US2758229A - Commutators and other electric current collectors - Google Patents

Description

Aug. 7, 1956 R. J. PERRY 2,758,229

COMMUTATORS AND OTHER ELECTRIC CURRENT COLLECTORS Filed Nov. 21, 1952 COLLECTOR COMPRISING S/NTERED COPPR./IND OTHER MET/4L 0F LOWER CONDUCT [V] T) THAN COPPER I CARBON BRUSH CflRBO/V BRUSH I X INVENTOR 512725245265 John Perify BY w /& ATTQRNEYS United States Patent COMIMUTATORS AND OTHER ELECTRIC CURRENT COLLECTORS Reginald John Perry, Wallington, England, assignor to The Morgan Crucible Company Limited, London, England, a company of Great Britain Application November 21, 1952, Serial No. 321,817

Claims priority, application Great Britain November 22, 1951 19 Claims. (Cl. 310-231) This invention relates to improvements in electric current collectors such, for example, as commutators and slip rings. The invention will be described herein with particular reference to commutators but it is to be understood that the invention is applicable in like manner to electric current collectors of other types.

It has been known for some time that the brushes of dynamo-electric machines on aircraft wear rapidly at high altitudes and that such brush wear has been so pronounced at altitudes of more than about 25,000 feet as to have presented a serious problem. Various attempts were made to solve this problem and it was discovered that the wear resistance properties of brushes could be considerably improved by the incorporation in the brush of certain substances or so-called adjuvants. In particular, the adjuvants proposed have been salts and oxides of alkaline earth metals, metal halides and sulphides, and metallic lead.

In the specification of the copending application Serial No. 298,470 an improved manufacture of brushes having resistance to wear at very high altitudes has been described.

The basis of the present invention is the discovery that brush resistance to wear at high altitudes can be enhanced to a remarkable degree by a departure from the ordinary method of manufacturing the commutator upon which the brushes operate. Such commutators, and like current collecting devices, used on aircraft are normally of small size compared with those used in electrical plant on larger vessels or on the ground, and the invention is especially applicable to commutators and the like which are relatively small.

According to the present invention, the current collecting portion of a commutator or like current collector is made from sintered copper in conjunction with other metal of substantially lower electrical conductivity than copper in an amount of at least 5% based on the weight of the whole. The practical upper limit for the amount of other metal may be as high as about 40% or in some cases even higher. For instance nickel may be used in amounts up to 70%. Generally, the optimum amount is between and Particularly suitable as the other metal are lead, iron, chromium, nickel, tin and cadmium. These may be used individually, or two or more together, alloyed or otherwise.

The sintered body constituting the current collector according to the invention may be produced in various ways. Generally the preferred method is to compact under pressure a mixture of fine powders of copper and the other metal or metals, and then to sinter the mixture at a high temperature appropriate to the nature of the mixture.

Another method which is applicable when the other metal e. g. lead, has a lower melting point than copper, is to introduce the other metal into an already sintered body of copper by infiltration at a temperature above the melting point of the other metal but below the 2,758,229 Patented Aug. 7, 1955 melting point of copper. Such infiltration may be carried out in a reducing atmosphere and may be facilitated by using a vacuum to draw the molten metal into the pores of the sintered copper body and/or by using pressure to force the molten metal into the pores.

A further method applicable in the case where the other metal or metals is or are capable of alloying with copper, is to produce the alloy and then to pulverize, compact and sinter it as such. The pulverizing is conveniently effected by solidifying an atomized spray of the molten alloy.

In any of the aforesaid methods the mass to be sintered may contain a small proportion, e. g. 1% by weight, of graphite. 1

The preferred amounts of the additional metal, in percentages of the total weight of the copper and the additional metal, are as follows:

If both iron and lead are used, the preferred percentage is 10% iron and 20% lead, whilst it nickel and lead are used together the preferred percentages are 20% nickel and 5% lead.

It will be appreciated that the sintered bodies produced according to the invention may be commutator segments to be mounted in the customary manner, or they may be complete commutator blanks which are subsequently split, or they may be rings.

The particle size of the powder to be sintered is preferably such that all the particles will pass through a sieve of meshes to a linear inch. A suitable pressure for compacting the powder is one of the order of 14 tons per square inch. The sintering temperature will be dependent on the composition of the powder. In the case of a mixture of copper and iron, copper and chromium, or copper and nickel, a sintering temperature of 800-1000 C. is suitable; for a mixture of copper and tin or copper and lead, or copper, iron and lead, or copper, nickel and lead, a sintering temperature of 700-850" C. is suitable; whilst for a mixture of copper and cadmium a sintering temperature of 400-600 C. is suitable.

I have found that a further improvement of the properties of the current collector made of a porous sintered body according to the invention is obtainable by impregnating the sintered body with an organic impregnant of a drying oil basis. Such organic impregnant may be of the nature of a varnish based on a drying oil which may contain a drier of the kind normally used to accelerate and improve the hardening of drying oils, e. g. naphthenates of cobalt and other metals.

The term drying oil denotes any oil of animal or vegetable or synthetic origin which will dry in air or harden or polymerize by heat. Examples of vegetable oils are linseed oil and tung oil. Examples of other oils are animal or fish oils which have been processed so as to be rendered driable or hardenable either as such or in the presence of metal driers. Natural or synthetic resins may be included in the impregnant to increase the hardness of the dried, oxidised or polymerized material. Examples of resin are wood rosin and copal resin. Examples of synthetic resins are those known as alkyd resins and these may be blended with the drying oil or combined therewith as in the case of oil-modified alkyd resins.

