US1326120A - Assigbiob to general electbic - Google Patents

Description

M. UN,GER.

'INDUCTION FURNACE- APPLICATION FILED APR-'21. I919.

' Patented Dec. 23,1919.

2 swans-sun? I.

Inventor. Magnus Linger, b 4. M

His fltLorneg.

, UNGER." moucnou FURNACE.

APPLICATION FILED APR.21. 1919.

71,326,120. Patented Dec. 23,1919.

2 SHEETS-SHEET 2- inventor 'Magnus Llnger,

MAG-NUS UN GER, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

To all whom it-mdy concern:

Be it known that I, MAGNUs UNGER, a citb zen of the United States, residing at Pittsfield, in the county of Berkshire, State of operation. It is possible that certain limita-' tions which were believed to be inherent in such a construction have interfered with the practical use of this structure, as for example, the belief that it is necessary to locate the legs of the core outside theessential parts of the leakage field ofthe primary winding and the charge constituting the secondary. Such a construction would necessitate a larger core with corresponding increase in cost, core loss and exciting cur rent. I have found that the reduction in stray flux would be negligible.

I have discovered that it makes no appreciable difference in the power factor of the furnace to place the legs of the core closely to the primary winding and the charge container.

It is the object of'my invention to provide an induction furnace having a primary winding located above the charge container and embodying the above and other improvements hereinafter pointed out with particularity in the appended claims.

A complete understanding of my invention may behad from the following description taken in connection with the accompanying drawings. Figure 1 is a top view; Fig. 2 1s a vertical section of a furnace embodying my invention; Figs. 3 and 4 illustrate structural details; and Fig. 5, Figs. 6,

6 and Figs. 7, 7 illustrate arrangements and electrical connection of the primary wi i g,

Specification of Letters Patent.

about 60 to- 90;

INDUCTIONFURN ACE.

Patented Dec. 2a, 1919.

Application filed April 21, 1919. Serial No. 291,615.

Referring to the dra-Wingand particularly to Fig. 2, the furnace comprises a magnetic core consisting of vertical legs .1, 2., 3, a

horizontal lower yoke 4 and a horizontal upper yoke 5 connecting the vertical legs 1, 2 and 3. The primary winding comprises a flat coil 6 consisting in some cases of several interconnected sections, as hereinafter described in connection with Figs. 5, 6 and 7. The terminals 7, 7 of the primary winding'are shown in Fig. 1.

. The charge to be treated is contained within an annular crucible 8 located beneath the primaryiwinding 6 and surrounding the central leg 2 of the core. The crucible 8' is provided with an' outer shell 9 of steel, or other suitable metal, which has one or more insulated joints to break the electric circuit. It is lined with a layer of fire brick 10, inside of which is'an inner lining 11, consisting of highly refractory material, as, for example, crystallized magnesia, preferably, n'iagnesia which has been molten, allowed to crystallize and thereupon powdered and rammed into place with a suitable: binder.

As shown in Fig. 20f the drawing, the sidewalls of the crucible are outwardly inclinedso as to make an-an'glewith respect to each other of about 60 to 90,that is, lines passing through. the intersection of a ver- 'tical plane with the opposite side walls meeting. at an angle within the l imits o'f This construction has the following advantages; It provides a shallow furnace chamber in which a given amount of charge, such as melted steel, can be brought closer to the primary winding 6 than ina deep narrow furnace chamber; (2) the position of the walls enables them to be easily repairedwhen cracked or worn out'by the action of the charge and the slag; the meniscus of the melted charge is more nearly flat and hence there is less slag required to completely cover the melted metal than in a deep narrow chamber in which the meniscus is driven down on one sideand up on the opposite side by the magnetic action of the stray flux to a greater degree than in a'shallow chamber; (4) the heating action of the current induced in the charge is greatest at the surface, that is,nearest the primary: winding. Hence in awlde, shalof the core being first removed.

The crucible is provided with a cover 1:5 I

of silica lire brick, crystallized niagi'iesia, or other suitable refractory material. l he cover 12 is preferably prorided with rings 13, ll, of iron or the lil e, on its inner and outer side. walls, and these rings may be provided with bands 1' to which hooks may be applied cciivcnience of removal of the cover if as indicated at 17.

