Knitting Performance of Wool Yarns: Instrumentation Studies 1

Abstract

The knitting performance of a yarn, in terms of the work Ty required to knit the yarn into jersey fabric, is measured hy use of a sensitive torque transducer located on the driving shaft of an experimental knitting machine. Using this technique, the knitting per formances of a variety of worsted wool yarns are studied, and the effects of input tension, yarn/metal friction, yarn/yarn friction, twist level, and the WURLAN shrink-resist treatment on knitting performance are investigated. By the use of a mathematical analysis, the knitting behavior of a worsted yarn with changes in input tension is shown to be essentially similar to that predicted. Under normal commercial knitting conditions, Ty is directly proportional to yarn/metal friction but independent of yarn/yarn friction. It is proposed that if the coefficient of yarn/metal friction ≤ 0.2, little trouble will be encountered in the knitting of wool yarns, and that the sometimes irregular appearance of knitted wool fabrics may be attributed to both spin ning irregularity and the magnitude of yarn/metal friction. The knitting performance of a multi-filament nylon yarn is also shown to be dependent on yarn/metal friction. The use of yarn feeding devices at the standard knit construction reduces Ty at any input tension, confirming that higher knitting speeds, increased efficiencies, and more regular fabric are attainable. The effect of yarn/metal friction on knitting performance is substantially decreased by the use of positive feed. An increase in twist factor from 1.8 to 2.8 had little effect on Ty, although slightly increased values are found for high- twist yarns. However, the WURLAN interfacial-polymerization wool shrink-resist treatment increased T y as much as 60% at normal input tensions. This effect seemed to be unrelated to measured changes in yarn/metal friction and yarn flexural rigidity, but could possibly be due to changes in yarn/yarn friction. Some interesting observations of the mechanical performance of knitting machinery are also reported in this paper.