For hot-dip galvanized cable trays, the zinc coating thickness should generally be at least 45µm for tray sheets 1.5–3mm thick, with heavier components requiring ≥55µm, in accordance with GB/T 13912-2020 and ASTM A123 standards.

Standard Requirements

Hot-dip galvanizing (HDG) provides a thick, durable zinc coating that protects steel from corrosion. The appropriate thickness depends on the steel thickness and component type:

• Tray sheet metal (1.5–3mm thick): Minimum local zinc thickness of 45µm, corresponding to a coating mass of at least 325 g/m² .
• Heavier components (brackets, supports >3mm): Minimum local zinc thickness of 55µm .
• Local thickness: The minimum value at any single test point, measured with a magnetic thickness gauge. All points must meet the requirement .
• Mean coating mass: Average zinc mass per unit area of the entire workpiece, determined gravimetrically, ensuring uniform coverage .

Relevant Standards

• GB/T 13912-2020: Specifies hot-dip galvanized coatings on fabricated iron and steel articles, including local thickness and mean coating mass requirements .
• ASTM A123: Covers zinc coatings on iron and steel products, providing minimum coating thickness based on material type and thickness .
• ISO 1461 / BS EN ISO 1461: International standard for HDG coatings, ensuring corrosion resistance and durability .

Measurement and Quality

• Magnetic thickness gauges are commonly used for non-destructive testing, while optical microscopy is used for dispute resolution .
• The coating should be continuous, uniform, and smooth, with minor dull or light grey areas permissible. Defects such as bare spots, blisters, or excessive zinc dross are not allowed .

Practical Considerations

• Thicker coatings provide longer corrosion protection, especially in harsh environments like coastal or industrial areas .
• The steel composition, surface condition, and galvanizing process affect the final coating thickness .
• For electro-galvanized trays, the minimum zinc thickness is much lower (≈12µm), but corrosion resistance is limited compared to HDG . In summary, for standard hot-dip galvanized cable trays, ensure a minimum zinc thickness of 45µm for typical tray sheets and 55µm for heavier components, following GB/T 13912-2020 and ASTM A123 specifications, with proper measurement and quality control to guarantee corrosion protection and compliance.