Electropolishing provides the solution by removing the peaks of the surface profile (if viewed at a microscopic level) leaving a smooth surface with a very low Ra.
It can be used for both decorative and functional applications. For decorative complex applications brightness can be achieved that is not possible to achieve by any other process.
Major applications are found in food and pharmaceutical industries or clean room environments; items like vessels, reactors, wire goods such as autoclave trays, baskets, filtration and catering equipment, where supreme cleanliness is required. Electropolished stainless steels are considerably more non-stick than can be achieved by other methods. Greatly enhanced ‘cleanability’ ensures both reduced downtime in plant maintenance and a high degree of product purity.
Pre-treatment for electropolishing
Degreasing, Pickling and Passivating is used as a pre-treatment for electropolishing to remove oils and greases, weld scale and heat tint. Degreasing is necessary for uniform pickling and electro-polishing. Weld scale and heat tint are removed with pickling prior to the electropolishing to ensure a uniform finish. Welded seams, hot rolled plate or any damage caused in fabrication are often polished mechanically prior to electropolishing. Moreover, mechanical polishing before electropolishing enables the lowest possible roughness to be achieved.
Removing embedded contamination in the process
With electropolishing the surface becomes contaminant free, because surface material can only be removed by dissolution. Electropolishing removes approximately 30/40 microns including all kinds of embedded surface contamination, producing an extremely clean, uniform and homogenous surface. The obtained smoothness and homogeneous surface are also beneficial for low friction applications.
The advantages of electropolishing are:
- Reduction of surface roughness (circa 50% in Ra)
- Removal of sharp edges (burrs, corners), sometimes referred to as chemical milling
- Results in a bright, reflecting surface, with removal of light scratches and a cosmetically desirable product with increased light reflection
- Improved resistance to corrosion due to chromium enrichment of the surface
- Reduced dirt adhesion making the surface easier to clean
- Reduced friction
- Removal of hydrogen from the alloy, called degassing (hydrogen may otherwise lead to embrittlement)