US3184530A - Process for the melting of metals, for example copper, and an electric furnace for the performance of said process - Google Patents

Description

May 18, 1965 l. PRoPl-:Rzl 3,184,530

PROCESS FOR THE MELTING OF METALS. FOR EXAMPLE COPPER. AND AN ELECTRIC FURNCE FOR THE PERFORMANCE OF SAID PROCESS Filed Feb. 25, 1962 6 Sheets-Sheet l COPPER, AND AN ELECTRIC FURNACE FOR THE PERFORMANCE OF SAID PROCESS PROCESS FOR THE MELTING OF METALS,

May 18, 1965 Filed Feb. 23, 1962 May 18, 1965 PROPERZI 3,184,530

PROCESS FOR THE MELTING OF METALS, FOR EXAMPLE COPPER, AND AN ELECTRIC FURNACE FOR THE PERFORMANCE OF SAID PROCESS Filed Feb. 25, 1962 e sheets-sheet s May 18, 1965 l. PRoPERzl 3,184,530

PROCESS FOR THE MELTINC OE METALS, FOR EXAMPLE COPPER, AND AN ELECTRIC FURNACE FOR THE PERFORMANCE OF SAID PROCESS Filed Feb. 25, 1962 6 Sheets-Sheet 4 1. PRoPERzl 3,184,530 PROCESS FOR THE MELTING OF METALS, FOR EXAMPLE May 18, 1965 COPPER, AND AN ELECTRIC FURNACE FOR v THE PERFORMANCE OF'4 SAID PROCESS Filed Feb. 25, 1962 6 Sheets-Sheet 5 N l ON u 0 nm u n, /lf/ 7 MN Hf., /f 1,/ l/ ,n o, 0M A ll Il. s m or... C

l. PROPERZI 3,184,530 PROCESS FOR THE MELTING OF METALS, FOR EXAMPLE May 18, 1965 COPPER, AND AN ELECTRIC FURNACE FOR THE PERFORMANCE OF SAID PROCESS 6 Sheets-Sheet 6 Filed Feb. 25, 1962 Fig United States Patent O PROCESS FOR THE MELTING F METALS, FOR

EXAMPLE COPPER, AND AN ELECTRIC FUR- NACE FR THE PERFORMANCE 0E SAID PRQCESS Ilario Properzi, Via Cosimo del Fante 10, Milan, Italy Filed Feb. 23, 1962, Ser. No. 175,225 Claims priority, application Italy, Mar. 4, 1961, Patent 649,374 7 Claims. (Cl. 13--23) The present invention relates to a process for the melting of metals and in particular for the melting of copper; the invention relates also to an electric furnace for the performance of said process.

One object of the present invention is to be able to provide for the melting of metals, and of copper in particular, in such a manner as to satisfy all the requirements of this operation, by economical means as regards both thermal eciency and low consumption of materials. The process according to the present invention is characterized in that the metal to be melted, for example copper, is completely covered by a layer of graphite or carbon powder, and in that an electric current is passed through the mass consisting of said powder and the metal.

Said conducting powder also constitutes a protective coat and, as will appear more clearly-hereinafter, keeps a controlled reducing atmosphere inside the furnace while at the same time insulating said furnace from the outside atmosphere; there is a minimum dispersion of heat and practically no wear on the furnace.

The difficulties that are encountered in the operation which goes by the name of melting metals are well known. In order to melt copper for example, it is found that this metal easily oxidizes and easily absorbs certain gases, so that it is necessary to control the atmosphere; again, when the copper to be melted is in the form of cathodes, these Often contain intolerable quantities of sulphur residue which has to be removed by refining operations, and it is furthermore necessary to bring the liquid metal to a very precise pouring temperature and keep it there for the whole time necessary. We therefore distinguish four stages in the operation which goes by the name of copper melting: convenient charging of the materials; melting in a controlled reducing atmosphere; analysis; refining, degassing, descaling; maintaining the temperature with the controlled atmosphere.

These requirements are perfectly satisfied if, as will be disclosed hereinafter, the furnace is divided into two parts at least one of which is movable; by shifting the two parts relatively to each other, the basin containing the metal is released but the liquid metal is perfectly protected by a layer of said conducting powder.

