US3752946A

US3752946A - Arcing contract for an electric circuit breaker and method of making same

Info

Publication number: US3752946A
Application number: US00230856A
Authority: US
Inventors: C Bailey; O Frederick
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14

Abstract

An arcing contact for an electric circuit breaker comprises a conductive support and an arcing part containing pressedtogether, sintered-together refractory metal particles. The support and the arcing part have substantially flat surfaces which are joined together by a welded bond between said flat surfaces. A coating of plasma-arc sprayed material containing partially-fused interlocking, flattened particles of refractory metal covers said support in the region adjacent said arcing part to protect said support from hot arcing products. The arcing part is so located that it bears the principal arc-erosion duty imposed on the contact by arcs established by circuit-breaker opening.

Description

United States Patent 1191 Bailey et a1.

[ Aug. 14, 1973 ARCING CONTRACT FOR AN ELECTRIC FOREIGN PATENTS OR APPLICATIONS C RCUI REAKE AND METHOD O 847,200 10/1958 Great Britain 200/166 0 MAKING SAME 1,048,520 10/1965 Great Britain 29/630 C [75] lnventors: Cecil Bailey, Woodlyn; Oscar C.

Frederick Springfield, both of Primary Exammer-Marvm A. Champion Assistant Examiner-Lawrence J. Staab Asslgneel General Electric p Attorney-J. Wesley l-laubner, William Freedman Philadelphia, Pa. etyalh V v 2 2 [22] Filed: Mar. 1, 1972 57 ABSTRACT [21] Appl. No.: 230,856 An arcing contact for an electric circuit breaker comprises a conductive support and an arcing part containing pressed-together, sintered-together refractory [52] US. Cl. 200/166 C, 29/630 C, 219/76 metal panicles The support and the arcing pa" have [51] Int. Cl. H0lh 1/00 substantially flat surfaces which are omed together by [58] Field of Search 29/630 C, 200/166 C, M d be d betw n t rf A f 200/166 CM' 219/76 121 P- 339/111 114 a e n a f plasma-arc sprayed matenal containing partially-fused interlocking, flattened particles of refractory metal covers said support in the region adjacent said arcing [56] References Cited part to protect said support from hot arcing products.

UNlTED STATES PATENTS The arcing part is so located that it bears the principal 2,504.906 4/1950 'lremblay. '2 C X arc-erosion duty imposed on the contact by arcs estab- 3,075,066 l/l963 YClll'll 6! al. .2. circuit breake opening 3,482,202 12/1969 Wallace et a1. 29/630 C UX 3,522,399 7/1970 Crouch 200/166 0 x :7 Clalms, 5 Drawing Flsures F- -I ll 1 I 1 I 1 1 Y- l Z 2 4 Patented Aug. 14, 1973 3,752,946

PR/O/F ART ARCING CONTRACT FOR AN ELECTRIC CIRCUIT BREAKER AND METHOD OF MAKING SAME BACKGROUND This invention relates to an arcing contact for an electric circuit breaker and also to a method of making such a contact. More particularly, the invention relates to an arcing contact which has a portion made of pressed-together, sintered-together refractory metal particles and another portion made of plasma-arc sprayed material containing refractory metal.

In most high current circuit breakers, the arcing contact is made of a pressed, sintered refractory metal body, suitably shaped, and brazed to a conductive support. To facilitate brazing, the mating surfaces of the contact and the support must be carefully matched, usually by machining each part to close tolerances. The above pressing, sintering, machining and brazing operations are relatively expensive, especially if the contact is large or of an odd shape. Also, where the mating surfaces of the contact and support are of an odd shape, the braze therebetween is sometimes not as reliable as might be desired. Still further, the brazing alloys typically contain high vapor pressure metals which the terminal of any arc on the contact tends to seek out and vaporize excessively, thus detracting from interrupting performance.

To overcome these disadvantages, it has been proposed in our US. Pat. No. 3,588,433, assigned to the assignee of the present invention, to form the contact by plasma-arc spraying a refractory metal on to the support. While such contacts are satisfactory for certain applications, it has been found that their resistance to arc-erosion and their ability to withstand closing impacts are not as great as might be desired in a high current power circuit breaker. The pressed, sintered type of contact appears to have substantially higher resistance to arc-erosion and superior ability to withstand closing impacts.

SUMMARY An object of our present invention is to provide an arcing contact constructed in such a manner that a pressed, sintered refractory metal element can be used to bear the major arcing and closing-impact duty but yet is incorporated in such a manner that the shaping and brazing problems referred to hereinabove are greatly reduced or eliminated.

