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.

As a continuation of the previous report which dealt with a mild steel sheet, this study covers the welding phenomena at a tool-work interface in deformation processing of aluminum sheet which has been investigated experimentally by using a two dimensional drawing-type friction testing machine. Variation mode of the frictional coefficient during the drawing process can be classified into four types, namely,- constant, increasing, decreasing and waving type. In both the increasing and decreasing types, the welding occurs at a die exit portion, similar to the case of mild steel reported previously. In the waving type, a process of growth and the peeling away of the welding layer is repeated at a central portion of the die, and corresponding frictional coefficient waves develop. The frictional shear stress on the welding region is constant (about 68.6 MPa), approximately equaling the yield shear stress of the aluminum. The ability to repair the welding has been examined by measurement of the frictional coefficient at the designated drawing travel for mineral oils with various viscosities and compositions.