Electropolishing is an electrochemical process just like, but the reverse of, electroplating. The electropolishing process smooths and streamlines the microscopic surface of a metal object like 304, 316, and therefore the 400 series stainless-steel. As a result, the surface of the metal is microscopically featureless, with not even the smallest speck of a torn surface remaining.
In electropolishing, the metal is removed ion by ion from the surface of the metal object being polished. Electrochemistry and also the fundamental principles of electrolysis (Faraday’s Law) replace traditional mechanical finishing techniques, including grinding, milling, blasting, and buffing as the final finish. In basic terms, the metal object to be electropolished is immersed in an electrolyte and subjected to direct electrical current. the object is maintained anodic, with the cathodic connection being made to a nearby metal conductor. During electropolishing, the polarized surface film is subjected to the combined effects of gassing (oxygen), which occurs with electrochemical metal removal, a saturation of the surface with dissolved metal, and also the agitation and temperature of the electrolyte.
The Benefits of Electropolishing
Improved Corrosion Resistance:
All sorts of corrosion begin on or near the surface. Unfortunately, all fabricating and handling practices invariably degrade surface conditions and surface properties. Surface contaminants, including grease, dirt, iron, and other metallic particles are inherent to machining, welding, and fabrication processes. Mechanical cutting, machining, handling, and polishing will leave iron and abrasive particles embedded within a material surface. These surface contaminants disrupt the formation of stainless steels’ present corrosion-resistant oxide layer and are often the origin site of corrosion. Electropolishing removes surface material and surface contaminants. Electropolishing dissolves free iron, inclusions, and embedded particles from the surface of the material surface.
Electropolishing improves the near-surface chemistry of stainless-steel. Not only does it remove embedded particles and inclusions, but it also improves the atomic ratios of the materials alloying elements. Figure 1 is an Auger Electron Spectroscopy (AES) analysis of electropolished stainless steel. It shows the effect of electropolishing on the near-surface atomic composition of stainless steel. Electropolishing preferentially dissolves Iron (Fe) from the fabric matrix and leaves the surface with a better relative concentration of Chromium (Cr). This improved surface will form a thicker and more uniform oxide layer with enhanced corrosion resistance properties. The improved oxide layer resulting from electropolishing will have a Chromium to an Iron ratio greater than 1.5 and a Chromium oxide to an Iron oxide ratio greater than 2.0. The oxide layer are going to be thicker than 30 Angstroms.
Improved Surface Finish:
Improved microfinishes can do quite improve the looks of a part. Superior microfinishes can improve seals, lower friction, reduce real area , allow for easier sanitation, and improve heat and light reflection.
The roughness of a surface are often measured and quantified by a profilometer.
A profilometer is an instrument that measures roughness by moving a diamond-tipped stylus across a surface. A profilometer will produce a reading of the surface roughness in either micro-inches (µin) or micrometers (µm). The electropolishing process may improve a surface finish reading by up to 50%. Because electropolishing isn’t a surface coating, there’s no risk of the surface distorting or peeling over time.
Reduced Product Adhesion & simple Cleaning:
The improved micro finish produced by electropolishing can reduce product adhesion and contamination build up. Reduced adhesion can limit product build-up and significantly lengthen duty cycles. When cleaning is important, cleaning operations are often completed in less time and with less effort.
Electropolishing facilitates sterilization and maintenance of hygienically clean surfaces. Research by the USDA has indicated that electropolishing reduces the build-up of bacterial biofilms.
Electropolishing reduces the looks of rouging on the within surfaces of distillation columns, storage vessels, and distribution systems for hot purified water and clean steam.
Electropolishing is naturally fitted to deburring. During the electropolishing process, this density is greater at high points and lesser at the low points within the surface profile. the rate of the electrochemical reaction is directly proportionate to the present density. The increased current density at the raised points forces the material to dissolve faster at these points and thus tends to level the surface. Electropolishing will simultaneously deburr and polish the surface.
Grinding, vibration, and tumbling techniques are often not suited to highly detailed or fragile parts. A properly controlled electropolishing process can remove burrs from such components. Because electropolishing may be a non-mechanical process, there’s no risk of distortion and therefore the material hardness has no bearing on the processing time or cost.
Burr removal by electropolishing is restricted to burr sizes of 0.002″ or less. Larger burrs require a longer process time to attain adequate material removal. These material removal levels may affect critical dimensions of the component. Large burr removal is often accomplished by first mechanically polishing the component then electropolishing.
The most striking advantage of electropolishing is that the resulting lustrous surface. Electropolishing may be a non-mechanical process. No tools come in contact with the piece so there’s no risk of making directional polishing lines. the material is treated electrochemically, leaving a microscopically smooth surface that’s highly lustrous.