GB2133810A - False twisting - Google Patents

Abstract

A method of false twist crimping a yarn comprises forwarding the yarn under tension from a feed device (12) through a heating zone (13) and a cooling zone (14) to a false twist device (15) whilst intermittently reducing and restoring the tension in the yarn to allow the twist inserted therein to travel around a yarn guide (20) which guides the yarn through a change of direction of travel between the heating zone (13) and the cooling zone (14). Guide 20 may comprise a disc (30) with fins (32), rotation of the disc thus causing the required tension variation in the yarn and allowing twist to run back past this point. <IMAGE>

Description

SPECIFICATION Texturing of yarn This invention relates to the texturing of yarn, and in particular to the texturing of yarn by the false twist crimping process.

In the false twist crimping process yarn is taken from a supply package by means of a first feed device and then passed through heating and cooling zones to a false twist device. It is preferable that the yarn travels in a straight yarn path between the first feed device and the false twist device in order that as much as possible of the twist imparted to the yarn by the false twist device can travel back to the heating zone and also to minimise the tension in the yarn required to forward the yarn through the heating and cooling zones and the false twist device.

However, in order that high yarn throughput speeds can be achieved, whilst the yarn reaches the required temperatures as it passes through the heating and cooling zones, it is necessary to provide long heating and cooling zones. If the desired straight line yarn path is maintained the machine becomes inconveniently or prohibitively high and for this reason it is customary in modern high-speed texturing machines to resort to 'bent' yarn paths, i.e. to cause the yarn to undergo one or more appreciable changes in path direction as it passes between the first feed device and the false twist device.

In order to provide such changes in path direction yarn guides are provided. If such guides are fixed there is of necessity a large increase in tension in the yarn as it passes around the or each guide. In order that the tension in the yarn in the heating zone is sufficient to avoid instability, i.e.

tension surging, at high processing speeds, the use of static yarn guides in the yarn path between the first feed device and the false twist device necessitates high tension levels at, and on the downstream side of, such guides. High tensions in yarn which is heated to or near to its softening temperature can cause flattening of the filaments, or even breakage thereof, as the yarn passes around a guide.

This results in a poor quality textured yarn.

Reducing the yarn tension in the region of such a guide can only be achieved at the expense of reducing the draw ratio or increasing the twist level, and possibly by increasing the guide radius, but such solutions lead to severe restrictions in process speed to avoid tension surging if product quality is to be maintained.

It is known that the above problems can be avoided to a large extent by the provision of simple rotating guides, but in that case other problems are encountered. By simple rotating guide is meant a guide rotating about an axis which is at right angles to the path of the yarn around the guide. Use of a simple rotating guide can lead to reduced twist transfer around the guide, i.e. the twist level in the heating zone may be considerably less than that inserted in the yarn by the false twist device. Again this leads to the production of a poor quality textured yarn. To overcome this problem it has been proposed to rotate the guide in the direction of the twist helix angle, but with such an arrangement the rotation angle would require changing for different processing parameters and for S as opposed to Z twist.

It is an object of the present invention to provide a process of false twist crimping yarn in which, whilst the yarn is caused to travel along a 'bent' yarn path between an input feed device and a false twist device, the aforementioned disadvantages are avoided or alleviated to a substantial extent.

The invention provides a method of false twist crimping yarn comprising forwarding the said yarn under tension from a feed device through a heating zone and a cooling zone to a false twist device, the yarn undergoing at least one change of direction of travel between the heating zone and the false twist device whilst being so forwarded, and intermittently reducing and restoring said tension.

Preferably said tension reduction and restoration is performed at successive regular time intervals, and may be effected by temporarily reducing the yarn path length between said heating zone and said false twist device.

The yarn may be caused to undergo at least one change of direction of travel between said heating zone and said cooling zone and said change of direction may be at least 900.

The invention will now be further described with reference to the accompanying drawings in which: Fig. 1 illustrates a typical false twist crimping machine incorporating a yarn path having a change of direction between the heating and cooling zones.

Fig. 2 is a cross-sectional view of one form of guide disposed between the heating and cooling zones of the machine of Fig. 1.

Figs. 3 and 4 are alternative forms of guide to that of Fig. 2.

Figs. 5, 6 and 7 show the effect on a yarn of processing using the following machine configurations respectively; the machine of Fig. 1 with static guides between the heating and cooling zones, the machine of Fig. 1 with the guide of Fig. 2 between the heating and cooling zones, and a machine having a straight line yarn path between the heating and cooling zones.

Fig. 8 is a table showing mean twist levels in a yarn in the heating zone and in the cooling zone using the machine configurations to which Figs. 5 and 6 relate.

Figs. 9 and 10 are graphs of yarn process tension against draw ratio and surge speed against process tension for each of the machine configurations to which Figs. 5 to 7 relate.

