Back Doubling

  • In rotor spinning, doubling takes place when fibres are fed & deposited one on the other in rotor.
  •  Since a fibre strand is first totally opened up & then reconstituted in the course of this operation , the term “ back-doubling” is used.
  •  The evenness obtained inthis way is of a high degree & is always better than that of ring spun yarn, for which feedstock with a high short-fibre content is used.
  • The only disadvantage is that all unevenness in sliver which are greater than internal periphery of the rotor {geneally=3.14*35=110 mm. Where 35mm. Is rotor diameter.} Pass straight into the yarn.
  • Schlafhorst formula of backdoubling:-.
    • Since the yarn is pulled out of the rotor , the yarn separation point shifts continually forward within the rotor.
    • It therefore has a higher peripheral speed than the rotor itself.
    • This lead  {x} is equal to the witdrawl speed of yarn / rotor circumference { c} .
    • The withdrawl speed in turn identical to the delivery speed {l} which is equal to the rotor rpm {n}   / twist per metre  {t}.
    •  Now according to the schafhorst ,
    • Back doubling =  n / x.
                                   =  Nc / l.

                                   =  Nct /  n.

                                   =  Ct.

                                   =  3.14 * DT  metres.

           {Since c=3.14 * d. Where d is diameter of the rotor}.

                                   = 3.14*DT /1000 mm.


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