In what follows there will be described a non-limiting embodiment of the furnace for the melting of metals, e.g. copper, according to the present invention, with reference to the accompanying schematic drawing wherein:

FIG. 1 shows a cross-section of the furnace taken along the line I-I of FIG. 3;

FIG. 2 shows another cross-section of the same furnace taken along the line II-II of FIG. 4, and in this crosssection, parts of said furnace are seen in a different recip rocal position from that of the foregoing figure;

FIG. 3 shows a longitudinal section of the furnace taken along the line III-III of FIG. 1;

FIG. 4 shows a plan of the furnace with said parts in said different reciprocal position in relation to FIGURES 1 and 3;

FIG. 5 shows a cross-section (like FIG. 1) of another example of a furnace according to the present invention;

FIGURES 6 and 7 show respectively the axial section and the plan of a variant of the electrode which can be employed in the furnace according to the invention.

FIGURES 8 and 9 show, in axial cross-sectional view, two further embodiments of the electrode, on a reduced scale with respect to that of FIGS. 6 and 7.

The furnace of the present example is a three-phase in-line furnace composed essentially of two distinct parts, a lower one and an upper one, respectively indicated by the numerals 16 and 4, supported and reciprocally joined by means whereof more will be said hereinafter.

The lower part 16 comprises a melting basin 1 on the bottom whereof there can also be provided a pressed down carbon or silicon carbide oor 2. Melting basin 1 is made from a suitable refractory material,

The presence of said floor 2 is not essential, since the metal load is a good conductor itself.

Said basin is adapted to receive the metal, which is then melted in the basin itself; in the present example, said metal consists of a bundle of copper cathodes 3; on one side of said basin there is provided a pouring spout 21.

The same lower part 16 extends over one side of the furnace into a part 18 on which the upper part 4 can be shifted as will be better disclosed hereinbelow.

Said part 4 carries rollers 22 which run on two rails 17; these are integral with supports 23 which are in turn integral with part 16 itself. l

In this manner, the upper part 4 is supported by part 16 itself and can perform horizontal movements in relation thereto.

The upper part 4 includes generally cylindrical openings or wells bounded by a surface 28 and lined with a refractory material 24. The wells contain the electrodes 5 which, in the present example, are three in number as the furnace is a three-phase one, as can be best seen from FIG. 3.

Each electrode 5 is housed in a well bounded by surface 28, and is integral with the current bars 6 embedded in said electrode; the latter is made of carbon or graphite.

Electrode 5 is formed with an axial passage 8 bounded by a surface 25, and the outer surface of the electrode, besides having a cylindrical part 26, has a lower frustoconical shape '7.

The current bars 6 of the electrodes are integral with the cross-beams 11 which are connected to bars 15 of the transformer supplying the furnace, through electrical conductors 14.

Each bar 11 is supported by means of two electrically insulated screws 12 and 13 resting on part 4 itself.

Each electrode 5 can therefore be lowered or raised by turning said screws 12 and 13.

The furnace is supported by means of columns 29 and a hydraulic piston 19 connected flexibly to part 16: to be precise, said part 16 is pivoted to said column 29 so that it can perform rotations on pins 20.

Since, as already stated, part 16 supports part 4 of the furnace, it follows that the whole furnace can rotate on said pins under the control of the piston 19.

The means actuating said piston can be provided in various ways and, for the sake of simplicity, are not shown.

It will be noted that axis A on which the furnace rotates, is relatively near to the pouring spout 21.

With regard to the working of the furnace, let us consider same in the configuration visible in FIGURES l and 3 the upper part 4 is in such a position that the electrodes 5 are situated above the basin 1.

In said basin is the charge of metal to be melted, consisting in this case of said bundle of copper cathodes 3.

All the space above the charge 3 is filled with graphite powder 9, including the space of the wells wherein the electrodes are situated, i.e. said electrodes are completely immersed in said powder.

adsense The surface 25 of each passage 8 serves to increase the area of contact with the graphite powder and to facilitate the filling and the flowing of said powder which must fill all the empty spaces inside the furnace and close all the cracks communicating with the outside, up to the top 1).

When current passes between the electrodes 5, the charge 3 is heated because said current, through the powder 9, also passes through the charge 3; thus, at a certain point, the melting of the metal in a reducing atmosphere is obtained.

The layer of powder, besides acting as a resistance, also serves as a useful protective coating.

In the practical employment of this furnace, it has been observed that the reduction of the oxides contained in the metal charge takes place automatically because of the high temperature (eg. 3500 C.) reached by the graphite powder in contact with the charge, and that, because of its fineness and the high temperature to which it is raised by the passage therethrough of powerful electric currents, said powder behaves as a liquid and is extremely effective in removing any impurities or scale due to oxidation, or any other impurities, scale or froth attributable to irnperfect reducing action or insufficiently high temperature.

