Compositions: coating or plastic – Coating or plastic compositions – Tractive or friction surface
Patent
1998-07-09
1999-10-26
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Tractive or friction surface
106600, 10628726, 427421, 427427, 427428, 427429, 4274301, C09K 314
Patent
active
059720905
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with stabilising friction levels. The invention is applicable, inter alia, to brakes for automotive, railway or industrial applications. The invention is particularly applicable to brake pads or linings of the type which comprise particulate material bonded together by a cured binder, eg a phenolic resin.
In brakes, a friction material is pressed against a surface to create frictional forces. The size of the frictional forces depends on the pressure applied, and on characteristics of the friction material and of the surface engaged thereby. The relevant characteristics of the friction material are referred to herein as its "friction level". For example, the braking force available from a disc brake depends on the frictional level of the pads which are pressed against the disc.
In service, it is desirable that a brake friction material exhibits a stable friction level in order to achieve consistent braking forces. However, it is found that the friction level of a newly-installed friction material, herein referred to as the "green friction level", is often lower than the friction level achieved after a period in service, herein referred to as the "nominal friction level". The increase in the friction level in service is caused by "bedding in" increasing the operative surface area, and by heat generated during braking altering the structure of the friction material. This leads to inconsistent friction levels between installation and achievement of the nominal friction level, herein referred to as the "initial friction level" and inconsistent braking.
Many brake pads and linings are manufactured from a mixture of various friction-enhancing particles and uncured phenolic resin which is compressed, and subjected to heat to cure the phenolic resin. It is known to attempt to stabilise the initial friction level by coating a newly-manufactured brake pad or lining of this type with phenolic resin containing particulate alumina. The resin acts as a carrier for the alumina which acts to enhance the friction. This type of coating gives a temporary increase in the friction level until it wears away, thereby resulting in an improvement in stability. However, while this type of coating increases the green friction level, it is found in practice that the coating often wears away before the pad achieves its nominal friction level. This results in the friction level of the pad or lining falling from its green level before recovering to its nominal friction level. This results in a period during which the friction level is not stable. Furthermore, such coatings may smell or even burn.
It is an object of the present invention to provide an improved method of stabilising the initial friction level of a brake friction material.
The invention provides a method of stabilising the initial friction level of a brake friction material, characterised in that the method comprises coating the friction material with a coating which is insoluble in water and which comprises a binder selected from alkali metal silicates and metal alkoxides.
It is found that a method according to the invention enables the initial friction level to be stabilised to a greater extent. Furthermore, no smell or burning problem is experienced. It is also found that the coating seals the surface of the pad or lining reducing corrosion during storage.
The binder may be applied with a solvent, eg as an aqueous solution.
The coating may also comprise particulate friction-enhancing material which forms a slurry with the binder. The particulate friction-enhancing material is preferably inorganic to avoid fading of the friction level and must not react with the pad. Fine particles are preferred which may, for example, be selected from minerals, ceramics, certain metal oxides, carbides, metal phosphates, and silicates. Preferred materials are alumina, and silicon carbide. Preferably, the particulate friction-enhancing material comprises a mixture of two or more materials, in order to allow the green friction level and, if desired, the visual ap
REFERENCES:
patent: 5433774 (1995-07-01), Kapl et al.
patent: 5482742 (1996-01-01), Takamiya et al.
Patent Abstracts of Japan, JP61106687 dated May 1986, entitled Frictional Material for Vehicle (Aisin Chem. Co. Ltd.) (2 pages).
Patent Abstracts of Japan, JP4151035 dated May 1992, entitled Frictional Member Pad (Sumitomo Electrical Ind. Ltd.) (1 page).
Patent Abstracts of Japan, JP4183774, dated Jun. 1992, entitled Friction Material (Toyota Motor Corp.) (2 pages).
Patent Abstracts of Japan, JP2008522 dated Jan. 1990, entitled Shim for Disc Brake (Akebono Brake Tes. & Dev. Centre Ltd.) (2 pages).
Patent Abstracts of Japan, JP60013875 dated Jan. 1985, entitled Surface-Treated Metallic Filler and Molding . . . (Matsushita Electric Works Ltd.) (1 page).
Derwent WPI, JP58077934 dated May 1983, entitled High Friction Material for Clutch Facings (Hitachi Chem. Co. Ltd.) (1 page).
Ferodo Bremsbelage Technik-Zentrum GmbH
Green Anthony
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