Galvanized steel products are made by cleansing and heat-treating rolled coils before dipping them into a bath of molten zinc. Through this process, the coils are plated with zinc only (GI), zinc and iron (GA) or zinc, aluminum and magnesium (PosMAC).
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Some rolling oil and other contaminants remain on the surface of cold rolled steel sheets following processing. These are removed by passing the electrically charged sheet through an alkaline solution which induces an electrochemical reaction.
The material properties of the pre-treated steel sheet can be altered and improved through recrystallization during the annealing process.
After passing through the annealing furnace, steel sheets are dipped into a zinc pot where molten Zn is coated onto the surface. The desired coating weight is achieved by removing excess zinc before solidification with high-pressure air from an air knife.
The surface of a steel sheet, after the air knife, can be coated with a zinc compound prior to reheating in an annealing process. Zn atoms diffuse into the Fe to create a Zn-Fe series alloy.
In order to achieve a flat surface and an elegant finish, the steel sheet is processed with a skin pass mill. In order to prevent the white rust, which often forms on the surface of activated zinc, and to improve corrosion resistance, the surface is coated with a Cr-free resin.
Located at the line’s exit section are a side trimmer, inspection table, oil coating machine and coiling equipment. At this station, all products are inspected and judged relative to material specifications required by the customer.