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.

Reference ID: 134234
Industry: Surface treatment industry
Application: Rinse water


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Technical data

  • Flow: recirculation: 1.7 m³/h
  • Conductivity: <20 µS/cm
  • Flow make-up water: 2.2 m³/h

Units in plant

  • Activated carbon filter FNSA 130 SE20
  • Demineralization units 2 x EMHE 602 SE30
  • Softening unit type SM 62-F
  • Reverse osmosis unit type RO B1-6 SE30
  • 1100 litre storage tank


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