Hot Dip Galvanized
All Calhoun Super Structures framework and other critical components are hot-dipped galvanized (HDG) after fabrication. This means you have the full protection of the HDG, inside and out, welds and all; nothing is exposed. The hot dip galvanization process creates metallurgical bond between the base steel and zinc-iron alloys. The result is a protective coating harder than the base steel and has up to 4 times the amount of zinc protection in that of in-line galvanizing. The HDG process is time tested. There is a reason why engineers in Canada spec hot dip galvanized steel in building high traffic bridges, it lasts!
We service the equestrian, agricultural, commercial, recreational and industrial markets of Canada and the United States of America. National Building Group will design and deliver straight from factory to site. Our implementation of new technology in administration, manufacturing, and delivery drives our efficiency which in turn saves you money!
Here's how it works
Galvanizing involves bonding zinc to steel, and surface preparation is extremely important. If it is not done correctly, the zinc won't adhere to the steel and sections will be left uncoated. Our steel undergoes three stages of preparation.
A hot alkali solution removes organic contaminants, such as dirt, paint markings, grease and oil from the metal surface. Epoxies, vinyl, asphalt, or welding slag must be removed before galvanizing by grit blasting, sand blasting or other mechanical means.
Scale and rust are removed from the steel surface by pickling in a dilute solution of hot sulphuric acid or ambient temperature hydrochloric acid.
Fluxing removes oxides and prevents further oxides from forming on the surface of the metal prior to galvanizing. The steel is dipped into an aqueous solution of zinc ammonium chloride. The material is then dried prior to immersion in molten zinc.
Each welded truss is completely immersed in a bath consisting of a minimum of 98% pure molten zinc at a temperature of about 840 ºF (449 ºC). The zinc metal then reacts with the iron on the steel surface to form a zinc/iron inter-metallic alloy.
The trusses are then withdrawn slowly from the galvanizing bath, and the excess zinc is removed by draining and vibrating.
Because the galvanization process involves total immersion, all surfaces are coated- providing protection for both the outside and the inside of the steel tubing used in the trusses.
After the trusses have dried, the galvanizer closely scrutinizes the coating thickness and appearance. Through a battery of physical and laboratory tests, they determine thickness uniformity, adherence and appearance.Every Calhoun super Structure is galvanized according to long-established, well accepted and approved standards of ASTM, the Canadian Standards Association (CSA), and the American Standards of State Highway and Transportation Officials (AASHTO). These standards cover everything from minimum required coating thickness for various categories of galvanized items to the composition of the zinc metal used in the process.