GB2027418A

GB2027418A - Carbon Friction Member

Info

Publication number: GB2027418A
Application number: GB7832680A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-08-08
Filing date: 1978-08-08
Publication date: 1980-02-20
Also published as: GB2027418B

Abstract

A carbon friction member for use in aircraft brakes is made by forming a reinforcing support of alternating layers of interwoven carbon fibers and layers of individual graphitized elementary fibers oriented to partially penetrate the interwoven fibre layers, impregnating the resultant reinforcing support with a binder and subjecting it to heat treatment to form a blank which is machined, saturated with pyrocarbon and heat treated at graphitization temperatures. The individual graphitized elementary fibers prevent interfiber void formation during firing and also prevent delamination during operation.

Description

SPECIFICATION Carbon Friction Product Manufacture The invention relates to carbon compositions, and more specifically to methods for making carbon friction products.

The invention may be most advantageously used, e.g. for making aircraft brakes.

It is an object of the invention to provide carbon friction products exhibiting stable performance during operation.

Another object of the invention is to increase coefficient of friction of a carbon friction product.

Still another object of the invention is to improve interlayer strength of carbon products.

Further object of the invention is to improve isotropy of physical properties of a carbon friction product.

The invention resides in that a method for making a carbon friction product comprises the steps of laying a reinforcing support by piling up a pack of alternating layers of interwoven carbon fibers and layers of individual graphitized elementary fibers, said elementary fibers being oriented in such a manner as to partially penetrate the layers of interwoven fibers, with subsequent impregnation of the resultant reinforcing support with a binder and heat treatment to obtain a blank which is machined to form a desired product, impregnating the product with pyrocarbon and heat treating it at graphitization temperature.

The above-described method for making a carbon friction product ensures an improvement of stability of friction performance of the product by eliminating layer-to-layer non-uniformity of the material which is associated with the presence of relatively thick films of non-reinforced binder therein.

In this method elementary graphitized fibers are incorporated in the binder layer, which are oriented during the laying of the reinforcing support in such a manner as to ensure their penetration into the layers of interwoven fibers.

Incorporation of individual graphitized elementary fibers in the binder layer lowers the probability of the formation of substantial interfibervoids resulting in the appearance of coarse pores, shells and laminations in the blank during roasting. Partial penetration of the scattered carbon fiber into the layer of interwoven fibers also prevents the products from stratifying during operation.

The use of this method with the pyrolytic deposition of binder from a gaseous phase enables the elimination of a thick layer of pyrocarbon in the finished product thus improving the stability of friction performance of the product.

Another advantage of the method according to the invention resides in that two types of reinforcing fillers with different elasticity modulus are most likely to participate in the operation at the friction surfaces of co-operating parts. This provides for a greater coefficient of friction since high-modulus components can penetrate a lowmodulus pattern to a greater depth.

Coefficient of friction of a carbon composition depends to a large degree on orientation of fibers relative to the friction surface. With the orientation at right angle to the friction surface, the coefficient of friction is generally at its maximum. With the fiber penetration by this method, the fibers are partially oriented at right angle to the friction surface which also contributes to an increase in the coefficient of friction, including the coefficient of static friction.

It is most important that the wear of friction members with such method of improving the coefficient of friction does not practically increase.

Piling up of reinforcing support into a pack is preferably effected by forcing an aqueous suspension containing individual elementary fibers sequentially through each layer of interwoven carbon fibers.

This facility ensures a partial orientation of individual carbon fibers enabling them to penetrate the layers of interwoven fibers.

The pack of reinforcing support may be piled up by forcing an air stream containing individual elementary fibers sequentially through each layer of interwoven fibers thus considerably reducing the time for piling up the reinforcing support by eliminating the drying step.

The main distinction of all products made in accordance with the invention resides in a highgrade friction performance. The stability of coefficient of friction of braking members of aircraft made by the method according to the invention, even under static conditions of engines is about 90% of what might be achieved during normal landing. During normal landing typical values of coefficient of friction for compositions on the basis of rayon fabric and individual polyacrylonitrile elementary fibers are from 0.38 to 0.40 and for compositions on the basis of interwoven polyacrylonitrile fibers and individual fibers of the same feedstock, the coefficient of friction is somewhat lower and amounts to 0.30-0.35.

Other objects and advantages of the invention will become apparent from the following specific examples of the method.

Example 1 Friction products were made of graphitized rayon cloth of 8-heald satin interweaving and a pitch blinder.

