Electric field analysis of the tribocharged fluidized bed powder coating process

Electrostatic powder coating in fluidized beds is a technique that has been known for more than 30 years. These systems are predominantly used for coating of wire-shaped objects and rely on corona charging of the powder. Experimental studies carried out in a tribocharged system have shown that the intersection points of a wire geometry rack are susceptible to insufficient coating. This paper attempts to explain why the intersection points may present coating difficulties. An analysis of the electric fields produced around a wire object immersed in a fluidized bed of charged powder is carried out using commercially available finite-element software. The finite-element results show that the intersection points suffer from Faraday-cage effects. However, if the powder is sufficiently charged, then, as powder deposits on the substrate in areas where the electric field is strong, the electric field is enhanced in the original weaker areas, thus promoting powder deposition toward the intersections. If a powder is insufficiently charged, no enhancement of the electric field occurs.