US1718172A - Electric furnace - Google Patents

Description

June 18, 1929. w. E. MOORE ELECTRIC FURNACE Original Filed Sept. 7, 1916 Willi awn/E Moo re,

Patented June 18, 1929. I

UNITED STATES WILLIAM E. MOORE, OI PITTSBURGH, PENNSY LVANIA.

ELECTRIC FURNACE.

Application filed September 7, 1916, SeriaI No. 118,890. Renewed-0ctober 3, 1928.

This invention relates more especially to improvements in arc type electric steel melting and refining furnaces.

In this class of furnace it has heretofore been customary to melt down the cold scrap with the same voltagewhich is used for refining, and on the refining operation to res duce the current, that is, the power in the furnace to keep the temperature within the liiiiits which the refractory linings and roof ofthe furnace will stand without toomuch deterioration. v

I-find that when melting steel, it is possible to run with much higher energy input and longer arcs without damage to the refractories so lot: as thereis unmelted steel in the furnace w ich keeps the temperature constant, but when refining it is best to materially reduce the power and shorten the arcs to keepwithinsafe temperature limits on the refractories. It is, however, desirable to run at much higher power for melting than for refining in order to reduce the'heat losses from radiation per ton melted and obtain a greater output per day from a given size furnace.

I have also found it extremely important when refining to run with a very short are, say volts, to prevent radiation at are temperature from in'uring the furnace. walls, whereas, when me ting a much longer are is permissible and-also desirable to prevent the fragments of scrap caving in to the cavities moltened by the arcs and contacting with the electrodes thus causing short circuits; and also to get increased power into the furnace without increasing the already enor-,

mously large currents, or requiring conductors and electrodes of unwieldy size in cross section. v

I have found too, that in an-arc playing from a carbon or graphite electrode to scrap metal or to a slag containing lime, silica, etc., there is a rectifying effect on the alternating-currents tending to permit heavier current to flow onedirection for one-half wave length than in the other, and that if this recti ed current be caused to flow down through the metal bath and furnace bottom,

it tends to agitate the metal and prevent hot spots or a .cold bottom by circulating the bath and brings it into more rapid circulation with the overlying highly heated slags which are depended upon in a large measure to refine stee i The primary object of this Invention may be stated generally to expedite or shorten the time involved in melting and refining steel, allowing the use of smaller-conductors and electrodes and more thorough heating and mixing thevbath, in this nace, and this I accomplish first by providmg means for obtaining a large variation of the power input in the furnace by varying the arc voltage without materially varying the current through the arcs, thus permitting rapid melting with electrodes and secondary leads-of minimum size. Second, by efi'ectmg an electrical connection between the conducting bottom of the furnace and a neutral point in the secondary windings of the trans "formers so as to permit a heavy flow of rectified or direct current for better heating and rmxmg the bottom of the bath, and third, by includlng in the secondary circuit of the transformer a reversing switch by which \still greater current flow may be effected through the bath in refining. In order' to more particularly describe my invention, reference will be had to the accompanying drawings in which,

Fig. 1 1s a. diagrammatic view illustratin one orm of my invention;

ig. 2, a diagram showing the star or Y connection of the transformer primaries when refinin and Fig. 3, a 'agram showing delta connections of the transformer primaries when melting. r

In the accompanying drawings, the furnace proper illustrated is of the three phase are type in which 1, 2 and 3 represent the three arcing electrodes. These electrodes extend .throu h the furnace top 4 and may be support in the usual or any desired way. They are usually mounted upon mechanism for adjusting them vertically. The arched top 4 of the furnace issupported upon side walls 5, composed of so-called ac-id brick down to a point several inches above the slaglevel, and preferably of so-called basic type of fur-- brick below this point. The bottom lining of the furnace is formed preferably in two or more layers 6 and 7, the former composed of magnesite, dolomite, or other refractory material, and the latter of avmixture of refractory material and such better conducting material as carbon, graphite or metal turnings or similar conducting material progressively increasing in conductivity towards the bottom and rammed or sintered in. I do not, however, limit my invention to this particular way of making the furnace hotthree transformers 11, 12 and 13, in wh i the secondaries connectedto the-eleetrode.

tom conducting. The sides and bottom of the furnace are enclosed in a metal shell 8.

In this drawing, 9 reprcsentsthe metal bath .and10tl 1e;slag. I i

(-urrcnt 1s supplied to the furnace from v shell 8.

Connected. in the secondary .c ircuit1 of transform-r.112 .is "a re-ve s1 The primaries of the-three transformers are connected to the -power mains -16, 17;

and 18 throughtwo switches 19 and 20, the former of which whenflclosedconnects the primaries in Y .'or star formation, and the latterwhen closed connects, them indelta. formation. T hose two switches may;be mter-connectcd by a .r'od 2l or other suitable In refining, switch 19 is. closed,-and switch 20.

open,- thus connectin" the primaries, in ,Y-

or star formation. y. means of-thisj Zarinput to the furnace may be-socured by vary-I ing the arc voltage withoutmaterially varying the current through the-arcs, thus per-f mitting more rapid.lneltingswith given size electrodes and secondary leads.

