Simply shaped parts may be electropolished by using general-purpose cathodes, located several inches or more away from the part.After processing, the parts must be thoroughly rinsed to remove the electropolishing solution. Some parts can be introduced directly into the electropolishing system, while others may require pretreatment to remove grease, soils, or scale.Part size varies from small (hollow needles) to large (15,000-gallon vessels).In most cases, the size and configuration of the parts to be electropolished is limited mainly by the imagination of the electropolishing technician. The electropolishing solution and cathode are brought to the part using a device colloquially called an electrified paint brush. In these cases, the part itself is the anode. Very large, unusually shaped parts that don’t fit into a tank or cannot become a tank require wand electropolishing. Some parts, such as large pipes or vessels, can themselves become the tank for internal electropolishing. The process is optimized by controlling the solution chemistry, temperature, current density, and time.Įlectropolishing generally is considered to be a tank process. The viscous boundary layer that results from the gassing contributes to the preferential dissolution of peaks and projections. Because of the tendency of electrical current to flow from points and projections, these areas are dissolved preferentially, resulting in a smoothing of the surface. Almost immediately large quantities of oxygen are liberated at the surface of the part, forming a dense gaseous layer. Both the part and the cathode are immersed in an acidic solution, and as the current flows through this circuit, metal is dissolved from the metal component. The part to be electropolished is connected to the anodic (+) side of a direct-current power supply, and the cathodic (-) side is connected to an inert metal, typically lead or stainless steel. The inherent strength and corrosion resistance of stainless steel make it the material of choice for process equipment and many consumer products. Nearly all metals and alloys can be electropolished, but in practice stainless steel accounts for the greatest portion of commercial electropolishing. As such, electropolishing isn’t a competitor with processes such as grinding, sanding, blasting, polishing, and buffing, but rather a complement. While conventional mechanical finishing processes are macro metal removal processes, electropolishing is a micro process. When applied to the ID of pipe system components used in high-purity and ultrahigh-purity applications, electropolishing helps to achieve and maintain the necessary cleanness. The process, the electrochemical dissolution of a metal surface, is used to improve the metal component’s smoothness, reflectivity, cleanliness, and passivity, or some combination of these surface characteristics. In recent years, the emphasis has shifted to engineering applications, especially in the food, medical, pharmaceutical, and semiconductor industries. The early use of electropolishing, practiced commercially since the 1930s, primarily concerned adding cosmetic appeal to consumer goods such as cookware and fountain pens.
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