LUDOX® Colloidal Silicas in Precision Investment Casting
Precision Investment Casting (PIC), also known as lost-wax casting, is a process used to create intricate metal parts with high accuracy and fine surface finish. This method is used to make metal parts as diverse as intricate components for airplane engines to large steel valves for chemical plants.
When the PIC process is undertaken using colloidal silica, the silica material serves the crucial function of being the ceramic binder that bonds to the refractory grain and forms a strong, cohesive casting. LUDOX® colloidal silica, a suspension of discrete fine and amorphous spherical silica particles in water has been used in PIC for decades as it provides several benefits, such as:
- Excellent adhesion and stability of the ceramic shell. This ensures that the mold maintains its shape and integrity during the casting process. This results in high-dimensional accuracy and smooth surface finishes of the final cast product.
- Enhanced thermal shock resistance of the mold. Reduces the risk of cracking and improving the overall durability and quality of the casting.
- No volatile organic compounds (VOC). Unlike ethyl-silicate used in some PIC processes, LUDOX® colloidal silica contains no VOCs.
- High compatibility with refractory grains. LUDOX® colloidal silica is highly compatible with a variety of refractory grains such as fused silica, zircon, alumina, etc., allowing it to be used effectively in a wide range of investment casting applications.
LUDOX® colloidal silica is indispensable in many modern precision investment casting processes. It is available in a wide variety of particle sizes, concentrations, and pH values, including:
- Acidic grades (LUDOX® SK) more suitable when lower drying temperatures are needed to achieve slower drying time, beneficial to build thicker shells and highly compatible with alumina and zircon grains.
- Alkaline grades (LUDOX® HS and SM) are particularly suitable in the initial stages of creating a ceramic shell (known as primary coat) because it provides excellent adhesion to wax patterns and has good wetting properties. These grades are also preferred for their faster drying rates and strong green (unfired) strength compared to acidic grades. Alkaline grades are highly compatible with a wide range of refractory grains including fused silica and zircon.
The LUDOX® colloidal silica portfolio offers a wide range of grades suitable to match the demand of specific casting applications and processes such as desired mold strength, drying time, surface finish and compatibility with different refractory grains.