Water glass casting is one of the most common investment casting processes in China, but is seldom in other countries. In Chinese investment casting foundries, about 80% foundries focus its business in water glass casting, while the rest are silica sol casting factories. So what is water glass casting?
Water glass casting, one kind of lost wax investment casting process, uses water glass as the binder for the shell. The origin of water glass casting is in Russia. Process of water glass casting is what we described in investment casting process, with this method, it is suitable for steel castings, especially for carbon steel and alloy steel castings. It allows to produce steel castings ranging from 0.5kg-60kg.
Water Glass Investment Casting Process
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.
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.
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.
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.
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.
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.
Why Water Glass Casting?
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.
Our Automatic Production Line
CFS is able to offer the water glass option through our own company in China, who has a rich experience in manufacturing components using this process. With water glass casting, we can meet size tolerance CT7-CT8. Our value added services (machining, surface treatment, and heat treatment, etc) can ensure us to supply finished castings to our customers eventually. To be more competitve, we have introuduced the automatic production line.
Currently, most of the water glass casting factories in China are making sand shell moulds, dewax manually. The products of quality can not be controlled statably because of labour changes. Different engineers or workers will make different products. Skills are different among workers. One worker may make the products well, but if changing another worker, there might be problems with quality of the products. To solve such problems, we’ve add an automatic production line to make the water glass castings.
With such automatice production line, we can keep the quality of the water glass castings stable. And help to save labour costs and short production time. Such production line is extremely suitable for casting parts with high volume requirements.
So, if you would like to make your products in such casting process, pls do not hesitate to contact us.