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Archive for April, 2009

Yarn Eveness

INTRODUCTION:

Non-uniformity in variety of properties exists in yarns. There can be variation twist.,bulk, strength, elongation , fineness etc. Yarn evenness deals with the variation in yarn fineness. Thisis the   property, commonly measured as the variation in mass per unit length along the yarn, is a basic  and important one, since it can influence so samy other properties of the yarn and offabric made  from it. Such variations are inevitable, because they arise from the fundamental nature of textile fibres and from their resulting arrangement.

The spinner tries to produce a yarn with the highest possible degree of homogeneity. In this connection, the evenness of the yarn mass is of the greatest importance. In order to produce an absolutely  regular yarn, all fibre characteristics would have to be uniformly distributed over the whole thread. However, that is ruled out by the inhomogeneity of the fibre material and by the mechanical constraints.
Accordingly, there are limits to the achievable yarn eveness.

IMPORTANCE OF YARNEVENNESS:
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. If the average mass per unitlength of two yarns is equal, but one yarn is less regular than the other, it is clear that the more even yarn will be the stronger of the two.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 where stress
is applied.

A second qality-related effect of uneven yarn is the presence of 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. The problem is particularly serious when a fault(i.e a thick or   thin place) appears at precisely regular intervals along the length of the yarn. 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. Such defects are usually compounded when the fabric is dyed or finished, as a result of  the twist variation accompanying them.

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 lowe 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. Thus, the effects of   irregularity are widespread throughout all areas of the production and use of textiles, and the topic is an important one in any areas of the industry.

“UNEVENNESS” OR “IRREGULARITY”:
The mass per unit length variation due to variation in fibre assembly is generally known as “IRREGULARITY” or “UNEVENNESS”. It is true that the diagram can represent a true relfection of the mass or weight per unit length  variation in a fibre assembly. For a complete analysis of the quality, however, the diagram alone is not enough. It is also necessary to have a numerical value which represents the mass variation.  The mathematical statistics offer 2 methods

  1. the irregularity U% : It is the percentage mass deviation of unit length of material and is caused by
    uneven fibre distribution along the length of the strand.
  2. the coefficient of variation C.V.%

In handling large quantities of data statistically, the coefficient of variation (C.V.%) is commonly used to define variability and is thus well-suited to the problem of expressing yarn evenness. It is currently probably the most widely accepted way of quantifying irregulariy. It is given by

coefficient variation (C.V.%) = (standard deviation/average) x 100

The irregularity U% is proportional to the intensity of the mass variations around the mean value. the U% is independent of the evaluating time or tested material length with homogeneously   distributed mass variation. the larger deviations from the mean value are much more intensively taken into consideration in the calculation of the coefficient of variation CV(squaring of the term) C.V.% has received more recognition in the modern statistics than the irregularity value U. The coefficient of variation CV can be determined extremely accurately by electronic means, whereas the calculation of the irregularity U is based on an approximation method. It can be considered that if the fibre assembly required to be tested is normally distributed with respect to its mass variation, a conversion possibility is available between the two types of calculation.

C.V.% = 1.25 * U%

INDEX OF IRREGULARITY”:
Index of irregularity expresses the ratio between the measured irregularity and the so-called limiting irregularity of an ideal yarn. The manner in which irregularity is assessed can lead to different ways of expressing the index.

In calculating the limit irregularity, the assumption is made that, in the ideal case, fibre distribution in a yarn is completely random and a practical yarn can never improve upon this situation.Thus, the   measured irregularity will be an indication of the extent to which fibre distribution falls short of  complete randomness. If all fibres are uniform in cross-sectional size, it can be shown that the  limiting irregularity expressed in terms of C.V is given by

C.V.(limit) = 100 / sqrt(N)

This expression also assumes a POISSON distribution in the values around “N”(the mean number of fibres  in the cross section)

Let
C.V.lim = the calculated limit irregularity
C.V. = the actual irreglarity
Then,
Index of Irregularity (I) = C.V / C.V.lim

By calculating the limit irregularity and then measuring the actual irregularity, we can judge the spinning performance.

DEVIATION RATE:

Deviation rate describes by what percentage a mass deviation exceeds or falls below a certain limit. The cut length factor in m averages out the shorter, higher deviations

DR (xy) =  (L1+l2..+Ln) x 100 / L tot

DR = Total relative length in (%) of all deviations of the mass signal which surpass the limit  +/- x% over a total test length of L meters, with the cut length of curve being y meters.

DR.jpg (29893 bytes)

FORMULA FOR DR PERCENTAGE:

DR1.jpg (4016 bytes)

The standard DR used for yarn is 1.5 m cutlength at a +/- 5% limit. The application of DR is similar to that of the CVm values. One has to take in to consideration that  the DR is based on threshhold values and changes more significantly than CV values when higher mass deviations over long stretches of test material arise.

THe deviation rate is calculated by comparing all the deviations of the positive range with the whole test length Ltot.  The same is valid for all deviations  in the negative range. As the zero line corresponds to the median , the Deviation Rate (DR) can reach the maximum of 5 0%.

DETERIORATION IN EVENNESS DURING PROCESSING:
In processing in the spinning mill, the unevenness of the product increases from stage to stage after drawframe. There are two reasons for this

  1. The number of fibres in the cross section steadily decreases. Uniform arrangement of the fibres becomes more difficult, the smaller their number.
  2. Each drafting operation increases the unevenness

Each machine in the spinning process adds a certain amount to the irregularity of finished yarn. The resultant irregularity at the output of any spinning process stage is equal to the square root of the sum of the squares of the irregularities of the material and the irregularity introduced in the process.

Let us assume that,
CVo – CV of output material
CV1 – CV of input material
CV – irregularity introduced by machine

then,

CVo = sqart(CV1 + CV)

UNEVENNESS OVER DIFFERENT CUT LENGTHS:
A length of yarn, for example of 10mm, contains only few fibres. Every irregular arrangement of only some of these fibres has a strong influence on the unevenness. In a length of yarn of 10m, incorrect arrangement of the same fibres would hardly be noticed against the background of the large number  of such fibres. Accordingly, the CV value of the same yarn can be, for example, 14% based on, 8mm, and only 2% based on 100 m. The degree of irregularity is dependent upon the regerence length.
Unevenness is therefore discussed in terms of short lengths(uster tester):medium lengths(seldom  used):long lengths(count variation).

Fabric stripiness and barre have been problematic fabric defects in the textile industry for many years. Though direct quantification has not been possible, the causes for such fabric defects have been studied. It has been shown that raw material quality and yarn mass variations (particularly medium and long term variations) contribute significantly to the guidance of such faults. Of these causes, there has been a general neglect of the control of medium term variations (variations over 1m, 3m,10m, etc). A mill needs to control the cut length variations of the yarn produced in order to ensure a fault free fabric.

If the variation of cut length C.V.% of 1 meter, 3 meters, 10 meters is high , when different cops are tested , the fabric appearance will be very badly affected. It will result in fabric defects such as stripiness.

IMPERFECTIONS:
Yarns spun from staple fibres contain “IMPERFECTIONS” . They are also referred to as frequently occurring yarn faults. They can be subdivided into three groups

  1. Think places
  2. Thick places
  3. Neps

The reasons for these different types of faults are due to rawmaterial or improper preparation process. A reliable analysis of these imperfections will provide some reference to the quality of the raw material used.

Thick places and thin places, lie in the range of +-100% with respect to the mean value of yarn cross-sectional size.The Neps will overstep +100% limit.

Thick places over +100% are analysed by the CLASSIMAT system, are cut by the clearers in winding depending upon the end use of the yarn.

Imperfection indicator record imperfections at different sensitive levels.

  1. Thin place
    1. -30% : yarn cross section is only 70% of yarn mean value
    2. -40% : yarn cross section is only 60% of yarn mean value
    3. -50% : yarn cross section is only 50% of yarn mean value
    4. -60% : yarn cross section is only 40% of yarn mean value
  2. Thick place
    1. +35% : the cross section at thick place is 135% of yarn mean value
    2. +50% : the cross section at thick place is 150% of yarn mean value
    3. +70% : the cross section at thick place is 170% of yarn mean value
    4. +100%: the cross section at thick place is 200% of yarn mean value
  3. Neps
    1. 400%: the cross section at the nep is 500% of the yarn mean value
    2. 280%: the cross section at the nep is 380% of the yarn mean value
    3. 200%: the cross section at the nep is 200% of the yarn mean value
    4. 140%: the cross section at the nep is 140% of the yarn mean value

Thick places and thin places which overstep teh minimum actuating sensitivity of +35% and -30% ,  respectively, correspond to their length to approximately the mean fibre length. Medium length or long thick and thin places are to be considred as mean value variations and are not counted by the instrument.

The standard sensitive levels are as follows

  • Thin place : -50%
  • Thick place : +50%
  • Neps : 200% ( 280% for open-end yarns)

    The reason for reducing the sensitivity of nep counting in rotor spun yarns is due to the fact that with these yarns, the neps tend to be spun into the core of the yarn and therefore are less visible to the human eye in the finished product. With ring spun yarns, on the other hand, the neps, in general  tend to remain on the surface of the yarn. Due to the above reasons, while a nep is considered serious
    for a ring spun yarn even if its size exceeds +200%, it becomes serious only after its size  exceeds +280% for open end yarns.

    It is however worth mentioning here that, though the imperfection values at standard sensitiviy levels i.e. +50% for thick places and -50% for thin places indicate the acceptable quality levels in terms  of fabric appearance, the quality of processing in terms of optimization of process parameters will  be better indicated by imperfections at higher sensitivity levels. It is commonly observed that while the thin places may be ‘0’ for any two mills at the standard sensitivity level of -50%, the  thin places at -40% sensitivity may show a big difference.

    Thin places and thick places in a yarn can, on the one hand, quite consdierably affect the appearance  of a woven or knitted fabric. Furthermore, an increase in the number of thin places and thick places   refer to a particularly valuable indication that the raw material or the method of processing has become worse. On the other hand, it cannot be concluded from the increased number of thin place faults that this yarn, the downtime of weaving or knitting machines will be increased to a similar degree.  Thin places usually exhibit a higher yarn twist, because of fewer fibres in the cross-section resulting in less resistance to torsion. The yarn tension does not become smaller proportionally with a reduced number
    of fibres. With thick plalce faults the contrary is the case. More fibres in the cross-section result  in a higher resistance to torsion. Thic places have therefore, in many cases, a yarn twist which is lower than the average. The yarn tension in the yarn at the position of the thick place is only in very few  cases proportional to the number of fibres. These considerations are valid primarily for ring-spun yarns.

    Neps can influence the appearance of woven or knitted fabrics quite considerably. Furthermore neps of a certain size can lead to processing difficulties, particularly in the knitting machines. Therefore the avoidance  of neps in the production of spun yarns is a fundamental textile technological problem.

    Neps can be divided, fundamentally , into two catergories:
    -raw material neps
    -processing neps

    The rawmaterial neps in coYtton yarn are primarily the result of vegetable matter and immature fibres in the raw material. The influence of the rawmaterial with wool and synthetic fibres in terms of nep production is negligible. Processing neps are produced at ginning and also in cotton , woollen and worsted carding. Their fabrication is influenced by the type of card clothing, the setting of the card flats, workers and strippers, and by the production speeds used.

    SPECTROGRAM:
    “DIAGRAM” is a representation of the mass variations in the time domain. Whereas SPECTROGRAM is a representation of the mass variation in the frequency domain. Spectrogram helps to recognize and analyse the periodic fault in the sliver, roving and yarn.

    For textile application, the frequency spectrum is not practical. A representaion which makes reference to the wavelength is preferred. Wavelength indicatres directly at which distance the periodic faults repeat. The more correct indication of the curve produced by the spectrograph is the wave-length spectrum.
    Frequency and wavelength are related as follows

    frequency = (wavelength)/(material speed)

    In the SPECTROGRAM, the X-axis represents the wavelength. Inorder to cover a maximum range of wavelengths, a logrithmic scale is used for the wavelength representation. The y-axis is without scale but represents the amplitude of the faults in yarn.

    The spectrogram consists of shaded and non-shaded areas. If a periodic fault passes through the measuring head for a minimum of 25 times, then it is considered as significant and it is shown in the shaded area. Wavelength ranges which are not statistically significant are not shaded. In this range the faults
    are displayed but not hatched. This happens when a fault repeats for about 6 to 25 times within the  tests length of the material.

    As far as those faults in the unshaded area is concerned, it is recommended to first confirm the seriousness of the fault before proceeding with the corrective action. This can be done by testing a longer length of yarn. Faults which occur less than 6 times will not appear in the spectrogram.

    A spectrogram starts at 1.1 cm if the testing speed is 25 to 200 m.min. It starts at 2.0cm if the  testing speed is 400 m/min and it starts at 4 cm if the speed is 800 m.min. For spun material the maximum wavelength range is 1.28 km. Maximum number of channels is 80

    Depending upon the wavelength of the periodic fault, the mass variations are classified as

    1. short-term variation( wavelength ranges from 1 cm to 50cm)
    2. medium-term variation( wavlength ranges from 50cm to 5 m)
    3. long-term variation(wavelength longer than 5 m)

  • periodic variations in the range of 1 cm to 50 cm are normally repeated a number of times within the  woven or knitted fabric width, which results in the fact periodic thick places or thin places will lie near to each other. This produces, in most cases, a “MOIRE EFFECT”. This effect is particularly  intensive for the naked eyes if the finished product is observed at a distance of approx. 50 cm to 1m.
  • Periodic mass variations in the range of 50cm to 5m are not recognizable in every case. Faults in this range are particularly effective if the single or double weave width, or the length of the stretched out yarn one circumference of the knitted fabric, is an integral number of wave-lengths of the periodic fault, or is near to an
    integral number of wave-lengths. In such cases, it is to be expected that weft stripes will appear in the woven fabric or rings in the knitted fabric.
  • Periodic mass variations with wave-lengths longer than 5m can result in quite distinct cross-stripes in woven and knitted fabrics, because the wave-length of the periodic fault will be longer than the width of the woven fabric or the circumference of the knitted fabric. The longer the wavelength, the wider will
    be the width of the cross-stripes.Such faults are quite easily recognizable in the finished product, particularly when this is observed from distances further away than 1 m.
    A periodic mass variation in a fibre assembly does not always result in a statistically significant  difference in the U/V value. Nevertheless, such a fault will result in a woven or knitted fabric and   deteriorate the quality of the fabric. Such patterning in the finished product can become intensified after dyeing. This is particularly the case with uni-coloured products and products consisting of
    synthetic fibre filament yarns.

