GB2478768A

GB2478768A - Wrapped woven fibrous structure with seamless woven tube sheath

Info

Publication number: GB2478768A
Application number: GB1004476A
Authority: GB
Inventors: Neil Saville; John Lynn Payne
Original assignee: Marathon Belting Ltd
Current assignee: Marathon Belting Ltd
Priority date: 2010-03-18
Filing date: 2010-03-18
Publication date: 2011-09-21
Anticipated expiration: 2030-03-18
Also published as: GB201004476D0; GB2478768B

Abstract

A fibrous structure comprises a tube with a plurality of layers of woven material wrapped around one another. The layers include an outer layer 3 comprising a sheath in the form of a seamless woven tube. An innermost layer 2 and an intermediate layer 4 may comprise seamless woven tubes with integral flaps (35, Figure 6a) which may be wound around the tube to form part of the intermediate layers. A web of woven material forming part of the intermediate layers may be tucked between the web and its integrally woven tube. Interengaging wells and ribs may be woven into the tubes and flaps to grip and stop the intermediate layers slipping over one another. The woven tubes may be formed from a multi-ply woven web which can be opened out to form the tube. The innermost layer and intermediate layers may comprise a rolled-up piece of woven material. Braided carbon or pre-cursor carbon yarn may be used. The structure is intended as a preform for friction products such as discs in brake mechanisms and hollow structures such as cones and nozzles for projectiles or aircraft. The structure may be formed on an inflatable former.

Description

A FIBROUS STRUCTURE AND

A METHOD OF MANUFACTURING SAME

The present invention relates to a fibrous structure and to a method of manufacturing such a fibrous structure. The invention is particularly, though not exclusively, applicable to the manufacture of preforms that are used to produce friction products such as discs for use in brake mechanisms, and to hollow structures such as cones, nozzles and the like for projectiles and aircraft.

Use of the term preform' indicates that fibrous structures in accordance with the present invention are heated in an autoclave in a methane or acetylene atmosphere at an appropriate temperature for an appropriate period of time in order to produce a hardened carbonaceous structure. Suitable carbonizable fibres for use in the manufacture of such a structure are well known to those in the art and are, for example, sold under the registered trade mark PANOX®. These fibres comprise oxidized polyacrylonitrile fibers or precursors of polyacrylonitrile fibers of various types. They are converted to carbon fibres by the heat treatment and produce carbon particles which enter and fill voids in the preform to densify the structure. Such fibres may be produced in a yarn form and comprise a large number of flexible filaments, for example between 3,000 and 25,000 filaments, in order that the preform can be manufactured using textile techniques, which in the present invention is weaving.

Conventional performs are manufactured in various ways. EP 0 748 781 (B.F. Goodrich) describes a method of making a preform wherein braided tapes are spirally wound and connected together by needle punching. WO 98/49382 (B. F. Goodrich) describes a method wherein a mass of loose fibre is accreted into a thick fibrous structure by repeatedly driving a multitude of felting needles into the loose fibre, the felting needles penetrating all the way through the fibrous material at the beginning of the process, and penetrating only part way through the fibrous material at the end of the process. EP 0 232 059 (P. G. Lawton Limited) describes a method of manufacturing a preform wherein a disc is built by adding segments, one by one, in a spiral, layer upon layer, these layers being connected by needling. GB 2 428 253 (P. G. Lawon (Industrial Services) Limited) describes a method of manufacturing a stack of fibrous material that is built up in the direction of the longitudinal axis of the stack by causing relative movement of a support for the stack and at least one feed of fibrous material adding fibrous material to build the stack. The stack is therefore built up in overlying layers which are connected by needling.

It will be appreciated that all of these fibrous structures invo've the needle-punching or felting to produce the fibrous structure. This means that the structure, in general, is comprised of a loose accretion of fibres, segments or tapes that are only held together by needle-punched fibres, which generally do not extend through all the layers of the structure. This can result in a stack or disc that has a propensity to fail owing to delamination. It can also be difficult to produce such structures with an homogeneous, optimum fibre fraction, which is a measure of the density of the structure. The fibre fraction is important as it affects the success of the carbonizing process. A homogeneous carbon fibre fraction of between 15% and 20% for the structure is the most preferable.

