WO1990008212A1

WO1990008212A1 - Yarn spinning

Info

Publication number: WO1990008212A1
Application number: PCT/GB1990/000086
Authority: WO
Inventors: James Lappage; Thomas Cassidy
Original assignee: Wool Research Organisation Of New Zealand Inc.; Scottish College Of Textiles
Priority date: 1989-01-20
Filing date: 1990-01-19
Publication date: 1990-07-26

Abstract

A method of transmitting real twist from a spindle area, through a nip of front drafting rollers, into a drafting zone, the method including the steps of: providing front drafting rollers, one of which is relieved around part of its circumference to provide an intermittent nip; dimensioning the relieved roller or rollers to control the amount of twist transmitted into the drafting zone; and drafting the yarn in the drafting zone. The invention also provides a means for drafting woollen slubbings, the means including a drafting zone between front drafting rollers and back drafting rollers, means for intermittently allowing a measured amount of real twist to run from a spindle area into the drafting zone, the arrangement being such that in use on a spinning machine the twist in the yarn within the drafting zone is intermittently topped-up to a preferred level.

Description

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The invention relates to yarn spinning and more^' particularly to the transmission of real twist from a spindle of a spinning system to a drafting zone to improve control of fibres during drafting. During the manufacture of spun textile yarns and the like the spinning process invariably includes a drafting stepr immediately prior to the insertion of twist into a yarn, to reduce the linear density of the feed material to that required in the finished yarn. In the yarn manufacturing system commonly known as woollen spinning the draft ^ratios used are usually of the order of 1.3:1, and rarely exceed 1.5:1. Significantly higher draft ratios than this may affect the quality of the yarn adversely since the draft is limited by the high degree of interfibre entanglement which is an important feature of woollen slubbings (or slivers). This interfibre entanglement, and its effects, are somewhat variable along the length of the slubbing (or feed material) and this tends to cause irregular drafting, resulting in undesirable thick places and thin places in the yarn.

In order to minimise the effects of irregular drafting it is necessary to take steps to control the individual fibres during the drafting process in such a way as to draft the slubbing as evenly as possible at every point along its length. A number of methods are available to control the fibres but in the woollen spinning process the most commonly used method is to insert twist into the slubbing in the drafting zone. Twist travels along the yarn, or that section of yarn between the drafting rollers, until the torque is the same at all points within the drafting zone. The rate of travel of the twist is in excess of 38 m/sec"*¹, which is at least an order of magnitude greater than the throughput speed of the yarn. In order to balance the torque at all points in the drafting zone the twist migrates preferentially and rapidly to the thinnest place or places in the yarn, leaving the thicker places with relatively little twist. The average level of twist in the drafting zone is chosen such that the amount of twist which migrates into the thinnest places in the yarn is sufficient to bind the fibres tightly together, prevents fibres slipping relative to one another at that point and thus inhibiting further drafting at the thin places. The amount of twist remaining in the thicker places is insufficient to prevent fibre slippage, so these thicker places are caused to draft preferentially. Depending upon the quality and properties of the slubbing, the drafting process can then have the effect of improving the overall evenness of the yarn.

The twist used to control the fibres in the drafting zone can be real twist or false twist, and whilst real twist is generally preferred, it is far more common to use false twist because of the problems involved in passing real twist into the drafting zone. Real twist is commonly used in the drafting zone of mule spinning machines, in which, by virtue of the design of both the machine and the process, it is simpler to use real twist than to use false twist, and this is one contributing factor to the generally superior quality of mule-spun yarns. Mule-spun yarns, however, are more expensive to produce than ring-spun yarns, so the latter are far more common in production.

In ring spinning, then, it is usual to use false twist in the drafting zone, and this twist is generated by a special mechanism included between a pair of front drafting rollers and a pair of back drafting rollers. The false- *»twist mechanism may be a false-twist spiral, a rotating tube or jaws or any rotating mechanism which grips the yarn is such a way that the yarn may be drawn through the mechanism by the front drafting rollers whilst the mechanism simultaneously inserts the desired level of twist upstream of the twisting point. All such mechanisms have attendant disadvantages including complexity in threading-up, the consumption of power etc., the inability to include false-twist right into the nip of the front drafting roller, and no facility to vary the average level of false twist to accommodate the longer term variations such as end-to-end variations in the slubbing.

