US2539215A - Electric furnace, including electromagnetic pump for molten metal - Google Patents

Description

2 c I T m G A M m K LT ABE IUL wm -F mm W c I m C E L E 3 Sheets-Sheet 1 Filed July 12, 1946 INVENTORS Walter M. mil

11 1 1.1 1 7 11 1 1 1 11, [/11 1 111 1 11 11 1111 1 111 1 1 1 111 1 111 11 1 11111 11 111 1111 1 1111 1 11 11 11 1 11 1111 f u 11111 1 1 111 1 1 1 11, 1 111 1 1 1 1 1111 1/ 1 1 1 1 l 1 111 11 1 1 1 1 1 1 11 111 1 1 11 1 Walter Bonsaclr Jan. 23, 1951 w. M. wan. EI'AL 2,539,215

ELECTRIC FURNACE. INCLUDING ELECTROMAGNETIC PUMP FOR MOLTEN METAL Filed July 12, 1946 3 Sheets-Sheet 3 III II INVENTORS Walter M PV'eiL Walter Bonsaclr ATTORNEYS Patented Jan. 1951 ELECTRIC FURNACE, INCLUDING ELECTRO- MAGNETIC PUMP FOR MOLTEN METAL Walter M. Weil, Shaker Heights, and Walter Bonsack, Lyndhurst, Ohio, assignors, by mesne assignments, to Ajax Engineering Corporation, Trenton, N. J a corporation of New Jersey Application July 12, 1946, Serial No. 683,115

25 Claims.

melting, lifting and conveyingmolten metal and in particular to a pump which can be utilized to lift and convey molten metals of various types. It is an object of the present invention to provide a device for lifting molten metal an appreciable distance, which will permit the withdrawal or raising of molten metal from beneath the surface of the molten metalbath and transferring the metal without appreciable oxidation to other locations where work is to be done with the metal or to'the metal.

Another object is to provide a pump for molten metal having no moving members and in which the parts may be fabricated of materials which are 'not subject to rapid deterioration when contacted with molten metal. For example in the case of molten aluminum it is not desirable to use any pump parts of metal since even a metal with a relatively high melting point such a iron will dissolve when contacted b molten aluminum, in spite of the fact that the molten aluminum is at a temperature approximately one-half the temperature at which iron melts.

A further object is to provide a pump for molten metal which will permit the lifting and .conveying of the metal through a closed conduit from a bath of molten metal directly to a mold or die.

Other objects and advantages will be apparent from the following detailed description accompanied by the drawings in which:

Fig. 1 is a fragmentary cross sectional elevational view of a bath of molen metal having installed in conjunction therewith a pump embodying the present invention;

Fig. 2 is an enlarged cross sectional elevational view taken substantially on line 2-2 of Fig. 1 to show further details of the pump mechanism;

Fig. 3 is a fragmen ary elevational cross sectional view of a modified form of pump embodying the present invention installed in a divided hearth reverberatory furnace, such as may be employed in the smelting of aluminum;

Fig. 4 is an enlarged cross sectional elevational view taken substantiall on line 4-4 of Fig. 3 to illustrate further details of the operation' of the pump;

Fig. 5 is an enlarged cross sectional View taken substantially on line 5'-5 of Fig. 3, illustrating details of the construction of the pump; and

Fig. 6 is a fragmentary elevaional View of a further modification of the present invention showing a bath of molten metal having installed in conjunction therewith another modified form of pump.

Figs. 1 and 2 show a molten metal bath I enclosed in a suitable container illustrated diagrammatically as a portion of a furnace having refractory lined side walls 2 and a suitable hearth 3.

Only a portion of a furnace is indicated, since the pump embodying the present invention may be applied to any container suitable for holding a supply of the molten metal which it is desired to pump. For example, the present pump may be used in conjunctionwith a melting furnace, in which the metal to be melted may be fed to the furnace and molten metal removed therefrom for transfer to another location where work is to be done with or to the metal. Or the pump may be utilized in conjunction with a holding furnace which ma be charged with molten metal and heat supplied thereto mainly for the purpose of preserving the metal at a point above its melting point for withdrawal as desired. In any case, it possible to use the pump embodying the present invention as the source of heat for the molten metal bath.

