Torque in Worsted Wool Yarns

Abstract

A direct technique developed for measuring yarn torque is explored for the case of worsted wool yarns. The technique balances the torque in a yarn hank against a wire of known torsional rigidity. It is shown that this technique gives a reliable measure of the torque per strand independent of the size of the hank. The torque per strand was found to be linearly dependent on the applied external tension and a finite torque exists even at zero applied tension. This leads to the concept of resolving the torque into two components, (a) the torque due to the applied tension and (b) the intrinsic torque that exists in the untensioned yarn. The torque due to the applied tension does not depend on the yarn history but only on yarn geometric factors such as the yarn twist and linear density. By comparison the intrinsic torque depends on factors such as the level of yarn set as well as the twist and linear density. These components of torque due to tension and intrinsic torque are shown to be consistent with literature models and lead to estimates of yarn specific volume, yarn packing fraction and relative fiber relaxation moduli after steaming.