GB1601891A

GB1601891A - Cycle brake blocks

Info

Publication number: GB1601891A
Application number: GB1528278A
Authority: GB
Original assignee: Shimano Industrial Co Ltd
Current assignee: Shimano Inc
Priority date: 1977-04-18
Filing date: 1978-04-18
Publication date: 1981-11-04
Also published as: FR2387838B1; DE2816887A1; DE2816887C2; FR2387838A1

Description

(54) CYCLE BRAKE BLOCKS (71) We, SHIMANO INDUSTRIAL COMPANY LIMITED, a company organized and existing under the laws of Japan. of 77, 3-cho, Oimatsu-cho, Sakai-shi, Osaka, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to cycle brake blocks for use in brakes provided on cycles including motorized cycles.

A caliper or rim brake on a cycle exerts its braking action by pressing a brake block composed of a suitable friction material against the rim of one of the wheels of the cycle. In rainy weather, this friction material is exppsed to water.

Brake blocks for such caliper brakes are conventionally formed of rubber, usually a synthetic rubber. When rubber. and especially synthetic rubber, is exposed to the atmosphere in the course of its use in a brake block, its coefficient of friction with respect to its contact with the wheel rim varies significantly between wet and dry conditions, thus affecting the braking action of the brake. In wet conditions, the braking action of synthetic rubber brake blocks greatly deteriorates and a dangerous time lag may occur between the moment a cyclist applies the brake and the moment at which proper braking begins. This can make cycling in wet weather very dangerous.

The present invention seeks to provide a brake block of a friction material such that loss of braking action under wet conditions is considerably reduced when compared with cycle brake blocks made of material hitherto used in brake blocks.

The present invention provides a brake block composed of a friction material comprising at least one synthetic rubber selected from a synthetic silicone rubber and a synthetic butadiene rubber, intimately admixed with from 50 to 75% by weight of the friction material of at least one of titanium oxide, tin oxide and cobalt oxide.

If the weight proportion of metal oxide in the friction material falls below 50%, the coefficient of friction between the brake block composed of the material and a wheel rim falls (as shown below) and the braking action still deteriorates too much in wet conditions.

No significant increase in the coefficient of friction under dry conditions is obtained when the proportion of metal oxide is raised above 50%, and the braking effect under wet conditions tends to reach its maximum value at about 70% metal oxide. If the proportion of metal oxide is raised above 75%, the friction material becomes difficult to mould into brake blocks and the surface of such blocks tends to peel off when they are pressed against wheel rims during braking. Also, the braking performance under wet conditions tends to deteriorate. Finally, if the proportion of metal oxide is 80% or more, the braking effect obtained is too low for safety, the wear resistance of the material is poor and contact of the material with a wheel rim causes vibrations which are uncomfortable for the cyclist.

Accordingly. the proportion of metal oxide used in the friction material of the invention is from 50 to 75-c bv weight of the material.

The synthetic rubber used in the friction material of the invention desirably is or includes a synthetic rubber, preferred synthetic rubbers being nitrile-butadiene and butadiene styrene rubbers. Alternatively a synthetic silicone rubber may be employed. The friction material may contain any one or more of carbon, a vulcanizing accelerator, an aging retarder, a plasticizer and a binder. The hardness of the friction material of the invention is desirably at least 85, and preferably at least 92, degrees IRH (International Rubber Hardness scale).

Preferably, in preparing a friction material of the invention, the metal oxides are blended with the synthetic rubber by being silane-coupled thereto, the weight of silane used in the coupling process being from 0.6 to 3.0% of the weight of the metal oxides.

Preferred embodiments of the invention will now be described, though by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is a graph showing the coefficient of friction between brake blocks formed of friction materials containing varying proportions of titanium oxide under dry conditions; Figure 2 is a graph of braking times against braking load for brake blocks formed of three different friction materials and of one conventional friction material, under wet conditions; and Figure 3 is a graph of the braking times obtained with brake blocks formed of a friction material of the invention under wet conditions during repeated braking.

