GB903027A - Process and apparatus for drawing synthetic linear polyester yarns - Google Patents

Abstract

Synthetic polyester multi-filament undrawn yarn with an optical birefringence not varying more than \sB0,0003 from a value lying between 0,002 and 0,015 is rapidly hot drawn three to six times its undrawn length between feed and draw rolls, heated between the feed and draw <PICT:0903027/IV(a)/1> <PICT:0903027/IV(a)/2> rolls by sliding contact to deflect it 50-270 degrees, preferably 90-180 degrees of arc, in a first zone comprising a stationary heated curved convex metal surface maintained at a temperature between 10 DEG C. below and 25 DEG C. above the second order transition temperature of the polyester, under a tension so that stretching is limited to less than 20% and so that no drawing occurs, passing the heated yarn without substantial cooling to a second zone comprising a small diameter non-rotatable snubbing pin, near to the first zone, causing the tension in the second zone to effect substantially all the drawing of the yarn, maintaining the second zone at the second order transition temperature or at a temperature between this and a temperature 45 DEG C. above the S.O.T.T. followed, if desired, by heating the yarn in a third zone maintained at a temperature 60 DEG -130 DEG C. above the S.O.T.T. but at least 30 DEG C. below the melting point of the polyester. The curved convex surface should be at least 1 1/2 inches but not more than 6 inches in radius, and may be provided with flat portions at ether or both ends. The snubbing pin should preferably be 1 to 2 inches from the first zone and have a diameter of 3/4 inch. Draw speeds up to 1,000 yards/minute may be used. As shown in Fig. 1, undrawn yarn from positive feed rolls is passed to a stationary convex surface (1) consisting of a heated segment of a metal cylinder for deflecting the yarn 90 degrees of arc. The segment has a sand-blasted chromed surface to reduce friction between it and the yarn. From the segment the yarn is passed to a snubbing pin 2 which may be positioned at A or B. The yarn is looped around the pin a number of turns which depend on the denier of the yarn and is then passed to the draw roll having a diameter 3 to 6 times that of the feed roll and mounted on the same shaft. The yarn is looped round the draw roll and a separating idler roll and then passed downwards where it is wound as to a rotating draw-twist bobbin (not shown). A further heating means in the form of a hot plate 3 may be provided between the snubbing pin 2 p and the draw roll. Alternatively the hot plate may be positioned beyond the draw rolls, as shown at 19 in Fig. 2, but in that case, the yarn is passed over slower rotating relaxing rolls 17 and 18 before winding up. The invention enables higher drawing speeds to be used without detriment to the yarn and provides yarns having more uniform dye uptake and more uniform shrinkage in boiling water. Examples are furnished of the drawing of polyethylene terephthalate yarns. U.S.A. Specifications 2,533,013 and 2,556,295 are referred to.