US3666867A - Smelting furnace - Google Patents

Abstract

An electric smelting furnace of the open hearth type suitable for producing ferrosilicon alloy and the like is described which has improved operating efficiency and heat and dust shielding of the electrical components. The furnace includes an open hearth for containing the melt, at least one carbon electrode extending vertically into the melt and an enclosed space suspended above the furnace and enclosing the upper portion of the electrode. Current-carrying interlaced conductors extend through the enclosed space to a point adjacent the upper portion of the electrode and are connected by means of flexible conductors to vertical conductors which extend to contact plates positioned around the electrode between the enclosed space and the melt. A water-cooled jacket forms an annular chamber around the vertical conductor. Super-atmospheric pressure is maintained within the enclosed space to thereby preclude the entry of airborne foreign particles into the enclosed space.

Description

United States Patent 1451 May 30,1972

Shaw

[54] SMELTING FURNACE [72] Inventor: Frank Walter Shaw, Welland, Ontario,

Canada [73] I Assignee: Union Carbide Canada Limited, Toronto,

Ontario, Canada [22] Filed: Apr. 28, 1971 [21] Appl. No.: 138,224

52 U.S.Cl ..13 9,13 14,13 1

. 13/17 [51] int. Cl ..F27d 1 1/08, HOSb 7/10, HOSb 7/ 12 [58] Field oiSearch ..l3/9,12,14,15,16,17

[56] References Cited UNITED STATES PATENTS 2,368,998 2/1945 Nissim ..13/9 2,929,858 3/1960 Koleda et al ..13/9

Primary ExaminerBernard A. Gilheany Assistant Examiner-Roy N. Envall, Jr. Attorney-William George Hopley ABSTRACT An electric smelting furnace of the open hearth type suitable for producing ferrosilicon alloy and the like is described which has improved operating efficiency and heat and dust shielding of the electrical components. The furnace includes an open hearth for containing the melt, at least one carbon electrode extending vertically into the melt and an enclosed space suspended above the furnace and enclosing the upper portion of the electrode. Current-carrying interlaced conductors extend through the enclosed space to a point adjacent the upper portion of the electrode and are connected by means of flexi ble conductors to vertical conductors which extend to contact plates positioned around the electrode between the enclosed space and the melt. A water-cooled jacket forms an annular chamber around the vertical conductor. Super-atmospheric pressure is maintained within the enclosed space to thereby preclude the entry of airborne foreign particles into the enclosed space.

4 Claims, 6 Drawing Figures Patented Ma 30, 1972 3,666,867

4 Sheets-Sheet 1 FIG. (Prior Art) INVENTOR.

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BY (Prlor Art) Patented May 30, 1972 3,666,867

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4 Sheets-Sheet 3 INVENTOR.

SMELTING FURNACE This invention relates to open electric smelting furnaces of the type used to produce pig iron, carbide, ferro alloys and the like, particularly ferrosilicon alloys. The furnace proper is usually a bucket-shaped enclosure which holds the melt, and a superstructure above the furnace proper supports and controls one or more carbon electrodes which are fed downwardly into the melt as the carbon of the electrode is consumed. Electrical bus bars and flexible copper conductors supply low-voltage high-ampere electric power to the free end of the electrode, and the circuit is completed downwardly through the electrode and the melt to the other electrical terminal. The electrical resistance within the melt, and at the carbon-metal juncture, generates heat which maintains the melt in the fluid or plastic condition. Usually, alternating current is utilized, being tapped off step-down transformers, to the primary of which is fed high-voltage line power.

The superstructure also includes a duct take-off system for removing generated gases from the area immediately above the open furnace proper.

In many conventional furnace constructions, a number of components are exposed to the heat generated in the melt, some of these components such as electrical conductors generating their ownheat by virtue of electrical resistance, and it has been found that costly, time-consuming breakdowns tend to occur at rather frequent intervals.

