US2394501A - Electrical contact - Google Patents

Description

Patented Feb. 5, 1946 2.894.501 ELECTRICAL CONTACT Paul a; w. New York. n. Square D net,

., gnor to No Dra. Application September 12, 1942,

, Serial No. 3

s (or. 15-22) This invention relates to electric contacts such as used on electric circuit controlling devices.

An object of the invention is to provide'an electric contact having long life and chemical stability under use.

Another object of the invention is to provide an electric contact containing a material which is chemically stable, does not tend to weld to the cooperating contact, is relatively hard, and has other desirable contact characteristics.

Another object of the invention is to provide an improved silver base contact incorporatin the contact material of the previous object.

Another object of the invention is to utilize iron oxide as a contact material either alone or admixed with silver, copper, or other conductive material. 1

Other objects and features of the invention will be readily apparent to those skilled in the art' from the following description taken in connection with the appended claims.

Iron oxide, when sintered or fused,- is a conductor which has many desirable characteristics from an electric contact standpoint. It is quite hard. It is chemically stable at high temperatures and has no tendency to increase its resistance from temperature or use under load. -It has no tendency to weld and does not oxidize or burn and shows no tendency to spatter at high temperatures. Perhaps its most important feature is its chemical stability in that no deterioration from further oxidation results from itsuse in an electric arc.

While it is contemplated that many of the varied oxides of iron or mixtures of the same may be utilized within the scope of the invention, a preferred embodiment of the invention will be described, although it is to be understood-that the invention is not limited thereto. In forming an ironoxide contact constituent a mixture of 15% iron powder and 85% ferric oxide (FeaOs) are pressed into a briquet and sintered by heating for one hour at 1800" F. in a neutral atmosphere such as carbon dioxide or nitrogen. Or, alternatively, the mixture may be heated to a sumcient temperature to form a fused product, although this is unnecessary to the formation of a satisfactory material. The resultant sintered or fused product will have a varied composition which is probably a mixture of ferrous oxide and ferric oxide, the indicated proportion being about 43% to 48% ferrous oxide (FeO) and the remaining 52% to 57% ferric oxide (FeaOa).

The purpose in sintering or fusing the omde is to render it conducting and the sintered or fused product after being so processed is ground into grains or particles whose size may vary over a wide range, but for a specific example would be all that would pass through 200 mesh. This iron oxide powder is then mixed with silver powder of a desired size such as the commercially obtainable 300 mesh in the proportions of about 5% to 15% (preferably 10%) iron oxide-remainder silver and is then compressed to a relatively high density and sintered for one hour at 500 F.' After this sintering operation, the contacts are repressed to increase their hardness and the contact is complete. The resulting contact may be attached to a backing or controlling arm in the usual manner by welding or brazing with a silver solderor by mechanical attachment. The silver, iron oxide contact so formed has very good wear qualities and gives a relatively long life under service operation. It is chemically stable and its resistance does not increase by deterioration under use such as might be caused by oxidation other than the oxidation of the silver, since the silver oxide is, of course, conducting. It has excellent non-welding characteristics and can be produced at relatively low cost compared with the cost of production of contacts using other rare and scarce admixtures with silver.

While a specific embodiment of the invention has been described herein, the invention is not limited thereto as it is clear that the process of manufacture may be varied as desired, and that the proportions of the ingredients may be varied within wide limits-since the materials are mechanical mixtures which do not form critical chemical compounds. Thus, even a very small proportion of iron oxide will have some beneficial effect, while for some specific applications it is contemplated that a very large proportion, or a contact formed entirely of iron oxide, might be suitable. K p

Further, while the specific embodiment employs silver, it is contemplated that copper and" other conductive materials may be used with iron oxide to form desirable electric contacts.

Accordingly, the invention is to be given its broadest possible interpretation in accordance with the appended claims.

I claim:

1. An electric contact composed of a mixture of finely divided particles of iron oxide and a metal having a highly conductive oxide.

2. An electric contact composed of a mixture of silver powder and powdered iron oxide.

3. A method of forming an electric contact g 5% e,eee,eo1

- comprising processing an oxide of iron into pertieiee in e conducting etete, admixing them with eiiver powder end compressing end heating the resultant mixture. i V v V 4. A'method (if-forming en electrical contact 5 which comprises forming a conductive mixture of ferrous oxide endierric oxide in pelrticle size, edmiizing the some with silver powder and'comcomprising mixing powdered iron and ferric oxide, heating the some to a temperature at ieest eumflcient to cause eintering and forming the mix-' ture into a conducting mixture of ferrous and ferric oxide, grinding the product into particles, admixing the oxide particles with silver powder, and compressing and heating the silver, oxide mixture.