GB924888A - Methods and apparatus for thermally shrinking thermoplastic yarns - Google Patents

Abstract

In a process for thermally shrinking thermoplastic, e.g. nylon or polyethylene, yarn, a running length thereof is positively overfed into and positively withdrawn from engagement with a heated surface by unheated feeding and withdrawing devices. The heater surface is positively driven so as to move in the same direction as the yarn at the points of contact with it and at a speed which is less than 5% different from the withdrawing speed and may be 5-40% less than the speed at which yarn is positively advanced to the surface. The temperature of the surface is at least 180 DEG F. but is not above the sticking temperature of the yarn. "Elasticising", e.g. edge-crimping, and processes for modifying bulk and/or stretch properties of the yarn product thereof by thermal shrinkage may be effected successively with apparatus providing two heating surfaces on a single structure for the respective heat treatments. As shown in Fig. 1, yarns 20 and 22 supplied from pirns 18, 19, are passed from guides 24, 26, through tension regulators 28 and 30 to assembly 32 (wherein the yarn is crimped and modified) thence about an oiling roller 34, and the lubricated, modified bulk/stretch yarns pass through a guide 40 and are plied and taken up by ring-twisting apparatus 42. Within the assembly 32, Figs. 3 and 6, yarns 20, 22, pass about multiple guides 62, 66, and wrap one or more spaced turns about larger diameter portions 84 and 90 of canted advancing rolls 74 and 82, thence through a guide comb 102 to a heater 108. The heater, Fig. 7, comprises a stepped roll 110 and an electrically heated member 128 which supports and distributes heat to rotary, coaxial, yarn contact members 130 and 132 grooved at 134 and 136 to receive the yarns. After passing in partial wrap about member 130, the yarns are withdrawn in a sharply angular manner about the edge of a blade 160 (the angularity and position in relation to the heater of which are adjustable and spring-located) under the guidance and tensioning control of an unheated, freely-rotatable roll 164, then pass <PICT:0924888/IV(a)/1> <PICT:0924888/IV(a)/2> <PICT:0924888/IV(a)/3> <PICT:0924888/IV(a)/4> over a separating guide 178, around the smaller diameter portions 88 and 92 of rolls 74 and 82 and thereafter through a guide comb 184 and in a partial wrap about member 132. The yarns are positively withdrawn from engagement with the heated surface of member 132 by a second yarn advancing device 188, comprising canted rolls 190 and 208 driven by a common belt 210, to which they are directed by a guide pin 186. A common drive shaft 212 driven in synchronism with the drive for take-up apparatus 42 may extend the length of a machine frame and serve a number of stations. The rate of operation of both yarn advancing devices 76 and 188 may be incrementally varied with respect to the rate of rotation of heater roll 110 through replaceable, adjustably mounted gear wheels and manually controlled clutches, the mechanism also being mechanically interlocked with apparatus 42 and subject to overriding control, through a solenoid-actuated link, by an electrical stop-motion (not shown) so that, upon yarn breakage, both edgecrimping and final yarn take-up automatically cease, Figs. 4 and 5 (not shown). The run of the yarn may be altered to restrict the function of the apparatus to a combined hot-stretching and thermal contraction, or shrinking or modification of a previously crimped yarn. Specification 823,047 is referred to.