By connecting the neutral point of the secondaries of the transformers to thesmetalshell of the furnace 8, a direct;current flow,

due tothe rectifying effect hereinbefore re-' ferred to, is effected from, the electrodes through the metal bath, whichcausesa bot tom-heating and agitation-ofthe batl1,-as'

above pointed out. 1

.VVhen the upper :layers of the'lining of the bottom ofthisfurnace become highly heated, they becomeelectrically conducting the metal bath to the toplayer-whiclris ren-:

dered electrically conducting'by the heat of the furnace, thence :to the lower layers of the bottom which are made conducting at lower temperatures by reason of their being intermixed with conducting materials such as carbon, graphite or other materialin' the manner above described, thence to' metal shell 8.

If switch 15 bet-brown in such direction the refining process by Without limitingmy invention to the at:

;cific form herein shown, what, I- .claim is:

1. .An electric furnace hayingtliree arcing tran. ormer secondas connected to'sai'd e at: odes, an electrical comlection from a neutral point in said conk'larie's to said conducting bottom, and

maries for varvingt-he arc voltage between v,the melting and refining operations. l v v i I I ng.switch glm p the funct on of wh ch willlater;bc;descr1bed.

An electric furnace having three. arcjing ,y c electrodes,anda:refractorybottoinrendered switch v20 is closed -3.lld1

, electrodes, and a refractory bottom rendered I ele t y.r0nsl. ctms 2. An electric furnace; having three arcingza electrodes, and a refratorysbottoiujrendered.: electrically conducting, .-trans former second.-

aries connected to saidpelectrodes'v in Y-. 'for- J matioma conductor-i.:leadingfronra neutral. point in thejsecondaryfconne'ctions.to said; -condiurting botton 'f'and :switchingmeans in. the transformer: primaries for. .varyin the arc. .volt age between ,the melting and refining =2 oberat-ions. means whereby when one is closed, theothe'r,

electrically conducting, .an-.=electrically con-.-

ducting shell, transformers for. supplying electric power to said: electrodes and having.

electrical connection from a .neutral point .or--

to the conducting .sh'ell'of said furnace, and

:secondaries connected to said-electrodes,- an

.neutral points in saidsecondaryconneetions rangenlenta largeflvariation of the power switching means for-i. connecting. the pri-:.-.-.

maries'ofsaid transformcrsfor varyin zthe; i

are voltage .b'etweenzthe melting and ref'ihing oPerat1ons.I

4. An electric furnace having arcing electrodes, and a refractory bottom rendered electrically conducting, transformers for supplying: electric-power; to. saidgelectrodes 1 and having secondaries-connected to said in said secondary 'connection to the conducting bottom of said :furnace, and switching means for connecting the primaries of-said..--' I transformer. in -high voltage formation .in low voltage formation -atiwill.'-,- and therefore form a path for current from i.

5.'-In the manufacture -voffstcel and other metals in an electrics furnace having three electrodes connected'in a three phase circuit;

and a bottom capable of conducting electpimity, the method which i 'consists in causing currentto pass fromsaidelectrodes through 2 the charge and. the material of the furnace bottom to a neutral point in'the three phase 7. The combination with an electric furnace for melting and refining iron and steel, such furnace having a refractory lining and three arcing electrodes, of a three phase transformer having a set of primary windings adapted to be connected to a source of current supply, and a set of secondary windings, a conductor extending from each of said secondary windings to one of said electrodes, switching means for changing the connections of one only of said sets of windings from star to delta, or vice versa, without altering the connections of the other set whereby the voltage at the arcs may be varied, and means providing a path through the furnace bottom for current flow between the molten charge and neutral point of the secondary windings.

8. An electric furnace having three arcing electrodes and a bottom susceptible of conducting electricity, a transformer comprising three-phase primary and secondary windings, said secondary windings being connected in star formation, connections be tween the terminals of said secondary windings and said arcing electrodes, a connection between the neutral point of said secondary windings and the bottom of said furnace, means for connecting said primary windings with a three-phase source of supply, and means for'reversing the normal relative direction of current flow through one of said electrodes, whereby a current is caused to flow through said furnace bottom.

9. An electric furnace having three arcing electrodes and a bottom susceptible of conducting electricity, a transformer comprising three-phase primary and secondary sets of windings, said secondary windings being connected in star formation, connections between the terminals of said secondary windings and said arcing electrodes, a connection between the neutral point of said secondary windings and the bottom of said furnace, means for connecting said primary windings with a three-phase source of supply, and means for reversing the connections of onephase of one of said sets of windings, whereby a current is caused to flow through said furnace bottom.

In testimony whereof I afiix my signature.

WILLIAM E. MOORE.

CERTIFICATE OF CORREC'IIOII.

Patent No. 1, 718,172.

Granted June 18, 1929, to

WILLIAM E. MOORE.

It is hereby certified that the above numbere n was said plten said Moore whoa Corporation of Delaware", and cm-pontwn t in said invention, and that the said Letters hat the same may conform to t to the inventor, "Pittsburgh Research Corporation, being assignee of the entire interes of assignments in this office; with this correction therein t case in the Patent Office.

Signed and sealed this th dsv of Julv.

(Seal) (1 patent was erroneously issued t should have been issued to as shown by the records Patent should be read he record of the M. l liners. Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,718,172. Granted June 18, 1929, to

WILLIAM E. MOORE.

It is hereby certified that the above numbered patent was erroneously issued to the inventor, said "Moore", whereas said patent should have been issued to "Pittsburgh Research Corporation, a Corporation of Delaware", said corporation being assignee of the entire interest in said invention, as shown by the records of assignments in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the. case in the Patent Office.

Signed and sealed this 30th day of Julv. A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents.

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