The object of the present invention is to provide a fibrous structure of the type under discussion and a method of manufacturing such a structure wherein the fibres of the structure are retained within the structure other than by needle punching and which is easier and more economical to produce than a needle-punched structure.

It is a further object of the present invention to provide method of manufacturing a fibrous structure of the type under discussion that can more readily be produced with a homogeneous, optimum fibre fraction than

prior art methods.

According to a first aspect of the present invention there is provided a fibrous structure comprising a tube made up of a plurality of layers of woven material wrapped around one another and defining at least an innermost layer and an outer layer, the outer layer comprising a sheath in the form of a seamless woven tube.

Preferably, the outer layer is formed from a multi-ply woven web which by virtue of the weave pattern can be opened out to form a tube. The cross-sectional profile of such a tube can be of any shape and the tube may taper along its length.

Preferably also, the innermost layer and one or more intermediate layers comprise a single rolled-up piece of woven material.

Alternatively, an innermost layer of the structure also comprises an seamless woven tube.

Preferably also, the structure comprises at least one intermediate layer of woven material. Advantageously, this intermediate layer also comprises a seamless woven tube.

Preferably also, the innermost layer and/or at least one intermediate layer comprises a seamless woven tube with an integrally woven flap that extends longitudinally along the length of the tube, the flap being wound around the tube and forming one or more of or part of one of the intermediate layers of the structure.

Preferably also, at least one intermediate layer of the structure comprises a web of material that is tucked, at least in part, between the flap and its integrally woven tube.

Preferably also, the flap and its integrally woven tube comprise a plurality of integrally woven ribs and wells that interengage with one another.

Alternatively or in addition, one or more layers of the structure comprise a honeycomb weave.

Preferably also, the structure is woven from braided carbon yarn and/or braided pre-cursor carbon yarn.

Preferably also, the structure is woven from carbon yarn or pre-cursor carbon yarn in conjunction with yarns made of any or a mixture of polyether ether ketone (PEEK), polyphenylene sulphide (PPS), polyester, nylon 6-6 and nylon 6.

According to a second aspect of the present invention there is provided a method of manufacturing a fibrous structure comprising providing a former; locating a first woven web around the former to form an innermost layer of the structure; providing a seamless woven tube with an inner diameter comparable to the outer diameter of the structure on the former; locating the tube over the structure on the former to form its outer layer; and removing the former to leave a free-standing fibrous structure.

Preferably, the first woven web is rolled around the former to form the innermost layer and one or more intermediate layers.

Alternatively, the method comprises the additional step of providing a seamless woven tube with an inner diameter comparable to the outer diameter of the former and using it as the innermost layer of the structure.

Preferably also, the method comprises the additional step of wrapping at least one intermediate layer of woven material around the innermost layer before locating the outer layer over the top of the intermediate layer or layers.

Preferably also, the former is mounted on a shaft and the method comprises the additional steps of rotating the shaft as each intermediate layer is wound around the former to tension the material forming the intermediate layer so that it conforms to the profile of the underlying layer.

Preferably also, the former is expandable and collapsible to facilitate the location of any layer that comprises a seamless woven tube around the former and any underlying portion of the structure and to facilitate removal of the former from the completed fibrous structure. Advantageously, the former is adapted to be inflatable and deflatable.

Preferably also, the method comprises the additional steps of providing a seamless woven tube with an integrally woven flap that extends longitudinally along the length of the tube, using the tube as the innermost layer and/or an intermediate layer of the structure and winding the flap around the exterior of the tube.

Preferably also, the method comprises the additional step of providing a web of material; tucking at least part of it between the flap and its integrally woven tube, and wrapping it around the former to form at least one intermediate layer of the structure.

