What is Powder Coating
Back to Painting Services
- Click Here
What is powder coating, why should
I consider using it, and how will it work in my
operation are questions that every finisher needs to be
asking today. Briefly, these questions can be answered
as follows:
1) powder is a dry, clean finish that gives a highly
durable coating,
2) in the long run, powder will save you money, and
3) a powder coating system can be designed to meet just
about any requirement your operation may have.
The purpose of this page is to explain quickly and
simply how powder coating delivers these highly
desirable solutions to many finishing problems, and to
provide you with a practical, worksheet approach, to
help you decide if moving to powder is the right move
for you.
Over the past decade powder coating has been
increasingly accepted as the preferred finishing process
for the future. The reasons for this conversion from wet
to dry can be attributed to three major forces: economy
— the high cost of energy and materials require a more
cost effective and less wasteful process; excellence —
consumers, and other end users, are demanding higher
quality and more durable finishes; and ecology —
progressively more stringent regulations are being
aggressively enforced in an effort to control air
pollution and hazardous waste disposal. Which in turn
goes back to economy. The cost of complying with the
Regulations and the disposal of toxic and flammable
waste are constantly rising.
Many companies have found that it is less expensive to
convert to powder than to bring their wet systems into
compliance!
With strong financial arguments providing the necessary
stimulus, therefore, powder coating technology has
evolved quickly. The quality and variety of powders
available have grown as an increasing number of
companies get involved with its production; and the
technology for spraying the powder, collecting it and
reusing it, is constantly improving transfer
efficiencies and material utilization, and reducing
color change times. Early perceptions that powder was
too difficult to control, too costly to install, too
time consuming for color change, or did not provide
enough choice of color are largely obsolete today.
But the move to a totally new technology can still be
confusing. This page is designed to make your decision
easier, providing both explanations and justifications
to help determine the right solution for you. So let's
start at the beginning and work through the questions.
What is Powder Coating?
Powder is a dry coating. Instead
of being dissolved or suspended in a liquid medium, such
as solvent or water, powder is applied in a granular
form. This material is finer than ground pepper but
coarser than flour, and is applied directly to the
surface to be coated.
The powder is created by blending the various components
(binders, resins, pigments, fillers and additives) and
processing them through an extruder into a continuous
mass. This homo-genous mass is cooled and broken into
small chips, which are then ground into the powder. Each
powder particle contains within it the necessary
components for reforming into the finished coating.
After the powder is applied to the part, typically using
an electrostatic spray process, the part passes through
an oven and cures, melting into a smooth film on the
surface of the part.
Powder
Formulation
There are two distinct types of
powder, Thermoset and Thermoplastic. The Thermoset
powders are reactive, which means that under cure
conditions there is a chemical "crosslinking", so that,
once cured, the coating will not remelt. Epoxies,
acrylics and most hybrids are examples of Thermoset
powders, making up over 90% of the current powder
market.
Thermoplastic powders do not "crosslink" when cured, but
simply melt and flow over the surface of the part. The
film hardens on cooling, but if it is reheated it will
remelt. Vinyls, nylons and fluorocarbons are examples of
thermoplastic powders.
Enamel powder is a specialized formulation used in
applications that previously used liquid porcelain
enamel. It utilizes glass in its formulation and is
cured, or fired, at a very high heat. The result is a
finish that is particularly resistant to heat,
scratching and harsh chemicals, and is typically used in
appliances, such as washers, dryers, ovens and ranges.
How is the Powder Applied?
The application process involves
applying a charge to the dry powder particles and
spraying them onto a grounded substrate. The substrate,
or part, is typically grounded through the conveyor or
hanger holding the part. The powder, once attracted to
the part, is then held on the surface until it is melted
and cured into a smooth coating film in the bake oven.
The spray process takes place inside a booth designed to
contain the oversprayed powder and makes it possible to
collect the overspray and ultimately reclaim it for
reuse.
The powder is fed pneumatically out of the powder
container, or hopper, into the powder applicator, or
gun. As the powder exits the gun, a low amperage, high
voltage charge is applied to the powder particles,
causing them to be attracted to the grounded workpiece.
This attraction may even cause the powder to "wrap"
around the piece, coating the back side.
The oversprayed powder, suspended in the air contained
inside the powder booth, is then passed through a
separation process that permits the powder particles to
be retrieved from the air. The clean air is fed back to
the work environment, eliminating the need for air
make-up. The reclaimed powder is mixed with a
proportionate amount of fresh, virgin powder for reuse
achieving consistent results and up to 98% material
utilization.
Now that we have covered the basics you should have a
better idea of what powder coating is all about.
|