Plating
Generally, plating refers to the deposition of one or more metals onto a base metal, or other material activated to behave as a metal surface. Our capabilities are limited to metallic substrates. The purpose of plating is either to prevent corrosion, make the part esthetically pleasing or to enhance the physical characteristics of the surface (such as increasing hardness). Electroplated metal applied by Kaehr is zinc. We can also apply electroless nickel. Since no external power is applied to the work, problems such as high current density buildup are avoided and all surfaces receive the same thickness of plating.
Electroless nickel plating takes place without an external power source, such as is required for electro-plated nickel. As a result, the high current density effects of electroplating are avoided and all surfaces in contact with the plating bath receive the same thickness of plating. Most deposits of electroless nickel are alloys of nickel and phosphorous (typically 4-12%). This results in excellent corrosion inhibiting properties for steel and aluminum parts. This can result in substantial savings over manufacturing in stainless steel. Combined with an attractive decorative appearance, electroless nickel is a good choice for plating such household items as bottle and can openers. Occasionally, electroless nickel is used for its hardness which as plated can range from 50-57 Rockwell C. With a post plate heat treat is can exceed Rockwell 60. Some companies will plate heavy deposits of low porosity nickel, then polish to obtain extremely flat, defect free mirror surfaces.
Zinc electroplate, or electro-galvanize, is most likely applied to steel surfaces to provide an inexpensive protective coating. The metal is sacrificial thereby corrosion is preferential for the zinc coating and spares the steel surface somewhat. To extend the life of the zinc coating, post treatments, most commonly chromates, are used. These react with and become part of the zinc surface. They are very stable and help the zinc withstand a wide variety of corrosive atmospheric conditions. Clear chromate gives the zinc a white or blue-chrome like appearance. Of the chromates it has the least protective value because of the lower hexavalent chromium content. Yellow chromate has a much better protective value due to a higher hexavalent chromium level. It usually has a "rainbow" appearance which varies depending on the depth of the chromate coating. Variations of the yellow chromate produce olive or black coating. The prior is used on military hardware or as a paint base, while the black is used commonly in the automotive industry. Bright decorative zinc deposits coated with a clear organic material are often used on such items as refrigerator trays because they provide looks and protective values almost equal to chrome plating at much less cost.