US1639340A

US1639340A - Combination induction furnace

Info

Publication number: US1639340A
Application number: US740034A
Authority: US
Inventors: Albert E Greene
Original assignee: Individual
Current assignee: Individual
Priority date: 1913-01-03
Filing date: 1913-01-03
Publication date: 1927-08-16
Anticipated expiration: 1944-08-16

Description

4 2 Sheets-Sheet 1 A E GREENE COMBINATION INDUCTION FURNACE Original Filed Jan; 5, 1913 A. E. GREENE Aug. 16, 1927. 1,639,340

COMBINATION INDUCTION FURNACE Original Filed Jan. 5, 1912, 2 Sheets-Sheet 2 lNVENTOR Patented Aug 16, 1927.

UNETED sraras lease .ALnnnT n. GREENE, or SEATTLE, WASHINGTON.

CQMBINATION INDUCTION FURNACE.

Application filed January 1913, SerialNo. 740,034. Renewed December 19, 1917. Serial No, 207,966.

My present invention relates to improvements in electrical induction furnaces and combination transformer furnaces.

It has. been suggested heretofore to combine the induction heating principle of heat-' ing melted metal with some other form of resistance heating to supply additional heat in local parts of the furnace. My present invention provides a; very simple and'novcl means of obtainingcurrent for an are or other'resistance heating circuit in combination with means for inducing current in a single turn secondary circuit of an induction furnace, without the use of a separate transformer or a special secondary winding on the induction furnace. contemplates a process and-apparatus for heating a bath of molten metal by current induced therein by means of a magnetic core encircling said bath, the core being magnetized by current in a primary winding; and it further contemplates a'process.

and apparatus for generating heat independently of the induction current heating, and of connecting asuitable number of turns of portions of the primary winding on said transformer core in series with anare or with electrodes, or with some other form of electricalresistanceto heat the charge.

One object of my invention is a combina tion transformer and electric furnace, the transformer of which constitutes an auto transformer whereby the apparatus may be connected to a standard voltage power circuit and at thesame time a desired proportion of the winding may be connected to an electrode circuit for generating heat in an are or other resistance,

A further object of my invention is a combination auto-transformer and electric furnace having adjustable electrodes and means for varying the electrode voltage taken from the transformer winding. v A still further object of my invention is an apparatus combining an electric furnace and an auto-transformer suitable for operation from a comparatively constant voltage source of current, and means for regulating the number of turns of the transformer windingin series with the supply voltage, thereby regulating-*the induced single turn voltage, and also incertain-cases, regulatin the number of turns of the auto-transformed which are connected to the electrode circuit. One purpose of my 1nvent1on is to use My invention a single transformer core in combination with an electric furnace, and a primary winding on said core whereby current may be'induced in a single turn secondary circuit around thesame core, and rat the same time whereby current may be drawn from this primary winding, and led to an electrode circuit operating in the same furnace.

further InOdlfiCtLf/lOH Of my invention consists in a polyphase transformer core in- .combination with a furnace, and comprising windings on the core, one for each phase connected in star,fthe separate windings and of incle- One featureof my invention is the combination of a channel for holding molten metal encircling a magnetic core, and a. primary winding on the core with a portion thereof enlarged so thata heavy current, may be drawn from this portion of the winding by means of taps connecting this portion of the winding 'to electrodes or to some form of electrical resistance.

A further feature of my invention relates to the method of control of the voltage induccd in the induction furnace molten secondary circuit and the voltage-of the current tapped from the windings of the primary and led to some suitable electrical resistance. r

In one embodiment of my invent-ion poly- .phase current is applied to the primary windings on the magnetic core or cores for inducing currents in molten metal secondary circuits encircling said cores, portions of the primary windings being provided with additional cross-sectional area of copper and taps taken off these portions of the primary windings and connected in series with suitable resistance for generating heat.

These and other features of my invention will be described with reference to the anncxcd drawings.

Fig. 3 is a'diagrammatic plan view of a two-phase furnace embodying my invention and which is supplied with three-phase current.

Fig. 4 is a diagrammatic view of a threephase combination transformer furnace showing thetaps on the windings for obtaining different voltages between electrodes, and also different voltages between each electrode and the neutral point of the star connected auto transformer.

In Fig. 1 I have shown a furnace which is suitable for the reduction of ore and the heating of the, reduced metal in accordance withmy invention. A primary winding 1 is wound around a magnetic core 2 and is coir, nected to a source of supply of single phase alternating current. core is a refractory crucible with a channel 3 encircling this core for holdingthe single turn molten metal secondary circuit of the induction furnace. One portion of this channel is enlarged to form a pot '4 in which the ore is reduced and. melted. This pot is made in the crucible or bottom of a shaft which may be designed in any suitable way. Into the top of this shaft ex-" tends an electrode 5 and in the bottom line ing is an electrode 6. The primary winding is provided with a portion T which consists of a suitable number of turns of copper or other conductor shown in the drawmg as four complete turns. One terminal of the primary coil 1 is connected by meanspf the wire .8 to the source of supply of alternating current and this same terminal is also connected by means of the conductor 9 to the bottom electrode of the furnace. Taps are shown as taken off the four lower turns which constitute the heavy portion of the. primary winding and any. number .of these turns may beiconnected to the top electrode 5 by means of the switchlO. In

this way it. is possible to apply any desired voltage to the arc'furnace circuit between the bottom electrode 6 and the top electrode 5.

