How Is Galvanized Steel Produced?
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The Objective of Galvanization
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"Galvanization" means the process of coating steel with a layer of zinc. The zinc is meant to protect the steel from corrosion. Depending on the type of galvanization needed, a thin or thick layer of zinc will be applied. However, in all cases, the zinc must bond firmly to the steel with no capability of chipping or peeling.
Hot-Dip Galvanization
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Hot-dip galvanization, a very common galvanizing technique, deposits a thick layer of zinc on a steel object. The process begins with heating zinc until it forms a molten bath at a temperature of around 850 degrees Fahrenheit. Then workers place the piece of steel to be galvanized in the bath and let it sit until it reaches the temperature of the bath. At that point, workers remove the object, which now has a layer of zinc carbonate firmly bonded to it. In some cases, the steel is then quenched in a dilute chromate solution. In all cases, the steel must be cleaned thoroughly before dipping in the hot bath.
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Electrogalvanization
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The electrogalvanization process uses electricity to bond zinc to steel. In this process, workers run DC electricity through a zinc-salt solution. The electricity runs through an anode and then to the steel, which acts as a cathode. The anode in electrogalvanization can be either a block of zinc, in which case it serves also as the zinc component of the zinc-salt solution. It can also be a block of lead, in which case workers must constantly add zinc to the solution. In both cases, the force of electricity running through the anode to the steel causes zinc to dissolve and bond to the steel. During this process, dissolved particles of zinc run along the line of current. This brings them to the steel and deposits them on it. The constant DC electricity causes zinc particles to bond tightly to the steel, creating a very thin layer. As in hot-dip galvanization, the steel must be thoroughly cleaned prior to this process.
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References
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