Product Overview

FINISHES
Zinc Coatings
Zinc protects steel in two ways. First it
protects the steel as a coating and
second as a sacrificial anode to repair
bare areas such as cut edges, scratches,
and gouges. The corrosion protection of
zinc is directly related to its thickness and
the environment.
This means a .2 mil
coating will last twice as long as a .1 mil
coating in the same environment.
Galvanizing also protects cut and drilled edges.
Electrogalvanized Zinc
Electrogalvanized Zinc (also known as
zinc plated or electroplated) is the process
by which a coating of zinc is deposited on
the steel by electrolysis from a bath of
zinc salts.
A rating of SC3, Cooper B-Line’s
standard, provides a minimum zinc
coating thickness of .5 mils (excluding
hardware, which is SC1 = .2 mils).
When exposed to air and moisture, zinc
forms a tough, adherent, protective film
consisting of a mixture of zinc oxides,
hydroxides, and carbonates. This film is in
itself a barrier coating which slows
subsequent corrosive attack on the zinc.
This coating is usually recommended for
indoor use in relatively dry areas, as it
provides ninety-six hours protection in salt
spray testing per ASTM B117.
Chromium/ Zinc
Chromium/ Zinc is a corrosion resistant
composition, which was developed to
protect fasteners and small bulk items for
automotive use.
The coating applications
have since been extended to larger parts
and other markets.
Chromium/Zinc composition is an
aqueous coating dispersion containing
chromium, proprietary organics, and zinc
flake.
This finish provides 500 hours protection
in salt spray testing per ASTM B117.
Pre-Galvanized Zinc
(Mill galvanized, hot dip mill galvanized or
continuous hot dip galvanized) Pre-
galvanized steel is produced by coating
coils of sheet steel with zinc by
continuously rolling the material through
molten zinc at the mills. This is also
known as mill galvanized or hot dip mill
galvanized. These coils are then slit to
size and fabricated by roll forming,
shearing, punching, or forming to produce
Cooper B-Line pre-galvanized strut
products.
The G90 specification calls for a coating
of .90 ounces of zinc per square foot of
steel. This results in a coating of .45
ounces per square foot on each side of
the sheet. This is important when
comparing this finish to hot dip galvanized
after fabrication.
During fabrication, cut edges and welded
areas are not normally zinc coated;
however, the zinc near the uncoated
metal becomes a sacrificial anode to
protect the bare areas after a short period
of time.
Hot Dip Galvanized After
Fabrication (Hot dip galvanized or
batch hot dip galvanized)
Hot dip galvanized strut products are
fabricated from steel and then completely
immersed in a bath of molten zinc.
A
metallic bond occurs resulting in a zinc
coating that completely coats all surfaces,
including edges and welds.
Another advantage of this method is
coating thickness. Strut products that are
hot dip galvanized after fabrication have a
minimum thickness of 1.50 ounces per
square foot on each side, or a total 3.0
ounces per square foot of steel, according
to ASTM A123.
The zinc thickness is controlled by the
amount of time each part is immersed in
the molten zinc bath as well as the speed
at which it is removed. The term "double
dipping" refers to parts too large to fit into
the galvanizing kettle and, therefore, must
be dipped one end at a time. It does not
refer to extra coating thickness.
The layer of zinc which bonds to steel
provides a dual protection against
corrosion. It protects first as an overall
barrier coating. If this coating happens to
be scratched or gouged, zinc's secondary
defense is called upon to protect the steel
by galvanic action.
Hot-Dip Galvanized After Fabrication is
recommended for prolonged outdoor
exposure and will usually protect steel for
20 years or more in most atmospheric
environments and in many industrial
environments. For best results, a zinc
rich paint (available from Cooper B-Line)
should be applied to field cuts. The
zinc rich paint will provide immediate
protection for these areas and eliminate
the short time period for galvanic action to
“heal” the damaged coating.
Anticipated Life of Zinc Coatings In Various Atmospheric Environments
Hot Dip Galvanized
Pre-Galvanized
= Zinc Coating 1.50 Oz./Ft.
2
(.0026”
Thick)
= Zinc Coating 0.45 Oz./Ft.
2
(.00075” Thick)
Rural
T
ropical
Marine
T
emperature
Marine
Highly
Industrial
Life
in
Y
ears
Suburban
Environment
Urban
10
20
30
40
10
36
8
29
7
25
6
21
5
18
3
11
Zn
Fe
ZnFe
ZnO
Technical Data
Technical Data
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