The science and technology of electrostatic powder spraying, transport andcoating

The electrostatic powder coating process is reviewed. Three basic regions o f a powder coating system are considered. The charged powder source region embraces corona and triboelectric guns. These are reviewed and particle cha rging processes considered. The second region where charged powder transpor t to the workpiece occurs is one in which aerodynamic, space charge, and gr avitational forces act to determine particle trajectories. With corona sour ces ions generally outnumber charged particles by 10 to 1 so that the space charge due to charged particles is negligible compared to that of ions. Ch arged particle deposition onto the workpiece, the third region, is affected by the electric held of particles already deposited. Back ionisation may o ccur if ions are present and lead to poor coating finish. The adhesion of c harged particles to a workpiece is often greater than expected by considera tion of image forces alone. (C) 1998 Elsevier Science B.V. All rights reser ved.