It is also known to use real twist in the drafting zone of ring spinning machines with-^the aid of specially designed front drafting rollers which are individual to each spindle point and which are designed to rotate about their own axis in order to draft and deliver yarn to the spindle. but also to. rotate about the yarn axis such that real twist is transmitted from the balloon zone into the drafting zone. Such mechanisms, however, are generally expensive to manuf cture, complex to thread-up and absorb a considerable amount of power_? they also do not include facility to vary the average twist level in the drafting zone according to the requirements of the individual ends of yarn.

An object of the present invention is to provide means of transmitting real twist from a spindle area into a drafting zone of a spinning apparatus to provide fibre control between front and back drafting rollers during a drafting step.

Further objects and advantages of the invention are to ameliorate the above identified disadvantages and to simplify the threading-up operation of woollen ringframes; to reduce machine construction costs and operating costs; to provide means of varying the average twist level in the drafting zone according to the needs of individual ends of yarn; and to produce woollen spun yarns of generally improved properties.

According to a first aspect of the invention there is- provided a method of transmitting real twist from a spindle area, through a nip of front drafting rollers, into a drafting zone, the method including the steps of: providing front drafting rollers, one of which is relieved around part of its circumference to provide an intermittent nip; dimensioning the relieved roller or rollers to control the amount of twist transmitted into the drafting zone; and drafting the yarn in the drafting zone.

According to a second aspect of the invention there is provided a means for drafting woollen slubbings, the means including a drafting zone between front drafting rollers and back drafting rollers, means for intermittently allowing a measured amount of real twist to run from a spindle area into the drafting zone, the arrangement being such that in use on a spinning machine the twist in the yarn within the drafting zone is intermittently topped-up to a preferred level. Further aspects of the invention which should be considered in all its novel aspects will become apparent from the following description which is given by way of example only.

An example of the invention will now be described with reference to the accompanying drawings in which:

Figure 1: depicts in cross-section a woollen drafting system according to the present invention and having a pair of front drafting rollers operating with an intermittent nip.

Figure 2: depicts in perspective a modified front drafting roller with part of its circumference relieved between shoulders formed by unrelieved parts of the roller; and

Figure 3: depicts in cross-section a woollen drafting system according to the present invention having two pairs of front drafting rollers. One roller of each pair being relieved around part of its circumference.

Referring firstly to Figure 1, woollen slubbing 1 is drafted between back drafting rollers 2 and front drafting rollers 3, from whence it passes as spun yarn 7 via a lappet guide 4 and a ring and traveller mechanisms 5 to be wound onto a rotating spindle 6. By virtue of rotation of spindle 6 twist is inserted into the yarn at 7 and this twist normally propagates upstream, against the flow of yarn, as far as_^ the nip^' of the front drafting rollers 3.

One of the front drafting rollers 3 is relieved around part of its circumference and near the middle of the roller space such that the slubbing 8 will be intermittently nipped by rollers 3 to effect an intermittent draft, and will also be intermittently released to allow twist to migrate from the spun yarn 7 into the drafting zone 8.

Preferably the nip of the back drafting rollers 2 , the nip of the front drafting rollers 3 and the lappet guide 4 should be in-line to allow unimpeded propagation of twist from the spun yarn phase 7 into the drafting slubbing phase - 8 when the nip between rollers 3 opens. The amount of twist propagating into the drafting zone 5 depends upon the twist in the spun yarn 7 and the time for-which the nip between rollers 3 is open. When the nip between rollers 3 is closed, twist will propagate with the yarn from the drafting zone 8 back into the spun yarn phase 7. The average level of twist in zone 8 is chosen for optimum drafting according to the dimensions of drafting and the spinning system and the properties of the slubbing and its constituent fibres, and can be controlled by the twist level in the spun yarn 7 ) the distance between the front drafting rollers 3 and the pigtail 4, and the extent to which one of the rollers 3 is relieved.

Referring now to Figure 2 is shown a front drafting roller 3 (top or bottom roller) which includes a relief 9 around part of its circumference and across the middle part of its_^ width at which the yarn is normally nipped, leaving shoulders on either side of the relief 9 to support the open nip and ensure the smooth running of the cooperating rollers. The relief 9 is wide enough to accommodate the usual cross-traverse imposed upon the drafting slubbing 8 for the purpose of spreading roller wear, and deep enough to accommodate the thickness of the yarn spun so that twist may propagate through the open nip unimpeded.

