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Fibre Separation And Transportation

 

  • To separate fibres from the sliver feed, the sliver is fed over a supporting surface towards the opening roller, the arrangement being similar to the taker-in region of a conventional card.
  • Thus to prevent damage to fibres , the supporting surface is machined to provide a curved but wedge shaped space in which the sliver fringe is held during separation of the fibres.
  • The optimum dimensions & position of the supporting surface relative to the sliver feed roller & to opening roller clothing will depend on the sliver count ,fibre fineness & the fibre length.
  •  Optimization of the support surface dimensions has shown that the distances designated g & h in fig.1 have the main effect on the yarn evenness & strength. For h = {1.5 to 2.2}t, where t is the linear density ktex of the sliver, & g={[2.3 to 4.2]^3}l, where l is the staple length [mm] of the fibre being processed, the resultant yarns were found to have well-above-average properties even at low opening-roller speeds.
  • In order to effect a high degree of fibre separation , pressing roller can be mounted on a pivot able bracket, which, through pressure from spring , makes the roller press lightly on the land of the clothing of the rotating opening roller.
  • When in operation , this arrangement enables  the fibres in the extreme end of the sliver fringe to be separated by the opening roller. After separation , not all the separated fibres remain attached to the opening roller.
  •  Some enter the thin layer of air {the boundary air-layer} that revolves with the opening roller .Only when all the fibres reach the separating edge of the transport tube .
  •  Those fibres that travel in the boundary air-layer to the transport tube can readily become caught on irregular projections on the inside wall of the opening roller housing.
  • Accumulations of fibre can result, which are eventually removed & follow the fibre flow to the rotor to form defects in the yarn, such as slubs or neps , or cause an end break.
  • To overcome this problem , an air-stream is directed downward through an additional inlet to remove any caught fibres from the wall of the opening roller housing.
  • Other designs have been reported, which prevent fibres from accumulating on the roller itself. Many of the irregular projections on the inside rotor wall of the opening roller housing result from the abrasive action of the fibres.
  •  Some designs  shows the use of a replaceable hard wearing metal band fitting the area where the fibres makes contact with opening roller housing.
  • Some designs illustrates how the action of fibre contact with the housing can be manipulated to give better fibre alignment. By using a similar notion to the stationary- top cards , two saw tooth-wire clothed inserts are positioned in the wall of the housing close to the opening roller. The carding action that results is presumed to give a more definite control of the fibres as they approach the transport tube. The claim is for better fibre alignment & parallelisation. One important major drawback with the design is the possible “flats-stripping effect". The fibres are likely to become caught in the additional clothing and build up to the point where they either bring about a deterioration in the yarn properties or cause excessive end breaks. No provisions have been made to prevent this situation from occurring. In obtaining good fibre separation, the design of the opening roller clothing predictably plays a major part.
  •  There are at present two kinds of clothing that are commonly used : saw tooth-wire & pinned-type clothing.
  • The saw tooth-wire clothing is usually wound in a helical manner around the surface of the roller drum, the drum having grooves cut into the circumferential surface to facilitate the fixing of the wire clothing.
  • The manufacture of the wire clothing is similar to that for cards in that the tooth shape, angle & size are cold-formed by press dies by using an already-rolled-mild steel bar.
  •  After forming, the working surfaces of the clothing are usually hardened to increase their wear resistance.
  •  For pinned rollers, the pins are made from polished hardened steel.
  •  The roller drum is made hallow i.e. Tubular , which enables the unpointed inner ends of the pins to project  & almost meet in the interior of the drum.
  •  The pins are held in place by a cured synthetic resin.
  •  Both types of roller have to be dynamically balanced; With the wire type, opening portions are removed from the solid drum; With the pinned type ,inert fillers may be added to the resin to give a density more comparable to that of the metal sections.
  •  These fillers can be colour-coded to indicate for which fibres the opening roller is best suited.
  • It has been reported that the pinned type of wire gives  the better all-round effect, that is to say, better fibre separation & longer working life.
  •  With some saw tooth -wire clothing it has proved impossible to spin certain blends , particularly synthetic fibres blends.
  •  In other cases ,it has been found that, although a yarn can be made, the distribution of the different fibres throughout the fibres is inhomogeneous.
  •  The flat land of tooth is unable to penetrate between individual fibres or small fibre bundles of the same fibre type, which are often in the sliver after drawframe blending, & intimate mixing of the fibre types is therefore prevented.
  •  The different working angles for both wire &pinned type rollers have been reported.
  • However, the results have now shown that 60 degrees angles, which are usually recommended for cotton, although effective in separation, give poor trash ejection & often cause trash build up in the rotor.
  • The sawtooth wire clothing is usually given a hardening treatment, but because this can only be done after cold forming of the tooth profile, & also because a degree of ductility is required for helical winding onto the drum, the effectiveness of the treatment is poorer than for the pinned clothing.
  •  It has , however, been found that a ceramic coating can be applied to the surface of both wire & pins to improve the resistance to wear.
  • In order to change the opening-roller drum rapidly without changing the bearing drive , several roller designs are available that allow the clothing section of the roller drum to be replaced by merely removing the 4 screws.
  •  This reduces not only the operatives time time taken up in changing rollers but also the cost in carrying spares , since the former practice of replacing a worn  damaged roller with a spare already fitted with new bearing drive - shafts was expensive.
  •  Further development in this area has lead to the refitting of a base roll component made from a plastics material.
  • This approach offers various advantages, in that the component can be injection moulded, which cuts the costs & with good quality control, the reduced weight could enable the rebalancing of the opening roller to be dispensed with.

 



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