GB2138898A - Friction lining for brakes - Google Patents

Abstract

The lining particularly for bicycle rim-brakes but also for disc- and drum-brakes consists at least in part of cork. The lining may consist entirely of compacted cork or may additionally comprise a binding agent (mixture) conveniently in proportion of from 1 to 80% by weight e.g. synthetic resin, elastomers. Filler materials may also be used such as organic and/or inorganic fibrous materials. In the illustrated embodiment, grains 1 of coarse-grained cork powder are embedded into a binding agent mixture 2 and arrive continuously at front face 3. The lining is said to provide improved braking under wet conditions for bicycle rim-brakes. <IMAGE>

Description

SPECIFICATION Friction lining for brakes This invention relates to a friction lining for brakes, in particular for brakes on bicycles or suchlike.

Bicycle brakes, particularly so-called rim brakes, have until now been in the form of friction brakes comprising blocks of rubber mixtures of various compositions. In dry weather, these brake linings cause sufficient deceleration. However, as soon as the friction surface of the brake rim is wet, for example in damp weather or when the roadway is wet, the braking effect of these friction linings greatly declines. The stopping distance on full braking may then be up to 10 times greater than when the roadway is dry. It makes difference in this connection which material is selected for the friction surface of the rim as a friction counterpart to the friction lining.

In order to remedy this disadvantage, it has been attempted to provide the brake blocks on rim brakes with tunnel- or slot-shaped profiling, to thereby improve the braking behaviour in a so-called "wet brake". However, these purely structural measures are not sufficient to shorten significantly the stopping distance of a "wet brake". The attempt at providing the friction surface on the rim with profiling has just as little success.

It is an object of the invention to provide a friction lining in which the deviations in friction behaviour between "dry brake" and "wet brake" conditions are no longer as extreme as is the case with the hitherto conventional friction linings.

According to the present invention there is provided a friction lining for brakes, wherein the lining material consists at least in part of cork.

Surprisingly, it has been shown that with a lining material containing cork, stopping distances are achieved both with a "wet brake" and a "dry brake" which are only able to be achieved on a "dry brake" with the conventional bicycle brake linings. Through this, a considerable improvement to the cyclist's safety is created. This applies in particular to sports cycles which have been widespread for some time, which are equipped with a rim brake both on the front and rear wheels and which until now represented a considerable safety risk in wet weather, presented by the insufficient braking power of the conventional brake linings.

In one embodiment of the invention, the lining material consists of compacted cork, in which the proportion of cork amounts to 100%-wt. Friction linings such as this are produced for example by compression moulding, in which it is immaterial in which external form the cork is used, whether in the form of a powder, a granular material, in coarse pieces or sheets.

In a preferred embodiment, however, the cork is bound with a binding agent. It is expedient to use those binding agents or binding agent mixtures which are conventional in the friction lining industry. Through this step, the intrinsic strength of the friction lining is further improved. Suitable binding agents include both synthetic resins, for example phenol-, cresol-, melamine-, novolac-, epoxy- and polyester- resins and the like or mixtures thereof, as well as elastomers, for example natural rubber or synthetic rubbers based on styrene, nitrile rubbers, butadiene, isoprene, chlorobutylene, latices or the like, and mixtures thereof. Binding agents are preferred which bind the cork in, largely maintaining its porosity.

The binding agent is conveniently used in a proportion of from 1 to 80, preferably 1 to 60 %-wt. With a proportion of binding agent of 1%, practically "pure" cork linings are produced, whereas with a proportion of binding agent of 60%-wt., filler materials may also be used in addition together with the cork, which modify the friction behaviour. With filler materials such as this it is possible to produce a friction lining with optimum braking properties, for the conventional friction surfaces in bicycle construction, for example on the rims.

Thus it is expedient to add additives for steel rims to improve the frictional performance, which increase the coefficient of friction. In the case of rims made of aluminium or aluminium alloy it is expedient to add filler materials which are known as so-called sliding aids. The mixture of binding agent and filler material may constitute from 1 to 98%-wt. of the lining. Whereas for normal operations two standard mixtures are sufficient, which are adapted to steel and aluminium rims, for racing cycles which are ridden at considerably higher speeds than a bicycle in normal operation, mixtures will be composed, as far as possible, which are adapted quite specifically to the rim material used. In combination with or in place of such filler materials, organic and/or inorganic fibrous materials may be added as filler materials in addition to the binding agent.The fibres here may have a systematic structure in the form of woven fabrics, twines or suchlike, or else they may be introduced in a random form, for example as fibre cuttings or the like. The fibres may serve to bring about a higher mechanical strength of the lining, and with a suitable selection of material, they can fulfill the functions of sliding and/or friction aids.

