Contribution to Yarn Irregularity in Spinning Operation

Last Updated on 27/05/2021

Contribution to Yarn Irregularity Or Variation in Spinning Operation

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


The random yarn irregularity is simply a function of fiber fineness and the periodic variation that of mechanical condition of the machine. The quasiperiodic irregularity is only one which is inherent to the drafting process and can’t be avoided. This is the main cause of excessive yarn unevenness and needs to the well understood.

The drafting wave is formed when the floating or short fibers move out of turn and get. Accelerated to front roller speed by the faster moving fibers. Its severity depends on the inter-fiber cohesion, fiber clustering and fiber entanglement with one another. Therefore, complete fiber individualization a parallelization is a must make each fiber move independently. In actual practice it is never completely realized even in combed materials.

Spinning Operation:
The spinning operation and some factors affecting yarn irregularity are discussed here.

1. Carding:
Its responsible for individualization and therefore contribute to unevenness at the drawing, roving and ring spinning stages. Factors like proper setting, well-grounded clothing, high cylinder speed etc. Which enhances fiber individualization will also result in more regular yarn.

carding process
Fig: Carding process

2. Combing:
It affects short fiber content, individualization and parallelization, all of which affects drafting operation. Therefore, this process should have great influence on yarn unevenness. Any impairment of combing quality can, therefore lead to poor yarn evenness.

fiber combing process
Fig: Combing process

3. Drawing:
The draw frame is essentially meet to parallelize the fiber and the facilitate proper drafting at the speed frame and the ring frame. It also minimizes the contribution of irregularity introduced in the previous processes.

drafting in draw frame
Fig: Drafting in draw frame

4. Fly frame and ring frame:
The drafting system of fly and ring frame have been considerably improved yarn unevenness. The improved drafting system and reduce irregularity of roving helps in minimizing yarn unevenness. The drafting system at the ring frame is the most important contributor to yarn unevenness. The modern drafting systems have significantly brought down the level of yarn irregularity by bringing down the amplitude of the drafting waves.

The total draft at the ring frame for counts up to 20s should be equal to count, 20-25 and 25-35 for 40s and finer yarns the break draft should be 1.84 drafts up to 25 and 1.5 for higher draft on top arm drafting system.

The spacer size should be 4.5 mm for counts up to 18s, 4.0 mm for 20s-26s, 3.5 mm for 28s-40s, 3.0 mm for 44s -80s and 2.5 mm for 100s and above. In fly frames, the draft in front apron zone should be 6 or more.

Measurement of Imperfections:
There are two categories of blemishes in yarn. The imperfection like thick place, thin place and neps are less severe in nature but occur more frequently then faults such as slubs, bad piecing and loose spuns in lint. Both types of blemishes may cause difficulties in post spinning operation can more fabric appearance.

The circuitry of the Uster imperfection indicator takes the average weight/1.25 mm of yarn preceding the imperfection for accessing the relative size of an imperfection. The measurement and assessment of each imperfection is done as under:

Types of imperfectionsTest length or cut lengthLevels of sensitivity
Thin place8 mm-30%, -40%, -50%, -60%
Thick place12 mm (effective)+35% (4), +50% (3), +70% (2), +100% (1)
NepsAbout 2 mm+140% (4), +200% (3), 280% (2), 400% (1)

The recommended choices for routine testing are -50%, 3(+50%) and 3(200%) for the thin place, thick place and neps respectively. The value of thin place or thick place is likely to shoot up for highly uneven yarn as – 50% and +75% would then fall inside the natural or normal variability due to spreading of the base of the distribution curve. The norms for imperfection in cotton and MMF yarns are given in the table:

Imperfection /1000 m
Count (Ne.)Thin (-50%)Thick (+50%)Neps (+200%)
20s – 29s300500600
Finer then 60s50010001200
81s-and finer100350450

Assessment of Unevenness and Imperfections:
The sample size required to estimate imperfection is same as for yarn unevenness i.e. 4 min test on 16 bobbins selected at random from a group of ring frames spinning a given count.

Yarn unevenness has a distribution and the CV of U% is around 6% for count yarn and 2-4% for MMF yarns. The % difference is real when more than

Imperfections of yarnThe imperfection can be expected to follow a poisson distribution. However, under industrial conditions the C.V of imperfection is 1.2-1.7 times more than expected. A good mill should strive to achieve parity with expected value i.e. variance/mean = 1.

The CV of imperfection is of the order of 20-25%. The difference is considered real when (A-B)2/(A+B)>4. Where A and B stands for total number of imperfections counted for equal number of samples in each case.

Causes of thick and thin place:
Several studies by ATIRA have shown that thin place correlate well with U%. The thick places have a fair correlation with U% but neps have no correlation at all with U%.

At sensitivity of -50% for thin and +3(50%) for thick, the number of thick and thin places produced at ring would be equal. The excess of thick or thin place comes from combing stage. One can thus say

  • Excessive thick and thin place: caused by poor drafting condition (mechanical conditions and process parameters) at ring frame.
  • Excessive (thick and thin place): caused by carding and combing.

Fibre neps: (Assessment and control)
The Uster neps count indicate the number of places where there is a sudden increase in weigh per unit length. Therefore, foreign matter like trash particularly seed coats will also get counted as neps besides the fibers neps. In fact, a very large proportion of neps in the Indian cotton yarns are formed around small seed coats. This is followed by a fair proportion of pure fiber neps

At carding the neps the counted conventionally in the web itself. The well-known Shirley template consisting of 34 holes, each of one sq. in area, is placed on the web taken from card on a board of the same size. In case of MMF a sample glass per plastic sheet without holes may be used and the neps counted on the total area of 40 sq. inches.

And is converted to neps per 100 sq. inches. By multiplying by 2.5. However, in cotton mixing, the number of holes with in or more neps is counted. This number is used to estimate the number of neps per 100 sq. in. formed by referring to table. Standardization nep count is then calculating for a 40 in. width called producing 0.12 hank sliver.

standard nep count

Number of holes with nepsNeps/100 sq. in.

The standard neps counts are directly comparable between different cards and mills. If need be, this can v converted to neps per unit weight as follows:

neps count

The standard neps count should normally lie between 20 and 25 for medium mixing and between 15 and 20 for fine and superfine mixing. For MMF, this should lie between 0.5 and 1.0 depending on the relative proportion if polyester and viscous fibers and whether they are grey and dyed.

The difference in two nep count is real when

difference in two nep count

A and B stands for total number of neps count for equal number of samples in each case.

The nep count at various stages of processes in cotton spinning. The points to be noted are:

  1. The bale cotton itself contains lot of neps
  2. The blow room substantially increase the nep level.
  3. The carding reduces neps by 30-40%.
  4. Combing reduces neps by 25%.
  5. There is a marginal reduction in nep level from fly frame to ring frame.

Factors of causing neps:

  1. Harsh treatment of fibers by beaters, openers etc.
  2. Poor conditions of beater’s blades, spikers, wires etc.
  3. More number of beaters in the line.
  4. Long length of material conveying ducts with bends and rough inner surface.


  1. Poor conditions of wires points.
  2. Improper machine settings.
  3. Less amount of flat strips extracted.
  4. Higher amount of extraction can help in nep reduction.

You may also like:

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

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