What Is Electropolishing?
Electropolishing is an electrochemical finishing technique for stainless steel and many other alloys that accomplishes a number of unique specific benefits. Essentially it is the opposite of electroplating, rather than depositing a metallic layer, metal is removed from the surface on a microscopic level.
The metal work piece to be electropolished is immersed in a temperature controlled electrolytic bath of a specifically blended acid formula and connected via a fixture or rack to the positive terminal of a DC power supply, making the part itself anodic (+). A series of stainless steel or copper plates in the bath are installed to the negative side of the power source making them cathodic (-). When direct current is applied, the electrolyte acts as a conductor to allow an electrical circuit and metal ions on the surface of the positively charged part are oxidized and dissolved by being attracted towards the negatively charged cathode. Electric fields naturally focus on microscopic peaks, increasing the local removal rate over that of the valleys, resulting in a significantly smoother, brighter more reflective surface even with minimal material removal (5-10 microns). Also while ions are drawn to the cathode, gassing in the form of oxygen occurs at the metal surface, furthering the cleaning process.
In addition to the improvement of surface topography, electropolishing improves the surface chemistry of stainless steel. Not only does it remove embedded particles and inclusions, elemental iron is removed preferentially leaving the surface with a higher relative concentration of chromium. Upon exposure to oxygen, this improved surface will form a thicker and more uniform chromium oxide layer achieving dramatically enhanced corrosion resistance properties. This makes electropolishing in many cases superior to traditional passivation.
In order to realize these results and the associated benefits, electropolishing must be properly executed. There is excellent, mediocre and poor quality electropolishing. To achieve the excellent, correct maintenance of the electrolyte, fixturing, current density and timing, pre-cleaning (degreasing) and post rinsing, cleaning and drying, are just some of the critical steps to the art and science of electropolishing. We have been achieving the excellent since 1993 while still meeting the the very strict environmental regulations of California, the Bay Area and Silicon Valley (San Jose-Santa Clara). We have the expertise, experience and of course all the necessary facilities and equipment to guarantee optimum results at a reasonable cost and timely delivery.
Benefits of Electropolishing
- Dramatically enhances corrosion resistance by preferentially removing free iron, embedded particles and inclusions introduced during manufacturing ( potential sources of crevice and pitting corrosion) as well as by increasing the chromium to iron oxide ratio.
- Improves surface smoothness by levelling microscopic peaks and valleys. 50% or better RA improvement on mechanically polished surfaces may be possible.
- Improves surface reflectivity and brightness. Besides a very attractive lustrous finish, improved heat and light reflection characteristics are tangible benefits.
- Provides the most superior form of passivation of stainless steels. Electropolishing is recognized by ASTM International in the Standard Specification B 912-02: Passivation of Stainless Steels Using Electropolishing.
- Facilitates maintenance of a hygienically clean surface that is resistant to bacteria growth or bacterial biofilms due to a smoother surface and the dissolution of embedded contaminants. Less friction and surface drag are features of electropolished surfaces. This results in reduced product adhesion and ease of cleaning. Because electropolishing is not a surface coating, there is no risk of the surface distortion or peeling over time.
- Unlike mechanical polishing, no directional lines, smearing, occlusions, or fracturing of crystalline metal surfaces.
- Reduces or eliminates stressed and disturbed layers caused by heat treating, decarburization, microscopic scratches, tool marks, grinding checks, cutting and abrasive finishing, thus greatly improving fatigue life. Electropolishing will not introduce new or different stresses that will adversely alter metal fatigue characteristics.
- Improved weldability: provides a low resistance surface for welding with less splatter and surface damage.
- Simultaneously micro-deburrs while it polishes. Ideal for delicate and intricate parts.
- Aesthetically appealing chrome-like appearance for formed sheet metal components without the high costs and environmental disadvantages of chrome plating.
- Economical polishing of large numbers of small parts and of intricate surfaces that are inaccessible to mechanical polishing.
Ultra-High Vacuum Components for the Semiconductor Industry
Electropolishing is considered the most desirable cleaning and surface preparation process for vacuum chambers and components. The most important resulting benefits are improved vacuum base pressures, and faster pumpdown speed as well as the lowest outgassing tates possible from stainless steel. Simultaneously corrosion resistance is dramatically improved.
For many years, the medical field has been a beneficiary of electropolishing. Electropolishing of stainless steel medical devices produces a smooth surface, free of contaminants and more passive, which allows for minimizing the foreign body response and cell adhesion. All hospital, medical and surgical equipment (scalpels, clamps, saws, bone and joint implants, prosthetic devices etc.) should be electropolished to facilitate cleaning and achieve high levels of non-contamination. All metal articles exposed to radiation and requiring regular decontamination are prime candidates for electropolishing.
Piping & Tubing
Electropolishing streamlines the microscopic surface of both the i.d. and o.d. of piping and tubing by removing the uppermost layer of the metal ion by ion, eliminating imperfections which trap and contain contaminants. In addition to dramatically enhanced corrosion resistance, the process is especially beneficial for the sterilization and maintenance of hygienically clean surfaces. Major beneficiaries of electropolished piping and tubing include the pharmaceutical, semi-conductor, food and beverage, nuclear, petrochemical industries.
Food & Beverage Processing
Electropolishing provides the smooth, easy cleaning and cosmetically pleasing surfaces demanded by this industry coupled with unmatched non-contamination and sanitary qualities. The process reduces oxidation and contamination of stainless steel components used in kitchen, dairy and automatic food processing equipment, and descales food and beverage containers. Overall, one can expect a significantly cleaner surface that resists the contaminating build-up of undesirable bacteria and product particles.
More Industrial Applications
- Dry Product Delivery Systems
- Filters, Screens and Strainers
- Product Trays and Dryers
- Pumps and Valves
- Compressors and Condensers
- Cooling and Plate Coils
- Turbine Blades, Wheels and Impellers
- Paper Mill Equipment — Paper slurry pipe systems and head boxes are two of many applications.
- Boating and Marine Industry
- Electronic and Communications Parts
- Offshore Oil field Applications — Instrumentation, down-hole safety equipment and other similar systems.
- Fouling Reduction of Screens and Springs
- Reduction of Oxidation and Corrosion — Crucial for preserving mechanical seals and parts located in chlorine environments.
- Electromachining — Occasionally, parts are made to improper tolerances or to tolerances needing a slight change. Electropolishing can be a valuable tool to alter tolerances by precisely controlling the removal of a small amount of metal.
- Passivation — Electropolishing serves as an excellent passivation process. The process removes contamination located on or just beneath the surface and passivates stainless steel to a much greater extent than any other treatment.
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