GB2208877A

GB2208877A - Drafting apparatus and method

Info

Publication number: GB2208877A
Application number: GB8818868A
Authority: GB
Inventors: James William Eke
Original assignee: Hollingsworth UK Ltd
Current assignee: Hollingsworth UK Ltd
Priority date: 1988-08-09
Filing date: 1988-08-09
Publication date: 1989-04-19
Also published as: GB8818868D0

Abstract

A drafting system uses a spring steel plate (20) tangential to first and second drafting rollers (21 and 22) of which the second drafting roller (22) has a higher peripheral speed than the first drafting roller (21) so that the sliver (23) is subjected both to drafting elongation and to slip between the advancing surface of the roller (21 or 22) and the blade (20) at each nip. One or both of the drafting rollers may be replaced by a drafting apron, and if desired the second nip may be defined by a pair of rollers or aprons or a roller and an apron. <IMAGE>

Description

DRAFTING APPARATUS AND METHOD The present invention relates to an apparatus for drafting staple fibre stock and to a method of drafting such material.

During the preparation of a staple fibre material for spinning, a sliver of the staple fibres is traditionally drafted, i.e. extended by slippage of the fibres over one another, in order to orientate the fibres in the sliver more nearly parallel to one another and to achieve a regularity of the matrix of fibres which is much improved with respect to the regularity encountered in the incoming bale of fibres, and in order to endeavour to reduce the number of hooked ends of the fibres in the sliver. Such drafting is frequently carried out together with a doubling of the material so that a plurality of incoming slivers can be combined together and immediately subjected to a drafting operation which imparts to the blended mass a cross-sectional dimension substantially equivalent to that of each of the incoming slivers.It will thus be seen that the drafting operation also allows for a certain measure of blending of slivers of different types of staple fibre material.

The normal method of drafting a sliver involves passing the sliver through at least two spaced nips (the spacing between them being greater than the length of the staple fibres in the sliver to be drafted) such that the speed of entrainment of the sliver at the first nip encountered by the sliver is lower than that at the next nip, and the same speed relationship applies to each or any subsequent pair of nips.

It is an object of the present invention to provide an alternative method and apparatus of drafting in which the fibre parallelisation, hook elimination, and sliver regularity are improved with respect to a conventional roller or apron drafting system.

Accordingly, the present invention provides a drafting system comprising at least first and second drafting nips, at least the first drafting nip being defined by a circulating drafting member and a stationary cooperating plate yieldably biased thereagainst.

A further aspect of the present invention provides a method of drafting a sliver comprising subjecting the sliver to elongation by passing it from a first drafting nip to a second drafting nip with a higher sliver-forwarding velocity, and simultaneously subjecting the sliver to slip at the first and second drafting nips, the slip at the first drafting nip being effected between a circulating drafting member and a cooperating stationary drafting plate dragging on the sliver.

In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings in which: FIGURE 1 is an elevational view of a drafting system in accordance with the present invention, with the cover removed; FIGURE 2 is a schematic view of an alternative embodiment of drafting system in accordance with the present invention; and FIGURE 3 is a view, similar to Figure 2, but showing yet a further embodiment in accordance with the invention.

The drafting system shown in Figure 1 comprises first and second rollers 1 and 2, of which roller 1 is an idler roller and roller 2 is provided with a high friction jacket 3 and is mounted on a driven shaft 4 for rotation in the clockwise direction.

The housing 5, defining a cylindrical recess for the driven roller 2 and having an open corner within which the idler roller 1 is mounted, also supports a mounting bracket 6 which is fastened to the housing by screws 7 and carries a spring steel plate 8 as well as a sliver guide member 9 intended to guide sliver into the nip between the spring steel plate 8 and the cylindrical surface of the idler roller 1.

Sliver from the nip between the plate 8 and roller 1 then passes leftwardly along an arc of the surface of the roller 1 subtending an angle 9 at its centre, to arrive at the nip 10 between the idler roller 1 and the driven roller 2. The drafted sliver then follows the surface of the driven roller 2 and eventually departs out through a discharge opening 11.

