Industrial electric heating furnaces – Electroslag remelting device – Power supply system
Patent
1980-09-30
1983-07-26
Envall, Jr., Roy N.
Industrial electric heating furnaces
Electroslag remelting device
Power supply system
373104, H05B 360, H05B 7148
Patent
active
043957714
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to electroslag melting, and more particularly to methods and apparatus for controlling a process of casting thin walled ingots using the electroslag melting process.
The method of the invention and the apparatus for practicing the same can be utilized in the manufacture of thin ingots-slabs, thin hollow ingots, and other thin walled products.
DESCRIPTION OF THE ART
Known in the art is a method of controlling the electroslag melting process by the resistance of the slab bath within the interelectrode gap, and the speed of electrode melting. The resistance of the slag bath in this method is controlled by varying the magnitude of the interelectrode gap so as to reduce to zero the difference between the voltage drop across the slag bath and the voltage drop across the resistance through which the current is flowing from the furnace transformer.
It has been found that the location of an electrode within the slag bath (its immersion) is determined by the resistance of the interelectrode gap which resistance is in linear dependence upon the magnitude of this gap within the limits of working draughts. To obtain a homogeneous ingot, the magnitude of the interelectrode gap should be constant in the process of electroslag melting, and must be equal to a predetermined process value.
There are also known a method and an apparatus to control the process of casting the ingots using the process of electroslag melting (Problemy spetsialnoj electrometallurgii-Problems of special electrometallurgy, issue 5, 1976, Kiev, B. E. Paton et al., Skhemy pitanija i upravlenija bifilljarnoj pechi -40 ( -105)-Feeding and control circuits for -40 ( -105) bifilar furnace, pp. 3-6, particularly 5-6), wherein the magnitude of the interelectrode gap is maintained constant, which is accomplished by measuring the resistance of the slag bath within the interelectrode gap, determining variation of said resistance from the predetermined value, and varying the power supplied to the slag bath depending upon said variation.
The apparatus for practicing the above method comprises a unit for measuring the resistance of the interelectrode gap, the output of said unit being connected to a unit for comparing the current value of the resistance against the predetermined value. The output of said unit for comparing is connected to a unit for forming a control action, the latter having its output connected to a drive for moving the consumable electrode.
In the prior art apparatus maintaining the magnitude of the interelectrode gap constant is effected by continuously measuring said gap in a unit for measuring said resistance. The output signal of this unit, corresponding to the value of the actual resistance, is fed into the unit for comparing wherein it is compared against the signal corresponding to the value of the predetermined resistance. Error signals are fed into the unit for forming a control action which governs the drive for moving the electrode.
It is well known that in the process of electroslag melting, stability of the melting current is determined by the location of an electrode within the slag bath (its draught).
Experience has proved that for a shallow slag bath, e.g. in melting thin walled ingots within an enlarged mould, the region of stable values of the melting current becomes narrower and is equal to several millimeters.
In this case controlling the process, as above described, does not ensure the location of the electrode within the region of stable current values. Current variations beyond this region result in an instability of operation of the control system (system wobbling) which results in a poor surface of the product being melted (corrugations, contractions) thereby considerably detriorating surface quality and structure of the ingots being cast.
SUMMARY OF THE INVENTION
The invention is directed to a method and an apparatus for controlling a process of casting thin walled ingots by applying the method of electroslag melting wherein by analyzing the time characterist
REFERENCES:
patent: 3890457 (1975-06-01), Fain
patent: 4194078 (1980-03-01), Thomas
patent: 4273948 (1981-06-01), Masucci
Problems of Special Electrometallurgy, Issue 5, 1976 Kiev, et al, Automatic Control System of Melting in the Electroslag Remelting Units, p. 711-Steel, No. 8, 1973.
Bondarenko Oleg P.
Chekotilo Leonty V.
Egorov Sergei P.
Gladky Evgeny D.
Medovar Boris I.
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