The paint on galvanized parts is easy to fall off. For example, galvanized water pipe, white galvanized iron sheet and so on, common alkyd paint is easy to fall off, some industrial galvanized structure, because of the high demand for paint adhesion,
ordinary epoxy paint is not competent, what paint used on galvanized parts has good adhesion, do not drop paint? Here, in the field of heavy-duty anti-corrosion coating, the anti-corrosion principle of zinc coating is summarized as follows :
1) Cathodic protection
The coating of cold galvanizing is mainly used to prevent steel corrosion by electrochemical protection. According to the theory of electrochemical corrosion, the anode with lower electrode potential is always corroded in
the corrosion battery. The standard electrode potential of zinc is -0.76v, which is more active than that of iron-0.44v. When the coating is eroded, zinc powder is corroded first as anode, and steel as cathode is protected. The zinc powder of cold galvanized
coating is gradually consumed in the process of protection, but the speed is very slow. The formation of corrosion products reduces the potential difference between the coating and the substrate. When the coating film is damaged, fresh metal zinc is exposed,
and the potential difference increases immediately, resulting in strong cathodic protection. It can also be called "self repairing" of cold galvanizing. The chemical reaction equation of zinc in natural environment is as follows: (2) the protective effect
of zinc salt, the chemical activity of zinc is greater than that of iron, and it is easier to lose electrons. As a sacrificial anode, it can protect the steel surface. At the same time, with the consumption of zinc powder, ZnO, Zn (OH) 2 and basic zinc
carbonate [2znco3 · 3zn (OH) 2] powders were deposited in the pores of the coating, which increased the compactness of the coating, played a shielding role, slowed down the electrochemical corrosion rate, greatly reduced the consumption rate of zinc powder,
and improved the durability. It is also reported that the existence of these alkaline sediments plays a chemical passivation role. (3) The shielding effect of organic resin cold galvanizing contains special organic mixed resin. After the film is formed,
it can prevent or inhibit water, oxygen and ions from passing through the coating, so as to isolate the corrosive medium from the steel. The shielding effect of the coating also slows down the corrosion rate of steel.
The excellent performance of
galvanized paint (cold galvanized paint) in steel structure: in China, hot-dip galvanized steel materials are mostly used in transmission poles and towers of transmission lines. However, the actual service life of zinc coating in recent years is far less
than the expected life at the time of design due to environmental pollution and global climate deterioration. In dry air, zinc coating has good protection performance, but in coastal, humid, acid rain environment, its corrosion resistance is significantly
reduced, in order to extend its service life, it has to be coated on its surface.