Henkel has developed a two-step phosphating process that applies the coating to steel and galvanized materials, while suppressing the deposition of a phosphate layer on aluminium parts. In the second step – at the passivation stage – a zirconium-based conversion coating is applied to the aluminium. Measuring between 20 and 50 nanometres, the layer is about a hundred times thinner than the crystalline layer obtained through zincphosphating.
The two-step process was used for the fi rst time in a dip process on the replacement and small parts line at Audi Ingolstadt. The line, including bath set up, was ready for production in a day and a half. A further benefit of the system is the reduction of dry sludge produced by phosphating, which has meant fi lter presses have to be cleaned less frequently.
The new process from Henkel has now been installed on the body production lines at Ingolstadt (spraying) and Neckarsulm (dip). Over 750,000 cars are manufactured at these locations each year. Experience of spraying and dipping on these lines has revealed a marked decrease in fluoride components, to about 50 ppm. In addition, the bath temperature in the phosphating zone has been reduced by 5°C.