US3525006A - Carbon fibre brush - Google Patents

Description

Aug. 18, 1970 L, ETAL CARBON FIBRE BRUSH Filed Feb. 29, 1968 QIQQ United States Patent Oflice 3,525,006 Patented Aug. 18, 1970 3,525,006 CARBON FIBRE BRUSH Norman Lawrence Parr, Wareham, Dorset, Sam Bolshaw,

Bath, Somerset, and Edwin Richard Wells May, Moordown, Bournemouth, England, assignors to National Research Development Corporation, London, England, a British corporation Filed Feb. 29, 1968, Ser. No. 709,444 Int. Cl. H011 39/26 U.S. Cl. 310251 4 Claims ABSTRACT OF THE DISCLOSURE A carbon brush comprising an aligned array of juxtaposed carbon or graphite fibres wherein the contact surface of said brush is formed by the ends of said fibres. The fibres may be bonded to each other for a part of their length either by means of an epoxy resin or by electroplating the ends of said fibres.

This invention relates to electrical brushes having an improved current carrying capacity by means of more efiicient surface contact.

According to the present invention a carbon brush comprises an aligned array of juxtaposed carbon or graphite fibres wherein the contact surface of the brush is formed by the ends of the fibres.

Referring, by way of example, to the accompanying drawing, which illustrates a brush according to the present invention, an aligned array of juxtaposed carbon or graphite fibres 1, which are bonded to each other over a portion of their length 2 by an epoxide resin, are encapsulated in a soft metal can 3 open at one end. Electrical conductivity at the non-contact end of the brush is ensured by electro-plating the ends 4 of the fibres which in turn are soldered to the closed end of the can 5.

Carbon brushes of dimensions /2" x 1" x 2 long have been produced in accordance with the invention. Sufficient carbon or graphite fibres of suitable length and diameter are placed in a three sided metal container and compressed with the fibres protruding from the container by about at one end and about 4 at the other. The fourth side of the container is then crimped and soldered into position whilst the fibres are under compression. The assembly is then placed vertically in a vessel containing diluted epoxy resin (e.g. Araldite MY 753 (registered trademark) diluted with %-10% acetone) in such a manner that resin is drawn, by capillary attraction, into the fibres to a predetermined height. The whole is then allowed to stand" until the resin cures. Excess resin is then removed and the resin-bond end of the fibre block faced level with the container to expose the ends of the fibres, which are electroplated to a continuous sheet of copper and then tinned with 60/40 solder. The end closure of the container, which has been previously tinned, is then folded down to meet the tinned end of the fibre block and the whole sweated together. A flexible electrical connection is then soldered to the container as desired. A suitable material for the container or can is copper sheet of 0.02 in gauge for this size of brush.

Experience has shown that resistance heating in individual fibres can lead to overheating of the brush and thus produce degradation of the epoxy resin. It has been found that this can be overcome by using shortened brushes and by bonding the fibres at the non-contaot end of the brush by low energy copper electro-plating of the tips of the fibres and thereby dispensing with the need to anchor the fibres with epoxy resin.

'In one example, small brushes in length by A" x 1" have been made without the use of epoxy resin. The fibres are encapsulated in a copper container as previously described and the assembly is then placed vertically in a copper plating bath. Electrolyte is drawn into the bundle of fibres by capillary attraction and the ends of the fibres are plated to a depth of .005. Further time in the plating bath results in the encasement of the ends of the fibres in a continuous matrix of copper, which is then tinned with /40 solder and the end closure of the container, which has been previously tinned, is then folded down to meet the tinned end of the fibre block and the whole sweated together.

It has also been found that control of the build-up of resistive oxide films on the commutator can be accomplished by the introduction of a selected number of fibres in the brush (e.g. glass, metals or other abrasive materials) to impart a limited degree of wear.

We claim:

1. A carbon brush comprising an aligned array of juxtaposed carbon fibres wherein the contact surface of said brush is formed by the ends of said fibres said array including a number of fibres of abrasive material.

2. A carbon brush according to claim 1 wherein said abrasive fibres are of glass.

3. A carbon brush comprising an aligned array of juxtaposed carbon fibres wherein the contact surface of said brush is formed by the ends of said fibres said fibres being bonded to each other for a part of their length by an epoxy resin.

4. A carbon brush according to claim 3 wherein said array includes a number of fibres of abrasive material.

References Cited UNITED STATES PATENTS 539,453 5/1895 Thomson 310--248 539,454 5/1895 Thomson 310-248 3,382,387 5/1968 Marshall 310-248 MILTON O. HIRSHFIELD, Primary Examiner L. L. SMITH, Assistant Examiner U.S. C1. X.R. 310252

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