Referring now to Fig. 1 , there is shown a false twist crimping machine 10 of conventional form.

The machine 10 comprises a creel 11, a first yarn feed device 12, a first heater 13, an yarn cooling plate 14, a false twist device 15, a second feed device 16, a second heater 17, a third feed device 18 and package wind up means 19.

Twist inserted into the yarn by false twist device 1 5 runs upstream through the cooling and heating zones 14, 13. The heater 13 must heat the yarn to a temperature at which it softens and the cooling zone 14 must allow the yarn to cool so that the twist is set in the yarn. For processing yarn at high throughput speeds it is necessary that the heating and cooling zone 1 3, 14 be relatively long in order that the yarn can reach the requisite temperatures within those zones. For this reason it is convenient to cause the yarn to undergo a change of direction of travel between the heating and cooling zone 13, 14. In consequence a yarn guide 20 is provided between these zones.Since the use of a stationary guide in such a location causes a large increase in tension in the yarn as it passes around such a guide it is possible to provide a rotatable guide at this position.

However, as herein before explained there are also disadvantages associated with the use of a rotating guide at such a location.

In order to avoid or alleviate to a substantial extent such disadvantages, in the process of the present invention a yarn guide 20 as shown in Fig.

2,3 or 4 is used between the heating zone 13 and the cooling zone 14. In Fig. 2 there is shown a guide 20a comprising a cylinder 21 which is rotatably mounted on a shaft 22, the latter being fixed to the frame of the machine 10 or preferably affixed to a sledge 23 which can be traversed along the heater 1 3 or the cooling plate 14 for ease of threading.

The cylinder 21 has an endless groove 24, extending around its periphery the base of the groove 24 defining a cylindrical surface whose axis is set at an angle to the rotating axis of the cylinder 21. In an alternative embodiment the groove 24 describes an endless but tortuous path around the cylinder 21 and in addition the inclination of the bottom of groove 24 relative to the axis of shaft 22 varies around the periphery so that the deepest part of the groove 24 can lie towards the outside or the inside of the curve of the groove path as desired.

With either embodiment one or more complete cycies per revolution of the cylinder 21 may be formed in groove 24 as desired. The tension in the yarn 25 as it passes around the guide 20a within the groove 24 will tend to cause movement of the yarn 25 towards the deepest part of the groove 24. In consequence the effective radius of the guide changes and the yarn path length between the exit end of heater 13 and the inlet end of cooling plate 14 will be varied as the cylinder 21 rotates, thereby intermittently releasing and then restoring the tension in the yarn 25.

In Fig. 3 there is shown a guide 20b comprising a pulley 26 rotatably mounted on a shaft 27. The shaft 27 is slidably mounted in a slot 28 in a mounting member 29 which is affixed to the frame of machine 10 or to a sledge 23. Pulley 26 on shaft 27 is caused to oscillate in the longitudinal direction of slot 28 so as to vary the length of the yarn path between heater 13 and cooling plate 14. In this way the tension in yarn 25 is intermittently released and restored.

In Fig. 4 there is shown a guide 20c comprising a disc 30 which is rotatably mounted on a shaft 31, the latter being mounted on the frame of machine 10 or a sledge 23. Mounted on disc 30 are a plurality, four being shown, of spigots 32, the yarn 25 passing around at least two of them.

As disc 30 rotates the yarn path length between the heater 13 and cooling plate 14 will vary, thereby intermittently releasing and restoring the tension in the yarn 25.

Referring now to Figs.5 to 7 there is shown a typical multifilament yarn having been subjected to false twist crimping on a machine generally of the type shown in Fig. 1. In the case of Fig. 5 the yarn 25a has been processed on a machine having two adjacent static guides between the heater 1 3 and the cooling plate 1 4. It can be seen that there has been a considerable amount of flattening of the filaments, particularly in the regions marked X, whereby a processed yarn of poor quality is obtained.

In the case of the yarn 25b shown in Fig. 6 the processing has been carried out using the yarn guide 20a of Fig. 2 on the sledge 23 of the machine 10 of Fig. 1. It will be seen that there is considerably less flattening of the filaments in this case than in the previous case, even though the two yarns have been subjected to the same temperature and twist level and processed at the same throughput speeds. In fact the yarn 25b of Fig. 6 is comparable with the yarn 25c of Fig. 7 which has been processed under the same processing conditions as yarns 25a and 25b but on a machine in which the heater 1 3 and cooling plate 14 are substantially in alignment so that the yarn 25c did not undergo a change of directions of travel between the heater 13 and the cooling plate 14.

