US2199240A - Silver faced contact - Google Patents

Description

I April30,1940. I B GWYN,JR Q I 2,199,240

SILQER FAGED CONTACT Original Filed Feb. 6, 1935 V Iii mn g I 'IIYQVENTOR ATTORNEY Patented:

um'rso ,s'rA'rEs PATENT orrics amass v i g f c iiiai eunomJamirmsm-amu eignorto 1'. R. Mallory & 00., Inc., Indianapolis, M, a corporation of Dehware application February 0, 1935, No. 5.21., now Patent No. 2,949,711, dated August Divided and this application 1986, Serial-No. 81,828

Hay,

120lai'ms. (caste-10o) y This invention relates to electrical contacts of silver and methods of fabrication thereof.

This application is a division of my copending application, Serial No. 5210, flied February 6, g 1935, now Patent #2,049,771, issued August 4,

1936 and a continuation in part of my copending application Serial No. 156,733, filed December 10, 1934, now'Patent' #2,086,221, issued July 6, 1937, both of which earlier flied copending appli- 10 cations disclose contacts having-a silver face integrally unitedto 'a steel backing.

An object of the invention is the provision of an electrical make and break contact assembly having a working face of silver composition and ii a backing or support of relatively hard and inexpensive material, and which due to its unique construction will function more eillciently than silver contacts of the prior art.

A further object is to provide a silver contact 3 assembly of higher mechanical strength and durability thanheretofore available.

A'still further object is to produce a contact assembly of superior operating characteristics at normal and elevated temperatures.

5 Another object is to produce a silver contact member at a substantially lower cost than has heretofore been possible by reducing the amount of expensive materials required for a satisfactory contact assembly.

, An additional object is to produce silver contacts or contact assemblies in quantities with an economy of labor and with resulting uniformity of product.

Other objects will be apparent from. the disa cig'isgire and drawing together with the appended cl s.

The present invention comprehends the provision of a contact element of silver composition fused to a metal backing. Preferably this is aco complished by utilizing a support or rivet blank of some hard base metal such as steel, which may or may not be first plated with a flashing of nickel, copper or silver, placing a quantity of silver or suitable silver composition on or against 5 the support, and heating the assembly in a suitable atmosphere such ashydrogen, until the silport, being rather soft, does not provide the strong hard backing desirable for'frequent make and break operations. Furthermore, the silver, being relatively weak, is not too well adapted to form a strong and durable mechanical attachment to the member or device to which it is connected. Since under certain operating conditions,

the contacts become quite hot, the difference in expansion between the silver and connected parts,

causes the entire contact body to loosen and has often resulted in loose "stacks" with consequent erratic operation. The loss of adjustment which results from this latter condition or from distortion of the soft metal backing, causes inefficient and unreliable service.

The above disadvantages are overcome by the present invention, which provides a structure in which forthe most part only the working face is of silver and which has a hard strong durable support integral with the silver facing, thus al-- 80 lowing the locating and attaching of the contact assembly in an electrical circuit in such manner as to insure dependable and efficient operation over along period of time without necessity of adjustment. Furthermore, bythe employment of 95 an inexpensive material, such as steel, for the greater part of the contact body, the cost of the contact is materially reduced.

t The invention accordingly comprises the fee.-

tures-of construction, combinationuof elements, arrangements of parts, and methods of manufacture referred to above-or which will be further brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawing, thescope of the invention being'indicated in the appended claims. 7

For a fuller understanding of the nature and objects of the invention as well as for specific fulfillment thereof, referencev should be had to the following detailed description taken in con- 40 nection with the accompanying drawing, in

which: I

"Figure 1 is a plan view of a rivet blank for use in forming the contact assembly} I Figure 2 is a side-view of the rivet blankshown in Figure 1;

Figure 3 is a top view of a disc of contact metal; v

Figure 4 is a side view of the disc shown in so we 3; g

Figure 5 is a sectional elevation of the rivet blank andcontact disc assembled in a receptacle preparatory to uniting said rivet and disc by heat treatment;

- element;

Figuredisasidevicwofacompleted'contact Figure 'l is a sectional elevation of the rivet blank and contact material assembled in a suitable receptacle for heat treatment according to a modified form of the invention;

