GB2340136A

GB2340136A - Dividing tows

Info

Publication number: GB2340136A
Application number: GB9816606A
Authority: GB
Inventors: Richard Graham Walker
Original assignee: PLASTIC DEV Ltd
Current assignee: PLASTIC DEV Ltd
Priority date: 1998-07-31
Filing date: 1998-07-31
Publication date: 2000-02-16
Also published as: GB9816606D0

Description

2340136 TOW DIVIDING The invention relates to tow dividing and primarily

(although not exclusively) relates to tow dividing of fibrous materials such as textile material, carbon fibre material or PAN material (which is the precursor to carbon fibre material, i.e. the raw material before having been processed to form carbon fibre). The invention is of particular application with materials which comprise a number of continuous filaments.

The tow of a material relates to the number of filaments in a length of fibrous material. Typically, there are available 500K tows, 50K tows, 24K tows, 12K tows, 6K tows and 3K tows, where 500K tow means 500,000 filaments running substantially continuously along the length of the tow.

In general, the larger the tow, the cheaper the material is per kilogram. To give some idea of the difference in price, a 24K tow might retail at, for instance, E18 per kilo for PAN precursor material whereas a 3K tow could easily retail for up to E45 per kilo. There is therefore a great incentive to be able to take precursor material with a large tow value and divide that material down into a number of smaller tow bundles or reels which can be sold at added value. As long as the tow dividing method is not too expensive, then the advantages of carrying out such a division are self evident.

Most continuous filaments, be they textile or for structural reinforcement applications have individual filament diameters of the order of 10 microns. This applies to fibres made from carbon/ graphite, kevlar/nomex, 2 glass and virtually all synthetic fibres. They are seldom used as individual filaments and are grouped into multifilament tows/yarns. It is always cheaper to obtain one 24K tow than it is to obtain eight 3K tows. A 24K tow wound under tension onto a bobbin/spool as supplied by a manufacturer is about 8mm wide and roughly 2mm thick, these dimensions encompassing 24, 000 individual fibres which are tightly packed together in this cross- section. These fibres are held together by a chemical surface coating (size) that can be an anti-static agent to prevent individual fibres from repelling each other or, in the case of a size, to protect the fibres in the tow from abrasion damage or make them more compatible with a plastic matrix into which these tows will be subsequently inserted e.g. with fibre reinforced plastics. Another method of ensuring that a tow retains its tightly packed cross-section is to impart a twist into the tow before it is wound onto the spool. The twist is def ined as the number of turns per metre and may be clockwise or anticlockwise (S or Z twist). Tows with a twist have a narrower and thicker cross-section and are difficult to spread unless the tow has been untwisted by an opposite rotation to the tow twist present. Tows can be supplied without size also.

A typical 24K carbon fibre tow weighs 1,600 tex (i.e. 1,600 grams per 1, 000 metres) and each of the 24,000 fibres has a diameter of 7 microns and a surface size of about 0.5 % of the tow weight. Although the tow is supplied as "never ever twisted" tow individual fibres are not in the same position in successive cross-sections since the tow is flexible and fibres are only loosely held in a tow.

There is a tolerance on tow tex. A 3K tow can have, for example, a tex of 200 + or - 2% which means that if the fibre diameter and density does not vary then the tow can have nominally 3,000 fibres + or - 60 (i.e. ranging from 2,940 to 3,060 per tow).

The larger tow sizes are widely available but there is a relative scarcity of and high demand for the smaller tow sizes such as 3K tows. There is therefore a good economic incentive for finding a method of reliably reducing the tex of a tow.

An existing method for attempting to reduce the tex of a tow (i.e. to divide the tow) is by stretch breaking the tow by applying a force in the direction of the fibres to cause them to break randomly along their length so that with further tension applied, the fibres will slide along side each other to produce a tow of discontinuous fibres with gaps between the end of each f ibre and its broke end.

