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Influencing the Structure of OE Rotor Yarns -Possibilities and Limits.   

By:- W.Kampen , J.Lunenschloss

  • It can be said that the yarn structure is influenced very considerably by the false twist imparted at the draw off tube.
  •  As more false twist is inserted , more wrapper fibre turns result.
  • Moreover at the draw off tube the yarn twists back to the true twist factor, causing parts of the wrapper fibres to become untwisted.
  • Under mechanical stressing at the draw off tube , the thread guides following or only in downstream processing , these fibres wound loosely round the yarn core are easily stripped back.
  • This becomes more likely as more false twist is inserted.
  • To produce yarns with the usual twist factors of 80-140 ,including a safety margin a certain false twist is needed.
  •  If the false twist is suppressed , as when working with a rotating draw-off tube, twist factors of 200 & more are required in order to spin without end breaks.
  •  Such yarns are similar in appearance to ring yarns; They have no wrapper fibres.
  • With increasing rotor speeds more false twist is inserted with all the attendant disadvantages mentioned, unless special precautions are taken, i.e., Matching the rotor diameter & draw off tube geometry.
  •  If for example the rotor speed is raised from 50000 rpm to 70000 rpm without increasing the insertion of false twist ,then either draw-off surface or the rotor diameter should be reduced.
  • In this way the properties of the yarn spun at higher speeds can be improved considerably.
  • The results quoted here may be improved still further by reducing the rotor diameter to 40mm. So that apart from the twist the yarn properties of the yarns s pun at rotor speeds of 70000 & 80000 rpm are quite comparable with the yarns spun at 50000rpm.
  • . Problems arise when starting up at lower speeds.
  • The false twist is too low.
  •  It might be raised briefly during the starting phase by increasing the surface of draw-off tube for example.
  • Another possibility would be a brief increase of the twist factor. Increasing the surface of the draw-off tube brings the advantage that the false twist remains roughly constant during start up, so that there is no or very little alteration in the yarn structure during the start up, while the rotor is running up to its full revolutions.
  • With the constant draw off tube surface employed industially up to now, from the commencement of spinning at low rotor rpm until nominal rotor speed is reached, the yarn length spun differs somewhat in its structure from the yarn produced at the nominal rotor speed.

 



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