First series of tests The results shown in Figure 1 were obtained as follows. A liquid silane having a functional group was dissolved with agitation in water or an organic solvent and titanium oxide added, the amount of silane used being from 0.6 to 3 weight per cent of the weight of the titanium oxide (wet process). Alternatively, the same relative amounts of silane may be added directly to titanium oxide in solution (dry process). The silane-coupled titanium oxide was then blended with the synthetic rubber and become strongly bonded thereto, thereby preventing it becoming separated therefrom in use. Finally the blended material was formed into brake blocks. The results shown in Figure 1 show that the coefficient of friction between the brake blocks and a bicycle rim increases as the proportion of titanium oxide is increased to 50% but thereafter remains substantially constant over the range 50 to 75% titanium oxide.

Second series of tests Three friction materials were prepared containing from 50 to 75% of titanium oxide, tin oxide and cobalt oxide respectively, all three materials having a hardness of 92 IRH. The preparation of the materials was effected substantially as in the first series of tests. The friction materials were then formed into brake blocks, and compared with a conventional brake block as follows.

The aforesaid brake blocks were used to brake a 26" diameter bicycle wheel rotating at 200.4 r.p.m. (corresponding to a bicycle speed of 25 k.p.h.). The moment of inertia of the wheel was J = 1.0 kg.m.sec2. and its kinetic energy at full speed 221.34 kg.m. The wheel was kept wet and the brake blocks applied thereto under pressures of 12, 32, 52, and 72 kg.

(corresponding to contact pressures of 10, 20, 30 and 40 kg.cm.-2 respectively). The times taken to bring the wheel to rest in seconds were as follows: Contact Pressure Block containing (kg.cm-) 10 20 30 40 Titanium oxide (Block A) 9.2 4.1 3.3 3.2 Tin oxide (Block B) 9.8 4.6 3.5 3.3 Cobalt oxide (Block C) 10.2 4.7 3.7 3.5 Conventional Block D (Control) 31.8 18.8 14.1 12.2 " (under dry conditions) 4.6 2.0 1.5 The results are presented graphically in Figure 2 and it will be seen that the braking effect of all three blocks of the invention is about three to four times that of the conventional block under wet conditions.

Third series of tests The four blocks used in the second series of tests were tested for repeated braking under the same conditions using a contact pressure of 20 kg.cm-2, the wheel of course being kept wet throughout. The interval between successive braking cycles was less than the time required to dry or half-dry the wheel. The results for all three blocks of the invention were similar and are represented by the solid line in Figure 3, the results for the conventional block D being shown by the dashed line. It will be seen that all the braking times obtained with the blocks of the invention were less than six seconds, as is required for satisfactory road use under wet conditions, whereas the times for the conventional block are far above this figure. Furthermore. the times for the blocks of the invention were relatively constant during repeated braking, whereas these for the conventional block increased rapidly.

Further tests using brake blocks of the invention containing 70% metal oxides yield results corresponding to the dash-dot line in Figure 3 with braking times consistently below four seconds.

EXAMPLES Example I 31.' parts by weight of a silicone rubber were blended with 65.2 parts by weight of silane-coupled titanium oxide and 6.3 parts by weight of additives comprising carbon, a vulcanizing accelerator. an aging retarder, a plasticizer and a binder, and formed into a brake block having a hardness of 91 degrees IRH. The braking performance of this brake block was substantially the same as that of block A in the second and third series of tests described above.

Exlzmple 2 32.5 parts by weight of a nitrile-butadiene rubber containing the same additives as mentioned in Example 1 were blended with 67.5 parts by weight of silane-coupled titanium oxide and formed into a brake block having a hardness of 89 degrees IRH.

The braking performance of this brake block was substantially the same as that of block A in the second set of tests described above, but in the third series of tests its performance was substantially as shown by the dash-dot line in Figure 3.

Exlrmple 3 30 parts by weight of a butadiene-styrene rubber containing the same additives as mentioned in Example 1 were blended with 70 parts by weight of silane-coupled titanium oxide and formed into a brake block having a hardness of 89 degrees IRH.

The braking performance of this block was substantially the same as that prepared in Example 2.

The above results show that the braking performance of brake blocks of the invention is at least as good as that of brake blocks made of conventional materials under dry conditions. and markedly superior to that of the latter under wet conditions, under which conditions the time lag experienced with conventional materials is substantially eliminated.

Furthermore. the brake blocks of the invention possess good wear resistance.

WHAT WE CLAIM IS: l. A brake block for a cycle which brake block is composed of a friction material comprising at least one synthetic rubber selected from a synthetic silicone rubber and a synthetic butadiene rubber, intimately admixed with from 50 to 75% by weight of the friction material of at least one of titanium oxide, tin oxide and cobalt oxide.

