US1804052A - Dynamo brush - Google Patents

Description

May 5, 1931. N. R. HAAs 1,804 @52 DYNAMO BRUSH l Filed ot. 10, 1925 EFAPH/ TE Patented May 1931 UNITED STATES PArEN'n OFFICE i N'ELSON ROBERT HAAS, OF DAYTON, OHIO, ASSIGNOR, BY MESNE ASSIGNNEELNTSQ T0 DELCO-BEMY CORPORATION, OF DAYTON, OHIO, A CORPORATION OF DELAWARE DYNAMO :BRUSH Application led October 10, 1925.

This invention relates to commutator brushes for dynamo electric machines and -particularly to brushes composed of a sintered mixture of graphite, a carbonized binder and an abrasive.

It has been known to shape into briquettes,

mixtures of graphite and synthetic resins and to heatthe briquettes in a non-oxidizing at- .mosphere at a temperature sufficient to drive olf the volatile matter from thel binder so that the particles of graphite will be held together only by the coked residue of the binder.

One of the objects of the present invention is to produce economically, brushes composed brush in accordance with my invention.

- With these objects in view, the present invention provides for the use of ingredients having a high degree of uniformity as regards their chemical and physical properties.

While artificial graphite has proved satisfactory, very vgood results can be obtained with certain grades of'natural graphite. One such grade is known to the trade as Dixonls No. .067 4 natural graphite. The graphite used should not contain more than 1% ash and should pass through a 200 mesh screen.

One species of synthetic resin which may be used as a binder Iis a phenol-formaldehyde. resin, one form of which is `lmown to the.

trade as bakelite, grade 2A.

One formula which has roduced a satisfactor brush is 91% graphite and 9% bakelite. n order that the bakelite will be uniformly distributed throughout the graphite l and thatthe granules of bakelite will be sepas Serial N'o. 61,842.

(82% in the example given) and then the entire mixture is mixed for one hour in a pot mill mixer. Previously computed quantities of this powdered mixture are pressed in a compound molding die having recesses for receiving a substantial quantity of briquettes, 40 to 50 for example. Before introducing the powder, the dies are previously .preheated (preferably by steam) to 250 F4. and then are cleaned oli with a cloth saturated with a volatile acid, such as stearicl acid; and the briquette punches and dies are lightly powdered with talcum.

Pressure is applied to the. punch until it enters the die recess a predetermined distance which. is determined by a suitable stop. Provided the closing distance of the punch with respect to the die is maintained uniform and uniform quantities of the powder are pressed in the die recess, the briquetting pressure will be uniform. This pressure should be ap- Kili proximately 3000 pounds per square inch.

This temperature and pressure is maintained .for six minutes, which is known as the curing time of the compound in the mold. The steam for heating the die is turned 0E and cool water between 60 and 7 0 Fahr; is turned into the die for three minutes while the briquetting pressure is still maintained. rlhe step of cooling while maintaining pres-l sure causes the set of the briquetted material.

to be more permanent and thus assists in eliminating blisters on the surface of the briquettes and hence renders the briquettes more uniform in density.

The briquettes are next packed with line charcoal preferably in a nichrome carbonizing pot. The briquettes are packed in layers and the layers are separated by a thin layer of charcoal. A number of these ots are heated for ten hours in a suitable ace at at least 900 F. or at a temperature for a time sucient to convert substantially all of the bakelite into carbon, so that the graphite particles will be bound together with particles of coked bakelite. If this is not done the briquettes will not give satisfaction as a commutator brush. The prsence of uncarbonized bakelite causes the brush to become soft in use and to wear away very rapidly. The

sinteriiig time and temperature specified have I proved satisfactory for brushes which are thick. Obviously brushes having a greater bakelite content or brushes which are thicker require a longer time or greater temperature to carbonize'all ofthe bakelite.V

After the sintering step the carbonizing pots are removed from the furnace but the lids are left on and the contents are undisturbed until the contents are cooled to roomV temperature. One purpose of this step isto render brushes less likely to crack or to have surface checks which are believed to be caused by exposing the brushes while heated, directly to room temperature. By 7keeping them packed in the carbonizing pots they are aly lowedto cool olf more gradually.

A modified and preferred form of the present invention results from substituting for vcrushed into sizes which will permit the maximum amountto be pressed'in a carbonizing pot. This scrap is heated ina non-oxidizing l. atmosphere from 6 to 7 hours 'at about 1700 F. which causes the bakelite material to be converted into carbon in the formy of coke. This carbon is removed from the ot and ground so that it will all pass a 65 mes screen.

vFor 10% of the 91%' graphite used in the preceding example 10% of bakelite coke is substituted, so that the formula in this example becomes 81% graphite, 10% bakelite coke and 9% bakelite grade 2A.' These ingredients are mixed in the following manner. As stated inthe previous example, 9% of bakelite and 9% grap ite are mixed in-a'pot mill mixer for 30 minutes in order that the granules of bakelite shall be thoroughly coated with graphite. To this mixture is added 72% graphite and 10% lbakelite coke and the total mixture is mixed for one hour in a pot mill mixer. The succeeding steps of the process are carried out as stated in the firstexample. The presence of the bakelite coke particles uniformly distributed in the briquette apparently assist in the escape of volatile matter during the sintering operation. There is usually less distortion or other changing in sha e when coke particles are used.

e present invention is notlimited to the use of natural graphite having the desired uniformity of physical andchemical charac- Vteristics'. lA uniform grade` of artificial graphite may be used, but when this is done it is necessary to add a small quantity of linel divided abrasive such as levigated alumina. 1y order that the alumina will be uniformly distributed throughout the mass, the alumina should be mixed with substantially an equal ortion of graphite in a pot mill mixer for at east an hour in order that the granules of alumina will be thorou hly coated with graplhite. The gran ules o bakeliteare thoroug ly coated with graphite by mixin bakelite with an equal amount of grap ite as already specified. Then these two mixtures are thoroughly mixed together with bakelite coke and with thev balance of the graphite, and the briquetting and sintering operations are carried out as previouslystated.

