Study On The Correlation Of Yarn Formation Mechanism And Yarn Structure In Self Twist Jet Vortex Spinning

Today, the high-tech spinning gradually develops towards a trend of high spinning speed, high efficiency, high automation, and low energy consumption, which is a necessary condition to improve the value-added of textile products. The jet vortex spinning technology with advantages of high-speed, short process, low carbon, has occupied the commanding heights of the world spinning technology. It is a very promising new spinning technology.Since the efficiency of vortex twisting manner is greatly improved relative to the mechanical twisting, but the fibers which have the lack of the yarn body control are easily to be pulled out by the high-pressure air pump. It may cause the fibers loss, which makes the weak points of yarn increased and yarn strength insufficient. And the jet vortex spinning yarn is built up by the core fibers and the wrapped fibers. Compared with the spiral structure of ring yarn, the parallel straight structure of core fibers makes the fibers have a poor cohesion between each other. The yarn breaking strength mainly comes from the wrapped fiber contribution, so that the yarn strength is lower. In addition, since 1995, the jet vortex spinning technology was developed and launched by Murata company in Japan, the MVS851 has developed into MVS870. During the 20 years, only the Rieter company in Swiss has researched and developed the J10 jet vortex spinning technology and equipment. C hina has not yet formed the jet vortex spinning technology processing systems and industrial equipment. The equipment is heavily dependent on imports and the technology upgrading is subject to foreign technology.This paper studies the status of jet vortex spinning technology based on the MVS870 spinning system developed by Murata company. This paper optimizes the lack of traditional jet vortex spinning process and yarn structure, and proposes a new technical theory of the self twist jet vortex spinning. Firstly, this paper has analyzed the air flow variation of jet vortex spinning twisting process and the movement of fiber, aid flow field numerical simulation and finite element model. then we has optimized and designed the structure parameters of the hollow spind le top area to achieve the self-twist of free fiber end, which could change the jet vortex spinning yarn structure, and improve the performance of jet vortex spinning yarn. The main contents and conclusions are as follows:?1? This paper established a three-dimensional computational fluid dynamics model of the internal twist nozzle zone based on the MVS870 spinning system developed by Murata company. We made the numerical simulation of the high speed, compressible and turbulent air flow field in twisting zone by the FLUENT module of ANSYS14.0 software. The Studies of airflow characteristics near the hollow spindle wall show that: the pressure of the internal twist nozzle zone distributes symmetry on the hollow spindle axis, and decreases from the nozzle inle t to the outlet. The static pressure of the hollow spindle inlet plane and the vertical upward is small and negative, which is better for the fiber sliver sucked into the hollow spindle inlet. The static pressure inside the nozzle distributes like U-shaped. The hollow spindle existence influences the internal nozzle flow field. The pressure near the hollow spindle wall is the smallest, and there is a small amount of reflux phenomenon on hollow spindle top. The airflow speed is in line with the theory of the swirling airflow. The tangential airflow mainly twists the free fiber end lodging around the entrance of hollow spindle; the axial airflow draws the fiber bundle, which can be ignored; the radial airflow mainly expanses the peripheral fiber, which with the tangential airflow can greatly increase the number of wrapped fibers.?2? Based on the results of three-dimensional fluid flow field simulation and the structural performance characteristics of the thin elastic rod model, we established the finite element model of fiber to simulate the trajectory of the free fiber end under the high speed airflow. Studies have shown that: the velocity of the fiber in the internal twist nozzle zone first increases with the H increases. At H = 5.25 mm it occurs a turn, and decreases with the H increases. Due to the special structure of the hollow spindle, the angle between the hollow spindle wall baseline and the axis has a significant change at H = 5.25 mm. the axis of the lodging fiber is determined by the angle between the hollow spindle wall baseline and the axis ?. within 0mm 5.25 mm of the hollow spindle top, the angle between the hollow spindle wall baseline and the free fiber end trajectory is ?1?53.5°; within 5.25 mm 11.15 mm of the hollow spindle top, the angle between the hollow spindle wall baseline and the free fiber end trajectory is ?1?59.3°.?3? According to the yarn mechanism of jet vortex spinning, we analyzed the force of the high speed jet vortex on the free fiber end by the mechanical torque and acceleration principles theory, and established the critical mechanics condition of the free fiber end gets self twist rotating around the top of hollow spindle. Studies have shown that: the critical mechanics condition of the free fiber end gets self twist rotating around the top of hollow spindle was ?d?