US1832483A

US1832483A - Electric furnace

Info

Publication number: US1832483A
Application number: US555907A
Authority: US
Inventors: Albert E Greene
Original assignee: Individual
Current assignee: Individual
Priority date: 1919-09-08
Filing date: 1931-08-08
Publication date: 1931-11-17
Anticipated expiration: 1948-11-17

Description

NOV. 17, 1931. GREENE 1,832,483

ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet l ATTORNEYS Nov. 17, 1931. A. E. GREENE 1,832,483

ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet 2 INVENTOR (P y w M ATTORNEYj Nov. 17, 1931.

A. E. GREENE ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet 3 I w w 7 m6 L. L /03 /06 //0 M A L p /13 INVENTOR i.

BY I

ATTORNEYS Nov. 17, 1931. E G'REENE 1,832,483

ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet 4 V0 6 Va/ifs [NVENTOR ATTORNEYS Nov. 17, 1931.

A. E. GREENE ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet 5 INVENTOR ATTORNEYS Nov. 17, 1931. GREENE 1,832,483

ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet 6 INVENTOR ATTORNEY-5 Nov. 17, 1931. A. E GREENE 1,832,483

ELECTRIC FURNACE Original Filed Sept. 8. 1919 8 Sheets-Sheet '7 INVENTOR Maw ATTORNEYS Nov. 17, 193 Q A. E. GREENE 1,832,483

ELECTRIC FURNAC E Original Filed Sept. 8. 1919 8 Sheets-Sheet 8 agwr Z76- 27f g6? j Z63 gg 264 W A??? 26g 272 27a 4 L 5 ATTORNEY5 Patented Nov. 17, 1931 UNITED STATE$ ALBERT E.- GREENE, 01? MEDINA, WASHINGTON ELECTRIC FURNACE Original application filed September 8, 1919, Serial No. 322,298. Divided and this application filed August 8, 1931. Serial No. 555,907.

My present invention relates to electrical apparatus and the operation thereof for the maintenance and control of electric arcs for electric heating, and more particularly to 5 the operation and control of electric arc fur-.

naces for the treatment of metals and ores, and also to the control of the voltage of the arc circuits and to the control of the current through the arc circuits. This application is a division of my application for patent Se-.

rial No. 322,298, filed September 8, 1 919.

My invention consists partly in a process of current control and independent arc voltage control and the necessary apparatus therefor for electric furnaces. More particularly my invention consists in improvements in methods of connecting arc resistance circuits of electric furnaces for the more cilicient control of temperature and heat conditions.

One object of my invention is to provlde means of generating heat electrically in an electric heating chamber and to control the location of the heat generation, or in other 213 words to control the location of the major part of the resistance. My invention contemplates generating heat electrically in the resistance of an arc and in the resistance of the other material present. One object of go my invention is-to so localize and control the heat generation that undesirable temperatures which might vaporize or otherwise unduly heat the charge may be avoided. Thus in the heating of volatile metals, such as copper or manganese or any other metal where-the temperature may become excessive after the bath is melted, my invention provides means for generating heat in the resistance of the are or charge at low voltage, so that high voltage arcs may be avoided and also the detrimental effects of such high voltage arcs.

One object of my invention is to provide a furnace of the arc type having means of con- 4.; ducting the current through. the bottom of the furnace into the charge and through the bath. I prefer to use a type of conductor or electrode which extends through the bottom from the outside of the furnace to the inside of the furnace chamber, but

in certain instances I may construct the bottom of the furnace of material which, like magnesite, becomes conducting when heated up to a sufliciently high temperature, but I do not limit myself to the use of such material for I may construct the bottom lining out of silica-containing material which is largely non-conducting as far as electric furnace operation is concernedand then I rely on the special bottom electrode conductor extending through the bottom, which may be of steel for example.

My invention also relates to the method and means of controlling and supplying the current to the electric resistance circuit whether the circuit be largely or partly, or only in small amount an arcresistance circuit, and the object of my invention in this regard is to provide means for controlling the electrode holders in accordance with the requirements of the resistance circuit and also to provide means for the use and control ofreactance in the circuit, whereby thetendency toward undesirable short circuit effects may be limited and controlled.

My invention further contemplates improved methods of connecting the transformer windings in polyphase' arc furnace circuits, both the primary and also the secondary circuits, and also combinations of the two which are in effect both primary and secondary windings combined as an auto transformer.

My invention further contemplates the method of controlling the temperature which consists of using a high voltage across the electrode terminals during the stage of operation when high energy input is desired and then in another stage when a high voltage are would cause undesirable heating, my invention contemplates the use of a lower voltage across the electrode terminals at which lower voltage the current may be regulated as desired. Thus my invention provides means of utilizing conductors which lead to the furnace electrodes and which have a given current carrying capacity in such a manner as to increase the energy development in the furnace by increasing the voltage across the electrodes and thus the energy per unit of time or the power may be increased almost in proportion to the increase an voltage assuming the maximum current carrying capacity of the conductor is not exceeded.

Another feature of my invention relates to the control of the number of arcs in series for a given electrode terminal voltage and more particularly this phase of my invention contemplates applying a given electrode voltage across a single are from an electrode to the charge, and subsequently applying the same electrode imltage across more than one are in series, whereby the several arcs will divide the electrode voltage between them and each will be of less voltage than the voltage of the single are. My invention also contemplates improved means of carrying out the process of starting the heat with a given electrode voltage applied across one are during one stage and subsequently applied through two arcs in series, or through more than two arcs in series, during another stage. My invention also contemplates apparatus for carrying out this process of single and multiple arcs whereby a bottom electrode may be utilized for one stage of the process and cut out of circuit in another stage of the process; and in certain modifications my apparatus provides for using a top electrode I in the second stage in place of the bottom electrode, whereby an arc may be formed during one stage and may be made to carry current in series with another are in another stage.

