Both the spring metal surface coating and the organic coating should meet the requirement that the coating (plating) layer be dense, uniform, and firmly bonded to the substrate. In coating (plating) layers, such as coating (plating) layer falling off, bubbling or hair flowering, and local non-coating layer, etc., in most cases due to the metal coating (plating) before the surface is not clean. Compared with organic solvent coatings, spring metal surface coating processes using water as solvent, such as electroplating, anodizing, phosphating, and water-based coating, are more sensitive to organic contamination on metal surfaces, even if monolayer contamination occurs. Things may lead to the failure of the entire process. Therefore, the cleanliness of the material before coating (plating) is very important.
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 an optical microscope. The disadvantage is that the passive oxide film on the metal surface and extremely thin oil stains will not be detected. For rough and shiny metal surfaces, the above method is powerless, but you can wipe the surface with clean, white cotton, cloth, and 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 the surface oil on the surface energy, the surface of the surface can be judged to be clean by determining whether the surface energy of the metal is infiltrated by a series of test solutions with different surface tensions. For example, a series of solutions prepared from 80% acetic acid 20% water (V/V, the same below) to 1% ethanol 99% water, the surface tension correspondingly increased from 24.5×10-5N/CM to 66.0×10-5N. /CM.
3, paint method
The degreaser was dropped on the metal surface and evaporated to dryness. If there was no trace, the surface metal surface was clean. If a ring appeared, there was oil stain.
4, wetting method
The clean metal surface is hydrophilic, so it can be completely wetted by water. When the metal surface contains oil, there will be areas of water cut that are not wetted by water. Based on the principle of whether it is hydrophilic or not, in addition to the simplest and most 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 or not the oxide film on the metal surface is desorbed.
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