A stretch broken discontinuous tow is therefore longer than it was before being broken and is lower in tex. A twist applied to this stretch broken tow helps to conceal the loose fibre ends and bind the tow together.

As will be appreciated, the abovementioned prior art method is rather brutal in that it relies upon forcibly breaking the fibres. Many industrial applications however prefer continuous filament tows and to separate a continuous filament tow into continuous filament sub-tows has not been successfully achieved in the prior art.

It is an aim of preferred embodiments of the present invention to enable a continuous filament tow to be separated into continuous filament subtows.

4 According to an aspect of the invention, there is provided a method of dividing a tow of material consisting of a large number of filaments into a plurality of subtows each having a smaller number of filaments, the method comprising longitudinally conveying the tow of filaments, spreading the filaments in a transverse direction and once the filaments have been spread, separating the spread filaments into a plurality of sub-tows.

Said step of spreading the filaments preferably comprises spreading the filaments by bringing them into contact with a fluid.

Spreading of the filaments may be accomplished by 15 conveying the tow over one or more gas jets.

Preferably, the tow of material is conveyed by means of first and second transportation means for conveying the tow in its longitudinal direction.

Said first and second transportation means are preferably synchronized such that the first and second transportation means convey the material in the longitudinal direction at the same rate.

Preferably, the material is arranged to be transported without tension, between the first and second means of transportation.

The transportation means may comprise a first and second set of pinch rollers.

The pinch rollers may be covered by a resilient material such as rubber.

The tow of material may be supplied on a spool of material, and fed from the spool to the transportation means.

The gas spreader may comprise an air spreader. The gas spreader is preferably arranged transversely with respect to the tow.

The gas from the jet or jets is preferably arranged to flow in a laminar fashion.

The separating means may comprise a plurality of pins arranged transversely with respect to the direction of motion of the spread tow, sub-tows being defined between adjacent pins.

Sub-tows may be separated by cross-stitching means, a stitch being required to be used once only for each subtow.

Preferably, during an initial phase, the tow of filaments is conveyed at reduced speed over said gas jet or jets and, once the filaments have been spread in a transverse direction by the gas jets, the spread filaments from a starting end of the tow are divided into said plurality of subtows and each sub-tow attached to take up means for collecting the respective sub-tow.

Preferably, during a second phase, the tow of filaments is conveyed at a normal running speed such that the filaments divided into sub-tows during the first phase may be rapidly collected.

Said takeup means may comprise a plurality of takeup spools.

6 Preferably, during collection of said sub-tows, the divided sub-tows are wound onto said takeup spools under tension.

Because the tow, and the sub-tows, comprise continuous filaments it is only necessary for the separation operation to be carried out once. In other words, once a tow has started to be separated into sub- tows, individual collection operations for the sub-tows should proceed without drama.

Preferably, each takeup spool is arranged to run at the same rate.

Preferably, the tow is provided in never ever twisted form. Alternatively, if the tow is twisted, the tow should be untwisted by the same amount of de-twisting to provide a twist free starting tow.

The separating means may be provided immediately subsequent to said transporting means or, may be provided intermediate the first and second transport means.

Preferably, the tow is cooled to a temperature in the range of +50C to -150C.

Thetow may be cooled by passing it through a cold chamber or by impinging jets of a cold gas, for instance, carbon dioxide from a pressurised liquid bottle. The gas spreader may comprise jets of a cold gas.

Cooling of the tow reduces the tack of the surface sizing applied to carbon fibres to enable fibre separation.

7 Preferably, the tow between the two transportation means is allowed to become slack and fall into a catenary.

The tow in the shape of a catenary is preferably gently blown with the gas spreader to cause filaments in the tow to separate and balloon apart.

The filaments can be spread apart by contacting two endless rubber belts that are stretched by increasing amounts perpendicular to the direction of transport of the fibre tow. The tow will follow the spread of the rubber belts.

