US999719A - Electric-furnace electrode. - Google Patents

Description

G. HERING. ELECTRIC FURNACE ELECTRODE. APPLICATION FILED FEB.17,1911.

IN VEN TOR Patented Aug. 1, 1911.

L A %E 3Q ATTORNEY a To (ZZZ whom it may-concern:

U I STATES PATENT 'onr on.

CARL HEBING, OF PHILADELBHIA, IENNSYLVANIA nnncrmc-runnaon ELECTRODE.

Specification of Letters Patent;

Patented Aug. 1,1911.

Original application fi led Iuly 6, 1909, Serial No. 505,963. Divided and this application filed February 17,

. 1911. Serial No; 609,123.

'Be it known that I, CARL Hninne, a citizen of the United States, residing'in thev city of Philadelphia, county. of Philadelphia, and State of Pennsylvania, have invented a certain new and useful Electric-Furnace Electrode, of which the following is a specification. r

, My invention relates to electrodes and more particularly to electrodes for conductmg current-to another -c0nductor,--such, for

example, as a heated conductor or a conductor wit-hm an electric furnace;

My invention resides in an electrode whose opposite ends are at substantially different temperatures while'current is passed through the electrode, and is so constructed that the current passing therethrough will prevent heat conduction from its hotter to its cooler end of heat generated externally to the electrode at its hotter end. To this end I so relate-the cross section of my electrode to its length that its resistance is such that the current passed therethrough will pre vent such heat conduction, by maintaining the hotter end of the electrode at a temperature substantially equal to the temperaturemaintained externally to the hotter end of the electrode.

for a givcnset of conditions, my electrode is far smaller and cheaper as compared with i'xn-merpractice; and by my improved construction I secure practically minimum electrode losses.

My in vcntion resides in the electrode hereinafter described and claimed.

For an understanding of my invention,

and for an illustration of some'of the applications of my invention, reference 15 to be had to the accompanying drawing, in which Figures 1 and 2 are views illustrative of the principle underlying my Improved electrodes.

Fig. 3 is a vertical sectional view of an electric furnace in which the resistor is in the form of a column or columns of molten material contacting with my improved electrodes. Fig. 4. is a vertical sectional view.

of an electric arc furnace, involving also resistors in contact with my improved e ectrodes. Fig. 5 is a side clcrational view of a metallic or conducting starter.

l-luwe'fo lmd-that the energy loss in the By my improved electrode constructiom electrodes of an electric furnace may. be reduced greatly below what has heretofore been common practice. I have discovered the law of the electrode losses and from it I have found. that for a minimumamountof loss in the electrodes, such electrodes must be so proportioned that the 0 R loss (heat generated by current in the resistance of the electrodes) shall be equal substantially or approximately to twice the heat conduction loss of the electrodes. Byheat conduction loss I mean the loss of heat from the interior of the furnace through the electrodes by heat conduction, when'no current is flowing.

"I have-found that for any other relation between these two losses the combined loss becomes greater. As a result of proportioning the electrodes so that thisrelation shall hold, the losses of energy in and through the electrodes become very small-as compared with .prior practlce. The total loss in the electrodes will then be equal to theelectrical resistance loss only, (C lt loss) as there will then be no heat lost by conduction, because 1 the temperature of the hot cnd of the electrode will then be equal to that of the furnace, and the electrode will therefore be the equivalent of a perfect heat insulator, allowmg no heat to pass through it from the furnace, although the electrode remains a very good electrical conductor. No material is known whlch has these two qualities combined, namely, heatinsulation and electrical conductivity; butby proportioning the electrodes-according to the lawswhich l have discovered, the practical equivalent of these two properties can nevertheless be realized. This may be bettcr-understood by reference .to Fig. I, in which a, b, is a conductor ot heaLand electricity,say an iron rod, embedded in a block of perfect heat insulating material 'i, except at the ends, which are kept at a low temperature, as by water cooling. Let s0 large'a current be passed through a, 7), that it will be melted for a short distance, a

