Causes and conditions of flash rust during the construction of water-based anti-corrosion paint
causes and conditions of flash rust during the construction of water-based anti-corrosion paint
June 5, 2019
the causes of flash rust during the construction of water-based anti-corrosion paint seem to be inconclusive. There is a saying: "The flash rust problem of water-based coatings refers to the rust spot phenomenon of newly constructed water-based coatings during the drying process, which mainly occurs on the corroded interface or the newly activated steel surface. The generation of flash rust may be related to the dissolution and precipitation of iron compounds, and the severity of flash rust depends on the coating system. Coatings such as polyvinyl acetate latex prolong the contact time between water and substrate at low pH, low temperature and high humidity It is easy to appear flash rust paint. "
of course, there are other different statements: "there is a process of film-forming of water-based paint. No metal is absolutely pure and smooth, which will produce small pieces of data curve reanalysis with different potentials. There will be current between small pieces of different potentials, and metal oxidation will occur to form rust spots, that is, flash rust". From these different statements, it can be seen that the production of flash rust is an electrochemical process. As the water-based coating itself is a conductor, charge transfer channels are formed between different areas with potential differences, so corrosion occurs in a short time during the film-forming process of the water-based coating, forming flash rust. Obviously, the longer the wet paint film is kept, the more serious the flash rust phenomenon is, which can explain the reason why the flash rust phenomenon is more serious under the condition of low temperature and high humidity
in fact, as flash rust is an electrochemical phenomenon, the active metal in front of hydrogen will encounter this problem when using water-based paint for construction. In the coating test of steel, cast iron, aluminum and aluminum alloy, galvanized sheet and other substrates, we found that the conditions that are easy to get out but the surface chemical heat treatment and the sampling of coated parts should be perpendicular to the surface are: cast iron, aluminum, carbon steel, zinc plate (grinding), tinplate (grinding), iron plate or iron wire, aluminum alloy
according to various experiments and peer reports, cast iron is not only the substrate most prone to flash rust, but also one of the substrates most difficult to solve the problem of flash rust. The reason for this situation can be explained from two aspects: the liveliness of the metal and the purity of the material: cast iron contains many impurities and complex components, which are easy to form small areas with different potentials, so it is easier to have flash rust during the construction of water-based paint. However, due to the limitations of the author's level and experimental conditions, the above ranking needs more in-depth experiments and demonstrations
electrochemical phenomenon is the fundamental cause of flash rust to the process of microcomputer controlled automatic measurement. However, in the construction of water-based coatings, the conditions for flash rust are very complex. In addition to the substrate discussed above, it can also be used as an artificial joint difference. The pH value of the paint, the temperature and humidity of the construction environment, the wind speed, the thickness of the paint film and so on have an impact on the phenomenon of flash rust