GB2177431A

GB2177431A - Process for manufacturing three-dimensional axisymmetrical structures of fibrous material, and fibrous material used therein

Info

Publication number: GB2177431A
Application number: GB08615601A
Authority: GB
Inventors: Pierre R Olry
Original assignee: Societe Europeenne de Propulsion SEP SA
Current assignee: Societe Europeenne de Propulsion SEP SA
Priority date: 1985-06-27
Filing date: 1986-06-26
Publication date: 1987-01-21
Also published as: FR2584107A1; IT8620901A0; GB2177431B; FR2584107B1; GB8615601D0; IT1193260B; JPS626957A; DE3620833C2; DE3620833A1; JPH0759783B2

Abstract

The process consists of winding on a mandrel (10) a strip (20) of fibrous material of width substantially equal to the axial dimension of the structure to be produced, and, simultaneously with the winding, needling the superposed layers formed by the strip (20) wound on the mandrel, the distance between the mandrel (10) and the needles (13) being caused to vary as the winding of the strip progresses, in order to keep the needling depth substantially constant. For every layer formed by a turn of the strip (20) about the mandrel (10), the mandrel is moved apart from the needles (13) by a distance (e) corresponding to the thickness of a needled layer. <IMAGE>

Description

SPECIFICATION Process for manufacturing three-dimensional axisymmetrical structures of fibrous material, and fibrous material used therein The present invention relates to the manufacture of three-dimensional structures formed by superposed flat layers of fibrous material bonded together by needling.

The field of application ofthe invention is more particularly, but not exclusively, that ofthe production ofthree-dimensional reinforcing structures used for manufacturing parts in composite material produced by densification of said reinforcing structures, and in particular,for manufacturing cylindrical orannular parts such as brake discs, in carbon-carbon.

One known process of manufacturing cylindrical structures by needling layers of fibrous material is described in French Patent 2 506 672. Said process consists in winding a web offibrous material in a cylindrical mandrel and carrying out a needling operation on the web while on the mandrel. This document, however, gives no indication as to what means to use in order to effectively produce a thick structure with a constant needling density right through the thickness ofthe structure. The same appliesto French Patent 2,378,888 and to U.S. Patent 3,772,125, as well as to the prior art documents relating to the production oftubular structures with thin walls (such as for example FR 1,570,992GB 2,048,424 and U.S. 3,909,893).

It has now been found thatthe techniques of needling through small thicknesses are not readily adaptable to thickthicknesses. One reason for this is that, once they have penetrated to a certain thickness in the superposed layers, the needles lose their effectivenessbecausetheirbarbs become clogged up with pieces offibers torn from the layers of materials gone through by the needles; the needles cannot thus fulfil theirfunction correctly, and as a result, the same needling characteristics cannot be obtained throughout the whole stack.

Yet, for materials which are destined to suffervery strong thermomechanical stresses, it is important to keep the properties constantthroughout the mass, in orderforexample,to prevent delamination.

It is therefore an object of the present invention to propose a process permitting the production ofthick three-dimensional structures by needling of superposed layers while keeping a constant density of needling throughoutthe thickness ofthe structure.

This object is reached with a process of the type comprising winding on a mandrel a strip offibrous material of width substantially equal to the axial dimension of the structure to be produced, and, simultaneously to the winding, needling the superposed layers formed by the strip wound on the mandrel, wherein, according to the invention, the distance between the mandrel and the needles is caused to vary as the winding of the strip progresses, in orderto keep the needling depth substantially constant.

Foreverylayerformed by a turn ofthe strip about the mandrel, said latter is moved apartfrom the needles by a distance corresponding to the thickness of a needled layer.

The needling is performed with a needle board which extends in parallel to the axis of the mandrel, preferably over a length at least equal to the length of the strip. The use of a shorter needle board is possible but requires a relative displacement between the mandrel and the needle board in the axial direction.

According to one particular embodiment ofthe process, the mandrel is rotatable and has a nonperforated surface coated with a base layer designed to allow the penetration of the needles without damaging them during the needling ofthefirst layer or layers ofthe structure. To preventthe formation of circumferential lines of the needle strokes which could impairthe homogeneity ofthe needling within the structure,the mandrel and the needle board can be subjected to a reciprocal displacement of small amplitude in an axial direction during the manufacture of the structure.

