Abstract:

Objective The reason for additional unevenness of output slivers after drafting is that the accelerating point of floating fibers fluctuates in a region during the drafting process. However, the existing models could not simulate the influence of the frictional force among fibers on the fiber acceleration process during the dynamic drafting process. In order to study the influence of drafting conditions on the accelerating point distribution of floating fibers, this paper established a dynamic drafting model and simulated the acceleration process of floating fibers with frictional force between fibers during the dynamic drafting process.

Method According to the velocity and the frictional force of fibers, the fibers in the drafting zone were divided into four types: back fiber, slow-floating fiber, fast-floating fiber, and front fiber. Further, back fiber and slow-floating fiber were called slow fiber, and fast-floating fiber and front fiber were referred as fast fiber. The dynamic drafting process of fibers was refined into five stages: entering the drafting zone, leaving the back roller nip line, accelerating, reaching the front roller nip line, and leaving the drafting zone. On this basis, the dynamic drafting process of fibers was simulated by calculating the time interval between adjacent fibers entering the drafting zone and the movement time of fibers at each stage. In addition, the acceleration process of fibers was simulated by calculating the guiding force and control force on floating fibers during the dynamic drafting process. The fibers in contact with floating fibers in the dynamic drafting process were determined by randomly selecting fibers from the drafting zone and calculating the contact length. The guiding force was obtained by calculating the contact length between floating fibers and surrounding slow fibers, and the control force was obtained by calculating the contact length between floating fibers and surrounding fast fibers. During the dynamic drafting process, the control force and guiding force changed dynamically as the floating fiber gradually moved to the front roller nip line. The floating fibers was accelerated instantaneously when the guiding force reached and exceeded the control force. At this moment, the leading end position of the floating fiber was the position of fiber accelerating point.

Results By weighting and cutting the strand in the drafting zone, the distribution of frictional field of simple roller device was calculated. On this basis, the dynamic drafting process with different drafting ratios and fiber lengths was simulated and the accelerating point distribution of floating fibers was obtained. The results showed that with the increase of drafting ratio, the distribution of accelerating points was gradually closer to the front roller nip line, and the distribution range of acceleration gradually reduced. This showed that the greater the drafting ratio, the more concentrated the slow-floating fiber accelerated in the area closer to the front roller nip line, and the longer the fiber length was, the closer the accelerated point distribution was to the front roller, and the smaller the range of accelerating point distribution was. This is because the longer the fiber length was, the shorter distance the fiber moved as floating fiber. In addition, the distribution of accelerating points in the simulation with different drafting conditions was roughly in the form of the normal distribution, which was close to the actual situation.

Conclusion This method could simulate the acceleration process of floating fibers affected by the frictional force among fibers during dynamic drafting process. In addition, the principle of the influence of different drafting conditions on the drafting process could be analyzed through this method because different drafting conditions changed the distribution of floating fiber accelerated points by affecting the frictional force between fibers. Therefore, this method could be adopted to predict the unevenness of the output sliver after drafting, and to design and optimize the process parameters of the actual drafting equipment.

Key words: dynamic drafting model, drafting, floating fiber, accelerated point distribution, fiber motion state, friction field distribution