    The degree to which a periodic fault can affect the finished product is not only dependent on its intensity but also on the width and type of the woven or knitted fabric, on the fibre material, on the yarn count, on the dye up-take of the fibre, etc. A considerable number of trials have shown that the height of the peak above the basic spectrum should not overstep 50% of the basic spectrum height
    at the wavelength position where the peak is available.

  • CHIMNEY TYPE FAULTS:
    The eccentricity roller results in a sinusoidal mass variation whereby the periodicity corresponds to full circumference of the roller. With one complete revolution of an OVAL roller, a sinusoidal mass variation also results, but 2 periodic faults are available. Chimney type of faults are mainly due to  -mechanical faults -eccentric rollers, gears etc -improper meshing of gears -missing gear teeth -missing teeth in the timing belts -damaged bearings etc
  • HILL TYPE FAULTS:
    These faults are due to drafting waves caused by -improper draft zone settings -improper top roller pressure -too many short fibres in the material, etc  Numerous measurements of staple-fibre materials have shown that there are rules for the correlation between the appearance of drafting waves in the spectrogram and the mean staple length. It is given below
    -yarn : 2.75 x fibre length
    -roving : 3.5 x fibre length
    -combed sliver : 4.0 x fibre length
    -drawframe sliver : 4.0 x fibre length
    A periodic fault which occurs at some stage or another in the spinning process is lengthened by subsequent drafting.If the front roller of the second drawframe is eccentric, then by knowing the  various drafts in the further processes, the position of the peak in the spectrogram of the yarn measurement can be calculated.

    The wavelength of a defective part is calculated by multiplying the circumference of the part and  the draft upto that part.

    The wavelength of a defective part can be calculated if the rotational speed of the defective part and the production speed are known.

    Doubling is no suitable means of eliminating periodic faults. Elimination is only possible in exceptional  cases. In most cases, doubling can, under the best conditions, only reduce the periodic faults.

    The influence of periodic mass variation is proportional to the draft.

    Due to the quadratic addition of the partial irregularities, the overall irregularity of staple-fibre yarns increases due to the periodic faults only to an unimportant amount.

Yarn testing

INTRODUCTION:
Yarn occupies the intermediate position in the manufacture of fabric from raw material. Yarn results are
therefore essential, both for estimating the quality of rawmaterial and for controlling the quality of
fabric produced. The important characteristics of yarn being tested are,

  1. yarn twist
  2. linear density
  3. yarn strength
  4. yarn elongation
  5. yarn evenness
  6. yarn hairiness etc.

SAMPLING:
In order that the results obtained are reproducible and give reliable information about the material,
the sampling must be true and representative of the bulk lot. The sampling procedure should be designed
to take account of and to minimise the known sources of variability such as the variation between
spindles, the variation along the length of the bobbin, etc. The procedure for sampling and the number
of test carried out are given under each characteristic.

AMBIENT CONDITIONS FOR YARN TESTING:
Some textile fibres are highly hygroscopic and their properties change notably as a function of the moisture
content. Moisture content is particularly critical in the case of properties, i.e yarn tenacity,
elongation, yarn evenness, imperfections, count etc. Therefore conditioning and testing must be carried out
under constant standard atmospheric conditions. The standard atmosphere for textile testing involves a
temperature of 20+-2 degree C, and 65+-2% Rh. In tropical regions, maintaining a temperature of 27+-2 degree C,
65+-2%RH is legitimate. Prior to testing, the samples must be conditioned under constant standard
atmospheric to attain the moisture equillibrium. To achieve this it requires at least 24 hours.

TWIST:

  • “Twist is defined asthe spiral disposition of the components of yarn, which is generally expressed
    as the number of turns per unit length of yarn, e.g turns per inch, turns per meter, etc.
  • Twist is essential to keep the component fibres together in a yarn.
  • The strength, dyeing, finishing properties, the feel of the finished product etc. are all dependent
    on the twist in the yarn.
  • With increase in twist, the yarn strength increases first , reaches a maximum and then decreases.
  • Depending on the end use, two or more single yarns are twisted together to form “plied yarns” or
    “folded yarns” and a number of plied yarns twisted together to form “cabled yarn”.
  • Among the plied yarns, the most commonly used are the doubled yarns, wherein two single yarns of
    identical twist are twisted together in a direction opposite to that of the single yarns.
  • Thus for cabled and plied yarns, the direction of twist and the number of turns per unit length of
    the resultant yarn as well as of each component have to be determined for a detailed analysis.
  • Direction of twist is expressed as “S”-Twist or “Z”-Twist. Direction depends upon the direction of rotation
    of the twisting element.
  • Twist take up is defined as, “The decrease in length of yarn on twisting, expressed as a percentage
    of the length of yarn before twisting. LINEAR DENSITY OR COUNT OF YARN:
  • The fineness of the yarn is usually expressed in terms of its linear density or count.
  • There are a number of systems and units for expressing yarn fineness. But they are classified as follows
    DIRECT SYSTEM:

    1. English count(Ne)
    2. Metric count(Nm)
    3. French count(Nf)

    INDIRECT SYSTEM:

    1. Tex
    2. Denier
    1. Ne : No of 840 yards yarn weighing in One pound
    2. Nm : No of one kilometer yarn weighing in One Kilogram
    3. Nf : No of one kilometer yarn weighing in 0.5 kilogram
    4. Tex : Weight in grams of 1000 meter(1 kilometer) yarn
    5. Denier: Weight in grams of 9000 meter(9 kilometer) yarn
  • For the determination of the count of yarn, it is necessary to determine the weight of a known length
    of the yarn. For taking out known lengths of yarns, a wrap-reel is used. The length of yarn reeled off depends upon the count system used.
  • Another factor which determines the length of yarn taken for testing is the type of balance used.
    Some balances like quadrant balance, Beesley’s blanace have been specially designed to indicate the yarn
    count directly from tests on specified short lengths of yarn and are very useful for determining the
    counts of yarn removed from the fabrics. The minimum accuracy of balance required is 0.001mg
  • One of the most important requirements for a spinner is to maintain the average count and count variation
    within control. The term count variation is generally used to express variation in the weight of a lea
    and this is expressed as C.V.%. This is affected by the number of samples and the length being considered
    for count checking. While assessing count variation, it is very important to test adequate number of leas.
    After reeling the appropriate length of yarn, the yarn is conditioned in the standard atmosphere
    for testing before it’s weight is determined.
  • The minimum number of sample required per count is 20 and per machine is 2.
    YARN STRENGTH AND ELONGATION:
  • Breaking strength, elongation, elastic modulus, resistance abrasion etc are some important factors which
    will represent the performance of the yarn during actual use or further processing. Strength testing
    is broadly classified into two methods

    1. single end strength testing
    2. skein strength or Lea strength

    Tensile strength of single strands of yarn:

  • During routine testing, both the breaking load and extension of yarn at break are usually recorded for
    assessing the yarn quality. Most of the instruments record the load-elongation diagram also.
  • Various parameters such as initial elastic modulus, the yield point, the tenacity or elongation at any stress
    or strain, breaking load, breaking extension etc can be obtained from the load-extension diagram.
  • Two types of strengths can be determined for a yarn
    1. Tensile strength -load is applied gradually
    2. Ballistic strength – applying load under rapid impact conditions
  • Tensile strength tests are the most common tests and these are carried out using either a single strand
    or a skein containing a definite number of strands as the test specimen.
  • An important factor which affects the test results is the length of the specimen actually used for
    carrying out the test. The strength of a test specimen is limited by that of the weakest link in it.If
    the test specimen is longer, it is likely to contain more weak spots, than a shorter test specimen. Hence
    the test results will be different for different test lengths due to the weak spots.
  • The amount of moisture in the yarn also influences the test results. Cotton yarn when fully wet show
    higher strength than when dry, while opposite is the case with viscose rayon yarns. Hence, to eliminate the
    effect of variation due to moisture content of the yarn, all yarn strengrth tests are carried out,
    after conditioning in a room where the standard atmospheric condition is maintained.
  • The rate of loading as determined by the “time-to-break”, which is the time interval between the
    commencement of the application of the load and the rupture of the yarn, is an important factor , which
    determines the strength value recorded by using any instrument. The same specimen will show a lower
    strength when the time-to-break is high, or higher when the time-to-break is low.
  • The instruments used for determining the tensile strengh are classified into three groups, based
    on the principle of working.

    1. CRT – Constant rate of traverse
    2. CRE – Constant rate of extension
    3. CRL – Constant rate of loading
  • In the instruments of CRE type, the application of load is made in such a way that the rate of elongation
    of the specimen is kep constant. In the instruments of the CRL type,the application of load is made
    in such a way that the rate of loading is constant througout the duration of the test. This type of
    instruments are usually preferred for accurate scientific work. In the CRE and CRL types of instruments,
    it is easy to adjust the “time-to-break” while this adjustment is not easy in the CRT types of instruments.
  • The uster Tensorapid applies the CRE principle of tensile testing. Constant Rate of Extension describes
    the simple fact that the moving clamp is displaced at a constant velocity. As a result, the specimen between
    the staionary and the moving clamp is extended by a constant distance per unit of time and the force
    required to do so is measured. Apart fron single values, this instrument also calculates mean value
    coefficient of variation and the 95% confidence range of maximum force, tenacity,elongation and work done
  • The total coefficient of variation describes the overall variability of a tested lot, i.e the within-sample
    variation plus the between-sample variation. If 20 individual single-end tensile test are performed
    on each of ten bobbins or packages in a sample lot, the total coefficient of variation is calculated
    from the pooled data of the total number of tests that were carried out.
  • In tensorapid, the breaking tenacity is calculated from the peak force which occurs anywhere
    between the beginning of the test and the final rupture of the specimen. The peak force or maximum force is
    not identical with the force measured at the very moment of rupture. The breaking elongation is calculated
    from the clamp displacement at the point of peak force. The elongation at peak force is no identical with the elongation at the very moment of rupture(elongation at rupture).
  • The work to break is defined as the area below the stress/strain curve drawn to the point of
    peak force and the corresponding elongation at peak force. The work at the point of peak force
    is not identical with the work at the very moment of rupture.
  • To compare tensorapid test results with other results,
    1. a measurement must be performed according the CRE princple
    2. testing speed must be exactly 5 m/min
    3. the gauge length or the length of the specimen should be 500 mm
    4. the pretension should be 0.5 cN/tex
  • There are two fundamental criteria which affect the compatibility between different measurements
    of tensile yarn properties.

    1. testing conditions, i.e the testing principle(CRE,CRL), testing speed, gauge length, and pre-tensioning.
    2. the second criteria,which also affects the magnitude of the differences, relates to the specific
      stress/strain characteristic of the yarn itself, which is determined by the fibrous materials, the
      blend ratio, and the yarn construction.

    Skein strength or Lea strength:

    The skein breaking strength was the most widely used measure of yarn quality in the cotton textile industry.
    The measurement of yarn quality by this method has certain drawbacks. Firstly, in most of the subsequent
    processing, such as winding, warping or weaving, yarn is used as single strand and not in the form of
    a skein except occasionally when sizing ,bleaching, mercerising or dyheing treatments are carrried out
    on hanks. Secondly, in the method used for testing skein strength, the rupture of a single strand at a weak
    place affects the result for the whole skein. Further, this method of test does not give an indication
    of the extensibility and elastic properties of a yarn, the characters which play and important role
    during the weaving operations. However, since a large size sample is used in a skein test as against
    that in a single strand test, the sampling error is less. The skein used for strength test can be used
    for determination of the linar density of the yarn as well.

  • In addition to the factors influencing the yarn strength, the size of the skein(lea) will affect to a
    large extent the strength recorded. The usual practice is to use a lea(120 yards) of yarn prepared by
    winding 80 turns on a wrap-reel having a perimeter of 1.5 yards(54 inches), so that during a test, there
    are 160 strands of 27 in.(“) length. There are different systems in use. But the actual breaking strength
    recorded on the machine would depend on the type of skein used as both the number of strands and
    test length may differ. The instruments most commonly used for this test is CRT type, where the
    bottom hook moves at 12 inches per min.
  • After findingout skein strength, broken skeins are also weighed to determine the linear density.
    The most common skein used is the lea and the results of lea strength tests are expressed as C.S.P.,
    which is the product of the linear density(count)of the yarn in the English system (Ne) and the lea breking
    strength expressed in lbs. In view of the fact that C.S.P. is much less dependent on yarn count
    than on strength, especially when count diffferences are small, C.S.P. is the mostg widely used
    measure of yarn qauality.
  • Spinning mill costing


    INTTRODUCTION:

    It is better to review the basics concepts, costing methods and techniques and elements of costing before we work out a costing for a spinning mill.

    Cost accounting is a system of determining the costs of products or services. It has primarily developed to meet the needs of management. It provides detailed cost information to various levels of management for efficient performance of their functions.

    Financial accounting provides information about profit , loss, cost etc., of the collective activities of the business as a whole. It does not give the data regarding costs by departments, products, processes and sales territories etc. Financial accounting does not fully analyse the losses due to idle time, idle plant capacity, inefficient labour, sub-standard materials, etc. Cost accounting is not restricted to past. It is concerned with the ascertainment of past, present and expected future costs of products manufactured or services supplied. Cost accounting provides detailed cost information to various levels of management for efficient performance of their functions.

    “A cost is the value of economic resources used as a result of producing or doing the things costed”

    Cost is ascertained by cost centres or cost units or by both.

    For the purpose of ascertaining cost, the whole organisation is divided into small parts of sections. Each small section is treated as a cost centre of which cost is ascertained. A cost centre is defined as ” a location, person, or item of equipment(or group of these) for which costs may be ascertained and used for the purpose of control. A cost accountant sets up cost centres to enable him to ascertain the costs he needs to know. A cost centre is charged with all the costs that relate to it. The purpose of ascertaining the cost of cost centre is cost control. The person in charge of a cost centre is held responsible for the control of cost of that centre.

