Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1995-01-11
1995-10-31
Kastler, Scott
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
266234, B22D 100
Patent
active
054625726
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and a device for stirring a molten metal. More specifically, the invention relates to inductive stirring of a molten metal which is contained in a container with a wall, which comprises at least one layer of a magnetic material.
BACKGROUND ART
To bring about homogenization and temperature equalization in a melt and to improve reaction conditions in connection with refining, degassing and alloying of the melt, the melt is stirred. By allowing a low-frequency magnetic travelling alternating field to act on the molten metal, sufficient electromagnetic forces are generated in the melt to achieve a good and controllable circulation in the melt. This circulation stirs the melt such that the desired improvements regarding homogenization and reaction conditions are achieved.
During the treatment, the melt is contained in a container, preferably an essentially cylindrical ladle or crucible, and a low-frequency magnetic travelling alternating field, which is generated in a coil arranged outside the container, is applied to the melt.
A problem which arises when a magnetic alternating wall is applied to act through a container wall are the losses which occur in the wall, especially when the wall comprises a magnetic material.
Usually, this problem is solved by designing at least that part of the container wall, through which the low-frequency magnetic alternating field has to pass to act on the melt, of a non-magnetic material. Especially in connection with ladles in which a molten metal is contained during transport, refining, degassing, alloying, holding and/or casting, this leads to increased costs because conventional steels cannot be used for that part of the shell of the ladle through which the magnetic alternating field is applied.
One object of the invention is to suggest a method, in inductive stirring of a melt, of applying a low-frequency magnetic travelling alternating field to act through a wall, which comprises at least one layer of a magnetic material.
Another object of the invention is to suggest a device suitable for inductively stirring a melt contained in a container whose walls comprise at least one layer of a magnetic material.
SUMMARY OF THE INVENTION
When a molten metal, which is contained in a container, is stirred inductively, magnetic fields are applied which, in order to act on the melt, must pass through the wall of the container.
During inductive stirring according to the invention, the above-mentioned container wall comprises at least one layer of a magnetic material. To thereby inductively stir the melt, at least one magnetic direct field is applied to act on part of the wall of magnetic material, such that an anisotropically directed magnetic saturation--a low relative permeability--is obtained in that part of the wall, in a direction--the saturation direction--which is substantially oriented in the plane of the wall and essentially parallel to the desired stirrer direction in the melt. According to the invention, a low-frequency magnetic travelling alternating field is further applied superposed on the magnetic direct field. This magnetic alternating field comprises components, which are substantially located in a plane oriented parallel to the saturation direction and perpendicular to the plane of the wall. The low-frequency alternating field thus passes through the part of the wall which is magnetically saturated by the direct field, with small losses and a low damping, whereby sufficient electromagnetic forces, in the form of a stirrer field, are generated in the molten metal to provide the desired circulation.
The above-mentioned method of stirring a molten melt is achieved by means of a device which according to the invention comprises at least comprises at least one layer of a magnetic material, one coil supplied with direct current or a permanent magnet, wherein the magnetic direct field is adapted to act on the magnetic material in the wall and to bring about an anisotropically directed magnetic saturation in one part of
REFERENCES:
patent: 3162710 (1964-12-01), Anderson
patent: 3230073 (1966-01-01), Ericsson
patent: 3314670 (1967-04-01), Kennedy
patent: 4183508 (1980-01-01), Michelet et al.
patent: 5164148 (1992-11-01), Kawasaki
Asea Brown Boveri AB
Kastler Scott
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