How is it Applied ?
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| How is it Applied ? |
The most common way of
applying the powder coating to metal objects is to spray the powder using an
electrostatic gun, or corona gun. The gun imparts a positive electric charge on
the powder, which is then sprayed at approximately at high speed towards the
grounded object by mechanical or compressed air spraying and then accelerated
toward the workpiece by the powerful electrostatic charge. A wide variety of
spray nozzles are available for use in electrostatic coating. The type of
nozzle used will depend on the shape of the workpiece to be painted and the
consistency of the paint. The object is then heated, and the powder melts into
a uniform film, and is then cooled to form a hard coating. It is also common to
heat the metal first and then spray the powder onto the hot substrate to
achieve a more uniform finish but can also create other problems, such as runs
caused by excess powder. Another type of gun is called a tribo gun, which
charges the powder by (triboelectric) friction. With a tribo gun, the powder picks
up a positive charge while rubbing along the wall of a Teflon tube inside the
barrel of the gun. These charged powder particles then adhere to the grounded
substrate. Using a tribo gun requires a different formulation of powder than a
corona. It is also possible to apply powder coatings using a dipping process.
The Powder Slurry process, combines the advantages of powder coatings and
liquid coatings by dispersing very fine powders of 1–5 micrometer particle size
into water, which then allows very smooth, low film thickness coatings to be
produced.
