Fibre matrix and a method of making a fibre matrix
A method of forming a three dimensional fiber structure is disclosed which comprises the steps of a) providing a starting material which comprises liquid carrier, fibers and binder; b) passing the starting material over a substrate so as to deposit fibers onto the substrate; c) forming a three dimensional fiber matrix; and d) curing the binder. The flow of material onto the substrate may be controlled such that the flow of a starting material over the substrate is chaotic and fibers are laid down in a three dimensional structure containing a high proportion of voids. The preform may be pressurized while moist and is cured under pressure. The fibers may comprise carbon fibers; recycled carbon fiber has been found to be particularly useful. The resulting preform may be stochastic and is suitable for use in ablative and braking applications.
1. A stochastic fibre preform, comprising a non woven substrate of fibres having a stochastic three dimensional matrix, wherein the preform has fibres arranged in the x, y and z directions, and these fibres are randomly oriented, and wherein the fibres are held together in the matrix formation by a cured binder and wherein the fibres comprise carbon fibres, and wherein the preform has a fibre volume fraction of 20% or higher.
2. A fibre preform according to claim 1 wherein 10 wt % or more of the fibres are carbon fibre.
3. A fibre preform according to claim 1 wherein the fibre preform is a fibre matrix obtainable by a method comprising the steps of:
a) providing a starting material which comprises liquid carrier, fibres and binder;
b) passing the starting material over a substrate so as to deposit fibres onto the substrate;
c) forming a three dimensional fibre matrix; and
d) curing the binder.
4. A fibre preform according to claim 3 wherein step d) comprises curing the binder by the application of heat whilst applying a pressure of 5 kPa or more.
5. A fibre preform according to claim 4 wherein step d) comprises curing the binder by the application of heat whilst applying a pressure of 50 kPa to 50000 kPa or more.
6. A fibre preform according to claim 5 wherein step d) comprises curing the binder by the application of heat whilst applying a pressure of such as from 100 kPa to 25000 kPa or more.
7. A fibre preform according to claim 4 wherein in step d) the pressure is applied to the fibrous matrix while the matrix contains moisture.
8. A fibre preform according to claim 1 in which the fibres are arranged in x, y and z directions and from 5 to 30 wt % of the fibres are arranged substantially in the z direction.
9. A fibre preform according to claim 1 wherein the preform is a monolithic structure.
10. A fibre preform according to claim 1 wherein the percentage of binder in the product is from 5% to 60% of the weight of the dried fibrous matrix.
11. A fibre preform according to claim 10 wherein the percentage of binder in the product is from 5% to 30% of the weight of the dried fibrous matrix.
12. A fibre preform according to claim 11 wherein the percentage of binder in the product is from 5% to 20% of the weight of the dried fibrous matrix.
13. A fibre preform according to claim 1 wherein the binder is selected from the group consisting of: epoxy novolac binders, urethanes, acrylics, methacrylates, styrenes, polyurethane co polymers, phenols, poly vinyl imides, poly vinyl alcohols, vinyl acetate/vinyl chloride copolymers, polyamides, PVC, PVDC, polyvinyl sulphones, PEEK (poly ether ketone) materials, polyesters, polyhydroxyether and epoxy materials, castor based hydroxy functional polyols, organic binders, silane binders, acrylic latex binders, highly carbonisable imide binders, and polyvinylpyrrilidone binders.
14. A fibre preform according to claim 13 wherein the binder is selected from the group consisting of: epoxy novolac binders, phenols, poly vinyl imides, poly vinyl alcohols, vinyl acetate/vinyl chloride copolymers, PEEK (poly ether ether ketone) materials, polyhydroxyether and epoxy materials, castor based hydroxy functional polyols, acrylic latex binders, highly carbonisable imide binders, and polyvinylpyrrilidone binders.
15. A fibre preform according to claim 1 in which the preform contains 20% or more of voids by volume.
16. A fibre preform according to claim 15 in which the preform contains 20% to 75% of voids by volume.
17. A fibre preform according to claim 1 wherein the preform has a fibre volume fraction of from 20% to 40%.
18. A carbon-composite product that comprises a fibre preform as defined in claim 1 .
19. A laminated fibre preform which comprises at least one layer of a fibre preform as defined in claim 1 and one or more layers of aramid fibres.
20. An article for use in high temperature applications comprising a preform as defined in claim 1 .
21. The article of claim 20 , which is an article for use in brakes or rocket motor housings.
22. The article of claim 21 , wherein the article is a brake shoe lining.
23. A method of producing an article for use in high temperature applications, the method comprising the steps of:
(i) providing a preform as defined in claim 1 ; and
(ii) carrying out a CVD or CVI process on the preform.
24. A method of making a fibre matrix, comprising the steps of:
a) providing a starting material which comprises liquid carrier, fibres and binder;
b) passing the starting material over a substrate so as to deposit fibres onto the substrate;
c) forming a three dimensional fibre matrix as defined in claim 1 ; and
d) curing the binder.