After rolling out sheets, for example for the automotive industry, these are wound into a so-called coil and are stress-relieved via annealing. When cooling the sheet-metal coils, the structure of the materials is changed in such a way that coil bending, edge waves, unilateral waves, coil breaks and central waves may arise
when unrolling the sheets. With these errors, the sheets cannot be further processed. Therefore, straightening machines are used prior to final processing of the sheets.
The material to be straightened is subjected to mechanical alternating bends in the machine. The intensity of the alternating bends is reduced at the outlet of the machine. The more straightening rollers there are, the higher the number of alternating bends, and the more bends, the better the straightening result. Straightening machines are result-oriented, and therefore there are straightening machines with five rolls for thicker sheets, and with up to 15 or more rolls for thin sheets.