The transportation means may be connected to a variable speed drive to enable initial separation of the tow to be carried out at low speed and, once the start of the sub-tows are separated, the transportation means may then be run at full speed.

Tow spreading may be carried out by inserting the tow into a viscous fluid flowing between closely spaced plates.

By supplying a viscous fluid at low pressure /velocity between such plates, fluid flow is effectively a twodimensional inviscid fluid flow which causes the fibres to align along stream lines as the fluid passes into a divergent channel.

A fluid flow device of this nature operates according to the Hele-shaw analogy which experimentally demonstrates inviscid two-dimensional flow using a viscous fluid such as water or air. Inviscid fluid flow between closely spaced plates causes the stream lines to fan out uniformly 8 down the divergent channel and take filaments of the tow along the stream lines and thereby separate the tow.

In view of the fact that some filaments within the tow may attempt to cross over from one sub-tow to another at the point of separation, cutting means may be provided for cutting those small number of filaments. Said cutting means may comprise oscillating blades.

The material may, for instance, comprise carbon fibres, carbon fibre precursers, aramid fibres or glass fibres.

According to a second aspect of the invention, there is provided apparatus for dividing a tow of material consisting of a large number of filaments into a plurality of sub-tows each having a smaller number of filaments, the apparatus comprising: means for conveying the tow of filaments; means for spreading the filaments in a transverse direction; and means for separating the spread filaments into a plurality of sub-tows.

Said means for spreading the filaments preferably comprises fluid means.

Said fluid means preferably comprises one or more gas jets.

Preferably, said means for conveying the tow of material comprises first and second transportation means for conveying the tow in its longitudinal direction.

9 Preferably, said first and second transportation means are synchronized such that the first and second transportation means convey the material in the longitudinal direction at the same rate.

Preferably, the first and second transportation means are set up with the tow of material such that the material is transported without tension between the first and second means of transportation.

Preferably, the transportation means comprises a first and second set of pinch rollers.

Preferably, the pinch rollers are covered by a resilient material such as rubber.

Preferably, the tow of material is provided on a spool and fed from the spool to the means for conveying the tow of filaments.

Thegas from the jet or jets is preferably arranged to flow in a laminar fashion.

Sub-tows may be separated by cross-stitching means, a stitch being required to be used once only for each sub- tow.

Preferably, takeup means are provided for collecting the sub-tows.

Preferably, said takeup means comprises a plurality 5 of takeup spools.

Preferably, the takeup spools are arranged to wind the divided sub-tows up under tension.

Preferably, each takeup spool is arranged to run at the same rate.

If the starting tow is twisted, then preferably detwisting means are provided between the starting spool and 15 the transportation means.

The separating means may be provided subsequent to said transportation means or, may be provided intermediate the first and second transportation means.

The tow may be arranged to pass through a cold chamber for cooling the tow to a temperature of between +5 to _150C.

Preferably, the tow between the two transportation means is allowed to become slack and fall into a catenary.

The transportation means may be connected to a variable speed drive.

Tow spreading may be carried out by inserting the tow into a viscous fluid between closely spaced plates.

By supplying a viscous fluid at low pressure /velocity between such plates, fluid flow is effectively a two- dimensional inviscid fluid flow which causes the fibres to align along stream lines as the fluid passes into a divergent channel.

Cutting means may be provided for cutting filaments within the tow which attempt to cross over from one sub tow to another.

Said cutting means may comprise oscillating blades.

The fibres may, for instance, comprise carbon fibres, carbon fibres precursors, aramid fibres or glass fibres.

In accordance with another aspect of the invention, a pair of continuous belt drives may be used to spread the tow, rather than using air spreading, the belts may be provided perpendicular to the direction of transport of the tow and contacting with the filaments such that the tow will follow the spread of the rubber belts.

According to a yet further aspect of the invention, tow spreading may be carried out by inserting the tow into a viscous fluid between closely spaced plates.

