Two traditional methods for cleaning stainless steel are Pickling Paste and mechanical abrasion. Both methods suffer from problems when used to clean stainless steel.
Pickling Paste comprises two very strong acids, which eat away the surface of the stainless steel. This process is called “etching”, which damages the surface of the stainless steel. Although Pickling Paste removes iron oxide discolouration, the metal surface is left without an oxide layer, which can allow contaminants to cause corrosion to take place. Therefore a separate “passivation” operation has to be performed. Due to the type of acids used, Picking Paste poses a very serious health risk to the operator, and is dangerous to the environment.
Mechanical abrasion, by definition, wears or scrapes away the surface of the stainless steel by linishing or other mechanical methods. The process does remove iron oxide layers, but also changes or damages the metal finish. Once again this method does not passivate the metal, so further processes are needed in order to protect the surface of the stainless steel. Abrasives and wire brushes also harbour contaminants which spreads damage further.
Conventional electrolytic pad and sock machines – great idea and still widely used, however due to the relatively low heat generated, the passive layer does not get restored as you clean and the main fundamental issue with them is the pads & socks wear away very quickly and it is very easy to catch the electrode on the workpiece which causes a black weld spot which is very difficult to remove.