In all of the examples given it has been specified that the granules of bakelite should be thoroughly coated Withgraphite before the bakelite is mixed with the balance of th graphite required b the formulae.

What is claimed is as follows:

1. A dynamo brush'in which lthe different ingredients contained in said brush are uniformly distributed therethrough and com- 2. A dynamo brush in which the different ingredients contained in saidA brush are uniformly distributed therethrough and comprisinv a sintered mixture of graphite, articles of previously coked phenolic-con ensation product and a binder of phenolic-condensation product.

3. The method of making a dynamo brush.

composed of a sintered mixture of graphite and a h drocarbon binder which consists first in mixing the binder with a portion onl of the graphite used in order to coat the particles o thoroughly mixing this mixture with the balance o the graphite, in shapin the mixture,

l d in heating' in a non-oxii phere.

4. Thev methodlof making a dynamo brush which includes briquetting a mixture of graphite and a binder under heat and pressure, cooling the briquette while maintain.- ing the briquetting pressure, and heating'the briquette in a non-oxidizing atmosphere.

5. The method of making a dynamo brush which includes briquettin in a heated mold a mixture of graphite an a binder, in coolzvi'ng atmosing the mold and briquette while the briquetting pressure is maintained, and in heating the briquette in a non-'oxidizin atmosphere. 6. The method of making a. ynamo brush which includes briquetting a mixture of graphite and a binder of synthetic resin in a mold heated to at least 250 Fahr., in coolin the briquette in theinold to at least 100 while the briquetting pressure is maintained, and in heating the briquette in a non-oxidizing atmosphere. I,

. The method of ,malng a dynamo brush the binder-with the graphite, then` los' 1h10Q leo l lesI iso

which includes briquetting a mixture of graphite and a phenolic-condensation product-in a mold heated to between 250 and 300 Fahr., in cooling the briquette in the mold to at least 100 Fahr., and in heating the briquette in a non-oxidizing atmosphere.

8.v The method of making a dynamo brush which includes brquetting a mixture' of graphite and phenolic-condensation product in a mold heated to'between 250 and 300 Fahr., .the briquetting pressure being about 3000 lbs. perpsquare inch and the heat being maintained for about 6 minutes, in cooling the mold to at least 100 Fahr. while maintainving the briquetting pressure, and in heating the briquette in a non-oxidizing atmosphere.

9. The method of making a dynamo brush which includes briquetting a mixture of graphite and phenolic-condensation product in a mold heated to between 250 and 300 Fahr., the briquetting pressure being about 3000 lbs. per square inch and the heat being maintained for about 6 minutes, and in cooling the mold by subjecting itffor about 3 minutes to cool running Water While maintaining the briquettingpressure, and in heating the briquette in a non-oxidizing atmosphere. y

10. The method of making a dynamo brush comprising graphite and a hydro-carbon binder, which consists in coking a part ot the binder, mixing graphite with the uncoired portion of the binder, then mixing the coiled portion of said binder with the mixture thus formed, shaping the mixture into the desire form and heating said mixture in a nonoxidizing atmospherelJ p 11. The method of making a dynamo brush comprising graphite and la hydro-carbon binder, which consists -in coking a part or the binder, mixing a part of the graphite Twith the uncoked portion of the binder, then mixing the coked portion of the binder and re- /mainder lof the graphite with the mixture thus formed, shaping the mixture into the desired form and heating said mixture in a non-oxidizing atmosphere. f

12. The method oi making a dynamo brush -i comprising graphite and a hydro-carbon binder which consists in coking substantially half of the binder, mixing the uncoked half of the binder Witha substantially equal quantity of graphite, then mixing the re- .mainder of the graphite and the coked portion of the binder ,with the mixture thus formed,-shaping the mixture into the desired form and heatln said mixture lin a non oxidizingatmosp ere.

` 13. The method of-making a dynamo brush comprising approximately 81% graphite and the coked portion of the Vbinder with the mixture thus formed, shapino' the mixture into the desired form and heating said mixture in,

vmixture of approximately') parts carbon including graphite and previously coked hydrocarbon binder and 1 part uncoked hydr'ocarbon binder. l

18.. dynamo brush comprising a sintered mixture of approximately 8 parts graphite, 1 part previously coked hydrocarbon binder, and 1 part uncoked binder.

19. A dynamo brush comprising a sintered mixture of 81% graphite, 10% previously eek-ed bakelite, and 9% uncoked bakelite. in testimony whereof hereto ax my signature..

NELSON ROBERT HAAS.

' 19% hydro-carbon binder, which consists in 7,-'

coking approximately one-halt the binder mixing substantially one-ninth of the graphite with the uncoked portion et the binder mixing the remainder of the graph'te and

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