Steady-State Unwinding of Yarn from Cylindrical Packages

Abstract

Over-end unwinding involves pulling yam from a fixed package to be used in textile processes such as knitting, sewing, twisting, weft insertion in weaving, and doubling. During unwinding, the yam slides on the package surface and lifts off into the balloon formed between the package and the guide eyelet. Variations in yam tension and bal loon shape can adversely affect process efficiency and final product quality. This paper investigates the steady-state motion of inextensible yam during unwinding. Previously developed models that predict the yam tension and motion in the unwinding balloon and on the package surface are modified to include the effects of nonzero wind angle packages and to allow comparison with experimental results. In the experiment, PC controlled video, tension, speed, and yam rotation sensors measure nine dynamic un winding process variables. Synchronized tension measurements and video images allow simultaneous measurement of eyelet and lift-off tension, balloon height, and lift-off and unwind height and angles. The optical balloon rotation sensor measures balloon rotation rate and balloon shape. In agreement with the theory, increased balloon height and decreased air drag lead to higher tension. Multiple loop balloons have lower tension and occur at larger balloon heights. Yam tension during forward unwinding (i.e., lift off point moving toward the guide eye) is significantly smaller than in backward un winding due to increased balloon rotation rate. A higher unwinding tension and liftoff angle result in a longer yam sliding path on the package surface.