GB2268502A

GB2268502A - Friction material

Info

Publication number: GB2268502A
Application number: GB9214137A
Authority: GB
Inventors: Mahmoud Lotfipour
Original assignee: Ferodo Ltd
Current assignee: Federal Mogul Friction Products Ltd
Priority date: 1992-07-03
Filing date: 1992-07-03
Publication date: 1994-01-12
Anticipated expiration: 2012-07-03
Also published as: GB9214137D0; GB2268502B

Abstract

A friction material comprises an organic resin, filler and a particulate inorganic material of Moh hardness 3 to 6 and a particle size in the range from 1 to 4mm. Preferred inorganic materials include magnesium oxide. Other suitable inorganic materials comprise titania, calcium carbonate, dolomite, magnesium-, iron- and zinccarbonates. The resin may be 8 rubber and/or a thermosetting resin, e.g. a phenolic resol. The filler may comprise a solid lubricant and reinforcing fibres e.g. steel, inorganic and/or organic fibres, and graphite. The friction material may be used in brake blocks and disc brake pads particularly for railway braking applications.

Description

Improved friction materials This invention relates to brake blocks and or disc brake pads particularly for use in railway braking applications.

Such blocks or pads are herein generally referred to as friction materials.

Traditional friction material formulations have included as an ingredient finely divided silica, typically ground sand with a particle size of less than 0.5mm. The silica forms about 50-60% by volume of the block or pad, the remainder of which comprises thermosetting resin, and/or rubber and usually also a solid lubricant, such as graphite, together with fibres and fillers.

In the case of disc brake pads, finely divided silica causes excessive wear to the disc. In the case of wheel tread braking, wheel wear is less important because wheel rims are less susceptible to wear because of their relatively great hardness, which is in part at least due to work hardening in use.

Silica is a relatively hard material with a Moh hardness of about 7. In use, braking also results in the release of silica in the form of a respirable dust. This is potentially hazardous, especially in the tunnels of an underground railway system. Reducing the level of silica present is helpful, but results in inferior braking performance in wet conditions. Increasing the silica particle size results in excessive wear, although it reduces dust formation. In fact, particle size and hardness are important factors in the formulation of a friction material of this.type.

According to this invention, a friction material comprises an organic resin, filler and a particulate inorganic material having a Moh hardness in the range 3 to 6 and a particle size of from about 1 to about 4mm. The particulate inorganic filler is preferably magnesium oxide, but may be selected from the group comprising titania, calcium carbonate, calcium/magnesium carbonate (dolomite), magnesium carbonate, iron carbonate and zinc carbonate.

The friction material preferably includes from 20-80% by volume of the particulate inorganic material, according to the intended operating or Service temperature, the higher amounts being appropriate for higher temperatures. For particularly severe applications, a range of from 40-80% by volume is preferred. Of the remainder, the organic resin may comprise a thermosetting resin, typically a phenolic resol, or it may comprise a mixture of such a resin and rubber. Typical rubbers include NBR. The filler may be any of the fillers conventionally used for such purposes, for example it may comprise a solid lubricant. Commonly used fillers include graphite (also as a lubricant), barium sulphate, reclaimed (cured) rubber particles. Minor amounts of curing agents such as sulphur, caustic soda and the like may also be present as required.The friction material may also comprise reinforcing fibres such as steel fibres, inorganic and/or organic fibres. The resin may be initially in liquid or solid form, or both, prior to manufacture of the block or pad.

The invention will now be described by way of example with reference to the following Examples.

Example I A brake block was made from the following formulation: Liquid cresol resin 28% (by volume) (80-85% resin solids by wt) Dry thermosettable cresol resin 12% (by volume) Organic fibres 2% (by volume) (50/50 mix of PAN fibres and aramid fibres) Filler 13% (by volume) (reclaimed cured rubber - 30 mesh - 600 micron particles) Magnesium oxide 45 (by volume) (particle size 1-3mm) The formulation was mixed in a Baker-Perkins mixer for about 15 minutes to produce a dough which was then press cured at 1500C under a pressure of 150 tonnes into railway brake blocks. Press curing was followed by open baking for 10 hours at 200"C to complete the cure. The blocks when tested on a dynamometer set up to simulate a railway wheel environment performed satisfactorily, both in wet and dry conditions.They did not yield unacceptable volumes of fine dust.

Example II A railway disc brake pad was made from the following formulation: Liquid phenolic resol resin 11% (by volume) (80% solids by wt) Liquid rubber 4% (by volume) (100% NBR oligomer) Solid lubricant 21% (by volume) (natural graphite, 75 micron particle size) Magnesium oxide 64% (by volume) (particle size 1-3mm) This was processed into railway disc brake pads, as follows.

The graphite and magnesium oxide were dry mixed for one minute prior to adding the resin and rubber and mixing for a further four minutes, in a Baker-Perkins mixer. The product was a coarse powder, which was dried for two hours prior to disintegrating by hammer milling on a 6mm screen.

The resultant powder was pressed into brake pads at 7 tsi for five seconds. The pads were then stack cured at 1500C for an hour. On testing on a dynamometer, they were satisfactory up to and above temperatures of 6000C.

Claims

1. A friction material comprising an organic resin, filler and a particulate inorganic material of Moh hardness 3 to 6 and a particle size of about 1 to about 4mm.

2. A friction material according to claim 1 wherein the particulate inorganic material is magnesium oxide.

3. A friction material according to claim 1 wherein the particulate inorganic material is selected from the group comprising titania calcium carbonate, calcium/magnesium carbonate (dolomite), magnesium carbonate, iron carbonate and zinc carbonate.

4. A friction material according to any preceding claim wherein the particulate inorganic material comprises from 20-80% by volume.

5. A friction material according to any of claims 1 to 3 wherein the particulate inorganic material comprises from 40-80% by volume.

6. A friction material according to any preceding claim wherein the organic resin is a rubber or . a thermosetting resin, or both.

7. A friction material according to any of Claims 1-6 wherein the filler comprises a solid lubricant.

8. A friction material substantially as described and illustrated by Example 1 or 2.

8. A friction material according to claim 7 wherein the filler further comprises fibres.

9. A friction material substantially as described and illustrated by Example 1 or 2.

Amendments to the claims have been filed as follows 1. A friction material comprising an organic resin, filler and a particulate inorganic material of Moh hardness 3 to 6 and a particle size of about 1 to about 4mm wherein said particulate inorganic material is selected from the group comprising magnesium oxide, titania, calcium carbonate, calcium/magnesium carbonate (dolomite), magnesium carbonate, iron carbonate and zinc carbonate.

3. A friction material according to any preceding claim wherein the particulate inorganic material comprises from 20-80% by volume.

4. A friction material according to any of claims 1 to 3 wherein the particulate inorganic material comprises from 40-80t by volume.

5. A friction material according to any preceding claim wherein the organic resin is a rubber or a thermosetting resin, or both.

6. A friction material according to any of Claims 1-6 wherein the filler comprises a solid lubricant.

7. A friction material according to claim 7 wherein the filler further comprises fibres.