Abstract: In view of the instability of round billet quality during continuous casting of a fivemachine fivestrand caster, especially the problem that the oxidizing stuffing sand continuously pollutes the molten steel and affects the cleanliness of molten steel during the ladle change process, the influence of the stuffing sand on the quality of molten steel was studied with the five-strand tundish as the research object through thermodynamic calculation and water simulation experiments, and the optimization scheme to improve the flow behavior of the stuffing sand was proposed. The results show that the stuffing sand during the open casting process increases the oxygen content of molten steel and reduces the cleanliness of molten steel. During the unsteady casting process, slag entrapment occurs when the stuffing sand enters into the molten steel. The removal rate of the stuffing sand is related to the insertion depth of the ladle shroud, the flow rate of the ladle and the liquid level of the tundish. When the flow rate of the ladle is 3 m³/h, the immersion depth of the ladle shroud is 160 mm, and the liquid level of the tundish is 400 mm, the removal rate of the stuffing sand is 94 % at the highest.The optimized flow control device improves the flow behavior of the stuffing sand, and its removal rate reaches 99.5 % at the maximum. In addition, during steady casting process,the divergence of the response time and the average residence time of each flow is small, and the consistency of each flow is improved, which is conducive to uniform composition and temperature of molten steel.

Key words: stuffing sand, unsteady state, inclusion, cleanliness of molten steel