US2987807A - Electrical conductor structures - Google Patents

Description

Jun 13, 1961 s, FOLDES ETAL 2,987,807

ELECTRICAL CONDUCTOR STRUCTURES Filed April 23, 1959 2,987,807 ELECTRICAL 'CONDUCTOR STRUCTURES Stephen Foldes and John Willard Reardon, Erie, Pa., as-

slgnors to General Electric Company, a corporation of New York 'Filed Apr. 23, 1959, Ser. No. 808,362 5 Claims. (Cl. 29-182.2)

This invention relates to new and improved electrically conductive structures; more particularly it relates to-commutators and commutator segments therefor, which are characterized by the strength of ferrous materials and the superior electrical qualities of copper.

The design and manufacture of commutator segments or bars is generally a compromise in terms of materials used. From the point of view of electrical characteristics, the metal used should be copper, copper alloys, or some other material possessed of superior electrical qualities. At the same time, copper and similar useful materials are not rigid and strong enough even when secured tightly to maintain a smooth contact surface under the temperatures and strains of actual service in an electrodynamic machine. Further complications are introduced by the fact that such materials have a different coetiicient of thermal expansion than the supporting different metal which is usually a ferrous material. Additionally, copper and similar alloys are relatively expensive and increase the cost of the commutator segments all out of proportion, when it is realized that only the contact surface of the segment or bar need be of a highly conductive metal.

Various attempts have been made to fabricate cornmutator segments having a copper wearing surface portion of reasonable depth with the remainder of the segment of ferrous or some similar metal. Such a structure would provide the strength and rigidity required, reduce costs, essentially reduce strains due to differences in coefficients of thermal expansion and between the segment and that part of the commutator to which it is clamped or xed, and at the same time present a copper or similar surface for electrical contact.

It has been suggested that copper strips be brazed or welded to a steel or iron base. Among the disadvantages of this method are inherent weaknesses in such joints and the cost of cutting and machining the segments from the bar so made. Another similar method of making segments is to cast molten copper over a steel or iron ingot and then to cut the segments therefrom as above. Segments so made are again relatively expensive and weak at the point of juncture between the cop- .50

per and the base material.

'From the above, it will be quite evident that there exists a need for economically fabricated bimetallic commutator segments which are electrically and physically desirable and a principal object of the invention is to provide such segments and means for making them.

Briey, the invention comprises sintered bimetallic copper-ferrous commutator segments which have -a contact surface of copper and a base section of ferrous material, such as iron or steel or of other high strength material. The invention also relates to the method of making such commutator segments.

Those features of the invention which are believed to be novel are specifically set forth in the claims attached hereto. The invention will, however, be better understood and further advantages thereof appreciated from a 2,987,807 Patented June 13, 1961 consideration of the following description and the drawing, in which FIG. 1 shows a typical segment of the inventoin, and FIG. 2 shows the segment in a typical application in a commutator.

It has been found that copper affords the best contact surface material consistent with such factors as cost, availability, strength, etc., although alloys of copper as well as other materials could be used. For base material, a ferrous alloy containing small amounts of copper and carbon provides the best mechanical or physical properties. Since the appropriate sintering temperature for iron powder is l C. or higher and the melting point of copper is 1083 C., -a temperature slightly below the melting point of copper was sought which would sinter the ferrous particles and bond them adequately, while at the same time not melt the copper but simply sinter it together as well as to the ferrous base. It was found that a sintering temperature of about l000 C. to 1060 C. preferably about 10607 C. would accomplish this purpose using compacting pressures up to l00,-

000 p.s.i. (lb./sq. in.) Iand then sintering as above for up to or over one hour in a reducing atmosphere such as that of hydrogen, dissociated ammonia, etc.` Preferably a lubricant such as zinc stearate or equivalent is added before mixing the powder. About l% of lubricant is suicient. coined or repressed to size at pressures of the order of the pre-sintering pressures.

As a practical matter, the ferrous powder is placed in one portion of a suitably divided horizontal die and the copper in another, and the partiton removed. ln some cases the partition can be dispensed with. The powders are then compressed while in the die, the compressed material removed from the die and sintered as above. If only a pre-sintering compacting is used, a pressure of the order of about 100,000 p.s.i. is found to be better than lower pressures from about 30,000 p.s.i. to 60,000 p.s.i. However, if lower pressures from about 30,000 p.s.i. to 60,000 p.s.i. are used in the pre-sintering stage, a post-sintering pressure or coining to shape at about 100,000 p.s.i. can advantageously be used. The green strength of material prepressed at below about 30,- 000 p.s.i. is normally too low for easy handling. This coining step not only results in a precisely sized and shaped product, but in general improves the mechanical qualities of the segment. It will be realized that the pressures may be varied to suit the particular needs and the physical requirements of the nal product.

