Galvanizing services involve the application of a protective zinc coating on metals such as steel or iron. The zinc layer forms a barrier that protects the underlying steel by providing sacrificial or galvanic corrosion protection on the steel surface. If the surface is scratched and the underlying steel exposed, the zinc layer functions like a galvanic cell with the steel. Since the zinc has a more negative or active electrochemical potential compared to the steel, the zinc act like a sacrificial anode in a cathodic protection system.
Galvanizing services are typically used to protect ferrous materials, such as iron or steel, from rust or other types of corrosion. There are a variety of galvanizing services available, including hot dip galvanizing; electrogalvanizing; vapor galvanizing, also known as sherardizing; and galvannealing. There are also galvanizing services that use special coatings to provide added corrosion resistance.
For hot dip galvanizing services, operators immerse the steel or iron metal in a bath of molten zinc, which is heated to a temperature of 860 degrees Fahrenheit (460 Celsius). The zinc-coated metal is then exposed to the atmosphere, and the pure zince reacts with oxygen to form zinc oxide. The zinc oxide reacts with water molecules in the air to form zinc hydroxide. Finally, the zinc hydroxide reacts with the carbon dioxide in the atmosphere to form zinc carbonate. The zinc carbonate is a very strong material that protects the underlying metal from a variety of elements. Hot dip galvanizing services provide a thick, durable coating on the steel surface, which is characterized by a crystalline pattern called spangle.
Electrogalvanizing is similar to electroplating and uses an electric current that is applied to the zinc bath. Electrogalvanizing typically deposits a thinner layer of zinc and is not as robust as hot dip galvanizing services. Vapor galvanizing services are used on small parts, or parts that require coating on inner surfaces. In vapor galvanizing, or sherardizing, the metal to be coated is heated inside an airtight container along with zinc powder. The zinc is then evaporated and diffuses into the metal, forming a protective layer. Galvannealing is a combination of galvanizing and annealing where the hot dipped, galvanized steel surface is heated so that the zinc and the top layer of the steel actually combine to form a very strong zinc-iron alloy.
Some galvanizing services also offer specialized coating techniques to provide additional corrosion resistance. While galvanized steel is very strong and corrosion resistant, some environments may require the addition of paints, powders, or coatings. For example, steel sheets or components that are used in marine environments are exposed to sea water, which has a high electrical conductivity and erodes the zinc layer more quickly. For the paint or powder coating to adhere to the surface of the metal, the galvanized coating is typically etched and primed.
Galvanizing services are used on all kinds of steel, iron, and aluminum components, sheet, and parts. They can be used on stock shapes, sheets, plates, rods, fasteners, fittings, pipes, tubes, or bars, as well as on fabricated parts.