Water glass, also known as sodium silicate, is a kind of soluble alkali metal silicate, solid state is glass, dissolved in water to form aqueous glass solution. According to the different alkali metal contained, there are potassium water glass and soda water glass two kinds. The latter is easily soluble in water, contains less impurities, and has a stable performance. Therefore, the water glass used for alloy steel casting is sodium water glass, namely Na₂₀.mSiO₂. Transparent or translucent aqueous colloidal solution formed after hydrolysis of water glass. The main chemical components of water glass are silicon oxide and sodium oxide, in addition to a small amount of impurities.Aqueous glass is not a single compound, but a mixture of multiple compounds. In the melt mold casting process, the water glass binder and coating performance is stable, low price, short shell cycle, easy to use. The production process of water glass shell is suitable for the production of carbon steel, low alloy steel, cast iron, copper, aluminum alloy and other precision castings with low surface quality requirements.