US1989376A - Electric induction apparatus - Google Patents

Description

-29, 1935. NQRTHRUP 1,989,376

ELECTRIC INDUCTION APPARATUS Filed Jan. 51, 1931 2 Sheets-Sheet l ELECTRIC INDUCTION APPARATUS Filed Jan. 31, 1951 2 Sheets-Sheet 2 14 MIMI/2361191? .17 4 kl I F. NQRTHRUP 1,989,376 I Patented Jan. 29, 1935 UNITED 'STATES PATENT- OFFICE 1,989,376 ELECTRIC INDUCTION APPARATUS Edwin Fitch Northrup, Princeton, N. J., assignor to Ajax Electrotherlnic Corporation, Ajax Park, N. .L, a corporation of New Jersey I Application January 31, 1931, Serial No. 512,536

23 Claims. (Cl. 219-43) My invention relates to induction electric furnaces and especially to spacing and focus inducto'rs and methods of using the same.

A purpose of my invention is to heat a metallic 5 charge in the solid state by progressing it through a spacing inductor, preferably carrying the charge through a soaking pit in prolongation of the spacing inductor so that the temperature throughout the charge cross section may become uniform.

A further purpose is to produce a plurality of heated billets by progressing a continuous charge through a spacing inductor heater and cutting from the heated end a suitable billet length.

A further purpose is to guide the progression of a charge through an inductor by a nonmagnetic metallic shell, slitted longitudinally and thin enough to avoid substantial inductive heating in the best form.

A further purpose is to employ a nonoxidizing atmosphere in a spacing inductor heater.

A further purpose is to arrange afocus in-' ductor heater with separate focus inductor loops on different axes, one beside the other, with a 'primary inductor included within one of the loops and that loop shielded so that workmen are 7 protected from contact with the primary inductor by the low voltage-focus inductor loop surrounding it and also by the shield, while the other focus inductor loop is accessible'and safe in use.

- A further purpose is to extend a primary inductor axially somewhat beyond a spacing inductor to increase the concentration of induction in the ends of the spacing inductor, thus allow ing for losses peculiar to the ends.

A further purpose is to construct a single turn focus inductor of a plurality of water cooled tubes electrically united by lateral strips in contact with the tubes.

A further purpose is to winda primary inductor of hollow flattened edgewound tubing while preferably using a spacing inductor in inductive relation with the primary inductor of hollow flattened flatwound tubing. i

A further purpose is to use alternatively guides of different kinds, w hether of ring shape or in the form of skids or otherwise.

Further purposes appear-in the specification and in the claims.

My inventionrelates both to the methods involved and to apparatus for carrying out the methods.

In the drawings I illustrate one only of the many constructions which may be used to embody my bread invention, choosing the form shown from the standpoint of satisfactory operation and convenient illustration of the principles involved Figure 1 is a diagrammatic central vertical section of my preferred form. v

Figure 1a is a fragmentary enlarged view of a portion of Figure 1, showing a modification in the charge.

Figure 2 is a section of Figure 2-2.

Figure 2a is a fragmentary enlargement of Figure 2.

Figure 2b is a fragmentary end elevation corresponding to Figure 2a and showing a variation of the charge supporting means.

Figure 3 is an end elevation of Figure 1 position 3-3.

The inductive heating of a solid metallic charge has ordinarily been accomplished by passing it through a primary inductor coil directly inducing current in the charge, or through a niufile 1 on the line whose walls are inductively heated. While both of these forms of heating are highly advantageous, each has features rendering it unsuitable in certain installations.

For example, where direct inductive heating is used, the inductor coil is ordinarily supplied with current at a fairly high voltage, requiring good insulation between the inductor and the charge and a considerable quantity of insulation. The insulation between the inductor coil and the charge must be capable of withstanding the temperature to which it is subjected by conduction from the charge. Frequently, it breaks down thermally before it ruptures electrically. The designer is not free to leave as much space for insulation between the inductor coil' and the charge as he might otherwise wish because close coupling is required for good power factor.

in the The high voltage inductor coil, being very close to the charge, is also likely to be inadvertently touched by a workman, and consequently special precautions in the way of shields and insulation are needed whereotherwise it might be desirable to have the parts left much more accessible.

In a direct induction furnace, the power factor drops very sharply when the charge is removed from thefurnace, with,a corresponding loss-in efficiency where it is not possible to operate the furnace continuously on full load.

The mufiie type of furnace has the inherent difficulty that the heat is not developed directly in the charge, and it is necessary to allow for conduction and radiation of heat to the charge.

