Process for casting a turbine wheel

摘要

A process for casting a turbine wheel includes steps of identifying a metal composition from which the turbine wheel is to be cast, providing a mold that defines a cavity into which molten metal composition is to be poured for casting the wheel, providing a seed member made of the metal composition and having an equiaxed grain structure, disposing at least a portion of the seed member within the cavity of the mold, pouring the molten metal composition into the cavity such that the molten metal composition envelops the portion of the seed member within the cavity, and controlling the process so that the portion of the seed member at least partially melts through contact with the molten metal composition and so that, upon cooling, the metal composition around the seed member solidifies with an equiaxed grain structure as precipitated by the equiaxed grain structure of the seed member.

主权项

1. A process for investment casting a turbine wheel to have an equiaxed grain structure, comprising steps of:
identifying a metal composition from which the turbine wheel is to be cast; providing a mold that defines a cavity into which the metal composition in molten form is to be poured for casting the turbine wheel, the cavity being configured for defining a hub portion of the turbine wheel and for defining blades extending from the hub portion; providing a seed member made of said metal composition, the seed member having an equiaxed grain structure; disposing at least a portion of the seed member within the cavity of the mold, the portion of the seed member within the cavity having a pin configuration and comprising a majority of the seed member, said majority of the seed member being disposed at a center of a region of the cavity that is configured for defining the hub portion of the turbine wheel; activating a heating device to pre-heat the mold and the seed member to a mold temperature within a range between a predefined minimum mold temperature and a predefined maximum mold temperature, followed by pouring the metal composition in molten form into the cavity such that the molten metal composition envelops said majority of the seed member; and once the pouring is completed, discontinuing the heating by the heating device and allowing the metal composition to cool and solidify; wherein said majority of the seed member acts (1) as a chill pin positioned at a center of the hub portion of the turbine wheel and able to absorb and dissipate heat via conduction along the length of said majority and (2) as a source of small grain nucleation sites for the surrounding liquid metal during cooling, so that said majority of the seed member at least partially melts through contact with the molten metal composition and so that, upon cooling, the metal composition around the seed member solidifies with an equiaxed grain structure as precipitated by the equiaxed grain structure of the seed member.