First, modern production line process analysis

1. Pre-treatment of key processes

Alkali wash degreasing: The NaOH solution of pH12.5 is used to remove 5-8g/m² of rolling oil

Reduction annealing: Heating to 720-850 ° C in H₂+N₂ atmosphere to eliminate work hardening

Zinc liquid composition: Modern production line adopts Zn-0.2% al-0.03mg formula, which improves fluidity by 15%

2. Coating control technology

The air knife system accurately controls the zinc layer thickness through 0.3-0.5MPa air pressure, and the error is controlled within ±3g/m². Wisco CGL production line adopts double air knife design to achieve single-sided differential thickness coating (such as 20/10g/m²).

2. Prevention and control of common quality defects

1. Surface defect map

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Zinc scar: Zinc slag particle size > 0.5mm need to replace the zinc pan

White rust: When the storage humidity is > 70%, the ZnO oxide layer is produced within 72 hours

2. Mechanical properties control

Automobile plate requires yield strength ≥140MPa, elongation ≥34%. Edge wave defects are eliminated by in-line tension straightening (elongation 0.5-1.5%). The 1200MPa galvanized sheet developed by Hangang has been commercialized.