US3476861A

US3476861A - Insulating nonconsumable arc electrode

Info

Publication number: US3476861A
Application number: US784327A
Authority: US
Inventors: Charles B Wolf
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1968-12-17
Filing date: 1968-12-17
Publication date: 1969-11-04
Anticipated expiration: 1986-11-04
Also published as: DE1962565A1; GB1277936A

Description

mum

Nov. 4, 1969 c. B. WOLF 3,476,861

INSULATING NONCONSUMABLE ARC ELECTRODE Filed Dec. 17, 1968 2 Sheets-Sheet 1 Nov. 4, 1969 Filed Dec. 17, 1968 c. B. WOLF 3,476,861

INSULATING NONCONSUMABLE ARC ELECTRODE 2 Sheets-Sheet 2 FIG. I8

INVENTOR C'norles BWolf BY M ATTORNEY 3,476,861 INSULATING NONCONSUMABLE ARC ELECTRODE Charles B. Wolf; Irwin, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 17, 1968, Ser. No. 784,327

Int. Cl. H0511 7/08 U.S. CI. 13-18 15 Claims ABSTRACT OF THE DISCLOSURE;

An electrode which fluid is brought through a supporting column to cool the electrode tip by paslsing the fiuid through a passageway in the tip near the aiicing surface, the fluid inroute to the tip is caused to flovijhrough an annular passageway existing between a tube of the supporting colun'in and a segmented heat shield; including a plurality of annular metal rings of similar diameter, electrically insulated from each other by rings ot'insulating material therebetween and electrically insulated from the supporting cjolumn, each of the rings haviri'g an annular groove therein and an O-ring disposed in the groove to provide a fluid tight seal between each ring the ad joining rings onfeach side thereof, all of the rings being removable by unthreading the electrode tip from'the supporting column fand sliding the rings from the bottom end of the electrode. There are peripherally spaced bolts passing through a flange adjacent the upper most ring of the heat shield and secured to the tube of the supporting column and secured against axial movement thr'eon, the bolts exerting pressure on the rings of the heat shield maintaining the O-rings in fluid tight sealing engagement.

BACKGROUND OF THE INVENTION ljescription of the prior art I The electrode is generally of the type designed to withstand an electric arc impinging on the electrodefgtip without any appreciable erosion of the tip surface an'djconsists mainly of a supporting column, a heat shield ahd a tip, and an internal field coil for setting up a magnetic field to move the are over the arcing surface of the tipsflfhe column serves the purpose of carrying electrical ciirrent to the tip, conducting cooling water to and from the tip and supporting the tip, and also contains the leads for the field coil which are electrically insulated from", the remainder of the structure.

Several patents have issued to the assignee of the instant invention on similar supporting column and electrode tip configurations including the following: 3,369,067; 3,377,418; 3,385,987 and 3,398,229.

One of the hazards with prior art electrodes in various applications such as in an arc furnace, is that the are sometimes goes up the outside of the column, which is sometimes at the same potential as the tip, or that material being "melted falls against the column and produces an arc to the column. When this happens the column may be punctured, and the apparatus has to be shut down. There is also the danger of a serious explosion due to the water spouting from the puncture coming in contact with hot reactive metals.

Various attempts at insulating the outside of the column have been made such as by coating with alumina or covering with a thick ceramic. These materials have a limited life at the high temperature conditions encountered. Also, it is possible that small particles of these insulating materials will fall into the melt and cause undesirable containination of the melt or discontinuities in an ingot being tormed by the electrode.

fired States Parent SUMMARY OF THE INVENTION In my invention, the problem of arcing to the column has been overcome by making the outside surface of the column of metallic ring-segments which are water cooled and electrically insulated from each other and the currentcarrying tubular member, of the column which carries the arc current to the tip. The heat shield ,performs no sup porting function and may be thought of as a separate entity from the column; on the other hand, the inside walls of the rings define an annular passageway for bringing fluid to the tip, so that the heat shield may be thought of as an integral part: of the supporting column structure. In the embodiment shown the power is brought to the tip through a separate tube inside the insulated segments and spaced therefrom. The metallic rings are separated from each other by thin" rings of insulating material such as mica. The ring segments are spaced from and coaxially aligned with respect to the current-carrying tube by means of spacer bars at peripherally spaced intervals, the bars being made of nylon or other insulating material. Sealing is accomplished by an O.-ring between each adjacent pair of rings of the segmented heat shield. Means are provided for compressing the :O-rings. Bellesville type spring washers are provided to allow for the difference in thermal expansion of the outer rings of the heat shield when heated in a furnacejenvironme'nt and the inner current-carrying tube which does not get hot. The inner current-carrying tube is strong enough to carry the Weight of the tip and the rings of the heat shield and to withstand the forces due to water pressure. The insulating spacers between the metal rings are thin so that very little of their area is exposed to the heat, and they are well cooled by the water cooled metal rings on either side of them. The metal of the heat shield will fioa't at or near electrode potential but very little current will flow through a ring due to the high resistance of the insulation and the high resistance of the water which comes in contact with the power supply tube and the insulating}. ring. My invention contemplates and includes electricallygbiasing the metal rings of the segmented heat shield at aljpotential other than the electrode tip potential to further; reduce the possibility of arcing from the metal rings ttfi the melt or the charge, as by an electrical lead extending through the fluid passageway and individually connected each of the segments, or Where a biasing potential is erriployed the insulating rings may bedispensed with except. for those two at the top and bottom of the stacks and biasing voltage;,applied near the top of the electrode be een the supporting column and the stacks.