When these break-downs occur, the furnace has to be shut down, the melt solidifies, and a great many hours are wasted.

In order to overcome the problem of recurrent break-downs resulting from excessive heat, it might appear that the sensitive components could be removed to a location further distant from the source of the heat. Such a solution, however, has been rejected in the past because it was thought that the greater length of the total electrical path thereby entailed would so increase the resistance losses that the furnace output per kilowatt hour would drop to an unprofitable level.

The present invention proceeds from the basic realization that reduced break-downs might compensate for the lower output per kilowatt hour, provided that the components which normally break down are sufficiently protected from the melt heat by appropriate protective structure.

The primary object of this invention, therefore, is to provide a shielded furnace construction in which the heat-sensitive components of the electrical system are sufficiently well protected from the melt heat that the decrease in break-downs tends to compensate for any decrease in profitability arising through the-longer electrical circuit path.

A further drawback of the conventional electric smelting furnace relates to the fact that, as the electrode is gradually fed down into the melt where it is consumed, the contact location at which the electric current is transmitted to the electrode must be repeatedly shifted longitudinally of the electrode. The contact is usually made through a series of contact plates which are pressed radially inwardly against the electrode at a given longitudinal location. In the conventional construction, the portion of the carbon electrode immediately above the contact plates is relatively open and exposed to the dust, gases and other impurities arising from the melt. The

dust-and other particles settle on the electrode in the area just above the contact plates, so that'when the contact plates are shifted upwardly into that region due to the continual consumption of the electrode, something less than an ideal electrical connection is made between the contact plates and the carbon electrode.

Thus, an object of a preferred form of this invention is to substantially eliminate the risk of dust and particle collection on the surface of the carbon electrode above the location of furnace and enclosing the upper portion of the carbon electrode, current-carrying interlaced bus means extending from a point remote from the furnace, through said enclosed space, to a point adjacent the upper portion of the carbon electrode, contact plates around and in electrical contact with the electrode at a location between the enclosed space and the melt, substantially vertical conductor means extending upwardly from said contact plates and into said enclosed space, said last-mentioned means lying adjacent to but spaced from the electrode, flexible conductor means connecting said interlaced bus means and the upper end of said substantially vertical conductor means, means for lowering the electrode into the melt as the electrode is consumed, and fan means for maintaining a super-atmospheric pressure within said enclosed spaced, thereby to preclude the entry of airborne foreign matter into said enclosed space.

The last-mentioned object of this invention is achieved by providing, in addition to the structure just recited, a watercooled jacket surrounding and shielding said substantially vertical conductor means, said jacket defining with the electrode an annular chamber containing said substantially vertical conductor means, said annular chamber being substantially closed at the top and open at the bottom adjacent said contact plate and air blowing means for urging air into the annular chamber so that a continuous outflow of air at the open bottom precludes the entry of airborne foreign matter into said annular chamber.

One embodiment of this invention is shown in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:

FIG. 1 is a plan view of a conventional electric smelting furnace exemplifying the prior art;

FIG. 2 is a vertical section taken at the line 2-2 of FIG. 1, showing the conventional electric smelting furnace in section and elevation;

FIG. 3 is a plan view of an electric smelting furnace constructed in accordance with this invention;

FIG. 4 is a sectional and elevational view of part of the structure shown in FIG. 3;

FIG. .5 is an enlarged view of a portion of the structure shown in FIG. 4; and

FIG. 6 is a graph showing the relationship of operating time and furnace output.

