Electropolishing is a process which electro-chemically strips off a thin layer of the base material, removing oxides and impurities. This is exaggerated at the ‘peaks’ of a machined finish and has the effect of reducing the surface roughness (Ra value) and improving the aesthetic appearance.
Whilst most metals can be treated, the process tends to focus on 300-series stainless steels. Electropolishing removes free iron and iron oxide which usually exist on the surface of stainless steel as contamination, especially after machining, grinding or fabrication. This 'free iron' is dissolved during the electropolishing process and at the same time a chromium-rich layer is formed on the surface improving corrosion resistance.
After electropolishing it is usual to passivate in a solution of nitric acid, this attacks any remaining free iron without attacking the chromium oxide or base metal. Areas such as tapped holes or crevices that might not have been exposed to the electropolishing process are now passivated.
Electropolishing smoothes, polishes, deburrs and cleans stainless steel parts, resulting in a high lustre finish. During processing the component is bathed in oxygen, removing all hydrogen from the surface. As bacteria cannot multiply on a surface without hydrogen, this makes the process ideal for medical, pharmaceutical, semi-conductor, and food processing equipment and parts.