US3075281A

US3075281A - Method for producing an electrical contact element

Info

Publication number: US3075281A
Application number: US765234A
Authority: US
Inventors: Howard E Spooner
Original assignee: Engelhard Industries Inc
Current assignee: Engelhard Industries Inc
Priority date: 1958-10-03
Filing date: 1958-10-03
Publication date: 1963-01-29
Anticipated expiration: 1980-01-29

Description

Jan. 29, 1963 H. E. SPOONER 3,075,281

METHOD FOR PRODUCING AN ELECTRICAL CONTACT ELEMENT Filed Oct. 3, 1958 FIG. 2 FIGJ mu-mm 1;

IIIIJIIII.

INVENTOR.

HOWARD E. SPOONER BY K642 flaw ATTOR EYS Patented Jan. 29, 1953 3,075,281 METHOD FUR PRQDUCING AN ELECTRICAL CGNTACT ELEMENT Howard E. Spooner, Lincoln, R.I., assignor, by mesne assignments, to Engelhard Industries, Inc., Newark, NJL, a corporation of Delaware Filed Oct. 3, 1958, Ser. No. 765,234 2 Claims. (Ci. 29-155.55)

This invention relates to a method for producing an electrical contact element and, more particularly, is con cerned with a method which permits the insertion of contact points of precious metal into a supporting base metal strip, the surface of the contact point contacting a base metal. oxide.

It is known that the properties of precious metal contacts are improved by additions of base metal oxides or mixtures thereof such as iron, cobalt, nickel, copper, cadmium, chromium, manganese, tin and many others. The contacts produced from precious metals with added base metal oxides show a decreased tendency to stick during performance and are used in a great number of applications. However, one of the main difiiculties encountered with this type of contact resides in the fact that the base metal oxide addition renders the material unsolderable and numerous methods exist to secure such contact points in supports. On the other hand, in US. Patent No. 2,625,737, a method has been described in which precious metal contacts are obtained by preparing a disc from a laminated stock sheet metal having a top layer of a precious metal. Subsequently, the disc is inserted into an aperture in a base metal strip, the aperture having a shape substantially identical with that of the disc, the strip serving as the support for the contact. The disc is bonded to the walls of the aperture and finally bent outwardly from the plane of the support, in order to form a raised contact point.

It has been found that this method, as described in US. Patent No. 2,625,737, can be successfully employed to produce electrical contact elements having a contacting surface of precious metal admixed with a base metal oxide. This invention therefore constitutes a further development of the method described in the aforementioned US. patent, thereby combining the advantages of precious metal contacts with added base metal oxides and those of the known method. Slight modifications of the method have been found useful, as described below.

In accordance with the invention, an electrical contact element, having at least one contact point of a precious metal with an added base metal oxide and being mounted in a supporting base metal strip, is obtained by forming a disc from a laminated metal sheet having two layers, bonded to each other, the first layer consisting of a precious metal containing a metal oxide whereas the second layer consists of any precious or base metal capable of being bonded to the desired support by means of a heat treatment, the second layer having a melting point not higher than that of the first layer. Good results have been obtained when using silver. Subsequently, the disc is inserted into an aperture in the support, of substantially identical shape to that of the disc, whereupon the assembly is subjected to a heat treatment in order to bond the sides of the second layer of the disc to the adjacent portions of the walls of the aperture. A raised contact point is finally obtained by bending the bonded disc outwardly from the plane of the adjacent portions of the support by means of dies and pressure.

In the following, the invention will be described in connection with contacts of fine silver with added base metal oxide, without being restricted thereto, and by reference to the accompanying drawing in which one embodiment of the invention is illustrated.

FIGURE 1 is a section through a laminated disc,

FIGURE 2 is a fragmentary section through the supporting base metal strip,

FIGURE 3 is a fragmentary section through the base metal strip of FIGURE 2 having a disc of FIGURE 1 inserted therein,

FIGURE 4 is a section through a finished contact element, and

FIGURE 5 is a section through a punch press suitable for applying the method of the invention and illustrating the combined steps of forming the disc and inserting the disc into the supporting strip.