Preferably also, the method comprises the step of weaving the seamless woven tube and integrally woven flap such that the longitudinal direction of the tube is parallel to the warp direction of the weave.

Alternatively, the method comprises the step of weaving the seamless woven tube and integrally woven flap such that the longitudinal direction of the tube is parallel to the weft direction of the weave. Advantageously, in this case the method comprises the steps of weaving a plurality of conjoined tubes and flaps, separating each of the woven tubes and integrally woven flaps from the others and using them to form the innermost and/or intermediate layers of the structure.

Preferably also, the tubes are woven such that their inner diameters are different so that they can be located one within another around the former.

According to a third aspect of the present invention there is provided a fibrous structure manufactured in accordance with the method of the second aspect of the present invention.

Other preferred but non-essential features of the various aspects of the present invention are described in the dependent claims appended hereto.

The various aspects of the present invention will now be described by way of example with reference to the accompanying drawings, in which:-Fig. 1 is a perspective view of a first embodiment of fibrous structure according to the first aspect of the present invention; Fig. 2 is a view similar to Fig. 1 but of a second embodiment of fibrous structure; Fig. 3 is a view similar to Figs 1 and 2 but of a third embodiment of fibrous structure; Fig. 4 is a perspective view of a piece of woven material woven in such a way that it is adapted to form the innermost or an intermediate layer of a fibrous structure, such as that shown in Fig. 3, according to the first aspect of the present invention; Fig. 5 is a view similar to Fig. 4 but of a piece of material woven in a different way and adapted to form a plurality of layers of the fibrous structure; and Figs. 6a to 6e show sequentially steps in the manufacture in accordance with the second aspect of the present invention of a fourth embodiment of fibrous structure as shown when completed in Fig. 6e.

In order to produce a carbon fibre-reinforced carbon structure or a silicon carbide structure that can be used to produce brake discs and the like, a fibrous structure in accordance with the invention is made of carbon yarn or pre-cursor carbon yarn. To produce a carbon resin structure, the fibrous structure of the invention may be made of carbon yarn in conjunction with yarns made of any or a mixture of polyether ether ketone (PEEK), polyphenylene sulphide (PPS), polyester, nylon 6-6 and nylon 6. Such combinations made be co-mingled, blended, twisted, braided or interwoven together. If pure carbon yarn is use, for example made from PANOX®, it is preferably used in a braided form. This has two advantages. First, it makes yarn easier to handle during weaving because PANOX® fibres are fine, brittle and slippery. Second braiding improves the product because it reduces the shedding of fibres from the fibrous structure during and after manufacture which improves its wear resistance.

Any of these yarns or others as appropriate for the ultimate use of the structure may be used to make fibrous structures in accordance with the invention. Various embodiments of such structures Will now be described.

All of them comprise a tube made up of a plurality of layers of woven material wrapped around one another, as is described below in more detail for each embodiment. All of these layers are woven in conventional fashion from yarns as described above that are suitable for the end purpose for which the structure is to be used. The fibre fraction required for the structure is achieved by a combination of appropriate choice of the yarns used together with the weave pattern and the number of picks and ends used per metre.

