Patent ID: 6019927
Filing Date: 2000-02-01
Classification: B22C,B33Y,Y10S

Abstract:
A method of producing an impeller of a high temperature casting material and having a complex geometry with curved blades defining undercut spaces, the method comprising the steps of forming a positive flexible pattern of the impeller with a curable resilient and flexible material to provide the pattern with flexible walls corresponding to the blades, dipping the flexible pattern into a liquid ceramic molding media capable of drying and hardening, removing the flexible pattern from the liquid ceramic molding media with a coated layer of the ceramic molding media, drying the layer of ceramic molding media on the flexible pattern to form a ceramic shell on the flexible pattern, repeating the dipping and drying steps to form a multiple layer ceramic shell on the flexible pattern, removing the flexible pattern from the ceramic shell by flexing the walls of the flexible pattern to form a first multiple layer ceramic shell mold defining a negative mold cavity corresponding to the impeller and to provide a reusable flexible pattern, forming a second pattern defining a back plate surface for the impeller and a sprue passage, dipping the second pattern into a liquid ceramic molding media, removing the second pattern from the liquid ceramic molding media with a coated layer of the ceramic molding media on the second pattern, drying the layer of ceramic molding media to form a ceramic shell on the second pattern, and repeating the dipping and drying steps to form a multiple layer ceramic shell on the second pattern to form a second multiple layer ceramic shell mold, connecting the second ceramic shell mold to the first ceramic shell mold, removing the second pattern from the second mold, pouring the casting material into the negative mold cavity of the first ceramic shell mold through the sprue passage within the second ceramic shell mold and allowing the casting material to harden to form a multiple blade impeller with a back plate, and removing the first and second shell molds from the impeller.