Both the spring metal surface coating and the organic coating should meet the requirements of the coating (plating) layer being dense, uniform, and firmly bonded to the substrate. In the coating (plating) layer, such as the coating (plating) layer peeling off, bubbling or blooming, and local non-coating layer, etc., in most cases, it is due to the unclean surface before metal coating (plating). Compared with organic solvent coatings, spring metal surface coating treatments using water as a solvent, such as electroplating, anodizing, phosphating, and water-based paint coating, are more sensitive to organic contamination on the metal surface, even if it is a monomolecular layer. can lead to the failure of the entire process. Therefore, the cleanliness of the material surface after coating (plating) is very important.
method:
1. Visual inspection and optical method
Oil stains on shiny metal surfaces can be observed with the naked eye and with the aid of a magnifying glass or optical microscope. The disadvantage is that the passive oxide film on the metal surface and the extremely thin oil pollution will not be detected. For rough and dull metal surfaces, the above methods are powerless, but you can wipe the surface with clean, white cotton, cloth, or paper, and then observe whether it is clean to determine whether the metal surface is clean.
2. Surface tension method
According to the influence of surface oil on its surface energy, the surface energy is determined by whether the metal is wetted in a series of test solutions with different surface tensions, and the cleanliness of the surface is judged accordingly. If a series of solutions from 80 percent acetic acid, 20 percent water) (V/V, the same below) to 1 percent ethanol and 99 percent water are prepared, the surface tension increases from 24.510-5N/CM to 66.010-5N accordingly. /CM.
3. Paint method
Drop the degreaser on the metal surface, and then evaporate to dryness. If there is no trace, the surface metal surface is clean. If a ring appears, it means that there is oil pollution.
4. Wetting method
Clean metal surfaces are hydrophilic and, therefore, can be completely wetted by water, and when the metal surface contains oil stains, there will be water-break areas that are not wetted by water. Based on the principle of whether it is hydrophilic or not, in addition to the simplest and commonly used exhalation method and atomizer spray method, there are the following detection methods. Since the metal oxide film is also hydrophilic, most of these methods cannot detect whether the oxide film on the metal surface has been removed.
