web 1 or drips off in order to catch this treatment fluid guide surfaces 34 35 are provided at both sides of the web 1 which catch any treatment fluid accumulating below and to the sides of the squeezing roller 32 33 and guide it to drainage surfaces 16 from where it is passed back to the flat channel 10 the drainage surface 16 is formed on the top of a drainage plate which is designated as a whole as 22 with one each being arranged in a mirror image relative to the web 1 the drainage plate 22 has a double wall structure and consists of a top flat wall 21 the top of which is the drainage surface 16 and another wall 23 arranged at a distance below the former in the exemplary embodiment the two walls 21 23 consist of panels of sheet metal made of corrosion resistant steel in principle the walls 21 23 can also consist of plastic but then simple forming by means of bending them at an angle is not possible a space 24 is left between the walls 21 23 through which a heat carrier medium such as hot water oil or air can flow in most cases the concern is to heat the drainage surface 16 in principle however cooling is also possible the structure of the drainage plate 22 is explained in greater detail using fig4 to 6 fig2 shows a different drainage plate 22 39 which can be used for the invention which rests against a roller 25 which rotates in the.