The Study On Improving Humidity Resistance Of Water Glass Sand

Because of innocuity, achromatism, insipidity and irritating gas not generated during the casting process such as mixing sand, moulding, coremaking, pouring, cooling and shakeout, the water glass as a foundry binder has become a promise green product and found wide applications in the spheres of bonding and coating. However, at recent, the general disadvantage of water glass is their humidity resistance in the moisture-laden air hindering the development in the foundry industry. It brings a lot of serious problems to moulding and coremaking of water glass sand. As a result, the humidity resistance of water glass sand has attracted the high attention of the foundry workers from all around the world.Based on hydration reaction of cement, a new conception on polycomponent modification of water glass using flyash, slag and amorphous silicon dioxide to improve their humidity resistance was put forward. Single factor experiment and orthogonal design on effects of modifying agents such as flyash, slag, amorphous silicon dioxide, borate, sorbierite and Al₂O₃ on properties of water glass modification have been indicated that the strength and humidity resistance of water glass sand modified by borate can probably be increased a little, but so did the retained strength of water glass sand. The humidity resistance of water glass sand can be also increased by adding amorphous silicon dioxide which is due to formation of a hydrophobic coated layer on the silica gel. The humidity resistance and 24h strength of water glass sand can be markedly raised by adding flyash and slag owing to the hydration reaction. The retained strength of water glass sand is considerably lowered as a result of addition of modifying agents.mixture ratio of amorphous modifying agents (including sorbierite) was optimized using regression analysis of uniform design, the optimum mixture ratio of modifying agents for water glass is as follows (wt%): 57.3 flyash, 24.2 amorphous silicon dioxide, 11.7 slag, 4.7 Al₂O₃ and 2.1 sorbierite. 24h strength of water glass sand modified by above-mentioned amorphous modifying agents can attained to 2.86MPa, the 72h strength at moist conditions is 2.32MPa, the retained strength at 1000℃is 0.9 MPa. The results of these tests explaine that the water glass sand modified using above-mentioned optimum modifying agents mixture has better processing properties to meet the demand for foundry.