Electropolishing is the reverse of electroplating process. In the process of electropolishing, metal is uniformly removed from the surface, resulting the development of smooth as well as bright surface finish. High quality acids and appropriate electrical current are applied on the surface to ensure the enhancement of the surface of components. Today, we have firmly positioned ourselves as one of the reliable providers of Stainless Steel Electropolishing Services, based in India. To meet the different demands of the clients, we offer Electropolishing Solution in various finishes. BASIC PRINCIPLES OF ELECTROPOLISHING Electropolishing is a process by which metal is removed from a work piece by passage of electric current while the work is submerged in a specially-designed solution. The process is essentially the reverse of electroplating. In a plating system, metal ions are deposited from the solution onto the work piece; in an electropolishing system, the work piece itself is dissolved, adding metal ions to the solution. Figure 1 is a schematic illustration of a typical electropolishing cell. The work piece is connected to the positive (or anodic) terminal, while the negative (cathodic) terminal is connected to a suitable conductor. Both positive and negative terminals are submerged in the solution, forming a complete electrical circuit. The current applied is direct (DC) current. The quantity of metal removed from the work piece is proportional to the amount of current applied and the time. Other factors, such as the geometry of the work piece, affect the distribution of the current and, consequently, have an important bearing upon the amount of metal removed in local areas. Figure 2 illustrates both high and low current density areas of the same part and notes the relative effects of electropolishing in these two areas. The principle of differential rates of metal removal is important to the concept of deburring accomplished by electropolishing. Fine burrs become very high current density areas and are, subsequently, rapidly dissolved. Low current density areas receive lesser amounts of current and may show negligible metal removal. In the course of electropolishing, the work piece is manipulated to control the amount of metal removal so that polishing is accomplished and, at the same time, dimensional tolerances are maintained. Electropolishing literally dissects the metal crystal atom by atom, with rapid attack on the high current density areas and lesser attack on the low current density areas. The result is an overall reduction of the surface profile with a simultaneous smoothing and brightening of the metal surface. In the case of stainless steel alloys, an important effect is caused by differences in the rates of removal of the components of the alloy. For example, iron and nickel atoms are more easily extracted from the crystal lattice than are chromium atoms. The electropolishing process removes the iron and nickel preferentially, leaving an enhanced surface layer consisting of corrosion-resistant chromium oxide. This phenomenon imparts the important property of "passivation" to electropolished surfaces. What are the Benefits of Electropolishing? Electropolishing produces a number of favorable changes in a metal part which are viewed as benefits to the buyer. All of these attributes translate into selling advantages depending upon the end&endash;use of the product. These include: Brightening Burr removal Total passivation Oxide and tarnish removal Reduction in surface profile Removal of surface occlusions Increased corrosion resistance Increased ratio of chromium to iron Improved adhesion in subsequent plating Reduced buffing and grinding costs Removal of directional lines Radiusing of sharp edges Reduced surface friction Stress relieved surface Removal of hydrogen Electropolishing produces the most spectacular results on 300 series stainless steels. The resulting finish often appears bright, shiny, and comparable to the mirror finishes of "bright chrome" automotive parts. On 400 series stainless steels, the cosmetic appearance of the parts is less spectacular, but deburring, cleaning, and passivation are comparable. Electropolishing produces a combination of properties which can be achieved by no other method of surface finishing. Mechanical grinding, belting, and buffing can produce beautiful mirror-like results on stainless steel, but the processes are labor intensive and leave the surface layer distorted, highly stressed, and contaminated with grinding media. The passivation methods commonly employed produce clean, corrosion resistant surfaces, but do not achieve the bright, lustrous appearance obtained by electropolishing. The corrosion resistance of electropolished stainless steel exceeds that of standard passivation processes. Electroplating can produce extremely bright finishes, but the finish is a coating which can chip or wear off. Electroplated surfaces may also exhibit hydrogen embrittlement which must be stress-relieved in a separate step. Neither passivation nor electroplating can accomplish burr removal. Processes are available for chemical deburring and brightening of steel and stainless steel, but these methods cannot match the surface improvement produced by electropolishing. The corrosion resistance produced by such processes is decidedly inferior to that produced by electropolishing. Electropolishing Process Requirements Electropolishing is accomplished in a series of wet processing steps using specially designed tanks, similar to electroplating or anodizing. The parts to be polished are mounted on a rack or jig which is moved from tank to tank. The three major process steps of the electropolishing system are: METAL PREPARATION: To remove all oils, lubricants, shop dirt, fingerprints, oxides, and other contaminants from the surface. Suitable methods include vapor degreasing, alkaline and/or acid cleaning, spray washing, abrasive blasting, wire brushing, and other types of mechanical steps. ELECTROPOLISH: To smooth, brighten, deburr, passivate, stress relieve, improve surface profile, hygienically clean, reduce friction, increase corrosion resistance. To remove and recover electropolishing solution. POST TREATMENT: To remove chemical residues or byproducts of electropolishing and to assist drying. Electropolishing processes are similar to other metal finishing processes such as electroplating, anodizing, or conversion coating. Each of the major operations requires a number of steps to accomplish the desired result, depending upon a number of factors. The typical flow chart for a stainless steel electropolishing system is shown in Figure 2.
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