US2412701A - Brush for electrical machinery - Google Patents

Description

I Patented Dec. 17, 19 46 addict! new BRUSH FOR ELECTRICAL MACHINERY Edward A. Williford, White Plains, N. Y., assignor to National Carbon Company, Inc., a corporation of New York No Drawing. Application February 27, 1941, Serial No. 380,889

10 Claims.

The invention relates to brushes for electrical machinery, of the type essentially composed of carbon, graphitized carbon, or mixtures of carbon and metal, and adapted to serve as conductor contacts to commutators or collector rings of motors, generators and the like. It is particularly concerned with impregnated motor and generator brushes of improved operating characteristics and life.

To diminish friction between a brush and rtating parts with which it contacts, it has been known to incorporate into the brush stock, usually by impregnation, a materia1 which will act as a lubricant. Different kinds of waxes have been proposed for this purpose, including paraffin, carnauba wax, beeswax, or sypt heticchlorinated hydrocarbon waxes, and impregnation has been 'eifected'irom solutions of these waxes in volatile organic solvents, or in a bath of the molten wax itself. It has, however, been difficult to obtain in this manner other than a transient improvement in brush operation, as the wax generally exudes from the brush under the heat developed during use, or it decomposes in a short time and loses its lubricating function. A complete and uniform distribution throughout the brush is also rarely obtained with prior known wax impregnants, as the organic solvents which must be used, to obtain a thorough penetration of the impregnant, carry the wax on evaporation toward the surface of the brush where the high concentrations thus efiected are deleterious to both the appearance and operation of the brush. The ultimate result has been that the commercial use of these prior wax impregnants to improve brush lubrication has been discontinued in all but a relatively few and unimportant applications.

In accordance with my invention, new and different waxes or wax-like materials are proposed for impregnation of brushes, which will impart to the brush a more eflicient lubricating function, with resultant improvement in durability and operating properties, without giving rise to the aforementioned disadvantages inherent in prior known impregnating materials.

I have found that waxes which are soluble in water are much better brush impregnants than water-insoluble materials, and that certain synthetic wax-like substances which have water solubility are excellently adapted as brush lubricants. These substances, which are comparatively new commercially, are highly polymerized chain-like hydrocarbon compounds which may be termed polyalkylene oxides. Since the polyboth ends of a long chain, the compounds have also been referred to as polyalkylene glycols, and in further modifications may consist of mixtures of different polyalkylene glycols or the polymers of monoethers of polyalkylene glycols. The products may be formed by the reaction, in the presence of an alkaline catalyst, of an alkylene oxide with an alkylene glycol or an alkylene glycol monoether, with the degree of polymerization controlled to produce the molecular size desired. Polymers varying in character from viscous liquids to pasty or solid materials are available, and the products as a class exhibit water solubility and wax-like properties. For the purpose of this disclosure the term polyalkylene oxides is intended to include broadly any of the polymer modifications indicated.

In a preferred embodiment of the invention the impregnants used are polyalkylene oxide compositions which have an average molecular weight in excess of 400; and a polyethylene oxide of an average molecular weight of about 1500 and another having an average molecular weight of about 4000 have both given an exceptionally good brush lubricating action. A complete and uniform penetration of the brush stock can be readily obtained by impregnation from an aqueous solution of the wax, using pressure if necessary to permeate completely brushes more dense in character. After air drying the wax is retained throughout the body of the brush, and does not exude or concentrate in the outer brush portions. Thus a persistent lubricating effect is obtained, creating a longer brush life, with reduction in friction, and a more stable film development on a commutator or collector ring.

The percentage of polyalkylene oxide impregnant in the brush, necessary for most efl'icient results, will vary with the brush stock treated and the service for which it is intended, but from both laboratory and commercial tests a range from about 0.1% to 1.0% by weight of the brush stock has proven suflicient to produce highly desirable improvements in brush life and operation. As specific examples, brush grades composed essentially of electro-graphitic lampblack were impregnated with polyethylene oxide of an average molecular weight of 4000, with the impregnant in one instance amounting to 0.44% by weight of the brush stock, and in another 0.50% by weight. Tests of these brushes on conunercial generators of a power substation showed immediate improvements in operating characteristics over similar brush grades unimpregnated, and

further showed that the beneficial lubricating action of the brushes was substantially permanent.

Within the broader scope of the invention numerous modifications will be evident, and are intended to be included, as many polyethylene oxides of different average molecular weights are readily available commercially. The brush stock composition can also vary within embodiments now customary, and in the claims where the brush is defined as a conductive carbonaceous body it is intended to include compositions comprising mixtures of carbon or graphite with metals, as well as brushes entirely of carbon in various forms. Impregnation is contemplated for brushes for any service where the lubricating qualities afforded thereby are of advantage to efllcient operation.

I claim 1. A brush for electrical machinery comprising a conductive carbonaceous body impregnated with polyalkylene oxide of an average molecular weight greater than about 400.

2. A brush for electrical machinery comprising a conductive carbonaceous body containing a polyalkylene oxide impregnant of an average molecular weight greater than about 400, the amount of said impregnant being from about 0.1% to about 1.0% by weight of the brush.

3. A brush for electrical machinery comprising a conductive carbonaceous body containing a polyethylene oxide impregnant of an average molecular weight greater than about 400, the amount of said impregnant being from about 0.1% to about 1.0% by weight of the brush.

4. A brush for electrical machinery as claimed in claim 3 comprising a conductive carbonaceous body impregnated with polyethylene oxide of an average molecular weight of about 1500.

5. A brush for electrical machinery as claimed in claim 3 comprising a conductive carbonaceous body impregnated with polyethylene oxide of an average molecular weight of about 4000.

6. Process of imparting lubricity to brushes which comprises impregnating the brush with an aqueous solution of polyalkylene oxide of an average molecular weight greater than about 400, and drying to distribute the wax uniformly throughout the body of the brush.

7. Process of imparting lubricity to carbonaceous brushes which comprises impregnating the brush with an aqueous solution of a polyalkylene oxide, and drying to distribute the polyalkylene oxide uniformly throughout the body of the brush.

8. Process of imparting lubricity to carbonaceous brushes which comprises impregnating the brush with an aqueous solution of a polyethylene oxide, and drying to distribute the polyethylene oxide uniformly throughout the body of the brush.

9. A brush for electrical machinery comprising a conductive carbonaceous body containing a polyalkylene oxide impregnant.

10. A brush for electrical machinery comprising a conductive body of graphite and metal, and 0.1% to 1% by weight of a polyalkylene oxide impregnant.

EDWARD A. WILLIFORD.