234
Fundamentals of Corrosion
Fluidized bed powder coating has the advantage of producing a uniform
and reproducible film thickness. It also has the advantage of producing a
heavy coating in one dip. The disadvantage of this method is the 3-mil minimum film thickness required to form a continuous coating.
An electrostatic fluidized-bed coater is essentially a fluidized bed with a
high-voltage DC grid installed above the porous plate to charge the finely
divided particles. The charged particles repel the grid and each other, forming a cloud. These particles are attracted to and coat products that are at
ground potential. Film thicknesses of 1.5 to 5 mil are possible on cold parts
and 20 to 25 mil are possible on heated parts.
The advantage of this method is that small parts such as electrical components can be coated uniformly and quickly. The disadvantage is that the
product size is limited and inside corners have low film thickness.
Electrostatic spray coating is a method for applying finely divided, electrostatically charged particles to products that are at ground potential. A
powder/air mixture from a small fluidized bed in a powder reservoir is
supplied by hose to a spray gun that has a charged electrode in the nozzle
fed by a high-voltage DC power pack. The spray guns can be manual or
automatic and mounted in a conveyorized spray booth. Film thicknesses
of 1.5 to 5 mil can be obtained on cold substrates. A 20- to 25-mil thickness
can be obtained on heated substrates. The advantage of this method is that
coatings using many resin types can be achieved in thicknesses of 1.5 to 3
mil, with no VOC emissions. Disadvantages include the difficulty in obtaining a continuous coating of less than 1 mil; and because of complex powder
reclaiming systems, color changes are more difficult to make than with liquid spray systems.
7.7.1.6 Electrodeposition of Polymers
The electrodeposition of polymers is an extension of painting techniques
into the field of plating and, like plating, is a dip coating process. In the case
of ionizable polymers, the deposition reaction is:
R NH OH
IF R N H O
3
3
+
−
+ →
+ 2
or the conversion of water-dispersed ammonium-type ions into ammoniatype, water-insoluble polymers known as cathodic deposition. Alternatively,
a large number of installations utilize the anodic deposition process:
RCOOH H less IF RCOOH
+
+
→
Fundamentals of Corrosion
Fluidized bed powder coating has the advantage of producing a uniform
and reproducible film thickness. It also has the advantage of producing a
heavy coating in one dip. The disadvantage of this method is the 3-mil minimum film thickness required to form a continuous coating.
An electrostatic fluidized-bed coater is essentially a fluidized bed with a
high-voltage DC grid installed above the porous plate to charge the finely
divided particles. The charged particles repel the grid and each other, forming a cloud. These particles are attracted to and coat products that are at
ground potential. Film thicknesses of 1.5 to 5 mil are possible on cold parts
and 20 to 25 mil are possible on heated parts.
The advantage of this method is that small parts such as electrical components can be coated uniformly and quickly. The disadvantage is that the
product size is limited and inside corners have low film thickness.
Electrostatic spray coating is a method for applying finely divided, electrostatically charged particles to products that are at ground potential. A
powder/air mixture from a small fluidized bed in a powder reservoir is
supplied by hose to a spray gun that has a charged electrode in the nozzle
fed by a high-voltage DC power pack. The spray guns can be manual or
automatic and mounted in a conveyorized spray booth. Film thicknesses
of 1.5 to 5 mil can be obtained on cold substrates. A 20- to 25-mil thickness
can be obtained on heated substrates. The advantage of this method is that
coatings using many resin types can be achieved in thicknesses of 1.5 to 3
mil, with no VOC emissions. Disadvantages include the difficulty in obtaining a continuous coating of less than 1 mil; and because of complex powder
reclaiming systems, color changes are more difficult to make than with liquid spray systems.
7.7.1.6 Electrodeposition of Polymers
The electrodeposition of polymers is an extension of painting techniques
into the field of plating and, like plating, is a dip coating process. In the case
of ionizable polymers, the deposition reaction is:
R NH OH
IF R N H O
3
3
+
−
+ →
+ 2
or the conversion of water-dispersed ammonium-type ions into ammoniatype, water-insoluble polymers known as cathodic deposition. Alternatively,
a large number of installations utilize the anodic deposition process:
RCOOH H less IF RCOOH
+
+
→