Installed beneath the molten metal bath I is a pump embodying the present invention. Such a pump may include the elements of an electric induction furnace of the submerged resistor type. A horizontally disposed rectangular core 4 made up of laminated sections on which the primary coil is wound is entwined with a secondary loop which comprises a vertically disposed double rectangle having a common side. The core surrounds the common leg of the double rectangle of the secondary loop with two legs of the core passing through the centers of the rectangles forming the secondar loop. Primary windings I 5 and 6 surround the legs of the core in the region where they pass through the centers of the rectangles of the secondary loop.

As sated the secondary loop of the transformer assembly may have the configuration of a double rectangle. At least a portion of the secondary loop should' comprise molten metal in communication with the molten metal bath. In order to obtain greater heating of themetal and to assure an adequate flow of metal to the pump it is preferable to form a large portion of the secondary loop as a channel of molten metal in communication with the molten metal bath.

As shown in Fig. 2, the secondary loop may be formed of outer vertical legs or channels 1 and 8 which open into the furnace proper in the region of the hearth 3 at their upper extremity and open into a lower horizontal channel In at their lower extremity. Approximately midway between the channels I and 8 is a central leg or channel H which also opens at its upper extremity into the molten metal bath and into the horizontal channel it at its lower extremity. A suitable plug E2 of a refractory material may be provided at one end of the horizontal channel It to permil; inspection and cleaning of the bottom channels when desired. The walls of the channels 1, 8, l0, and H are lined with a suitable refractory material [3 which will resist deleterious attack by the molten metal in the furnace. Adjacent the layer of refractory material and outwardly thereof may be disposed a suitable layer of insulating material M to decrease heat flow from the channels. If desired, the insulating material It may then be encased in a metal housing l5. In order to cool the core l and the primary windings 5 and 6, air may be circulated through the housing i5 and removed through an aperture to therein by a suitable fan (not shown). Since the housing 85 does not enclose one side of the rectangular primary loop, air may enter the housing 415 by traveling around the legs of the core which have the windings 5 and ti thereon, being exhausted through the aperture it.

The channels ll, 3, it and it may have any desired cross sectional contour, but are preferably straight to facilitate their being cleaned during the operation of the furnace without the necessity of shutting down and removing the molten metal bath from the furnace. Cleaning may be accomplished by suitable tools which are passed through the channels to dislodge or scrape foreign material, slag, and the like from the side walls.

As current is applied to the primary loop from any suitable source (not shown) a corresponding current is induced in the secondary loop, and

since the secondary loop is a channel of molten metal, current will flow therethrough and create heat due to the resistance of the molten metal conductor.

A conduit or pipe l'l depends into the molten metal bath and has its terminus within the central channel 6 i in the region of the mouth of the channel where it is surrounded by molten metal. Preferably the conduit may be formed of a suitable refractory material, such as graphite or silicon carbide, so that it will not be subject to deterioration due to its contact with the molten metal. The conduit it extends upwardly to a point above the level of the metal bath where it may be joined to a horizontal run or section it of the conduit by means of the right angle elbow 2&3. The horizontal section it may extend through an aperture in the side wall 2 of the furnace so that the furnace wall supports the conduit it in its position depending into the molten metal bath.

In induction furnaces of the submerged resistor type, where the molten metal comprises at least a portion of the secondary loop, the electromagnetic forces cause a movement or circulation of the molten metal bath. For many applications, a certain amount of circulation of the'molten metal bath is considered desirable, as it keeps the molten metal throughout the furnace at a nearly uniform temperature, and a homogeneous mixture of the bath is assured. Where the metal is an alloy or is undergoing refining, modification, purification, alloying, or fluxing, it is desirable that the molten metal bath be as homogeneous as possible.

It has long been known that there is considerable agitation of the molten metal in such furnaces due to electromagnetic forces; in fact, as

illustrated by the Tama et a1. Patent 3,342,617,

granted February 22, 1944, considerable attention has been given to reducing the turbulence of the metal, so that the protective oxide or slag coating at the surface of the molten metal bath is not continually ruptured.

