GB2099365A

GB2099365A - Process for the production of friction discs

Info

Publication number: GB2099365A
Application number: GB8215631A
Authority: GB
Original assignee: Carbone Lorraine SA
Current assignee: Mersen SA
Priority date: 1981-06-02
Filing date: 1982-05-28
Publication date: 1982-12-08
Also published as: NL181888B; CA1198268A; GB2099365B; IT8221473A0; IT1151237B; DE3220306C2; NL181888C; JPS58643A; FR2506672A1; NL8202003A; FR2506672B1; DE3220306A1

Abstract

Friction discs of carbon-carbon composite materials are produced by winding a strip of material 8 composed of fibres around a cylindrical mandrel 13, and carrying out one or both of the following operations: (a) at the time as the strip of material 8 composed of fibres is wound around the mandrel 13, it is subjected to a radial needling operation, the strip then comprising two or more layers of fibres of different orientations and lengths according to the layers formed, and (b) the winding produced is radially compressed by 12a, 12b so as to produce circumferential undulations in all the layers forming the winding 8. The invention is particularly intended for the manufacture of brake and clutch discs. <IMAGE>

Description

SPECIFICATION Process for the production of friction discs The present invention concerns the production of friction discs of carbon-carbon composite materials, which are particuiarly intended for use as friction members having structural strength in brakes or clutches comprising one or more discs associated with other discs or with pads or shoes.

It is known that a member comprising carboncarbon composite material may be produced by preparing a fibrous substrate of carbon or carbon precursor material which is carbonised, then followed by densification of the substrate. This operation results in a member comprising carbon fibres embedded in a carbonaceous "matrix".

Densification of the substrate may be effected for example by chemical deposit of carbon in the vapour phase, by means of one or more cycles comprising liquid impregnation of carbonisable materials, carbonisation and graphitation, or by a combination of those two methods.

It is also known that the properties of the member that is finally produced largely depend on the arrangement of the initial fibrous substrate.

In accordance with the present invention, there is provided a process for the production of friction discs of carbon-carbon composite material by winding a strip of material composed of fibres around a cylindrical mandrel, in which at least one of the following operations is carried out: (a) at the same time as the strip of material composed of fibres is wound around the mandrel, it is subjected to a radial needling operation, the strip then comprising two or more layers of fibres of different orientations and lengths according to the layers formed, and (b) the winding produced is radially compressed so as to produce circumferential undulations in all the layers forming the winding.

The present invention can be carried out easily and economically to produce, after convention carbonisation and/or densification, friction discs with a good performance.

The roll produced after one or other or both operations is optionally carbonised, if the fibres used comprise a carbon precursor material, and then cut up perpendicularly to its axis to form a large number of disc members which form the substrate of a plurality of discs, if the width of the strip is sufficient for that purpose.

The roll or the disc members is/are then subjected to a densification treatment, either by putting them in a furnace so that they receive, at a temperature of 1000"C, a chemical deposit of carbon in the vapour phase, which forms the matrix of the material, or by impregnating them at least once with liquid hydrocarbons such as coal tar, followed by carbonisation and graphitation.

This second possible process, which is intended if necessary to remove local porosity in the substrate or to reduce the total period of time required for producing the matrix, may be effected between a third and four-fifths of production of the finai density by chemical vapour-phase deposition.

The densified discs are then subjected to a heat treatment at a temperature of from 1600 to 2500 C, depending on the use to which they are to be put.

The brake discs produced in accordance with the present invention can have the following advantages: no wastage of fibres during production of the disc; speed and ease of deposit of the matrix, due to the form of the substrate; ease of production of the substrate on an industrial scale; very good mechanical strength in respect of braking couple; good resistance to wear, due to the generally highly inclined orientation of the fibres with respect to the friction surfaces; excellent dimensional stability of the disc during the heating effect caused by braking; in regard to the disc, the condition of parellelism of the faces is retained because of the zero coefficient of expansion in respect of thickness; in regard to the fibres or groups of fibres, there cannot be any local geometrical change in the surface that could promote the occurrence of hot spots;; very good resistance to radial delamination due to the radical needling action and/orthe undulations, those two processes separately or in combination reducing the adverse effects of the polar anisotropy of the winding; a very high level of compression and tensile strength in the axial direction of the disc; and the heat due to the friction effect can be very easily removed towards the interior of the disc.

It should be noted that the above-indicated process includes a number of variations, which are also part of the present invention.

In the accompanying drawings, which are given to illustrate but not to limit the invention, Figure lisa diagrammatic view of the windingneedling operation, Figure 2 is a diagrammatic view of a preferred type of circumferential undulation, Figures 3A and 3B are diagrammatic view of means for producing the circumferential undulations shown in Figure 2, and Figure 4 shows the operation of winding a particular strip of fibres.

Referring to Figure 1, four layers of fibres are wound simultaneously around a cylindrical mandrel 1. The mat layers 2a and 2b are formed by short fibres (for example from 3 to 5 cm) which are disposed randomly in the plane of the layer.

