GB2031038A - Fibre Drafting Apparatus and Method - Google Patents

Abstract

A method of drafting fibres which comprises drawing out fibres from a sliver by means of a succession of discrete bites which draw the fibres from a feed position to a release position, the nips being timed to ensure continuity of the fibres so drafted, and causing or allowing the tension of the fibres to drop to substantially zero immediately prior to each successive nipping action. In apparatus for use in the method, a fibrous sliver is supplied by feed rollers 10, 12 to a porcupine roller 16 from which the fibres are intermittently drafted by reciprocating jaws 20 carried on a rocking arm 22. Retaining rollers 92 and 94 take up the slack in the drafted sliver released by the jaws 20 at such a rate that the slack is just taken up when the jaws return to the proximity of the roller 16 for a further bite. <IMAGE>

Description

SPECIFICATION Fibre Drafting Apparatus and Method This invention relates to a method of fibre drafting and to apparatus for use therein.

The purpose of fibre drafting is to reduce the thickness of the fibre sliver from that at which it is presented to the drafting apparatus, the ultimate purpose being to produce yarn of the required thickness. In worsted drawing, for example, the sliver is first drawn from the top, and from the top to the yarn a total draft in the order of 1000 may be required. With the conventional roller drafting arrangements, total drafts of this order could only be achieved by repeated passes of the sliver, although by using relatively modern apparatus such as the Autoleveller Drawbox or Superdraft, giving drafts of up to 120 between front and back rollers, the number of passes could be as low as 3,4,or5.

It is the principal object of the present invention to provide a method of drafting fibres which enables very large drafts to be obtained at a single pass, whereby yarn can be produced directly from undrafted top or gilled comb sliver in a very even manner. The expression "undrafted top" refers to a thick sliver in which the fibres may have been subjected to combing, carding, gilling or like fibre preparation treatments (which may of themseives, involve an element of attenuation) but which have not been subjected to the action of "pure" drafting arrangements such as drafting roller, aprons, or pressure drafters. Generally the fibre preparation treatments involve drafts of no more that about 12 whereas the "pure" drafting arrangements involve drafts in excess of 30.It may be said therefore than an "undrafted top" is a sliver of fibres which has not at any one stage been subjected toa draft in excess of 12. Thus it can be said that the invention in its broadest aspect provides mechanically the drafting effect of hand spinning. It is a further object of the invention to provide apparatus for carrying out the method.

According to the present invention there is provided a method of drafting fibres which comprises drawing out fibres from a sliver by means of a succession of discrete bites which draw the fibres from a feed position to a release position, the nips being timed to ensure continuity of the fibres so-drafted, and causing or allowing the tension of the fibres to substantially zero immediately prior to each successive nipping action.

The invention also provides a drafting device comprising a fibre feeding means adapted to present a sliver at a feed position, a drafting mechanism comprising a nip for gripping the sliver at the feed position, a mechanism for causing the drafting mechanism to travel away from the feed position to a release position whilst maintaining the gripping action, and for releasing the gripping action and returning the drafting mechanism to the feed position without gripping the sliver, and a retaining mechanism adapted to grip the sliver at a position beyond the release position in the direction of travel of the sliver and so constructed that the tension on the sliver between the retaining mechanism and the feed position is substantially zero immediately before the drafting mechanism grips the sliver at the feed position.

One way in which this can be achieved is for the retaining mechanism to comprise a pair of nip rollers which grip the attenuated fibres of the drafted sliver. The peripheral speed of the nip rollers in relation to the drafting mechanism is adjusted so that as the drafting mechanism moves towards the nip rollers a reservoir of sliver is built up which is just used up during the time taken for the drafting mechanism to return to the feed position to grip a fresh portion of the sliver.

Thus at the point when the drafting mechanism grips the sliver each time, the tension on the sliver is effectively zero.

Preferably the silver is presented at the feed position in a compact form by feeding it, for example, through a constraining apparatus. Such a constraining apparatus may be arranged so that the forward flow of fibres from the sliver into the through the feed position during the travel of the drafting mechanism is restricted. For instance, the sliver may be constricted in width as it approaches the feed position.

