Fluid Bed Powder Coating Application Process
Fluid bed powder coating consists of immersing a hot part into a bed of powder, allowing the powder to melt on the part and build a film, and subsequently providing enough time and heat for this film to flow into a continuous coating.
The part should be immersed in the fluidized bed as quickly as possible after removing it from the preheat oven to keep heat loss at a minimum. A time cycle should be established to keep this time interval constant. While in the powder, the part should be kept in motion to keep powder moving over the hot part. The motion for a particular part depends on its configuration.
Improper or inadequate motion can be the cause of several problems:pinholes, especially on the underside of flat horizontal surfaces and at wire intersections; “orange peel” appearance; and inadequate coverage of corners\or crevices. Improper motion also can lead to nonuniform coating thickness, such as an oval coating on round wires. Normal immersion time in a fluidized powder is three to 20 seconds.
Excess powder must be removed immediately after coating to prevent excessive buildup.This can be done with a blast of air from a regulated air jet, tapping or vibrating the part, or tilting it to dump off the excess. If the excess powder is not contaminated with other powder or dirt, it can be reused. If the part has sufficient residual heat, the coating may flow out to acceptable levels without post heating. On thinner parts, or heat sensitive parts, a post heat may be required.