US999720A - Electric furnace. - Google Patents

Description

G. HERING.

ELBCTBIG FURNACE.

Arrmonlon FILED an 2, 1911.

999,720 Patented Aug. 1, 1911.

UNITED STATES PATENT OFFICE.

CARL HERING, 0F PHILADELPHIA, PENNSYLVANIA.

ELECTRIC FURNACE.

To all whom it may concern:

Be it, known that I, CARL Hennvo, a citizen of the United States, residin in the city 0'. Philadelphia, county of P liladelphia, and State of Pennsylvania, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to electric furnaces. and more particularly to electric furnaces employing electrodes of certain proportions.

My invention resides in an electric furnace comprising improved electrodes. for securing minimum electrode loss, in connection with electric furnace resistors. preferably liquid or molten: and the employment of my said improved electrodes in combination with an electric furnace in such arrangement that the power factor of the furnace is great. when alternating: current is employed.

For an illustration of some forms of application of my invention. reference is to he had to the accompanying drawing, in which:

Figure l 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 in combination with my improved electrodes. Fig. 2 is a vertical sectional VlQW of an electric arc furnace. involving, also resistors in combination with my improved electrodes. Fig. 3 is a side elem tional View of a metallic or conducting starter.

I. have found that the energy loss in the electrodes of an electric furnace may be reduced greatly below what has heretofore been common practice. 1 have discovered the law of the electrode losses and from it I have found that for a minimum amount of loss' in the electrodes, such electrodes must he so proportioned that the (FR 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. By heat 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 co bined loss be- Specification of Letters Patent. Original application filed February 17, 1911, Serial No. 809,123.

Patented Aug. 1, 1911. Divided and this application filed May 2,

Serial No. 624,616.

comes greater. Asa result of roportioning the electrodes so that this relation shall hold, the losses of energy in and through the electrodes become very small as compared with prior practice. The total loss in the electrodes will then be equal to the electrical resistance loss only (0 R loss) as there will then he no heat lost by conduction. because the temperature of the hot. end of the electrode willthen be equal to that of the furnace, and the electrode will therefore he the equivalent of a perfect heat insulator. allowing no heat to pass through it from the furnace. although the electrode remains a very good electrical conductor. No material is known which has these two qualities co1nhined, namely. heat insulation and electrical conductivity: hut hy proportioning the electrodes according to the laws which I have discovered. the practical equivalent of these two properties can nevertheless he realized. hile the equations and proportions herein given are for electrode materials with ideal properties, such as zero co-etticicnts for both electric and heat conductivities. these co-ettieients of actual materials available wary somewhat and. therefore. the results in practice are not exactly those indicated by the equations and proportions given. but are, for all practical purposes. substantially those indicated hy 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 material this minimum electrode loss is dependent upon the furnace temperature and the current, but not on the electrode dimensions, except. that the ratio of the length to the cross section of the electrode must he 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 the dimensions of the electrodc. For different materials I find that. this minimnm-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 usual materials carbon and graphite.

It is a part of my invention, therefore, that metal electrodes are employed, preferably of the same metal as is melted in the furnace, or of metal or material which does not contaminate the material or metal fused in the furnace, and thereby I can greatly reduce the electrode losses. To obtain this advantage of a lower minimum loss for metal electrodes they must be proportioned so that the heat conduction loss, with no current flowing, will be equal to half the (PR loss approximately or substantially. But my improvement is not limited to metal electrodes, for, by observing the novel proortions herein described, carbon and graphite electrodes, giving minimum losses for those materials, may be employed, and the loss will be found to be much smaller than for the carbon and graphite electrodes as heretofore used. I have stated above that this minimum loss is independentof the actual dimensions of the electrodes, that is, they may be lar e or small and yet have the same minimum oss. To get this minimum loss, however, I find that they must have a certain proportion between their length and their cross section. In order to obtain the best economy of electrode material, therefore, the-electrode should be made as short-as possible, as the economy increases inversely as the square of the length. The cross section is then made to correspond with this length in accordance with the laws which I have discovered, in order to obtain the minimum loss. From the laws which I have discovered it follows that this economy of material will be greatest, that is, for any given length the cross section will be least, when the square root of the product of the electrical and the thermal conductivities is greatest. Hence, I find that as far as economy of material is concerned, those matcrialsare best in which this product is greatest. In any given material, therefore, the desirable qualitiesare, to a certain ektent, opposed, with respect to economy of power as compared with economy of material. I have discovered that if K and ll: represent the electrical and thermal conductivities of the material,'then the minimum power loss in them, in the form of the heat which leaves them at the outside terminals, is least when K divided by k is greatest. On