The present invention is not concerned with the reduction of turbulence of the molten metal but is rather concerned with the utilization of the electromagnetic forces for the commercial lifting and pumping of the metal to a zone usually outside of the current path. Even though the turbulence of the metal has long been known and the cause of the turbulence has long been understood, it has not been recognized prior to the present invention that this pressure within the molten metal could be utilized to cause the molten metal to flow in a conduit in a single direction so that pumping or lifting of large masses of molten metal could be accomplished successfully. At least as far as we are aware, no methodhad been proposed prior to the present invention for obtaining directionalized flow of the metal due to the pressure created by electromagnetic force suflicient to permit utilization thereof for commercially conveying the molten metal upwardly out 21f the molten metal bath to another desired loca- Referring principally to Figure 2 which shows a cross section of a portion of a secondary loop made up of molten metal within the passageways or channels 1, 8, II], II and the portion of the molten bath lying between the channels 7 and 8, it is apparent from elementary electromagnetic principles that when current flows in the primary loop a current is induced in the secondary loop. It is also apparent that inasmuch as the molten metal constitutes a single closed turn of conductor about the metal core 4 that the current flowing through the molten metal will be many times that of the primary and, in the secondary loop shown, the entire current must pass through the central channel or passageway ll. The quantity of current flowing being large, every portion of the metal occupying passageway M will be subjected to relatively high current density.

Since conductors carrying currents in the same general direction are heavily attracted toward each other, and considering the molten metal in the channels comprising the secondary loop as made up of a large number of tubes of molten metal each being an independent conductor, it is seen that each of these tubes is pinched or squeezed together by the current flowing through the secondary loop. This effect is more noticeable in confined passageways such as the channels l, 8, it, and l i The pressure within the molten metal located in the central channel it is increased over that in other portions of the secondary loop since the channel it carries currents induced by each of the windings 5 and 6 of the primary loop 6. The molten metal within the channel I I is also subjected to an additional force caused by its location between the windings of the primary coils. The repelling force of the current in a primary coil upon the sec ondary has a tendency to shift the line of highest pressure away from the fixed primary. Thus the forces in the metal surrounding the axis. The insertion of conduit I'I into the region of the mouth of the channel II, or into the channel II, serves to provide a path by which the pressure within the metal in the channel II may be relieved resulting in the flow of the metal from the channel into and through the conduit to an area of lower pressure. The pressure within the channel I I is sufficient to lift molten metal into the conduit and upwardly out of the molten metal bath where it may be conveyed through the conduit to a desired location.

While the forces acting on the metal are strongest in the central channel II, they are also present in the channels I and 8 and can be utilized in the same fashion either independently of or in conjunction with those in the central channel. For example, conduits maybe disposed in either or both of the channels I and 8 and molten metal pumped through such conduits.

To obtain the maximum lift from the pump it is believed preferable to insert the end of the conduit wholly within a region of high current density in the secondary loop, such as the channel I I, in a position so that the conduit displaces as small a portion of the secondary loop as is feasible. In other words, by inserting the conduit, the electrical conductivity of which will generally be lower than that of the molten metal, so that its end is surrounded by the molten metal in the secondary loop, the decrease incurrent flow through the secondary loop, due to the insertion of the conduit, is less than if the conduit were inserted so that it stopped off the mouth of the channel II.

In the embodiment of the invention shown in Figs. 3, 4 and 5, the pump is illustrated as being installed in the subhearth or charging compartment of a divided hearth reverberatory furnace, such as is used in the smelting of aluminum. Only a portion of the main hearth is shown, and this is indicated by the numeral 2| in Fig. 4. The main hearth may be enclosed by suitable refractory side walls (one of which is indicated by the numeral 22). Suitable burners (not shown) may be provided to introduce fuel for heating the molten metal bath in the main portion of the furnace with a flue or flues to lead combustion gases from the furnace. The side wall 22 is provided with apertures 23 and 24 7 into the hearth 25 and extend between the hearth and a lower horizontal channel 3I. Entwined with the double rectangle formed by the secondary loop is a core 32 in the shape of a rectangle having primary windings 33 and 34 disposed around the legs of the rectangle which extend through the double rectangle of the secondary loop as in the form of pump disclosed in Figs. 1 and 2. The side walls of the channels of the secondary loop may be provided with a lining of a suitable refractory material 35 having a layer of insulating material 36 disposed exteriorly 8 thereof and a suitable housing 31 incasing the insulating material.

