| The air jet vortex spinning has become the focus study both at home and abroad because of the high-speed and high-yield characteristics, and it not only overcome the difficulty that the spinning speed of traditional ring spun cannot be increased greatly with the mechanical twisting parts, but also a series of questions such as damaged twisting parts because of friction and a big rotary inertia by adopting the high-speed airflow to twist the free end of fiber, in addition, although the integration process of roving, spinning and spooling is more to save manpower, occupied area and investment of capital equipment, the particular yarn structure of air jet vortex spinning leads to weak yarn strength which is a major problem that the whole textile industry must face at present In this paper, we will comprehensively and systematically investigate to solve this problem. Because the mechanism and process of yam forming of the air jet vortex spinning, decide the structure of the yarn, therefore in this paper we will take yarn forming mechanism of air jet vortex spinning, yarn structure and the mechanical behavior between air and solid as the research subject.In this paper, the development of new spinning technology and the current research situation of air jet vortex spinning will be expounded at first, and it shows that the history of the air jet vortex spinning technology development is short, the researches of predecessors on how yarn structure and process parameters of air jet vortex spinning affect these aspects such as yarn strength and levelness are insufficient and systemic, they also do not have reasonable and feasible measures on how to enhance the yarn strength. In this paper we will deeply analyse and discuss these problems. The research work mainly includes the following aspects:(1) Based on nozzle internal computational fluid dynamics modeling of jet vortex spinning, numerical simulation computed with the fluid calculation software FLUENT 6.3 will be made to simulate airflow of three-dimensional flow field, which represents and analyzes flowing law of the internal flow field of nozzle, analyses and compares the flow distribution of different nozzle air pressure. The results of the study show that the compressed gas spraying from nozzle holes form three-dimensional rotation flow in nozzle interior, and the pressure distribution in general is symmetric on the nozzle axis. Total pressure decrease gradually from inlet to outlet. The center area of the hollow spindle head end presents obvious negative pressure, the negative pressure is helpful for fiber sucked smoothly into yarn end. In the annular region between the hollow spindle external surface and internal surface, the air pressure of region near wall is lower, the pressure is higher in the central part between two wall. Tangential airflow twists the free end of fiber, axial airflow makes fiber end move attached with hollow spindle surface, radial airflow forms certain positive pressure.(2) Based on spinning principle of jet vortex spinning and numerical simulation of nozzle internal flow, the action trajectory of fiber which is affected by rotating airflow and stress distribution in the twisting cavity is expounded theoretically, the results of the study show that the space locus of the fiber is made up of core fiber situating yarn core, the transfer and wrapped fiber from inside to outside and the wrapped fiber twisting inner fiber, fiber length of the three parts is a function about spinning speed, angular velocity of fiber end, fiber length, yarn diameter and the distance between front roller nip to hollow spindle fore-end. Under airflow role, fiber is at the same time variously forced, in addition to acting force produced by tangential, axial and radial airflow, also the centrifugal force produced by the rotation of fiber, supportiveness and friction forced between wall and fiber, and gripping force produced by tangential friction resistance between fibers produces to the head of fiber, etc. In addition, with the torque description of fiber end, analyzed the conditions fiber itself twisting. And on this basis, we will design a method that can improve yarn strength, that is to say, roughen hollow spindle surface to improve friction coefficient of its surface, and achieve fiber itself twisting.(3) In the base of developing 14.7tex blended yarn with 55/45 Jutecell/PLA fibers in Murata Vortex Spinning, the main processing parameters which affect the MVS yarn were discussed. These parameters include delivery speed v, distance L between the nip of front roller and the inlet of the hollow spindle, nozzle pressure p, inner diameterΦof spindle and nozzles models. According to the yarn strength and elongation as well as evenness the processing parameters have been optimized and evaluated. The results show that the yarn strength and elongation as well as evenness are good. Also it has good wear resistance.(4) Based on the idea of reformation of hollow spindle, we will use three hollow spindle to make different types of yarn with the same process parameters and the same types of yarn with different yarn spinning process parameters to get the experimental contrast, the results show that: after using three hollow spindle to spin different types of yam with the same process parameters,we find the yarn strength got by using hollow spindle surface treated is lower than the yarn with the original untreated hollow spindle, evenness is also slightly worse than the latter. After using three hollow spindles to spin the same yarn with different process parameters, the results show we can improve the yarn strength after treatments of the hollow spindle by increasing the nozzle air pressure and reduce the spinning speed, but the yarn evenness is still worse than the yam with untreated hollow spindle. Overall, surface rough treatment on the hollow spindle, to some extent, can improve yarn strength, it is a positive effect, but on the other hand it worsened the yarn evenness. The spinning effect of 40 grooves dealing process of hollow spindle is not better than 60 grooves.In summary, based on jet vortex spinning mechanism and flowing rule inside the nozzle, non-linear relationship between a jet vortex spinning process and yarn strength is built through the description of the trajectory of the fibers and mechanical analysis, and we also do some exploratory testing on the transformation of hollow spindle. In order to further improve the yarn strength, so it provides a strong theoretical support and a new direction. |
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