Contribution to the Study of the B–L Curve of Cotton Yarns

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Abstract
For the worsted system of processing Grosberg [9] has developed an equation which makes possible the derivation of the variance–length curve of a yarn from the total variance of each of the slivers made during the manufacture of the yarn. The present study is an attempt to evaluate the suitability of this equation for cotton processing. For this purpose, two cottons were spun to 40s and one to 30s using the orthodox system of processing consisting of 3 speed frame passages. The irregularity of the material at different stages of processing was determined with the Uster evenness tester, and the B–L curve of the yarn was deduced using Grosberg's equation. The actual B–L curve of the yarn was also determined with the evenness tester by the “inert test” method. On plotting the results it is found that there is considerable discrepancy between theory and experiment—the predicted curve is seen to be too high in every case. The reasons for this discrepancy are discussed. A preliminary study on two yarn samples showed that there is good agreement between the B–L curves obtained by the Uster evenness tester and the cut-and-weigh method. The log B (L)–log L plot is found to be fairly linear, except for short lengths, for cotton yarns.

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