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Surface Finishing Tutorial

#186 Powder Painting (Fluidized Bed Coating Method)

Category : Painting
June 6, 2014
Fluidized Bed Coating Method is also known as fluid bed method. As shown in [Fig.1], powder paint is put in a fluidized tank with a perforated bottom plate. and compressed air or inert gas is pressure fed. The powder paint whirls up through the perforated plate and the tank is fluidized.

When a paint subject preheated to temperature above the melting temperature of the powder paint is immersed, the melted (or semi-melted) paint forms a film on the subject's surface. The paint subject then is heated afterward to be finished as needed.

The perforated plate is made of ceramic, expanded form resin, sintered metal, filter cloth, and etc. with uniform sized perforations of 10〜60μm based on required particle size for the paint to be used.

The factors for the fluidized bed coating method are said to be [1] preheating temperature of the paint subject, [2] immersion duration, [3] shape and heat capacity of the paint subject, [4] particle size (80〜150μm) and melting point. The factor that determines the coating film thickness is the immersion time duration, and is typically 5~20 seconds.
[Table 1]

Examples of process conditions are shown in [Table 1].

[Table 1] Fluidized Bed Coating process condition examples
Powder paint resinPreheating Temp. (℃)PrimerPost heating Temp. (℃)Post heating time (Minutes)
Epoxy resin120〜230None120〜2305〜60
Vinyl resin230〜290Yes200〜3201〜3
C.A.B.260〜320Yes200〜2901〜3
Nylon340〜430Yes340〜3701
Polyethylene260〜320None200〜3201〜5
Polypropylene260〜370None200〜3201〜3
Teflon430〜540None430〜4801〜3

The characteristics of this method are as follows.

1. It is possible to obtain 250〜1500μm thick film in 1 coat.
2. Less paint losses.
3. Spray booth and recovery device are not needed.
4. Simple and economical system device.
5. Preheating is required.
6. Limitations on paint subject sizes and shapes.
7. A certain amount of paint is needed even for a small job.

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