What is Electropolishing?

Electropolishing is the controlled electrochemical removal of surface metal, resulting in a brilliant appearance and improved properties. Sometimes described as "reverse plating," the process has a leveling effect, which produces smoothness and increased reflectivity. When properly performed, the process is completely safe, does not cause pitting or etching, and, in contrast to pickling or acidic cleaning, does not produce hydrogen embrittlement due to the release of oxygen at the surface.

How does it work?

Electropolishing is the process of smoothing a metal surface anodically in a concentrated acid or alkaline solution (electrolyte). Electropolishing is accomplished by connecting the metal part to be processed to the positive terminal (the anode) of a DC power supply. The part is then immersed in a heated electrolytic bath that contains metal plates connected to the negative terminal (the cathode). With the application of electrical current, a film forms on the metal surface being treated, thus allowing metal ions to diffuse through the film. For normal stainless steel, 300 series, the process can take place in under twenty minutes.

The high spots or "peaks" are attacked more rapidly than the low spots or "valleys" to create a smoother, bright surface. At the same time, all impurities such as scale, rust, foreign debris, oils, grinding compounds and other materials are removed as the surface material is dissolved.

Electropolishing can be performed on a range of metals such as copper alloys, aluminium alloys, stainless steel, tool steels, mild steel, etc.

Picture Left: Is a corrosion test, this stainless steel soccer ball was electropolished and used in a salt water pool for three years.

Made of 304 - 18/10 grade stainless steel, this ball can still be used in this pool for 50 more years.

Click on the image to enlarge.

The following diagrams shows the microscopic results of Electropolishing:

In a nutshell there are three basic steps to Electropolishing :
1. Metal preparation and cleaning/pickling
2. Electropolishing
3. Post-treatment - hot water rinse

The Advantages

Mechanical finishing systems tend to smear, bend, stress, and even fracture the crystalline metal surface to achieve smoothness. Electropolishing removes surface metal in a unidirectional pattern that is both stress- and occlusion-free, microscopically smooth, and often highly reflective.

Unlike paints, plating or other coatings, an electro-polished surface cannot flake off or chip. This is especially important for food or pharmaceutical processing, high vacuum assemblies, and pure gas/water systems. The ultimate benefits of electropolishing are manifest by improved appearance, micro smoothness, corrosion resistance, cleanability, and resistance to further contamination and bacteria growth.

Electropolishing gives us:

• Chemically clean parts
• Improved corrosion resistance
• De-stressing and de-burring
• Highly reflective surface finishing
• Removal of oxides
• Passification of stainless steel
• Hygienically clean surfaces - easier cleaning
• No Hydrogen embrittlement
• Reduced friction and wear
• Reduced radioactive contamination
• Optimum welding and soldering surface
• Polishes and deburrs odd-shaped parts simultaneously