The physical and chemical parameters of silica sol mainly include: SIO2 content, density, Na2o content, PH value, kinematic viscosity, colloidal particle diameter, etc. These physical and chemical parameters mainly affect the shell strength, the stability of the coating and the powder-liquid ratio of the coating.
As it is difficult for precision castings machining enterprises 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, the surface layer and back layer should choose to use different specifications of silica sol, The layer is S-830 silica sol, and the back layer is S-1430 silica sol. The coating preparation method will directly affect the quality of machining castings in precision casting, so we first understand the coating preparation.
Generally, the coating is prepared by first adding silica sol, then adding a wetting agent, and adding a refractory powder to the stirring, and finally adding a defoaming agent. In order to ensure the quality of the coating, when the top coating is all new, the stirring time should be greater than 24h. If it is new ingredients, the stirring time can be shortened to 12h. The mixing time of the transition layer and back coating can be less than the top coating. When all new coatings are used, the stirring time is greater than 10h, and when some are new, the cnc machining stirring time can be reduced by half. If the formulated paint is not used, it should be sealed to prevent water evaporation.
It is best not to mix paint during shell-making operation, but to set up special paint preparation equipment.