Abstract: The market for fancy yarns is showing a steady growth trend, and with the increasing pursuit of textile quality and design by consumers, fancy yarns have received widespread attention and favor due to their unique characteristics. In 2023, the global market revenue for fancy yarns reached 34.223 billion yuan, of which the market size for Chinese fancy yarns reached 16.756 billion yuan. With the expansion of market size, diversification of product types, and expansion of application fields, the development and refurbishment of traditional fancy yarns have become an inevitable trend. The big belly yarn, as a traditional fancy yarn, also faces updates and iterations. However, current research both domestically and internationally has focused on the influence of process parameters on the performance and quality of big belly yarns, and there is relatively little research on how the draft ratio affects the diameter of these yarns and, in turn, the texture and relief of the fabric surface, especially in the context of big belly yarns with a dual-color structure..
To explore the relationship between the spinning draft ratio and the diameter of the big belly yarn, which in turn affects the appearance of the fabric, this study investigates the spinning of the big belly yarn based on the dual-color structure. Starting from the perspectives of yarn effect and fabric effect, the study firstly designs a big belly yarn with a dual-color structure in the cross-section and axial direction, varying length and thickness of the bulge. The study also selects two different colors of coarse yarns, and determines the final process parameters through trial spinning. The factors that affect the yarn quality are controlled during spinning, and the coarse yarns are placed reasonably to prevent entanglement and impact of the yarn quality when the two coarse yarns are fed. The speed ratio between the front roller and the groove tube is maintained at 1:1.1, which can not only ensure good yarn winding by coordinating the groove barrel with the front roller but also maintain tension between the front roller and the groove barrel, ultimately successfully spinning the target sample. On this basis, with 1.5 as the starting value and 0.3 as the increment, the draft ratio is set to study the diameter changes of yarns under different draft ratios. Data analysis software is used to regress the draft ratio in the spinning process parameters with the corresponding big belly yarn diameter, and the optimal function model is obtained. Research has found that adjusting the movement time of the back roller can simultaneously control the color and diameter changes of the yarn, and setting the width reasonably during weaving can achieve staggered changes of different colors. There is a power function relationship between the draft ratio and the diameter of the big belly yarn, with the function equation being y=0.7693×x(-0.3864); there is a corresponding relationship between the diameter of the big belly yarn and the unevenness effect of the fabric surface, that is, the thickness of the fabric surface. Under weaving conditions with warp and weft tightness of 37.31% and 80.93%, respectively, there is a non-linear relationship between the diameter of the yarn and the thickness of the fabric surface, with the equation being y=0.1466-75.2459×(5.64×10-8)x.
The influence of draft ratio on the final fabric effect provides insights for the development of big belly yarn products. The spinning process parameters can be quickly determined based on the expected fabric effect, so as to reduce the frequency of manual adjustment and improve production efficiency.

Key words: big belly yarn, color changes, draft ratio, feeding position, fancy yarn

摘要： 为了研究牵伸倍数和后罗拉运动对大肚纱大肚形态和拼色效果的影响，分析了纺纱过程中后罗拉的运动规律，并通过增加粗纱的数量，得到截面和轴向均具有双色效果的大肚纱；同时基于该大肚纱改变牵伸倍数，得到大肚纱直径数据，从而对数据进行分析，得到牵伸倍数与大肚直径之间的函数关系。结果表明：通过改变工艺参数调控后罗拉的运动，可以成功纺制出双色结构大肚纱，且其牵伸倍数同大肚直径之间存在幂函数关系，实验所得函数关系式为：y=0.7693x-0.3864。用所纺纱线织造的机织布表面呈现色彩变幻及凹凸不平的外观，达到预期效果。

关键词: 大肚纱, 颜色变化, 牵伸倍数, 喂入位置, 花式纱线