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:
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.
To smooth, brighten, deburr, passivate, stress relieve, improve surface profile, hygienically clean, reduce friction, increase corrosion resistance. To remove and recover electropolishing solution.
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.
Electropolishing systems require rinse water to remove solution from the parts after each chemical operation. These rinses usually go to drain, and are subject to Federal, State, and Local regulations affecting discharge to public sewer treatment systems. Most modern electropolishing systems now incorporate evaporative recovery and/or multiple rinse technologies to minimize the amount of rinse water used. KEPCO can furnish simple waste treatment packages guaranteed to meet the current restrictions. For the solutions commonly used to polish stainless steels, the KEPCO system includes assistance with disposal of recovered electropolishing solution, thereby relieving the KEPCO customer of a major capital investment in waste treatment equipment.
Electropolishing baths generate both hydrogen and oxygen gases, producing an acid mist which must be ventilated to meet OSHA requirements. Other solutions in the line, such as cleaners and pickles, may also require ventilation to meet this regulations. KEPCO can furnish installed ventilation systems constructed entirely of PVC which meet or exceed such regulations.
High quality surface finishing also requires some analytical effort to ensure that solutions are chemically balanced. KEPCO will furnish analytical services free of charge to its chemical customers in good standing; however, each customer should also budget space, equipment, and reagents for the chemical controls needed to achieve the desired finish specification.
Special equipment may be needed to ensure that quality criteria specified by the end-user are being met. Many end-uses require only visual examination of the parts to evaluate brightness, luster, or clarity of the finish. Others may require sophisticated instrumentation to determine surface profile, degree of passivation, surface layer composition, or other specified performance characteristic.