In this study, a quasi-static model is built to theoretically analyze the distribution of twists and spinning tension in embeddable and locatable spun (ELS) yarn formation zone. Important equations are also derived to determine inner mechanics and external configurations of the ELS yarn formation zones 1, 2 and 3. Analysis results demonstrate that in zones 1 and 2 the tension distribution on the filament and staple strand is directly proportional to their linear mass and square of delivery speed; the larger weight causes a smaller angle between the responding component and the composite strand axis line. The angle between the composite strands 1 and 2 can be simply calculated by dividing the composite yarn velocity by composite strand velocity. Online photographs are provided to validate theoretical analysis of the ELS yarn formation zone configuration and twist distribution in zones 1 and 2.

In this study, Photoshop software was used to do image analysis on the photos of spun yarns. The result showed that yarn could be divided into two parts: the surface hairs and the stem. Based on this finding, a mathematical model of yarn unevenness was built to analyze the relationship between yarn unevenness and surface hairiness. The relationships among the coefficients of mass variance of the yarn, the stem and the surface hairs, expressed as CV t , CV s and CV h , respectively, were investigated in detail. Results indicate that the CV s of an uneven yarn always coincides with the irregularity of the yarn hairiness. More specifically, the CV t of a yarn cannot be better than those of both yarn hairiness and stem (CV h and CV s ), even if one of them is excessive. It is rare for CV t to be higher than CV s after removal of yarn hairs. In particular, it is irrational for the CV t value to be higher than both CV s and CV h , which prompts a rethinking of the exact distribution of yarn hairs on the yarn body.

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