Studies On Fiber Self-Twisted Technique In Air-Jet Vortex Spinning

Air-jet vortex spinning has currently become one of the most advanced spinning technologies because of the high production, high speed, short process, automation, small occupational room and less labor characteristics. Compared with other spinning process, the twisting process of air-jet vortex spinning belonged to free-end spinning technology is achieved by high-speed rotating airflow. Due to the difference of twisting between ring spinning and air-jet vortex spinning, fibers can be pulled out of the yarn easily during the twisting process in air-jet vortex spinning which causes much more snicks and reduces the strength of yarn. Based on the analysis of yarn twisting and structure, this article proposes fiber self-twisted technique in air-jet vortex spinning, and studies the mechanical behavior between the airflow and the fiber, the process of fiber self-twisted and flow field characteristics.Based on the yarn structure and numerical simulation of flow filed, this article discusses the development status of spinning technology and the research status of air jet vortex spinning firstly, then analyses the reason of yarn snick and the process of fiber self-twisted in depth. The research mainly includes the following parts:(1) Based on the motor process of fiber and the yarn structure, the twisting system of fiber in air-jet vortex spinning is established. From the system we can know, the wrapping effect of yarn is affected by spinning speed, the mean angular velocity of the free end fiber, length of fiber, yarn radius and the distance from the bottom of rotating surface to the inlet of hollow spindle. The results show that the wrapping effect will be strengthened by decreasing spinning speed, or increasing the mean angular velocity of the free end fiber, or increasing length of fiber, or increasing the distance from the bottom of rotating surface to the inlet of hollow spindle, or decreasing yarn radius, etc.(2) Based on the stress condition analysis of free-end fiber, the critical condition of pulling fiber out of yarn by airflow during twisting is established. The condition shows that fiber self-twisting is favorable to improve the force between fibers, and also decrease the number of fibers pulled out of the yarn. According to morphological model of free-end fiber in the airflow, the rolling friction between fiber and the wall of hollow spindle is established which is also the theoretical basis of designing the fiber self-twisted hollow spindle.(3) On the basis of the structure of nozzle and hollow spindle in Murata No.861, the computational fluid dynamics model of air-jet vortex spinning computed by the fluid calculation software FLUENT6.3in compressible style is built. The distribution regularity of compressed airflow in the flow flied is characterized. The results show that the pressure and the velocity distribution are symmetric on the nozzle axis; the lowest pressure is near the inlet of hollow spindle which is conducive to draw the fibers into hollow spindle; the tangential velocity and axial velocity conform to the rotating flow theory; the fluctuation of radial velocity is apparent at the top of hollow spindle which disperses the fiber assembly. In the flow flied of fiber self-twisted, the region of negative pressure is increased obviously, and the velocity is decreased little which the tangential velocity is reduced by ten percent increasing the wrap angle of free-end fiber.(4) The groove of the fiber self-twisted hollow spindle reformed by laser is designed into different quantity of vertical, clockwise slant and anticlockwise slant. Compared with the different kinds of yarn from the different kinds of hollow spindle, the suitable structure of fiber self-twisted hollow spindle is conducive to improve the strength of yarn. The quality of yarn spun by20grooves is better than40, and clockwise slant groove is better than vertical and anticlockwise slant. With the friction coefficient of the hollow spindle wall increasing, hairiness index of the yarn is increased, and the distribution of unevenness value is presented like’V, and the wrap effect and the abrasive resistance are reduced because of the wrap angle is increased. The fiber on the surface of the yarn is tangled obviously which increases the strength of yarn.