Aluminum casting method with helium insertion

Abstract

Helium gas at ambient pressure is inserted into an expendable mold at a fill tube or other port exiting the bottom of the mold. The helium displaces atmospheric air in the mold cavity, and the displaced air exits the cavity through the fill tube. When the air in the mold cavity and fill tube has been completely displaced by the helium, the fill tube is submerged in molten aluminum, and the aluminum is drawn into the mold cavity through the fill tube to form a casting having significantly reduced oxide inclusions and significantly improved fatigue strength.

Description

TECHNICAL FIELD [0001] The present invention relates to aluminium casting processes, and more particularly to a casting method in which atmospheric air in a mold cavity is replaced with helium gas to minimize oxide formation in the casting. BACKGROUND OF THE INVENTION [0002] Various casting processes have been utilized to produce high-strength aluminum parts. Intricate, high precision parts such turbocharger impeller wheels are typically produced using an expendable mold process where molten aluminum is poured or drawn into a plaster or sand mold which is then destroyed to release the casting. Although high quality impeller wheels may be produced very cost effectively in this way, care must be taken to limit exposure of the molten aluminum to atmospheric air in order to minimize the formation of aluminum-oxide in the casting. Oxide inclusions in a casting impair fatigue strength and are believed to be responsible for the majority of fatigue failures that occur in the field. [0003] O...

AI Technical Summary

Benefits of technology

[0005] The present invention is directed to an improved aluminum casting method in which atmospheric air in the cavity of an expendable mold is replaced with helium gas prior to introducing aluminium into the mold cavity. The mold is sealed at its top if gas permeable, and helium gas at ambient pressure is inserted into the mold cavity through a fill tube or other port exiting the bottom of the mold. The helium naturally rises into the mold cavity and drives atmospheric air out of the mold cavity and through the fill tube. When the air in the mold cavity and fill tube has been completely displaced by the helium, the fill tube is submerged in molten aluminum, and the aluminum is drawn into the mold cavity through the fill tube to form a casting having significantly reduced oxide inclusions and significantly improved fatigue strength.

Problems solved by technology

Oxide inclusions in a casting impair fatigue strength and are believed to be responsible for the majority of fatigue failures that occur in the field.

However, this technique is not totally satisfactory due to air resident in the mold cavity and fill tube.

However, these known techniques require sealed chambers and various other special equipment that make them both difficult to implement and costly to practice.

Images