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What is Hot Dipped Galvanizing?
The hot dip galvanizing process is relatively simple. It involves cleaning steel and immersing it in molten zinc to obtain a coating.
Hot dip galvanizing is the process of coating iron or steel with a layer of zinc by immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). During the process, a metallurgically bonded coating is formed which protects the steel from harsh environments, whether they be external or internal.
Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel and can be identified by the crystallised pattern on the surface (often called a ‘spangle’).
What Is Hot-Dipped Galvanized Steel Used For?
Hot-dip galvanized steel is used where steel is being used in a corrosive environment. This could be in salt-laden air or marine applications, but could also apply when steel is embedded in soil, concrete, or water. Galvanized steel is a versatile metal that is used in car bodies, bikes, fasteners, structural beams in buildings, rebar in concrete, metal fencing, and electrical pylons.
Hot Dipped Galvanizing Benefits
Hot-dip galvanizing provides a number of benefits to the steel it protects. The metallurgically-bonded zinc-iron alloy layers not only create a barrier between the steel and the environment, but also cathodically protect the steel. The cathodic protection offered by zinc means the galvanized coating sacrifices itself to protect the underlying base steel from corrosion.
DURABILITY The hot-dip galvanized coating has excellent durability. This is an important characteristic for fasteners, which are often packaged in bulk and handled frequently, during which less durable coatings might be scraped off.
COMPLETE COVERAGE The nature of the hot-dip galvanizing process creates a uniform coating. Molten zinc flows over and into all areas of an item, reacting with the steel in a diffusion process that proceeds perpendicularly into the surface, producing a consistent coating thickness on all surfaces including corners and edges. This is of particular importance for fasteners, where the peaks and valleys of threads must receive equally thick coatings to prevent early failure of the coating, as well as to ensure proper fit of the thread into mating fasteners.
LONG SERVICE LIFE Hot-dip galvanized coatings have excellent service lives in a variety of environments, including in fresh and saltwater, in soils and in contact with concrete and treated wood. The lifetime of galvanized coatings is proportional to the thickness of the coating. Thicker zinc coatings will last longer, as the corrosion process must penetrate more material before reaching the base steel.
Hot Dipped Galvanizing Specifications
ASTM Standards (ASTM A123/A123M)
Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products
ASTM Standards (ASTM A153/A153M)
Zinc Coating (Hot-Dip) on Iron and Steel Hardware
ASTM Standards (A767/A767M)
Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement
ISO 1461
Hot-Dip Galvanized Coatings on Fabricated Iron and Steel Articles - Specifications and Test Methods
ISO 14713
Zinc Coatings - Guidelines and Recommendations for the Protection Against Corrosion of Iron and Steel in Structures