Galvanizing

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This is the application of a thin layer of zinc or zinc-aluminium alloy to steel to provide corrosion resistance. The two principal coating methods are continuous galvanizing and batch (or general) galvanizing.

Continuous galvanizing is used to coat flat-rolled steel (mostly cold reduced, but some hot rolled), and also wire and tube. Zinc is applied either by hot-dip coating (the steel passes through a pot of molten zinc) or electrolytic coating (deposition takes place in a series of electrolytic cells). Hot dip is the most common method as it is cheaper.

The key stages on a continuous hot-dip line for strip are pre-cleaning, heating, coating, air-knife (to control coating thickness), cooling and re-coiling. An electrolytic line has no heating or cooling stages.

Continuous lines operate with an endless steel strip created by welding the end of one coil to the start of the next. This highly productive coating process can typically throughput 200,000-500,000 tonnes/year of coil. Batch galvanizing is the coating of individual finished items or components (typically street furniture) by dipping them in a large bath of molten zinc. And for more detail click and see wikipedia entry.

Galvanized steel

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