Water glass casting

Water glass casting is also called sodium silicate casting. Its casting process is very similar to investment casting (that is the lost wax investment casting method). It is a technology that uses water glass as the binder for the shell to cast. The process provides a far superior surface finish and dimensional precision to that achieved through sand casting. And more complex shapes can be achieved.

It is particularly suited to larger castings and is cheaper to produce. The raw materials are mainly steel and iron.

The Water glass casting technology is from Russia. Now it is one of the most common investments casting processes in China. About 75% of foundries focus their business on water glass casting. the rest are silica sol casting factories.

The water glass casting process is very similar to investment casting (ie the lost wax method), but is particularly suited to larger castings, and is cheaper to produce. The process provides a far superior surface finish and dimensional precision to that achieved through sand casting, and more complex shapes can be achieved. In addition to steels, it is possible to cast alternative materials such as iron and SG iron using this method. The process only differs from the lost wax method at the point where the wax is removed from the ceramic mould. Investment casting uses high temperature autoclaves to melt the wax, whereas, with the water glass process, the moulds are submersed in hot water. The wax then melts away from the moulds and floats on the surface of the water, enabling it to be skimmed off and reused for wax making purposes. Obviously, this also provides environmental advantages and the wax is completely recyclable.

Here’s a list of the benefits of Water Glass Casting:

Better surface finish than sand casting.
Better and more precise dimension than sand casting.
Complex parts are more achievable.
Larger parts than the usual investment casting method.
Inexpensive
Better choice of metals
Safe for the environment.

Wax Injection

For each casting to be made, melted wax is injected into a mold to produce a wax pattern of the casting. The wax molds are constructed of Aluminum and sized to account for shrinkage in the wax and metal that are being used. Wax tooling ranges from simple two piece dies, to multi-cavity automated dies and complex dies featuring water soluble or ceramic cores.

Wax Assembly

Once the wax patterns have cooled and settled to a stable size and shape, they are mounted onto a sprue or tree. The sprue, also made of wax, contains all of the necessary gates, runners and supports to adequately feed the part during the casting process.

Shell Building

The wax sprue is now “invested” in ceramics to create the mold for the metal to be poured into. The ceramic consists of two parts, a liquid slurry covered with a dry sand. Each sprue is covered in multiple layers of slurry and sand until the ceramic shell is thick enough to hold up during the casting process. The shell building process usually takes 24 hours, with anywhere from 2 days to almost 2 weeks for the shells to fully dry.

Dewax

Once the shell has fully dried, the wax is melted out using an autoclave to counteract the expansion of the wax. The shells are then fired to remove any remaining wax residue and cure the ceramic shell. Once the shells have been fired, they are now ready for the casting process.

Casting

The processed shells are placed back in the oven to be pre-heated prior to casting. Once the shells are at the proper temperature and the molten metal has been prepared and qualified, the shells are removed from the oven and the metal is poured into the shells.

Finishing

The shell is hammered, media blasted, vibrated, waterjeted, or chemically dissolved (sometimes with liquid nitrogen) to release the casting. The sprue is cut off and recycled. The casting may then be cleaned up to remove signs of the casting process, usually by grinding.

Water glass casting process was introduced to our country in the mid of 1950 by the former Soviet union, it is different from the ethyl silicate binder investment casting process. Due to the advantages of material cost and production cycle, water glass casting was quickly applied in civil machinery manufacturing. With the development of water glass casting process in our country for more than 60 years, in terms of its production scale and application field, it has become the mainstream of investment casting industry of China.

By adding 0.5% penetrant, the surface quality of water glass casting is greatly improved, and surface finish can even be comparable to the silica sol casting technology. It can avoid defects caused by traditional shell making technology. At the same time, the working environment is improved obviously. In addition, the process parameters and operation requirements are not so complicated and strict, general workers are available to operate shortly. This reduced the loss of skilled workers and new workers are also feasible, which stabilized the normal production efficiency of the factory. In terms of costs, shell making material cost of water glass casting is not added compared with traditional hardening process, and this process decreased the weld repair processing significantly, improve the product rate shortens, and thus to reduces the production cost and the production effeciency.

Challenges in Water Glass Casting

1. Mold Strength and Integrity

Achieving the right balance between mold strength and ease of breakaway can be challenging. The mold needs to be strong enough to withstand the forces of the molten metal but not so strong that it is difficult to remove after casting.

2. Surface Quality

Surface defects such as scabs or inclusions can occur if the mold material reacts with the molten metal or if the molding sand is not properly prepared. Ensuring a high-quality surface finish often requires additional finishing processes, increasing the overall production cost.

3. Environmental Impact

The use of sodium silicate and the generation of used sand molds present significant environmental challenges. Proper disposal or recycling of these materials is crucial to minimizing the environmental impact of the casting process.

Innovations in Water Glass Casting

1. Advanced Binder Systems

Research and development efforts are ongoing to create binder systems that provide excellent mold strength and integrity while being easier to remove and more environmentally friendly.

2. Automation and Process Control

The integration of automated systems for mold making, pouring, and quality control helps to improve consistency and reduce labor costs. Real-time monitoring and control systems ensure that each step of the process is executed with precision, resulting in higher quality castings.

3. Enhanced Quality Assurance

Advancements in non-destructive testing and quality assurance techniques allow for thorough inspection of the final parts, ensuring they meet all required specifications and quality standards.

Applications of Water Glass Casting

1. Automotive Industry

Water Glass Casting is extensively used to produce engine components, transmission parts, and other critical automotive components. The process’s ability to handle large parts and complex geometries makes it ideal for this sector.

2. Heavy Machinery and Equipment

Large components for agricultural machinery, construction equipment, and industrial machines are often produced using Water Glass Casting, benefiting from the process’s cost-effectiveness and capability to produce robust parts.

3. Railways

Components for trains, tracks, and other railway infrastructure are frequently manufactured using this casting process, taking advantage of its ability to handle large, complex parts.

4. Valves and Pumps

The process is well-suited for producing large valves and pumps used in various industries, providing the required strength and durability.

5. General Engineering and Manufacturing

Water Glass Casting finds applications across a broad spectrum of industries, producing components for machinery, equipment, and structures that require strong, durable parts.