Investment casting with improved melt feeding

Abstract

Method and apparatus for casting of molten metallic material wherein the metallic material is introduced into a mold and a pressure cap then is clamped on the mold by a cam/cam follower mechanism to form a seal such that pressurizing gas can be introduced into the mold on the molten metallic material therein. The pressure cap includes an inlet for pressurizing gas, which is introduced on the molten metallic material in the mold after the pressure cap is sealed thereon. Application of gas pressure on the molten metallic material in the mold improves filling of mold with the molten material and reduces or eliminates non-fill voids in the solidified casting.

I claim:  
     
         1 . Apparatus for casting a molten metallic material, comprising: 
 a mold having a mold cavity to receive the molten metallic material, and    a pressure cap having a seal-carrying member disposed on said mold and having a cam member disposed on the seal-carrying member, said seal-carrying member including a seal for sealing on a surface of said mold, said cam member having a cam surface, said pressure cap including a cam follower that engages said cam surface and said mold in a manner that said seal is compressed against said surface between said seal-carrying member and said mold when said cam member is moved, said pressure cap including a gas inlet for introducing pressurizing gas into the mold on a surface of the molten metallic material therein.    
     
     
         2 . The apparatus of  claim 1  wherein said cam follower is disposed for movement on said seal-carrying member.  
     
     
         3 . The apparatus of  claim 2  wherein said cam follower includes a follower surface that engages the cam surface and a mold-gripping surface that grips the mold in a manner to urge said seal-carrying member toward said mold when the cam member is rotated.  
     
     
         4 . The apparatus of  claim 3  wherein the mold-gripping surface engages a frusto-conical pour cup of the mold.  
     
     
         5 . The apparatus of  claim 3  wherein said cam member includes a pair of said cam surfaces that are engaged by a respective said cam follower.  
     
     
         6 . The apparatus of  claim 3  wherein said cam follower includes an upstanding follower member having the follower surface and the mold-gripping surface thereon, said cam follower member being disposed for up and down movement between a pair of brackets connected to said seal-carrying member.  
     
     
         7 . The apparatus of  claim 1  where the seal resides on a lip of a mold pour cup so as to seal thereon when the cam member is moved.  
     
     
         8 . The apparatus of  claim 1  wherein said cam member is circular cam plate and said seal-carrying member is a circular plate having said seal on a side facing the mold.  
     
     
         9 . The apparatus of  claim 8  wherein the cam member includes a handle by which it is rotated relative to the seal-carrying member.  
     
     
         10 . The apparatus of  claim 1  including a source of inert gas communicated to said gas inlet.  
     
     
         11 . The apparatus of  claim 1  wherein said gas inlet extends with clearance through an aperture in the cam member and is connected to the seal-carrying member to communicate to a mold interior.  
     
     
         12 . Method of casting, comprising introducing molten metallic material into a mold, placing a pressure cap on the mold after the melt is introduced therein with a seal of said pressure cap disposed on a mold surface, camming the pressure cap toward the mold to compress the seal against the mold surface, and introducing gas through an inlet in the pressure cap on the melt residing in the mold to provide gas pressure on said melt.  
     
     
         13 . The method of  claim 12  wherein the pressure cap is cammed toward the mold by movement of a cam follower that engages a cam surface on the pressure cap and that also engages the mold.  
     
     
         14 . The method of  claim 13  wherein the cam surface is moved relative to the cam follower while the cam follower engages the mold.  
     
     
         15 . The method of  claim 13  wherein the cam follower engages a frusto-conical pour cup of the mold.  
     
     
         16 . The method of  claim 12  wherein an inert gas is introduced through the inlet into the mold.  
     
     
         17 . The method of  claim 12  wherein the molten metallic material is introduced into the mold in a vacuum casting chamber, the mold is removed from the vacuum casting chamber, and the pressure cap is placed on the mold after the mold is removed from the vacuum casting chamber.