US1496299A - Electric furnace - Google Patents

Description

June 3, 1924; 1,496,299

H. E. CLIFFORD ELECTRIC FURNACE Filed Oct. 4, 1921 Patented `lune 3, 1924i.

UNITED v STATES PATENT fil-Fica HARRY ENCLIFFORD, OF NEWTON, MASSACHUSETTS, AASSIGNO'B. TO SCO'VILL MANU- FACTURING COMPANY, OF WATERBURY, CONNECTICUT, A CORPORATION OIF CON- -Nnc'rrt um,

ELECTRIC FURNACE.

Application led October 4, 1921. lSerial No; 505,274.

` To all whom it may concern:

Be it known that I, HARRY E. CLIFFORD,

a citizen of the United States, residing 'at Newton, county of Middlesex, and State of Massachusetts, have invented certain new and useful Improvements in Electric Furnaces, fully described and represented in the following specification and the accompanying drawings, forming a part of the same` This invention relates to improvements in electric furnaces.

. In furnaces employing a polyphase current which is delivered directly to the charge, as by electrodes, when the electrodes are properly'set, a rotating magnetic eld is set up in the metal constituting the furnace charge. The lines of this rotating magnetic field concentrate within the space enclosed by the electrodes and the action of the field causes a circulation or stirring of the metal within the space surrounded by the electrodes. However, the lines of this field diverge in the space outside the electrodes, and the effect of the field in producing a circulation or stirring action in the space between the electrodes and the furnace wall is so slight as to be in general practically negligible. Y

Constructions have been employed in which conductors carrying a polyphase current are located' in or near the furnace wall and opposite or nearly opposite the electrodes.

The flow of current in these conductors sets up a rotating magnetic field or fields additional to those referred to as being set up by the electrodes. The rotating field or fields -set up by the current in the conductors coact with the fields set up by the current in the electrodes, and the coaction of these fields produces valuable results in furnace operation, such as improved mixing and additional heating effects.

The present invention has for .its principal object to produce an improved furnace, generally of the type referred to, in which the rotating magnetic field which coacts .with the rotating field of the heating current delivery means is produced by a flow of current having different characteristics from the heating current.

A further object of the invention is to produce a furnace having certain improved features of construction which are applicable generally to electric furnaces in which two coacting magnetic fields are einployed. n

With the objects referred to and others in view, the invention consists in certain constructions, improvements, and combinations of parts herein fully described and then speciiically pointed out.

Referring to the accompanying drawing- Figure 1 is a diagrammatic plan view of a furnace embodying the invention, the furnace wall being shown in section and the circuits being diagrammatically indicated;

Figure 2 is a sectional side elevation of the furnace shown in Figure 1, the plane of spction being indicated by the line 2 2 in Figure 3 is a perspective view of the conductlors and certain parts connected there wit The" furnace which has been selected to illustrate the invention is of the'usual ty e, the body of the furnace being markedP 1 and the cover 2.

Furnaces embodying the invention will employ a polyphase heating current which will be so delivered to the charge as to set up a rotating magnetic field in the charge. In the furnace shown, the heating current-is three-phase and it is delivered to the charge by electrodes 3 in circuit with a suitable current source, the generator being diagrammatically indicated at 4, the transformers not being shown. The electrodes 3, asillustrat-ed, are set about 120 apart, and the flow of heating current through them into the charge causesy a rotating magnetic eld -to be set up. The lines of this rotating magnetic field are concentrated within the space enclosed by the electrodes and the field causes a rotating and stirring movement of the metal in the space enclosed by the electrodes. The magnetic lines of this electrode field, however, diverge in the space between the electrodes and the furnace wall, and the' motor effect of this field on the metal in this space is practically negligible.

As has been pointed out,furnace constructions have been employed in Avwhich conductors are located inor alongside the fur'- nace wall, a polyphase currfitbeing sent through them. This current produces a rotating. magnetic eld the lines of which converge within the space enclosed by the conductors. This rotating field coacts with the rotating field set up by the flow .of current in the electrodes and produces-valuable esults as improved mixing and-heating efects.

In accordance with the present invention, as in the construction'just referredY to, conductors are employed to set u an additional rotating magnetic field, but t ese conductors are in circuit with a source of polyphase current which has different 'characteristics from those ofthe heatin current. For instance, the frequency o the current thus supplied to the conductors may dier from that of the main heating current; it may differ in wave shape, in voltage, in phase, in amperage, or it may differ in combinationspofthese characteristics. In the particular construction illustrated, conductors 5, 6, 7 are employed. In what are regarded as the best constructions, these conductors, as in the rior construction referred to, are insulate from the charge and .are located inthe furnace wall. Further, such conductors are carried down underneath the bottom of the furnace', and meet y at a common point, as 8, beneath the furnace. By thus causing the conductors to meet at a' common oint, weakening of the furnace bottom such as might result from leading the conductors through it, is avoided. This feature of construction is of ralue not only in furnaces Yin which the additional rotating magnetic field is set up by -a current having characteristics different from the main heating current, but is also of utility in the prior furnaces referred to wherein the current which assists the rotating magnetic field has the same characteristics as the main heatin current. Where, as in the construction siown, the furnace has a detachable cover, the upper ends of the conductors 5, 6, 7 may well terminate below the joint between the cover and the main body ofl the furnace. This permits Aremoval of the Acover without disturbing the conductors and their circuit connections. In thev furnace illustrated, a threefphasc heating current is employed-and the current inthe conductors is also a three-phase current. The conductors 5, 6, 7 are in circuit with the polyphase generator 13 which supplies a current having different vcharacteristics from the heating current.

