The physical and chemical parameters of silica sol are mainly composed of SIO2 content, density, Na2o content, PH value, kinematic viscosity and colloidal particle diameter. These physical and chemical parameters mainly affect the shell strength, the stability of the coating and the powder ratio of the coating.
As the precision casting enterprises are difficult to test these physical and chemical parameters, so on the one hand to strengthen the supplier's choice, evaluation and confirmation, on the other hand, the surface layer and back layer should choose to use different specifications of silica sol, Select the S-830 silica sol and the back layer to select the S-1430 silica sol. Paint preparation method in the precision casting will directly affect the quality of castings, then we first understand the preparation of paint.
Paint preparation generally first add silica sol, coupled with wetting agent mixing, adding fire in the mixing powder, and finally add defoamer. In order to ensure the quality of the coating, the surface coating is all the new material, the stirring time should be more than 24h to use, such as part of the new ingredients, mixing time can be shortened to 12h. Transition layer and back paint mixing time can be less than the surface coating, All with the new coating, the mixing time is greater than 10h, part of the new allocation, the mixing time can be reduced by half. With a good paint if not used, should be sealed to prevent moisture evaporation.
It is best not to operate in the shell with paint, and set up a special paint preparation equipment.