Friction lining compositions of cork and binding agents or of cork and binding agentfiller material mixtures also have the advantage that the workability is improved compared with pure cork, since through the addition of the binding agents, depending on the type of binding agent which is added, the lining material is able to be worked by cold pressing, hot-pressing, extrusion pressing or by injection or extruding, calendering or roll ing.

In order to enable the invention to be more readily understood reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is perspective view, partly in section, of a brake block for a rim brake, Figure 2 is a test stand measurement dia gram for a conventional lining with a "dry brake", Figure 3 is a test stand measurement diagram for a conventional ling with a "wet brake", Figure 4 is a test stand measurement diagram for a lining according to the invention with a "dry brake", Figure 5 is a test stand measurement diagram for a lining according to the invention with a "wet brake".

Referring now to Fig. 1, there is shown a cross section on enlarged scale through a brake block for a bicycle rim brake. On this embodiment, the grains 1 of a coarse-grained cork powder are embedded into and distributed throughout a binding agent mixture 2.

In operation, the front face 3 of the block comes to rest against an associated friction surface of the bicycle rim in the braking process. Owing to the even distribution of the cork grains in the binding agent matrix 2, despite the wear, cork grains continuously arrive at the surface 3 and thereby come into contact with the rim in the braking process.

Figs. 2 to 5 are measurement diagrams determined on a bicycle simulation test stand both for dry and wet braking. The following test conditions were given: At a given speed 16 km/h, a weight to be braked (cyclist plus cycle) of 100 kg., and with aluminium rims, a braking cycle of 30 sec. in each case was run until standstill.

Fig. 2 shows a stopping distance of approximately 2.5 to 3 m. With a conventional lining material for bicycle rim brakes with a "dry brake" on 20 successive stop braking actions.

Fig. 3 shows the measurements with a wet brake" for the same conventional lining material. Here, even at the first braking action, a stopping distance of approximately 12 m. was required, whereas on the 20th braking action a stopping distance of approximately 23 m. was required.

In comparison with this, a friction brake according to the invention was tested under the same conditions. Fig. 4 and Fig. 5 show that both for the "dry brake" and also for the "wet brake" constant stopping distances of approximately 3 m. were maintained over the entire testing cycle, i.e., the frictional behaviour was almost the same in both cases.

The present "cork" friction lining is not only suitable for the example of the bicycle rim brake which is described, but in the same way is also able to be used advantageously for disc- and drum-brakes of different instances of application. In the latter case, the linings are not made up in the form of pads or blocks, but in the form of strips which are fastened to the lining support of the drum brake. The present friction lining can be made free of asbestos.

Claims (11)

1. A friction lining for brakes, wherein the lining material consists at least in part of cork.

2. A friction lining as claimed in Claim 1, wherein the lining material consists of compacted cork, in which the proportion of cork amounts to 1 00%-wt. of the lining.

3. A friction lining as claimed in Claim 1, wherein the cork is bound with a binding agent.

4. A friction lining as claimed in Claim 3, wherein the cork is embedded in a binding agent matrix in the form of pieces or grains.

5. A friction lining as claimed in Claim 3 or 4, wherein the binding agent constitutes from 1 to 80%-wt. of the linings.

6. A friction lining as claimed in any one of Claims 3 to 5, wherein the binding agent constitutes from 1 to 60%-wt. of the lining.

7. A friction lining as claimed in any one of Claims 3 to 6, wherein the binding agent is mixed in addition with filler materials, which modify the frictional behaviour of the lining.

8. A friction lining as claimed in any one of Claims 3 to 7, wherein the binding agent is mixed in addition with a fibrous material as filler material.

9. A friction lining as claimed in Claim 7 or 8, wherein the mixture of binding agent and filler material constitutes from 1 to 98%wt. of the lining.

10. A friction lining as claimed in any one of Claims 1 to 9, wherein the friction lining is for a bicycle brake.

11. A friction lining for brakes substantially as hereinbefore described with reference to Figs. 1, 4 and 5 of the accompanying drawings.