manufacturers still have reservations about applying a water-based product directly to metal. High-solids are liquid coatings that have a solids content
of at least 65 percent, which means minimal solvents are present. But fewer solvents also means
that the coating is more viscous. ;at has led to the
development of multipart application systems (
referred to as 2K systems if two parts are mixed, 3K if
three parts are mixed, etc.) that are formulated to
be mixed only seconds before application.
All finishers that apply liquid coatings spray to
waste. ;e overspray can’t be reclaimed. If filters
are used to capture the overspray, the finisher has
to dispose of the filters according to regulations established by local authorities.
Powder. ;e powder booth does not require an
exhaust. As stated previously, if any VOCs are emitted during the powder coating process, they are
typically very low.
Powder coatings can be recycled with the right
reclamation equipment. Companies looking for
Class A finishes have reclamation systems that depend on thorough cleaning and maintenance because any cross-contamination of reclaimed material ruins the original material’s ability to deliver a
Again, disposal of unreclaimed powder coating
material is governed by local regulations. In some
instances, local law may require disposal in sealed
containers or require that the powder coating material be baked into the form of a brick for disposal
in a local landfill.
What Are the Characteristics
of the Final Coating?
Liquid. When someone talks about a Class A finish, typically used to define the coating quality on a
new automobile, most people think of liquid coatings. Specialty finishes, such as
those incorporating metallic
flakes, also are possible in liquid
Durability has improved over
the years as well, especially with
the emergence of 2K coatings.
;ese are typically used on
large metal parts that can’t be
powder-coated because they
can’t fit into a typical booth
and oven setup.
Liquid coating finishes can be
applied in various thicknesses.
Obviously, the more mils applied, the better the protection.
In many instances, a manufacturer, such as an automaker,
will seek to balance maximum
protection with the minimum
amount of paint mil thickness.
Powder. Powder coatings
o;er the same characteristics
that come with liquid coatings.
Properly cured powder coat-
ings can o;er superior protec-
tion against chipping, scratching, UV rays, and cor-
rosive elements. ;is is why powder coatings are
often specified to coat metal products destined for
Material development has progressed to the
point where powder coatings can deliver a Class
A finish. In fact, a major European automaker and
a U.S. motorcycle manufacturer are using powder
coatings for their clear coating. However, many
manufacturers, including automakers, still prefer
liquid coatings for that topnotch finish.
Standard powder coating finishes are applied in
the thickness range of 2 to 4 mils. Specialty finishes
like a hammertone or a texture are usually 3 to 5
mils thick. Functional coatings can be 10 to 40 mils
What Type of Cleaning Is Necessary
Before Parts Are Coated?
Liquid. A lot of fabricators simply wipe the part
clean with a rag soaked in solvent. Others rely on
a wash of some kind with pretreatment chemicals.
Solvent helps to prepare the metal surface because it has aggressive cleaning action and actually
prepares the surface for adhering to the paint. New
coatings that have less solvent content may require
much more formalized pretreatment processes to
achieve a quality finish.
Powder. Pretreatment is critical when it comes
to powder coating. If a powder coating is going to
last, the part needs to be thoroughly cleaned.
Pretreatment can range from a simple abrasive
media blasting chamber to a multistage pretreat-
ment system with several chemical application
and rinse stations and an oven. (Parts have to be
dried and cooled before any application of powder
takes place.) Some of the pretreatment chemicals,
such as zinc phosphate, have to be treated before
disposal, but newer, environmentally friendly pre-
treatment chemicals have emerged in recent years
to ease the disposal hassles. ;e Environmental
Protection Agency, however, likely will seek chang-
es in the near future that will call for treatment of
all wastewater prior to discharge.
What Are the Basic
Liquid. Booths or stations used in liquid coating are
typically made of metal. Whether in a manual or
an automated setup, the paint is often sprayed to
Fumes are exhausted outside during the painting process to keep the work environment in and
around the paint booth free from the strong odors.
Powder. In some instances, particularly if batch
finishing is occurring, a shop might use the same
booth for both liquid and powder coating. But fabricators need to keep in mind that if they choose
to powder coat in a liquid application booth and
exhaust overspray outside the building, employees
could be walking out to cars with all new finishes
at the end of the shift on a very hot day—
depending on where that powder overspray landed. For
the most part, however, filters and correct powder
coating technique should prevent most powder
overspray from going outside.
If a company is doing any kind of high-volume
powder coating, it should consider a reclamation
system. Single-color reclamation systems are car-tridge-based and typically made of stainless steel.
Multicolor systems, which are designed for fast
color changeout, are plastic, making them easier to
clean. Sophisticated fan setups keep the overspray
in the booth, and the polymer-based interior walls
prevent the powder from adhering to them. ;e
overspray is collected and recycled for another application.
2013_07 Ad Fabricator Trilogy Schwarze-Robitec Oct and Nov 7x4, 875.indd 1 07.08.2013 09:46: 10