Steady-state unwinding of yarn from cylindrical packages

Over-end unwinding involves pulling yam from a fixed package to be used in textile processes such as knitting, sewing, twisting, weft insertion in wea ving, and doubling. During unwinding, the yam slides on the package surface and lifts off into the balloon formed between the package and the guide ey elet. Variations in yam tension and balloon shape can adversely affect proc ess efficiency and final product quality. This paper investigates the stead y-state motion of inextensible yam during unwinding. Previously developed m odels 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 ex periment, pc controlled video, tension, speed, and yam rotation sensors mea sure nine dynamic unwinding process variables. Synchronized tension measure ments and video images allow simultaneous measurement of eyelet and lift-of f tension, balloon height, and lift-off and unwind height and angles. The o ptical balloon rotation sensor measures balloon rotation rate and balloon s hape. 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 t han in backward unwinding due to increased balloon rotation rate. A higher unwinding tension and liftoff angle result in a longer yam sliding path on the package surface.