Degreasing and pickling of aluminium in a pre-treatment unit

Phosphoric acid, inhibitors, auxiliary substances, Na-Isooctyl sulphate, Na-Amyl sulphate

In surface treatment the quality of rinsing water after an acid pickle degreasing demands high standards, as salt residues or traces of oil and surface active agents on the work pieces considerably worsen absorption upon later varnishing or powder coating. Through the processing of the rinsing water with the VACUDEST® process, impurities such as salts, oils or surface active agents are safely removed and a permanent high quality of rinsing water is achieved. Only via the VACUDEST® process with direct vapour compression is a germ free, desalted distillate available as rinsing water. The rinsing water is taken from the first rinsing bath, distilled and directed to the last rinse, i. e., demineralised water post-rinse nozzles. This creates a closed water cycle. To compensate for the evaporation losses, water from a reverse osmosis is added to the last rinse stage. In the case of fluoride-containing pickling, a neutralisation is added to the distillation. Processing of the active bath in the case of corrosion is not economical, as there is so much metal and acid in the content, that only a low rate of concentration is achievable.

Practical experience in continuous operation shows that a 100 % recycling and circulation process of the rinsing waters leads to optimal cleaning results. In applications in which there is an existing danger that traces of oil or surface active agents might pan in to the distillate, VACUDEST® can post-connect a combined gravitational coalescence and active carbon filter. During rinsing water processing, waste disposal of concentrate is < 1 %. This means that the waste volume is reduced by factor 100.

The VACUDEST® process has proved itself in practice to be the most economical process in the treatment of rinsing waters from acid pickle degreasing.

If the acid pickle degreasing contains phosphoric acid as a pickling acid as well as sulphuric acid, then the choice of material used in the evaporator must be investigated.