US1309045A - Electric fubnace and pbocess of opebating same - Google Patents

Description

w. E. MOORE. ELECTRIC FURNACE AND PROCESS OF OPERATING SAME.

APPLICATION FILED AUG.9, I918- Patented J uly 8, 1919.

314mm oz MZZiamEMW-L,

' wrLLIhm E. moon's, or PITTSBURGH, PENNSYLVANIA.

. ELECTBIC'-FUBNACE AND PROCESS OF OPERATING SAME.

Specification of Letters Patent.

Patented July 8, 1919;

Application filed August 9, 1918. Serial No. 249,073.

To all whom it may concern:

Be it known that I, WILLIAM E. Moons, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Electric' Furnaces and Processes of Operating Same, of which the following is a specification.

My invention relates to improvement in electric furnaces and the method of operating the same, and'it consists in the constructions, combinations and arrangements hereinafter described, and in the steps for controlling the heat as hereafter indicated.

In the manufacture of steel, its alloys and other metals, in an electric furnace of the arc type, in which the current, or part of it, passes through the molten mass and through the bottom of the furnace, it is an advantage ,to be able to readily effect a variation in the current to meet varying operating conditions, and to provide. for a reasonably wide variation in the current without having to manipulate heavy current carrying leads.

In those electrieffurnaces of the type mentioned where thei fientire current returns through the bottom of the furnace, portions of the charge may become overheated; On the other hand, in furnaces where no part of the current is returned through the bottom of the furnace, difficulties are experi enced attimes due to-sluggish circulation in the bath which prevents a rapid diffusion of the alloys, and often forms a skull on the bottom. At other times the bottom fills up from an accumulation of oxids and slag, making the bath shallow, as for instance, in running a basic lime furnace in making high carbon steel.

* The primary object of the present invention is to provide a furnace of the arc type,

having a conducting bottom by means of which the current may be passed through the bath, and having comparatively simple means for varying the amount of current passin through the bath.

A f rther object of my invention is to provide a novel process or method of varying the current and thereby regulating the heat, by unbalancing one or .more of the polyp ase arcs. ,As will be seen hereinafter, this may be done in a number of ways, the effect in each case being to regulate the current flow through the bottom of'the furnace and through the bath.

Other objects and advantages will appear in the following specification, and the novel features of the invention will be articularly pointed out in the appended c aims.

My invention is illustrated in the accompanying drawings, in which Figure 1 is a diagram illustrating one em- 'bodiment of my invention; and

Fig. Qais a diagram illustrating another embodiment thereof.

Referring now particularly to Fig. 1, I have shown therein a furnace comprising, among other parts, an arched top 1, and side walls 2 of suitable refractory brick. The bot-tom of the furnace comprises a lin- .ing formed preferably of two layers 3 and 4, the former being composed of magnesite, dolomite, chromite, ganister, or other suitable refractory materials, and the latter of a mixture of refractory material and better electrically conducting material, such, for example, as carbon, graphite, or other suitable conducting materials, the mixture preferably increasing in conductivity toward the bottom and being rammed or sintered in. My invention, however, is not limited to any particular construction of furnace crucible further than that the said construction shall embody characteristics which will permit the carrying out of my invention. The sides and bottom of the furnace are inclosed in a metal casing or shell 5.

In the present instance the furnace is provided with three arcing electrodes 6, 7 and 8 respectively, which extend vertically through the furnace roof, and are supported in the usual, or in any desired manner, for vertical adjustment, asby means of the cables 9. The electrical power for the furnace is supplied from a three phase circuit A, B and C, which is connected with the primaries a, b and 0 respectively, of the transformer T. It will be understood that this arrangement is for purposes of illustration only, since series or multiple primaries may be used. The secondary windings d, f and e, are connected to the electrodes. 6, 7 and 8, bythe conductors 10, 11 and-12 respectively.

A conductor 14 is connected to the bottom of the furnace through the,medium of the metal casing 5, at one end, and at the other end to a switch arm S which is pivotally mounted at 15, and which may be moved to engage stationary contacts 16, each contact being connected at a difl'erentpoint to one are affected. This produces anunbalancing of the neutral terminal, 11. (2., it makes it eccentric to the terminal voltage. By this adjustable means of tappingthe neutral connection in a variable eccentric position as related to the terminal voltages of the.

star connected secondary polyphase transformer winding, a heavy current may be thus maintained in one or more of the electrodes, thus forcing the unbalanced current to return through the bottom to the neutral connection on the transformer. At the same time a uniform power flow is maintained through each electrode, thus balancing the load on each of the phases of the power supply system which feeds-the furnace.

