THE ROLE OF FALSE TWIST IN WRAP SPINNING

Using a false twister for hollow spindle wrap yarn spinning is suppose d to facilitate operations. However, our investigation shows that a hi gh level of false twist can significantly influence yarn appearance an d mechanical properties. Wrap yarn spun with a false twister has a tor tuous structure, while wrap yarn spun without a false twister is smoot h. Compared with equivalent zero false twist wrap yarns, false twist w rap yarns display a similar twist-strength relationship, but lower mod uli and bending rigidities at increased wrap twist. Twist contraction of the yarn core during initial wrapping is the primary cause for the tortuous structure of the false twist wrap yams. When a false twister is used, the yarn core first contracts under false twist, and at the s ame 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.