US3395240A - Fluid cooled arc electrode having means for utilizing the current which produces and sustains the arc to generate a magnetic field which continuously moves the arc in a csed path - Google Patents

Description

3 ,395,240 0 TILIZING THE T ARC TO OUSLY July 30, 1968 G KEMENY ET AL FLUID COOLED ARC ELECTRODE HAVING MEAN CURRENT wHIcH PRODUCES D SUSTA GENERATE A MAGNETIC PI v ICH CONTINU MOVES THE ARC IN A CLOSED PATH Filed Aug. 27. 1965 FIG.3.

INVENTORS Serufino M. De Corso a George A. Kemeny fiw/ M ATTORNEY SOURCE OF POTENTIAL United States Patent-O 3,395,240 FLUID COOLED ARC ELECTRODE HAVING MEANS FOR UTILIZING THE CURRENT WHICH PRODUCES AND SUSTAINS THE ARC TO GENERATE A MAGNETIC FIELD WHICH CONTINUOUSLY MOVES THE ARC IN A CLOSED PATH George A. Kemeny, Franklin Township, Export, and Seralino M. De Corso, Wilkins Township, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 27, 1965, Ser. No. 483,111 19 Claims. (Cl. 13-48) ABSTRACT OF THE DISCLOSURE An electrode for use in an arc furnace includes a fluid cooled hollow conduit having a portion thereof formed into a coil preferably with a plurality of turns, the axis of the coil normally extending perpendicular to the melt of the furnace or to a surface of opposite polarity, one or more turns of the coil forming an arcing surface. The conduit is connected to a source of potential at a point thereon where are current flows through at least a portion of the coil and produces a magnetic field which causes the arc to the surface of opposite polarity to rotate substantially continuously around the surface or surfaces of one or more turns of the coil at the end thereof near the surface of opposite polarity. In some embodiments the conduit contains means internal thereto for forcing the cooling fluid to follow a path closely adjacent the wall of the conduit. In other embodiments certain turns of the coil are electrically insulated on their outsid'es to limit the arc to one particular turn thereof. In all embodiments the bottom turn of the coil, the turn nearest the surface of opposite polarity, does not form a continuous annular electric current path or a continuous annular magnetic flux path.

This invention relates to improvements in electrodes for electric arc furnaces, and more particularly to an improved electrode for producing and sustaining an arc, and having an arc-moving magnetic field producing coil energized by the same current which produces and sustains the arc.

It has been known for some time that a water-cooled electrode could be constructed which was suitable for use in an arc furnace, the electrode having means forming a water-cooled or other fluid-cooled annular arcing surface, and having disposed near the arcing surface a magnetic field producing coil, usually energized by direct current, for setting up a magnetic field transverse to the arc path and transverse to the arc current for creating forces on the are which cause the arc to move in a closed path substantially continuously around the arcing surface, thereby avoiding burning through the wall of the arcing surface forming means by the intensely hot are spot. The successful operation of such an electrode depends upon the simultaneous meeting or satisfaction of a number of essential conditions: the arc must move at a suflicient speed so that the arc spot does not remain in any one position long enough to sublimate sufficient material to cause a burn through, and yet the are spot must not return to the same place after one complete revolution on the arcing surface until the material at the place has had time to cool to a safe temperature. These conditions are met, in accordance with the physical dimensions of the arcing surface and the current of the arc, by providing a magnetic field of the desired strength to rotate the are at a speed which is neither too great nor too small. These conditions are set forth more fully in a copending application of A. M.

3,395,240 Patented July 30, 1968 Bruning for Electric Arc Furnace and Nonconsumable Electrode Suitable for Use Therein, filed Oct. 29, 1964, Ser. No. 407,332, and assigned to the assignee of the instant invention.

We have discovered that where alternating current or direct current is employed to produce and sustain the arc, the same current which produces the arc may be passed through a series-connected coil of a few turns and utilized to set up a magnetic field for rotating the arc. To accomplish this, we have devised an electrode composed. entirely of hollow conduit, the conduit being composed of highly heat conductive and electrically conductive material, such as copper, and preferably of nonmagnetic material, with a cooling fluid flowing through the conduit, the portion of the conduit at the end of the electrode from which an arc is to be produced being shaped in the form of a coil, the source of electric current being connected to that terminal of the coil which causes the arc current to flow through substantially all the turns of the coil to the lowest turn thereof, or turn nearest to the surface of opposite polarity, from which lowest turn the arc takes place to a melt or another electrode.