to (l, at the middle. .Under these com'litions and when the stable state is reached, the only loss will be the CIt loss which will flow out as heat at the two ends. If this block i be now supposed to be cut in two atthe middle plane a, f, and separated to form the two walls of a furnace-which contains that same material ina melted state, as illustrated in Fig. 2, the rods now forming the two electrodes, there will evidently be no'more heat conducted by the electrodes from the melted mass in the interior of the furnace to the outside than there was before, because the ends of the electrodes and the melted materialare at the same temperature. I find thatit follows from the'laws ofheat and electricity that the conduction loss when the current stops, would then be equal to approximately half the C 11 loss, as heretofore pointed out. Also that for any other than .these conditions, the electrode loss will be increased and not be a ninimum. \Vhile the equations and proportions herein given are 'for electrode materials with ideal properties,

such as zero temperature co-etiicients for both electric and heat conductivities, these co-cfiicients of actual materials available vary somewhat and,jtherefore,.the results in practice arenot'exactly those indicated by the equations and proportions given, but are,

for all practical purposes, substantially those indicated by the equations and proportions given. I have found that for each electrode material, this minimum loss is a constant per ampere of current and per degree of furnace temperature. Also that for a given ma-- reduce the ele 'trode losses.

tcrial this minimum electrode loss is dependent upon the furnace temperature andthe current, but not on the electrode dimensions, except that the ratio ofthe length to thecross section of the electrode must be a certain quantity, as hereinafter pointed out. For any given electrode material, temperature, and current, this minimum electrode loss is'fixed and cannot be further reduced by any change in tliedimeiisions of the electrode. For different materials I find that this minimum loss is proportional to the square root of the ratio of the thermal to the electrical conductivities of the electrodes. From these laws I find that the minimum loss is generally least for the metals, and

that it is very considerably less than for the current flowing, will be equal to half the.

(5R loss approximately or substantially.

llut. my improvement is not limited to metal electrodes, for, by observing the novel proportions herein described, carbon and graphite electrodes, givingminirnuin losses for thosc-materials, maybe employed, and the loss will. be found to' be much smaller than for the carbon and graphite electrodes,

as heretofore used. I have statedabovethat this minimum loss is independent. of theaetual dimensions of the electrodes,- that is,

they may be large or small and yet have the same minimum loss. To get this-minimum loss, however,I find that they must-have a certain proportion between. .theirlength and their cross section. Inorder to obtain the best economy-of electrode material, therefore, the electrode should be made as short as possible, as theeconomy'increases inversely as the square of the length. The cross section is then nade to correspond.-

with this length. in accordance with the laws which I have discovered, in order to.

From the laws which. I have discovered it'followsthat thisobtain the minimum loss.

economy of material will be greatest, that is,

for any given length the cross section will be least, when the. square root of the prod-..

net .of the electrical and ,the thermal conductivities is greatest. Hence, I find thatas far as economy ofjmaterial is. concerned, those mater als are best n which thisprod-' net is greatest. In any given. iii'tltfillttl,

therefore, the desirable qualities are, to a certain extent, opposed, with respect to' economy of power as compared with econ-- omy of material. I have discovered that if" K and I: represent the electrical aiidthernial.

conductivities of the-material, then the ininimum power loss in them, in the form of-.' the heat which leaves them at the outside r terminals, 18 least when ls. divided by A: 13 greatest On the other hand, the economy of material is best. when the product of k .[t is, therefore, the

and K- is greatest.

quotient and the product ofthe electrical and thermal conductivities whiclrdetermine their suitability for'electrode materials, and

not either of these alone. Incompuring different materials quantitatively -\\'ith each other, it is the square root of'th is quotient or this product which mustbe compared and not the quotients and-products directly.

From the conductivities of dill'erent ma terials as far as thev are known, I lind. from the law which I have discovered, that the square root of these qiioticntsiuid products are as a. rule greatest for. the metals as distinguished from the fusual electrode mate-.

rials, carbon and graphite. The .ditlerence. I

is great. Hence, I- have found it much more economical to use .metal electrodes whenever possible.

portioiied iii-accordancewith the laws which I have discovered, they will reu'iuin solid at' the-external endsalthough they will be at thetemperature,ofafusion at the inside or furnace ends. The reason is that whenso proportioned there will v be no heat renducted by the 'clecti'ode'qfrointhe interior of the furnace, and all'the heat-generated in them by the current .willbe' led' off at the 4 120. I When metal electrodes are used and pr'o- 1 will not contaminate the latter.

cool or outside end'just as fast as it is generated in it; hence their temperature will not increase and they will remain unfused except at their extreme inside ends. 5 tinuously covered with fused metal at their inside or hot ends they will not be consumed and if made of the same metal as thatfused in the furnace, or of one which is nonmiscible with the fused l'naterial, they This state. as Ighave found, is also the state of least total loss in the electrodes.

