31 Yarn Tests

S. Sundaresan

epgp books





In spinning mill the yarn is the final product. The yarn is graded and marketed according to the linear density (count).The yarn quality is decided by its strength and count. The price of the yarn will be based on the quality only.

  1. Learning objectives

At the end of this lesson you will be able to

  • Identify yarn test methods
  • Various test methods of yarn
  • Quality level of yarn according to specification
  1. Range of tests

The following are the test done for yarn to assess its quality and specification

  1. Count definition and system
  2. Linear density (Yarn count)
  3. Strength (Tenacity): Single yarn, Lea strength
  4. CSP
  5. Yarn twist ( TPI)
  6. Yarn appearance
  7. Yarn hairiness
  8. Classimatt faults
  9. Evenness The non-technical used to identify the fibres are


YARN COUNT: It indicates the weight per unit length or length per unit weight. In English system count denotes the number of hanks of 840 yards that will weigh one pound.

Count can be classified according to its numbering system followed. It may broadly have classified into direct count system and indirect count system. Tex, Denier are the examples for direct numbering system, while English count system (Ne), worsted system of numbering can be the example for indirect numbering system.

Count Determination

Irrespective of the system of yarn numbering employed, two basic requirements for the determination of yarn number are an accurate value for the sample length and an accurate value for its weight.The methods determination of yarn count depends to a large extent on the form in which the yarn is available for testing.For example,when yarn is in form of ring bobbin a long sample length is possible and when yarn is in form of fabric, only a number of short lengths are available.

Weight Measurement




The analytical balances and any other balances used in determination of count must be accurate and calibrated time to time in order to get the exact readings




Moisture content can affect the results largely so it is very important to do 24 hrs conditioning of the sample in standard atmospheric condition

Beesley Balance: The Beesley Balance consists of a lightweight beam pivoted on jewel bearings with a hook at one end and a pointer at the other.The beam is initially levelled to bring the pointer against a datum line. A standard weight is suspended in a notch on the beam arm on the pointer side.A template is used to cut short lengths of yarn, the length depending upon the count system required. These lengths are placed on the hook until the pointer comes against the datum line. The number of short lengths required to balance the beam gives the count of the yarn.


YARN STRENGTH: It is measured in terms of lea strength or skein strength and expressed as count strength product.




The lea tester is a simple and versatile machine. They are made in different capacities up to 100,200,300 and 500 lbs. The unit records tensile strength and extension at breaking. The rate of traverse is 12” per minute.

Preparation of test specimens


  1. Number the selected cones/cops and fix them on the bobbin holder of the wrap reel.
  2. Reel out the required length of 120 yards for wrap reel.
  3. Cut and tie the trailing end of the lea to its leading end.
  4. Similarly take 30 leas making a total of 40 leas from the same 10 bobbins.
  5. Condition the sample in a conditioning box for about 12 hours.
  6. Determine the mass in grams of the leas and calculate the count

Cotton count = 64.80 / Weight of lea in gms


Lea strength test procedure

  1. Bring the hooks of the testing machine to zero position.
  2. Take a particular lea with count known and fix it on to the hooks and carefully separate the yarn to avoid overlapping on individual strands.
  3. Start the m/c and carry out the test up to rupture.
  4. The lea strength is automatically recorded in the system. The count CV%, the strength CV%, Lea CSP, maximum and minimum values of count and strength are obtained in the form of printouts.
  5. Similarly find the breaking load of the remaining leas and record them against their respective counts.
  6. Calculate the avg.breaking load of the, avg.linear density(count) of all the observations taken, coefficient of variation (CV) of breaking load and CSP

Computation of corrected CSP  C2 S2    = C1 S1 – 13.0 (C2 – C1)




S1=observed lea strength (lbs)


S2 = corrected strength to nominal count (lbs)


C1 = observed count (Ne)


C2 = nominal count (Ne)


Sample tabulation for lea count, strength, CSP

Twist measurement: Expressed as the number of turns per unit length, e.g. TPM or TPI.


