Effect of Additives on the Sand Burning of Inorganic Binder in Al-Si7Mg Alloy Casting

Traditional organic binders used by the foundry industry produce problems such as generation of volatile organic compounds(VOCs), smoke and etc. A water glass binder system has been developed to improve the casting strength and to solve the environmental problems. However the water glass binder has a serious problem of sand burning. In this study, a commercial water glass binder was modified to reduce sand burning during aluminium casting by the addition of Calcium carbonate, activated carbon, and monosaccharide. The modified water glass binder was characterized by XRF, viscometer and TGA-DTA. We then evaluated the water glass binder core strength. Casting tests were conducted using Al-Si7Mg alloy to compare the ability to prevent sand burning in a sand mold. The XRF results of the prepared modified water glass binder showed a similar molar ratio of SiO2/Na2O to the commercial one. From the TGA-DTA analysis and gas emission calculation, it was considered that gas generation and corresponding inhibition of sand burning would be maximized with the monosaccharide-added water glass binder. Casting evaluation showed reduced sand burning for the water glass binder with mono saccharide. Also, core strength was found to be similar to the commercial water glass binder. These results prove that the monosaccharide-added water glass binder could replace the traditional organic binder.