If the feed device 1 6 of the machine 10 is driven at a higher speed than feed device 1 2 the yarn 25 will be drawn simultaneously with being false twisted. From the table shown in Fig. 8 it can be seen that generally, and at least for lower draw ratios, the twist level in the yarn in the heating zone is more nearly equal to that in the cooling zone when the yarn tension is intermittently released and restored using the yarn guide 20a than when using two static guides. This shows that generally such tension release allows the twist to travel upstream to the heating zone more readily than is the case with static guides. The facility of twist transfer is of particular advantage on start up of the machine when the yarn is untwisted, since static yarn guides 20, would resist passage of twist from the cooling zone to the heating zone during that part of the operation.

From Fig. 9 it can again be seen that use of an intermittently tension releasing yarn guide 20a reduces the yarn processing tension, curve 9b, from that required for processing using two static guides 20, curve 9a, almost to the tension value required when using a straight line yarn path between the heating zone and the cooling zone, curve 9c. Since there is such a reduction of processing tension it is to be expected that there would be less flattening of the filaments of the yarn 25b than yarn 25a and that yarns 25b and 25c would be comparable, as is shown in Figs. 5 to 7.

The curve 9a is that obtained when using an alumina surfaced static guide. The process tensions shown for the static guide can be reduced, to values only about 2 grms above the values shown by curve 9b, if a material having a lower friction co-efficient with the yarn is used, e.g. titanium. However such guides have the disadvantages of reduced service life and being unsuitable during start-up as discussed below.

From Fig. 10 it may also be seen that processing the yarn by releasing the tension intermittently is comparable with using a straight line yarn path between the heating zone and the cooling zone. In this case it can be seen that for a given yarn throughput speed the process tension at which surge occurs is higher in the case of the use of static guides, curve 1 Oa than with periodic tension release curve 1 Ob or with a straight line yarn path, curve 1 Oc. This means that in either of the latter cases the yarn can be processed without surge occurring, with less chance of filament flattening or damage than with the use of static guides.

The present invention is particularly advantageous during start up of the textile machine. If static yarn guides are used at the direction change locations of the yarn paths between the heaters and the false twist devices then for normal running smooth surfaced guides are required to reduce friction between the twisted yarn and the guide surface and to keep the tension around the guide to a minimum. However during start up a rougher surfaced guide is required because the yarn is in its untwisted, i.e.

flat, state. A simple rotating guide at this location, as previously mentioned, is satisfactory at start up when the yarn is untwisted but is not satisfactory for normal running when the yarn is twisted since there is insufficient transfer of twist around the guide. These effects are particularly significant at the higher processing speeds generally desired for modern yarn processing.

Claims (14)

1. A method of false twist crimping yarn comprising forwarding the said yarn under tension from a feed device through a heating zone and a cooling zone to a false twist device, the yarn undergoing at least one change of direction of travel between the heating zone and the false twist device whilst being so forwarded, and intermittently reducing and restoring said tension.

2. A method according to claim 1 wherein said tension reducing and restoring are performed at successive regular time intervals.

3. A method according to claim 1 or claim 2 wherein said tension reducing and restoring are effected by temporarily reducing the yarn path length between said heating zone and said false twist device.

4. A method according to any one of claims 1 to 3 wherein said yarn is caused to undergo a change of direction of travel between said heating zone and said cooling zone.

5. A method according to any one of claims 1 to 4 wherein said at least one change of direction is of at least 90 .

6. A method according to any one of claims 1 to 5 wherein said at least one change of direction is effected by passing said yarn around a rotatably mounted yarn guide.

7. A method according to claim 6 comprising oscillating said yarn guide whilst the yarn is forwarded therearound.

8. A textile machine for performing the method of claim 1 comprising a feed device, means defining a heating zone, means defining a cooling zone, a false twist device, guide means operable to guide the yarn through at least one change in direction of travel between the heating zone and the false twist device and means operable intermittently to reduce and restore tension in said yarn.

9. A machine according to claim 8 wherein said tension reducing and restoring means is operable to reduce temporarily the yarn path length between said heating zone and said false twist device.

10. A machine according to claim 8 or claim 9 wherein said guide means is located between said heating zone and said cooling zone.

11. A machine according to any one of claims 8 to 10 wherein said guide means is rotatable.

12. A machine according to claim 11 wherein said guide means comprises a cylinder having an endless groove extending therearound, the base of which defines a cylindrical surface whose axis is inclined relative to the axis of rotation of said cylinder.

13. A machine according to claim 11 wherein said guide means comprises a pulley mounted for rotation and for reciprocating sliding motion relative to pulley support means.

14. A machine according to claim 11 wherein said guide means comprises a plurality of spigots mounted on a rotatable disc.

1 5. A method of false twist crimping yarn substantially as hereinbefore described with reference to and as illustrated in Fig. 1 when modified by any one of Figs. 2 to 4.

1 6. A textile machine for false twist crimping yarn substantially as hereinbefore described with reference to and as illustrated in Fig. 1 when modified by any one of Figs. 2 to 4.