How Are Powder Coatings Applied?
The two most common methods of applying powder coatings are spraying and dipping.
Powder coatings are ideally suited to high efficiency, fully automated application lines. The powder coating process is equally adaptable to applications requiring flexible manual operations.
The electrostatic spray method is used to apply thin (25-125 microns) powder films. In some cases heavier (150-375 microns) films can also be applied. Powder coatings are typically fed as a powder/air mixture from a feed hopper to the spray gun, which imparts an electrostatic charge on each powder particle by the application of a high voltage. The charged powder particles are attracted to the earthed workpiece to be coated and are deposited onto any conductive object within the spray area. However, some of the particles do not deposit on the workpiece and it is here that a major benefit of the powder coating process is identified. The so called overspray particles are recovered to the feed hopper for re-use, which can result in recovery efficiencies of up to 99%.
The coated workpiece is then conveyed to the curing oven. Being solvent free this eliminates the need for solvent flash off zones, environmental control equipment or other abatement costs associated with traditional liquid paints. Arising from this are lower fire insurance premiums, and a safer work environment.
Another method of charging in some spray gun designs is Tribo Charging. Tribo Charging does not use high voltage, but instead uses the principal of high velocity friction to give the powder particles a static charge.
Powder coatings can also be applied by dipping into a fluidised bed of powder, made to flow like a liquid by bubbling air through it. A bed of powder is fluidised by blowing air from below through a porous plate. The object to be painted is pre-heated to, typically 70-2000C, and immersed in the bed. depending on the heat sink, the object may require post-heating to effect the curing of the film.
This method is often