As shown in Fig. 1, a first embodiment of fibrous structure 1 according to the invention comprises an innermost layer 2 and an outer layer 3 which both comprise a sheath in the form of a seamless woven tube. As mentioned above, a seamless woven tube is a tube is formed from a multi-ply woven web that by virtue of the weave pattern can be opened out to form a tube. Such weave patterns are known to persons skilled in the art. Between the layers 2 and 3 are intermediate ayers 4 of materia' that are formed by a sing'e piece of woven material that is rolled-up around the layer 2 before being secured in position by location of the outer layer 3 over the top of it. The number of layers 4 equating to the number of turns in the roll together with the thickness of the material comprising the layers 4 determines the diameter of the finished structure 1 and the latter is chosen according to the structure's end purpose. Typically, the inner diameter of the tubular structure 1 is of the order of 70 to 80 mm but its outer diameter may be made between 250 mm 600 mm. The thickness of the material comprising the layers 4 is chosen dependent on the yarn and weave pattern used so that the material 4 can be tightly woven around the inner layer 2. If the material is too thick, then it becomes too difficult to roll satisfactorily, especially close to the inner layer 2 when the diameter of the layer 4 is small. Typically, therefore, the thickness of the material 4 comprising the layers will be between 2 mm and 6 mm. In order that the structure 1 is rigid and self-supporting, preferably the depth or thickness of inner layer 2 is made of the order of 6 mm. This means that the woven web produced to make the layer 2 must be of the order of 12 mm in thickness. However, the outer layer 3 only has to hold the intermediate layers 4 in place and is preferably significantly thinner in depth, for example of the order of 3 mm. Keeping the outer layer 3 relatively thin also facilitates its location over the top of the intermediate layers 4.

In a modification of the first embodiment, the innermost layer 2 is not made from a seamless woven tube but from a single piece of material that is rolled so that two opposite edges butt up to one another. The material is then secured in this position by a tie, for example a length of the same yarn as is being used to weave the layer 2, or a peg or staple made from a material such as wood that will burn away or carbonize when the structure 1 itself is carbonized.

In a different modification, the innermost layer 2 and the intermediate layers 4 are made from a single, rolled-up piece of woven material. In this case, to ensure the innermost layer remains in a tubular form, preferably its longitudinal edge running along the length of the inner diameter of the tube is secured to the intermediate layer 4 immediately overlying it by one or more pegs or staples as described above. In this modification, the inner circumference of the tube is stepped. Generally, this will not matter in the final carbonized structure as the inner diameter of the tube is usually machined away when the structure is fashioned into its final shape. However, it will be appreciated that in this case the inner diameter of the tube must be made an appropriate size to take this into account.

A second embodiment of structure 5 is shown in Fig. 2. This structure again comprises an innermost layer 6 and an outer layer 7 in the form of seamless woven tubes. However, in this embodiment each of the intermediate layers 8 also comprises a seamless woven tube. All of the tubes 6, 7 and 8 are woven with an inner diameter, when opened out, such that they can be assembled, as described below, as a series of concentric tubes over the top of one another to produce a structure as shown in Fig. 2. The thickness of the woven material used for each of the tubes 6, 7 and 8 can be as described above for the first embodiment.

Preferably, for both the first and second embodiments, the seamless woven tubes used for the structures 1 and are woven such that the warp direction of the weave pattern runs circumferentially around the tube, as -10 -indicated by the arrow 9 in Fig, 2. This means that the edges of the ends of the tubes can be made selvedge edges, which reduces fraying and shedding of fibres from the structures 1, 5. The width of the material woven to produce the tubes is therefore the same as the length of the tubular fibrous structure 1,5.

A third embodiment of structure 10 is shown in Fig. 3. This structure again comprises an innermost layer ii and an outer layer 12 in the form of seamless woven tubes. The intermediate layers 13 also comprise seamless woven tubes but they and the innermost layer ii also each comprise an integrally woven flap 14 that extends longitudinally along the length of the tube. Each flap 14 is wound around the underlying layers of the structure and forms one or pare of one of the intermediate layers 13.

A first embodiment of a woven piece of material i that will form one of the seamless woven tubes with an integrally woven flap is shown in Fig. 4.

The material i is a multi-ply material woven with the warp direction as indicated by the arrow i6 and with a selvedge at each side. One side 17 of the material 15 is woven so that two of the plies i8 of the fabric 15 can be separated to form a tube. The other side 19 of the material is woven so that the plies i8 are integrated by binder threads 20 so that they cannot be separated and so that they form the flap 14. It will be appreciated that in this embodiment the tubes making up the structure 10 can be made any length as the material i is simply cut to this length, as required. However, the diameter of the tube and the overall width of the material i will determine the length of the flap and therefore the degree to which the flap will roll around the layers underlying it when it is in position in the structure 10. If it is desired that the structure 10 have a large diameter, then flaps 14 of those intermediate layers 13 close to the outer layer 12 may not be sufficiently wide to wind around the whole of the circumference of the underlying intermediate layers 13. This problem can be overcome in two ways.