33 my present invention I avoid many of the difficulties met in direct induction from a primary inductor and in inductive muiile heating, while at the same time I retain many of the advantages of these other forms. My invention is to some extent a continuation of those disclosed in my patents, No. 1,378,187 for Focus inductor furnace, granted May 17, 1921 and No. 1,378,138 for ladle heating by high frequency currents, granted May v an explanation of the general principles involved.

As in these patents, I transfer energy-to a charge from a primary inductor through a spacing inductor, or; in some cases, a focus inductor;

By a spacing inductor I mean to designate broadly an inductor in inductive relation to a primary inductor and also in inductive relation to a charge, which transmits energy over a relatively short distance from the primary inductorto the charge, without regard to whether or not any concentration of input takes place, either because the spacing inductor has fewer turns than the primary inductor and therefore carries a larger current, or because the length of the spacing inductor in inductive relation to the charge is less than the length of the spacing inductor'in inductive relation to the primary inductor, or for any other reason.

By a focus inductor, on the other hand, I mean to designate one of a class of spacing inductors which focuses or concentrates energy, either because it has fewer turns than the primary inductor with which it is coupled, or because it has a smaller length in inductive relation to the charge than in inductive relation to the primary inductor, or for any other reason.

Certain aspects of my invention are applicable broadly to induction furnaces, and even in the narrower aspects of my invention, I do not restrict myself to the type of spacing inductor or of focus inductor in which the spacing or focus inductor loops have separate axes or to the type in which the loops are concentric, except in those features applicable only to the nonconcentric form.

In the drawings I show a source of alternating current 6 connected by leads 7 and 8 to a primary inductor 10 of hollow flattened edgewound tubing, supplied with water through suitable connections at 11 and 12. The power factor is desirably corrected by capacitative reactance 9. In inductive relation to the primary inductor 10 is located a spacing inductor 13 having loops l4 and 15. The spacing inductor 13 is made up of a plurality .of bands, each comprising a flattened flatwound tube, connected by bars 16 and 17 welded respectively at the top and bottom of each band, so that electrically the spacing inductor comprises only one turn axially as well as annularly. The spacing inductor is cooled by water flowing from a I plurality of inlet connections 18 to a plurality of outlet connections 19.

, Since the primary inductor and the spacing inductor are stationary with respect to one another, and since no heating takes place close to the surface of contact between them, the separating insulation 20 between the primary inductor and the spacing inductor loop 14 may be extremely thin, insuring very close coupling. I find that in practice a few sheets of mica are satisfactory.

The loop 15 of the spacing inductor surrounds the charge 21. The charge 21 is guided'through the spacing inductor by the walls of a thin non- I magnetic metallic shell 22, preferably of austenitic iron. The shell 22 .will ordinarily be of a thickness less than the depth of penetration for the frequency chosen. The shell 22 conforms closely to the cross section of the ,charge 21 and is slitted longitudinally at 23 to avoid excessive inductive heating of the shell itself. Because of its'thin,

walls, nonmagnetic characterand longitudinal slit, the shell 22 is in no'sense a muilie, but is rather a heat resisting guide for the charge and guard for the interior of the inductor coil.

Between the spacing inductor loop 15 and the shell 22 I'place suitable electrical insulation 24.

vented by ears 25 extending from the ends of the shell and bent over the-ends of the spacing inductor as shown in Figure 2a.

- The utility of the shell 22, while it is likely to begreatest in focus inductor furnaces because of the low voltage on the inductor close to the charge, is by no means restricted to such furnaces, and will be present to some extent in induction furnaces generally.

As an alternative means of support and guidance of the charge I may use rods or tubes as skids 22', as seen in Figure 2b. The skids 22 may be insulated from the inductor coil or may be in direct contact with the inductor coil.

In the latter'case, the skids will be cooled by heat transfer to the inductor coil.

At-26 I show an inlet to the interior of the shell 22 suitable for admitting a 'nonoxidizing gas to prevent oxidation of the shell and scaling of the charge. The charge 21 may be uncut as shown in Figure 1,'or it may be already cut to length as shown at 21' in Figure la. The charge is directed into the shell 22 by a guide 27, and as soon .as the charge enters the shell it is concurrently shell, preferably being protected in the meantime by nonoxidizing gas.

Particularly at the higher frequencies, but to some extent even at moderate and low frequency,

inductive heating is largely concentrated in the outside of the charge. If the inductive heating be'very rapid,'the outside portions of the charge cross section will be at higher temperature than the inside portions after heating. To permit uniform-distribution'of the heat, I provide a soaking pit 28, axially beyond the heating chamber in the direction of charge travel and preferably formed of heat insulating material to prevent too rapid loss of heat. The length of the soaking pit will of course depend upon the rate of heating and the degree of uniformity required.