' to the switch 11 independently'of thevoltage lVhenthe primary coil 1 is connected to,

aiconstant voltage circuit, as for exampleyto a 5140 volt. line, I may by means of taps, any" oneofwhich may be connected to the switch;

11, vary" the potential inducedin-the molten metal secondary circuit. 1 The current in-.

duced in the molten metalconsequently may be controlled by means of the taps connectedv applied between the electrodes-5 and 6 thru the controlling switch 10,; As to the 'e;ra ct number of turns to be usedin each case, this Around the magnetic of some20 volts or more.

nest-3,340

forms no part of my invention since it is determined entirely by the several voltages which it isdesired to use in the induction current circuit and in the resistance circuit.

The are circuit may be of very high potential if desired, therefore requiring more turns on main pot, or shaft, or crucible, 4, themolten metal being kept heated to the desired temperature by the currents induced therein. The ore charged into the shaft 4 is heated by means of an arc and resistance heating from the top electrode to the bottom electrode, and as above stated, the power, and consequently the temperature developed in the two parts of the furnace, namely the resistance portion and the induction current portion, may be controlled and regulated separately and independently of each other. The electrode circuit is in no way dependent on the induction heating circuit. In fact, one feature of my invention is the combination of a transformer which maybe used to induce current in a secondary single turn heating circuit with means of controlling the proportion of it to electrodes or some form of I electrical resistance, without any limitation as to where the'electrode circuit be located.

-However, in the operation above described in the furnace of Fig. 1, it is. to be noted that the charge is first heated by means of current in the arc circuit from the top electrode 5 to the bottom electrode 6, the are terminating of course on the charge resting on the bottom of the crucible. After the charge is heated'and melted by theheat from thepar'c, the molten charge then enters the bath below and becomes a part of the induction circuit and has current induced therein. The development of heat in the molten bath is by means of a relatively low voltage current. I windings shown in Fig. 1, there are about 20 turns on the winding which can be connected to the 440 volt supplycircuit for example, thus inducing a single turn voltage Without making allowance for magnetic leakage, the single turn secondary induced voltage would be in the neighborhood of 20 volts; and if four of the twenty turns of the winding were connected to the electrodes the electrode voltage under the above conditions would be about volts. Under these conditions the arc circuit would serve to melt the charge with about an 80 volt arc circuit and then In the diagram of the the melted charge would have current induced in it at a much lower voltage. It is understood that any desired voltage may be applied to the arc circuit-and the are circuit may be of relatively high potential requiring more turns of the winding connected to it. F or example, if the supply circuit be 110 volts and a voltage of 130 volts isdesired for the arc circuit, then morev turns would be required on the winding for the arc circuit than would be required for the induced single turn secondary circuit.

Considering the transformer andeiectrode circuits shown in Fig. 1 independently of the secondary induction circuit, the transformer shown in this Fig. 1 connected to the arc circuit in fact constitutes an, auto-transformer by means of the connections with the supply circuit and with the electrodes. The number of windings connected between the supply lines may be varied by switch 11.

In the same manner the switch 10 controls heating chamber.

thenumber of windings connected to the" electrodes 5 and 6. The upper electrode is adjustable in elevation by means of the flexible suspension which passes over the pulley mounted on an axis shown inFig. 1, whereby the electrode may be raised or lowered. The lower electrode 6 passes thru the bottom of the electric furnace chamber so that its upper endwill be exposed in .positionto come in contact with the molten metal or other charge.

It will thus be seen that Fig. 1 shows an electric furnace. adaptedflto heat a charge by means of heat generated by the current from the electrodes 5 and 6 entering the The current is supplied to the electrodes by means of an auto transformer. By manipulating switch .10 or switch 11, or both, the potential between the electrodes may be varied in accordance with operating conditions;' or in other words'by way of example, if-thevoltage first tried is not high enough to force the desired current thru the resistance, obviously the voltage may be increased by means of the switches 10 or 11 or both and vice versa. Furthermore the upper electrode may be adjusted in elevation to vary the resistance between the electrodes 5 and 6 and thereby vary the currentflowing thru the electrodes. By means of the switch 11 the number of turns of the windings of the-transformer connected to the source of alternating current supply may be varied; and furthermore, the number of windings of the/transformer connected to the electrodes may be varied by the switch. 10. The switch 11' will vary the single turn induced voltage and the switch 10 will vary the number of turns connected to the electrodes. Obviously the switch 11 willvary,

the voltage applied to the electrodesfor anygiven connection of switch 10- In Fig. 2 is shown a polyphase autotransformer which is arranged to supply current to a plurality of electrodes entering the heating chamber. By supplying each of the separate windings shown in Fig. 2 with switches similar to those indicated at 10 and 11 in Fig.1, the electrodes shown in Fig. 2,

at 25, 26 and 27 may be connected to'the' '17 and. interconnected passages '29, 30 and 31 corresponding to the induction circuit 3 of Fig. 1, the' polyphase auto-transformer and electrode circuits will operate entirely independently of the induction circuits.

