Abstract:

Objective In the spinning process, slivers need to be drafted for several times to achieve a certain fineness. At present, this process is mainly performed through the roller drafting mechanism. Due to the limitation of the deceleration ratio of transmission system, the velocity ratio of front and rear rollers is generally small, hence the slivers need to be drafted for several times to achieve the needed drafting ratio. In the process of drafting, the friction force between fibers changes dynamically and so does the drawing force. In order to solve the above problems, an airflow assisted drafting method is proposed, and the performance of such a system is modeled and simulated.

Method It was proposed that the sliver from the airflow drafting channel goes directly into the twisting channel of the air-jet vortex spinning machine. The drafting ratio was set to 140 according to the drafting ratio of roving frame and spinning frame. The outlet air velocity of airflow drafting channel was set to 420 m/s, according to the air-jet vortex spinning speed. The inlet air velocity of airflow drafting channel was calculated as 3 m/s. The model of the airflow drafting channel was established (Fig. 4). The fluid-solid coupling simulation platform was built based on ANSYS Workbench software, and the fluid-solid coupling effects of single straight fiber, two parallel straight fibers and a single hooked fiber were numerically simulated, respectively.

Results The motion trajectories of a single straight fiber, two parallel straight fibers and a single hooked fiber in the drafting channel were obtained by simulation (Fig. 12-14). The fiber was accelerated forward in the drafting channel, and its motion track was wavy (Fig. 12). Due to the large velocity gradient of the air in the drafting channel, the air velocity at the fiber head was higher than that at the fiber tail. As a result, the fiber straightens again when it flew out of drafting channel. When two straight parallel fibers moved in the drafting channel, they got close and eventually contacted each other (Fig. 13). Because of different air velocities at different positions in the drafting channel, the two fibers stagger with each other in the forward process. Compared with straight fibers, the single hooked fiber moved faster in the drafting channel, and the total moving time was greatly reduced (Fig. 14). At the same time, Because of the influence of the friction force of the air, the hooked fibers gradually extend straight during the forward motion.

Conclusion Through the analysis of the above results, these conclusions can be attained. Firstly, velocity gradient of the air in the drafting channel is large, which makes fibers accelerate forward and straighten again when they exit the drafting channel. Secondly, when multiple fibers move in the drafting channel, different fibers stagger forward by means of different air velocities at different positions. That is, the fibers are redistributed in the advancing process. Thirdly, in the process of movement, the hooked fibers will be gradually straightened due to the friction force of the air. So the purpose of straightening fibers is realized similar to that of roller drafting. Finally, Becaust of the boundary layer effect of the air, the air velocity close to the inner wall of the drafting channel is smaller than that in the center of the drafting channel, and the farther away from the center, the lower the air velocity, suggesting that the fibers tend to move close to the inner wall as they move forward. In summary, in the airflow drafting channel, fibers can be accelerated, redistributed and straightened, that is, the purpose of drafting can be achieved, verifying the effectiveness of the airflow drafting method.

Key words: airflow drafting method, fluid-solid coupling, numerical simulation, flow field characteristic, law of fiber motion, spinning technique