Thermal stress analysis of defect formation in fused-cast alumina refractories

• Main Author: Au, Dominic Ka Man
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/9383

Mathematical models have been developed to predict the temperature, stress and strain evolution during the manufacture of fused-cast αβ-alumina refractories approximately consistent with the process used at Monofrax Inc.. An uncoupled thermal stress model, which consists of a heat transfer model to predict the temperature evolution and a mechanical model to predict the stress and strain evolution, has been formulated. The commercial finite element code ABAQUS was employed in the thermal stress analysis. The thermal model was validated against industrial thermocouple and pyrometer measurements obtained at Monofrax Inc., located in Falconer, NY. The model predictions were in good agreement with the thermocouple data obtained at several locations from within the graphite mold, during Stage I cooling, and in the alumina annealing ore, during Stage II cooling. In Stage I cooling, it has been necessary to augment the conductivity of the liquid alumina to account for convective heat transport. In Stage II cooling, it proved necessary to account for asymmetric placement of the block in the annealing bin. The temperatures obtained from the thermal model were utilized as input to the mechanical model. Elastic and elastic-plastic stress analyses were conducted to assess the evolution of stress and strain during the casting process. The strain rate independent inelastic behavior of the casting based on the flexural tests performed at Oak Ridge National Laboratory was incorporated into the elastic-plastic stress model. The results obtained from the elastic-plastic stress model were more realistic than those predicted by the elastic analyses. However, the plastic strain may be under-predicted during Stage II cooling owing to the strain rate independent plasticity employed in the analysis. The preliminary stress/strain predictions indicate that the β-alumina core plays an important role in the generation of tensile stresses and likely gives rise to the generation of cracks. Since high tensile stress/strain was found to develop within the refractory, it is likely that crack initiates subsurface and propagates outwards. Overall, the results of the present research show the importance and usefulness of developing the ability to predict temperature, stress and strain evolution in the fused-cast αβ-alumina refractories during the manufacturing process. === Applied Science, Faculty of === Materials Engineering, Department of === Graduate