The Science of Corrugated Metal

Corrugated metal provides a lightweight, portable, low-cost and durable architectural material that can withstand hail and windstorms while resisting corrosion for years. Corrugated steel can be painted or coated and is a popular choice for decking, roofing, and siding in commercial, agricultural and even residential buildings.

Corrugated metal starts with carbon steel sheet which is then pressed into three-dimensional patterns, called corrugations, using a series of rollers in a cold roll forming process. Different roller die arrangements produce different types of corrugation, including waves, squares and angles. Cold rolling allows a thicker and stronger product that also presents a better appearance than hot-formed steel. Finished sheet is then sheared off to the desired length.

For artistic effect, corrugated steel sheet may formed with uncoated steel or corten steel, a weathering steel that gives a rusted look right off the shelf! But most building applications require protection from the environment. There are different ways to achieve this, depending on cost and application, e.g., galvanization, painting or coating.

According to the American Galvanizers Association, galvanization is a method of protecting steel from corrosion by dipping it in a vat of molten zinc. The iron in the steel reacts with the zinc, forming a tightly bonded alloy coating that provides a shiny finish. As the galvanized finish ages, it will grow a white oxide coating which protects the metal from further corrosion, even at scratches or the sheared edges on galvanized corrugated sheet.

In addition to applying the zinc in this hot-dip batch process, galvanization can also be accomplished with continuous sheet galvanizing. During this process, rolls of sheet steel are passed through an annealing furnace to clean and prepare the surface, then rolled through a zinc bath, pulled up vertically and allowed to dry. This type of galvanized coating is thinner and less protective, and so should be used indoors only.

An alternate version of galvanization is the patented Galvalume process. First discovered by Bethlehem Steel in 1972, Galvalume steel coating contains about 55 percent aluminum and 45 percent zinc, along with a tiny percentage of silicon. The silicon helps the coating adhere to the steel, even during the corrugation process.

The aluminum in Galvalume provides corrosion resistance against atmospheric conditions. When the coating is applied, microscopic areas of aluminum and zinc form. The aluminum areas provide a barrier of protection from corrosion while the zinc areas provide galvanization. In most applications, Galvalume provides greater protection than galvanization, but there are exceptions, such as in the alkaline environments of concrete and mortar, or in agricultural or animal confinement areas.

For more information or to order, contact Industrial Metal Supply.


What is Galvanized Steel?

Galvanized steel is coated with zinc oxide to prevent rusting, since the chemical compound takes far longer to corrode than steel. It also changes the steel’s appearance, giving it a rugged look that some people prefer. All in all, galvanization makes the steel stronger and harder to scratch, so it’s ideal for outdoor use.

How does galvanization work?

Typically, manufacturers will dip the steel into molten zinc, which bonds itself to the steel like any other alloy would. This makes zinc more than just a protective coating, because it’s actually becoming part of the steel’s chemical composition. The interior may be steel, and the exterior may be zinc, but in between are gradient mixtures of steel and zinc that combine both metals’ properties. This dipping process is the most common form of galvanization, called hot-dipped galvanization. It’s also possible to spray zinc onto the steel, but this method creates a weaker layer of zinc.

Advantages

  • Rust Resistance: Iron in steel is incredibly prone to rusting, but zinc acts as a protective buffer between moisture, oxygen, and the steel.
  • Easy Inspection: It’s fairly simple to tell how strong a galvanized coating is, just by looking at it. There are also quick stress tests that can tell you how thick the zinc is.
  • Sacrificial Anode: This ensures that any damaged steel is protected by the surrounding zinc coating. It doesn’t matter if the steel section is completely exposed; the zinc will still corrode first.
  • Longer Life: With galvanization, a piece of industrial steel is expected to last more than 50 years in average environments, and can last over 20 years with severe water exposure. No maintenance required.

Disadvantages

  • Impractical to Dip Certain Items: Some steel pieces are too tiny or too huge to be hot-dipped, and it doesn’t make sense to galvanize them using other methods.
  • Zinc Can Be Temperamental: It’s important to take enough time to let galvanized steel cool down and settle in, so that the zinc doesn’t peel off. Galvanization isn’t nearly as effective if the zinc is not binding to the steel. The right coating thickness must be applied.