Abstract:

Objective The purpose of this paper is to explore the shape change of roving whisker in the back drafting area of spinning frame and the influence of roving performance on the drawing effect of the back drafting area of spinning frame. It has certain beneficial effect for producers to set the roving production process and optimize the spinning production parameters.

Method In this research, polyester fiber (1.67 dtex×38 mm) and viscose fiber (1.67 dtex×51 mm) were used as raw materials to prepare roving samples with different roving weights, roving twist and fiber length. The roving section was observed by resin embedding method, and the roving mechanical properties were measured by stretching method. The drawing experiment was carried out on the digital spinning machine SSP-01 to observe the shape change of the roving whisker and cut off the drawing sample. The drawing effect of the back area of the spinning yarns was analyzed, based on the isometric cutting and weighing method.

Results The section of roving whiskers in the rear drafting area was round at first, became a flat ribbon after extrusion by roller pliers, and then gradually shirked and recovered to a circular shape with a certain tightness. Roving (450 tex, 4.01 twist/m or 4.48 twist/m) had better mechanical properties than another samples. The additional friction boundary generated by roving twist back was found to control effectively the movement of fibers, so that the fiber accelerated points was concentrated and close to the clamp mouth of the middle roller, and the drafting effect was stable. The variation of roving strength indirectly proved that the roving strength was better at the twist of 4.01 twist/m and 4.48 twist/m, indicating that the additional friction boundary generated by roving twist back could effectively control the fiber movement. The drafting effect of 350 tex roving whisker met the draft requirement of concentration of the fiber accelerated point and as close as possible to the jaws of the middle roller when the draft multiple of the back area was 1.1 times and the draft spacing was 50 mm. However, under the same drafting conditions, the fiber accelerated points of 600 tex roving fiber was in region Ⅰ, even earlier, which seriously affect yarn quality. Furthermore, without increasing the pressure of the roller, the high weight of the roving was not conducive to the drafting of the roving, while the speed difference between fast fiber and slow fiber leads to more and more obvious delamination behavior with the increase of roving weight. At small drafting multiples (1.10 times and 1.22 times), the fiber weight ratio of each block in the whole post-drafting area changed slightly, indicating that only a small relative displacement occurred between fibers. When the draft ratio was 1.36 times, the fiber weight ratio of each block decreased greatly, indicating that the fiber accelerating points occurred earlier. Even at large draft multiples (1.50 and 1.65 times), the proportion of fiber weight was decreased sharply between zone Ⅲ and zone Ⅳ, indicating that the relative displacement between fibers was too large, resulting in draft instability.

Conclusion The shape of the roving whisker section was constantly changing during the drafting process in the back area, which was accompanied by a slight twist redistribution. The additional friction boundary created by roving twist can effectively control the movement of the fiber, so that the fiber accelerated points were concentrated and closed to the jaws of the middle roller, which was beneficial to the stable drafting. In addition, the small weight of roving facilitated stable drafting. As for heavy roving, it was recommended to increase the roller pressure and roving twist to control fiber movement. The draft factor of the back area should be small, within 1.10 to 1.36 times was appropriate.

Key words: back draft, roving whisker movement, roving strength, distribution of fiber accelerated point, isometric cutting and weighing method