Transcript Slide 1
Yarns Now that you have the fibers what do you do next? Spinning Spinning • Different connotation for natural & manufactured fibers – Natural: making long yarn from short fibers – Manufactured: making fibers and yarn simultaneously • Sometimes manufactured fibers are “chopped” up into short fibers and then treated as if they were natural fibers Manufactured Fibers - Spinning Spinneret Spinning Dope Spinne re t Polymer Reservoir Take -up Take-up Pump Coagulating Bath Wet Spinning Spinning Dope Mo lten Poly mer Pump Pu mp Spinne re t Sp in n er et Warm air Coo l air Take -up Dry Spinning Tak e- u p Me lt S pin nin g Manufactured Fibers - Summary Summary of Major Fiber Spinning Methods DRY MELT WET Polymer before spinning solution solution molten Spinning Environment solution warm air cool air rayon acetate, acrylic polyester, nylon Example Natural Fibers - Twisting • Fibers are put in a parallel bundle and the bundle is drawn down and twisted to form a yarn • 2 competing effects – Cohesion: friction as fibers are pressed into one another produces strength – Obliquity: fibers can carry the most load along their axis; twisting causes the fiber axis and yarn axis to be different Yarn Strength cohesion yarn strength obliquity Twist Twist Direction S Z S - twist Z - twist • No effect on yarn strength • Can affect other properties – Untwisting in larger structures – Fabric thickness Complex Yarn Structures • • Very large textile structures can be built up by twisting together other structures. For example, two or more single yarns can be twisted together to form a plied yarn; two or more plied yarns twisted together form a cord; two or more cords form a cable ad infinitum. The twist in each of the parts is alternated so, for example, if the twist in the single yarn is 'Z', the plied yarn will have 'S', the cord 'Z'; the cable 'S' … The twist is alternated to help prevent the larger structure from untwisting. Yarn Numbering Systems • Direct (ND) – Our “old friends” from linear density – As yarn gets larger its yarn number increases – Usually used with manufactured yarns ND = WS L ND S denier (Nd) 9000 m/g tex (Nt) 1000 m/g decitex/dtex (Ndt) 10000 m/g Yarn Numbering Systems • Indirect (NI) – As yarn gets larger its yarn number decreases – Usually used with twisted yarns NI = L WS NI S English cotton (Ne) 840 yd/lb worsted (Nw) 560 yd/lb woolen run (Nwr) 1600 yd/lb