US2300286A - Electrical contact - Google Patents

Description

' claims.

, contacts.

Patented Oct. 27, 1942 UNITED STATES PATENT OFFICE,

ELECTRICAL CONTACT Childress B. Gwyn, In, Bannockburn, I lL, assignor to Fansteel Metallurgical Corporation, North Chicago, 111., a corporation of New York No Drawing. Application May 3, 1941,

Serial No. 392,487

6 Claims. (01.200-166) tion of elements, methods of manufacture, and

the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention bein indicated in the appended While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements without departing from the spirit of the invention.

In voltage regulators or relays the contacts should'be non-fusing, have a low contact resistance with a relative small contact pressure and be capable of maintaining low resistance in serviceafter a large number of operations.

It is of importance in contact applications to consider the type of current load placed upon the This load will normally be through a resistive circuit in voltage regulators. I applications, on the other hand, the load may varyfrom purely resistive to purely inductive. It may be a combination of resistance and inductance. It may also include capacitative loads as well.

It has. been found that contacts in such services as mentioned above frequently fail on account of excessive material transfer. This transfer is a function of the electrical conditions at the time of make or break and it is also dependent upon the materials which are used for the contacts. It is well known that difierent metals and different alloys have widely diflferent characteristics in their ability to withstand transfer.

It is known that the tendency of the contact materials to transfer and of the contacts to fail is also dependent upon the contact polarity. That be difierent from a combination in which the ma- I terials of the positive and negative contacts are reversed. This is apparently dependent upon the characteristics of the different materials in the composition, including such factors as the arcing voltages, ionization potentials, sticking or nonfusing characteristics and the like.

According to the present invention, there is proposed the use of contact combinations for D. C. purposes wherein the contact on the posi- For relay tive side is characterized by the presenceof an appreciable quantity of a platinum group element and the contact on the negative side is made up of a refractory metal such as tungsten in combination with silver and in some cases modifying element.

I have found the most'suitable materials for the positive side to be alloys of a precious metal,

e. g. of the platinum group or gold with or without silver, which may also include small amounts of hardening metals such as the metals of the iron group or copper.

For most applications the contacts for the positive side may be formed of alloys in the following The .preferred contact materials for the negative side are' hard alloys of high conductivity characterized by a wear-resisting ingredient such as tungsten, molybdenum or their carbides or borides, plus a conductive ingredient such as silver, copper or alloys made up principally of these elements modified by lesser amounts of other elements such a one of the iron group metals, cadmium, zinc, arsenic or the alkali or alkaliearth metals.

For most uses the negative contacts may be formed of alloys having their ingredients present in the following range of proportions:

Tungsten, molybdenum or the carbides thereof- 20-80 Silver or copper -15 Modifying element 0-5 Examples of preferred compositions for use according to the invention are:

Positive side:

Per cent 1 range of compositions: I

' Per cent Platinum and/or palladium and/or gold" 0-98 Other metals of the platinum group 0-15 Silver 0-50, Iron group or copper 0-5 nickel, copper -5 Negative side:

a. Molybdenum 35 Tungsten carbide 25 Silver 20 Copper 20 b. Molybdenum 64 Silver- 35 Nickel 1 c, Tungsten 75 Copper 24 Cobalt 1 d. Tungsten carbide -l- 75 Silver 24.6 Copper 0.4

e. Tungsten Silver 45 Cadmium 5 In comparison tests of various of the preferred combinations of the present invention with other contact combinations, it has been found that combinations selected according to the invention operate for periods of the order of 300 to 5,000 hours which is far in excess of known previous combinations.

While the present invention as to its objects and advantages has been described here as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention as broadly as the spirit and scope of the appended claims permit.

What is claimed is:

1. In combination a co-operating pair of electric make-and-break contacts, one contact being formed of an alloy rich in at least one noble metal and the other contact being made up of a wearresistant constituent selected from the sixth group of the periodic system and a conductive constituent of the class consisting of silver, copper and alloys predominating in these metals.

2. An electric contact combination for D. C. operation the contact on one side of said combination having the composition Per cent At least one metal of the group platin palladium, gold 0-98 At least one metal of the group ruthenium,

rhodium, osmium, iridium 0-15 Silver 0-50 At least one metal of the group iron cobalt,

and the contact on the other side being made up of a wear-resistant constituent selected from the sixth group or the periodic system and a conductive constituent of the class consisting of silver, copper and alloys predominating in these metals.

3. An electric contact combination for D. C. operation, the contact on one side of said combination being formed of an alloy rich in at least one noble metal and the contact on the other side of said combination having the composition I Percent Tungsten, molybdenum or the carbides thereof 20-80 Silver or copper 15-75 Modifying agent selected from the class consisting of iron, cobalt, nickel, cadmium, zinc, arsenic, the alkali metals and the alkaline earth metals 0-5 contact is made of a platinum group alloy and the other contact is made up of a tungsten group metal, a small amount of a modifying agent for said metal selected from the class consisting of carbon and boron and silver.

CHILDRESS B; GWYN, JR.