Canadian Finishing & Coatings Manufacturing - July/August '24 - 14

INDUSTRIAL FINISHING: SURFACE PREPARATION
ESSENTIAL
PREP STEPS
BY MARK FREELS
S
urface preparation is a primary part of the coating
application process. Before metal products can be
powder coated or sprayed with liquid paint, the
part surface should be cleaned and prepped for the
specific coating application. Proper surface preparation is
essential to ensuring powder or paint adheres properly to
products. It also lays the groundwork for consistent, quality
finishes and prevents corrosion from forming on products.
Which method of surface preparation is required depends on
the condition of the substrate and performance requirements
of your coating-including appearance, durability, adhesion
and corrosion resistance. By understanding what is needed to
pretreat your product, you can ensure optimal results.
Surface preparation requirements for metal parts range
from simple to complex. Manufacturers typically work with
coating suppliers, who recommend appropriate surface
preparation prior to coating application. There is a range of
surface preparation processes for parts:
* Simple: The surface of the parts is already prepped/ primed.
Parts require minimal prep-manual blow off, wipe off or
power cleaning-to remove road grime, dust or oils.
* Advanced: Parts that are low-volume production
(batch order) require minimal adhesion and corrosion
specifications. Some manual surface preparation is still
required, with options including a chemical wipe, sand/
grind/wire brushing, light blasting and spraying with a
cleaner and/or pretreatment/conversion.
* Complex:
Manufacture of
high-production
parts
with high-performance coating specifications.
Typical automated processes include surface
blasting and surface pretreatment/conversion.
Commonly used pretreatment methods and
recommended environments
Spraying Methods
When metal products are manufactured or transported,
they are often covered in grease, oils or dirt. For powder or
paint to adhere to a product, it must be washed to remove the
contaminants. Otherwise, a majority of powder or paint that
is sprayed will not adhere to the product. Even if powder or
paint does adhere, the finish quality will be less than ideal.
Washing and cleaning requires soaps or specialty
chemicals, such as alkaline, solvent and acidic cleaners.
Steam cleaning or hot water helps break down the soils and
can reach difficult spots or gaps in the surface. Detergent is
usually used to clean metal containing oils, waxes, polishing
compounds or other substances that prevent the coating from
sticking to the metal.
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For part surfaces (substrates) that require increased
performance beyond what cleaning the surface can provide,
chemical processes improve coating adhesion and corrosion
protection performance. Phosphate and non-phosphate
chemical processes provide a seal between porous paint and
the metal surface, greatly increasing corrosion protection.
The most common chemical pre- treatment applications
include:
Iron Phosphate: Used on steel and aluminum
Zinc Phosphate: Used on steel and aluminum; typical in
higher salt spray protection
Zirconium: New phosphate-free chemistry with equivalent
salt spray of iron phosphate but no heat required
Manual wash processes require an open face or enclosed
booth with a drain in the floor (known as wash booths),
depending on pressures and the chemicals to be contained.
Parts
are
sprayed
(liquid
blasted)
with
cleaning and
rinsing solutions, then dried with ambient air or in an oven
before coating application. Low-temperature ovens with
recirculating air movement typically range from 43 to 82
degrees Celcius to rapidly dry the parts.
An alternative to manual washing, continuous throughput
automatic pretreatment washers are widely used for highproduction
throughput for precise surface preparation.
Pretreatment washers automatically clean the part, apply
the surface preparation and rinse/seal the part, which is then
conveyed through a multi-stage spray washer-ranging from
three to eight stages-to be dried and coated.
Methods and equipment to
prepare parts for coatings
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Canadian Finishing & Coatings Manufacturing - July/August '24

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