Expendable cap device to minimize dross inclusions in the vacuum casting process

摘要

A closed mold assembly having a mold cavity therein, an ingate extending from the mold cavity through the mold assembly with an opening having an outer wall for immersion into a bath of molten metal, and an expendable cap fitting around the outer wall of the ingate having a continuously upward tapering dimension to urge the top larger of the molten metal in a bath away from the ingate opening during the immersion process to minimize impurity inclusion in the mold. The expendable cap is preferably made from a non-contaminating sacrificial material intended to be melted after immersion into the molten metal bath without being detrimental to the quality of the workpiece. The closed mold assembly may also include upflow channels formed within the bottom of the mold assembly to further urge impurities in the top layer to flow away from the ingate opening and may further include downwardly extending ribs in the mold assembly with flat surfaces on the bottom to form a level surface to facilitate easy mold handling such that the molds may be stacked upon one another.