Countergravity Casting Apparatus and Desulfurization Methods

Abstract

An apparatus for countergravity casting a metallic material, has: a crucible for holding melted metallic material; a casting chamber for containing a mold; a fill tube capable of extending into the crucible to communicate melted metallic material to the casting chamber; and a gas source coupled to a headspace of the melting vessel to allow the gas source to pressurize the headspace to establish a pressure differential to force the melted metallic material upwardly through said fill tube into the mold. Extraneous sulfur is prevented from entering the molten metal from the mold by solidifying metal in the fill tube.

What is claimed is: 
     
         1 . A method for using an apparatus for countergravity casting a metallic material, the apparatus comprising:
 a melting vessel;   a casting chamber containing a mold;   a fill tube capable of extending into the melting vessel to communicate melted metallic material to the casting chamber; and   a gas source coupled a headspace of the melting vessel to allow the gas source to pressurize said headspace to establish a pressure differential to force the melted metallic material upwardly through said fill tube into said mold,   the method comprising:   melting a nickel-based superalloy in the melting vessel;   disposing the mold under subambient pressure on a mold base with the fill tube extending through an opening in said base;   relatively moving said melting vessel and said base to immerse an opening of said fill tube in the melted nickel-based superalloy in said melting vessel and to engage said melting vessel and said base with seal means therebetween such that a sealed gas pressurizable space is formed between the melted nickel-based superalloy and said base;   gas pressurizing said space to establish a pressure differential on the melted nickel-based superalloy to force it upwardly through said fill tube into said casting mold, the melted nickel-based superalloy passing through the filter which filters the sulfur-containing particles; and   a step for preventing sulfur pick-up by the melted nickel-based superalloy in the melting vessel from the material of the mold.   
     
     
         2 . The method of  claim 1  wherein:
 the step comprises solidifying melted nickel a superalloy in the fill tube. 
 
     
     
         3 . The method of  claim 1  wherein:
 the mold has a cavity shaped to form a gas turbine engine component. 
 
     
     
         4 . The method of  claim 1  wherein:
 the mold has a cavity shaped to form a gas turbine engine combustor panel. 
 
     
     
         5 . The method of  claim 1  wherein at least one of:
 the filter comprises a sulfur-gettering material; and 
 a source of sulfur-gettering particles is upstream of the filter and the filter is effective to filter the sulfur-gettering particles. 
 
     
     
         6 . The method of  claim 1  wherein:
 the melting vessel has a removable crucible; and 
 at least one of the crucible, fill tube, and mold has at least a surface layer of a sulfur-gettering material of greater sulfur-gettering ability than alumina and zirconia. 
 
     
     
         7 . The method of  claim 6  wherein:
 the surface layer is along the crucible; and 
 the sulfur gettering ability is at least that of 20 weight percent MgO in ZrO 2 . A method for using an apparatus for countergravity casting a metallic material, the apparatus comprising: 
 a melting vessel having a crucible for holding melted metallic material; 
 a casting chamber for containing a mold; 
 a fill tube capable of extending into the crucible to communicate melted metallic material to the casting chamber; and 
 a gas source coupled a headspace of the melting vessel to allow the gas source to pressurize said headspace to establish a pressure differential to force the melted metallic material upwardly through said fill tube into said mold, 
 the method comprising: 
 melting a nickel-based superalloy in the melting crucible; 
 disposing the mold under subambient pressure on a mold base with the fill tube extending through an opening in said base; 
 relatively moving said melting vessel and said base to immerse an opening of said fill tube in the melted nickel-based superalloy in said melting vessel and to engage said melting vessel and said base with seal means therebetween such that a sealed gas pressurizable space is formed between the melted nickel-based superalloy and said base; 
 gas pressurizing said space to establish a pressure differential on the melted nickel-based superalloy to force it upwardly through said fill tube into said casting mold, the melted nickel-based superalloy passing through the filter which filters the sulfur-containing particles; and 
 solidifying the nickel-based superalloy in the fill tube. 
 
     
     
         9 . The method of claim  8  wherein:
 the solidifying acts to prevent sulfur pickup by the nickel-based superalloy in the melting vessel from mold material. 
 
     
     
         10 . The method of claim  8  further comprising:
 releasing the pressure differential; 
 removing the mold and the fill tube; and 
 replacing the removed mold and fill tube with a new mold and fill tube. 
 
     
     
         11 . The method of claim  8  wherein:
 the fill tube comprises a ceramic filter. 
 
     
     
         12 . The method of  claim 11  wherein at least one of:
 the filter comprises a sulfur-gettering material; and 
 a source of sulfur-gettering particles is upstream of the filter and the filter is effective to filter the sulfur-gettering particles. 
 
     
     
         13 . The method of claim  8  wherein:
 at least one of the crucible, fill tube, and mold has at least a surface layer of a sulfur-gettering material of greater sulfur-gettering ability than alumina and zirconia. 
 
     
     
         14 . The method of  claim 13  wherein:
 the surface layer is along the crucible; and 
 the sulfur gettering ability is at least that of 20 weight percent MgO in ZrO 2 . 
 
     
     
         15 . The method of  claim 13  wherein:
 the surface layer comprises CaO.