Galvanizing uses electric current to bond metals like zinc, chromium, or gold to a piece. It provides rust protection and improves appearance. Zinc plating is cheaper but hot-dip galvanizing is better for corrosion. The process involves cleaning, electrolytic bath, and multiple anodes. The final product may require polishing.
Galvanizing is one of several plating processes that uses electric current to bond the material to be plated, usually a metal such as zinc, chromium or gold, to a piece. Careful preparation and strict adherence to safety procedures are common to all plating processes, as the chemicals involved are both toxic and caustic. However, galvanizing involves less hazardous chemicals than most other forms of plating and is successfully done in small shops and even home metal shops.
One of the most common uses for galvanizing is to provide durable and inexpensive rust protection for steel. An alternative to zinc plating is zinc plating, which involves immersing hot steel in a bath of liquid zinc. A piece that has been electroplated with zinc will often have a “shiny” looking surface because the zinc crystallizes as it cools. Hot-dip galvanizing, as it’s called, requires special furnaces, vats, and process rooms that generally exceed the capabilities of many small shops. An additional consideration is that the fumes given off by molten zinc are toxic. Electroplating, therefore, is a much cheaper way to plate zinc onto a piece. However, because hot-dip galvanizing applies a much thicker layer of zinc to a work surface—about 50 microns for 3 to 15 micron plating—if corrosion is a major concern, hot-dip galvanizing is a better choice.
Even small shops can galvanize zinc on workpieces, such as fasteners like nails, nuts, and bolts, as well as other hardware like hinges. Galvanizing is also used for other pieces, both to provide rust protection and to improve the appearance. Applied correctly, zinc plating can be polished to a smooth, nearly as bright finish as chrome. The first step in the process, as with all plating work, is to thoroughly clean the piece. This is a two-step process, starting with a caustic alkaline cleaning bath, followed by a “pickle” in an acid bath. The piece can subsequently be rinsed with water, but not touched with bare hands; any contamination, even microscopic, can interfere with the plating process.
After the piece has been cleaned, it is connected to the negative pole of an electrical source, usually via copper wire, and suspended in a heated and stirred electrolytic bath. Zinc can be dissolved in the bath in the form of zinc salts, or solid zinc plates can be attached to the positive pole of the same source of electricity. In both cases, the initiation of an electric current triggers a response in the zinc such that it is attracted to the negatively charged piece: the cathode. The zinc atoms will migrate through the bath to the workpiece and bond with it. The process takes about 100 milliamperes per square inch (6.4516 square centimeters) of piece to be plated and, after about an hour, should result in a plate about 3 microns thick. A stronger current will speed up the plating process, but the surface won’t be as smooth and will require significant polishing.
It is difficult to plate metals with a uniform thickness of zinc and the shape of the piece being plated contributes to this difficulty. The cracks and grooves in the workpiece will not develop to the thickness of a plate like exposed surfaces and edges. Therefore, many platers use multiple anodes and place them in the electrolyte bath to target problem areas. Some jobs may require a combination plate, such as nickel-zinc. One way to achieve this is to connect two anodes to the positive pole, one zinc and one nickel. The plate on the piece will be a combination of nickel and zinc.
Once the plating process is finished, the piece can be removed from the bath and rinsed. Hardware, such as fasteners, hinges, or plumbing components, are usually available for immediate use. Workpieces such as automotive trim, which require a high gloss finish, may require polishing and polishing before they can be used for their final use.
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