It was found that a material containing from about 0.2% to 0.8% carbon and from about 1% to 10% copper, with the remainder iron, provided a very suitable base segment portion from a physical point of view, with a material containing 0.2% carbon and 5% copper, with the remainder iron having the best qualities. The carbon serves to deoxidize the surface of the iron and copper and, of course, most or all of it passes ot in gaseous form during the heating step. The minimum stated amount of carbon is preferred because more tends to make the final product harder and hence harder to shape or Work.

Iron alloys containing 0.2% carbon, 0.4% carbon and 0.8% carbon along with varying amounts of copper were prepared by compacting at 100,000 p.s.i. and sintered for one hour at 1060 C. The physical characteristics of such an alloy are shown in Table I below.

The segments after sintering are preferably Table I Tensile Yield Elonga- Strength, Strength, tion,

p.s.i. p.s.i. Percent ou, 0.2% o 22,000 15,000 3. 4 0% ou, 0.4% o 20, 000 10,000 2. s 0% 0u, 0.8% o 20,000 15,000 2. o 1% ou, 0.2% o 25,000 16,000 4. s 1% Cu, 0.4% C 19, 000 9, 000 3. 8 17 Cu, 0.8% O ,000 16,000 2.1 2 L; ou, 0.2% o 33,000 1s, 500 6. 0 2 o Cu, 0.4% C 30,000 13, 500 4. 8 2% Gu, 0.8% C 26,000 17,000 3. 4 5% Cu, 0.2% o 29,000 22,000 2.0 5% Cu, 0.4% C 28,000 16,000 2. 7 5% Cu, 0.8% C 25,000 19, 000 2. 2

Shown in Table II are similar physical characteristics of materials compressed at 60,000 p.s.i., sintered for one hour at 1060 C., and repressed or coined to size at 100,000 p.s.i., compared with copper so treated and wrought copper containing about 0.08% silver.

Table II Tensile Yield Elonga- Strength, Strength, tion,

p.s.L p.s.L Percent 0% Cu, 0.2% C 41, 000 45,000 0.4 0% Cu, 0.4% O 41, 000 39,000 0.4 0'7 Cu, 0.8% o 40,000 37,000 0.3 2 o Cu, 0.2% C 45, 000 48, 000 1.0 2% Cu, 0.4% o 44, 000 41,000 0. s 2% ou, 0.8% o 45,000 39,000 o. 4 5% Cu, 0.2% C.. 47, 000 48,000 0.8 5% Cu, 0.4% C.. 47, 000 43, 000 0.5 5% ou, 0.8% C 50,000 40, 000 0. 3 Cu, sLntered and coined 38, 000 35, 000 Wrought [Silver (0.08%) bearing copper 32, 000 32, 000

Table III Tensile Yield Elongn- Sintering Time (hrs.) Strength, Strength, tion,

p.s.i. p.s.i. Percent The data in Table III indicates that longer times of sintering result in better physical characteristics. While sintering times of over one hour can be used, the propenties after one hour are adequate for the present purpose.

The preferred method of preparing the present commutator segments is as follows. There is placed in a horizon-tally disposed die of suitable size and coniguration copper powder and ferrous alloy powder consisting of 5% copper and 0.2% carbon, the two powders being separated by a partition of metal, plastic, etc., which is removed after the powders are in place. Usually the copper powder is added in sucient quantity so that about one-third of the finished segment measuring from 4the contact surface is copper. This, of course, can be varied within limits, depending upon the particular job, keeping in mind that the ferrous alloy should form at least that part of the segment which is subjected to greater physical stress, consistent with having a sufficiently deep copper section adequately to conduct the current used without undue heating. After conipacting at 60,000

p.s.i., sintering for about one hour at 1060 C. and re- -pressingor coining at 100,000 p.s.i., there results a material of the characteristics shown in Table III above. It is found that when segments so made are subjected to tensile test, they ultimately fail not at the juncture between the copper and the ferrous alloy, but within the copper itself, thus indicating an extremely strong copperto-iron bond.