Types of twist is S or Z

The twist in the yarn is found by using twist tester. It is working on tension imparted on during testing. It is a tension type twist tester. Based on the count yarn the appropriate weight in gms is added to the tester before testing the yarn. The instrument can be used to test the single yarn twist as well as double yarn twist. In case of testing of twist for single yarn first the twist is released in the parent yarn and again the twist inserted in the yarn in the opposite direction. The twist in the single yarn is calculate using the formula


TPI = dial reading/(gauge length in inches x 2)


In case of testing the twist of double yarn or ply yarn all the twist is released in the parent yarn and it is ensured by inserting a needle in the parent so that it freely travels from one end to other end, which indicates the end point of testing. The TPI is calculated by using the formula

TPI= Dial reading/Gauge length in inches

Single Yarn:

Untwist and Retwist method (twist contraction).

Suppose a yarn is twisted in Z direction and has a length “L” . Let the twist be completely removed to produce an untwisted strand of length “L+C” (C being the contraction due to twist).

If the strand is now twisted in S way with a number of turns equal to those removed, it can be expected that the strand will again contract to the original length “L”.


Suppose Z twist yarn length =  L

After Untwisting yarn length =  L+C

Again twisted in S direction   =  L


To give Z twist ,the strand should be rotated in clock wise rotation.


To untwist the Z twisted yarn ,yarn should be rotated in anti-clockwise rotation



To give S twist ,the strand should be rotated in anticlockwise rotation.


To untwist the S twisted yarn, yarn should be rotated in clockwise rotation


Yarn appearance ( ASTM Board)


Fabric appearance depends on yarn appearance.It includes yarn’s short term variation, imperfections, faults, presence of foreign particles and yarn hairiness.The method generally followed is to wrap the yarn around a black board(25cm X 14 cm).No. of wraps/cm is selected between 8-19 depending on the yarn count.After winding board is compared with standard photograph.

Yarn hairiness

Hairiness is one of the very important properties of staple yarns. It gives pleasant hand to the materials as well as creates processing problems during the further technological operations. Hairiness occurs because some fibre ends protrude from the yarn body, some looped fibres arch out from the yarn core and some wild fibres in the yarn


Yarn evenness and yarn faults are very important characteristics affecting spun yarn ability process and fabric appearance. New generation high speed looms and knitting machines place more stringent demands on the quality of the yarn. The importance of faults lies in the fact that they are a major factor responsible for rejection and down grading of yarn and fabrics and low productivity due to higher end breakage in further process. Yarn faults of various shapes and sizes can be introduced at all stages of spinning process, ever how these need to be controlled or extracted. Normally in most of the mills, since extraction of these faults which is done at winding is a simple process, control of generation of faults does not get prime importance. It is well known that to control anything one should know the characteristic, the causes and the effect. The measurement of the seldom occurring faults is essential but it is rarely done as the length required for testing is more.The frequently occurring faults are measured on imperfection testers that count number of the yarn imperfection i.e. thin places, thick places and neps which occur over certain specific meters of yarn. Determination and control of imperfection in the yarn is basic and important since it can influence many other properties of the yarn as well as of the fabric made from it. The most obvious consequence of high imperfection mainly thin and thick places is the variation of strengths along the length of yarn and production of patchy defective fabric, while higher neps reflect prominently in the fabric as specks. These imperfections however do not always  result in an end breakage during processing of the yarn. Therefore, over past many decades the imperfection indicator has been in extensive use in the Indian textile industry for day to day control and as an aid to improves the quality of yarn.

  • The purpose of classimat is of analysing the seldom occurring or disturbing thick places.
  • To eliminate the really disturbing yarn faults.
  • To simultaneously keep the efficiency of the winding machines as high as possible. This system act as a tool to separate yarns into 1st,2nd grades.

It is a capacitor type sensing unit and is used to count the various types ofyarn faults.With this instrument on a winding machine, large quantities of yarn can be examined in a non-wasteful way.According to the classimat faults yarn classifying installation detects yarn faults.In this way, thick and thin place faults are analysed according to their cross-sectional size and length.

Short thick faults:


A4, B4, C3, C4, D3, D4 are objectionable faults.

Stricter norms: A3, B3, C2, D2 are also considered as objectionable.

Long thick faults:

E & G are objectionable.


Thin faults:


H2, I1 & I2 are more critical, because they cause break during further processing. They also show up as thin lines in fabric.

The objectionable faults are cleared by yarn clearer


Yarn evenness : Capacitance principle

Yarn Unevenness: The variation in weight per unit length of the yarn or as the variation in its thickness. It shows the degree of uniformity of a product. For exampleTextile products: laps, sliver, roving and yarn.


