FIBRE TESTING PROCEDURE

FIBRE TESTING

IMPORTANCE OF RAWMATERIAL IN YARN 

MANUFACTURING

Raw material represents about 50 to 70% of the production cost of a short-staple yarn. This fact is sufficient to indicate the significance of the rawmaterial for the yarn producer. It is not possible to use a problem-free raw material always , because cotton is a natural fibre and there are many properties which will affect the performance. If all the properties have to be good for the cotton, the rawmaterial would be too expensive. To produce a good yarn with this difficulties, an intimate knowledge of the raw material and its behaviour in processing is a must.

Fibre characteristics must be classified according to a certain sequence of importance with respect to the end product and the spinning process. Moreover, such quantified characteristics must also be assessed with reference to the following

• what is the ideal value?
• what amount of variation is acceptable in the bale material?
• what amount of variation is acceptable in the final blend

Such valuable experience, which allows one to determine the most suitable use for the raw material, can only be obtained by means of a long, intensified and direct association with the raw material, the spinning process and the end product.

Low cost yarn manufacture, fulfilling of all quality requirements and a controlled fibre feed with known fibre properties are necessary in order to compete on the world's textile markets. Yarn prodcution begins with the rawmaterial in bales, whereby success or failure is determined by the fibre quality, its price and availability. Successful yarn producers optimise profits by a process oriented selection and mixing of the rawmaterial, followed by optimisation of the machine settings, production rates, operating elements, etc. Simultaneously, quality is ensured
by means of a closed loop control system, which requires the application of supervisory system at spinning and spinning preparation, as well as a means of selecting the most sutable bale mix.

BASIC FIBRE CHARACTERISTICS:
A textile fibre is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibres or prodction factors of manmade fibres are responsible for this situation. An individual fibre, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrient-supply, seasonal, weather, or other factors influencing the rate of cell development in natural fibres. Surface characteristics also play some part in increasing the variablity of fibre shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals along the cellulosic natural fibres etc.

Following are the basic chareteristics of cotton fibre

• fibre length
• fineness
• strength
• maturity
• Rigidity
• fibre friction
• structural features

STANDARD ATMOSPHERE FOR TESTING:
The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C,
may be used.

FIBRE LENGTH:
The "length" of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries

• mean length
• upper quartile
• effective length
• Modal length
• 2.5% span length
• 50% span length

Mean length:
It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight.

Upper quartile length:
It is that value of length for which 75% of all the observed values are lower, and 25% higher.

Effective length:
It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a
numerical length distribution
eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length.

Modal length:
It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the follwing way.

(Mode-Mean) = 3(Median-Mean)

where,
Median is the particular value of length above and below which exactly 50% of the fibres lie.

2.5% Span length:
It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH".

50% Span length:
It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH".

The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths.

Effective length = 1.013 x 2.5% Span length + 4.39
Mean length = 1.242 x 50% Span length + 9.78

FIBRE LENGTH VARIATION:
Eventhough, the long and short fibres both contribute towards the length irregularity of cotton, the short fibres are particularly responsible for increasing the waste losses, and cause unevenness and reduction in strength in the yarn spun. The relative proportions of short fibres are usually different in cottons having different mean lengths; they may even differ in two cottons having nearly the same mean fibre length, rendering one cotton more irregular than the other.It is therefore important that in addition to the fibre length of a cotton, the degree of irregularity of its length should also be known. Variability is denoted by any one of the following attributes

1. Co-efficient of variation of length (by weight or number)
2. irregularity percentage
3. Dispersion percentage and percentage of short fibres
4. Uniformity ratio

Uniformity ratio is defined as the ratio of 50% span length to 2.5% span length expressed as a percentage. Several instruments and methods are available for determination of length. Following are some

• shirley comb sorter
• Baer sorter
• A.N. Stapling apparatus
• Fibrograph

uniformity ration = (50% span length / 2.5% span length) x 100
uniformity index = (mean length / upper half mean length) x 100

