Introduction galvanized coils
For galvanized coils, the thin steel plate is immersed in the molten zinc tank, so that a thin steel plate with a layer of zinc is adhered to the surface. It is mainly produced by continuous galvanizing process, that is, the coiled steel sheet is continuously immersed in a galvanized bath with molten zinc to make galvanized steel sheet; alloyed galvanized steel sheet. This kind of steel plate is also manufactured by hot dipping method, but immediately after leaving the tank, it is heated to about 500°C to form an alloy film of zinc and iron. This galvanized coil has good paint adhesion and weldability.
Passivation treatment of the galvanized layer can reduce folding rust (white rust) under moisture storage and transportation conditions. However, the anti-corrosion performance of this chemical treatment is limited, and it hinders the adhesion of most coatings. This kind of treatment is generally not used on the zinc-iron alloy coating. In addition to the smooth surface, as a rule, the manufacturer performs passivation treatment on other types of zinc coatings.
Oiling can reduce the corrosion of steel plates under humid storage and transportation conditions. After passivation treatment of steel plates and steel strips, repainting oil will further reduce the corrosion under humid storage conditions. The oil layer should be able to be removed with a degreaser that does not damage the zinc layer.
3. Lacquer seal
By coating a very thin transparent organic coating film, it can provide an additional anti-corrosion effect, especially fingerprint resistance. It can improve lubricity during molding and serve as an adhesion base layer for subsequent coatings.
Through phosphating treatment, galvanized steel sheets of various coating types can be coated without further treatment except for normal cleaning. This treatment can improve the adhesion and corrosion resistance of the coating and reduce the risk of corrosion during storage and transportation. After phosphating, it can be used with a suitable lubricant to improve the molding performance.
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.