PURPOSE: To prevent the generation of longitudinal cracks in the slab by setting an immersion nozzle at a shallow depth in the initial period of casting, increasing the depth gradually with an increase in casting speed and adjusting the depth to the prescribed depth when the prescribed speed is attained.
CONSTITUTION: A molten steel is supplied through the immersion nozzle into a casting mold and is continuously cast. The depth of the immersion nozzle is set at the shallow depth in the initial period of casting until the casting speed attains the prescribed speed at this time. The immersion depth is increased gradually with an increase of casting speed. The immersion nozzle is set at the prescribed depth when the prescribed casting speed is attained. The depth of the immersion nozzle is controlled in such a manner. The control of the immersion nozzle depth is so executed as to maintain the superheat degree of the molten steel in respective meniscus parts at ≥0°C. The control is also so executed that the difference in the temp. of the molten steel in the respective meniscus parts is kept at ≤5°C. The generation of the longitudinal crack in the slab is prevented in this way.
NAKAI TAKESHI
SAKASHITA TSUTOMU
