WO2007007045A1

WO2007007045A1 - Production of shaped filamentary structures

Info

Publication number: WO2007007045A1
Application number: PCT/GB2006/002491
Authority: WO
Inventors: John Pritchard; Richard Ward; Lloyd Thomas Halstead
Original assignee: P.G. Lawton (Industrial Services) Limited
Priority date: 2005-07-09
Filing date: 2006-07-04
Publication date: 2007-01-18
Also published as: GB0613246D0; GB2428253A8; GB2428253A; JP2009500533A; GB0514141D0

Abstract

Circumferential fibres (28) are added and needled into a stack by a needle head (23). Radially extending fibres (34A to 34E) are also added into the stack. Production is continuous. The continuous fibres (28, 34) are added such that there is a common density of fibres all of the way over the surface of the stack. The stack is built up to be greater than the overall depth required of a preform and the stack is later cut to form a plurality of preforms.

Description

PRODUCTION OF SHAPED FILAMENTARY STRUCTURES

The present invention relates to methods of forming shaped fibrous structures and to structures. The present invention is particularly, although not exclusively, applicable to friction products that are formed by the method such as for example brakes, such as disc brakes for aircraft.

EP 0 748 781 (B. F. Goodrich) discloses a method of making a preform in which braided tapes are spirally wound and connected together by needle punching. As the braid has helical fibre along its length none of the fibre ever extends in from the inside to the outside in a radial direction or at a tangent thereto. The fibre is of necessity always extending from the inside to the outside or back again in a curved direction.

WO 98/49382 (B. F. Goodrich) discloses cross-lapping tow and needling that tow and then adding disordered tow and then further cross-lapped tow before needling again. No fibre is disposed in the chordal direction.

Furthermore in both of the above B. F. G. publications there will be more fibres at the inner region than the outer region as a result of the shorter circumferential distance at the inner region.

It is well known to effect a finishing step to the preform which inevitably results in different operations being effected at different parts of the preform. For instance WO 98/49382 effects a final finishing needling step consisting of three full revolutions without adding fibre. EP 232 059 (P. G. Lawton Limited) discloses another known method of making a carbon fibre disc. The disc is built by adding segments, one by one, in a spiral, layer upon layer. Some segments have continuous filaments extending chordally and others radially. The layers of segments are connected by a needling head. As the preform (as it is known before it is heated and carbonised) is built up, a foam base is lowered inside a metal cylinder which surrounds the outer circumference of the preform. During initial needling the needles penetrate the foam base. After a time the needles no longer penetrate the descending foam base. However lowering, adding segments and needling continue. After the finished preform, of perhaps 120 mm in depth, has been built up it is removed together with the foam base, which base is then cut off.

Preforms are put in an autoclave and heated to perhaps 1400 to 2000° to carbonise and harden the product. During the heating, natural gas with carbon particles is present in the autoclave, which is under a reduded pressure. The carbon particles enter the voids in the preform to fill the voids to thereby densify the structure. The voids in the top and bottom surfaces soon become clogged with carbon particles. Thus the preform has to be removed from the oven and cooled. Then the top and bottom of the disc are machined to remove the clogged region. Then the densification process is repeated, perhaps two or three times .

The densification process with the repeated skimming of the top and bottom surfaces is wasteful of material and necessitates extra preform building time as the preform has to be built higher than required for the subsequent reduction in height. In addition manufacturing time is increased.

The densification process is inefficient and most of the carbon particles are lost with perhaps 5 - 7% of the particles entering preforms to densify them.

It is an object of the present invention to attempt to overcome at least one of the above or other disadvantages.

According to one aspect of the present invention a method of manufacturing a shaped fibrous structure from fibrous material to form a stack of fibrous material comprises causing relative movement of a support and while the stack is being built and at least one feed of fibrous material adding fibrous material to build the stack, the stack being built in the axial direction of the relative rotational movement, the method comprising causing layers of the feed to overlap each other and interconnecting overlapping layers.

The present invention is at least partly defined in the claims appended hereto.