I am aware that it has been disclosed in United States specification No. 2,053,662 to form commutator segments by compressing and sintering a mixture of copper powders with certain other metal powders but in that case the object in view is the production of a material which is harder than ordinary cold worked copper. The proportion of the added metal according to the said specification, for achieving the purpose disclosed therein, is of the order of 3% or less, and the manufacture is such that the sintered mass is substantially nonporous.

In contradistinction, the present invention employs a higher proportion of added metal and the sintered mass may be porous. It would not appear, however, that the sintered metal structure is the basic reason for the improved resistance to wear of brushes working on the commutator because a commutator made of sintered copper alone does not produce the improvement.

The single figure of the accompanying drawing schematically illustrates a representative embodiment of the invention.

I claim: 1

1. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other conductive metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least percent based on the weight of the whole, wherein copper is sintered and carries said other metal.

2. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other conductive metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount between 10 percent and 30 percent based on the weight of the whole, said current collecting portion being a sintered body of copper particles having said other metal incorporated therein.

3. A rotatable electric current collector for dynamoelectric machines usedat high altitudes, said current collector having a peripheral current collecting portion comprising compacted copper and nickel in an amount between 10 percent and 70 percent based on the weight of the whole, wherein said copper is sintered and carries said nickel.

4. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion cornprising copper and lead in an amount between 10 percent and 40 percent based on the weight of the whole, said current collecting portion being a sintered body of copper particles having said lead incorporated therein.

5. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion com prising copper and iron in an amount between 10 percent and 30 percent based on the weight of the whole, said current collecting portion being a sintered body of copper particles having said iron incorporated therein.

6. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising compacted copper and chromium in an amount between 10 percent and 30 percent based on the Weight of the whole, wherein said copper is sintered and carries said chromium.

7. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and tin in an amount between 10 percent and 30 percent based on the weight of the whole, said current collecting portion being a sintered body of copper particles having said tin incorporated therein.

8. A rotatable electric current collector for dynamo-- electric machines used at high altitudes, said-current collector having a peripheral current collecting portion comprising copper and cadmium in an amount between 10 percent and 25 percent based on the weight of the whole, said current collecting portion being a sintered body of copper particles having said cadmium incorporated therein.

9. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and at least one metal of the group consisting of lead, iron, chromium, nickel, tin and cadmium in an amount of at least 10 percent based on the weight of the whole, wherein said copper is sintered and carries at least one metal of said group.

10. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other conductive metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole, said current collecting portion consisting of a sintered mixture of copper powder and powder of said other metal.

11. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper, iron and lead, wherein said copper is sintered and carries iron and lead.

12. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper, nickel and lead, said current collecting portion being a sintered body of copper particles having said nickel and lead incorporated therein.

13. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other metal of lower melting point than copper and of substantially lower electrical conductivity than copper and from the group consisting of lead, iron,

chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole, said current collecting portion consisting of a sintered body of copper impregnated with said metal.

14. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other metal of lower melting point than copper and of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole, wherein said current collecting portion consists of a sintered body of copper alloyed with said other metal. 157 A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion com prising copper and other metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole and impregnated with an organic impregnant of a drying oil basis, said current collecting portion being a sintered body of copper particles having said other metal incorporated therein.

16. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current col lector having a peripheral current collecting portion comprising copper and other metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole and impregnated with a varnish based on a drying oil, wherein said copper is sintered and carries said other metal.

17. A rotatable electric current collector for dynamoelcctric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole and impregnated with a Varnish based on a drying oil and incorporating a drier, said current collecting portion being a sintered body of copper particles having said other metal incorporated therein.

18. A rotatable electric current collector for dynamoelectric machines used at high altitudes, said current collector having a peripheral current collecting portion comprising copper and other conductive metal of substantially lower electrical conductivity than copper and from the group consisting of lead, iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the whole and impregnated with a varnish based on a drying oil and incorporating resin, said current collecting portion being a sintered body of copper particles having said other metal incorporated therein.

19. In a dynamo-electric machine for use at high altitudes the combination of a carbon brush and a commutator having a compacted current collecting portion comprising copper and other conductive metal of substan- 6 tially lower electrical conductivity than copper and from the group consisting of lead. iron, chromium, nickel, tin and cadmium and in an amount of at least 10 percent based on the weight of the Whole, wherein said copper is sintered and carries said other metal.

References Cited in the file of this patent UNITED STATES PATENTS 276,233 Edison Apr. 24, 1883 1,177,407 Gilson Mar. 28, 1916 1,248,924 Sandell Dec. 4, 1917 1,937,465 Sherwood Nov. 28, 1933 2,053,662 Hardy Sept. 8, 1936 2,075,444 Koehring Mar. 30, 1937 2,096,252 Koehring Oct. 19, 1937 2,129,844 Kiefer Sept. 13, 1938 2,157,596 Davis May 9, 1939 2,182,741 Bolesky Dec. 5, 1939 2,362,007 Hensel Nov. 7, 1944 2,370,400 Graves Feb. 27, 1945 2,376,706 Lum May 22, 1945 2,379,232 Hensel June 26, 1945 FOREIGN PATENTS 101,993 Sweden July 8, 1941 456,018 Great Britain Nov. 2, 1936

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