A NEW CERAMIC CASTING MOLD MADE BY GEL CASTING USING SILICA SOL AS A BINDER

Abstract

This Paper presents a new ceramic casting mold made by gel casting using silica sol as a binder. The new ceramic mold is consisted of an alumina-mullite-zirconia matrix with the ratios of 38.332 wt. % alumina, 34.378 wt. % mullite, and 27.294 wt. % zirconia respectively, the slurry is mixed then the gelling agent is added and poured into the pattern. After gelation the mold is extracted and left to dry, then sintered. There are three main defects appear in the mold fabrication process. The 1st defect is the mold cracking, as a result of forced shrinkage of mold into pattern. The 2nd defect is the bad gelation behavior of mold, as a result of non equal gelling time. The last defect is mold surface cracks, due to increased silica ratio added to the mixture. As zirconia increased the bulk density and apparent porosity is increased, leading to higher mold permeability which is important to eliminate trapping of residual gases. The increased zirconia content decreases the micro hardness and the cold crushing strength, but increases the thermal shock resistance due to phase transformation during sintering. The ceramic mold is applicable for nodular cast iron so that the mold is hard enough to withstand the forces of spheroidal graphite formation when nodular cast iron is poured into the ceramic mold. The surface roughness no. of metal cast into ceramic mold is 0.582 μm, while of the metal cast into sand mold is 5.187 μm.