Shown in FIG. 1 is a typical commutator segment 1 made according to this invention. The copper or contact portion 2 is of copper while the lower part, which is subjected to stress and strain is of ferrous alloy containing typically from 1 to 10% copper and from about 0.2% to 0.8% carbon, preferably 5% copper and 0.2% carbon. The projection at 4 is for electrical connection purposes. The segment shown is illustrative only, any variations in size vor shape being possible as is well known in the art.

FIG. 2 is an arrangement of a portion of a commutator showing a typical installation of commutator segment 1 therein. The segment 1, having copper face portion 2, ferrous metal base portion 3, and contact portion 4, is fitted in the periphery of the commutator part 6, with its recessed portion being gripped securely by a mating portion of the periphery of the commutator portion S, and by an adjustable ring 6 which latter can be tightened against Vpart 5 as by means of bolt 7 to hold the segment securely in place. The segment is insulated by usual insulation strips 8. It will be realized that this method of clamping the segment in place is illustrative only and that other methods of accomplishing this purpose, such as by shrink rings, etc. may be used. Generally, the commutator portions 5 and 6 are made of some relatively high strength metal, such as a ferrous alloy, in order lto withstand the forces exerted upon it during high speed rotation, and under high temperatures. Since the portion of the segment gripped is also of ferrous metal with a generally similar coeiicient of thermal expansion, no undue heat-generated forces are exerted on any one part of the system, in preference to another. At the same time, the lower portion of the segment is able to resist physical stresses and strains where they are actually applied and does not deform under the pressure of the holding and other forces. Y

By the present invention, there are provided commutator segments which are economically fabricated, are resistant to physically applied forces, and forces generated by high temperatures under operating conditions. In the process of fabrication, the copper and ferrous powders are separated and compressed as a unit, to provide a composite segment, each portion of which performs a particular function in a superior manner, but which at the same time is so Strongly bonded together that under tension the segment fails in the copper portion rather than at the copper-iron alloy-interface.

It will be appreciated that this invention is also applicable to electrically conducting or collecting structures other than commutator segments where a highly conductive surface or portion is desired along with a high strength base portion. When the powdered materials are compacted separately and then placed together and sintered, the bond between the two portions is weak. This is as compared to the present invention wherein the powders are compacted together at the same time causing the boundary layers to interlock forming a strong mechanical bond.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The process of making a commutator segment which comprises placing copper powder in that part of a horizontally disposed partitioned die of proper size and shape which corresponds to the contact surface portion of the segment and a ferrous powder containing from 1 to` powders, compacting said powders, sintering said powders and coining the sintered product.

2. The process of forming a commutator segment which comprises placing separately in a horizontally disposed partitioned die of suitable size and shape copper powder and a ferrous powder containing from 1 to 10% copper and up to about 0.8% carbon, removing the partition separating said powders, compacting said powders under a pressure of about 60,000 lbs. per sq. in., sintering said powders at a temperature of about 1060" C. for about one hour and thereafter recompacting the sintered product under a pressure of about 100,000 lbs. per Sq. in.

3. The process of making a commutator segment which comprises placing copper powder in that part of a horizontally disposed partitioned die of suitable size and shape which corresponds to the contact surface portion of the segment and placing a ferrous powder containing from 1 to 10% copper and up to about 0.8% carbon in the other portion of said die, removing the partition between the powders, compacting said powders under a pressure of from about 30,000 p.s.i to about 60,000 p.s.i, sintering said powders at a temperature of from about 100()u C. to about 1060 C. and coining the sintered product at a pressure of about 100,000 p.s.i.

4. The process of making a commutator segment which comprises placing copper powder in that part of a partitioned die of suitable size and shape which corresponds to the contact surface portion of the segment and placing a ferrous powder in the other portion of said die, removing the partition between the powders, compacting said powders at pressures from about 30,000 p.s.i to about 100,000 p.s.i, sintering said powders at temperatures of from about 1000 C. to about 1060" C. and coining the sintered product at about 100,000 p.s.i.

5. A commutator segment formed by placing copper powder in that part of a horizontally disposed partitioned die of suitable size and shape which corresponds to the Contact surface portion of the segment, and a ferrous powder containing from 1 to 10% copper and up to about 0.8% carbon in the other portion of said die, removing the partition between the powders, compacting said powders, sintering said powders, and coining the sintered product.

References Cited in the file of this patent UNITED STATES PATENTS Talmage June 29, 1943 Perry Aug. 7, 1956 Goetzel: Treatise on Powder Metallurgy, lvol. 2, pages 310, 311 (1950).

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