Degreasing and phosphatizing during the powder coating pre treatment

phosphoric acid, sodium phosphate, oxidation agent (nitrite, nitrate, chlorate, fluoride)

In surface treatment the rinsing water quality following a Zn-phophatizing is subject to high demands, as salt residues or traces of oil and surface active agents on the work pieces significantly reduce the absorption during the later varnishing or powder coating. Through the processing of rinsing water with the VACUDEST®-process, impurities such as salts, oil and surface active agents are safely removed and allow a constant high rinsing water quality to be achieved. Only via the VACUDEST®-process with direct vapour compression is the germ free, desalted distillate available as rinsing water. The rinsing water is taken from the first rinse, distilled and directed to the last rinse, i.e., demineralised water post-rinse zone. This creates a closed water cycle. To compensate for the evaporation losses, water from a reverse osmosis is added to the last rinse stage.

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 be imported into the system via evaporation, VACUDEST®, can post-connect a combined gravitational coalescence and active carbon filter. The concentrate from the VACUDEST® can be directed back into the active bath during the distillation of rinsing water dependent of the chemicals used.

The VACUDEST® procedure has proved itself in practice to be the most economical procedure in the pre-treatment of rinsing waters from Zn-phosphatizing.

With sodium/sodium coating phosphatizing, the rinsing water must be neutralised before the distillation in order to avoid corrosion damage to the vacuum pump. Besides this, neutralisation of the rinsing waters leads to a better distillation quality, as there can be no creation of azeotropics in a neutral area. Active baths used for Zinc phosphatizing often contain sludge, which necessitates the use of a separation system, such as centrifuge. For this reason, the collection containers should be processed prior to the VACUDEST® with conical bottoms, in order to remove the toxic sludge. With phosphatizing containing fluorides, special attention must be paid to the selection of materials employed, for there is the danger of fluoride caused pitting corrosion to occur to stainless steel.