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ArkNovin

Engineering Contrivance , Performance Sustainability
Ark Novin Hot-Dip Galvanizing

Hot-dip galvanizing defects Possible Causes
Rough surface condition

Presence of impurities in the base metal, lengthy pickling process, prolonged immersion time in molten zinc bath, too high temperature of molten zinc bath, presence of dross in the melt, high impurity content of zinc ingot
Peeling

 

Slow cooling, piling up the galvanized components on top of one another
Flaking

 The coating is too thick; high silicon content of the galvanized component; prolonged immersion time in molten zinc bath
 Bare spots

 The degreasing and pickling processes are not done properly and paint markings, oil and oxide are not removed from the component surface; the protective flux layer is damaged due to the components clashing during the process; high impurity of the components
 Blistering

The hydrogen produced during pickling is entrapped at the surface of the steel component and adsorbed by steel during the immersion in molten bath. Such blistering is accompanied by the embrittlement of steel.
 Gray coating

 The gray coating is an impure coating with layers of zinc and iron alloys being visible. The reasons for this defect are attributed to the high content of impurities in base metal, such as oxide and silicon, lengthy immersion in molten bath, slow cooling, and uneven surfaces.
Dross pimples

  Entrapment of dross particles underneath the pure zinc coating during the withdrawal of the component from the melt
 Rust stain

 Presence of iron hydroxide at the surface in form of brownish red stains due to the storage of galvanized pieces adjacent to rusty components, or oozing acid solution from the gaps, which is entrapped during the degreasing stage
 White rust

 Conversion of the pure surface zinc to zinc carbonate due to exposure to air; the carbonates react with moisture in the environment and form a white layer of zinc hydroxide.
 Zinc skimmings

 Presence of burnt ashes at the surface of molten zinc bath
Flux inclusions

Burning of the flux layer, presence of impurities at the surface of the molten zinc bath