Referring now to Figure 3 which shows in cross-section - _a preferred practical optional embodiment of the invention and which includes a second pair of front drafting rollers 10, one of which is also relieved around part of its circumference. In this embodiment of the invention the relieved rollers 9 of roller pairs 3 and 10 preferably cooperate and are mechanically linked to ensure a fixed phase relationship is retained between them. The relieved rollers are thus preferably the bottom or driven rollers of each pair which are both relieved around less than half the circumference, and are driven at equal rotational speeds with the relieved portions operating precisely 180° out-of-phase. In operation then as the nip between rollers 10 opens the nip between 3 closes, and twist propagates from the yarn 7 in the spindle area into the partially drafted slubbing in zone 11 between the nips of rollers pairs 3 and 10. When the nip between rollers 10 closes the nip between rollers 3 opens, allowing the twist in zone 11 to propagate onward into zone 8. Thus the average level of twist in the drafting zone can be precisely controlled by choosing the distance in zone 11 between the nips of rollers 3 and

*% rollers 10.

A further advantage of this preferred embodiment of the invention is that by including two pairs of front drafting rollers the drafting action becomes continuous for when the nip between rollers 10 is open, that between rollers 3 is closed and drafting takes places between rollers 2 and rollers 3; similarly when the nip 10 is closed, and drafting then takes place between rollers 2 and rollers 10. A further advantage of the present invention arises from the way in which real twist is propagated into the drafting zone and how that twist is controlled, in part, by the linear density of each individual end of slubbings. Thus in the case of a lighter-than average area in an end of slubbing a higher level of twist will be accepted into the drafting zone, tending to inhibit further drafting of that area. A heavier-than-average area in the_slubbing will accept a lower level of twist and this promotes easier drafting of such thick areas. Similarly constantly thin ends of slubbing can be expected to accept a higher average level of twist into the drafting zone resulting in some reduction in the actual average draft, whilst constantly thick ends of slubbing are able to accept less twist into the drafting zone and can be expected to draft more readily with a higher actual draft.

By this invention is provided a method and apparatus by which real twist can be propagated from the spindle area into the slubbing in the drafting zone of a woollen drafting system* for the purpose of controlling the fibres during the drafting process.

Particular examples have been described for effecting the purpose of this invention which is to continuously transfer real twist from the spindle area into the drafting zone of a woollen drafting system, and it is understood that there can be variations in the methods used without departing from the spirit and scope of the invention. For example it is possible and practical to affect an intermittent nip, thereby allowing the propagation of twist upstream into the drafting zone, by using a standard, unrelieved roller nip but intermittently guiding the yarn into and out of that nip.

Claims

1. A method of transmitting real twist from a spindle area, through a nip of front drafting rollers, into a drafting zone, the method including the steps of: providing front drafting rollers(3), one of which is relieved around part of its circumference to provide an intermittent nip; dimensioning the relieved roller or rollers to control the amount of twist transmitted into the drafting zone; and drafting the yarn in the drafting zone.

2. A method as claimed in claim 1 wherein the draf ing zone has two pairs of front drafting rollers(3) (10), one roller of each pair being relieved around part of its circumference.

3. A method as claimed in claim 1 or claim 2 wherein the roller or rollers are relieved near the middle of the roller space.

4. A method as claimed in any one of the preceding claims wherein a woolen slubbing is drafted between back drafting rollers(2) and front drafting rollers(3) before it passes via a lappet guide(4) and ring and traveller mechanism(5) to a rotating spindle(β), the nip of the back drafting rollers(2), the nip of the front drafting rollers(3) and the lappet guide(4) are in-line to allow unimpeded propagation of twist from the spun yarn phase into the drafting slubbing phase when the nip between roller opens.

5. A means for drafting woollen slubbings, the means including a drafting zone between front drafting rollers(3) and back dra ing rollers(2) , means for intermittently allowing a measured amount of real twist to run from a spindle area into the drafting zone, the arrangement being such that in use on a spinning machine the twist in the yarn within the drafting zone is intermittently topped-up to a preferred level.

6. A means as claimed in claim 5 wherein the drafting zone has two pairs of front drafting rollers(3) (10) , one roller of each pair being relieved around part of its circumference.

7. A means as claimed in claim 5 wherein the propagation of twist upstream of the drafting zone is created by an unrelieved roller nip by intermittently guiding the yarn into and out of the nip.

8. A means as claimed in claim 6 wherein the roller or rollers are relieved near the middle of the roller space.

9. A means as claimed in claims 5,6 or 7 wherein woolen slubbing is drafted between back drafting rollers(2) and front drafting rollers(3) before it passes via a lappet guide(4) and ring and traveller mechanism(5) to a rotating spindle, the nip of the back drafting rollers(2), the nip of the front drafting rollers(3) and the lappet guide(4) are in-line to allow unimpeded propagation of twist from the spun yarn phase into the drafting slubbing phase when the nip between