Method and device for bending section-sheet, plate, strip and like material

A method of bending a section-sheet comprising alternating longitudinal ridges and valleys, the side portions of which valleys also constitute side portions of the ridges, perpendicularly to the longitudinal directions of the ridges and valleys, characterized in that the lower surface of the valley bottoms is impressed from below on its entire width along a straight line in parallel with the valley bottoms, which line extends perpendicularly relative to said longitudinal direction, that the impression is made in radial direction relative to a shaft in parallel with and located on the same side of the sheet as said line between holding-up members positioned in relatively small spaced relationship, which members prior to the beginning of the impressing operation are tightened only to the upper surface of the valley bottoms to permit the sides of the lateral portions of the valleys forming a part of the lower surface of the sheet to bulge outward when the impression is being made, and after such an impression the relative position between the holding-up members and the sheet is changed for carrying out a second impression in parallel with the first one, whereafter this operation is repeated until the desired bending angle has been obtained.