Silica sol casting is a type of investment casting process, also known as lost wax casting. The process starts with a wax model that is coated with refractory material to make a mold, then the wax is melted out, leaving a cavity for molten metal to be poured into. The silica sol slurry is used in the shell building process, providing excellent surface finish and dimensional accuracy.
Silica sol is a colloidal dispersion of silicon dioxide (SiO2) particles in water. It is used as a binder in the ceramic shell building process. The silica sol coating provides a smooth surface finish and high dimensional accuracy to the final casting.
This process is ideal for parts requiring tight tolerances, smooth surface finishes, and complex geometries. It is commonly used in aerospace, automotive and medical industries.
A metal die or mold is created. This die will be used to produce wax patterns. The die is precision-machined to ensure accurate dimensions.
Wax patterns are injected into the metalmould. The wax is heated until it is liquid, then injected under pressure. Once cooled, the wax pattern is removed from the die.
The wax patterns are assembled onto a wax tree. This tree structure allows multiple parts to be cast at once. The tree is then cleaned and prepared for shell building.
The wax tree is dipped into a silica sol slurry. The slurry coats the entire tree. After dipping, the tree is coated with refractory sand. This process is repeated several times until a shell of sufficient thickness is built.
The dipping process is critical. The shell must have enough strength to hold the molten metal. Each layer must dry completely before the next layer is applied. This ensures a strong, defect-free shell.
Once the shell is built, the wax is melted out. This leaves a hollow cavity in the shape of the desired part.The shell is then fired to burn out any remaining wax and to strengthen the ceramic.
Molten metal is poured into the hollow shell. The metal fills the cavity, taking the shape of the original wax pattern. After cooling, the ceramic shell is broken away to reveal the metal casting.
Why is Silica Sol Casting So Capable?
Silica sol casting utilizes colloidal silica as the binder for the ceramic shell, offering several advantages over traditional water glass casting:
Superior Surface Finish: Silica sol produces castings with excellent surface quality (typically Ra 3.2-6.3 μm), reducing or eliminating the need for machining.
High Dimensional Accuracy: Tolerances of ±0.5% or better can be achieved, making it ideal for complex, precision components.
Excellent Material Properties: The slow cooling rate in ceramic molds allows for better metallurgical structure and mechanical properties.
Complex Geometries: Intricate shapes, thin walls (down to 0.5mm), and internal features can be cast with high repeatability.
Wide Material Compatibility: Suitable for carbon steel, stainless steel, alloy steel, aluminum alloys, and superalloys.
Limitations of the process:
Higher cost compared to water glass casting due to longer shell building time (typically 7-15 days)
Longer production lead times
Generally limited to smaller castings (typically under 50kg)
More complex process control requirements
Ningbo Qianhao Metal Products Co., Ltd. is a professional precision casting and machining manufacturer that owns two foundries and two machining facilities and has all comprehensive investment casting capabilities as well as powerful precision machining capabilities. The machining base one is located at the headquarters and is equipped with comprehensive and advanced CNC machining equipment including more than 60 vertical and horizontal machining centers, and more than 70 CNC machine tools and 50 other machines. Our new machining factory- machining base two was established in the Fenghua Binhai Development Zone, equipped with more advanced and high-end machining equipment, including gantry machining centers, more than 30 horizontal and vertical machining centers (Okuma brand), over 50 CNC machine tools, three laser cutting machines, flame cutting machine, CNC bending machines, hydraulic presses, welding robot lines, intelligent painting lines and electrocoating lines. The factory integrates a smart logistics system based on AGVs, as well as PLM, ERP and MES systems, delivering high-value-added assemblies and one-stop services.