The feed may move relative to the stack to and fro in a direction transverse to the circumferential direction over the stack. Successive such movements may always include the outer region of the stack and the inner movements of the to and fro movements may vary in distance from an inner region of the stack. Successive to and fro movements may periodically miss an outer region of the stack or successive movements may be different in their extent at different radial extents of the stack or may- increase as the distance from the centre of the stack increases. The feed may move in a direction transverse to the circumferential direction as the feed moves to and fro in a direction transverse to the radial direction.

The stack may be cylindrical and may comprise a hollow cylinder.

The present invention also includes a shaped fibrous structure having an axial and a radial extent, the structure including a plurality of overlapping layers comprising continuous fibre extending circumferentially and continuous fibre extending radially.

The present invention also includes a shaped fibrous structure including continuous fibre extending circumferentially and continuous fibre extending radially throughout the complete axial extent of the structure.

According to another aspect of the present invention a method of forming a plurality of shaped fibrous structures comprises building a stack from fibrous material with the stack having an axial and a radial extent and subsequently dividing the stack across the axial extent to form a plurality of structures from the stack.

The present invention also includes causing a shaped fibrous structure to harden prior to division.

According to a further aspect of the present invention, a shaped fibrous structure has an axial length to the outside diameter ratio greater than 2:3 or 1:1 or 2:1 or 3:1 or 4:1.

The present invention also includes a shaped fibrous structure that has been made by a method as anywhere herein referred to.

According to another aspect of the present invention a method of densifying a shaped fibrous disc including carbonisable fibres comprises causing gas and carbon particles to flow from the inner diameter of the disc, through the disc and out through the outer diameter with at least some of the carbon particles remaining in the disc.

The flow may be in the plane of layers that the structure has been built up in.

The present invention also includes a disc that has been densified by a method as herein referred to.

The present specification includes various different statements of invention and independent claims. Any of these may be combined in any combination whatsoever and any of the dependent features or claims could be made dependent upon any such combined independent claims.

In the specification and in the claims reference is made to a stack. The stack could be one that is about to be built, a partially completed stack - that is the stack may not necessarily have had all of the layers added to the stack - and also a complete stack. Also, where the movement of the stack is referred to, for instance relative to needling, it is the already formed partially completed stack that is moved, such as the bottom of the stack, such that material can continue to be added, such as to the top.

Reference is also made to a feed of material. There may be at least two feeds . For ease of reference at a later date these may be referred to a first feed and a second feed which may feed material in direction transverse to each other such as a generally radial direction and a generally circumferential direction, which may be radial and circumferential.

The present invention can be carried into practice in various ways but one embodiment will now be described with reference to and as shown in the accompanying drawings, in which: -

Figure 1 is a schematic perspective view of a first embodiment of a preform building machine 10;

Figure 2 is a schematic perspective view of a second embodiment of a preform building machine 110;

Figure 3 is a side view of a stack 12 of fibres made from either of the machines 10 or 110, and

Figure 4 is a perspective view of a container 14 for the stack 12.

The machine 10 that is used to form the preform comprises an elongate steel drum 16. A hollow cylinder of foam 18 lies against the inwardly facing surface of the drum and a cylinder of foam 20 is spaced centrally within the drum. The foam cylinder 18 and, alternatively or additionally, the foam cylinder 20 may extend the full depth of the drum 16 or may rest on or be secured to supports provided by the drum such as a central pedestal extending from the base of the drum for the cylinder 20 or a radial flange extending inwardly from the interior of the drum surface for the hollow cylinder 18.

A movable base 19 shown in Figure 2 is located in the space between the foam cylinders which is able to move down, during manufacture, either continuously or stepwise. The base is disc shaped and supports a layer of foam 22 which travels down with the base. The movement of the base and the function of the foam on the base is as described in WO 95/05502 (P. G. Lawton) the contents of which are hereby incorporated.

