PREFOAMING GRAIN USED TO PRODUCTION OF EXPENDABLE PATTERN FOR CASTING AND EXPENDABLE PATTERN MADE OF IT

摘要

PURPOSE:To prevent generation of soot at the time of burning a pattern and to obtain a casting having beautiful casting surface by heating synthetic resin containing foaming agent, introducing or replacing with inert gas in grain during pre-foaming forming or in grain obtd. by pre-foaming forming and using to an expendable pattern for casting. CONSTITUTION:At the time of pre-foaming by heating the synthetic resin grain containing foaming agent, by mixing the inert gas in steam or hot blast as heating medium, the inert gas is contained in the pre-foaming grain. Or, after pre-foaming, the pre-foaming grain is charged into a vessel under condition of reducing pressure without replacing air, and the inert gas is introduced into the vessel and is absorbed in the grain. Then, at least one kind of gas selected among nitrogen, argon, helium, carbon dioxide and hydrogen fluoride is used as the inert gas. Next, the pre-foaming grain is packed into a metallic mold, which is possible to shut but not possible to close, and heated to foaming-form and is made to the expendable pattern for casting. Therefore, as the pattern contains the inert gas, the soot is scarcely generated at the time of burning at pouring.