ZnCoat is a revolutionary new finish that offers effective solutions for the problems that have been encountered by users of zinc plating for fasteners and small parts.
NOF Metal Coatings North America Inc. and Curtis Metal
Finishing Company have launched ZnCoat, a revolutionary new
finish that offers effective solutions for the problems that have been
encountered by users of zinc plating for fasteners
and small parts. ZnCoat, a zinc-rich coating for
ferrous metals, offers several major advantages for high-strength fasteners
when compared to electroplated zinc. The
finish is entirely chromium-free (no hexavalent or trivalent chromium), and
provides superior corrosion resistance with a thin film, without risk of hydrogen embrittlement. Most
importantly, these features and more are available at no extra
cost when compared to zinc plating, baked for
hydrogen embrittlement relief. ZnCoat is applicable
for industries such as agriculture, construction,
appliance, recreation, marine, etc.
The zinc in the ZnCoat
is passivated without the use of toxic materials. ZnCoat is free of chromium, nickel, cadmium, lead, barium and
mercury, and meets RoHS, REACH and WEEE environmental regulations. By comparison, conventional zinc plating is passivated by the use of
hexavalent or trivalent chromates. Chromates provide a thin-film passivation
layer, but only on the surface of the zinc plating. Subsequently, during
installation or in-use, this fragile film may be damaged and lead to premature
zinc oxidation. ZnCoat offers a
solution to this problem: environmentally friendly passivation agents and
corrosion inhibitors are found throughout the film, and so the coating is far less susceptible to early
failure. Furthermore, the unique corrosion inhibitors found in ZnCoat allow for continuous release
throughout the life of the coating.
ZnCoat provides sacrificial
protection as the zinc corrodes to protect the steel substrate. The coating is
further enhanced by a self-repairing
mechanism. If a coated fastener is abraded during installation, zinc oxides and
carbonates form at a controlled rate at the damaged area, sealing the breach in
the coating, and thus restoring barrier protection. Compared to conventional zinc plating, ZnCoat consistently achieves over 240 hours of ASTM-B117 salt spray corrosion protection, as well as higher cyclical corrosion performance
and real-world outdoor weathering resistance.
ZnCoat is applied to steel parts through a non-electrolytic
dip spin coating process. In contrast, the process of zinc electroplating
produces hydrogen as a byproduct. Some of this hydrogen can be trapped beneath the plated layer and cannot escape. For hardened parts,
this can cause hydrogen embrittlement of the steel
substrate, leading to delayed fracture of the
part after installation. For this reason, high-hardness parts must be baked to
relieve the entrapped hydrogen, but this step adds cost, and does not guarantee
the part is free from embrittlement. The ZnCoat
process is intrinsically free from the risk of hydrogen embrittlement, thus
reducing a processing step for high-hardness fasteners.
For
threaded fastener applications, ZnCoat has a tight, consistent
friction coefficient (CoF). Lower CoF can be achieved with conventional wax-type topcoats, as is common
with electroplated fasteners. ZnCoat is compatible with microencapsulated, anaerobic and
nylon type thread adhesive and sealant patches. Because the dry film is thin (8-10 microns /
0.3-0.4 mils), no adjustments to thread tolerances are
necessary.
ZnCoat provides
excellent UV protection for
outdoor applications. The coating performs to greater than 2,000 hours with no change in appearance in Q-Panel ultraviolet (QUV) testing (UVB at 158
oF / 70 oC). Fluorescent
UV lamps simulate the damaging effects of sunlight. In a few days or weeks, the
QUV test
can produce damage that would
occur over months or years of outdoor exposure. ZnCoat resists fading, chalking, cracking, crazing, hazing,
blistering, gloss loss, strength loss and embrittlement.
ZnCoat is applied under
license by Curtis Metal Finishing, which took the lead in bringing ZnCoat to market. “ZnCoat
has a number of performance advantages for high strength fasteners in
comparison to zinc trivalent plating, at no
additional cost. The superior rheology of this coating allows for
consistent, uniform application – a definite must for thin films,” says Brian
Lowry, Vice President, Technical Services at Curtis Metal Finishing. “The finished product has an aesthetically pleasing,
metallic silver appearance and it retains that appearance much longer than
electroplated zinc.” Curtis provides the coating at two locations, Sterling
Heights, Michigan, and Machesney Park,
Illinois. For more information,
contact Brian Lowry at Curtis Metal Finishing at 586/939.2850, or go to www.zncoat.com.