Relation between surface quality of cast strips and meniscus profile of molten pool in the twin roll casting process

Experiments of laboratory scale twin roll casting to observe strip surface quality and to detect contact point between molten metal and roll by immersing a refractory bar into the molten metal pool have been done using stainless and carbon steels and copper alloy to elucidate the relation between surface quality and meniscus behavior of molten metal. Furthermore, dynamic meniscus profile near the roll surface and critical casting speed controlling surface wrinkles have been theoretically analyzed. With increasing casting speed, the depth of surface wrinkles becomes shallow and the flat surface is obtained. The observed critical speed for the wrinkle-free surface is roughly 0.45 to 0.6 m/s for the cast metals. By the immersion of refractory bar over a depth, the solidification of columnar dendrite zone is delayed and the surface wrinkle is resultantly formed. With increasing casting speed, the depth of bar to result in surface wrinkles increases and the contact point between molten metal and roll moves downward. It has been theoretically found that the descent of meniscus increases with increasing casting speed and surface tension of molten metal and with decreasing the density. The surface wrinkle does not appear when the descent of meniscus is deeper than a critical value, because vibration of the molten pool surface due to the teeming flow becomes less influential at the contact point. A theoretical equation of the critical speed for preventing surface wrinkles has been presented to show that it increases with increasing the critical descent of meniscus and the density and with decreasing the surface tension.