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Six functions of mold flux for continuous casting

　　The real meaning of protective casting is not only to produce a certain thickness of liquid protective slag layer on the upper layer of molten steel in the mold to isolate the atmospheric erosion of liquid metal. After the completion of this task, a certain thickness of protective slag layer should be wrapped on the surface of the shell. On the steel slag interface in the mold, a protective slag shell made of non-metallic materials is formed first, and then the liquid metal is attached to the inner cavity of the protective slag shell to form a primary metal shell, which gradually develops and increases its thickness. After leaving the copper tube of the mold, a shell with sufficient safe thickness is formed, which wraps the internal molten steel and continues to descend. Figuratively speaking, the protective slag layer is equivalent to wearing a layer of tights on the outer wall of the metal shell. This layer of solid and molten protective slag shell separates the high-temperature metal shell from the copper tube and plays the following roles:

　　1. Improve the friction relationship: change the contact friction between the metal shell and the inner surface of the copper tube into the contact friction between the slag shell and the copper tube formed by the non-metallic protective slag. This is a stable friction contact relationship, which greatly reduces the wear of the copper tube and greatly improves the service life of the copper tube.

　　2. Reduce the fluctuation of molten steel: from the perspective of open casting, the fluctuation of molten steel level is very large. However, due to the thickness of the protective slag, the effect of the self weight on the molten steel level greatly reduces the fluctuation of molten steel on the whole liquid level. Of course, it also has the effect of the large depth of the immersion nozzle, so a stable liquid level is formed, so the vibration marks formed by the protective slag are regular.

　　3. Change the heat transfer mode and efficiency of the casting slab: the slag shell formed by the mold flux is closely combined with the surface of the metal shell, creating conditions for the stability of the heat transfer of the whole shell, which is conducive to the uniform generation and development of the shell.

　　4. It is conducive to filling the air gap: the blank shell in the transition from liquid state to solid state shrinks, causing local depression of the blank shell, and then the air gap is formed. The molten mold flux is squeezed into the air gap under the action of regular mold drawing to fill the air gap and maintain continuous and stable heat transfer of the mold flux layer;

　　5. Good surface quality is obtained: it is precisely because the uniform protective slag shell is generated, which wraps the surface of the metal shell, and good and uniform heat transfer is obtained. The solid metal shell does not contact the copper tube, resulting in bonding defects. The surface quality of protective casting is much better than that of open casting;

　　6. Reduce the superheat during shell formation: the liquid mold flux is on the upper layer of the mold steel slag interface. First, the mold flux shell is formed. The metal primary shell is formed by attaching to the non-metallic mold flux shell. The process of metal solidification is not as intense as open casting, but the molten steel is in contact with the non-metallic mold flux shell. At this time, the mold flux shell temperature for the formation of glass and crystal is much higher than the inner wall temperature of the copper tube, In this way, the conditions for the formation and growth of relatively balanced and stable primary shell are obtained, and uniform and defect free primary shell is obtained, which is the prerequisite for high-quality slab production.