Description of Prior Art Attention is now directed to FIGS. 1 and 2, which illustrate the conventional electric smelting furnace exemplifying the prior art. In FIG. 1, three carbon electrodes 10, 11 and 12 are vertically arranged for controlled downward feeding into the melt 14 in the furnace 16. In FIG. 2, only the electrode 10 is shown. The open top of the furnace 16 is exposed, such that the heat generated in the melt radiates upwardly therefrom. A floor 18 elevated above the furnace 16 has roller guide means 19 which control in its vertical path a collar guide 20 which grips the electrode 10 in a manner not shown. As the electrode 10 is gradually consumed at its contact with the melt 14, the roller guide means 19 permit progressive downward movement of both the collar guide 20 and the carbon electrode 10, until the point is reached where it is necessary to index the collar guide 20 upwardly along the carbon electrode so that another progressive downward movement can begin. The differential vertical movements of the collar guide 20 and the electrode 10 at the time of realignment are usually controlled by hydraulic means which are not shown.

Suspended over the open furnace 16 is a roof 22 which is stationary with respect to the floor 18 and is suspended therefrom, and which has a suitable opening 23 for the passage of the collar guide 20. The roof 22 has side skirts 24 so that the roof 22 with the side skirts 24 define a hood 26 over the open furnace 16 adapted to collect the evolved gases. Ductwork 28 is provided for both admitting cooler air for admixture with the hot evolved gases and extracting the mixture of cooler air and gases from the area of the hood 26.

A floor 30 at the level of the open furnace l6 permits access to the furnace for maintenance, stoking, the breaking of furnace banks, etc.

A plurality of contact plates 31 are pressed tightly into electrical contact with the electrode by conventional means not shown, and in turn communicate electrically with watercooled copper tubing 32 which includes horizontal looped portions 33. The loops are welded into solid electrical contact with a vertically slidable plate 34. The horizontal loop portions 33 of the tubing 32 and the vertically slidable plate 34 are fixed with relation to a support arm 36 which is securely attached to the collar guide and moves vertically therewith. Also attached to the support arm 36 is suitable water pipe connections 38 which supplies cooling water to the loops of the.

water-cooled copper tubing 32, but does not participate in the electrical circuit.

Thus, as the carbon electrode 10 is fed gradually downward into the melt 14 because of electrode consumption, the collar guide 20, the support arm 36, the contact plates 31, the copper tubing 32, the water pipe connections 38 and the vertically slidable plate 34 all move-as a single unit therewith. Each electrode is fed electrically from an interlaced bus bar 40, from the end of each of which two positive and negative bars 42 extend into separator boxes 43.

Either the positive or negative bars 42 are then connected to a fixed plate 45, which is fixed with respect to the roof 22 and is positioned at approximately the edge of the furnace 16. The fixed plate 45 is in spaced, juxtaposed relation with the vertically slidable plate 34, as seen in FIG. 2, and electrical connection takes place between them by virtue of flexible copper straps 46. Likewise, water supply mains 48 are fixed with respect to the roof 22 just above the fixed plate 45, and have attached thereto flexible hoses 50 which in turn communicate with the water pipe connections 38. Thus, the flexible hoses 50 and the flexible copper straps 46 permit the vertically slidable portions to move with respect to the roof 22, without severing either the water or electrical connections.

In order to protect the flexible hoses 50 and the flexible copper straps 46 from the deleterious effects of the heat from the melt, a water-cooled jacket 52 is suspended from the roof 22 and surrounds these components. A vertical slot 54 on the inside wall of the water-cooled jacket 52 permits the vertically slidable plate 34 to move vertically with respect to the jacket 52. As can be seen, the water-cooled jacket 52 has a double wall, the intermediate space being filled with circulating water.

Essentially, there are two sources of heat on ferrous components which are taken care by water cooling. The first of these is the heat generated in the copper conductor and copper plates due to the resistance to the electrical current. The second source is the radiant heat and the hot gases from the furnace. The heat attacks exposed copper, exposed circuits, the smokehood and other furnace components.

A number of problems arise in the conventional electric smelting furnace shown in FIGS. 1 and 2. Some of these problems are listed below.

1. The flexible water hoses 50 and the flexible copper straps 46 are exposed to a certain degree of heat, depending upon how efficiently the water-cooled jacket 52 protects them.

