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Abstract
The variation in fibre length of a worsted roving has been found to have a significant effect on the spinning properties and on the levelness and strength of the yarn. Contrary to traditional ideas, it has been shown that, if a top is too ‘square’ (i.e., too uniform in fibre length as shown in a cumulative frequency diagram), it will give an inferior spin; in other words, there is an optimum fibre-length distribution for best spinning performance and yarn properties.
The drawing and spinning of some 48/50s crossbred and 58/60s fine halfbred tops, produced from wools with various levels of staple strength, are described. Various commercial tops and the yarns spun from them have also been examined.
Fibre breakage was least in the lots made from the wools of highest staple strength, which had previously given the best combing performance. However, it was found that these lots (made from wools sorted for length as well as strength) were too uniform in fibre length for optimum spinning performance. Commercial tops are not likely to reach this degree of fibre-length uniformity unless straight lines of very sound wool are being used, when it is clearly undesirable to sort for length.
Over-all, fibre breakage in drawing and spinning (calculated from the change in mean fibre length from top to yarn) increased with increasing fineness of the wool, averaging 14% for 48/50s and 23% for 58/60s.
End-breakage rates increased as the r.h. decreased below 50%, and a fall in r.h. to 35% increased the end-breakage rate by about 50%.
For the same mean number of fibres in the cross-section of a yarn, the mean fibre length has a significant effect on the levelness and strength of a yarn.