There are two methods to determine the cleanliness of color coated sheets: laboratory instrument method and production site simple method. Instrumentation methods include electron microscopy, laser scattering and surface analysis. These methods are mainly
used in the case of high requirements for cleanliness of color coated plate substrate and mechanical properties of coatings, but these methods are subject to many objective restrictions. At present, most of them remain in the scope of laboratory research.
In the production and application of color coated sheets, the cleanliness of the substrate is mainly determined by the following methods.
(1) Wiping method. Wipe the surface of the strip with clean, white, non-wool cloth (such as gauze), cotton and filter paper, and then observe the degree of dirt on the cloth, cotton and filter paper to judge the cleanliness of the surface of the strip. This method is simple but not accurate enough.
(2) Droplet method. It is an application of contact angle to evaluate cleanliness. Under certain conditions, the larger the diameter of the droplet (a certain volume) on the surface, the smaller the contact angle and the higher the cleanliness. That is to say, the diameter and shape of water droplets formed on the surface are taken as the basis of cleanliness.
(3) infiltration method. Clean metal surfaces are hydrophilic, so they can be completely wetted by water. When dirt or oil blocks are treated on the surface of steel strips, there will be a "water loss zone" that will not be wetted by water. But because the metal oxide film is also hydrophilic, the wetting method can not detect whether the oxide film can be removed.
(4) Exhalation. After degreasing and drying, exhale on the surface of strip sample. If the surface is clean, it will form a uniform and continuous fog-water shape. When the cleanliness is high, the fog spots are uniform, but there is no fog water in the greasy areas. When the surface is very smooth and clean, the fog spots will disappear in a very short time.
(5) Water cut-off method. Immerse the cleaned sample in water, make the sample vertical to the water surface, then move out of the water surface. Observe whether there is a water drop or no water area on the surface of the sample after leaving the water surface from an inclined angle of 45. If there is dirt on the surface of the steel strip, if the water film formed on the surface of the sample can evenly cover all the surfaces, then explain. High cleanliness.
(6) Drop test method. Referring to CB/1332-19, two drops of standard G-type polar solution (about 0.mL) were applied on the surface of the tested specimen. The covered area of 20 mm *40 mm was immediately coated with glass rod. The special type A oil test paper was attached to the solution film, and the pornography was observed after 1 minute. If the color of type A oil test paper is uniform and continuous and complete, it is high cleanliness, and vice versa, it is not qualified.