By supplying a viscous fluid at low pressure /velocity between such plates, fluid flow is effectively a two dimensional inviscid fluid flow which causes the fibres to align along stream lines as the fluid passes into a divergent channel.

A fluid flow device of this nature operates according to the Hele-shaw analogy.

12 The method of the last two mentioned aspects of the invention, may utilise any of the features of the first described aspects.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, in which:

Figure 1 illustrates in schematic form a method and apparatus for use in dividing a tow of material into a plurality of sub-tows.

Figure 2 illustrate in schematic form an optional tow spreading step which may be substituted for the air spreading step illustrated in Figure 1; and Figures 3 and 4 illustrates apparatus which operates according to the hele-shaw analogy to provide tow spreading.

Referring to Figure 1, there is shown on the left hand side a starting spool 1 carrying a tow 2 of never ever twisted continuous fibre material. The continuous fibres run in the direction of the tow, i.e. in a longitudinal direction. The tow 2 passes through an eyelet guide 3 to a first set 4 of rubber covered driven pinch rolls. The function of the first set of pinch rolls 4 is to feed material from the starting spool. The tow material 2 then subsequently passes towards a second set 5 of rubber covered pinch rolls-running at the same speed as the f irst set 4. Intermediate the f irst set 4 and second set 5, the tow of material is allowed to be slack so as -to form a catenary and an air jet (not shown) is applied from underneath to the tow 2 to allow it to 13 balloon out and spread transversely as shown. Spreading of the tow in this fashion facilitates separation of the tow into sub-tows. Separation could initially be carried out, for instance, by eye and the sub-tows fed through eyelets 71 to 78 to keep them bundled together and aid their passage from the second set of pinch rollers 5 to wind-up spools 61 to 68. An alternative and more accurate method of separation is to pass the spread material through separating pins, the gap between each separating pin defining a sub-tow. Other methods of separating the tow into sub-tows are envisaged. For instance, a crossstitching machine may be used to provide the initial separation of the spread out material, one looped crossstitch being required at the start of each sub-tow.

Once initial separation has taken place then, because the tow is of never ever twisted material which is comprised substantially of continuous filaments, each individual group of continuous fibres forming a sub-tow may be simply wound up on the individual wind up spools 61 to 68.

The above describes the general method in which a tow may be separated into a number of sub-tows (8 in the example given).

Specific details of the method will now be given. To separate a 3K subtow to an accuracy of + or - 60 filaments, successful separation may be achieved if the tow is spread to a width of, for instance, 100 fibres per mm width. By then sewing a cross-stich thread across the width of the tow to an accuracy of 0. 5mm each stitch would pull a bundle of 3000 + or 50 fibres together. To form such 3K sub-tows, a 24K starting tow must first be spread 14 from 8mm wide to 240mm wide so that on average 100 fibres occupy each mm of width.

When carrying out air jet spreading, it should be noted that turbulent air flow will tend to cause chaotic motion of the spread fibres in the tow whereas a lamina flow will avoid this. Another method of helping a tow to spread (and to bring a spread tow back together again) is to pass the tow between a pair of endless rubber belts that are stretched by increasing amounts perpendicular to the fibre movement by using edge to spread and vice versa to contract the tow width. Also, cooling the tow down will make the surface size temporarily brittle and thereby reduce the tack between fibres. The tack can be reintroduced after separation by warming up the separated tows before winding on the take-up spools 61 to 68.

In the example given above, when separated a spread 3K tow will be 30mm wide and needs to be reduced in width by applying tension and passing the tow through a circular ceramic eyelet guide (e.g. 71 to 78 as described above) to help the tow to reduce to a width of around 3mm bef ore wind-up. It should be noted that the width of a tow does not increase proportionally to the number of filaments and that, for instance, a 24K tow packs thicker and narrower than eight 3K tows added together.