In this form of the invention the three legs 21, 28 and of the secondary loop are disposed at an acute angle to the vertical. A suitable conduit 38 is disposed at the junction of the central channel 30 and the hearth and has a passage 40 therethrough for the molten metal. The passage 40 is disposed at an acute angle to the vertical and tapers outwardly as it extends upwardly. to a point above the normal level of the molten metal bath. The conduit 38 merges at its top with a dividing wall 4| which extends across the open compartment from the side wall 22 of the main hearth 2| to the side wall 26 of the open compartment. A suitable pouring lip or spout 42 is provided at the end of the passage 10 of the conduit 38, so that the metal being conveyed upwardly through the passage 40 will leave the conduit 38 and pass over the wall 4| into the open compartment. The conduit 38 is indicated as being formed of a refractory material having a melting point higher than that of the metal to be melted, so that it will resist deleterious attack by the molten metal. Since suitable refractory materials such as silicon carbide are generally not considered relatively good conductors of electricity, inserts 43 may be provided at the intake end of the conduit 38, which are made of a material having relatively high conductivity. These inserts 43 are shown in Figs. 3 and 4 and serve to minimize the decrease in the flow of current through the secondary loop caused by the insertion of the conduit 38 into the secondary loop. The inserts could be made, for example, of graphite or of a metal having a melting point higher than the metal in the molten metal bath and preferably a metal which will not be deletriously affected by such molten metal.

The embodiment of the invention shown in Figs. 3 and 4 may be utilized in the smelting of metal withextremely beneficial results. In a divided hearth reverberatory furnace such as shown in Figs. 3 and 4 the open compartment may be used for the purpose of charging the furnace and, when the metal to be melted becomes molten, it will be in communication with and flow through the passage 24 into the main hearth of the furnace. For example in the smelting of aluminum, aluminum scrap or ingots may be charged to the open compartment where simultaneously with the charging of the metal the metal to be melted may be covered with a stream of molten metal pumped through the passage 40 of the conduit 38 out of the spout 42. Thus the metal to be melted will be immersed very rapidly, reducing oxidation of the metal during the melting process and providing a very rapid rate of heat flow to the metal to be mefted. As the metal becomes molten and flows into the main furnace, the circulation of the metal will assist in creating homogeneity of the molten metal bath. The metal in the main furnace may be tapped and withdrawn for useor may be pumped therefrom by the use of the same or another pump embodying the present invention installed in the main furnace.

Fig. 6 indicates another modification of a pump embodying the present invention. In this instance the core 50 of the transformer assembly is in the shape of a double rectangle composed of laminated sections intertwined with a single rectangular secondary loop composed of the vertical channels SI and 52, the horizontal bottom channel 53 and a portion of the molten metal bath disposed in a hearth 54 in the region between the openings of channels and 52 into the hearth 54. The leg of the double rectangular core 50 which passes between the channels 5! and 52 is provided with a primary winding 55. A conduit 56 may be disposed with its extremity positioned in the mouth of either or both of the vertical channels 5! and 52.

While the present invention has been illustrated in connection with a transformer assembly similar to that used in a submerged resistor type induction furnace, it is to be understood that the pressures resulting in the molten metal from the electrical forces may be obtained by other methods. For example, the flowing of suflicient current through a channel or a constricted portion of a molten metal bath to create a region in which the molten metal is subjected to a high current density will create pressure and thus cause the flow of molten metal into and through a suitably disposed conduit. The present invention is therefore not limited in scope to the use of a transformer assembly similar to that used in a submerged resistor type induction furnace to create by electrical means the desired pressure within the molten metal to accomplish pumping of molten metal.

