Manufacturing: Metal Casting

Introduction

Casting Methods

Online Resources

Metal Casting Techniques - Sodium Silicate CO2 InOrganic Shell Molding

Instead of using an oil or resin that requires heat for bonding or curing, this process uses a sand which has been mixed with sodium silicate (NA2SiO3).

In this process, the CO2 gas forms a weak acid which hydrolyzes the sodium silicate, thus forming an amorphous silica that becomes the bond. There is also a bonding action from the sodium silicate itself. The use of CO2 gives an almost instantaneous set. The mold is fully hardened before the pattern is drawn from the mold sections.

Advantages

• Materials for the sodium silicate process tend to be low cost.
• All sands can be used as the base aggregate for the silicate sand mixture. These include silica sands, bank sands, lake sands as well as zircon, chromite and olivine sands.

Disadvantages

• The more alkaline the binder, the longer it takes to gas and the greater the tendency for the core to remain rubbery instead of firm.