Pre-treatment of aluminum by DI water

The quality of the pre-treatment is critical to the final result of the powder coating process. The surface pre-treatment at Indulak in Denmark is handled in a 56 meter long spray tunnel. The treatment is done according to the GSB AL 631 standard. The aluminum workpieces go through the following treatment steps:  

• Alkaline degreasing and etching at 55 °C
• Rinse
• DI rinse (deionized water with a conductivity less than 30 µS/cm)
• Chromium-free passivation
• Rinse
• DI rinse (deionized water with a conductivity less than 30 µS/cm)

The rinse water is lead through the line in a reverse cascade rinse to minimize the consumption of rinse water. Furthermore, the used rinse water is recycled over two parallel demineralizers to ensure continous operation. Fresh make-up water is added by reverse osmosis unit.