Apparatus and method for folding over an edge portion of thin sheet

Apparatus for folding over along a crease line an edge portion of a thin sheet of material, which sheet comprises on opposite sides of said crease line a body portion and an edge portion integral with the body portion and extending between the body portion and an edge of the sheet, the edge portion being substantially in line with the body portion when the sheet is unfolded and being doubled back into an overlapping position with respect to said body portion when the sheet is fully folded, said apparatus comprising:

• (a) a pair of support rolls having laterally spaced-apart axes and peripheries over which said sheet is caused to pass so that a predetermined region of said sheet extends between said peripheries as the sheet travels from a first one of said support rolls to a second one of said support rolls,
• (b) an air film roll having a longitudinal axis and positioned between said support rolls and exerting on said predetermined region of said sheet a force that causes the body portion of the sheet in said predetermined region to be deflected toward a reference plane in which said support roll axes are located, and in which:
• (c) said air film roll has an outer end that is located at said crease line so that said edge portion folds along said crease line from said in-line position at said first support roll to a position substantially perpendicular to said body portion at said outer end of the air film roll and folds along said crease line from said perpendicular position to said overlapping position in the zone of said sheet extending between said outer end of the air film roll and said second support roll, said edge and said edge portion when said edge portion is in said substantially perpendicular position are disposed in close proximity to said outer end of the air film roll,
• (d) said outer end of said air film roll has a substantially planar configuration and angles in two directions with respect to an adjacent end plane perpendicular to the longitudinal axis of the air film roll,
• (e) there is a first viewing plane parallel to said reference plane on the outer side of said air film roll,
• (f) when said air film roll and said predetermined region of said sheet are viewed from said first viewing plane, said outer end of the air film roll angles in a first of said two directions with respect to said perpendicular end plane that allows said edge of the sheet to pass said outer end via a straight line path extending between said support rolls, and
• (g) when viewed from a second viewing plane perpendicular to said first viewing plane and extending through the longitudinal axis of said air film roll, said outer end of the air film roll angles in a second of said two directions with respect to said perpendicular end plane to recess away from the perpendicular end plane the portion of said outer end nearest said first viewing plane.