A reinforcing support was prepared by piling upy a pack consisting of alternating layers of graphitized rayon cloth and layers of individual graphitized elementary fibers. Individual elementary fibers of a length from 0.1 to 5 mm were obtained in a nutsch filter under an intense stirring by means of a propeller stirrer of chipped graphitized thread on the basis of polyacrylonitrile.

Then a pack was piled up by forcing a stream of an aqueous suspension containing particles of fiber and pitch through which cloth layers by means of a vacuum pump. The following proportioning of components was used (in % by weight): carbonic cloth-1 5, individual graphitized elementary fibers-25, coal pitch with softening point 650C-the balance.

After compression moulding and heat treatment of the pack a blank was obtained which was roasted to 1 2000C at an average rate of temperature raise 200C/h, re-impregnated with pitch and roasted. To make friction products, the blanks were machined, saturated with pyrocarbon at 950-9800C during 90 hours and heat treated at 2000cm. The resultant carbonic friction products may be used as friction members for an aircraft wheel. The density of products is 1.65 g/m3.

Example 2 Friction products were made of a carbonized polyacrylonitrile fiber which is laid in such a manner as to orient individual fibers in the direction of application of maximum stresses in a braking disc; for instance, a spiral winding with radial interweaving can be used.

Then a reinforcing support was prepared by piling up a pack consisting of alternating layers of interwoven polyacrylonitrile thread and layers of elementary graphitized fibers. Individual graphitized elementary fibers were obtained as described in Example 1 and dried to achieve a constant weight.

Then a pack was piled up by the dry method by forcing an air stream containing individual elementary fibers by means of a high-pressure pump through layers of interwoven carbon fibers.

The pack was fixed in a clamp and saturated with pyrocarbon until the density increased to 1.6 g/cm3. The blank was heat treated at 20000C and machined to remove the surface layer, than saturated with pyrocarbon again to the density of 1.7 g/cm3. Repeated heat treatment and pyrocompaction steps with removal of surface layers can ensure the density of discs to be as high as 1.75-1.80 g/cm3. The friction products obtained by this method are most preferably used as friction discs in heavily loaded aircraft wheels.

Claims

Claims 1. A method for making a carbon friction product, comprising laying a reinforcing support by piling up a pack of alternating layers of interwoven carbon fibers and layers of individual graphitized elementary fibers, said elementary individual fibers being oriented in such a manner as to partially penetrate the layers of the interwoven fibers, impregnating the resultant reinforcing support with a binder and subjecting it to a heat treatment to form a blank which is machined to obtain a desired product, saturating it with pyrocarbon and heat treating at graphitization temperature. 2. A method as claimed in Claim 1, wherein the pack piling of reinforcing support is effected by forcing an aqueous suspension containing individual elementary fibers sequentially through each layer of the interwoven carbon fibers. 3. A method according to Claim 1, wherein said pack piling is effected by forcing an air stream containing said individual elementary fibers sequentially through each layer of said interwoven fibers. 4. A method of making a carbon friction product substantially as hereinabove described. New Claims or Amendments to Claims Filed on 30 July 79 Superseded Claims 1 to 4 New or Amended Claims:

1. A method of making a carbon friction element, comprising forming a support structure of two types of layers of fibres with different elasticity moduli arranged alternately, one type of layer comprising interwoven carbon fibres and the other type comprising individual graphitized elementary fibres, said elementary individual fibres being oriented and arranged in such a manner as to partially penetrate the layers of the interwoven fibres, impregnating the support structure with a binder, subjecting the support structure to heat treatment to form a blank, machining the blank, saturating the blank with pyrocarbon and heat treating at graphitization temperature.

2. A method as claimed in claim 1, wherein support structure is formed by forcing an aqueous suspension containing said individual elementary fibres through said layers of the interwoven carbon fibres.

3. A method as claimed in claim 2, wherein the aqueous suspension also contains a binder whereby the impregnation of the support structure with a binder is performed simultaneously with the introduction of individual elementary fibres in the support structure.

4. A method according to claim 1, wherein said support structure is formed by forcing an air stream containing said individual elementary fibres through each layer of said interwoven fibres.

5. A method of making a carbon friction element substantially as herainabove described.

6. A carbon friction element comprising a alternate layers of interwoven carbonised fibres and layers of individual graphitized elementary fibres, said elementary fibres being orientated in such a manner as to partially penetrate the layers of interwoven fibres, the layers being bound together by a graphitized binder.

7. A carbon friction element substantially as' hereinbefore described with reference to Example 1 or2.