I have found that high voltage arcs may be used to advantage in electric arc furnaces, but that after the furnace charge and chamber become sufliciently heated, there is danger of excessive and undesirable heating due to the long arc which results from a high volt age, and I have found that when it is important to maintain limited temperatures, for example in the melting or treating of volatile metals, then it is important to regulate and control the electrode voltage so as to operate with a lower voltage across the electrode terminals, and at this lower voltage the current may be regulated as desired: for example, a current of low voltage and high amperage may be utilized.

In general the regulation of the current is accomplished by the movement of the electrode in my present invention; the electrode is raised to increase the resistance and therefore to decrease the current; the electrode is lowered to increase the current. When the electrode is raised the arc is lengthened, and may be lengthened until the breaking distance of the arc is reached, beyond which point the arc breaks and ceases to exist. As long as there is an arc, the length of the arc is determined by the distance between the are terminals and this distance is manually or mechanically controlled by the move- -ment of the electrode with respect to the Lesaaes other terminal of the arc from this electrode; in other words the length of an arc is a factor which is controlled by the manual or other operation of the furnace electrodes. In my present invention the electrodes may be moved either by regulation with respect to the furnace proper by any suitable means such as a drum hoist or a rack and pinion, or by the movement of the furnace whereby the charge is moved from the end of the electrode to a greater or less distance, or by both of these means'in combination.

My invention may be carried out by the use of either single phase, or two phase, or three phase power circuits or by means of direct current. In three phase furnaces I may use three top movable electrodes and connect one phase between each top electrode and a corresponding bottom electrode which conducts the current through the furnace bottom into or out from the charge; and I may provide means for cutting out the bottom electrodes and generating the heat by passage of the current between the top electrodes only through arcs in series with each other.

This arrangement provides a relatively high are voltage in one stage, that is in the stage in which the electrode voltage is applied through a single arc, and then a lower voltage are by dividing the electrode voltage between two arcs in series.

Two phase current may be applied to a furnace with two top electrodes and a bottom electrode during one stage and between three top electrodes during another stage, whereby the voltage of a single phase is applied through two arcs in series in the last mentioned stage and each arc will be of lower voltage than when the voltage of a single phase is applied through a single arc.

Another object of my process of using higher voltage across the electrode terminals is to overcome any unusually or excessive resistance from the furnace charge, as for example, to overcome the resistance of the pieces of scrap metal, or to overcome the re sistance of a silica-containing slag which might freeze over or cover the metallic charge or the metallic contact in the bottom of the furnace. I have found it very advantageous to be able to increase the electrode voltage at will. Sometimes during the course of the heat, the temperature of the charge may drop and it is desirable to increase the voltage and operate at higher voltage until the charge is heated to the desired point. Sometimes a silica slag may cover the metal and if it happens to become chilled it may easily insulate the bottom electrode so thoroughly that forty or fifty volts will not cause any appreciable current to flow and then it is possible to raise the voltage to say 110 volts, which will usually be sufiicient to overcome any such resistance. Then again where a large amount of rustyscrap is charged into a furnace, a low voltage current will not pass. through the scrap and this is especially noticeable in furnaces of the induction type, .where the voltage may drop to as low as eight or ten volts, and this voltage is insufficient to cause the necessary current for melting the charge to pass through it, and then the high voltage is especially advantageous. In certain instances, I have utilized this method of starting the melting in an induction furnace and after the charge had become molten I'have used the low voltage of the induced current to advantage.

Another instance where my invention is especially advantageous is in the melting of copper or copper-containing metal to prevent vaporization 'a ft er the metal is melted. I have found direct current especially advantageous in this connection, and I regulate the voltage of the direct current applied across the electrode terminals or through the are so as to use a low voltage during the stage when undesirable heating might otherwise occur if I were to use a high voltage and long arc during such stage.

In order that the processes and apparatus of my invention may be more clearly understood I have made a number of dia rammatic" drawings to make all stages and features of my invention clear and easy to understand.

Fig. 1 is a diagrammatic view of a furnace and transformer winding designed to operate in accordance with my present invention.

Fig. 2 is a sectional elevatio'n'taken longitudinally through the axis of a cylindrically shaped furnace built in accordance with my invention.

Fig. 3 is a sectional elevationthrough the center electrode of the furnace shown in Fig. 2, but with the electrode at a different elevation.

Fig. 4 is a sectional elevation of another modification showing a bottom electrode through the side lining of the furnace.

Fig. 5 is a diagrammatic view of atransformer system and a three electrode furnace in which the transformers and top and bottom electrodes may be connected in various ways.

Fig. 6 represents diagrammatically the conncctions between the transformer windings and the electrode for one particular stage of operation.

Fig. 7 represents diagrammatically the arrangement of electrical circuitsdncluding the transformer windings and the electrodes for another stage of operation.

Fig. 8 represents the arrangement of transformer windings and electrodes for still another stage of operation.

Fig. 9 represents diagrammatically the arrangement of a three-phase, two-phase transformer system in connection wlth a three electrode furnace and also shows a switching arrangement and the re-actanoe.

Fig. 10 represents diagrammatically the arrangement of a three phase transformer system operated in open delta connection and connected to a three electrode furnace.

Fig. 11 represents diagrammatically the electrode voltages and the lengths of arcs in a furnace built in accordance with my invention when operated according to one stage of operation.

Fig. 12 represents diagrammatically a three electrode furnace in which the arcs are in series across the same electrode voltage as shown in Fig. 11.

Figs. 13, 14. 15, 1,6, 17 and18 represent diagrammatically different stages of operation of a two electrode furnace and transformer windings embodying my present invention.

Fig. 13 is a diagrammatic view of a furnace showing two relatively high voltage and correspondingly long arcs in series with each other.