From the laws above stated I have deduced the following formula:

X: macaw inwhich X is the total minimum loss in watts in or through the electrodes, 2.8% is a constant involving no physical properties, C is the current in amperes, is the heat con- (lucti-vity in gram calories per second. cubic inch units, 1 the electrical resistivity in ohms, cubic inch units, and T the temperature difference between the inside and outside ends of the electrode in centigrade degrees. And I have deduced the following formulafor determining the condition of proper proportions of the electrodes for minimum loss:

nies the factor 7:, so that these formulae take the form, respectively, as follows:

a This second formula gives the ratio of the section to the length of the electrodes and therefore leaves a choice of either, but not of both. The length should be made as short as possible; it is usually determined by the general design and thickness of the furnace walls or other considerations. The quantity of electrode material increases as the square of the length. It follows, there fore, that in accordance with my discoveries and invention, I may greatly reduce the size of, and therefore cheapen, the electrodes heretofore used in the art and at the same time secure ammnnum loss of energy in the electrodes, thus leavlng greater amounts of If conenergy for useful work within the furnace and, in consequence, increasing the efficiency of the furnace.

If by the electrode efliciency is meant the ratio of the energy set free in the interior of 79 the furnace, that is, between-thehot ends of the two electrodes, divided by the total. energy between the two, cold ends, then for a given minimum loss in the electrodes, this efficiency will evidently be higher the greater the drop of Volta e between the hot ends, as compared with t e drop of voltage in one of the electrodes. By my invention the latter may be made very small, much smaller than heretofore, hence for a given 80 current and voltage of a furnace there will. be more useful heat generated in the furnace. But to increase this efliciency still more the drop of voltage between thetwo hot ends should be made as great as possible. To do this with a liquid resistor may require this resistor to be made longand small in section, hence I may in those cases prefer to use the are as this has a relatively high drop of potential in a small space. Or still better I may use several arcs in series.

My improved electrodes may therefore be used in any electric furnace irrespective of whether the resistor is a column of molten material, an are, or what its form or char- 5 acter maybe. In Fig. 3 is shown an electric furnace in vertical section, having a hearth A; this hearth may take any suitable ordesired form, as the heat producing resistor is 10 practically independent of the proportions of this hearth or the amount ofmolten material. in it. Upon the hearth A is a mass, B,

of molten iron orjother material under treatment, the molten material extending also downwardly into the columns C and D, the molten material In these columns majkmg electrical end-on contact wlth the furw nace electrodes E, E, proportioned and-com: structed as herembefore described, which .110

extend through the bottom or wall Of thej furnace, and may terminate outside in conducting enlargements F, F, which may be cooled, if desired, by a water jacket. The

furnace extends upwardly in thelform of a 115.'

dome G, preferably enlarging toward the bottom, such dome being preferably filled with the charging material 11, as iron ore or other material, which may. be introduced through the opening I at the top, which is thereby preheated.

The furnace may be started by a charge of molten material or by a casting of preferably the same material as that to be" treated, extending downwardly in the col.- unms C and D into contact with the electrodes E, E, such casting being continuous and bridging the columns C and D at the top. When the currentis turned on, it flows from one electrodethrough one of the columns and out through the other column veyed to it, thereby hastening the chemical action, such as the combination of iron and carbon on the one hand, and the combination of the carbid, thus formed, with the iron oxid on the other hand, as is well understood in the art. J represents the slag. And a further opening L may be provided for the introduction. of air, as by a blast, for burning any possible unburned gases which may be formed, like carbon monoxid, thus preheating the ore and increasing the economy of heat of the furnace.

M is a tap hole communicating with the column C for drawing off the finished material, and a similar tap hole N may be provided for communicating with the other column D for the same purpose, if desired. 01' the tap hole may communicate with the bottom of the hearth, if desired, or tap holes may be placed at both places.

In operation, a minimum amourn of energy is lost in the electrodes E, E, and the heat is produced by the current in the columns C and D, the molten masses in these columns constituting the resistor. 'Ihis heat is then supplied to the mass B by the columns C and D.

