to the sliding surface 12 2 the drive shaft 6 is pivoted by the bearing 23 within the bearing bore 18 the drive shaft 6 is coupled on one end to a drive 19 through which the nozzle ring 1 can be driven with predetermined rotational speed the drive 19 could for example be formed by an electrical motor which is arranged laterally on the stator 2 as can be seen from the representation in fig1 a cover 13 is associated with the nozzle ring 1 on the periphery and the cover is movably held on the carrier 3 via a pivot axis 14 as can be seen from the representation in fig2 the cover 13 extends in a radial direction on the periphery of the nozzle ring 1 over a region including the chamber opening 10 of the stator 2 the cover 13 has an adapted covering surface on the side facing the nozzle ring 1 the covering surface completely covers the guide groove 7 on the outer casing 31 of the nozzle ring 1 and hence forms a treatment channel in this region a thread 20 is guided in the guide groove 7 on the periphery of the nozzle ring 1 to this end on the nozzle ring 1 an inlet side 21 is associated with an inlet thread guide 15 and an outlet thread guide 16 is associated with an outlet side 22 thus the thread 20 can be guided between.