GB2230491A

GB2230491A - Homogeneously needled three dimensional structures of fibrous material

Info

Publication number: GB2230491A
Application number: GB9004904A
Authority: GB
Inventors: Michel Malfetes
Original assignee: Scapa Group Ltd
Current assignee: Scapa Group Ltd
Priority date: 1989-03-04
Filing date: 1990-03-05
Publication date: 1990-10-24
Also published as: GB9004904D0; DE4006717A1; JPH0351353A; GB8905006D0; FR2647475A1

Abstract

An intermediate textile fabric for use in the manufacture of a three dimensional reinforcement for composite materials capable of sustaining high thermomechanical forces, for example for use as brake pads and heat shields, is proposed, the fabric (11) comprising a coherent textile structure, preferably comprising warp and weft yarns (12, 13) woven together, the surfaces of the fabric being subjected to a textile raising operation to provide a nap (14). The three dimensional reinforcement is produced by the progressive needling of successively superimposed such fabrics. <IMAGE>

Description

MANUFACTURE OF HOMOGENEOUSLY NEEDLED THREE DIMENSIONAL STRUCTURE OF FIBROUS MATERIAL The invention concerns the production of highly uniform needled structures intended for use as reinforcement in forming high performance braking elements, rocket motor parts or other rigid heat resistant structures and has more particular reference to the provision of an intermediate textile element for use in the manufacture of such reinforcing structures.

Brake discs for use in the braking systems of high speed vehicles, for example racing cars and aircraft are subjected to particularly heavy braking loads and must be capable of reliably sustaining those loads. More particularly, the discs must be of such physical characteristics as to be able to endure the high stress forces met with in this context.

A particular method of producing threedimensional structures of fibrous materials for use as a reinforcement in composite materials is disclosed in U.S. Patent specification No. 4790052 and involves the individual needling together of successive layers of fibrous sheet material.

The degree of homogeneity demanded of the three-dimensional structure which is to form the reinforcement is such as to require that the needling operation whereby the individual layers are combined together be applied with constant effect as the successive layers are applied in the build up of the structure, U.S. Patent Specification No. 4790052 disclosing a particular method of achieving this end.

In the self-same way as uniformity in the manner of needling is of paramount importance in achieving the requisite degree of homogeneity in the threedimensional structure, so too is the utilisation of individual layers of fibrous sheet material which are closely similar one to another as to physical characteristics.

Conventionally, the individual layers which are combined to form the three-dimensional structure each include carded webs or lapped webs comprising continuous yarns or tows applied to a woven layer as by needling, and by their very nature the webs are lacking in uniformity. Accordingly, difficulty is experienced in achieving optimum homogeneity in the three-dimensional structure.

The object of the present invention is to provide an improved form of fibrous sheet material for use in the production of reinforcing structures as aforesaid.

Thus, in accordance with the present invention, the method of producing an intermediate textile element for use in the manufacture of an homogeneous reinforcing structure by the progressive needling together of superimposed such elements is characterised in that, in creat ing the intermediate textile element, a coherent structure is subjected to a raising operation at one face at least thereof. The coherent structure will preferably be of woven form, although such structure may comprise, for example, a needled fibrous mass which may, if preferred include a woven base cloth or be reinforced simply by spaced parallel yarns fed from a creel.

The invention also includes an intermediate textile element, for use as aforesaid comprising a textile structure, preferably constructed from multi-filament carbon or ceramic precursor yarns, having a raised surface at one face at least thereof.

The invention will now be described further, by way of example only, with reference to the accompanying diagrammatic drawings in which : Fig. 1 is a perspective view of the fabric of the invention a part only of the surface of which has been raised; Fig. 2 is a schematic representation of the build-up of a stack of fabric layers and the needling thereof to give a homogeneous structure; and Fig. 3 is a weave structure appropriate to the use of pure carbon yarns.

In one embodiment of the invention, see now Fig. 1, we propose a fabric 11, preferably a twill but for convenience not shown as such, wherein the warp yarns 12 and the weft yarns 13 each comprise multifilament P.A.N. yarns (polyacrylonitrile, a carbon precursor).