When building of a stack is started, fibre is deposited on the foam 22 with the base rotating and with a needle head 23 reciprocating so that the needles drive some of the fibres into the foam. There may be one or more revolutions of the base without lowering of the base or the base may start to lower from the initial needling. Fibre may be added continously initially or may be added for one revolution, for instance, and then stopped whilst needling starts or continues for a further revolution, for instance, before fibre is added again. Fibre may be added from a first, circumferential feed 24 or from a radial feed 26 or both either simultaneously or at separate times. Preferably though the fibre is added simultaneously from both feeds 24 and 26 and preferably whilst needling simultaneously occurs. One or more layers from either or both feeds may take place before needling starts, if desired.

As the fibre is added and the base descends it will be appreciated that, at least in the initial needling stages, the needles will penetrate the foam 22 on the base. There will come a time though when the base will have descended a sufficient distance for the needles to be clear of the foam on the base. During that movement between initial needling and foam penetration to the time when the needles are clear of the foam approximately 8 to 10 layers of fibres comprising 4 or 5 layers from the feed 24 and 4 or 5 layers from the feed 26 may have been added. It will be appreciated though that the needles may penetrate the foam for less revolutions or numbers of layers and may only penetrate the foam on the base for 1 or 2 or 3 rotations, for instance.

The needles may, at least during early needling, such as when the needles penetrate the foam on the base, be reciprocated through less distance than when the needles no longer penetrate the base. For instance, the needles may initially be reciprocated through 10mm for the first or first few revolutions with the needles subsequently being reciprocated through 14 mm. The extent of the reciprocation may be increased in a single step from one depth to another, such as from 10 mm to 14 mm.

Alternatively there may be a plurality of step changes such as from 10 mm to 11 mm to 12 mm to 13 mm to 14 mm or from 10mm to 11 mm to 14 mm. Alternatively or additionally the needling reciprocation increase may be continuous for at least some of the change in reciprocal movement and possibly for all of the reciprocal change in movement .

Needling continues with the stack having layers added to it until the desired depth of the complete stack has been reached. That depth may comprise the full operation depth or may comprise a preselected depth less than the maximum operational possible depth of the machine.

The circumferential feed 24 includes a series of openings 28 that extend in a line, radially with respect to the rotational axis of the base. Eight openings 24 are shown. There may be any number though such as twelve openings . Tows 30 of continuous fibre are feed through each of the openings 28 to lay continuous fibre onto the foam base or onto a previously laid layer.

The substantially radial feed 26 comprises a tow 32 of continuous fibres that are fed through a tube 34 which is reciprocated in a radial direction about a pivot 36 located above the base midway between the inside and outside diameter of the base. In this way, when the tube 34 is reciprocated continuous fibres are laid in a radial direction.

Preferably the tows 30 and 32 comprise continuous fibre only. However, either or both of the tows may include staple fibre or staple fibre may be added separately, for instance at a different circumferential location.

The tows of continuous fibre may comprise continuous tows that have been subject to a degree of needling to assist in their handling, for instance, or separate continuous filaments. The tows may comprise or include crimped or uncrimped fibre, or instead the fibre that is fed may comprise or include rovings or slivers or braids or any combination thereof.

The fibre may comprise carbonisable fibres such as carbon fibres or may comprise a non-carbonisable fibre or carbonised fibre such as PANNOX. One such fibre is sold by SGL Carbon Ltd under the registered trade mark SIGRAFIL under code C30T50. Each tow of continuous fibre 30 or 32 may include 3OK to 70K fibres, for instance and preferably 5OK. The tows may be fed under an air velocity directed at the tow or under gravity or both. Each tow of 5OK may weigh 4,5g/m. The rate of feed may be 2.5 to βm/min. The rate of rotation of the drum is preferably 0.4m/min at the outside diameter of fibre feed which is 535 mm from the centre of rotation.