Obviously, it is also possible to use a non-rotating mandrel, with a surface presenting perforations facing the needles of the needle board. In this case, the strip is wound by moving the structure being produced by its outer face.

At each needling stroke, the needles go through several superposed layers. Then, in orderto obtain a material which is homogeneous throughout its thickness, finishing needling steps are conducted after winding and needling ofthe last layer, so that the needling density in the lastly deposited layer is substantially equal to that in the other layers. During the finishing needling steps, the mandrel and needles are mutually moved apart as if new layers were being wound. Due to the fact that for part of the finishing step, the needles travel through the air, said needles are more efficient towards the upper layers of the winding than if they had had to go through other layers beforehand, with a more or less important clogging up oftheir barbs.Forthis reason, the number offinishing steps is preferably less than what is necessaryto reach the moment when the needles can no longer reach the last layer of the stack.

Another object of the invention is a fibrous material suitable for use with the process.

The choice of the fibrous material is guided bythe proposed application, while making sure that the needled structure will lend itselftothe densification operation, namely that it has a rather widely open porosity.

For example, the layer of material can comprise at least one layer formed of single discontinuous fibers and obtained by carding, or one layer of continuous fibers obtained by a lapping of tows or yarnsfollowed by a pre-needling.

In addition, the material must be suitable for needling, which is not really the case of carbon or ceramic fibers composing the composite materials currently used in applications requiring highthermomechanical resistance. In this latter case, at least part of the fibers constituting the material are fibers precursors of carbon or ceramics which are very suitable for needling and which are subsequently converted into carbon or ceramic by treatment of the structure.

The invention will be more readily understood on reading the following description of examples of the process and materials in accordance with the invention, with reference to the accompanying drawings, in which: - Figure 1 is a very diagrammatical view of a device for carrying out an example of the process according to the invention; and - Figures 2 to 4 are cross-sectional views illustrating different stages in the production of a structure in the example of Figure 1.

Astrip 20 of fibrous material is brought in continuous manner over a mandrel 10 driven in rotation about a horizontal axis. The mandrel, which in this case is cylindrical with circular cross-section, has a profile corresponding to that ofthe axisymmetrical structure to be produced, whereas the strip 20 has a width corresponding substantially to that of said structure. Said strip 20 is wound on the mandrel to form superposed layers which are joined together by needling, by means of a needle board 12. Said needle board is situated above the upper generatrix ofthe mandrel 10 and extends in parallel to the axis ofthe latter over a length at least equal to the width of the strip 20, the needles 13 being directed vertically downward.

The needle board and the mandrel 10 are moveable one with respectto the other in a vertical direction. To this effect, the shaft of the madrel passes through bearings mounted on supports 14 movablevertically with respectto the frame on which is mounted the needle board. The vertical displacement ofthe supports 14 is achieved by means of stepper motors which are con rolled synchronouslyto each other and which drive toothed wheels on which mesh endless chains 16, the support 14 being fixed on the latter. The mandrel 10 is driven in rotation by a motor 17 provided at one end of the axis ofthe madrel.

Each time another layer is formed by winding the strip 20 on one turn of the mandrel 10, said mandrel is lowered with respect to the needle board by a distance corresponding to the thickness "e" ofthe needled layer.

Simultaneously to the winding, the strip 20 is needled onto the preceding layer atthe very level where the strip is superpose thereon. At each penetration of the needles, their asperities or barbs carry with them fibers from the material of traversed layers, these fibers creating radial bonds between the superposed sheets.

Figures 2 and3 showthe needles respectively in high position and in low position. The needles penetrate into the structurethrough a depth equal to several timesthethickness of a needled layer (for example, eighttimes). Due to the progressive lowering ofthe mandrel 10 with respectto the needles, the needling depth is keptconstantthroughoutthe operation In orderto be able to needle he first layers on the mandrel 10, it is necessaryto providemeansthat prevent the needles 1 3from hitting the hard surface of the mandrel 10. To this effect, the mandrel 10 is coated with a base layer 11 which the needles can penetrate without being damaged and without carrying particles orfibers into the structure to be produced.

