Defects in Galvanized Coil

1. The main defects:

Peeling, scratches, passivation spots, zinc particles, thick edges, air knife striations, air knife scratches, steel exposure, inclusions, mechanical damage, poor performance of steel base, wave edges, clamps, dimension, stamping, zinc layer thickness, roll printing, etc.

2. The main cause of zinc layer shedding:

Surface oxidation, silicon compounds, cold rolled emulsion is too dirty, NOF section of oxidizing atmosphere and dew point of shielding gas is too high, unreasonable air-fuel ratio, hydrogen flow rate is low, aerobic infiltration, the stove temperature is low, the strip into the pan RW3 -p section of the furnace pressure is low and the oven door suction, NOF section of furnace temperature is low, oil evaporation is endless, zinc pot aluminum content is low, the unit too fast, inadequate reduction, in zinc liquid residence time is too short and thick coating.

3.The causes of white rust and black spot are as follows: Black spot is formed by further oxidation of white rust.

4. The causes of white rust mainly include:

(1) Poor passivation, insufficient or uneven passivation film thickness;

(2) There is no oil on the surface or residual moisture on the surface of the strip;

(3) The surface of strip steel contains moisture when coiling;

(4) Passivation is not completely dried;

(5) Get wet or wet from rain during transportation or storage;

(6) The storage time of finished products is too long;

(7) Galvanized plate and other corrosive media contact or stored together.

The finished products are allowed to be stored for up to three months in the storage to avoid oxidation.