The layers 3 and 4 are formed by unidirectional fibres 5 which are possibly disposed on a thin plastic carrier which can be removed by heat, and which are oriented, with respect to the axis of the mandrel: - towards the right, in respect of the layer 3, and - towards the left, in respect of the layer 4.

The angles at which the fibres are oriented may be for example between 30 and 60 , according to circumstances. Figure 1 shows the angles as being equal at 45D The mandrel 1 rotates in the direction indicated by arrow 9.

While the winding 8 is progressively being formed, a needling bar 6 provided with a large number of needles 7 continuaily alternatively perforates the winding 8. By virtue of the projections or spurs on the needies, the result of the needling operation isto pull out shortfibres which are initially disposed on the mat layers comprising short fibres 2a and 2b, and to arrange them in radial directions with respect to the winding 8.

When the needled winding S is sufficiently large in diameter, the mandrel 1 is removed.

The winding 8 enjoys very good cohesion and can be handled without having to take special precautions. It is advantageous for the winding 8 to be made from layers of fibres of carbon precursor material such as cross-linked polyacrylonitrile. This results in the winding being less fragile, which permits both the needling operation and the radial compression operation. In that case, the substrate is subjected to an additional carbonisation operation.

Figure 2 shows undulations in the layers at the inside periphery pf of the radially compressed winding, which are as marked as the undulations in the layers at the outside periphery Pf. In order to produce that type of undulation, it will be seen that it is essential in the radial compression operation substantially and simultaneously to reduce the diameters of the outside and inside peripheries Pi and p ofthe winding.

Figure 2 also shows that there are real undulations around any circumference of the winding, thereby forming notches or recesses which are disposed in a staggered arrangement relative to each other, atthe inside and outside peripheries.

Referring now to Figures 3A and 3B, the needled winding 8 is disposed within a rigid cylinder 10, coaxially therewith (axis 11). Radial compression sector members 12a and 12b are disposed between the cylinder 10 and the winding 8. The longitudinal direction of the sector members is and remains parallel to the axis of the cylinder throughout the compression operation. The sector members are identical in length to the winding 8 and the cylinder 10.

A radial force and a radial movement are imparted to the sector members 12a and 12b in such a way that the sector members 12b are displaced radially at a higher speed than the sector members 1 2a.

Disposed at the centre of the needled winding 8, coaxiallytherewith and with the cylinder 10, is a compressible cylindrical core member 13 which is of the same axial length as the members 10 and 8.

The core member 13 may either comprise an elastomer or an assembly of mechanical compo nents, but in both cases the diameter of the core member must be reduced during the radial com pression operation. At its periphery (and over its entire axial length), the core member 13 has raised surface portions 13a, the longitudinal direction of which is parallel to the axis of the core member 13.

There is a regular alternation as between sector members 12b and raised surface portions 13a in the angular space which is around the axis 11, thereby to produce properly repetitive undulations such as those which can be seen in Figures 2 and 3B, in the radial compression operation.

The resulting winding with undulations is then cut up perpendicularly to its axis into ring or disc members which form substrates for discs and which are subjected to a densification treatment.

The discs which are finally produced, being provided with their notches or recesses, can be put to many uses. Mention may be made of the following: when the disc is used as a rotor or rotary member, it will be driven in rotation by key or pin members which are fixed to the inside of an aircraft wheel rim, for example, by way of all or some of the notches formed by the undulations in the outside periphery of the disc, and when the disc is used as a stator, it will be immobilised by means of key or pin members which are fixed to a non-rotating shaft, by means of all or some of the notches formed by undulations in the inside periphery of the disc.

A first alternative form in accordance with the invention concerns producing discs, the wound substrate of which is subjected only to the operations disclosed in Figure 1. Therefore, that substrate is not subjected to the operation of forming the undulations by radial compression as described with reference to Figures 2, 3A and 3B, but except for that step, the method of producing the discs is strictly the same.

A second alternative form according to the invention concerns the production of discs wherein the wound substrate is not subjected to the radial needling operation, but on the other hand is subjected to the operation of forming undulations by radial compression and all the operations described hereinbefore.

In this second alternative form of the process, referring to Figure 1, the substrate may comprise: - either the succession of layers 2a, 3, 2b, 4 as described hereinbefore (but without being radially needled), - or the succession of layers 3 and 4, the layers 2a and 2b thus being omitted, - or a strip as illustrated in Figure 4.

In the single case of the strip shown in Figure 4, the substrate is made disc by disc and not by long cylinder members which can subsequently be cut up into discs, as in all the other embodiments.

The strip illustrated in Figure 4 comprises a warp 14, the width b of which is only two thirds of the total width a of the disc. The weft 15 of the strip on the other hand is of a width corresponding to the full width a of the finished disc.

Thus, the friction surfaces of the disc will be subjected to wear, in braking operations, in regard to a disc thickness which has only weft threads which are therefore perpendicular to the disc surfaces. In order to enhance the final operational stability of the surfaces of the disc, the weft threads are notwoven with warp threads but are simply assembled by two sets of stitches which are produced by machine parallel to the longitudinal axis of the strip.

