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Prolonged tests and extensive operating experience for channel furnaces for melting aluminum alloys have shown that their good economic performance is accompanied by major shortcomings, which are due to the poor stability in the refractory lining in the longitudinal and transverse blocks of the tapoff induction unit, particularly on operation at high power. Often, these tapoff units fail because of trapping in the arch coating in the transverse blocks and the flow of liquid into lining junctions in the longitudinal channel and in the transverse block.Cracks arise in the lining for the transverse block because of the large temperature differences over the cross section, particularly in emergency situations, as when a channel blocks or needs to be cleaned or one of the tapoff units needs to be replaced.The lining is made of heat-resistant concrete or refractories; the thermal stresses arising in monolithic refractories relax less than those in sintered ones [i], so heat resistance has to be considered in choosing the refractories.Thermal failure in refractories can be evaluated from a criterion [2] that estimates the resistance to cracking and crack growth. That method has been used to evaluate the stability in unshaped refractories, which were chosen to resist molten aluminum-base alloys. MK-90 mullite-corundum refractory with phosphate bonding agent is resistant to such alloys [3], as is our MKBS mullite-corundummaterial based on a combined bonding agent consisting of lignin sulfonate and borosilicate glass. These materials have been compared with heat-resistant magnesian concrete bonded by waterglass, which is fairly heat-resistant but not very resistant to the metal.The thermal deformation resistance has been evaluated from the R 0 criterion, which is defined by Ots(l -~)/E=, in which Ots is the tensile strength, ~ Poisson's ratio, E elastic modulus, and ~ the linear expansion coefficient. The thermal resistance coefficient R has been determined by the [4] method on the basis of the brittleness measure.The thermal resistance was judged from the capacity to resist crack propagation.Griffiths' theory indi-

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