Assessment of heat transfer through mold slag film considering radiative absorption behavior of mold fluxes

Abstract

Controlling the heat transfer rate from solidifying shell to copper mold is one of the important role of mold flux film during continuous casting of steels. It is highly desirable to regulate the thermal resistance of mold flux film not to exceed the critical quantity of mold heat transfer rate to prevent cast steel products from surface defects. In order to examine the effect of thermal radiation on the overall heat transfer rate through slag film in the continuous casting mold, the absorption coefficient has been investigated for various mold fluxes using a UV and an FT-IR spectrometer, followed by numerical calculations based on gray gas assumption. It is estimated that the heat transfer rate will decrease in 2-4% by addition of 3.2 mass% NiO into the conventional mold flux system with basicity (CaO/SiO 2 ) of 1.07. As the increase of absorption coefficients will not be harmful to any casting performances such as friction in a casting mold, it is highly recommended to enhance the thermal radiative absorption behavior of mold slag film by optimizing the chemistry of mold fluxes, especially in the wavelength range of 1 to 3 μm at which the emitted energy intensity from steel shell will be maximized.

Heat transfer control by dispersed metallic particles in glassy mold flux film for continuous steel casting

“…Mie scattering by MPs increased the β as the content of FeO (Figure 3A) and Fe (Figure 3B) increased. Samples that contained FeO had an additional increase in β as a result of the characteristic charge‐transfer absorption by the transition metal in FeO, 20,24 over that of the samples that contained Fe. The increase in β data in the range of 3.83‐3.87 µm may be a result of ring stretching in the cyclic meta‐borate ion 20,25 .…”

“…In this study, a similar concept to Mie theory is also applied to explain the mechanism by which the particles affect radiative heat transfer because the size of the spherical MPs of the designed mold flux is similar to the incident beam wavelength from steel shell 10,17‐20 …”

“…Therefore, maximizing β is very important for the heat transfer control through the liquid mold flux film. β is the sum of the scattering coefficient s and absorption coefficient α 20‐23 : …”

Mold Simulator Study of Heat Transfer Phenomenon During the Initial Solidification in Continuous Casting Mold

“…[4,[12][13][14][15] Generally, the high basicity mold flux (high tendency for crystallization) is applied to the crack-sensitive steel grades to optimize the mold heat flux and the liquid/glassy slag film with transition metal oxides is desired to suppress the radiative heat transfer and provide the lubrication. [16][17][18] In principle, a glass film adjacent to mold is formed at first, as the cooling rate is high enough to prevent the growth of any nuclei. Then the glassy slag would transform into a crystalline layer with time, [1,19] and this solid slag film eventually will consist of crystals in a glass matrix.…”

“…Thermal conductivity of liquid slag k sl 1.2 [18] W/m K Apparent thermal conductivity of solid slag k eff 2.4 [2] W/m K Thermal conductivity of air k a 0.032 W/m K Crystallization temperature T sol 1323.15 (1050) K (°C) resistance R l , and the solid film thermal resistance R s over the total mold/shell thermal resistance, and they are 27.5 to 34.4 pct (R int /R tot ), 17.2 to 34.0 pct (R l /R tot ), and 38.5 to 48.8 pct (R s /R tot ), respectively. Therefore, the interfacial thermal resistance, R int , and the solid film thermal resistance, R s , are regarded as the dominant factors to control the heat transfer from the shell to the mold.…”