Method of preparing ceramic molds

Claim 1

AN IMPROVED PROCESS FOR FORMING A HOLLOW CERAMIC SHELL CASTING MOLD WHICH COMPRISES: BLENDING A RAPIDDRYING BINDER COMPOSITION WITH A REFRACTORY MATERIAL, SAID BINDER COMPRISING 40-90% BY WEIGHT OF AN ACIDIC, STABLE, SALT-FREE SILICA SOL COMPRISING AN AQUEOUS LIQUID HAVING COLLOIDALLY DISPERSED THEREIN 25-50% BY WEIGHT OF SUBSTANTIALLY DISCRETE, DENSE, NON-AGGLOMERATED PARTICLES OF SILICA HAVING AN AVERAGE PARTICLE DIAMETER OF 5-150 MU, SAID SILICA SOL HAVING A PH RANGING FROM 2.6 TO 3.8 AND A SPECIFIC CONDUCTIVITY NOT GREATER THAN 1000 MICROMBOS/ CM., AT 77*F., AND 10-60% BY WEIGHT OF A LOWER ALKYL POLAR ORGANIC ALCOHOL HAVING A CARBON ATOM CONTENT NO GREATER THAN 4, SAID ALCOHOL BEING COMPATIBLE WITH SAID SILICA SOL; AND POURING SAID BLEND INT THE CAVITY OF A HOLLOW EXPENDABLE PATTERN; ALLOWING SAID BLEND TO GEL SUFFICIENTLY TO FORM A GELLED CORE; AND THEREAFTER COATING THE PATTERN WITH A CERAMIC MATERIAL TO BUILD-UP A PLURALITY OF COATS AROUND THE PATTERN TO FORM A CERAMIC SHELL.