the reason of galvanized steel,zinc coating steel appear rust and zinc falls off

 galvanized steel,zinc coating steel 

The main reasons for zinc layer shedding are as follows:  Surface oxidation, silicon compounds, cold binding emulsion is too dirty, NOF oxidation atmosphere and protective gas dew point is too high, air fuel ratio is unreasonable, hydrogen flow is low, the furnace oxygen infiltration, the temperature of the strip into the pot is low, RWP section furnace pressure is low and the door air absorption, NOF section furnace temperature is low,  Oil evaporation is not enough, zinc pot aluminum content is low, the unit speed is too fast, insufficient reduction, zinc liquid residence time is too short, thick coating.  

The causes of white rust and black spots are as follows: black spots are formed by further oxidation of white rust.  
The main reasons for white rust are as follows:  
(1) Poor passivation, passivation film thickness is not enough or uneven;  
(2) the surface is not coated with oil or there is residual water on the surface of the strip;  
(3) the surface of the strip contains moisture when coiling;  
(4) Passivation is not completely dried;  
(5) damp or rain during transportation or storage;  
(6) The storage time of finished products is too long;  
(7) Galvanized sheet and other acid and alkali and other corrosive medium contact or stored together.  

Finished products are allowed to be stored in the warehouse for a maximum of three months to avoid oxidation.  

 galvanized steel,zinc coating steel