In Fig. 3 Ihave shown two

magnetic cores

40, 40 each with windings thereon toconstitute auto-transformers. ings areconnected to a source of alternating current, indicated at 14. The

windings

42 and 43 are connected to three elec trodes 48, A) and 50, two of which enter the heating chamber from above, and that designated entering the heating chamber thru one of its upright walls or thru the bottom in a.manner similar to that indicated at 6 in Fig. 1. The two

separate windings

42 and 43 are interconnected to separate phases of a polyphase' supply circuit.

These wind- However, when the furnace of Fig. 3 is operated as an arc induction furnace, the

arc circuit and the induction circuit are energized from the same transformer and they .arealso in this Fig. 3energized from the same winding, on a magnetic core attached to the, furnace In other words Flg. 3 shows an induction arc furnace com prising a plurality of magnetic cores and seconda' k channels in refractory material surroun ingeach core. Eachcore has a primary winding thereon and the induction channels connect-- with the main chamber into which;.-tlie electrodes project. In fact both-the arrangement shown in Fig. 2 and the arrangement shown in Fig. 3, both include an arc induction furnace operating from a three phase supply circuit and each furnace comprises a ,plurality of magnetic cores withwindings on each core connected to the electrodes which enter the furnace and arranged so that current will be in duced inthe molten metal secondary cirper electrode 5. By means of these sets of taps and the switches 10 and 11 the ratio of the voltage applied to the electrodes and 6 to the voltage applied to the winding 1 from the source of supply may be regulated. lVhen the transformer winding 1 is energized so that a given voltage is generated in such winding any given proportion of this total transformer voltage may be applied to the electrodes 5 and 6 by connecting the switch to the desired tap of those taps connected to the heavier portion of the windings 7 tion.

By means of the switch 11 and the taps associated therewith it is possible to apply the given supply line voltage either to the whole winding 1 or the supply line voltage may be applied to the desired proportion of the winding 1. Thus itis possible to vary and control the voltage of, the transformer winding within the limits of the apparatus.

The inherent regulation of the transformer. will depend upon its design, If there be considerable leakage of magnetic flux there may be a lowering of the induced voltage applied to the electrode circuit, as the current thru the electrode circuit increases. This drop involtage may be augmented or oil-set by the independent means of voltage control by means of the taps on the windings. Thus when the upper electrode 5'is lowered and the. current thru it increases, the voltage betweenv the electrodes 5 and 6 will drop due to the inherent reactance and resistance ,of the transformer circuits but the electrode voltage may be regulated independently of this drop by means of the switches 10 and 11 or either of them. Thus, for example, if the inherent re'actance of the transformer is high, and a heating is largely by resistance.

given voltage is applied across the electrodes 5 and 6 and this voltage is found to be'too low to force the desired currentthrn the. resistance, then the electrode voltage may be raised by means of the switches 11 or 10. i

The arrangements shownin the drawings provide for regulation of the voltage so that eithera high voltage or a .low voltage are may be used, or the voltage on the elec trode circuit may be made so low that/the An arc of suitable voltage may be used in one stage,

fonexample inm elting the charge in the shaft of the furnace of Fig. 1, and then after the charge is melted it may be kept heated or further heated by means of low voltage current thru it as a resistor.

Fig. 2 shows a 'polyphase arc electric furnace comprising a plurality of arcing electrodes and when the auto=transfo rmers as shown in this view are supplied'with switches corresponding to those indi'catedat l0 and 1 1 inFig. 1,;the cnrrentor voltage ,which are of larger cross sec-' of any one are maybe regulated as already described with regard to Fig. 1. In fact the voltage supplied to any one electrode may be regulated by the switch in the circuit to that electrode.

Ina furnace in which the induction and are circuits are used simultaneously it may be necessary to use both sets of switches, one serving to control the induced single turn voltage and the other set to control the electrode voltage.

My invention may be applied in a 3 phase furnace as' shown in Fig. 2. A suitable core having three legs shown in plan at 15,

16 and 17 is provided and a primary windingor windings are shown as connected in star or Y and having a neutral or common connection 18 and three

terminals

19, 20 and 21 which go to the 8 phase source of power. The neutral connection is of suitably heavy cross sectional area to carry the heavy currents which may be drawn from the heavy portions of the three windings 22, 23 and 24, and the current taken from the taps on these windings may be led to electrodes 25, 26 and 27 between which the power may be applied in any desired way to heat the ore or to heat a bath of metal. The neutral wire 18 may also be connected .to a neutral bottom electrode 28 if desired.

The secondary channels holding the molten metal are shown at 29, and 31, encircling the several legs of the magnetic core and uniting in a main chamber 32.

In Fig. 2 the cores shown at 15, 16 and 17 are the vertical legsof a single polyphase v(in this case three-phase) magnetic core.