Figure 8 is a sectional elevation of a rivet blank and contact disc assembled in a receptacle preparatory to uniting by heat treatment;

Figure 9 is a sectional elevation of a completed contact element of modified form and the receptacle used in forming the same:

Figure 10 is a sectional elevation of parts assembled for formation of a contact element according to a still further modified form of the invention;

Figure 11- is a side view of a contact element formed according to the method illustrated in Figure 10;

Figure 12 is a sectional elevation showing parts arranged for the simultaneous production of a plurality of contact elements; and

Figure 13 is a perspective view of a multiple receptacle containing contact assemblies preparatory to the heating treatment.

Like reference characters indicate like parts in the several figures of the drawing.

While a preferred embodiment of the invention will be described herein, it is contemplated that considerable variations may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. 7

Referring to the drawing, the rivet blank 2| illustrated in Figures 1 and 2 is preferably formed of a base metal having the mechanical characteristics necessary to form a mechanically strong and'durable assembly when secured to backing members to form part of electrical apparatus. The rivet blank may be made of steel, for exam ple, by upsetting, cold heading, or by other meth- Ods of fabrication, well known in the art, to form a head 22 and shank 25 of desired diameter and length. The steel rivets are preferably plated with a thin film or flashing of copper from 0.0001" to 0.0005" thick. A, wide variety of other base metals having a melting point higher than the desired facing, may of course be had, instead of the steel.

The contact metal may be prepared for assembly in a variety of ways, such as forming it into a disc24asshownlnFigum3and-i. Thedise is preferably slightly less in diameter than the rivet head and may be formed y p nching, heading or otherwise forming the disc from a measured amount of silver. 7

The rivet blank 2| and contact disc 24 are assembled in a suitable receptacle 2! as illustrated in Figure 5, prior to uniting. Receptacle 25 may preferably be formed of a materia1 which does not unite or adhere to the contact metal when it is in a molten or solid state, such as carbon, graphite, or other suitable refractory material.

The receptacle containing the contact parts assembled in a suitable manner as shown, with the contact metal placed against the face of the rivet desired to be coated, is placed in a heating chamber and heated, the temperature being raised high enough for a sufilcient period of time for the contact metal to fuse onto or partly alloy with the rivet member. If an iron or steel rivet is used and the contact metal is silver a temperature of 985 C. for approximately two minutes is satisfactory to allow the capillary attraction between the'melted silver and iron to cause a "wetting'or uniting of the two materials. While it is possibleto carry on the heating without any special precautions as to the type of atmosphere used, it is preferred that the atmosphere in the heating chamber shall be neutral or reducing in nature, or that the heating shall be done in a vrcuum. A hydrogen atmosphere is very satisfactory.

Upon cooling. the contact parts will be found to have united to form a contact element, such as illustrated in Figure 6. The contact metal, due to its capillary attraction for the base metal backing member and its own tendency to ball up" or form a spherical or hemi-spherieal shape, will produce a rounded surface 26 on the contact element when it cools and solidifies.

According to a modified form of the invention, the contact metal, such as silver, instead of being preformed in the shape of a disc for uniting with the rivet blank, may be used in the form of powder or shavings 21, which are placed in the bottom of receptacle 2! as shown in Figure 7. The rivet blank 2| is placed over these as shown in this figure and the heat treatment applied as previously described.

Figure 8 illustrates an alternate method of forming the contact assembly. Carbon recepta cle 25 houses rivet blank 28 upon the head of which is placed silver disc 29. When this assembly is heated, the silver melts, unites with the steel and forms a convex shaped contact face similar to that shown in Figure 6.

When a rounded face is desired, such as that illustrated in Figure 6, the operation is carried out as previously described. If, however, it is desired to produce contact faces of special shapes, such as oval, pointed, square, etc., the receptacle 25 may be suitably recessed to produce the shapes desired. In Figure 9, for example, a method of forming a pointed contact is illustrated, this flgure showing the receptacle 2! containing the contact assembled after the heating operation. It will be noted that the contact surface '30 has assumed a somewhat pointed form due to the shape of recess ilin receptacle 2!.

