Research of Compound Additives on Moisture Resistance of Sand Cores Bonded by Sodium Silicate

In this research, the storage performance of sodium silicate-bonded sand core was significantly improved by adding compound additives, including micro-silica powder, PVB ethanol solution and cement. The orthogonal test determined that the optimal addition percentage for sodium silicate binder, micro-silica powder, PVB ethanol solution and cement was 100:35:35:17.5. The storage tensile strength for prepared sand cores was 0.98 MPa under condition of 25 °C and 70% RH for 4 h. According to SEM observation, the bonded bridges inside sand cores with additives were still well connected under humid environment. As suggested by the FT-IR analysis, a complex and dense Si–O–Si network containing more Q3 and Q4 type silicon atoms was formed inside bonding bridges enhancing the connection between sand particles, and the hydrolysis of Si-O-Si network was relieved. Therefore, the storage tensile strength of sand cores was enhanced by adding compound additives.