If desired, our electrode structure consisting of a relatively rigid hollow conduit with a coil at one end and having .a cooling fluid flowing therethr-ough may be disposed in a substantially cylindrical casing or shield having cylindrical fluid inlet and fluid outlet passages for the flow of a cooling fluid, the cylindrical casing or shield being composed of nonmagnetic material, and possibly of material which is not electrically conductive, and being enclosed by a heat shield consisting of a highly heat resistant material such as, for example, a ceramic, although the entire electrode may consist solely of at least one elongated portion of conduit and a coil portion. This summarizes our invention according to one embodiment thereof.

In other embodiments of the invention, We employ either square or round conduit having filler means for forcing the fluid to flow near the inner wall of the conduit to thereby increase the heat flux transferred away from the coil by the cooling fluid. In still another embodiment, we enclose all the turns of the coil, except the one from which the arc occurs, in a ceramic or plastic coating.

Accordingly, a primary object of our invention is to provide a new and improved electrode for an electric arc furnace.

Another object is to provide a new and improved electrode in which the current which produces and sustains the are also creates a magnetic field for rotating the arc.

A further object is to provide a new and improved electrode for an electric arc furnace consisting essentially of a hollow conduit through which a cooling fluid flows, the conduit at the arcing end of the electrode being shaped to form a coil of at least a few turns through which the current flows thereby creating a magnetic field for rotating the arc, the are taking place from the turn or turns at the end of the coil nearest the surface of opposite polarity.

These and other objects will become more clearly apparent after a study of the following specification, when read. in connection with the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view of an electrode according to one embodiment of our invention;

FIG. 2 is a cross-section through a conduit suitable for us in the embodiment of FIG. 1;

FIG. 3 is a cross-section of a portion of a coil suitable for use in the embodiment of FIG. 1, in which the turns of the coil are spaced from each other by electrically insulating material, whereas in FIG. 1 they are spaced from each other and electrically insulated by air;

FIG. 4 is a cross-section through round conduit suitable for use in the electrode of FIG. 1;

- FIG. is a view illustrating arc jumping of a space in the turn of a coil; and

FIG. 6 is a view of a modified mounting arrangement of the coil portion of the conduit.

Referring now to the drawings, in which like reference numerals are used throughout to designate like parts for a more detailed understanding of the invention, and in particular to FIG. 1 thereof, an electrode generally designated 10 has an outer heat shield generally designated 11 composed of a heat resistant or refractory material such as acerami'c, a split cylindrical'fluid-cooled portion generally designated" 12 providing concentric cylindraceous passageways for the flow 'of a cooling fluid from a fluid inlet header at the top of the electrode to the arcing region thereof and back to a fluid outlet header, and a portion forming an arcing surface generally designated 13 and seen to comprise a hollow conduit through which a cooling fluid flows, a portion of which is bent to form a magnetic field producing coil.

If the walls of the fluid cooled portion 12 are composed of electrically conductive material, preferably there are circumferentially aligned breaks therein as at 24 to prevent the formation of large circulating current therein which might cancel or reduce a magnetic field set up for rotating the arc, the fluid passage-ways being closed on both sides of the break or air gap 24.

In particular, the electrode which forms an arcing surface of. an are 14 to melt 15 is seen to comprise two spaced elongated portions of conduit 16 and 17, illustrated as extending down substantially near the middle of the cylindrical cooling portion 12. The conduit por tions 16 and 17 have elbows 18 and 19 at the upper ends thereof and are connected by hydraulic insulators 20 and 21 respectively, to other conduit means 22 and 23, one of which supplies a cooling fluid to the electrode, this being conduit 22, and the other of which conducts fluid from the electrode, the latter being designated 23. The hydraulic insulators 20 and 21 are necessary since the portion of the conduit which forms the electrode is at a substantial electrical potential, this electrical potential being applied to conduit portion 16 by means symbolized by lead 25 connected to source 26, which may be direct current or alternating current, the source also being electrically connected by means symbolized by lead to melt 15 which is electrically conductive at least to some degree. The two conduit portions 16 and 17 extending down into the furnace are seen to be electrically insulated from each other by electrically insulated mounting means 27 and 28 mounted upon a cross bar 29 which extends across the interior of the cylindrical portion 12.

