46 and 47 a coating agent is supplied to the coating supply pipe 32 from one or both ends of said pipe via connecting members 45 a plurality of arms 34 are connected to the sides of the box beams 46 and 47 that face the nip n the filling pieces 37 and 38 of the invention are connected to the arms 34 via a t joint 35 or the equivalent as shown in fig3 the filling pieces 37 and 38 have an essentially triangular cross section and their tip parts 39 face the nip n the filling pieces 37 and 38 are affixed to the arms 34 by a metal strip 36 or the equivalent sufficiently strong fixing a plurality of nozzle pipes 33 lead from the transverse coating supply pipes 32 toward the pools l 1 and l 2 supplying the coating via their ends 33a and 33b to said pools the pools l 1 and l 2 have a surface s the surface s of the pools is preferably essentially at the level of the upper side of the filling pieces 37 and 38 the filling pieces 37 and 38 constitute liquid permable porous material or corresponding perforated material such as for example teflon rubber or plastics for example polyethylene the diameters of the holes of the filling pieces 37 and 38 are for example 1 10 mm and the share of holes.