Adhesion
Below the name of each layer
in the figure above (magnified cross-section
of hot-dip galvanized coating) appears its
respective hardness, expressed by a Diamond
Pyramid Number (DPN). The DPN is a progressive
measure of hardness; the higher the number,
the greater the hardness. Typically, the Gamma,
Delta and Zeta layers are harder than the
underlying steel. The hardness of these inner
layers provides exceptional protection against
coating damage by abrasion. The Eta layer
is quite ductile, providing the coating with
some impact resistance. The galvanized coating
is adherent to the underlying steel on the
order of several thousand pounds per square
inch (psi). Other coatings typically offer
adhesion rated at several hundred psi at best.
Hardness, ductility and adherence combine
to provide the galvanized coating with unmatched
protection against damage caused by rough
handling during transportation to and/or at
the job site, as well as in service. The toughness
of the galvanized coating is extremely important
since barrier protection is dependent upon
the integrity of the coating.
Abrasion
Resistance
