Silica sol physico-chemical parameters is mainly composed of: SIO2 content, density, content of Na2o, PH, kinematic viscosity, colloid particle diameter, etc., the physical and chemical parameters of the main affects the stability of shell strength, coating and coating powder liquid ratio.As the precision casting enterprise hard to these physical and chemical parameters for testing, so, on the one hand, to strengthen the supplier selection, evaluation and validation, on the other hand, the surface layer and back layer should choose to use different specifications of the silicon sol, into the surface of S - 830 silicon sol choice, choice of S - 1430 silicon sol back layer.The preparation of the coating method in precision casting will directly affect the quality of the castings, that we first understand the preparation of the coating. Coating preparation and silica sol first commonly, plus, wetting agent and mixed into mixing refractory powder, add defoaming agent.To ensure the quality of coating, surface coating are all new material, stirring time should be more than 24 h to use, such as part of new ingredients, mixing time can be shorten to 12 h. transition layer and back layer of paint mixing time can be less than the surface coating, all for the new match paint, stirring time is more than 10 h, part for the new timing, mixing time can be shorten the half.If you don't use with good coating, seal shall be affixed to prevent evaporation.