Athird alternative form in accordance with the invention is concerned with the production of discs from a substrate which is wound and radially needled in a manner strictly in accordance with the description relating to Figure 1. The substrate is then placed in the equipment described with reference to Figures 3A and 3B, except that the equipment is slightly modified: all the parts outside the winding (cylinder member 10 and section members 12a and 12b) are unchanged, but the compressible core member 13 with the raised surface portions 13a is replaced by an incompressible core member, the diameter of which is identical to that of the mandrel 1 shown in Figure 1.The radial compression operation is then performed, which has the effect of producing undulations which are clearly marked in the peripheral regions of the winding 8, and undulations which are increasingly less marked at diameters which progressively move towards the diameter of the mandrel 1.

This third embodiment of the process of the invention therefore makes use of a property of radial compressibility of the wound needled substrate, which makes it possible to reduce and form undulations in the initial outside periphery of the winding, without reducing or forming undulations in the inside periphery.

Such radial compressibility of the substrate will be enhanced (see Figure 1) if on the one hand the thickness of the short4ibre layers 2a and 2b is increased and if on the other hand no circumferential tension is applied to the layers of fibre during the winding and needling operations.

The attraction of the alternative forms of the invention may be that they permit a saving in production, if use of the discs is limited in each of the cases in question, to particular situations of use.

Claims

1. A process for the production of friction discs of carbon-carbon composite material by winding a strip of material composed of fibres around a cylindrical mandrel, in which at least one of the following operations is carried out: (a) at the same time as the strip of material composed of fibres is wound around the mandrel, it is subjected to a radial needling operation, the strip then comprising two or more layers of fibres of different orientations and lengths according to the layers formed, and (b) the winding produced is radially compressed so as to produce circumferential undulations in all the layers forming the winding.

2. A process according to Claim 1 in which, in order to produce the circumferential undulations, a cylindrical core member of the same length as the winding is introduced without clearance into the winding and coaxially with it, and sector members that are alternately long and short are applied to the periphery of the winding and subjected to a centripetal radial force.

3. A process according to Claim 2 in which the cylindrical core member comprises a compressible material which thus permits of simultaneous reduction in its internal and external diameters when the winding is radially compressed.

4. A process according to Claim 3 in which the cylindrical core member carries raised surface portions.

5. A process according to Claim 2,3 or 4 in which the circumferential undulations are so formed that they produce notches disposed in a staggered arrangement relative to one another on the external and internal peripheries of the winding such that each notch of a periphery is disposed facing the middle of the arc between two successive notches of the other periphery.

6. A process according to Claim 5 in which the notches are distributed and shaped such that at least some of them serve as key-way grooves.

7. A process according to Claim 2 in which the cylindrical core member comprises incompressible material.

8. A process according to any one of Claims 1 to 7 in which the strip of material composed of fibres is formed by four layers, viz.

(a) a layer of randomly disposed short fibres, (b) a layer of unidirectional fibres oriented in a direction inclined with respect to the axis of the mandrel, (c) another layer of short randomly disposed fibres, and (d) a layer of unidirectional fibres oriented in another inclined direction with respect to the axis of the mandrel, the four layers being wound simultaneously and needled during the same period and the winding produced not being subjected to the radial compression operation.

9. A process according to any one of Claims 1 to 7 in which the strip of material composed of fibres is formed by four layers, viz.

(a) a layer of randomly disposed short fibres, (b) a layer of unidirectional fibres oriented in a direction inclined with respect to the axis of the mandrel, (c) another layer of short randomly disposed fibres, and (d) a layer of unidirectional fibres oriented in another inclined direction with respect to the axis of the mandrel, the four layers being wound simultaneously and then being subjected to the radial compression operation.

10. A process according to any one of Claims 1 to 7 in which the strip of material composed of fibres is formed by layers of unidirectional fibres that are not needled, and the resulting winding is then subjected to the radial compression operation.

11. A process according to any one of Claims 8 to 10 in which the fibres comprise carbon precursor material.

12. A process according to Claim 11 in which the material is cross-linked polyacrylonitrile.

13. A process according to any one of Claims 8 to 10 in which the winding produced is cut into disc members and subsequently subjected to densification.

14. A process according to Claim 11 or 12 in which the winding produced is carbonised and then cut into disc members and subsequently subjected to densification.

15. A process according to any one of Claims 1 to 7 in which the strip of material composed of fibres is formed by a strip of carbon threads, the warp width of which is less than that of the carbon thread strip and the weft width of which is equal to that of the carbon thread strip, the said carbon thread strip not being needled and the winding formed by it then being subjected to the radial compression operation and subsequently to densification.

16. A process according to Claim 15 in which the warp and weft threads of the carbon thread strip are straight and intersect one another at right angles.

17. A process according to Claim 15in which the warp and weft threads are joined by stitching.