Fiber Orientation and Twists of the Half-yarn on the Drum Surface in Friction Spinning

Abstract

In a yarn formation process, twist is a very important yarn factor, and at the same time an important process variable either. The twist is topologically described by the orientation of the constituent fiber orientation, which is usually defined by turns per length or twist angle. But in friction yarn spinning, twist insertion is complicated. In the spinning zone consisting of two drums, the staples are delivered and accumulated around the half yarn surface, while after the friction drum the half yarn undergoes a real twisting operation between the drum exit and the take-up roller. Therefore the twist in the friction yarn is difficult to define. This study reports on the twist behavior of the half yarn on the friction drum during the yarn forming process. As the twist is directly coupled with the yarn thickness, the dynamic behavior of yarn thickness is taken into account. Therefore a mathematical model, describing the changes of yarn thickness and twist, was established. Introducing a slippage factor between friction drum and half yarn surface, the continuities of fiber mass and twists on the friction drum were c1onsidered. With some assumptions the equation system was simplified and the transient responses of the yarn thickness and twists were simulated numerically by FDM, especially by applying Forward Time Backward Space method. Dynamic behaviors of yarn thickness showed a saturated exponential form for the step change in the input rate of the fiber fleece. However, twists showed a much complicated way of behavior because of the fiber allocation and real twist effect by radial thickness increase on the friction drum. The fluctuation of the input fiber fleece rate has an influence on the twist distribution through the half yarn thickness change.