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PROCESS PARAMETERS IN DRAW FRAME

draw frame

 

INTRODUCTION:
Drawframe is a very critical machine in the spinning process. It's influence on quality, especially on evenness is very big.If drawframe is not set properly, it will also result in drop in yarn strength and yarn elongation at break.The faults in the sliver that come out of drawframe can not be corrected . It will pass into the yarn.

The factors that affect the yarn quality are

  • the total draft
  • no of drawframe passages
  • break draft
  • no of doublings
  • grams/meter of sliver fed to the drawframe
  • fibre length
  • fibre fineness
  • delivery speed
  • type of drafting
  • type of autoleveller
  • autoleveller settings
  • The total draft depends upon
    1. material processed
    2. short fibre content
    3. fibre length
  • Following are some facts derived from trials
    1. wider back roller setting will result in lower yarn strength
    2. wider back roller setting will affect yarn evenness
    3. wider back roller setting will increase imperfections
    4. higher back top roller loading will reduce yarn strength
    5. higher back top roller loading will reduce end breakage rate
    6. wider front roller setting will improve yarn strength
  • Higher draft in drawframe will reduce sliver uniformity, but will imrprove fibre parallelisation. Somtimes the improvement in fibre parallelisation will overcome the detrimental effects of sliver irregularity.
  • Most of the improvement in fibre parallelization and reduction in hooks takes place at first drawframe passage than at second passage.
  • Better fibre parallelisation generally results in more uniform yarns and a lower end breakage rate in spinning.
  • Higher the weight of sliver fed to drawframe, lower the yarn strength, yarn evenness, and it leads to higher imperfections in the yarn and more end breakages in ring spinning
  • Irregularities arise owing to the instability of the acceleration point over time. The aprons and rollers are used in the drafting zone to keep the fibre at the back roller velocity until the leading end is firmly gripped by the front roller, but individual fibre control is not achieved.
 
  • Drafting wave is caused primarily not by mechanical defects as such but by the uncontrolled fibre movement of a periodic type resulting from the defects. As the fibre-accelerating point moves towards the front rollers, the draft increases( and vice versa), so that a periodic variation in linear density inevitably results.
  • With variable fibre-length distribution(with more short fibre content), the drafting irregularity will be high.
  • More the number of doublings , lower the irregularity caused due to random variations. Doublings does not normally eliminate periodic faults.But it reduces the effects of random pulses. Doubling does not have any effect on Index of Irregularity also, since both the irregularities are reduced by square root of the number of doublings.
  • Fibre hooks influences the effective fibre length or fibre extent. This will affect the drafting performance. For carded material normally a draft 7.5 in both breaker and finisher drawframe is recommended. Seven of a draft can be tried in breaker, since it is a carded material.
 
  • For combed material, if single passage is used, it is better to employ draft of 7.5 to 8.
  • If combers with four doublings are used, it is better to use two drawframe passages after combing. This will reudce long thick places in the yarn.
 
  • In case of two drawframe passage, first drawframe passage will reduce the periodic variation due to piecing. Therefore the life of servomotor and servo amplifier will be more , if two drawframe passage is used. Quality of sliver will also be good, because of less and stable feed variation.
 
  • For synthetic fibres (44 mm to 51 mm), 8 of a total draft can be employed both in breaker and finisher passage.
  • The number of doublings depends upon the feeding hank and the total draft employed. Most of the modern drawframes are capable of drafting the material without any problem, even if the sliver fed is around 36 to 40 grams per meter.
 
  • Especially for synthetic fibres with very high drafting resistance, it is better to feed less than 38 grams per meter to the drawframe.
  • Break draft setting for 3/3, or 4/3, drafting system is as follows
    1. For cotton, longest fibre +(8 to 12 mm)
    2. For synthetic fibre, fibre length + (20 to 30% of fibre length)

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