2. The water piping is exposed to radiant heat and a corrosive atmosphere. Maintenance work is difficult as a result of heat, dust and smoke. I

3. The water-cooled copper tubing 32 is exposed to high heat and a corrosive atmosphere.

4. The water-cooled jacket 52 is prone to developing leaks due to the proximity to the furnace heat. Also, it is necessary to introduce pressurized air into the water-cooled jacket 52 in order to keep out the dust.

5. The roller guide means 19 have a close vertical spacing, and this results in high stresses and continuing maintenance.

6. In order to remove the contact plates 31, it is necessary to shut off the water for a complete circuit and to disconnect the piping, which results in leaks on other sections from steam generation and overheating.

7. The fume flow pattern within the hood 26 is not uniform due to the presence of the jacket 52, the supporting members and the associated piping.

8. It is not possible to introduce extra water circuits to the contact plates 31 if this is considered necessary, due to the configuration of the copper tubing 32.

9. Because of the slot 54 in the water-cooled jacket 52, it is impossible to prevent a certain amount of radiant heat and dust from entering the jacket 52 and causing problems with the flexible hoses 50 and the flexible copper straps 46.

10. Because the vertical slidable plate 34 is live" electrically, it is necessary to provide insulated guide rollers (not shown) to prevent grounding on the jacket 52 a high maintenance item.

DESCRIPTION OF INVENTION Attention is now directed to FIGS. 3 and 4 in which can be seen anopen-top furnace 56 having three carbon electrodes 58, 59 and 60, only the electrode 60 being visible in FIG. 4. An enclosed space 62 is defined between a rigid ceiling structure 63, downwardly depending side walls 64 and a suspended floor 66. The floor 66 has openings 68 for the passage of chutes 70, the chutes 70 being employed in the charging of the furnace 56. Because the charging procedure does not form any part of this invention, the rest of the charging structure is not shown.

As seen in FIG. 3, three interlaced bus bars 72 are adapted to carry low-voltage high-ampere electrical power from conventional step-down transformers (not shown) to locations within the enclosed space 62 adjacent the carbon electrodes 58, 59 and 60. At these locations, the positive and negative plates of each interlaced bus bar are separated and connected to two stationary plates 74 (only one shown in FIG. 4). The stationary plates 74 for each bus bar are adapted to deliver current to two different electrodes, in the usual manner for a three-phase system. Flexible conductors 76 similar to the flexible copper straps 46 in FIG. 2 conduct the current from the stationary plates 74 (FIG. 3) to movable plates 78. From each movable plate 78 the current is conducted to a conductive ring bus bar 80 (shown in FIG. 4) which encircles each electrode but is spaced therefrom. From the conductive ring bus bar 80 the current is conducted downwardly adjacent the periphery of the electrode 60 by means of conductive, watercooled piping 82 which loops downwardly and upwardly in a substantially vertical boustrophedonic configuration, with the lower ends 84 communicating electrically with contact plates 86 similar to the contact plates 31 shown in FIG. 2. The watercooled piping defines a water passageway of the said boustrophedonic configuration, such that the water passes through the water-cooled piping 82, and the contact plates 86 as well.

A cylindrical water-cooled jacket 88 surrounds and shields the water-cooled piping 82 and defines with the electrode 60 an annular chamber 90 which is substantially closed at the top in a manner shortly to be described, but which is open at the bottom adjacent the contact plates 86, thereby defining an open annular mouth 92 opening downwardly adjacent the contact plates. Cooling water is fed to the water-cooled jacket 88 by means of water connections (not shown) within the enclosed space 62. The water connections are thus protected from the heat of the melt in the furnace 56. As seen in FIG. 4, the water-cooled jacket 88 extends upwardly through an opening 94 into the enclosed space 62, and terminates in a ledge 96 through which the piping 82 extends. The piping'82 is thus exposed above the ledge 96 within the enclosed space 62. The ledge 96 does not extend inwardly into contact with the electrode 60, but adjoins the lower end of a cylindrical encasement 96 which extends upwardly around and in spaced relationship with the electrode 60 to terminate in an inward flange 98 which contacts the electrode 60 in a non-conductive manner, and thus closes the upper end of the annular chamber 90. Air-blowing means 100, preferably an air impeller, is provided for urging air into and pressurizing the annular chamber 90, such that a continuous outflow of air through the open annular mouth 92 adjacent the contact plates 86 will preclude the entry of airborne foreign matter into the said annular chamber 90.