    Cost unit breaks up the cost into smaller sub-divisions and helps in ascertaining the cost of saleable products or services. A cost unit is defined as a ” unit of product , service or time in relation to which cost may be ascertained or expressed.” For example in a spinning mill the cost per kg of yarn may be ascertained. Kg of yarn is cost unit. In short Cost unit is unit of measurement of cost.

    METHODS OF COSTING:

    Method of costing refers to the techniques and processes employed in the ascertainment of costs. The method of costing to be applied in a particular concern depends upon the type and nature of manufacturing activity. Basically there are two methods of costing

    1.Job costing: Cost unit in job order costing is taken to be a job or work order for which costs are separetely collected and computed.

    2.Process costing: This is used in mass production industries manufacturing standardised products in continuous processes of manufacutring. Cost are accumulated for each process or department. For spinning mills , process costing is employed.

    TECHNIQUES OF COSTING:

    These techniques may be used for special pupose of control and policy in any business irrespective of the method of costing being used there.

    Standard costing: This is the valuable technique to control the cost. In this technique, standard cost is predetermined as target of performance and actual performance is measured against the standard. The difference between standard and actual costs are analysed to know teh reasons for the difference so that corrective actions may be taken.

    Marginal costing: In this technique, cost is divided into fixed and variable and the variable is of special interest and importance. This is because, marginal costing regards only variable costs as the costs of products. Fixed cost is treated as period cost and no attempt is made to allocate or apportion this cost to individual cost centres or cost units.

    Cost Ascertainment is concerned with computation of actual costs. Ascertainment of actual costs reveals unprofitable activities losses and inefficiencies .

    Cost Estimation is the process of predetermining costs of goods or services. The costs are determined in advance of production and precede the operations. Estimated costs are definitely the future costs and are based on teh average of the past actual costs adjusted for future anticipated changes in future. Cost estimates are used in the preparation of the budgets. It helps in evaulating performance. It is used in preparing projected financial statements. Cost estimates may serve as targets in controlling the costs.

    CLASSIFICATION OF COSTS:

    Costs are classified into direct costs and indirect costs on the basis of their identifiability with cost units or processesses or cost centres.

    DIRECT COST: These are the costs which are incurred for and conveniently indentified with a particular cost unit, process or equipment. For a spinning mill, costs of rawmaterial used, packing material, freight etc are direct costs

    INDIRECT COST: These are general costs and are incurred for the benefit of a number of cost units, processes or departments. These costs cannot be conveniently identified with a particular cost unit or cost centre. In a spining mill, power cost, administrative wages, managerial salaries, materials used in repairs etc are indirect costs.

    The terms direct and indirect should be used in relation to the object of costing. An item of cost may be direct cost in one case and the same may be indirect in the other case.It is the nature of business and the cost unit chosen that will determine whether a particular cost is direct or indirect.

    FIXED AND VARIABLE COSTS; Costs behave differently when level of production rises or falls. Certain costs change in sympathy with production level while other costs remain unchanged. As such on the basis of behaviour or variability, costs are classifed into fixed, variable and sem-variable.

    FIXEDCOSTS; These costs remain constant in “total” amount over a wide range of activity for a specified period of time. They do not increase or decrease when the volume of production changes.

    VARIABLE COSTS: These costs tend to vary in direct proportion to the volume of output. In other words, when volume of output increases, total variable cost also increases and vice-versa.

    ELEMENTS OF COST: A cost is composed of three elements i.e. material , labour and expense. Each of these elements may be direct or indirect.

    DIRECT COST INDIRECT COST
    Direct material Indirect material
    Direct labour Indirect labour
    Direct expenses Indirect expenses

    MATERIAL COST:

    DIRECT MATERIAL is that which can be conveniently identified with and allocated to cost units. Direct materials generally become a part of the finished product. For example, cotton used in a spinning mill is a direct material.

    INDIRECT MATERIAL is that which can not be conveniently identified with individual cost units. In a spinning mill, engineering department spares, maintenance spares, lubricating oils, greases, ring travellers etc

    LABOUR COST:

    DIRECT LABOUR cost consists of wages paid to workers directly engaged in converting raw materials into finished products. These wages can be conveniently identified with a particular product, job or process.

    INDIRECT LABOUR is of general character and cannot be conveniently identified with a particular cost unit. In other words, indirect labour is not directly engaged in the production operations but only to assist or help in proudciton operations. For example in a spinning mill, the number of maintenance workers, no of workers in utility department etc

    EXPENSES; All costs other than material and labour are termed as expenses.

    DIRECT EXPENSES are those expenses which are specifically incurred in connection with a particular job or cost unit. Direct expenses are also known as chargeable expenses.

    INDIRECT EXPENSES can not be directly identified with a particular job, process and are common to cost units and cost centres.

    PRIME COST = Direct material +Direct labour + Direct expenses

    OVERHEAD = Indirect material + Indirect labour + Indirect expenses

    TOTAL COST = PRIME COST + OVERHEAD

    ADVANTAGES OF COST ACCOUNTING:

    • It reveals profitabale and unprofitable activities.
    • It helps in controlling costs with special techniques like standard costing and budgetary control
    • It supplies suitable cost data and other related information for managerial decision making such as introduction of a new product, replacement of machinery with an automatic plant etc
    • It helps in deciding the selling prices, particularly during depression period when prices may have to be fixed below cost
    • It helps in inventory control
    • It helps in the introduction of a cost reduction programme and finding out new and improved ways to reduce costs
    • Cost audit system which is a part of cost accountancy helps in preventing manipulation and frauds and thus reliable cost can be furnished to management

    ESSENTIALS OF A GOOD COST ACCOUNTING SYSTEM:

    • The method of costing adopted. It should be suitable to the industry
    • It should be tailor made according to the requirements of a business. A ready made system can not be suitable
    • It must be fully supported by executives of various departments and every one should participate in it
    • In order to derive maximum benefits from a costing system, well defined cost centres and responsibility centres should be built within the organisation
    • controllable and uncontrollable costs of each responsiblity centre should be separately shown
    • cost and financial accounts may be integrated in order to avoid duplication of accounts
    • well trained and educated staff should be employed to operte the system
    • It should prepare an accurate reports and promptly submit teh same to appropriate level of management so that action may be taken without delay
    • resources should not be wasted on collecting and compiling cost data not required. Only useful cost information should be compiled and used whenever required.

    CASE 1. Project costing for a POLY/COTTON PLANT with autodoffing and link to autoconer:(IN INDONESIA)

    Following information is required to work out a costing for a new plant:

    • The average count of the plant
    • Capacity of the plant – No of spindles to be installed and the number of back process and winding machines required
    • Investment on machineries
    • Investment on land
    • Investment on building
    • working capital required
    • product lay out, the count pattern
    • Selling price of individual counts
    • rawmaterial cost(including freight, duty etc)
    • packing cost per kg of yarn
    • freight per kg of yarn
    • direct labour cost
    • indirect labour cost
    • fixed power cost
    • variable power cost
    • spares consumption
    • administration costs
    • selling overheads

    Let us work out a project cost:

    For this , i have used the details of the modern mill which is running in Indonesia from year 2000

    STEP NO.1: Contribution to be calculated. In general for a spinning mill ,contribution per kg ofa particular count is calculated to work out the economics for a new project as well as for a running mill.

    Cotribution = selling price – direct cost

    Direct cost for a spinning mill includes rawmaterial price, packing cost, freight. All other costs are either fixed costs or semi variable costs. The other costs can not be conveniently allocated to per kg of a particular count.

    The basic idea of a new project or a running plant is to maximise this contribution. Because once the plant is designed, spares cost, power cost, administration cost,labour cost etc almost remain constant. There will not be significant changes in these costs for different count patterns if the plant is utilisation is same.

    The following table gives the details of count pattern, selling price, rawmaterial price, packing cost and contribution per kg of different counts for a particular period ( year 2000). This is just an example , one should understand that the selling price, rawmaterial price and all other costs keep changing. THis is the reason why costing is important for a running mill. All the costs are changing. Some costs change every month, some once in a year. Therefore costing plays a major role to run the plant efficiently.

    count no. of spls no of mcs prdn/mc prdn kgs/day raw material cost/kg packing cost /kg freight per kg commn 2% on selling price selling price / kg contribn per kg
    20s CVC 4480 4 1109 4436 1.456 0.046 0.051 0.04 2.2 2674
    24s CVC 4480 4 881 3525 1.456 0.046 0.051 0.05 2.3 2470
    30s CVC 5600 5 679 3394 1.456 0.046 0.051 0.05 2.4 2712
    30s TC 4480 4 679 2716 1.240 0.046 0.051 0.04 2.15 2091
    36s TC 6720 6 552 3315 1.240 0.046 0.051 0.05 2.4 3365
    23 17385 contrbn/ day 13312

    In the above table, all the costs are in US$. The ringframes are with 1120 spindles per machine with automatic doffing and link to autoconer. Packing cost is based on indonesian packing material prices for carton packing.

    The ultimate aim of the project is to maximise the contribution. Looking into the cotribution per kg of yarn, the project should produce only 36s TC. But in this project they have considered 5 different counts. Because

    • yarn market is not stable. It needs a lot felxibility
    • customers are not same, the price depends on the customers
    • the end uses are not same, the price depends on the enduse
    • this unit exports 80% of the yarn, it can not depend on one country, eg. 36sTc is only for Philippines market, it can not be sold in Malaysia, eventhough the quality is good
    • the count pattern depends upon the market requirement and the major counts in the market, not only on the contribution
    • A linear programming technique can be used to maximise the contribution, considering all market constraints, and production constraints.
    • flexibility needs more investment and more day to day expenses, if a project has to be more flexible, it has to invest more money on infrastructure
    • the major factor which will make the project feasible with less felexibility is YARN QUALITY in a spinning mill
    • Since this is a critical step for a new project, management should be clear about their Yarn quality , Flexibility required for marketing and should make use of Linear Programming Techniques to find out the best product mix to maximise the contribution.

    STEP NO. 2: To work out the Total Investment cost ( machineries, accessories, land and builidng, humdification and electrical instruments)

    The following table gives the requirement of produciton machines. To calculate the number of back proess and winding drums required, a detailed spin plan should be worked out with speeds and efficiencies to be achieved in each machine.

    While calculating the no of machines required, m/c utilisation, m/c efficiency , waste percentage, twist multipliers, delivery speeds etc should be considered properly. These factors should be decided based on yarn quality required, end breakge rates and the capacity of machine.

    INVESTMENT ON MACHINERY

    MACHINERY NO. OF MCS RATE / MC TOTAL COST
    Trutzschler Blowrrom line for cotton 1 line 416,640 416,640
    Trutschler Blowrrom line for Polyester 1 Line 321,365 321,365
    Trutshcler DK-903 cards 22 92,500 2,035,000
    Rieter RSB-D30 draw frames (with autoleveller) 6 1,648,000
    Rieter double delivery drawframe 10
    Rieter unilap 2
    Rieter E62 combers 10
    Howa speed frames with overhead blower 7 144530 1,011,710
    Ring frames with autodoffer 23 148,960 3,426,080
    winding machines ( 26 drums per mc) 23 93,200 2,143,600
    Roving transport ( manual) 1 150,000 150,000
    Argus fire system 1 50,000 50,000
    TOTAL 11,202,395

    Some of the following points can be considered while deciding the machines.

    From the above table it is clear that, 23 ringframes with 1120 spindles are working with auto doffing and with link to autoconer. The major advantage of this automation is to reduce labour and to reduce the problems related to material handling. One has to really work out the benefits achieved because of this and the pay back for the extra investment.

    Drawframe contributes a lot to the yarn quality and the ringframe and winding machine working. It is always better to go in for the best drawframes like RSB-D30 drawframes with autoleveller. It is not wise to buy a cheaper drawframe and save money.

    It is always better to keep excess carding and autoleveller drawframes, so that flexibility of the project is also maintained. If the coarser counts contributes more and the market is good, overall production can be increased. If the market is for finer count, both the machines (carding and drawframes)can be run at slower speeds, which will surely contribute to yarn quality.

    Speeds of speedframe , combers and ringframes do not affect the yarn quality as it is affected by card and drawframe speeds.

    Blow room capacity should be utilised to the maximum, as it consumes a lot of power ,space and money.

    Ringframe specification should be perfect, because the working performance and power consumption of the ringframe depends on the specifications like, lift, ring dia, no of spindles etc. Ring frame specification should be decided to get the maximum production per spindle and to reduce the power consumed per kg of yarn produced by that spindle. Because the investment cost and the power consumption for the ringframe is the highest in a spinning mill.

    INVESTMENT ON ACCESSORIES:

    The following table gives the details of the accessories like cans for carding, drawframe, bobbins, trollies etc

    ACCESSORIES NO. OF MCS RATE / MC TOTAL COST
    Carding cans 36″ x 48″ 120 160 19,200
    comber cans 24″ x 48″ 350 85 29750
    Drawframe cans 20″ x 48″ 1100 53 58,300
    Identification bands 20″ 400 1.2 480
    Identification bands 24″ 50 1.8 90
    Roving and spinning bobbins 36,000
    Plastic crates 400 6 2,400
    trolleys 10,000
    Cone trolly 80 200 16,000
    Fork lift 1 27,000 27,000
    hand truck 3 1000 3,000
    TOTAL 202,220

    SERVICE AND MAINTENANCE EQUIPMENTS:

    The following table gives the details about the investments required on service and maintenance equipments

    SERVICE AND MAINTENANCE EQUIPEMENTS NO OF MCS RATE/MC TOTAL PRICE
    Cots buffing machine and accessories 1 20000 20000
    Card room accessories 1 set 60,000 60,000
    Spindle oil lubricator 1 4000 4000
    Clearer roller cleaning machine 1 3000 3000
    Vacuum cleaner 5 3000 15000
    pneumatic cleaners 6 500 3000
    Weighing balance 3 2000 6000
    Strapping machine 2 2000 4000
    Premier autosorter 1 2500 2500
    Premier uster tester 1 45000 45000
    Premier strength tester 1 45000 45000
    premier fiber testing 1 45000 45000
    Premier Classidata 1 25000 25000
    Erection charges 150000
    TOTAL 427500

    Card service machines like Flat tops clipping machine and flats grinding machine are very important for yarn quality. One should not look for cheaper machine. It is always better to go for reputed manufacturers like GRAF, HOLLINGSWORTH etc.

