Considering the production process of hot-dip galvanized steel sheet and the packaging of finished products, the hot-dip galvanized steel sheet may have some surface appearance defects. The following are some defects that may appear on some galvanized steel sheet summary by Galvanized Steel Sheet Manufacturer.
1. Original plate defect
Surface defects, such as creases, pits, and wavy edges, of the galvanized original sheet continue to affect the galvanized sheet and become surface defects. Therefore, the producer must inspect the original board before production.
2. Dark spots
a. The purity of the galvanized layer is not enough. Metal impurities form a galvanic cell on the zinc surface. When it is beneficial to hydrogen evolution, it is easy to cause black spots on the surface of the zinc layer.
b. When the content of impurities such as copper, iron, arsenic in the galvanized layer is high, after passivation treatment, these impurities appear black.
c. Insufficient treatment of the dirt on the surface of the original board, resulting in residues, making some areas not coated with zinc, which causes problems with the galvanized layer and easily falls off, resulting in dark spots.
d. Miss plating occurs during galvanizing, and black spots are easily formed during post-treatment.
e. Residues or small black ash (carbon or carbon compounds) are contained in the galvanizing solution, adhere to the surface of the zinc layer or reside in the zinc layer, and are firmly combined with the zinc layer. Black spots are visible on the finished galvanized sheet.
f. Abrasive dark spots. It is caused by rough operation during transportation and storage.
The surface of the galvanized steel is wet or rain-soaked. At a certain temperature, zinc is oxidized to produce a white powder. The surface that produces white rust has a greatly reduced anticorrosive ability, which affects its use.
4. Uneven galvanized layer
The zinc layer on the surface of Galvanized Steel Sheet is uneven, uneven in thickness, and even small particles appear on the surface. There is excess zinc liquid on the surface of the strip from the galvanizing pot. These excess zinc liquid is blown off with an air knife (jet high pressure gas) to control the thickness of the zinc layer. The gas pressure of the air knife, the distance between the air knife and the strip, and the speed of the strip will directly affect the thickness of the zinc layer. If the air knife air supply is unstable or the air knife pressure is insufficient, it will cause galvanization layer accumulation, that is, zinc scar.
Galvanized Steel Sheet
There are residues or dross (metal or non-metallic inclusions) in the galvanizing solution. Sometimes these slags are mixed in the galvanized layer. The Shanghai model ship model mechanical model industrial model makes small round spots on the surface, and even makes the original board not stain Zinc coating can easily cause iron spots.
6. Scratches and abrasions
When the galvanized coil passes the tension leveler, foreign matter on the leveler causes surface scratches and abrasions.
7.Chromic acid dirt
In order to improve the anti-corrosion ability of galvanized steel, a thin passivation layer is formed on the surface of the strip, which can be completed by chromic acid treatment, that is, chromizing treatment. However, if the chromic acid treatment is not good and there is residual liquid, there will be light yellow bands or stains on the surface of the galvanized sheet, and even black spots.
In addition to the surface defects mentioned above, the surface of the coating sometimes has damage, scratches, white rust, roll marks, pits, creases, black spots, unwashed salt marks, water marks, removable or rendered Defects such as brown, brown passivation film, and dendritic, sponge and stripe plating. All these defects will have an impact on the use of galvanized sheet.
The above are the surface defects of the galvanized steel sheet introduced by the Cold Rolled Steel Sheet supplier. Hope to help you.