Both GALVALUME and galvanized sheet steels are made by a "continuous hot dip" process. Coils of cold rolled steel are welded end-to-end and processed continuously on the coating line at speeds up to 600 feet per minute. The uncoiled sheet is first cleaned to remove rolling oils and mill dirt, and to reduce surface oxides so that the surface will accept the coating. These continuous sheets are first fed into a molten coating bath contained in an open top, brick-lined heated pot. The sheet then passes around a roller submerged in the coating bath and exits the bath vertically, pulling out with it an envelope of the coating material. As it exits, the sheet proceeds through a pair of opposing air knives, which are positioned above the bath and equidistant from the surface of the sheet. Most modern production lines have a coating thickness gauge feed-back control, which automatically adjusts knife air pressure and position to ensure that a uniform coating is applied. Various finishing steps are carried out to complete the process, after which the sheet is wrapped around a reel into a coated steel coil.