PROFESSIONAL COATINGS LIMITED

Powder coating is by far the youngest of the surface finishing techniques in common use today.

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 electrostatic-ally charged, or The powdered paint is electro-statically 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 re-melt when heated, and Thermosetting powders that will not re-melt 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.

How is it done -- electrostatic spray?

The powder is applied with an electrostatic spray gun to a part that is at earth (or ground) potential.

Before the powder is sent to the gun it is fluidised:

to separate the individual grains of powder and so improve the electrostatic charge that can be applied to the powder and so that the powder flows more easily to the gun. Because the powder particles are electrostatic-ally charged, the powder wraps around to the back of the part as it passes by towards the air
off take system. By collecting the powder, which passes by the job, and filtering it, the efficiency of the process can be increased to 95% material usage.

The powder will remain attached to the part as long as some of the electrostatic charge remains on the powder. To obtain the final solid, tough, abrasion resistant coating the powder coated items are placed in
an oven and heated to temperatures that range from 160 to 210 degrees C (depending on the powder).
 

Under the influence of heat a thermosetting powder goes through 4 stages to full cure.

MELT, FLOW, GEL, CURE

The final coating is continuous and will vary from high gloss to flat matt depending on the design of the powder by the supplier.

How is colour introduced?

Colour is added to powder coatings during the manufacturing process, i.e. before the powder reaches the powder coater. There is little that can be done to change the colour consistently, once the powder leaves the manufacturing plant.

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 standard, Thermo-set 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.

Installations and maintenance

During installations, the powder coating should be protected from damage due to abrasion and materials of construction such as mortar and brick cleaning chemicals.

Once installed, maintaining the initial appearance of a powder coating is a simple matter. The soot and grime which builds up on surfaces from time to time contains moisture and salts which will adversely affect the
powder coating and must be removed. Powder coatings should be washed down regularly (at least once each 6 months in less severe applications and more often in marine and industrial environments). The coating should be washed down with soapy water -- use a neutral detergent -- and rinsed off with clean water.

When powder coated items are installed without damage to the powder coating and they are maintained regularly, they should be relatively permanent. The correctly applied coating, although not metallurgic ally
bonded to the metal will not crack, chip or peel as with conventional paint films.