It may also be desirable to vary the length of stroke of the nip, and/or its speed of travel in relation to the quantity of fibres gripped by the nip at the feed position, as measured by a fibre quantity detector. Thus, for example, the nip could be caused to increase its stroke for increasing quantities of fibres gripped and vice versa. The quantity of fibres may be measured by mechanically, optically or electrically responsive detection apparatus.

It has been found desirable however to limit the length of the travel of the nip in the fibredrawing direction to a distance less than the length of the longest fibres present in the sliver. In this connection it will be understood, by those skilled in the art, that any particular sliver will have a range of fibre lengths and that the bulk of the fibres in the sliver will be within this range.

There may be occasional fibres longer than the upper limit of this range, but for the purpose of deciding on the length of the longest fibres present in the sliver such occasional and exceptional fibres should be ignored.

The fibre feeding means may be adapted to feed fibres either continuously or intermittently to the feed position, and in a simple form of the invention, the fibre feeding means may incorporate a pair of rollers which operate in similar fashion to the back rollers of a conventional roller drafting apparatus. However, since the apparatus is intended to operate at very high drafts, the pair of back rollers will rotate at a very slow speed.

The fibre feeding means preferably also includes a sliver restraining apparatus, which may for example take the form of an open-topped trough through which the sliver is fed the feed position whereby the width of the sliver is constrained. The sliver restraining apparatus preferably includes a toothed member having its teeth passing through substantially the entire thickness of the sliver so that all parts of the cross-section of the sliver are subjected to the restraining action. This toothed member may be a porcupine roller set with its teeth projecting into the trough.

In the preferred arrangement, the drafting mechanism is adapted to travel in a substantially rectilinear path and this may pe provided by carrying the drafting mechanism on an oscillating arm so that the drafting mechanism travels in an arc which approximates to a straight line.

Preferably the mechanism for producing movement of the drafting mechanism is camoperated.

Also in the preferred arrangement, the drafting mechanism includes a pair of jaws for actually gripping the fibres of the sliver. The driving mechanism for the drafting mechanism may be arranged to produce a reciprocation of the jaws, and to hold the jaws closed in their forward travel (i.e. away from the feed position) but open in their return travel. The jaw operating machanism is preferably also cam operated. The preferred construction may be realised by a driving mechanism for producing substantially rectilinear reciprocation of one jaw, and a rectangular motion of the other jaw, one side of the rectangle representing movement of the second jaw in contact with the first jaw as the latter moves forwardly.

In an alternative construction, the drafting mechanism comprises two rotary elements one or both of which has radial projections adapted to meet part of the other element to produce the nip.

Thus the mechanism may consist of two continuously driven rollers, rotating about parallel axes, one of the rollers having one or more projections resiliently loaded radially outwards, so that each time the projection is passing through the gap between the two rollers, it is pressed on to the surface of the other roller. Alternatively the drafting mechanism may comprise a pair of endless belts or chains carrying jaws and having parallel runs where the jaws of the two belts or chains meet each other to provide the forwardly travelling nip.

In the preferred arrangement, the drafting mechanism comprises a pair of jaws disposed on opposite sides of the path of the sliver through the apparatus, each jaw being carried by a camoperated mechanism, which is adapted to be driven continuously to produce the following movements:- (1) The lower jaw slides in a rectilinear path parallel with the path of the sliver and simply reciprocates in this path.

(2) The upper jaw travels in a rectangular path, of which the horizontal runs are parallel with the traverse of the lower jaw, and the disposition of the path is such that when the upper jaw is travelling along its lower horizontal run, it engages with the lower jaw and travels with that jaw towards the front of the apparatus, one of the jaws being spring loaded towards the other, so that the fibres being drafted can be nipped between them when they are moving forwardly.

