US2750308A - Process of filming commutator segments and compositions therefor - Google Patents

Description

PROCESS OF FILIVHNG COMMUTATOR SEGMENTS AND COMPOSITIONS THEREFOR Willard F. Burchfield, Maple Heights, Ohio, assignor to Jack & Heintz, inc, Cleveland, Ohio, a corporation of Delaware No Drawing. Application May 19, 1953, Serial No. 356,100

Claims. (Cl. 117--224) This invention relates in general to rotating electrical machines and has for one of its primary objects to provide an improved commutating, or current conducting, film on the commutator segments, or slip rings, that will be durable and electrically stable and that will have the proper lubricating and current conducting characteristics for the brushes of the machine that engage it.

Another object is to provide a material for treating the commutator segments, or slip rings, in such a manner as to obtain an improved commutating, or current conducting, durable and electrically stable film thereon so as to provide the proper lubricating and current conducting characteristics, whereby with the use of conventional brushes, whether specially treated or not, such a film will be provided within the minimum running-in time under regular operating conditions.

With the foregoing and other objects in View, my invention resides in the agents used in my novel aqueous mixture and in my novel method of application thereof directly to the running commutator segments, or slip rings, of the rotating electrical machine.

With the conventional practices employed, it is necessary to run rotating electrical machines employing either commutators, or slip rings, made of copper, in conjunction with brushes, regardless of its composition or treatment, for a considerable period of time in order to build up a proper commutating, or current conducting, film on the commutator, or slip rings, so as to obtain a film that will provide the proper lubricating and current conducting characteristics.

it is desirable to be able to build up such a film in a short period of time, instead of running the machinery under operating conditions for a long period of time, such as for example, 20 to 50 hours, or longer, in order to obtain the proper operating characteristics. I have found a material that answers the above problem to a highly satisfactory degree, hitherto unobtainable. Such a material preferably contains the following components, in the proper concentrations, for rapidly forming a constant commutation promoting chemical, or conductive film, on copper matrix commutators and slip rings:

. Sodium acetate Ammonium chloride Ammonium persulfate Barium nitrate Hydrogen peroxide Water awa n- 2. Ammonium chloride (NH4Cl).This serves as a dual purpose component: The primary purpose served by ammonium chloride in my mixture is that of providing a highly ionizable component usable as an electrolyte in the conduction of the necessary electrical current during film formation in actual operation of the machine.

3. Sodilmz acetate (NaC2HaO2).-This acts as stabilizer for my compound, serving to buffer the compound s'ufiiciently to prevent undue metal erosion.

4. Barium nitrate (Ba(NOs)z).-This serves as the primary film forming component. It is carried in my compound as a partial suspensoid and is deposited uniformly upon the clean metallic surface. The other components of my compound are preferably present in correctly balanced proportions in order to promote the necessary uniform film deposit.

5. Ammonium persulfate (NH4)2S2Os).This acts as a component of the surface preparation portion of my compound, serving a dual purpose. Due to the fact that ammonium persulfate attacks the metal, copper, it is used as a matrix eroding agent. Thus, when present in the desired concentration, it produces a fine micro-etched surface.

One of the conventional approaches to a solution of the problem has been the provision of brushes which contain such inorganic fillers as barium nitrate, calcium sulfate dihydrate, and various reaction agents suitable for use in atmosphere containing little or no moisture, such as occurs at high altitudes. Brushes made in this manner are structurally porous, and moisture is stored by absorption within their capillaries only under high moisture conditions and not under low moisture conditions. The purpose of the use of calcium sulfate dihydrate in the mixture is for it to be converted to hygroscopic calcium sulfate during processing so as to furnish a means of collecting moisture by the hydrating of this salt.

The use of barium nitrate in treated brushes is twofold. One use is as a source of nitrogen gas during processing so as to increase the porosity of the formed brush. The second use is as a source of barium oxide as a pyrometric reaction product. This hygroscopic barium oxide serves as a further means of moisture storage, and this moisture is released as needed at the interface between the brush and the commutator segment. This stored moisture serves two purposes. It prevents dusting or wearing of brush due to lack of moisture at high altitudes. The residual moisture serves to catalyze the formation of cuprous oxide on the commutator surface. This cuprous oxide, in conjunction with the graphite from the brush, serves as a lubricant during commutation.