The method of the invention is intended to be used especially in connection with silver contacts having a base metal oxide added to the contact surface and therefore will be described in connection therewith, without being limited to silver contacts. Referring to FIGURE 1, a disc 8 is provided which consists of a bottom layer 10 of silver having a top layer 12 of silver thereon with which a selected base metal oxide is in admixture. For the purpose of mass production, the discs 8 are blanked out from laminated sheet metal stock, as described hereinafter in connection with FIGURE 5. However, when desired, the top layer may be a layer of silver containing a metal capable of forming an oxide and the oxidation of this metal can be effected at any time during the process and even after the contact element is finished.

FIGURE 2 illustrates the base metal strip 14 forming the support for the contact and which is fabricated from any desired material such as copper, brass or the like. At the location where the contact is to be inserted, the strip 14 is provided with an aperture of a shape substantially identical with that of the disc, generally in the form of a circle. Subsequently, the disc 8 is inserted into the aperture as shown in FIGURE 3 and subjected to a heat treatment in a furnace at a temperature within or above the softening range of silver, whereby the wall 16 of the layer 1b of the disc is firmly bonded to the adjacent portion of the wall 18 of the aperture in the support 14. N0 bonding occurs between the comparatively narrow edge of the layer 12 and the adjacent portion of the aperture wall 18 since this layer contains a base metal or a base metal oxide but it has been found that, for all practical purposes, when making the layer 10 sufficiently thick, a firm bonding between the disc 8 and the support 14 is obtained. Especially when using silver, the bond is strong enough to permit the final shaping effected by die pressing and illustrated in FIGURE 4, whereby the disc 8 is bent outwardly from the plane of the adjacent portion 2% of the support to form a raised contact point.

In the aforementioned U.S. Patent No. 2,625,737, the disc described therein has a third layer on its bottom consisting of a solder, which is partly drawn up around the sides of the disc when the disc is punched out from the laminated metal stock, and serves to accomplish the bond. Such a solder layer may be used in connection with the present invention as well, but it has been found that, when the layer 10 is made from a metal having a melting point not higher than that of the first layer, e.g. silver, no solder is required and a sufficiently strong bond is obtained.

Referring to FIGURE 5, a die press suitable for manufacturing contacts in accordance with the invention consists of a die 22 passing through a guide plate 24 and cooperating with a die plate 26 having a bore 23 therethrough, the diameter of the bore 28 corresponding to the diameter of the disc 8 punched out by the device. A laminated metal sheet consisting of a layer 10 of pure silver and a second layer 12 of silver combined with the In the drawbase metal oxide and bondedto the pure silver layer is passed between the guide plate 24 andthe die- 26.- Sirnultaneously, the base metal strip 14 forming the support is passed through a recess 36 in the lower surface of the'die 26 in such a vvay that the aperture18 is aligned with the bore 28. The punch 22, when moving downwardly, punches'out the disc 8 andimmediately' inserts the disc-into the aperture in'the supporting strip" 14 in one operation. The strip 14 carrying one or more discs 8- within one or more apertures is subsequently introduced into a fur'nace andheatedto a temperature suitable to insure the bond between the layer 1% of the disc 8- and the wall 13 of'the-ap'ertures in'the'strip 14. Finally, the contact elements are blanked out-fromthe strip 14 and-shapedby suitable die pressingto the'forrn shown inFIGURE 4, for example, by bending-over the edges of the-strip 14 as shown at 32'and- 34 and by displacing the initial disc 8 outwardly frornthe plane of the surrounding portions 211.

It has been pointed out above that-the base metaloxide canbe incorporated intothetop layer 12 f the laminatedstock before blanking out the' discs 8. However, good results have been obtained when using a layer 12made frorn silverand containing ab-ase meta-lcapableofforming an oxide whereby theforrnation oi the oxide in'the layer can be etfeeted at anymoment during the process of manufacturing the contact and: even when the contact elerne'ntis finishedi- In'anyevent; astrongbonding of the side wall-16 of the" layer w theadjacent-portions of'the wall 180i the aperture w'ill be-obtained,-which results in a precious metal contact surface containing a base metal oxide supported by a base metal strip, without the necessity of soldering the oxide-containing material.

