GB1037997A - Drawing synthetic filaments - Google Patents

Abstract

A process for drawing a yarn of undrawn synthetic linear polymer filaments between feed and draw rolls comprises elongating the filaments to at least twice their length while subjecting the undrawn filaments to a high velocity turbulent heated fluid stream which is capable of transferring sufficient heat to the individual filaments to localize the draw point, said fluid stream deflecting the individual filaments in the yarn from their paths and separating them from each other at a critical position where drawing is taking place so that there is substantially no coupling between the filaments at the draw point. The undrawn state is defined in that the natural draw ratio at room temperature makes the filaments capable of elongating at least twice their length. The fluid stream may impinge at right angles, obliquely, or parallel to the filaments and may be arranged to exit preferentially at one end of a jet device so as to cause tension in the filaments. The fluid stream may also be caused to heat the filaments beyond the draw point e.g. by use of a tube or shroud, and also to intermingle the filaments to form a cohesive yarn. The filaments before being wound may be subjected to a continuous crimping operation by e.g. false-twisting (see Specification 777,625) or by passage over a narrow surface (see Specification 1,028,979). In one embodiment (Fig. 1 not shown) undrawn yarn 1 from spin bobbin 2 is passed from a feed roll 4 and idler roll 5 via a double air jet 6 to a draw roll 8 driven at a surface speed at least twice that of roll 4. The yarn is wound up on draw twist bobbin 12. The jet device is associated with air stream valve 7, electric heater 7a and reducing valve 7b. If a crimped yarn is desired, a heated narrow surface may be located at B, C or D. A heat-relaxing device in association with further sets of driven rolls may then be provided before wind-up. If a false-twister is inserted at B to form the crimp, the false twist is prevented from running back into the draw zone by a pin or guide 13. The fibre-forming polymers may be polyesters e.g. derived from terephthalic acid, polyamides e.g. nylon or polyolefines, in particular those containing 70-100% isotactic polypropylene. In Examples, melt-spun polyethylene terephthalate yarn having a birefringence of 8.0 x 10-3 is heated, between feed and draw rolls, by a turbulent air jet at 120-320 DEG C. from a pressure vessel at 60 p.s.i. Draw ratios of 1 : 3.34 are used at wind-up speeds of 1500 ft/min. The amount of coherence of the filaments on the yarn brought about by the false-plaiting caused by the turbulent air stream is preferably 6-12 i.p.m. (as defined) but separation of the filaments by the air jets during drawing may also be achieved without causing coherence in the issueing yarn or tow (see Specification 758,398).