Silica sol ceramic mold was made at room temperature with JN-30 silica sol, silica powder and NH4Cl. It is found that the harden time of silica sol ceramic mold is only 0.5 to 1.5 h under the amount of NH4Cl solution of 7% to 8% with 15% concentration, and less surface cracks occur by using vacuum drying. The proper
vacuum drying process parameters: vacuum drying temperature is 80 to 100±C, drying time is 5 h and vacuum is 0.06 to 0.07 MPa. The harden mechanics , vacuum drying mechanics and the reason of less surface cracks of silica sol ceramic mold by vacuum drying were also analyzed in this paper.