US2165481A - Electrical make and break contacts - Google Patents

Description

Patented July ll, 1939 ELECTRICAL Franz It. Hensel and Kenneth L.

AKE AND BREAK CONTACTS Emmert, In-

dianapolis, Hnd., assignors to P. R. Mallory 86 00., Inc, Indianapolis, Ind., a corporation of Delaware No Drawing. Application January 19, 1939, Serial No. 251,706

4 Claims.

The present invention relates to electric contacts.

An object of the invention is to improve the characteristics of electric contact elements, containing silver.

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

The present invention comprises the combination of elements, methods of manufacture, and the' product thereof, brought out and exemplifled in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

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 inventlon.

The present invention comprises an improvement in silver electric contact pecially of contact elements formed of at least 70% silver.

According to the invention, the contacts are improved by the addition of thorium. While these alloys may vary in their physical characteristics, according to their specific compositions, they will generally be characterized by a high conductivity, satisfactory hardness and low materlal transfer or build-up characteristics.

It is contemplated that alloys may be produced for electrical contacting purposes, according to the invention, having the ingredients combined in the following range of proportions:

Thorium .005 to 25% Balance substantially all silver.

It is likewise possible to improve the characteristics of silver alloys containing additional ingredients, by the addition of thorium. Such el'ements are primarily copper and gold, and elements taken from the second group of the periodicsystem. We have also found that iron group metals may be added up to several percentages, and that the alloys may contain considerable percentages of precious metals, taken from the palladium and platinum groups.

Tests which we made with silver alloys, containing 2.12% thorium, indicated that the addition of thorium to silver for inductive load applications substantially maintained the critical current of fine silver, while reducing the transfer tendency by about 50%. The silver-thorium alloys were prepared by melting the silver first elements and cs and then adding the thorium in the form of a silver-thorium master alloy of pure thorium powder mixed with silver powder and pressed into the form of pellets to form the silver-thorium master alloy, showing a. high concentration of thorium. No difficulty was encountered to dissolve the thorium in the silver..'

The alloys containing lower percentages of thorium, can be worked into suitable shapes from which contacts can be prepared either by head-- ing, machining or punching. The preferred materials are those containing .005 to 5% thorium.

In a number of applications, silver is mixed with the refractory materials taken from the group of tungsten, molybdenum and/or their compounds and metals from the iron group, consisting of iron, cobalt and nickel. These materials are prepared either by mixing the powdeis together, pressing'same, and hot and cold working same into suitable forms, from which contacts can be made. We have found that the addition of thorium, to the silver base, used in such contact combination, is very beneficial. In certain circumstances, it is also possible to add the thorium to the refractory metal base, and form the silver-thorium alloy by impregnating this mixture with silver or a suitable silver alloy.

Materials of the type described show a structure which is more uniform and homogeneous, and shows higher specific density and less tendency to transfer than materials made according to the prior art.

While the present invention as to its objects and advantages 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.

What'is claimed is: I 1. An electric contact member, containing as an essential ingredient, silver, to which has been added thorium, in quantities ranging from .005 to 25%.

2. An electric contact member, composed of a refractory metal base of the nature of tungsten, molybdenum, iron, cobalt and nickel, and a silver alloy containing .005 to 25% of thorium.

3. An electric contact member composed of .005 to 25% thorium and the balance substantially all silver.

4. An electric contact formed of an alloy containing .005 to 5% thorium and the balance substantially all silver. FRANZ R. HENSEL.

KENNETH L. EMMERT.