Abstract:

Objective The yarn quality produced from a single component often faces limitations imposed by the material itself. These limitations can be addressed by utilizing a combination of multiple materials to enhance the performance. Composite yarns are typically manufactured using methods such as ring spinning, which results in high twist rates and substantial residual torque. These factors contribute to an increased number of kinks which necessitates additional processes to reduce residual torque, thereby incurring higher time and resource costs. In contrast, self-twisting spinning leverages the principle of de-twisting during yarn formation, naturally reducing residual torque and offering significant research potential.

Method This study utilized a composite filament approach to investigate the properties of self-twisted yarns, aiming to control the yarn structure and produce low-torque, high-quality composite yarns. Wool fiber and nylon filament served as the raw materials, the improved S300 self-twist spinning system was used for large-scale manufacture of embedded in-phase self-twisted yarns and heterogeneous self-twisted yarns. A stress analysis was conducted on the in-phase self-twisted yarns to examine the influence of the angle and spacing of the embedded filaments on the self-twist torque of the composite yarns. Additionally, the effects of filament and roving spacing on the yarn formation performance of both types of self-twisted yarns were analyzed.

Results Eight groups of spun yarns were rigorously tested using 3-D microscope, evenness tester, hairiness tester, strength tester, and hanging kink test. When the spacing between the filament and the roving was set at 0 mm, the resulting yarns formed a core structure, exhibiting poor quality due to uncontrolled hairiness. At a spacing of 2 mm, the yarns became wrapped yarns, in which the filament exerted inward pressure on the fibers to control the surface fibers and enhance internal strength. This configuration provided optimal strength and evenness properties, validating the effectiveness of the compound twisting followed by retwisting yarn formation scheme. As the spacing between the filament and roving increased, the orientation of the filament was decreased, leading to improvement of the wrapping effect on the fibers and enhancement of the surface hairiness control. However, the filament struggled to maintain internal tensile resistance, resulting in a gradual decline in strength. Furthermore, an increase in the self-twisting torque of the embedded composite self-twisted yarns led to non-uniform twisting distribution, adversely affecting the yarn evenness. When the spacing became excessively large, the filament and roving could not effectively compound under the grip of the twisting roller. On the contrary, they converged at the hook, resulting in a unique yarn formation structure characterized by an initial twist followed by a retwist. In this specific configuration, referred to as Scheme D, both filaments periodically migrated toward the same side. During half a twist cycle, the left filament moved away from the fibers while the right filament remained close, causing the right single yarn to wrap around the yarn body and form a composite single yarn. The left single yarn twisted with the composite yarn, but the filament could not regulate the internal and external transfer of fibers effectively.

Conclusion The embedded self-twisted yarns significantly reduced the residual torque to below one kink in composite yarns. The optimal configuration for achieving superior tensile properties and yarn structure was identified at a filament-roving spacing of 2 mm. In comparison, heterogeneous self-twisted yarns exhibited better evenness and tensile properties than the homogeneous self-twisted yarns. Therefore, the heterogeneous self-twisting spinning method is preferred in practical production. When the spacing between filament and roving exceeded 6 mm, achieving a tensile homophase self-twisted yarns displayed a unique structure with both core and wrapped characteristics, achieving a strength of 7.39 cN/tex, surpassing that of close heterogeneous self-twisted yarns.

Key words: self-twisting spinning, embedded composite yarn, low torque, yarn structure model, yarn property