US2418710A - Electric contact and brush - Google Patents

Description

Patented Apr. 8, 1947 2,418,710 ELECTRIC CONTACT AND BRUSH Franz R. Hensel, Indianapolis, Ind., assignor to P. R. Mallory & Co., Inc., Indianapolis, hit, a

corporation of Delaware No Drawing. Application November 10, 1944, Serial No. 562,917

Claims. 1

This invention relates to electric contacts and brushes, particularly to sliding electric contacts for use in Variable resistance devices, slip rings. commutator segments and brushes for cooperation with slip rings, and commutator segments.

This application is a 00ntinuati0n-in-part of copending application Serial No. 457,113, filed September 3, 1942.

An object of the invention is to improve electric contacts and brushes and the composition thereof.

Other objects will be apparent from the description and claims.

The present invention contemplates contacts formed of an alloy of palladium and/or platinum together with lead. I have found that these alloys have better wear resistance and operating characteristics than contacts of pure palladium or platinum.

While all compositions containing above 60% of platinum or palladium are suitable for such purposes, the preferred material for sliding contacts are composed of:

Per cent Palladium '75 to 99 Lead Balance Per cent Palladium 93 Lead '7 was formed by melting palladium in a beryllium oxide crucible and then adding lead to the melt to produce the desired composition. The alloy was then allowed to solidify in the crucible after which the piece was swaged and drawn and then formed into contact discs and plates.

Tests were performed on these contacts mounted as sliding contacts of a wire wound potentiometer of 20,000 ohms resistance using Nichrome wire having a diameter of .0025".

The palladium-lead contact had a diameter of .040". This potentiometer was tested under electrical load for 60,000 operating cycles after which it was determined that the contact face had worn down .002". Very little metallic powder was observed between the turns of the resistance wire. The potentiometer was then further tested for an additional 60,000-cycles without any further measurable wear being observable. The general appearance of the contact and potentiometer was.

2 the same for 120,000 as it had been for 60,000 cycles.

For purposeof comparison a pure palladium contact of similar dimension was tested on a similar potentiometer under the same conditions for 60,000 cycles. At the end of the test the pure palladium contact had worn .020" or ten times as much as the wear observed on the palladium-lead contact. Moreover, considerable palladium powder was observed between the turns of the wire.

While melting and casting is the preferred alloying method it is contemplated that the contacts may in some cases be produced by other methods such as by sintering the mixed powders, metal spraying, alloy plating or alloy deposition from metallic vapors.

An important advantage in using platinum and palladium base contact materials results from their low thermal coefflcient of expansion. This reduces the tendency toward distortion or binding if a portion of contact or slipring becomes overheated.

Where the contact is bonded to a backing of other composition the support may also be formed of material of low coefiicient of expansion such as nickel steel containing between 30 and 48% nickel. It is possible to select steels within this range having coefficients of expansion which exactly match that of the contact material.

Another alloy which is useful for sliding contacts and slip rings may contain:

Per cent Palladium Lead Balance For most sliding-contact purposes it is preferred that the platinum or palladium base alloy be used in the annealed condition under which it is extremely soft and affords an excellent sliding surface. This condition may be arrived at by annealing, the annealing temperature depending upon composition. In the case of an alloy of Per cent Palladium Lead 10 3 I 4 to 99% of metal selected from the group consist- 5. A sliding electric contact formed of an alloy ing of platinum and palladium. balance substanof about 70% palladium and the balance lead.

tially all lead. 1 FRANZ R. HENSEL.

2. A sliding electric contact formed of an al 0y of 75 to 99% palladium and the balance substan- 5 REFERENCES CITED tially all lead. The following references are of record in the 3. A sliding electric contact formegiflandalloy fil of 118' patent; of about 93% palladium and about 0 ea 4. A sliding electric contact formed of an alloy UNITED STATES PATENTS of'about 90% palladium and about 10% lead. 10 Number Name Date 1,358,908 Williams Nov. 16, 1920