The coating 11 can, for example, be constituted by a sleeve 11 a in reinforced elastomer (such as for example a sheet of"Hypalon" reinforced by a "Nylon" fabric) fixed to the mandrel 10 and on which is adhesively fixed a layer 11 b formed of a felt base (for example a polypropylene felt) of sufficient thickness forthe needles to penetrate, during the first needling strokes, through the preset needling depth without touching the mandrel 10. On the felt base is adhesively fixed another sleeve 11 c, for example in polyvinychloride. During the needling, the sleeve llcis traversed through by the needles but prevents fibers from the material of the strip 20 from being embedded in the felt base, which would complicate the removal ofthecompleted structure.

To preventtheformation ofcircumerential lines of needle strokes which impairthe homogeneity of the resulting structure, a reciprocal displacement of small amplitude in axial direction is made between the mandrel 10 and the needle board 12. This is achieved forexample by imparting tothe needle board a horizontal to-and-fro movement over a small distance.

It will be noted as a variant that it is possible to carry out the needling on a perforated mandrel having perforations corresponding to the needles ofthe board 12. In this case, it is not necessaryto coat the mandrel with a surface layersuch as 11.The mandrel is then immobile with respecttothe needle board except vertically and it is the sheet, deposited on the mandrel, which is driven in orderto be wound overthe mandrel. In a manner known per so, the driving ofthe strip 20 may be caused by one orseveral members such as a cylinder acting by friction on the outer surface ofthe structure being produced; itwill be further noted that this particular driving method is applicable when using a mandrel equipped with a layer 11.This device which acts by friction on the outer surface ofthe structure then replaces the driving movement imparted on the end of the shaft of the mandrel by the motor 17.

In orderto obtain a constant needling density through thewhole thickness of the structure, it is necessaryto conductfinishing needling steps once the last layer has been positioned and needled. The procedure then is the same as if new layers had been positioned. Due to the fact thatthe needles traverse a certain distance dthrough the air before reaching the structure and arriving at the end of their downward stroke (Figure 4), their barbs are less clogged than if they had to travel an equal distance "d" through the fibrous fabric. The needles are thus increasingly effective duringthe finishing needling steps. Then, to avoid denser needling in the upper layers, the number offinishing layers produced (four for example) is less than that (eight) which would have been necessaryto reach the time when the needles can no longer reach the last layer deposited.

The sheet offibrous material may be supplied in differentforms, particularly depending on the proposed application.

For example, the fibrous material may be at least partly constituted by a layer of discontinuous fibers obtained by carding (card webs), or by a layer of continuous fibers obtained bycriss-crossing un idirectionalwebsofcontiunuousyarnsortowsand by low density needling (pro-needling) of the layer together. In the latter case, the criss-crossing can be achieved as already known per so, namely by lapping; one ofthe unidirectional webs ofyarns ortows is continuously supplied whereas another unidirectional web of yarns or tows is superposed thereon by reciprocal movement in a direction perpendicular to the movement ofthe first web.Due to the relative displacement between the unidirectional webs, what is obtained is in factth roe superposed webs forming between them angles different from 90% for example angles of 60% When greater mechanical strength is required for thestructure,in particularasafunctionofthe propertiesrequiredforthefinalcompositefabricto be produced, or simply to provide a correct supply ofthe mandrel, the fibrous material is constituted by at least one woven layer, which is, for example:: -a complex constituted by a fabric of continuous or discontinuous fibers (satin or plain weave type) on which has been needled, with low needling density, a web of discontinuous fibers obtained by carding (card webs) or a web of continuous fibers, such as a web being deposited over the fabric by lapping, -a single fabric constituted, in warp and weft directions, of yarns formed of continuous of discontinuous filaments, or - a single fabric, constituted in the warp direction, of yarns formed of continuous or discontinous filaments, and by a roving in the weft direction.

The fibers constituting the materials described hereinabove may be any natural, artificial of synthetic fibers, used either such as they are or after a heat treatment, the choice of the nature of these fibers being dependent on the proposed application.

Inthocasoofthe manufacture of reinforcement structures for composite materials destined to withstand greatthermomochanical forces, the most advantageous fibers are the carbon fibers and the ceramic fibers (alumina, silicon carbide, etc.) as well as any fibers precursors of such fibers, or any fibers constituting an intermediary between such precursor fibers and thefully heat-treated fibers.

When the three-dimensional structure is entirely or partly produced from precursor or intermediate fibers, it has to undergo a subsequent heat-treatmentto confertothefibersthemaximum mechanical properties.