As previously stated, fluid flows in conduit 16 and this conduit is shaped at the lower or arcing end of the electrode to form, for example, a coil 38 of four turns, the turns being designated 31, 32, 33 and 34, the hollow passage through the conduit being designated 35. The are 14 takes place from the bottom of the lowest turn 34 which is preferably wound or formed so that most of the portions of the lowest turn are substantially equidistant from the melt, that is, the plane of the turn is substantially perpendicular to the axis of the electrode and parallel to the surface of opposite polarity. The fluid in the hollow passageway 35 then, after passing around turn 34, follows the bend 37 upward and thence passes through conduit portion 17, through hydraulic insulator 21, and out the conduit 23. The current brought to the electrode by lead 25 flows down conduit portion 16 and around all of the four turns 31, 32, 33 and 34 of the coil portion of the conduit, creating a magnetic field which causes the are 14 to move or rotate in a substantially continuous fashion in a closed path around the arcing surface formed by the bottom of turn 34. The arc jumps any gap in the turn, or may jump between turns 33 and 34 in the region designated B-C.

The aforementioned cylindrical fluid cooling portion of the electrode generally designated 12 is seen to comprise 4, three coaxial or concentric walls 41, 42 and 43 with circumferentially aligned air gaps or breaks 24 therein on both sides of which the spaces between walls are closed, forming enclosed passageway 44 between walls 41 and 42 and enclosed passageway 45 between walls 42 and 43. An annular space 46 exists between the end of cylindrical Wall 42 and the substantially annular ring closing portion 47 extending between wall portions 41 and 43 at the bottom thereof, so that fluid entering fluid header 49 from inlet 50 flows down substantially cylindrical passageway 44 through substantially annular space 46 up substantially cylindrical passageway 45 into fluid header 52 and thence to-outlet 5 3. i v

The aforementioned heat shield generally designated 11 is seen to have a portion 55 at the upper end thereof of increased inner diameter for accommodating water headers 49 and 52. The heat shield 1'1 may be maintained in place on the cylindricalwall portion 41 by any convenient means as by having studs, not shown, extending from the wall.

It will be understood that if fluid cooled portion 12 is employed as part of the electrode, preferably the cylindrical tubes 41, 42, 43 and the annular ring 47 which closes the ends of the tubes, are all preferably composed of nonmagnetic material so as not to interfere with the formation of a magnetic field by the coil 38 of turns 31 to 34, inclusive, which will rotate the are 14. Tubes 41, 42 and 43 and ring 47 may be made of non-conductive material if desired to avoid having currents inducedtherein which might tend to cancel the magnetic field produced by the coil 38 in which case gap 24 may be eliminated; or the tubes 41, 42, '43 may be composed of material having a high electrical resistance to minimize induced currents. One suitable material for the tubes of FIG. 1 is stainless steel.

It will further be understood that the entire electrode may, if desired, consist solely of the two rigid hollow conduits 16 and 17 extending down into the furnace and having formed at the ends thereof several turns to form a magnetic field producingcoil, the conduit connected to the top turn of the coil, or the turn farthestfrom the surface of opposite polarity, as seen in FIG. 1, being connected to the source of potential, .so that current will have to flow around substantially all the turns of the coil before forming an are from the bottom turn, that is, the turn nearest to the surface of opposite polarity.

It will be further understood that if any metallic supporting structure is employed in conjunction with the hollow conduit which forms the coil and the arcing surface, precautions are taken to prevent the electrode metal from acting as a single turn transformer coil, that is, as a secondary coil with the field coil 38 as the primary winding, where source 26 is alternating current. It has been found in practice that where a magnetic field 'coil is disposed in an electrode tip or in electrode face means forming an electrode arcing surface that where'alternating current was applied to the coil, the current induced in the electrode tip metal results impractical cancellation-of the magnetic field strength available for spinning the arc.

