US2354081A

US2354081A - Method of forming contacts

Info

Publication number: US2354081A
Application number: US314826A
Authority: US
Inventors: William J Weder
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1940-01-20
Filing date: 1940-01-20
Publication date: 1944-07-18
Anticipated expiration: 1961-07-18
Also published as: GB542342A

Description

July 18, 1944. WE 2,354,081

METHOD OF FORMING CONTACTS Filed Jan. 20, 1940 F'igAa.

Inventor: William J. Weder,

by Jv ad w His Attorney.

Liaeaea Myra. 1944 barren/grates PATENT {fort-me I mrrnop or time CONT-ACTS I A i v William J. Weller, Philadelphia, Pa., asslgnor to i General Electric Company, a corporation of New York Application January 20, 1940, Serial No. 314,826

4 Claims. (Cl.

v invention relates to electric switches and more particularly to the contacts of such 1 switches and the method of forming the contacts upon the engaging parts of the switches.

' One object of my invention is'to provide a new and improved electric switch, having contacts of a material the oxide of which either has a low resistance or is physically or' chemically unstable so as not to interfere with electrical current conduction, which is simple in construction, easy to manufacture, and capable of carrying large currents without excessive heating or physical damage to the contacts of the switch.

A further object of my invention is to provide a new and improved electric switch of large current-carrying capacity and having contacts of a material the oxide of which either has a low resistance or is physically or. chemically unstable so as not to interfere with electrical current con-.

duction, which can be manufactured from comareas of the contacting members and increasing the contact pressure, the size and 'cost of the switches could be materially reduced without effecting the maximum current-carrying capacities thereof. However, it was found in ,practice that, under certain high current-carrying conditions, an objectionable amount of heating occurred at the contacts which caused the contacting surfaces to oxidize. Usually the contacting areas were formed of copper and since the resistance of copper oxide is relatively high commercial stock materials by simple mechanical operations with substantially no waste of the materials. V

-A still further object of my invention is to pro vide a new and improved electric switch, the contacts of which can be easily and quickly formed on the current-carrying member of the switch in any desired shape, thickness, and size from commercial silver wire or strips.

Another object of my invention is to provide a switch having a contact surface of appreciable pared with copper, the presence of copper oxide on the contacting surfaces caused increased heating of the contacts so that in some cases the contacts became overheated and damaged when carrying abnormally large currents. To overcome this diiliculty due to oxidation 'of the contacting surfaces, it has been proposed that the contacts be made of a material, the oxide of which has a low' resistance which is not materially different from the resistance of the material itself, or from a metaLsuch as silver, the oxide of which is both physically and chemically unstable so as to be either decomposed or rubbed off by the high width whereby the current density under normal conditions is maintained under 10,000 amperes per square inch.

Still another object of my invention is to provide ,a new method of forming on a currentconducting member of an electric switchoi one material, such as copper, a contact of a different material, such as silver, of any desired size, thickness, and shape andhaving any desired width of contacting surface.

It is another object of my invention to provide a new and improved method of simulta neously. forming by one operation with a minimum amount of apparatus aplurality of contacts .on a current-conducting member of an contact pressures, thereby providing substantially no impedance to the flow of electric current.

ing conditions, the silver plating sometimes bllstered and was torn from the copper or other cooperating surface. Whenever such blistering occurred, even though only in minute spots, the

electric switch, which same apparatus may be used for manufacturing switches of diflerent ratings. ,1

These and other objects of myinvention will appear from the following description when taken in connectionwiththe accompanying drawing,

. and the scope of my invention will be pointed out' in the appended claim.

It was the practice for manyyears to make the contacting members of electric switches of copper and to vary the contacting area of the members in accordance with the current-carrying' capacities of the switches. Subsequently it was discoveredv that, by decreasing the contact undesirable conditions were aggravated due to the increased resistance and consequent increased heating resulting in further blisterings. In accordance with my invention, I have provided a new switch contact having restricted contacting surfaces of a metal. such as silver for overcoming the above disadvantages and maintaining the current density at the contacts below 10,000

amperes per square inch. I have constructed, in

accordance with myinvention, various switches having ampere ratings from 200 to 6,000 amperes wherein the current density under normal conditions was always maintained considerably below 10,000 amperes per square inch. The following tabulation, sets forth the normal switch ratings, contact areas, and current densities for-a number of switches'constructed in accordance with my invention:

Total con- Current density 22% tact area, at contacts square amperes per mpem inches square inch 200 0. 16 l, 250 400 0. 23 l, 740 600 v o. 39 1, 540 800 0. 39 2, 050 1, 200 0. 63 1, 900 1, 600 0. 63 2, 540 2, 000 l. 26 1, 590 3, 000 l. 89 l, 590 4, 000 2. 83 1, 410 6, 000 3. 3O 1, 820

los of stiffness.

