with three active segments 82 83 84 respectively distributed uniformly over the periphery of the disk and each having the same characteristics as those of the active segments of the disks in fig3 in fig6 there is shown another modification which differs from the embodiments of fig1 to 4 by virtue of the fact that the grooves are no longer formed by spaces between the side by side sheet metal disks but by deep recesses 91 helically cut in the cylindrical surface of a solid drum of external diameter d the grooves thus formed determine together the fibre separating ridges they may be at a single thread or else several threads and form fibre separating ridges corresponding to one thread or several threads the operation of the fibre separating drum is always substantially the same that is to say that the narrow fibre separating ridges constituted in this example by the outer surfaces of the threads form with the continuous cylindrical surface of the upper pressure roller 42 nip points which are constantly displaced in the axial direction during the rotation of the fibre separating drum 18 in fig7 there is shown another embodiment which differs from that of fig1 on the one hand by the inversion of the positions of the fibre separating drum and.