/dl?×R_t. we proposed that increasing the frictional force between the top wall surface of the hollow spindle and the free fiber end was better for the fiber getting self twist, and increasing the deformation of self twisted fiber involved into the yarn body. we analyzed the movement of the free fiber end getting self twist, and the deformation of self twisted fiber involved into the yarn body would change with the roll time t_max of the free fiber end. When t_max <T_f, the deformation of self twisted fiber involved into the yarn body is ?d?/dl?×t_max. When the self twisted fiber got the maximum deformation, the fiber would take pure sliding movement around the hollow spindle wall; when t_max = T_f, the free fiber end got the maximum deformation and at the same time ended the rotational movement on the hollow spindle; when t_max> T_f, the deformation of self twisted fiber involved into the yarn body is?d?/dl?×T_t. The free fiber end is failed to reach the largest deformation before the end of the rotational movement around the hollow spindle. This analyzes the feasibility of self- twist jet vortex spinning techniques theoretically.?4? Combined with the critical mechanics condition of the free fiber end gets self twist rotating around the top of hollow spindle and the free fiber end trajectory, we has optimized and designed the structure parameters of the hollow spindle top area. We made the numerical simulation of the air flow field in self twisting zone to verify the rationality of the design. Combined with the actual production, we produced the self-twist jet vortex spinning hollow spindle in different designs by 3D printing technology, and compared the performance of yarn. Studies have s hown that: the groove structure on the self-twist jet vortex spinning hollow spindle makes the air have a briefly stagnation in itself. The pressure around the groove structure decreases as the angle between the groove and the hollow spindle wall baseline decreases, and the groove number increases. Airflow thrust entrainment capacity and airflow velocity components?tangential, radial and axial velocity? increases with pressure decreasing. Compared with the traditional jet vortex spinning yarn sample, to a certain range, increasing the surface friction between the top wall surface of the hollow spindle and the free fiber end is better for the lodging fiber to get self twist. The tensile properties and evenness performance of the yarn would improve. But out of the certain range, the friction will discourage the twisting movement, which makes the tensile performance of yarn weakened, the structure become loose, and the hairiness of yarn increase.?5? Based on self- twist jet vortex spinning yarn, we studied its structure by high-powered microscope and some other methods. We analyzed the fracture mechanism of self-twist jet vortex spinning yarn by methods of calculus, mechanics torque. Studies have shown that: the self- twist jet vortex spinning yarn has a similar appearance with the ring-spun yarn. the self twist jet vortex spinning yarn has a bigger wrapped angle than the traditional jet vortex spinning yarn; the core fiber is straight and parallel; the wrapped fibers wrapped on the outside of the core fiber, and the wrapped angle is not consistent; in the middle of the two parts is the transfer wrapped fibers, and it has a short length. Most fibers of the self- twist jet vortex spinning yarn have a self- twist deformation. The breaking strength of the self-twist jet vortex spun yarn is constituted of two parts; one is the friction force of the slipping fibers; the other is the breaking strength of the breaking fibers. In the self twist jet vortex spun yarn, the self twist will get elastic recovery, which will make the normal compressive stress q increase. The self twist of fibers will make the friction mutual contact area A increase. When the normal compressive stress q and the friction mutual contact area A increase at the same time, the slipp ing length lc will be reduced. When the slipping length lc decreases, the number of the slipping fibers NS will be reduced. When the number of the slipping fibers NS decreases, the number of the breaking fibers will increase. The breaking strength of self twist jet spinning vortex yarn will increase with the number of breaking fibers increasing. Therefore, the self twist jet vortex spinning could keep high spinning speed of the jet vortex spinning, and improve breaking strength of yarn effectively.Based on the above findings, we can see that, the self- twist jet vortex spinning can make the fiber have self twist by changing the parameters of the hollow spindle. The self-twist jet vortex spinning effectively compensates the shortcomings of traditional jet vortex spinning processing technology, optimizes the yarn structure of traditional jet vortex spinning, and improves the performance of traditional jet vortex yarn spinning. The self- twist jet vortex spinning underlys a basis for the research and development of new jet vortex spinning technology and equipment with independent property rights.