US2032926A

US2032926A - Electrical contact

Info

Publication number: US2032926A
Application number: US4483A
Authority: US
Inventors: John B Ford
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1935-02-01
Filing date: 1935-02-01
Publication date: 1936-03-03
Anticipated expiration: 1953-03-03
Also published as: GB449797A; DE670594C

Description

J. B. FORD ELECTRICAL CONTACT March 3, 1936.

Filed Feb. 1, 1955 Inventor: John B. For" by W His Attorney.

Patented Mar. 3, 1936 PATENT, OFFICE ELECTRICAL CONTACT John B. Ford, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 1, 1935, Serial No. 4,483

3 Claims.

My invention relates to electrical contacts of the silver contact type and has for an object the provision of an inexpensive low resistance silver contact provided with a backing member which may be readily united integrally with an iron or steel supporting member. I

Whilesilver has been commonly recognized as a good contact making and breaking material, its use has been restricted due to the difliculties of securing the silver metal to steel supporting members. Heretofore the silver contacts have been formed as by coining or by the flowing of the silver metal under pressure into predetermined size, the pre-formed contact then being applied to the supporting member either by riveting or brazing. While silver can be welded to iron or steel by exercising a great deal of care, welding is not practical for quantity production of switch members where the silver tips are welded directly to the switch members due to the .high percentage of rejects, i. e., switch members to which the silver contacts have not been welded securely. If the silver is secured to the switch member by brazing a flux must be used and the temperature controlled very accurately. This method is too costly to be satisfactory. Riveting is unsatisfactory since additional operations are necessary and under the repeated stress of the opening and closing of the contacts the rivets often are loosened sufficiently to interfere with the circuit making and breaking functions. It has been heretofore proposed to provide silver contacts with backing metals of copper or an alloy of copper and zinc, the backing metals being used to decrease the cost of the contact and to afford a surface metal which can be secured to a supporting member by brazing or soldering. As I have said, however, brazing or soldering operations are not desirable in quantity production due to the great care demanded to insure a minimum number of rejects.

In carrying out my invention in one form thereof I provide a pre-formed electrical contact having a body portion formed of silver and a backing member integrally united to the silver, the backing member being formed of steel. With such a pre-formed contact the steel membar can be resistance welded to a supporting switch member of steel or the like without the use of flux or other complicated manufacturing methods. Iv have found that by integrally uniting the steel backing member and the silver contact members prior to the mounting of the silver contacts to the switch members that the pre-formed contacts can be resistance welded to their supporting members by an automatic welding machine, the union between the steel supporting member and the steel backing member in all cases affording a strong and rigid connection. The result is that the life of the contacts is lengthened, the resistance is decreased, and the cost of the preformed contact is decreased over a silver contact of corresponding size.

In order to assist in the positioning of the preformed contacts with reference to the switch member, the backing member is provided with one or more positioning projections which are arranged to nest within a centering groove provided in the switch member. Due to the thinning of the material inthe switch member by the groove and the relatively small cross'sectional area of the projections, the maximum heat during the resistance welding is produced at the projections. During the welding these projections flow into the groove, the flowing of the metal rapidly extending to the adjoining surfaces of the switch member and the backing member to provide an extremely strong union between the two.

For a more complete understanding of my invention reference should now be had to the accompanying drawing wherein I have shown in Fig. 1 my invention applied to a switch member provided with a pair of silver contacts each having a backing member of steel; Fig. "2 is a perspective view of a pre-fornied silver-steel contact and one end of the switch member shown in Fig. 1 prior to the union of the steel backing member with the switch member; Fig. 3 is a sectional elevation of the contact shown in Fig. 2; while Fig. 4 illustrates a modified form of the invention.

Referring to the drawing, I have shown my invention in one form as applied to a steel switch member ID provided with silver-steel contacts H and [2 of identical construction. The silver con-' tact ll consists of a body portion l3 formed of fine silver and a ferrous backing member H formed of free flowing steel composed mainly of iron. Preferablyrthessteel is heat treated for maximum ductility, i. e., free flowing. The high ductility is desirable since it facilitates the preferred method of integrally uniting the silver to the steel by rolling together under pressure silver and steel bars-which have been heated to a predetermined temperature. After the relatively large bars have been thus integrally united and rolled to a predetermined thickness, composite members approximately the size of the contacts are stamped from the composite metal.

The finishing operation is performed by placing the composite members in dies and applying pressure of a magnitude suflicient to cause the metals to flow into the dies and form the finished contacts.

Instead of the hot rolling method, the bars or plates may be integrally united by other suitable methods well known to those skilled in the art such, for example, as by brazing.

The steel backing member ll of the finished contact is provided with a plurality of frustroconical projections it, each of which is located the same distance from the center of the backing member. These projections of gradually increasing cross-sectional area from their extremities to their base cooperate with a groove !6 formed in the end I! of the switch member l and serve to position the contact I l on the switch member preparatory to the welding operation. The groove l6 shown as circular in form is complementary to the projections; that is to say, it

of the resistance "welding machine are then brought to bear on the outer faces of the respective contact members to'complete an electrical connection and to apply a predetermined pressure .on the contacts. By reason of the groove l6 and the dimensioningof-the projections 15 the welding current flowing from one electrode to the other tends to concentrate through the path of lowest resistance provided by the projections I and the thinned portion of the switch member III at the bottom of the groove. -The result is that the projections II are first melted, the metal flowing along the groove and uniting with the melted walls of the groove. A strong union of the steel backing member M to the switch member III is therefore in everycase assured and I have found that faulty switch members have been practically eliminated because of improper welding of the parts. in fact, after the steel backing member I has been welded to the switch member it is practically impossible to separate them.

As shown in Fig. 3, the thickness of the silver body portion ll is preferably somewhat greater 10 than the thickness of the backing member I 4 although it is understood that the relative thicknesses can be varied as desired. Preferably, the backing member I4 is formed slightly concave so that the outer rim Ha overlaps somewhat the face of the switch member III. This construction is desirable because it reduces the thickness of the resulting switch member and contact assembly.

If desired, the silver body portion it can be 2 formed to overlap the outer edges of the backing member l4, this construction being shown in Fig. 4. v

While I have shown a particular embodiment of my invention, it will be understood, of course, 2s- -that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:--

1. An electrical contact member comprising a body portion formed of silver and a backing member formed of a ferrous metal integrally secured to said body portion.

2. An electrical contact member comprising a body portion formed of silver, a backing member for said body portion formed of steel, the adjoiningsurfaces of said body portion and said back- 40 ing member being integrally secured together.