Characterization of particle size evolution of the deposited layer during electrostatic powder coating processes

This experimental study investigated particle size evolution in deposited layers during typical electrostatic powder coating processes, using two powder (coarse and ultrafine) systems. Results disclosed that powder coating is a size-selective process in which the motions of in-flight particles are size-dependent. As a result, particles deposited on different regions of the substrate present some size discrepancy which accounts for a size-decreasing tendency along radial direction for both powders. In comparison with coarse powder, however, ultrafine powder can greatly alleviate the size discrepancy. Furthermore, it was also revealed that, due to the size-selective effect, locally deposited particles are with narrower size distributions than the original particles. The study still demonstrated that small particles are more prone to adhere on the substrate in coarse powder coating processes while large particles take the priority to deposit in ultrafine powder coating processes, due to different dominant factors. However, because of the intensifying back corona, the deposited particles show a size-decreasing tendency with extended spraying duration, which is commonly exhibited in both coarse and ultrafine powder coating processes. Nevertheless, in this study it was also found that charging voltage plays a limited influence on the size evolution.