The invention will be described further by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial diagrammatic side view of an apparatus constructed according to the invention; Figure 2 is a detail view of back roller tensioning system; Figure 3 is a detail view of the jaw rotating mechanism; Figure 4 is a detail of the jaw operating mechanism; Figure 5 is a front view of a rocking arm assembly looking in the direction of arrow V in Figure 1; Figure 6 is a plan view, partly in section, of the jaw operating and rocking mechanisms; Figure 7 is a perspective view on an enlarged scale of the nip rollers of the apparatus; and Figure 8 is a plan view of the apparatus of Figure 1.

Referring to the drawings, untwisted sliver or top is fed to a pair of nip rollers 10, 12. The roller 10 is a driven roller and is formed with a peripheral groove within which the sliver is guided. The top roller 12 is received within the peripheral groove and rests on the sliver passing therethrough. A load is applied to the top roller 12 in any convenient manner to compact and restrain the sliver.

From the rollers 10, 12 the sliver passes through a channel 14 to a porcupine roller 1 6 the teeth of which engage the sliver. The roller 1 6 is driven at a slightly greater peripheral speed than the rollers 10, 12 thus putting the sliver under slight tension. From the roller 1 6 the fibres of the sliver project from the end of the channel 14 forming a "beard".

A drafting mechanism 1 8 comprises controllable jaws 20 on a rocking arm 22. The mechanism is driven so as to rock from the position shown in full in Figure 1 to the position shown in dotted lines and back again. During the cycle the jaws 20 are operated to close on the beard when the mechanism is adjacent to the channel 14 and remain closed during the traverse to the left (as viewed in Figure 1), opening at the left hand extremity of the rocking motion and remaining open for the remainder of the cycle.

The mechanism for effecting drafting of the sliver is illustrated in Figures 3 to 6, and in general it comprises the pair of jaws 20 which are adapted to move towards and away from each other for the purpose of closing to nip the sliver, or opening to release the sliver, the jaws being also mounted for forward and backward reciprocatory motion as will be hereinafter described.

The jaws 20 are carried by the rocking arm assembly 18, which includes a bolster 24, having aligned stub shafts 26 (see Figure 5) journalled in bearings in the machine frame (not shown) whereby, the rocking arm 1 8 is permitted to oscillate about the common axis of the stub shafts 26.

A cam shaft 28 extends transversely of the machine, and is driven from the machine driving mechanism (not shown). An oscillating cam 30 is fixed on the cam shaft 28, and engages with a follower 32 on a short lever 34, pivoted about a spindle 36 fixed to the machine frame. The short lever 34 has an abutment 38 on which there rests a screw abutment 40, carried by a bracket 42, which projects from and is secured to the bolster 24. It will be observed that the screw abutment 40 is located by a pair of lock-nuts, one on each side of the bracket 42, so that it is possible to ajdust the relative positions between the rocking arm 18 and the short lever 34. The bracket 42 is connected to one end of a tension spring 44, the other end of which is anchored to a part of the machine frame, so that the screw abutment 40 is pulied into engagement with the abutment on the short lever.

When the cam shaft 28 is rotated, the cam 30 raises the lever 34, thus lifting the bracket 42 against the action of the tension spring 44, and causing the rocking arm 1 8 to turn about its pivotal axis, to carry the jaws 20 in a forward direction. The position illustrated in Figure 1 is the rear-most position, wherein the jaws 20 are in close juxtaposition to the front end of the channel 14. This is the feed position at which fibres emerge from the fornt of the channel 14, and are able to be gripped between the jaws 20.

The combined action of the cam 30 and the tension spring 44 produces an oscillation of the rocking arm assembly 18, and hence causes the jaws 20 to oscillate in a forward and rearward direction. It is possible to adjust the magnitude of this oscillation, by adjusting the position of the abutment screw 40 in the bracket 42, a slot 46 (see Figure 6) being provided in the bracket 42 for this purpose. In practice, the angle through which the jaws 20 move is relatively small, and in a specific example it is about 8 . It will also be appreciated, that although this movement of the jaws 20 is strictly an arcuate movement about the axis of ths stub shafts 26, in practice, because of the relatively large radius at which the nip of the jaws is situated, this forward and reverse movement of the jaws approximates to a rectilinear motion.

