PROCESS PARAMETERS IN COMBING

Collected By: Muhammad Abid Farooq

INTRODUCTION
Combing is a process which is meant for upgrading the cotton raw material so that the following yarn
properties will improve compared to the normal carded yarn. U% of yarn tenacity gms/tex trash in the yarn(or kitties in the yarn) Lustre and visual appearance   POINTS TO BE CONSIDERED
Following parameters are very critical as far as the yarn quality of combed yarn is concerned

• Noil percentage(waste percentage)
• Type of feed
• feed length
• feed wight in grams per meter
• Piecing length
• Top comb penetration depth
• The distance between unicomb to nipper
• unicomb specification
• Number of needles in top comb
• The cleaning of unicomb
• Variation in nipper grip
• Variation in noil percentage
• type of lap preparation
• total draft between carding and comber i.e total draft employed in lap preparation
• Drafting roller settings in comber
• Drafting roller settings in lap prepartion machines
• No of doublings in lap preparation
• Short fibre content
• Fibre micronaire
• the type and the amount of trash in the card sliver
  WASTE PERCENTAGE
  
  The noil percentage from a comber depends upon the following
  
• short fibre content
• detaching distance
• feed length
• top comb penetration
• The distance between unicomb to top comb
• The basic idea of removing the waste is to remove the short fibres i.e to improve 50% span length
  or mean length.
• 
  The two impartant basic parameters to be considered in deciding the waste percentage are,
• 1.Yarn quality requirement and
• 2.Short fibre content in the raw material
• 
  Let us assume that the following cotton is used/> 2.5 span lenth = 28 to 30 mm
  uniformity ratio = 50 to 53%
  FFI % = 6 to 14
  Micronaire = 3.8 to 4.2
  fibre strength = 24 to 28 gms/tex
  and the quality requirement for counts 30s to 40s, is to meet 5% uster standards in U%, imperfection,
  strength and classimate faults.
• 
  To meet this quality requirement with the above rawmaterial ,the amount of noil to be extracted
  may be around 16 to 18% if E7/4(RIETER MAKE)comber is used or 15 to 16 % if E-62(RIETER MAKE) comber
  is used. The above example is given to highlight the effect of noil removed and the quality achieved.
  This is just an approximate figure, the parameters may vary depending upon the application.
  
• Combing efficiency is calculated based on the improvement in 50% span length, expressed as a percentage
  over 50% span length of the lap fed to the comber multplied with waste percentage.
  i.e.
  ((S-L)/(L*W))*100
  
  where
  S- 50% span length of comber sliver
  L- 50% span length of comber lap
  W- waste percentage
  
  
• Higher the noil %ge , lower will be the combing efficiency.
• Given a chance, it is better to remove waste more from top comb penetration than increasing the
  waste percentage by increasing the detaching distance. When the detaching distance is more the control
  during detaching will be less.
• Given a chance, it is better to work with backward feed than forward feed for the same waste
  percentage.Nep removal will be better, loss of long fibres in the waste during detaching will
  be less.
• With backward feed, top comb penetrates into the fibre fringe which is already combed by the unicomb,
•  therefore combing action done by top comb will be better and there will not be longer fibres in the
  waste
• Waste percentage depends upon the feed length and type of feed. In backward feed, higher the feed
  length, higher the waste percentage. In forward feed, higher the feed length, lower the waste
  percentage.
• With backward feed, the detaching distance will be less for the same waste percentage compared to
  forward feed. Therefore fibre control during detaching and during top comb action will be better.
• Higher the noil, higher the yarn strength. But this is true upto certain level of waste. Further increase
  may not increase the yarn strength. Very high %ge of noil will reduce the yarn strength and will
  increase the breakage rate in ring frames.
•