How to Specify Electropolishing

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For many years, the lack of accepted specifications for electropolishing left many uncertain as to how to specify the finish desired on the metal surface. There are four primary and generally accepted finish standards for electropolishing.

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To achieve quality electropolishing:

Step One must be the specification of the correct metal alloy. For example, a general materials specification to manufacture a part from "300 series stainless steel" alloys can create problems. Some 300 series stainless steels Electropolish better than others. Type 316 generally polishes better than Type 304. Type 303 stainless possesses sulfide inclusions, which presents an obstacle to high-grade electropolishing. Selection of the material should be discussed with the Electropolisher.

Step Two is the selection of the final finish required for the application being considered. An intermediate step of mechanical abrasive polishing may be required to achieve the final finish desired. Generally, electropolishing can reduce the Ra or RMS reading on a mechanically polished surface by approximately 50 percent. For example, if the existing mill or mechanically polished surface shows a surface reading of 50 Ra, one can expect an electropolished surface reading of approximately 25 Ra. There are factors, however, that can depress or elevate the final Ra reading. Quality Electropolishers use sample coupons of the metals to be electropolished in order to help determine the final finish.

Step Three: Any mechanical polishing required to achieve the specified final finish must be considered. Multiple passes of ever-finer abrasive grits are recommended as mandatory for best results. Very coarse grits (less than 80 grit) should be avoided. Surface quality obtained by Electropolishing is directly related to the quality of the pre-electropolished surface. Electropolishing cannot remove digs, gouges, scratches or other similar surface distortions. Discussion of the mechanical polishing requirements with the Electropolisher will help assure the quality of the desired final finish.

Delstar recognized some time ago that the creation and implementation of nationally accepted standards regarding electropolished finishes was desperately needed in order to establish and maintain quality. Working closely with an independent research institute, our research and development teams led the industry's response to this challenge by establishing the Electropolish Finish Standards (EFS). Each standard contains specifications in order to enable customers to accurately specify the final finish desired. Details on grades EFS-1, EFS-2, EFS-3 and EFS-4.


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