Process for casting a metal

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 low-density riser insert comprised of hollow aluminosilicate microspheres having a density of from about 0.3 g/cc to about 1.6 g/cc into the cavity of the riser low-density riser insert comprised of hollow aluminosilicate microspheres 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 . (canceled)

6 . The process of claim 6 4 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.