The most widely used metallic coating is zinc. Galvanized steel is produced when the steel is covered in molten zinc or zinc alloy, either by hot dipping or the electrolytic process. In the case of hot dipping, the adherence of the zinc to the steel depends on the steel and zinc temperature, immersion time, alloying elements, and surface preparation. The thickness of the zinc coating also is controlled by the same factors, as well as by the distance of the applicators or wipers during continuous hot-dip galvanizing.
Galvanized steel can be roll formed just as well as uncoated steel, but the zinc pickup on tooling and damage to the coating must be prevented. Zinc pickup is due mainly to the smearing or cold welding effect caused by the speed differential between the rolls and the formed strip and is accelerated by the roll pressure. It is cumbersome and dangerous to remove the built-up zinc from the rolls. The best way to prevent zinc buildup is to use good lubrication combined with properly designed and set up tools.
There is almost no difference between roll forming hot-dipped or electrolytically coated steel if the coating has the proper adherence. Careless metal preparation and incorrect coating procedures can lead to the zinc peeling off the product. Wiped coated steels (the zinc is wiped off after hot dipping) create no problems during roll forming.
Zinc alloy and aluminum-coated steels behave similarly to the galvanized steel and can create the same problems. Metal pickup can be avoided by using the same precautions as those recommended for zinc coating.