Fig. 14 shows the same furnace with a lower electrode voltage and the electrodes lowered so that they are nearer the charge and showing shorter arcs than are shown in former connections.

Fig. 15 shows the same furnace represented in Fig. 13, but with one electrode making contact with the'metal in the bottom of the furnace chamber and the other electrode arcing to the charge with a relatively long arc.

Fig. 16 shows the same furnace that is in Fig. 15 with one electrode contact with the charge andthe other electrode arcing to the charge with a relatively shorter arc and lower electrode holder. I

Fig. 17 shows the same furnace as in Fig. 16 with both electrodes in. the slag and formiilig What is known as buried-arcs to the s ag. v

Fig. 18 shows the same furnace as in Fig. 17, but with the electrodes making contact with the metallic charge beneath the slag and with the lowest available electrode voltage from the transformer winding.

Fig. 19 represents diagrammatically a direct'current arc furnace and generator and variable resistance.

Fig. 20 represents diagrammatically a modification of the apparatus shown in Fig.

Fig. 21 represents the rimary windings of three transformers w ich may be connected either in star or in delta to a three phase power line.

- Fig. 22 represents the secondary windings of thesesame transformers shown diagrammatically in Fig. 21.

Fig. 23 is a dlagrammatic view of a single hase furnace and a transformer winding tted with means of connecting different numbers of turns to the electrodes and also dilferent numbers of turns to the power supply line.

Fig. 2st a diagrammatic view of a threephase are furnace and three separate auto transformers which may be intercollected in either star or delta relation.

Fig. is a diagrammatic View of a singlephase combination are furnace and auto transformer winding and induction device.

To avoid ambiguity, I use the term electrode voltage to mean the voltage supplied by the electrical circuit between two given electrodes and this voltage is not necessarily constant but necessarily does vary of itself as the current through the circuit varies and this variation in voltage across the electrodes results from the inherent regulation of the electrical circuit through the said electrodes.

The resistance between the electrodes is made up of the resistance of the arc and the resistance of the charge, and both of these are variable factors; and ofcourse the resistance of the electrical conductors is a part of the resistance of the whole circuit but is relatively small compared to the resistance of the arc and other material in the furnace chamber.

I have used the term series arcs to mean two or more arcs through which the same current flows, not necessarily the same amperage, for part of the current flowing through one are may not pass through the second arc, but nevertheless if some of the current in one are passes through a second arc, I say these arcs are in series.

I use the term parallel arcs or the term arcs in parallel to mean two or more arcs, both or all of which carry current which in another part of the circuit flows through a single common conductor.

In order to more fully explain my invention I will make reference to the drawings already referred to.

Referring, to Fig. 1, this view shows a furnace shell 1 resting on rails 2, so that the furnace may be tilted in the manner desired for example by means of a hydraulic cylinder 3, shown mounted on a pin 4, so as to allow for movement of the cylinder when the furnace rolls over. The furnace is lined with a suitable refractory bottom 7 and the crucible G is provided with refractory walls 5, and a removable roof 8 of suitable refractory material. This roof is held in a frame shown partly at 9.

Electrodes

10 and 11 extend through the roof and wall of the furnace chamber in such a manner that they may are to or cause current to pass through the charge. They may make contact with the slag, or one of them may make contact and the other may arc to the charge. The various stages of operation possible withthis modification of my invention will be more fully described and referred to further on with reference to Figs. 13 to 18 inclusive. In this Fig. 1, an are 12 is shown between the electrode 10 and the slag, and the electrode 11 is shown dipping through the slag into the metal beneath the slag. These electrodes may be independently operated longitudinally and their location with respect to the charge varied as desired; and this location or movement with respect to the charge may be further or independently controlled by tilting the furnace. For example, the furnace may be operated by tipping it to such an angle that the electrode 11 makes contact with the charge, and the other electrode 10 is above the charge. This particular stage of operation is also shown in Fig. 15. The control of the furnace may be changed to operate in a different stage whereby both electrodes must arc to the charge and this phase of operation is shown in Fig. 13. Both electrodes may be regulated to make contact with or form buried arcs in the charge as shown in Fig. 17, and in this stage a low voltage would beinsed by the proper connection of the transformer taps to the electrode.

In Fig. 1 the medium "oltage tap is shown connected through the switch 17 to the electrode 10. The transformer 18 is provided with taps 1st, 15 and 16 designed to give dillerent transformer voltages which may be applied to the electrodes and thus furnish dili'erent electrode voltages, and the change in 'oltage may be accomplished through the switch 17.

This furnace may be operated in various ways. It may be started with one electrode in contact with the charge and a relatively high voltage applied across a single are as shown diagramn'iatically in Fig. 15. It may subsequently be operated in another stage by lowering the voltage and having a shorter are, for example as shown in Fig. 16. And it may be ope 'ated in another stage by using a still lower voltage and one or more buried arcs as shown in Fig. 17. If desired, the voltage between electrodes may be still further lowered so that both electrodes actually make contact with the metallic charge, in which case the resistance will be largely in the charge itself. These charges are carried out by selecting the desired electrode voltage, for example by theuse of the switch 17, to connect to the desired tap of the transformer 13 in Fig. 1; and the further control of the operation is had by the manipulation or operation of the electrode or of both of the electrodes.

This furnace may be operated in any of these different stages according to the results desired: it may be started with high power. for example with the highest volta 'e available from the transformer and the eIectrodes manipulated to carry the maximum current allowed by the given conductors with their mamas limited current carrying capacity; and when the temperature becomes sufliciently high in the furnace chamber, so that it becomes necessary to lower the power, then I prefer to use a lower electrode voltage so as to localize the heat and to not operate with a high Voltage and long'arc'which tends to cause undesirable heating after the charge is raised to the desired temperature. However, my invention is not limited to starting with high voltage for I often find it advantageous when operating to raise the power during the course of operation, for example where I want to carry out chemical reactions which require a higher temperature, and then I may raise'the voltage and regulate the power as desired, and accomplish the same advantage in way of increased power input, without increasing the carrying capacity of the electrical conductors. I may, in certain -instances, use direct current as shown for example in Fig. 19 and Fig. 20 and may use this kind of current to assist in the chemical reaction desired.