' Current transformers 10, 11 and 12- are provided, one-for each current hase. These transformers may be and shou d -be located lclose to the leading-in terminals of ,the conductors, `so that the secondary leads from the transformers to the conductors may be made short. The location of the current transformers close to .the leading-in terminals ofthe conductors has advantages in the wayof preventing losses. High voltage curren-t can be brought up to the transformers on comparatively light conductors which can be arranged to securel minimum ma netic and electric losses, and the short lea s .l from the transformers to -theconductors also cut down suchV losses materially. A

In what are regarded as the best constructions, the secondary leadsare formed by a metal annulus 9 which connects the upper ends of lthe conductors, the trans-YK formers being arranged around this metal v annulus, and the annulus Aand conductors being arranged in the furnace wall. This forms a compact construction which is particularly efiicient in theA way lof'preventing losses.

Further, while this construction is of special value in furnaces in which the additional rotating magnetic field is set up by a current flow vhaving characteristics -which are different from those of the main heating current, it ma also be used to advantage in furnaces in w ich the current which sets up the additional rotating magnetic field hasV the same characteristics as those of the main heating current.

A furnace construction -such as has been described, in which the additional rotating magnetic field referred to vis set up by a current which has different characteristics from that of the main heating current, en' ables many useful results to be obtained. For instance, if thecurrent supplied to the conductors be of a lower voltage than that of the main heating current, the problems connected with the insulation of the conductors are simplified. When the current in theconductors has the same voltage as the heating current in the electrodes, there is considerable danger of short circuiting, and great care has t'o be taken with the insula tion, particularly 'in view of the high temperatures to ,which the furnace walls are subjected. With a current in the conductors f of lower voltage than that of the current in the electrodes, this danger of short circuiting is practically eliminated and the insulating problems are simpler. Further, while the heating current sent through the electrodes into the charge necessarily has fixed characteristics because it must effect the heating of the metal, the current sent throughI the conductors may be selected with respect to the particular additional results it is desired to produce. Thus, as has been indicated, if itbe desired to simplify the problems connected with insulation,- a current of lower voltage than the 'voltage of the main current will be employed, and` if additional heating or mixing results are desired, the current in the conductors will be selected with particular reference to the roduction of theseeffects, or, if a comblnation of the various results are desired, the additional current will be selected accordingly.l

Changes andyvariations may be made in 130 the construction herein shown for carrying the invention into'effect, and it is to be understood that the invention is not confined to the particular construction herein shown and described,-

What is claimed is:

l. In an electric furnace, the combination with means for so delivering a polyphase heating current to the charge as to set up a rotating vmagnetic field therein, of conductors,l means for supplying to said conductors a polyphase current -having different characteristics from the heating current, the current fiow in the conductors also setting up a rotating magnetic field, said conductors being located in such proximity to the charge` and in such relation to the heatingcurrent delivering means that the conductor field coacts with the heating-current field to increase the stirring effect.

2. In an electric furnace, the combination iwith electrodes for delivering a polyphase heating current to the charge, the electrodes being so arranged that the fiow of current therein sets up a rotating magnetic field in the charge, of conductors, transformers, one for each current phase, for delivering polyphase current to the conductors, the conductors being located in such proXlmity tothe charge and in such relation to the electrodes that the conductor-field coacts with the heating-current field to increase the stirring effect.

3. In an electric furnace, the combination with electrodes for deliverin polyphase heating current to the charge, t e electrodes being` so arranged that the flow of current` transformers being arranged close to the conductor terminals, the conductors being so located in such proximity to the charge 'and in such relation to the electrodes that -therein sets up a rotating magnetic field Vin the Acharge,'of conductors;transformers,

one for each current phase, for delivering polyphase current to said conductors, said transformers being arranged close to the conductor terminals and in the furnace wall,

the conductors being so located in such proximity to the charge and in such relation to the electrodes that the conductorfield coacts with the heating-current field to increase the stirring effect.

5. In an electric furnace, the combination with electrodes for deliverin polyphase heating current to the charge, t e electrodes being so arranged that the lfiow of current therein sets up a rotating magnetic field in the charge, of conductors located in the furnace wall, lsaid conductors being carried down alongside the charge and underneath it and meeting at a common point, and means for supplying a lyphase current to said conductors, where y'the current flow in the conductors sets up a rotating magnetic field which coacts with the rotating magnetic eld established by the current in the electrodes.

