STIRRER FOR STIRRING OF MOLTEN METAL IN CONTINOUS CASTING

Abstract: Stirrer for stirring of molten metal in continuous casting. According to the invention at least two stirrers or sub-­ stirrers (1,2) are placed outside the mould (3) on opposite sides thereof, said stirrers being provided with iron cores surrounding parts of the mould. Between adjoining parts of the stirrers/sub-stirrers intermediate iron cores (5) can be arranged, which together with the stirrers/sub-stirrers form a closed magnetic circuit around the mould, the stir­ rers/sub-stirrers (1,2) forming a closed magnetic circuit around the mould (3), the stirrers/sub-stirrers being adapted to create a horizontal rotation of the molten metal in the mould or metal strand.

Description: The present invention relates to a stirrer for stirring of molten metal in continuous casting according to the precharacterising part of Claim 1. Such a stirrer is known from the Patent Abstracts of Japan, vol 7, no.187, 16.08.83 (JP-A-58 86963). Stirrers of the kind refered to in this patent are usually made with a round or rectangular geometry. Further, they are usually made in one piece and surround the mould and/or the strand. One problem with such stirrers is their restriction to a specific dimension of the mould/strand. It is desirable to be able to make the mould stirrers adjustable to different dimensions. Sub-stirrers ar known per se, which may cooperate with other sub-stirrers to bring about stirring of the non solidified parts of a continuous strand in a portion along the mould. Such a combination of sub-stirrers is described in the Patent Abstracts of Japan, vol 7, no.187, 16.08.83 (JP-A-58 86963), where two sub-stirrers are arranged in parallel along each of the long sides of the mold. The two sub-stirrers generate a horizontally rotating movement in the melt. However, this arrangement does not solve the problem of adjustability between different cross-sectional areas, neither at the strand nor at the mould. The Patent Abstracts of Japan, vol 11, no.102, 31.03.83 (JP-A-61 249652) discloses stirring means at the strand outside of a continuous casting mold consisting of two sub-stirrers, each being U-shaped and surrounding one end side each of the flattly shaped strand. Coils on the sub-stirrers bring about a horizontally rotating force on the molten melt in the strand. Between the two sub-stirrers there are considerable gaps in the stirrer cores which make the design less effective and also bulky. The invention aims to provide a solution enabling the stirrer to be more effective and adjustable to different cross-sectional sizes of the mould or the strand. To achieve this aim the invention suggests a stirrer for stirring of molten metal in continuous casting according to the indroductory part of claim 1, which is characterized by the features of the characterizing part of Claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention, it is possible, by exchange of intermediate cores, to adapt the mould stirrer to different mould and strand dimensions. By a suitable choice of phase sequence for the different phases in the stirrer, a horizontal rotation of molten metal can be obtained inside the mould. In case of sub-stirrers, these are allowed to contain coils for half a stirrer, two cooperating sub-stirrers acting as one whole stirrer. The intermediate iron cores ar suitably exchangeable and/or dimensioned for different strand and mould areas. The invention will now be described in greater detail with reference to the accompanying drawings showing - by way of example - in Figure 1 a view of two sub-stirrers at a mould and a continuous strand, seen from above, Figure 2 a section B-B through the stirrers shown in Figure 1. Figure 1 shows two sub-stirrers 1,2, each of which partially surrounding a mould 3. Inside the mould 3 there are placed copper plates 4 in the usual manner, which may be laminated. The sub-stirrers 1,2 also comprise iron cores. Between ad joining parts of the two sub-stirrers 1,2 intermediate iron cores 5 of such a dimension are inserted that the sub-stirrers 1,2 along with the intermediate iron cores 5 surround the mould 3. The melt 6 in the mould 3 is surrounded by copper plates. By a suitable choice of the phase sequence for the complete two-phase or three-phase stirrers formed by the two sub-stirrers 1 and 2 a horizontal rotation of the melt as indicated by the arrows can be obtained for the non-solidified portion of the strand. Also Figure 2 shows the stirrers 1,2, the mould 3 and the copper plates 4. Numeral 7 designates the direction of the advancing cast strand. The sub-stirrers 1,2 are suitably arranged so that their iron cores will be connected to the intermediate iron cores 5. The intermediate iron cores 5 can be replaced by cores of a different dimension when the mould area is changed. The stirrers can thus be used for several different dimensions of the strand and hence of the mould. The mould stirrer according to Figure 1 and 2 thus consists of two main parts or sub-stirrers, each of which form half a stirrer. These stirrers are electrically connected together so as to form one complete stirrer adapted to generate a normal travelling magnetic field. For larger sizes of the strand, intermediate iron cores 5 of appropriate size may then be fitted between these main parts to obtain an external closed iron core. It is also possible to compose each of the two iron cores 5 from two or more different sub-cores in order to facilitate adjustment of the stirrer to different cross-sectional areas of the mould or strand. It would also be possible to replace the sub-stirrers 1 and 2 by two complete stirrers, each individual stirrer thus comprising all the phase coils required to generate a travelling field of its own. Also in this case the intermediate iron cores 5 are beneficial. By a suitable choice of phase sequence, i.e. opposite phase sequences in the arrangement according to Figure 1, a stirring scheme according to the arrows can be obtained. The arrangement according to the above can be varied in many ways within the scope of the appended claims.

Claims: Stirrer for stirring of molten metal in continuous casting with at least two stirrers or sub-stirrers (1,2) being placed outside the mould (3) or strand on opposite sides thereof, said stirrers being provided with iron cores each of which surrounds part of the mould (3) or strand, characterized in that intermediate iron cores (5) are provided which are placed between adjoining parts of the stirrers/sub-stirrers (1,2), said intermediate iron cores (5) together with the stirrers/sub-stirrers (1,2) forming a closed magnetic circuit around the mould (3) or the strand, the stirrers/sub-stirrers being adapted to create a horizontal rotation of the molten metal in the mould or metal strand. Stirrer according to Claim 1, characterized in that two sub-stirrers (1,2), each one comprising coils for half a stirrer, are arranged to act jointly as one complete stirrer. Stirrer according to Claim 1 or 2, characterized in that the intermediate iron cores (5) are exchangeable and/or dimensioned for different areas of the mould or the strand. Stirrer according to any of the preceding claims, characterized in that copper plates (4), possibly laminated, are disposed between the stirrers/sub-stirrers (1,2) and the continuous strand (6). Stirrer according to any cf the preceding claims, characterized in that each of said two intermediate iron cores (5) consists of two or more sub-cores of identical or different size.

Inventors: ANDERSEN, INGVAR-THORN, ERIKSSON, JAN ERIK
Applicants: ASEA BROWN BOVERI AB
Application year: 1988
Main classification: B22D11
IPC codes: B22D11