Electropolishing is the “reverse of electro-plating”. Instead of depositing a coating of another material on a surface, the action of electropolishing removes a surface layer, typically between 10 and 40 microns in the case of stainless steel. That way, all contamination is removed acting deeper than pickling. Passivation of the surfaces is achieved simultaneously with electropolishing.
Electropolishing is an “electroplating process in reverse”. Instead of coating another material onto a surface, the electropolishing action removes a surface layer of a typical thickness of between 20 and 40 microns in the case of stainless steel. Passivation of the surfaces takes place simultaneously during the electropolishing when operating under suitable conditions. The quality of passivation depends on the grade of the stainless steel (AISI 304, AISI 316, etc..), the electrolyte formulation and the operating conditions. Free iron on the surface of the stainless steel is removed, giving the surface a higher resistance to corrosion.
The smoothing of the micro-surface achieved by electropolishing also helps to improve corrosion resistance. The electropolished material thus becomes passive as specified in ASTM B912/02. Electropolishing needs an electrical current source and a rectifier to convert it from alternating current to direct current. The direct current is transmitted through metal bus-bars to act on an anode and cathodes suspended in a tank of a acid-based electrolyte solution. The part to be treated (positive pole) is suspended on the anode bar facing the cathode (negative pole). When the current is transmitted the material on the part to be processed begins to be removed, with this removal process focusing most intensely on microscopic peaks on the material. This has a smoothing effect on the surface within the micro-profile while the macro-profile is unchanged. Careful selection of the electrolytes to be used enables the electropolishing technique to be employed on various materials, including aluminium, titanium and copper
The application that has proved most interesting in commercial terms, however, is electropolishing of stainless steel. Hastelloy©, Inconel© and other nickel-chromium alloys have been successfully electropolished. In the majority of cases the electropolished surfaces of stainless steel are smooth and bright due to the removal of an often contaminated surface layer, and also due to the electrochemical action of micro-deburring. There are many advantages in achieving such a smooth, bright surface. Since the total surface area is reduced as a result of micro-deburring, products coming into contact with an electropolished stainless steel surface adhere less easily. For the same reason the surfaces can be cleaned and kept clean more easily.
Friction is lower on electropolished surfaces due to the smoothing action, which makes electropolishing an excellent technique for eliminating burrs caused by machining that can be difficult to remove mechanically. This bright, smooth finish is suitable and ideal for a huge variety of aesthetic applications, particularly where a mechanical cleaning process is difficult. Applications benefitting from the characteristics of electropolishing are many, and continue to increase every day!