    Rubber cots contributes a lot to yarn quality. Bad buffing in ring frame can increase the imperfections by 15%. Poor quality of buffing in drawframe and speedframes can affect both production and quality. It is better to go for the best cots mounting machine and cots buffing machine.

    HUMIDIFICATION AND ELECTRICAL EQUIPMENTS:

    The following table gives the details about the investments required on humdification and electrical istruments

    Electrical installation including transformer, incoming and outgoing panels, bus duct, capacitor, etc for 3800 KVA 350,000
    Cables 125,000
    Compressor, Dryer and pipe lines 180,000
    humidifaction system 767,000
    chillers 176,000
    Ducting and installation for humidification system 125,000
    workshops, hydrant and other equipments 100,000

    TOTAL

    1,823,000

    In indonesia, most of the units use PLN power and some of the spinning mills use Gensets. A detailed costing has to be done to compare the cost per unit to decide, Whether to use the PLN power or to go in for Gensets. while working out the costing finance cost on investment , overhauling cost, running cost, efficiency of the machine should be considered for cost caluculation in the case of Genset. In case of PLN power, the losses due to power interruption( based on the area data), finance cost on initial investment, md charges, unit charges to be considered. It is better to use 50% PLN and 50 % own generation.

    The following table gives the details about land and builiding investments

    Land cost 200,000
    Land development 40,000
    Factory building Including Service ally 192 x 62 meters 11,712 Square meter @ 120 usd/sq meter 1,405,440
    Road and others 40,000

    TOTAL

    1,445,440

    STEP NO.3: To calculate the expenses ( labour, power, stores,working capital, insurance etc)

    Working capital = 3,000,000

    LABOUR:The following table gives the details about labour requirement

    DEPARTMENT No of people required
    Production 140
    packing 15
    maintenance 30
    utility 17
    administration and personal dept 20

    Total no of people required per day

    222
    wages at 50 usd/month including bonus and insurance 111,00
    other facilities at 35 % 3,885
    salaries for managerial staff 10000
    Other facilities at 35 % 3500

    Total labour cost / month

    28485

    POWER: The following table gives the details about the power

    Total units(KWH) produced (consumed)per day 69559
    Unit cost (cost / KWH) 0.03
    Total production in Kgs 17,390
    KWH/ Kg of yarn 4.0
    TOTAL POWER COST /DAY 2087

    SPARES:The following table shows the spares cost, repair , and insurance

    spares cost at usd 8/1000 spindle shift 222,566
    repairs and other overheads 200,000
    Insurance at 0.175% on investment and working capital 31320
    TOTAL cost per year 453886

    STEP NO.4: PAY BACK CALCULATION

    DETAILS IN USD
    INVESTMENT:
    Land and building 1,444,440
    Machinery, accessories & service equipments 11,832,115
    Electrical and Humidification ducts 1,823,000

    TOTAL INVESTMENT

    15,099,555
    WORKING CAPITAL 3,000,000

    GRAND TOTAL

    18,099,555
    RECURRING EXPENDITURES PER DAY
    Salaries and Wages 949.5
    Power cost 2087
    Stores , repairs and insurance 1260.8

    TOTAL

    4297.3
    INTEREST CALCULATION (per day)
    On capital 8% 3355.5
    on working capital 9% 750
    TOTAL EXPENSES INCLUDING INTEREST 8402.8
    TOTAL CONTRIBUTION PER DAY 13312
    NET PROFIT( before depreciation & taxation) 4909.2
    PAY BACK PERIOD 8.54 years

    Cheese yarn dying reciepe

    Reactive Dyeing of cotton yarn in cheese form:

    Whether it is Vinylsulphone or Bifunctional dyestuff, you may follow the following dyeing cycle for yarn dyeing:

    The Chemical table shown below contains a Code No. that has to be included time to time when the dyeing process is going on.

    Code No Name of Chemical Grams/liter
    1 Acetic Acid 0.5
    Sequestering Agent 0.5
    2 Acetic Acid 0.5
    Vacuum Salt or Glauber’s Salt As Recommended
    3 Dyestuff O.W.F.
    4 Soda Ash As Recommended
    5 Acetic Acid 0.5
    6 Sequestering Agent 0.5
    Anionic Soap 0.5
    7 Acetic Acid 0.5
    8 Dye fixing Agent Not Necessary
    9 Softener 1.0


    Processing Cycle for Yarn Dyeing:

    • Set the dye bath with soft water at ambient temperature and as per MLR
    • Enter the RFD (Ready For Dyeing) yarn in to the processing vessel.
    • Add Chemical [Code-1]. Circulate for 3 minutes (In -> Out) and hold for 10 minutes. Drain.
    • Check pH. It should be 6 – 7. Check for channeling.
    • Fill cold water, add chemicals [Code-2], Circulate for 5 minutes (In -> Out) and hold for 10 minutes.
    • Raise temperature to 40°C and hold for 5 minutes.
    • Add dissolved dyestuff [Code-3] in 2 to 3 portions with Out -> In circulation at 40°C.
    • Raise temperature to 60°C @ 1.5°C/minute and hold for 15 minutes.
    • Add Chemicals [Code-4] in two parts with In->Out circulation and run for 45 minutes.
    • Check the sample and drain the dye bath.
    • Rinse at room temperature for 5 minutes and drain.
    • Give overflow rinse as per the dept of shade – 3 to 5 minutes.
    • Fill fresh water, add chemicals [Code-5] and hold for 5 minutes. Drain.
    • Fill hot water (60°C), add chemicals [Code-6] and circulate for 3 minutes.
    • Raise the temperature to 95°C and run for 15 minutes. Drain.
    • Rinse at 70°C for 10 minutes followed by 5 minutes overflow wash. Drain.
    • Fill fresh cold water, add chemicals [Code-7] & [Code-8] and circulate for 3 minutes, hold for 15 minutes and then drain.
    • Fill Cold water, add chemicals [Code-9], circulate for 3 minutes and hold for 10 minutes. Drain.
    • Unload the batch.

    Notes on Dyeing:

    1. For Shades above 7%, two soaping operations are necessary.
    2. Dye fixing is optional but not a substitute for thorough washing.
    3. Pressure difference during In->Out and Out ->In operations has to maintain a constant.

    Engineering of Denim Fabric

    Denim mills are searching for ways to produce denim fabrics of the highest quality at competitive prices. The engineering from raw fiber to finished fabric results in superior denims when modern fiber and manufacturing technologies are consistently applied throughout the processing chain. However, the cost of these engineered products delivered to the market place demands, in addition the prudence in tackling the volatility associated with the raw material, mainly cotton.

    The Raw Material Cost [RMC] per metre of 150 cm width basic OE denim, for various denim weights over a decade is depicted below in equation, for the sake of simplicity:

    RMC/metre = 2.3 x ozs per sq.yd. + 8.4
    +/-0.4

    That is cotton cost per metre for a 10ozs OE denim is Rs.31.4 [Ranging 27.4 to 35.4]

    The engineering of denim fabrics utilizes, ring spinning or open end rotor spinning or their differentiated innumerable characteristic yarns + modern fabric forming and finishing techniques and commonly available but selected cotton fibers. The mixing specifications for different yarns are given in Table-13.3. Cotton Mixing Specifications of Important Fibre Characteristics for Denim Yarns (HVI Mode).

    The following equation depicts the cost differentials between Ring denim and Rotor denim in a simplified way:

    RMC Ring per metre = RMC OE per metre x [1+ozs per sq.yd/100]

    That is cotton cost for a 10 ozs ring denim is Rs.31.4 + [1+10/100] = Rs.31.4 x 1.1 = Rs34.54.

    Engineering

    Hence the engineering of denim fabrics begins with the selection of appropriate combination of cotton fibre characteristics for different yarn types with the aid of modern HVI instruments. The mixing specifications for different yarns are given in Table-13.3. Cotton Mixing Specifications of Important Fibre Characteristics for Denim Yarns (HVI Mode).

    Once fibre characteristics are known, yarn quality and processing performance can be predicted. Last column in the Table-13.3 provides an iNDEX for various yarn types which can be used as a composite measure to arrive at a variance with respect to actual yarn quality of various yarn types including individual characteristic yarns.

    The equation for calculating

    iNDEX=735 x [UHML x Str - 3 x Str -255 -6.6 x UHML]^0.22

    Where UHML is Upper Half Mean Length in mm and
    Str is Strength in grams per tex as tested using HVI Mode

    The above iNDEX which uses Fibre characteristics as tested using HVI Mode is deduced from earlier ATIRA equation for predicting CSP of Open-end yarns using Fibre characteristics using ICC Mode.

    CSP =720 x [2.5% SL x S - 300]^0.22 – [72.5 x Mc/2.5% SL + 16] x C
    Where 2.5% SL is 2.5% Span Length in mm
    S is Strength in grams per tex as tested using ICC mode
    Mc is Micronaire and
    C is Count in Ne

    The spinning parameter Twist Multiplier and important yarn parameters, such as strength, count and their variability’s of various yarn types are provided in Table-13.4. Spinning Parameters and Yarn Quality.
    Rope dyeing technology demands less torque yarns in warp which are made from “U”rotors. The H values of Yarns made from “U” rotors as tested in Uster evenness testers are higher by 2.0 to 2.5 numbers in comparison with the yarns produced from “T” rotors

    Cover Factor

    To obtain better performance on the loom and fabric yield, a guideline for cover factor in developing new fabric constructions is given in Table-13.5 and classified under 3 categories for

    i) Rings
    ii) Bulky Open-ends and
    iii) Shrinking Stretches.

    B.Grey construction is used for calculations.

    C.The formula used = Threads per inch
    ————————— ——– X 100
    [28 X Square root of Count]
    Changing Trend in Yarn Preferences

    Beginning of twenty first century saw the explorations in different yarn options. The below list is arranged by their usage in volume, starting with warp followed by their use in weft.

    Crosshatch / Streak / Rain Denims

    Recently, the usage of characteristic yarns, such as slubby and multi count yarns, both in ring spinning and open end rotor spinning system in denims are on the rise. These yarns need additional monitoring of Slub parameters. Fancy yarn module of UT-5 serves this purpose with testing of Slub parameters -Slub frequency, Slub Length and Mass increase in addition to yarn diameter, yarn density and shape. Aggressive slub parameters tend to lower Yarn Strength and poor performance at subsequent processes. The minimum tenacity values as tested using Uster Tensorapid for satisfactory performance level is given in Table-10.4 in Row 3 and 7. Beyond which compromise needs to be made among Slub parameters or performance levels or cotton fibre characteristics.

    Chinos

    Two ply chino denims in indigo dyed shade have a unique soft hand feel, Fabric cover and a luxurious appeal.

    Tencel Denim

    Woven century luxury cellulosic fibre made from specially grown woods and transformed in non-chemical process which give feel of silk and comfort of cotton.

    Stretch Denims

    For stretch denims, Core-Spun Cotton Spandex, Poly Spandex and Type -400 yarns are generally employed. Core-Spun Cotton Spandex yarns in denims range 10s to 16s Ne and uses generally 70 denier filament; though 40, 55 and 120 denier filaments are also available. The Spandex % of Core-spun cotton spandex yarn ranges from 3.5 to 5.5 %. The twist multiplier is 4.4.

    Union Denims

    Denims are differentiated with weft yarns to create Union Fabrics. The union denims produced in large volumes uses the following weft yarns in the same order – Polyester Texturised Filament, Stretch yarns of Poly Spandex and Type -400 yarns, and Pre-bleached Linen Yarns.

    Poly Denim

    Polyester Texturised Yarns in denim applications range 300 to 600 denier, with a tenacity of 4.0 g/tex and 20 to 27% extension. Bulk which is expressed in %HCC (Hot Crimp Contraction) is about 40 and nips per metre ranges from 70 to 90 for better performance.
    Grey as well as dyed yarns are being used.

    Poly Stretch Denim

    Poly spandex yarns used in denims range 150 to 300 denier with 6 to 12 % spandex. Nips per metre for better weaving performance is 100 to 130. Type -400 yarns from Invista used in denim applications range 150 to 600 denier with a bulk of 50% HCC and nips per metre of 35 to 50.

    Linen Vintages

    Pre-bleached Linen yarns range 9s to 16s Ne [or 25 to 44 Lea]. Though these yarns have very high strength of over 3000 csp and 20 cN/tex, due to low elongation of 2% and the natural variation in yarn, the loom performance as well as full width defects is poor in comparison with normal denim.

    Value Engineering

    In accordance with the value engineering, quality fabrics can also be produced from Value mixings given in Table -11.3 Row 5. However the denim fabrics produced out of such yarns should not be meant for elaborate destructive garment washes.

    Addition of 10% Recycled Waste

    The full recycling of all opening and carding wastes, using a new line of machinery from Trutzschler and others, is attempted by few with a success . Its obvious importance in Denim manufacture lies in the overall weight on the final cost represented by the cost of cotton .Because of heavy yarns and fabrics, if one can save 3 or 4% on cotton costs, the impact on the bottom line can be remarkable.

    This clean material has some residual trash in it not too different from the cotton used. Naturally there are more short fibres. The yield will be approximately 50%, in other words from each 2 kgs of raw waste we get 1 kg of clean recycled cotton. This material is baled again and fed to the mix at the lay down. Normally 10% is used. A loss of some 0.5 to 1.0 cN/tex is then unavoidable, but with 10% it will be manageable.

    Control of Yarn Realization

    A one percent reduction in yarn realization has almost the same economic impact on the mill’s profit as an increase of one percent in the mixing cost. The control of yarn realization is thus as important to a mill as the control of cotton and mixing costs. One may find the detailed procedures for the control of yarn realization in Chapter 3, ATIRA Silver Jubilee Monograph “Process Control in Spinning”.

    Mock Rings

    Various attempts to duplicate superior denims made from ring yarns with rotor yarns of mock or slubby have always failed in fabric strength properties, fabric hand and appearance due to differences in yarn structure and yarn properties. Still one wonders how much of the present so-called ring spun Denims are such and how many are mock ring made in open end.

