The coatings used in precision casting are mainly composed of silica sol.

Silica sol is mainly composed of silicon dioxide, high-density substances, sodium dioxide, substances that adjust acidity and alkalinity, moving adhesives, colloidal particles, etc. The physical and chemical parameters of these substances mainly affect the strength of precision casting shells and the stability of coatings.

Due to the difficulty for precision casting manufacturers to detect these physical and chemical parameters, it is necessary to strengthen the selection, evaluation, and confirmation of suppliers on one hand. On the other hand, different specifications of silica sol should be used for the surface and back, with S-830 silica sol used for the surface and S-1430 silica sol used for the back. In precision casting production, the preparation method of coatings directly affects the quality of castings.

The preparation of coatings usually involves adding silica sol first, followed by wetting agents, adding refractory powders to the mixture, and finally adding defoamers. To ensure the quality of the coating, all surface coatings are made of new materials, and the mixing time should exceed 24 hours before use. For some new ingredients, the mixing time can be shortened to 12 hours. The mixing time of the transition layer and the back layer of the coating can be shorter than that of the surface coating, all of which are newly prepared coatings, and the mixing time can exceed 12 hours. For some newly prepared coatings, the mixing time can be shortened by more than half. If the coating is not used, it should be capped to prevent moisture evaporation.