Investment CastingLost-wax castings · Stainless, carbon & alloy steel
Water glass process
Water glass casting: an economical route for steel parts
In water glass investment casting the shell is bonded with sodium silicate. Each coat is hardened chemically, typically in an ammonium chloride or aluminum chloride solution, instead of being dried for hours, so a shell of 4–6 coats can be built in about a day. Patterns are usually made from low-temperature wax (paraffin and stearic acid) that is melted out in hot water and reclaimed, and shells are fired at about 850–950 °C.
The shell is cheaper and quicker to make, but the surface is rougher and tolerances are wider than with silica sol. That makes water glass a good fit for carbon and low-alloy steel parts whose functional faces are machined anyway: machinery and agricultural parts, levers, brackets, hardware and construction machinery components. Some foundries use a silica sol face coat with water glass back-up coats to improve the surface at moderate cost.
Where water glass casting fits best
- Carbon steel and low-alloy steel parts
- Larger and heavier castings
- Parts machined on their functional faces
- General tolerances around ISO 8062-3 DCTG 7–9 (typical)
- Machinery, agricultural and hardware parts
Water glass casting at a glance (typical)
| Shell binder | Sodium silicate (water glass) |
|---|---|
| Coats and hardening | Typically 4–6 coats, each hardened in ammonium chloride or aluminum chloride solution |
| Refractories | Quartz or zircon face coat; quartz, chamotte or mullite back-up sand |
| Pattern wax / dewax | Low-temperature wax (paraffin and stearic acid); hot-water dewaxing at about 90–95 °C |
| Shell firing | Typically about 850–950 °C |
| Surface finish | Typically Ra 6.3–12.5 µm as-cast |
| Tolerance | Typically ISO 8062-3 DCTG 7–9 |
| Common alloys | Carbon steels and low-alloy steels |
Water glass casting FAQ
When should I choose water glass instead of silica sol?
When the part is carbon or low-alloy steel, the functional surfaces will be machined anyway, and cost matters more than the as-cast finish.
Can stainless steel be cast by the water glass process?
It is possible, but stainless parts are usually cast in silica sol. Water glass shells give a rougher surface and more surface pitting on stainless, which then needs extra grinding or polishing.