To produce a flat .face contact or a contact with a very slight radius, I find it desirable to apply a nickel flash or plating to the rivet, the thickness of the plating being from 0.0001" to 0.0005", the thinnest plating being preferred. The capillary action of nickel is so much greater than that of copper or silver that, complete silver coverage maybesecuredwithadiscaslowas50% ofthe diameter of the rivet head. When a nickel plating is employed, it is desirable to have a recess in the back of, the blank around the shank such as shown in Figure 10, in which carbon receptacle 2! houses nickel plated steel rivet blank 2 I which rests upon silver disc 32. The nickel plating, about 0.0002" is shown in exaggerated form at ll- When heated in the manner hereinabove described, the silver will be found to have spread evenly over the rivet face to form a substantially flat contact surface 33 as shown in Figure 11. The recess ll in the blank prevents the silver from flowing down the side of the shank. This recess, it will be noted, is between the area of the rivet to which the facing is fused and the area to be protected. The capillary flow of the molten metal out over the surface of the rivet is halted by the groove apparently due to the surface disconformity produced by it. This is not required when flashings of copper or silver are employed as the capillary action with these'metals tends to draw the facing on the contacts into a natural radius.

Anotheradvantagederivedfromtheuseof 'nickellsthatthinnerflatsilverfacingscanbe produced. The nickel may be sprayed on the surface of the rivet instead. of plating, in which case'thewettingacti'ontakesplaceonlyontbe head of the rivet and the recess is unnecessary.

The above described method of producing contact elements lends itself extremely well to automatic or semi-automatic operation and to si- .1 multaneous production of a large number of elev ments. This may be carried out as illustrated in Figure 12, for example. In this figure is iliustrated a punch press member 84, having punching projections 35, shown more clearly at It.

is A punching plate :1, having holes is, registering with projections 35, is located immediately below the punching member 34. A sheet 39 of contact facing material, such as silver or silver alloy suitable for contact materiaL'such ascoln silver, etc., rests upon the upper surface of plate 31. Immediately below plate 31 is .a boat or other suitable receptacle ll provided with a corresponding plurality of recesses ll located immediately I below said holes ll. In thepunching operation,

After the contact discs 24 have .been punched into the recesses I, the rivet blanks ii are inserted on top of these discs This may conveniently be done by merely placing a number of rivet blanks upon theupper surface of boat 40 and shaking the boat in such a manner that the rivet blanks will fall into the holes. Due to their rivet shape, it is found that the rivet blanks will readily fall into the holes with the desired orientation without further precautions being taken. The boat 40, containing the contact assemblies ready for insertion into the heating chamber is shown in perspective in Figure 13, parts being cut away to better illustrate the relationship of the contact parts.

If desired, union of the contact material with therivet blank may be aided and the appearance of the completed contact element may be improved by applying a light plating of silver to the entire rivet blank 2i before formation of the silver facing on the rivet head. When this-is done, the copper or: nickel plating is omitted.

The nickel, copper, or silver plating which is applied to the rivet blanks prevents oxidation and also increases the capillary action of the silver so that a uniform bonding action is obtained. Where unplated blanks are employed, I have found that it is usually necessary to utilize a silver disc or powder which covers the entire face of the contact in order to obtain complete coverage; y using a plating, the disc size can be as much as 25% smaller in diameter than the face of the finished contact and still provide complete coverage. Furthermore, the shape of the silver disc is not of importance as long as the required amount of silver is available.

The platings or flashlngs which I employ are not to be confused with brazing discs which have been employed in uniting dissimilar metals. In the present invention, the plating is used merely sea method of controlling the mechanical how of the-silver facings. It deleterious edfects'of hydrogen or other reducing or inert gases. ,Inthe priorart, where contact'facings of tungstenor metal discs have appliedto steel'backims. MW or silver brazing discs have been inserted therebetween to produce a deiinite between two comparatively non-melting elements, whereas in the contactassemblies of .my invention, the contact face material is which will melt and flow at a lower temperature than. the base metal backings. The plating, in the instant case, is for convenience and is not of necessity,

as under proper production control, it may, if ll necessary, be eliminated.

