US1879361A - Electric induction furnace - Google Patents

Description

Sept. 27, 1932. F. LlNNHoFF 1,879,361

ELECTRIC INDUCTION FURNACE Filed July 22. 192g Inventor'.- Franz L inrzzofff Attorney Patented Sept. 27, 1932 UNITED STATES PATENT OFFICE FRANZ LINNHOFF, F EBERSWALDE, GERMANY, ASSIGNOR TO AJAX ELECTROTHERMIC CORPORATION, 0F AJAX PARK, NEW JERSEY, A CORPORATION 0F NEW JERSEY ELECTRIC INDUCTION FURNACE Application led J'uly 22, 1929, Serial No. 380,140, and in Germany July 24, 1928.

My invention rela-tes to electric induction furnaces, more particularly to coreless induction furnaces, in which the melting material is surrounded by an induction coil and heated 1by the eddy currents induced in it by the It is known to decrease the leakage of the induction coil by surrounding it with a yoke by which the magnetic circuit is closed. The

yoke must consist of laminated iron to avoid high losses caused by the eddy currents induced in it. Such yokes have been made in form of several columns arranged round about the coil, the single columns having been connected one to another at the top and at the bottom. It would be much more advantageous to provide a yoke of hollow cylindrical shape, but the production of such yokes of laminated iron causes very high costs and gives great constructive diiculties. This is ,the case even with the known columnated yokes of laminated iron.

The object of my invention is to provide a yoke which does not cause any eddy current losses and can be made in any form without difficulties.

My invention consists in a yoke of pressed powder with little magnetic and high electric resistance. Such powder, which may consist f. i. in a mixture of iron parts with zinc oxide or chromium oxide, with or without application of a binding substance, can be pressed into any convenient form with little cost and is adapted for magnetic yokes even better than laminated iron since its electric resistance is higher. The powder can easily be pressed into a hollow cylindrical form so that using such a yoke of magnetic powder the best magnetic conditions can be attained. Moreover, the yoke of magnetic powder makes it possible, owing to its high electric resistance, to imbed the windings of the induction coil immediately into the yoke without any insulation. Thereby the supporting devices for the coil become available and the side-leakage of the coil is entirely prevented.

In the accompanying drawing there is illustrated one embodiment of the invention.

Figure 1 is a vertical central section of a coreless induction furnace embodying my invention.

Figure la is a fragmentary vertical section showing a modified form.

Figure 2 is a top plan view of the structure seen in Figure 1.

The Crucible 1 of an induction furnace is surrounded by an induction coil 2 and provided with a cover 3. The coil2 is surrounded by a magnetic yoke 4 of magnetic powder pressed into a hollow cylindrical form The magnetic. powder preferred by me consists of a mixture of iron parts and zinc oxide or chrome oxide with or without a binder vhich cheaply can be pressed into convenient orm.

The furnace is supported by a frame 5 and can be poured out through the spout 6 by tilting itover the trunnions 7.

In the modification shown in Fi re 1a the magnetic powder has been insert d between and about the individual turns of the induction coil.

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:

1. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said crucible and a yoke of pressed magnetic powder arrangedaround said coil.

2. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said CrucibleV and a yoke of pressed magnetic powder arranged around said coil, said powder consisting 1n a mixture of iron parts and zinc oxide.

3. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said crucible and a, yoke of pressed ma netic powder arranged around said coil, sai powder consisting 1n a mixture of iron parts and chrom oxide.

4. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said crucible and a hollow cylindrical yoke of pressed magnetic material surrounding said coil.

5. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said crucible and a yoke of magnetic powder forming a return magnetic circuit for the induction coil having substantially continuous poor electrical conductivity and good magnetic permeability in a direction parallel to the axis of the coil.

6. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said Crucible and a yoke of pressed lo magnetic powder arranged around said coil, said powder consisting in a mixture of iron parts and zinc oxide.

7. In an electric induction furnace, in combination, a crucible, an induction coil surrounding said Crucible and a yoke of magnetic powder with high electric. resistance, the windings of said induction coil being embedded into said yoke.

8. The method of facilitating magnetic return about a furnace inductor which consists in reducing the reluctance of the magnetic path between individual turns of the inductor and concurrently reducing the reluctance of the return path outside of the turns of the inductor.

9. In an electric induction furnace, a crucible, an inductor coil surrounding the crucible and an annular powdered magnetic path of high electrical resistance surroundsu ing the inductor coil.

10. In an electric induction furnace, a crucible, an inductor coil surrounding the crucible and powdered magnetic material against the outside of the inductor coil throughout its length.

11. In an electric induction furnace, a crucible, an inductor coil surrounding the Crucible and a. magnetic return circuit of high resistance for the flux induced by the coil 0 including powdered magnetic material of high electrical resistance between the'turns of the inductor coil.

12. In an electric induction furnace, a crucible, an inductor coil surrounding the crucible and magnetic material of high electrical resistance about the inductor coil and between its turns near their outside edges.

In testimony whereof I affix my signature.

FRANZ LINNHOFF.

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