US2186245A - Electrical contact member - Google Patents

Description

Patented Jan. 9, 1940 r 2,186,245

II'UNITEDCSTATES PJTENT OFlCE ELECTRICAL CONTACT MEMBER James M. Kelly, Traffcrd, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa, a corporation of Penn sylvania No Drawing. Application May 5, 1939, Serial No. 271,934.

Claims. (01. 200-166) This invention relates to electrical make and melting point so formed as to have interstices break contact members. therein, and which of itself does not possess the Contacts formed from refractory metal powdesired mechanical strength, is impregnated with ders and a metal having good conductivity, '2. silver base alloy of lower melting point, as will 5 such as copper or silver, have been employed -be disclosed more fully hereinafter.

heretofore. Such metals having high conduc- Informing themetal base here employed, tivity, are, however, not of themselves entirely refractory metal powders of predetermined size satisfactory for this purpose, since the resulting ranging from 150 to 250 mesh are mixed with contact member does not have as high physical sufficient organic bond to form a plastic putty- 1 properties as are required in certain applications. :like mass which is moldable, or which can be 1.0

Carbon has been so added to the composition rolled orcast to a desired shape. Any suitable of the contact members that when heat treated organic bond which can be removed by drying it will combine with the refractory metal and or sintering the shaped mass to leave a porous form a refractory carbide, thereby increasing the structure may be employed. It is desirable to hardness of the contact members. Such refracemploy a bond which can be substantially'com-glfi affect the oxidation rate of the contact members leaving the desired porous structure.

tory carbides are undesirable in the contact mempletely removed so as not to leave a carbon resibers since they increase the resistivity of the due which may combine with the refractory metal metal and lower the melting point of the refracin the form of. a carbide, since such carbides are tory with which the carbon combines. undesirable. An organic bond composed of about Other alloying metals have been added in addi- 75% of shellac and of alcohol is entirely=:2o tion to the copper or silver in making the contact satisfactory in forming the putty-like mass, and member in an effort to enhance the physical ,When the mass is heated at a temperature of properties of the resulting contact member, but about 1000" C. to 1100 C. in a reducing atmossuch additionshave the disadvantage that they phere, it is substantially completely removed,

:25 and introduce impurities therein without appre- In order to impart the desired characteristics ciably increasing the physical properties of the to the contact member, the porous refractory contact member. Further, where some of these metal base or body is then filled with theimalloying metals have been utilized, it has been pregnating silver base alloy. The alloy employed 130 found that a satisfactory bond is not perfected in forming the contact members of this invention go between the refractory metal and the alloying is a silver base alloy which contains between 1% metals, it being difiicult to secure a satisfactory and 10% of each of the alloying elements, copper wetting action of the alloy with refractory metal. and antimony. It is desired that at least 1% of An object of this invention is to provide a coneach of copper and antimony be present in the ,35 tact b r having high physical properties and silver base, sincellower contents of copper and,

good wear characteristics. antimony are not effective for imparting the de-" Another object of this invention is to provide sired strength to the alloy and consequently to a composite contact member formed from refracthe resulting contact member impregnated with tory metal powders and a silver base alloy conthe silver basealloy. taming copper and antimony. In practice, it is found that a silver base alloy 0 A further object of this invention is to provide containing about 7.5% of copper and about 8% a contact member formed from refractory metal of antimony is effective in producing the desired powders and a silver base alloy containing copper mechanical strength in the resulting alloy. For and antimony, and which is susceptible to an practical purposes, however, it is found that a age-hardening heat treatment to improve the silver base alloy containing an optimum composimechanical strength of the contact member. tion of from 3.5% to 4% of each of copper and Other objects of this invention will become apantimony is satisfactory for the purpose of this parent from the following description and the invention, since comparable strengths are obappended claims. tained as in the contact members impregnated 5 In practicing this invention, a contact member with the silver base alloy having larger contents 550 is formed from a plurality of metals which have of the alloying elements, copper and antimony. been found to cooperate to give certain desired It is thought that this is because copper and anticharacteristics. A base body of refractory metal mony in excess of about 4% in the silver base of selected from the group consisting of tungsten the alloy does not go into solution in the silver and molybdenum, and which has a relatively high base. 55

