Hot Dipped Galvanised Coil

Hot-dip galvanised coil is the process of coating fabricated steel by immersing it in a bath of molten zinc. There are three fundamental steps in the hot-dip galvanizing process; surface preparation, galvanizing, and inspection when the fabricated steel arrives at the galvanizing facility, it is hung by wire or placed in a racking system which can be lifted and moved through the process by overhead cranes. The steel then goes through a series of three cleaning steps; degreasing, pickling, and fluxing. Degreasing removes dirt, oil, and organic residues, while the acidic pickling bath will remove mill scale and iron oxide. The final surface preparation step, fluxing, will remove any remaining oxides and coat the steel with a protective layer to prevent any further oxide formation prior to galvanizing.

Hot-dip galvanised coil proper surface preparation is critical, as zinc will not react with unclean steel. After surface preparation, the steel is dipped in the molten (830 F) bath of at least 98% zinc. The steel is lowered into the kettle at an angle that allows air to escape from tubular shapes or other pockets, and the zinc to flow into, over, and through the entire piece. While immersed in the kettle, the iron in the steel metallurgic ally reacts with the zinc to form a series of zinc-iron intermetallic layers and an outer layer of pure zinc. The final step is an inspection of the coating. A very accurate determination of the quality of the coating can be achieved by a visual inspection, as zinc does not react with unclean steel, which would leave an uncoated area on the part. Additionally, a magnetic thickness gauge can be used to verify the coating thickness complies with specification requirements.

A hot dip galvanized finish gives steel a long life and durability which lasts for decades. In addition, it creates a maintenance-free finish, which lessens the costs and carbon emissions usually associated with the upkeep of non-galvanized steel. The galvanizing process itself is also environmentally friendly.

Construction: Roofing, siding, structural beams.

Automotive: Chassis, exhaust systems (galvannealed).

Agriculture: Grain bins, fencing, irrigation pipes.

Utilities: Transmission towers, cable trays.

Household Appliances: Air ducts, water heaters.

(A) By Coating Weight (ASTM A653)

G60 (Z180): 180 g/m² total coating – General purpose.

G90 (Z275): 275 g/m² – Heavy-duty outdoor use.

Z600: 600 g/m² – Extreme environments (e.g., marine).

(B) By Surface Treatment

Regular Spangle: Visible zinc crystals (aesthetic, less uniform).

Minimized Spangle: Smoother for painting/coating.

Galvannealed (GA): Heat-treated for better paint adhesion.

(C) International Standards

ASTM A653 (USA) – Grades CS, DS, SS.

EN 10346 (Europe) – DX51D, DX52D, DX53D.

JIS G3302 (Japan) – SGCC, SGCH.

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