In addition t the means for regulating the current flow through the bottom of the furnace and through the bath, a greater current flow may be produced by unbalancing the power through the variation of the individual arc lengths of one or more phases of the power system. This may be done by shortenin the arc, that is to say, by adjusting the istance of one of the electrodes from the surface of the bath. It may also sup lying the electrode with voltage equal.

be done by the manipulationof the switch arm S .and the shortening of the arc.

While in each case a variation in the current flow to the bottom of the furnace and the bath is produced, it will be noted that the variation is effected under three distinctconditions; first, by making the length of the arc of one electrode relatively less while to t at supplied to the others; second, by

varying the voltage in one or more of the arcs and maintaining. the length of the arcs equal or balanced; and third, by unbalancing both the length of the arc and the voltage.

In Fig. 2 I'have shown an arrangement in which a three-phase circuit A B and C is connected up with the primary windings a, b, to change from three phase to two phase. The secondary coils, c, d, are connected with the four electrodes 6', 7', 8, and 9, in-the manner indicated. The conductor 14' is connected with two switch arms S and S which are arranged to engage contacts 16' connected with the coils c and d respectively at one end of the latter.

The operation of this form of the device is substantially the same as that illustrated in Fig. 1. The current may be varied by the manipulation of one or both of the switch arms so as to unbalance the voltage. As in the arrangement shown; in Fig. 1, the electrodes may be adjusted so as to cause the variation of the current through the bottom of the furnace and of the bath by varying the length of are.

It will be seen from the description that I have provided a furnace having relatively simple means for effecting a comparatively wide variation in the flow of the current through the bottom; of the furnace and through the bath. Furthermore, by using the means described I attain a flexibility of adjustment which permits the regulation of the current to the exact point to suit operating conditions;

I claim:

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 the polyphase arcs.

9.. A polyphase are electric furnace com-' prising a. plurality of arcing electrodes, a conducting bottom arranged to hold a metal bath, a conductorconnected with said-conducting bottom, and means for varying the current through said conductor and through said bath, by unbalancing the voltage or current in one or more of said arcing electrodes.

3. A lyphase electric furnace comprising a p urality of arcing electrodes, a conducting bottom arranged to hold a metal bath, a conductor connected with said conductingbottom, and means for varying the current through said conductor and through said conducting bottom, said means comprising an adjustable device for unbalancing the voltage supplied to one of said elec;

trodes. I

4. A polyphase electric furnace, compris ing a plurallty of arcing electrodes, a polyphase circuit connected with said electrodes, and means for unbalancing the voltage supplied to one of said electrodes.

5. An electric furnace comprising a plurality of electrodes, a conducting bottom arranged to hold a molten bath, said electrodes being spaced from'the bath to form arcs, a source of polyphase current and means for unbalancing the voltage of one of said arcs while maintaining the length of the are uniform. I

6. In an electric furnace, a plurality of arcing electrodes, a conducting bottom, a conductor connected with said bottom, a secondary source of polyphase current comprising a plurality of transformer windings, each of said windings being connected with one of said electrodes, and means for adjustably connecting said conductor with different points along one of said transformer windings.

7. In an electric furnace; a plurality of arcing electrodes, a conducting bottom arranged to hold a metal bath, a conductor connected with said conducting bottom, a plurality of secondary transformer coils,- each of said coils being connected with one of said electrodes, contacts connected with one of said secondary coils at different points therealong, and a switch connected with said conductor and movable to connect any of said contacts.

-8. The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, which consists in unbalancing the current or voltage of one or more of the polyphase arcs.

9. The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, whichconsists' in .unbalancing the voltage in one or more of the arcs while maintaining the length of the arcs equal or balanced.

10. The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, which consists in unbalancing' both the Voltage and the length of the arc of one or more of the electrodes.

11. The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, which consists in varying the length of the arc of one or more electrodes while maintaining an equal voltage on all electrodes.

12. The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, which consists in varyin the voltage between the electrode and the ath on one or more of the arcs While maintaining auniform power flow through each electrode,v between the electrode and thebath.

13,, The herein described process of controlling the current flow through the bottom of a polyphase are electric furnace of the neutral star connected type, which consists in varying the voltage on one or more of the arcs while maintaining the load on each of the phases of the power supply system balanced.

In testimony whereof I afiix my signature.

' WILLIAM E. MOORE.

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