Galvanized coating

Galvanized coating has a number of characteristics that make it a well-suited corrosion protective coating for iron and steel products in most environments.

Th excellent field performance of Galvanized coating results from its ability to form dense, adherent corrosion product films of corrosion considerably below that of ferrous materials (some 10 to 100 times slower depending upon the environment). While a fresh zinc surface is quite reactive when exposed to the atmosphere, a thin film of corrosion products develops rapidly, greatly reducing the rate of further corrosion. In addition to creating a barrier between steel and the environment, zinc also has the ability to cathodically protect the base metal. Zinc, which is anodic to iron and steel, will preferentially corrode and protect the iron or steel against rusting when the coating is damaged.

Many different types of zinc and each has unique characteristics. These characteristics not only affect applicability but also the relative economics and expected service life.The method of processing, adhesion to the base metal, protection aff orded at corners, edges, and threads, hardness, coating density, and thickness can vary greatly among the diff erent coatings.This is practical aid discusses each of the major types of zinc coatings, applied by batch hot-dip galvanizing, continuous sheet galvanizing,electro galvanizing, zinc plating, mechanical plating, zinc spraying, and zinc painting, to help specialists assess and select zinc coatings for corrosion protection.

After deciding to use a Galvanized coating for corrosion protection, some factors must be considered to ensure the proper coating is selected for the intended application and service environment. Obviously, zinc coating processes which are limited to small parts, and operations limited to continuous lines in steel mills (i.e. continuous galvanizing and electrogalvanizing) cannot be considered for the protective coating of structural steel members. Each Galvanized coating reviewed provides various degrees of corrosion protection. When selecting a coating, it is important to investigate the corrosiveness of the exposure environment to ensure the Galvanized coating selected will provide adequate service life for the cost.

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