In operation of the drafting system shown in Figure 1, the presence of sliver at the nip 10 may allow some slippage in the driving of the idler roller 1 by the driven roller 2, despite the high friction surface coating of the jacket 3 of the roller 2, but will nevertheless effect frictional driving of the idler roller 1 in the anticlockwise direction generating further shear or slip at the nip between the plate 8 and the roller 1 which define the first nip of the drafting system involving the blade 8 and both of the rollers 1 and 2.

The slip occurring at the nip 10 will result in further shear in the sliver so that while the sliver is being drafted in the arc 9 of the surface of the idler roller 1 its fibres are also being realigned due to fibre-to-fibre slip occurring at both the first nip (between the plate 8 and the roller 1), and the second nip 10 (between the roller 1 and the roller 2).

It will of course be important to ensure that the arc length of the sector e of the idler roller 1 is at least as great as the staple fibre length of the sliver being drafted. For this purpose the angle 9 may be adjustable as will be described later.

We have found that with this double slip action at the two drafting nips the sliver leaving the discharge opening 11 has greatly improved fibre parallelisation, hook elimination, and sliver uniformity, as compared with the product of a conventional drafting system.

If desired, still further drafting nips may be incorporated in the drafting apparatus, while maintaining the relationship of increasing fibre entrainment speed from each nip to the following nip, and maintaining sliver slip at-each nip.

In order to adapt the device of Figure 1 for different staple lengths, the bracket 6 may be replaced by an alternative bracket having the mounting for the sliver guide member and the spring steel blade 8 displaced in the clockwise direction about the centre of the idler roller 1, thereby allowing the point of tangency between the blade 8 and the roller 1 to be moved in the clockwise direction and hence increasing the angle e subtended at the centre of the roller 1, to correspond to the new staple length.

Alternatively, the value of the angle e may be so great as to be at least equal to the longest staple length to be encountered by the drafting system, with the result that any staple length of sliver can be tolerated on the same drafting system.

The new drafting action is notable in that a relatively small biasing force is sufficient to press the planar blade of Figure 1 against the drafting roller 1 sufficiently firmly to effect the fibre straightening during the drafting action.

The fact that the blade 8 is planar is considered particularly advantageous in that it ensures that the sliver being condensed between the blade 8 and the roller 1, in anticlockwise rotation of the roller 1, it progressively undergoes slip (i.e. fibre-to-fibre shear) before arriving at the nip line, and then at the nip line the sliver gripping action gradually releases. Had the plate 8 been convex the sliver slip would occur much more abruptly, and had it been concave the spreading of the contact between the blade 8 and the roller 1 would require a much greater contact force in order to generate the desired sliver drag to achieve slip.

An alternative embodiment is shown schematically in Figure 2 as comprising a pair of nips both formed by a spring steel plate 20 on one side and a respective driven roller 21 for the upstream nip and 22 for the downstream nip. The clockwise driving of the two rollers 21 and 22 is such that roller 22 has a higher surface speed than that of roller 21, and in this particular case as their diameters are substantially identical this difference is achieved by virtue of difference in angular velocity of the two rollers. As a result of the pressing action of the spring steel plate 20 tangentially against the two rollers 21 and 22 there is sliver slip at both of the drafting nips simultaneously with the drafting action between the two nips.

In this particular embodiment the sliver 23 is guided towards the first drafting nip by a sliver guide chute 24. The discharging fibre from the second drafting nip is immediately introduced into a fibre feed duct 25 of an open end spinning system, for example a friction spinning unit or a rotor spinning unit.

A third embodiment of drafting system in accordance with the present invention is illustrated in Figure 3 where the reference numerals of Figure 2 have been maintained but increased by ten. Thus in this case the sliver 33 passes by way of the guide chute 34 to the first nip between the spring steel plate 30 and roller 31 from whence it is guided onwardly to the second nip between the roller 32 and a further driven roller 36 which together discharge the sliver directly into the fibre feed duct 35 of an open end spinning unit.