It can be seen that if the circumferential tows 30 are added at the same rate then the inner region on the base would have a greater density than the outer region. Consequently the tows at an outer region can be fed at a greater rate than the tows at the inner region or, alternatively or additionally the outer tows may include more fibres than the inner tows. The greater number of the fibres or the increase in speed may take place from the inner opening 28, radially outwardly from each adjacent opening 28. The needles attach each tow to the foam base or to a lower layer that has already been needled. Thus the tows may be pulled through the openings 28 as a result of the preattachment . Consequently the outer tow will move at an increased speed as a result of the arc that the outer attached tow is caused to move through compared to an inner arc for a given degree of rotation.

The same factor applies to the radial feed 26. Given a constant tow 32 rate of feed and a constant rate of reciprocal pivotal movement of the feed 26 about the pivot

36 and a constant rate of rotation of the base then the outer radial region may have a lower density of fibres than the inner radial region. However by varying any of those factors or any combination of those factors or other factors then the density disparity can be compensated for, at least partially.

For instance, the rate of rotation of the base could be greater when tow is being dispensed at an inner radial region than at an outer region or the rate of feed of tow could be greater at an outer radial regional than the inner radial region or the feed could rotate about the pivot 36 at a slower rate when depositing tow at an outer region than that rate of rotation when depositing tow at an inner region or any combination thereof.

Alternatively or additionally, the radial feed 26 could be reciprocated from the outermost radial position partly towards the innermost radial position and then out again before moving back towards the radially innermost position. Indeed there may be several partial inwards movements getting successively nearer to the innermost position before the innermost position is reached as shown by the inner turning points 34A, 34B, 34C and 34D. Successive inner or to and fro turning points may be of the same measurement from each other (that is the distance between 34A and 34B may be the same distance as that between 34B and 34C or may decrease going inwards or may increase going inwards.

In an alternative embodiment (not shown) there may be more than one radial feed. One or more radial feeds may be arranged to cover only part of the radial extent of the stack.

Thus the stack, as it is being built up, may not tend to have a greater thickness of an inner or outer region than at another region and the stack has a generally planar upper surface. Alternatively the radial feed could comprise the tube 34 or 128 reciprocating each time between the inside and outside of the preform without stopping short or without a variation in the speed of feed or fibre of speed of rotation. This would appear to add significantly more fibre to the inside of the preform.

However, in practice such additional fibre at the inner region has not been found to cause any detrimental effect to the preform.

The needle head 23 may be in an arc shape, as shown, or may have the density of needles increasing towards an outer region of the head or may effect a greater needling action at an outer region such that the needling effect is substantially the same at each location of the stack. Good results have been achieved using approximately 250 needles, pitched at approximately lcm and oscillating at a rate of around 580rpm.

The needling action will tend to move each or some tows 30 radially inwards to a small extent. That is thought to be because the outlet of the openings and the first series of circumferential needles can not be on the same radius. Consequently there will be a tendency for the distance between the outlets of the openings and the needles to decrease to a direct line thereby pulling the tow inwards to be a tangent. Thus the rate or amount of circumferential tow may be adjusted to attempt to compensate for this such as by making an adjustment to increase the tow being added in a radially outwards direction of the circumferential feed 28.

The needling takes place over the entire radial extent of the disc. In addition the needles penetrate the foam 18 and 20. Thus the needling of the stack as it is being built up and at the completion of the stack at the inner and outer edges may be homogenous. Upon completion of the stack the foam 32 may be cut from the base and the foam 18 and 20 may be cut from the upper inner and outer sides of the base. Alternatively or additionally at least some of the attached foam may be burnt off in a subsequent step in the manufacturing process.

Figure 2 shows an alternative way of adding the circumferentially orientated fibre 130. All other parts of the machine and the operation thereof are as previously described.

The fibre is added from a reciprocating tube 128 that has its pivot mounting 140 located above the stack at a position between the inner and outer radius of the stack and preferably mid way between those two radii.

The tube reciprocates, preferably whilst the stack is rotating to add the fibre between the radial lines 142. Thus more fibre is added towards the outside of the stack than towards the inside to compensate for the greater distance moved at the outside during a rotation of the disc than at the inside. The rate of pivotal movement of the tube 128 or the rate of needle of the fibre through the tube may be varied, if desired, to vary the deposition rate of the fibre at different radial positions such as, for example, to add more fibre at an outer region than at an inner region. As the tube moves to and fro between the radii 142 the tube also moves radially outwards and then radially inwards.

