Patent ID: 9333546
Filing Date: 2016-05-10
CPC Classification: B21B,B21D

Claim Text:
1. A metal sheet flattening method of flattening a metal sheet having a cut-sheet form in a roller leveler, which includes a plurality of leveling rolls disposed in a staggered state on upper and lower sides of a pass line of the metal sheet to be flattened and configured to rotate to sandwich and flatten the metal sheet while passing the metal sheet therethrough, a hydraulic pressing cylinder configured to press the metal sheet via the leveling rolls, a drive unit configured to rotate the leveling rolls to pass the metal sheet, and a pinch roll unit disposed on one side of a leveling roll array area, in which the leveling rolls are disposed along the pass line of the metal sheet, and including a pair of pinch rolls configured so that a clearance between the pair of pinch rolls is adjusted by a pinch roll cylinder, and configured to pinch the metal sheet using a pinch roll cylinder and apply a drawing force by the application of a pinch roll drive unit thereto, the method comprising, in the following order: passing the metal sheet that is a steel sheet having a thickness of 2.0 to 25.4 mm and a yield stress of 400 to 1,800 MPa through the leveling roll array area in a state where the steel sheet is not pressed or in a state where the steel sheet is pressed by the pressing cylinder of the leveling rolls with a pressing amount small enough to allow the steel sheet to be passed by the drive unit of the leveling rolls; when a leading end of the steel sheet reaches the pinch roll unit, increasing the pressing amount given by the pressing cylinder of the leveling rolls to a value necessary for flattening the steel sheet and driving the pinch roll cylinder to pinch the steel sheet by the pair of pinch rolls; and passing the steel sheet between the leveling rolls by a driving force applied by the drive unit of the leveling rolls and the drawing force applied by the pinch rolls using the pinch roll drive unit; wherein the pinch rolls and the leveling rolls apply respective drawing forces which pull the steel sheet in the same direction through the leveling rolls.