These vertical legs are connected together at the top andbottom to form the complete magnetic circuits, which encircle portions of the molten metal in the induction channels. It will be seen that the metal in channel 29 forms a part of a single turn circuit around core leg 15; likewise the metal in channel 30 forms part of a singleturn circuit around core leg 16; and also the metal 'in channel 31 formspart of a single turn eircuitaround core leg 17. l

It Wlll be seen that a vertical section through these vertical core legs and corresponding channels would show four sectionsof the channels,or in other words, a section of each of four different channels, this numher being one more than the number of vertical core legs. Fig. 4, shows approximately what such a vertical section would be like, and also shows the arrangement of the taps above mentioned in connection with the winding on each phase of the core.

It is understood that where I have re ferred to copper in this specification that I may use any suitable electrical conductor for carrying the current.

\Vith reference to the three phase furnace, shown in Fig. 2, and also in Fig. 4, it

other form of resistance heat.

connected togetherby a neutral connection neaas ro" 5 phase furnace may be operated as an arc furnace or as an induction furnace, or both methods of heating may be used together, and the heat developed in the arc circuits may be controlled as desired independently of heat developed in the induction circuits,

and likewise the development of heat in the "flinductioncurrent circuitsmay be controlled as desired independently of current through the are circuits.

V In the use of 3 phase current, the'primary windings may be connected in delta instead of star and the terminals from the heavy sections of the primary may be led to suitable electrodes for generating an are or The several voltages may be controlled independently of each other as shown in Fig. 1. My invention may be used in a 2 phase furnace, as shown in Fig. 3, having two separate cores 40 with prnnary WVlIldlIlgS thereon 42 and 43. In the furnace shown, the connections are arranged to take power from a 3 phase circuit 44 and to transform this in the electrical part of the furnace to 2 39 phase power. For this purpose the approximate center of the primary 42 is connected to one end of the primary 43 and the number of turns so connected are such as will give M the desired voltages in the secondary induction circuits of the furnace. The connection between the two coils is made ofga suitabl heavy conductor and a heavy portion of eac r winding is provided from'the two terminals of this connecting conductor 4.5.- From the 4) other terminals of these two portions 46 and.

tom of the lining of the furnace or as a bottom electrode. Thus there will be a current flow between the

electrodes

50 and 48, and 50 and 49, and also between the two electrodes 48 and 49.

In Fig. 4 I have shown a diagram of the windings and electrode circuits for a star connected 3 phase auto-transformer furnace combination. The three primary windings are shown at 51, 52 and 53 andthey are 54. Three movable electrodes are shown at 55,56 and. 57 adjustable in elevation-,and

these have conductors leading to switches so that the number of turns of the winding between the neutral and the connection to the electrode may be adjusted. This would be serve to conucchthe desired proportion of the total winding to the corresponding conductor of the power circuit and have shown three switches 11 for this purpose. Switches 10 serve to connect the taps desired to the three electrodes respectively. The bottom electrode 28 may be connected to the neutral connection 54 if desired. I

have shown also four sections, 115, 116, 117 and 118 which diagrammatically represent the sectionsof the metal in the single turn induction circuits similar to

sections

29, 30, 31 and 32 of Fig. 2 and have also shown back of the windings the general arrangement of the three-phase core having three vertical legs and connecting yokes above and beneath. This construction-of apparatus is very'inexpensive to construct and is efiicient to operate and has very great advantagesover any other furnace apparatus heretofore used.

It'is understood that the several details of my invention may be applied in any combination ofthe methods described herein.

It is also understood that I do not limit myself to'making the separate heating circuit of less or greater voltage than the sup ply circuit.

The term are circuit as used in this specification and claims is intended to include any circuit in which the current passes to the charge through an electrode as well as circuits in which the arc constitutes the essential resistance and is not limited to the formation of an are above the charge, sincewhen an electrode makes contact with a slag or other charge it may happen that no visible arc is formed, yet the term arc circult is intended to include such a circuit.

One of the important advantages of my present invention is that it provides an apparatus which will serve as an induction furnace to heat a single turn secondary circuit and at the same time current may be transformed in the same apparatus and used in an independent electric, heating circuit. Thus where before my invention it was customary to provide a transformer tosupply current to electrodes and an independent transformer to supply current to the single turn induction circuit, my presentinvention makes it possible to use the transforn'ier ofthe induction furnace to supply both circuits and yet control either separately and independently of the other. In other words the two separate circuits are energized from the same transformer.

While I have described the heating and melting and reduction of a charge of ere, it is to be'unders'tood that my invention is notby any means limited to such use but may be applied for heating ormelting any kind of material or metal within the limits of the apparatus. I have used the term resistance to include arc circuits;

The determination of the proper voltage to use between electrodes of the electrode circuit is a matter dependent on the particular treatment desired, and the range of voltage to be used may be from a very high are volt age down to practically nothing, and includes very lOW are voltages. The voltage may be so low across the electrodes as to avoid much of any arcing. The useof a low voltage in the treatment of metal is described in my copending application for patent Serial No. 20,336 filed J an. 2, 1909.