. the other hand, the economy of material is best when the product of k and K is greatest; It is, therefore, the quotient and the prodiict of the electrical and thermal conductivities which determine their suitability for which must be compared and not the quo tients and products irectly. From the conductivities of different materials as far as they are known, I find, from the law which I have discovered, that the square root' of these quotients and products are as a rule greatest for the metals. as distinguished from the usual electrode1naterials, carbon and graphite. The difference is great. Hence, I have found it much more economical to use metal electrodes Whenever possible.

\Vhen metal electrodes are used and proportioned in accordance with the laws which I have discovered, they will remain solid at the external ends although they will be at the temperature of fusion at the inside or furnace ends. The reason is that when so proportioned there will be no heat conducted by the electrodes from the interior of the furnace, and all the heat generated in them by the current will be led off at the cool or outside end just asfast as it is generated in it; hence their temperature will not increase and they will remain unfused except at their extreme inside ends. lf continuously covered with fused metal at their inside or hot ends they will not be consumed and if made of the same metal as that fused in the furnace, or of one which is nonmisciblc with the fused material, they will not contaminate the latter. This state, as I have found, is also the state of least total loss in the electrodes.

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

X 2.8940 {MT in which X is the total minimum loss in watts in or through the clectrodrs. 2.894: is a constant involving no physical properties, C is the current in amperes, is is the heat conductivity in gram calories per second, cubic inch units, 7 the electrical resistivity in ohms, cubic inch units, and T the temperature difference between the inside and outside ends of the elcctr'ode in centigrade dcgrccs. And I have deduced the followin formula for determining, the condition 0 proper proportions of the electrodes for minimum loss:

r lcT in which S is the cross section of the electrodes in square inches, L their length in inches, the current in amperes, r, In and T being the same as above. The electrodes must have this proportion in order to obtain the minimum loss given in the first formula.

Then the thermal conductivity is in the above formulae is expressed in watts in place of in calories per second, the numerical constants in these formulae, namely, 2.894 and 0.3456, disappear, and a factor 2 accomsection to the length 0 panics the factor It, so that these formulae take the form, respectively, as follows:

ives the ratio of the 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, therefore, 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 a minimum loss of energy in the electrodes, thus leavin greater amounts of energy for useful wori within the furnace and, in consequence, increasingthe efliciency of the furnace. V I

If by the electrode elliciency is meant the ratio of the energy set free 1n the interior of the furnace, that is, between the hot ends of the two electrodes, divided b the total energy between the two cold on s, then for a iven minimum loss in the electrodes, this eth ciency will evidently be higher the greater between the hot ends, as e drop of voltage in one e electrodes. By my invention the latter may be made very small, much smaller than heretofore, hence for a given current and voltage of a furnace there will be more useful heat generated in the furnace. But to increase this efficiency still more the dro of voltage between the two hot ends should To do this with a liqui resistor may require this resister to be made long and small in section, hence I may in those cases refer to use the are as this has a relative y high drop of potential in a small space. Or still-better may use several arcs in series.

In Fig. 1 is shown an electric furnace in vertical section having a hearth. A; this hearth may ta e an suitable or desired form, as the heat pro ucing resistor'is practical] independent of the proportions of this iearth or the amount iof molten material in it. Upon the hearth A is a mass B, of molten iron or other-material under treatment, the molten material extendin also downwardly into the columns C and I), the molten material in these columns making electrical end-on contactwith the furnace electrodes .E, E, roportioned and constructed as hereinbe ore described, which extend through the bottom or wall.of the furnace, and may terminate outside in conduct- This second formula the drop of volta com ared with t f th be made as rest as possible.

iempltiyed. The dividing member S 1n co led, if desired, by a water jacket. The furnace extends upwardly in the form of a dome G, preferably enlarging toward the bottom, such dome being lpreferably filled with the charging n'lateria H, 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 materia as that to be treated, extending downwardly in the columns C and D into contact with the electrodes E, E, such casting bein continuous and bridging the columns C- an D at the top. When the current is turned on, it flows from one electrode through one of the columns and out through the other column and other electrode, the casting, when such is employed for starting, becoming hotter and hotter until finally melted.

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

Ill operation, a minimum amount of energy is lost in the electrodes I), E, and the heat is produced by the current in the columns C and D, the molten masses in these columns constituting the resistor.

