WO1994019518A1

WO1994019518A1 - Improvements relating to knitted fabrics

Info

Publication number: WO1994019518A1
Application number: PCT/GB1994/000303
Authority: WO
Inventors: Anthony Primentas
Original assignee: The University Of Leeds
Priority date: 1993-02-20
Filing date: 1994-02-15
Publication date: 1994-09-01
Also published as: AU6008094A; GB9303425D0

Abstract

The invention relates to a method and apparatus for manufacturing a yarn which when knitted into a fabric does not exhibit Spirality. Further, the invention provides for a yarn and a knitted fabric when manufactured by the method or apparatus of the invention. Spirality in the knitted fabric is eliminated as a result of treatment of the yarn, which involves balancing torsional forces in the yarn such that twist in a first direction is counter balanced by twist in a second opposite direction.

Description

IMPROVEMENTS RELATING TO KNITTED FABRICS

The invention relates to a method and apparatus for treating yarns to be used for the production of knitted fabric, and also a yarn and a fabric produced by the method and apparatus.

In the textile industry there is well known an undesirable effect called

SPIRALITY which commonly appears in single tubular knitted fabrics. Spirality results due to a lack of perpendicularity between courses and wales as the latter follow a spiral path along the axis of the produced fabric. In the case of flat knitted fabrics, the wales follow a sideways direction at an angle to the perpendicular. According to the direction of the inclined wales, two types of Spirality exist, positive or Z-spirality where there is an inclination to the right side of the vertical fabric axis and negative or S-spirality where there is an inclination to the left side of the vertical fabric axis.

It is know that Spirality is mainly due to the yarn "twist liveliness". Highly twisted yarns have a high residual torque providing the knitted fabrics with an increased tendency to spiral (skew). The "twist liveliness" property of a yarn, by acting in each of the individual loops of the knitted structure, causes the lifting of one side of the knitted loop from the plane of the fabric which results in an overall distortion of the fabric surface. Hitherto, a number of methods have been developed to overcome Spirality. These can conveniently be divided into two types; mechanical and chemical methods.

Mechanical methods include a way of using balanced doubled (plied - fold) yarns, that is, two component single yarns having equal twist amount and same twist direction are combined and twisted as one unit, in the opposite direction, with an appropriate twist amount. This first method has drawbacks in that, although Spirality is eliminated, the two-fold yarn production is expensive and further a garment, knitted by such yam, is heavier, in fact double in weight.

Another method includes knitting two single yarns, of equal and opposite twist liveliness values, per feeder. This method, (similar to the "plating" process) has drawbacks as aforedescribed. Alternatively, two single yarns of equal and opposite twist liveliness values can be used in a method of knitting alternate courses. Even though this method eliminates the overall

Spirality of a knitted fabric, it provides the fabric surface with an undesirable "cockling" effect.

Furthermore, for the above methods, the production of two types of yarns having equal twist amount and opposite twist direction, as well as the actual fabric production process, is costly. In addition, the method is also labour intensive because it requires yarn package marking and inspection for the avoidance of mixing up the yam types during the fabric production.

Chemical methods of eliminating Spirality include correction of the problem by imposing distortion of the fabric so that the wales straighten out and are subsequently set in a straightened form. Setting can be achieved by using resins, heat, steam or mercerization. However, setting by resin, steam or dry heat is a transient measure, because as soon as the fabric is wet the fault returns. Moreover, setting the twist of a cotton yam which contains a small percentage of low melt polyester fibres reduces the fibre movements in the yarn but the latter becomes stiff.

It follows from the above that, to date, no single method has been successful in permanently eliminating Spirality without disadvantage.

It is therefore an object of the invention to provide a method which both eliminates or at least substantially mitigates Spirality and which does not suffer from the aforementioned drawbacks.

According to a first aspect of the invention there is therefore provided a method for treating a yarn so as to eliminate Spirality in a knitted fabric comprising:

a) taking a single yarn that has been twisted in a first direction and thereafter set in said first direction; and

b) twisting said yarn in a second opposite direction with respect to said first direction.

According to a further aspect of the invention there is provided a method for treating a yam so as to eliminate Spirality in a knitted fabric comprising:

a) taking a single yarn and twisting it in a first direction or taking a single yam that has been twisted in a first direction;

b) setting the said twisted yarn; and

c) twisting said set yarn in a second opposite direction with respect to said first direction.

