Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip)

This practice covers the precautions that should be taken to obtain high-quality galvanized coatings. Assemblies should consist of elements of similar chemistry and surface condition. Whenever different analyses of steel or different surfaces of steel are united in an assembly the galvanized finish is not generally uniform in appearance. These differences include excessively rusted surfaces, pitted surfaces, machined surfaces, cast iron especially with sand inclusion, cast steel, malleable iron, hot-rolled steel, and cold-rolled steel. All oil or grease should be removed from both the sheet steel and wire or rod before rolling. Welding flux residues shall be removed by standard galvanizing cleaning techniques and are best removed at the gun. All fabricated assemblies shall be so designed with vent and drain holes such that no air is trapped during immersion of the assemblies into cleaning solutions or molten zinc. Moving parts such as handles or hinges should be galvanized separately and assembled after galvanizing. All markings shall remain legible after galvanizing. When an assembly of steel parts or an individual steel part has been designed and fabricated with critical dimensions and must be subsequently hot-dip galvanized, the designer should be aware that the hot-dip galvanizing process chemical cleaning to prepare the surfaces for coating and this may alter the critical dimensions.