The surface coating and plating of spring metal materials shall meet the requirements that the coating (plating) shall be fine, uniform and solid with the base material. However, in the coating (plating) layer, for example, the coating (plating) layer drops, bulges or hairiness, and part of it has no coating layer. In most cases, it is caused by the unclean surface of the metal material before coating (plating). Compared with the solvent coating, the surface coating of spring metal materials with water as the organic solvent can solve the physical environment pollution on the surface of metal materials, such as electroplating process, air oxidation, phosphating treatment and water-based paint spraying. Even the pollutants of single molecular layer are likely to cause the failure of all processing processes. Therefore, the cleanliness of raw material surface before and after coating is particularly important
method:
1. Estimation and electron optics method
Oil stains on the surface of bright metal materials can be viewed by human eyes and with high-power magnifying glass or microscope. Its disadvantage is that the passive air oxide film and thin oil stains on the surface of metal materials can not be found. For the surface of unsmooth and unsmooth metal materials, the above methods seem helpless, but the surface can be cleaned with clean and snow-white cotton wool, cloth and paper, and then check whether it is clean to recognize whether the surface of metal materials is clean.
2. Surface tension method
According to the harm of surface oil stain on its surface energy, it is necessary to determine whether the metal material is wetted in a series of standard solutions with different surface supporting forces to recognize its surface energy, so as to determine its surface cleanliness level. If a series of product aqueous solutions from 80% formic acid and 20% water (V / V, the same) to 1% alcohol and 99% water are prepared, the surface support force correspondingly increases from 24.5 × 10-5n / cm to 66.0 × 10-5N/CM。
3. Paint method
Drop the detergent on the surface of the metal material and then evaporate it. If there is no trace, the surface of the metal material is clean. If it is round, it is marked with oil stains.
4. Wet method
The clean metal material surface is hydrophilic, so it can be wetted by water. When the metal material surface has oil stains, it will show a water stop area that is not wetted by water. According to the basic principle of hydrophilicity, in addition to the general simple and common breath method and the electronic atomizer spray method, there are also the following types of inspection methods. Since the air oxide film of metal materials is also hydrophilic, most of these methods can not test whether the air oxide film on the surface of metal materials is faded.