It will be appreciated according to the method described above that a tow having a large number of continuous fibres in it may be separated into a plurality of sub-tows having a smaller number of continuous fibres within them advantageously. The method described is relatively low-cost and is therefore immediately attractive since the commercial value of, for instance, - 15 three 8K tows is much greater than the commercial value of a single 24 K tow.

Referring now to Figure 2, there are shown a pair of conveyor belts 81, 82 which are driven in opposing directions. The tow is arranged to pass over the two conveyor belts and the action of those belts acts to spread the tow. Such apparatus is placed between the elements 4 and 5 of Figure 1, to take the place of the air spreading apparatus.

Referring now to Figures 3 and 4, there is shown a further variant in which apparatus for demonstrating the well know hele-shaw analogy is used to spread the tow.

Such apparatus comprises a pair of closely spaced plates 91, 92, which at their peripheries are fixed together and have a divergent channel 93 defined between them. This divergent channel is therefore of a fan type shape, and of very little thickness (approximately 2mm). The tow is fed in from the left, with respect to Figure 4 and emerges spread from the right hand side of the apparatus' of Figure 4. Spreading of the tow is arranged to take place by means of applying a low pressure/velocity fluid supply to an inlet 94. This low pressure fluid supply acts in accordance with experimental theory to give an effectively two- dimensional flow which automatically aligns the fibres being passed through the apparatus along stream lines as the flow passes into the divergent channel 93.

In the above discussion, it will be appreciated that the apparatus of Figure 2, as well as the apparatus of Figures 3 and 4 may be utilised with the apparatus of Figure 1, taking the place of the air spreadi ng jets.

N 16 The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

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Claims

1. A method of dividing a tow of material consisting of a large number of filaments into a plurality of sub-tows each having -a smaller number of filaments, the method comprising conveying the tow of filaments longitudinally, spreading the filaments in a transverse direction and, once the filaments have been spread, separating the spread filaments into a plurality of sub-tows.

2. A method according to claim 1, wherein the tow of material is conveyed by means of first and second transportation means for conveying the tow in its longitudinal direction.

3. A method according to claim 2, wherein said first and second transportation means are synchronized such that the first and second transportation means convey the material in the longitudinal direction at the same rate.

4. A method according to claim 2 or 3, wherein the material is arranged to be transported without tension between the first and second transportation means.

5. A method according to any of the preceding claims, wherein the tow is conveyed by means of a f irst and second set of pinch rollers.

6. A method according to claim 5, wherein the pinch rollers are covered by a resilient material, for instance, rubber.

7. A method according to claim 2, or any of claims 3 to 6 as dependent upon claim 2, wherein the tow of material is supplied on a spool, and fed from the spool.

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8. A method according to any of the preceding claims, wherein one or more gas jets are provided to form part of a gas spreader over which said tow of filaments are conveyed, spreading being brought about by flow of gas 5 through the tow.

9. A method according to claim 8, wherein the gas spreader is an air spreader.

10. A method according to claim 8 or 9, wherein the gas spreader is arranged transversely with respect to the tow.

11. A method according to any of the preceding claims, wherein gas from the jet or jets is arranged to flow in a laminar fashion.

12. A method according to any of the preceding claims, wherein during an initial phase, the tow of filaments is conveyed at reduced speed over said gas jet or jets and, once the filaments have been spread in a transverse direction by the gas jets, the spread filaments from a starting end of the tow are divided into said plurality of sub-tows and each sub-tow attached to take up means for collecting the respective sub-tow.

13. A method according to claim 14, wherein during a second phase, the tow of filaments is conveyed at a normal running speed such that the filaments divided into subtows during the first phase may be rapidly collected.

14. A method according to any of claims I to 7, wherein the said step of spreading the filaments comprises feeding the tow between a pair of closely spaced plates, into which a viscous fluid is injected.

N 19

15. A method according to claim 14, wherein said closely spaced plates define a divergent channel, said channel being widest at an exit point of the tow, and narrowest at the entry point of the tow.

