ELECTROSTATIC COATING

Electrostatic spray 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.