Controllability of Radiative Heat Flux across Mould Flux Films by Cuspidine Grain Size

Abstract

Apparent reflectivities and transmissivities have been measured as functions of cuspidine grain diameter for mould fluxes having constant degrees of crystallinity. Samples used were two types of synthesised mould flux with the basicity of 1, one of which samples contained 1 mass% of Fe2O3, and the grain diameter was varied in the range 1-3.5 μm. The optical measurements were carried out in the wavelength range 300-2 600 nm at room temperature using a spectrophotometer with an integrating sphere. With increasing grain diameter, the apparent reflectivity tended to increase and the apparent transmissivity tended to decrease at higher wavelengths for iron oxide free mould fluxes: it seemed that the apparent reflectivity showed a maximum value and the apparent transmissivity showed a minimum value in the grain diameter range 2-3 μm. In contrast, there was less significant dependence on grain size for mould fluxes containing iron oxides. The total radiative heat flux which may reach the mould from the steel shell has been evaluated using apparent reflectivity and transmissivity data on the basis of an optical process model. It has been found that the total radiative heat flux would be smallest in iron oxide free mould fluxes having the highest apparent reflectivity and the lowest apparent transmissivity at higher wavelengths. Effects of grain size on the radiative heat flux are smaller for mould flux containing iron oxides. Comparison of the total radiative heat flux with the total heat flux including conductive contribution suggests that control of cuspidine grain diameter would lead to reduction of the total heat flux by 7-8% for iron oxide free mould fluxes. In addition, the air gap layer would affect the total heat flux more efficiently where the volume fraction of air in the layer exceeds 85%.

Use of ornamental rock residues for mould flux development

“…The formation of other phases is related to Na 2 O, MgO and Al 2 O 3 contents and, therefore, some variations among the fluxes were observed. Some of these phases, such as akermanite and gehlenite, were also found by other authors (Susa et al, 2011). Similarly as in X-ray diffraction, cuspidine and nepheline formation was observed in the thermodynamic simulation ( Figure 6).…”

“…Therefore, it is believed that CP could lead to a small decrease in heat transfer by radiation due to larger grains in relation to NP (Susa et al, 2011).…”

“…Moreover, when comparing Figures 5-(a) and 5-(b), it was found that CP has larger grain sizes than NP. According to Susa et al (2011), bigger grain size may decrease heat transfer by radiation.…”

Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders

“…FeO 9) and (ii) scattering of IR radiation by crystals. 10,11) Thus increasing f cryst in the slag film results in increased k lat but decreased k R ; since overall, increased f cryst reduces the hear flux (q hor ), it is the effect of f cryst on k R which is dominant. The effect of adding FeO to the slag is also complicated since the reduction of k R is partially-offset by the promotion of the glass phase by FeO (i.e.…”

“…it reduces f cryst ). 11) Thus the principal properties of the slag film affecting the heat transfer are (i) the break (or solidification) temperature (T br or T sol ) since the film thicknesses (d s and d l ) increase and decrease, respectively, with increasing T br (ii) f cryst and (iii) the optical properties of the slag. Crystallisation of the initially-glassy slag film occurs over time and is accompanied by an increase in density (ρ cryst > ρ glass ).…”