US1991487A - Impregnating carbonaceous brushes with abrasive material - Google Patents

Description

@@arch @mm A. S. BEMIS Feb. 19, 1935.

IMPREGNATING CARBONACEOUS BRUSHES WITH ABRASIVE MATERIAL Filed Feb. 20, 1933 Contnkns deposited obmswe INVENToR rur Bem/s BY RNEY' Patented Feb. 191, 1935 UNITED STATES PATENT OFFICE IMPREGNATING CARBONACEOUS BRUSHES WITH ABRASIVE MATERIAL Arthur S. Bemis, St. Marys, Pa., assignor to Speer Carbon Company, a corporation of Pennsylvana Application February 20, 1933, Serial No. 657,618

6 Claims.

This invention relates to dynamo electric brushes and other contacts and particularly to the impregnating of such articles with an abrasive or polishing substance.

An object of the invention is to impregnato carbonaceous articles such as brushes or other contacts with a minutely divided abrasive or polishing agent preferably uniformly distributed throughout the article.

Another object is to saturate a brush with a liquid that is deccmposable by moderate heat into a solid substance having polishing or abrasive qualities.

Another object is to employ such an abrasive or polishing agent that will not eloresce on the surface in the forming process, or subsequent thereto.

Another object is to use as such agent a material that will not attack, discolor or otherwise harm the copper or other metal contacting therewith.

Another object is to use an abrasive or polishing material that will not have a deleterious effect on the compound usedA to tamp around the flexible cable in fastening it to a carbon article such as a brush, for example.

Movable contacts of copper or brass with ordinary carbon or graphite have long been used in switches and as brushes in dynamo electric machines.

The sole gure of the drawing illustrates a brush containing the invention.

The forms of carbon used are ordinary or amorphous carbon, natural graphite and electrically produced graphite, such as was originally referred to as Acheson graphite either with or Without powdered metal distributed therethrough. Brushes of carbon have been made of amorphous carbon in comminuted form with a binder such as pitch and then baked to cause the pitch to bind the materials together. Both ordinary or amorphous carbon and natural graphite usually contain sufficient quantities of ash to act as an abrasive agent to keep the copper commutator or other contact in clean condition. Additional abrasive materials have sometimes been added to the brush mix for further abrasive eiect. These abrasive materials remain in the brush during the baking process as the baking temperature is not high enough to volatilize them.

Electrical graphite has been used for brushes and other contacts by forming the desired shapes, either the brush itself or larger slabs of carbon stock from which the desired shape may be later sawed, and then heating them to a very high temperature. To produce graphite this temperature must in general be from substantially 2500 C. to 3000 C.

Brushes thus made from electrical graphite are substantially pure carbon, speaking generically, and contain practically no ash as the latter is volatilized at the excessive graphitizing temperature. Such brushes seldom contain more than 0.05 to 0.50 per cent. ash. These materials therefore are practically free of polishing material.

Electrical graphite is an excellent material for making brushes It excells all other forms of carbon except for the lack of a polishing material. Various attempts have been made to eliminate this one defect by incorporating an excess amount of abrasive material in the carbon before graphitization in the hope that enough would survive the high graphitizing temperature to furnish the abrasive for the brush. With all materials thus far tried this has proven impractical. Other attempts have been made to add abrasive' by impregnating the brush with boric acid, calcium chloride and other soluble compounds and then drying out the solvent to leave in the solute.

Boric acid and calcium chloride have high vapor pressures and must be dried slowly after impregnating the brush stock therewith and at carefully controlled temperatures. By this prior process it takes at least a month to prepare the brush without causing the abrasive to eforesce on the surface of the brush, which action would deplete the interior of the impregnating compound.

Also attempts have been made to precipitate an abrasive by soaking a precipitating agent into a brush previously impregnated with a suitable precipitatablc compound but this causes precipitation only at the surface because the precipitated material prevents the reagent from further entering the pores.

Various other attempts have been made to incorporate abrasive material in a brush of electrical graphite but without practical success as far as I am aware.

