What is hot galvanized steel?
Galvanized steel (HDG) is a steel that has been immersed in molten zinc to form a resistant coating. The term galvanization usually refers to a hot dive method; Sometimes it is also called zinc hot immersion . A characteristic crystalline pattern is often left on the steel surface, called spangling . Hot galvanized steel is used in applications where the weather can be exposed, but where stainless steel is too expensive. It is then immersed in the kettle of molten zinc at 815-850 ° F (435-455 ° C). Hot zinc reacts with steel and creates a alloy surface with four different layers. The inner layer is about 75% zinc and 25% steel; The outer layer is 100% zinc. The excess zinc is then exhausted and coated steel is cooled with cold air or water.
When exposed to air, zinc with oxygen, water and carbon dioxide reacts to form a hard carbonate layer (ZNCO 3 ). This protects the underlying steel in two ways: noIt only provides a mechanical barrier between steel and atmosphere and minimizes oxygen exposure. Second, zinc acts as sacrificial anode . Zinc oxidizes faster than iron and gives up electrons in this process. These electrons rather than traveling to steel, where they reduce chemical reactivity of iron and slow down the corrosion process. The term sacrificial concerns the fact that a well of zinc available for oxidation is used over time, preventing iron in steel in the same fate.
Despite this two -point defense, all hot galvanized steel will eventually be. The zinc coating only slows down this process. Because zinc free zinc is used by oxidation, its role of sacrificial anode becomes dimennik. The coating will also physically erode due to the exposure of abrasives and chemicals in the environment, thereby reducing its efficiency as a mechanical barrier for air. Sour rain and salt water will increase the speed at which the coated metal breaks.
galvanizing process is over 150 years and in the wholeMany applications are used by a hot dip galvanized steel. It is used, among other things, for structural steel beams, undulating steel leaves, nuts, screws, pipes, grid, railing and steel sidewalks. Industry claims that galvanized steel can take more than 100 years in typical installations. If steel should be used in places where it will be exposed to seawater, mechanical abrasion, acids or other hard conditions, stainless steel for long -term choice can be a better choice.