At the end of the heating chamber or at the outlet end of the soaking pit where soakingis used, the charge may be put to any use required. Where a continuous charge, such as a long rod, is to be shaped, I may very desirably cut the heated charge to the size desired for the shaping machine. As an illustrationI show a circular saw 29, on a movable support 30, for periodically cutting the charge. It will of course be understood that I may heat a succession'of relatively small separate charges instead of a continuous charge, and that where separate charges of proper size are used, no cutting subsequent to heating will be needed. I show a small unit charge in Figure 1a.

I will preferably use as many turns as possible in the primary inductor and as few turns as possible in the spacing inductor. In Figure 1 I illus trate a large number of primary inductor turns and only one spacing inductor turn. I make the individual spacing inductor tubes flatwound as seen at 31 sothat they will cover as wide a space as possible, while I edgewindthe primary inductor in my preferred form so. that a maximum number of primary'turns may be in inductive relation Where a high voltage is impressed on the primary inductor, as will normally be the case, the spacing inductor voltage will nevertheless be quite low, so that workmen will not be endangered. In the structure shown, the sides of the primary inductor 10 are very largely covered by the spacing inductor 13. This is distinctly advantageous from the standpoint of safety.

in operation and can be handled freely and with safety. In case a charge sticks, a' workman may safely insert a metal rod into the furnace without danger to himself even in case of breakdown in the insulation.

Since cooling is more rapid at the ends of the heating chamber, I preferably somewhat increase the inductive input at the endsby extending the primary inductor 10 axially at 33 somewhat beyond the spacing inductor 13. In this way end tubes 34 of the spacing inductor, in spite of the strips 16 and 1'7, carry slightly heavier current than other tubes, inducing more current in the charge.

Actual experiments made by me show a remarkably good power factor regulation. From full load to no load the change in power factor has been only about 7%.

It is diflicult to explain this very lowpower factor change when the charge is removed, but I consider that, among other factors, it is due to the fact that the spacing'inductor provides a secondary circuit for the primary inductor which is closed at all times without regard to the presence ,of the charge in the spacing inductor or its absence therefrom. The spacing inductor/voltage is low, and this permits very close coupling between the spacing inductor and the charge. The coupling between the primary inductor and the spacing inductor is also extremely good. 1' There are doubtless other influences. Of those mentioned, the fact that the spacing inductor always extends forth as a load on the primary inductor is probably the most important.

With a magnetic charge and high frequency current the current is induced in an extreme outer layer first with the result that viewed from the end an annulus of the material is readily heated to a cherry red. Apparently as soon as this outer layer loses its magnetism the current is induced within a corresponding outer layer of charge which still remains magnetic so that an adjoining annulus as viewed from the end is raisedin temperature to correspond with a cherryred color. With continued application of a high frequency current the cherry red zone increases progressively from a mere ring at the extreme outer surface to a wide ring ultimately closing at the center. With lower frequencies of course the depth of ring initially heated would be increased and the progressionof the color inwardly would be much less noticeable, with quite low frequencies heating much more nearly uniformly all the way through.

It would appear that certainly with the higher frequencies and to a lesser extent as the frequencies are reduced the path of the induction lies within the outer shell of the magnetic material and continues there until this portion of the charge loses its magnetism when the current is induced primarily not in this now non-magnetic rim but .in the outermost part of that portion of the charge which still remains magnetic, be-

ing progressively maintained in the' magnetic material as long as any of the material is magnetic.

Whatever be the exact fact, whether the theory suggested above be. correct or not, the fact remains that the temperature is not uniform throughout the entire'thickness of a cylindrical charge-at the time that it is first raised in its entirety to a cherry red; and this gives opportunity for considerable advantage in uniformity of temperature from soaking the charge in a non-oxidizing atmosphere protected against heat leakage but free from any considerable current induction or at least not having more current I induction than will equalize the cooling from the surface. My invention contemplates the possibility of using some induction for this purpose if desired;

I will preferably employ moderate or high frequency current, desirably of the order of several thousand cycles, in the furnace shown. However, many of the aspects of my invention are equally applicable to low frequency, and may be so employed. 4

In view of my invention and disclosure variations and modifications to meet individual whim 'or particular need will doubtless become evident to others skilled in the art, to obtain part or all of the benefits of my invention without copying thestructure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having .thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In an electric induction fu-rnace for heating a travelling charge, a source of alternating current, an inductor coil supplied with current from the source and a nonmagnetic metallic guide within the inductor coil adapted to pass the charge.

k 2. man electric induction furnace for heating a travelling charge, a source of alternating current, an inductor coil supplied with current from the source and non-magnetic metallic guide within the inductor and electrically insulated from it, for guiding the charge travel through the inductor.

