
OUR ESTABILISHMENTS
An immersion of steel manufactured goods in a molten zinc bath, which allows the realization of a protective coating.
The
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.
Download
Cappello Group hot dip galvanizing Manual