Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1983-08-04
1986-01-21
Godici, Nicholas P.
Metal founding
Process
Shaping liquid metal against a forming surface
164504, B22D 2702
Patent
active
045652384
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of stirring molten steel in a continuous casting mold and an apparatus therefor. More particularly, the present invention provides a novel technique in production of steel by continuous casting. The technique includes molten steel poured into a continuous casting mold from a tundish and moved along the inner wall of the mold at different flow rates depending upon its position in the mold while being stirred moderately into a smooth flow. The present invention, by providing for moving the moderately stirred molten steel in a smooth flow along the inner wall of the mold, promotes the degassing of the resulting cast steel.
BACKGROUND ART
Continuous casting of non-deoxidized steel and weakly deoxidized steel, such as rimmed steel and semi-rimmed steel, has a drawback reflected in the operation and quality of the steel. This drawback, which involves the generation of bubbles during the casting of the steel, or the fact that bubbles remain in the cast steel to cause trouble, has prevented the continuous casting of non-deoxidized steel and weakly deoxidized steel from being practically carried out. However, various investigations have recently been made with respect to the technique for removing gas in molten steel by circularly moving (stirring) the molten steel in a continuous casting mold by means of an electromagnetic stirrer (a large number of the investigations have been actually reported). Similar to the above described method and apparatus for stirring electromagnetically molten steel in a casting mold, there are other various methods and apparatuses. However, when the effect for improving the operability and the quality of cast steel was taken into consideration, a circular flow which rotates on a horizontal plane as illustrated in FIG. 1 was most effective. In the stirring technique illustrated in FIG. 1, electromagnetic stirrers 3 and 3' are oppositely arranged on the walls of both long sides 2a and 2a' of a casting mold 2, and electromagnetic forces 4 and 4' which are in reverse directions with each other act on the molten steel flow, whereby the molten steel 1 is moved in a direction indicated by the arrows 5 and 5' and is stirred. When such flow is caused in the molten steel, bubbles caught in the vicinity of the solidifying interface are again washed and moved and are promoted to be floated up to the molten steel surface so that the bubbles contained in the molten steel are effectively removed. The flow rate of the molten steel necessary for removing bubbles is about 0.2-1.0 m/sec, and is generally preferred to be at least 0.5 m/sec.
FIGS. 2 and 3 illustrate the distribution of flow rate of molten steel in the flow illustrated in FIG. 1. FIGS. 2 and 3 illustrate the distribution of flow rate at the initial stage of acceleration when the average flow rate of the molten steel is 0.5 m/sec. Furthermore, the flow rate distribution is not constant even in the thickness direction (y direction in FIG. 1) of the cast steel, but has a distribution illustrated in FIG. 3. Accordingly, when the flow rate distribution in the width direction (x direction in FIG. 1) of cast steel is shown by using positions (a and b in FIG. 3), at which the flow rate becomes maximum (v.sub.max) and the average flow rate becomes minimum (v.sub.mean) (as representative points), the flow rate distribution shown in FIG. 2 is obtained.
It can be seen from FIG. 2 that, in such prior techniques, the flow rate is short in the first half (E-L) of acceleration, and is excessively high in the second half (L-F) thereof. Particularly, the flow rate becomes a maximum flow rate of 1.4 m/sec and is about 3 times the amount of the average flow rate at the position at which the molten steel collides with the short side wall (2b) in the finishing stage (F-B) of acceleration. When the rate of the circulating flow of molten steel in a casting mold along the wall in the horizontal direction is not uniform, the following troubles occur. That is, at a short flow rate position, bubbles can not
REFERENCES:
patent: 4030534 (1977-06-01), Ito et al.
patent: 4298050 (1981-11-01), Ohashi et al.
Kodama Masanori
Kojima Shinji
Miyazaki Yasuharu
Mizota Hisakazu
Asea AB
Godici Nicholas P.
Kawasaki Steel Corporation
Seidel Richard K.
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