| Over-end unwinding involves pulling yarn from a fixed package to be used in textile processes such as knitting, sewing, twisting, weft insertion in weaving, and doubling. During unwinding, the yarn slides on the package surface and flies into the balloon formed between the package and guide eyelet. Variations in the yarn tension and balloon shape can adversely affect process efficiency and final product quality. This dissertation theoretically and experimentally investigates the quasi-steady state motion of inextensible yarn during unwinding. Models are developed to predict the yarn tension and motion in the unwinding balloon and on the package surface. The models depend on diameter, wind angle, frictional coefficient, and residual tension of the package and the transport speed, air drag, and material properties of the yarn.; The numerical results show that increasing balloon height and decreasing air drag lead to higher unwinding tension. Multiple balloons have lower tension and smaller maximum balloon radius as compared to single balloons. Higher unwinding tension and larger package frictional coefficient result in a longer yarn sliding path on the package surface.; An experimental device consisting of a camera and tension, speed, and yarn rotation sensors is used to verify the model. The mechanical and geometrical properties of the unwinding balloon and sliding yarn are determined from synchronized tension measurements and video images. Comparisons of the experimental results with the unwinding balloon and sliding motion models validate the theoretical predictions. |