I claim:

1. In an electric furnace, the combination of a channel for holding molten metal encircling a magnetic core, a primary w nding thereon, meanso'f connecting this Winding to a source of alternating current power, and means of connecting portions of the Winding to an arc circuit for generating heatin the furnace.

2. In an. electric induction furnace, the combination of a channel forming a single turn secondary circuit, a core encircling same with a primary winding thereon, taps on the primary for connecting to electrodes the aortion of the primary between said taps eing made of suitable cross-section to carry heavy currents. I I

3. In a polyphase induction furnace, the combination of a plurality of secondary channels, magnetic cores encircling these channels with primary windings thereon, these windings'being interconnected to take polyphase current and provided with taps for supplying currents to an electrical arc circuit for generating additional heat.

4. In a polyphase induction furnace, the combinatio of secondary channels, cores encircling these with primary coils thereon, the primary coils being provided with suitable turns for carryin additional current and taps on these sections for taking current at the desired voltage to electrodes for additional heatin 5. In a electric induction furnace, the combination of a magnetic core and refractory channel encircling same, of a primary winding on the core, means of connecting a variable umber of turns to a source of alternating current, and independent means for connecting a variable number of turns to an electric arc circuit for generating additional heat in the furnace chamber.

6. In an electric induction furnace, the combination of a main chamber in refractory material having a channel communicating with the main chamber, a magnetic core encircling the channel, a primary winding on the core, a pair of electrodes entering said chamber. and adjustable means for connecting a suitable number of turns of the primary winding to said electrodes.

7. A combination electric furnace com prising a main chamber provided with an electrode for forming an arc to the charge therein and an electrode for completing the are circuit thru the charge, a channel in refractory material connecting with the main chamber, a magnetic core encircled by said channel, said core having a primary windingthereon, and independent means for connecting a suitable number of turns of the primary winding to a source of alternating current and to the said electrodes respectively.

8. A combination electric furnace comprising a main chamber, a shaft above the same, a channel in refractory material connecting with said main chamber, an electrode entering said shaftand an electrode for contacting with the charge and completing the are circiut, means of inducing current in the metal in the refractory channel including a magnetic core having a primary winding thereon, means of connecting said primary winding to a source of alternating current, and means of connecting suitable portions of said winding to electrodes.

9. A combination electric furnace comprising an arc heating chamber an induction heating channel in refractory material connecting with said are chamber, a magnetic core encircled by said channel, a primary Winding on said core, an electrode entering the arc chamber thru' the roof thereof, an electrode in the hearth of said chamber, and means of connecting said electrodes to a suitable number of turns of said primary winding.

' 10. An electric furnace comprising a main chamber, an induction channel opening into said chamber and encircling a magnetic core, an electrode entering the main chamberfor generating heat therein, another electrode arranged for completing the arc circuit thru said first electrode, a primary winding on the magnetic. core for magnetizing same, said winding and core comprising an auto transformer having terminals which may be tapped onto the electrodes of the are circuit.

ll. An electric furnace comprising a magnetic core, and a primary winding thereon constituting an auto-transformer, a single turn molten metal secondary circuit for heating the charge, and means of taking current from the primary winding and gencrating additional heat in an arc circuit in proximity to the charge.

12. The combination of an electric furnacc having an arc. heating chamber with electrodes entering therein, an induction heating channel magnetic core encircling said induction channel, a prin'iary winding on said core coust'ituting an auto transformer for supplymg current to the electric arc circuit, and means of control ccusistiug of independent means for varying the number of turns of the primary winding connected to the supconnecting therewith, a

ply circuit and ,thenumbe'r of turns of said winding'connected to the electrodes, there by independently controlling the current induced in the molten metal and the current thru the arc circuit.

13. A combination are and induction furnace in which the arccircuiband the induction circuit are energized from the same primary Winding on a magnetic core attached to said furnace.

14:. Pin-induction arc furnacecomprising a plurality of magnetic cores, secondary channels in refractory material surrounding each core, primary windings on said cores, a main chamber with which said channels connect, a polyphase supply circuit, means of connecting the separate windings to separate phases of said polyphase supply circuit, means for connecting electrodes in circuit with the windingson said cores, said electrodes entering said main chamber, and means for controlling the voltage applied to the electrode circuit as desire g 15. An induction furnace for operation from a three phase supply circuit, said furnace comprising-a plurality. of magnetic...

cores,-windings on each. of said cores, means for interconnecting said windings to a three phase supply circuit, means for connecting three electrodes entering said furnace to said windings, and means for inducing current in a molten metal secondary circuit in combination with said furnace.

16. The combination with an electric furnace comprising a chamber with electrodes entering the same, of a magnetic core, a winding thereon, a channel encircling said core for containing molten metal, and means of connecting the said winding-to said elec-' trodes, and means of connecting said wind-- ing to a source of alternating current.

17. A. combination are and induction furnace comprising an are or resistance, chaniber, an induction channel connected to and communicating with said chamber, and means for melting charge in the arc chamber and causing it to enter said channel and have current induced therein, and means for varying theelectric energy developed in the arc chamber and in the induction circuit in dependently. 18. T he method of operating an induction arc' furnace having two ma 'netic cores which consists in so connecting the primary windings. to a three phase current supply as to keep the three phase load balanced while transforming to twophase in the secondary channels, and when desired, connecting three electrodes to the windings and operating by. auto transformer.

