October 18, 2008

Electropolishing

Electropolishing is an excellent preparation of metals for electroplating this is a kind of metal surface treatment before anodizing process or other kind of process. In addition to providing a chemically and physically clean surface, electropolishing removes mechanically surface damage. As a result, subsequent electroplates have the best adhesion possible and a decreased tendency toward developing pits and voids that lower corrosion protection. Metal surfaces that have been machined, ground, picked and rolled, abrasive polished, and buffed, have asperities that are detrimental to uniform and pit-free electroplates, adhesion of the plate, and strength of the interface region of the plate basis metal.

Electropolishing removes light tarnish films and light oil or grease. However, removal of oils and grease by cleaners is preferred before electropolishing. This is because such oils and grease eventually form a floating layer of oily-tarry degradation products on the surface of the electropolishing bath. Such a layer contaminates clean surfaces as they pass through the layer on entering the bath. The contamination becomes an irregular stopoff that is revealed as a pattern in the electropolished surface. Heavy rust and heat scale should be removed before electropolishing. These surface oxides also have a nonuniform stopoff effect.

For electropolishing, part are racked as they are for electroplating. Because the current density is five to ten times higher, contacts and splines are heavier. Equipment, racks, and power sources are analogous to those for chromium plating, except that usually the work rod is moved in back and forth motion as for bright plating. The same racks can carry the parts through cleaning and plating. In the electroplating step, excess plate is removed from contact areas. Therefore, the racks are stripped.

Post by Aluminum Anodizing.

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