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Definition of plating

(1) Normal spangle coating
In the normal solidification process of the zinc layer, zinc grains grow freely to form a coating with obvious spangle morphology.

(2) minimized spangle coating
During the solidification of the zinc layer, the zinc crystal grains are artificially restricted to form the smallest possible spangle coating.

(3) Spangle-free coating spangle-free
It is obtained by adjusting the chemical composition of the plating solution, does not have a visible spangle morphology, and has a uniform surface coating.

(4) Zinc-iron alloy coating
The steel strip after passing through the galvanizing bath is heat treated to form an alloy layer of zinc and iron throughout the coating. This coating has a dark gray appearance without metallic luster, and is easy to powder during the violent forming process. In addition to cleaning, the coating can be painted directly without further treatment.

(5) differential coating
For both sides of the galvanized steel sheet, coatings with different zinc layer weights are required.

(6) Smooth skin pass
Smoothing is a kind of cold rolling of galvanized steel sheet with a small amount of deformation for one or several of the following purposes.
Improve the appearance of the galvanized steel sheet surface or be suitable for decorative coating; temporarily minimize the slip line (Lüdes line) or wrinkles produced when the finished product is processed.

Defect

Mainly 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, wavy edges, buckling, size incompatibility, Embossing, inconsistent zinc layer thickness, 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 oxidizing 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 as follows: 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.

Storage

The finished product is allowed to be stored in the warehouse for a maximum of three months to avoid oxidation due to excessive storage.

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