Electrostatic fluidized bed deposition of a high performance polymeric powder on metallic substrates

The electrostatic fluidized bed deposition of a single-layer PPA 571 coating onto low carbon steel rods is reported. A full factorial experimental design was developed in order to study the influence of several operative variables on the effectiveness of the coating process and on the coating thickness and uniformity. The operative variables included exposure time, air flow, the applied voltage, attitude, and the radial and vertical location of the work-piece in the fluid bed. After the experimentation, several process maps were developed as a support to identify the best way to lead the coating process. Finally, by using a statistical approach, the reliability and repeatability of the coating process was also established. Experimental trends were consistent with theoretical expectation. A significant growth in achievable coating thickness was obtained by increasing voltage and air flow. Furthermore, at higher values of exposure time and applied voltage, relevant back ionization phenomena occurred, which simultaneously caused a top limit in coating thickness and a worsening of surface finishing. Process characteristics, leading mechanisms, and some practical aspects are also discussed in detail. (c) 2005 Elsevier B.V. All rights reserved.