However, I have found that a run-in period of or more operating hours is required under normal atmospheric conditions to form a complete, uniform, durable and electrically stable film that will give a constant operational performance on a commutator, or slip ring, surface even with such a specially constructed brush.

In contrast, by the use of my mixture and my method of application thereof, I form a film having the desired properties in from four to fifteen minutes of operating time. Instead of using a special brush, I may use a conventional brush. My compound is preferably applied directly to the commutator, or slip ring, surface by immersing, wiping, daubing or brushing. Any treated or untreated brush may be utilized with my compound, and the brush will be more rapidly seated than by any other method, with the added advantage of obtaining an effective, durable and electrically stable commutating film on the commutator, or slip ring.

By the use of my improved filming aqueous mixture,

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the commutator, or slip ring, surface is properly prepared for the formation of a uniform, durable and electrically stable film over the entire commutating surface, and the complete film is rapidly formed as a permanent component of the commutator, or slip ring, surface, that is to be engaged by the brush. The film provides for a constant rate of commutation, whether tested immediately after the brush seating period or after a considerable lapse of time from such period.

Due to the efficiency of the commutation film formed by this method, brushes may be initially operated at high current densities. This fact, coupled with the fact that as film-forming operation is initiated, the frictional coefiicient between the brush and commutator, or slip ring, is extremely high, the brush seating time may be drastically reduced. However, by the time the brush is seated, sufficient glazing is present to reduce friction to the lowest possible value. Thus, minimum brush wear is assured and maximum brush life is attained.

I have found that with generators using this method of film formation, a peak load can be applied after only five minutes of run-in time has elapsed, and that the brushes will be completely seated after an average of seven hours of continuous operation. Thus, by using my compound, a commutating film may be formed in four to fifteen minutes, depending on concentration which is the equivalent of a film having qualities requiring onehundred hours or more to form by conventional means. Moreover, by using this method of film formation, brushes may be adequately seated in an average of seven hours,

instead of from ten to fifty hours of operation. The use of my compound is directly aimed toward increasing the speed of film formation and decreasing the time of brush seating, obtaining a durable and electrically stable current conducting film and providing for efficient operational testing and performance.

My film forming aqueous mixture preferably consists of five chemical reagents present in a balanced ration utilizing water as a solvent, or carrier. These five reagents are preferably sodium acetate, ammonium chloride, ammonium persulfate, barium nitrate and hydrogen peroxide.

The optimum working compound including ingredients by weight has been found to be as follows:

Sodium acetate, NaCzHaOz 4.0 grams. Barium nitrate, Bz(NOs)z -a 3.0 grams. Ammonium chloride, NH4Cl 4.0 grams. Hydrogen peroxide, H202 5.0 oz.-5%

solution. Ammonium persulfate, (lJH4)2S20B---. 6.0 grams. H2O 24.0 oz.

Distilled water is added to make one quart of stock compound.

The preferred operating range of limits of composition operating range limits of my compound for best operation are approximately as follows:

Per cent 1. Soduim acetate 0.125 to 0.50 2. Ammonium chloride 0.125 to 0.50 3. Ammonium persulfate 0.250 to 1.00 4. Barium nitrate 0.065 to 0.39 5. Hydrogen peroxide 0.65 to 2.50 6. Water 98.785 to 95.11

load may be supplied to the rotating electrical machine. Thus, by the use of the cfiicient film formed by my compound, brushes may be operated at high current densities much sooner than is possible with the less efiicient films formed by conventional means.

