Method and apparatus for evaporative pattern casting

Abstract

The method and apparatus are based on the use of a casting process in which expendable patterns are made of a low density material, then evaporated by molten metal as the metal advances into the cavity created by the evaporation of the pattern material. The outer supporting material of the cavity is an unbonded granular material of sufficient grain size distribution. This unbonded material is vibrated in defined partial volumes of the whole volume of a holding vessel called a pouring container and compacted to a predetermined density around the expendable pattern so that it fills all cavities of the expendable pattern prior to the introduction of molten metal into the container to displace the pattern. The compacting vibration is performed in several independent zones to achieve uniform compaction and to prevent pattern deformation. The pouring container follows a loop via a conveyor system preferably through four operation stations. At a first station, the apparatus inserts the pattern and vibrates and compacts the molding medium around the same. At a second station, the actual pouring of the molten metal into the pattern within the molding medium takes place. Preferably, the gases from the evaporation of the pattern are recovered and rendered environmentally safe. After a cooling period, the pouring container continues to a third station where the final casting is removed from the molding medium. The molding medium is recycled and recovered at a fourth station and the empty pouring container can then be used for a new casting.