US2137617A - Electrical contact and method of making the same - Google Patents

Description

Nov. 22, 1538. R, 'H' MEs ET AL 2,137,617

ELECTRICAL CONTACT METHOD OF MAKING THE SAME Filed March 4, 1936 I k '4 INVENTQRS jwm ,9, [W5 f/ l Ffzfa/k TTORNEY Patented Nov 22, 1938 7 i 4 UNITED STATES PATENT OFFlCE ELECTRICAL CONTACT AND METHOD OF MAKING THE SAME Robert 11. lines and Hal F. Fruth, Indianapolis,

Ind., asdgnors to P. R. Mallory & 00., Inc., Indianapolis, Ind., avcorporation of Delaware Application March 4, 1936, Serial No. 67,010

13 Claims. (01. 29-15555) This invention relates to electrical contacts contacts wherein a contact face of silver or a.

and methods of making the same. silver alloy is integrally united to a steel backing. An object of the invention is to improve the In prior practice such contacts have been made methods of making electrical contacts. by punching the contact discs out of bimetallic Another object is to produce an improved elecsheet stock consisting of a sheet of steel havin 5 trical contact. a uniform layer of silver welded to its surface. Other objects of the invention will be appar- It will be readily apparent that this procedure ent from the following description and accomis wasteful and uneconomical because of the panying drawing taken in connection with the fact that a sizeable proportion of the silver is appended claims. left onthescrap material from which the con- 10 The invention comprises the features of contact discs have been punched. These prior struction, combination of elements, arrangemethods, therefore, require a considerable inment of parts, and methods of manufacture and vestment in material which is converted into operation referred to above or which will be scrap which requires further processing in order brought out and exemplified in the disclosure to recover the precious metal; The present ill-'15 hereinafter set forth, including the illustrations vention provides an improved method of making in the drawing, the scope of the invention being contacts which does not have these objections.

indicated in the appended claims. Referring to the drawing, a silver-faced con- For a fuller understanding of the nature and fact i0 is illustrated in Figures 1 and -2 and the objects of the invention as well as for specific method of making the contact is illustrated in 0 fulfillment thereof, reference should be had to Figures 3 to 8. In this method a strip .of sheet the following detailed description taken in consteel II is run through a stamping machine or nection with the accompanying drawing in punch press wherein a series of annular grooves which: 12 are stamped in the strip. In the same opera Figure 1 is a face view of an electrical contact tion an indentation I3 is formed on the same 25 made according to the present invention; face with the annular groove and preferably Figure 2 is a section on the line 2-2 of Figconcentric therewith. A corresponding projecure 1; tion 14 is thereby provided on the opposite face Figure 3 is a face view of a steel blank us d in ofthe strip. A series of locating or centering fabricating contacts of the kind shown in Figholes i 5 is also punched in the strip in a line 30 ure 1; parallel to the line of centers of the annular Figure 4 is a section on the line H of Figgrooves, the centering holes being spaced apart ure 3; I by the same distances as the annular grooves. Figure 5 is a section through a preliminary After the above operation the steel strip will have 85 assembly comprising the steel blank and a disc the form Shown in Figures 3 and of contact metal; The next step in the procedure is to place Figure 6 is a section through the assembly a piece It of the contact metal, such as silver, after fusion of the contact metal to the steel on or in contact with the steel strip within the backing; area enclosed by each annular groove l2. The

Figure 7 shows the coining operation; nd pieces each contain a definite predetermined 4.0

gure 8 shows the operation of punching th quantity of metal and may be in the form of discs contact from the steel strip on which t was punched from sheet, slugs punched from wire formed. or small pieces formed in other ways.

While a preferred embodiment of the inv nti The steel strip ll, carrying pieces iii in con- 5 is described herein, it is contemplated th t tact, is then passed through a'furnace where siderable variation may be made in th m th d the assembly is heated to a temperature above of procedure and the construction of parts iththe melting point of the silver or silver alloy. ut. departing from th Spirit 0f t invention When the silver is in the molten condition it flows In the following description and in the clai out over the surface of steel strip H until it Parts will be identified by specific names fo reaches-the inner edge of groove l2, where the 50 convenience, but they are intended to be as is d, p a y a e the Surface generic in their application to similar pa t as tension of the molten silver is greater than the the art will permit. attraction of the silver for the steel at this point. An important use of the present invention is Should the silver flow over the inner edge of 56 in the production of steel-backed silver-faced the groove it will be stopped at the outer edge.

' the edges thereof.

There results a body of molten silver which solidifies, on removal from the furnace, into a solidlayer l'l adhering to the steel backing within the area bounded bythe annular groove, the silver layer having a convex circular face l8 (Fig. 6).

The convex face l'l may, in some instances, be suitable for use as a contact face without extra treatment. It is generally desirable, however, to insure perfect uniformityof dimensions and to obtain the exact radius of curvature desired, to coin the surface. This is accomplished, as indicated in Figure '7, by a pair of punches l9 and 20 held. in a suitable pressing arrangement. Punch l9 has a face shaped to receive the projection It on the back of the strip and punch 20 has a face 30 of the curvature necessary to apply the desired radius 21 to the silver face. In the coining operation the contact can be centered with respect to the punches by one or more locating pins 22 adapted to fit into holes I5.