    Other Value Offerings

    Cotton rich polyester denims are with superior hand feel, luster and colour contrast for fashion market. One may find a deep value in using dyed polyester texturised filament yarn in place of costly yarn dyed cotton weft for high fashion denim. Poly Spandex yarns are replacing core spun lycra yarns in the value universe. Within Poly Denims, the denier is getting coarser day by day from 300 to 450 to 600. Though, Linen Vintage denims are not in high volume, there are efforts to replace it with Jute (Indian Linen) in the value proposition.

    Successful strategies in denim mean profit, often (now) even survival. Engineering the fabrics on continual basis provides a way to achieve both quality and cost benefits of substantial proportions. At the same time full manufacturing flexibility through modularization is being maintained, enabling the denim mill to meet new and changing trends in raw material and fashion.

    Evalution of Denim Fabric

    The following standards for denim fabric quality in terms of inspection, packing, shade and physical requirements are of general nature considering varied requirements of end-uses / customers, however holds good for major universe.

    This chapter details classifying fabrics according to color and defects so that the fabrics are made to garments at ease with defects eliminated, grouped according to shade and perform satisfactorily.

    INSPECTION REQUIREMENTS

    Fabric Group Classification According to Yarn Type

    Group One

    All Basic Denims (OE/OE)

    Group Two

    All Denims (RING/OE) & (RING/RING)

    Group Three

    Specialty Denims: Linen Denims, Vintage

    Acceptable Defect Point Levels According to Yarn Type

    TABLE-11.1:DEFECT POINTS PER 100 SQUARE YARDS
    TABLE-11.2:DEFECT POINTS PER 100 SQUARE METRES
    TABLE 11.3: QUALITY CATEGORISATION OF DENIM FABRICS

    Defect Grading:

    A. Point Grading System: Denim fabrics are normally graded using the “4-Point” system. This numeric grading system is endorsed by ASTM, AAMA (American Apparel Manufacturer’s Association) and ECMA (European Cloth Manufacturers Association). All defects which are clearly visible from one meter (three feet) are scored as defects and demerit points assigned according to severity.

    B. Length of Defect Points: Demerit points are assigned to warp and filling defects as follows (Defects in any direction)

    v 1 point – Defects 7.5 cm(3”) or less
    v 2 points – Defects exceeding 7.5 cm(3”) up to 15 cm(6”)
    v 3 points – Defects exceeding 15cm (6”) up to 22.5cm(9”)
    v 4 points – Defects exceeding 22.5 cm(9”)

    C.Counting of Lengthwise 4 Point Defects: No linear meter is penalized more than 4 points.

    v Defect length 22.6cm (9”) to 100cm (40”) – 1 no of 4 point defect
    v Defect length 100.1cm (40.1”) to 200cm (80”)–2 no of 4 point defects
    v Defect length 200.1cm (80.1”) to 300cm (120”)–3 no of 4 point defects
    v If length of defect is more than 3 meters (120”) the length containing the defect is removed.

    D. Full Width Defects:

    v A full width defect running over 6” in length shall be removed.
    v More than four full width defects per one hundred linear meters shall not be accepted as first quality.
    v A full width defect in first or last three meters of roll shall not be allowed.

    E. Flagging of Defects:

    v Only 4 point defects are flagged with a metallic sticker. One may find the metallic sticker at the start of the defect. Metallic flags should be a minimum of 2 cm wide and 7.5 cm length.
    v Defect points 1, 2, 3 shall be counted but not flagged.
    v All splices shall be flagged.
    v All holes shall be removed. There must be two or more yarns broken at the same place to consider a defect as a hole.

    F. Roll Length and Splicing:

    v Roll length tolerance should be agreed upon the first delivery. Say maximum 135 meters and minimum 85 meters.
    v No pieces shall be accepted as first quality with length less than 30 meters.
    v No roll shall be accepted as first quality containing more than one splice.
    v The shade continuity between parts must allow for the mixing of garment components within a garment.
    v Two part rolls should be identified as such, No more than 25% two part roll should be allowed in any shipment.

    G.Shading:

    v No pieces shall be accepted as first quality that exhibits a noticeable degree of shading from side- to -side or side- to –centre.
    v No pieces shall be accepted as first quality that exhibits a noticeable degree of shading from end– to –end.

    Skew

    A. All 3/1 and some 2/1 twill fabrics for bottoms require skewing. Since the optimum skew varies depending on the fabric (anywhere from 5% to 9%), this must first be determined by the supplier and agreed upon before bulk fabric orders are placed. Target for individual rolls = +/- 3%

    B. No fabric shall be accepted as first quality exhibiting more than 3% skew movement.

    Waviness

    No roll shall be accepted as first quality exhibiting a noticeable degree of looseness (waviness) or tightness along either or both selvages.

    Ripples or puckers in the body of the fabric, which prevents the fabric from lying flat when spread in a conventional manner, is unacceptable.

    The woven selvage or fringe should be the same on both sides of the fabric.
    Tolerance wavy selvage: 2% in length

    Width

    Cuttable width variations must meet the minimum fabric width specification. In addition width variation within a roll should not exceed 2 cm.

    PACKING REQUIREMENTS:

    Put- up- Specifications

    A. Fabric shall be rolled onto a spiral-wound tube with necessary wall thickness [OD: 60 mm; ID: 45 mm] and strength [Radial Crushing Strength > 500 Kgf for 8” length] to insure it reaching to customers in good condition, provided it is handled by reasonable and acceptable methods.

    B. Rolls are wrapped in such a manner that will protect the fabric from all types of damage during transportation and storage.

    C. The outer edge of each roll shall be taped down to prevent unrolling during shipment and storage.

    D. Roll Identification

    Two stickers must be attached one to the end of the roll and another on side of the roll. The stickers shall contain the following information.
    1. Roll /Bale Number.
    2. Fabric Style number
    3. Shade Group
    4. Roll length in meters
    5. Roll length in yards
    6. Fabric width in inches
    7. Total square meters
    8. Demerit points per 100 square Yards
    9. No of fabric pieces
    10. Gross weight in Kg
    11. Net weight in Kg
    12. Quality Category
    13. Total number of 4 point defects
    14. Total number of Demerit points
    15. Security code

    COLOUR EVALUATION / SHADE GROUPING

    Option 1: Instrumental Shade Evaluation Procedure of Wash Swatches

    Instrumental Color Measurement: The color measurement shall be carried out using Spectrophotometer.

    Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll – Instrumental Evaluation”

    Blanket Preparation: The blanket preparation procedure is given under the head “Blanket Preparation”

    Shade Evaluation: The color measurement shall be carried out using Spectrophotometer and shade grouping shall be carried out according to wash color reference of master roll. Before assessment, all fabric swatches must be conditioned for at lease 1 hour in a controlled atmosphere. Samples must be conditioned from a dry state. All measurements must be done as soon as possible after conditioning.

    Classifying Rolls by Color Groups: LMD grouping shall be followed. (L= Light, M = Medium, Dark = D), the taper standards are defined as color difference (dEcmc) by Standard, Average, Range and Roll to Roll. L: C [Lightness: Chroma]

    The tolerance to be followed is

    Average : 1.2
    Standard : 2.0
    Range : 1.5
    Roll : 0.5
    L: C Ratio : 2.0

    Visual Evaluation: All roll sequences shall be evaluated visually by laying the swatches in standard lighting conditions and remove abnormal rolls.

    Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux.

    Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D and the same shade group shall be mentioned in the packing list by tracking via roll number.

    Swatch Service: The system shall be to send two set of unwashed and washed swatches to customers. The washed swatches are being sent so that customer can review the shade at their end and the unwashed swatches will be used for additional use if any.

    Option 2: Visual Shade Evaluation Procedure of Wash Swatches

    Visual Color Assessment: Each wash swatch representing one roll in the shipment needs to be compared to the master swatch under standard light conditions.

    Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll – Visual Evaluation”

    Blanket Preparation: The blanket preparation procedure is given under the head “Blanket Preparation”

    Shade Evaluation: Each wash swatch shall be evaluated versus reference shade swatch on shade, color, wash-down, abrasion and overall appearance. Based on this comparison swatches representing rolls shall be accepted/ rejected.

    Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux. Make sure a matt grey background is used with reference of Munshell grey N5 or N7 to assess colors.

    Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D and the same shade group shall be mentioned in the packing list by tracking via roll number.

    Swatch Service: The system shall be to send two set of unwashed and washed swatches to customers. The washed swatches are being sent so that customer can review the shade at their end and the unwashed swatches will be used for additional use if any.

    Option 3: Visual Shade Evaluation Procedure of Unwashed Swatches

    Visual Color Assessment: Each wash swatch representing one roll in the shipment needs to be compared to the master swatch under standard light conditions.

    Master Roll: Master roll shall be established during initial stages and will remain during the entire life cycle of the product. The procedure for selecting the master roll is given under the head “Procedure for Selecting the Master Roll”

    Shade Evaluation: Each unwashed swatch shall be evaluated versus reference shade swatch on shade, color and overall appearance. Based on this comparison swatches representing rolls shall be accepted/ rejected.

    Light Conditions: Only D65 lamps are to be used to assess color. Make sure appropriate Number of lamps is used to obtain luminosity of minimum 1500 lux. Make sure a matt grey background is used with reference of Munshell grey N5 or N7 to assess colors.

    Identifying Color Groups: To facilitate classification of rolls, the rolls shall be identified with appropriate color stickers of L, M and D or D+, D, D- and the same shade group shall be mentioned in the packing list by tracking via roll number..

    Swatch Service: The system shall be to send three set of unwashed swatches to customers.

    Blanket Preparation

    Swatch Size: Use uniform swatch size of 8” x 6”

    Preparation of Blankets: All blankets for washing shall have standard shade swatch from Master Roll. Swatch shall be cut from every roll of a shipment each 8” x 6”. Identify each roll no at the back of the swatch. In case of light weights identify by serial nos at the backside corner with indelible ink.
    Waste material of same style

    Wherever less number of swatches is available use dummy swatches of same style nos.

    Do not use washed swatches for dummies.

    v Dummy swatch size shall be of same size as that of blanket swatches.

    v To make wash load if required, use dummy swatches of same style only.

    v Sew the two panels together to avoid entangled panels in washing.

    v All panels from one shipment to be washed in same wash load.

    Washing of the Blankets: Wash blankets according to the recipe for various classes of products.

    Procedure for Selecting the Master Roll

    Instrumental Evaluation

    v From the average of the washed lot select about five roll which are near to the average values.
    v Check their UNWASHEDED L*a*b* values, these must belong to 555 block. If not then select 5 more rolls near to average values from the washed lot.
    v The roll which belongs to 555 shade block, check the preceding and succeeding rolls L*a*b* values, these must also belong to 555 shade block. This will ensure that there is no shade variation within the roll.
    v Now check the consistency of the complete beam. There should not be much variation within the beam.
    v The dyer will use the yarn latti of this particular beam as shade reference for dyeing.

    Visual Evaluation

    v Select about five rolls which represent middle of the washed lot.
    v Check unwashed swatches as well, for their true representation of the middle of the lot.
    v Check the preceding and succeeding swatches. These must also belong to the same shade. This will ensure that there is no shade variation within the roll.
    v Now check the consistency of the complete beam. There should not be much variation within the beam.
    v The dyer will use the yarn latti of this particular beam as shade reference for dyeing.

    Weaving with Denim yarn

    Traditional denim weaving had been done with the rapier looms and projectile looms for a long time. But with the development of the air jet weaving technology, the main flow of the denim weaving has been changed to Air Jet Loom due to its suitability to mass production.

    The general guidelines in selection of various types of shuttle less weaving machines are as follows:

    Rapier is known for its versatility in weaving fancy fashion materials of different constructions like suiting, upholstery, furnishing etc.

    Air Jet weaving machine is most suitable for mass production.

    Projectile is suited for dress material, industrial fabrics, heavy denim and geotextiles in single or multiple widths.

    An evaluation on the application of various methods of weft insertion carried out by the Textile Machinery Society of Japan is given in Table 5.1

    As can be seen from the Table that Air Jet Weaving scores in high productivity and labour savings however suffers in high energy costs and yarn wastage. Projectile scores well on both parameters, that is energy saving and fabric quality. More over, running cost will be the lowest for projectile during extended machine’s economic life beyond capital life. However, these ratings may be different in Indian context and for specific denim applications.

    ON AIR JET LOOM

    The important features of Denim weaving on Air Jet Loom are as follows:

    a. High Productivity: As an actual production in the mill, 900 rpm is achieved already with the latest models of different makes.

    b. Start Marks: The rush motor emits 1200% torque at the time of start and avoids start marks. Electronic let off, ensures the even warp tension from the full beam to the empty beam. Electronic let off is also equipped with the programmable kick back function which controls the cloth fell position at the start according to the loom stop duration. The second feeler is equipped to detect blow off of weft yarn.

    c. Special arrangements for the Denim Weaving of Coarse Yarns:

    I. Reinforced loom structure for heavy duty weaving.
    II. Reinforced let-off motion for heavy warp.
    III. Intermediate rocking supporter to make a strong beat without bending for heavy fabric.
    IV. Positive cam motion for high speed operation for the heavy load of warp.

    d. Stop Market Prevention:

    i) Automatic Leveling Device: It automatically closes the shed after a loom stop by leveling all the shafts and prevents warp strain which may create corrugate marks.

    ii)One Pick Insertion System: To minimize stop marks, a special weft insertion system functioning at the time of restart can be equipped with. When the loom is started first pick is automatically inserted just before the first beat. By avoiding the beat- up without yarn at reverse rotation, this system prevents the corruption of the fabric construction and prevents corrugate marks.

    e. Devices for a coarse count weft:

    The following are some of the arrangements equipped to use a coarse count yarn for weft.
    i) Balloon Breaker reduces the weft tension due to ballooning.
    ii) Auxiliary main nozzle is installed before the main nozzle to insert a coarse weft with less air pressure.
    iii)Stretch nozzle is furnished to give adequate stretch to the weft for a perfect insertion of a coarse weft.

    f. Labour Saving:

    This is realized with a large size packages and loom automation. Automation includes automatic pick finding for easier weft repair and automatic defective pick remover.

