Zinc metal used in the galvanizing process provides an impervious barrier between the steel substrate and corrosive elements in the atmosphere. It stops moisture, corrosive chlorides, and sulfides from attacking the steel.
Oil and Grease Removal
A hot alkaline cleaner is used to remove dirt, oil, grease, and soluble markings. Paint and welding contaminants must be removed by sandblasting, which we can arrange for you.
Pickling-A dilute solution of hot sulfuric acid is used to remove surface rust and mill scale to provide a chemically clean metallic surface, readying the metal for the hot-dip process. This portion of the process can take anywhere from 30 minutes to 1½ hours, depending on the complexity or the thickness of the part.
Fluxing-Fluxing is the final surface preparation step in the galvanizing process. Fluxing removes oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing. The steel or iron is dipped in an aqueous solution of zinc ammonium chloride. The material is then dried prior to immersion in molten zinc.
This is where the steel gets the zinc coating. The steel is immersed into a bath of molten zinc, which is heated between 820° F and 850° F. During the galvanizing process, the steel comes up to the bath temperature and the zinc metallurgically bonds to the steel, creating a series of highly abrasion-resistant zinc-iron alloy layers, topped by an impact resistant pure zinc layer. In this step, the material is completely immersed in a bath consisting of a minimum of 99% pure molten zinc at a temperature of about 840°F (449°C). The zinc metal then reacts with the iron on the steel surface to form a zinc/iron inter-metallic alloy.
The articles are withdrawn slowly from the galvanizing bath and the excess zinc is removed by draining, vibrating and/or centrifuging. The articles are cooled in either water or ambient air immediately after withdrawal from the bath. Because the galvanizing process involves total material immersion, it is a complete process: all surfaces are coated.
Galvanizing provides both outside and inside protection for hollow structures. Hollow structures that are painted have no interior corrosion protection.
Galvanizing is performed at the factory under any weather or humidity conditions. Most brush-applied and spray-applied coatings depend upon proper weather and humidity conditions for correct application. This dependence on atmospheric conditions often translates into costly construction delays. The galvanizer’s ability to work in any type of weather allows a higher degree of assurance of on-time delivery. Working under these circumstances, galvanizing can be completed quickly and with short lead times. Two-day or three-day turnaround times for galvanizing are common.
The final step in the hot-dip process is to ensure compliance with the specifications.
Inspection is perhaps the most important step in the process!
The two properties of the hot-dip galvanized coating that are closely scrutinized after galvanizing are coating thickness and coating appearance. A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity, adherence and appearance. Products are galvanized according to long-established, well-accepted and approved standards of ASTM, the Canadian Standards Association (CSA), and the American Association of State Highway and Transportation Officials (AASHTO).
These standards cover everything from minimum required coating thicknesses for various categories of galvanized items to the composition of the zinc metal used in the process. The inspection process for galvanized items is simple and fast, and requires minimal labor.
We have AGA-approved certified inspectors, and can provide material certs upon request