Modelling of fused cast alumina refractory

Abstract

Finite difference computer modelling of a 2D cast mould insulation annealing system (CMIA) was used to investigate the temperature gradient and thermal stress distribution during cooling of a fused cast α,β-Al₂O₃ refractory. It was found that, of the various materials comprising the system, the mould material has the largest influence on the temperature gradient and thermal stress distribution, particularly at the beginning of cooling. The insulation layer has a large influence over the whole cooling cycle. The influence of the annealing layer mainly occurs in the later stage of cooling. As the thermal conductivity of any layer in the CMIA system increases, the peak temperature gradient and peak thermal stress in the cast increase rapidly, and move to a lower temperature region. This is obvious in the case where all the layers except the cast are of the same material. As the thermal conductivity of the mould in the cast mould system increases, the peak temperature gradient increases rapidly and moves to a lower temperature region until a maximum occurs at about 1310°C. The largest temperature gradient and thermal stress, therefore, appear in the temperature range 1310 to 1580°C for cooling fused cast α,β-Al₂O₃ refractory. An optimum thickness exists for any layer in the CMIA system to give minimum temperature gradient and thermal stress. Deviation from the optimum thickness leads to proportionate increases in the temperature gradient and thermal stress. In addition, optimum thicknesses are related to each other, and also to the size of the cast. This is also obvious in the case where the system, except for the cast, consists of the same material. The temperature gradient is proportional to (x_r /d_x )(y_{r r} /d_y ) for a cast mould system. A second peak in temperature gradient, in addition to a major peak in the high temperature region, appears below 1580°C, and is closely related to the thickness of each layer in the system. The second peak can be eliminated if the thickness of each layer in the system is optimum, and its elimination would decrease the possibility of cracks forming in the cast.