Abstract:

Objective Compared with the traditional ring spinning, Sirofil two-component yarn possesses higher strength and smoother surface. In order to optimize the performance of Sirofil wrapped yarn, including hairiness, evenness and strength, the influence of the relative position and spacing distance of filament and staple strand on the yarn properties was explored. Additionally, the combination of theoretical modeling and experiment were employed to quantitatively analyse and predict the performance of ring spun Sirofil wrapped yarn in practical manufacturing.
Method To analyze the twisting process and characteristics of the Sirofil wrapped yarn, the numerical analysis of the twisting triangle were carried out, and the model is established based on the geometric relationship of filament and staple strand in the twisting triangle and the force analysis of the twisting triangle. The hairiness, evenness and strength of sirofil wrapped yarn were tested by experiments, the results of which were used to validate the model.
Results The relationship between the offset distance of the centroid of the Sirofil wrapped yarn relative to the spindle axis and the yarn twisting angle in the triangle area was deduced and the equation for calculating the quality of half twisted yarn was established. In accordance with the force analysis of the twisting triangle, the moment balance equation was attained and the twist transfer rule of Z-twisting yarn was explained. The analysis results showed that with the increase of the distance, the offset distance of the centroid of the twisting triangle relative to the spindle axis was increased, and the twist angle of the staple strand was decreased(Tab. 3). Therefore, the slippage length of the staple fibers became longer and the proportion of the strength of the short fiber bundles in the axial direction of the yarn got larger, making greater contribution of the fiber to the yarn strength leading to improved yarn strength. Torque contributed by filament and staple strand shows that the twist angle of the filament was smaller than that of the staple strand, and the proportion of the torque in the axial direction of the yarn was larger(Tab. 4). Therefore, the filament is regarded as the main contributor to the strength of the Sirofil wrapped yarn. Furthermore, when the filament position was on the right, the staple strand would obtain a larger number of twists with better wrapping effect which is conducive to enhance the yarn quality. Through the comparison of 3 mm, 4 mm and 5 mm spacing distances, it was seen that 5 mm was the best spacing distance between filament and staple strand of Sirofil wrapped yarn. It is evident that the experimental results showed good consistency with the conclusion of model analysis(Fig. 5).
Conclusion In this paper, the force model of twisting triangle zone is established based on results from mechanical analysis and experimental investigation, and the influence of the relative position and distance between filament and staple fiber on the yarn properties is studied. The calculation and verification results show that the larger the yarn centroid offset distance is, the smaller the twist return angle is, and the twist direction above the convergence point is the same as the real twist direction below the convergence point. The twist of the staple filament is greater when it is on the left side of the filament. The model provides theoretical and experimental guidance for practical quantitative analysis and process design.

Key words: Sirofil wrapped yarn, ring spinning, yarn structure, twisting triangle area, twist angle