3. In an electric induction furnace for heating a travelling charge, a source of alternating current, an inductor coil supplied with current from the source and a nonmagnetic metallic guide within the. inductor and electrically insulated.

from it.

4. In an electric induction furnace for heat-' -a spacing inductor in inductive relation with the primary inductor and also with a charge and walls within the spacing inductor guiding the charge travel through it.

6. In an electric induction furnace for heating a travelling charge, a source of alternating with the primary inductor and also with a charge,

:wallsguiding the charge into the spacing ina travelling charge, a source of alternating cur-.

rent, an inductor supplied with current directly or inductively from the source, non magnetic metallic guides within the inductor guiding travel of the charge through itand heat confining walls in prolongation of the path through the inductor and wherein the charge is free from electric induction.

8. In an electric induction furnace for heating a travelling charge, a source of alternating current, a primary inductor connected to the source, a spacing inductor in inductive relation with the primary inductor and also with a charge, walls within the spacing inductor guiding travel of the charge through it and heat confining walls in prolongation of the path through the spacing inductor. I

9. In an electric induction furnace, a source of alternating current, a primary inductor connected to the source, a spacing inductor in inductive relation with the primary inductorand also with a continuous metallic charge, walls within the spacing inductor guiding the travel of the charge and means operable at a point axially beyond the spacing inductor in the direction of travel of the charge for cutting off a portion 'of the charge periodically.

10. In an electric induction furnace, a source of alternating current, a primary inductor connected to the source, a spacing inductor in inductive relation with the primary inductor and also with a charge, walls within the spacing inductor guiding travel of the charge through it and a charge of nonoxidizinggas within th interior of the spacing inductor.

11. In an electric induction furnace a source of alternating current, a primary inductor con nected to the source, a spacing inductor in inductive relation with the primary inductor and also with a charge and consisting of a single turn from an electrical standpoint and walls within the spacing inductor guiding travel of the charge through the spacing inductor.

12. In an electric induction furnace. a source of alternating current, a primary inductor consisting of a plurality of turns connected to the source, a spacing inductor in inductive relation with the primary inductor and also with acharge and comprising one turn from an electrical standpoint and'walls Within the spacing inductor guiding travel of the charge through the spacing of alternating current, a primary inductor con-. nected to the source and a spacing inductor surrounding the primary inductor comprising inductor bands electrically in parallel and in the aggregate axially shorter than the primary inductor. v v

15. man electric induction furnace, a source of "alternating current, a primary inductor connected to the source and a focus inductor surcurrent, a primary inductor connected to thesource, a spacing inductor in inductive relation rounding the primary inductor and comprising a plurality of bands arranged side by side and united into a single turn in length by strips extending-across the bands.

16. In an electric induction furnace, a. source of alternating current. a primary inductor connected to the source and comprising hollow fiattened edgewound tubing and a spacing inductor in inductive relation with the primary inductor and also with the charge.

1'7. In an electric induction furnace, a source of alternating current, a primary inductor connected to the source and a spacing inductor in inductive relation with the primary inductor and also with the charge comprising hollow flattened flatwound tubing.

18. In an electric induction furnace, a source of alternating current, a primary inductor connected to the source and comprising hollow flattened edgewound tubing and a spacing inductor in inductive relation with the primary inductor and also with the charge comprising hollow flattened flatwound tubing.

19. In an 'electnc induction furnace, a source of alternating current, a primary inductor connected to the source and comprising hollow fiattened edgewound tubing and a spacing inductor in inductive relation to the primary inductor and also with the charge comprising hollow flattened fiatwound tubing, a plurality being laterally connected to form a single turn.

20. In an electric induction furnace, a source of alternating current, a primary inductor connected to the source, a focus inductor in inductive relation with the primary inductor and with the charge, having two loops, one. of which is coaxial with and surrounding the primary inductor and the other of which is bodily at one side of the primary inductor, means for passing a metallic charge in the solid state through the side' focus inductor loop, and a shield enclosing the other focus inductor loop, whereby the oper- .tact with the stock within the heating coil and extending longitudinally of the coil and adapted to receive the weight of the stock.

v22. In an induction heater for travelling st ck,

a plurality of inductor turns in parallel, a p r ary and connections for inducing current in said turns as a secondary and a non-magnetic metallic guide and support for the travellingstock, extending transversely of the lower parts of the turns.

23. In an electric induction furnace for heat-. ing a travelling charge, a source of alternating current, an inductor coil supplied with current I from the source and a non-magnetic metallic guide in contact with and supporting the charge within the inductor coil whereby direct contact between the charge and the inductor coil is prevented and the charge is supported within the inductor coil, so that deformation of the portion of the charge within the induction coil due to its own weight is prevented.

EDWIN FITCH NORTHRUP.

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