Effect of argon blowing at tundish upper nozzle on the multiphase flow behavior of sub entry nozzle

In steel continuous casting, tundish nozzle can control the flow of steel injected into the crystallizer from the tndish as well as the melt flow behavior in the crystallizer. When used in conjunction with protective slag, sub entry nozzle can avoid secondary oxidation of the liquid steel, which has a significant effect on improving labor conditions, stabilizing continuous casting operation, and preventing surface defects on slabs.

However, when casting certain steel grades, solid inclusions with high melting points may be attached and deposited on the inner wall of the tundish nozzle, causing the nozzle to be clogged. Once the tundish nozzle clogging, the tundish nozzle will appear in the bias flow, the clogging may be suddenly rushed into the crystallizer, resulting in violent fluctuations in the liquid level in the crystallizer and slag roll. This not only affects the continuous casting operation, but also seriously affects the quality of cast billet, which may produce subcutaneous bubbles and slag in the cast billet.

Argon blowing is widely used to prevent tundish nozzle clogging and includes argon blowing from plug bars, tundish upper nozzle and sub entry nozzle. Argon blowing from the tundish upper nozzle is performed by adjusting the process parameters to form a stable and continuous gas curtain between the inner wall of the spout and the molten steel. This in turn inhibits the buildup of inclusions such as Al2O3 on the inner wall of the nozzle and reduces the risk of nozzle clogging.

By establishing a three-dimensional model of the tundish-nozzle outlet-crystallizer, numerical simulations were performed to investigate the effect of argon blowing in the tundish upper nozzle on the multi-phase flow behavior in the sub entry nozzle.

The study shows that the argon gas bubbles injected from the inner wall of tundish upper nozzle under the action of the liquid steel first downward movement along the water outlet wall. With the increase of distance from the tundish upper nozzle, argon bubbles gradually spread to the center of the nozzle. Compared with not blowing argon, when blowing argon, the liquid steel velocity increases in the center of the spout and decreases near the wall. As the argon flow rate increases, the bubble concentration inside the immersed spout increases, and the process of diffusion of the bubble population to the center region of the spout is accelerated. This in turn increases the steel velocity at the center of the spout but decreases near the wall of the spout. As the pulling speed increases, the bubble concentration inside the spout decreases, the length of the bubble cluster near the spout wall is extended, and the liquid steel flow rate in the center and near-wall areas of the spout increases. The mechanism of argon blowing on the water spout of the intermediate package to prevent the nozzle from blocking is mainly realized by the isolation of the argon bubble group on the inner wall of the nozzle.