Classification of Yarn Faults and Its Removal

Last Updated on 24/05/2021

Yarn Faults: Types, Classification and Remedies

Ramandeep Singh
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India


Yarn Faults / Defects:
A yarn which is not uniform is said to be irregular or to contain yarn defects or faults. These faults vary in their cross-sectional size and length. Yarn quality is influenced by various types of yarn faults which also affects the quality of fabric produced. During the yarn manufacturing process various types of irregularities are generated in the yarn diameter regularly or at intervals which are known as yarn faults. Yarn faults are represented based on their size, length and their frequency of occurrence.

“Unevenness” or “irregularity”
In all staple spun material (yarn, rovings and slivers), the fiber distribution along the material varies. The mass per unit length variation due to variation in fiber assembly is generally known as “Irregularity” or “Unevenness” (in practice the Um% or CVm% value). It is the skill of the spinner to arrange all machine settings in such a way that all fibers are spread as even as possible over the length of the material.

The extremes of variations, i.e., the thin places, thick places and neps, are usually referred to as “Imperfections”. These “imperfections” are determined according to a frequency figure or number per 1000 m or yards.

Objectionable yarn faults
If one now considers faults larger than +100% based on the mean yarn cross-section, one moves into the range of ‘yarn faults’ and correspondingly a further reduction in the frequency. Yarn defects have sizes from +100% and larger and lengths of 1 mm and longer.

Classification of Yarn Faults / Defects
Yarn faults are mainly categorized as below:

  1. Frequently Occurring Faults (Analyzed by Uster Evenness Tester)
  2. Seldom Occurring Faults (Scanned by Uster Classimat Tester)

A. Frequently Occurring Faults:
These are faults occurring in the range of 10 to 5000 times per 1000 m of yarn. Yarns spun from staple fibers contain imperfections, which can be subdivided into three groups:

  1. Thick Places
  2. Thin Places
  3. Neps

Thick places: Cross-sectional size +30% to +100% of normal yarn with fault length ranging from 4 to 25 mm.

Thick and thin places in yarn
Fig: Thick and thin places in yarn

Thin places: Cross-sectional size -30% to -60% of normal yarn with fault length ranging from 4 to 25 mm.

Neps: Neps are defined as small, tight balls of entangled fibers seen in linear textile strands. Cross-sectional size +140% to +400% of normal yarn with a fault length of 1 mm.

neps in yarn
Fig: Neps in yarn

Thin and thick places are produced due to drafting irregularities and neps are generated due to immature fibers in raw material.

B. Seldom Occurring Faults:

  1. Slubs
  2. Spun in fly
  3. Long thin places
Slubs in yarn
Fig: Slubs in yarn

These are the thick and thin places in yam which occur so rarely that spotting them would require testing at least 100,000 m of yarn. These faults may be classified further into the following types:

  1. Short thick places: 1 to 8 cm and above +100%
  2. Long thick places: Above 8 cm and above +45%
  3. Long thin places: Above 8 cm and less than -30%
Spun in fly
Fig: Spun in fly

These faults are also known as objectionable faults.

Why These Yarn Faults to be Avoided?

  • Causes breaks during post spinning operations.
  • Detract aesthetic appeal of the fabric, if allowed to pass.

Objectionable yarn faults can be categorized in three groups:

  1. Faults due to raw material
  2. Faults due to piecing
  3. Faults due to Spinning machine

1. Faults due to raw material: The number of objectionable faults due to raw material varies from 16% to 30% with different yarns.

2. Faults due to piecing: The number of objectionable faults due to piecing varies from 9% to 16% of the total objectionable faults.

Bad piecing in yarn
Fig: Bad piecing

3. Faults due to spinning machine: The spinning frame (R/F) is responsible for about 50% to 60% of the total objectionable yarn defects.

Remedies of Yarn Faults:

  1. Machine surfaces to be maintained clean.
  2. Broken teeth gear wheel to be avoided and proper meshing to be ensured.
  3. Setting at ring frame to be maintained.
  4. Proper functioning of pnemafil/roller clearers to be ensured.
  5. Removal of foreign matters (such as jute fibers, color cloth bits) to be ensured during preparation of mixing.
  6. Better fiber individualization at cards to be achieved.
  7. Correct tension weights and slub catcher settings to be employed at winding.
  8. Optimum twist to be used for the type of cotton processed.
  9. The yarn to be conditioned.
  10. Vibration of bobbins on the spindles to be avoided.
  11. Use of optimum roller settings.
  12. Optimum top roller pressure to be maintained.
  13. Use of travellars of correct size and shape and rings in good condition to be ensured.
  14. Optimum relative humidity to be maintained in the spinning room.

You may also like:

  1. Measurement of Yarn Unevenness | Types of Yarn Irregularity
  2. Reasons for Increasing Imperfection Index of Yarn
  3. Effect of Spacer on the Quality of Roving and Yarn
  4. Determination of Cotton Yarn Strength and C.S.P. by Lea Strength Tester
  5. Effect of Fiber Properties on Yarn Hairiness in Ring Spun Yarn
  6. Reasons for Poor Quality in Ring Spinning

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