A pump embodying the present invention may be used to convey molten metal from the molten metal bath through a conduit directly to a mold or a die or to a container provided with multiple sprues leading to a plurality of molds or dies. The molten metal may also be transferred by such a pump to another location where additional work may be carried out with or on the metal.

A pump comprising the present invention is highly advantageous and susceptible to many uses. The molten metal withdrawn is substantially homogeneous, due to the circulation created in the molten metal bath. Further, the metal withdrawn is relatively free from impurities and while being conveyed is not subjected to oxidation, since it is pumped from below the surface of the molten metal bath and is conveyed in a closed conduit.

Molten metal may be pumped to a point for use and will arrive at a temperature closely corresponding to that within the molten metal bath. In this connection it may be desired to insulate the conduit or to provide a means for heating the conduit to maintain the metal conveyed therethrough at a uniform temperature. It has sometimes been necessary to overheat the moten metal because of loss of heat occurring while transferring the molten metal in open conduits or containers. In casting processes the use of the present invention permits drawing the metal directly from the molten bath and introducing it at a substantially uniform temperature into molds or dies.

It will be understood that the foregoing description is not intended to limit the present invention.

What we claim is:

1. A pump for molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop, a secondary loop of said transformer assembly at least a portion of which comprises a channel of molten metal, a molten metal bath in communication with said channel, and a conduit having one end disposed in communication with said channel and positioned to receive molten metal from said channel and convey it upwardly to a point above the molten metal bath when current is supplied to said primary loop.

2. A. pump for conveying an electrically conductive molten metal which comprises a primary loop of a transformer assembly, means for supplyin current to the primary loop, a secondary loop of the transformer assembly formed of a conductor, at least a portion of said conductor comprising a channel containing molten metal in a region of high current density, means for feeding molten metal to said channel, and a conduit having one end disposed adjacent said region of high current density and in communication with the molten metal therein to receive, lead upwardly and convey molten metal away from said secondary loop.

3. A pump for molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop, a secondary loop of said transformer assembly, at least a portion of which comprises a channel of molten metal in communication with a molten metal bath, and a conduit having one open end disposed in communication with the opposite end of said channel for receiving molten metal and conveying it upwardly to a point. outside of the molten metal bath when current is applied to said primary loop.

4. A pump for molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop, a secondary loop of a transformer assembly, at least a portion of which comprises a molten metal bath and a channel of molten metal in communication therewith, and a conduit communicating with said secondary loop and forming a continuation of said channel of molten metal in position to receive, lead upwardly and convey molten metal from said secondary loop, the side wall portions of said conduit in the region of the secondary p havin the capacity of conducting electricity.

5. A pump for lifting and conveying molten metal from a bath of molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop, a secondary loop of said transformer assembly entwined with said primary loop, at least a portion of said secondary loop comprising a molten metal bath and a channel of molten metal having at least one of its ends in communication with the molten metal bath and disposed beneath the surface of said bath, and a conduit forming a continuation of said channel, said conduit being surrounded by the molten metal in said molten metal bath and being .in position to receive, lead upwardly and convey molten metal from said channel to a point above said molten metal bath.

6. A pump for lifting and conveying molten metal from a bath of molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop, a series of channels disposed beneath said molten metal bath and entwined with said primary loop, said channels being connected together and in communication with said bath to form at least a portion of a secondary loop of the transformer assembly, and a conduit depending into said bath and having one end communicating with one of said channels in a region of high current density to receive and convey molten metal to a point above the molten metal bath.

'7. A pump for lifting and conveying molten metal from a bath of molten metal which comprises a primary loop of a transformer assembly, means for supplying current to said primary loop,

. coil.

both of said series, and a conduit depending into said bath with an end in communication with said common channel to receive and convey molten metal to a point above the molten metal bath.

