GB700176A - Improvements relating to methods of stretching threads and filaments composed of synthetic linear polymers and apparatus therefor - Google Patents

Abstract

Threads or filaments of synthetic linear polymers are stretched by passing them under tension at least once round a snubbing member, which may or may not be rotated, in such a way that the position of the draw point is restricted to a fixed zone of limited extent in the path of the threads or filaments round the member. For this purpose, the latter has a number of spaced peripheral projections, so that the threads or filaments come into contact only with the projections and are spaced from the surface of the snubbing member intermediate the projections. The member may consist of a cylinder of good heat conducting material into the surface of which are sunk, at spaced intervals around its periphery, a number of pins, e.g. 6 or 10, parallel with the axis of the cylinder, only a sufficient portion of each pin being above the surface of the cylinder periphery to permit a small part of the surface of each pin to come into contact with the thread or filament and exert friction thereon, the thread or filament not contacting the cylinder itself. The cylinder may be of sufficiently large diameter to enable heating or cooling means, e.g. tubes through which a heating or cooling liquid is passed, to be arranged within it. The pins may be of abrasion-resistant material such as agate, corundum, hard porcelain, quartz, glass, silver steel or tungsten. They are preferably of circular cross section but may be elliptical. The cylinder may be mechanically rotated in the same direction as or the opposite direction to the direction of travel of the thread or filament round the cylinder. The pins may all be of the same diameter or may decrease in diameter in the direction in which the thread or filament travels round the cylinder. They may be fixed in the cylinder in such a manner that when required they can be turned or longitudinally displaced, so that worn places can be moved out of the path of the thread or filament. In an example a poly-e -caprolactam yarn is delivered at a speed of 50 metres per minute from a pair of rollers, passed once round a snubbing member 18 mm. in diameter having six equal sized frictional pins and drawn off the member at a speed of 175 metres per minute. The denier of the yarn is thereby reduced from 105 to 30 with an average deviation of titre of only + 1 per cent. Specification 543,466 is referred to.