Removal of physically bound impurities. The industrial degreasing of metal surfaces includes not only the removal of grease, oil, waxes, but also of layers of dirt (e.g. polishing wheel and paste residues, drawing aids, drilling oil, rust inhibitors) of any kind (except oxide coatings, the removal of which is called pickling, descaling or derusting).
There are various degreasing agents and processes for metals: alkaline cleaners (decocting degreasing), emulsion cleaners, solvent degreasing, electrolytic degreasing and the less common mechanical and thermal processes. The processes are often used in combination; e.g. before electroplating, degreasing is first carried out with an alkaline cleaner or an organic solvent and then electrolytically. In some cases, degreasing is assisted by the application of movement, elevated temperature and above all ultrasound. This has proved to be very effective, especially when cleaning places that are difficult to access (drill holes, blind holes or similar).
The selection of the degreasing process or the sequence of processes depends mainly on the type and thickness of the contamination, but also on the base material. In any case, however, degreasing must precede pickling, because the pickling cannot attack the areas of the workpiece covered with grease.