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FIBRE TESTING

fibre testing

FIBRE ELONGATION:
There are three types of elongation

  • Permanent elongation: the length which extended during loading did not recover during relaxation
  • Elastic elongation:The extensions through which the fibres does return
  • Breaking elongation:the maximum extension at which the yarn breaks i.e.permanent and elastic elongation together Elongation is specified as a percentage of the starting length. The elastic elongation is of deceisive importance, since textile products without elasticity would hardly be usable. They must be able to deforme, In order to withstand high loading, but they must also return to shatpe. The greater resistance to crease
    for wool compared to cotton arises, from the difference in their elongation. For cotton it is 6 -10% and for wool it is aroun 25 - 45%. For normal textile goods, higher elongation are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations.

FIBRE RIGIDITY:

The Torsional rigidity of a fibre may be defined as the torque or twisting force required to twist 1 cm length of the fibre through 360 degrees and is proportional to the product of the modulus of rigidity and square of the area of cross-section, the constant of proportionality being dependent upon the shape of the cross-section of the fibre. The torsional rigidity of cotton has therefore been found to be very much dependent upon the gravimetric fineness of the fibres. As the rigidity of fibres is sensitive to the relative humidity of the surrounding atmosphere, it is essential that the tests are carried out in a conditional room where the relative
humidity is kept constant.

THE SLENDERNESS RATIO:
Fibre stiffness plays a significant role mainly when rolling, revolving, twisting movements are involved. A fibre which is too stiff has difficulty adapting to the movements. It is difficult to get bound into the yarn, which results in higher hairiness. Fibres which are not stiff enough have too little springiness. They do not return to shape after deformation. They have no longitudinal resistance. In most cases this leads to formation of neps. Fibre stiffness is dependent upon fibre substance and also upon the relationship between fibre length and fibre fineness. Fibres having the same structure will be stiffer, the shorter they are. The slendernesss ratio can serve as a measure of stiffness,

slender ratio = fibre length /fibre diameter

Since the fibres must wind as they are bound-in during yarn formation in the ring spinning machine, the slenderness ratio also determines to some extent where the fibres will finish up.fine and/or long fibres in the middle coarse and/or short fibres at the yarn periphery.

TRASH CONTENT:
In additon to usuable fibres, cotton stock contains foreign matter of various kinds. This foreign material can lead to extreme disturbances during processing. Trash affects yarn and fabric quality. Cottons with two different trash contents should not be mixed together, as it will lead to processing difficulties. Optimising process paramters will be of great difficulty under this situation, therefore it is a must to know the amount of trash and the type of trash before deciding the mixing.

SHIRLEY TRASH ANLAYSER:
A popular trash measuring device is the Shirley Analyser, which separates trash and foreign matter from lint by mechanical methods. The result is an expression of trash as a percentage of the combined weight of trash and lint of a sample. This instrument is used

  • to give the exact value of waste figures and also the proportion of clean cotton and trash in the material
  • to select the proper processing sequence based upon the trash content
  • to assess the cleaning efficiency of each machine
  • to determine the loss of good fibre in the sequence of opening and cleaning.

Stricter sliver quality requirements led to the gradual evolution of opening and cleaning machinery leading to a situation where blow room and carding machinery were designed to remove exclusively certain specific types of trash particles. This necessitated the segregation of the trash in the cotton sample to different grades determined by their size. This was achieved in the instruments like the Trash Separator and the Micro Dust Trash Analyser which could be considered as modified versions of the Shirley Analyser.

The high volume instruments introduced the concept of optical methods of trash measurement which utilised video scanning trash-meters to identify areas darker than normal on a cotton sample surface. Here, the trash content was expressed as the percentage area covered by the trash particles. However in such methods, comparability with the conventional method could not be established in view of the non-uniform distribution of trash in a given cotton sample and the relatively smaller sample size to determine such a parameter. Consequently, it is yet to establish any significant name in the industry.

RAW MATERIAL AS A FACTOR AFFECTING SPINNING:
Fineness determines how many fibres are present in the cross-section of a yarn of particular linear density. 30 to 50 fibres are needed minimum to produce a yarn fibre fineness influences

  • spinning limit
  • yarn strength
  • yarn evenness
  • yarn fullness
  • drape of the fabric
  • lustre
  • handle
  • productivity

productivity is influenced by the end breakage rate and twist per inch required in the yarn

Immature fibres(unripe fibres) have neither adequate strength nor adequate longitudinal siffness. They therefore lead to the following,

  • loss of yarn strength
  • neppiness
  • high proportion of short fibres
  • varying dyeability
  • processing difficulties at the card and blowroom

Fibre length is one among the most important characteristics. It influences

  • spinning limit
  • yarn strength
  • handle of the product
  • lustre of the product
  • yarn hairiness
  • productivity

It can be assumed that fibres of under 4 - 5 mm will be lost in processing(as waste and fly). fibres upto about 12 - 15 mm do not contribute to strength but only to fullness of the yarn. But fibres above these lengths produce the other positive characteristics in the yarn.

The proportion of short fibres has extremely great influence on the following parameters

  • spinning limit
  • yarn strength
  • handle of the product
  • lustre of the product
  • yarn hairiness
  • productivity

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