The fabric is subjected to a conventional raising operation to create a nap 14 at each face of the fabric (one face only being shown), the degree of raising being determined by the amount of nap required.

By virtue of the regular nature of the weave structure, the nap density will be substantially constant, and, more-over, will be readily reproducible.

The raised fabric of Fig. 1 is used in building up a sensibly homogeneous body of a requisite thickness by progressively applying successive layers thereof to a stack and needling the stack through each successive layer, the needling being such as to give uniformity thereof for the full thickness of the stack, the method being schematically illustrated in Figs. 2A to 2C and being generally in accordance with that shown in U.S.

Patent specification No. 4790052. Fig. 2A shows an intermediate stage in the building up of the stack 21 on a platen 22, the reciprocable needles 23 carried by needle bar 24 being shown at their full depth of penetration, the lowermost layers of the stack no longer being subjected to the needling operation. Figs. 2B and 2C show the manner in which the platen 22 is progressively lowered as the stack builds up and that the needling operation is restricted to the upper region 25 only of the stack. In the initial build up of the stack the reciprocating needles will pass fully through the stack into engagement with holes 26 in the platen, but as that build up progresses the platen will move downwardly with respect to the bottom dead centre position of the needle stroke such that, in due course, the lowermost fabric layers are no longer subjected to needling.

Needling continues after the stack has reached a requisite thickness, the platen being progressively lowered during the needling process until such time as the uppermost layer 27A has been subjected to a like degree of needling as the lowermost layer 27B and the intermediate layers 27C.

The needled fabric is subjected to a conventional carbonization step (to transform the pre-oxidised P.A.N. into carbon) and to a conventional densification step by chemical vapour infiltration of pyrocarbon, the resultant material being suitable for use as a brake pad in extreme load environments. The regularity of the nap formed on the individual layers provides a high degree of homogeneity in the brake pad and contributes to the strength of the pad and its ability to resist stress loads.

The nap itself may be laid flat prior to application of the layer to the existing build up of layers on the needling machine, as by subjecting the fabric to a hot calendering operation, or may be treated to maintain the same in a condition in which it extends outwardly from and perpendicular to the woven structure.

In this latter situation it may be found desirable to crop the raised surface to give a nap of sensibly uniform height.

It is to be observed that by selection of an appropriate twill, it is possible to create a pattern in the raised surface having regular napped and un-napped areas, these male and female areas being capable of receiving complementary un-napped and napped areas of a similar fabric arranged in superimposed disposition relative thereto. Preferably, the napped and un-napped areas exist in complementary positions at the respective surfaces of the fabric. In this way a degree of natural interlocking is attained between successive layers which further contributes to the shear strength of the end product.

Furthermore, by utilising, say, a weft satin weave and raising the surfaces unequally, a fabric layer having a different degree of nap at the respective surfaces could readily be achieved.

The wide range of possible weave structures does, of course, permit of the possibility of achieving a corresponding variety of napped fabrics and, more particularly, of providing any required degree or distribution of nap or nap combination. Thus, for example, a broken twill with dominant weft, and particularly one having plural weft yarns woven together, could be used to produce a fabric having a heavy nap at each surface.

In the case of an intermediate textile element comprised of pure or substantially pure carbon yarns, it has been found desirable to utilise a weave such as will give a multilayer structure, the creation of a nap at a surface of the fabric having no adverse effect on layers remote from that surface notwithstanding the fragile nature of the carbon yarns and the damage to the yarns at the fabric surface caused by the raising operation. A typical weave pattern of use in the context of elements woven from pure or substantially pure carbon yarns is shown in Fig. 3.

Other weave structures will, of course, present themselves to one skilled in the art.

Although the invention is described by reference to a woven structure which is raised to provide a nap, a multiplicity of fabric layers of this kind being needled together, it is to be observed that a fabric layer for use in the production of a three-dimensional reinforcement may comprise a carded web of fibres intermediate two raised fabrics, the whole being made integral on a fibre locking machine.

