Steel strip can be hot-dip galvanized in a continuous line. A third, declining method is to use low Z5 grade zinc. Lead is either added to primary Z1 grade zinc or already contained in used secondary zinc. Environmental regulations in the United States disapprove of lead in the kettle bath. Lead is often added to the molten zinc bath to improve the fluidity of the bath (thus limiting excess zinc on the dipped product by improved drainage properties), help prevent floating dross, make dross recycling easier and protect the kettle from uneven heat distribution from the burners. The steel is cooled in a quench tank to reduce its temperature and inhibit undesirable reactions of the newly formed coating with the atmosphere.The steel is dipped into the molten zinc bath and held there until the temperature of the steel equilibrates with that of the bath.The flux is allowed to dry on the steel and aids in the process of the liquid zinc wetting and adhering to the steel. A flux, often zinc ammonium chloride is applied to the steel to inhibit oxidation of the cleaned surface upon exposure to air.The steel is pickled in an acidic solution to remove mill scale.The caustic cleaning solution is rinsed off.This removes oil/grease, dirt, and paint. Steel is cleaned using a caustic solution.The resulting coated steel can be used in much the same way as uncoated.Ī typical hot-dip galvanizing line operates as follows: The process of hot-dip galvanizing results in a metallurgical bond between zinc and steel, with a series of distinct iron-zinc alloys. This is a unique characteristic for galvanizing, which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of 5 mm, above which electron transfer rate decreases). However, zinc is a more electropositive (active) metal in comparison to steel. Like other corrosion protection systems, galvanizing protects steel by acting as a barrier between steel and the atmosphere. Electrogalvanized sheet steel is often used in automotive manufacturing to enhance the corrosion performance of exterior body panels this is, however, a completely different process which tends to achieve lower coating thicknesses of zinc. The use of galvanized steel at temperatures above this will result in peeling of the zinc at the inter-metallic layer. In long-term, continuous exposure, the recommended maximum temperature for hot-dip galvanized steel is 200 ☌ (392 ☏), according to the American Galvanizers Association. This temperature varies by the galvanization process used. Galvanized fumes are released when the galvanized metal reaches a certain temperature. Galvanized steel can be welded however, one must exercise caution around the resulting toxic zinc fumes. It can be identified by the crystallization patterning on the surface (often called a "spangle"). ![]() Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. ![]() When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen ( O 2) to form zinc oxide ( ZnO), which further reacts with carbon dioxide ( CO 2) to form zinc carbonate ( ZnCO 3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 ☌ (842 ☏). Hot-dip galvanization is a form of galvanization. Galvanised hand rail Crystalline surface of a hot-dip galvanized handrail, known as "spangle" Protective effect: completely rusted letter box mounted to a hot-dip galvanized wall
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