In Fig. 1-, I have shown an arc furnace having the electrodes E, E, in accordance with my invention, which may be metallic, comn'iunicating with the separated baths B and B of molten material, a dividing wall or member S being provided. The are may be started by a bridge piece m, such shown in Fig. 5, made of the same metal that in the baths B and B, by placing the same over the dividing member S; thememher then melts and an are 0 is formed between the two baths B and B. Or the arc may be started by granular conducting material extending over the member S into contact with the two baths, or the baths may be agitated to come momentarily into contact with each other above the member S, or any other means may be employed. The dividil'ig member S may be kept from fusing by a circulation of water or other cooling material through the opening or tube T. Or the n'iagnetic blow-out principle may be used to keep the arcs farther from the dividing member S.

In both the forms of furnaces herein shown, itwill be noticed that the two terminals or electrodes may be brought out close together, because of their small size, due to my invention, thereby facilitating the connections to the transformer and thus in creasing the power factor, when alternating current is used, since the area inclosed by the conducting loop formed within the. furnace is greatly reduced.

'ifhe electrodes are. not consumed and therefore do not contaminate the fused product and do not have to be advanced into the furnace. In consequence, the construction of the furnace is greatly simplitied and cheapened. Unless proportioned as I have shown, the losses through metal electrodes may become very large, due to their high heat conductivity.

By constructing a furnace electrode as hereinbefore described, the electrode section is not so large that heat conduction can occur therethrough from the furnace; nor is the section of the electrode so small that the electrode is raised within the furnace wall to a temperature higher than the furnace temperature.

This application is a division from my application Serial No. 505,963, filed July 6, 1909, upon which was issued Letters Patentof the United States No. 988,936.

\Vhile I have herein shown and described my nnprovcd electrodes applied in several relations in electric furnaces, I claim herein my improved electrode only, and in my co pending application Serial No. (524,616, filed May 2, 1911, I claim my said improved electrode in those relations in electric furnaces disclosed but not claimed herein.

\Vhat I claim is:

1. In an electric furnace, an electrode having a resistance such that the (FR heat. de veloped therein by current transmitted therethrough to said furnace shall be substantially equal to twice the heat conduction loss when no current flows.

2. In an electric furnace, an electrode having such length and cross section that the furnace current [lowing through said electrode raises said electrode at its furnace end by its own resistance to a temperature substantially equal to furnace temperature.

3. In an electric furnace, an electrode having the ratio of its electrical to its thermal conductivities and the product of its electrical and thermal comhuztivities great, and such thatv the (Flt heat developed therein by furnace current is substantially equal to twice the heat. conduction loss through said electrode when no current is flowing.

l. .\n electric furnace electrode having an electrical resistance suilicient to cause the generation, throughout its whole length between its outer and inner terminals, by the passage thcrethrough of furnace current of the hcatnecessary to prevent loss by conduction toward its outer terminal, of the heat generated in the furnace.

5. An electric furnace electrode having a substantially uniform cross section and having an electrical resistance sufiicient to cause thegeueration, by the passage thcrethrough of furnace current, of the heat necessary to prevent loss by conduction toward its outer end, of the heat generated in the interior of the furnace.

6. An electric furnace electrode having such a thermal resistance that durii'ig normal furnace operation only that heat is conductedto its outer terminal which is generated within said electrode by the passage therethrough of furnace current.

7. An electric furnace electrode having such a length and uniform cross section that Substantially no heat will flow into or out of the furnace through the hot end of said electrode.

the current passing through said electrode to said heated conductor raises said electrode.

at its end in communication with said heated conductor by the resistance of said electrode to a temperature substantially equal to that of said heated conductor.

10. An electrode for carrying current while its opposite ends are at different temperatures having such resistance that the C 11 heat developed therein by the current transmitted therethrough shall be substantially equal to twice the heat conduction loss through said electrode when no current is flowing through said electrode.

11. An electrode for cala'ying current while its opposite ends are at different temperatures, said electrode having such relation of its cross sectionto its length, sul stantially as described, that the current flowing through said electrode raises'said'electrode at its hotter end to a temperature we venting conduction through said electrode of heat generated external to said electrode at its hotter end.

In testimony whereof I have hereunto athxcd my signature in the presence of the two subscribing witnesses.

CARL HERING.

Vitnesses:

Anna E. S'rumnocn, ELEANOR 'l. MGCALL.

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