The main defects of hot-dip galvanized sheet include: shedding, scratches, passivation spots, zinc particles, thick edges, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of the steel base, wave edges, scoops Curves, size irregularities, embossing, zinc layer thickness irregularities, roll printing, etc.
The main reasons for the zinc layer to fall off are: surface oxidation, silicon compounds, too dirty cold rolled emulsion, too high oxidation atmosphere and protective gas dew point in the NOF section, unreasonable air-fuel ratio, low hydrogen flow, oxygen infiltration in the furnace, strip steel The temperature of entering the pot is low, the furnace pressure in the RWP section is low, and the furnace door suction, the furnace temperature in the NOF section is low, the grease does not evaporate, the aluminum content of the zinc pot is low, the unit speed is too fast, the reduction is insufficient, and the zinc liquid stays The time is too short and the coating is too thick.
The causes of 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 oiled or there is residual moisture on the surface of the strip;
(3) The surface of the strip steel contains moisture during coiling;
(4) The passivation is not completely dried;
(5) Moisture or rain during transportation or storage;
(6) The finished product has been stored for too long;
(7) The galvanized sheet is in contact with or stored together with other corrosive media such as acid and alkali.
The finished product is allowed to be stored in the warehouse for up to three months to avoid oxidation due to excessive storage.
