suction devices 3 it is here further indicated that in the arrangement of fig i and as viewed in the direction of movement 50 of the upper and lower wires 8 and 9 the length of the vacuum suction box 4 provided in the upper wire 8 is greater than the length of the suction box 2 provided in the lower wire 9 downstream of the vacuum suction box 4 there is located a separation or separating element 5 which is located upstream of the horizontally extending rear portion 56 of the lower wire 9 in the embodiment of fig1 this separation or separating element 5 comprises a curved box containing ledges extending over the width thereof in the cross machine direction and having a radius of curvature in the order of between 1 5 meters and 20 meters this separation or separating element 5 has an active surface 5a which here is located at a position intermediate the planes extending through the upper apex point 58 and lower apex point 60 of the forming roll 1 as a modification this box defining the separation or separating element 5 can comprise a linear or straight box which is operated under vacuum conditions it is also conceivable to use a register roll as the separation or separating element 5 fig2 schematically depicts and without greater detail a different possible course of the converging or joined together upper and lower wires 8 and 9 at the region between the forming roll 1.