The primary winding (3 is provided with a CtlSllli? or housing 20, consisting of noin magnetic ni-rtcrial, such for example, as brass, or 25)? nickel steel. The central leg; 2 of the core is provided with casino; ll. spaced away from the core and providin e space for the passage of the cooling: fluid,

The lowerL finally emerging thr ugh outlet openin at the pcriph of the casino ".20.

ably openings are provided for the passage of some oi: the cooling air over the top of the cover 12. I

Circular angle irons it) and :3? rest upon the yoke .5. and act supports for the pri mary coil ti and Sll1ll ll11(llll2f casing which are connected thereto by studs 2b. lheforably. the cover 12 is also connected to one of the angle iron supports, for exam-- pic, by connecting; rods already referred to. This construction enables the yoke, primary coil, its casing and the cover of the furnace to be removed as a unit. the bolts to connecting' the yoke to the vertical lc in this manner convenient access may be had to the charge within the crucible. which is then entirely exposed.

The entire furnace is supported within a frame 31. hungby the shaft 32 on trunnions 33, so as to cnablelhe furnace to be tilled by any convenient means. such as the hand wheel ill. for the removal of the charge.

As shown in Fig. 1, a number of charging doors 35. 36. and 37 maybe provided for the introduction of metal to be melted. slag forming materials and the like. Convenient, access is provided thereby to all parts of the such as air. end of the 21 connects with an inlet tube the upper end reg as with an inlet o into the casing 20. A. blast of air rel through the inlet tube 2;. passes .oin l the core 12 and from thence around the ci charge in the crucible, rendering convern lent the supervision of slagging operations and the like. A pouring spout 38 provided for the discharge of the metal. and slag.

Cihe magnetic core of the furnace is so proportioned and designed that the mag; nctic flux density will be substantially uniform when the furnace is under load. The limiting feature determining the size of the core of an induction furnace is generally not the core loss which is relatively low on accountof the low frequencies used. On the other hand. the factor which is of considerable importance is the exciting current required for the primary windings. The greater-the exciting; current the lower will be the power factor at which the furnace will.

operate. By proportioning the core to give a substantially uniform flux density at load current. there will be a substantial reduction .in the core loss as well as in the exciting current render load conditions. The lower yoke l; of the core because of its more remote location from the. primary and secondary winding' has a lower flux density than the upper yoke This is not only in accord with theoretical considerations taking into account the leakage iclds but has been {13(- ariincntally determined by me.

in order to operate the furnace substantially uniform flux density largest cross-sect on to the top 'hc same flux with a.

yoke I) is illla will have nearly density as at. no load. The vciucal lo 1. 2 and 3 bottom \'()l\'@ 4- will have cross-section 503% less than the. cross section of the top yoke. The actual proporticni of the sections will depend upon the particular design and is based upon the distribution of the stray tin ln this manner the weight of the core may be reduced .without sacrifice of ciliciency. For example, in a ill-ton induction furnace a core designed to give a uniform 't'iulv density of no load. would weigh forty tons. The weight of such a core in a furnace of the design illustrated herewith could be reduced about 15')? or more in weight of material with a correspoiulingly reduced cost.

There is always some danger in an induction furnace of a fracture of the lining and the escape. of molten metal through the break with consequent oamac'c to the core and other parts of the furnace. As already indicated above. I have provided a shield about the core to obviate damage by the escape of molten metal.

Figs. 3 and -l illustrate in section specific forms of shields en'ibodying my improvement. The shield illustrated comprises a metal form i1 upon which are located a layer 42 of refractory fire-proof material such, for example, as mica, and an; outer I gri vo I 21 5 culatoiji current"being set-up in the bath 111 some sizes of furnaces a layer of asbestos aprlmary winding, upon sald core and a layer 43 of fibrous refractory material, such as'asbestos. As asbestos fabric loses part of its mechanical strength at a temperature ofabout 200 to'300 C. due to a burn-out of the cotton binder commonly used, I prefer to impregnate the asbestos with'a binder, such as a phenolic condensation product. The heat insulating properties of asbestos and mica serve as adequate protection even for molten steel at 1600 C. In some cases the metal backing may be omitted and in fact alone will furnish adequate protection.

