Patent ID: 8308909
Filing Date: 2012-11-13
Classification: D21F

Abstract:
1. A sheet forming system for a machine for producing a multilayer fibrous web from at least two fibrous stock suspensions, the multilayer fibrous web being one of a multilayer paper web and a multilayer cardboard web, said sheet forming system comprising: a multilayer headbox with a headbox nozzle which includes at least one separating wedge and at least two converging nozzle chambers extending over a width of the machine and separated from one another by said at least one separating wedge, said at least two converging nozzle chambers including a first nozzle chamber and a second nozzle chamber, said first nozzle chamber carrying a first fibrous stock suspension of the at least two fibrous stock suspensions in a form of a first fibrous stock suspension stream during an operation of said multilayer headbox, said second nozzle chamber carrying a second fibrous stock suspension of the at least two fibrous stock suspensions in a form of a second fibrous stock suspension stream during said operation of said multilayer headbox, said first nozzle chamber being equipped with a first upstream feed device and a first downstream outlet gap extending over said width and including a first gap width, said second nozzle chamber being equipped with a second upstream feed device and a second downstream outlet gap extending over said width and including a second gap width, said first and second nozzle chambers each being an outer nozzle chamber, said first nozzle chamber having a first outside wall on an outside of said first nozzle chamber, said second nozzle chamber having a second outside wall on an outside of said second nozzle chamber, said at least one separating wedge having a first separating wedge surface and a second separating wedge surface, said first separating wedge surface being in contact with said first fibrous stock suspension stream which is adjacent said first separating wedge surface during said operation of said multilayer headbox, said second separating wedge surface being in contact with said second fibrous stock suspension stream which is adjacent said second separating wedge surface during said operation of said multilayer headbox, said at least one separating wedge arranged in said headbox nozzle having a separating wedge protrusion in a range of 0.5 to 3.0 times a largest individual gap width of said at least two converging nozzle chambers, said at least one separating wedge including two separating wedge areas which are an upstream separating wedge starting area and a downstream separating wedge end area, said upstream separating wedge starting area having a separating wedge starting angle, said downstream separating wedge end area having a second separating wedge end angle, said separating wedge starting and end angles of said two separating wedge areas having different angular values, said separating wedge starting angle of said upstream separating wedge starting area having a greater angular value than said separating wedge end angle of said downstream separating wedge end area, at least one of said first separating wedge surface and said second separating wedge surface respectively including a non-planar transition area between said two separating wedge areas of said at least one separating wedge; and one gap former which is located immediately downstream from said multilayer headbox and which has a continuous revolving first wire and a continuous revolving second wire, said gap former further including a forming roll and a breast roll, said forming roll including a circumferential area and being an open forming roll, said breast roll including a circumferential area, said first wire running over said circumferential area of said forming roll, said second wire running over said circumferential area of said breast roll and then running onto said first wire in an area of the sheet forming system of said forming roll, thus forming a wedge shaped stock inlet gap which immediately receives said first and second fibrous stock suspension streams emerging from said headbox nozzle of said multilayer headbox as one common fibrous stock suspension free jet having a free jet length, said first and second wires with the at least two fibrous stock suspensions therebetween forming a twin wire zone at least in a plurality of sections, said common fibrous stock suspension free jet which includes at least said first and second fibrous stock suspension streams having a free jet length in a range of 100 mm to 500 mm, said open forming roll having a diameter in a range of 1,200 mm to 2,500 mm.