The use of my compound provides the commutating surface with a film possessing optimum characteristics for the seating of brushes. Initially the commutator, or slip ring, surface, due to chemically induced copper surface oxidation, will be of such a nature as to provide an initial. high coefficient of friction at the brush-commutator, or slip ring, interface. This results in the rapid formation on the commutator, or slip ring, surface of a glaze composed of various reaction products combined with micro particles of graphite from the brush. This glaze serves as a permanent film on the surface of the commutator, or slip ring, which requires no further treatment, such as rinsing, or cleaning. it serves as an excellent lubricant and permanently electrically stable current conducting film between the brush face and the metal surface of the commutator, or slip ring. The coefficient of friction at the blush-commutator. or brush-slip ring, interface is thus reduced to a minimum in a very short time.

The brushes may be operated at high current densities virtually immediately because of the film present, and the fact that the prepared commutating surface offers the optimum properties for glazing, the unit operating time necessary for the seating of the brush is drastically reduced.

Thus, it will be seen that I have provided a means and method, whereby a complete and efiicient commutating film will be formed virtually immediately upon application of my compound to the commutator, or slip ring, surface. It is therefore not necessary to wear the brushes away in order to build up a film, such as is the case in the conventional manner of film formation. As the above factor allows high current densities to be impressed on the brushes from the start and as my applied film natural- 1y ofiers a high friction condition prior to the time of glazing, brushes may be seated in a drastically reduced run-in time. Glazing time on my film is relatively short and a lubricating component is rapidly produced, reducing the frictional value to a desired minimum. Moreover, my film is embedded in the commutator, or slip ring, and forms a durable protective coating. The factors, combined, necessarily extend brush life is well as to allow unit operational testing as soon as the brushes are seated. Due to the completeness and stability of the film formed by my method, the test results will be an accurate indication of the units characteristics and the resulting values will remain constant, even though the unit should be idle for an extended period of time after the initial test. Furthermore, these desire-d qualities will be present at the time that the machine is actually put into service.

It will be understood that while referring to my mixture of ingredients as a compound, I prefer to form it as an aqueous mixture. 1 have also found it to not be the best practice to apply my compound directly to the brushes, instead of the commutator, or slip rings, as a uniform film deposit is not insured. inasmuch as my compound is preferably applied directly to the commutator, or slip ring, surface, this may readily be done while the commutator, or slip ring, is actually being rotated and engaged by the brushes. A relatively small amount of the compound is applied directly to the com mutator, or slip ring, surface by applying it longitudinally'back and forth on the surface while the latter is rotating. Initial chemically induced copper oxidation in creases the friction between the surface and the brushes, which lessens rapidly after the brief time necessary for the film to form, and the film to be embedded in the surface.

I have described the compound as preferably having five ingredients, in addition to water and the preferable proportions for optimum results, as well as percentage variations, within a reasonable operating range.

I claim:

1. The method of providing a current conducting film on commutator segments, or slip rings, of a rotating electrical machine having brushes, which consists in the application of an aqueous mixture consisting of the following ingredients, in approximate proportions by weight, sodium acetate, NaCzi-lsOz, 4.0 grams, barium nitrate, Ba(N'Os)2, 3.0 grams, ammonium chloride, NHiCl, 4.0 grams, hydrogen peroxide, H202, 5.0 oz. of 6% solution, ammonium persulfate, (NHQzSzOs, 6.0 grams, and distilled water (H2O), 24.0 02., directly onto said segments and rings and the running of said machine under operating conditions with the brushes of said machine in contact with said aqueous mixture on said segments, or rings, to provide a lubricant and current conducting film on said segments, or rings.

2. The method of providing a current conducting film on commutator segments, or slip rings, of a rotating electrical machine having brushes, which consists in the application of an aqueous mixture consisting of the following ingredients, in proportions by percentage by weight, Within approximate ranges of sodium acetate, from 0.125 to 0.50%, ammonium chloride, from 0.125% to 0.50%, ammonium persultate, from 0.250% to 1.00, barium nitrate, from 0.065% to 0.39%, hydrogen peroxide, from 0.650% to 2.50%, and water, from 98.785 to 95.11%, directly onto said commutator segments, or slip rings, and the running of said machine under operating conditions with the brushes of said machine in contact with said aqueous mixture on said segments, or rings, to provide a lubricant and current conducting film on said segments, or rings.