This last manner of proceeding protects the fibers against breaking during needling in the case where the heat-treated fibers have modules that are too high, and the transversal strengths that are too low to be needled without any damage, as this is the case with carbon and ceramic fibers. Thus the materials described hereinabove can be constituted at least partly with carbon ceramic precursor fibers, any remaining fibers being in carbon or ceramic.

For example, the fibrous material destined for needling is constituted by a complexformed of a highly resistant fabric of carbon fibers, pre-needled with a card web of stabilized P.A.N. fibers (polyacrylonitryl, a carbon precu rsor). In this complex, the fabric brings the required mechanical strength whereas the web of fibers permits the non-destructive needling of the superposed sheets, since the barbs ofthe needles, in loading themselves with the stabilized P.A.N., cannot seriously damage carbon fibers. For economical reasons, the fabricwill be selected to be as light as possible in view of the required mechanical properties, for example with a surface weight varying between 100 and 600g/m2.

Itis of course possible in the preceding exampleto replace carbon fibers and/or precursors, independently, by ceramic fibers and/or precursors. And, in reverse, a fabric in carbon or ceramic precursorfibers may be combined with a card web in carbon or ceramic fibers.

Inthosameway, carbon orcoramicfibers and carbonorceramicprocursorfiberscan be combined and form, independently one from the other, the warp and weft of a fabric constituted byyarns of continuous or discontinuous filaments in the warp direction, and by a roving oryarns of continuous or discontinuous filaments in the weft direction.

Claims

1. A process for manufacturing three-dimensional axisymmetrical structures by needling layers offibrous material, ofthe type comprising winding on a mandrel a strip offibrous material of width substantially equal to the axial dimension ofthe structure to be produced, and, simultaneously to the winding, needling the superposed layers formed by the strip wound on the mandrel,wherein the distance between the mandrel and the needles is caused to vary as the winding ofthestrip progresses, in orderto keep the needling depth substantially constant.

2. A process according to claim 1, wherein for every layer formed by a turn ofthe strip about the mandrel, the latter is moved apartfromthe needles by a distance corresponding to the thickness of the needled layer.

3. A process according to claim 1 or claim 2, wherein the mandrel is rotatable and has a nonperforated surface coatedwith a basolayerdesignod to allow the penetration ofthe needles without damaging them during the needling of the first layer or layers of the structure.

4. A process according to claim 3, wherein the mandrel and the needle board are subjected to a reciprocal displacement of small amplitude in the axial direction duringthe manufactureofthestructure.

5. A process according to claim 1 or claim 2, wherein the mandrel is fixed and presents surface perforations in facing relationship to the needles.

6. A process according to any one of the preceding claims, wherein the winding ofthe strip is performed by driving the strip on the outside of the structure being formed.

7. A process according to any one of claims 1 to 4, wherein the winding of the strip is performed by driving the mandrel in rotation.

8. A process according to any one of the preceding claims, wherein finishing needling steps are conducted afterwinding and needling ofthe lastlayer,so that the needling density in the lastly deposited layer is substantially equal to that in the other layers.

9. A process according to claim 8, wherein the numberoffinishing steps is less than what is necessaryto reach the momentwhen the needles can no longer reach the last layer of the stack.

10. Afibrous material for use in carrying out the process according to any one of the preceding claims, wherein said material is at least partly constituted by criss-crossed unidirectional webs of tows oryarns, said webs being needled together.

11. A material according to claim 10, wherein the webs are criss-crossed so as to form angles of about 600.

12. A material according to claim 10 or claim 11, wherein the webs areformed, independently one from the other, by cables or tows, comprising fibres selected from carbon, ceramics, carbon precursors or ceramic precursors.

13. Afibrous material for use in carrying outthe process according to any one of claims 1 to 9, wherein said material comprises at least one woven layer.

14. A material according to claim 13, wherein said material is at least partly constituted by a fabric of continuous ordiscontinuous yarns on which a card web has been pre-needled.

15. A material according to claim 14,wherein said fabric and card web are constituted, independently one from the other, of fibres selected from carbon, ceramics, carbon precursorsorceramic precursors.

16. A material according to claim 13,wherein said material is at least partly constituted by a fabric of which the warp is formed of continuous ordiscontinuous yarns, and the web is formed of rovings.

17. A material according to claim 16, wherein the warp and weft are formed, independently one from the other, of fibres selected from carbon ceramics, carbon precursorsorceramic precursors.

18. A process according to claim 1, substantially as described with reference to the accompanying drawings.