Galvanized coil production process easily lead to defects
They are: off, scratches, spots passivation, zinc tablets, thick edge, air knife streaks, air knife scratches, exposed steel, inclusions, mechanical damage, poor performance of the steel substrate, wave edge, buckling, size or not, imprint, zinc layer thickness or not, roll printing and the like.
The main reason for falling zinc layer: surface oxidation, silicon compound, cold rolling emulsion dirty, NOF segment oxidizing atmosphere and shielding gas dew point is too high, air-fuel ratio is irrational, the low flow rate of hydrogen, oxygen furnace infiltration, strip wok temperature is low, RWP segment furnace pressure is low and the door suction, NOF section furnace low fat evaporated endless, low aluminum content of the zinc pot, the unit too fast, reduction is insufficient, zinc liquid residence Time is too short, partial thickness coating.
White rust and causes spots produced are: white rust spots are formed by further oxidation.
The main reasons of white rust are:
(1) passivation poor, insufficient or uneven thickness of the passivation film;
(2) The surface is not coated with oil or residual moisture of the strip surface;
(3) coiling strip surface contains moisture;
(4) passivation is not completely dry;
(5) The moisture or rain water during transport or storage;
(6) Finished stored for too long;
(7) galvanized sheet and other acid and other corrosive media contact or stored together.
Finished in the library the maximum allowable 2 months, stored for too long in order to avoid oxidation.