    REQUIREMENTS FOR HIGH INSERTION RATES IN AIR JET WEAVING

    weaving profitability is the result of weaving productivity. The higher the weaving machine speed and efficiency the higher the productivity. As soon as speed is increased however, weaving machine efficiency, which is affected by loom down time on warp and product changing on repairs and yarn break repair times and also quit markedly by the number of warp and weft stoppages falls a rule.

    The standards for loom stops per hour is given in Table-5.2

    In air jet weaving, the proportion of weft stoppages to total is high, and their reduction is therefore of great importance for increased efficiency in air jet weaving processes. In addition, fewer warp yarn breaks, their faster repair and short setting times are the key for high production. It is not the speed of the machine, but the number of picks actually produced that is the deciding factor in modern weaving. The important points are i)the factors which guarantee high insertion rates ii) the humidity levels iii) the factors which lead to a high fabric quality.

    Influence of Yarn:

    The yarn breaks in spinning are correlated to the yarn breaks on the weaving machine. It is important to maintain count and strength variability to the lowest. The standards for Count CV% and Strength CV% is given in Table- 5.3.
    The count CV% will be higher by +0.5 where auto levelers are not existing on finisher draw frame. Therefore it is necessary to use two passage draw frames where finisher draw frame is equipped with auto levelers particularly fine, ring and characteristic yarns.

    In case of OE spinning there is an interesting correlation between high residual trash- content and increased yarn breaks in weaving. The norms for residual trash content at feed sliver are 0.5%.

    The weft insertion performance depends to a large extent on the level of weak spots. The standards for Uster Tensojet Tensile properties are given in Table-5.4. Percentile 0.1% values given in Col 5 and 6 for Elongation% and Force in cN is a tool for identifying the weak spots in the yarn lot and estimated performance on loom.

    Influence of Weaving Preparatory on the Cloth Production System:
    Tight ends, lost ends, pieces of yarn or lint dragged onto the warper beam are performance killers in air jet weaving. Therefore the accurate functioning of the stop motion on the creel plays a key role.

    Warper beams should not contain any grooves, high edges or crossed ends. They should be made with bobbins of adjusted length and run off the creel without crossing ends and at uniform tension. In this manner yarn breaks on the sizing machine can be almost eliminated.

    During sizing, the lengths run at creep speed should present less than 4% and a moderate size application control system should be used. For air jet weaving, two size boxes and real wet splitting should be used in case of warps with more than 70% cover density, in order to reduce the hairiness of the yarn.
    The use of size add on control seems to be essential when operating with two size boxes, because there are no two size boxes, because there are no two size boxes which, in spite of exactly identical setting, produce exactly the same size add on. The differences measured may reach as much as 4% in absolute figures.

    Over drying, particularly when sizing cotton yarns should absolutely be avoided.

    After waxing, (0.2 to 0.5%) of the warp ends generally improves its performance.

    Finally the warp ends should be fixed by tapes in such a way that they can be entered into the harness without crossing.

    Factors influencing the performance of the warp in the weaving machine:

    The shed geometry in front of the reed is to a large extent designed by the builder of the machine. When setting the back shed and harness stroke the weaver is required to choose the proper setting, also when determining the warp tension. These settings have an important impact on the performance of the machine. It is therefore essential that these settings are optimized with utmost care and by using modern measuring instruments.

    Following two factors have a particular influence on the behaviour of the warp:
    i) yarn traction force
    ii) yarn hairiness

    A too high warp yarn traction force is leading to overloading the warp ends. As the yarn traction force is not constant during weaving, the peak tensions which generally appear in the bottom shed, particularly in the middle of the warp should be taken into consideration. These peak values should not exceed 5 to 6 cN/tex, depending on the quality of the yarn.

    The importance of the setting of the warp stop motion is often under estimated. Its position has a direct influence on the back shed and thus on the yarn traction forces in the bottom and top sheds. The vertical position of the warp stop motion should therefore be set very precisely. It changes the asymmetry of the shed.

    Atmospheric Conditions

    Relative humidity have a great impart on the performance of the weaving machines. The optimal dissipation of temperature and humidity over the machines, that is the warp, is generally not reached, because the sources of heat within the weaving machine disturb the climatic conditions. Numerous yarn breaks are caused by dust, lint and fibre accumulations. The best experiences have been made with air conditioning systems whereby humidified air is conducted over the machine, whilst the dust – loaded exhaust air is evacuated through floor opening under the back shed, and because the descending flow of the conditioned air is assisting the sedimentation of the lint. At the same working conditions for the personnel are improved. It is surprising how much cleaner the machines and the whole weave room are, compared with systems whereby the exhaust air is evacuated in the alleys, or worse, through the outside walls.

    Table -7.6: Weaving – Typical Denim Constructions

    TABLE-7.7 : PRODUCTION CALCULATION

    The following information is an estimated performance for weaving 14.5 ozs indigo denim.

    a)Fabric : Indigo Denim 14.5 ozs/square yard
    Warp Yarn : 100% Cotton Ne 7s Indigo Dyed
    Weft Yarn : 100% Cotton Ne 6s Grey
    Warp Density: 60 ends/inch
    Weft Density : 40 picks/inch
    Width : 66.5 inches
    Weave : 3/1
    b)Reed Space : 68.5 inches
    2 Colour Weft Mixing
    Positive cam shedding Motion, 4 shafts
    -Denim Weaving Arrangement
    c)Estimated Loom Speed : 900 rpm
    d)Estimated Production Per Loom:
    i)Daily Production (linear length)
    = 900 rpm x 60min x 24h x 0.92 eff x 0.0254 / 40 ppi
    = 757 metres/day/loom
    ii)Monthly Production (linear length)
    = 757 m x 30 days
    =22713 metres/month/loom

    Spinning of Denim Yarn

    The denim units have a high production output. According to international standards a unit of 50 million metres per annum capacity is considered to be of an economic size. In India however units of 10 million metres per annum capacity have been operating.

    The spinning capacity is usually determined by the performance in the dyeing range. For a 10 million metre capacity unit producing 12 ozs average fabric weight with a standard width of 150cms require denim yarn of 16 to 17 tonnes per day. Extending it further, the raw material requirement will be about 19 to 20 tonnes of cotton per day. Thus, spinning of denim yarn is really a large scale business because of heavy yarns and fabrics.

    PLANT & MACHINERY

    The following features in plant and machinery have become prerequisites for producing top quality denims:

    A. Modern Blow room line with 4 to 5 beating points with micro dust extractor and very efficient automatic waste evacuation system.
    B. Modern High Production Chute feed cards with autolevellers and efficient automatic waste evacuation system.
    C. High Speed autoleveller Draw frame at finisher passage.

    Open End Spinning

    D. Modern Open End Spinning machine with automatic piecing and yarn monitoring devices like Corolab or Uster Polyguards.

    Ring Spinning

    E. High speed frames with bigger doff packages.
    F. Ring Spinning machines with Longer Lift and Larger Ring dia.
    G. Cone winding machines with efficient yarn clearers

    COTTONS USED

    Let us first start with the raw material. Cotton fibre specifications of important Indian varieties used in denim yarns are given in Table-3.1.Various cottons are used, ranging from irrigated J-34 from North, hybrid Shankar-6 from Gujarat, windy V-797 of Saurashtra, lean season rescuer NHH-44 from federation, quilty Bengal desi to cosmic bunny to name a few from the Table [Table 3.1].

    Often recycled waste, purchased comber noil of other mixings is also added.

    Cotton fibre specifications of some imported cottons used in denim yarns are given in Table-3.2. Here again cotton used, ranging from 32s to 36s of US upland cottons, trashy CIS cottons, to sticky Sudanese cotton.

    This is because, denim fabrics that, whether we like it or not, are somehow getting close to commodity status, cannot ignore the very high raw material cost. In addition, over the years, process and technology improvements allowed the operational flexibility to use various cottons, leading to cost savings still meeting the quality standards required by customers. In addition, India has the sole distinction of producing many varieties covering all four species and their hybrids, each with limited availability. For example, V-797, [which is considered to be the seismic test for installing a wind mill, in the lighter sense] with higher Uniformity Ratio translating to better yarn, has limited availability geographically. With the increased demand from large scale denim businesses, the relative price cannot go beyond the better value cotton, say J-34. Cost, proximity and availability over-ride the variety preference.

    Cotton Mixing Requirements For Denim Yarns

    Cotton mixing specifications of important fibre characteristics for denim yarns engineered to meet seven major end-uses are given in Table- 3.3.

    Upper Half Mean Length, Uniformity Index, Strength at 1/8” and Micronaire values as tested in HVI mode are to be maintained in a lay down. [Row 1 in Table 3.3]

    Uniformity of average fibre properties in successive lay downs is far more important and desirable than a level of certain properties, that being difficult to achieve, is not easily maintained day in and day out.

    Open End

    Coarse count yarn in denim refers to less than 8s Ne. and fine count is 9s to 16s. Mixing requirements for rope dyed warp open end yarns are higher and normally made from “U” rotors. [Row 2 in Table 3.3]

    Mock-ring yarns are made in open end by the various devices available (amsler, caipo etc). Strength variability due to character (slubs) demands slightly better mixing. [Row 3 in Table 3.3]. Strength uniformity is far more important for Weft yarns used in very high speed air jets.

    For fine counts and ring spinning, no doubt a good length and appropriate micronaire are a must. [Row 4, 6 and 7 in Table 3.3]

    Quality fabrics can also be produced from Value mixings. This is because of the realization that heavy denim has strength far above realistic requirements. However the denim fabrics produced out of such yarns should not be meant for elaborate destructive garment washes. [Row 5 in Table 3.3]

    Ring Spun

    In spite of open end yarns have lower strength than ring spun yarns it has been enjoying mass market denim products due to cost angle. The raw material costs and the cost differential between ring and open end is discussed in “Engineering of Denim Products”

    For aesthetic reasons, at least in the warp, several denim products are actually ring spun. Also core-spun elastic yarns for weft will always be made in rings.

    Yarn Strength from Fibre Selection

    Since the yarn strength is of special significance when processing denim yarns, especially open end yarns, it is important to know the effects fibre strength, fibre length and fibre fineness have on the yarn strength.

    The relationship between fibre properties and yarn strength of open end yarns for various counts are expressed in the form of equation.

    The equation for calculating

    CSP =735 x [UHML x Str - 3 x Str -255 -6.6 x UHML]^0.22– [72.5 x Mc/UHML + 16] x C

    Where, UHML is Upper Half Mean Length in mm and
    Str is Strength in grams per tex as tested using HVI Mode
    Mc is Micronaire and
    C is Count in Ne

    The above equation which uses Fibre characteristics as tested using HVI Mode is deduced from earlier ATIRA equation for predicting CSP of Open-end yarns using Fibre characteristics using ICC Mode.

    CSP =720 x [2.5% SL x S - 300]^0.22 – [72.5 x Mc/2.5% SL + 16] x C
    Where, 2.5% SL is 2.5% Span Length in mm
    S is Strength in grams per tex as tested using ICC mode
    Mc is Micronaire and
    C is Count in Ne

    Cotton From Dyer’s Perspective

    The colour of cotton fibre is important in gradation of cotton fibres. The calorimeter of HVI measures two colour components of cotton – lightness and yellowness. Lightness is expressed as a percent reflectance (%Rd), and yellowness is expressed in Hunter’s scale (+b) values.

    These values affect dye ability of denim warp yarn. With cost savings, proximity and availability taking more focus on selection of cotton, the dyer has to leverage operational flexibility to use various cottons and still hits the target shade.

    The % Rd, +b values of typical Indian and imported cottons are given in Table-3.4.

    TABLE -3.4 : COLOUR COMPONENTS OF TYPICAL INDIAN AND IMPORTED COTTONS
    As can be seen from the Table, that V-797 is yellowier than J-34 and necessary corrections need to be done when switching over from yarn set made from J-34 to V-797.

    Norms For Yarn Realization

    The percentage yarn realization depends primarily on the process waste taken out at the blow room and cards. Of these the waste taken out in the blow room depends on the trash content of the mixing, the waste in cards and on the type of cards. It is therefore, necessary to use a separate norm for yarn realization for each mixing. Over and above the type of cotton used in denim mixings range from J-34 to trashy V-797. The norms for yarn realization which depends on the trash content in the mixing is given in the Table as a guideline.

    A one percent reduction in yarn realization has almost the same economic impact on the mill’s profit as an increase of one percent in the mixing cost. The control of yarn realization is thus as important to a mill as the control of cotton and mixing costs. One may find the detailed pcedures for the control of yarn realization in Chapter 3, ATIRA Silver Jubilee Monograph “Process Control in Spinning”.

    TABLE – 3.5 : NORMS FOR YARN REALIZATION
    Notes:

    Yarn Production
    1.Yarn realization (%)= ——————————————————————– x 100
    Bale Cotton +Waste of other mixings +Purchased Wastes

    2. Usable wastes of the same mixing, added back are not considered while determining the yarn realization.

    3. Yarn realization can also be obtained from the following formulae. These can be used for quick estimates.
    Yarn Realization (%) = 93.44 – 1.30 x Trash in mixing (%)

    4. The values given in the table are arrived at by considering the waste levels as follows:
    Invisible loss: 1.5% on mixing fed
    Sweepings : 1.5% on mixing fed
    Usable Waste: (% is based on material fed at each process)
    Card Sliver 0.5%,
    Draw frame Sliver: 0.6%,
    Speed frame: 0.5%.
    Ring frame Pnemafil 1.0%,
    Roving ends: 0.4%
    Open End Sliver: 0.3%

    5. The percentage trash in the mixing is for the mixing inclusive of usable waste and waste of other mixings added.

    6. When comber noil is added to the mixing, the yarn realization will be lower than that given in the Table. For every 10% comber noil addition in the mixing, the yarn realization will come down by 1%

    7. The yarn realization values given the Table are for ring doffs weighed without conditioning, wherein the time lapse between doffing and weighing is very short. If doffs are conditioned and weighed, the realization will be higher by about 1.0 to 1.5%.

    Managing Waste

    There was a time when blow room and carding non-re workable wastes used to be just that: non-re workable, except perhaps for surgical cotton. Attempts have always been made to re-use flat strips.