Roller guide means 102 which bear against the outside of the water-cooled jacket 88 serve to align the electrode 60 properly in the vertical position for downward progression.

Fan means 104 are provided for maintaining a super-atmospheric pressure within the enclosed space 62, thereby to preclude the entry of airborne foreign matter into said enclosed space through openings such as 68 and 94.

It will be noted that, in the construction shown in FIGS. 3, 4 and 5, there are no flexible water hoses or flexible copper strips exposed to the heat of the melt of fumace 56, and that no water piping is located in an area where heat and the corrosive atmosphere can attack it. The enclosed space 62, which is large enough for maintenance personnel to move around comfortably, permits continuous inspection of these parts. Also, there are no support arms or water-cooled jackets such as the jacket 52, and thus the problems related to the high heat in the water-cooled jackets are eliminated. Furthermore, because the support arms and the water-cooled jackets 52 of the conventional construction are now removed, the gas hood structure 105 defines an area within which there is unrestricted gas flow to the take-off ducts.

With the design of this invention, it is possible to have separate water circuits to each contact plate 86 if required, and this can be carried out simply by modifying flexible water hoses (not shown).

THEORETICAL CONSIDERATIONS With regard to the electrical circuitry of the furnace, the construction shown in FIGS. 3, 4 and 5 requires that the bus bars and water-cooled pipes or cables be removed to an area further up along the electrode than was the case with the conventional design shown in FIGS. 1 and 2. When moved to this higher location, as explained above, it is possible to erect a protective environment, in the form of an enclosed space 62, around these components, whereby they are shielded from the heat and corrosive atmosphere emanating from the melt in the furnace 56.

Although it might appear at first glance that the removal of the electrical circuitry (flexible water pipes and conductors) to a higher location with respect to the melt would be an obvious step to overcome the problems arising because of the excessive heat and corrosive atmosphere, the person skilled in this art would reject such an apparently obvious solution because of the nature and characteristics of the electrical circuit involved. Because AC current is used in this kind of furnace, the bus bars and the water-cooled piping which carries the power down to the contact plates 86 are arranged in a manner called interlacing. In this system, common to all installations of this kind, the cables or conductors are positioned side-by-side in an alternating positive and negative field arrangement whenever possible, so that the magnetic drag (hysteresis losses) can be minimized. Without the interlacing arrangement, the magnetic drag or hysteresis losses established in a single isolated conductor through which AC was being conducted would set up a considerable 97 and reduce the amount of electric power available for activating the electrode, in the case of an electric smelting furnace. In the construction according to the present invention, the greater part of the electrical circuitry is removed upwardly from the electrode contact plates 86, in this case about or 12 feet farther up from its conventional position, and because of this the circuitry in the enclosed space 62 must be connected to the contact plates 86 by means of a straight line cable. Because of the high resistance to be expected in such straight line cables, it would generally be assumed by those skilled in this art that the power losses arising from magnetic drag would be so great as to render this design impractical.

In the actual reduction to practice of this invention, however, it was found that while there is considerable power loss in the straight line cable portion (the piping 82), there was actually less power loss between the two bus bars and the water cooled piping because these can now be placed closer together since they do not require individual shielding and extension arms from shielded boxes.