Numerical Results

  • Unevenness or Irregularity
  • U% , CV%
  • CV at different cut lengths
  • Imperfections
  • Maximum and Minimum mass variations
  • Relative Count
  • Hairiness Value ‘H’

Impact of Unevenness on Quality


1.Strength of yarn


Irregularity can adversely affect many of the properties of textile materials .The most obvious consequence of yarn evenness is the variation of strength along the yarn. The uneven one should have more thin regions than the even one as a result of irregularity, since the average linear density is the same. Thus, an irregular yarn will tend to break more easily during spinning, winding, weaving, knitting, or any other process.


2.Fabric appearance due to Unevenness


Visible faults on the surface of fabrics. If a large amount of irregularity is present in the yarn, the variation in fineness can easily be detected in the finished cloth. In such cases, fabric construction geometry ensures that the faults will be located in a pattern that is very clearly apparent to the eye, and defects such as streaks, stripes, barre, or other visual groupings develop in the cloth.


3.Twist variation due to unevenness


Twist tends to be higher at thin places in a yarn. Thus, at such locations, the penetration of a dye or finish is likely to be lower than at the thick regions of lower twist. In consequence, the thicker yarn region will tend to be deeper in shade than the thinner ones and, if a visual fault appears in a pattern on the fabric, the pattern will tend to be emphasized by the presence of colour or by some variation in a visible property, such as crease-resistance controlled by a finish.

Other fabric properties, such as abrasion or pill-resistance, soil retention, drape, absorbency, reflectance, or lustre, may also be directly influenced by yarn evenness

Classification of Variation


Random variation: variation occurring without any definite pattern of repetition or definite sequence of thick and thin places.

Periodic variation: Variation show definite sequences of thick and thin places in strand of material.

Classification of periodic variation

If the wavelength of the periodic variation is

1 to 10 times the fibre length= short term

10 to 100 times the fibre length = medium term

100 to 1000 times the fibre length =long term

Evenness & Imperfections


Yarns spun from staple fibres, besides the normal irregularity also contain certain extremes of variations, referred to as ‘imperfections’.

These imperfections are subdivided into three categories – thin places, thick places and neps.

Imperfections are caused either due to poor raw material quality or due to imperfect process parameters.

A reliable estimation and analysis of these imperfections will therefore help in achievement of optimum processing conditions and also provide some reference for the purchase of good quality raw material.







“B‟ faults seed coats fragments account for 30 to 60 % of the total „B‟ faults. Seed coats fragments account for most of the ‘A’ faults but only for about 50% of the „B‟ faults. In other words, apart from seed coats fragments some other factors contributes significantly to „B‟ faults

piecing etc. are known to


contribute to „C‟ &‟D‟ faults. Drafting deficiencies are not likely to have a very significant contribution to the frequency of „C‟&‟D‟ faults in the yarn, as these faults are recorded at a level of yarn weight per unit length +100 % or more. Unopened fiber Cluster that are present in the sliver and are potential slubs in yarn, have the largest processing contribution for „C‟ and „D‟ types of faults.


Factor contributing to the high incidence of the classimat fault.

a)   Faults due to raw material are about 8 times greater in cotton than in staple fibres whereas the drafting faults are only 1.5 times greater. The numbers of objectionable faults are also 1.5 times higher in cotton than in staple fibre yarn, and staple fibre yarn give these C and D type of faults when compared to cotton.

b)   The number of faults systematically increases with increase in count both in carded and combed yarn however percentage increase is lower for the latter than the former.

c)   Use of high production and tandem cards as compared with semi-high production card as well as flexible fillet carded yarn, significantly reduce yarn faults. Higher percentage of waste removed in carding and combing lowered the fault level appreciably.

d)  According to them19 the total number at faults in combed yarns is about 65 to 85% lower than those in corresponding carded yarn.

e)  As the percentage of noil removed increased, objectionable fault reduced considerably.

f)  Conventional drawing gives lowest number of faults per 100km, & semi high production & high production drawing give substantial increase in the incidence of faults.

g)   Overhead clearer generally used by mills to keep the department clean and prevent fly and dust depositing on the yarns help in reducing the incidence of different type of yarn faults. In general, it is observed that total faults in cotton yarn are reduced by about 50% & in staple yarn by 50%. The reduction in other types of faults does not show any specific trend.

h) No firm conclusion could be drawn regarding the effect of drafting system and spindle speeds on yarn faults.


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