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The Navel

  • The  yarn leaves the rotor via a tube in the middle of the rotor .

  • Turning of the rotor causes the yarn to roll continually on the surface of the specially formed mouthpiece {navel} of this tube .

  • The false-twist effect previously descibed is generated , & , in addition the navel exerts an influence on the yarn structure.

  • The magnitude of these effects are dependent upon the surface of the navel.

  •  A rough surface , for example , one that is grooved, increases false twist but simultaneously leads to a rougher , hairier & more voluminous yarn and also leads to more deposits in the rotor , because fibre fragments or spin finish already bound into the yarn are separated again at the navel.

  • A rough navel surface enables spinning to be done with a lower twist coefficient , giving a softer yarn.While smooth navels give somewhat better yarn characteristics, coupled with very low yarn hairyness, so that ,for several types of end-product, required fluffiness is lacking .

  • Furthermore , running problems can arise for the yarn in the package because the yarn layers exhibit inadequate adherence.

  • This can cause slipping of layers , loops & snarl formation, and sometimes over-large yarn balloons.

  •  Accordingly , in the production of some yarn types ,especially knitting yarns , the navel is deliberately selected to give a degree of yarn hairyness.

  • The radius of the arc of wrap on the navel also exerts an influence on the yarn-production process.

  •  A large radius permits spinning with a lower twist coefficient .

  •  a smaller radius gives a notably higher yarn stregth , but yarn twist has to be raised in order to maintain practicable running conditions.

 

  • The mouthpiece of the withdrawl tube , the navel is made up of steel , while the surface contacting the yarn is of steel or chrome-plated steel or ceramic.

  • Furthermore , distinctions are drawn between surfaces that are ; smooth [fig. A] ,GROOVED{3-8 GROOVES} [fig.B –d],, KNURLED, WITH SPIRALS [fig.E]  & RIBBED.

  • Smooth navels give a smooth yarn of high strength , good evenness , & low tendency to slub under axial forces . such navels are used mainly in the production of yarn for weaving & in the processing of severaltypes of the synthetic fibre.

  • Grooved navels enable voluminous , rough & rather hairy yarn to be produced. The effect is more marked the greater the number of grooves. The typical field of application for this navel type is in the production of knitting yarn. It has the adv antage that the yarn repeatedly lifts off the navel surface as it rolls around .This gives better distribution of twist along the yarn.

  • Knurled {& grooved} navels are chiefly used only in the processing of coarse synthetic fibres.

  • Spirally modified navels are suited to the production of rather voluminous yarns with low twist levels,similar to those obtained from ceramic navels  with four grooves . however , in comparision with the latter , the spiral version gives higher strength, fewer ends down , & a smoother conduct.

  • Ceramic are more wear resistant than grooved steel navels.But due to the  better heat conduction ,steel navels are used in synthetic fibres processing as there is less heating of fibres & less damage to the fibres.

 



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