Chrome Electroplating
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In chrome plating a thin layer of chromium is plated onto an object, which may be iron,copper or other metals to protect from rust and to give a decorative finish. Although chromium is a reactive metal it reacts with oxygen in the air to form a protective coating of chromium oxide. Unlike iron oxide (rust) the layer formed is stable and hard and protects the underlying metal from corrosion. Bright chrome is the familiar shiny finish but black chrome can also be used. The thickness of the chrome layer varies depending on the purpose. Decorative finishes are thinner than hard chrome finishes for protection.
Decorative Chrome Plating
Bright Chrome
Decorative chrome plating is usually applied to a nickel plated deposit which is applied to steel, plastic, copper alloys, steel or aluminium. Surface hardness is provided by the chrome and lustre is provided by the nickel. It is used for appliances, hand tool, hardware, auto trims and jewelry.
Black Chrome
Black Chrome is plated onto bright or matte nickel. It is less wear resistant than bright chrome and not as hard. To improve the appearance it may be oiled or waxed. It can be used in solar panels as it has a high absorption of solar energy. Some automotive parts are made from black chrome and it is also used in gun sights and some optical components.
Hard Chrome
Hard chrome plating is used for protection when a decorative finish is not required. The plating is thicker and is used for pistons, crankshafts, hydraulic rods and cylinders printing plates etc.
Electroplating Procedure
The object to be plated is cleaned thoroughly by degreasing then manually cleaning to remove impurities and dirt. Etching solutions of sulphuric acid, hydrochloric acid and hydrofluoric acid nmay be used. On Nimonic alloys ferric chloride is often used. Depending on the object to be plated some pre-treatments may be performed then the object is suspended in a plating solution containing chromic acid and sulphuric acid for bright chrome and a chromic acid, acetic acid, barium acetate mix is used for black chrome. For bright chrome the temperature of the bath is kept at 45 to 50 degrees C, for black chrome 32 to 46 degrees C. The current used is adjusted depending on the thickness of plating required.
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[...] the vehicle. Chrome rims are more expensive than metal wheels covered with a silver finish as the electroplating process takes much longer and is more [...]