US3297811A

US3297811A - Cooling system

Info

Publication number: US3297811A
Application number: US338940A
Authority: US
Inventors: Kugler Walter
Original assignee: Deutsche Edelstahlwerke AG; AEG AG
Current assignee: Deutsche Edelstahlwerke AG; AEG AG
Priority date: 1963-01-18
Filing date: 1964-01-20
Publication date: 1967-01-10
Anticipated expiration: 1984-01-10
Also published as: GB1043002A

Description

Jan. 1.0, 1967 w. KUGLl-:R 3,297,811

COOLING SYSTEM Filed Jan. 2o, 1964 (QuitarV Kugler uw mmff United States Patent O 11 claims. (ci. 13-29) The present invention relates to a system for cooling induction coils by means of a gaseous coolant.

More particularly, the present invention relates to a system for cooling the induction coil of -a trough-type induction furnace.

FIGURES 1 and 2 are sectional views showing -a typical trough-type induction furnace equipped with la conventional cooling arrangement. Such an induction furnace comprises a metallic housing 1 within which is a packed refractory lining 2. The lining 2 is provided with -a trough 3 containing the liquid material to 'be heated, this material itself constituting the secondary winding, heat being produced within this trough induction. The heating system is arranged within a cylindrical openin-g 4 and comprises the induction coil 5 and the magnetic yoke 6 of the transformer 7. The induction coil 5 is centered in the opening 4 by means of suitable spacers 8.

The liquid melt, as well as the joulean heat loss of induction coil and the iron losses of yoke 6, all contribute to yliberate substantial amounts of heat in opening 4, and this would unduly increase the temperature of the coil. In order to prevent this, cold air is blown through the interspace 9 that is formed Ibetween the wall of opening 4 and the coil 5, as well as through the interspace 10 between the coil 5 and the yoke 6.

i Experience has shown that this type of 'cooling is inadequ-ate at higher `melt temperatures and at increased power of the heating arrangement. Accordingly, the air-cooled system is replaced by a water-cooled system. Such a water-cooled system takes the form of a doublewalled jacket arranged in the space 9, the outer wall of which jacket lies against the wall of opening 4. The coil 5 abuts against the inner wall of the double-walled jacket by means of the spacers 8. This cooling jacket carries off the heat derived from the melt in trough 3, as well as the major portion of the heat produced by coil 5, so that all the air Iblown through interspace 10 has to do is to cool the yoke 6.

Water-cooled systems have been found to be very efficient, but they have a number of inherent drawbacks which have been found to be particularly bothersome in the case of electrical melting furnaces'for iron or metal. These drawbacks are, for example, that the welded seams of the water jacket are vulnerable to rup` ture in the event the supply of water is even briefly interrupted. Also, scales or other incrustations form on the walls of the jacket which makes it necessary periodically to shut down the furnace in order to clean the nside of the cooling jacket. Furthermore, the position of the cooling jacket is such that the welded seams can not be inspected visually. More serious difficulties arise in the event the jacket and/or the coolant supply and exhaust conduits leak, because this may result in a short circuit. Leakage brings with it yet another and even more serious danger, namely, that of an explosion, should the water come into contact with the hot lining or, worse still, the liquid metal.

It is, therefore, an object of the present invention to provide a cooling system for induction furnaces which overcomes the above-outlined drawbacks of the prior art, namely, a cooling system which does not use any liquid ice but which is nevertheless eicient enough to enable the furnace to operate -at very high maximum power. Accordingly, the present invention resides in an induction furnace which is provided with a Ihigh-efficiency cooling `system that makes use of -gaseous coolant. This is accomplished by dividing the interspace between the lining and the induction coil by means of an auxiliary cooling surface, and by providing between this auxiliary cooling surface and -a main cooling surface, which itself abuts against the wall of the opening, a third cooling surface which divides the space between the main and auxiliary cooling surface into coolant channeling of reduced cross section. In one embodiment of the present invention, the third cooling surface is undulate and weaves back and forth between the main and auxiliary cooling surfaces.

According to a further feature of the present invention, the cooling system is divided radially into a plurality of segments, there being electrical insulation between the circumferential ends of the segments. This insulation may constitute a core into which the lining is packed.