2. A brake block as claimed in claim 1, in which said at least one synthetic rubber is nitrile-butadiene or butadiene-styrene rubber.

3. A brake block as claimed in claim 1 or claim 2, in which the friction material includes any one or more of carbon. a vulcanizing accelerator, an aging retarder, a plasticizer and a binder.

4. A brake block as claimed in any one of the preceding claims in which the friction material has a hardness of at least 85 degrees IRH.

5. A brake block as claimed in claim A. in which the friction material has a hardness of at least 92 degrees IRH.

6. A brake block as claimed in any one of the preceding claims, in which the said oxide or oxides are silane-coupled to said synthetic rubber.

7. A brake block as claimed in claim 6. in which the weight of silane used in the coupling process is from 0.6 to 3Xc of the combined weight of the said oxide or oxides.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Third series of tests The four blocks used in the second series of tests were tested for repeated braking under the same conditions using a contact pressure of 20 kg.cm-2, the wheel of course being kept wet throughout. The interval between successive braking cycles was less than the time required to dry or half-dry the wheel. The results for all three blocks of the invention were similar and are represented by the solid line in Figure 3, the results for the conventional block D being shown by the dashed line. It will be seen that all the braking times obtained with the blocks of the invention were less than six seconds, as is required for satisfactory road use under wet conditions, whereas the times for the conventional block are far above this figure. Furthermore. the times for the blocks of the invention were relatively constant during repeated braking, whereas these for the conventional block increased rapidly.

Further tests using brake blocks of the invention containing 70% metal oxides yield results corresponding to the dash-dot line in Figure 3 with braking times consistently below four seconds.

EXAMPLES Example I

31.' parts by weight of a silicone rubber were blended with 65.2 parts by weight of silane-coupled titanium oxide and 6.3 parts by weight of additives comprising carbon, a vulcanizing accelerator. an aging retarder, a plasticizer and a binder, and formed into a brake block having a hardness of 91 degrees IRH. The braking performance of this brake block was substantially the same as that of block A in the second and third series of tests described above.

Exlzmple 2 32.5 parts by weight of a nitrile-butadiene rubber containing the same additives as mentioned in Example 1 were blended with 67.5 parts by weight of silane-coupled titanium oxide and formed into a brake block having a hardness of 89 degrees IRH.

The braking performance of this brake block was substantially the same as that of block A in the second set of tests described above, but in the third series of tests its performance was substantially as shown by the dash-dot line in Figure 3.

Exlrmple 3 30 parts by weight of a butadiene-styrene rubber containing the same additives as mentioned in Example 1 were blended with 70 parts by weight of silane-coupled titanium oxide and formed into a brake block having a hardness of 89 degrees IRH.

The braking performance of this block was substantially the same as that prepared in Example 2.

The above results show that the braking performance of brake blocks of the invention is at least as good as that of brake blocks made of conventional materials under dry conditions. and markedly superior to that of the latter under wet conditions, under which conditions the time lag experienced with conventional materials is substantially eliminated.

Furthermore. the brake blocks of the invention possess good wear resistance.

WHAT WE CLAIM IS: l. A brake block for a cycle which brake block is composed of a friction material comprising at least one synthetic rubber selected from a synthetic silicone rubber and a synthetic butadiene rubber, intimately admixed with from 50 to 75% by weight of the friction material of at least one of titanium oxide, tin oxide and cobalt oxide.
2. A brake block as claimed in claim 1, in which said at least one synthetic rubber is nitrile-butadiene or butadiene-styrene rubber.
3. A brake block as claimed in claim 1 or claim 2, in which the friction material includes any one or more of carbon. a vulcanizing accelerator, an aging retarder, a plasticizer and a binder.
4. A brake block as claimed in any one of the preceding claims in which the friction material has a hardness of at least 85 degrees IRH.
5. A brake block as claimed in claim A. in which the friction material has a hardness of at least 92 degrees IRH.
6. A brake block as claimed in any one of the preceding claims, in which the said oxide or oxides are silane-coupled to said synthetic rubber.
7. A brake block as claimed in claim 6. in which the weight of silane used in the coupling process is from 0.6 to 3Xc of the combined weight of the said oxide or oxides.
8. A brake block as claimed in claim 1 and substantially as herein described with

particular reference to any one of Examples 1 to 3 and Figures 1 to 3 of the accompanying drawings.