Another object is to construct an arcing contact by plasma-arc spraying but in such a manner that the plasma-arc sprayed portion of the contact is not subjected to the principal arcing duty and to the principal closing impacts.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view, partly in section, showing a portion of an arcing contact and its support prior to their being joined together.

FIG. 2 shows the parts of FIG. 1 as they are being joined together.

FIG. 3 shows an added step in forming the arcing contact.

FIG. 4 shows the final contact and the manner in which it cooperates with a mating contact.

FIG. 5 shows a prior art contact.

DETAILED DESCRIPTION OF PREFERRE EMBODIMENT Referring now to FIG. 1, there is shown a conductive support 10 of tubular rod form, at the upper end of which an arcing contact is to be provided. In one form of the invention, the rod 10, or at least its upper portion, is of low-oxygen content copper, e.g., American Metal Climax Company's OFHC copper. The uppermost, or end, surface 16 of the rod is flat. The rod 10 has a shoulder 17 thereon so that the exterior 19 of the rod located above the shoulder has a reduced diameter as compared to the rest of the rod.

In one form of the invention, the arcing contact that is to be joined to the rod 10 comprises a circular element 12 of disk form that has a flat lower surface 14. This element 12 comprises a porous skeleton of a refractory metal, such as tungsten, impregnated with a high conductivity metal such as copper. The porous skeleton is made in a conventional manner by pressing together powdered tungsten particles under high pressure in a mold of the desired shape to form a briquette, after which the briquette is heated to a high temperature to sinter the particles together. The resulting product is a porous skeleton of sintered'together tungsten particles, which is thereafter suitably impregnated with the high conductivity metal. By way of example, in one form of the invention, we utilize for element 12 a material containing approximately percent tungsten and 30 percent copper by weight.

This element 12 of pressed-together, sinteredtogether refractory metal particles is placed in engagement with the flat upper surface 16 of the rod 10, and thereafter element 12 and rod 10 are joined together along their contacting

flat surfaces

14 and 16. This joining operation can be performed in any suitable manner, but we prefer to rely upon electron-beam welding. Referring to FIG. 2, such electron-beam welding is accomplished by directing the electron beam 20 from a conventional electron-beam welding gun 22 ra dially inward along the flat

engaging surfaces

14 and 16. This causes one of the surfaces, where exposed to the electron beam, to fuse and thereafter to bond to the other surface when it solidifies. With the electron beam directed as shown in FIG. 2, the rod 10 is suitably rotated about its central longitudinal axis 24 to expose its entire surface 16 to the electron beam, thus producing a welded bond between

surfaces

14 and 16 over substantially the entire surface 16.

Although electron-beam welding is preferred, other welding procedures, such as magnetic force percussion welding, can be used for bonding the

surfaces

14 and 16 together. This latter type of welding is described in the Welding Handbook, sixth Edition, Section 2, pages 27.38-27.50, published in 1969 by the American Welding Society.

The subassembly comprising the

parts

10 and 12 welded together as above described may be thought as comprising an annular groove or recess 26 between the shoulder 17 and the surface 14. The next major step in forming the arcing contact is to fill this recess with metal applied by plasma-arc spraying. Prior to such spraying, however, all the exposed surfaces of recess 26 are suitably roughened, preferably by a grit blasting operation, to provide for an improved bond with the subsequently-applied sprayed-on material.

The plasma-arc spraying operation is performed as shown in FIG. 3, using for this operation a conventional plasma-arc spray gun 30, which is preferably of the type shown and described in our aforesaid U.S. Pat. No. 3,588,433 and in our U.S. Pat. No. 3,588,405. As described in these patents, inside such a gun, a high current electric arc is formed and a suitable gas is passed through the region of the arc to form a stream of extremely hot arc plasma. Metal, preferably in powdered form, is fed into the arc plasma stream, where it is melted and converted into atomized droplets of molten metal, which are ejected through a suitable nozzle at high velocity in the plasma stream. In FIG. 3 such a plasma stream containing the molten droplets is shown at 34. This plasma stream is projected onto the surfaces of recess 26, and upon striking these surfaces, the molten particles flatten and freeze into an adherent coating 36. The microstructure of such a coating comprises partially-fused flattened particles interlocking with each other.

In one embodiment of our invention, we use as a source material for the plasma-arc sprayed coating a combination of molybdenum and silver powders, present in approximately equal percentages by weight. A mixture of these powders is fed into the plasma stream, andmolten particles of the two metals are entrained in the plasma stream and projected onto the surface being coated. The resulting coating 36 may be thought of as comprising partially-fused flattened, interlocking particles of molybdenum forming a porous refractory metal structure and silver contained within the pores of this structure.

