The Role of False Twist in Wrap Spinning

Abstract

Using a false twister for hollow spindle wrap yam spinning is supposed to facilitate operations. However, our investigation shows that a high level of false twist can sig nificantly influence yarn appearance and mechanical properties. Wrap yarn spun with a false twister has a tortuous structure, while wrap yarn spun without a false twister is smooth. Compared with equivalent zero false twist wrap yarns, false twist wrap yarns display a similar twist-strength relationship, but lower moduli and bending rig idities at increased wrap twist. Twist contraction of the yam core during initial wrapping is the primary cause for the tortuous structure of the false twist wrap yarns. When a false twister is used, the yarn core first contracts under false twist, and at the same time is wrapped with a low wrap twist because of the difference in rotational speed between the wrapper balloon and the yarn core. Then, as the false twist is removed from the core and further wrap twist is formed at the exit side of the false twister, the core recovers from twist contraction and buckles to form a helix under the tension of the wrapper.