GB1380467A - Electroslag refining - Google Patents

Abstract

1380467 Electroslag refining processes BRITISH STEEL CORP 10 April 1973 [11 April 1972] 16677/72 Heading B3F [Also in Divisions G3 and H5] In an electroslag refining process in which one or more electrodes depend into a vessel 1 having an upper reservoir portion 2 and a lower mould portion 3 having a cross-sectional area less than that of the electrode(s), the level of the molten metal pool 18 is maintained at or adjacent the interface of the reservoir and mould portions of the vessel. This is achieved by detecting the formation within the reservoir portion 2 of a pool of molten metal having a surface area equal to or greater than that of the electrode(s) and causing relative movement between the vessel 1 and the ingot 20 formed. When the surface of the molten metal pool is within the mould portion 3, further melting of the electrode 4 results in a decrease in the distance between the end of the electrode and the said surface due to the difference in the cross-sectional areas of the electrode and mould portion 3. As the distance decreases a corresponding increase in current will occur if the voltage is maintained constant. When the surface of the pool 18 is within the reservoir portion 2, further melting of the electrode results in an increase in the said distance and thus a decrease in current. Such reversals in the direction of current change are detected by a device 17 which activates a motor 13 to move the vessel 1 upwardly to lower the level of the pool 18 to a position at or adjacent the interface between the reservoir and mould portions. Alternatively, the motor 13 may be activated when the current reaches a maximum value or when a change in the rate of current variation is detected. In a modification the voltage is maintained constant and variations in the voltage are monitored. At start-up, the vessel 1 rests on a base-plate 5 having a member 7 which extends into the lower end of the mould cavity and is made of a material weldably compatible with the metal -to be refined. The annular space between the wall of the mould cavity and the member 7 is filled with crushed slag 8. A ring 9 of asbestos or steel is placed above the slag 8. The base-plate 5 rests on load cells 6 which monitor the weight of the ingot 20. The height of the ingot and the position of the vessel 1 may also be measured. The vessel 1 may be provided with more than one mould cavity so that a plurality of ingots may be formed simultaneously from a single electrode.