US Patent 7270172 Process for casting a metal

This invention relates to an improved process for casting a metal by pouring molten metal into and around a casting assembly, where a riser containing a sleeve is a component of the casting assembly. The process comprises (a) inserting a riser insert into the cavity of the riser containing the sleeve, and (b) then allowing molten metal to flow into the cavity of the riser containing the riser insert. 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 and provides a thermal barrier to reduce heat loss from the riser. The sleeve is shaped such that the riser insert will not be forced out or float off of the riser cavity when the metal is poured.