In addition to the forward and reverse motion of the jaws 20, provision is made for closing and opening these laws. Referring now particularly to Figure 5, a column 48 is fixed to the bolster 24, and at its upper end, it carries the lower jaw 20, which hence is fixed relatively to the bolster 24. A pair of slide bearings 50 is provided on the top of the bolster 24, and a slide rod 52 passes through each of these bearings 50. At their upper ends, the slide rods 52 carry a moveable bolster 54, having a slide bearing 56 at its centre, which slides on a reduced diameter portion of the column 48. Hence, the slide rods 52 with their moveable bolster 54, are guided for vertical reciprocation relatively to the bolster 24 and the column 48.

The bolster 54 itself carries a pair of upstanding rods 58, having reduced diameter portions at their upper ends, the upper extremities of these rods 58, being secured by screwing into a presser head 60. Consequently, the presser head 60 is fixed relatively to the moveable bolster 54. The top jaw 20 is carried by a plate 62, which is a loose sliding fit on the reduced diameter upper portions of the rods 58, and a centrally situated ball bearing 64, is positioned between the underside of the presser member 60, and the top side of the jaw plate 62.

The lower ends of the slide rods 52 project below the top part of the bolster 24, and are connected to a lifter plate 63. Tension springs 65 are attached to the lifter plate 63, the other ends of the tension springs being anchored to part of the machine frame, so that these springs tend to pull the lifter plate and its slide rods 52 downwardly. This in turn causes the pressure member 60 to press on the jaw plate 62 via the ball bearing 64, thus forcing the upper jaw down into nipping contact with the lower jaw.

In this lowest position of the top jaw, the jaw plate 62 is still clear of the shoulder between the lower part and the upper part of each rod 58. By virtue of the ball bearing 64, and the losse fit of the jaw plate 62 on the reduced diameter portions of the rods 58, it is possible for the lower jaw to rock slightly relatively to the upper jaw, so as to accommodate any irregularity in the thickness of a sliver trapped between the two jaws across the width of the sliver. Alternatively, with the proper selection of jaw surfacing material the upper jaw may be fixed in a horizontal position dispersing with the ball bearing arrangement.

A jaw operating cam 66 is fixed on the camshaft 28, and this cam 66 engages with a follower 68 on a lever 70, which is also pivoted about the spindle 36. This is illustrated in Figures 4 and 6.

The lever 70 carries an arm 72, and a lifting roller 78 is mounted at the free end of the arm 72. As shown in Figures 3 and 5 the roller 78 is capable of engagement with the underside of the lifter plate. The effective length of the lever 70 and its arm 72 (i.e. the distance between the axis of the spindle 36 and position at which the roller 78 engages with the lifter plate 64) can be varied by adjusting the position of the arm 72 relatively to the lever 70. This is permitted by screws 80 and 82, which pass through slots (not shown) in the lever 70. Hence, it is possible to vary the effective lifting stroke of the lifter roller 78.

When the cam shaft 28 rotates, the cam 66 causes the arm 70 to oscillate, and this in turn causes the lifter roller 78 to press the lifter plate 63 upwardly against the action of the spring 65, and then allows the lifter plate to descend under the action of the springs 65. When the lifter plate 63 is lifted, the pressure member 60 is immediately lifted, thus relieving the pressure applied to the upper jaw, but there is a short lost motion of the lifter plate 63, before the shoulders on the rods 52 engage with the underside of the jaw plate 62, and lift that plate together with the top jaw away from the bottom jaw. Hence, when the cam 66 lifts the lever 70, the jaws 20 are opened, and when the cam 66 allows the lever 70 to lower, the jaws 20 are closed.

It will be appreciated that since the cams 50 and 66 are mounted on a common cam shaft, the motions of oscillating the jaws 20 and closing and opening those jaws are synchronized. The setting of the cams on the cam-shaft is such, that during the forward movement of the jaws 20 away from the feed position illustrated in Figure 1, the jaws are closed, to nip the sliver, but as soon as the jaws arrive at the forward end of their traverse, they are allowd to open, and remain in the opened condition, until they arrive again at the feed position.