-11 -The first way of overcoming the problem is by using a second embodiment of tube and integral flap as will now be described with reference to Fig. 5. In this embodiment material 21 for the flap and integral flap woven with the weft direction as indicated by the arrow 22. In the warp direction, at right angles to the arrow 22, the material 21 is woven with a plurality of conjoined tubes and flaps by weaving a section 23 of material 21 wherein two plies 24 of the material are left separate to form a tube and then by weaving a section 25 of material 21 wherein the two plies 24 are integrated by binder threads 26 so that they cannot be separated and form the flap 14. These sections 23, 25 are woven alternately along the warp direction of the material 21 as it is woven. The finished material 21 can then be cut up to provide a plurality of tubes with integrally woven flaps. The width of the material 21 in the weft direction will determine the length of the tube comprising the structure 10.

It will be appreciated that in this case the lengths of the sections 23 will determine the diameter of the tube being produced and the lengths of the sections 25 will determine the length of the flaps 14. Hence, in this case, the lengths of the sections 23 and 25 can be woven successively longer, or shorter, when producing the material 21, in order to provide a series of tubes and integral flaps that will nest within one another when producing the structure 10.

In modification, the material can be produced with a first section 23 that will form the innermost layer ii of the structure 10, a long section 25 that will form a single long flap 14 and then a second section 23 of a sufficient length to form the outer layer 12 of the structure 10. This length of material is then cut to sever off the second section 23 to leave the first section 23 and conjoined section 25. In this case the section 25 can be woven long enough to provide a flap 14 that will can be wrapped several times around the innermost layer 11 to form all of the intermediate layers 13 of the structure 10.

-12 -The second way of overcoming the aforesaid problem is by manufacturing a fourth embodiment of structure 27 as shown in Fig. 6e. The manufacturing steps required to produce this structure 27 Will now be described by reference to Figs. 6a to 6d and to Fig. 6e itself.

The structure 27 shown in Fig. 6e comprises an innermost layer 28 and an outer layer 29 in the form of seamless woven tubes. Intermediate layers 30 also comprise seamless woven tubes but they and the innermost layer 28 also each comprise an integrally woven flap 14 as described above with reference to Figs. 3 and 4. However, in this embodiment the intermediate ayers 30 of the structure 27 a'so comprise separate webs 32a, 32b, 32 of material that are tucked, at least in part, between each flap and its integrally woven tube. The manufacture of such an arrangement will now be described in more detail.

As shown in Fig. 6a, the manufacture of the structure 27 commences with the location over a former 33 of an innermost layer 28 comprising a first tube 34 and integral flap 35. This tube 34 comprises the innermost layer 28 of the structure 27. Typically, the former 33 will be cylindrical With a circular cross-sectional proffle but it should be appreciated that it could be made With any cross-sectional profile that may vary along its length and that may taper long its length. If the profile is complex, then it is likely all the layers of structure 27 Will be made thin enough to enable them to closely follow the profile as they are built up on the former.

In order to facilitate the location of each tubular layer over the former 33 and over underlying layers, the former 33 may be mounted on a rotatable shaft 36 and made expandable and collapsible, for example by being inflatable and deflatable. In its deflated state it is possible to locate the first tube 34 around the former 33 with ease and without damage. Inflation of the former 33 to a predetermined cross-sectional size in conformity with the inner diameter of the tube 34 then holds the tube 34 rigid. The integral flap can then be wrapped tightly around the tube 34. However, as shown in -13 -Fig. 6b, in order to increase the number of intermediate layers in the structure 27, a first web 32 is located between the flap 35 and the tube 34.

