A systematic study of a modified drafting system based on the ring spinning frame, which is called the SDS (soft drafting system), is reported in this article to raise yarn quality. Two parts of an experiment were conducted to investigate differences between the conventional and modified drafting systems by spinning three kinds of yarns (in part I) and the effects of process parameters (block gauge, pressure on the front rollers and break draft) on the SDS by using response surface methodology (RSM) to spin 18.2 tex cotton yarn (in part II). The results show that the SDS can significantly improve yarn evenness and reduce yarn imperfections of thick places by +35% and +50%, respectively, and neps by +140% per km. In addition, it is noted that the three parameters are all statistically significant for the SDS to spin yarns, while interactions between them are not. More importantly, RSM predicted a minimum CVm% of 13.95% under the optimum conditions of 1.75 mm, 190 N and 1.21 for the block gauge, pressure on the front rollers and break draft, respectively, which is very close to the conditions of the practical spinning test.
A modified drafting system, named the soft drafting system, based on the ring spinning frame, has been introduced in the previous paper. In order to compare with the conventional drafting system, this paper analyzed pressure distributions of the two drafting systems and compared apron slippages based on the condition of spinning 18.2 tex combed cotton yarns. The results show that the floating area of the soft drafting system is only 6 mm, much smaller than that of the conventional drafting system at 12 mm. In addition, the soft drafting system can provide a longer and more stable friction zone and the curved channel is more conducive to the separation of fiber bundles to reduce yarn imperfections. The soft drafting system does not have the problem of apron-to-apron slippage that may cause deterioration of yarn quality. The slip rate of the soft drafting system between the lattice apron and the middle bottom roller is 0.03%, while the slip rate of the conventional drafting system between the bottom apron and the middle bottom roller is 8.58%, resulting in a reduction in drafting efficiency and poor stability of yarn quality. The experimental results show that the soft drafting system can significantly improve yarn evenness with CVm% of the soft drafting system decreasing 10.2% over the conventional drafting system. Also, the soft drafting system can reduce yarn imperfections, especially thick places with +35% thick places decreasing 71.9% and +50% thick places decreasing 70.4%.
A model using the iterative method is introduced in this paper to simulate the drafting process, including roller drafting and apron drafting. This proven model is established based on the relationship between the controlling force and the guiding force on a single fiber at different positions in the drafting zone. Through simulation, the effects of fiber length distribution, roller gauge and draft ratio on fiber accelerated points are discussed. The result proves that the accelerated point of a fiber is related to its own length, but has nothing to do with the lengths of other fibers in the sliver. The smaller the roller gauge, the closer the fiber accelerated point is to the front-roller nip and the more concentrated the accelerated-point distribution. Under the condition that a sliver can be drafted, the draft ratio only affects the fiber accelerated points slightly. The distribution of all accelerated points and distributions of different types of fibers in the drafting zone can also be obtained, including floating fibers and fibers that are controlled by the front and back rollers. The model can be applied not only to the roller drafting system, but also to the apron drafting system as a theoretical guide for practice.
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