It will be implicit from the above that the invention involves taking a single yarn that has either been twisted and set in a first direction or taking a single yarn which may or may not have been twisted and twisting and/or setting said yarn in a first direction and then treating the yarn as per the above so that said twisted and set yarn is twisted in a second opposite direction with respect to said first direction.

In the above described method where a twist in a first direction results in the yam being Z twisted then the said twist in the second direction will be in an S direction and effectively "untwisting" the yarn. Ideally, the amount of twist and untwist, or counter twist, will be balanced so as to ensure that torque created by Z twisting and remaining in the yarn will be balanced by torque created by S twisting so providing for a "balanced yarn". It follows, that the degree of first and second twisting, and the respective directions of same, will vary according to the nature of yarn to be twisted but in any event, will be so practised as to produce a balanced yarn.

Fabrics produced from yarns treated as per the above method typically exhibit no, or at least very little, Spirality before and after processing.

It will be apparent to those skilled in the art that Z twisted yarns produce knitted fabric presenting Z spirality. However, when yarn treated as per the above described method is knitted, and the ensuing knitted fabric is wet processed and dried it can be seen that the Spirality almost disappears depending on the amount of S twist there was inserted. This can be explained if the two counter torsional forces balance each other during the wetting process as was described previously.

We have noticed a curious phenomenon associated with the invention in that, before washing a fabric we can sometimes see Spirality in a direction opposite to that normally anticipated for a given yam, eg a Z twisted yam normally exhibits Z-spirality before and after processing, but surprisingly, a Z twisted yarn treated in accordance with the invention exhibits S- spirality of low order before washing. It follows that yam treated in accordance with the invention is free of any distorting forces and a permanent twist setting usually is achieved, resulting in the knitted fabric being free of Spirality. Further, we have noticed that the yarn and consequently the knitted fabric is more bulky, fuller and has an unusual handle, similar to that given by a twistiess yam.

It was thought that, since twist supplies the yarn with strength, the treated yarn would be "untwisted" and therefore reduced in strength. It was found that the strength was reduced, as was expected due to the untwisting process, but not seriously. Accordingly, use of the method does not deleteriously affect the yarn and the garment subsequently produced therefrom.

The invention also provides for an apparatus that is adapted to treat the yarn according to the aforementioned methods.

Accordingly, the invention provides for an apparatus for treating a yarn so as to eliminate Spirality in a knitted fabric by said yarn comprising; a feed means for feeding a single yam, that has been twisted in a first direction and set therein, to a reverse twisting means which twists said yarn in a second opposite direction with respect to said first direction.

Further aspects of the invention include an apparatus which is adapted to treat a yarn that has been twisted in a first direction but not yet set and which therefore further includes a setting means for the purpose of setting said yam in said first direction prior to transferring said yarn to said reverse twisting means.

A yet further aspect of the invention involves the provision of an apparatus which further includes a first twisting means whereby the apparatus is adapted to feed a single yarn to said first twisting means so as to twist the yarn in a first direction and which also includes a first transfer means which transfers said twisted yarn to a setting means where said yarn is set; and also a second transfer means which transfers said twisted and set yarn to a reverse twisting means which twists said yarn in a second opposite direction with respect to said first direction.

In preferred embodiments of the invention said apparatus includes a means for extracting said yarn from the spinning frame and/or a means for feeding said treated yam to a knitting machine.

According to a further aspect of the invention, there is provided an apparatus for eliminating Spirality in a knitted fabric comprising:

a) means for extracting yarn from a spinning frame;

b) means for twisting said yarn in a first direction as it is wrapped about a first reel member;

c) means for setting the said twisted yarn; and

d) means for twisting said set yarn in a second opposite direction with respect to said first direction as it is wrapped about a second reel member.

Yarn thus treated as aforedescribed can then be stored on the second reel member prior to use.

Preferably said apparatus includes a knitting machine to which said treated yam is transferred so as to produce a knitted fabric.

Ideally, the apparatus will be designed to operate so that yam in accordance with the invention is produced at a rate compatible to the operating rate of the knitting machine. Embodiments of the invention will now be described by way of example only. With reference to the following examples wherein;

Figure 1 and Table 1 show the Spirality characteristics of a normal and two processed yarns, which processed yarns have been treated in accordance with the method of the invention.

Figure 2 and Table 2 show the Spirality characteristics of further yarns treated in accordance with the invention compared to untreated yarns.

