GB1352520A - Process for crimping filaments - Google Patents

Abstract

1352520 Crimped filaments ERNEST SCRAGG & SONS Ltd 14 Dec 1971 [17 Dec 1970] 59873/70 Heading B5B A method of crimping drawable filaments comprises the steps of advancing the filament through the nip between two rollers which are both heated but to different temperatures: subjecting said filament to a predetermined pressure during passage through said nip, differentially treating said filament by means of said rollers during passage through said nip so as to establish a temperature gradient across the cross-section of the filament; and drawing the thus treated filament so that the draw point is at least close to the nip. As shown, filaments 10 extruded from spinneret 13 are passed via guide rollers 14, 15 to driven forwarding rollers 16. A guide 17, adjustable, as indicated by the chain line 18, enables the filaments to enter the nip of the rollers 11 and 12 along the common tangent to the rollers, or to have a short arc of pre-wrap upon either of the nip rollers in advance of the nip. Further driven forwarding rollers 19 draw the filaments 10 from the nip rollers 11 and 12, via another guide 20 which is adjustable, as indicated by the chain line 21, to enable the filaments to leave the nip rollers 11 and 12 along the common tangent to the two rollers, or to have a short arc of post-wrap, beyond the nip, upon either of the nip rollers. From the draw rollers 19 the filaments pass to a wind-up 22, passing if desired through an optional oven 23 in which they can be annealed. Cooling means for the filaments may be provided downstream of the nip rollers 11 and 12, as indicated at 24, and may be a water bath or air quencher. Preferably the nip rollers are driven at a higher peripheral speed than that of the forwarding rollers 16, so that the yarn is drawn by drawing means operating upstream of the nip of the rollers 11 and 12, the draw point or region of necking being at or close to the nip. The filaments 10 are then drawn from the nip of the nip rollers 11 and 12, along the common tangent to the nip roller, by the further forwarding rollers 19 the peripheral speed of which exceeds that of the nip rollers, so that the yarn is also drawn by drawing means operating downstream of the nip, the draw point or region of necking again being at or close to the nip. The difference between the peripheral speeds of the forwarding rollers 16 and the nip rollers 11 and 12 is equal to the difference between the peripheral speeds of the nip rollers and the further drawing rollers 19, so that the total draw imparted to the filaments is effected in substantially equal proportions by the drawing means operating both upstream and downstream of the nip. In this way the highest crimp levels are obtained. In operation, nip pressure is gradually increased until crimp appears and the pressure then held at this value for maximum crimp; further increase in pressure reduces the crimping effect. Overall temperatures of 125-160‹ C. for the hot roller and 70-110‹ C. for the cooler roller are preferred, depending upon the filamentary material used and the speed of travel of the filaments. With a filament input speed of 30 m./min. polyamides and polypropylene crimp well with a hot nip roller temperature of 128-160‹ C., preferably 145‹ C., and a cooler nip roller temperature of 90-95‹ C; with polyesters hot nip roller temperatures of 125-140‹ C., preferably 135‹ C., and cooler nip roller temperatures of 80-85‹ C. are preferred. A variety of other means of operation are described. In the zone between the roller 19 and the wind-up 22, the extensibility of the crimped yarn can be reduced by passing it through an annealing oven 23 under conditions of controlled overfeed of the yarn, suitably 10-40% overfeed. Auxiliary yarn feed rollers (not shown) may be provided between oven 23 and wind-up 22 to provide an appropriate speed differential between rollers 19 and the auxiliary yarn feed rollers. Profiled nip rollers having spaced shallow circumferential grooves may be used to avoid the tendency of unprofiled rollers to distort the filaments. A wide range of textured effects may be imparted to continuous filament yarn using the apparatus of the invention.