1.What is the oxidation process of zinc?
During the galvanizing process, molten zinc, when exposed to air, rapidly reacts with oxygen, forming a thin, dense protective film of zinc oxide (ZnO) on the surface. This film, usually invisible, protects the zinc within from further corrosion.
However, during the cooling, coiling, and subsequent transportation and uncoiling of the galvanized coil, this oxide film is scraped off by friction, compression, and relative sliding between the steel sheets, forming a fine powder. Therefore, a large portion of the "dust" you see is composed of this abraded zinc oxide particles.
2.How does zinc react with other substances?
Zinc also reacts with carbon dioxide and water vapor in the air to form basic zinc carbonate (Zn₅(CO₃)₂(OH)₆).
In humid environments, zinc hydroxide (Zn(OH)₂) may also be formed.
These compounds also appear as powder on the surface.
3.What are other possible impurities?
Ambient Dust: In a factory or warehouse environment, common airborne dust (such as silicates and carbides) may settle on the strip surface.
Process Residues: Small amounts of residue from the galvanizing line itself, such as zinc slag particles from the zinc pot or reaction products from the shielding gas.
Other Metal Particles: If the line also processes galvanized or aluminum-coated products, cross-contamination may occur.
4.What are the impacts?
Appearance: Dust can affect the gloss and appearance of the galvanized coil surface.
Post-processing: During post-processing steps such as spraying and laminating, surface dust can impair coating adhesion, leading to quality issues.
Welding: Dust may affect spot welding quality and electrode life.
Health: Inhalation of zinc oxide dust may cause mild respiratory irritation (commonly known as "metal fume fever"), but under normal storage and processing conditions, with proper ventilation, the risk is low.
5.HOW TO HANDLE?
For demanding applications, the strip surface is cleaned prior to processing using a washing line or wiping device.
Light dust can be removed with dry compressed air or wiped with a clean, soft cloth.