SiO2 content
This is a very important parameter of silica sol. The strength of silica sol shell (normal temperature strength, high temperature strength, residual strength) basically depends on the SiO2 content of silica sol. The higher the SiO2 content, the greater the strength of the shell. The silica sol used for general investment casting is a silica sol with a SiO2 content of 30%. According to the product structure and casting material, the silica sol silicon dioxide content can be diluted to a minimum of 20%. It is recommended that the surface layer silica sol of aluminum alloy castings can be diluted to 25%, and the back layer can be diluted to 20%. The silicon dioxide content is also a factor in the gelation of silica sol. The information shows that the conventional 30% silica sol has a silicon dioxide content of 34%-36% due to the evaporation of water, which may cause the silica sol coating to age and deteriorate, and lose its bonding properties. This is also the origin of the regular water replenishment of silica sol coating, especially the water replenishment of the surface slurry, which is particularly important.