In accordance with my invention, I provide an electric switch having a current-conducting member formed of a metal of high electrical and thermal conductivity, such as copper, on which are formed one or more contacts of a material, such as silver, the oxide of which is physically and chemically unstable so as not to interfere with electrical current conduction, bybonding in any suitable manner a piece of commercial wire of the contacting material' to the current-conducting member and, at the same time, deforming the wire so as to produce a contact of the desired thickness and having a contacting surface 'of the desired width. Preferably a shallow groove of sufficient depth to hold the wire in the desired position on the current-conducting member during the manufacturing process is formed in the member priorto thebonding of the contact to the member. While various types of bonding may be used for securing the contact to the current-conducting member, I prefer to use an amalgamation process of the type disclosed and claimed in my prior United States Letters Patent 2,094,482 and 2,094,483, granted September 28, 1937, to the assignee of this application.

For a better understanding of my invention,

- reference may be had to the following description taken in connection with the accompanying drawing inwhich Fig. 1 illustrates a switch blade showing two different types of contact surfaces; Fig. 2 is a cross-sectional view of Fig. 1;Figs. 3a and 3b are enlarged views of th contact structures shown in Figs. 1 and 2 to illustrate one step in the process of manufacture thereof; Figs. 4c and 4b are views similar to Figs. 3a and 3b showing another step in the process; Fig. 5 illustrates a side view .of a representative switch to which 7 In the specific example illustrated in Figs. 5 and 6,

two blades l0 are mounted parallel with one an-- other and provided with openings H (see Fig. 1)

for the insertion of a bolt I2 which provides a transverse axis about which the blade members 10 pivot during the opening and closing operations of the switch. A tongue is is provided for pivotally supporting switch blades ll and this tongue is connected to a suitable electrical terminal ll. Spring washers I! are placed on the ends of bolt l2 so that the desired contact pressure-between tongue "andblades I 0 may be conventional disconnecting eye H. A bolt I! passes through the openings in switch blades llland, together with spring washers 21 mounted on either end of bolt I9, provide the means for obtaining proper contact pressure at the. contacting-surfaces of blades l0 and cooperating tongue 22 which is connected to terminal member 23. The entire switch structure in Fig. 5 is illustrated as vertically mounted on a suitable base of insulating material 24. Although I have described a particular disconnecting switch in order better to describe my inventionhereinafter, it will be understood by those skilled in the art that any switch having a plurality of relatively movable contacts could just as well have been chosen.

The contacting surfaces of switch blade In with ,which my invention is particularly concerned will now be described with reference to Figs. 1 to 4b in which two different contact surfaces 25 and 26' are illustrated. Contact surface 25' is illustrated as being annular in form and is concentrically arranged about the transverse axis upon which switch blade I0 pivots. Thi annular contact surface 25' is the surface of a ring of deformed commercial wir 25 of a metal, such as silver, whose oxide does not substantially interfere with electrical current conduction, which is bonded to the switch blade I0,- preferably in a shallow registering groove 21 formed in the surface of the switch blade ill by any suitable means. Although the groove 21 is illustrated in the drawing as V shaped, it, will be understood that the shape is not critical and should be determined by cheapness and ease of manufacture and the cross section of the commercial wire that is used. The other contacting surface 26' of switch blade I. is the surface of a straight piece of deformed commercial wire 26, similar to the wire 25, which is bonded to the switch blade Ill preferably in a transverse shallow registering groove 28 formed in the surface of switch blade 10.

The

grooves

21 and 28 are relatively shallow so that the majority of the silver wire extends beyond.the surface of the switch blade It in. order to provide a maximum of material 'both for contact and wearing purposes.

In accordance with my new and improved method of manufacturing contact surfaces, the

silver ring 25 and the straight length of silver wire 26, preferably of cylindrical cross section,'

are simultaneously bonded to the switch blade I0 and deformed to produce the contact surfaces 25' and 26', respectively, of the desired character in a single plane.

In manufacturing an electric switch according to my invention, one of the two relatively. movable switch members which is to be provided with raised contacts of restricted area formed of a metal whoseoxide does not substantially interfere with electrical current conduction is first prepared or cut to the proper sizeand shape from a metal, preferably copper. In view ofzthe improved process of my invention, as will be set forth in greater detail hereinafter, a relatively.

cheap grade of copper may be used for forming the switch elements which will hereinafter be referred to as blades although it will be understood by those skilled in the art that my invention may equally well be applied to either of the relatively movable switch members. After the copper switch blade has been cut to the proper sizeand shape and provided with the necessary openings, shallow registering grooves, such as 21 and 28, are formed in the surface thereof by any suitable means. It will be under stood that the shaping of the switch blade, the punching of the openings and the forming of the grooves can all be accomplished with a single operation. Commercial wire of a metal whose oxide does not substantially interfere with electrical current conduction, preferably silver, is then cut to the proper use in connection with an annular contact, is constructed in ring form similar to ring 25. A straight length of wire 26 is cut for forming a contact surface similar to 26'. It will be obvious to those skilled in the art that, by this arrangement, substantially no waste of the silver occurs.

