ZERMEG II – Zero emission retrofitting method ... - Fabrik der Zukunft

5.3 Pickling, Etching and DescalingDuring the pickling and descaling process oxid-layers, scales and swarfs are removed bychemical reaction of the components surface and the pickling/descaling solution. Thesolution consists usually of hydrochloric or sulfuric acid and different pickling agents. Inspecial cases nitric, phosphoric or hydroflouric acid, or combinations of these acids are used.The removed oxide layer dissolves as ion in the solution and raises its ion concentration. Toassure the removal of the oxide layer effectivly the acid concentration, temperature, picklingtime and ion concentration in the solution has to be in certain ranges.The ion concentration for an effective pickling process depend on the process solution andvary between 2,5 % and 12 %. A common value for pickling solutions using sulfuric acid is aconcentration of 25 % and a temperature of 60 °C. Hydrochloric acid baths are used withconcentrations of 18 - 22 % and a temperature range of 30 – 35 °C.5.4 PhosphatingPhosphating can be either a pre-treatment process or the main electroplating process itself.The process forms a layer of insoluble phosphates on a metal surface using an agentcontaining phosphoric acid and/or phosphates. The pH value, rising on the surface, allowsthe formation and precipitation of the phosphates on it. The thinkness of the layer liestypically between 3 and 50 µm.Zinc-phosphating is used as a pre-treatment process. It forms a layer on iron or aluminiumsurfaces prior to painting or oiling for cold flow pressing processes. Zinc-phosphating canalso be used as galvanising process itself against corrosion. Iron phosphating is usedbecause of its good adhesion to paints.5.5 Electrolytic ProcessElectrolytic Processes are most of the time the main process of an electroplating plant.During the process a defined metal layer is build up on the component to change itscharacteristics. The process consists of different steps, which are the dissolution of metalions into the electrolyte, the movement from the ions in the electrolyte and the deposit ofthe metal ions on the component. The electrolyte is necessary for closing the current circuitand the ability of movement, and consists of acids or bases, which differ in theirconcentration and combination from process to process. The attributes of the coating are afunction of the process parameters.Most of the time the coating is build up on the cathode (-), but in special cases at the anode(+), i.e. anodising of aluminium or titanium. Several requirements are needed, which are An electrolytic solution At least two conducters and the ability to form a circuit An electrical currentCommon electroplating processes use copper, nickel, chromium, zinc, gold, silver,aluminium, as coatings.9