The critical part of ring spinning machine, at which yarn evenness and tensile strength can be greatly influenced is by the drafting arrangement. The main components in drafting have been subject to various studies in order to make a uniform even yarn. In this study an investigation was done on altering the front top roller cot diameter by grinding and adjusting top roller pressure. The study was undertaken in an industrial setup, 15 different combinations of rubber cot diameter and top roller pressure were tried to optimize the utility of rubber cots with enhanced cot service life without compromising the yarn quality to benefit Bahir Dar Textile Share Company, Ethiopia. The unevenness and tensile strength of 20s Ne 100% cotton yarn were investigated. The test results were subjected for statistical analysis and the worldwide quality standard of the results was also determined by USTER ® STATISTICS 2013 v1.1. The result showed that, the decrease in cot diameter by grinding critically influences the mass unevenness and imperfection of the yarns. It does not apparently influence the yarns tensile strength. Accordingly, cot diameters of 29.9mm and 29.6mm at pressure of 2.2bar and 29.3mm at pressure of 2.3bar was found as optimal pressure and cot diameter combinations which can be able to maintain consistency of yarn unevenness and extends the service life of the rubber cot.

Keywords : Rubber cot, Grinding, Roller pressure, Uster statistics, evenness, and Tenacity.