Predicting the Nep Number in Cotton Yarn—Determining the Critical Nep Size

Neppiness is one of the most important aspects of cotton yarn quality and significantly influences the appearance of woven and knitted fabrics produced from that yarn. The direct sources are neps and trash contained in the cotton fiber sliver feeding the spinning frame. Nevertheless, not all neps cause yarn faults. For each yarn linear density, there exists a critical nep size above which neps are registered by an Uster tester as yarn imperfections. Determining the critical nep size is important from the point of view of predicting the nep number per 1000 m of cotton yarn. We consider and elaborate on theoretical models of critical nep size as a function of the linear density of cotton ring spun and OE yarns. On the basis of our equations, we calculate the critical nep size for different yarn linear densities. The experimentally obtained results confirm our theoretical models.