Chrome rims and other chrome parts are often used to improve the appearance of vehicles. The bright decorative finish of chrome plating is very familiar and enhances the appearance as no other method of customising your ride can. Chrome plating is used on exhausts, handles, mirrors and trims as well as on the very popular chrome rims. Chrome plating is not just used for decoration however. The protective coating of the chrome makes the technique of chrome plating useful for other applications. Chrome plating can be used to protect pistons and other engine parts.

Chrome plating consists of applying a thin layer of chromium on to an iron, copper or other base metal to give a protective and decorative finish. Chromium itself is a reactive metal that reacts readily with the oxygen in the air. Unlike iron which forms a very unstable oxide that flakes and falls apart chromium oxide is hard and stable and forms a protective layer which prevents the underlying metal from corroding.

Different electroplating techniques are used to produce different effects. The shiny highly decorative finish that we are all familiar with on chrome rims and other auto parts is known as bright chrome. Other variations are black chrome and hard chrome.

Bright chrome is used when a decorative finish is required, on car rims for instance, and is applied fairly thinly. Decorative chrome is applied after a nickel coating is plated to a base of steel, copper alloys, steel and aluminum alloys and plastic. The nickel provides the luster and the chrome provides the hardness and protection. This kind of process is used for auto parts, jewelry, hardware, hand tools and appliances.

Black Chrome

For black chrome an underlying base of metal is plated with bright or mate nickel then the chromium plating applied over this. Black chrome is not as hard as bright chrome and not so long lasting. It is often oiled or waxed to improve the appearance. Black chrome is used in some auto parts, solar panels and some gun sights and other optical components.

Hard Chrome

Unlike the other types hard chrome is not used to give a decorative finish but to give a very long lasting protective coating for pistons, hydraulic rods, cylinders and other engine parts. The chrome is plated more thickly than for the decorative finishes to make a strong protective layer.

The Electroplating Procedure

Before the object can be plated it must be cleaned thoroughly by degreasing the cleaning manually to remove any debris and impurities. Sulphuric acid or other strong acids are also used. Other pre-treatments may also be used. Once cleaned the object is suspended in the plating solution. For bright chrome a solution of sulphuric acid and chromic acid is used and for black chrome, chromic acid with acetic acid and barium acetate. The temperature of the bath must be kept within 45C to 50C for bright chrome and 32C to 46C for black chrome. The thickness of the plating is controlled by the current used..

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