Process for casting a metal

Abstract

This invention relates to an improved process for casting a metal by pouring molten metal into and around a mold assembly, where a riser is a component of the mold assembly. The process comprises (a) inserting a riser insert into the cavity of the riser, and (b) then allowing molten metal to flow into the cavity of the riser containing the riser insert. The process is carried out in a manner such that the density and the shape of the riser insert enables the riser insert to float on the surface of the molten metal when the molten metal enters the cavity of the riser.

We claim:  
     
         1 . A process, for forming a metal casting by pouring molten metal into and around a casting assembly comprising an open riser having a cavity, wherein said process comprises: 
 (a) inserting a riser insert into the cavity of the riser, and    (b) then allowing molten metal to flow into the cavity of the riser containing the riser insert, wherein, 
 the riser is shaped such that, or contains a barrier such that, the riser insert does not fall into other parts of the casting assembly before the molten metal is poured, and  
 the density of the riser insert is such that the riser insert floats on the surface of the molten metal when the molten metal enters the cavity of the riser.  
   
     
     
         2 . The process of  claim 1  where the riser insert acts as a barrier to heat loss from the metal in the riser by radiation and/or convection to the atmosphere.  
     
     
         3 . The process of  claim 2  wherein the riser insert has insulating properties, exothermic properties, or both.  
     
     
         4 . The process of  claim 3  wherein the riser is a component of a casting assembly.  
     
     
         5 . The process of  claim 4  wherein the material used to make the riser insert comprises hollow aluminosilicate microspheres.  
     
     
         6 . The process of  claim 6  where the riser contains a physical barrier to keep the riser insert in the riser and prevent the riser insert from falling out.  
     
     
         7 . The process of  claim 6  wherein the riser contains a breaker core or is a neckdown riser.  
     
     
         8 . The process of  claim 7  wherein the riser insert retains insulating properties until the metal in riser solidifies.