Filters made from chemical binders and microspheres

A process for casting a metal part which comprises:

• (a) inserting a filter into a pouring cup or directly in a sprue of a mold assembly, wherein said filter comprises (1) a refractory material wherein said refractory material comprises at least 50 weight percent of hollow insulating aluminosilicate microspheres having an average diameter of about 10 microns to 350 microns, based upon the weight of the refractory material, and (2) an effective bonding amount of a foundry binder selected from the group consisting of phenolic resin binders, phenolic urethane binders, furan binders, alkaline phenolic resole binders, epoxy-acrylic binders, and sodium silicate binders, and
• (b) pouring metal, while in the liquid state, through said filter;
• (c) allowing said metal to cool and solidify;
• and
• (d) then separating the cast metal part from the casting assembly.