Friday, February 1, 2008

Hard Chromium Plating

The success of chromium plate in industrial applications may probably be attributed to its unique combination of properties not possessed by any other one material available commercially. The most important of these are hardness, adhesion, corrosion resistance, non galling and non wetting qualities, and low coefficient of friction. In many instances all these properties are important for successful commercial applications. The properties of hard chrome plating process produce a metal with hard chrome plating.

The hardness alone would not be sufficient to secure widespread use, become a number of other hard materials or hardening process are available. It is the combination of very great hardness with extremely good corrosion resistance (equal or superior under most conditions to that of such noble metals as gold or platinum), and very low coefficient of friction or unique surface qualities, which has given such remarkable result in many applications of chromium plate. To this should also be added relative ease of application and control, which ensures the maintenance of fixed standards of quality and durability, together with moderate cost. There is also be ease of stripping permissible limits.

The benefit of the hardness of chromium deposits is not effectively obtained unless the coating is deposited on a sufficiently hard basis metal and to a satisfactory thickness. Generally, hardened steel is used for the basis metal. Even a relatively heavy deposit of chromium may be crushed or indented if applied over a soft basis metal such as copper. The best possible adhesion is also important in many uses where the surface may be subjected to severe stress or shock, and any chipping of the deposit would be injurious.

Sometimes a bright deposit is applied to a smooth surface and used without further mechanical treatment. By means of careful operation it is possible to plate to size within very close limits. Worn machine parts are salvaged by chromium plating oversize and grinding back to size.

The stable wetting agents used to control fumes from chromium baths were found to encourage the formation of pits in heavy hard chromium deposits more than 35 micro meter thick, at basis metal defects. Some fume suppressants or wetting agents partially overcome this difficulty.

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