In stainless steelPrecision castingIn inquiries, customers often ask: Why do some quotes use "silica sol" while others use "water glass" for lost-wax casting? This isn't just a simple difference in terminology; the shell material, dimensional stability, surface quality, post-processing costs, and suitability for the product are completely different. Choosing the wrong process can lead to anything from larger machining allowances and more surface rework to failing to meet dimensional and airtightness requirements as specified in the drawings.
To summarize: the core difference between the two processes
The silica sol process uses silica sol as a binder, resulting in better shell strength and thermal stability, and a finer shell surface, making it suitable for castings with high requirements for dimensional accuracy, surface roughness, and material consistency. The water glass process uses water glass as a binder, offering lower process costs and a relatively shorter production cycle, making it more suitable for medium to large-sized castings with simpler structures, less demanding surface finishes, and requiring extensive subsequent machining or sandblasting for corrosion protection.
A table to understand the difference between silica sol and water glass
| Comparison Projects | Silica sol process | Water glass process |
|---|---|---|
| Surface quality | The surface is finer, with a relatively lower risk of pinholes and sand adhesion, making it suitable for visible surfaces and assembly surfaces. | The surface is relatively rough and usually requires sandblasting, grinding, or a larger machining allowance. |
| Dimensional accuracy | It offers better dimensional stability and makes it easier to control small holes, thin walls, and complex contours. | Suitable for general tolerance requirements, but riskier for complex thin-walled parts. |
| Material compatibility | More suitable for materials with high requirements for composition and surface, such as stainless steel, duplex steel, and heat-resistant steel. | Commonly used in carbon steel, low alloy steel, and some stainless steel parts with general requirements. |
| cost | The shell manufacturing process is lengthy, with higher material and management costs, resulting in a typically higher price per unit. | Low overall cost, suitable for price-sensitive or high-volume standard parts |
| Post-processing | It can reduce the amount of grinding and machining allowance, and is suitable for direct assembly or a small amount of finishing. | Post-processing involves a larger workload, requiring the inclusion of machining allowances and rework costs. |
When should you choose the silica sol process?
If the product is a pump and valve accessory, fluid equipment accessory, food machinery part, medical machinery part, marine hardware, precision connector, or if the material involves 304, 316, 2205 duplex steel, heat-resistant steel, etc., silica sol is generally more stable. Especially for parts with sealing surfaces, threaded hole perimeters, thin-walled flow channels, assembly positioning surfaces, and visible surfaces, it is not recommended to only look at the casting unit price.
Another situation where silica sol is suitable is when the customer's drawings don't explicitly state "silica sol," but specify smaller dimensional tolerances, lower surface roughness, or require reduced machining allowances. In this case, castings made with water glass might be cheaper, but the subsequent machining, polishing, and scrap costs will negate the advantage.
When can you choose the water glass process?
Water glass is not synonymous with low-end; it is suitable for products that explicitly do not require a high surface finish. Examples include large brackets, general mechanical structural parts, pipe fitting blanks, engineering machinery parts, some valve body shells, and parts requiring subsequent full-surface milling and turning. If the drawings allow for a large machining allowance, and the product prioritizes strength and delivery time rather than appearance and small-dimensional details, the water glass process offers a cost advantage.
It's important to note that when quoting prices for water glass components, you can't just compare the "cast blank price." If the part has many assembly surfaces, sealing surfaces, or appearance surfaces, the costs of sandblasting, grinding, welding repairs, machining allowances, and inspection should be evaluated together. In many projects, it's not that water glass can't be made, but rather that the total cost isn't as low as initially expected.
Make a practical choice based on product type.
Small stainless steel precision parts, thin-walled parts, appearance parts, food machinery parts, medical machinery accessories, pumps and valvesimpellerFor valve bodies with complex fluid channels, silica sol is the preferred option. For large load-bearing supports, general mechanical blanks, thick-walled pipes, and parts with most surfaces covered by subsequent machining, water glass can be evaluated. For products with high requirements for airtightness, corrosion resistance, weld repair limitations, or export appearance, silica sol should be the primary benchmark solution.
Haijin Casting's suggestion: First consider the usage scenario, then discuss the price.
We typically start by looking at the material grade, wall thickness, minimum aperture, critical assembly surfaces, annual usage, and post-processing requirements in the drawings before determining the process. For customers, a more reasonable approach is not to directly ask "How much does silica sol cost?" or "How much does water glass cost?", but rather to send samples, drawings, or the usage environment to the factory so that process engineers can determine which dimensions must be guaranteed and which surfaces can be addressed through post-processing.
Simply put: silica sol is suitable for making "precise, delicate, and stable" stainless steel castings; water glass is suitable for making "thick, heavy, and economical" general cast steel parts. The truly suitable solution is to find a balance between performance, appearance, machining allowance, delivery time, and total cost.
