Defects in Galvanized Coils

There are mainly: peeling, scratches, passivation spots, zinc particles, thick edges, air knife marks, air knife scratches, exposed steel, inclusions, mechanical damage, poor steel base performance, wave edges, curling, size mismatch, imprinting, zinc layer thickness mismatch, roller printing, etc.
The main reasons for the detachment of the zinc layer include surface oxidation, presence of silicon compounds, dirty cold rolled emulsion, high oxidation atmosphere and protective gas dew point in the NOF section, unreasonable air fuel ratio, low hydrogen flow rate, oxygen infiltration into the furnace, low temperature of the steel strip entering the furnace, low furnace pressure in the RWP section, low furnace door suction, low furnace temperature in the NOF section, incomplete oil evaporation, low aluminum content in the zinc pot, fast unit speed, insufficient reduction, and short residence time in the zinc liquid The coating is too thick.
The reasons for white rust and black spots are: black spots are formed by further oxidation of white rust.
The main causes of white rust are:
(1) Poor passivation, insufficient or uneven passivation film thickness;
(2) The surface is not coated with oil or there is residual moisture on the surface of the strip steel;
(3) During coiling, the surface of the strip steel contains moisture;
(4) Passivation not completely dried;
(5) Suffering from dampness or rainwater during transportation or storage;
(6) Long storage time of finished products;
(7) Galvanized sheets come into contact with or are stored together with other corrosive media such as acids and alkalis.
The finished product is allowed to be stored in the warehouse for a maximum of three months to avoid oxidation caused by prolonged storage.