As the continuous production of coil technology, galvanized steel roofing sheet can be divided into electric galvanized and hot dip galvanized two methods, one of the electric galvanized way is the method of electrodeposition of gold paint on - "layer of zinc metal or zinc alloy. Hot dip galvanizing, also known as hot dip, is the dipping of a protected metal product into a molten zinc metal so that its surface forms a protective metal coating. Compared with electroplating, the hot coating of metal is thicker. In the same environment, its life is longer. The corrosion of hot-dip galvanized steel surface is equivalent to the corrosion of pure zinc. The corrosion of zinc in the atmosphere is similar to the corrosion process of steel under atmospheric conditions. Chemical oxidation corrosion occurs.
In the neutral or slightly acidic atmospheric environment, the corrosion products formed after the corrosion of steel plate galvanized layer is non-soluble compounds (zinc hydroxide, zinc oxide and zinc carbonate), these products will be precipitated form, form a dense thin layer, generally up to 8 microns "thickness. The film has a certain thickness, and not easy to dissolve in water, adhesion and strong. Therefore, it can play a barrier role between the atmosphere and galvanized sheet, prevent the further development of corrosion. The protective zinc coating was damaged. Part of the surface of the steel is exposed to an atmospheric environment. At this time, zinc and iron form a micro-battery, and the potential of zinc is significantly lower than that of iron. As an anode, zinc can protect the plate substrate at the expense of anode and prevent the corrosion of the steel plate.
PPGI corrugated roofing sheet is the liquid coating, with brush or roll coating method on the clean metal surface, add temperature curing can get the same thickness of paint film. The function of the paint film is not only to separate metal from a corrosive medium but also to passivate the metal by means of some pigments (such as lead, zinc chromate, etc.) to achieve a permanent anticorrosive effect.
From the perspective of anti-corrosion mechanism of color-coated steel plate, organic coating (including solid coating and bottom coating) is a kind of isolated material, which isolates the substrate from corrosive medium to achieve the function of anti-corrosion.