The jaws therefore apply a series of mechanical pulses to the sliver as it is travelling through the apparatus. The driving mechanism is preferably so arranged that the speed of travel of the nip or pulses in the forward direction is in excess of forty feet per minute.

It will be observed that a brush 84 is fixed to the top jaw, or to the pressure member 60, and this brush engages with the teeth of the porcupine roller each time the jaws arrive at the feed position. Hence the brush 84 is used to clean the teeth of the porcupine roller, as they are moving away from the sliver within the channel 14.

As can be seen in Figure 2, the roller 12 is biased towards the roller 10 by means of a spring 86 acting through levers 88 and 90.

The apparatus also includes a retaining mechanism which is illustrated in Figures 1,8 and 9. This comprises a pair of retaining rollers 92, 94 which nip the fibres drawn from the sliver by rocker and jaw mechanism 18. The pheripheral speed of these rollers 92,94 is adjusted in relation to the speed of operation of the apparatus so that slack in the drawn fibres is just taken up as the rocker 1 8 reaches the feed position and the jaws 20 close on the beard. Since the films contain crimp and the rocker removes this, the roller speed may be some 8% slower than half the rocker motion.Since the rocker 1 8 moves forward at approximately twice the speed of the rollers 92, 94 a reservoir of drawn fibres is built up each cycle between the rocker 1 8 and the rollers 92, 94 which is just taken up by the rollers 92, 94 as the rocker returns to the feed position.

A guide 96 which narrows towards the nip of rollers 92, 94 (see Figure 9) is provided to control the take-up of the drafted fibres.

A spinning device 24 is also provided on the machine (not illustrated) and this spinning device takes the form of a ring spinner. It is to be understood however that any twist inducer for applying twist to the sliver to create a yarn could be employed for example a flyer spinning apparatus.

Before describing the operation of the apparatus, it is necessary to consider the action of conventional drafting arrangements.

In all known drafting apparatus, a relatively thick sliver of fibres is fed forwardly by a pair of back rollers. A pair of front rollers rotating with a surface speed greater than that of the back rollers, withdraws fibres at a predetermined rate to produce the required thin sliver or yarn. For the purpose of the present theoretical consideration, the line joining the axes of the front rollers is referred to as the nip line, and the sliver approaching this nip line from the back rollers is referred to as the ingoing sliver, whilst the sliver leaving the nip line is referred to as the outgoing sliver.

If the leading fibre ends arrive regularly (i.e. at finite intervals) at the nip line, and change at that point from a slow to a fast speed of travel, then the thickness of the outgoing sliver will be as regular as it is theoretically possible. In practice, this does not happen for two reasons:- (a) Due to slight eccentricity of the front rollers, and due to pressure variations on the top roller (which generally has a compressible surface) the nip line oscillates backwards and forwards by a distance of several thousands of an inch.

(b) The mass of slow moving fibres between the back rollers and front rollers is extensible, and reacts like a tension spring, to the drag of those fibres which are gripped by the nip of the front rollers. This drag is variable, due to movement of the nip line as mentioned above, and due to variations in the thickness of the ingoing sliver, and varying degrees of fibre entanglement. Thus, the leading fibre ends arrive at the nip line at a varying rate, more per second if the slow fibre mass is extending, and vice versa. Furthermore, an increasing rate of arrival of the fibres, means an increasing rate of withdrawal, and hence increases the drag on the remainder of the slow mass, and so causes still further extension. In extreme cases, oscillation of the fibre mass occurs.

In the known drafting apparatus, the higher the draft, the worse the irregularity of the outgoing sliver. For this reason, normal drafts are in the range 6 to 10, although these have been raised by use of the Ambler Superdraft to about 80, or even in extreme cases 1 80. By using apparatus constructed as described with reference to the drawings, it is possible to raise the draft to over 700 and perhaps as high as 1000, without seriously impairing the regularity of the outgoing sliver. By means of the apparatus, it is now possible to spin of all counts from coarse to fine yarns direct form worsted tops, or thick gill sliver, in only a single pass as compared with the three of five passes required with known apparatus.

