Abstract
For the development of exhaust gas purifying devices of automobiles, the development of cast products with excellent heat characteristics in terms of anti-heat cracking and anti-oxidation properties is urgent. In this study, the possibility of heat insulating casting was considered and metal-ceramic composite material which is produced by pouring molten metal outside the ceramic pipe placed in advance in a mold was examined as a typical example. Ceramic pipes having 50mm outside diameter with four different materials were placed in molds afterwhich aluminum alloy or gray cast iron was poured. All of the alumina group ceramic pipes broke at the time of pouring due to thermal shock. All of the mixed alumina-silica group cracked. Some of silica group broke and others cracked. By contrast, the special group containing alumina cement was enveloped soundly without any cracks irrespective of the kind of metal. This is due to the reason that the special ceramic containing alumina cement has low modulus of elasticity and optimum range of compressive strength, that is, it has high flexibility, and therefore the diameter of the ceramic pipe can be reduced close to the elastic limit due to the force of contraction of the cast metal, as a result of which excess stress is released by the elastic deformation of the ceramic to give a sound composite structured pipe. The surface of the metal has shrunk to fit that of the ceramic due to contraction of the metal poured. Since the compressive stress in the ceramic is balanced with the tensile stress in the metal within the range of elasticity, the metal-ceramic composite structure can withstand mechanical vibration with sufficient durability so that uses in internal combusion engines and other uses can be expected.
