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What is powder coating?
Powder coating is by far the youngest of the surface finishing techniques in common use today. It was first used in Australia about 1967.
Powder coating is the technique of applying dry paint to a part. The final cured coating is the same as a 2-pack wet paint. In normal wet painting such as house paints, the solids are in suspension in a liquid carrier, which must evaporate before the solid paint coating is produced.
In powder coating, the powdered paint may be applied by either of two techniques.
The item is lowered into a fluidised bed of the powder, which may or may not be electrostatically charged, or
The powdered paint is electrostatically charged and sprayed onto the part.
The part is then placed in an oven and the powder particles melt and coalesce to form a continuous film.
There are two main types of powder available to the surface finisher:
Thermoplastic powders that will remelt when heated, and
Thermosetting powders that will not remelt upon reheating. During the curing process (in the oven) a chemical cross-linking reaction is triggered at the curing temperature and it is this chemical reaction which gives the powder coating many of its desirable properties.
Why powder coat?
Powder coating produces a high specification coating which is relatively hard, abrasion resistant (depending on the specification) and tough. Thin powder coatings can be bent but this is not recommended for exterior applications.
The choice of colours and finishes is almost limitless, if you have the time and money to have the powder produced by the powder manufacturer.
Powder coatings can be applied over a wide range of thickness. The new Australian Standard, "AS/NZS 4506 - Thermoset powder coatings", will recommend 25 micron minimum for mild interior applications and up to 60 micron minimum for exterior applications. Care must be exercised when quoting minimum thickness because some powder will not give "coverage" below 60 or even 80 micron. "Coverage" is the ability to cover the colour of the metal with the powder. Some of the white colours require about 75 micron to give full "coverage". One of the orange colours must be applied at 80 micron.
Colour matching is quite acceptable batch to batch.
-Mario S. Pennisi
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