For said powder placed above the charge, by behaving like a liquid of great reducing power, can iow and penetrate everywhere, removing impurities and scale which are reduceable because of the presence of carbon at a very high temperature and a strongly reducing gaseous atmosphere.

It will be noted that, since electrodes 5 are contained in wells, the electric currents are constrained to a greater extent to pass through the powder in the direction of the metal charge. It will also be noted that said bottom 2 of the basin represents a conducting fioor which ensures the closure of the circuits when the charge, at the commencement of heating, has not yet formed an integral electrical conductor.

The dispersion of heat is very small because only a thin layer of powder in contact with the charge is brought to a high temperature, this being the layer between the bottom surface 7 of the electrodes and the top surface of the charge 3; the rest of the powder, right up to the top 10 thereof, constitutes a heat-insulating protective mantle which isolates the charge from the outside atmosphere. In addition, the furnace is subject to practically no wear since the action of the high temperatures involves only the surface of the metal and the lower part of the electrodes, as well as said interposed layer of powder 9.

It will be noted that said frusto-conical surfaces 7 serve to reduce the cross-sectional area of the electrode tips in order to reduce the losses due to heat transfer therewithin.

It will also be noted that the carbon or graphite electrodes immersed in and protected by the powder, are subjected to practically no wear, which means that they can retain their reduced terminal cross-section which is in contact with the hot graphite powder.

And it will be seen that the electrodes shown in FIG- URES 1 to 5 have tapering terminal cross-sections corresponding to the outer frusto-conical surface 7; the type of electrode, also included in the scope of this invention, and illustrated in FIGURES 6 and 7 also has a decreasing cross-section, but has an inner frusto-conical surface 27. Two further electrodes, having a decreasing terminal cross-sectional area, are shown in FIGS. 8 and 9. rI`he loss of heat which strongly affects the thermal efficiency of electric furnaces with electrodes because of the thermal conductivity of the electrodes themselves, is thus considerably reduced, whilst the resistance to the passage of electric current along the electrodes' remains practically unchanged.

By lowering or raising electrodes 5 by means of said screws 12 and 13, `the thickness of the layer of powder separating said electrodes from the metal mass 3, can be varied. With the consequent variation in the electrical resistance, the electrical input between the phases and the total power absorbed by the furnace can be balanced.

It will be noted that the operation of lowering and raising the electrodes which, on account of the considerable size of said electrodes, would not appear to be easy in the mass of powder, is, on the contrary, quite possible during the working of the furnace since, as already stated, the high temperature of the graphite powder causes same to behave substantially like a liquid.

The pointed shape of the electrode facilitates the descent thereof.

FIG. 2 shows the same section as FIG. 1 but with the upper part i (which runs on said rails 17) in the recharging position, i.e. with said upper part 4 taken to the right (looking at FIG. 2) whilst the graphite powder rests on the bed 1S of refractory material.

Suitable means are provided for providing the thrust for this movement. In this position, the operations of controlling, refining, etc., if necessary, take place, and when they have been completed, the liquid metal is taken to be used, whilst the powder in the wells cannot come down into the basin during the discharging phase.

The new charge can therefore be introduced into basin 1 after same has been cleaned of residue.

Body 4 is taken back to the position shown in FIG. l to start a new heat.

The lower part 16, containing the melting basin 1, is manoeuvred, at the moment of pouring, by means of said hydraulic piston 1.9 which obliges the furnace to rotate on said pins 20. Any suitable means can be employed to retain or cover the powder which is thus uncovered.

FIG. 5 shows a variant of an embodiment of the furnace described hereinabove. In this variant there is provided a double basin, i.e. besides the above-described part 16, there is provided a second part 16 at the side of the rst and integral therewith. In said embodiment shown in FIG. 5, part 13 is missing and is replaced by the new part 16; the latter is in all respects the same as the first, i.e. it comprises the same basin 1 with conducting floor 2 and pouring spout 21.

Above parts 16 there is provided a part 4 which is in all respects the same as the part 4 described hereinabove. Part 4 in the embodiment under examination can be so shifted as to dispose itself alternately on one and on the other part 16. In substance we have a furnace with a double sprue basin and a single part 4 with its related electrodes and accessories thereto. The whole assembly is actuated by means of two hydraulic pistons 19 and can rotate on pins 20 about its axis A.

With the furnace of FIG. 5 a continuous heating cycle is obtained.