The finished contacts are punched from strip II by a punch 23, having a face shaped to receive projection 14, in cooperation with a die 24. The punch 23 and die 24 have a diameter 26 slightly less than that of annular ring 12 so that some of the silver contact metal is drawn down around the sides of the punched disc to cover the edges as is apparent from Figure 2. In the punching operation locating pin 25 co-operates with hole I5 in the steel strip to center the contact in the die.

The finished contact I0 is thereby produced having a circular silver face with a curvature 2|, the silver face being integrally attached to a steel backing disc 21 and extending down over The steel disc 21 also has welding projection l4 whereby the contact can be electrically welded to a switch spring, circuit breaker armature, breaker arm, relay armature or any other metal part on which it is desired to provide contacts.

It will be obvious that other contact materials, in some instances, can be used in place of silver and other backing materials can be used in place of steel. Composite facings may also be formed. The metal in contact with the backing must, of course, be of lower melting point than the backing metal.

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:

1. The method of making an electric contact which comprises providing an annular groove in one face of a sheet of backing metal, placing a quantity of lower melting point contact metal in contact with said face in the area surrounded by said groove, heating the assembly thus produced to a temperature above the melting point of said contact metal, whereby itis fused to said backing metal, cooling said assembly and punching a disc from an area of said backing metal sheet including at least part of the area within said annular groove, said groove serving to limit the flow of the melted contact metal during said heating.

2.-The method of making an electric contact which comprises providing a groove in one face of a backing metal member, said groove enclosing a portion of the area of said surface, placing contact metal of lower melting point than said backing metal against said portion, heating said assembly above the melting point of said contact metal but below the melting point of said backing metal, and cooling the integral assembly thus produced, said groove serving to limit the flow of the melted contact metal during said heating.

3. The method of making an electric contact which comprises providing a groove in one face of a metal backing member, said groove enclosing a portion of the area of said face so as to prevent the flow of molten metal of lower melting point than the backing metal away from said area, placing facing metal in contact with said area, at least a portion of said facing metal being suitable for a contact facing and at least a portion of said facing metal being of lower melting point than said backing metal, heating the assembly thus produced above the melting point of said lower melting point metal but below the melting point of said backing metal whereby said lower melting metal will fuse to the surface of said backing metal within said area, and cooling the integral assembly thus produced.

4. The method of making an electrical contact assembly which comprises forming a moat in a face of a backing metal member, placing a lower melting metal in contact with said face inside said moat, heating to fuse said lower melting metal and cooling to solidify the integral assembly thus produced, said moat serving to limit the flow of the melted contact metal during said heating.

5. The method of making an electrical contact which comprises stamping a circular groove in a face of a backing metal member, placing a piece of contact metal of lower melting point than said backing metal within the area enclosed by said groove, heating the assembly to a temperature high enough to melt said lower melting metal only, and cooling the integral assembly thus produced, said groove serving to limit the fiow of the melted contact metal during said heating.

6. The method of making an electrical contact which comprises stamping a moat in a face of a backing metal member, placing a piece of silver metal within the area enclosed by said moat, heating the assembly sufliciently to fuse said silver metal without fusing said backing metal, then cooling the assembly below the melting point of said silver metal, said moat serving to limit theflow of the fused silver metal during said heating.

7. The method of making an electrical contact which comprises stamping a circular groove on one face of a piece of sheet steel, placing a piece of silver metal within the area enclosed by said groove, and heating the assembly to fuse the silver to the steel, said groove serving to limit the flow of the fused silver metal during said heating.

8. The method of making an electrical contact which comprises stamping a circular groove on one face of a piece of sheet steel and raising a welding projection on the other face opposite the area enclosed by said circular groove, placing a quantity of silver in contact with the area enclosed by the circular groove, heating the assembly sufllciently to fuse said silver to said area and cooling the integral assembly thus produced, said groove serving to limit the flow of the fused silver during said heating.

9. The method of making an electrical contact which comprises stamping a circular groove on one face of a piece of sheet backing metal, fusing a body of silver metal to said face within the area enclosed by said groove, and punching a bi-metal disc from the silver-backing metal assembly, said groove serving to limit the flow of the fused silver metal during said heating.

10. The method of making an electrical contact which comprises stamping a circular groove on one face of a piece of sheet backing metal, fusing a body of silver metal to said face within the areaenclosed by said groove, coining a contact face on said silver metal and punching a bimetal contact from the assembly, said groove serving to limit the flow of said silver metal during fusing.

11. The method of making an electrical contact which comprises stamping a circular grooveon one face of a piece of sheet steel, raising a welding projection on the other face of said sheet opposite the area enclosed bysaid groove, fusing a body of silver metal to said face within the area enclosed by said groove, coining a contact face on said'silver metal and punching a bi-metaicontact disc from an area including said silver and said welding projection, said groove serving to limit the flow of said'silver metal during fusing. v

12. A blank for producing a contact backing comprising a strip of sheet metal having a row of locating holes punched therein, said row being on a line parallel to one edge of said strip, said strip also having a row of annularly grooved portions parallel .to said holes.

13. The method of making a bimetal electric contact disk having a curved edge, without wastage of the contactmetal facing, which comprises integrally securing a layer of contact metal to a sheet metal backing in an area correspondingto an i ndividual contact surrounded by an area of backing metal substantially free from contact metal and then punchingsaid bimetal contact disc out of said sheet metal backing by severing said backing along a line substantially at the boundary of the area to which said contact metal is secured and simultaneously drawing said contact'metal down over the edgeof the backing along the curved edge of said disc thereby to produce said bimetal contact having a.

curved edge and with the entire face'and edge thereof covered with contact metal.

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