The webs 32a, 32b and 32C are manufactured or cut so that they have the same dimensions as the length of the tube 34 but are made sufficiently long that they project beyond the edge of the flap under which they are tucked so that they can be wound further than the flap around the underlying structure. Location of the web between the flap and the tube anchors it in position along one edge and enables it to be tensioned as it is wound around the structure. Preferably, the shaft 36 is rotated as the flap and web are being wound to tension them and force them to conform to the profile of the underlying layer. The free edge of the flap and the web may be tied into the structure using a tie, peg or staple as described above.

As shown in Figs. 6c and 6d, additional intermediate layers 30 are built up over the top of the first tube 34, flap 35 and web 32a. Preferably these layers comprise a second tube 37 with integral flap 38 and a second web 32b. To facilitate the location of the second tube 37, the former 33 may be deflated slightly and once the tube 37 is in position inflated back to its previous state to enable the flap 38 and second web 32b to be tensioned.

Any number of additional intermediate layers can be built up. Fig. 6e shows a third tube 39, flap 40 and web 32C located over the top of the second tube 34. This is positioned in the same way. Finally, when the structure 37 has achieved the desired circumference, the outer layer 29 in the form of a seamless tube without a flap is positioned. Once this is in place, the former 33 can be deflated and the finished structure 37 removed therefrom.

In the finished structure it is preferably if the layers grip one another as this improves the integrity of the structure as a whole and ensures that the structure remains self-supporting. Gripping between the layers is influenced by the type of weave pattern used to produce the tubes and webs of the intermediate layers of the structure. In some embodiments, the woven tubes -14 -and integral flaps can be woven with a plurality of integrally woven ribs and wells located in series across or along the length of the material. These ribs and wells interengage when the structure is being built up and help to stop the intermediate layers from slipping or sliding over one another. Other weave patterns can also be used. For example a honeycomb weave provides a material than facilitates conformity to an underlying profile and this may be appropriate for use in some structures, particular ones when a former with a complex shape is used.

In addition to the foregoing, it is possible to weave material that is thicker at one side than the other and this can be used to produce tubes and flaps that vary significantly in thickness from one another. Similarly, it is possible to weave tubes that taper from one end to the other so that they fit over a tapering former. This is useful in the production of conical shapes such as may be required to produce a preform for a nose-cone or similar.

Fibrous structures according to the present invention have several advantages, as follows.

1. Their production is simple and minimises waste of yarn and material, which is important as the yarn may be expensive to produce.

2. They are well-defined structures so that there is little or no waste in the production of a preform as very little, if any, material has to be machined away from the preform structure after carbonization.

3. The use of braided yarn when weaving the material for the structure reduces the likelihood of fibre damage during weaving.

4. The use of woven materials to produce the structure assists in the achievement of precise fibre fractions, as required, in the preform.

Claims

-15 -Claims 1. A fibrous structure comprising a tube made up of a plurality of layers of woven material wrapped around one another and defining at least an innermost layer and an outer layer, the outer layer comprising a sheath in the form of a seamless woven tube.

2. A structure as claimed in Claim 1, wherein the outer layer is formed from a multi-ply woven web which by virtue of the weave pattern can be opened out to form a tube.

3. A structure as claimed in any one of Claims 1 and 2, wherein the innermost layer and one or more intermediate layers comprise a single rolled-up piece of woven material.

4. A structure as claimed in any one of Claims 1 and 2, wherein an innermost layer of the structure also comprises a seamless woven tube.

5. A structure as claimed in Claim 4, wherein comprising at least one intermediate layer of woven material.

6. A structure as claimed in Claim 5, wherein this intermediate layer also comprises a seamless woven tube.

A structure as claimed in any of Claims 4 to 6, wherein the innermost layer and/or at least one intermediate layer comprises a seamless woven tube with an integrally woven flap that extends longitudinally along the length of the tube, the flap being wound around the tube and forming one or more of or pare of one of the intermediate layers of the structure.