Fig. 2 shows a rolling cylinder type of furnace which consists of a shell 21 with refractory lining 22. Entering through the roof 23 are three

electrodes

25, 26 and 27, which are all adjustable longitudinally so that the height of the electrodes and the distance between the end of each electrode and the charge in the furnace chamber 14 may be independently varied and controlled as desired. In the bottom of the furnace chamber extending through. the lining 22are three

bottom electrodes

28, 29 and 30, which extend from the outside of the furnace through the bottom and make contact with the charge 31 lying on the'hearth of the furnace chamber. A slag 32 is shown on top of the metal bath 31. An are 33 is shown between the electrode 25 and the charge. The lower end of the electrode 26 is shown beneath the top level of the slag 32. An are 34 is shown between the electrode 27 and the charge. A doorway and door are shown at 35, the doorway entering the furnace chamber through the re fractory wall. Another doorway is shownin the other view of this furnace at 36 in Fig.

Also in Fig. 3, a spout 37 isshown at the side of the furnace. This Fig. 3 is a diagram of a section through the center electrode of Fig. 2, but the electrode 26 in Fig. 3 is shown at a-lower elevation and a shorter are 38 is shown between the end of this electrode and the charge. The furnace may be tilted by any suitable meanssuch as a hydraulic cylinder, the connecting rod 39 of which is shown in this Fig. 3.

Fig. 4 represents a furnace similar to that in Fig. 3 except that the bottom electrode 4].. 'nntersthrough the bottom side wall of the furnacechamber. A top movable electrode is shownjat42 arcing (43) from its lower end tothe' 'unmelted charge 44 resting on a metallic charge 45 in the hearth of the furnace chamber. This furnace may be rotated by any suitable means,,not shown, and in this way the electrodes may be changed in their relation to the charge and the bottom electrode may be raised out of .the charge if desired, so that the current no longer passes through it, but must enter and leave through the several top electrodes as shown in Fig. 1. Referring to Figs. 5, 6 and 7. the furnace shown in Fig. 5 is provided with three top movable electrodes 49. and 51 and three bottom electrodes 52. 53 and 54. Three separate transformer windings are shown at 55, 56 and 57 Each transformer winding is provided with taps. Transformer has three taps shown at 63, 64 and 65. In my drawings the voltage between a given tap and the other end of the transformer winding'is roughly proportional to the amount of winding inserted. A switch 66'is provided to make connection between any one of these taps, and the conductor from the switch 66 leads to adouble-throw switch 75 and when this switch is thrown to the right it serves to connect the switch 66 with the central bottom electrode 52 which is directlv underneath the top electrode 50 from which a conductor leads-to the other terminal 78 of the transformer 55.

Transformer winding 56 is likewise-provided with

taps

67, 68 and 69 and a switch 70 is provided to make contact withany one of these taps as desired according to the electrode voltage desired. This switch is connected to a conductor which leads to a doublethrow switch 76, which when thrown to the right will make contact with the bottom electrode -53'which is directly beneath the top electrode 49. and a conductor leads from this electrode 49 to the other terminal 79 of the transformer 56.

The third transformer of this system is age are. the three switches 75. 7 6 and 7 7 may be thrown to the right and then the three transformers which are shown in three-phase relation to each other will be connected in star relation with the metallic furnace charge as the-neutral point of the circuit. and the transformer voltage of each transformer will then be applied between the charge and the top electrode directly above the bottom electrode of the given transformer circuit. For example, if these transformers furnish approxi mately 110 volts on open circuit between the .trode outside taps, the voltage between each top electrode and its corresponding bottom elec trode on open circuit will be approximately 110, and this voltage will drop as the load is increased in accordance with the regulation of the transformer circuit and depending upon the amount of reactance in this circuit.

Fig. 6 shows diagrammatically the connections which have just been described with three transformers connected in star, the same numerals representing the same parts, but arcs are shown at 82. 83 and 84; of relatively long len th, and for convenience the bottom electrodes are shown as connected toge her.

When it is desired to operate the furnace of Fig. 5 so as to use a lower voltage and so as to generate more of the heat in the charge itself, the transformers may be connected in a different relation. One way of doing this is bV throwing the double-throw switches 75., 76 and 7? to the left instead of to the right. and when th s is done the tap of the transformer which is connected to the switch 66 will through the switch 75. be then connected to the terminal 79 of the next transformer 56. And the tap of the trans ormer 56 which is connected to the switch will then be connected through the switch '76 to the terminal 80 of the other transformer 57. The tap of the transformer 57 which is connected to the switch 7 1- and to the double-throw switch '1? will then be connected with the terminal 76 of the transformer 55. lhe transformers will be in delta connection. The e ec voltage will then be approximately canal to the transformer voltage and as this electrode voltage will then pass through two arcs in series. for example from the electrode 50 into the charge and out through the elec trode 49. each the arcs will be of considerahly lower voltage and necessarily shorter.

T? shows diagrammatica ly the connections which have just been described with three transformers connected in delta. the same numerals representing the same parts, but the arcs shown at 85, 86 and 87 are of relatively short" lengths; and the bottom electrodes are shown disconnected'from the transformers by having a switch 81 open.

Fig. I? shows a switch 88 in the line leading from the transformer to the central electrode 50. This switch maybe thrown to disconnect electrode 50 from circuit and malre connection through the switch 81 (when closed) to the bottom electrodes. Then the transformer voltage, for example 110 volts of each of the

transformers

55 and, 56 will be applied through single arcs which will he of relatively higher voltage than when in the delta relation.