In order to bond the silver wire to the copper blade without adversely affecting the blade or the silver wire, I preferably utilize a mercury alloying or amalgamation process by means of which the wire is amalgamated to the blade. This amalgamation process of joining the silver wire to the copper blade is accomplished by completely covering either the silver wire or the cooperating part of the switch blade or both with mercury. The parts to be coated may be dipped in the mercury or they may be electroplated by using a mercury cyanide solution or one of the parts may-be electroplated with mercury while the other is merely dipped in mercury. The mercury-coated silver'wire to be used to form contact surfaces 25' or 26' is then placed in the registering

grooves

21 or 28, respectively, so as tc appear like the arrangement shown in Figs. 3a an 3b, which do not show the mercury coating. The mercury-coated switch blade "I and

silver wires

25 and 26. are then placed between the heated platens of a suitable ress. Proper spacing plates are provided so as to get the desired height of silver above the switch blade. Pressure is then supplied by the press; causing the silver to be amalgamated to the copper blade and flattened so as to produce a contact area of subr stantial width whereby current densities under normal conditions are maintained below 10,090 amperes per square inch at the contact surfaces. The pressing surfaces of the platens are mounted parallel with one another and both contact surfaces 25' and 26' are formed simultaneously so that, in deforming the s lver wire or strip, the final contact surfaces will be in the same plane whereby optimum conditions may be obtained at the contacting surfaces even though the copper switch blade II is slightly warped as is frequently the case or in spite of irregularities in the silver wire or registering grooves within which it lies. It will be understood by those skilled in the art that such accurately formed contact surfaces may be obtained by my invention using cheaper copper blade material than was possible in prior art arrangements. Furthermore, by this arrangement, a minimum amount of pressing equipment isrequired since switch members of different lengths may be produced with the same press without auxiliary equipment and also diflerentthicknesses of the length and, if desired for I of varied thickness. The completed contact surfaces 2! and 2! are shown enlarged in Figs. 4a. and 41:, respectively. The excess mercury is driven off by the heat during the pressing process and-a bond 28, which comprises an alloy of mercury and copper adjacent and an alloy of mercury and silver

adjacent silver wires

25 and 26, is formed.

Although I have described my invention in connection with a pivoted type disconnecting switch employing a pair of blades, it will be understood, of course, that the invention may be applied to any other types of switches employing relatively, movable contacts. Furthermore, although I have illustrated my invention as applied to the switch blade itself, it will be understood that it may be applied to either one of the cooperating contacts of the switch.

Theterms metal," silver, and copper as used hereinbefore and inthe claims which follow include both substantially pure metal of the particular genus and species stated and alloys thereof.

It should be understood that my invention is not limited to the specific details of construction and arrangement thereof herein illustrated and T intend in'the appended claims to cover all such press requiring only a plurality of spacing plates ing pressure to all changes and modifications which fall within the spirit and scope of my invention.

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

l. The method of manufacturing a contacting surface on a current-conducting member of an electric switch comprising molecularly bonding a strip of material whose oxide does not substantially interfere with electrical current conduction longitudinally to said member and simultaneously deforming said strip to produce a contact surface of a predetermined character.

2. The method of manufacturing contacting surfaces for an electric switch employing relatively movable switch members which comprises bonding a plurality of pieces of silver to one of said switch members and simultaneously applyof said pieces of silver so as to produce a plurality of contact surfaces of ap preciable width accurately formed in a single plane.

3. The-method of manufacturing contacting surfaces for an electric switch employing relatively movable switch members which comprises forming a plurality of shallow grooves in one of said switch members, placing strips of metal formedof a metal whose oxide does not substantially. interfere .with electrical current conduction in said grooves, bonding said strips to said member, and simultaneously applying pressure to all of said strips so as to produce contact surfaces of appreciable width accurately formed in a single plane. I

4. The method of manufacturing a contacting surface for an electric switch employing relatively movable switch members which comprises forming a shallow grooiie in one of said members, coating said member with mercury, Placing a mercury-coated strip formed .of a metal whose oxide does not substantially interfere with electrical current conduction in said groove, and applying heat and. pressure said strip so as simultaneously to bond the two together and to prod ce a contact surface of a predetermined character.

WILLIAM J. WEBER.

switch blade llv to said member and