In summarizing the operation of the apparatus of FIG. 1, or the operation of an electrode consisting solely of the conduit-coil portion of the-apparatus of FIG. 1, as previously stated, the invention comprises asmall number of turns of a high conductivity Water-cooled co-il. Water enters the coil at one'end and leaves at the other end. Alternating current (or direct current) are power is connected to one end of the structure, point A or lead 25, and the alternating current flows through the coil from point A to the-lowestturn, and from there arcs to the charge or melt in the furnace, or to an opposingelectrode at opposite polarityi'Arcin'g'can be expected to take place at the lower turns in'area s marked B'to C and'D to E. The number of effective turns pfoducing magnetic flu'x may vary slightly as the af c move'siaround the coil, but sufficient turns are always available reproduce an adequate field flux. For example, a direct current energized field coil for use in a 16-inch diameter electrode, as described and claimed in a copending patent application of S. M. De Corso and C. B. Wolf, Ser. No. 440,425, filed Mar. 17, 1965, and assigned to the assignee of the instant invention, produces a magnetizing force of about 200,000 ampere turns. This is in an electrode where the arcing current is about 50,000 to 80,000 amperes. With a similar arcing current of 50,000 to 80,000 amperes in the electrode of the instant invention, it is seen that four effective turns are required to get substantially the same magnetizing force as was obtained with the direct current field coil described and claimed in the last-named copending application.

Because the coil of the instant invention has to carry very large currents, and because the lower turn will have to remove arc contact and radiation losses, adequate cooling is provided. Particular reference is made now to FIG. 2, which shows a typical conduit cross-section for the coil involving an outer tube and a filler which directs the water flow against the inside wall of the hollow conduit, the outer tube or conduit being designated 61 and the filler 62. By using a filler 62, water velocity is increased which results in increased heat transfer capability.

In a conduit having this configuration, for the lowest turns, the arc may rotate in such a manner that practically all the arc contact losses have to be removed by a single coolant passage such as, for example, passage F, which might result in a burnout since all the arc contact losses may be removed by a single passage; this may result in excessive water heating and ultimate water boiling and burnout.

Particular reference is made now to FIG. 4, which shows a further improved conduit configuration using a circular cross-section in which cooling passages such as passages G spiral about the center line or axis of the conduit. In FIG. 4, the tubing or conduit is designated 63 and the filler 64. In this manner, tube G is in or near bottom position or closest to the surface of opposite polarity for only a fraction of a turn of the coil, and therefore overheating and burnout is less likely because less heat has to be removed by the water flowing through the particular passage G. Furthermore, due to centrifugal effects, spiralling of the water flow will result in improved heat transfer.

In FIGS. 2 and 4, the desired conduit cross-sections can be produced by inserting a machined filler inside of the tube or conduit and bending the conduit to the desired coil shape. Also for better heat transfer and rigidity, the filler and tube may be joined or produced integral by brazing, rib-bonding, electron beam welding, or extrusion in one piece.

It is to be noted that the bottom turns of the coil, that is, the turns closest to the melt, will be subjected to the highest heat fluxes and should therefore be provided with the best water cooling. Since high heat transfer rates require high water velocities, and since high water velocities result in high frictional pressure drops per unit of length, it is desirable from a pumping power viewpoint, to provide high heat flux capability only in as little of the length of the conduit as is required to prevent burnouts. For example, the conduit-filler configuration shown in FIG. 4 may be utilized only in the bottom turns of the coil of FIG. 1 while for the rest of the coil the tube or conduit may be left without filler, thus resulting in lower water velocities and correspondingly lower pressure drops in those parts of the coil where less heat has to be removed.

Alternately, the same type of conduit configuration may be used throughout the length of the coil, by swaging the area down for the bottom turns, which results in smaller water passage size and hence higher water velocities and better cooling.

For scrap melting and ore reduction, it is desirable that the space between turns be insulated to prevent electrical shorting as a result of some of the furnace charge or melt being deposited on the coil or thrown upon the coil. Particular reference is made now to FIG. 3 showing a coil wound with a gap between turns, this gap being filled with ceramic or other electrically insulating and refractory material, the turns of the coil being shown at 66, 67 and 68 and the ceramic insulation at 69. The ceramic may also aid in holding adjacent turns together. The ceramic may be applied by dipping the coil in a ceramic slurry, thus coating all parts, and then removing the coating from the surface of the bottom turn of the coil which forms the arching surface of the electrode. Alternately, the bottom surface can be masked during the coating operation.

