1. Normal spangle coating
In the normal solidification process of the galvanized coiled zinc layer, the zinc crystal grains freely grow to form a coating with obvious spangle morphology.
2. Small spangle coating
During the solidification of the zinc layer, the zinc crystal grains are artificially restricted to form the smallest possible spangle coating.
3. Zinc-free coating
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. It is suitable for removing general In addition to cleaning, the coating can be painted directly without further treatment.
5. Poor thickness coating
For both sides of the galvanized steel sheet, coatings with different zinc layer weights are required.
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 phenomenon of slip lines or creases generated when the finished product is not seen during processing.
What is the purpose of galvanized coil
Galvanized coil is a thin steel sheet with a layer of zinc adhered to the surface by immersing a thin steel sheet in a molten zinc tank. Galvanized coils can be divided into hot-rolled galvanized coils and cold-rolled hot-dip galvanized coils. At present, the continuous galvanizing process is mainly used, that is, the coiled steel sheet is continuously immersed in a galvanized bath with molten zinc to make galvanized Steel plate.
Because galvanized coils have the characteristics of strong corrosion resistance, good surface quality, deep processing, economical and practical, etc., they are widely used in construction, home appliances, automobiles, containers, transportation and home industry and other fields. Especially in steel structure construction, automobile manufacturing, steel silo manufacturing and other industries.
Defects of galvanized coil
Galvanized coils are easy to fall off, 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, sag, size Incompatibility, embossing, zinc layer thickness incompatibility, roller printing and other defects.
The main reasons for the shedding of the zinc layer of the galvanized coil 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, and oxygen infiltration in the furnace. The temperature of the strip steel 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 The medium residence time is too short and the coating is too thick.