Transcript Powder Coating

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Powder Coating
One of the most
common methods
of finishing metal
surfaces.
Many items used
everyday are
powder coated.
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Examples of Powder Coating
Everyday items such
as mailboxes, chairs,
appliances,
automotive parts,
tools, and
construction materials.
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Topics
We will examine..
–how the process works
–the benefits
–what major equipment it involves
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The Process
A simple process, involving “spray painting”
a fine plastic powder paint onto a metal
surface.
Typically the surface is steel, aluminum or
iron.
Most any surfaces can be coated, however,
they must be able to withstand the high
temperatures of the baking oven.
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Before coating the part, the surface must be
cleaned. Often a sand blaster is used for
this purpose. Parts must be totally free of
contaminants that might effect the process
such as grease, rust, oils, etc.
As the powder leaves the gun it is charged
with static electricity. This charge then
attracts the powder to the surface that is
being coated.
After the parts are coated, they are then
baked in an oven at about 400 degrees
Fahrenheit for 10 to 45 minutes depending
on the part. The actual part itself must reach
these temperatures in order for curing to
occur properly.
While in the oven, the powder melts and
flows into a smooth finish. Curing time is
critical, because under curing will cause loss
of adhesion, and over curing will cause the
strength characteristics of the powder to
decrease.
Walk in oven
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Unlike painting, there are no runs or drips with
powder coating, and due to the static charge,
there is no need for primers.
Additional clear coating and primers can be
added to improve protection and depth.
If a mistake is made before baking, the powder
can simply be blown off with an air nozzle and
reapplied. If the mistake is realized after baking,
the part must be sandblasted or the coating
must be burned off.
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Types of Powders
There are two main
types of powders
used for different
applications.
Both types outperform
most wet paint
finishes and they both
come in many
varieties of colors,
textures, and glosses.
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Most indoor powders
are made of epoxy.
Epoxy is the most
durable powder, but it
will chalk and dull from
the sun’s ultraviolet
rays.
Polyester powders are not as durable, but
since they are unaffected by the sun, they
should be used for most outdoor
applications.
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Equipment Used
Obviously the most important and expensive
item to purchase is the oven.
The oven must be able to heat a part to around
400 degrees Fahrenheit for at least 10 minutes,
sometimes more depending on the part.
The size of the oven depends on the sizes of
parts the consumer wishes to coat. Obviously
the larger the oven, the larger the part that can
be coated.
With a larger oven, several parts can be baked
at one time.
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Ovens vary in style
and price.
– A small 6’x 8’x 10’
walk in gas oven is
priced around
$30,000.
– A 100’ oven with a
pass through
conveyer can be as
much as $100,000.
Small walk in oven
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There are three main types of ovens;
gas, electric, and infrared. Infrared
ovens work well if designed properly,
however gas and electric tend to be
more dependable. Electric ovens
take longer to heat up, thus delaying
the coating process. Obviously, the
faster the oven heats, the faster the
product will be coated.
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Spray Guns
There are two types of spray guns, a
Corona and a Tribo spray gun.
Most Corona spray guns charge the
powder negatively, meaning an electron is
added to the powder by a high voltage
power device to induce a negative charge.
When the powder is negatively charged
with excessive electrons, it is attracted to a
surface with fewer electrons.
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The other type of gun is the Tribo
powder gun.
In a Tribo gun, as the powder goes
through a Teflon lined gun barrel and
rubs against the lining, an electron is
transferred from the powder to the
lining. This creates a positive charge
in the powder. When a powder has a
positive charge and a deficiency in
electrons it will be attracted to a
surface with more electrons.
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Other equipment needed:
the powder supplies
an air operated vacuum cleaner to
retrieve any overspray
a spray booth.
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Drawbacks to powder coating
The major drawback is the initial investment to
begin the operation.
Powder coating does not have the strength or
hardness characteristics that some other coating
processes such as chrome or zinc have.
Chipping is another main problem with powder
coating. This often results because the part was
not baked long enough or kept at the proper
cure temperature.
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Benefits of Powder Coating
The biggest benefit of powder coating is
that it is environmentally friendly.
– There are no solvents as in paints, and thus
no harmful air pollution. There is absolutely
no hazardous waste created with this process.
Economic
– Overspray can be air vacuumed and reused,
thus reducing the amount of waste produced
as well as saving cost.
Analysis
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As can be seen for certain applications,
powder coating is the most durable
decorative finish available at this time.
A variety of different textures, colors,
and glosses can be used.
The process is fairly simple and the
cost is much less than other processes
like chroming or zinc plating.
Also the initial investment is minimal
compared to other processes.
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Conclusion
With all the benefits of powder
coating, it can be seen why it is such
a widely applied technique. Obviously,
if a person has the resources and
demand for the procedure, they
should think seriously about investing
in the operation.
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