Vacuum casting apparatus using flange-free stalk

Abstract

A vacuum casting apparatus secures gas tightness of the die cavity without welding together a straight-tubular stalk and a flange or flanges, thus permitting an excellent quality casting. Two flanges are mounted in a mutually spaced-apart relation on an outer periphery of a stalk, and secured between a gas-tight chamber and a die. The gas-tight chamber is fitted on the die from above to form a gas-tight space between the two flanges. The space is evacuated to a pressure close to an inner pressure formed in a cavity of the die during vacuum casting. Thus, air that intrudes into the cavity of the die through small gaps between the flanges and the stalk is reduced, thereby preventing casting defects which might otherwise result. An end of the stalk inserted into the die is also spread to bring an outer periphery of the stalk into close contact with an inner periphery of a flange mounted on the stalk. A first degree of vacuum is applied to the gas-tight chamber to draw molten metal through the stalk to a level above the insertion end of the stalk, and below an inlet of the die cavity, so that the molten metal cools and forms a gas-tight seal about the insertion end of the stalk, before a second degree of vacuum is applied to withdraw molten metal into the die cavity.