My invention includes coating the outside surfaces of the metal ring segments with an insulating material such as alumina to limit the heat transferred to the column. Since this thermal insulation is not depended on for electrical insulation, if it becomes damaged or deteriorates no harm is done to the electrical insulating capabilities of the heat shield. If desired, the full length of the column may be insulated in this manner to further reduce the possibility of arcing at a location far removed from the electrode tip. The number of insulated gaps and the thickness of the insulating rings are selected in accord ance with the arc voltage and the environment in which the electrode is to 'be used.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 1a and 1b taken together show a view par tially in section and partially in elevation of an electrode according to the preferred embodiment of my invention.

DESCRIPTION OF THE INVENTION In the drawings the reference numeral 10 generally designates the electrode tip, while the insulated metallic grooves 24 in the various rings. Rings 11 to 21 are composed of metal and it is seen that each of the metal rings is electrically insulated from the adjacent metal ring on both sides thereof by thin rings of insulating material, for example mica, these rings being designated 26.

The column for the electrode tip is seen to include three concentric tubes including supporting tube 31, these being designated 31,32 and 33; a fluid outlet passageway is formed between

tubes

33 and 32 whereas fluid is admitted on the inside of tube 31. In the annular space between

tubes

31 and 32 there pass two conduits each enclosed in a sleeve of insulating'material for bringing cooling fluid and electrical current to the field coil and conducting fluid therefrom and completing the electrical circuit to the field coil, one of these conduits with its insulating sleeve being shown in the plane selected for illustration, the conduit being designated 35 and the insulating sleeve 36. While the passageway 38 appears in FIGURES la and 1b to be generally cylindrical in shape, in actuality fluid may be admittedaround the entire inside wall of the tube 31 with the space between the outer wall of tube 32 and the inner wall tube 31 not occupied by the insulating sleeves 36 being filled with fluid which will ultimately fill the area 40 and the water therein will reach the level of and pass through peripherally spaced apertures 41 into a substantially cylindrical passageway 44 formed between the outside wall of tube 31 of the supporting column and the inner wall portions of the stacked rings including rings 11 through 21. Peripherally spaced spacer members 46 composed of insulating material and screwed to tube 31 are provided to insure the proper width of the passageway 44. The ex= ternal surface of the lower end of tube 31 is threaded as shown at 48' to engage threads in the electrode tip generally designated 10. Additionally the tube 31 has a plurality of peripherally spaced portions of decreased thickness, one of these being shown at 50, said portions of decreased thickness also being shortened in length to provide peripherally spaced gaps 52, the portions of reduced thickness of the tube providing peripherally spaced passageways 54 communicating with the aforementioned peripherally spaced gaps 52 and providing for the flow of fluid from the annular passageway 44 between the rings and the tube 31, through the peripherally spaced passageways 54 and associated gaps 52 into a passageway generally U-shaped in cross-section which extends around the entire tip, this last-named passageway being shown at 60 and providing for the flow of cooling fluid near the arcing surface 61 of the tip to remove heat flux gen= erated by the are spot of are 62.