3. The method of providing a current conducting film on commutator segments, or slip rings, of a rotating elec trical machine having brushes, which consists in the application of an aqueous mixture consisting of the following ingredients, in proportions by percentage by weight, Within approximate ranges of sodium acetate, from 0.125% to 0.50%, ammonium chloride, from 0.125% to 0.50%, ammonium persulfate, from 0.250% to 1.00%, barium nitrate, from 0.065% to 0.39%, hydrogen peroxide, from 0.650% to 2.50%, and water, from 98.785 to 95.11%, directly onto said commutator segments, or slip rings, and the subsequent running of said machine under operating conditions with the brushes of said machine in contact with said aqueous mixture on said segments, or rings, to provide a lubricant and current conducting film on said segments, or rings.

4. An aqueous mixture for use in providing a current conducting film on commutator segments, or slip rings, of a rotating electrical machine having brushes, and which consists in the following ingredients, in approximate proportions by weight, sodium acetate, NaCzHsOz, 4.0 grams, barium nitrate, Ba(NO3)z, 3.0 grams, ammonium chloride, NH4C1, 4.0 grams, hydrogen peroxide, H202, 5.0 oz. of 6% solution, ammonium persulfate, (NH4)2S2OB, 6.0 grams, and distilled water (H2O), 24.0 oz. for direct application to said segments, or rings, while the machine is running under operating conditions with the brushes of said machine in contact with said aqueous mixture on said segments, or rings, to provide a lubricant and current conducting film on said segments, or rings.

5. An aqueous mixture for use in providing a current conducting film on commutator segments, or slip rings, of a rotating electrical machine having brushes, and which consists in the following ingredients, in approximate proportions by percentage weight, Within ranges of sodium acetate, from 0.125% to 0.50%, ammonium chloride, from 0.125 to 0.50%, ammonium persulfate, from 0.250% to 1.00%, barium nitrate, from 0.065% to 0.39%, hydrogen peroxide, from 0.650% to 2.50%, and water, from 98.785% to 95.11% for direct application to said segments, or rings, while said machine is running under operating conditions with the brushes of said machine in contact with said aqueous mixture on said segments, or rings, to provide a lubricant and current conducting film on said segments, or rings.

References Cited in the file of this patent UNITED STATES PATENTS 1,750,990 Briel Mar. 18, 1930 1,750,657 Adolph et al Mar. 18, 1930 2,291,202 Bassett et al July 28, 1942 2,501,321 Elsey Mar. 21, 1950 2,656,475 Diehl et a1. Oct. 20, 1953 2,703,372 Savage Mar. 1, 1955 FOREIGN PATENTS 601,446 Great Britain May 6, 1948

Claims (1)

1. THE METHOD OF PROVIDING A CURRENT CONDUCTING FILM ON COMMUTATOR SEGMENTS, OR SLIP RINGS, OF A ROTATING ELECTRICAL MACHINE HAVING BRUSHES, WHICH CONSISTS IN THE APPLICATION OF AN AQUEOUS MIXTURE CONSISTING OF THE FOLLOWING INGREDIENTS, IN APPROXIMATE PROPORTIONS BY WEIGHT, SODIUM ACETATE, NAC2H3O2 4.0 GRAMS, BARIUM NITRATE, BA(NO3)2, 3.0 GRAMS, AMMONIUM CHLORIDE, NH4CI, 4.0 GRAMS, HYDROGEN PEROXIDE, H2O2, 5.0 OZ. OF 6% SOLUTION AMMONIUM PERSULFATE, (NH4)2S2O8, 6.0 GRAMS, AND DISTILLED WATER (H2O), 24.0 OZ., DIRECTLY ONTO SAID SEGMENTS AND RINGS AND THE RUNNING OF SAID MACHINE UNDER OPERATING CONDITIONS WITH THE BRUSHES OF SAID MACHINE IN CONTACT WITH SAID AQUEOUS MIXTURE ON SAID SEGMENTS, OR RINGS, TO PROVIDE A LUBRICANT AND CURRENT CONDUCTING FILM ON SAID SEGMENTS, OR RINGS.