During the heating `of one of the basins 1, whilst part e with its electrodes is above same, Ithe loading `of the other basin is canried out; thereafter, when the heating of the first basin has been completed, i.e. when the metal therein has melted, part 4 is moved on to the other basin and the heating of its basin is immediately commenced.

With this continuous working there is, in the double basin furnace, a considerable saving of time and energy.

As regards the time, there are in fact no idle times due to the loading of the basins. Furthermore, because there are no dead times, the installed power is fully utilized. As regards energy, it will be noted that, when part 4 is moved from one basin to the other, as soon as lthe heating of the first has been completed, i.e. when part 4 still contains a considerable amount `of heat, this residual heat from the previous operation is exploited.

The electric current can, naturally, have any number of phases; in the case of a single-phase furnace, 'there may be a single electrode immersed in the graphite, the circuit being capable of being closed either through the Hoor or through another electrode.

I claim:

1. An electrical furnace for melting readily oxidizable metals in a reducing atmosphere, including in combination, a furnace body of refractory material, a melting basin recessed in the top surface of said furnace body, said melting basin .adapted to receive a charge of metal to be melted, with said charge covered with an incoherent carbonaceous material, a movable roof of refractory material disposed above said melting basin means for horizontally transporting said roof in a linear path over the top surface of said furnace body, at least two vertical wells extending through said roof, a carbon electrode disposed coaxially in cach said well and extending a substantial distance along the axial length thereof, each said electrode having a bottom portion terminating near the bottom of each said well and positioned over said melting basin, at least one metal member secured to and extending vertically from the top portion of each said electrode for securing said electrodes in place in said wells and providing terminal means for application of an electrical potential thereto, and an incoherent carbonaceous material disposed around each said electrode so as to completely fill each said well, so that current flow through said carbonaceous material results in heating to thereby melt said metal, with said carbonaceous material providing a reducing atmosphere and insulating said melted metal from oxidizing gases.

2. An electric furnace according to claim 1 wherein each said electrode has a generally hollow cylindrical configuration with a tapered rbottom portion.

3. An electric furnace according to claim 1 wherein said melting basin is provided with a pouring spout, `and wherein means are provided for rotating said furnace body in a vertical plane for removal of said melted metal from said melting basin.

4. An electric furnace according to claim 1 wherein said metal members supporting said electrodes are adjustably mountedso that the proximity of the bottom portion of each said electrode may be varied with respect to the top of said melting basin.

5. An electrical furnace for melting -readily Koxidizable metals in a reducing atmosphere, including in combination, a furnace body of refractory material, a melting basin recessed in the top surface of said furnace body, said melting basin adapted to receive a charge of metal to be melted, with said charge covered with an incoherent carbonaceous material, a movable roof of refractory material disposed above said melting basin, said roof having three vertical wells extending therethrough, means for horizontally transporting said roof in a linear path over the top surface of said furnace body, a generally cylindrical hollow carbon electrode disposed c0- axially in each said well and extending a substantial distance along the axial length thereof, each said electrode having a tapered bottom portion of reduced cross-section terminating near the bottom of each said well and juxtaposed near the top surface of said melting basin, at least one metal rod secured to each said electrode and extending vertically from the top thereof, means for adjustably holding said rods in place above said wells to thereby position said electrodes and to provide terminal means for application of an electrical potential thereto, and an incoherent carbonaceous material disposed around the inner and outer surfaces of each said cylindrical electrode so as Ito completely fill each said well, `so that current flow through said ca-rbonaceous material results in heating to thereby mel-t said metal, with said carbonaceous material providing a reducing atmosphere and insulating said melted metal from oxidizing gases.

6. An electrical furnace for melting copper in a reducing atmosphere, including in combination, a furnace body of refractory material, an elongated rectangular melting basin recessed in the -top portion of said furnace body, said melting basin adapted to receive a charge of copper CTI stock to be melted, with said charge completely covered with powdered graphite, a movable roof of refractory material disposed above said inciting basin, means for transporting said roof horizontally over the -top surface of said furnace body in a linear path to thereby make said melting basin accessible for removal of melted copper and to receive additional stoclr to be melted, a plurality of vertical wells extending through said roof, said wells disposed in a row coextensive with Athe elongated length of said melting basin, a generally cylindrical hollow carbon electrode disposed coaxially in each said well `and extending a substantial distance along the axial length thereof, each Isaid electrode terminating in a bottom portion of reduced cross-section near the bottom of each said well and juxtaposed near the top surface of said melting basin, at least one metal rod secured to the top portion of each said electrode for adjustably holding each said electrode in place in each said well and providing terminal means for application of an electrical potential thereto, and powdered graphite material disposed around the inner and outer surfaces of each said cylindrical electrode so as to completely fill each said well, whereby current flow thro-ugh said powdered graphite material results in heating to thereby melt said copper stock, with said powdered graphite material providing a reducing atmosphere and insulating said melted copper from oxidizing gases.

