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Metal Casting Technologies : September 2006
82 TECHNICAL FEATURE In the critical temperature range up to 850°C (1560°F) R1, R2 and R3 of Phosphate bonded SB shows better numbers compared to Andalusite HS. Basically this is a confirmation of the results from FEM analysis and means the phosphate bonded material allows a higher temperature change; heat flux and temperature increase at the surface without exceeding the failure stress compared to the cement bonded material. However, a material ranking based on these results is difficult because above 1100°C (2000°F) both materials form melted phases and show plastic behavior. Hasselmann assumes only elastic properties. Hence the quality of a material choice based on thermal stress resistance parameter calculations would increase with the data base and comparative FEM analysis. CONCLUSION Comparative FEM analysis of a burner tile made of low cement bonded andalusite and a phosphate bonded castable have been conducted. Under given thermal boundary conditions it is likely that the cement bonded material would show cracking because the calculated stresses (Figure 6) are close to the yield stress limit (Table 6). It can be concluded that improved properties can be achieved by using a cement bonded castable of higher cement content in order to lower the stiffness in this temperature range. The results of the phosphate bonded material "SB" show a lower V-modulus, higher thermal conductivity and a lower coefficient of thermal expansion compared to the low cement bonded andalusite material. The determining low V- modulus is characteristic for phosphate bonded material and can be explained Figure 8. Temperature contours after one hour of heat up. A displacement-scaling factor of 50 was used. Figure 9. Calculated stresses in circumferential direction. www.metals.rala.com.au