False twisting machines must operate under a variety of processing conditions involving high-speed production to facilitate mass fabrication. However, high processing speeds increase the likelihood of “surging” events. Surging is a phenomenon in which yarn oscillates unstably, causing the quality of textured yarn to deteriorate. Therefore, the suppression of surging in false twisting machines is an important issue. In our previous paper yarn conditions with and without surging were reported from the perspective of 4T (Twist, Tension, Temperature, Time of heating). However, the causes of surging are not yet to be clarified. In this study, yarn conditions due to changing the speed ratio D / V_d (ratio of tangential disc velocity to delivery roller velocity) were monitored when surging occurred, then revealing the effect of speed ratio D / V_d on surging. As a result, it is found that surging tends to be suppressed owing to the stabilization of the twisting action when the speed ratio is increased. This is because the contact condition between yarn and the disc is improved. Moreover, the results obtained here also indicate that surging is induced by insufficient twisting tension.

Bending of carbon fibers around the needle during the integrated piercing process for preparing carbon cloth preforms was analyzed. The mechanical behavior of carbon cloth under the moving steel needle tip was investigated using well established mathematical models of carbon fiber bending and elongation and the interaction between the carbon fiber and steel needle. Based on the analysis of the puncture of carbon fiber fabric by the needle tip, four equations satisfying the morphology of the needle tip puncture were selected, then the particle swarm algorithm was used to optimize the curve of the steel needle tip. Curves of the pressure, horizontal tension of the fiber due to the needle tip and frictional resistance between the fiber and the needle tip were compared. The results show that the reconstructed steel needle tip with optimized curve improves the mechanical behavior of the needle tip during the puncture process. Furthermore, this research provides a theoretical basis for studying the overall puncture process parameters of the steel needle.