Carbon Dioxide Casting

The sand mixture used in this process is pure silica and sodium silicate. The molding mixture thus obtained is rammed around the pattern and gassed with carbon dioxide (CO2). The molding mixture gets hardened due to the formation of silica gel. After passing CO2, the pattern is removed and the mold cavity is ready for pouring.
Properties of silicates vary according to the silica (SiO2)-soda (NaO) ratio of the sodium silicate base that is used to formulate the binder. Considerable care must be used when gassing with CO2 since overgassing and undergassing adversely affect the properties of the cured binding system. The amount of silicate binder used for cores and molds varies from 3% to 6% depending on the type of sand, grain fineness, and degree of sand contaminants.