In Fig. 2, I have shown an arc furnace having the electrodes E, E, proportioned as herein described, which may be metallic, communicating with the separated baths B and B of moltenmaterial, a dividing wall or member S being provided. The are may be started by a bridge piece m, such as shown in Fig. 3, made of the same metal as that in the baths B and B, by placing the same over the dividing memer S; the member then melts and an arc ois formed between the two baths B and- Or the are may be started by granular oonducti material extending over the member 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 may be kept om fusing by a circulatlonof water or other cooling material through the-opening or tubeT. Or the magnetic blow-out principle may be used to kee the arcs far-- ther from the dividing mcm er S.

In both the forms of furnaces herein shown, it will 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 enlargements, F, F, which may be 66 connections to the transformer and thus increasing the power factor, when alternating current 15 used, since the area inclosed by the conducting 100 formed within the furnace is reatl re uced.-

The e ectro es 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 sim lifted and cheapcned. Unless proportionc 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 herembefore described, the electrode section selves, proportioned, as herein described, for i minimum loss, but claim said electrodes herein only in combination with other features; the electrodes themselves, roportioned for minimum loss, are claims in the above-mentioned application Serial No. 009,123.

What I claim is: '1. In an electric furnace, molten conduct ing matelial serving as a furnace resistor,

and an electrode in electrical commnnication with said resistor for communicating heating current to said resistoiy-the length and cross section of said electrode being so related that the resistor heating current passed through said electrode raises said electrode to a temperature preventing heat conduction through said electrode from said molten material. i

2'. In an electric furnace,a resistor, a plurality of electrodes electrically communicatin withsaid resistor, and an insulating 'divi ing wall between said electrodes, said electrodes; pro ortioned" for minimum electrode lose an ntially as described, whereby the distance between said electrodes is small and the area. inclosed by the furnace circuit is small and the power factor great when alternating current is passed through said electrodes.

3. In an electric furnace, axesistor, and an electrode for communicating heating current to said resistor, said electrode being so proportioned-that the CPR heat developed in said electrode by the resistor heating current passed through said electrode raises posed in end on contact with said mass of molten metal, said metal electrode having is resistance such that the CR heat developed therein by current transmitted therethrough to said mass shall be substantially equal to twice the heat conduction loss when no current flows.

5 In an electric furnace, an insulating dividing wall, columns ofconductin material on opposite sides of said wall, an electrodes on opposite sides of said wall electrically communicating with said conducting columns, saidclectrodes proportioned for minimum electrode losses substantially as described, whereby the distance between said electrodes is small and the area of the furnace circuit is small and the power factor great when alternating current is passed through aid electrodes.

6'. In an electric furnace, a. dividing wall within said, furnace. containers for molten material on opposite sides of said dividing wall within the furnace wall, electrodes proportioncd for minimum electrcde'losses sub,-

fillllli t lh. as herein described extending through tilt. furnace wall and disposed in oml on cont-act with said separate masses on either side of said dividing wall, said masses being adapted to be connected b an are extending over said dividing we. 1.

7. In an electric furnace, a container for a mass of molten metal, a metal electrode extending through the furnace wall in electrical communication with said mass, the:

cross section of said'clectrode so related to the length of said electrode that the CR heat developed in said electrode by current transmitted t-herethrough to said mass raises said electrode to a temperature preventing heat conduction through said electrode from said mass.

8. In an electric furnace, a molten-resistor, an electrode in end-0n contact therewith for communicating heating current to acid resister, said electrode having such resistance that the (FR heat developed in said electrode by said resistor heating current raises the end of said electrode in contact with said resistor to a temperature substantially equal to the temperature of said resistor.

9'. In an electric furnace, the combination with a container for material to-Ue treated within the furnace wall, of an electrode ex- I tending throughsaid walhand disposed in electrical commui'iicat-lon with'sald mater al,- the cross sect-ion"'of said electrode being so small that the C'R heat developed in said electrode by current passed therethough to said material raises said electrode to a temperature preventing heat conduction through said electrode from said material within said furnace.

10. In an electric furnace, the combination with a container for material to be treated within the furnace wall, of an electrode extending through said wall and disposed in clectrlcnl communication with said nmterial, the cross section of said electrode being uniform and so small that the (PR heat developed in said electrode by current passed therethrough to said material raises said electrode to a temperature preventing heat conduction outwardly through said electrode.

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

CA RL H ERI NG.

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