Figure 3 shows the Spirality characteristics of an untreated yarn compared to a set yarn and a treated yarn.

Figure 4 shows the Spirality characteristics of a further yarn compared to a normal yam, a set yarn and a treated yam.

Figure 5 shows the Spirality characteristics of a further yarn when treated in accordance with the invention compared to an untreated yarn.

Example 1

The yarn used was a quantity of cotton ring-spun single yarn which was unwaxed and Z-twisted. The yarn had a count of Nee 20 (30 Tex) and a twist amount of 734 tpm (=18.6 tpi) or twist factor (tpi/VNec) of 4.17.

This yarn was steam set in a steaming machine Sanderson under pressure of 10 psi in 105°C for a time of 20 minutes.

The "untwisting" process took place on a two-for-one Volkmann VTS-08 twisting frame. The least tension was used in the "yarn tensioning" accessory in the used spindle of the machine. The twist amount of 111 tpm in S-direction was inserted in the set yarn, leaving the yam with a Z direction twist and an actual measured net twist amount of approximately 620 tpm.

Following conventional processing the yarn was then knitted on a Wildt Model 5 circular, one feeder (single jersey) machine. The machine had a diameter of 9" and a number of 420 needles (gauge E14). This machine had a cam box revolving in the anti-clockwise direction (as looked at from above) and no arrangement for positive feed of the yarn to the knitting point had been done. After calculation, the loop length was found to be 4.83 mm.

The produced fabric was fully wetted by immersion in a basin full of warm water (40-45°C) and dried in normal atmospheric conditions (20°C, 65%)

The Spirality angle of this "processed 1" fabric, before and after the wetting process was measured. For comparison, a non processed yarn ("normal"), having the same original specifications as the "processed 1" yam, was also knitted and subjected to the same wetting and drying processes keeping exactly the same settings in all the processing stages. The obtained results are shown in Table 1.

Example 2

The above experiment was repeated except in that the amount of S direction twist in the "untwisting" stage was 163 tpm, resulting in a net twist of approximately 576 tpm (14.6 tpi). The Spirality angles of this "process 2" fabric are also shown in Table 1.

Bssulis

It can be seen from Table 1 that the Spirality of an untreated cotton ring- spun yam both before and after wetting is 23 degrees. In contrast, treating the yarn according to the first method and thus inserting twist in the order of 111 tpm in S direction reduced Spirality to 3 degrees before wetting and 3 degrees after wetting. Further, treating the yarn such that twist of a magnitude of 163 tpm in the S direction was inserted resulted in Spirality of -2 degrees before wetting and 1 degree after wetting. Clearly, by selectively controlling the amount of twist inserted into the yam one can control the degree of Spirality in the knitted fabric.

These results are illustrated graphically in Figure A.

Further experimental results are shown in Table 2, Figures 2, 3, 4 and 5.

Turning firstly to Table 2, it can be seen that row 1 shows the results of a normal yam both before and after wetting. The angle of Spirality being 31 degrees and 26 degrees respectively.

On row 2, it can be seen that steaming this yarn results in a reduction in Spirality from 31 degrees to 13.5 degrees before wetting, and from 26 degrees to 13.5 degrees after wetting. Further, it can be seen that the wetting process has no effect on the Spirality of a steamed yarn.

In contrast, towards the bottom of Table 2, it can be seen that yarns treated in accordance with the invention, having a variable degrees of untwist, as referenced by numbers 154, 163, and 175, have a significantly reduced angle of Spirality both before and after wetting, the Spirality before wetting being 2 degrees or less from the vertical fabric axis.

These results are illustrated in Figure 2 where it can be graphically seen that untwisting of the yarns in the method in accordance with the invention produces a significant reduction in the angle of Spirality.

In Figure 3 a comparison is made between a) a yarn which came directly from a spinning frame; b) the same yarn as a) after steaming (setting process); and c) the yam processed with the new method. As can be seen again, the new method produces significantly enhanced results both before and after wetting. The best results being achieved before wetting.

Using a different yarn, these results were repeated and are illustrated in Figure 4.

The difference in Spirality between normal and processed yarns is illustrated in Figure 5 where it can be seen that treating the yarns in accordance with the invention produces a significant decrease in the angle of spirality.

The working of the aforementioned method, when using a single yam that has been twisted in a first direction and set, involves the provision of at least a reverse twisting means which is adapted to twist said yarn in a second opposite direction with respect to said first direction. Further, said reverse twisting means incorporates a control means such that an operator can determine the degree of reverse twist to be inserted into the yam.