6. In an electric furnace, the combination with electrodes for delivering polyphase heating current to the charge, the electrodes being so arranged that the flow of current sets up a rotating magnetic field in the charge, of conductors located in the furnace wall, said conductors being carried down alongside and underneath the charge and meeting at a common point, means for supplying a polyphase currentto said conductors, and transformers, one for each current phase, located in the furnace wall and close to the leading-in terminals of the conduct ors` wherebyv the current flow in the conductors sets up a rotating magnetic field which coacts with the rotating magnetic field established by the current, in the elec-.

trodes.

7. In an electric furnace, the combination with electrodes for delivering polyphase heating current to the charge, the electrodes being so arranged that the flow of "current therein sets up a rotating magnetic field in the charge, of conductors located in the furnace Wall, said conductors being carried -down alongside the charge and underneath it and meeting at a common point, and means for supplying polyphase current to said conductors having different characteristics from the heating-current, whereby the current fiow in the conductors sets up a rotating magnetic field which coacts with the rotating magnetic field established by `the current in the electrodes.

8. In an electric furnace,'. the combination with electrodes for delivering polyphase heating current to the charge, the electrodes being so arranged that the flow of current sets up a rotating magnetic field in the charge, of conductors located in the furnace wall, said conductors being carried down alongside and underneath the charge and meeting at a common point, means for supplying polynhase current to said conductors having different characteristicsl from the heating-current, and transformers, one for each current phase,located in the furnace wall and close to the leading-in terminals ofthe conductors, whereby the current ow in the conductors sets up a rotating magnetic field which coacts with the rotating magnetic field established by the :current in the electrodes.

9. In an electric furnace, the combination with means for so delivering polyphase heating current directly to tlie charge as to set up a rotating magnetic field i in the 5 charge, of conductors -insulated from the Charge and in circuit with a source of polyphase current, the conductors being so ar ranged that the flow oficurrenttherein sets up' an additional rotating magnetic field in 1U the charg which coacts with the rotating set up arotating magnetic field in the charge, of conductors arranged around the heating-current delivering means, a source of polyphase current of different characteristics from that of the heating-current, con- 20 nections including a current transformer, one

for each current phase,.between said source and the conductors, the conductrs bein so located as-to set up a rotating magnetic eld or fields in lthe charge which coact with the Y 25 rotating field set up bythe heating current.

11. In an electric furnace, the combination with means for soy delivering polyphase heating current directly to the charge as to set up a rotating magnetic field in` the charge, of conductors arranged around the heating current delivering means and insu- Y lated from the charge, a source of polyphase current 'of lower voltage than the heating current, and connections between said source and the conductors including a transformer for each phase of the current, the conductors being so located as to set up an additional rotating magnetic eld or fields in the charge which coact with .the rotating field set up by the heatin -current.

12.l In an electric urnace havinga detachable cover, the combination with electrodes for so delivering polyphase heating current directlyv to the charge as to set up a rotating magnetic field inthe charge, of conductors arranged around the electrodes and havin their upper ends below the 'joint between the cover andthefurnace, means for delivering polyphase lcurrent to said conductors, said means including a transformer for each co'nductor, the conductors being so -arranged that the current iiow therein sets upa rotatingI magnetic eld or fields in the charge .Which coact with the rotating eld set up by the heating-current. g

13. In an electric furnace having av detachable cover, the combination Awith electrodes for so delivering ,polyphase heating current directly to the charge as to' set up l al rotating magnetic'eld in the charge, of 60 conductors arranged around the electrodes and having their upper ends below the joint between the cover and `the furnace, Vmeans for delivering polyphase current to said conductors, said current having different characteristics from the main heating current, said current delivering means for the 00nductors ,including a. transformer for each conductor, the conductors being so arranged that the current fiow therein sets up a rotat- I- ing magnetic field or fields infthe char which coact with the rotating field set up y the heating current.

14'. In an electric, furnace having a detachable cover,'the combination with electrades for Vso delivering polyphase'heating current directly to the charge as to set up a rotating magnetic field in the charge, of conductors arranged around the electrodes,

said conductors having their lower ends bey neath the furnace and their upper ends terl trodes for so delivering polyphase heating,r 95

current directly to the charge as to set upa rotating magnetic fieldv in the charge, of conductors arranged around the electrodes, said conductors having their lower ends be' yneath the furnace and their upper ends terminating below the joint of the cover and the furnace, and`means including a transformery for .each conductor for deliver-in to the conductors polyphasecurrent of di ferent characteristics .from the main heating-current, the ,transformers being located .in the furnace walls andclose tothe lead-l ing-in terminals of the conductors,.and the conductors being so located thatI the current ow therein sets u a rotating magnetic elduor fieldsuin tlg) current.

In testimony whereof, I have hereunto set m hand. n y `HARRY E. CLIFFGRD.

e charge which coact with the rotating field sct up by the healing-

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