Yarn Faults | Defects of Yarn

Defects present in yarn can be classified in to five categories:

1) Count Variation: Variation in diameter along the length of yarn beyond acceptable range.

2) Unevenness or Irregularity: It is mass variation per unit length (cm). This fault is expressed as U% or CV% and evenness tester is used to measure it.

Various fault in yarn
Fig: Various fault in yarn
3) Frequently Occurring Faults: These are the faults that occur in range of the 10 to 5000 times per 1000 m of yarn. Yarns spun from staple fibers contain imperfections, which can be subdivided into three groups:

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

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

Neps: Cross sectional size +140% to +400% of normal yarn with fault length of 1 mm. Neps are defined as small tight balls of entangled fibres on linear textile strands.

4) Seldom Occurring Faults: These are the thick and thin places in yarn which occur so seldom that for their determination at least 100,000 m of yarn must be tested. This faults may be classified into the following classes:

A. Short thick places: 1 to 8 cm and above +100%
B. Long thick places: Above 8 cm and above +45%
C. Long thin places: Above 8 cm and less than -30%

5) Periodic Faults: If any fault repeats after a certain length/time then the fault is called periodic or systematic fault.

6) Hairiness: This is the measure for the protruding fibers from the yarn body.

7) Lot Mixing: Some times yarn lot can be mixed at the stages of spinning process as well as in the preparatory section of weaving/knitting mill. This type of mixing causes severe problem in subsequent processes. 
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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