"on the Mechanics of Twist Inserti

ON THE MECHANICS OF TWIST INSERTION by ALY H. M. EL-SHIEKH Submitted to the Department of Mechanical Engineering Fibers and Polymers Division, on May 14, 1965 in Partial Fulfillment of the Requirements for the Degree of Doctor of Science in Mechanical Engineering This investigation is directed toward an improved understanding of the mechanisms and actions taking place in the textile twisting process. During conventional twisting, material is fed into the system at a constant rate and in the form of a flat ribbon, composed either of continuous filaments or short discontinuous fibers such as cotton or wool. Upon passing the delivery point, the ribbon is continuously twisted into a compact yarn structure. During twisting, the different filaments comprising the ribbon compete for the central position in the yarn structure. The difference in fiber path lengths between inner and outer yarn layers leads to tension variation between the fibers and this, in turn, causes a continuous change of fiber position along the yarn length. The mechanism of this fiber interchange, or migration, was studied theoretically and experimentally. It was found that in open structures outward migration occurs when predetermined slack develops in the pretwist zone. In closed structures, outward migration occurs when the central fiber buckles compressively against the surrounding fiber matrix. The experimentally measured migration frequencies agreed well (within 10-20%) with the theoretically predicted values.