Precision casting coating preparation method
The physical parameters of silica sol mainly consist of: SIO2 content, density, Na2o content, pH value, kinematic viscosity, colloidal particle diameter, etc. These physicochemical parameters mainly affect the shell strength, the stability of the coating and the powder to liquid ratio of the coating.
Since 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 the supplier. On the other hand, the surface layer and the back layer should choose different sizes of silica sol to enter the surface layer. S-830 silica sol was selected and the back layer was selected from S-1430 silica sol. The preparation method of the coating will directly affect the quality of the casting in the precision casting, then we first understand the preparation of the coating.
The coating preparation is generally first added with a silica sol, then mixed with a wetting agent, a refractory powder is added during the stirring, and finally a defoaming agent is added. In order to ensure the quality of the paint, when the top coat is all new, the mixing time should be more than 24h. If the part is new, the mixing time can be shortened to 12h. The mixing time of the transition layer and the back layer coating can be less than the surface coating. When all are new paints, the mixing time is more than 10h, and when it is new, the mixing time can be shortened by half. If the coating is not used, it should be sealed to prevent evaporation of water.
It is best not to use a coating in the shelling operation and set up a special coating preparation equipment.