Torsional properties of staple fibre plied yarns

Abstract

A mathematical analysis of the mechanical governing equations applying to the torsional behaviour of multi-ply yarns under tension has been carried out. This analysis clearly shows that there are two components, a geometric component that determines the slope or gradient of the torque due to tension and a component that determines the yarn torque at zero applied tension (intrinsic torque) that depends on the fibre number, fibre moduli and diameter as well as the strand structural geometry. The effect of the ratio of the ply twist to the spinning twist on the two components of yarn torque has been numerically analysed for two-, three- and four-ply yarns prepared from singles 31 yarns spun with different spinning twists and for two different fibre diameters. Other comparisons are made for two-ply yarns prepared from 40 and 80 tex singles yarn. The model allows the effects of the various yarn and fibre parameters to be assessed and compared with experimental data. Experimental torque data for a range of two-ply yarns plied at different percentages of the singles spinning twist and also with different yarn histories and test environments are consistent with the trends identified by the model.