The principles of yarn quality improvement of the double S curves soft drafting techno-logy (doubles S soft drafting) were analyzed from the perspective of devices. The same types of yarns were produced by ring spinning and double S soft drafting, respectively, and the yarn samples were measured and compared. Then the characteristics of yarns produced by soft drafting were summarized and the reasons were discussed. In conventional ring spinning, the surface speed difference between the upper and lower aprons caused friction and static electricity, which resulted in decrease of yarn quality. However, in the double S soft drafting system, the upper and lower aprons and bins were removed, and the yarn body was well controlled and drafted by the S-shaped plates, curve pipes and lattice aprons. By using the ring spinning and doubles soft drafting technology respectively, the yarn of combed cotton/polyester(60/40)with fineness of 18. 4 tex was produced, and yarn evenness and defaults were tested. The data were analyzed using single factor variance analysis. The results show that double S soft drafting technology can clearly improve yarn evenness, and reduce the occurrence probability of neps, thin places and thick places per kilometer. Double S soft drafting is especially useful for reduction of thickness ( +35%) defaults index. The reason is considered to lie in the facts that double S soft drafting technology can optimize the distribution of drafting area friction and shorten the length of floating zone, and thus performing more effective control on floating fibers.%从装置结构方面阐述双S曲线软牵伸纺纱技术(简称双S软牵纺)改善纱线质量的原理,对比环锭纺和双S软牵纺纺制同规格纱线的测试数据,分析双S软牵纺的成纱质量特点,并分析原因.传统环锭纺在牵伸区由于上下胶圈表面线速度差造成摩擦和静电,影响成纱质量.双S软牵纺去掉了上下胶圈及上下销,通过S形曲线板、曲线管和网格圈实现对纤维须条的控制.分别用双S软牵纺和环锭纺纺制精梳棉/涤纶(60/40)混纺的18.4 tex纱线,测试其条干、纱疵等指标,用单因素方差分析法对数据进行分析.结果表明,双S软牵纺因可优化牵伸区摩擦力界的分布,缩短浮游区长度,因此控制浮游纤维更为有效,可较显著地改善成纱条干,降低千米棉结、千米细节、千米粗节等常发性纱疵的数量,其中粗节(+35%)纱疵改善尤其显著.
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