SHORT FIBRES:
The negative effects of the presence of a high proportion of short fibres is well known. A high percentage of short fibres is usually associated with,
- Increased yarn irregularity and ends dddown which reduce quality and increase processing costs
- Increased number of neps and slubs whiiich is detrimental to the yarn appearance
- Higher fly liberation and machine contttamination in spinning, weaving and knitting operations.
- Higher wastage in combing and other oppperations.
While the detrimental effects of short fibres have been well established, there is still considerable debate on what constitutes a 'short fibre'. In the simplest way, short fibres are defined as those fibres which are less than 12 mm long. Initially, an estimate of the short fibres was made from the staple diagram obtained in the Baer Sorter method

Short fibre content = (UB/OB) x 100

While such a simple definition of short fibres is perhaps adequate for characterising raw cotton samples, it is too simple a definition to use with regard to the spinning process. The setting of all spinning machines is based on either the staple length of fibres or its equivalent which does not take into account the effect of short fibres. In this regard, the concept of 'Floating Fibre Index' defined by Hertel (1962) can be considered to be a better parameter to consider the effect of short fibres on spinning performance. Floating fibres are defined as those fibres which are not clamped by either pair of rollers in a drafting zone.

Floating Fibre Index (FFI) was defined as

FFI = ((2.5% span length/mean length)-1)x(100)

The proportion of short fibres has an extremely great impact on yarn quality and production. The proportion of short fibres has increased substantially in recent years due to mechanical picking and hard ginning. In most of the cases the absolute short fibre proportion is specified today as the percentage of fibres shorter than 12mm. Fibrograph is the most widely used instrument in the textile industry , some information regarding fibrograph is given below.

FIBROGRAPH:
Fibrograph measurements provide a relatively fast method for determining the length uniformity of the fibres in a sample of cotton in a reproducible manner.

Results of fibrograph length test do not necessarily agree with those obtained by other methods for measuring lengths of cotton fibres because of the effect of fibre crimp and other factors.

Fibrograph tests are more objective than commercial staple length classifications and also provide additional information on fibre length uniformity of cotoon fibres. The cotton quality information provided by these results is used in research studies and quality surveys, in checking commercial staple length classifications, in assembling bales of cotton into uniform lots, and for other purposes.

Fibrograph measurements are based on the assumptions that a fibre is caught on the comb in proportion to its length as compared to toal length of all fibres in the sample and that the point of catch for a fibre is at random along its length.

FIBRE FINENESS:
Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres.

Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is microgrammes per inch and the various air-flow instruments developed for measuring fibre fineness are calibrated in this unit.

Following are some methods of determining fibre fineness.

• gravimetric or dimensional measurements
• air-flow method
• vibrating string method

Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value.

It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres.

AIR-FLOW METHOD(MICRONAIRE INSTRUMENT):
The resistance offered to the flow of air through a plug of fibres is dpendent upon the specific surface area of the fibres. Fineness tester have been evolved on this principle for determininG fineness of cotton. The specific surface area which determines the flow of air through a cotton plug, is dependent not only upon the linear density of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with caution particularly when testing samples varying widely in maturity.

In the micronaire instrument, a weighed quantity of 3.24 gms of well opened cotton sample is compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample, at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flowmeter. The sample for Micronaire test should be well opened cleaned and thoroughly mixed( by hand fluffing and opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy to operate and presents little difficulty as regards its maintenance.

FIBRE MATURITY:

Fibre maturity is another important characteristic of cotton and is an index of the extent of
development of the fibres. As is the case with other fibre properties, the maturity of cotton fibres varies not only between fibres of different samples but also between fibres of the same seed. The causes for the differences observed in maturity, is due to variations in the degree of the secondary thickening or deposition of cellulose in a fibre.

A cotton fibre consists of a cuticle, a primary layer and secondary layers of cellulose surrounding the lumen or central canal. In the case of mature fibres, the secondary thickening is very high, and in some cases, the lumen is not visible. In the case of immature fibres, due to some physiological causes, the secondary deposition of cellulose has not taken sufficiently and in extreme cases the secondary thickening is practically absent, leaving a wide lumen throughout the fibre. Hence to a cotton breeder, the presence of excessive immature
fibres in a sample would indicate some defect in the plant growth. To a technologist, the presence of excessive percentage of immature fibres in a sample is undesirable as this causes excessive waste losses in processing lowering of the yarn appearance grade due to formation of neps, uneven dyeing, etc.

