Preparation Tips

Recommended Process and Process Control Requirements

for Coating of Architectural Aluminium Alloys

  1. Area of Application
    1. Aluminum pressings, sheetings and extrusions for exterior application
    2. The aluminum or aluminum alloy materials must be suitable for the coating processes specified in this document
      It must be free from corrosion and must not have any anodic or organic coating. The radii of the angles must be as large as possible
  2. Laboratory Equipment
    1. Equipment necessary for testing the pre-treatment chemicals, rinsing water and final results
      1. Tests of pre-treatment chemicals to be performed according to suppliers' instructions
      2. Conductivity measurement gauge for evaluation of final rinse
      3. Temperature recorder
      4. Coating weight equipment, DIN 50939 or equal
    2. Equipment necessary for testing the powder coating
      1. Film thickness gauge suitable for use on aluminum (e.g. ISO 2360, DIN 50984)
      2. Cross hatch equipment, DIN-EN ISO 2409 – 2mm
      3. Bending test equipment, DIN-EN ISO 1519
      4. Indentation test equipment, DIN-EN ISO 2815
      5. Impact test equipment, ASTM D 2794 (5/8”ball) or ECCA T5 (1985)
      6. Erichsen Cupping test equipment, DIN-EN ISO 1520
      7. Gloss measurement equipment, DIN 67530, ISO 2813 (using a 60 head)
      8. Equipment for boiling water test
      9. Temperature recorder
      10. Equipment for test of curing (MEK-test)
  3. Procedure for Surface Treatment
    1. Handling
      1. Handling of details should be done carefully and contamination (dust, oil, at, finger marks, etc.)
      2. Care should be taken to secure proper treatment of the total area
    2. Pre-treatment
      1. As a minimum, the following pre-treatment should be performed:
        • Degreasing / etching – alkaline
        • Rinsing
        • Acid Wash
        • Rinsing
        • Chromating
        • Rinsing
        • Rinsing, demineralized water. (The last running water from the object should be tested at 20°C. The readings should measure below 30 micro Siemens/cm)
        • Drying, max, object temperatures: 100°C
      2. Coating thickness of the chromate conversion layer between 0.4 – 1.0 g/m2
    3. Powder application and curing
      1. The pre-treated parts are to be transferred to the coating process immediately in a clean and dry state and before the integrity of the pre-treatment process has deteriorated
      2. Application shall be done in one operation to a minimum thickness of 60 microns for exposed areas. On details which are to be treated mechanically (e.g. sawing, milling, drilling) after coating, the coating film thickness must not exceed 120 microns (100 microns for Corro-Coat PE-SDF)
      3. The Powder coating shall be cured as specified by Corro-Coat Powder Coatings for the product used. The metal temperature must be recorded on the area with greatest metal thickness and with the oven fully loaded.
      4. At no single point in the curing zone must air temperature deviate from adjusted nominal by more that ±10°C
    4. Handling after curing
      1. Coated items should be cooled to less than 40°C before handling.
      2. Precaution should be taken to avoid damages on the finished coating during stacking, packing, storing and transportation
  4. Testing Procedure
    1. Operation and raw materials
      1. Prior to start of a running production and by start-up after stops, necessary test panels shall be pre-treated, coated and cured, to control equipment and materials. Tests as under 5.a. The temperature shall also be recorded.
      2. The same procedure (4.a.1) shall be performed for each separate color
      3. Testing of pre-treatment chemicals and rinsing stages shall be done according to written instructions from supplier
      4. The final rinsing stage must be constantly monitored and adjusted regarding conductivity
      5. Testing of the last running water from the object (3.b.1) shall be done at least once per shift, color or job (if less than one shift is required). The conductivity of the rinsing bath must be adjusted accordingly
      6. Testing of the drying oven at least once per shift, color or job (if less than one shift is required according to 3.b.1
      7. Testing of the chromate conversion layer (3.b.2 at least once per shift, color or job if less than one shift is required) according to procedures given in DIN 50939 or equal
    2. Production control
      1. When the oven is fully loaded, the temperature shall be recorded. Temperature to be measured in air and on greatest metal thickness. The temperature shall also be recorded prior to shutting production in fully loaded oven
      2. At least once per shift, color or job (if less than one shift is required), necessary panels shall be coated for testing purposes. Panels to be coated and cured under current working conditions
    3. Coated materials
      1. At least once per shift, color or job (if less than one shift is required), tests shall be performed according to 5.b
      2. On parts with variable thickness and shape, test shall be performed according to 5.b on a representative selection
  5. Test Performance
    1. Test on panels (Panel thickness 0.8 mm. Film thickness 60 microns)
      1. Measuring of gloss DIN 67530, ISO 2813 (using a 60° head) Specification: as specified for the product
      2. Adhesion, cross hatch/tape test, DIN-EN ISO 2409 - 2mm. Specification: Gt.0
      3. Falling weight impact. Specification: as specified for the product
      4. Erichsen Cupping Test. Specification: as specified for the product
      5. Bend test. Specification: as specified for the product
      6. Indentation test, DIN-EN ISO 2815. Specification: Min. 80
      7. Color shall be controlled visually according to specification
      8. Pre-treatment shall be controlled in distilled boiling water test for 2 hours. Specification: no blistering or loss of adhesion (according to 5.a.2)
      9. Cure test by MEK resistance. 30 double rubs according to Corro-Coat Powder Coatings procedures
    2. Finished material
      1. The surface coating shall be continuous, free from damage, even in color and gloss visually controlled
      2. Decorative appearance shall be visually evaluated on a distance of 5 meter (15 feet) for material for exterior use, and 3 meter (9 feet) for interior use
      3. Fill thickness. Specifications: as 3.c.2
      4. Adhesion, cross hatch/tape. To be tested according to 5.a.2. Specification: Gt.0
      5. Indentation test according to 5.a.6. Specification: as specified for the product
      6. Cure test by MEK resistance. Specification as 5.a.9
  6. Registration and Documentation
    1. Full powder products identification, processing data and test panels, to be kept for the duration of the warranty period
  7. Miscellaneous
    1. When a failure is detected, the coating process shall stop and necessary steps be taken
    2. The powder coating must be handled and stored under dry conditions at a temperature not exceeding 25°C. Storage stability to be controlled after 6 months from the date of receipt
    3. Special care must be taken when loading and unloading the coated components and reasonable care exercised during handling and transport on site. Each coated component should be packed separately and separated from the other components by tissue paper, plastic sheeting, or foam padding to prevent damage during transport.
      Regular adhesive tapes must not be allowed to come into direct contact with the polyester coating. Should protective tape must be required, then only tape designed for the protection of coated aluminum shall be used. The responsibility of compliance is our clients' as well as ensuring that no residue of any nature is left on the finished product