16. A method according to claim 14 or 15, wherein said viscous fluid is supplied at low pressure and velocity between the closely spaced plates.

17. A method according to claim 14 or 15, wherein tow spreading is brought about in accordance with the Hele Shaw analogy, whereby the tow fans out uniformly along streamlines defined by the fluid flow.

18. A method according to claim 14, 15, 16 or 17, wherein said fluid comprises air.

19. A method according to any of claims 1 to 7, wherein said tow of filaments are conveyed over a pair of continuous belt drives, said belt drives being arranged transversely with respect to the direction of the tow and being driven in opposing directions to one another, spreading being brought about by said opposing motion of the continuous belts.

20. A method according to claim 19, wherein said belt drives are arranged perpendicular to the direction of transport of the tow.

21. A method according to any of the preceding claims, wherein the spread fibres are separated into sub-tows by means of a plurality of pins arranged transversely with respect to the direction of motion of the spread tow, subtows being defined between adjacent pins.

22. A method according to any of the preceding claims, wherein crossstitching means are provided, said crossstitching means being arranged to perform separation of the spread fibres.

23. A method of according to any of the preceding claims, wherein takeup means are provided for collecting individual sub-tows.

24. A method according to claim 23, wherein said takeup means comprises a plurality of takeup spools.

25. A method according to claim 23, wherein during collection of said subtows, the divided sub-tows are wound onto said takeup spools under tension.

26. A method according to claim 24 or 25, wherein each takeup spool is arranged to run at the same rate.

27. A method according to any of the preceding claims, wherein the tow is provided in never ever twisted form.

28. A method according to any of claims 1 to 26, wherein the tow is provided with a twist and the method further comprises a de-twisting step for untwisting the twisted tow prior to the step of conveying.

29. A method according to any of the preceding claims, wherein the spread filaments are separated into sub-tows subsequent to the conveying step.

30. A method according to claim 2, or any of claims 3 to 29 as dependent upon claim 2, wherein the filaments are spread at a point intermediate said first and second transportation means.

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31. A method according to any of the preceding claims, wherein the tow is cooled to a temperature in the range of +511C to -150C.

32. A method according to claim 31, wherein the tow is cooled by passing it through a cold chamber prior to said spreading.

33. A method according to claim 31, wherein the tow is cooled by impinging jets of a cold gas.

34. A method according to claim 33, wherein said cold gas comprises carbon dioxide from a pressurised liquid bottle.

35. A method according to claim 2, or any of claims 3 to 13 or 19 to 34 as dependent upon claim 2, wherein the tow between the two transportation means is slack so as to form a catenary.

36. A method according to claim 35, wherein the tow is gently blown by said gas jet or jets to cause filaments in the tow to balloon apart.

37. A method according to any of the preceding claims, wherein any filaments within adjacent sub-tows attempting to cross over to neighbouring sub-tows are cut.

38. A method according to claim 37, wherein such filaments attempting to cross over are cut by rotating blades.

39. A method according to any of the preceding claims, wherein the material comprises any one of the following: carbon fibres, carbon fibre precursors, aramid fibres or glass fibres.

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40. A method substantially as herein described with reference to the accompanying drawing.

41. Apparatus for dividing a tow of material consisting of a large number of filaments into a plurality of subtows each having a smaller number of filaments, the apparatus comprising: means for conveying the tow of filaments in a lengthwise direction; means for spreading the filaments in a transverse direction; and means for separating the spread filaments into a plurality of subtows.

42. Apparatus according to claim 41, wherein said means for conveying the tow of material comprises first and second transportation means for conveying the tow in its longitudinal direction.

43. Apparatus according to claim 42, wherein said first and second transportation means are synchronized such that the first and second transportation means convey the material in the longitudinal direction at the same rate.

44. Apparatus according to claim 42 or 43, wherein the first and second transportation means are set up with the tow of material such that the material is transported without tension between the first and second means of transportation.

