Dewax method for investment casting

Abstract

A method for controlling the dewaxing of a ceramic investment casting shell assembly is provided whereby the shells are immersed in a fluid having a relatively low boiling point, e.g., below about 230° F. The fluid must be hot enough to transfer heat though the shell assembly so as to melt the wax pattern, but low enough so as to limit steam generation as a result of moisture in the shell. By controlling the rate of immersion of the shell in the hot fluid bath, shell cracking can be greatly reduced.

1 . A method for dewaxing a casting shell assembly including a wax pattern, said method comprising the steps of:
 a) providing a bath containing a fluid heated above the melting point of the wax pattern but below a boiling point temperature of about 230°; and   b) means for immersing the casting shell assembly into the hot fluid at a controlled rate of speed to melt away the wax pattern.   
     
     
         2 . The method of  claim 1  in which the hot fluid is water. 
     
     
         3 . The method of  claim 2  wherein the hot water is heated to a temperature of between about 190° F. and 230° F. 
     
     
         4 . The method of  claim 3  wherein the hot water is heated to a temperature of between about 190° F. and 210° F. 
     
     
         5 . The method of  claim 2  in which a soluble salt is added to the water to enable higher operating temperatures. 
     
     
         6 . The method of  claim 1  in which the shell is moistened with water prior to immersion in the hot fluid. 
     
     
         7 . The method of  claim 6  in which a fan is added to the apparatus to further cool the non-immersed portion of the shell assembly. 
     
     
         8 . The method of  claim 1  in which the hot fluid is di methyl silicone. 
     
     
         9 . The method of  claim 1  in which the hot fluid is a wax having the same composition as that of the wax pattern. 
     
     
         10 . The method of  claim 1  wherein the rate of immersion of the shell assemblies into the hot fluid is between about 0.2 inches/minute and about 5.0 inches/minute. 
     
     
         11 . A system for dewaxing comprising:
 a ceramic shell mold;   a wax pattern located within the ceramic shell mold;   a hot fluid bath maintained at a temperature below about 230° F. but above the melting point temperature of the wax pattern, and configured to receive the ceramic shell mold therein;   a pour cup engaging the ceramic shell mold and arranged such that melted wax of the wax pattern flows out of the ceramic shell mold and through the pour cup, and   means for immersing the ceramic shell mold within the hot fluid bath at a controlled rate of speed.   
     
     
         12 . The system of  claim 11  in which the hot fluid is water. 
     
     
         13 . The system of  claim 12  wherein the hot water is heated to a temperature of between about 190° F. and 230° F. 
     
     
         14 . The system of  claim 13  wherein the hot water is heated to a temperature of between about 190° F. and 210° F. 
     
     
         15 . The system of  claim 12  in which a soluble salt is added to the water to enable higher operating temperatures. 
     
     
         16 . The system of  claim 11  in which the shell is moistened with water prior to immersion in the hot fluid. 
     
     
         17 . The system of  claim 16  in which a fan is added to the apparatus to further cool the non-immersed portion of the shell assembly. 
     
     
         18 . The system of  claim 11  in which the hot fluid is di methyl silicone. 
     
     
         19 . The system of  claim 11  in which the hot fluid is a wax having the same composition as that of the wax pattern. 
     
     
         20 . The system of  claim 11  wherein the rate of immersion of the shell assemblies into the hot fluid is between about 0.2 inches/minute and about 5.0 inches/minute.