Additional objects -and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1, already referred to above, is a sectional view of an induction furnace equipped with Ia convention-al cooling arrangement.

FIGURE 2, also referred to above, is a sectional View taken on line 2 2 of FIGURE 1.

FIGURE 3 is a sectional view essentially similar to FIGURE l but shows the induction furnace as being equipped with a cooling system according to the present invention.

Referring now once again to the drawing, the same shows the cooling arrangement as incorporating an iron outer jacket 11 which lmay be considered as the main cooling surface. Arranged nteriorly of and spaced from jacket 11 is a second, inner jacket 12 which acts as an auxiliary cooling surface. A third, intermediate cooling surface 13 is arranged between jackets 11 and 12. As shown in FIGURE 3, the intermediate surface 13 is undulate, thereby to sub-divide the interspace between jackets 11 and 12 into a plurality of coolant channels 9a of smaller cross section and thereby also to increase the total surface area of surface 13. The induction coil 5 is arranged close to the inner jacket 12 and is spaced therefrom by means of thes spacers 8a. Air is blown through the channels 9a and the interspace 10 between the coil 5 and the yoke 6.

Thanks to the above arrangement, the cooling area is increased threefold and the heat transfer coefficient is increased `by almost one half. Inasmuch as the heat removal may be expressed mathematically by the equation Q=F--At (where Q=the heat removal, F=the effective area, a=the heat transfer coefficient, and At=the temperature differential), and since (F wx) has `been increased `by approximately (31.5)=4.5, the heat removal will be seen to have been substantially increased in cornparison with the prior art arrangement shown in FIG-

URES

1 and 2. Thus, an induction coil cooling system of greatly increased eiciency is obtained Iby very simple structural means.

For reasons relating to the electrical characteristics of the furnace, it is advisable to divide the coil cooling system radially into two or more individual segments 14, 15. The circumferential ends of the segments are separated by electrical insulation 16, a very effective structure ybeing obtained if the insulation 16 also serves as the core onto which the lining 2 is packed.

Yet another advantage of the cooling system acc-ording to the present invention, over the prior art systems,

isthat the auxiliary cooling surfaces catch the radiant heat put out by the hot inner wall of opening 4 and the surface of the coil 5, which radiant heat is not otherwise picked up by the stream of cold fair. The radiant heat thus picked 4up by the auxiliary cooling surfaces is carried faway by convection. In this way, the effective cooling area is substantially increased. Furthermore, the invention makes use of the fact that, :at the same air velocity, the heat transfer coeflicient is greater in the case -o-f air channels of smaller cross section than air channels of larger cross section.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations and the same are intended to be comprehended within the'meaning 4and range of equivalents of the appended claims. For example, it is no-t absolutely essential that the auxiliary cooling surfacelift` be undulate, instead, the wall can be so configured as to provide helical or meandering channeling between the jackets 11 and 12, the cold air being blown through this channel.

What is claimed is:

1. In a trough-type induction lfurnace lhaving a lining provided with an opening, within which opening there is arranged an induction coil which itself is spaced from the wall of the opening thereby to forrn` an interspace between the induction coil and the wall of the opening, a convection cooling system adapted for use with a gaseous coolant, said sooling system comprising, in combination: means forming an auxiliary cooling surface and divi-din-g sai-d interspace between the induction coill and tliewall f the opening; means forming a main cooling surface spaced lfrom said auxiliary cooling surface and arranged against the wall of the opening; means forming a third cooling surface arranged |between said main and auxiliary cooling surfaces for dividing the space between said main and auxiliary cooling surfaces into coolant channeling of reduced cross section; and means for permitting a -gaseous coolant to flow over said cooling surfaces so as to cool the same by c-onvection.

2. A cooling system .as dened in claim 1, said system being'divided intov a plurality of segments, and electrical insulating means interposed between the circumferential ends Iofsaid segments.

3. A cooling system as defined in claim 1 wherein said third cooling surface is un-dulate and divides said space` between said main and auxiliary cooling surfaces into a plurality of individual air channels of reduced cross section.