In addition to this factor, it was noted that while there is a slightly greater power loss in the construction of the present invention than is found in the conventional design shown in FIGS. 1 and 2, this loss is more than compensated for by the reduction in maintenance to the furnace and the fact that the furnace can now be operated on a continual basis for periods up to thirty days without shut-down, as compared to conventional furnace operation with which operation at high temperatures normally cannot be extended beyond about 10 days without shut-down.

It will also be appreciated that the elimination of the watercooled jackets 52 of the conventional furnace shown in FIGS. 1 and 2 means that it is possible to establish take-off ducts from the gashood structure 105 at any desired positions around the open furnace, thereby permitting more efiicient collection of discharge gases.

In FIG. 6 is shown a graph with percentage of operating I time O.T.) above 85 percent on the horizontal axis, and percent increase in production on the vertical axis. The graph shows the relationship between these two variables at a constant power input. It will be noted, for example, that for every increase in operating time of 1 percent gives a resulting increase in production of 5 percent for the same power input. Thus a small increase in operating time has a disproportionately large impact on the output of a furnace of the kind here involved, and thus that measures, such as those incorporated in the present invention, which tend to increase the percentage of operating time by lowering the frequency of shut-down, will add materially to the efficiency of the furnace.

I claim: I. An electric smelting apparatus comprising: an upwardly opening furnace for containing the melt, at least one carbon electrode extending vertically downwardly into the melt, means defining an enclosed space suspended above the furnace and enclosing the upper portion of the carbon electrode, current-carrying interlaced bus means extending from a point remote from the furnace, through said enclosed space, to a point adjacent the upper portion of the carbon electrode, contact plates around and in electrical contact with the electrode at a location between the enclosed space and the melt, substantially vertical conductor means extending upwardly from said contact plates and into said enclosed space, said last-mentioned means lying adjacent to but spaced from the electrode, flexible conductor means connecting said interlaced bus means and the upper end of said substantially vertical conductor means, means for lowering the electrode into the melt as the electrode is consumed, and fan means for maintaining a super-atmospheric pressure within said enclosed space, thereby to preclude the entry of airborne foreign matter into said enclosed space. 2. The combination claimed in claim 1 which further includes a water-cooled jacket surrounding and shielding said substantially vertical conductor means, said jacket defining with the electrode an annular chamber containing said substantially verticle conductor means, said annular chamber being substantially closed at the top and open at the bottom adjacent said contact plates, and air-blowing means for urging air into the annular chamber so that a continuous outlfow of air at the open bottom precludes the entry of airborne foreign matter into said annular chamber.

3. The combination claimed in claim 2, which further includes a conductive ring bus bar encircling but spaced from the upper portion of the electrode within said enclosed space, said ring bus bar constituting said upper end of the substantially vertical conductor means, the latter being further constituted by electrically conductive, water-cooled piping arranged in a vertical boustrophedonic configuration encircling the electrode, each downward loop of the boustrophedonic configuration being in conductive contact with one of said contact plates, each upward loop of the boustrophedonic configuration being in conductive contact with said ring bus bar.

4. An electric smelting apparatus comprising:

an upwardly opening furnace for containing the melt,

three carbon electrodes extending vertically downwardly into the melt,

means defining an enclosedspace suspended above the furnace and enclosing the upper portions of the three carbon electrodes,

each electrode having a plurality of contact plates around and in contact with it at a location between the enclosed space and the melt,

the upper portion of each electrode within said enclosed space being encircled by a conductive ring bus bar which is spaced from its respective electrode,

each electrode having an encircling arrangement of electrically conductive, water-cooled piping defining with the contact plates and with the conductive ring bus bar a water passageway of vertical boustrophedonic configuration, the piping being spaced from the electrode and being in electrically conductive contact with both the contact plates and the conductive ring bus bar, the

current-carrying interlaced bus means extending from a location remote from the furnace, through said enclosed space, to points adjacent the upper portions of each of the carbon electrodes,

flexible conductor means connecting the interlaced bus means to the three conductive ring bus bars,

means for lowering the electrode into the melt in a controlled way to compensate for electrode consumption,

fan means for maintaining a super-atmospheric pressure within said enclosed space, thereby to preclude the entry of airborne foreign matter into said enclosed space,

a water-cooled jacket surrounding and shielding said watercooled piping, said jacket defining with the electrode an annular chamber substantially closed at the top and open at the bottom adjacent said contact plates,

and air-blowing means for urging air into said annular chamber so that a continuous outflow of air at the open bottom precludes the entry of airborne foreign matter into said annular chamber.

