Tensile drawing behavior of rotor spun yarn.

摘要

Rotor spun yarn, despite of its growing popularity, suffers the disadvantages of lower tenacity, limited count range, and especially harsh hand of its end fabrics. This project is thus conducted with an aim to probe the possibility of amending these drawbacks by a tensile drawing process.; Yarns produced with different specifications from cotton and Tencel fibers are used. The results are encouraging since it is confirmed that staple yarn treated this way can still serve its proper function. Especially, it is found that the tensile drawing process can improve rotor spun yarn quality in terms of structural/mechanical evenness and processability.; A specially designed device is also prepared to improve the drawing effect in terms of tenacity enhancement and breaking elongation loss moderation. The device comprises a two-roller drawing system, with an air jet nozzle in between. In the two-roller drawing system, the feed roller is always at a speed lower than the delivery roller, and thus the rotor spun yarn would undergo tensile stretching when passing through these two rollers. The adoption of the air jet nozzle can subject rotor spun yarn to the action of false twisting when it travels along a path predetermined by two rollers so as to improve tensile drawing effect via yarn restructuring. Experimental results demonstrate that the designed device is a success as reflected by the rise in yarn tenacity and even some improvements in breaking elongation. This device enhances the potential of commercial applicability of the proposed tensile drawing process.; Although millions of yarn models must have been developed, the feasibility of these models to rotor spun yarns is still doubtful in consideration of the peculiar structure of rotor spun yarn. A new tensile model specially for rotor spun yarn is thus necessary, which may contribute to an in-depth understanding of the tensile drawing behavior of rotor spun yarn so as to optimize the proposed tensile drawing process. The study is carried out on the basis of a coaxial-helix structural model, taking account of non-uniform yarn packing density. Especially, a changing-pitch system is for the first time introduced in yarn modeling. A pitch function has thus been determined by the aid of non-linear regression method and curve-fitting approach on the basis of fiber lengthwise images using tracer fiber technique. Fundamental approaches adopted in modeling include discrete-fiber-modeling principle, an energy method, and a “shortest-path” hypothesis. (Abstract shortened by UMI.)