GB1601203A - Continuous casting - Google Patents

Description

(54) CONTINUOUS CASTING (71) We, ACIÉRIES RESUMES DE BURBACH-EICH-DUDELANGE S.A., Arbed, a Company incorporated in accordance with the laws of the Grand Duchy of Luxembourg, of Avenue de la Liberty, Luxembourg, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention concerns a process and an apparatus for electromagnetic stirring of molten metal, for example, steel, in a plant for the continuous casting of slabs.

In order to improve the solid state structure and homogeneity of slabs produced by continuous casting it has been known for some time to mix the molten metal contained in a mould by centrifuging, i.e.

by imparting to the metal rotational movement about the longitudinal axis of the ingot mould.

Nowadays one method for effecting this mixing consists in circulating the molten metal by means of a rotating magnetic field produced by an annular inductor surrounding the mould. Compared to mechanical centrifuging by rotation of the mould this method has the advantage that it can be applied to curved and/or oscillating moulds, and can be operated without moving mechanical parts.

Previously, electro-rotative procedures for continuous casting have always had the disadvantage that they can only be used effectively for the production of round or tubular products, or for products of square section with rounded corners or of polygonal section with substantially equal sides.

In particular they cannot be easily adapted to the continuous casting of slabs, i.e.

ingots of rectangular section with adjacent sides of substantially different length.

The present invention aims to improve the structure and homogeneity of continuously cast slabs.

In accordance with the invention there is provided a method for stirring molten metal in a mould of a continuous slab casting installation, the method comprising engendering in the molten metal rectilinear magnetic fields which cause formation of at least two zones in which the molten metal circulates about respective axes parallel to the direction of passage of the metal through the mould.

In order to obtain optimum homogeneity of the central part of the slab produced, the intensity and frequency of at least one of the fields may vary periodically or aperiodically with time. The intermediate strata which separate the zones and which are substantially stationary in the absence of such variation, are continuously being displaced towards one or other side of the mould so that no preferential zone of inhomogeneity can form.

Also in accordance with the invention there is provided a continuous slab casting installation including an apparatus for stirring molten metal in a mould of the installation, the apparatus comprising means for engendering in the molten metal rectilinear magnetic fields to cause, in operation, the formation of at least two zones in which the molten metal circulates about axes parallel to the direction of the metal through the mould.

The apparatus may include an inductor comprising several straight stators each of which is similar to the stator of a translatory field linear motor. Such stators are fed with polyphase alternating current and are suitably disposed perpendicular to the longitudinal axis of the mould and parallel to its wider pair of walls. Straight stators may equally well be provided parallel to the narrower walls of the mould when the slab produced is relatively thick.

The use of straight stators extending across the wider walls of the mould has the advantage that the dimensions of the slab may vary over a wide range without necessitating any change in the inductor used.

The current used to induce the field is preferably of low frequency as this allows conventional copper moulds to be retained without incurring appreciable loss due to the formation of Foucault currents in the walls of the mould.

WHAT WE CLAIM IS: - 1. A method for stirring molten metal in a mould of a continuous slab casting installation, the method comprising engendering in the molten metal rectilinear magnetic fields which cause formation of at least two zones in which the molten metal circulates about respective axes parallel to the direction of passage of the metal through the mould.

2. A method according to claim 1 in which the engendered fields cause the molten metal in each zone to circulate in a generally elliptical path.

3. A method according to claim 1 or 2 in which the intensity or frequency of at least one of the fields is varied with time.

4. A continuous slab casting installation including an apparatus for stirring molten metal in a mould of the installation, the apparatus comprising means for engendering in the molten metal rectilinear magnetic fields to cause, in operation, the formation of at least two zones in which the molten metal circulates about axes parallel to the direction of passage of the metal through the mould.

5. A continuous slab casting installation according to claim 4 wherein the apparatus includes a plurality of inductors and means for feeding the inductors with polyphase current.

6. A method according to claim 1 and substantially as hereinbefore described.

7. A continuous slab casting installation according to claim 4 and substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. without incurring appreciable loss due to the formation of Foucault currents in the walls of the mould. WHAT WE CLAIM IS: -

1. A method for stirring molten metal in a mould of a continuous slab casting installation, the method comprising engendering in the molten metal rectilinear magnetic fields which cause formation of at least two zones in which the molten metal circulates about respective axes parallel to the direction of passage of the metal through the mould.

2. A method according to claim 1 in which the engendered fields cause the molten metal in each zone to circulate in a generally elliptical path.

3. A method according to claim 1 or 2 in which the intensity or frequency of at least one of the fields is varied with time.

4. A continuous slab casting installation including an apparatus for stirring molten metal in a mould of the installation, the apparatus comprising means for engendering in the molten metal rectilinear magnetic fields to cause, in operation, the formation of at least two zones in which the molten metal circulates about axes parallel to the direction of passage of the metal through the mould.

5. A continuous slab casting installation according to claim 4 wherein the apparatus includes a plurality of inductors and means for feeding the inductors with polyphase current.

6. A method according to claim 1 and substantially as hereinbefore described.

7. A continuous slab casting installation according to claim 4 and substantially as hereinbefore described.