Industrial electric heating furnaces – Electroslag remelting device – Power supply system
Patent
1985-10-21
1987-10-06
Envall, Jr., Roy N.
Industrial electric heating furnaces
Electroslag remelting device
Power supply system
373104, H05B 7148
Patent
active
046988246
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the control of electrothermal processes, and more specifically to those processes in which heat is generated by passing an electric current through a plurality of electrodes into and through a resistance medium in which the electrodes are placed. The invention can be applied to particular advantage in electric reduction furnaces in which the resistance medium comprises the furnace charge or burden. It is emphasized, however, that the invention can also be applied when carrying out other electrothermal processes based on resistance heat, including arc heat. For example, appropriate parts of the invention can also be utilized in electric steel furnaces. However, since the advantages afforded by the invention are particularly large in number and most pronounced when applying the invention to processes carried out in reduction furnaces, particular reference will be made to such a furnace, and then especially to a three-phase furnace, often used in practice, in which the electric current normally passes through one or more electrodes and thereupon through the furnace charge and finally through the metal bath lying therebeneath. In principle, however, the invention can also be applied irrespective of whether the current takes this path or travels totally or partially between the electrodes.
TECHNICAL BACKGROUND
In order to effect a satisfactory process in electrometallurgical furnaces and to satisfactorily utilize their electric capacity, it is a fundamental condition that the resistance factors of the furnace and of the electrode circuits are mastered. This applies both when the process heat is generated totally or partially by direct resistance heating of the charge, as with reduction and slag smelting furnaces, and when the heat is generated totally or partially by arcs, as with steel furnaces. The composition of the charge and its conductivity interplay with internal processes (e.g. varying SiO-formations) and with purely electrical conditions, resulting in changes in the positions of the electrodes and in displacement of the electrical zero point in the furnace.
Thus, the ability of the furnace to function is predominantly dependent on the ability to measure, monitor and consciously control the resistance conditions of the electrodes. Normally, endeavours are made to achieve this control by adjusting the height of the electrode tips in the furnace charge with the aid of automatic regulators.
The electrical resistances are both electrically and metallurgically dependent. Optimum furnace performance therefore presumes contemporary electrical and metallurgical stability. It is imperative that a metallurgical balance prevails, if the electrical capacity of the furnace is to be utilized to the full. The mutual relationships of the electrical circuits and the position and stability of the electric zero point are also of special importance.
Consequently, with respect to electrode control it is particularly important to be able to use control magnitudes which correctly reflect the electrical resistance conditions.
Attempts have been made previously to control the electrodes with the aid of various control magnitudes: rather often used, does not afford stability in the electrode positions when variations in voltage occur, but leads to so-called "dancing electrodes". most reliable control method, but assumes that the electrical resistance between electrodes and the electrical zero point can be measured with sufficient accuracy. While this is simple in the case of single-phase furnaces, it is more complicated in the case of three-phase furnaces, because of the difficulty of access of the zero point.
In a number of processes involving a highly conductive metal bath (e.g. pig-iron), where the zero point is in all probability practically anchored within the bath, it has been possible passably to consider the furnace as three single-phase furnaces connected in parallel. In such cases it has been endeavoured to place a measuring zero at the bottom of the furnace, which i
REFERENCES:
patent: 4000361 (1976-12-01), Bondarenko et al.
Kjolseth Ove
Willners Harry
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