Particular reference is made now to FIG. 5. As will be readily understood by those skilled in the art, where an alternating current is used to supply the arc current and an alternating current of the same frequency, or more precisely the same alternating current, is used to generate the magnetic field for rotating the arc, both the magnetic field and the current change polarity every half-cycle so that the are always rotates in the same direction around the arcing surface. This also occurs when source 26 is direct current. This means that the arc and are contact spot will have to jump between turns, or across a gap in one turn, at least once each revolution, but experiments have demonstrated that where a coil has the configuration shown in FIG. 5, the arc jumps between turns or across a gap at the point x very readily, and this necessity for jumping between turns does not present any serious problem.

Whereas the invention has been described largely with respect to operation from an alternating current power supply, it should be understood that source 26 connected to lead 25 may be a direct current source, that the current of are 14 may be supplied by the direct current from the source and the magnetic field set up by the coil including turns 31 to 34 may be a direct current field. It will be understood that the magnetic field of this arrangement is in such a direction as to cause continual rotation of the are 14 about the bottom turn of the coil, the direction of rotation being unvarying.

In summary, the electrode of this invention is less expensive to construct than some of the prior art fluidcooled electrodes utilizing direct current magnetic filed coils and alternating current for supplying the arc. The need for two power supplies, both direct current and alternating current, is eliminated. The need for cooling the field coil is eliminated. The electrode support structure is greatly simplified as only two tubes are required for each electrode tip or coil. Attaching coil to structure is simplified as only two fittings or braze joints are needed. It was previously stated that the cooling means 12 of cylinders or tubes 41, 42 and 43 and heat shield 11, may be omitted entirely and that the electrode may consist solely of conduits 16 and 17 and the coil 38 having turns 31 to 34, with means for suspending the electrode in the furnace whereby the arcing surface of the lowest turn is maintained a predetermined distance from the melt.

It will be readily understood that in the type of construction shown, the magnetic field will not be as easily directed as in a structure described and claimed in the aforementioned copending patent applications. However, since the field can be made stronger by simply adding a few turns, this is not a handicap.

Particular reference is made now to FIG. 6, which shows another arrangement for mounting the coil. Elongated conduit portions 55 and 56 rest upon or pass through the walls of furnace 60 and support coil 57 in the position shown. Arc 58 takes place from the nearest turn to conductive melt 59 or another electrode. Conduit 55 and electrode 54 in contact with the melt are connected to a source of potential.

It will be understood that, Where the coil may be adjacent the wall of the furnace, only one substantially 7 elongated portion of conduit may be required, the coil discharging fluid outside the wall.

Whereas the coil 38 has been shown as helical it could be flat or of the pancake variety, with the turn most electrically remote from the source 26 being slightly misaligned to be slightly nearer the surface of opposite polarity.

Whereas we have shown and described our invention with respect to some embodiments thereof which give satisfactory results, it should be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

We claim as our invention:

1. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, comprising a length of hollow conduit composed of electrically conductive, heat conductive and non-magnetic material the conduit having a cooling fluid flowing therethrough, the length of conduit including two spaced elongated portions adapted to extend into the furnace and a substantially helical coil portion intermediate the elongated portions, that elongated portion merging into that turn of the coil farthest from the surface of opposite polarity being adapted to be electrically connected to one terminal of a source of potential to produce an arc to the surface of opposite polarity, the arc current flowing through the coil and setting up a magnetic field which causes the arc to rotate substantially continuously around the surface of at least one of the turns of the coil near the surface of opposite polarity.

2. An electrode according to claim 1 in which said hollow conduit is additionally characterized as having a filler therein forming a plurality of spiraling fluid flow passageways near the inside Walls of the conduit.

3. An electrode according to claim 1 including in addition means attached to the elongated portions for mounting the electrode in a furnace with a predetermined distance between said last-named turn and the surface of opposite polarity.

4. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, comprising a length of hollow conduit composed of electrically conductive and heat conductive material, the conduit having a cooling fluid flowing therethrough, the length of the conduit including two spaced elongated portions adapted to extend into the furnace and a coil portion intermediate the elongated portions, the axis of the coil being substantially perpendicular to the surface of opposite polarity, that elongated portion which merges into that turn of the coil farthest from the surface of opposite polarity being adapted to be electrically connected to one terminal of a source of potential to produce an arc from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through the coil and setting up a magnetic field which causes the arc to rotate substantially continuously around the surface of said lastnamed turn, all of the turns of the coil except the lastnamed turn being encased in a refractory insulating material which spaces and electrically insulates the turns of the coil from each other and provides a heat shield for the turns of the coil.

5. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, said surface being selectively the melt in the furnace or another electrode, comprising a length of hollow conduit composed of electrically conductive, heat conductive, and non-magnetic material, the conduit being substantially circular in cross-section and being adapted to have a cooling fluid flow therethrough, the length of conduit including two spaced elongated portions and a coil portion intermediate the elongated portions, the axis of the coil being substantially perpendicular to the surface of opposite polarity, the two spaced elongated portions being adapted to extend into the furnace and support the coil portion in position therein, that elongated portion merging into that turn of the coil farthest from the surface of opposite polarity being adapted to be electrically connected to one terminal of a source of potential toproduce an are from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through the coil and setting up a magnetic field, the number of turns of the coil being selected in accordance with the arc current to provide a magnetizing force of at least a predetermined number of ampere turns whereby the arc rotates substantially continuously around the surface of said last-named turn of the coil at at least a predetermined speed.

6. An electrode according to claim 5 in which at least that portion of the hollow conduit which forms the coil is additionally characterized as having filler material therein which forces the fluid which flows through the conduit to pass adjacent the inside surfaces of the walls of the conduit.

7. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, comprising a length of hollow conduit composed of electrically conductive, heat conductive and non-magnetic material, the conduit being substantially square in crosssection and having a cooling fluid flowing therethrough, the length of conduit including two spaced elongated portions and a coil portion intermediate the elongated portions, the elongated portions being adapted to support the coil portion in predetermined position in the furnace, the coil being disposed in the furnace with its axis substantially perpendicular to the surface of opposite polarity and having a plurality of turns with a turn closest to the surface of opposite polarity and a turn farthest from the surface of opposite polarity, that elongated conduit portion merging into the turn farthest from the surface of opposite polarity being adapted to be electrically connected to one terminal of a source of potential to produce an arc to said surface of opposite polarity, the arc current flowing through the coil and setting up a magnetic field which causes the arc to rotate substantially continuously around the surface of at least one of the turns of the coil near the surface of opposite polarity.

8. An electrode according to claim 7 in which the coil is additionally characterized as having a predetermined number of turns to produce a predetermined magnetizing force of at least a given number of ampere turns in accordance with the current producing the arc.

9. An electrode according to claim 7 including in addition a ceramic material substantially enclosing the entire coil except for the turns comprising that portion of the coil nearest to the surface of opposite polarity, the ceramic material insulating the turns of the coil and separating the turns of the coil from each other.

10. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, the electrode being adapted to be electrically connected to one terminal of a source of potential having the other terminal connected to the surface of opposite polarity, comprising in combination, an electrode including an elongated supporting portion and a coil portion, both the elongated supporting portion and the coil portion being composed of hollow conduit, the conduit being composed of electrically conductive, heat conductive and nonmagnetic material, the coil portion and supporting portion being connected together to form a through passageway for the flow of a cooling fluid through the elongated portion and through the coil portion and thence to a fluid outlet, the coil portion being adapted to be disposed in the furnace in predetermined position with respect to the surface of opposite polarity, the coil being shaped whereby one turn of the coil is nearer to the surface of opposite polarity than the remainder of the turns, another turn farthest from the surface of opposite polarity being operatively connected to the source of potential, the arc taking place from the turn'neare'st to the surface of opposite polarity, the current which produces the arc flowing through the coil and creating a magnetic field which causes the arc to rotate substantially continuously around the surface of said last-named turn.