An immature fibre will show a lower weight per unit length than a mature fibre of the same cotton, as the former will have less deposition of cellulose inside the fibre. This analogy can be extended in some cases to fibres belonging to different samples of cotton also. Hence it is essential to measure the maturity of a cotton sample in addition to determining its fineness, to check whether the observed fineness is an inherent characteristic or is a result of the maturity.

DIFFERENT METHODS OF TESTING MATURITY:
MATURITY RATIO:
The fibres after being swollen with 18% caustic soda are examined under the microscope with suitable magnification. The fibres are classified into different maturity groups depending upon the relative dimensions of wall-thickness and lumen. However the procedures followed in different countries for sampling and classification differ in certain respects. The swollen fibres are classed into three groups as follows

1. Normal : rod like fibres with no convolution and no continuous lumen are classed as "normal"
2. Dead : convoluted fibres with wall thickness one-fifth or less of the maximum ribbon width are classed as "Dead"
3. Thin-walled: The intermediate ones are classed as "thin-walled"

A combined index known as maturity ratio is used to express the results.

Maturity ratio = ((Normal - Dead)/200) + 0.70
where,
N - %ge of Normal fibres
D - %ge of Dead fibres

MATURITY CO-EFFICIENT:
Around 100 fibres from Baer sorter combs are spread across the glass slide(maturity slide) and the overlapping fibres are again separated with the help of a teasing needle. The free ends of the fibres are then held in the clamp on the second strip of the maturity slide which is adjustable to keep the fibres stretched to the desired extent. The fibres are then irrigated with 18% caustic soda solution and covered with a suitable slip. The slide is then placed on the microscope and examined. Fibres are classed into the following three categories

1. Mature : (Lumen width "L")/(wall thickness"W") is less than 1
2. Half mature : (Lumen width "L")/(wall thickness "W") is less than 2 and more than 1
3. Immature : (Lumen width "L")/(wall thickness "W") is more than 2

About four to eight slides are prepared from each sample and examined. The results are presented as percentage of mature, half-mature and immature fibres in a sample. The results are also expressed in terms of "Maturity Coefficient"

Maturity Coefficient = (M + 0.6H + 0.4 I)/100 Where,

M is percentage of Mature fibres
H is percentage of Half mature fibres
I is percentage of Immature fibres

If maturity coefficient is

• less than 0.7, it is called as immature cotton
• between 0.7 to 0.9, it is called as medium mature cotton
• above 0.9, it is called as mature cotton

AIR FLOW METHOD FOR MEASURING MATURITY:

There are other techniques for measuring maturity using Micronaire instrument. As the fineness value determined by the Micronaire is dependent both on the intrinsic fineness(perimeter of the fibre) and the maturity, it may be assumed that if the intrinsic fineness is constant then the Micronaire value is a measure of the maturity

DYEING METHODS:
Mature and immature fibers differ in their behaviour towards various dyes. Certain dyes are preferentially taken up by the mature fibres while some dyes are preferentially absorbed by the immature fibres. Based on this observation, a differential dyeing technique was developed in the United States of America for estimating the maturity of cotton. In this technique, the sample is dyed in a bath containing a mixture of two dyes, namely Diphenyl Fast Red 5 BL and Chlorantine Fast Green BLL. The mature fibres take up the red dye preferentially, while the thin walled immature fibres take up the green dye. An estimate of the average of the sample can be visually assessed by the amount of red and green fibres.

FIBRE STRENGTH:
The different measures available for reporting fibre strength are

1. breaking strength
2. tensile strength and
3. tenacity or intrinsic strength

Coarse cottons generally give higher values for fibre strength than finer ones. In order, to compare strength of two cottons differing in fineness, it is necessary to eliminate the effect of the difference in cross-sectional area by dividing the observed fibre strength by the fibre weight per unit length. The value so obtained is known as "INTRINSIC STRENGTH or TENACITY". Tenacity is found to be better related to spinning than the breaking strength.

The strength characteristics can be determined either on individual fibres or on bundle of fibres.

