PURPOSE: To improve the thermal shock resistance of a casting mold by a method wherein high purity silicon dioxide porous body is heat-treated so as to control the porosity and pore diameter of the porous body to specified values.
CONSTITUTION: A silicon dioxide porous body 12 consisting of a mold 10 is provided by VAD method in advance and then worked roughly into a roughly worked body 13, which is then heat-treated into a roughly worked body after heat treatment 14 and finally precision-work it into a casting mold 10. The resultant purity silicon dioxide porous body is made of minute particles having the average particle diameter of 0.01-10μm and controlled by heat treatment so as to realize the porosity of 30-70vol.%, the pore diameter of 1.0-30μm and high purity such as the impurity content of 1ppm or less. By heating the casting mold 10 made of the above-mentioned porous body at 1,100°C, silicon dioxide particles are softened, resulting in producing partial sintering, enhancing the bonding force between particles and improving the strength of the casting mold. Accordingly, the excellent casting moldability and thermal shock resistance. Further, no metallic pollution and the like is recognized in cast moldings.
ARAHORI TADAHISA
HAYASHI SHIGETOSHI
