Coating Preparation Method for Precision Casting

The physicochemical parameters of silica sol are mainly determined by the foundry: SiO2 content, density, Na2O content, pH value, kinematic viscosity, colloidal particle diameter, etc. These physicochemical parameters mainly affect the shell strength, coating stability and powder liquid ratio of the coating.

Because it is difficult for precision casting 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 foundry should choose different specifications of silica sol for surface layer and back layer, s-830 silica sol for surface layer and s-1430 silica sol for back layer. The preparation method of coating will directly affect the quality of castings in precision casting. Let's first understand the preparation of coating.

In coating preparation, silica sol is added first, then wetting agent is added and mixed evenly, refractory powder is added during mixing, and finally defoamer is added. In order to ensure the coating quality, when the surface coating is all new, the mixing time shall be more than 24h before use. If some are new, the mixing time can be shortened to 12h. The mixing time of transition layer and back layer coating can be less than that of surface coating. When all are new, the mixing time shall be more than 10h, and when some are new, the mixing time can be shortened by half. If the coating prepared by the foundry is not used, it shall be covered and sealed to prevent moisture evaporation.

It is better not to prepare coating in shell making operation, and the foundry should set up special coating preparation equipment.