' Spraying onto the rod portion 19 is continued until a coating 36 of the desired thickness is obtained. In this particular case, we prefer to continue the coating operation until the recess 26 is completely filled and,preferably, until the exterior diameter of the coated portion of the rod slightly exceeds that of the rod portion below shoulder 17. When this coating operation has been completed, the resulting assembly is suitably machined so that a smooth cylindrical external surface of uniform diameter is present along the entire length of the illustrated portion of the assembly. Thereafter, the upper edge 37 of the assembly is suitably rounded.

Although the electron-beam welding operation of FIG. 2 produces some roughness of surface 14 where it is exposed, this is no significant disadvantage because such roughness does not interfere with providing a good bond with the sprayed metal coating and, as a matter of fact, even improves this bond.

Referring to FIG. 3, the illustrated contact is intended for use in a high current circuit breaker as a movable rod contact that is vertically movable into and out of engagement with a stationary contact assembly comprising fingers 40 biased radially inwardly by suitable springs (not shown). Reference may be had to U.S. Pat. Nos. 2,717,294-Balentine or 2,749,412- McBride et al., both assigned to theassignee of the present invention, for more detailed showings of such stationary contact assemblies. FIG..4 shows in solid lines the movable contact in a fully-closed position, where the fingers 40 are shown pressed against the sprayed coating portion 36 of the movable rod contact. When the rod contact is driven downwardly from its solid-line position of FIG. 4 toward its dotted-line open position, fingers 40 slide first along the external surface of portion 36 and then along the external surface of disk 12. The contacts finally part when the upper surface of the movable rod contact moves below a horizontal line 42, thus drawing an are between one of the fingers 40 and the disk portion 12. Until the arc is extinguished, its lower terminal usually remains on the disk portion 12, typically moving about at random on this disk portion. Since the most severe arc-erosion duty usually occurs at the localized region where the arc terminal is located, it will be apparent that the disk portion 12 bears the most severe arc-erosion duty. This disk portion is particularly well-suited for bearing this duty because its principal constituent is the pressedtogether sintered-together refractory metal particles described hereinabove. Although a plasma-arc sprayed coating of refractory particles, such as 36, has relatively good resistance to arc-erosion, we have found that the arc-erosion resistance of such a coating is appreciably less than that of a part made of pressedtogether sintered-together refractory metal particles. Thus, in our contact, the portion (12) that is subjected to the most severe arc-erosion duty is of a material most suited to hear such duty.

Prior contacts of this general configuration have typically been made of the design shown in FIG. 5. In this prior contact, a one-piece cup-shaped element made of pressed-together sintered-together refractory particles is brazed to a rod support 10 along the juxtaposed surfaces of the two parts. This brazed joint is indicated at 53. In order to make a good brazed joint between the

parts

50 and 10, it is necessary that the mating surfaces of the two parts be machined to close tolerances. To facilitate such machining, the sidewall of cup 50 must be relatively thick in comparison to the thickness of our coating 36, thus adding appreciably to the cost of such contact. Another reason why extra thickness is needed for sidewall 55 is that not infrequently there are voids and misses'in the brazed joint 53, and added thickness is needed to carry current around any such voids and misses. The plasma-arc sprayed coating, on the other hand, provides a better bond, much freer of such voids and misses, thus reducing the need for the extra thickness.

The improved bond between the portion 19 and the surrounding contact material 36 is important because when the circuit breaker is closed, the stationary contact fingers 40 are pressed radially against portion 36 and most of the current passing through the closed circuit breaker passes through the cylindrical portion 36 directly into the rod portion 19 surrounded by portion 36 via the bond between

portions

19 and 36.

It is to be noted that our contact of FIG. 4 does not rely upon any brazing to join its parts together. This is desirable because the terminal of the electric arc established upon circuit breaker opening seems to actively seek out any nearby braze material that is present, especially if this braze material is at all exposed. Not only can this weaken the braze joint, but it .can detract from the interrupting performance of the circuit breaker, probably because the braze material typically has a rel atively high vapor pressure and tends to vaporize more profusely than the basic contact materials.

We are able to dispense with brazed joints, partially because our element 12 is of a very simple shape that readily lends itself to a welding operation such as illustrated in FIG. 2. Note in this respect that the weld takes place entirely along

flat surfaces

14 and 16 located essentially in a single plane. There are no corners around which the weld must extend. This feature facilitates not only electron-beam welding but also magnetic-force percussion welding.