Basically, it will be appreciated that the invention avoids the use of the front rollers, or the intervention of any other continuously and evenly applied nip which are at the root of yarn irregularity, and substituting an intermittent nipping device (namely the jaws 20) for drawing the fibres forwardly. The intermittent nipping device substantially reproduces the finger action used in hand spinning.

The sliver is fed from a top (not shown) as required through a funnel 98, and the back rollers 10, 12, the rollers acting to pull the sliver from the top. The sliver is then fed forwardly through the channel 14 and is stretched by the porcupine roller 1 6. As has been previously described, the jaws 20 have a cyclic action, and at the commencement of the cycle the jaws are at the feed position illustrated in Figure 1, and the jaws are open.

At this stage, there is no tension in the outgoing sliver, that is to say the sliver on the forward side of the drafting jaws 20 and hence there is no tendency to extend the ingoing sliver, that is the sliver on the rearward side of the jaws.

Hence only the leading fibre ends, which have been advanced during the previous drafting cycle, are lying at the feed position and these form a "beard". (The expression "beard" is used herein to describe a projecting fringe of fibre ends which are less in number than all the fibres in a crosssection through the full undrafted sliver). As the jaws 20 close, they only close on to the "beard" which lay just behind the nip of these jaws on the previous ciosure, but which has now been advanced by a determined amount, during the previous drafting cycle. The nip of the jaws 20 thus only adds to the outgoing sliver on each stroke, those fibres, whose ends have been determinedly fed beyond the nip line.

As the jaws 20 close, and move forwardly through a predetermined drafting stoke, the outgoing fibres are being pulled by the jaws 20 due to frictional contact, slightly stretch the mass of ingoing fibres, so that their ends project momentarily beyond the feed position, but at the front end of the motion of the jaws, the jaws open, and release the outgoing sliver.

Consequently, the ingoing sliver contracts to its normal position whilst the jaws a-e open and during their rearward travel. It is important to note, that in its drawing out stroke, the drafting mechanism opens to release the sliver after drawing a distance less than the longest fibre length which is present in the sliver, so that it does not sever the sliver between the ingoing and outgoing fibres.

The retaining mechanism nipping rollers 92, 94 hold the outgoing yarn, when the jaws are open and on their return stroke, so that the drag produced by the twisting parting mechanism 24 does not sever the yarn and so that this spinning tension does not extend to the sliver beard.

It has been found, that apparatus constructed as described above, can be used to produce worsted yarn direct form a wool top down to a count of say 70's worsted in a single pass. Such yarns are particularly suitable for producing fine knitted garments and worsted suiting. It will be appreciated that a number of sets of apparatus similar to that described above with reference to the drawings, can be provided in a side-by-side arrangement, each being adapted to deal with a separate sliver.

The above described apparatus for drafting a sliver of untwisted and undrafted top in a single step to a count which is capable of being spun, comprises a fibre feeding means adapted to present the undrafted sliver at a feed position, a fibre drafting mechanism comprising mechanical nip means adapted to create a succession of discrete nips travelling away from a position close to the feed position to a release position spaced forwardly of the feed position in the direction of travel of the sliver, the operation of the fibre feeding means and the drafting mechanism being so related that on the one hand the nip means can only grip a proportion of the cross-section of the undrafted sliver at the feed station and on the other hand the sliver will not be broken by the forward pull of the nip means.

It will be understood that the apparatus is capable of various refinements. For example, a pair of straightening rollers may be provided to the rear of the rollers 10 and 12, that is to say between the funnel 98, and the rollers 10 and 12.

In fact, such straightening rollers may be used instead of the funnel 98. If provided, straightening rollers must be disposed so that their nip is set at a distance from the nip of the back rollers greater than the length of the longest fibres to be drafted.

