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.
