Page 28 - CFCM Sept-Oct-2020_Neat

ZINC PLATING

chromate or passivate which runs the trivalent chromium coatings is to the zinc plating. Corrosion resistance
range of color from blue bright or “Chromite”, the term chromate has is good with the new generations of
clear, to iridescent, yellow, bronze, been around so long people use it chromates, typically reaching 48 to 120
olive drab, and black. Most chromates interchangeably and simply refer to hours neutral salt spray to white corro-
today are trivalent (+3) due to the tox- the coating as “Trivalent Chromate”. sion. Yellow trivalent chromates
icity of hexavalent chromium (+6). The chromate is a conversion coat- perform equally well, however, unlike
Though the correct technical term for ing on top of the zinc that is sacrificial their hexavalent predecessors, trivalent
yellows are made yellow with a dye.
These dyed systems usually result in
Regulations have changed very poor adhesion for subsequent
processes such as paints, powder coats,
in Surface Tension Measurements adhesives, and other coatings.
Thick film or high-performance
chromates can exceed 240 hours to
white corrosion. Hexavalent chromates
are still available but capacity is limited
Fast and Precise - the Kibron as most platers do not use or offer
AquaPi+ Tensionmeter. hexavalent chromate options for zinc
due to environmental and heath
regulations coupled with mandates
such as RoHS and ELV Directives.
The appearance of red rust is a func-
tion of the zinc thickness once white
corrosion occurs.
Zinc plated and chromated parts
may also have topcoat seal applied.
These seals, which are normally either
silicate-based organic topcoats or lac-
quers, have two primary functions.
They offer added corrosion resistance
to the chromate and zinc system by
providing a barrier to the chromate
and, depending on the formulation,
some protection to bare surfaces such
as deep holes and tube IDs.
The other benefit these seals can
provide is modification of torque ten-
Chromium Electroplating sion properties to provide a consistent
coefficient of friction. This is important
Chromium Anodizing in robotic/automated assembly where
Reverse Etching torque tension and torque retention
can be critical properties in safety.
Substrate preparation is the most
QAS INTERNATIONAL
ISO 9001:2015 critical factor in achieving a top-notch
REGISTERED COMPANY
Certificate No. CAN1641
finish and maximum corrosion resist-
Distributed Exclusively in Canada by Dynamix Inc. ance. Certain parts may require addi-
tional pretreatment outside the normal
91 Esna Park Drive, Unit #7 process. If parts are heavily covered
Markham, Ontario L3R 2S2 in excess machining coolant or stamp-
Phone: (905) 477-0900 ing oils, a degreasing operation is
usually needed to remove the excess
www.dynamix-inc.com oils and to avoid contamination of
the plating line baths. This can be
done online or offline depending on

28 CAnADIAn FInISHInG & COATInGS MAnuFACTuRInG SEPTEMbER/OCTObER 2020