GB2420124A

GB2420124A - Fibre drafting apparatus

Info

Publication number: GB2420124A
Application number: GB0424896A
Authority: GB
Inventors: Cherian Iype
Original assignee: Super Spinning Mills Ltd
Current assignee: Super Spinning Mills Ltd
Priority date: 2004-11-11
Filing date: 2004-11-11
Publication date: 2006-05-17
Also published as: ES2315924T3; CN101061266B; WO2006051294A1; GB0522808D0; CN101061266A; US20090094793A1; GB2420566A; GB0424896D0; DE602005010467D1; GB2420566B; ATE411420T1; EP1809795B1; EP1809795A1

Abstract

A drafting assembly for drafting a fibre web, the drafting assembly comprising ```a lower rear apron 28 having a first support surface; ```an upper rear apron 27 having a second support surface; ```the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons ```upper and lower front aprons 29, 30 having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons ```the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web. The drafting assembly may be associated with a carding machine.

Description

A Drafting Assembly and Method of Drafting The present invention relates

to a drafting assembly and method of drafting. More particularly, but not exclusively, the present invention relates to a drafting apparatus comprising two pairs of drafting aprons separated by a gap and arranged to generate a drafting force on fibres in a web which span the gap.

It is known to draft slivers, rovings or strands by roller drafting. The drafting apparatus comprises front and rear roller pairs. The front roller pair rotate more quickly than the rear pair so creating a drafting force on the fibres in the sliver or strand.

Such an apparatus is suitable for drafting slivers, rovings or strands since the sliver, or roving strand is thick enough or is immediately twisted so that there is little problem of the fibres lapping around the front rollers. There is evidence that drafting of the fibre web particularly the carded web, rather than the sliver can result in overall higher quality of yarn. Small front rollers are to be preferred since it enables shorter fibres to be drafted.

However, the tendency of the fibres to lap around the front rollers increases with decreasing front roller size. Web drafting is therefore currently restricted to drafting longer fibres in a web. For the avoidance of doubt, it should be stated that reference to long and short fibres does not refer to the intrinsic length of the fibres but the extension of the fibres along the length of the web. For example an intrinsically long fibre may be looped or twisted upon itself or may be inclined to the length of the web. In such a case an intrinsically long fibre may be classed as a short fibre.

The present invention seeks to alleviate this problem.

Accordingly, in the first aspect, the present invention provides: a drafting assembly for drafting a fibre web, the drafting assembly comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons; upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons; the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web.

The nip points can be arranged such that drafting of fibre web takes place.

The two pairs of drafting aprons significantly reduce the fibre lapping even when very small diameter rollers are used. This enables much shorter fibres within the web to be drafted significantly improving the properties of the drafted web.

Preferably, the drafting assembly further comprises a drive assembly for displacing the aprons, the drive assembly being adapted to displace the front aprons more rapidly than the rear aprons so generating a drafting force on the fibres in the web gripped by the front and rear nip points.

At least one of the aprons can comprise a loop of flexible material, a planar portion of the loop defining a support surface. The loop can be nylon, PVC or rubber, preferably reinforced rubber. The ioop can be a composite material.

Preferably, the drafting assembly comprises upper and lower rear nip rollers arranged to nip the upper and lower rear aprons between them to create the rear nip point. The drafting assembly could also comprise upper and lower front nip rollers arranged to nip the upper and lower front aprons between them to create the front nip point. The front nip rollers can be smaller than the rear nip rollers. Alternatively the rear nip rollers can be smaller than the front nip rollers.

The drive assembly can comprise at least one drive roller which abuts an apron and is adapted to displace the apron on rotation of the drive roller. The drive roller can be positioned within the loop.

In a further aspect of the invention there is provided a carding assembly comprising at least one carding roller for creating a fibre web; and a drafting assembly for drafting the fibre web the drafting assembly comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons; upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons; the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web.

The carding assembly can further comprise consolidating means for partially reducing the width of the web before it is received by the drafting assembly. The carding assembly could also comprise a further consolidating means for receiving the drafted web from the drafting assembly and further reducing its width to a sliver.

In a further aspect of the invention there is provided a method of drafting a fibre web comprising the steps of (a) providing a drafting apparatus, the drafting apparatus comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web; and (b) providing a fibre web to the drafting apparatus for drafting.

The present invention will now be described by way of example only, and not in any limitative sense with reference to the accompanying drawings in which figures 1 and 2 show, in schematic form, a known drafting assembly for drafting slivers, rovings or strands; figures 3 and 4 show further known drafting assemblies in cross section; figure 5 shows a drafting assembly according the invention in cross section; and figure 6 shows a carding assembly according to the invention.

