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Powder Coating Process and Standards

We at Rainbow adhere to the latest industry standards “BS EN 12206-1:2004- ‘Paints and varnishes - Coating of aluminium and aluminium alloys for architectural purposes’ ” for our pretreatment and testing methods in powder coating.
This replaces the earlier British Standard BS 6496:1984.
The 2004 BS EN standard covers primarily the pre-treatment process and the testing of suitable test samples which accompany the material throughout the process.


Items for powder coating are stored in a solvent and contaminant free environment away from the treatment area.


Aluminium supplied direct from the extrusion process is often contaminated with oil and other residues which will effect the longevity of the final coating. Unfinished aluminium supplied from stock will have traces of natural oxidisation on the surface. It is vital therefore that the pretreatment is correctly carried out to a very high standard.
The vast majority of powder coat failures can be put down to poor or inconsistent pre-treatment methods.

Our Pre-treatment offers two main benefits:

  • Offers an air and watertight ‘seal’ to the aluminium
  • Offers a good ‘key’ surface for the powder to adhere to

The basic procedure carried out in our plant is as follows

  1. Clean with a caustic agent
  2. Water Rinse
  3. Etch
  4. Water Rinse
  5. Water Rinse
  6. Chromate Conversion
  7. Water Rinse
  8. Water Rinse
  9. Dry

At all times during the process the concentration of chemicals used in the baths are strictly monitored according to international standards.


After treatment, the substrate items are transferred onto an automatic linear conveyor which passes the items through two powder coating booths equipped with state of the art GEMA Optiflex 2 guns on either sides.


The linear conveyor passes the items through a fuel powered oven using twin Baltur burners and an advanced heat exchange system maintaining a steady temperature cycle throughout the oven of 230- 240 degrees centigrade.

Post Coating Test Results

Gloss ENISO2813 Gloss cat.1( MATT) :0–30+/‐ 5units Gloss cat.2
(SEMI GLOSS) :31 ‐70+/‐7units Gloss cat.3
(GLOSS) :71–100+/‐ 10units
Thickness ENISO2360 60-90μmN
Adhesion ENISO2409 0
Indentation ENISO2815 80
Cupping ENISO1520 5mm
Bend ENISO1519 No cracking or detachment
Impact ENISO6272ASTMD2794 No cracking or detachment
Drilling, milling and sawing No flaking of coating
Neutral salt spray resistance ASTM B117 No blistering or loss of adhesion after 1000 hours
Acetic Acid Salt Spray Resistance ISO 9227 After 1000 hours testing- maximum 16 mm infiltration over a scratch length of 10 cm.