On the surface of the paint film, there are concavities and convexities with a diameter of (05~3) mm like a crater. The difference between the pits, depressions and shrinkage holes and fish eyes is that the coated surface is not exposed. This disadvantage is also called depression. , pitted. The causes and prevention methods are similar to shrinkage cavities.

Pinhole A phenomenon in which needle-like holes or leather-like holes are created in the paint film. The diameter of the holes is about 10 microns.

Reason:

(1) The coating has poor fluidity, poor leveling, and poor release of bubbles.

(2) The paint deteriorates during storage and transportation.

(3) Impurities are mixed into the paint, such as water mixed into the solvent-based paint.

(4) Insufficient drying after painting, too fast heating during drying, and too fast surface drying.

(5) The temperature of the coated object is too high and there is dirt (such as welding flux, etc.) on the coated surface. The coating has small holes.

(6) The ambient air temperature is too high.

Prevention:

(1) Select the appropriate paint, and strengthen the inspection of the paint that is prone to pinholes to prevent unqualified materials from being put into production.

(2) Pay attention to the cleanliness of paint storage containers and painting tools and the quality of solvents to prevent impurities from being mixed into the paint.

(3) After painting, dry according to the specifications, and add a solvent that evaporates slowly to slow down the surface drying of the wet paint film.

(4) Pay attention to the temperature and cleanliness of the coated object. Eliminate small holes in the coated surface.

(5) Improve the coating environment.