Application of a Large-Sized Pressureless-Sintered Silicon Carbide for the Immersion Tube of Molten Metal

Abstract

We have developed a gas-fired immersion heater tube for use with melting furnaces for the processing of molten zinc. The tubes are made out of a pressureless sintered silicon carbide. The tubes single-ended have dimensions of either φ230 × φ210 × 2300mm or φ310 × φ290 × 1000mm. In this study, we examined thermal shock resistance upon water quenching, measured the gas temperature along the tubes, and simulated their tube wall temperature strength/stress distributions. Maximum stress of tube occurs just above the ring of contact with the surface of the molten zinc, where the temperature differential is the maximum. By inserting a thermal insulation sleeve (alumina silicate cloth) within the immersion heater tube, stress is decreased from 51.5MPa to 22.5MPa. The stress on dipping slant, which occurred at mechanical fixing part of tube, were not so large. We also checked the resistance of immersion heater tubes to molten zinc corrosion within actual production furnaces. We have found that within industrial zinc furnaces, the tubes can keep to operate on good condition (i.e., corrode only partially) after 6 years of service with normal burners and 4 years of service with regenerative burners.