    The full recycling of all opening and carding wastes, using a new line of machinery from Trutzschler and others, is attempted by few with a success . Its obvious importance in Denim manufacture lies in the overall weight on the final cost represented by the cost of cotton .Because of heavy yarns and fabrics, if one can save 3 or 4% on cotton costs, the impact on the bottom line can be remarkable.

    This clean material has some residual trash in it not too different from the cotton used. Naturally there are more short fibres. The yield will be approximately 50%, in other words from each 2 kgs of raw waste we get 1 kg of clean recycled cotton. This material is baled again and fed to the mix at the lay down. Normally 10% is used. A loss of some 0.5 to 1.0 cN/tex is then unavoidable, but with 10% it will be manageable.

    SPINNING PREPARATORY PROCESSES

    Blow Room

    The raw material for Denim yarn is cotton, the type and quality of which varies tremendously, not only from country to country but within India and even within regions. Because of this variation it is difficult to envisage a standard line to meet all cases and manufacturers of opening and cleaning machinery have to be able to configure a line to meet the requirements of each individual customer. In general, Modern Blow room line with 4 to 5 beating points with micro dust extractor and very efficient automatic waste evacuation system will be adequate to ensure satisfactory opening and cleaning.

    In the case of variations within regions it is not uncommon to have fluctuation of colour from bale and therefore blending becomes very critical if shade variations from lot to lot in the finished cloth are to be kept to a minimum.

    It is already mentioned in the beginning that denim units have a high production output This necessitates, the modern method of opening bales. That is to use an automatic bale plucking machine which removes small size tufts of raw material from a line of bales and feeds these pneumatically to a blending machine. This ensures a uniform tuft size being fed to the blending and cleaning machines. However, the disadvantage is that removal of foreign material. In traditional blow rooms it is the practice to pre-open the bales and create a stack mixing. This ensures easy removal of foreign matters. It is important to have both options available to maintain the ability to satisfy all the variables.

    For feeding recoverable waste and small blends of fibre material it is recommendable to integrate a pre-mixer.

    V-797 and CIS cottons have considerable amount of trash, as high as 15%, as a result of geographic conditions and bad picking practices. In addition to trash, the fine clay of the soil, on which the cotton grows, permeates everything. It is also important to use pre cleaners to handle trashy cottons. Tandem cards used in the past, was successful in yarn quality considerations, but cost considerations turned it into an impossible proposition. The yarn realization as well as the clean cotton cost will be impacted by the use of high trashy cottons. [See 3.2.3 Norms for Yarn Realization]

    It is also possible to integrate a waste recycling line to recycle non re workable wastes from blow room line and cards to bring down cotton cost [See 3.2.4 Managing Waste]

    For denim yarns produced from open end spinning systems, probably the most important characteristic of the sliver is its cleanliness with particular care to be given to dust removal.

    Particularly in ring spun Denim yarn, a high incidence of nep in the yarn will cause uneven dye uptake during the warp yarn preparation. It is observed that modern blow room lines create neps, upto an increase of 100% over neps in raw cotton that will still allow the carding machine to be able to remove most of these objectionable faults.

    Cards

    The card is absolutely decisive for the quality of the denim yarns and for the efficiency of the production. It was possible to double the card production during the past 25 years.

    The carding quality is decisively influenced in the areas of cylinder, flat. Cylinder speed, clothing fineness and distance between cylinder and flat are deciding factors.

    Monitoring and controlling the carding process is critical in ensuring minimal fibre damage. Instruments such as AFIS [Advanced Fibre Information System] can be used to generate information of processes that precede yarn manufacturing. The carding process is very aggressive and, if not adjusted properly, can reduce fibre length causing short fibre. This phenomenon is especially true in the new high speed carding machines. If card flats are adjusted too close to the main cylinder, the nep and trash removal is improved, however the result can also be a reduction in fibre length and an increase in short fibre content. Replacing new cylinder wire or regrinding the wire will cause a temporary increase in short fibre content but this should return to normal in a relatively short time.

    The measurement of short fibre content will have some variability due to the natural variation in raw cotton. The following guideline will give an idea on how much increase is significant.

    SFC(w) SFC(n)
    Significant Increase >3% >6%

    Increase in short fibre content less than these values are not significant and should not be considered a processing problem.

    Draw frames

    The requirements of Draw Frames are as follows:

    i) Drawing mixes stock coming from different cards, producing a more even sliver of a more uniform quality.

    ii) The high friction between fibres, especially in modern high speed frames, tends to eliminate remaining dust adhering to fibre surfaces.

    iii) The fibre parallelization induced by drawing (remember a card web has fibres randomly oriented) is essential for ring roving and spinning and is helpful in open end to achieve a combination of high draft at the opening roll and good yarn uniformity.

    One or Two Process of Drawing:

    No doubt, the making of ring yarn with good staple cotton needs the parallelization at two drawing passages.

    Several studies have been conducted to see the effect of the number of draw frame passages on the yarn properties of rotor yarn. The original general rule suggested is

    i) If you make fine counts, maintain the two processes.
    ii) If you go to coarse counts, one process all you required.
    iii)If you are processing very short fibre material you are better off straight from the card.

    Because most cotton drawing system need a fairly uniform fibre length diagram to produce slivers of good short term evenness, it is obvious that materials with short fibre contents have little to gain from even a single passage.

    On the other hand, use of draw frames is also advantageous from the point of view of blending and cleaning.

    It has already been several years since cards have been offered with auto-levellers. Most of these can be classified as:

    -truly short term auto-levellers
    -long and short term auto-levellers

    The truly short term auto-regulation, now virtually abandoned, measures the sliver thickness coming out of the card by means of short variable drafting zone which attempts to adjust sliver weight to the nominal value. But as card speeds increased, and also can sizes and weights, the increased inertia of the system made accurate corrections very difficult. Even the speed of the coiler has to follow what the correction dictates. Also even if the average sliver weight could be maintained, the short term sliver evenness does deteriorate from the lack of fibre control at the small drafting zone.

    Nowadays, all long and medium term auto levelers operate by adjusting the rate of feed to the card, in fact adjusting the total draft of the machine. It is sound in principle, but does not guarantee short term uniformity and is not so easy in many cases to have every card adjusted to exactly the same average value.

    This is one reason why the averaging effect of at least one passage of drawing is still necessary. The new high response short term auto-levellers provide an ideal complement and very even slivers are now possible, totally free of count drift and with very acceptable short term irregularity.

    It has also been observed that the direction of majority hooks has little influence whereas the number of draw frame passage has a marked effect on yarn strength. It is also important to maintain count and strength variability to the lowest as the yarn breaks in spinning are correlated to the yarn breaks on the weaving machine.

    Thus, we can modify the original rule as

    i) Two passages for ring spinning and
    ii)one passage for coarse count open end spinning provided, the Count CV% of yarns produced is about 1.0% [or not exceeding 1.2%] and warping breaks per million metres of warp is about 0.3 [or not exceeding 0.5]

    Quality of Feed Sliver

    Standards for Trash and Nep Levels

    In ring spinning, trash particles are thrown harmlessly off the yarn as it balloons whereas in rotor spinning, they tend to become embedded along with dust particles in the rotor groove. The impurities and dust which accumulate in the rotor groove not only impair the operating conditions of the machine and cause rapid wear of the rotor surface but are also responsible for lower yarn quality and increased yarn breakage rate. In order to minimize end breaks, the total trash percentage of sliver fed to the rotor machine should not exceed 0.5% as tested using MDTA.

    Particularly in ring spun Denim yarn, a high incidence of nep in the yarn will cause uneven dye uptake during the warp yarn preparation. It is observed that modern blow room lines create neps, upto an increase of 100% over neps in raw cotton, that will still allow the carding machine to be able to remove most of these objectionable faults. The nep content expressed in neps/gram as tested using AFIS should not exceed 150.

    Mill Studies: Health Checks at Spinning Preparation Processes

    In addition to level of neps at feed sliver, AFIS [Advanced Fibre Information System] can also be used as a powerful process control tool for scanning the processes that precede yarn manufacturing periodically.-
    One such analysis, done Product wise and Process wise in seven different mills, four open end spinning and three ring spinning, is summarized in Table – 3.6.

    TABLE – 3.6 : NEP LEVELS AT SPINNING PREPARATION AND PROCESS ANALYSIS
    The product wise analysis refers to Level of neps at mixing, Blow room and Card sliver. The process wise analysis refers to nep increase at Blow room and nep reduction at card.

    It is important to arrive the product standards, considering the end use requirement for card sliver. Once the level of card sliver neps required are decided, the level of neps required at blow room material and target level at mixing can be arrived. This is by working backwards with the use of process standards for nep increase in blow room and nep reduction at cards.

    The standards used in the analysis are as follows:

    Nep/gram at Card Sliver : 120
    Card Feed : 400
    Mixing : 200
    Nep increase at Blowroom: 200%
    Nep reduction at Card : 70%

    As can be seen from the Table, the blow room nep generation was high at OE Mill1, OE Mill2 and OE Mill 4 Feeder 2. It is observed that Long and bent material transport duct lines were the reasons for nep generation in OE Mill 4 Feeder 2.

    Slivers made from OE Mill1, OE Mill2, OE Mill 4 Feeders 1, 2 and , RS Mill 5 feeder1 had excessive neps. It is also observed, that the overall rep removal efficiency of cards in OE Mill 1 and 4 were very poor due to poor condition of wire points.

    In addition, the cards who’s performance was too poor than the rest were identified and given in remark – though individual values could not find place in this summarized report.

    SPINNING PROCESS

    Denim plants have both open-end and ring denim capabilities, although a majority of the capacities are open-end, which historically cater to mass-market denim products. However, open-end plants are also able to manufacture specialty denim fabric with changes to their processes. Ring spun denim is of a higher quality and commands higher prices in the denim fabric market.

    The following pages describe the merits and limitations of the systems in general, inclusive of non denim yarns, so as to understand and derive maximum benefit from both systems.

    Ring Spinning: Merits and Limitations:

    Ring spinning had remained unchallenged for almost 150 years, since its inception. However its limitation in regard to production speeds was well realized which made its position quite vulnerable to new spinning technologies like rotor spinning. Subsequent to this realization, renewed attempts made the maximum production speed has increased to 25000 rpm by i)by extending the maximum traveller speed to 45m/sec and using ii)smaller ring diameter and bobbin lift. However, this has not prevented rotor spinning applications in coarse denim yarns as these yarns demand higher ring diameter and bobbin lift. Today the problem of excessive knots due to smaller ring package is of little consequence due to efficient splicing systems available at winding. Another serious problem of excessive initial end breaks due to greater number of doffs has been solved by the employment of efficient automatic piecing devices. Additionally there are support systems such as automatic roving transport to the ring frame, automatic roving rupture if the yarn is not pieced in three successive attempts in order to reduce incidence of roller lapping.

    The merits which makes it unique ever are i)It produces the strongest yarn, it is the bench mark among all 100% staple fibre spinning systems for various types of fibres and their blends. ii)It can produce yarns with a large range of twist, density from very low to very high. No other spinning system can match this unique capability of catering from knit to voile yarns. iii) It can be used for all types of fibres and can spin from very coarse to extremely fine yarns. iv) The desired hand, crisp or soft as per requirements can be imparted using the ring yarns.

    Open End Rotor Spinning: Merits and Limitations:

    The rotor spinning system has the following merits and possibilities:
    As can be seen from the process sequence, i)the speed frames and cone winding machines can be dispensed with. ii)the productivity per position is 6 to 8 times that of ring spinning. iii) It is extremely amenable to automation – viz auto piecing, auto cleaning and auto doffing. Features like Online Quality Monitoring can also be opted for. iv) The rotor yarns are extremely regular and have much lower levels of imperfections and faults as compared to ring yarns.

    The inherent drawbacks / limitations of the rotor spinning system are:
    i)The rotor yarn strength is lower than ring yarns.
    ii)Longer fibres (>32mm) offer no advantage in regards to yarn quality and /or productivity.
    iii) the yarn twist required for optimum strength is higher than ring yarns.
    iv)the biggest drawback of rotor yarns is the harsh feel of the fabrics made out of them.
    v) The minimum number of fibres required in the cross section of rotor yarn is around 100 to 110 compared to 50 required for ring yarns. Therefore the quality of rotor yarn deteriorates when finer yarns are spun on this system.

    Rotor Selection:

    Rotor size, rotor groove configuration, rotor speed and rotor surface treatment all have a decisive influence on the structure and properties of a rotor yarn.

    30, 33 and 36mm rotor diameters are used for finer yarns and 40 and 46mm rotors are useful for coarser yarns. A small rotor cannot accommodate the fibre mass needed for a coarse count in its narrow groove, and a possible overfeeds in case of yarn rupture would quickly choke the rotor cup.

    It is a common misconception that yarn quality deteriorates with small smaller rotors and higher rotor speeds.

    The grove configuration determines whether a yarn is bulky or compact, weak or strong, more or less ring-yarn-like etc. Most manufacturers of rotor spinning machines offer an array of different rotors. The grooves normally used in Denim applications are as follows:

    “S” Groove Rotors produces a bulky yarn which is weaker than yarn spin in any other rotor. It yields an excellent uniformity and is suitable for cotton with above-average trash content and for all synthetic fibres.

    “U” Groove Rotors possesses good self-cleaning properties as far as dust is concerned, but trash particles can still jam the groove and cause moiré. The yarn strength is higher than that from an S-rotor. For these reasons U-rotor is preferred for denim yarns.

    “T” Groove furnishes the strongest yarn due to its narrow, recessed groove, especially in fine counts. It is also the leanest, most compact yarn, having a low number of hairs per yarn cross section. Yarn torques is also higher, indicating a more ring-yarn-like structure.
    It is susceptible to initial deposits, but then the self cleaning effect sets in, maintaining uniform yarn properties. It is unsuitable for trashy cottons. It may also not be useful for denim warp yarns for rope dyeing where the higher yarn torque may cause problems in rebeaming.

    Opening Zone

    The opening roller wire specifications should be chosen as per fibre specifications, The general principle to be followed for deciding opening roller speed is that the higher the speed, the lower the yarn unevenness, the faults, the yarn strength and the breaking extension, Lower opening roller speeds should be used normally be used for the following:
    i) longer, finer and crimped fibres
    ii) coarser and cleaner sliver
    iii) lower rotor speed

    The range of speeds normally ranges from 5000 to 8000 rpm.