A number of different types of machine are known for processing cotton type and worsted type fibres into yarn. In general these machines provide the steps of: (1) The opening, cleaning and reducing fibres to small tufts; (2) "carding" the fibres to open or individualise fibres. This process forms a web of fibres which is consolidated at the output end into a rope like form called a sliver; and, (3) aligning the disordered carded fibres and progressively reducing the sliver thickness or linear density by a series of machines until in the final "spinning" machine a strand of fibres is formed which is consolidated by twisting to form a yarn.

Short fibres are not conducive to the production of high quality yarns. The yarns are therefore combed to remove these. Combing takes place after carding but before spinning.

The fibres need to be aligned before they can be subjected to the combing process. This is done by drafting.

Shown in figures 1 and 2 in schematic form are known as roller drafting assemblies (1).

The drafting assembly (1) of figure 1 comprises a pair of front rollers (2) and a pair of rear rollers (3). The front rollers (2) are arranged to rotate more rapidly than the rear rollers (3) so producing a drafting force on the fibres (4) as they move between the two sets of rollers (2, 3). The assembly (1) shown in figure 2 includes a pair of rear aprons (5, 6) for better control of fibres.

Roller drafting is typically performed on slivers and rovings or occasionally on webs. It is known that a large proportion of the fibres in the sliver or web are hooked as a result of the earlier carding process. Hook free material can lead to better quality of yarn and/or lower the amount of comber waste.

Shown in figures 3 and 4 are further known drafting assemblies. Each of the assemblies comprises upper and lower rear aprons (7, 8). The upper and lower rear aprons (7, 8) each comprise a flexible loop of material (9, 10), typically pvc, nylon, rubber or a composite material. Positioned within each loop (9, 10) is a drive assembly (11, 12) comprising a drive roller (13, 14) which abuts the loop (9, 10). Turning the drive roller (13, 14) turns the loop (9, 10). Each of the aprons (7, 8) includes a planar support portion (15, 16). The two planar support portions (15, 16) are arranged to grip the fibres of a sliver received at an entrance (17) between them. As the drive rollers (13, 14) turn the fibres of the input fibre sliver are drawn from the entrance (17) to a rear nip point (18). The rear nip point (18) is created by upper and lower rear nip rollers (19, 20) which nip the upper and lower aprons (7, 8) between them.

The embodiment of figure 3 does not include a front apron. The drafting assembly of figure 4 further comprises a front apron (21) in the form of a loop (22) having a shape defined by tensioning means (23). In the drafting assembly of figure 4 a lower front nip roller (24) is positioned within and abuts against the front apron loop (22). An upper nip roller (25) nips the apron (21) between it and the lower nip roller (24) creating a front nip point (26). The front and rear nip points (26, 18) are arranged such that the fibres which exit the rear nip point (18) are received by the front nip point (26).

Such drafting assemblies can be used for sliver drafting or web drafting.

It has been found drafting the card web, by a relatively small draft whilst in the web state or at least in an open state in comparison to the sliver, followed by the normal process of producing the sliver package for the combing machine has a beneficial effect of better preparing the sliver package as it results in a reduction in the noil extracted by the combing machine. Furthermore, there is evidence that the drafting of the card web results in overall higher quality of yarn. It appears that the process of web drafting partially or in some cases completely removes hooks but also re-arranges the fibres so that the subsequent drafting is more efficient in removing hooks that remain in the material.

In order for this drafting to be beneficial, it is essential that drafting occurs whilst the fibres, including the short fibres, remain under positive control as far as possible. This is essential as the fibres in the web state or substantially in the web state lends itself to better control as it interacts with less fibres whilst enabling more fibres under intimate control by appropriately designed control surfaces. It is this extra degree of control possible which enables the fibre hooks to be unhooked, or rearranged such that it is removed in subsequent doubling or drafting, as against doubling and drafting alone as implied in normal sliver drafting and yarn manufacture. In order to achieve the degree of control necessary whilst ensuring that the fibres can be processed without the lapping of fibres being a problem, it is necessary that fibres are under positive control by appropriate surfaces.

The drafting assemblies of figures 3 and 4 are only suitable for drafting long fibres in the web. The relatively large upper nip rollers (25) in figures 3 and 4, necessary to avoid fibre lapping, places a limit on how close together the front and rear nip point (26, 18) can be.

