Precision casting is a general term for the process of obtaining accurate dimensional castings. Compared to the traditional sand casting process, precision casting yields castings with more accurate dimensions and better surface finishes.
Silica sol or water glass is used in the third step of the process, together with other refractory materials (mostly zirconium or mullite powder), reinforcing agents, defoamers and wetting agents to make a slurry, which is soaked and dried several dozen or tens of times to make the mould. The differences are.
First of all, both belong to lost wax precision casting, the difference is the difference in the surface quality of the mould shells made, the surface of the moulds made by silica sol casting is better and the dimensional accuracy is higher, which is more suitable for use in precision casting. It produces products with good surface smoothness, small deformation, small shrinkage ratio, and precise dimensions, and does not require secondary processing, the corresponding cost is also higher than water glass casting.
Secondly, the silica sol is basically a small product, while the water glass disappearing mould is a relatively large product.
Once again, the drying and hardening of the shell mould is not the same, water glass to use ammonium chloride and other hardening agents, while the silica sol shell mould on the constant temperature and humidity in the space can be dried and hardened. Generally speaking, the water glass process has low production costs, short production cycle, poor surface quality, mainly for carbon steel and low alloy cast steel parts; silica sol process has high production costs, but long production cycle, good surface quality, mainly for high alloy steel and stainless steel products.
To sum up, the castings produced by the silica-sol casting process have high dimensional accuracy and can reach the CT4-8 level specified in GB/6414-1986, with low surface roughness values of Ra0.8-6.3um and small machining allowances, even without cutting; the silica-sol casting process can produce castings with more complex geometric switches, with a minimum wall thickness of 2.5mm and a minimum hole diameter of 1mm, casting weight: max. 20kg, min. 0.003kg Casting length: max. 500mm, min. 10mm; cost double that of the water-glass casting process.
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