US1920325A - Electric induction furnace - Google Patents

Description

Aug. 1, 1933. K. SCHMIDT ELECTRIC INDUCTION FURNACE Filed Oct. 25. 1929 Patented Aug. 1, 1933 UNITED STATES ELECTRIC INDUCTION FURNACE Tempelhof, Germany Application October 25,

1929, Serial No. 402,526,

and in Germany October 25, 1928 2 Claims.

Application has been filed in Germany October This application relates to electric furnaces and more particularly to an improved form of induction furnace. having a circular closed'core.

Heretofore it has been the practice to use induction furnaces either operating with high frequency current in the absence of iron parts, or low frequency current furnaces having a surrounding iron core usually with an air gap in which the crucible is located. The first type has the advantage' that it permits the heating of any form of material, but on the other hand it is not economical due to considerable inductive leakage. Further drawbacks to low frequency furnaces employing crucibles now in use are that they require annular or ring-shaped crucibles, the core is so situated that the heat from the crucible comes into contact therewith, causing it to bend, and the difiiculty of removing the crucibles.

The principal object of this invention is to provide a furnace having a laminated core so positioned that the lines of magneto-motive force act perpendicularly to the axis of the working chamber.

A further object is to provide a furnace from which the crucible or work may be removed with ease and which is economical to operate, due to the reduction of bending of the core. A clearer conception of the construction, operation and further objects of the invention may be had from thefollowing specification taken in conjunction with the accompanying drawing in which:

Figure 1 is a View of the invention. in cross section.

Figure 2 is a top view of Figure 1, and

Figure 3 is a perspective view of the core showing the method of winding the coil on the core.

The furnace comprises a crucible i surrounded by a laminated sheet metal core 2 formed of circular plates having holes 3 therein, in each of which a portion of the winding may be positioned. The heating chamber formed by the core is filled as far as possible by the material or crucible to be heated and the heat rising therefrom does not come in contact with the core. The whole construction is exceedingly compact and of high stability. The crucible proper or material to be heated may be withdrawn vertically by means of a crane or hoist, thereby reducing the possibility'of spilling which often occurs when the crucible is withdrawn horizontally, as has formerly been the practice and which has thereby necessitated the use of a car or other device. It

is also apparent that, if desired, the crucible may be permanently built into the core and the entire structure tipped to permit drawing the melt.

The use of a cylindrical core prevents the heat which rises out of the crucible from damaging the core and thereby greatly reduces bending effects and, as set forth above, facilitates removal of the crucible. The inductive winding of the core may be distributed in a manner similar to that used in a three phase alternating current generator as is shown in Figure 3. The windings consist of three wires 5, 6 and 7 which are positioned as shown. one wire in each aperture 3.

In Figs. 1 and 2 the windings are shown as insulated copper tubes 4., with only one tube in each hole 3. The insulation is mica or other material of low thermal conductivity. The tubular. form of the winding provides a ready means for cooling the winding as well as the surrounding magnetic material of the core. The cooling medium may be either airor Water passing through the tubular windings. Where a solid conductor, as in Fig. 3, is employed cooling channels may be provided in the magnetic core. By positioning the windings in the hole 3 parallel with the vertical axis of the furnace, the magnetcmotive force is concentrated at the vertical axis.

The frequency of the alternating currents used may vary within wide limits and thus normal frequencies from the line as well as lower or higher frequencies may be used. The latter course naturally requires a very careful insulation of the iron sheets employed. Multiphase currents may also be employed and, as is known, they will produce a rotating field which, as with multiphase generators or motors, will create a rotary action on the material to be fused, so that a considerable motion is imparted to the molten metal. By changing the amplitude of the phases, by reversing the windings or by changing the angle of the phase, the rotating field can be infiu enced in any desired manner, or'it may be altogether eliminated. Consequently, the-movement of the metal can be regulated in any desired way without the necessity of materially reducing the heat generated, or of cooling the metal by the introduction of agitating apparatus.

The use of a multi-phase system renders possible the connection of such a furnace to a normal three phase line, a property which is of the greatest importance in the interest of a uniform loading of the three phases of the network. A furnace according to this invention may also be used to advantage for glowing, tempering and so on,

by removing the crucible and directly substituting the work to be heated. A special advantage in connection with all the purposes mentioned is .that the whole furnace may be constructed of continuous sheets of metal in contradistinction to the known low frequency furnaces, so that a solid furnace body is obtained, which can easily be handled, and which is also economical to oper- I ate.

What is claimed is:

1. An electric induction furnace comprising a laminated ring of magnetic material having openings therethrough near the inner periphery and parallel to the axis of the ring, heating means for reducing metal to a molten state and for causing its rotation consisting of a single set of multiphase windings arranged in said openings, and a removable crucible positioned within and surrounded by the ring of magnetic material and 1 having an unobstructed interior.

2. An electric induction furnace comprising a crucible having an unobstructed interior and pro- 1

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