Closed hot-dip galvanizing production line

I. Process Flow

1. Pre-Treatment Stage

- Degreasing and Cleaning: Alkaline solutions remove oil and contaminants from the steel surface.

- Pickling and Rust Removal: Hydrochloric or sulfuric acid dissolves oxides and activates the metal surface.

- Flux Treatment: Immersion in a zinc ammonium chloride solution to prevent re-oxidation and enhance coating adhesion.

2. Hot-Dip Galvanizing Stage

- Closed Galvanizing Tank: Steel is immersed in molten zinc (~450°C). The sealed tank minimizes zinc vapor leakage, with exhaust recovery systems.

- Automatic Temperature Control: Ensures precise zinc bath temperature for uniform coating.

3. Post-Treatment Stage

- Cooling: Water or air cooling solidifies the zinc layer.

- Passivation/Oiling: Enhances corrosion resistance or lubrication.

- Quality Inspection: Tests coating thickness, adhesion, and surface quality.

II. Core Equipment

1. Closed Galvanizing Tank

- Made of high-temperature-resistant materials, equipped with sealed covers and negative-pressure ventilation to reduce zinc mist emissions.

2. Exhaust Treatment System

- Scrubbers, bag filters, and activated carbon adsorbers to treat acid mist, zinc fumes, and pollutants.

3. Automated Conveyance System

- Robotic arms or conveyors automate material handling, minimizing manual operations.

4. Intelligent Control System

- PLC or DCS integrates control of temperature, timing, and solution concentration for process stability.

III. Technical Advantages

1. Eco-Friendliness

- Over 95% exhaust recovery rate, compliant with strict standards like EU RoHS.

2. Energy Efficiency

- Waste heat recovery reduces energy consumption; zinc utilization exceeds 90%.

3. Consistent Quality

- Sealed environment minimizes oxidation; coating thickness (50-150 μm) ensures 30+ years of corrosion resistance.

4. Safety

- Isolates high-temperature/hazardous zones, reducing occupational health risks.

IV. Applications

- Infrastructure: Power transmission towers, bridge steel structures, highway guardrails.

- Automotive: Anti-corrosion treatment for chassis parts and fasteners.

- Appliances & Construction: AC housings, color-coated panels, solar mounting systems.

V. Comparison with Open Processes

Metric	Closed Production Line	Traditional Open Process
Eco-Friendliness	Centralized exhaust treatment, meets emission standards	Zinc fumes dispersion, severe pollution
Zinc Consumption	00-800 kg/1,000 tons of steel	1,000-1,200 kg/1,000 tons of steel
Automation Level	Full automation, 70% labor reduction	Manual operations dominate
Initial Investment	High (≈20-50 million RMB)	Low (≈5-15 million RMB)

VI. Development Trends

- Green Technology: Ammonia-free flux agents, low-zinc-consumption methods.

- Smart Manufacturing: AI vision for coating defect detection; digital twins optimize parameters.

- Material Innovation: Zinc-aluminum alloy coatings for enhanced corrosion resistance.

VII. Challenges & Solutions

- High Costs: Scale production to dilute equipment investments.

- Complex Maintenance: Modular designs simplify repair workflows.

The closed hot-dip galvanizing line represents an advanced direction in metal anti-corrosion technology. With tightening environmental regulations, its efficiency and eco-friendly features will drive broader adoption in high-end manufacturing.

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