In the instance where a single yarn which has been twisted in a first direction but not yet set is to be used, then the apparatus is further provided with a setting means so that said twisted yarn can be set prior to transferring to said reverse twisting means.

In a further instance where a single yarn has neither been set or twisted, the apparatus includes a first twisting means for twisting said yam in a first direction; and suitable means for transferring said yam to a setting means where said yarn is set in said first direction; suitable means for transferring said set twisted yarn to a reverse twisting means where said yam is twisted in a second opposite direction with respect to said first direction.

The amount of reverse twist inserted into the yarn will be determined by the amount of twist provided in, and remaining in, the yarn by twisting in said first direction. Ideally, the amount of reverse twist or "untwisting" will equal the amount of first twist provided in, and remaining in said yarn, so as to provide a yarn which is balanced and thus not exhibiting Spirality when a knitted fabric is provided.

Claims

1. A method for treating a yarn so as to eliminate Spirality in a knitted fabric comprising; a) taking a single yarn which has been twisted in a first direction and thereafter set in said first direction; and b) twisting said set yarn in a second opposite direction with respect to said first direction.

2. A method according to Claim 1 wherein the stage; a) involves; i) taking a single yarn that has been twisted in a first direction; and ii) setting said twisted yarn in said first direction; and then b) twisting said set yarn in a second opposite direction with respect to said first direction.

3. A method according to Claim 1 wherein said stage; a) involves; i) taking a single yarn; ii) twisting said yarn in a first direction; iii) setting said twisted yarn; and then b) twisting said set yarn in a second opposite direction with respect to said first direction.

4. A method according to any preceding Claim wherein the amount of twist in said first direction, and remaining in said yarn, determines the amount of twist in said second direction so that twist in said second direction is equal to said twist in the yarn from the said first direction.

5. A method according to any preceding Claim which further includes an initial stage of extracting yarn from a spinning frame and then treating the yarn as described in Claims 1-4 above.

6. A method according to any preceding Claim which further includes a final stage of feeding said treated yarn to a knitting machine.

7. An apparatus for treating a yarn so as to eliminate Spirality in a knitted fabric comprising; a feed means for feeding a single yarn, that has been twisted in a first direction and set therein, to a reverse twisting means which twists said yarn in a second opposite direction with respect to said first direction.

8. An apparatus according to Claim 7 wherein the feed means is adapted to feed a single yarn that has been twisted in a first direction to a setting means which sets the twisted yarn and which further includes; a transfer means which transfers said twisted and set yarn to a reverse twisting means which twists said yarn in a second opposite direction with respect to said first direction.

9. An apparatus according to Claims 7 or 8 wherein the feeding means is adapted to feed a single yarn to a first twisting means which twists said yarn in a first direction and which further includes; a first transfer means which transfers said twisted yarn to a setting means which sets said twisted yarn; and a second transfer means which transfers said set twisted yarn to a reverse twisting means which twists said yarn in a second opposite direction with respect to said first direction.

10. An apparatus according to Claims 7-9 wherein there is further provided a control means which determines the amount of twist in the yarn from the first twisting process and adjusts the reverse twisting means so that the amount of twist conferred by twisting in said second opposite direction can be selectively controlled and adjusted until it approximately equals the amount of twist provided, and remaining in said yarn, by twisting in said first direction.

11. An apparatus according to Claim 9 wherein there is further provided an initial extraction means for extracting yarn from a spinning means.

12. An apparatus according to Claims 7-11 wherein there is further provided a means for transferring said treated yarn to a knitting machine.

13. An apparatus according to Claim 12 wherein there is further provided a knitting machine.

14. An apparatus for treating a yarn so as to eliminate Spirality in a knitted fabric comprising a means for feeding a single set yarn that has been twisted in a first direction to a twisting means where said yarn is twisted in a second opposite direction with respect to said first direction; a transfer means for transferring said oppositely twisted yarn to a knitting means; and a knitting means where said yarn is knitted into a fabric.

15. A yarn produced by a method in accordance with the invention.

16. A yarn produced by the apparatus in accordance with the invention.

17. A knitted fabric produced in accordance with the method of the invention.

18. A knitted fabric produced by the apparatus in accordance with the invention.

19. A knitted garment produced in accordance with the method of the invention.

20. A knitted garment produced by the apparatus in accordance with the invention.