, weaving and knitting operations. – Higher wastage in combing and other oppperations. While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a ‘short fibre'.In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. An estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method Short fibre content = (RB/OB) x 100References: 1. â€Å"TE05046PhysicalTextileTestingandQualityControl. doc. † Www. most. gov. mm. MINISTRY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF TECHNICAL AND VOCATIONAL EDUCATION GOVERNMENT TECHNOLOGICAL COLLEGES/INSTITUTES DEPARTMENT OF TEXTILE ENGINEERING, n. d. Web. ;lt;http://www. most. gov. m/techuni/media/TE05046PhysicalTextileTestingandQualityControl. doc;gt;. 2. Kohli, Nitesh. Fibre Testing. Scribd. com. N. p. , 18 May 2009. Web. ;lt;http://www. scribd. com/doc/15569730/F ibre-Testing;gt;. 3. â€Å"FIBRE TESTING. † Textiletechinfo. com. N. p. , n. d. Web. 25 July 2012. ;lt;http://textiletechinfo. com/spinning/fibretesting. htm;gt;. 4. Tirumalai, Radhakrishna S. â€Å"General Chapters: COTTON. † Http://www. pharmacopeia. cn. N. p. , n. d. Web. 25 July 2012. ;lt;http://www. pharmacopeia. cn/v29240/usp29nf24s0_c691. html;gt;