Galvanized sheet, immersed the thin steel sheet in a molten zinc bath, so that the surface of the sheet is adhered with a layer of zinc. It is mainly produced by continuous galvanizing process, that is, galvanized steel plate is made by continuously immersing the rolled steel plate in a plating tank with molten zinc. Alloy galvanized steel sheet. This kind of steel plate is also made by hot-dip method, but after it is out of the tank, it is heated to about 500 ℃ immediately to form an alloy film of zinc and iron. This galvanized sheet has good paint adhesion and weldability.
Its disadvantages are mainly falling off, scratches, passivation spots, zinc particles, thick edges, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of steel base, wave edges, buckling, and inappropriate sizes. , embossing, different thickness of zinc layer, roll printing, etc.
The black spot is formed by the further oxidation of white rust.
The main reasons for white rust are as follows:
(1) Poor passivation, insufficient or uneven thickness of the passivation film
(2) The surface is not oiled or there is residual moisture on the surface of the strip
(3) The strip surface contains moisture during coiling
(4) Passivation is not completely dried
(5) damp or rain-drenched during transportation or storage
(6) The storage time of finished products is too long
(7) The galvanized sheet is in contact with or stored together with other corrosive media such as acid and alkali.