Whilst the feed from the tube 128, and or the tube 34 may cover the stack from the inside to the outside on each rotation of the stack it is also possible for the tube to only cover part of the radial extent. Furthermore, it is possible for the needling not to be continuous and to act only periodically such as every alternate revolution or every third revolution, for instance, throughout the rotation and build up of the stack. Such alternate revolution or periodic revolution as used in this embodiment may also be used in the first embodiment.

The addition of the radially orientated foam and the needling or the remainder of the process or the various possibilities for adding fibre may be as previously described or as previously described in relation to the possible modifications.

The fibre is blown through the radial feed 26 and 128 by air. This air tends to blow the fibres apart from each other as they exit the radial feed. Thus, although the tow passes through the tube in a fairly small diameter of, for instance, 4 ram in average cross sectional direction when the tow exits the tube and is deposited on the perform, the fibres in the tow are blown out to have, for instance, a dimension over the surface of the stack of 15 mm to 20 mm. Advantageously, this spreading of the fibres may assist in the even build-up of the stack, as opposed to having tight bundles of fibres located over the stack with the possibility that one region may have a greater concentration of fibres than another such as may occur if tight tows are laid.

In addition, it can be of advantage to lay the generally radial fibres in a figure of "8" pattern. This pattern is very much an elongated such pattern with the majority of fibres extending mostly if not completely in the radial direction. The pattern can be effected by the fibre overlapping at at least one of the inner or outer changes of direction of supply of fibre. Thus a return sweep of the fibre may initially turn over itself and at least partially overlap a portion of fibre that was laid previously, just before the return sweep was made. In order to achieve the pattern, the rate at which the reciprocating tube traverses to and fro needs to be controlled relative to the rate of revolution of the base. For example a ratio of the tube reciprocating to and fro around 60 times per revolution of the base may be used.

During the build up of the stack it may be desirable to have a compressive radial force imparted into the stack. This will be caused, or result in forces tending to push the inner and outer retaining walls away from each other. This may result in the uppermost layer of the stack or finished stack (be the finished stack a single perform or be the stack long enough to be cut into a plurality of performs) having a slightly domed appearance, as shown in Figure 2 by the dashed line 150.

Figure 3 shows the finished stack 12, once it has been removed from the machine. The removal may be effected by raising the platform carrying the foam base that descends as the stack is being added to and is being built up (in which case the fibre feeds and needle be may be moved clear from the top of the machine) , or may be effected by lowering the stack out through the bottom of the drum 16.

In the prior art, discs made by each machine are removed one by one. In the present embodiment the stack 12 may be a single perform or disc or may be longer in the axial extent of the disc than the thickness of a preform for subsequent manufacture into a single disc and may be longer by a multiple of individual preform and lengths and may be more than 2, or 4 or 6 or 8 or 10 or 12 times the thickness of an individual preform for subsequent manufacture into a disc or less than 20 or 18 or 16 or 14 times such a thickness. Consequently the manufacturing time is reduced. The disc may have an axial length of a multiple of any individual preform to be made into a disc which may have an axial length of 120 mm. Thus the disc may have an axial length of 1200 mm. The ratio of the axial length to the outside diameter may be greater than 2:3 or 1:1 or 2:1 or 3:1 or 4:1

When the disc is made of carbonised or precarbonised fibre, the disc may be located in an autoclave to effect the hardening of the fibres. Either before or after such treatment the individual discs may be cut off the stack about planes parallel to the perpendicular to the axial extent, as shown by the lines 44 in Figure 3.

If the stack is made from carbonisable fibres then the stack can be placed in the container 14 shown in Figure 4. The container 14 includes a solid bottom wall 46 and perforations 48 in the cylindrical wall. The top is closed by a removable cover 50 having an inlet 52 in the centre. During densification natural gas in an autoclave that contain carbon particles is drawn through the inlet 52 and then out through the stack from the internal diameter to the external diameter. This causes the carbon particles to enter and fill voids within the stack. Thus the whole stack can be densified prior to the discs being cut from the stack.