    The influence of other machine and process parameters on rotor spinning yarn properties in general are well documented in two references given at the end which we suggest for further reading.

    YARN QUALITY PROFILES

    Yarn quality profiles can be presented in many different ways. E.g. in table or graphic form. One example, shown here in Tables 3.7, 3.8 and 3.9 details the properties of yarn spun on both the rotor spinning and ring spinning systems and tabulate the yarn quality levels achieved with different yarn counts. The specific information on rotor groove and end use, whether it is meant for warp/weft, rope/ slasher are provided for interesting comparisons. Each of these Tables corresponds to the Fibre characteristics of different mixings, coarse count open end, fine count open end and ring spinning mixings , as provided earlier in Table -3.3 in this treatise.

    If one studies critically, the data shown in these Tables confirm many of the statements made throughout this book.

    COTTON, PROCESS AND YARN TESTING

    In order to monitor yarn quality consistently and efficiently, a testing laboratory equipped with modern instruments is an indispensable tool for the spinner. A good sampling plan (size and frequency of test samples) keeps track of sliver quality and yarn quality in such a way that in case of deviation from set quality standards, corrective action can be taken immediately. The sampling plan usually varies from plant to plant and should represent a careful balance between the prevailing quality requirements and the cost of testing. The Table – 3.10 lists the most commonly used testing instruments to determine specific cotton, process tests and yarn properties. These instruments are fairly well standardized throughout the world; they are not operated not only in yarn spinning plants, but also in research laboratories, textile institutes, universities and at machinery manufacturers. The following brief describes the uncommon tests – yarn torque and fancy yarn testing.

    Determination of Yarn Torque

    A simple and fast method to evaluate yarn kinkiness, bulk, and hand is the so-called Torque Test.

    Two leas (skeins) of the same yarn are connected by slipping an O-ring in each end as the skeins are pulled off the reel. This double skein, suspended in a vertical position with the lower ring released turns due to its own torque. The number of turns reveals very useful information about the yarn structure, internal dynamics and its behavior in subsequent processes, such as kinking and snarling, as well as fabric properties such as skew, bulk and hand.

    Torque measurements range from near 0 (no torque) to 6 (very high torque). Subjectively comparing the soft or harsh feel of yarn skeins provides good clues to the hand of the fabric.

    Determination of Fancy Yarn Parameters:

    Recently, the usage of characteristic yarns, such as slubby and multi count yarns, both in ring spinning and open end rotor spinning system in denims are on the rise. These yarns need additional monitoring of Slub parameters. Fancy yarn module of UT-5 serves this purpose with testing of Slub parameters -Slub frequency, Slub Length and Mass increase in addition to yarn diameter, yarn density and shape. The fancy yarn properties of typical characteristic yarns are given in Table-3.11

    Denim production technologies

    DENIM PROCESS SIMPLIFIED: FROM FIBRE TO FABRIC

    Denim process begins with the spinning of raw cotton to cotton yarn. Hundred percent cotton still remains the preferred fabric despite attempts made by denim manufacturers in India and abroad to introduce union denims which has not found any wide acceptance either in the international or Indian market. Spinning is followed by dyeing of warp yarn to required shades and other weaving preparatory treatments like sizing etc. The yarn is woven into fabric and the fabric is subjected to various finishing processes. The finished material is then checked, packaged and delivered to customers. The production of fabric mainly involves spinning, dyeing and sizing, weaving and processing.

    TABLE 2.1 : DENIM PRODUCTION TECHNOLOGIES

    CHOICE OF TECHNOLOGY & THE PROCESS SEQUENCE

    Open End Spinning – v – Ring Spinning

    Denim plants have both open-end and ring denim capabilities, although a majority of the capacities are open-end, which historically cater to mass-market denim products. However, open-end plants are also able to manufacture specialty denim fabric with changes to their processes. Ring spun denim is of a higher quality and commands higher prices in the denim fabric market. The process sequence of OE and ring spinning are given in the following Table 2.2

    TABLE 2.2 : SPINNING – PROCESS SEQUENCE
    The rope method is generally used in the mass production of fabrics with set specifications. The slasher method is generally used in smaller scale production of fabrics and allows for modification of specifications. Rope-dyeing technology provides a uniform dye to denim fabric when compared to the slasher-dyeing process. Steps involved in the Slasher Process and Rope process are as follows:

    TABLE 2.3 : DYEING – PROCESS SEQUENCE

    Wet and Foam Finishing

    While application and distribution of chemicals is quite uniform in wet finishing, the practical alternative to reduce energy bill is to use foam technology. The foam finishing is environmentally-friendlier and reduces pollution. The Table below depicts the process sequence adopted.

    TABLE 2.4 : FINISHING – PROCESS SEQUENCE

    Denim History

    This venerable fabric has in almost 150 years, run the gamut from a basic work wear fabric to a fashion trend setter.

    People around the globe love denim. It has become symbolic of a casual lifestyle for many. Denim is affordable, comfortable, and durable and offer variety of style and colour. It is fashionable and can be dressed up or down. There’s a fit for everybody.

    Denim offers something for everyone.

    How Denim Evolved?

    The history of denim is as colourful as the fabric that has ruled the fashion chart of the world for the past fifteen decades. Denim as a fabric was introduced first in the USA during the Californian Gold Rush. Levi Strauss was a tent salesman in America who thought the miners in Sanfrancisco needed a rugged pair of trousers that could withstand the rigours of their job. So he offered them what he had trousers made out of canvas. Across the Atlantic the French were already using such heavy fabric known by the name Serge-de-Nimes, a name of French city. Since the French alternative was better and tougher, the Americans too started buying the fabrics from France, discarding the canvas and used the same fabric for trousers with studs etc. Given the American penchant for cutting the names short the elaborate Serge-de-Nimes quickly became “Denim”. These trousers caught on and the rest is history.

    Fashion-wise denim has gone through many phases. From its initial indigo dye blue it went through various washes, was over-dyed into colours as vivid as brown, yellow, orange, green and even pink. It went into streaks and prints and it also turned totally black or remained in its natural state that is ecru or off-white. But no doubt it is the indigo colour that has returned to every time it has got over a current fad. Indigo unlike most of the dyes is a crystalline substance. It gets absorbed by the yarn to limited extent. It dyes merely the outer layer of the yarn leaving its core white. In between it imparts several shades of blue. The crystalline nature of the dye is the reason why the fabric appears bright even when the dye has faded. The indigo crystals reflect light. Hence even faded jeans look bright and not dull.

    How Jeans Evolved?

    The word jeans is believed to have been coined by Genoese sailors who found it difficult to keep their white trousers clean. They dyed them with cheapest available colour – Indigo blue. The Invariably humid and often hot atmosphere on the high seas resulted in the colour fading quite fast. However, indigo being a crystalline substance some brightness remained even after fading. This was subsequently became everyday wear for industrial workers and cowhands in 19th century America. This is how the present day “Denim Jeans” were born.

    By World War II, denim jeans had come to be identified with male machoism and celebrated stars like Wayne, Gary Cooper and Clark Gable further pushed the popularity of the jeans by wearing them in their many successful films. To look manly, thereafter one simply had to wear jeans.

    Denim and Jeans Defined

    Denim is defined as a 3/1 warp-faced twill fabric made from yarn dyed warp and undyed weft (Textile Terms and Definitions. The Textile Institute, 1992). Denim is distinguished from chambray, a flat weave made from similar yarns, by its 3/1 construction which exposes the dyed warp predominantly on one side and the paler unbleached weft on the other. Traditionally, denim was dyed with indigo a blue dye originally obtained from natural sources but now manufactured chemically. While most denim remains’ blue a growing market for other colours has developed. Most denim is still 100 percent cotton, although a relatively small volume of union denims are produced and traded worldwide.

    Jeans are harder to define than denim. Unless described as denim, they are sometimes made in other fabrics-notably corduroy and lighter flat fabrics for summer wear. Most manufacturers define jeans as trousers for both sexes with a number of distinctive characteristics, some or all of which may be present. These include:

    - the so-called waist yoke inserted below the self-supporting waist band at the rear, ensuring a close fit over the buttocks;
    – patch pockets at the rear;
    – double rows of stitches on folded seaming; and
    – in classic versions, metal riverts.

    The cut of the rest of the garment may vary to include flares, baggy legs, narrow drain pipes or pleated fullness from the waist at the front of the jeans.

    112 Years Pre-Indian Denim History

    The story of how the law of gravity was discovered is well known. Newton was sitting under a tree, under an apple tree, and then one apple fell down. Because of this he started thinking, and he felt that something is pulling the apple downwards. But the law of gravity is only one law. There is another law, which science has yet to uncover it. It is called levitation – “How did the apple reach upwards in the first place? How?”. That must be explained first – how the apple reached the upward position, how the tree is growing upwards. The apple was not there; it was hidden in a seed, and then the apple traveled the whole journey. It reached the upward position and only then did it fall down. So gravity is a secondary law. Levitation was the first and powerful.Similarly, the water flows downwards; it is under the law of gravity. When it evaporates, suddenly the law also evaporates. Now it is under levitation, it rises upwards.In denim history, Levi Strauss, the Bavarian with alpine tradition, in 1873, simply become available for the higher law of levitation. In Indian context, it is Sanjay Lalbhai in 1986. The below is the sequence of events between 112 years

    1873 Levi Strauss makes in San Francisco the first jeans using a heavy brown duck fabric for the Californian mine workers.
    1873 Levi Strauss produces the first jeans with the designation “501-Indigo”.
    1904 Founding of the Blue-Bell Co. in Greensboro, North Carolina.
    1950 The first zipper-jeans are introduced in the market.
    1954 Marlon Brando and James Dean appear in jeans and thus created a new image for denim.
    1960 Denim starts to conquer the world.
    1974 The first “pre-washed” jeans appear on the market.
    1978 The industry developed a new washing process for denim clothing “stone-wash”.
    1986 Birth of Indian denim.

    Blue Revolution in India Fashion Industry

    The Blue Revolution has taken the Indian industry by storm. It is a rage among the young and old alike. The ever blue fabric- Denim- shares the ups and downs of consumers – big and small and is the favourite for fabric designers of clothes and casuals. No wonder it evokes romance, craze and thrill.

    Birth of Indian Denim

    The year 1986 marked the birth of Indian denim when Arvind Mills, a member of the Lalbhai Group, set up the first denim plant in Ahmedabad. Taking this clue from Arvind others K.G, Ashima, Soma, Mafatlals, Aarvee, Century, Raymond Suryalakshmi, Malwa, LNJ, Nahar etc followed.

    The one quality of denims which has endeared this material to the vast multitude is its toughness. It does not crease easily. Besides it grows brighter with every wash. While other cotton materials fade and loose their luster with subsequent washes, denim’s luster increases with every wash.

    Colour Options

    With different weights in denims – 6 to 16 ozs and a variety of colours ranging from light blue to dark blue the utility of denims has increased. To name a few

    Super Dark Denim :Stay blue and stay black indigo products with differential tonal effects for younger generation.

    Tinted Denim Cotton denims enriched with different colour cast by tinting or over dyeing technology .

    Vintage Dusk Grey cast effect or give unique, second hand look.

    Added to this are the different washes – stone wash, bleach wash, hand wash, acid wash, rinse wash, water wash, ink wash, camel wash etc. and over-dyed, printed denims and even coated denims. Today we have colours like olive, hunter green and over-dyed black.

    Fibre and Yarn Options

    Beginning of twenty first century saw the explorations in different yarn options with the development of wide range of characteristic yarns, and their usage in rains, streaks and crosshatch denims. To name a few

    Tencel Denim: Woven century luxury cellulosic fibre made from specially grown woods and transformed in non-chemical process which give feel of silk and comfort of cotton.

    Stretch Denim: Woven with lycra from Dupont, stretch is the established fashion fabric for women and recently in menswear niche segments too who believes in exact fit and comfort.

    Chinos: Two ply chino denims in indigo dyed shade have an unique soft hand feel, Fabric cover and a luxurious appeal.

    Polyester Blends: Cotton rich polyester denims with superior hand feel, luster and colour contrast for fashion market.

    Rain Denim: Novelty loom denim with a fine weave & premium ‘Run’ effect for an unique appearance.

    Crosshatch Denim: high fashion denim with enhanced fabric texture

    Denim for Kids

    Today denim is the basis of the Indian fashion industry in many cases. Children’s wear is one of the largest consumers of the fabric after men’s wear discovered the benefits of this fabric. No fabric has been as suitable for the rough and tumble use of children’s wear as denim has been. It is durable and tough and when used in different weights the designing possibilities are limitless.

    Denim for Teens

    To the present generation jeans means disco. They mean casual wear or party wear. The teenagers consider it fit to even jeans at weddings, parties, office etc. Jeans has different connotations for different people. In the U.S. of America there have been reports of several bride-grooms wearing jeans at the nupitals. With film stars seeing the trend the present day jet-setter feels that you can appear at the “Rock Around the Clock” only if you are donning the “in” apparel – jeans.

    Denim For all

    Today denims don’t just mean jeans. It means a multitude of things-skirts, jackets, bags, accessories and even shoes. Cotton dresses have patches of denim material. The age group which considers denims as fashion wear is 16 to 28. The high profile jeans culture is finally here and urban youngsters particularly are lapping them up as soon as they appear on shop-shelves. Sarees and even Salwar Kameez are being discarded in favour of jeans; something very elegant and more in keeping with the youngish look of the mini-skirted young. Minis moved out to be replaced by jeans.

    The emergence of international brands of jeans in India such as Lee, Wrangler, Levis, Calvin, Klien, Jordache and Pepe further supports the potential of jeans in India. Indian brands which are already popular in jeans are Flying Machine, Numero, Blue Lagoon, Unnex, Buffalo, UFO, Avis etc. Besides there are atleast 150 brands which are in the market on dealer support.

    Indian denim is constantly scaling new heights. It is successfully competing with the other brands which are popular abroad and has carved a niche for itself in the world market by catering to international standards. No fabric has been as hardsold by it’s manufacturers as denim has been and it is not surprising to read of overnight successes in the readymade garment business with denim as the base fabric.

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