Hot-dipped galvanized (HDG) chains are a must for applications such as construction, agriculture, and oceanic rigging, where corrosion resistance is not an option. This guide dissects the whole HDG chain manufacturing process—from raw steel selection to final inspection. We delve into surface preparation, zinc bath dynamics, and adherence to ISO 1461/ASTM A123 standards, so you can appreciate how each process adds up to chain durability. Regardless of whether you are a buyer or manufacturer, this technical step-by-step unmasks the science that goes into creating durable galvanized chains.

1. Carbon Steel Selection for HDG Chains

Start with high-carbon steel (typically SAE 1045) for weldability and strength. Low-sulfur alloys (＜0.05%) are preferred by producers to prevent zinc bath contamination, and carbon content (0.4-0.6%) allows a balance between ductility and hardness.

2. Surface Cleaning: Degreasing & Pickling Stages

Before galvanizing, chains undergo dual cleaning:

·Degreasing: Alkaline solutions strip oils from forming operations.

·Pickling: 10-15% hydrochloric acid dissolves mill scale, creating a reactive iron surface for bonding by zinc.

3. Flux Immersion: Zinc Adhesion Prep

Following cleaning, chains are dipped in ammonium chloride flux (pH 4-6) to:

·Prevent oxidation during drying

·Activate the steel surface for zinc bonding

·Minimize dross formation in the zinc bath

4. Zinc Bath Composition & Temperature Control

The bath contains 98.5% pure zinc + 0.1-0.3% aluminum to improve adhesion of the coating. The temperature is stabilized between 450-460°C (842-860°F), maximizing the coating thickness (15-100μm) and manufacturing speed.

5. Hot-Dip Timing: 460°C Immersion Process

Chains are immersed for 3-5 minutes to enable the iron-zinc intermetallic layer (FeZn₇) to develop. Increased duration adds thickness at the cost of brittleness, so the timing is coordinated with chain diameter (e.g., 6mm chains 3 mins dip, 20mm 5 mins dip).

6. Centrifugal Spin: Excess Zinc Removal

Following dip, chains are spun at 60-100 RPM to eliminate surplus zinc for an even coating. This process prevents thick brittle edges and guarantees minimum thickness (ASTM A123: 45μm for ＜6mm chains).

7. Air Cooling and Water Quenching Processes

·Air cooling (30-60 mins): Ideal for big chains to prevent thermal stress.

·Water quenching (5-10 mins): Faster but requires controlled rates (＜20°C/s) to prevent coating cracks.

Coating Thickness Measurement (ASTM A123)

Measure using magnetic induction gauges to confirm thickness:

·＜6mm chains: ≥45μm

·6-12mm chains: ≥60μm

·>12mm chains: ≥70μm

Corrosion Resistance through Salt Spray Testing

Chains are subjected to 72-168 hours of ASTM B117 salt spray testing (35°C, 5% NaCl). Passing requirements: ＜5% white rust at 120 hours, ＜1% red rust at 240 hours.

ISO 1461 Compliance & Quality Certification

Final chains meet ISO 1461 (coating adhesion by bend test) and ASTM A123 (thickness) requirements. Certificates are marked with batch numbers, zinc weight, and test results for traceability.

Conclusion

HDG chain manufacturing combines metallurgy, chemistry, and precision engineering to produce corrosion-resistant and long-lasting products. Every process, from steel selection to salt spray testing, is customized to meet international standards. For tailor-made HDG chain specifications or technical data sheets, reach out to our team at [email protected]—we combine 20+ years of galvanizing experience with ISO 9001 certification to serve your industrial requirements.