Device for the flattening of sheets by means of suction

In a device for removing curling tendency in sheets in sheet-fed machines, particularly printing presses, having means for conveying a sheet edgewise in a transport plane, the combination comprising upstream and downstream beam-like supporting members arranged transversely with respect to the direction of sheet movement and presenting supporting surfaces which are spaced parallel to one another on one side of the transport plane to define a groove in between, means for applying vacuum within the groove to draw a passing sheet downwardly into the groove to produce a relatively sharp concave bend in the sheet thereby to counteract normal curling tendency, the supporting surfaces being cylindrically rounded to lead the sheet gradually into and out of the groove, a filler strip in the groove normally defining the bottom of the groove and which is adjustable broadwise for varying the depth of the groove, the filer strip being elevatable into a position in which it extends clear of the groove and having a presented edge with a small radius of curvature so that when the sheet is drawn over the presented edge a final convex bend is imparted to the sheet thereby to remove curling tendency in the opposite direction.

In a device for removing curling tendency in sheets in sheet-fed machines, particularly printing presses, having means for conveying a sheet edgewise in a transport plane, the combination comprising upstream and downstream beam-like supporting members arranged transversely with respect to the direction of sheet movement and presenting supporting surfaces which are spaced parallel to one another on one side of the transport plane to define a groove in between them, the upstream supporting member being hollow to form a vacuum plenum and having ports leading from the plenum into the groove, the plenum being connected to a source of vacuum for drawing a passing sheet downwardly into the groove to produce a relatively sharp concave bend in the sheet having a predetermined included angle to counteract the curling tendency, and means including a manually movable member for changing the profile of the groove to vary the sharpness of the included angle thereby varying the degree of correction while enabling the degree of vacuum to be kept substantially constant.