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Electropolishing: An electrochemical finishing process for metal surfaces

Publication date: 31 Gennaio 2018

Electropolishing is an electrochemical process of surface finish that is applied, in particular to steels, copper and aluminium and is based on the selective removal of metal in anodic phase (usually 0.5-1 micron).

This process is the exact opposite of the galvanic deposition occurring, instead, in the cathodic phase.

The process

The electropolishing consists of a direct current passage provided by a rectifier in a mixture of properly inhibited strong inorganic acids, and allows a gradual levelling of the roughness peaks.

Through the electrochemical process applied to stainless steel, the nickel and iron atoms are deported faster, leaving the surface rich in chromium: a corrosion-resistant surface layer formed by chromium oxide is formed. This operation that improves the passive surface layer of stainless steel is also included in ASTM A380, A967, A967-99  norms and is described as a method of passivation.

The treatment of electropolishing therefore allows to separate the crystalline grid constituent the metal atom by atom, with a quicker attack in the areas of high current density (zones corresponding to Microbave) and a milder attack in those low Current density. The final result is a reduction of the roughness profile and a brightening of the surface.

The treatment creates a progressive leveling of the peaks of roughness.

The times of permanence of the articles to be treated are different depending on the thickness, the size, and the aesthetic result that one wants to obtain.
With the electrolytic treatment articles of various shapes and sizes can be treated, reaching points that would be difficult to achieve with other processes.

Therefore through this process we obtain surfaces with the following characteristics:

  • Surfaces without microscopic burrs
  • Easily cleanable surfaces
  • Low friction surfaces
  • Reflective and aesthetically pleasing surfaces

Industrial applications

For various reasons the electropolishing covers all sectors in which stainless steel is used and can satisfy both aesthetic and functional requirements.
The aesthetic requirements are related to gloss, leveling effect on the surface, reflectivity and elimination of burrs and small imperfections.

The functional requirements, in addition to the increase in corrosion resistance, concern:

  • The cleaning and the aseptic of the metal for applications in the food field.
  • The anti-stick action for all manufactured products come into contact with solid or viscous liquids.
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