An immersion of steel manufactured goods in a molten zinc bath, which allows the realization of a protective coating.
most appropriate term is "hot dip galvanizing or galvanization".
It is the oldest and widespread method for metal coating and it underwent a further evolution thanks to the invention of a Polish engineer SENDZIMIR, in 1937, concerning the continuous galvanizing of tape laminated steel.
Today, with fully automatic plants, this system is applied in Cappello Group S.p.A. estabilishments for the galvanizing of iron, for the structure work and for all those manufactured goods that require a protection layer.
The artefacts, before being subjected to the treatment, go through a cleaning cycle, in order to eliminate fat slags, paint and welding, by means of degreasing tanks. Subsequently the products are pickled in hydrochloric acid (the time of pickling is long enough to allow iron oxides to turn into iron chloride).
In this way the metals get to the molten zinc bath, after having undergone a final treatment, a step in preheating furnaces.
Of major importance, on the success of the galvanizing, is the temperature of the galvanizing bath, if too high there is the risk of formation of slags with the result of rough and opaque deposits, on the contrary, a too low temperature is likely to give the manufactured good a brittle zinc thickness, with the risk of easily splitting apart when the good is subjected to further treatments.
The ideal temperature for thin sheet metal is between 455 and 465°C, while for greater thickness materials the galvanizing must be performed at lower temperatures.
A further element that plays an important factor in the success of the galvanizing is given by the quality of the material to be galvanized.
Steels with low carbon content and no silicon produce uniform coatings and with various regular iron-zinc layers, the surface of the galvanized product will look shiny, whereas a poor quality steel after the galvanizing will look dull and rough, this will not however affect the duration of protection.
The immersion time of the artefacts varies according to the thickness that is expected to obtain, but the extraction from the bath must allow the maximum casting surplus zinc, to ensure a smooth and uniform surface.
Hollow objects must have sufficiently large openings to allow an easy passing of the liquid zinc.
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