US2518872A - Induction furnace - Google Patents

Description

i middle portion of the winding.

' Patented Aug. 15, 1950 INDUCTION FURNACE Ludwig A. Dreyfus, Vasteras, Sweden, assignor to Allm anna

Svenska Elektriska Aktiebolaget,

Vasteras, Sweden, a Swedish corporation Application November 12, 1948, Serial No. 59,63 In Sweden November 15, 1947 v 2 Claims. 1

In many electric eddy current furnaces a substantially uniform body. for instance a molten bath, is to be heated, and in such cases it is generally of minor importance if the electric induction inthe furnace decreases towards its ends, as is usually the case. In certain cases, however, it may be of great importance that the induction be kept practically uniform for the whole length of the furnace, especially when a common inducing winding influences a plurality of electrically more or less independent bodies which, however, are to be heated uniformly, for

instance for metallurgical reasons, or when there is only one body which for instance should be uniformly heat treated throughout its mass.

ing the same by 2. Fig. 1 shows inserted into the furnace a number of bodies 3 to be heated, said bodies being only diagrammatically shown. The said bodies 3 may consist for instance of crucibles of conducting material or with a conducting content, of solid bodies for instance to be heat treated or of conducting carbonpieces for carburating a traversing gas current.

With a constant number of ampereturns per unit of length of the winding l, the flux image shown in Fig. 2 is obtained, in which the fulldrawn lines a designate magnetic lines of flux and the dotted lines D the level surfaces of the When using a common cylindrical winding, it is known that the induction therein decreases to- If a uniform induction in the wards the ends. whole operative region of the furnace is desirable without any particular steps being taken as regards the winding, it will therefore be necessary to make the said operative region essentially shorter than the winding, so that the end portions having a reduced induction will be in-' active. This implies, however, an imperfect utilization of the possibilities of thefurnace.

According to the present invention, a more uniform distribution of the induction along the eddy current furnace is obtained by the provision of an inducing winding, which as a whole is connected in parallel with a condenser for compensating the main portion of its reactive power demand, while certain portions of the winding, especially the ends and the1middle winding portions can be adjusted to values other v than the mean value of the winding- Thus for instance, negative reactances (capacities) may be connected in parallel to the end-portions and T a positive reactance (inductor) in parallel to'the induction which are perpendicular to the flux lines. As shown, the distance between these level surfaces is essentially larger towards the ends of the furnace than in the middle height thereof, especially near the axis of the furnace, and as the induction is proportional to the inverse value of the said distance, it decreases essentially towards the ends of the furnace. In many cases it is, however, desirable that the induction is maintained at substantially the same value at the ends of the furnace as between the ends, and the present invention comprises means for increasing the number of ampereturns per unit of length of the furnace winding towards the ends for this purpose. In the form of the invention illustrated, condensers 4 are connected in parallel with the end portions of the furnace winding I and are preferably adjustable, while a middle portion is connected in parallel to an inductance 5, preferably also adjustable. The

entire winding is as usual connected in parallel with a large condenser 6 which delivers the main portion of the necessary reactive power, while the vactive'power is delivered by agenerator I. The result will be, that the number of ampereturns per unit of length of the winding, instead of being normally constant as in induction furnaces, will vary according to Fig; 4, in which In the accompanying drawing, Fig. I shows diagrammatically in plan view an eddy current furnace having a plurality of bodies to be heated and Fig. 2 shows a vertical section thereof with the said bodies omitted but with lines of flux and level surfaces of the induction shown in the case of the invention not being applied. Fig. 3 shows I a diagram of connections for one form of the somewhat increased and the said number of the the width of the hatched surface represents the said number, i. e'., the number of ampereturns of the portions parallel with condensers 'will be portion parallel to an inductance will be somewhat reduced as compared with the portions without any parallel current path. By suitable adjustment of the members 4, I, for instance under theinfluence of a pyrometer measuring the temperature in the diiferent portions of the furnace, the specific number of ampereturns along the furnace winding can be varied so that the reduction of tbemasnetic induction towards the ends of the furnace illustrated in Fig. 2 is essentially compensated.

The invention may of course be combined with other means for equalizing the induction in the furnace body, for instance with the internal inductor winding surrounded by the bodies heated by the induction described in my patent application Serial No. 59,705 of even date. In such case also certain portions of the internal winding, for instance in the middle and at the ends, may be provided with parallel reactances in the same way as the portions of thewinding I.

I claim as my invention:

1. An eddy current furnace comprising a coilshaped inductor winding, a source of high frequency current, means connecting the ends of the coil to said source, conducting means inside said winding adapted to be uniformly heated by eddy currents induced therein by said winding, a variable inductance connected in parallel with the middle portion of said winding and variable capacitors connected in parallel respectively with each end portion of said winding beyond the points of connection of the inductance.

2. In a furnace as claimed in claim 1, a laminated iron shell surrounding said winding.

LUDWIG A. DREYFUS.

4 REFERENCES crrnn The following references are of record in the tile or this patent:

UNITED STATES PATENTS Number Name Date 1,642,198 Gerth et a1. Sept. 13, 1927 1,828,291 Northrup Oct. 20, 1931 1,852,215 Northrup Apr. 5, 1932 1,943,802 Northrup Jan. 16, 1934 1,948,704 Fischer Feb. 27, 1934 1,961,621 Northrup June 5, 1934 2,452,197 Kennedy Oct. 26, 1948 2,490,104 Strickland, Jr. Dec. 6, 1949 FOREIGN PATENTS Number Country Date 305,620 Great Britain Feb. 8, 1929 310,031 Great Britain Jan. 16, 1930 386,387 Great Britain Jan. 19, 1933 393,958 Great Britain June 12, 1933 586,822 Germany Oct. 26, 1933 764,178 France Feb. 26, 1934

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