19. An electric induction furnace comprising a transformer core, a primary winding thereon, a channel in refractory material oncircling said core for containing a molten charge therein. said electrodes being connected to a winding on said transformer core, and means for operating either the electrode circuit or the ,induction circuit separately or together as desired.

20. An nduction furnace comprising a plurality of magnetic cores, secondary chan nels in refractory material respectively surrounding said cores, primary windings on said cores respectively for magnetizing them, a main chamber for holding a charge, said chamber connected with said channels, means for connecting the separate windings to separate phases of a polyphase circuit, means for connecting an electrode in circuit with windings on each of said cores, means for. supporting said electrodes in position to enter the main chamber for generating heat in the charge therein. and means for con trolling the voltage induced in the separate circuits of the furnace.

21. An induction furnace for operation froina three phase-power circuit,--said furnace comprising two magnetic cores, a primary winding on each core, means for interconnecting said primary windings to a threephase circuit, means for connecting three electrodes to the respective windings on the said two magnetic cores. means for supporting electrodes to enter the main chamber, induction channels connected with the main chamber and respectively encircling the said cores, and means for passing three phase current thru the electrodes into the charge in the main chamber at the desired voltage between the electrodes.

22. An induction arc furnace comprising a main chamber, a plurality of magnetic cores. primary windings thereon, channels in refractory material encircling said cores and connecting with the main chamber, means for connecting the windings on the separate cores to separate phases of a polyphasc power circuit, electrodes mounted .in position to enter said chamber, and means for effecting the generation of heat in said main chamber by passing current thru said electrodes from the windings on said magnetic cores.

23. In combination, in an electric induction furnace, a single turn secondary heating circuit around the core of'said furnace. an electrode circuit taking current from a winding on said core, and iudcpcmhmt means for regulating the single turn voltage and the electrode voltage.

24. In combination, in an electric induc tion furnacc,.a single turn secondary heating circuit around the core of said furnace, and an electrode circuit, com rising one or more movable electrodes entering ,the chamber of said furnace and means for regulating the voltage applied to the electrode circuit from a winding on said core.

25. In an electric induction furnace, the

combination of three separate interconnected ings each having taps, and means of connecting the desired number of turns of each winding in star between the three conductors of a three phase supply system, whereby the single turn induced voltage may be regulated. 1

27. In combination, a three phase induction furnace comprising a three phase magnetic core having three legs extending thru corresponding single turn secondary heating circuits, the ends of said three legs being connected together to complete the magnetic circuits, the number of the channel sections in the plane of the said extending legs being one more than the number of said extending legs.

28. A combination three phase induction furnace, con'iprising an elongated chamber for holding metal, four channels connecting therewith on one side thereof, the other ends of said channels having a common con necting channel thus forming three single turn circuits, a leg of a magnetic core extending thru each of said circuits, and Windings on each of said cores connected to a three phase system.

29. In combination, an arc and induction furnace comprising a main chamber, induction channels connecting therewithand encircling magnetic cores, adjustable electrodes entering said main chamber for heating charge therein, and means for supplying current at the desired voltage to said electrodesfrom windings on saI'l magnetic cores.

30. An electrode furnace comprising a refractory channel, arranged to hold molten metal, said metal constituting the secondary circuit of a transformer, a chamber associated with said channel and arranged to hold molten metal. and electric heating means in said chamber above the surface of the metal and actuated by said transformer.

3 An electric furnace comprising a refractory channel arranged to hold molten metal, said metal constituting the secondary circuit of a transformer, a chamber associated with said channel and constituting a continuation thereof, and arranged to hold circuit of a transformer, a chamber associ-- ated with said channel and constituting a continuation thereof and arranged to hold molten metal, the metal in the channel and in the chamber constituting a continuous circuit, and electric heating means in said chamber above the surface of the metal and actuated by said transformer. i

An electric induction furnace comprisin a main chamber, a loop channel communicating with said main chamber and adapted to receive molten metal from said main chamber, electrodes extending thru the top and bottom of the furnace for effecting heating in said main chamber, and transformer windings and connections for elfecting the energization of said magnetic core to induce current in the molten metal in said loop channel and for supplying current to said electrodes to effect heating in said main chamber.

34:. An electric induction furnaceccmprising a three phaset ansformer core, a winding on each phase of said core, taps on said Winding and adjustable means for connecting said windings in star connection to a three phase power circuit.

35.'The method of operating an induction furnace, said method consisting in supplying current from a winding on the transformer of said induction furnace to electrodes in a heating chamber, and controlling the electrode'voltage and the single turn transformer voltage independently of each other.

36. In an electric induction furnace the combination of a single turn secondary heating circuit of a transformer and an electrode heating circuit supplied with current from the same transformer, and means for con trolling the heating in said circuits separately and independently.

37. An electric induction furnace comprising a magnetic core, a winding on said core. an electrode circuit comprising electrodes entering a chamber of said furnace, and circuits and connections for supplying current to said electrode circuit from a winding on said core and for varying the electrode voltage.

