To suggest a guideline for designing a mould flux for mild cooling, the radiative heat transfer characteristic of mould fluxes has been investigated using apparent reflectivity and transmissivity data on the basis of an optical-process model. The apparent reflectivities and transmissivities of mould fluxes were measured systematically as functions of the degree of crystallinity and the concentration of iron oxides, where the degree of crystallinity ranged between 0% and about 60%, and the concentration of iron oxides ranged between 0% and 2.0% on a mass basis. The apparent reflectivities and transmissivities were measured over the wavelength range 300-2 600 nm using a spectrophotometer with an integrating sphere. It has been found that crystallisation for mould fluxes increases the apparent reflectivity and decreases the apparent transmissivity, and that additions of iron oxides increase the apparent absorptivity of crystallised mould fluxes and instead decrease the apparent reflectivity. The radiative heat transfer characteristic has been evaluated using apparent reflectivity and transmissivity data on the basis of an optical-process model, which has suggested that crystallisation of mould fluxes leads to mild cooling due to increased apparent reflectivities and decreased apparent transmissivities. Furthermore, it has also been suggested that crystallised mould fluxes with no iron oxides can reduce radiative heat transfer even more by decreasing the apparent absorptivity and increasing the apparent reflectivity.
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