-16 - 8. A structure as claimed in Claim 7, wherein at least one intermediate layer of the structure comprises a web of material that is tucked, at least in part between the flap and its integrally woven tube.

9. A structure as claimed in Claim 7 or Claim 8, wherein the flap and its integrally woven tube comprise a plurality of integrally woven ribs and wells that interengage with one another.

10. A structure as claimed in any of Claims 1 to 9, wherein one or more layers of the structure comprise a honeycomb weave.ii. A structure as claimed in any of Claims 1 to 10, wherein the structure is woven from braided carbon yarn and/or braided pre-cursor carbon yarn.12. A structure as claimed in any of Claims 1 to 10, wherein the structure is woven from carbon yarn or pre-cursor carbon yarn in conjunction with yarns made of any or a mixture of polyether ether ketone (PEEK), polyphenylene sulphide (PPS), polyester, nylon 6-6 and nylon 6.13. A method of manufacturing a fibrous structure comprising providing a former; locating a first woven web around the former to form an innermost layer of the structure; providing a seamless woven tube with an inner diameter comparable to the outer diameter of the structure on the former; locating the tube over the structure on the former to form its outer layer; and removing the former to leave a free-standing fibrous structure.-17 - 14. A method as claimed in Claim 13, wherein the first woven web is rolled around the former to form the innermost layer and one or more intermediate layers.15. A method as claimed in Claim 13, comprising the additional step of providing a seamless woven tube with an inner diameter comparable to the outer diameter of the former and using it as the innermost layer of the structure.i6. A method as claimed in any of Claims 13 to 15, comprising the additional step of wrapping at least one intermediate layer of woven material around the innermost layer before locating the outer layer over the top of the intermediate layer or layers.17. A method as claimed in Claim i6, wherein the former is mounted on a shaft and the method comprises the additional steps of rotating the shaft as each intermediate layer is wound around the former to tension the material forming the intermediate layer so that it conforms to the profile of the underlying layer.i8. A method as claimed in any of Claims 13 to 17, wherein the former is expandable and collapsible to facilitate the location of any layer that comprises a seamless woven tube around the former and any underlying portion of the structure and to facilitate removal of the former from the completed fibrous structure.19. A method as claimed in Claim i8, wherein the former is adapted to be inflatable and deflatable.20. A method as claimed in any of Claims 13 to 20, comprising the additional steps of providing a seamless woven tube with an integrally woven flap that extends longitudinally along the length of the tube, -18 -using the tube as the innermost layer and/or an intermediate layer of the structure and winding the flap around the exterior of the tube.21. A method as claimed in Claim 20, comprising the additional step of providing a web of material; tucking at least part of it between the flap and its integrally woven tube, and wrapping it around the former to form at least one intermediate layer of the structure.22. A method as claimed in Claim 20 or Claim 21, comprising the step of weaving the seamless woven tube and integrally woven flap such that the ongitudina direction of the tube is paralle' to the warp direction of the weave.23. A method as claimed in Claim 20 or Claim 21, comprising the step of weaving the seamless woven tube and integrally woven flap such that the longitudinal direction of the tube is parallel to the weft direction of the weave.24. A method as claimed in Claim 23, comprising the steps of weaving a plurality of conjoined tubes and flaps, separating each of the woven tubes and integrally woven flaps from the others and using them to form the innermost and/or intermediate layers of the structure.25. A method as claimed in Claim 24, wherein the tubes are woven such that their inner diameters are different so that they can be located one within another around the former.26. A fibrous structure manufactured in accordance with the method as claimed in any of Claims 13 to 25.27. A fibrous structure substantially as described herein with reference to Fig. 1, Fig. 2, Figs 3 and 4, Figs. 3 and 5 or Fig. 6e of the accompanying drawings.-19 - 28. A method of manufacturing a fibrous structure substantiafly as described herein with reference to Fig. 1, Fig. 2, Figs 3 and 4, Figs. 3 and 5 or Figs. 6a to 6e of the accompanying drawings.