powder coating uses a powder-air mixture from a small fluidized bed in a powder
feed hopper. In some cases, the feed hoppers vibrate to help prevent clogging or
clumping of powders prior to entry into the transport lines. The powder is supplied
by a hose to the spray gun, which has a charged electrode in the nozzle fed by a
high voltage dc power.
Electrostatic powder spray guns direct the flow of powder; control the deposition
rate; control the pattern size, shape, and density of the spray; and charge the
powder being sprayed .The spray guns can be manual (hand-held) or automatic, fixed
or reciprocating, and mounted on one or both sides of a conveyorized spray booth.
Electrostatic spray powder coating operations use collectors to reclaim over-spray.
This reclaimed powder is then reused, adding significantly to the powder coating's
high transfer efficiency.
There are various gun designs that mainly differ in the method of applying electrostatic
charge to the powder. In some cases, the powder is electrostatically charged by
friction. The advantage is that the powder is free to deposit in an even layer over
the entire surface of the part, and deposition into recesses is improved.
The film thickness is dependent on the powder chemistry, preheat temperature, and
dwell time. Film thicknesses of 1.5 - 5.0 mils (37.5 - 125 µm) can generally
be applied on cold products. If the products are preheated slightly, 20 - 25 mils
(500 - 625 µm) coatings can easily be applied in a single coat.