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The simplest description of Electropolishing (EP) is that it is the opposite of electroplating a metal. Rather than depositing a metallic layer as done in electroplating, metal is removed from the surface when electropolishing. The part to be electropolished is made anodic by connecting to the positive side of a DC power circuit while the cathode, usually copper, is connected to the negative side of the DC power source . An electrical circuit is completed through an acidic blend of electrolyte removing metal ions from the anode, producing a bright, shiny surface typically associated with an electropolished surface.
There are a number of process parameters which are critical in a proper electropolishing procedure that must be controlled to produce a quality surface. These parameters are identified as “essential variables” and a change in any one essential variable may affect the outcome of the process. The essential variables are:
- Amperage/time as defined in ampere-minutes per square inch - This determines metal removal, allows for removal calculation, and establishes a repeatable process on a variety of part shapes and sizes.
- The temperature range of the bath during operation - This Variable affects distribution which in turn controls uniformity of surface metal removal. Good practice includes maintaining the bath temperature within a specific range, for example +/- 10 degrees (+/- 5 degrees C).
- Bath monitoring - The electrolyte must be maintained to a controlled composition, Factors of greatest concern are metal pick up and the water content, both of which if not controlled can affect EP quality. During use, metal salts increase in the electrolyte and are controlled by decanting and adding new electrolyte. Also the electrolyte is hygroscopic and takes on water or loses water depending up on the operating operating environment. The water content can be controlled by increasing bath temperature to “cooking off” excess water or by adding water as required.
Requiring vendors to produce an electropolishing procedure specification with proper control of essential variables is a major step in assuring quality electropolishing workmanship.
Ultraclean Electropolish, Inc. utilizes over 30 years experience and meets all the criteria set forth in the current edition of the
ASME-BPE Non Mandatory Appendix "H" Electropolish Procedure Qualification