Thread-guiding unit, open-end spinning machine and method for operating a spinning station

1. A thread guide unit for drawing off a thread out of a rotor of a spinning unit of an open-end spinning machine, comprising:

a draw-off tube, the draw-off tube having a first end, an opposite second end, and a continuous inner diameter surface between the first end and the opposite second end, wherein the draw-off tube is configured such that during spinning operations at the spinning unit, the first end is adjacent and concentric with an open-end of the rotor to draw a spun yarn out from a center of the rotor and into the draw-off tube;

a compressed air nozzle configured with the draw-off tube;

a thread outlet element extending into the second end of the draw-off tube;

the compressed air nozzle comprising a mouth formed as a gap between the inner diameter surface of the draw-off tube and the thread outlet element, wherein compressed air is directed into and along the gap from the compressed air nozzle; and

means for generating a vortex in the compressed air flowing through the gap and into the draw-off tube to generate or maintain a twist in the thread in the draw-off tube.

2. The thread guide unit according to claim 1 , wherein the mouth of the compressed air nozzle has one of a ring or semi-circular shape and comprises a plurality of openings arranged along a ring that extends radially outward towards the inner diameter surface of the draw-off tube.

3. The thread guide unit according to claim 1 wherein the vortex generating means comprises air directing elements in the gap formed on one or both of the inner diameter surface of the draw-off tube or an outer diameter surface of the thread outlet element.

4. The thread guide unit according to claim 1 , wherein the vortex generating means comprises an offset of the compressed air nozzle relative to an axis of the draw-off tube so as to introduce the compressed air to the mouth with a tangential component to generate the vortex.

5. The thread guide unit according to claim 1 , further comprising a compressed air coupling on the compressed air nozzle to connect a compressed air hose.

6. The thread guide unit according to claim 1 , wherein a ring-shaped air chamber is formed between the draw-off tube and the thread outlet element.

7. The thread guide unit according to claim 1 , wherein the draw-off tube comprises a bend such that a direction of a part of the draw-off tube on which the thread outlet element is arranged corresponds to a draw-off angle of thread from the thread guide unit.

8. The thread guide unit according to claim 1 , wherein the draw-off tube further comprises a twist stop device.

9. The thread guide unit according to claim 1 , wherein the draw-off tube further comprises a thread sensor.

10. The thread guide unit according to claim 1 , further comprising a fastening device that connects the thread guide unit to the spinning unit.

11. The thread guide unit according to claim 1 , further comprising a negative pressure connection provided on the draw-off tube.

12. The thread guide unit according to claim 1 , wherein the inner diameter surface of the draw-off tube comprises a cylindrical surface with a diameter (D) between 2 mm and 4 mm and the gap has a thickness (T) that is between 0.5% and 15% of the inner diameter (D) of the draw-off tube.

13. An open-end spinning machine with a plurality of spinning units, wherein each spinning unit comprises a spinning assembly, draw-off rollers, a winding unit, a thread piecing unit, and the thread guide unit according to claim 1 .