The oldest method of powder application is the Fluidised Bed process.
In this process, a preheated substrate is immersed into a fluidised powder bed. The action of heat and the powder coming into contact with the substrate results in the melting of the powder and its adherence to the substrate.
The fluidised bed is constructed as a two-compartment container with the top open for dipping substrates to be coated into the powder fluidised within the bed. The fluidised bed utilises an upper compartment for storage and fluidisation of powder; a lower compartment is provided as air space where the compressed air is regulated through a porous membrane separating the lower and upper compartment.
The thickness of a coating is determined by the temperature of the preheated substrate and the total immersion time.
Generally a coating of 150 microns – 300 microns is obtained.
The compressed air must be clean, dry and oil-free, and regulated to achieve an optimum level of fluidisation.