Silica Sol Casting
What is Silica Sol Casting?
An introduction to the Silica Sol Casting process.
Silica sol casting is a form of investment casting. The process is very similar except that the investment mould is made from silica sol zircon sand mixed with refractory powder. Silica sol zircon sand is exceptionally fine-grained (10-20 Microns) and can be mixed to a slurry with very low viscosity when creating the mould. The result is a casting method that delivers dimensionally accurate castings with excellent as-cast surface finishes. Crucially, the silica sol zircon moulds can withstand temperatures up to 2000°C, making them very useful when casting high temperature alloy steels and stainless steels.
The term investment casting is derived from the process of “investing” (surrounding) a pattern with refractory materials. Investment casting is often selected over other molding methods because the resulting castings present fine detail and excellent as-cast surface finishes. They can also be cast with thin walls and complex internal passageways. Unlike sand casting, investment casting does not require a draft.
Why Choose Investment Silica Sol Casting?
The Investment casting process Silica sol castings is similar to the water glass process for but different in the Wax type there is called Silicone glue. Silica sol castings are mainly used for products with high corrosion resistance and precision dimensions. The Silica sol castings gives the possibilities to eliminate the need for secondary machining after casting. The alloys typical produces is carbon steel and stainless steel castings. The casting surface of stainless steel is very smooth even meet requirement on Ra 3.2 µ or better, wish make it ideal for industries like Food, pump and water applications.
Benefits of Silica Sol Investment Casting
1.Great versatility; suitable for casting most metals.
2.Will allow very intricate castings to be produced with thin walls.
3.Smooth surface finishes are possible with no parting line so machining and finishing are reduced or eliminated.
4.Allows un-machinable parts to be cast accurately instead.
5.Excellent dimensional accuracy
Silica Sol Casting Process
1.A metal die is made, the impression being the same as required in the final mould.
2.Molten wax is injected into the metal die to create a pattern, allowed to solidify and then removed. Some complex wax patterns are fabricated by joining several separate patterns together using an adhesive.
3.The waxes are then assembled on a wax tree, many parts can be put on the tree depending on size, it is common for components to be in the weight range 0.1kg up to 50kg.
4.The tree is then immersed in silica sol zircon slurry to coat the wax, the slurry is exceptionally fine with low viscosity resulting in an excellent as-cast surface finish. The slurry is coated with a refractory material and the process is repeated several times until a shell is created around the wax pattern.
5.The drying process is critical. The shells must be allowed to dry naturally in a constant temperature to allow the silica sol gels and refractory particles to bond, the result is a strong, high quality shell mould. The trees of wax are put into ovens of about 200 degrees to melt out the wax.
6.When all wax is removed the trees are heated up to over 1000 degrees to complete preparation for casting.
7.The metal is then poured into the hot moulds, which allows the alloy to reach the thinnest sections of the mould before it solidifies.
Capability of Silica Sol Casting
1.Liner tolerance of silica sol castings can be controlled with ±0.1mm, and the surface finish is Ra6.3.
2.Min. weight 0.01kg, Max. weight 50kg.
3.Cast min. hole: Φ2mm
4.Cast min. round corner: R0.1mm
5.Cast min thickness: 0.7mm
Silica Sol Casting VS Water Glass Casting
The silica sol investment castings have better dimensions and surface quality, but just more expensive than water glass casting. Cost of solica sol casting is almost twice than the cost of water glass casting. Both silica sol casting and water glass casting belong to investment casting or lost wax casting. So process of silica sol casting is almost the same as water glass casting. But silica sol investment casting process uses silica sol zircon sand as the molding material, which can stand temperature up to 2000 degree. Below are the main differences between solica sol casting and water glass casting.
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