7. An electrical furnace for melting readily oxidizable metals in a reducing atmosphere, including in combination, a furnace body of refractory material, first and second melting basins recessed side by side in the top surface of said furnace body, said melting basins adapted to receive a charge of metal to be melted, with said charge being covered with finely divided carbon powder, a movable roof of refractory material disposed above said furnace body and positioned over one of said melting basins, means to horizontally transport said roof from sai-d position over one said melting basin to a corresponding position over the other said melting basin, a plurality of vertical `wells extending through said roof, .a generally cylindrical hollow carbon electrode disposed coaxially in each said Well and extending a substantial distance along the axial length thereof, each said electrode having a bottom por-tion of reduced cross-section terminating near the bottom of each said well such that it is positioned above one of said first and second melting basins, at lease one vertically extending metal rod secured to the top portion of each said electrode, means for receiving said rod to position said electrodes in said wells and to provide terminal means for application of an electrical potential thereto, and finely divided carbon powder disposed around the inner and outer surfaces of each said electrode to thereby lill said bores, whereby said movable roof may be positioned above either said first or said second melting basin so that current flow through said finely divided carbon powder results in heating to thereby melt said metal in one said melting basin in a reducing atmosphere which is free from oxidizing gases, with the other `said mel-ting basin being accessible for recharging thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,812,357 6/31 Mills 13-9 1,901,524 5/33 Moschel 13-20 1,924,201 8/33 Schuffler 13-20 2,290,028 7/42 Brooke 13-9 2,298,055 10/42 Hulme et al. 75-65 2,446,637 8/48 Crampton et al. 75-65 2,448,886 9/48 Hopkins 13-9 3,025,385 5/62 Tanaka 219-50 RICHARD M. WOOD, Primary Examiner.

Claims (1)

1. AN ELECTRICAL FURNACE FOR MELTING READILY OXIDIZABLE METALS IN A REDUCING ATMOSPHERE, INCLUDING IN COMBINATION A FURNACE BODY OF REFRACTORY MATERIAL, A MELTING BASIN RECESSED IN THE TOP SURFACE OF SAID FURNACE BODY, SAID MELTING BASIN ADAPTED TO RECEIVE A CHARGE OF METAL TO BE MELTED, WITH SAID CHARGE COVERED WITH AN INCOHERENT CARBONACEOUS MATERIAL, A MOVABLE ROOF OF REFRACTORY MATERIAL DISPOSED ABOVE SAID MELTING BASIN MEANS FOR HORIZONTALLY TRANSPORTING SAID ROOF IN A LINEAR PATH OVER THE TOP SURFACE OF SAID FURNACE BODY, AT LEAST TWO VERTICAL WELLS EXTENDING THROUGH SAID ROOF, A CARBON ELECTRODE DISPOSED COAXIALLY IN EACH SAID WELL AND EXTENDING A SUBSTANTIAL DISTANCE ALONG THE AXIAL LENGTH THEREOF, EACH SAID ELECTRODE HAVING A BOTTOM PORTION TERMINATING NEAR THE BOTTOM OF EACH SAID WELL AND POSITIONED OVER SAID MELTING BASIN, AT LEAST ONE METAL MEMBER SECURED TO AND EXTENDING VERTICALLY FROM THE TOP PORTION OF EACH SAID ELECTRODE FOR SECURING SAID ELECTRODES IN PLACE IN SAID WELLS AND PROVIDING TERMINAL MEANS FOR APPLICATION OF AN ELECTRICAL POTENTIAL THERETO, AND AN INCOHERENT CARBONACEOUS MATERIAL DISPOSED AROUND EACH SAID ELECTRODE SO AS TO COMPLETELY FILL EACH SAID WELL, SO THAT CURRENT FLOW THROUGH SAID CARBONACEOUS MATERIAL RESULTS IN HEATING TO THEREBY MELT SAID METAL, WITH SAID CARBONACEOUS MATERIAL PROVIDING A REDUCING ATMOSPHERE AND INSULATING SAID MELTED METAL FROM OXIDIZING GASES.

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