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What is the role of silica sol casting in precision foundries?
2021-09-22
Silica sol casting is a casting process that we often hear about today, and precision casting manufacturers are quite familiar with it. Precision casting can be divided into three types:
1. Silica sol casting;
2. Water-glass castings;
3. Composite casting;
What is the role of silica sol casting in precision foundries?
The three silicon sol casting methods differ in the materials used to fabricate the wax patterns and the shell molds. In the silicon sol process, low-temperature and medium-temperature waxes are employed to produce the wax patterns, followed by the formation of the shell mold using mismatched sand, mullite sand, mismatched powder, and silicon sol. Depending on the specific requirements of each product, 4 to 8 shell layers may be applied. In the sodium silicate process, low-temperature wax is used for the wax pattern, and the shell mold is then built up using sodium hydroxide, quartz sand, and other materials. The composite process combines elements of the first two: the initial two to three layers are formed with silicon sol, while the final two layers utilize sodium silicate.
When comparing these three processes in terms of dimensions, silica sol casting is particularly well suited for producing small castings with exceptionally fine surface finishes, achieving surface roughness values in the range of Ra 3.2–6.4 and offering superior dimensional tolerance control. Moreover, when using the silica sol process, certain features can be formed in a single step without subsequent machining, resulting in significant cost savings. In contrast, composite casting falls short of silica sol casting in both surface finish and dimensional accuracy; however, it is capable of producing larger castings and generally delivers better dimensional and surface quality than sodium silicate casting, with surface roughness sometimes reaching around Ra 6.4–12.5. Compared with composite casting, sodium silicate casting lags one grade behind in terms of overall performance.
So, what are the applications of silica sol in precision casting for precision casting manufacturers?
Silica sol is primarily used as a binder in silica-sol-based investment casting and can also serve as an reinforcing coating and a surface finish for shell molds. Precision casting foundries are increasingly replacing ethyl silicate with fine-particle silica sol in precision casting processes, which not only reduces casting costs but also improves working conditions and the overall work environment. When silica sol is employed in thin-shell precision casting, the shell mold exhibits higher strength, while the surface finish and dimensional accuracy of the castings are significantly enhanced. Moreover, the molding quality achieved with silica sol surpasses that obtained using sodium silicate, yet the cost is lower than that of ethyl silicate. Silica sol casting is particularly well suited for large castings, those with stringent surface-finish requirements, and applications where minimal or no draft allowance is needed. In addition, silica sol is utilized in precision casting as a high-temperature-resistant coating, imparting excellent wear resistance and thermal stability to the coating, reducing the loss of molten metal into the mold at elevated temperatures, and facilitating easier demolding of the castings.
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