Investment CastingLost-wax castings · Stainless, carbon & alloy steel
Silica sol process
Silica sol casting: fine surfaces and tight dimensions
In silica sol investment casting the shell is bonded with colloidal silica. The face coats are zircon flour slurry with fine zircon sand; the back-up coats use fused silica or mullite (aluminosilicate) sand. A shell typically has 5–7 coats, and each coat dries for several hours at controlled temperature and humidity, so building one takes about two to three days. Dewaxing is done in a steam autoclave and the shell is fired at about 1,000–1,100 °C before pouring.
The fine zircon face copies the wax pattern closely, which gives the best surface and dimensional accuracy of the two shell routes. Silica sol is the usual route for 304, 316 and 17-4PH parts, thin walls and fine detail, and for surfaces left as-cast: pump and valve parts, food machinery parts, marine hardware and instrument parts.
Where silica sol casting fits best
- Stainless steel and high-alloy parts
- Fine detail, lettering and thin walls
- Surfaces left as-cast
- General tolerances around ISO 8062-3 DCTG 4–6 (typical)
- Small and medium-size parts
Silica sol casting at a glance (typical)
| Shell binder | Colloidal silica (silica sol) |
|---|---|
| Face coat | Zircon flour slurry, fine zircon sand stucco |
| Back-up coats | Fused silica or mullite (aluminosilicate) slurry and sand |
| Coats and drying | Typically 5–7 coats, each dried for several hours at controlled humidity |
| Pattern wax / dewax | Medium-temperature pattern wax; steam autoclave dewaxing |
| Shell firing | Typically about 1,000–1,100 °C |
| Surface finish | Typically Ra 3.2–6.3 µm as-cast, about 1.6 µm on favorable faces |
| Tolerance | Typically ISO 8062-3 DCTG 4–6 |
| Common alloys | Stainless steels, alloy steels, tool steels |
Silica sol casting FAQ
Why is silica sol casting more expensive than water glass?
The shell uses zircon face coats, more coats in total and hours of controlled drying per coat, so it takes two to three days to build instead of about one. In return it gives a smoother surface and tighter dimensions.
Is silica sol casting only for stainless steel?
No. It is the usual route for stainless steel, but carbon, alloy and tool steels are also cast in silica sol shells when the surface or accuracy matters.