Industrial electric heating furnaces – Arc furnace device – Power supply system
Patent
1991-11-19
1993-03-02
Evans, Geoffrey S.
Industrial electric heating furnaces
Arc furnace device
Power supply system
373108, H05B 7102
Patent
active
051915928
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a direct current electric furnace for the melting of metal raw material, especially scrap iron.
BACKGROUND OF THE INVENTION
Electric furnaces used for the melting of scrap iron or other raw material and the reduction of the bath of metal obtained, with optional addition of alloy elements until a metal of determined composition is obtained, have long been known in the art.
An electric furnace is generally constituted by a vessel delimited by a lateral wall and a bottom covered with a sole of refractory material and closed with a removable dome-shaped lid.
At least one electrode, called consumable, generally constituted by a bar of graphite, penetrates inside the vessel. Each electrode is supported by an arm extending above the dome and is mounted for vertical movement, so as to pass through the dome and descend into the raw material loaded into the furnace. This raw material, which is generally constituted by scrap iron, is in contact with at least one fixed electrode passing through the bottom and the refractory sole.
In the case of a single-phase alternating current furnace or of a direct current furnace, the consumable electrode and the sole electrode are connected to the two poles of a current source.
In the case of a two- or three-phase alternating current furnace, the consumable electrodes are connected to the poles of the current source and the charge is in contact with the sole electrode which constitutes the neutral of the system.
There are thus formed between the charge and each consumable electrode one or more electric arcs, which produce the melting of the scrap iron and the formation of a bath of metal in the bottom of the vessel.
Until recently, furnaces supplied with alternating current in particular were used, but it was found that the supply of direct current to the electrodes brought a number of advantages such as reduced noise and increased energy efficiency because it is possible to use higher voltages than those permitted with alternating current.
Provided that the charge is in scrap-iron form, the electrodes penetrate the latter by digging holes in it which determine a sort of insulation of the arcs from one another and tend to stabilize them. On the other hand, when the charge is entirely melted, the arcs which are subject to the magnetic effects created by the current passing through the electrodes, through the conductors which connect the electrodes to the current source and through other parts of the installation, may form in unpredictable directions and are therefore very unstable.
The zone in which the arcs form, which is at the highest temperature, can therefore not be kept at the center of the furnace, the walls and bottom of which may be subjected to excessive temperatures and substantial wear of the refractory lining.
Applicants have already disclosed, in U.S. Pat. No. 4,821,284, a process for controlling the direction of the electric arcs in a direct current furnace, even at high power levels.
To this end, instead of separating the conductors as far as possible from the furnace in order to avoid the influence of the magnetic fields produced by the passing of the current, the conductors connected to the fixed electrodes are, on the contrary, made to pass along the lower face of the bottom and as close as possible to the latter determining the profile and orientation of the path followed by the conductors so that the passing of the current produces magnetic fields, the mutual effects of which, with respect to deviation of the arcs, and taking into account all of the magnetic influences exerted in operation by the other conductors and the various parts of the installation, are such, that the arcs tend to converge towards a predetermined zone of the bath of metal.
The intensities which can be made to pass in the conductors and the electrodes, in particular the sole electrodes, are limited, and several consumable electrodes and several sole electrodes must therefore be used. In U.S. Pat. No. 4,821,284, several arrangements were
REFERENCES:
patent: 1983544 (1934-12-01), Ingelsrud
patent: 4016355 (1977-04-01), Stenkuist
patent: 4821284 (1989-04-01), Janiak et al.
patent: 4907244 (1990-03-01), Konig et al.
Janiak Robert A.
Meysson Nicolas
Clecim
Evans Geoffrey S.
Jeffery John A.
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