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Galvanized Steel Coil Process | HengZe Manufacturer

Galvanized steel coils are a cornerstone of modern industry—offering superior corrosion resistance, cost-efficiency, and high processability. In this guide, HengZe Steel explains the professional and technical process behind galvanizing steel coils, focusing on both continuous hot-dip galvanizing and batch galvanizing, with an emphasis on quality control and zinc layer formation. Whether you’re in construction, automotive, or appliance manufacturing, understanding this process is critical for selecting the right product for your application.

🏗️ 1. Raw Material Preparation

The process begins with selecting high-grade carbon steel coils. These coils must be free of large-scale rust, scale, oil, or surface defects. Prior to galvanization, the coils are typically:

Uncoiled and Welded into continuous strip lines
Edge Trimmed to achieve dimensional uniformity
Inspected for surface integrity

This stage ensures that only steel substrates with optimal chemical and mechanical properties proceed into the coating phase.

🔬 2. Surface Treatment (Pre-Galvanizing)

Surface preparation is essential to ensure a strong metallurgical bond between the steel substrate and the zinc layer. The following steps are performed on a continuous galvanizing line (CGL):

Degreasing: Using alkaline or solvent solutions to remove oils and lubricants
Pickling: Acid baths (HCl or H₂SO₄) remove oxides and mill scale
Rinsing & Drying: Multiple rinses with deionized water followed by air knives to eliminate residuals
Fluxing: Application of a ZnCl₂–NH₄Cl solution forms a thin protective layer that promotes zinc adhesion

This multi-step process is critical to preventing coating defects like bare spots, blisters, and poor adhesion.

🔥 3. Hot-Dip Galvanizing Process

At the heart of the process is immersion into a molten zinc bath at 450–460°C. Here’s what happens:

➤ Metallurgical Reaction:

A zinc-iron alloy layer forms via diffusion between steel and zinc.
This creates a layered structure: Fe-Zn alloy layers + pure zinc top layer.

➤ Coating Control:

Air knives precisely control coating thickness, often between 45–275 g/m² (G30–G90), depending on application and standards (ASTM A653, EN 10346, JIS G3302).

➤ Options:

Spangle control: By adjusting bath chemistry and cooling rates (minimized spangle, regular spangle, zero spangle)
Alloyed galvanized (GA) or Galvannealed steel is created by reheating after dipping to improve paintability.

🌡️ 4. Cooling, Passivation & Post-Treatment

After galvanizing:

Rapid Cooling: Using water quenching or air blast coolers to fix the zinc layer.
Passivation: Chromate or non-chromate solutions are applied to improve corrosion resistance and storage life.
Oiling (Optional): Light oil film application prevents white rust during transport and storage.

Advanced coil lines use electrostatic oilers and drying tunnels to ensure even application without compromising downstream processability.

🎯 5. Finishing: Tension Leveling, Slitting & Packaging

Once galvanized, the coil undergoes:

Tension leveling: Corrects shape defects and improves flatness
Inspection: Online cameras and X-ray thickness gauges ensure uniformity and defect-free surfaces
Slitting or recoiling: Depending on customer requirements
Packaging: Moisture-proof paper, edge protectors, and steel strapping ensure safe international shipment

🔍 6. Batch vs. Continuous Galvanizing (Comparison)

Feature	Continuous Galvanizing (CGL)	Batch Hot-Dip Galvanizing
Coating Control	Precise (air knives)	Thicker, less uniform
Surface Finish	Smooth, spangle adjustable	Matte, irregular spangle
Productivity	High-speed, mass production	Flexible, lower volume
Applications	Roofing, appliances, auto panels	Gratings, poles, fabrication parts

🛡️ 7. Why Zinc? Corrosion Protection Mechanism

Zinc offers dual corrosion protection:

Barrier Protection: Prevents contact between steel and external elements (O₂, H₂O, chlorides)
Cathodic Protection: Zinc sacrifices itself to protect exposed steel (anodic reaction)

Even when the coating is scratched, zinc corrosion products (ZnO, Zn(OH)₂) act as a natural sealant, slowing down further oxidation—a critical property in outdoor and marine environments.

📦 8. Applications of Galvanized Steel Coils

Construction: Roofing, wall panels, rain gutters
Automotive: Body panels, underbody components
Home Appliances: Refrigerator backs, washing machines
Agriculture & Infrastructure: Silos, fencing, steel pipes

At HengZe Steel, we offer customized galvanized steel coil solutions with various coatings (Z100–Z350), spangle control, and slit widths tailored to your specifications.

Why Choose HengZe Steel?

As a trusted galvanized steel coil manufacturer in China, HengZe Steel operates with advanced production lines, ISO-certified processes, and strict quality inspection protocols. Whether you need regular spangle, zero spangle, or galvanized and color-coated steel coils, we deliver:

High tensile strength steel coils
Uniform zinc coating with long-lasting durability
Fast lead times and international shipping
OEM and private label support

👉 Visit HengZe Steel’s official website to explore our full product range and request a free quote.