Modelling of fused cast alumina refractory

Finite difference computer modelling of a 20 cast mould insulation annealing system (CMIA),vas used to investigate the temperature gradient and thermal stress distribution during cooling of a fused cast alpha,beta-Al2O3 refractory. It was found that, of the carious materials comprising the system, the mould material has the largest influence on the temperature gradient and thermal sti ess 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 ther mal str ess 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 degrees C. The largest temperature gradient and thermal stress, therefore, appeal in the temperature range 1310 to 1580 degrees C for cooling fused cast alpha,beta-Al2O3 refractory. An optimum thickness exists for and layer in the CMIA system to give minimum temperature gradient and thermal stress. Deviation from the optimum thickness lends 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)/d(y))for a cast mould sq stern. A second peak in temperature gradient, in addition to a major peak in the high temperature region, appears below 1580 degrees 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.