38. In an electric induction furnace, the combination with a chamber for containing a charge of metal to be treated, of electrodes entering said chamber, channels adapted to contain molten metal communicating with said chamber and for induction of current therein, a magnetic core encircling one of said channels, and a winding on said core connected to said electrodes.

39. The process of trading charge in an aeeaaao electric furnace provided with top adjust able electrodes supplied with current from a variable voltage source, said process consisting insfirst subjecting the charge to heat from one or more arcs from saidelectrodes to the charge and subsequently heating the melted charge by means of a lower voltage voltage and current thru said charge, and regulating the current independent y.

v4'0. In combination, an electric furnace, two or more magnetic cores, windings there 011, means for connecting said windings to a source of alternatin current, and means for connecting said windings torthree elec-' trodes entering the chamber of said furnace. 41. In combination with a three electrode electric furnace, a polyphase supply'circuit,

an auto transformer comprlsing'two or more magnetic cores, windings thereon connected to said polyphase circuit, and connections from said windings to the said three electrodes.

42. In combination, an electric furnace, "a

. polyphase supply circuit, an auto transformer having two or more separate wind.-

lugs interconnected to separate phases of 'a po yphase' circuit, and means of connecting a plurality of electrodes to said windings.

43. In an electric arc furnace, the combination with a furnace chamber having refractory walls, of an arcresistor, an upper electrode adjustable in elevation and in position for melting and heating a charge in said chamber, and a variable voltagesource of power connected to said electrode to supply current thru said are resistor, and in dependent means of adjusting the voltage of the circuit supplying the current to said are circuit.

44. In an electric furnace. a plurality of arcingelectrodes, a source of polyphase current comprisinga plurality of transformer windings, a circuit connecting each of said windings to a corresponding electrode, said windings having a common or neutral connection, and means of adjusting thenumber "of turns of said windings connected between the common connection and each electrode.

45. A polyphase electric furnace comprising a heatin' chamber, three adjustable electrodes entermg said chamber for arcing to charge therein, a conducting bottom electrode extending thru-the hearth of said chamber and means for supplying a variable voltage between said adjustable electrodes and said bottom electrode, independently of I the ad'ustment of 'said electrodes.

46. n combination,jan induction furnace having a main chamber, two electrodes enterin said chamber thru the top and adjusta le in elevation, a bottom electrode thru the lining of'said chamber for making con-.

cores to said top electrodes and said bottom electrode. I 47. In combination, an electric furnace, two magnetic cores, windings thereon, means of connecting said windingsto a source of alternating current, and means of connecting saidwindings to three electrodes entering the chamber of said furnace, and single turn secondary heating circuits around said cores.

48. A polyphase induction furnace comprising a magnetic core and winding thereon for eaclrphase, anelectrode for each phase entering a chamber of said furnace, and means of connecting each electrode to a winding on each core respectively.

49. In an electric furnace structure, a crucible electric heating means therein, 'a metal holding conduit in communication with said crucible, a transformer in inductive relation to said conduit, a coil on said transformer, said coil provided with a multiplicity of taps, switchv connections to vary the active length of said coil, and other switch connections connected to said heating'means and arranged to independently vary'the uantity of electric energy supplied to the eating means in the crucible. 50. The process of treating metal in an electric furnace provided with a top adjustable electrode for arcing to the charge, said process consisting in supplying-current of comparatively high voltage to form the arc, form said electrode to the charge,cand subsequently heating the melted charge by charge in an electric furnace, said method consisting in subjecting the charge first to the action of a high voltage are and subse quently introducing a lower voltage current thru the molten charge, and regulating the current independently of the electrode volta maintaining a relatively high electrodii'voltage, maintaining arcs from the electrodes to e. 53. The'method of operating a polyphase electric furnace, said method consisting in the charge, and subsequently heating the melted metal by passing lower voltage-cur rent therethrn, and regulating the electrode voltage and current independently.

54.. In apparatus for treating metal by the use of an electric arc, the combination of a pair of electrodes, one of which is movable relatively to the other one, and means for delivering to said. electrodes when positioned for a relatively long are a given kilowatt load, and then substantially the same kilowatt load with reduced voltage and increased amperage' when the electrodesare positioned for a shorter arc.

In apparatus for treating metal by the use of an electric arc, the combination of a pair of electrodes, one of which is movarc type electric furnace, the combination with are electrodes of means for varying the amount of current through the metal bath while maintaining substantially the same k. w. load in theelectriccircuit.

57. In combination, an electric furnace, a plurality of arcing electrodes, a source of polyphase current, a plurality of transformer windings comprising primary and secondary circuits for each phase, a connection between each of said electrodes and a secondary windin and means of adjusting the number of turns of the primary windings connected to the source ofpower. I

58. In an electric furnace a three phase transformer having secondaryzcircuits connected to the electrodes of-said furnace and means of adjusting the number of primary turns in circuit between three conductors of v a three phase power supply circuit.