The silver base alloy employed in forming the contact member of this invention is susceptible to precipitation hardening, and when heat treated, as by quenching at from a temperature of between 600 C. and 775 0., and aged at a temperature of between 100 C. and 400 0., has a hardness greater than '70 Rockwell B. The same eifect is found when a contact member formed of the refractory metal powders and impregnated with the silver base alloy containing copper and antimony is subjected to a similar heat treatment, giving a contact member having high mechanical strength.

In forming the contact members, from 45% to 75% by weight of the refractory metal powders is impregnated with from 55% to by weight of the silver base alloy containingbetween 1% and 10% of each of copper and antimonyr-In impregnating the refractory metal powders, it is found that, in addition to imparting strength to the alloy, the antimony constitiuent of the silver base allow aids in securing a .bond between the refractory metal powders and the impregnating alloy. It is thought that the antimony in the silver base alloy acts asa fluxing agent, promoting and so accelerating the wetting characteristics of the silver base alloy that it readily impregnates the porous refractory structure, giving a contact member having a uniform structure in which the refractory metal is securely bonded by the silver base alloy. Such contact members are resistant to corrosion, and'when precipitation hardened, as hereinbefore described, have high physical properties, that is, high hardness, high tensile strength, and resistance to wear or deformation.

A particular ccntact member formed in accordance with this invention, and which is satisfactory for use where it is desired to interrupt heavy currents, is formed from about 60% of molybdenum powders impregnated with about 40% of the silver base alloy which contains about 4% of each of the alloying elements, copper and I antimony. As quenched from 700 0., this contact member has a Rockwell B harness of 20,

whereas when aged for only 10 hours at 200 C.,

the hardness and consequently the strength of the resulting contact member is increased to a Rockwell B hardness of 71. The resulting contact "member is particularly resistant to corrosion and has a long life when measured in terms of interrupting operations.

By practicing this invention, contact members and which are free from carbon contaminations .blows such as are encountered in service.

micro-examination of the contact members emof a silver base alloy containing from 1% sometimes employed heretofore for improving the wearing characteristics of the contact members. With the combination of metals employed, a contact member is produced which can readily be machined to shape prior to the described precipitation hardening treatment, and which afterwards can be heat treated to render them resistant to deformation when subjected to repeated A bodying the teachings of this invention reveals that the silver base alloy containing copper and antimony is distributed very uniformly throughout the matrixof refractory metal in a very finely divided state of subdivision. Such contact members are resistant to corrosion and can be utilized in service where it is necessary to inter- -rupt heavy currents without danger of contact failure.

Although this invention has been described with reference toa particular embodiment thereof, it is, of course, not to be limited thereto except insofaras is necessary in accordance with the teachings of the prior art and the scope of the appended claims.

I claim as my invention:

1. An electrical contact member comprising from-% to 75% by weight of refractory metal powders bonded together with from to 25% to 10% of copper and 1% to 10% of antimony.

2. An electrical contact member comprising from 45% to by weight of refractory metal powders formed to a predetermined shape and impregnated with a silver base alloy having a copper content of from 1% to 10% by weight and an antimony content of from 1% to 10% by weight, and which has been precipitation hardened subsequent to the impregnation.

3. An electrical contact member comprising about 60% of molybdenum and about 40% of a silver base alloy which contains between 1% and 10% of each of copper and antimony.

4. An electrical contact member as in claim 1 which has been quenched from a temperature of between 600 C. and 775 C. and aged at a temperature of between C. and 400 C.

5. An electrical contact member comprising a major proportion of refractory metal powders bonded together with a minor proportion of a" silver base alloy which contains from 1% to 4% of each of the allowing elements copper and antimony.

JAMES M. KELLY.