Aother advantage of these welding processes, as compared to brazing, is that the temperature of the parts remains relatively low during the joining operation, thus making it possible to use lower cost materials which might be annealed if exposed to brazing temperatures.

When the circuit breaker is operated to closed position, the rod contact is driven upwardly from its dottedline open position into the solid-line closed position shown in FIG. 4. The fingers 40 are then somewhat closer together than as illustrated, and the upper surface of the movable contact therefore impacts against the lower ends of the fingers before wedging them radially outward. It is to be noted that this closing impact is borne primarily by the pressed, sintered disk 12 rather than by the plasma-arc sprayed coating 36. This is desirable because the pressed, sintered material seems to be able to better withstand such impacts without damage than can a sprayed-on coating.

Because our contact has its two major components formed by two entirely different processes, we can readily use different materials for the two components, selecting each material according to its ability to best perform the particular function that is called for in the final contact. Along these lines, we use for the disk 12 a mixture of tungsten and copper and for the portion 36 a mixture of molybdenum and silver. The tungsten of the part 12 imparts exceptionally high arc-erosion resistance to this part; and the silver of part 36 imparts to this part an exceptionally low electrical resistance that is maintained despite oxide films thereon. The refractory constituent of coating 36 is needed to protect this coating from the hot arcing products that, during an opening operation, are projected along the rod away from the arcing gap between the contacts. Molybdenum is satisfactory for this refractory constituent because this duty is relatively light compared to that encountered when the terminal of a high current arc persistently burns on the surface. For such surfaces, tungsten, a more expensive refractory metal having a higher melting point, is preferred to molybdenum for the refractory constituent.

Although we have shown an arcing contact of a particular configuration, it is to be understood that our invention in its broader aspects is applicable to arcing contacts of other configurations wherein the principal arc-erosion duty is borne by a pressed, sintered refractory metal part and the adjacent region is protected from the hot arcing products by a plasma-arc sprayed coating containing refractory metal.

While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects; and we, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of our invention.

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

1. An arcing contact for a power circuit breaker comprising:

a. a rod-shaped support of conductive material having an end surface, said support having a shoulder spaced from said end surface and a portion of reduced external dimension extending between said shoulder and said end surface,

b. a disk of conductive material containing pressedtogether, sintered-together refractory metal particles,

c. said disk having a surface that is joined to said end surface of said support by a welded bond between said surfaces,

d. a coating of plasma-arc sprayed metal surrounding said rod-shaped support between said shoulder and said disk and bonded to said rod-shaped support, said coating comprising interlocking flattened particles of refractory metal,

e. said coating having an external surface that substantially aligns with the external surface of said disk,

f. said coating being in a location wherein the principal current through said circuit breaker when full yclosed passes through the bond between said coating and said support,

g. said disk being in such a location that a terminal of any are produced by a circuit-breaker opening operation is located on said disk, whereby the principal arc-erosion duty imposed on said contact is borne by said disk.

2. The arcing contact of claim 1 in which said end surface and said disk surface are substantially flat to fa cilitate formation of a weld therebetween.

3. The circuit breaker of claim 1 in combination with:

a. a cooperating contact comprising fingers pressing against said coating when said circuit-breaker is fully closed,

b. said fingers being so located that circuit-breaker opening causes said fingers to slide first along said coating and then along the exterior of said disk and then to part from said disk, whereby the arc developed by circuit-breaker opening is developed between said disk and one of said fingers.

4. An arcing contact for a power circuit breaker comprising:

a. a support of conductive material having a substantially fiat surface,

b. an arcing part of conductive material containing pressed-together, sintered-together refractory metal particles, said arcing part having a substantially flat surface that is joined to said flat surface of said support by a welded bond between said surfaces,

c. a plasma-arc sprayed coating on said support adjacent said arcing part, said coating comprising interlocking flattened particles of refractory metal,

d. said coating being in a location to protect said support from hot arcing products developed by an are having its terminal on said arcing part,

e. said arcing part being in a location where it bears the principal arc-erosion duty imposed on said contact by arcs established by a circuit-breaker opening operation.

5. The arcing contact of claim 4 in which the refractory metal in said arcing part is tungsten and the refrac tory metal in said coating is molybdenum.