59. In an electricarc furnace the combina tion with a furnace having an adjustable top electrode for arcing to the charge and another electrode for completing the arc circuit, of a transformer having primary, and

secondary circuits, the secondary circuit be-,

ing connected to the electrodes, and means of adjusting the number of turns of the primary in circuit with the power supply.

60. Incombination with an electric furnace, an auto-transformer, a relatively constant voltage source of alternating current, means for connecting the desired number of turns of the auto-transformer to this current supply, and means including said autotra'nsformer for-varying the electrode volt-' age applied to the electrodes of the electric furnace.

61. In. combination with an electric arc furnace, a source of alternating current of relatively low voltage such as 440 volts or less, and an auto transformer having taps for varying the-voltage applied to the elec trodes'of said arofurnace. 62. In combination with an electric arc furnace, a source'of lowyoltage alternating former Ihaving current which voltage is near one of the voltages used on the electrodes, and an auto transformer connected to this low voltage alternating'current supply circuit for ad justing and varying the voltages applied to the electrodes.

63. In combination with an electric arc furnace, a source of alternating current for supplying power to the electrodes. an auto transformer having a winding connected to said alternating current supply and another winding connected to the electrodes and -means for applying different voltages-between the electrodes.

64. In combination with an electric arc furnace, a source of relatively low voltage alternating current for operating said are furnace, a polyphase auto transformer, means for connecting the primary windings of said auto transformer to the said supply and means for arranging the phases and windings so as to furnish difi'erent voltages to the electrodes of said are furnace. v

65. In combination, a three phase electric arc furnace having three electrodes adjust;- able in elevation, a source of low voltage alternating current supply, an auto "transrimary windings for con meeting to the, different phases of the three phase supply and having connections from windingsto the electrodes of said arc furmice, and means for changing the connections to change the voltage applied to the electrodes.

.66. In combination with an electric arc furnace. a source of alternating current supply, a magnetic-core and windings thereon for connection to the alternating current supply and tothe e'ectrodes of said arofurnace, means for connecting different taps to the supply or electrode circuits and said arrangement of windings on said core being such as to introduce magnetic leakage 1n more than normal amounts into the circuit supplying current to the electrodes.

67. In combination with an electric furnace, a source of alternating current power for supplying current to the terminals of said furnace, a booster transformer having a windingin ,series between a terminal of said furnace and the power supply circuit, and means of energizing the booster transformer.

68. In combination with an electric furnace, a source of alternating current power for supplying current to the terminals of said furnace. a transformer having a rela tively low voltage winding in series between the power supply circuit and a terminal of the furnace, and. means for connecting a winding on said transformer between the lines of said power supply circuit.

rent to said electrodes, a separate trans: former having a winding in series'between the supply circuit and an electrode and means for controlling the voltage induced in said transformer winding. v

70. In combination with an electric furnace having a plurality of electrodes, a source of alternating current power, a low voltage transformer secondary winding in series between each electrode of said furnace and a phase of said alternating current supply circuit and means for controlling the voltage induced in said secondary windings.

'71. In combination with an electric furnace, two separate induced voltages in circuit in series with each other and with the electrodes of said furnace, and means for controlling the relative direction of induced vollltage in one circuit with respect to the ot e 72. The combination with an electric furnace of meansfor supplying current to the terminals of said furnace thru an auto transformer, means for varying the induced voltage in the windings of said auto transformer and means for connecting the desired taps to the furnace terminals.

73. The combination with an electric furnace of a transformer supplying current to said furnace, a booster transformer having a winding in series between the power supply and the furnace, and means for connecting the booster transformer primary between the power supply lines for controlling the induced current.

74. In combination with an electric furnace. a source of alternating current power for supplying current to the terminals of said furnace, a booster transformer having a secondary winding inseries between the furv n'ace terminal and the power supply, and a primary winding for said booster, this latter connected so as to control the direction of the booster secondary to that of the supply circuit.

voltage in relation 75. In combination with the electrodes of an electric arc furnace, a transformer core, primary and secondary windings thereon, taps on saidwindings whereby a comparatively high voltage may be impressed on the secondary circuit for maintaining an arc, reactance in the secondary circuit, and taps on the windings for impressing a lower voltage on the secondary circuit to the electrodes.

76. The method of melting and refining metal in an electric furnace. which method consists in supplying current of comparatively. high voltage to the electrodes thru a reactance in the electrode circuit and maintaining an arc with said relatively high voltage.

77. The combination with an electric furnace having a plurality of electrodes, of a three phase transformer having both primary and secondary Windings'connected in star, both of said windings having series of taps whereby the voltage applied to the electrodes may be varie 78. In combination with the electrodes of anelectric furnace. a three phase transformer set having taps on the primary and secondary windings of each phase, means for connecting any given primary 'tap on each phase to the corresponding phase-of an alternating current supply circuit, and means for connecting any given tap on the secondary part of each phase to a corresponding electrode of said furnace to regulate the electrode to electrode voltage.

79. The combination ofan electric arc furnace, a three phase transformer system having secondary windings connected together in star and having a conductor leading from the neutral connection to the furnace bottom, and means for changing ,the connections to vary the secondary voltage on the electrodes.

. ALBERT E. GREENE.