45. Apparatus according to claim 42, 43 or 44, wherein the transportation means comprises a first and second set of pinch rollers.

46. Apparatus according to claim 45, wherein the pinch rollers are covered by a resilient material such as rubber.

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47. Apparatus according to any of claims 41 to 46, wherein the tow of material is provided on a spool and fed from the spool to the means for conveying the tow of filaments.

48. Apparatus according to any of claims 41 to 47, wherein said spreading means comprises one or more gas jets which are provided to form part of a gas spreader over which said tow of filaments are conveyed, the gas spreader being arranged transversely with respect to the tow.

49. Apparatus according to claim 48, wherein the gas spreader comprises an air spreader.

50. Apparatus according to claim 48 to 49, wherein the gas from the jet or jets is arranged to flow in a laminar fashion.

51. Apparatus according to any of claims 40 to 47, wherein said spreading means comprise a pair of closely spaced plates, through which the tow of filaments is passed, and between which a viscous fluid is injected.

52. Apparatus according to claim 51, wherein said closely spaced plates define a divergent channel, the channel being widest at an exit point of the tow, and narrowest at an entry point of the tow.

53. Apparatus according to claim 51 or 52, wherein said viscous fluid is supplied at low pressure and velocity between the closely spaced plates.

54. Apparatus according to any of claims 51 to 53, wherein the tow spreading is brought about in accordance 24 with the Hele Shaw analogy, wherein the tow f ans out uniformly along streamlines defined by the fluid flow.

55. Apparatus according to any of claims 51 to 54, 5 wherein said fluid comprises air.

56. Apparatus according to any of claims 40 to 50, wherein said means for spreading comprises a pair of continuous belt drives over which said tow of filaments are conveyed, said belt drives being arranged transversely with respect to the direction of the tow and being driven in opposing directions to one another, spreading being brought about by said opposing motion of the continuous belts.

57. Apparatus according to claim 56, wherein said belt drives are arranged perpendicular to the direction of transport of the two.

58. Apparatus according to any of claims 41 to 58, wherein the separating means comprises a plurality of pins arranged transversely with respect to the direction of motion of the spread tow, sub-tows being defined between adjacent pins. 25

59. Apparatus according to any of claims 41 to 58, wherein sub-tows are separated by cross-stitching means, a stitch being required to be used once only for each subtow. 30

60. Apparatus according to any of claims 41 to 59, wherein takeup means are provided for collecting the subtows.

I

61. Apparatus according to claim 60, wherein said takeup means comprises a plurality of takeup spools.

62. Apparatus according to claim 61, wherein the takeup spools are arranged to wind the divided sub-tows up under tension.

63. Apparatus according to claim 61 or 62, wherein each takeup spool is arranged to run at the same rate.

64. Apparatus according to any of claims 41 to 63, wherein if the starting tow is twisted, then de-twisting means are provided.

65. Apparatus according to any of claims 41 to 64, wherein the separating means are provided subsequent to said transportation means.

66. Apparatus according to claim 42 or any of claims 43 to 51 as dependent upon claim 36, wherein the separation means are provided intermediate the first and second transportation means.

67. Apparatus according to any of claims 41 to 66, wherein the tow is arranged to pass through a cold chamber for cooling the tow to a temperature of between +5 to 150C.

68. Apparatus according to claim 42 or any of claims 43 to 67 as dependent upon claim 36, wherein the tow between the two transportation means is allowed to become slack and fall into a catenary.

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69. Apparatus according to any of claims 41 to 68, wherein the means for conveying the tow is connected to a variable speed drive.

70. Apparatus according to any of claims 41 to 69, wherein cutting means are provided for cutting filaments within the tow which attempt to cross over from one subtow to another.

71. Apparatus according to claim 70, wherein said cutting means comprise oscillating blades.

72. Apparatus as herein described with reference to the accompanying drawings.