The bulging of casting coating is usually the size of fingernail or larger area, which often occurs after the last layer of coating is dried, and it is easy to fall off. Why does this happen? How to solve it?
This phenomenon is mostly an operational problem. The root cause is that when the first layer of coating is applied, the slurry fails to fully infiltrate the surface of the white mold, and the gas in the small groove on the surface of the white mold cannot be fully removed. During the drying process, the gas in the small groove is heated and agglomerated and expanded. Because the first layer of coating is very thin and can be well ventilated, there is often no obvious bulging phenomenon. However, the second or third layer is different. When the second or third layer is applied, the water seeps to the first layer, while the gas in the groove under the first layer still exists. After the third layer is applied, the thickness of the coating increases, and the drying degree of the inner and outer layers is different. The outer layer of slurry first forms a film in the drying room, while the inner layer is still wet. At this time, the inner layer is seeped by the outer layer during the worst air permeability period After the water is moistened, the adhesion with the white mold is also in the weakest state. At this time, the gas under the inner layer must bulge the local (nail size) coating (about 1-2mm), which is the root cause of the formation of “blister”.
Of course, the source of “blow gas” is closely related to the amount and type of mold release agent remaining on the surface of the white mold. Its existence weakens the permeability and adhesion of the paint slurry, and it is easy to volatilize and produce gas when heated, which is often ignored.
terms of settlement:
① The first coating must be as much friction as possible with the surface of the white mold – hand friction, repeated spray coating, brush coating, flow state dip coating, etc. are effective.
② For the phenomenon that the surface of the white mold is polluted by the release agent, it is advisable to wipe the surface of the white mold once with detergent or alcohol.
③ It is effective to add 2-3% silica sol to improve the adhesion and permeability of the coating. It is easy to find out the cause of its formation and the source of its Qi, and to eliminate it. This phenomenon is very common in China, but it is not difficult to solve it.