The transformer circuits in these lastdescribed Iigureshave not' shown the primary windings, but have shown only the secondary windings. The primary windings of these transformers may be inter-connected with each other in the same way as the secondary windings and Figs. 21 and 22 show diagrammatically both the primary and secondary windings of a three phase transformer system.

Fig. 9 represents a furnace which I have shown for convenience as having three top

movable electrodes

49, 50 and 51 and corresponding

bottom electrodes

52, 53 and 54; but this furnace is connected to a transformer system adapted to transform three phase current at one valtage into two phase current at suitable furnace voltages.

I will subsequently describe a furnace provided with only two top movable electrodes which may be used on this same transformer system.

Referring to the transformers in this Fig. 9, the three phase supply line is shown at 101 of the switch 102 for connecting to the primary windings of two

transformers

103 and 104. The secondary winding of trans former 104 is shown at 105 as consisting of two

coils

105 and 106; a double-throw switch 107 when thrown toward the top in the drawing will conncctthe two

transformer windings

105 and 106 in series and will apply between the bottom electrode 53 and the top electrode 49 the voltage of each one of these coils. When the switch 10'? is thrown downwardly. the

windings

105 and 106 will be connected in parallel with each other and the voltage then applied between the bottom electrode 53 and the top electrode 49 will be approximately equal to the sum of the voltages of the

coils

105 and 106. A reactance 108 is shown in circuit and it may be short circuited by a switch 109. Vlhen the power is varied, the electrode voltage will of course correspondingly vary through the reactance and the regulation of the transformer circuit.

The secondary windings of the other transformer are shown at 110 and 111 with a corresponding doublethrow switch 112, which serves to throw these coils in either series or parallel with corresponding regulation of the electrode voltage between the electrodes 51 and A switch 113 is shown by which either of the single phase circuits may be operated independently of the other. A double-throw switch 114 is provided whereby a third top electrode may be used in place of a bottom connection and then the electrode voltage would be used through two arcs in series with each other instead of what may be called parallel arcs when the current passing through the switch 114-, when it is thrownto the right, divides and part of the current. goes through the electrode 49 and the other partthrough the electrode 51 (dis- -';or refining. lln Fig. 19 there is, showh diaregarding the phase relations of the current through these different electrodes).

The

reactances

108 and 115 are preferably used when the higher voltage is applied to the furnace electrode and subsequently when a lower voltage is used, for example during the finishing or refining of metal in the furn'a'ce chamber, the reactances may be short circuited by means of the

switches

109 and 116.

Fig. 11 shows diagrammatically the length of arcs and voltages for the high voltage stage of operation with 100 volts between the top electrode and corresponding bottom electrode.

Fig. 12 shows the voltages when series arcs are. used and the bottom electrodes are cut out of circuit, the arcs as shown being shorter with 100 volts as the electrode voltage applied through two arcs in series.

In Figs. 21 and 22 I have shown transformer windings, Fig. 22 representing primary windings which may be connected to a three phase line as-shown at 121, and the secondary windings which may be connected by suitable leads 122 to the electrodes of a furnace. The three transformer windings 124,125 and 126 may be interconnected in any suitable way either star or delta. The switches for making such changes are not. shown as similar switches have been shown in other figures on the drawings in this case. The

secondary windings

127, 128 and 129 may likewise be connected in any suitable way, either in star or in delta, and the switches for these changes also are not shown for similar switches have been shown in the drawings already. These two figures, Fig. 21 and Fig. 22 are shown for the purpose of making it clear that the voltages available on the lines 122 may be varied or changed by any method described in this specification, either by manipulating the primary connections of the separate transformers, or

by manipulating the secondary connections. Switches are of course not essential to such changes for it has been often the case that the leads themselves are removed from one terminal of a transformer and connected to another terminal to accomplish the desired new connection. Furthermore, no taps are shown on these separate transformer primary and secondary windings, such taps having already been shown in the drawings and their use described, and it of course clear that taps on any of these t 'ansformer windings may be used in addition to the different connections between the dilferent. transformer windings themselves.

I have referred to the use of direct current as preferable in some instances for melting grammatically a view of the arc circuit of a direct Icurrent'furnace and also thedirect current generator. 130- represents the direct current generator; 131 is the field wind ing which may be used for varying or controlling the field current and therefore the voltage at the generator terminals in a manner well known in the operation of direct current generators; and the voltage from the generator may be applied to the electrodes, one terminal being connected to the top movable electrode 133 and the other to the bottom electrode shown diagrammatically at 134; and in circuit with the top electrode a resistance may be used so that thevoltage of the generator may be partly used up in this resistance when desired. T his resistance is shown at 132 and may be a variaole-resistance as for example a water barrel containing two terminals which may be more or less separated to vary the resistance between them, or it may be a simple resistor and the terminal leading to the electrode 133 may be connected to it at any suitable point to provide the desired amount of resistance to be in series with the arc circuit. The electrode 133 may be raised or lowered to manip ulate the length of the are. r The electrode is dropped as usual toward the charge 135 until an arm forms which may be drawn out as shown at 136.

In Fig. 20 I have shown another well known modification of direct current generator having both series and shunt field windings. Either field winding may be controlled by means of resistance not shown to vary or control the voltage of the generator. '1 his generator may also operate like any compound wound direct current generator so that increase of current in the series winding may produce a field opposing the shunt field and thuhtlrop the voltage at the generator terminals. The series field winding is shown at 141; the shunt field winding at 142; and the terminals of the generator may be connected. one to a top electrode 143 which is movable for the purpose of manipulating the length of the are 146 fronkthe electrode to the chargel il' and the other terminal from the generator may lead to the bottom electrode shown diagrammatically at 1 rd.