The aforementioned tip generally designated 10 is seen in FIG. lb to be composed of inner and

outer shells

64 and 65 both generally annular in shape and generally U-shaped in cross-section, the outer wall of the inner shell 64 being spaced from the inner wall of the outer shell 65 to provide the aforementioned passageway 60 for the flow of cooling fluid near the arcing surface. The outer shell 65 may be thought off as having an inner wall portion and an outer wall portion which as aforementioned is threaded at 48 to the end of tubular member 31, while the inner wall portion of smallerdiameter is threaded at 66 to a tubular member 67 having grooves 122 formed therein. An O-ring 71 seated in an annular groove 72 provides fluid tight sealing engagement. Tubu lar member 67 has the passageway generally designated 82 thcrethrough. At the upper end of the tubular member 67 there is seen to be a tapering portion 74 whereas the outside diameter of the tubular member '67 is reduced sharply culminating in an upper end portion 75 of small diameter threaded at 77 to the lower extremity of he aforementioned tube 33, it b ing noted hat th re is a passageway extending axially through the electrode from the upper end of the tube 33, the passageway -be comingof relatively small inside diameter at the portion 79 and thereafter increasing indiameter as aforementioned to provide a passageway of relatively large di ameter 82 which communicates with Qthe central passageway through the annular electrode tip, the tube 33 and the tubular member 67 being provided for bringing ma= terial through the central aperture of the electrode tip for anysuitable purpose.

Disposed within the electrode coluj mn above the tip is a cylindrical member 81 snugly fitting in the space between the inner wall of tube 31 and the outside wall of tubular member 67, the cylindricalmember 81 having two passageways therethrough for conduit connections to a magnetic field coil generally designated 84, one of these passageways 86 being shown {in the plane of the cross-section selected for illustration'fiand having a lower portion of relatively small diameter 87 and an upper portiori88 of relatively large diameter. Thereby a shoulder 89 is formed upon which abuts the lower end of the aforementioned insulating sleeve 36, "the sleeve having an O-ring' seated in an annular groove near the end thereof to provide a fluid tight seal betweenthe insulating sleeve and the" adjacent wall of member 81. Conduit 35 passes through-the portion of small diameter 86 of the aperture being spaced therefrom and electrically insulated therefrom and brings electrical current and cooling fluid to the field coil which it is understood is composed of a number of turns of hollow conduit, electrically insulated from each other, these not being shown for convenience to illustration. The conduit 35 is "seen to have shallow annula'iv grooves 91 and 92 therein in which are seated O-

rings

93 and 94 for providing sealing engagement between the outside surface of the conduit and the inside wall of insulating sleeve 36. v

The 'aforementioned cylindrical member 81 has a lower portioniof reduced outer and reduced inner diameter 95 forming two shoulders 96 and 97 against which abut respective ly the upper edge of the wall of smaller diameter ofthe' inner shell and the upperl edge of the wall of larger diameter of the inner shell. O-rings in annular grooves" provide sealing engagement between both the wall o f'smaller diameter and the wall of larger diameter and the; aforementioned cylindrical member 81. Peripherally spaced set screws 99 secure the wall of larger diameter ofthe inner shell to the aforementioned member 81.

As previously stated means is provided for applying tension-to the various ring members of the heat shield to insure-good sealing at the various -:O-rings between each shield :ring and the adjacent shield rings on both sides thereof. To this end a retaining ring 101 is seated in an annular-groove 102 in the outer wall of the aforementioned Tubular member 31 of the supporting column, and abutting against this retaining ring is an annular clamp member 103 having a plurality of peripherally spaced threaded bores 104 thcrethrough in which are disposed bolts, two of these being shown at 106 and 107, for ap plying pressure to an annular member 108 slidable on. the outside surface of the wall of the aforementioned tubular member 31 and within limits having an outside annular surface slidable with respect to the adjacent inside annular surface of the uppermost specially shaped ringmember 21. O-

rings

126 and 127 in annular grooves provide sealing engagement between member 108 and the adjacent wall of member 21 and the adjacent wall of tubular member 31. interposed between the lower end of member 108 and a shoulder 110 formed in the inner wall eta-ring member 21 is a Bellesville washer 112 permitting compensation for the thermal expansion of ring members. 11 through 20 as they become heated in the environment. of the furnace.

The upper end of the aforementioned tubular member 31 of the supporting column is seen to have an outwardly exten mg fla ge p rti n 114 and the outer surface of tubular member 31 is seen to have a collar 115 threaded on the outer surface thereof abutting against the flange portion 114, the collar being provided for mounting the electrode in supporting structure. O-rings 117,118,119 and 120 seated in annular grooves are provided for convenience in making fluid tight connections to fluid inlet and outlet means for the magnetic field coil and fluid inlet and outlet means for bringing fluid to and from the electrode tip and the heat'shield for cooling the same.

Cooling fluid passes around the tip from the outcr wall around the bottom and up the inner wall thereof and thence passes through peripherally spacedcut-away portions 122 thence through an annular passageway 123 between the inside wall of tubular member 32 and the outside wall of tubular member 67 thence into the portion of the passageway of larger area 124 between

members

32 and 33 and out of the upper end of the electrode.