This in turn places a relatively large lower limit on the length of fibre which can be controlled in the drafting process. Fibres below this limit either because of their length or because of their relative orientation or configuration will tend to be uncontrolled.

However, reducing of the size of the upper front drafting roller would result in the fibres from the web lapping around the roller.

Shown in figure 5 is a drafting assembly according to the invention. The drafting assembly comprises upper and lower rear aprons (27, 28). The drafting assembly further comprises upper and lower front aprons (29, 30) in the form of loops. Associated with each apron (27-30) is a drive assembly (31) within the ioop. Each drive assembly (31) comprises a drive roller (32) which abuts against the inside of each respective loop and which drives rotation of the loop. The upper and lower front aprons (29, 30) have third and fourth support surfaces (33, 34) respectively. These are arranged to grip the fibre web received at a front nip point (35) and transport it to an exit point (36).

The front nip point (35) is created by upper and lower front nip rollers (37, 38). These nip the upper and lower front aprons (29, 30) between them.

In use the above drive assembly (31) rotates the upper and lower rear aprons (27, 28) transporting the web from the entrance (39) to the rear nip point (40). The web exits the rear nip point (40) and is received by the front nip point (35). From here it is transported to the exit point (36). The drive rollers (32) rotate the front aprons (29, 30) more rapidly than the rear (27, 28) so producing a drafting action on fibres as they span the gap between the front and rear nip points (35, 40). The apparatus according to the invention has no need of a larger front roller to avoid fibre lapping. The apparatus can therefore be used to draft shorter fibres under control in webs than known drafting apparatus. This results in a commercially significant improvement in the web with a significant reduction in noil in the subsequent combing process.

Shown in figure 6 is a carding assembly (41) according to the invention. The carding assembly (41) comprises a carding roller (42) for producing a web which is received by the drafting assembly of figure 5. Arranged between the carding roller (42) and drafting assembly is a consolidating means (not shown). The consolidating means reduces the width of the web. The web is however still maintained wider and more open than a sliver.

In a further embodiment of the invention (not shown) the carding assembly comprises a further consolidating means which further consolidates the drafted web as it leaves the drafting assembly.

In a further embodiment of the invention (not shown) the carding assemb'y does not include a consolidating means for reducing the width of the web.

Claims

1. A drafting assembly for drafting a fibre web, the drafting assembly comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web.

2. A drafting assembly as claimed in claim 1 further comprising a drive assembly for displacing the aprons, the drive assembly being adapted to displace the front aprons more rapidly than the rear aprons so generating a drafting force in fibres in the web gripped between the front and rear nip points.

3. A drafting assembly as claimed in either of claims 1 or 2, at least one of the aprons comprising a loop of flexible material, a planar portion of the loop defining the support surface.

4. A drafting assembly as claimed in claim 3 wherein the ioop is nylon, PVC or rubber, preferably reinforced rubber.

5. A drafting assembly as claimed in any one of claims I to 4 further comprising upper and lower rear nip rollers arranged to nip the upper rear aprons between them to create the rear nip point.

6. A drafting assembly as claimed in any one of claims 1 to 5 further comprising upper and lower front nip rollers arranged to nip the upper and lower front aprons between them to create the front nip point.

7. A drafting assembly as claimed in claim 6 when dependant on claim 5 wherein the front nip rollers are smaller than the rear nip rollers.

8. A drafting assembly as claimed in claim 2 wherein the drive assembly comprises at least one drive roller which abuts the apron and is adapted to displace the apron on rotation of the drive roller.

9. A drafting assembly as claimed in claim 8 wherein the drive roller is positioned within the loop.

10. A carding assembly comprising at least one carding roller for creating a fibre web; and a drafting assembly for drafting the fibre web the drafting assembly comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web.

11. A carding assembly as claimed in claim 10 comprising consolidating means for partially reducing the width of the web before it is received by the drafting assembly.

12. A carding assembly as claimed as claim 11 comprising a further consolidating means for receiving the drafted web from the drafting assembly and further reducing its width to a sliver.

13. A method of drafting a fibre web comprising the steps of (a) providing a drafting apparatus, the drafting apparatus comprising a lower rear apron having a first support surface; an upper rear apron having a second support surface; the first and second support surfaces being arranged to grip the fibre web and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons upper and lower front aprons having third and fourth support surfaces respectively being arranged to grip the fibre web and transport the web from a front nip point to an exit on displacement of the front aprons the aprons being arranged such that the front nip point receives fibre web which exits the rear nip point to draft the fibre web; and (b) providing a fibre web to the drafting apparatus for drafting.