LUDOX® Colloidal Silicas in Precision Investment Casting
Investment casting involves pouring hot molten metal into a mold and allowing it to solidify as it allows for the creation of finely detailed metal objects. The craft was traditionally the domain of artisans until the late 1930s when it expanded into the industrial realm in World War II. This method is used to make metal parts as diverse as intricate components for airplane engines to large steel valves for chemical plants.
The investment casting process consists of encasing an expendable wax pattern of the part to be produced in a ceramic shell. Encasing is done by repeatedly dipping the wax pattern in a slurry containing refractory grain and LUDOX® colloidal silica, followed by stuccoing with coarser refractory grain, and drying.
The expendable pattern is melted out, the ceramic shell is fired, and metal is poured into the hollow shell. After solidification of the metal, the shell is broken away and discarded.
LUDOX® colloidal silica has high bonding power with a variety of refractory grains such as:
- Fused silica
The resulting shells are strong, with low coefficients of thermal expansion and excellent surface reproduction. Unlike ethyl silicate systems, LUDOX® colloidal silica contains no volatile organic compounds (VOC).
Refractory grains readily disperse in LUDOX® colloidal silica to form slurries that have consistent properties and long pot life. LUDOX® HS and SM products are the most frequently used alkaline grades. The acidic LUDOX® SK binders result in superior pot life and green strength in many systems.