* i l i

Claims (4)

1. An electric smelting apparatus comprising: an upwardly opening furnace for containing the melt, at least one carbon electrode extending vertically downwardly into the melt, means defining an enclosed space suspended above the furnace and enclosing the upper portion of the carbon electrode, current-carrying interlaced bus means extending from a point remote from the furnace, through said enclosed space, to a point adjacent the upper portion of the carbon electrode, contact plates around and in electrical contact with the electrode at a location between the enclosed space and the melt, substantially vertical conductor means extending upwardly from said contact plates and into said enclosed space, said lastmentioned means lying adjacent to but spaced from the electrode, flexible conductor means connecting said interlaced bus means and the upper end of said substantially vertical conductor means, means for lowering the electrode into the melt as the electrode is consumed, and fan means for maintaining a super-atmospheric pressure within said enclosed space, thereby to preclude the entry of airborne foreign matter into said enclosed space.

2. The combination claimed in claim 1 which further includes a water-cooled jacket surrounding and shielding said substantially vertical conductor means, said jacket defining with the electrode an annular chamber containing said substantially verticle conductor means, said annular chamber being substantially closed at the top and open at the bottom adjacent said contact plates, and air-blowing means for urging air into the annular chamber so that a continuous outlfow of air at the open bottom precludes the entry of airborne foreign matter into said annular chamber.

3. The combination claimed in claim 2, which further includes a conductive ring bus bar encircling but spaced from the upper portion of the electrode within said enclosed space, said ring bus bar constituting said upper end of the substantially vertical conductor means, the latter being further constituted by electrically conductive, water-cooled piping arranged in a vertical boustrophedonic configuration encircling the electrode, each downward loop of the boustrophedonic configuration being in conductive contact with one of said contact plates, each upward loop of the boustrophedonic configuration being in conductive contact with said ring bus bar.

4. An electric smelting apparatus comprising: an upwardly opening furnace for containing the melt, three carbon electrodes extending vertically downwardly into the melt, means defining an enclosedspace suspended above the furnace and enclosing the upper portions of the three carbon electrodes, each electrode having a plurality of contact plates around and in contact with it at a location between the enclosed space and the melt, the upper portion of each electrode within said enclosed space being encircled by a conductive ring bus bar which is spaced from its respective electrode, each electrode having an encircling arrangement of electrically conductive, water-cooled piping defining with the contact plates and with the conductive ring bus bar a water passageway of vertical boustrophedonic configuration, the piping being spaced from the electrode and being in electrically conductive contact with both the contact plates and the conductive ring bus bar, the current-carrying interlaced bus means extending from a location remote from the furnace, through said enclosed space, to points adjacent the upper portions of each of the carbon electrodes, flexible conductor means connecting the interlaced bus means to the three conductive ring bus bars, means for lowering the electrode into the melt in a controlled way to compensate for electrode consumption, fan means for maintaining a super-atmospheric pressure within said enclosed space, thereby to preclude the entry of airborne foreign matter into said enclosed space, a water-cooled jacket surrounding and shielding said water-cooled piping, said jacket defining with the electrode an annular chamber substantially closed at the top and open at the bottom adjacent said contact plates, and air-blowing means for urging air into said annular chamber so that a continuous outflow of air at the open bottom precludes the entry of airborne foreign matter into said annular chamber.

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