The straightening rollers may be driven at a surface speed s!ightly less than that of the back rollers 10,12, to produce a slight drafting effect on the sliver before it arrives at the rollers. The principal purpose however of these straightening rollers is to straighten the sliver and remove variations.

Again, instead of having the jaws 20 carried by the oscillating arm mechanism illustrated, they could be carried for example on upper and lower endless belts or chains, so that they are pressed into contact with each other on the inner runs of the belts or chains, as they travel forwardly, but are released from each other at the front end of the inner runs of the belts or chains. Alternatively, the jaws could be carried by rotating members, although in that case, the rotating members should preferably be of considerable diameter, in order to ensure that the forward movement of the jaws is substantially rectilinear. In some circumstances it might be possible to operate with an arcuate forward motion of the drafting jaws, but it is thought that a rectilinear motion will be desired.

With a view to producing yarn of a consistent quality, it is important to exercise careful control over the sliver which is presented to the jaws 20.

Several additional features of the apparatus may be directed to this end.

For example, it is very important that the rollers 10, 12 and the porcupine roller 1 6 should be rotated very smoothly and at a constant angular velocity. The required roller speeds are very low (e.g. with a draft of 1000 and yarn leaving the machine at 2 metres per minute, the top has to be advanced by the rollers 10, 12 and the porcupine roller 16, at a speed of only 2 m.m. per minute) and hence even very slight variations in the regularity of the drive to these rollers could have a significant effect on the consistency of the yarn. It is desirable therefore, that the drive to the rollers 10, 12 and 1 6 should be as direct and positive as possible. For instance, a drive which employs a speed reduction gear train with a final worm gear drive is preferable to say a chain drive.It is also useful to apply a braking device to the porcupine roller 1 6 (and possibly to the delivery rollers 10 and 12) to smooth out yarn irregularities produced by the jaws snatching the fibres from the porcupine roller.

Another feature which improves the control over the delivery of the fibres to the jaws, is that the clearance between tEfeeth of the porcupine roller and the base of the channel 14 should be uniform and very small - in the order of a few fibre diameters. Effectively, therefore, the teeth of the porcupine should extend at their lowest point substantially to the base of the channel.

Further, in order that the porcupine roller can exercise the necessary control over the delivery of the sliver, it is preferable that the size of the roller and/or the shape of the channel shall be such that a considerable length of the sliver (say up to 1 5 centimetres) shall be engaged by the teeth of the porcupine roller at any one time. This can be achieved for example by providing that the channel 14 has a part which is arcuate about the axis of the porcupine roller - and in a particular example, part of the channel 14 is curved through approximately 900 about the roller axis, the entering part of the channel being vertical (so that the sliver flows vertically down through this part) and the exit end of the channel being horizontal.

In view of the small differences in peripheral speed at various points along porcupine fins, the base of the channel 14 may be curved to prevent shearing of the sliver.

For high speed operation, the mechanism comprising the cam 30, follower 32 and spring 44 may be replaced by a mechanism (not illustrated) comprising an eccentric crank pin carried by the shaft 28 and engaging in a bearing in one end of a lever which fulfils the same function as the lever 34. This alternative mechanism is not limited by the recovery rate of the spring 44, and consequently can operate at higher speeds than that shown in Figure 3.

Furthermore, the cam 66 (Figure 4) can advantageously be replaced by a cam profiled to provide two complete opening and closing cycles per 3600 revolution of the shaft 28. The camshaft 28 may then rotate at half the speed which would be required by the mechanism shown in Fig. 2 to produce the same number of working strokes per minute.

Claims (21)

Claims

1. A method of drafting fibres which comprise drawing out fibres from a sliver by means of a succession of discrete bites which draw the fibres from a feed position to a release position, the nips being timed to ensure continuity of the fibres so drafted and causing or allowing the tension of the fibres to return to substantially zero immediately prior to each successive nipping action.