The Belle-sville washer, shown at 112 as a single washer, may in fact be two or three stacked Bellesville washers.

If desired, a small groove may be cut in each' of the metal rings just outside the'O-ring sealing areato act as a thermal barrier and limit the heat the O-ring is exposed to.

If desired, the top and bottom surfaces of rings 11-21 may be sprayed with a ceramic insulating material; instead of using'insulating rings of mica or similar material.

The foregoing written description and the drawing are illustrative and exemplary only and are not to be interpreted in a limiting sense.

I claim as my invention:

1. An electrode comprising in combination an electrode tip having a fluid flow passageway therein near the arcing surface for removing heat flux from the tip resulting from the arc thereto, a supporting structure for the tip including an outer tubular member and fluid channeling means within the outer tubular member for conducting fluid from the tip, a heat shield enclosing at least a portion of the outer tubular member and including a plurality of coaxially aligned metallic rings all having an inside diameter greater than the outside diameter of said tubular member of the supporting structure, said rings providing an annular passageway between the inner walls of the rings and the outer wall of said tubular member, means for bringing fluid to said annular passageway, and means for causing the fluid'after it passes through said annular passageway to pass through the passageway in the electrode tip near the arcing surface and thence through the fluid channeling means, the electrode including means for supporting the rings of the heat shield.

2. An electrode according to claim 1 including in addition electrical insulating means disposed between each ring of the heat shield and the adjacent rings on both sides thereof whereby all of the rings are electrically insulated from each other and from the supporting structure.

3. An electrode according to claim 1 wherein each ring of the heat shield is additionally described as having an annular groove therein and including in addition an O- ring disposed in the annular groove for providing fluid tight seals between adjacent rings.

4. An electrode according to claim 3 including in addition means for applying a clamping force to the rings to enhance the seals provided by the O-rings.

5. An electrode according to claim 1 in which the electrode tip is additionally described as having an outer wall portion extending out substantially flush with the outside wall of the lowest ring and forming a shoulder upon which the lowest ring abuts, the tip supporting the stacked rings of the heat shield.

6. An electrode according to claim 1 including in addition a magnetic field coil disposed at least partially within the electrode tip to set up a magnetic field for causing the arc ito move substantially continuouslyover the arcing surface.

7. An electrode according to claim 6 in which said magnetic field coil is composed of hollow conduit.

8. An electrode according to claim 7 in which the conduit passes through the supporting structure being electrically insulated therefrom for bringing an energizing current to the coil and conducting a cooling fluid to and from the coil.

9. An electrode according to claim 1 in which the ,electrode tip is threaded securely to said tubular member of the supporting structure. 1

10. An electrode according to claim 4 in whichv the tubular member' has an annular groove in the outside wall thereof arid the clamping means includes an annular retaining ring seated in said groove in the outside wall of the tubular member of the supporting structure, a clamp ing member retained by the clamping ring, the clamping member having a plurality of peripherally spaced threaded bores" therethrough, a plurality of clamping bolts passing through said bores, and an annular clamping member slidable on the outside surface of the tubfular member and interposed between the bolts and an adjacent surface -'of the next adjacent ring member of the heat shield.

11. An electrode according to claim 1 in which the outer walls of said ring member are coated with an electrically insulating material.

12. An electrode according to claim 1 in which the tip is annular fwith a central aperture therethrough and including in addition other tubular means extending through the electrode and communicating with the central passageway through the annular electrode tip.

13. An electrode according to claim 12 in which the annular tip is generally U-shaped in cross-section and the wall of smaller diameter thereof is threaded to said last-named tubular means.

14. An electrode according to claim 1 including spacer means interposed between the stacked rings of the heat shield and the 'outer surface of the tubular member of the supporting structure to correctly space the rings and provide an annular passageway of the desired width.

15. An electrode according to claim 1 in which the supporting structure includes in addition a cylindrical member near the electrode tip, in which the electrode tip is composed of inner and outer shells with a passageway therebetween for the flow of cooling fluid, both the wall of smaller diameter of the inner shell and the wall of larger diameter'of the inner shell being supported by said cylindrical member of the supporting structure.

References Cited UNITED STATES PATENTS 2,472,851 6/1949 Landis et al. l. 315-347 3,194,941 7/1965 Baird 219-121 3,130,292 4/ 1964 Gage et al 219- 3,201,560 8/1965 Mayo et al. a... 219-123 X BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner US. Cl. X.R.. 219-75, 121.