11. An electrode according to claim in which the coil has a predetermined number of turns to provide a magnetizing force of at least a predetermined number of ampere turns in accordance with the strength of the current creating and sustaining the arc.

12. An electrode according to claim 10 in which at least the coil portion of the conduit has means extending therethrough which forces the fluid flowing through the coil portion to flow in a path adjacent the inside wall of the conduit.

13. An electrode according to claim 10 including in addition insulating material substantially coating all of the turns of the coil except that portion of the turn nearest the surface of opposite polarity which forms an arcing surface, and electrically insulating the turns of the coil from each other while thermally insulating the turns from the heat of radiation and convection in the furnace.

14. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, comprising a length of conduit composed of electrically conductive and heat conductive material, the conduit having a cooling fluid flowing therethrough, the length of conduit including two spaced elongated portions and a coil portion intermediate the elongated portions, one elongated portion being adapted to have fluid admitted thereto and the other elongated portion being adapted to have fluid taken therefrom, the elongated portions supporting the coil portion in predetermined position in the furnace, that elongated portion merging into that turn of the coil farthest from the surface of opposite polarity being adapted to be electrically connected to one terminal of a source of potential to produce an arc from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through the coil and setting up a magnetic field which causes the arc to rotate substantially continuously around the surface of said last-named turn.

15. An electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, the electrode comprising a length of hollow conduit comprising a first extended portion and a second portion shaped to form the turns of a coil, the second portion being disposed at the arcing end of the electrode, the first and second portions being adapted to be operatively connected to hydraulic insulators and thence to fluid inlet and fluid outlet means, the turn of the coil farthest from the surface of opposite polarity being adapted to be connected to a source of potential, current flowing from the source of potential through the coil and forming an arc from at least one of the two turns of the coil nearest to the surface of opposite polarity.

16. An electrode according to claim in which the coil portion of the conduit is additionally characterized as having ceramic insulating material between turns of the coil.

17. In an electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, a length of hollow conduit composed of electrically conductive and heat conductive material, the conduit being adapted to have a cooling fluid flow therethrough, at least a portion of the conduit being shaped to form a coil having a predetermined number of turns, the coil being adapted to be supported in the furnace in predetermined position with respect to the surface of opposite polarity, the coil being so shaped that one turn of the coil is nearer to the surface of opposite polarity than the remainder of the turns, and means operatively connected to another turn of the coil farther from the surface of opposite polarity for producing an arc from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through at least a portion of the coil and setting up a magnetic field which causes the arc to move.

18. In an electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, a length of hollow conduit composed of electrically conductive and heat conductive material, and means connected to the conduit for causing a cooling fluid to flow therethrough, at least a portion of the conduit being shaped to form a coil having a predetermined number of turns, the coil being adapted to be supported in the furnace in predetermined position with respect to the surface of opposite polarity, the coil being so shaped that one turn of the coil is nearer to the surface of opposite polarity than the remainder of the turns, another turn of the coil farther from the surface of opposite polarity being adapted to have a potential applied thereto for producing an arc from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through at least a portion of the coil and setting up a magnetic field which causes the arc to move.

19. In an electrode for producing and sustaining an arc to a surface of opposite polarity in an electric arc furnace, a length of hollow conduit composed of electrically conductive and heat conductive material, means connected to the conduit for causing a cooling fluid to flow therethrough, at least a portion of the conduit being shaped to form a coil having a predetermined number of turns, the coil being adapted to be supported in the furnace in predetermined position respect to the surface of opposite polarity, the coil being so shaped that one turn of the coil is nearer to the surface of opposite polarity than the remainder of the turns, and means operatively connected to another turn of the coil farther from the surface of opposite polarity for producing an arc from the turn of the coil nearest to the surface of opposite polarity, the arc current flowing through at least a portion of the coil and setting up a magnetic field which causes the arc to move.

References Cited UNITED STATES PATENTS 2,093,821 9/1937 Southgate 219- X 2,286,210 6/1942 Klemperer et al. 219- X 2,286,211 6/ 1942 Dawson et a1 219-100 X 2,472,851 6/1949 Landis et a1 219--123 X 2,727,937 12/ 1955 Boyer 13-9 X BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

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