2. A method as claimed in claim 1, wherein the drafting apparatus includes a retaining mechanism for gripping the sliver during return of the drafting mechanism towards the feed position, the retaining mechanism comprising a pair of nip rollers which grip the attenuated fibres of the drafted sliver, the peripheral speed of the nip rollers in relation to the drafting mechanism being adjusted so that as the drafting mechanism moves towards the nip rollers a reservoir of sliver is built up which is just used up during the time taken for the drafting mechanism to return to the feed position to grip a fresh portion of the sliver.

3. A method as claimed in claim 1 or claim 2, wherein the sliver is presented at the feed position in a compact form.

4. A method as claimed in claim 3, wherein the sliver is fed to the feed position through a constraining apparatus.

5. A method as claimed in any one of claims 1 to 4, wherein the length of stroke of the nip and/or its speed of travel is varied in relation to the quantity of fibres gripped by the nip at the feed position.

6. A method as claimed in claim 5, wherein the length of travel of the nip in the fibre drawing direction is limited to a distance less from the length of the longest fibres present in the sliver.

7. A method as claimed in claim 1 substantially as described herein with reference to the accompanying drawings.

8. A drafting device comprising a fibre feeding means for presenting a sliver at a feed position, a mechanism for causing the drafting mechanism to travel away from the feed position to a release position whilst maintaining the gripping action, and for releasing the gripping action and returning the drafting mechanism to the feed position without gripping the sliver, and a retaining mechanism adapted to grip the sliver at a position beyond the release position in the direction of travel of the sliver and so constructed that the tension on the sliver between the retaining mechanism and the feed position is substantially zero immediately before the drafting mechanism grips the sliver at the fee position.

9. Apparatus as claimed in claim 8, wherein means are provided by which the length of stroke of the nip and/or its speed of travel can be altered.

10. Apparatus as claimed in claim 8 or claim 9, wherein the fibre feeding means include a sliver restraining apparatus.

11. Apparatus as claimed in claim 10, wherein the sliver restraining apparatus takes the form of an open-topped trough through which the sliver is fed to the feed position whereby the width of the sliver is constrained.

12. Apparatus as claimed in claim 10 or claim 11, wherein the sliver restraining apparatus includes a toothed member having its teeth passing through substantially the entire thickness of the sliver so that all parts of the cross-section of the sliver are subjected to the restraining action.

13. Apparatus as claimed in any one of claims 8 to 12, wherein the drafting mechanism is adapted to travel in a substantially rectilinear path.

14. Apparatus as claimed in claim 13, wherein the drafting mechanism is carried on an oscillating arm so that the drafting mechanism travels in an arc which approximates to a straight line.

1 5. Apparatus as claimed in any one of claims 8 to 14, wherein the drafting mechanism includes a pair of jaws for gripping the fibres of the sliver.

1 6. Apparatus as claimed in claim 15, wherein the driving mechanism for the drafting mechanism is arranged to produce reciprocation of the jaws and to hold the jaws closed in their travel away from the feed position to open them in their return travel.

1 7. Apparatus as claimed in claim 16, wherein the driving mechanism produces substantially rectilinear reciprocation of one jaw and a rectangular motion of the other jaw, one side of the rectangle representing movement of the second jaw in contact with the first jaw as the latter moves away from the feed position.

1 8. Apparatus as claimed in any one of claims 8 to 14, wherein the drafting mechanism comprises two rotary elements one or both of which has radial projections adapted to meet part of the other element to produce the nip.

1 9. Apparatus as claimed in any one of claims 8 to 14, wherein the drafting mechanism comprises a pair of endless belts or chains carrying jaws and having parallel runs where the jaws of the two belts or chains meet each other to provide the forwardly travelling nip.

20. Apparatus as claimed in any of claims 8 to 1 9 wherein the retaining mechanism comprises a pair of nip rollers and peripheral speed of which is controllable such that a reservoir of sliver built up during travel of the drafting mechanism from the feed position is just taken up when the drafting mechanism returns to the feed position.

21. Apparatus as claimed in claim 8, substantially as described herein with reference to and as shown in the drawings.