Any of the fibre described as being added in this specification may be added whilst the stack is rotating or, alternatively, without the stack rotating or both.

Before densification, whether the performs are built one at a time or cut from a stack to create different performs, the fibres may fill 20% or less of the value of the perform.

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.

Claims

1. A method of manufacturing a shaped fibrous structure from fibrous material to form a stack of fibrous material comprising:

- causing relative rotational movement of a support on which the stack is being built and at least one feed of fibrous material adding fibrous material to build the stack, the stack being built in the axial direction of the relative rotational movement, causing layers of the feed to overlap each other as a result of the relative rotational movement and interconnecting overlapping layers .

2. A method as claimed in Claim 1 in which a plurality of overlapping layers have been supplied from the feed without interruption of the feed.

3. A method as claimed in Claim 1 or 2 comprising adding fibrous material from the feed whereby a greater amount of fibre is added at an outer region than at an inner region.

4. A method as claimed in Claim 3 in which the amount of added fibre increases from the inner region to an intermediate region and the amount of added material increases from an intermediate region to an outer region.

5. A method as claimed in Claim 3 or 4 in which the feed deposits more fibrous material at the outer region than at the inner region.

6. A method as claimed in Claim 5 in which the rate of feed is increased when the feed deposits material at the outer region as compared to the rate of feed when the feed deposits material at the inner region of the stack.

7. A method as claimed in Claim 5 or 6 in which the feed spends more time depositing feed at the outer region than at the inner region.

8. A method as claimed in any preceding Claim in which the feed moves relative to the stack to and fro in a direction transverse to the circumferential direction over the stack.

9. A method as claimed in Claim 8 in which the to and fro movements of the feed deposits material to an innermost and outermost region of the stack at each to and fro movement .

10. A method as claimed in Claim 9 in which the rate of deposition of fibre is constant during each to and fro movement.

11. A method as claimed in Claim 8 when dependent on any of Claims 5 to 7 in which successive to and fro movements periodically miss the innermost region of the stack.

12. A method as claimed in any of Claims 5 to 11 in which the feed pivots relative to the stack at a location spaced from the axially facing surface of the stack whereby the feed is deposited over different regions of the stack.

13. A method as claimed in Claim 12 in which the feed pivots relative to the stack about an axis parallel with the axially facing surface of the stack.

14. A method as claimed in any preceding claim in which the feed adds material to the stack in a direction that extends at least partly and preferably substantially or completely in a radial direction.

15. A method as claimed in any of Claims 8 to 14 in which a plurality of feeds move relative to the stack to and fro in a direction transverse to the circumferential direction over the stack.

16. A method as claimed in any of Claims 8 to 15 in which the feed is caused to overlap itself during at least some successive to and fro movements.

17. A method as claimed in any of Claims 8 to 16 in which fibres of the fibrous material in the feed are dispersed from each other as the material is added to the stack.

18. A method as claimed in Claim 17 in which the fibres are dispersed from each other by being blown apart from each other.

19. A method as claimed in any preceding claim in which the feed adds material to the stack in a direction that extends at least partly and preferably substantially or completely in the circumferential direction.

20. A method as claimed in Claim 19 comprising adding material from a plurality of feeds of fibrous material adjacent to each other in a radial extent.

21. A method as claimed in Claim 19 comprising supplying more material from a radially outer feed than from a radially inner feed.

22. A method as claimed in Claim 21 comprising supplying material faster from the radially outer feed than from the radially inner feed.

23. A method as claimed in Claim 21 or 22 comprising supplying a greater bulk of material from the radially outer feed than from the radially inner feed.

24. A method as claimed in any of Claims 18 to 22 comprising adding material to the stack to at least partially compensate for radially inwards movement of the material occurring as a result of interconnecting overlapping layers .

25. A method as claimed in claim 24 comprising determining the compensation required and adding additional material at at least one location spaced from the innermost location when material is fed.

