US1879360A

US1879360A - Electric induction furnace

Info

Publication number: US1879360A
Application number: US380139A
Authority: US
Inventors: Linnhoff Franz
Original assignee: Ajax Electrothermic Corp
Current assignee: Ajax Electrothermic Corp
Priority date: 1928-07-24
Filing date: 1929-07-22
Publication date: 1932-09-27
Anticipated expiration: 1949-09-27

Description

3 .Sheets-Sheet 2 F. LINNHOFF sLscTRIc INDUCTION Fummc `Ftlsd July 22.

Fig 3.

Sept. 27, 1932.

3 Sheets-Sheet 3 Filed Ju'ly 22. 1929 Franz Linnhoff By Patented Sept. 27, -1932 `UNITED STATES PATENT OFFICE FRANZ LINN'HOFF, OF E'BERSWALDE, GERMANY, ASSIGNOR TO AJAX ELECTROTHERMIC CORPORATION, OF AJAX PARK, NEW JERSEY, A CORPORATION 0F NEW JERSEY ELECTRIC INDUCTION FURNACE Application led .Tuly 22, 1929, Serial No. 380,139, and in Germany July 24,1928.

My invention relates to electric induction furnaces, more particularly to coreless induction furnaces.

These furnaces have the disadvantage that a considerable part of the magnetic force lines does not flow through the melting bath, but takes its way through the air outside of the coil. This strong magnetic leakage makes the power factor of the furnace worse and increases the operating costs; moreover, it makes it impossible to provide the furnace with an iron supporting frame because such a frame would be heated highly by the eddy currents induced in it by the leakage flux.

It has been tried to prevent the leakage by arranging a yoke of laminated iron round the coil. These yokes consist either in a cylinder surrounding'the coil or in columns of laminated iron extending parallel to the axis of the coil. Experience has shown that even with such furnaces provided with yokes a considerable leakage takes place. The reason for this leakage lies in the fact, that, with both yoke types, the magnetic force lines which follow the yoke change their direction abruptly at the top of the yoke between it and the bath.Y As a result considerable leakage takes place in this part of the magnetic circuit giving a large leakage field.

The object of my invention is to eliminate the magnetic leakage entirely and to increase the power factor of the furnace.

Figure l is an approximately central vertical section through the structure of Figure 2 taken upon line l-l of that figure.

Figures 2 and l are top plan views of variant forms of my furnace.

Figure 3 is a section corresponding in position with Figure l but taken upon line 3-3' of Figure 4.

Figure 5 is a central vertical section showing a further modified form.

Figure 6 is a fragment of Figure l, modified to show a somewhat different form.

My invention consists in a coreless induction furnace with a yoke arranged round the coil, the yoke being formed so that the magnetic force lines can pass from the yoke to the melting bath and inversely without considerable changement of their direction. With this arrangement any leakage is avoided, since the path of the magnetic force lines in the air and in the melting bath represents the short` est way between both yoke ends so that they are not inclined to leave it.

By the concentration of the flux on the 'melting bath the power factor is increased melting bath. The ends of thc yoke may ap-I proach the crucible from the side,'but in order to utilize the magnetic iiuX entirely it is particularly favourable to lead the ends of the yoke above and below the melting bath. In furnaces which are charged from above, the yoke can be subdivided in such a manner that its upper part be removable together with the cover of the furnace.

The yoke may consist in several arms of laminated iron arranged round the coil, as usual. In order to attain a good distribution of the magnetic fiux, the single arms can be connected one to another at one or both ends by means of rings of magnetic material.

The iron of the yoke can be laminated in radial or tangential planes. For avoiding a too strong heating of the innerparts of the yoke by the leakageiiux fiowmcr in these parts, they may be provided with horizontal slits S, Figure 6, of Convenient depth. These slits increase the magnetic. resistance of the inner parts of the `yoke .and thereby cause the'flux to distribute more uniformly in the inner and outer part of the yoke.

The slits S are shown as extending hori- Zontally outwardly from the inside of the vertical leg of the yoke, extending part way only through the leg.

In the accompanying drawings there are illustrated some embodiments of the innention.

Figs.. l and 2 show an induction furnace 10c with the crucible 1,-the cover 2 and the suporting ring 3. The Crucible is surrounded y the induction coil 4 arranged between

rings

5 and 6. The yoke'consists of several arms 7 distributed round the coil, the arms being C-shaped and extending above and below the Crucible. The furnace is supported by-a frame 9 and can be tilted over the 'axis 10. The cover and the upper part :of the yoke can be removed by means of the loo 13 fastened to the plate l2 which is insufated from the yoke by a disk 11.

Figs. 3 and 4 show a furnace witha yoke consisting of arms 7 which are connected one to another at their upper end lower ends by rings 15.

Fig. 5 shows a furnace with a yoke which does not interfere with the cover since its ends are inclined toward the furnace approaching it from the side.

Having now particularly described and:

ascertained the nature of my invention and in what manner the same is to be performed, what I claim is:

l. In an electric induction fur-nace, in combination, a Crucible, an induction coil surrounding said Crucible and a C-shaped yoke surrounding said coil, the inner part of the yoke being provided with horizontal slits and being removable bodily at the top from the side members.

2. A pot-type of induction furnace including a coil surrounding the furnace, ring pole pieces respectively across the topand bottom ofthe metal of the furnace and laminated connections between the pole pieces.

3. A pot-type of induction furnace including a. coil surrounding the furnace, rinU pole pieces respectively across the top and bottom of the metal of the furnace and laminated connections between the polev pieces,-`

the upper pole piece being removable.

4. A pot-type of furnace having a removable lid, an induction coil surrounding the furnace and a'niagnetic pole piece across the bottom of the furnace, a removable cover upon the top of the furnace, upright laminated magnetic conductors spaced around the sides of the furnace and connecting at their lower ends with the bottom pole pieces and a ring pole piece above the cover directly above the metal of the furnace and having laminated extensions to the upright members.

In testimony whereof I affix my signature.

FRANZ LI'NNHOFF.