I prefer to use direct current in operating with easily volatile metals such as copper alloys, and manganese alloys. The tendency to vaporize in an arc furnace is not strong until the whole chamber and charge become sutli- Mid current arc tends to draw out-longer for the same electrode voltage than an alternating 13% current are under the same conditions of operation. After the charge becomes sufliciently hot the direct current are may become excessively long, that is when the electrodes are separated by raising the top electrode to cut down the current the arc may become quite long. At this time the temperature may become excessive in the upper parts of the furnace, and when the temperature becomes excessive due to the localization of the heat of the are in the upper part of the furnace chamber it is likely to cause undesirable volatilization of the metal of the charge or of the ingredients of the charge. Then I prefor to change the voltage applied to the electrodes by any of the means I have described, or any means, and operate with a lower electrode voltage. Then I manipulate the electrode so as to control the current through it and lower the electrode to operate with a shorter are or even with a buried arc. The electrode may be lowered until the end is even with the slag or dips into the slag or charge. The current may be regulated by the comined means of manipulating the electrode and independently manipulating the electrode voltage. I may operate with a current of low voltage and comparatively high amperage. The important feature, however, is that I control the location of heat development, and instead of generating most of the heat in the long are above the metal, the heat may be generated more in the charge itself and thus lessen the tendency to vaporize the metal, for a current of low voltage and high amperage will cause more heat to be developed in the resistance of the solid or molten charge. I may so control the direct current as to make it flow in either direction in accordance with the desired electrol tic efiect on the in redients of the molten bath.

In Fig. 23 l have shown diagrammatically a single phase are furnace having a top movable electrode 151 in a chamber 152 containin g charge 153 and molten charge in the lower part of this chamber at 154 and a bottom electrode contacting with the charge in the bottom of the chamber and leading through the bottom lining of the furnace. The bottom electrode 155 passes through the bottom 156 of the furnace chamber. A trans ormer is shown to the left of the furnace; This transformer consists of a suitable winding 157. The transformer core is not shown. The winding is provided with two sets of taps; one set is on the right hand side of the winding and there are shown the following taps on this ri ht hand side. namely.-158,

159, 160. 161, 1 62 and 163. The bottom terminal of the transformer is 164. This bottom terminal 164 is connected to the bottom electrode 155 of the furnace by a suitable conductor. This bottom terminal 164 is also connected to the supply circuit by the lead 173. Any one of the taps 158 to 165 may be connected through a suitable switch or terminal connection 174 to the top electrode 151. VVhenthe transformer winding is energized so that a given voltage is generated in the winding any given proportion of this total transformer voltage between the terminal 164 at the bottom and the terminal 163 at the top may be applied to the electrodes, by connecting the terminal 17 4 to the desired top on the right hand side of the transformer.

On the left hand side of the transformer winding are other taps 165 to 17 0 inclusive. These taps are shown arranged so that a switch 171 may connect any one of them to the conductor 175 leading to the supply line 172. Thus this transformer winding 157 is provided with taps which make it possible to apply the given supply line voltage either to the whole winding, for example when the supply line voltage is applied between the terminal 164 and the top terminal 170; or the supply line voltage may be applied to any portion of the winding by selecting the desired tap and connecting it through the switch 171 to the supply line. Thus it is possible to vary and control the voltage of the transformer winding between the terminals 16 i and 163 within the limits of the apparatus. If a voltage between 163 and 164 is desired not greater than the supply line voltage applied between 164% and 170 then these two

terminals

164 and 170 would be .connected to the supply voltage. If the voltage between 163 and 164 is desired not greater than the'supply line voltage applied between 164 and 170 then these two

terminals

164 and 170 would be connected to the supply voltage. Ifthe voltage desired on the

terminals

164 and 163, that is between them, is desired greater than the supply line voltage, then other taps would be selected on the left hand side of the winding and connected to the supply line voltage; for exam le it might be desired to obtain a high voltage to use on the furnace and then the terminals 164 and 165 might be connected to the supply circuit and a very high voltage a pl ed to the furnace electrodes by' using the

taps

164 and 163 to connect to the electrodes.

ll'he electrode voltage may be manipulated and controlled as des red by regulating the co nections of the transformer.

'The inherent regulation of the transformer will depend on its design. If there is consi erable leakage of magnetic flux there will of course be a considerable lowering of the voltage applied to the electrodes as the current through the transformer increases. This drop of voltage may be augmented or lessened or controlled independently of the operat on of the electrodes Thus when the electrode is lowered and the current through it increases, then the voltage on the electrodes -furnac'e operation.

will drop due to the-inherent reactance of the transformer circuit, 'but the electrode voltage may be regulated independently of this drop and for example the electrode voltage maybe raised by varying or manipulating the connections on either side of the transformer winding. This manipulation may be accomplished without breaking the circuit so that the operation may not be disturbed. The reactance of the circuit may be so high that when the electrode is lowered to produce a current of low voltage and high amperage, the voltage across the electrodes may be too low and then a different transformer connection may be used.

This transformer is essentially an auto transformer.- It has especial advantages in My invention contemplates the control of the current so that in the stage of operation when long or high voltage areas are undesirable, I may operate'with a low voltage current, and may so regulate the voltage'that itmay be of'very low potential so as to practically avoid any appreciable are. I have found that when the voltage is only about 10 volts between an electrode and the,

charge there is still an are or arcing between the electrode and the charge although they are practically in contact with each other. My invention contemplates, however, still lower voltages so that the heat is generated.

largely by resistance or in the resistance of the charge itself when this is desired. And my invention contemplates using an arc of suitable voltage in one stage of the heating and then in another stage when the are voltage is too high for convenience my invention contemplates using a low voltage current through the charge'as a resistor; and my invention contemplates voltage regulation of the electrode voltage between any desired limits that may be appropriate for the different stages of operation.

