SoSi casting or water glass casting (Lost wax)

Sodium silicate casting, also known as SoSi casting or water glass casting, is one of the lost wax casting processes used by Castmetal Advanced Services to produce high-quality metal parts at competitive prices. It is particularly suited to complex parts requiring good precision and surface quality, at a lower cost than colloidal investment casting.

What is Sodium Silicate casting?

It is a lost wax casting process that uses sodium silicate – commonly known as water glass – as the binder to build the ceramic shell around the wax model.

When carbon dioxide is added to the sodium silicate, it rapidly transitions from liquid to solid state, losing water in the process. This reaction creates a rigid ceramic shell that is used to produce the final metal part.

The process produces complex parts with good dimensional accuracy and a clean surface finish, at a cost significantly lower than colloidal investment casting.

How does the process work?

The first stage involves creating a wax model of the part to be manufactured. This wax model is then coated with sodium silicate combined with sand to form the ceramic shell. Carbon dioxide is applied to harden the shell rapidly. The shell is then heated to melt and remove the wax, leaving a hollow mould. Finally, this mould is filled with molten metal to form the final part. After cooling, the shell is broken to reveal the casting.

Sodium silicate casting vs colloidal investment casting

Both are lost wax processes, but they serve different requirements.

Sodium silicate uses sodium silicate as the binder. It offers good surface quality and dimensional accuracy at a competitive price point. It is the right choice when cost efficiency is the primary requirement.

Colloidal investment casting uses a colloidal ceramic slip. It achieves tighter dimensional tolerances, a superior surface finish and greater repeatability – preferred for aerospace, medical and defence applications, but at a higher cost.