| Solidification contraction during crystallization of molten mold fluxes has been observed in a laboratory scale mold. Mold fluxes with larger contraction show smaller mold heat flux in thin slab caster. This implies that thermal resistance at mold/mold flux interface arises from the solidification and crystallization of the flux film. Also, the effect of chemical composition on the solidification contraction has been clarified using synthetic mold fluxes of 1.25∼1.45 basicity, 8∼12 mass % Na_2O, 7∼11 mass % F, 2∼6 mass % Al_2O_3, 1.5∼4.5 mass % MgO. Larger basicity and Na_2O/F ratio yield larger contraction. Especially, mold flux of 12% Na_2O and 7% F shows larger contraction than that of 8% Na_2O and 11% F. Microphotograph analysis shows that the crystallization of sodium fluoride dicalcium silicate (NaF.2CaO.SiO_2) is the main reason for the increase of solidification contraction. |
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