The invention is not limited to the exact detail of the embodiments hereinbefore set forth, since further alternatives will present themselves to one skilled in the art. Thus, for example, the relative weights of the warp and weft may differ and the weave structure be such that, after raising, the actual weight of the yarns in the warp and weft are equivalent, the surplus from the predominant yarn becoming the nap or fibrous reinforcement.

Indeed, an appropriate fabric may be formed by other than weaving, and may comprise, for example, a needled mass of fibres, for example of a weight of 500 grammes per square metre, the surface of which is lightly raised to give a surface "fuzz" for bonding purposes. The needled mass may include a reinforcement, such reinforcement typically comprising a woven structure disposed within the fibre mass or merely spaced, parallel yarns provided for a like purpose.

Whilst the primary interest is in providing an intermediate fabric for use in the manufacture of an homogeneous reinforcing structure intended to withstand high thermomechanical forces, and thus the fabric will comprise carbon or ceramic fibres (or precursors of such fibres) or combinations thereof, it is to be understood that the invention provides a fabric of advantageous use in less demanding situations wherein the materials used will be dependent upon the intended context in which the homogeneous structure will be used. Thus, according to context, natural, artificial or synthetic fibres may be used, whether in combination or otherwise.

Claims

1. In the production of an intermediate textile element for use in the manufacture of an homogeneous reinforcing structure formed by the progressive needling together of successively superimposed such elements, the step of subjecting at least one face of a coherent textile structure defining the said element to a textile raising operation.

2. The method of producing an homogeneous reinforcing structure comprising the steps of applying successive layers of a coherent textile structure to a progr- essively needled stack of similar structures and needling each successive layer to the said stack to give a stack of a requisite thickness, the needling being such as to provide substantial uniformity of needling throughout the full thickness of the stack, characterised in that one face at least of the coherent textile structure is subjected to a textile raising operation prior to application to the stack.

3. The method as claimed in claim 1 or 2, wherein both faces of the coherent textile structure are raised.

4. The method as claimed in claim 3, wherein each surface of the coherent textile structure is selectively raised to provide napped and un-napped regions thereto.

5. The method as claimed in claim 4, wherein the napped and un-napped regions are complementarily positioned at the two faces of the coherent textile structure.

6. The method as claimed in claim 2 or in any one of claims 3 to 5, when dependent on claim 2, wherein each coherent textile structure comprises a fabric constructed from carbon or ceramic fibres (or precursors thereof) and the method includes a densification step.

7. An intermediate textile element for use in the manufacture of an homogeneous reinforcing structure formed by the progressive needling together of successively superimposed such elements, characterised in that the element comprises a coherent textile structure of which one face at least has been subjected to a textile raising operation.

8. An intermediate textile element as claimed in claim 7, wherein both faces of the coherent textile structure are raised.

9. An intermediate textile element as claimed in claim 8, wherein each surface of the structure is selectively raised to provide napped and un-napped regions thereto.

10. An intermediate textile element as claimed in claim 9, wherein the napped and un-napped regions are complementarily positioned at the two faces of the coherent textile structure.

11. An intermediate textile structure as claimed in any one of claims 7 to 10, wherein said structure comprises a woven fabric.

12. An intermediate textile structure as claimed in claim 11, wherein the said structure comprises a punched laminate of two woven fabrics and a fibrous batt disposed therebetween.

13. An intermediate textile structure as claimed in any one of claims 7 to 12, comprising carbon or ceramic fibres or precursors thereof.

14. An intermediate textile structure as claimed in claim 13 comprising a multilayer woven fabric.

15. A plurality of intermediate structures as claimed in any one of claims 7 to 14, arranged in superimposed overlying disposition and needled together to provide an homogeneous three dimensional reinforcing fabric.

16. The method of producing an intermediate textile element, for use in the manufacture of an homogeneous reinforcing structure formed by the progressive needling together of successively superimposed such elements, substantially as hereinbefore described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

17. The method of producing an homogeneous reinforcing structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

18. An intermediate textile element for use in the manufacture of an homogeneous reinforcing structure formed by the progressive needling together of successively superimposed such elements, substantially as hereinbefore described with reference to and as illustrated in Fig. 1 of the accompanying drawings.

19. An homogeneous reinforcing structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.