There is of'course more or less'reactance in the leads from the transformer terminals to the electrodes, both to the topelect'rode and to the bottom electrode; and there is of course more or less reactance in the circuit due to the inductance of the shell itself in the bottom thereof, for the current passes through the metal of the shell and the metal of the shell forms a circuit around the current which of necessity causes inductance in the circuit and tends to act'asa resistor.

I may use reactance in the circuit as described in connection witlpFigs. 9 and 10. I

that are light circuits are operated, that is with high reactance when a high voltage is applied, so that the reactance absorbs part of this voltage and simplifies the operation and to steadfy the current. Then again in another stage 0 operation when it is desired to operate with lower electrode voltage, at which time large reactance in circuit wouldcause objectionable operation or power factor, I may then'cut out the reactance from the cm cuit or short circuit the reactance and operate without it.

In Fig. 24 I have shownthe connectionsfor a combination of auto-transformers connected to a poly-phase circuit. This figure shows three auto transformers similar to the ,one shown in Fig. 23. These transformers are shown at 180, 181 and 182. .Each transformer is provided with taps for connecting to the furnace electrodes; thus transformer 182 has taps shown at 189, 190, 191, 192, 193 and switch or conductor 195 to the electrode 183. I The'bottom terminal 196 of this transformer 182 is connected to a switch 197 which i a double throw switch. This double thr w switch 197 may be thrown to the top and connect to a terminal 198 which leads through a conductor to the terminal or switch 200 and also to the electrode 185. This double throw switch 197 may be thrown to the bottom and connect to a terminal 199 which leads to the bottom electrode 186 of the furnace.

The other two

transformers

180 and 181 are provided .also with similar taps which may be connected to the switches or terminals 200 and 201. The lower terminals of these transformers are also connected to

switches

202 and 203 and these may be connected to the

top terminals

204 and 205 respectively or to the bottom terminals 206 and 207 respectively; and the switches are all inde endently operable so that any one'doub e throw switch may be operated independently of the others.

These three

transformers

180, 181 and 182 are also provided with taps on the opposite any way permissable by the switches so that I they may be operated either in star or in delta arrangement. The primary windings are shown as part or the same as the secondary windin the primary circuit 'belng that which is connected to the primary line or source of sup ly voltage shown as three conductors 208. lLach of the three conductors of the supply circuit 208 connect through

terminals

209, 210 and 211 to the taps on the separate windings so that any desired taps may be selected.

This last described arrangement of connections provides for any desired manipulation of the various voltages and for starting with higher voltages on the arcs and formanipulating the voltage and the heights of the electrodes to operate at a given stage with a lower voltage and to control the location of greatest heat development.

In my Fig. 25, I have shown a modification of my invention involving the combination of an arc furnace and an induction furnace. In this figure I have shown an arc furnace chamher 269 with an induction channel 279 in a refractory lining 278. This induction channel encircles a magnetic core 281. On the magnetic core is a winding 262, provided with taps, one of which is marked 263, which may be connected to one conductor 277 of a power circuit. This conductor may be connected through the terminal 264 to one of the taps as shown. The electrode circuit is connected between the portion of the coil marked 280 and one of the taps 265, through a conductor 266 which leads to the top electrode 261. The bottom contact beneath this top movable electrode is marked 268 and is connected through the conductor 267 to the transformer winding. On another part of the core are additional coils 270, which may be cut in or out of circuit as desired, that is the other com ductor 276 of the power line is arranged to make contact by means of a switch 271 with one of the

taps

272, 273, 274 of this coil 270, or with the conductor 275 which leads to the tap 280.

The electrode voltage applied between the bottom electrode and the top electrode in this are furnace circuit may be varied as desired, for example, at the start of a heat, the magnetic core may be energized by having the portion of the coil marked 270 in circuit as well as the other part of the coil marked 262 between the two

power supply lines

276 and 277. Under these conditions the voltage applied to the electrodes of the arc furnace may be raised as high as desired for the starting of the heat. The leakage flux through part of the winding is sufiiciently great to act as a steadying reactance. When the temperature has become suiiiciently high in the arc chamber of the furnace, then the electrode voltage may be lowered. This may be done by manipulation of the connections so as to include a smaller number of turns of the transformer winding in circuit with the electrodes, andalso the number of turns of the winding connected to the supply circuit may 1 be varied so as to cut out part of the coils.

Under these conditions the reactance may be lessened during this stage of operation.

If desired, the use of the are may be discontinued altogether and only a very low voltage current used to heat the charge at the finish by induction.

My process described in this specification and the apparatus therefor has numerous advantages. I have shown how a charge may be heated at the start with a high voltage on theelectrodes during the melting down period and a lower voltage at the finish; and also the use of reacta'nce in circuit, either in the primary circuit or in the secondary circuit, when a high voltage is used, and I have shown means for cutting the reactance out of circuit, when it is no longer required. My process has the advantage that the low Voltage current at the finish of the heat when lower energy input is desired will not cause detri mental effects on the lining; also it is possible to heat volatile metals by means of a low voltage current at the finish of the heat, where the use of a high voltage are would be undesirable.

My invention provides means for varying the voltage on any single electrode circuit and also for varying or unbalancing the current in one circuit with respect to others. The phase of the current and voltage in any of the single circuits with reactanceis not the same. that is the current is out of phase with the voltage. In my specification I have described a conductor through the bottom of the furnace and I call such a furnace bottom a conducting bottom. I may vary the amount of current through this conductor through the bottom as desired by means of the switches shown and I preferably varv the amount of current through this bottom by disconnecting the bottom conductor altogether during certain periods of operation. and thus change from all the current flowing through the bottom during one stage to another stage when no current flows through the bottom conductor.