8. A pump for molten metal which comprises a rectangular core member, a primary transformer coil disposed around a portion of said coremember, a secondary loop formed of a conductor, at least a portion of said secondary loop comprising a channel of molten metal in communication with a source of supply of molten metal, and a conduit having one end opening into the secondary loop to receive, lead upwardly and convey molten metal when current is supplied to 9. An electromagnetic induction pump for mol ten metal comprising a receptacle to hold a molten metal bath, a transformer assembly located in a restricted section of said bath to induce current in said section, to thereby hold the metal in the molten state and to superimpose in said restricted bath section an. electromagnetic pressure upon the hydraulic bath pressure, a refractory tube reaching with the one end into said restricted section of superimposed pressure and leading with its other end into a location which is substantially free from said superimposed pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into said restricted section of superimposed pressure to said location substantially free from superimposed pressure.

10. An electromagnetic induction pump for molten metal comprising a receptacle to hold a molten metal bath, a transformer assembly located in a restricted lower section of said bath to induce current in said section, to thereby hold the metal in the molten state and to superimpose in said restricted lower bath section an electromagnetic pressure upon the hydraulic bath pressure, a refractory tube reaching with the one end into said lower restricted section of superimposed pressure and leading with its other end into a location which is situated outside of the receptacle, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into said restricted ,lower section of superimposed pressure to said location situated outside of the receptacle.

11. An electromagnetic induction pump for molten metal comprising a receptacle and a secondary melting loop to hold a molten metal bath, a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pres-. sure upon the hydraulic bath pressure, a refractory tube reaching with the one end into the proximity of said secondary melting loop and leading with its other end into a locationwhich is substantially free from said superimposed pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into the proximity of said secondary melting loop to said said primary location substantially free from superimposed pressure. I

12. An electromagnetic induction pump for molten metal comprising a receptacle to hold a molten metal bath, a transformer assembly located in a restricted lower section of said bath to induce current in said section, to thereby hold the metal in the molten state and to superimpose in said restricted lower bath section an electromagnetic pressure upon the hydraulic bath pressure, a refractory current conductive tube reaching with the one end into said lower restricted section of superimposed pressure and leading with its other end into a location which is substantially free from said superimposed pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into said restricted lower section of superimposed pressure to said location substantially free from superimposed pressure.

13. An electromagnetic induction pump for molten metal comprising a receptacle and a secondary melting loop to hold a molten metal bath, the said melting loop consistent of a channel spaced from said receptacle and three channels including one center channel and two lateral channels connecting said spaced channel with said receptacle, a transformer assembly to induce current in said secondary melting loop, to hold the metal in the molten state and to superimpose in said melting loop an electromagnetic pressure upon the hydraulic bath pressure, a refractory tube reaching with the one end into said center channel and leading with its other end into a location which is substantially free from said superimposed pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from said center channel to said location substantially free from superimposed pressure.

14. In an induction furnace having a hearth, a secondary melting loop opening into said hearth, at least one primary transformer assembly threading said loop and adapted to hold a metal charge in the molten state, a refractory tube located with the one end in communication with an opening of the melting loop and being elevated with the other end above the floor of the hearth.

15. In an induction furnace having a hearth, a secondary melting loop opening into. said hearth, at least one primary transformer assembly threading said loop and adapted to hold a metal charge in the molten state, a refractory current conductive tube located with the one end in communication with an opening of the melting loop and being elevated with the other end above the floor of the hearth.

, 16. In an induction furnace chambers for holding metal, a secondary loop com-posed of melting channels, at least one primary transformer unit threading the said secondary melting loop, an inclined refractory tube connected with its one end to an outlet of the melting loop into achamber and extending with the other end into a section of said chamber which is substantially free from the influence of the electromagnetic fields. 1'7. In an induction furnace a chamber for holding molten metals, a secondary loop composed of melting channels, at least one primary transformer unit threading the said secondary melting loop, an inclined refractory tube connected with its one end to an outlet of the melting loop into a chamber and extending with the other 11 end into a section of said chamber which is substantially free from the influence of the electromagnetic fields.

