US2184741A - High frequency smelting furnace - Google Patents

Description

Dec. 26, 1939; F. HARTMANN HIGH FREQUENCY SMELTING FURNACE Filed Nov. 17, '1938 Patented Dec. 26, 19 39 HIGH FREQUENCY SMELTING FURNACE Fritz Hartmanm-Dortmund, Germany, assignor to Kohle-und Eisentorschung G.-m. b. 11., Dusseldon, Germany, a limited-liability company Application November 17, 1938, Serial No. 249,930 In Germany November 19, 1937 4 Claims; (Cl. 13-27) To counteract the danger of breaking out, it and'the outflow temperature of the water can be 20 is proposed according to the invention to utilize read at any time. The interposing of a secondary the change of temperature of the cooling water, circuit 8 is recommended as the thermo-currents caused by the penetration of the hot metal into are too weak to attain the direct actuation of the the wall of the crucible, by arranging in the main switch.

cooling water current temperature-influenced Instead 'of the thermo electric couple 3, other 26 devices, such as thermo-electric couples, redevices may be fitted according to the invention sistance coils or bimetal strips, which in the provided they canbe influenced by changes in event of inadmissible rise in temperature cut temperature. For example a resistance coil may out the furnace switch by means of known mebe provided which presents the advantage that 30 chanical or electrical transmission elements. It an intermediate relay between resistance coil 30 is advisable to arrange a thermo-electric couple and cut out of the main switch can be dispensed or the like not only at the cooling water outlet with. Thermometers with cut off contacts may but also at the cooling water inlet. Thus, it is also be employed. By using bimetal strips as possible to control the actual rise in temperatemperature influenced devices a mechanical 5 ture of the cooling water in the furnace indetransmission of the movement of the bimetal pendently of the inlet temperature of the coolstrip under changes of temperature to the main ing water which mostly fluctuates. If the two switch may also be attained. thermo-electric couples in differential connec- According to Fig. 2 thermo-electric couples are tion are jointly actuated, even a considerable inarranged one 6' in the outlet 6 and another 6 crease in the sensitivity of the cut out canv be in the inlet 3 for the cooling water. The two 40 thereby attained so that it. is possible to indicate thermo-currents, in the case of differential conbreaking out in its inception. nection, indicate the difference in the tempera- Two embodiments of the invention are illustures of the cooling water at the inlet and outlet trated by way of example in the accompanying points. By the diiferential connection on the drawing, in which:-- electromagnet 'l the protecting arrangement is 45 Fig. 1 is a diagrammaticalview showing the rendered independent of temperature fluctuations arrangement of a thermo-electric couple in the of the inflowing cooling water. Furthermore, by cooling water inlet, the differential connection the sensitivity of the Fig. 2 is a similar view showing the arrangeindication or of the adjustment of the cut out ment of a thermo-electric couple in the inlet point of the main switch can beconsiderably in- 60 and another in the outlet of the cooling water. creased. This is perhaps advantageous for show- In the drawing l designates a crucible in ing on an indicating instrument the relatively whose wall a current conducting coil 2 is em slight increase in temperature already at the bedded and is connected to asource' 9' of high beginning of a break out. The protecting arfrequency alternating current through the con- When smelting metals in high-frequency furnaces of large capacity there exists, owing to the relatively thin walls of the crucible, the danger of the liquid metal breaking out through the crucible wall. In the case of such breaking out, apart from the destruction of the coils, explosions might occur, and the liquid metal may come into contact with the cooling water.

Experience has shown; that a breaking out is preparcd'by the formation of small cracks or crevices in the crucible wall which cracks and crevices flll with metal and spread in outward direction. It is evident that such cracks cannot be detected during the smelting.

In most cases the breaking outtakes place so suddenly that, even if the threatening breaking out canmake itself apparent in some way by external signs, there is nevertheless not enough time to cut out the furnace.

tacts II and II. In the example illustrated the coil consists of a tube, through which the cooling water flows. The cooling water enters at 3 and passes out at 4. The electric connection of the induction furnace is effected in the usual 5 manner over fuses ill and a main switch 5. According to Fig. 1 the protecting device consists of a thermo-electric couple 6 which acts on a relay I. The relay 1 in responding, closes a secondary circuit 8 to energize an electromagnet 10 I l to attract a detent armature l5 by which the main switch 5 is switched ofi through the action of a spring i6.

An indicating instrument may be used instead of the relay I, if this instrument has in known manner cut off contacts by which the secondary circuit 8 is controlled. The use of an indicating instrument instead of a relay presents the advantage that the heating process can be observed rangement cuts out the furnace only when the difl'erence in temperature of the water at the inlet and outlet points increases. In most cases this will take place only when the metal breaking out is already near the coil whereby electromagnet I will be energized sufiiciently to attract its armature I! for closing the secondary circuit 8, as in the previously described embodiment, to actuate switch 5 through the release of detent :2 by electromagnet M and the action of spring I claim:

1. In a high frequency smelting furnace, means for avoiding breaking through, comprising in combination with a crucible and an electric circuit for heating said crucible, a main switch in said circuit, a cooling water conduit surrounding said crucible, at least one heat influenced device inserted in the cooling water, arranged in said circuit and influenced by an excessive rise in temperature in the cooling water circulating through said conduit, and transmission elements between said device and switch and adapted to cut out said circuit through the actuation of said switch at the influencing of said device, by an excessive rise in temperature in the cooling water.

2. In a high frequency smelting furnace of the nature'set forth in claim 1, two heat influenced devices in the circuit, a difierential relay connected to both of said devices and cooperatively connected to the main switch.

3. In a high frequency smelting furnace, means for avoiding breaking through, comprising in combination with a crucible and an electric circuit for heating said crucible, a main switch in said circuit, a cooling water conduit surrounding said crucible and connected with said circuit to constitute the induction heating coil of the furnace, at least one heat influenced device inserted in the cooling water, arranged in said circuit and influenced by an excessive rise in temperature in the cooling water circulating through said con- I

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