Abstract: Apparatus for molding expanded polymer beads by the steam-fusion technique including mold segments having perforate walls, steam chests confronting the mold segments, and thermal insulation located at the junction between the mold segments and the steam chests to reduce conductive heat transfer therebetween.

Abstract: A method is disclosed for heating pre-expanded foundry pattern molding beads of polystyrene or the like in a stream of hot air to reduce the vapor-forming expansion agent content for the purpose of producing more dimensionally accurate, molded foam bead casting patterns.

Abstract: A vaporizable pattern for casting reduced porosity metal by a lost foam process is coated first with a thermally insulative, refractory layer characterized by a relatively high gas permeability and thereafter with a vaporizable polymeric layer characterized by a relatively low gas permeability. During metal casting, the refractory layer insulates the polymeric layer to delay vaporization, whereupon the low permeability causes pattern decomposition vapors to build up and slow metal replacement of the pattern to reduce vapor-entrapping turbulence. After vaporization of the polymeric layer, the vapors readily vent through the high permeability, refractory layer to avoid entrapment in the metal.