The key technical indexes of casting coating have great influence on the quality of casting, as follows.
Influencing factors of sand sticking defects of castings:
(1) The chemical composition of casting coating is unreasonable;
(2) Insufficient fire resistance;
(3) Insufficient coating thickness;
(4) The adhesive strength of casting coating is insufficient.
The influencing factors of porosity in the skin of casting are as follows:
(1) The coating layer of casting is too thick and not dry enough;
(2) The permeability of coating is too strong and drying is not enough;
(3) Excessive binder of casting coating;
(4) The moisture absorption of casting coating is too high.
Factors affecting the surface roughness of castings:
(1) The thickness of casting coating is insufficient;
(2) The viscosity of casting coating is not suitable;
(3) The Baume degree of casting coating is not suitable;
(4) The casting coating is polluted by sand mold or casting coating with poor dispersion.
Influencing factors of brush mark defect on casting surface:
(1) The viscosity of casting coating is too high;
(2) The leveling property of casting coating is too poor;
(3) The coating is too thick at one time.
The trend of the double effect of coating thickness on the risk of casting defects. It can be seen that with the increase of coating thickness, the beneficial effect of coating on preventing casting defects is increasing, but the risk of casting defects caused by the use of coating is increasing gradually. When the coating thickness exceeds a certain value, the risk of casting defects caused by coating will increase significantly. Therefore, the thickness of casting coating is not the better. There is an optimal value for different casting coating applications.
For the treatment time of surface brush mark defects. After the core is treated by coating operation, the leveling property of the coating attached to the core will gradually decrease with the extension of the placing time. When the levelness is reduced to a certain degree, brush marks will be left when painting. The leveling property of the coating meets the period of time when no brush mark is left during the coating operation, which is usually called the operable time of the coating. The treatment time of surface brush mark defects shall be within the operable time range of the coating.