The final electrolytic cleaning removes the last traces of residual soils. In this step the very adherent solid soils and the residual hydrophobic soils, which have survived both the precleaning and the intermediate cleaning, are removed by the efficient agitation provided by the gas generation and evolution on the surface. The usual treatment is 1 to 3 min as cathode followed by a 3 to 20 sec treatment as anode for nonferrous alloys.
Steel are generally cleaned anodically, which in the trade is often called reverse current cleaning. Reverse current cleaning removes smuts, some oxides, and other metallic contaminants that will be dissolved in the cleaning solution. Where both cathodic and anodic cleaning are included in a cleaning cycle, separate cleaning tanks are recommended for each operation. If a single tank is used, smuts will form during cathodic cleaning because of metal contamination of the cleaner. This is especially true if chelated cleaners are used.
Alkaline cleaning is usually followed by an acid dip, this dip neutralizes alkaline films, removes any oxides that form during the alkaline cleaning, and provides a microetch on the surface which improves adhesion of the electroplate. The strength of the acid dip varies with each metal. One percent sulfuric acid by volume or less is adequate for zinc die castings, but copper and cold rolled steel required 4 to 10 %. If the surface requires considerable activation for plating, as do nickel and stainless steel, special treatment may be required.