Rieter

Yarn take-off

Index

The yarn is taken from the rotor by the delivery shaft and pressure roller (a in Fig. 30), diverted virtually at right angles in the process by draw-off nozzle (b) projecting into the rotor and guided out by draw-off tube (c) immediately following this. However, as has already been said, the draw-off nozzle is far more than a mere guide device. At take-off the yarn continuously rolls off on the surface of the draw-off nozzle due to the rotation of the rotor. This rolling-off temporarily inserts additional twist into the yarn (contrary to the direction of twist of the yarn), thus creating the false-twist effect required for spinning stability, which can be up to 60% of the set yarn twist (see section  Genuine and false twist). The greater the false-twist effect, the higher the spinning tension.

While rolling off on the surface of the nozzle, the yarn is repeatedly raised briefly in rapid succession, depending on the surface structure. This high-frequency vibration – together with the false-twist effect – promotes twist propagation into the rotor groove. The more pronounced the structure of the nozzle surface, the more vigorously the yarn vibrates, thus supporting twist propagation and the falsetwist effect extending into the rotor all the more. As a result of this, the greater the false-twist effect, the lower the genuine yarn twist that can be selected and the bulkier and softer the yarns that can be spun. The draw-off nozzles are held firmly in the rotor cover by either a screw or magnetic lock. Draw-off nozzles can be replaced very easily and in some cases without using tools. Since draw-off nozzles are now usually made of high-quality ceramics, service lives of several years can be achieved under normal spinning conditions.

Section  Range of application of draw-off nozzles and draw-off tubes deals in detail with the ranges of application of the different nozzle surfaces, the positioning of the draw-off nozzle relative to the thread collecting groove of the rotor and the influence of the different thread draw-off tubes on yarn quality, yarn structure and spinning stability.

Fig. 30 – Yarn take-off with take-off rollers (a), draw-off nozzle (b) and yarn draw-off tube (c)