Continuous Hot-Dip Galvanizing Process
In short: Cold rolled steel coil → Cleaning & Annealing → Hot-dip Galvanizing → Air Knife Thickness Control → Cooling & Leveling → Passivation & Oiling → Finished Coiling
Raw Material Feeding & Uncoiling
Raw material: Cold rolled steel coil (CR) with smooth surface and high dimensional accuracy.Proceed with uncoiling, head and tail cutting, and strip welding to form a continuous steel strip for non-stop production.
Surface Cleaning
Process: Alkali washing, brushing, electrolytic cleaning, rinsing and drying.It thoroughly removes oil, iron powder and impurities. Unclean surface will cause peeling and falling off of the zinc coating.
Continuous Annealing
The steel strip is heated in an annealing furnace at 700–850 ℃ under protective atmosphere (N₂+H₂).It eliminates cold rolling stress, improves ductility, and reduces surface oxide to pure iron, so as to enhance the adhesion of zinc coating.
Hot-Dip Galvanizing (Core Process)
The steel strip is immersed in a molten zinc pot at 450–460 ℃ with zinc purity over 99.99%.Metallurgical reaction occurs between steel and zinc to form a firm bonded zinc layer, instead of simple surface coating.
Air Knife Blowing & Zinc Thickness Control
After leaving the zinc pot, high-pressure nitrogen or air knives blow off excess molten zinc.Precisely control zinc coating weight (Z40 / Z80 / Z120) with uniform and bright surface.
Cooling, Leveling & Straightening
Cool down to room temperature by air cooling and water quenching.Skin pass rolling optimizes flatness, eliminates yield lines and adjusts surface roughness.Straightening process ensures flat sheet without warping.
Post-Treatment
Passivation treatment with chromium-free or chromate solution to prevent white rust and improve corrosion resistance.Anti-fingerprint treatment or oil coating protects the surface from scratches and facilitates subsequent processing.
Coiling, Inspection & Packaging
Cut to required length or recoil, with full inspection on coating, color difference and surface defects.Final procedures include weighing, packaging and warehouse storage.
| Production Line | Product Thickness (mm) | Product Width (mm) | Coating Weight (GSM) | Surface Treatment Options | Annual Capacity (MT) |
| Zero-spangle Galvanizing Line | 0.2–2.0 | 750–1250 | ≥ 60 | Chromate-free passivation, anti-fingerprint, oiling | 150,000 |