18. A submerged resistor type induction furnace comprising an upper hearth, a secondary duct system located below said upper hearth, said duct system consisting of a substantially horizontal bottom duct and a plurality of adjoining ducts extending between said upper hearth and said bottom duct, a primary current inducing transformer assembly associated with said ducts for inducing an electrical current to flow through said upper hearth and said duct system in series, a refractory tube inserted in said upper hearth and forming an extension of one of said adjoining ducts in such a manner as tointerrupt fluid flow therefrom into the upper hearth, said tube extending to a point outside of said upper hearth and above said vertical ducts.

19. A submerged resistor type induction furnace comprising an upper hearth, a secondary duct system located below said upper hearth, said duct system being composed ofa substantially horizontal bottom duct and a center and two lateral adjoining ducts extending between the upper hearth and said bottom duct, a primary current inducing transformer assembly associated with said ducts for inducing an electrical current to flow around loops extending through said upper hearth and said ducts, a refractory tube disposed in said upper hearth in communication with said center duct in such manner as to prevent fluid flow from the center duct into the upper hearth, said tube extending from said center duct to a' point outside of said hearth and above the upper end of said center duct.

20. The method of pumping molten metal from a hearth having a secondary duct system communicating therewith adjacent the bottom thereof and a primary transformer coil for inducing an electric current through molten metal in said hearth and said duct system, comprising maintaining in said hearth a refractory tube in communication at one end with said duct system and extending away from the duct system, and energizing said primary transformer coil to induce a current in said duct system and thereby create an electromagnetically induced pressure superimposed on the hydraulic bath pressure in said duct .system, whereby metal is caused to flow through said tube away from the region of superimposed pressure. I

21. The method of pumping molten metal from a hearth having a secondary duct system communicating therewith adjacent the bottom thereof and a primary transformer coil for inducing an electric current through molten metal in said hearth and said duct system, comprising maintaining in said hearth a refractory tube in communication at one end with said duct system and extending upwardly away from the duct system,

munlcating therewith adjacent the bottom thereof and a primary transformer coil for inducing an electric current through molten metal in said hearth and said duct system, comprising maintaining in said hearth a refractory tube in comsome metal level in the hearth, and energizing said primary transformer coil to induce a current in said duct system and thereby create an electromagnetically induced pressure superimposed on the hydraulic bath pressure in said duct system, whereby metal is caused to flow upwardly through said tube from the region ofsuperimposed pressure.

23. The method of pumping molten metal from a hearth having a secondary duct system communicating therewith adjacent the bottom thereof and a primary transformer coil for inducing an electric current through molten metal in said hearth and said duct system, comprising maintaining in said hearth a refractory tube in communication at one end with said duct system and extending upwardly and out of said hearth, and energizing said primary transformer coil to induce a current in said duct system and thereby superimpose an electromagnetically induced pressure upon the hydraulic bath pressure in said duct system, whereby metal is caused to flow through said tube from the region of superimposed pressure.

24. The method of pumping molten metal from a hearth having a secondary duct system communicating therewith adjacent the bottom thereof and a primary transformer coil for inducing an electric current through molten metal in said hearth and said duct system, comprisin maintaining in said hearth a refractory tube having an electrically conductive end portion connected to said duct system and its opposite end disposed in a region remote from the duct system, and energizing said primary transformer coil to induce a current in said duct system and thereby superimpose an electromagnetically induced pressure upon the hydraulic bath pressure in said duct system/whereby metal is caused to flow through said tube from the region of superimposed pressure.

25. The method of pumping molten metal from a hearth having a secondary duct system communicating therewith adjacent the bottom thereof and a primary transformer coil for inducingan electric current through molten metal in said hearth and said duct system, comprising maintaining in said hearth an upwardly extending refractory tube having an electrically conductive end portion connected to said duct system and its opposite end disposed outside of said hearth, and energizing said primary transformer coil to induce a current in said duct system and thereby create an electromagnetically induced pressure superimposed on the hydraulic bath pressure in said duct system, whereby metal is caused to flow through said tube from the region of superimposed pressure.

WALTER M. WElL.

WALTER BONSACK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,602 Tama Feb. 13, 1945 2,339,964 Tama Jan. 25, 1944 2,381,523 Tama et al. Aug. 7, 1945 FOREIGN PATENTS Number Country Date 126,947 Great Britain of 1919

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