I have found an entirely practical way of incorporating a polishing or abrasive material in a brush of electrical graphite in a comparatively brief period.

The brushes are made up in the desired form of carbonaceous material, or a slab of brush stock is formed, and then heated electrically to the temperature of graphitization for a sufficient period to convert the carbon into graphite. The graphite brushes, or graphite stock, as the case may be, is then impregnated or saturated with a silicon ester such as ethyl silicate, (C2H4)4Si304. The silicon ester may be readily made by adding anhydrous ethyl alcohol to silicon tetra-chloride. The impregnation is preferably carried on under vacuum with later applied pressure to saturate the brush or stock throughout with the compound. After impregnation the stock is dried in the air for several days and then bake-d to 600 C. or even somewhat higher. This transforms the ethyl silicate into silicon dioxide (SiOz) in extremely ne condition in the pores of the graphite and the whole process may be completed in three days. The quantity of SiOz precipitated in the brush depends among other things, upon the concentration of the ethyl silicate in the ethyl alcohol. Various other esters may also be used, for example, the esters of tin and titanium. These may be made by adding ethyl alcohol to the chlorides of tin and titanium respectively. All these, and similarly acting campounds, are regarded as equivalents of silicon ester and the resulting abrasives are equivalents.

The silicon or other oxide formed from the esters is in very minute size, much finer than the silicon dioxide produced from sodium silicate and consequently it does not mar or scratch the commutator. It merely polishes the commutator and keeps it bright and clean, though it can be called an abrasive in the sense that it does Wear the surface of the commutator enough to keep it smooth. The polishing or abrasive action can be controlled 5y varying nt of 'thersilicon dioxide, or stannic or titanium dioxide, incorporated' in the material by the new process. As has been said, a convenient Way to accomplish this is to vary the concentration of the ester in the ethyl alcohol. In the drawing the brush 1 contains the evenly distributed abrasive and may have any form of cable desired. I have illustrated the cable 2 as being held in a recess 3 by tamped metal but this forms no part of the invention.

The invention is also not limited to esters or any specific compound, as any liquid compound can be used to saturate the brush if it is decomposable by heat to an abrasive or polishing solid 0 in situ.

A brush made from the treated stock does not eiiioresce and does not chemically attack the commutator or the material used to tamp the pigtail cable therein.

While I prefer to use electric graphite as the brush stock on account of its excellent qualities, I may nevertheless, secure some of the results of the novel invention by using ordinary carbon, or natural graphite, either mixed with powdered metal or not, and precipitate the abrasive therein. This would be especially advantageous where the carbon or natural graphite has been puriiied and its ash content accordingly reduced.

Various modifications may be devised and the invention is not to be limited to the specific disclosure.

Having described my invention, what I claim l. The process of making a brush for dynamo electric machines which consists in first forming a brush body of carbonaceous material, saturating the body with a liquid compound decomposable by moderate heat into a polishing or abrasive solid and heating said body to form said abrasive solid directly within the body.

2. 'I'he process of incorporating abrasive material in a brush containing carbon which consists in adding ethyl silicate thereto, and forming silicon dioxide therefrom.

3. The process of incorporating polishing ma.- terial in a brush composed in part of carbonaceous material which consists in soaking the brush in ethyl silicate, drying and baking the brush to form silicon dioxide therein.

4. The process of making a brush which consists in forming electrical graphite into the desired shape, soaking the graphite shape with ethyl silicate solution, drying out the solvent and baking to form silicon dioxide in minute particles in the pores of the electrical graphite.

5. A brush for dynamo electric machines consisting of a graphitized body and a graphitized binder and having minute particles of an insoluble abrasive oxide exceeding 0.5% in amount uniformly distributed throughout the graphite material.

6. A brush for dynamo electric machines consisting of a graphitized body and a graphitized binder and having minute particles of silicon dioxide exceeding 0.5% in amount uniformly distributed throughout the graphite material.

ARTHUR S. BEMIS.

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