Coating configuration and drying is one of the important links to obtain high quality castings. The role ofcoating is to reduce the surface roughness of castings, prevent or reduce the sand sticking of castings, which is conducive to improving the efficiency of sand removal. After using high quality coating, the surface roughness of the casting can be reduced, so as to improve the surface quality and service performance of the casting; help to reduce the defects such as sand sticking and sand hole of the casting; help to improve the efficiency of sand dropping and cleaning of the casting. In addition to the function of sand casting, EPC coating can also improve the strength and rigidity of foam pattern and prevent deformation and damage of the mould when filling sand.
For the impeller production, the effect of coating on the foam foam blade is different. After the molding process is finished, the foam blades need to be burned to form cavity by flame, and residual carbides will be left due to incomplete combustion of foam. If there is no coating layer on the blade, the carbide will adhere to the sand mold, which is not easy to clean. This is not only not conducive to the smooth surface of the casting, but also leads to surface carburization, which seriously affects the performance of the casting. Therefore, it is necessary to coat the blade with a thickness of 1.5mm before molding, so that after the foam is lost, the residue will be attached to the coating, so it is easy to clean up.
The technical indexes of the coating are: ① main refractory aggregate: Zircon powder and high alumina powder; ② solid content 60%; ③ service density 1.5-1.7g/cm3; ④ suspension 99%; ⑤ pH value 8-9; ⑥ gas generation 157.7l/g. Before coating, the coating shall be stirred evenly.
In the coating process of blade coating, because the positioning requirements of the bottom and upper part of blade cannot be coated, the coating process can only be applied by flow coating. After coating, put it into the drying room for drying. The temperature of the drying room is controlled at about 45 ℃, and the time is about 24 hours. After drying, apply the second coating with the same method. The second coating shall be thinner than the first one. After drying, check whether the pattern and pouring system coating have defects. If there is repair drying, store in the drying room to avoid moisture regain. The foam after coating is shown in the picture.