Although in Fig. 2 the primary winding of the furnace has been indicated asconsisting of two sections, it is desirable in some cases .to provide more than two sect1ons. In any event, whether two sectlons or agreater number are used I provide 0on v,magnetlccore, a primary wmding thereon s5 nections and switching means for supplying one of these sections or a combination of sections with current to the e zclusion of the; I other sections in order to ad uStthe shape of the meniscus of the molten charge in the furnace'brucible. For example, in Fig. 5

-I have shown a primary coil consisting of I sections 45$) 4'8 provided'with separate conductors 49 'to..53', and respective switches "54:

to 58. By closingswitches 5,4.and 55 current can be sent through section. while the remainingxsections remain open-cir- -cuited, and in the same way by closing switches '54: and .56 while the remaining switches remain. open current may be sent through the sections 4E5and 46 in series. In

this-'maiiner the magnetic center of they excitation may be shifted from the inner toward the outer periphery of thefurnace crucible. The effect of this is'illustrated more clearly in Figs. 6 and 6 and? and 7 In Fig.5 two groups of coils 59 to 62 and 63 .to' 66. are connected electrically in parallel 2 through the conductors GZand 68. In that case} wtheemolten charge; assumes a shape somewhat-as shown in Fig. 6, a single ciras indicated by arrows. This single cir- L I culatory efi'ect lasjdisti nguished from the double circulation is. distinctive-ofa fur-' nace built in accordance with-my invention having a shallow crucible with-{diverging walls A single circulation as illustrated obviate the deleterious suction effect on the allrcaused by a'double circulation.

69. 'This UQQYQIQIiQSS- iIi thG shape-of the meniscus requires a larger amount of slag to fully cover. jfthe m'etal at-the High point of'the bath than wouldberequired with a more level-meniscus. .It is preferable;

therefore for some-metallurgical o 'erations to change' the connections by shi ing-the switches 71, 72, 73, 74' and 75 to conne ct',the

coils 59, 60, 63' and 64 in series, asiiiidicated shape of a; meniscus .shown in ere '1s.a;.depress1on at th'e'po'int I in- Fig. 7. 70

What I claim as new and desire to secure by Letters Patent of the United States, is 1. An induction furnace having a melting chamber, the side walls of which are outwardly inclined and makean angle of about 75 '60 towith respect to each other.

2; An induction furnace comprising acore,

furnace chamber located below said primary Winding and adapted to contain a charge, the 0 -Walls of said chamber being outwardly inclinedabout 60 to 90 with respect to each other.

3. An lnductlo'n furnace comprlsing a and a crucible located beneath said winding for containing a charge constituting a secondary winding, the legs of said core being placed closely about said primary and secondary windings within the leakage fields of 90 said windings. I 4. An lnductlon furnace comprislng a core I having a removable yoke, a primary winding upon said core, a charge-containing chamber located upon said core, a cover therefor, '-means mechanlcally connectlng together said yoke, cover and all parts above said chamber -1I1 order toenable the same to be removed'as a unit in the operation of said furnace to expose a charge within said crucible. 1 5. An inductipn furnace comprisinga core, 'a primary winding interlinked .magneti cally With said core, a housing for said winding, a removable yoke for said core,.means for mechanically connecting said yoke, winding and housing, and a .charge "containing chamber located beneathsaid primary wind- .6. An inductionfurnacecomprising acore, a remova ble yoke for said core, a primary wlnd no" interlinked ina'gnetically with said core, a ousing'for said winding, havin in- .let and outlet openings, means" attac ing said wlndlng, and houslng to said yoke and a housing'for said core providing space for a "cooling fluid and communicating with the inletof the housing for the primary coil. 7{' jAn:1nduction furnace comprising a core 'having a' disengageableyoke, a. primary winding for, said core, a crucible for contaminga charge constltuting a secondary windingnafcover' for said crucible and means connecting said yoke, primary winding and cover to enablethe same to be removed as 8 Aninduction furnace comprising a core,

a charge container surrounding-said core,

a primary-Winding consistingv of a plurality ofsections located upon said core abovesaid 13o container, and switching means for varying the electrical connection of said coils to each other. v

9. An induction furnace comprising a core, a refractory container adapted to contain the charge constituting the secondary" winding of the furnace and a primarv \Yindino' for said furnace consisting of a plurality of sections, and switching means exciting one or more of said sections to the exclusion of other sections in order to vary the relation of the magnetic center of said primary Winding to the furnace charge.

10. An induction furnace comprising a primary winding thereon, a crucible adapted to contain the charge constituting the secondary Winding, a core of magnetic material linking said windings, said core being located in part beneath said crucible thereby subject to contact with the accidental escape of molten material through a fracture in said crucible, and a shield located between said crucible and parts of said core exposed to crucible adapted to contain a charge constituting a secondary winding, the cross-section of said core being proportioned to give substantially uniform flux density when said furnace is operated at load.

In witness whereof I have hereunto set my hand tliis'lSth day of April, 1919.

' MAGNUS UNGER.

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