The physical and chemical parameters of silica sol are mainly composed of: SIO2 content, density, Na2o content, PH value, kinematic viscosity, colloidal particle diameter, etc. These physical and chemical parameters mainly affect the strength of the shell, the stability of the coating and the powder-to-liquid ratio of the coating.
Because it is difficult for precision casting companies to detect these physical and chemical parameters, on the one hand, it is necessary to strengthen the selection, evaluation and confirmation of suppliers. On the other hand, different specifications of silica sol should be used for the surface layer and back layer. Choose S-830 silica sol and S-1430 silica sol for the back layer. The preparation method of coatings will directly affect the quality of castings in precision casting, so let us first understand the preparation of coatings.
For coating preparation, silica sol is added first, then wetting agent is added to mix well, refractory powder is added during stirring, and defoamer is added finally. In order to ensure the quality of the paint, when all the surface coatings are new materials, the stirring time should be longer than 24h before they can be used. If some are new ingredients, the stirring time can be shortened to 12h. The mixing time of transition layer and back layer coatings can be less than that of the surface coating. When all coatings are newly prepared, the stirring time is longer than 10h, and when some are new coatings, the stirring time can be reduced by half. If the prepared paint is not in use, it should be sealed and sealed to prevent water evaporation.
It is best not to mix paint in the shell making operation, but to set up special paint preparation equipment.