6. A method of making an arcing contact for a power circuit breaker, comprising:

a. providing a rod of conductive material that has a shoulder adjacent one end, a flat surface at said one end, and a portion of reduced external dimension between said shoulder and said one end,

b. providing a disk of conductive material containing stantially aligns with the external surface of said pressed-together, sintered-together refractory disk in the region adjacent said recess. metal particles, siad disk having. a flat surface at 7. A method of making an arcing contact for a power one side thereof, V circuit breaker, comprising:

c. positioning the flat surface of said disk in juxtaposia. providing a conductive support that has a substantion to the flat surface of said rod, tially flat surface,

(1. welding said disk and said rod together along said b. providing an arcing part of conductive material juxtaposed flat surfaces, thereby forming a subascontainipg pressed-together, sintered-together resembly having a recess present between said disk fractory metal particles, said arcing'part having a and said shoulder, a 10 flat surface at one side thereof,

e. depositing within said recess by plasma-arc sprayc. placing said flat surfaces in juxtaposition and welding a conductive material containing refractory ing said arcing part to said support along said juxtametal, said plasma-arc spraying being continued posed flat surfaces, until said recess has been tilled with said plasmad. plasma-arc spraying onto the region of said suparc sprayed material, port immediately adjacent said arcing part a def, machining the external surface of said disk and said posit of plasma-arc sprayed material containing a sprayed material until the external surface of said refractory metal. sprayed material is substantially smooth and sub-

Claims

1. An arcing contact for a power circuit breaker comprising: a. a rod-shaped support of conductive material having an end surface, said support having a shoulder spaced from said end surface and a portion of reduced external dimension extending between said shoulder and said end surface, b. a disk of conductive material containing pressed-together, sintered-together refractory metal particles, c. said disk having a surface that is joined to said end surface of said support by a welded bond between said surfaces, d. a coating of plasma-arc sprayed metal surrounding said rodshaped support between said shoulder and said disk and bonded to said rod-shaped support, said coating comprising interlocking flattened particles of refractory metal, e. said coating having an external surface that substantially aligns with the external surface of said disk, f. said coating being in a location wherein the principal current through said circuit breaker when fully-closed passes through the bond between said coating and said support, g. said disk being in such a location that a terminal of any arc produced by a circuit-breaker opening operation is located on said disk, whereby the principal arc-erosion duty imposed on said contact is borne by said disk.

2. The arcing contact of claim 1 in which said end surface and said disk surface are substantially flat to facilitate formation of a weld therebetween.

3. The circuit breaker of claim 1 in combination with: a. a cooperating contact comprising fingers pressing against said coating when said circuit-breaker is fully closed, b. said fingers being so located that circuit-breaker opening causes said fingers to slide first along said coating and then along the exterior of said disk and then to Part from said disk, whereby the arc developed by circuit-breaker opening is developed between said disk and one of said fingers.

4. An arcing contact for a power circuit breaker comprising: a. a support of conductive material having a substantially flat surface, b. an arcing part of conductive material containing pressed-together, sintered-together refractory metal particles, said arcing part having a substantially flat surface that is joined to said flat surface of said support by a welded bond between said surfaces, c. a plasma-arc sprayed coating on said support adjacent said arcing part, said coating comprising interlocking flattened particles of refractory metal, d. said coating being in a location to protect said support from hot arcing products developed by an arc having its terminal on said arcing part, e. said arcing part being in a location where it bears the principal arc-erosion duty imposed on said contact by arcs established by a circuit-breaker opening operation.

5. The arcing contact of claim 4 in which the refractory metal in said arcing part is tungsten and the refractory metal in said coating is molybdenum.

6. A method of making an arcing contact for a power circuit breaker, comprising: a. providing a rod of conductive material that has a shoulder adjacent one end, a flat surface at said one end, and a portion of reduced external dimension between said shoulder and said one end, b. providing a disk of conductive material containing pressed-together, sintered-together refractory metal particles, siad disk having a flat surface at one side thereof, c. positioning the flat surface of said disk in juxtaposition to the flat surface of said rod, d. welding said disk and said rod together along said juxtaposed flat surfaces, thereby forming a subassembly having a recess present between said disk and said shoulder, e. depositing within said recess by plasma-arc spraying a conductive material containing refractory metal, said plasma-arc spraying being continued until said recess has been filled with said plasma-arc sprayed material, f. machining the external surface of said disk and said sprayed material until the external surface of said sprayed material is substantially smooth and substantially aligns with the external surface of said disk in the region adjacent said recess.

7. A method of making an arcing contact for a power circuit breaker, comprising: a. providing a conductive support that has a substantially flat surface, b. providing an arcing part of conductive material containing pressed-together, sintered-together refractory metal particles, said arcing part having a flat surface at one side thereof, c. placing said flat surfaces in juxtaposition and welding said arcing part to said support along said juxtaposed flat surfaces, d. plasma-arc spraying onto the region of said support immediately adjacent said arcing part a deposit of plasma-arc sprayed material containing a refractory metal.