26. A method as claimed in any of Claims 19 to 25 comprising adding material to the stack adjacent to where the layers are interconnected.

27. A method as claimed in any preceding Claim comprising causing radial compression of the fibres as the stack is being built.

28. A method as claimed in Claim 27 comprising causing the axially facing upper surface of the stack to be deformed from a planer surface as a result of that compression.

29. A method as disclosed in Claim 28 comprising causing an intermediate radial extent of the axially facing upper surface to extend higher than at least one of the radially inner or outer extents.

30. A method as claimed in any preceding claim comprising interconnecting overlapping layers by needling the overlapping layers .

31. A method as claimed in Claim 30 comprising, during the connection of what will be lower layers of the stack, varying the extent of reciprocal movement of needles to effect the needling such that the extent of reciprocation increases as layers are added.

32. A method as claimed in Claim 31 comprising varying the extent in at least one step.

33. A method as claimed in Claim 31 or 32 comprising varying the extent continually during at least part of the increase in the extent.

34. A method as claimed in any of Claims 31 to 33 comprising needling with sacrificed material during the early stages of the build of the stack with the extent of the reciprocal movement being greater when the needles no longer penetrate the stack as a result of the number of layers that have been added.

35. A method as claimed in any of Claims 30 to 34 comprising needling occurring beyond at least one side of the stack.

36. A method as claimed in Claim 35 in which fibrous material that has been added at the side of the stack is needled into a sacrificial material adjacent to a radial side of the stack.

37. A method as claimed in any preceding claim in which the stack comprises a disc having an opening including the axial centre of the disc.

38. A method as claimed in Claims 34 and 35 or 36 in which the needling occurs beyond a radially inner side of the stack.

39. A method as claimed in any of Claims 35 to 38 in which needling occurs beyond a radially outer side of the stack.

40. A method as claimed in any of Claims 30 to 39 in which relative movement of the location where needling occurs and the initially interconnected overlapping layers in the axial extent of the stack occurs as the stack is being built up.

41. A method as claimed in any of Claims 30 to 40 comprising needling during at least one selective rotation and ceasing needling during at least one rotation.

42. A method as claimed in Claim 41 including repeatedly needling and ceasing needling during the complete build up of the stack.

43. A method as claimed in Claim 36 or any claim when dependent on Claim 36 in which relative axial movement of the sacrificial material and the support occurs as the stack is being built up.

44. A method as claimed in any preceding claim comprising causing the structure to harden after the stack has been formed.

45. A method as claimed in any preceding claim comprising dividing the stack in a direction across the axial extent of the stack in order to provide a plurality of shaped fibrous structures.

46. A method as claimed in Claim 45 comprising dividing the structure after the structure has hardened.

47. A method as claimed in any preceding claim comprising adding fibrous material at the same time that relative movement of the stack and the feed occurs about the axial extent of the stack.

48. A method as claimed in Claim 47 comprising adding fibrous material to the stack without relative movement about the axial extent of the stack occurring.

49. A method as claimed in any preceding claim comprising the feed covering only a partial radial extent of the stack during one relative rotation of the stack.

50. A method as claimed in any preceding claim comprising adding continuous fibre.

51. A method as claimed in Claim 50 comprising adding continuous fibre in both the radial and the circumferential direction.

52. A method as claimed in Claim 50 or 51 comprising adding only continuous fibre.

53. A method as claimed in any preceding claim comprising continuously feeding material to the stack from the feed when the first material is fed to when the last of the material is fed to the stack.

54. A shaped fibrous structure including an axial extent and layers that extend in a generally radial direction and that are interconnected in the axial direction.

55. A structure as claimed in Claim 54 in which the layers include continuous fibres extending circumferentially at each radial extent of the structure.

56. A structure as claimed in Claim 54 or 55 including continuous fibre extending in a generally radial direction at each circumferential extent of the structure.

57. A structure as claimed in any of Claims 55 to 56 when made by a method as claimed in any of Claims 1 to 54.