Although in the description of Figure 2 and Figure 3 herein we refer to a sliver being advanced from the second nip, it will be appreciated that the fibres entering the fibre feed duct 25 or 35 are separated one from another so that a continuous stream of airborne fibres may be apparent in the fibre feed duct after delivery from the downstream drafting nip.

The drafting system in accordance with the present invention has been found to give particularly good fibre straightening action and presents the fibres in the form of a highly uniform flow of straight parallel fibres to be entrained along the fibre feed duct (25 or 35) towards the open end of the yarn in an open end spinning unit.

The existence of sliver slip at the downstream nip between the rolls 32 and 36 in Figure 3 is ensured by virtue of the fact that the surface speed of the roller 36 is different from that of the roller 32. Its surface speed may be greater than that of roller 32 or it may be less than the speed of the roller 32, as desired. Preferably the surface speed of the roller 32 is higher than that of the roller 36 so that the fibre shear or sliver slip is the same as that encountered at the first nip, i.e. that the right hand side of the sliver 33 is accelerated while the left hand side is retarded (by the spring steel plate 30 at the first nip and by the cooperating roller 36 of the second nip).

Although in the embodiments described thus far we have referred to the drafting plate as a spring steel blade, it will of course be appreciated that the plate can be of any other construction, preferably planar, and can be biased against the surface of the cooperating roller by any suitable yieldable biasing means.

Claims

C L A 1 M S

1. A drafting system comprising at least first and second drafting nips, at least the first drafting nip being defined by a circulating drafting member and a stationary cooperating plate yieldably biased thereagainst.

2. A drafting system according to claim 1, wherein the second drafting nip is also defined by a circulating drafting member and a stationary cooperating plate.

3. A drafting system according to claim 2, wherein a single drafting plate is effective at both the first and second nips.

4. A drafting system according to claim 3 wherein the sliver path between the first and second nips is defined by said common drafting plate.

5. A drafting system according to claim 1, wherein the path of the sliver being drafted between the first nip and the second nip is defined by the drafting roller of the first nip.

6. A drafting system according to any one of the preceding claims, wherein said drafting plate is a planar member yieldably biased against the surface of the drafting member with which it cooperates.

7. a drafting system according to any one of the preceding claims, wherein the or at least one said circulating drafting member is a drafting apron.

8. A drafting system according to any one of the preceding claims, wherein the or at least one said circulating drafting member is a drafting roller.

9. A drafting system according to claim 8, when appendant to any of claims 1 to 6, wherein the circulating drafting member at the first nip is common to the second nip and is an idler roller driven by frictional contract with the sliver at said second nip where the sliver is driven by a cooperating said drafting roller.

10. A drafting system according to any one of the preceding claims, wherein said drafting plate is a spring steel blade.

11. A drafting system according to any one of the preceding claims including means for adjusting the sliver path length between said first and second nips.

12. A drafting system substantially as hereinbefore described with reference to, and as illustrated in, Figure 1, or Figure 2, or Figure 3 of the accompanying drawings.

13. A method of drafting a: sliver comprising subjecting the sliver to elongation by passing it from a first drafting nip to a second drafting nip with a higher sliver-forwarding velocity, and simultaneously subjecting the sliver to slip at the first and second drafting nips, the slip at the first drafting nip being effected between a circulating drafting member and a cooperating stationary drafting plate dragging on the sliver.

14. A method according to claim 11, wherein the second drafting nip is defined by a first further circulating drafting member moving with a peripheral speed higher than that of the circulating drafting member at the first nip, and by a second further circulating drafting member having a speed different from that of said first further circulating drafting member, thereby subjecting the sliver to slip between the circulating drafting member and the stationary drafting plate at the first nip and again to slip between the first and second further circulating drafting members at the second nip.

15. A method of drafting substantially as hereinbefore described with reference to the accompanying drawings.