Process Overview

Process Overview

The Galvanizing Process

Incorporating hot-dip galvanization to protect metals from corrosion has been a mainstay of industry for about 150 years, and the science of galvanization goes back even further. French chemist Paul Jacques Malouin made a presentation about galvanization before the French Royal Academy in 1742. In 1836, another French chemist, Stanislas Sorel, obtained a patent for his process that used zinc to coat iron.

Although the basics of hot-dip galvanization—coating metal with zinc to inhibit corrosion—have remained the same over the years, we’ve come a long way in terms of equipment and technology. We hot-dip entire coils of steel sheet (weighing as much as 22 tons each) in a continuous process on our galvanizing lines, which average close to three football fields in length.

First, a coil is placed on a payoff reel, and the steel sheet is fed into a gas-operated direct-fire furnace that has four functions: to heat, clean, anneal, and remove oxide. Initially, direct flames clean the steel and raise its temperature to 1,200 degrees Fahrenheit. The temperature is then raised to 1,400 F in an annealing process that makes the steel stronger and harder while making it more pliable for forming as well.

Still in the furnace, the temperature of the steel is reduced to 870 F to match the temperature of the molten zinc awaiting it. In the fourth function of the furnace, hydrogen gas is injected to remove oxide.

The steel is then hot-dipped in the zinc bath, and the two metals bond during a chemical reaction. As the steel leaves the bath, high-velocity air knives blow off excess zinc to achieve the desired coating weight (thickness). Next in line, the steel may undergo temper rolling and leveling to further improve its mechanical properties.

After any mechanical treatments occur, the steel sheet goes past a continuous-scanning radiation gage that measures the coating weight to ensure it’s to specifications and consistent. All results are monitored in real time, and all coating information for each coil is stored in a database.

If requested by the customer, the steel may then undergo chemical treatment that provides addition protection against corrosion.

At various points in the process, a closed-loop water system is used to cool both the steel sheet and the equipment on the line. In fact, we use more than 3 million gallons of water in our operations each year.

Finally, the steel sheet is rewound on the recoiler and readied for shipment. The product is strong, has the mechanical properties necessary for the intended application, and is ready to withstand the years and harsh environments.