Plating, Electroplating, and Brush Plating

Two common processes used to coat and protect metal are plating and electroplating. The processes are different but when done properly can provide protection for a long time.

1. Plating is the process of mechanically bonding a protective coating onto a parent piece of metal. This can be done by different means such as dipping, spraying, brushing or the use of fasteners.
2. Electroplating is a process that uses an electrical current to transfer a protective metal coating through a specialized chemical solution and then bond it onto the parent piece of metal (also referred to as the deposition of metal).

A third process called brush plating uses a brush that has been activated by an electrical current to apply different metals to different surfaces. It is not a very sophisticated process, but can deposit large amounts of metal in a short time.

Galvanizing

Galvanizing is the process of putting zinc onto iron, steel sheets, plates, components and fasteners to prevent corrosion. Once attached the zinc slowly wears, "sacrificing' itself so the steel or iron will not corrode. (This process is similar to the sacrificial anodes that are found on the underwater hulls of ships). The crucial step in galvanizing metal components is to make sure the parent metal is clean so that the zinc will attach.

Galvanizing can be applied in two ways:

1. hot zinc dipping, is a process whereby metals such as steel are first chemically cleaned and then immersed in vats of hot molten zinc. Girders, beams, pipes, and mechanical parts can be treated in this fashion and also nuts, bolts, washers, and other fasteners that would otherwise corrode if not protected.
2. cold galvanizing, involves brushing a zinc-rich coating onto metals. The finish is usually much thicker and coarser than the hot-dipping process, so it tends to last longer.

Zinc cannot be painted easily without special preparation, but when aesthetics are an issue, special additives can be added to the solutions to better prepare it to accept coatings.

Anodizing

Anodizing is used to protect aluminum sheets, plates, components and fasteners by providing a tough layer of protection on the surface that can either be left natural or painted. Anodizing involves putting the metal into a sulphuric acid solution and then directing an electrical current through the solution. The metal (or anode) will react vigorously with the acid and form a very tough film on its surface. This film is thicker than what would occur naturally and it helps aluminum survive in tough marine environments. The acidic solution can also be tinted with dyes for cosmetic purposes and deposited on the metal . Many non-ferrous metals can be anodized, but aluminum is the most common.

Electroplating

There are many small metal components and fixtures onboard ships that need protection from corrosion: valve wheels, small switchboards, equipment activators/knobs, identification plaques. These pieces are initially fabricated from plate (flat or round stock), or cast in metals such as brass or cast iron. Once they have been fitted and their function has been proven, they will be electroplated with a suitable metal such as nickel or chrome to make them withstand harsh environments.

When pieces are sent to the electroplating area, they are first chemically cleaned to remove all traces of oil, grease or other contaminants. The component is hooked to a fixture or wire and lowered into a vat. When a current is introduced into the solution, the metal used for plating will flow through the solution in microscopic amounts and be deposited on the component. The longer the item is left in the solution with the current on, the more metal is deposited. When the correct thickness has been achieved, the part is taken out and washed to remove any residual solution.

Repeated or multiple layered electroplating can be very useful when it comes to repairing older equipment that is no longer supported by the manufacturer (parts such as crankshafts, camshafts, or metal gears). Electroplating can be used to build up a damaged surface with a suitable metal such as chrome or nickel. This type of repair can save thousands of dollars if replacement parts are no longer available.

Hot Metal Spray

Hot metal spray is the process of spraying any kind of metal onto large components that cannot easily be placed in electro-plating tanks. Hot metal spray involves spraying powdered metal onto a preheated surface to provide protection, or to provide some sort of property the parent metal does not have. An example would be the restoration of a steel ship's ladder. The first step would be to sandblast the surface to a white metal finish to ensure adhesion, heat the surface with oxy-acetylene torches, and then spray with aluminum to provide corrosion protection and a textured non-skid surface.