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Surface Finishing Tutorial

#187 Powder Painting (Air Electrostatic Fluidized-bed Coating Method)

Category : Painting
June20, 2014
Although similar to the fluidized-bed coating method, this method does not immerse the paint subjects in the fluidized layer of powder paint. Rather, the electrically charged powder paint particle layer that forms on top of the fluidized layer is electrically deposited onto the subjects.

The system, as shown in [Fig.1], has a perforated plate with electrodes, and high voltage DC of 30~100kv is applied between the electrodes and the earth.

As the result, a strong electrical field is generated between the grounded paint subject and the electrodes. The air in the tank is ionized by the corona discharge from the electrodes. The powder paint particles are electrically charged, repelling each other, floating on the top section of the fluidized bed, getting absorbed onto the paint subject as the opposing pole.

The powder paint amount to be used would suffice at 50~100mm high from the perforated plate, much less compared with the fluidized-bed coating method. The powder paint of 20〜100μm granularity is used to obtain 50〜150μm thick coating layer.
image

The characteristics of this method are as follows.

1. Since preheating is not required, loss of heat energy is little.
2. Since preheating is not required, paint subject's heat capacity and heat conductivity are not of concern.
3. Requires 1/10 of the paint amount compared with the fluidized bed coating method.
4. Since the film is electrically formed, thick film such as fluidized bed method can not be obtained.

The method is applicable on steel pipe fittings, metal mesh, resistors, clasps, sprigs, and wire, etc.


Cost comparisons are shown on [Table 1]. As can be seen, the powder painting is highly economical compared with the conventional solvent based painting. Furthermore, when considering solvent pollutions on the work and general environments by the conventional painting, switching to powder painting can be considered as urgent.

[Table 1] Cost comparisons of painting methods
 Powder paint
(Polyester)
Solvent based pint
(Acrylic)
Electrostatic paint
(Acrylic)
Paint solids (%)10060100
Paint loss (%)2402
Paint film thickness(μm) 50/405030
Paint price (index)100/8024999
Number of layers (times)121
Painting cost (index)100/80220100

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