If you’ve ever purchased inexpensive jewelry with a fine coating of precious metal, then you’ve witnessed the end result of electroplating. It’s an electrochemical reaction used to put a fine metallic coating on an object. Aside from making cheap jewelry, electroplating has important uses in the automotive industry for chrome plating, and in the electronics industry for optics and sensors.
The process of electroplating (also referred to as electrodeposition) is fairly simple. To start, a negative charge is placed on the object that will be coated. The object is then immersed in a salt solution of the metal that will be used to plate the object. From there, it’s simply a matter of attraction; the metallic ions of the salt are positively charged and are thus attracted to the negatively charged object. Once they connect, the positively charged ions revert back to their metallic form again and you have a newly electroplated object.
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In another form of barrel plating operation, the parts lie at the bottom of an open cup-shaped tub rotatable about an axis at about 45o to the horizontal. There is a negative contact sited centrally in the base, and an anode is hung above the parts. The tub is filled with plating solution and rotated. For removal, the contents are dumped out through a sieve. Barrel plating does not produce such satisfactory deposits as tank plating, for the action on any one parts is at best intermittent and some parts may receive an inordinately thin deposit.
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The development of modern continuous sheet galvanizing lines has led to the disappearance of most of the old manual mills for galvanizing cut sheets. There are however still some machines that galvanize cut-to-length sheets; they use chemical pretreatment sequence similar to those for wire or tube galvanizing.
At the beginning of the line, the end of one coil is welded to the start of the next coil. Then there are two basic methods for continuously galvanizing sheet which differ in the way that the strip is cleaned before galvanizing-chemically or by thermal treatments. Coils of annealed cold reduced sheet may be fed directly to the galvanizing line, or alternatively, coiled sheet is continuously heat treated in the pretreatment line. After leaving the galvanizing bath, in which strip only stays for a few seconds, the surface is wiped to remove excess zinc and may be further treated to after the surface appearance, composition, smoothness or mechanical properties.
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