It will-be obvious-to those skilled in the'art that many modifications may be made within the scope ofthe present invention withoutdepartingfrom the spirit thereof; and the invention includes all such modifications.

What'is claimed-is:

l. A method for producing an electrical-contact ele-- merit having atleast one contact point of silver conta'ining a base metaloxide and-mounted'ina base metal support, which comprises forming adisc froma laminated metal sheet having first and second layersbonded to each other, the first layer consisting essentially of a thinlayerof silver in admixture with an oxide of a base metal selected from the group consisting of iron, cobalt, nickel, copper, cadmium, chromium, manganese, tin and admixtures thereof, the second layer consisting essentially of a comparatively thicker layer of silver; inserting the disc into an aperture in said-support; bonding the side wall of the second layer of the disc directly tothe adjacent wall of the aperture by means, of a heat treatment; and displacing. the bonded disc outwardly from the plane of the-support, to form a raised contact point.

2. A method for producing an electrical contact ele ment having atleastone contact point of silver containinga base metal oxide andmounted in a base metal support, which comprises forming a disc from a laminatedmetal sheet having first and'second layers bonded toeach other, the first layer consisting essentially of a thin layer of silver in admixture with an oxidizable metal selected'from the group consisting of iron, cobalt, nickel, copper, cadmium, chromium, manganese, tin and admixturesthereof, the secondv layer consisting. essentially of a comparatively thicker layer of silver; inserting the disc'into an'aperturein said support; bonding the side wallof the secondlayer of the disc directly to the adjacent wall of the aperture by means of a heat treatment; and, displacing the bondeddisc outwardly firomthe plane of'th'e support to form araised-contact point; the method also including oxidizing-at leasta portion of the oxidizable metal content in the firstplayer.

References Citedin-the file of this patent UNITEDSTATES PATENTS 2,148,040 Schwarzkopf Feb. 21, 1939 2,226,944 Reeve Dec. 31, 1940 2,360,522 Shobert Oct; 17, 1944 2,365,249 Co'mstock; Dec. 19, l944- 2,373,861; Van Inwagen Apr. 17,, 1945 2,382,338 Shobert Aug. 14, 1945 2,425,052 Swinehart Aug. 5', 1947 25,425,053- Swinehart Aug. 5, 1947 2,625,737 Spooner Jan. 20, 1953 2,861,155 Farnham Nov. 18, 1958

Claims

1. A METHOD FOR PRODUCING AN ELECTRICAL CONTACT ELEMENT HAVING AT LEAST ONE CONTACT POINT OF SILVER CONTAINING A BASE METAL OXIDE AND MOUNTED IN A BASE METAL SUPPORT, WHICH COMPRISES FORMING A DISC FROM A LIMINATED METAL SHEET HAVING FIRST AND SECOND LAYERS BONDED TO EACH OTHER, THE FIRST LAYER CONSISTING ESSENTIALLY OF A THIN LAYER OF SILVER IN ADMIXTURE WITH AN OXIDE OF A BASE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKLE, COPPER, CADMIUM, CHROMIUM, MANGANESE, TIN AND ADMIXTURES THEREOF, THE SECOND LAYER CONSISTING ESSENTIALLY OF A COMPARATIVELY THICKER LAYER OF SILVER; INSERTING THE DISC INTO AN APERTURE IN SAID SUPPORT; BONDING THE SIDE WALL OFF THE SECOND LAYER OF THE DISC DIRECTLY TO THE ADJACENT WALL OT HE APERTURE BY MEANS OF A HEAT TREATMENT; AND DISPLACING THE BONDED DISC OUTWARDLY FROM THE PLANE OF THE SUPPORT TO FORM A RAISED CONTACT POINT.