Chrome free powder coating pre-treatment for aluminium and aluminium alloys on the basis of hexafluoric titanium acids, no rinse procedure

Hexafluoric titanium acids, polymer

This type of surface pre-treatment is characterised by the fact that no rinses are required after the chrome free passivation. However, this makes a high rinsing water quality before the no rinse procedure even more important. The first step is always the cleaning of the surface with pickling degreasing. After that there are several rinsing steps, as well as a rinse zone with demineralised water. The rinsed surfaces of the work pieces have to be free from outside ions, so that the chrome free conversion layer can be laid on optimally and no deposits go into the passivation bath. Through the treatment of rinsing water according to the VACUDEST® process, impurities such as salts, oils and surface active agents are safely removed and a constant high rinsing water quality is achieved. It is only by applying the VACUDEST® process with direct vapour compression that germ free, desalinated distillate is available as rinsing water. The rinsing water is taken from the first rinse, distilled and led back to the last rinse, i. e. a demineralised water after rinse zone. This creates a closed water cycle. To compensate for losses through evaporation, water from a reverse osmosis is added to the final rinsing step.

Practical experience with vacuum distillation over a lasting operation shows that a 100 % reuse and recycling of rinsing water produces optimal cleaning results. Combined gravity coalescence and active carbon filters can be added to applications in which there is a danger that traces of oils or surface active agents may be imported with the steam and deposited in the system. The chrome free Al pre-treatment is rarely added to and due to the long standing time is seldom faulty. However, if this is the case, the pH value of the Al pre-treatment used before the distillation should be increased from the normal 2.4 - 3.0 to 7, as the chrome free Al pre-treatment contains relevant amounts of fluoride. Through the distillation pre-treatment of the active baths the amount of waste can be lowered down to 2 %. Due to its high quality, the distillate can be recycled into the process. A minimisation of water use and a reduction in the disposal costs can be achieved by using the VACUDEST® for the treatment of the chrome free Al pre-treatment.