painting, coating & hot dipping of metals (3479-ct)

overview of painting, coating & hot dipping of metals (3479-ct)

— painting, coating & hot dipping of metals - there are four commonly used methods of applying metal coating to steel surfaces. these are hot-dip galvanizing, thermal spraying, electroplating and sherardizing. the latter two processes are not used for structural steelwork but are used for fittings, fasteners and other small items. in general the corrosion protection afforded by metallic coatings is largely dependent upon the choice of coating metal and its thickness and is not greatly influenced by the method of application. hot-dip galvanizing is a process that involves immersing the steel component to be coated in a bath of molten zinc (at about 450°c) after pickling and fluxing, and then withdrawing it. the immersed surfaces are uniformly coated with zinc alloy and zinc layers that form a metallurgical bond with the substrate. the resulting coating is durable, tough, abrasion resistant, and provides cathodic (sacrificial) protection to any small damaged areas where the steel substrate is exposed. thermally sprayed coatings of zinc, aluminium, and zinc-aluminium alloys provide long-term corrosion protection to steel structures exposed to aggressive environments. they are an important component of coating systems that are currently specified by network rail and they are commonly used on steel bridge decks prior to surfacing with mastic asphalt systems.