The fluidized bed coating process is a simple dipping process that can be either
conventional or electrostatic. In the convention fluidized bed process, the fluidized
bed is a tank with a porous bottom plate. The plenum below the porous plate supplies
low pressure air uniformly across the plate. The rising air surrounds and suspends
the finely divided plastic powder particles, so the powder-air mixture resembles
a boiling liquid as shown in Figure 1. Products that are preheated above the melt
temperatures of the powder are dipped in the fluidized bed, where the powder melts
and fuses into a continuous coating. A high transfer efficiency results from little
drag out and no dripping.
Figure 1: Illustration of the fluidized bed process.
The fluidized bed powder coating method is used to apply heavy coats in one dip,
3 - 10 mils (75 - 250 µm), uniformly to complex shaped products. It is possible
to build a film thickness of 100 mils (2500 µm) using higher preheat temperatures
and multiple dips. An example of film build-up is presented in Figure 2.
Figure 2: Effects of preheat temperature and dipping time on the film build in coating a steel bar with epoxy resin.