In a three-phase furnace with the transformers connected in star and the bottom of the furnace serving as a neutral point, I may vary the length of any one of the arcs with respect to others and maintain the electrode voltage approximately constant; also I may vary the lengths of the arc where two arcs are in series by shortening one and lengthening another as for example by tilting the furnace and vet maintain the current approximately constant.

When I use very low voltage on the arc circuit and heavy currents. the reactance dron through the transformer circuit may exceed the arc voltage.

Any reactance in the circuit of the bottom electrode due to the'passage of the current through the magnetic circuit of the shell will of course have its effect on the saving of the arc. Such voltage drop caused bv this reactance is of course out of phase with the current passing through the arc.

In some of the figures of the drawings, I have shown three electrodes-although only two electrodes are used. It is understood that my invention contemplates the use of furnaces having only two top electrodes, which together with one or more bottom electrodes,

will be connected to a three-phase transformer system. I

The apparatus which I have described may be operated in a great variety. of ways and it is thought these different ways have been fully described in the claim.

The shell of the furnace usually consists of iron which is of course magnetic and therefore serves more or less as a reactance.

I claim: I

1. A polyphase are electric furnace comprising a plurality of arcing electrodes, and means for unbalancing the current or voltage of one or more of thepolyphase arcs.

2. A polyphase electric furnace, comprising a plurality of arcing electrodes, a polyphase circuiteonnected with said electrodes, and means for unbalancing the-voltage supplied to one of said electrodes.

- I 3. The herein described process of controlling the current flowthrough the bottom of-fa' polyphase arc electric furnace of the neutial star connected type, which consists in unbalancing the current or voltage of one or more of the polyphase arcs.

4. The method of o crating multi-phase electric arc furnaces w ich consists in stabiwhich is out of phase with the current causing said are.

5. The combination with a source of threephase current, of an electric furnace having two upper electrodes and a third terminal in conducting relation with the ,molten bath,

each of said three terminals being directly connected with one of said phas'es.

6. The combination with an electric furnace having a plurality of electrodes and a bottom contact, of circuits supplying said electrodes and said contact,said electrode circuits being closetogetherand separated from the circuits supplying said contact.-

7 The combination with an electric fur nace having a' plurality of arcing electrodes, and a bottom susceptible of conducting electricity, of a three phase transformer having star connected secondary windings, each provided with a series of taps, the neutral point of said windings being connected to said bot-' tom, and means for selectively connectin said electrodes to any desired one of eac series of taps so as to varythe voltage supplied to the electrodes."

8. The combination wlth an electric furnace having arcing electrodes, of a three phase transformer having primary windings connected in delta andsecondary windin s connected 'instar, both of said windings aving taps whereby voltage supplied to the electrodes may bevaried.

9. The combination wlthanelectricfurnace,

of means of supplying alternating current.

thereto at varying voltages, a reactance in the supply circuit, and means for varying such 'reactance as the voltage is varied.

10. The herein described method of operating an electric furnace having an arcing electrode which consists in supplying current to said electrode at one voltage during a given stage of operation, and then simultaneously changing both the voltage and the reactance of the supply circuit during another stage of operation as the metallurgical conditions in the furnace may require.

11. The herein described ating an electric furnace having an arcing electrode, which consists in supplying current to said electrode at a relatively high voltage during the melting stage, and reducing such voltage and at the same time reducing the reactance of the supply circuit during the refining stage. I

12. The combination with a three phase electrode furnace, of transformer means for supplying power to said electrodes compristhe melting down period, and a lower voltllzing the are by means of a voltage drop age for refining, said high and intermediate voltages being obtained by delta connections and said low voltage being obtained by means of a star connection.

13. The combination with .a three phase.

electrode furnace, of transformer means for supplying power to said furnace provided with a set of three primary windings, switching means whereby portions of said primary windings may be connected in delta to give a high voltage and larger amounts of said primary windings connected 'in-d'elta for an intermediate voltage, and switching means whereby portions of said prlmary wmdmgs may beconnected in star for a low voltage.

14. The combination with a three phase electrode furnace, of transformer means for supplying power to said furnace prov ded with a set of three primary windings, switching means whereby portions of said primary windings may be connected in delta to give a high voltage and the entire windlngs connected in delta for an intermediate voltage, and switching means whereby portions of said windings maybe connected in star for a low voltage.

15. In combination with the electrodes of an electric arc furnace, a transformer having a magnetic core and primary and secondary windings thereon, taps'on one of said windings for regulation and control of the voltage supplied to the electrodes, arrangement of said windings whereby more than normal reactance is introduced into the transformer circuit whensurges occur, and separate external reactance outside the transformer but in the circuit of 'said apparatus.

fig essence an electric arc furnace, a transformer hav ing primary and secondary windings, means for changing the connections between different parts of the windings for effecting a change in reactance, and means for l11d6 pendently regulating the secondary voltage applied to the electrodes.

17. In combination with an electric arc furnace having arcing electrodes, a transformer having a magnetic core and primary and secondary windings thereon, taps on one of said windings for efi'ecting a change in the magnetic leakage of said transformer, and independent means of regulating the second- 15 ary voltage applied to the electrodes.

18. The combination with an electric furnace having adjustable electrodes, of a transformer having a plurality of primary windings and secondary windings, means for con necting portions of the primary windings to a supply circuit whereby a high secondary voltage is induced and whereby high magnetic leakage takes place inoperatlon, and means for connecting other and larger portions of the; primary windings to the supply circuit to produce a lower secondary voltage with less magnetic leakage.

19. The combination with a three phase electrode furnace, of a transformer for supplying power thereto provided with primary windings certain portions of which constitute reactance coils, means for connecting portions of the primary windings including said reactance coils to the supply circuit to give a high secondary voltage and high reactance and means for connecting other portions oi the primary windings to give a lower secondary voltage and less reactance.

In testimony whereof I afiix my signature.

ALBERT E. GREENE.