Patent GB-960500-A (GB)
Title: Process for stretching yarns
IPC: D02J1/22
Filed: 1962-03-08
Abstract: 960,500. Stretching yarns and filaments. FARBENFABRIKEN BAYER A.G. March 8, 1962 [March 9, 1961], No. 8965/62. Heading B5B. [Also in Division D1] Yarns and filaments of synthetic linear polymers are stretched at temperatures up to the melting point of the yarn material by passing the yarn while under stretching tension helically around a heated straight stretching rod, the longitudinal axis of which is disposed in the stretching direction. Stretching may be carried out on freshly spun yarns or filaments immediately after leaving the spinning shaft, and may take place in the stretching zone of a stretching or drawing frame between the supply mechanism and withdrawal mechanism. Highly stretched material, which has been spun at a speed of more than 1,000 m/min. may be used as starting material. The temperature of the stretching rod is suitably between the melting point of the yarn material and 50 ‹ C. below said melting point, and specified yarn materials include polyamides, e.g. polycaprolactam, polyesters and polyurethanes. The yarn may be wrapped 0.5-5 times around the stretching rod, which may be fitted with a thread guide (e.g. 9, Fig. 3) for determining the number of helical windings longitudinally of the axis of the stretching rod. In apparatus as shown, Figs. 1 and 2 are side and front elevations of a rod comprising a single heated resistance wire, bent to the required shape. Yarn is looped around upper part 1 and lower part 2 and forms a helix around the adjacently disposed wires 3 and 4, being prevented from running off by the bentover ends 5. The space between wires 3 and 4 is filled with adhesive. Current is supplied at the ends 7, and a thermocouple may be attached at 6. In Fig. 3, the rod is constructed of a single wire of semi-circular cross-section, the curved surfaces of the wires facing outwards and the space between the wires being filled with adhesive. Current is supplied at the ends 8. Yarn can be threaded through a lateral slot in thread guide 9 which is rotatable about pin 10 by screw 11, so as to determine the number of windings around the stretching rod. Fig. 5 illustrates a tubular stretching rod. Current is supplied by a wire soldered to the inside of the tube at 13, the other terminal 14 being movable along the tube, and 15 is a resistance thermometer. To prevent a temperature drop at the yarn input end when using thick yarns or filaments, a tube tapered at the input end, so as to raise its electrical resistance at this end, may be used. The stretching rods may be made of nickel-containing steel, hardened or hard-chromium plated on the exterior surfaces. Ceramic surfaces may also be used. In Fig. 7, the stretching rod 16 is incorporated in a conventional stretching frame, comprising feed rolls 20 and draw roll 18 and positioning roll 17. In Fig. 8, freshly-spun yarn leaving the spinning shaft 21 passes over thread guide 22, roll 23 and brake 24 before reaching the stretching rod 25, from which it is withdrawn by the foil mechanism 26, passing via roll 27 to the winding mechanism 28. The stretching process of the invention enables yarn to be obtained having a very low shrinkage on boiling, a very small amount of immediate recovery and a very high workability under impact, while using high spinning speels. Specifications 598,820, 850,899 and U.S.A. Specification 2,533,013 are referred to.