US2145690A - Electric contact material - Google Patents

Description

Patented Jan. 31, 1939 PATENT OFFICE smc'rmo CONTACT MATERIAL ,Franz R. Hensel, Indianapolis, Ind., assignor to P. B. Mallory & 00., 1110., Indianapolis, Ind., a corporation of Delaware No Drawing. Application September 24, 1931 Serial No. 165,568

7 Claims.

This invention relates to electric contacts.

The, general objects of this invention are the provision of electrical make-and-break contacts having improved operating characteristics and the provision of the composition from which such contacts are formed.

A more specific object of the invention is the provision of electrical make-and-break contacts which have, due to the composition thereof, a

10 reduced contact resistance; less tendency for arcin'g, pitting and transferring during the operation, and which overcome particularly the danger of sticking or fusing together of contacts.

Among other objects, the invention contemplatesthe composition of such electrical makeand-break contacts to which is attributable improved operating characteristics. 7

Other objects of the invention will be apparent from the following description taken in go connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the productthereof brought out and exemplified in the disclosure, hereinafter set forth, the scope a of the invention being indicated in the appended claims.

. The present invention contemplates the use of cadmium oxide in proportions ranging from the least useful amounts up to 50% in contact alloys 30 and compositions.

It is contemplatedthat the addition of cadmium oxide can be utilized to effect improvements in all of the various contact materials of the prior art. In particular, I have discovered that it produces desirable improvements when incorporated in silver and silver alloy contacts, noble metal contacts, refractory metal contacts, nickel contacts, copper contacts, and contacts formed of mixtures of refractory materials and 40 lower melting point metals.

Silver is comparatively cheap and has advantageous characteristics for contacts when used alone or in its alloys. Silver is accordingly one of the principal contact materials to which I 5 propose the addition of cadmium oxide. Other specific materials which can be improved by cadmium oxide are gold, platinum, palladium, tungsten, molybdenum, chromium, copper, nickel, the carbides, borides and nitrides of tungsten, molyb- 50 denum, titanium and zirconium and mixtures of the various metals and compounds, such as mixtures of the refractory metals and compounds with silver or copper or their alloys. These may, for example, be sintered compositions of tungsten 5 and tungsten carbide with copper or silver. The

.cadmium oxide additions may also improve such mixtures as silver and graphite or copper and graphite. One class of contacts of this group are composed of copper containing up to graphite.

Where a contact of cadmium oxide and silver is prepared, the usual method of manufacture consists of mixing the powders, pressing same and then sintering them in air atmosphere at 825 to 850 degrees C. for one hour. Under cer- 10 taincircumstances,..I have found it advisable to carry out sintering in a neutral atmosphere. If a reducing atmosphere is used, there exists a possibility that part of the cadmium oxide is being reduced to metallic cadmium. By regulatl5 ing the time and temperature at which sintering is carried out, the ratios of metallic cadmium to cadmium-oxide can be accurately controlled.

Cadmium oxide, due to its fine amorphous condition, is an excellent material to separate the 20 metallic particles which are the current conducting parts of an electrical contact. It' is generally accepted today that the fusing together of these metallic particles must be prevented if a nonsticking contact is to be produced. Cadmium oxide is excellently suited for this purpose and has given better results than most of the other materials tried. 7

Cadmium oxide also has the advantage that it will not form layers of high contact resistance during operation .of the contact, and therefore relatively light pressures can be used in the construction of a contact which in turn again tends to prolong the life of the contact because the mechanical wear is decreased.

Any cadmium oxide which, due to the method of manufacture, might have been converted partly to metallic cadmium, will again be re-converted to cadmium oxide in service and therefore will carry out the same function as the cadmium oxide contained as such in the mixture.

Tests were made on a regular relay test bank and it was found that with the relay working on 110 volt D. C. and 1.9 ampere current, a contact consisting of 20% cadmium oxide and balanoe silver or a contact of cadmium oxide and balance silver, did not fail on this test.

Almost all other silver base materials will fall after very fewoperations. The new cadmium oxide bearing materials, however, stood up during 50 the entire length of the test, which is '72 hours. On low voltage D. C. applications, such as 6 volt-l2 volt, the contact resistance did not increase appreciably. In the case of a material containing 50% cadmium oxide and balance 66 silver, the contact resistance increased at 12 volts D. C. 2.3 amperes from .93 milliohm to 1.41 milliohms. I

It has also been possible to increase the hardness of a soft metal, say for instance, pure silver, by adding cadmium oxide. The Rockwell H hardness of a material containing 95% silver and 5% cadmium oxide is 5. Byincreasing the cadmium oxide content to 20%, the hardness can be increased to 59. By further increasing the cadmium oxide to a hardness of 81 can be obtained.

In order to obtain particularly dense combinations, it is possible to press the mixtureof metal powder and cadmium oxide powder at a slightly elevated temperature. It is also possible to press the metal cadmium oxide powders cold, sinter same in oxidizing or neutral atmosphere, repressing same after sintering, either at room or elevated temperature and then finally subject the material to another heat treatment either in oxidizing or reducing atmosphere, at a temperature lower than the first sintering temperature.

It is also possible to use the metal cadmium oxide mixtures of sufliciently low cadmium oxide concentration for rolling purposes. This can be accomplished by pressing a bar, preferably at an elevated temperature, and then carefully working it down to smaller cross sections by either a swaging, forging or rolling process. In some cases it might be advisable to back up the cadmium oxide metal mixture by a solid metal layer and produce a bimetallic structure con sisting of one side of cadmium oxide metal and on the other side, of a metal or alloy not containing any cadmium oxide.

These bimetallic strips can be cut in suitable sizes and fastened to contact arms or other contact structures by means of a brazing operation or a welding operation in general Since certain changes may be made in the above composition and diiferent embodiments of the invention could be made without departing from the scope thereof. it is intended that all matter contained in the above disclosure shall be interpreted as illustrative and not in a limiting sense.

While the present invention as to its objects has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the appended claims. v v 7 What is claimed is:

1. An electric contact composed of a contact material characterized by the addition of cadmium oxide.

2. An electric contact composed of a contact material characterized bythe addition of an appreciable amount of cadmium oxide.

3. An electric contact formed of a contact metal I composition containing cadmium oxide in the least useful amounts up to 50%.

4. A sintered electrical contacting element, containing cadmium oxide in quantities ranging from more than incidental percentages, up to 50%, the balance being a metal composition comprising, elements taken from either the group of silver, gold, copper, or tungsten and molybdenum,

or platinum and palladium, or compounds of titanium, zirconium, molybdenum and tungsten of the nature of carbides, nitrides and borides.

5. A sintered contacting element consisting substantially of silver and cadmium oxide, the

cadmium oxide comprising from more than incidental percentages to 50% of the composition.

6. A sintered contacting element consisting substantially of silver and cadmium oxide, the said cadmium oxide ranging from more than incidental percentages to 50%, and containing graphite up to 20%.

'7. A sintered contacting element consisting substantially of copper and cadmium oxide, the said cadmium oxide ranging from more than incidental percentages to 50% and containing graphite up to 20%. FRANZ R. HENSEL.