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Zinc plating is a process of coating corrosive metals with a non-corrosive metal, usually zinc, to prevent corrosion and increase strength. Hot dipping and electrogalvanizing are common methods. Galvanized nails and screws prevent unsightly stains on house siding. The hot dip procedure involves immersing metals in a bath of molten zinc, while electrogalvanizing uses an electrolytic process to apply a thinner layer of zinc. Galvanized metals are thicker and guidelines for thickness are provided by ASTM specifications. Magnesium is added for marine environments.
A process by which zinc is coated onto corrosive metals is known as zinc plating. It’s actually a method of coating corrosive metals, such as steel and iron, with a non-corrosive metal. Zinc is melted and applied, usually by so-called hot dipping, to the metal, providing a corrosion protection coating of one mil (0.001 inch or 0.0254 mm) to just over four mils (0.004 inch or 0.1016 mm) thick . When hardened, zinc, by reaction with the coated metal, becomes zinc carbonate.
The galvanizing process not only prevents corrosion of various “soft” metals, but increases the strength of the original uncoated metal. Obviously, galvanized metal is thicker than uncoated metal, so fittings and fixings are usually sized to take into account the thickness of the additional coating. Various American Society for Testing and Materials (ASTM) specifications provide guidelines and continuity for the thickness of galvanized metals.
Galvanizing nails and screws is the most common method of preventing the unsightly stains found on many types of house siding. Non-galvanized steel nails and screws, when used outdoors, “bleed” as they corrode, causing dark spots on the coating. This stain is eliminated only by repainting the siding. Stains on a building’s facade from corroded nails, screws, or other types of fasteners are not only unsightly, but they also indicate that because they aren’t galvanized, the fasteners are deteriorating and need to be replaced.
The hot dip procedure for galvanizing metals is essentially a bath of molten zinc. The zinc is held liquefied at a temperature of approximately 860°C (460°F) and the metals to be coated are immersed or, in some cases, fed through this zinc bath. Prior to dipping, the metals are cleaned and prepared for hot dipping by pickling in a mild acid solution. The zinc coating is normally distinguishable from bright bare steel or iron in that it is a dull medium gray. Magnesium is put into the hot dip solution when galvanized metals are to be used in a marine environment.
Electrogalvanizing is an electrolytic process in which a thinner, more adherent layer of zinc is applied to a metal via electroplating. In this process, an electric current is passed through a zinc compound, positively charging the zinc ions to adhere more firmly to the conductive primary metal. Provides a somewhat stronger tensile strength to the coated metal by virtually impregnating the metal with zinc. This process is most commonly employed with iron or steel beams, angles, and other items that are to be used in building construction. Hot-dip and electro-galvanizing are the most common of several metal galvanizing methods.
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