Abstract:
There is disclosed a method for false twist texturing comprising the steps of supplying a yarn hot (11) to a twist trap (12) upstream of a false twist device (13) instead of supplying heat to the yarn intermediate the twist trap and the false twist device.

Description:
TECHNICAL FIELD 
     This invention relates to false twist texturing of yarns. 
     BACKGROUND OF THE INVENTION 
     Conventionally, yarns are textured by the false twisting process in a false twist zone which extends from a twist trap that defines the upstream limit of false twist, and contains a heater that raises the temperature of the false twisted yarn, a cooling zone in which the false twisted yarn is cooled, a false twisting device and an output roller arrangement that hauls the yarn through the false twist zone. The yarn may optionally then be wound up as stretch yarn without further processing, though with some relaxation in an overfeed zone to control the wind-up tension, or, with further heat processing in a relaxation zone, to produce a set textured yarn. 
     The supply yarn may be fully drawn or oriented yarn, or more usually nowadays, partially oriented yarn produced by high speed extrusion from the spinneret, in which case the false twist texturing may involve sequential drawing, in which the yarn is drawn in an in-line operation before passing into the false twist zone or, more usually, simultaneous drawing in which the partially oriented yarn is drawn in the false twist zone itself. 
     As false twist devices have been developed which operate at higher and higher twisting speeds, the rate at which yarn can be processed--which is limited by the false twisting speed, since false twist texturing requires high rates of twist per unit length--has increased correspondingly. The threadline of a false twisting machine as described is necessarily straight or substantially so--a gently curved heater track can be tolerated--between twist trap and false twist device--and because the twisted yarn must remain in contact with the heater for a certain time in order to reach an effective temperature, the heater has become very long and much ingenuity has been put into the design of false twist texturing machines to cope with the long heaters--which can be several metres in length. Eventually, limitations on practical heater length have limited processing rates. For example, 167 dtex yarn could be false twisted at a speed corresponding to a throughput speed of 1500 metres/minute, but is rarely processed at speeds in excess of 900 metres/minute because of heater limitations. 
     SUMMARY OF THE INVENTION 
     The present invention provides a false twist texturing method that avoids such problems. 
     The invention comprises false twist texturing comprising supplying a yarn hot to a twist trap upstream of a false twist device instead of supplying heat to the yarn intermediate the twist trap and the false twist device. 
     The yarn may be cooled between the twist trap and the false twist device. 
     The yarn may pass through a heating zone as an untwisted yarn prior to the twist trap. The heating zone may comprise a Jet heater, which may be supplied with steam and/or hot air. The yarn may be heated in a plug. Jet heaters can operate on untwisted yarn at speeds in excess of 6000 metres/minute. 
     A feed back control arrangement may be used to control the texturing. The feed back control may comprise a bulk measurement after the false twisting device and which may be effected in a relaxation zone, as by measuring yarn speed or yarn tension in the relaxation zone. 
     The feed back control may act on a yarn heater, which may be a supplementary yarn heater--that is to say a readily controllable heater that is additional to a primary, uncontrolled heater. The feed back control may, however, act on a yarn hauling device, which may be the output roller of the false twist zone or a false twisting device. 
     The yarn may be draw-textured. The supply yarn may be taken from a spinneret over a twist trap into a false twisting zone, the heat remaining in the yarn from the spinning operation being sufficient to avoid the need for a separate heating arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of false twist texturing apparatus and methods according to the invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic illustration of a first arrangement; 
     FIG. 2 is a diagrammatic illustration of a second arrangement; and 
     FIG. 3 is a diagrammatic illustration of a third arrangement. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawings illustrate false twist texturing comprising supplying a hot yarn 11 to a twist trap 12 upstream of a false twist device 13 instead of supplying heat to the yarn intermediate the twist trap 12 and the false twist device. 
     It is, of course, to be understood that heat could still, additionally, be supplied to the yarn 11 downstream of the twist trap 12--the invention does not exclude that, but renders it, rather, unnecessary so to do or a matter of choice as to whether and if so how much heat to supply, but in particular renders it unnecessary to use long heaters as are conventionally used. The process however is simplified both from an operating and a control point of view if the conventional twisted yarn heaters are eliminated altogether, as in the embodiments particularly described and illustrated herein and the false twist texturing machine is considerably reduced in capital and operating costs because of the cost savings on providing the heaters and the framework necessary to accommodate them. 
     Moreover, without such long contact heaters, the machinery can be started and stopped readily. Conventional heaters cannot be so operated without waste of time or yarn before reaching equilibrium temperature. This facility for ready stop/start operation introduces a large measure of flexibility into the operation of the machinery--no longer is it necessary to keep the machinery running on a continuous basis for economic operation, so that single shift or two shift operation becomes viable. 
     Between the twist trap 12 and the false twisting device 13 is a cooling zone 14--which may simply be an air gap or which may comprise a forced cooling arrangement such as a cold contact block or forced air cooling. 
     FIGS. 1 and 2 illustrate the yarn 11 passing through a heating step prior to the twist trap 12. In FIG. 2, the yarn 11 is fed by a hot air and/or steam jet 16 into a plug 17 in a tube or plug constraint 18 with a heater jacket 19. Such arrangements are known from other methods of yarn treatment. 
     In FIG. 1, yarn is supplied through a jet heater 16 without forming a plug. It is desirable, of course, to heat the yarn to such a temperature as will, allowing for any cooling prior to and at the twist trap 12, leave the yarn still at an appropriate temperature for the false twist process. The use of steam, for some yarns at least, enables a lower temperature to be used than if hot air alone is used. The appropriate temperatures are well known from the literature--what does not appear to have been generally recognised hitherto is that such temperatures produced at the twist trap 11 by feeding to it an already hot yarn can suffice for false twist texturing without the need to add post-twist trap heat. Such a suggestion is made in GB-A-2 026 560, but does not appear to have been adopted in practice. 
     The hot yarn will, of course, heat up the twist trap, but the thermal capacity of the twist trap which will normally comprise a godet roll or a nip roll arrangement may be arranged to be quite small so that equilibrium is rapidly achieved, and indeed the twist trap itself may be heated--heated godets are of course well known in yarn processing. 
     It is, of course, known in yarn texturing and in particular in false twist texturing to have a relaxation zone for the yarn prior to wind--up-in producing set-textured yarn, the relaxation zone includes stretch-relaxing heating. In the embodiments of FIGS. 1 to 3, such a zone 21 is provided in which bulk develops and comprises a bulk measuring device 22 comprising a yarn speed measuring wheel or tension measuring device connected to a feed back control 23 acting on the system to maintain a constant wheel speed and hence bulk. 
     The feed back control 23, in FIGS. 1 and 2, acts on a supplemental heater 24 for the steam and/or hot air input to the jet heater 16. This effects fine tuning on the yarn temperature at false twisting and is able to control the bulk. The relatively short feed back loop resulting from avoiding the need for the conventional metres-long false twisting heater aids the feed back control operation materially. 
     FIG. 3 illutrates an arrangement in which freshly spun yarn is supplied to an on-line false twist texturing operation utilising the heat remaining in the yarn from the spinning operation. Filaments 31 from the spinneret 32 are gathered together at the twist trap godet 12 and draw-textured as before. The feed back control 23 is shown as controlling the input godet to zone 21 or alternatively the false twist device 13, but the feed back could operate on the extrusion process as by controlling the cooling chimney or the godet 12. 
     Any kind of false twist device may be used, but really high speeds are attainable with roller twisting devices of the Positorq (RTM) type.