Colloidal silica , also known as silicic sol solution, is a colloidal dispersion of amorphous silica aggregate particles in water. Colloidal silica has a wide range of water loss temperatures, which not only destroys its binding strength, but also makes its three-dimensional structure more stable, resulting in higher binding strength. It is a good inorganic binder for precision casting.

In the 60s of the 20th century, colloidal silica began to be used as a binder for precision casting. Since the 90s of the 20th century, due to the increase in environmental protection pressure, colloidal silica has gradually replaced the widely used ethyl silicate hydrolysate, which is seriously polluted and expensive. At present, polymer-reinforced fast-drying colloidal silica is widely used as a binder in the world's investment casting industry.

Precision casting is a general term for the process of obtaining castings with precise dimensions. Precision casting is also known as lost wax casting. Its products are precise and complex, close to the final shape of the part, and can be used directly without machining or a small amount of machining. This is an advanced near-net-shape process. The process includes: selecting a suitable investment material (such as paraffin) to make the investment mold, repeating the steps of impregnating refractory paint (the main component is silica sol) and spraying refractory sand, hardening the shell and drying on the investment mold, melting the inner investment mold to obtain the mold cavity, baking the shell to obtain sufficient strength and burning off the residual investment material, pouring the required metal material, solidifying and cooling, shelling, and sand removal to obtain a high-precision finished product.

Colloidal silica is used for precision casting. Due to its good adhesion ability and filling performance, the shell made of high strength, high gloss and easy release of mold is widely used in this field. According to the different requirements of specific use, it is divided into surface silica sol and back silica sol, which consumes a huge amount.

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