The present invention makes possible. the pro duction of con st e ements ate greatly reduced cost, both by making it possible for the shank of the contact rivet to be made of a. cheaper materlal and also by reducing the thichiess of 811-5.

ver required in the rivet head. As an example of this, it has previously been necessary for manufacturing and mechanical reasons to make the head of a certain type of rivet from silver .025" thick or greater. According to the present invention, a contact having sufficiently long life may be made with a silver facing .010" in thickness or less, with equally satisfactory results.

The difliculty experienced in the past of :providing contact. elements which will provide satisfactory operation underihigh temperature conditions has been entirely overcome by the present invention. since the rivet blank may be made of the same material or of material having substantially the same expansion characteristics as the backing member to which it is to be attached, no or erratic operation will be obtained. Likewise, much higher mechanical strength will be obtained in the resulting. structure and no loosening after long operation will take place.

The improved qualities inherent in the contact of this invention maybe said to be derived from the fact that the silver face is completely united and fused with its support. This is brought about by the flowing or melting of the-silver to the support, as distinguished, for example, from welding or soldering where junctionis effected at a plurality of points.

The present invention provides for automatic on semi-automatic fabrication of the contact elements and it has the advantage of low cost from a manufacturing standpoint. Other advantages will be readily apparent from the preceding description of the invention.

The term silver".or silver composition" as used herein includes pure silver as -well as compositions of silver with other metals, where the product is suitable for use as a silver contact and where it has a melting point sufliciently low to vbe adapted for use in the contact and method of 4 V 101 silver individually r m to the had of said I rivet cooled as a unit from the liquid molten state,

the external surface of said silver body forming the contact working surface.

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

4. An electrical contact member comprising a body portion formed of silver, a backing member for said body portion formed of steel, the adjoining surfaces 'of said body portion and said backing member being integrally secured together.

5. An electrical contact comprising a body portion of silver and a backing plate formed of a free flowing metal composed mainly of iron integrally united with said body portion.

6. An electrical contact'button comprising a disc having a silver facing and a ferrous metal backing, and a thin layer of nickel interposed between said silver and said ferrous metal, said nickel preventing diffusion of said ferrous metal and saidsilver.

7. An electric contact member comprising a base metal backing and a contact metal facing bonded to a first portion of said backing, metal of a lower melting point than said base metal effecting said bond, and a capillary flow stopping molten metal trap between said contact metal facing and a second portion of said backing to halt the capillary flow of molten metal from said first to said second portion of said backing.

8. An electric contact member comprising a base metal backing, a contact metal face integrally bondedto a first portion of said backing, said contact metal being of lower melting point than said base metal, and a capillary flow stopping molten metal trap between said contact metal .attaching portion for attaching the assembly to face and a second portion of said backing adapted to halt the capillary how of molten metal from said first to said second portion ofsaid backing.

9. A support blank for an electric contact element comprising a base metal rivet having a I head portion adapted to receive a contact metal facing by metal fusion thereto, said rivet having a shank portion for securing it to a support and an annular metal flow stopping disconformity in the region between said head portion and said [1 shank portion to stop the capillary flow of molten metal onto said shank-portion during the fusion of metal for application of said contact facing.

10. A contact assembly comprising a columnar backing member terminating ,at one end in a contact supporting face and at the other end in an attaching portion for attaching the assembly to a support and a contact element secured to said supporting face by metal fusion, said backing member having a metal flow limiting dis- Q conformity encircling the portion thereof between said contact supporting face and said attaching portion, said disconformity being adapted to stop the capillary now of fused metal down the side of said backing member.

11. A contact assembly comprising a columnar backing member terminating at one end in a contactsgpporting face and at the other end in 'an'attaching portion for attaching the assembly to a support and a contact element secured to said supporting face by metal fusion, said backing member having a groove formed in and encircling the portion thereof between said contact supporting face and said attaching portion, said groove being adapted to stop the capillary ilow of fused metal down the side of said-backing member. I

12. .A contact backing blank comprising a base metal member terminating at one end in a contact supporting face and at the other end in an a support, said backing blank having a metal flow limiting disconformity encircling the portion thereof between said contact supporting face and said attac g portion, said discon'formity being adapted top the capillary flow of fused metal from the contact supporting face to the attaching portion.

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