4. A cooling system as defined in claim `1 wherein sai-d third cooling surface divides said space between said main and auxiliary cooling surfaces int-o a helical cooling channel.

55.' A cooling system as dened in claim 1 wherein said third cooling surface divides said space between said main and auxiliary cooling surfaces into a meandering channel. v

6.` An induction furnace c-omprising, in combination: (a)`means forming a lining which is provided with an opening; (b) an induction coil arranged in said opening but spaced from the wall thereof so that an interspace is formed between said induction coil and said wall of l said opening; and (c) a convection cooling system adapted for use with is packed.

a gaseous coolant, said cooling system incorporating `(l) means forming an auxiliary cooling surface and dividing said interspace between said ind-uction coil and said wall of said opening,

(2) means forming a main cooling surface spaced from said auxiliary cooling surface and arranged 7. An induction furnace as defined in claim 6 where` in said cooling system is divide-d into a plurality of segments; and electrical insulating means interposed between the circumferential ends of said segments.

8. An induction furnace as defined in claim 7 wherein said lining is a packed lining and said electrical insulating means constitute a core ont-o which said lining is 9. An induction furnace comprising, in combination:

(a) means forming a lining which is provided with a cylindrical openin (b) an induction coil arranged in `said opening but spaced `from the ,cylindrical wall thereof so that an annular interspace is formed and betwen said induction -coil and said wall of .said opening; and

(c) a convection cooling system adapted `for use with a gaseous coolant, said cooling system incorporating (l) means forming an annular auxiliary cooling surface and dividing said interspace between said induction coil and said wall of said openlllg, y (2) means forming an annular main cooling surface spaced lfrom said auxiliary cooling surface and arranged against said wall of said opening, (3) means `forming a third cooling surface :ar-

ranged between said main and auxiliary cooling surfaces for dividing the annular space therebetween into coolant channeling of reduced cross section, and (4) means for permitting .a gaseous coolant to flow over said cooling surfaces so as to cool the same by convection.

10. An induction furnace as defined in claim 9 wherein said cooling system is divided radially into a plurality o-f segments, there .bein-g electrical insulating mea-ns interposed between the circumferential ends of said segments.

11. An induction furnace as defined in claim 10 wherel:in said lining is a packed lining and said electrical insulating means constitute a core onto which said lining References Cited bythe Examiner UNITED STATES PATENTS 8/1958 Limpel .M9-10.49

7/1961 Cooke a 13-29 11/1965 Wenzel Zl9-l0.49

RICHARD M. WOOD, Primary Examiner.V A. BARTIS, Acting Examiner.

L. H. BENDER, Assistant Examiner.

Claims

1. IN A TROUGH-TYPE INDUCTION FURNACE HAVING A LINING PROVIDED WITH AN OPENING, WITHIN WHICH OPENING THERE IS ARRANGED AN INDUCTION COIL WHICH ITSELF IS SPACED FROM THE WALL OF THE OPENING THEREBY TO FORM AN INTERSPACE BETWEEN THE INDUCTION COIL AND THE WALL OF THE OPENING, A CONVECTION COOLING SYSTEM ADAPTED FOR USE WITH A GASEOUS COOLANT, SAID SOOLING SYSTEM COMPRISING, IN COMBINATION: MEANS FORMING AN AUXILIARY COOLING SURFACE AND DIVIDING SAID INTERSPACE BETWEEN THE INDUCTION COIL AND THE WALL OF THE OPENING; MEANS FORMING A MAIN COOLING SURFACE SPACED FROM SAID AUXILIARY COOLING SURFACE AND ARRANGED AGAINST THE WALL OF THE OPENING; MEANS FORMING A THIRD COOLING SURFACE ARRANGED BETWEEN SAID MAIN AND AUXILIARY COOLING SURFACES FOR DIVIDING THE SPACE BETWEEN SAID MAIN AND AUXILIARY COOLING SURFACES INTO COOLANT CHANNELING OF REDUCED CROSS SECTION; AND MEANS FOR PERMITTING A GASEOUS COOLANT TO FLOW OVER SAID COOLING SURFACES SO AS TO COOL THE SAME BY CONVECTION.