SINGLE FIBRE STRENGTH:
The tenacity of fibre is dependent upon the following factors

chain length of molecules in the fibre orientation of molecules size of the crystallites distribution of the crystallites gauge length used the rate of loading type of instrument used and atmospheric conditions

The mean single fibre strength determined is expressed in units of "grams/tex". As it is seen the the unit for tenacity has the dimension of length only, and hence this property is also expressed as the "BREAKING LENGTH", which can be considered as the length of the specimen equivalent in weight to the breaking load. Since tex is the mass in grams of one kilometer of the specimen, the tenacity values expressed in grams/tex will correspond to the breaking length in kilometers.

BUNDLE FIBRE STRENGTH:
In practice, fibres are not used individually but in groups, such as in yarns or fabrics. Thus, bundles or groups of fibres come into play during the tensile break of yarns or fabrics. Further,the correlation between spinning performance and bundle strength is atleast as high as that between spinning performance and intrinsic strength determined by testing individual fibres. The testing of bundles of fibres takes less time and involves less strain than testing individual fibres. In view of these considerations, determination of breaking strength of fibre bundles has assumed greater importance than single fibre strength tests.

fibre fineness

FIBRE FINENESS:

Fibre fineness is another important quality characteristic which plays a prominent part in determining the spinning value of cottons. If the same count of yarn is spun from two varieties of cotton, the yarn spun from the variety having finer fibres will have a larger number of fibres in its cross-section and hence it will be more even and strong than that spun from the sample with coarser fibres.
Fineness denotes the size of the cross-section dimensions of the fibre. AS the cross-sectional features of cotton fibres are irregular, direct determination of the area of croo-section is difficult and laborious. The Index of fineness which is more commonly used is the linear density or weight per unit length of the fibre. The unit in which this quantity is expressed varies in different parts of the world. The common unit used by many countries for cotton is microgrammes per inch and the various air-flow instruments developed for measuring fibre fineness are calibrated in this unit.
Following are some methods of determining fibre fineness.

• gravimetric or dimensional measurements
• air-flow method
• vibrating string method
Some of the above methods are applicable to single fibres while the majority of them deal with a mass of fibres. As there is considerable variation in the linear density from fibre to fibre, even amongst fibres of the same seed, single fibre methods are time-consuming and laborious as a large number of fibres have to be tested to get a fairly reliable average value.
It should be pointed out here that most of the fineness determinations are likely to be affected by fibre maturity, which is an another important characteristic of cotton fibres.
AIR-FLOW METHOD(MICRONAIRE INSTRUMENT):
The resistance offered to the flow of air through a plug of fibres is dpendent upon the specific surface area of the fibres. Fineness tester have been evolved on this principle for determininG fineness of cotton. The specific surface area which determines the flow of air through a cotton plug, is dependent not only upon the linear density of the fibres in the sample but also upon their maturity. Hence the micronaire readings have to be treated with caution particularly when testing samples varying widely in maturity.
In the micronaire instrument, a weighed quantity of 3.24 gms of well opened cotton sample is compressed into a cylindrical container of fixed dimensions. Compressed air is forced through the sample, at a definite pressure and the volume-rate of flow of air is measured by a rotometer type flowmeter. The sample for Micronaire test should be well opened cleaned and thoroughly mixed( by hand fluffing and opening method). Out of the various air-flow instruments, the Micronaire is robust in construction, easy to operate and presents little difficulty as regards its maintenance

yarn testing procedure in spinning

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.

yarn hairiness( compact spinning)

YARN HAIRINESS

INTRODUCTION:

Yarn hairiness is a complex concept, which generally cannot be completely defined by a single figure.
The effect of yarn hairiness on the textile operations following spinning, especially weaving and
knitting, and its influence on the characteristics of the product obtained and on some fabric faults
has led to the introduction of measurement of hairiness.

FACTS ABOUT YARN HAIRINESS:

Hairiness occurs because some fibre ends protrude from the yarn body, some looped fibres arch
out from the yarn core and some wild fibres in the yarn.

• Pillay proved that there is a high correlation between the number of protruding ends and the
number of fibres in the yarn cross-section.

• Torsion rigidity of the fibres is the most important single property affecting yarn hairiness. Other factors are flexural rigidity, fibre length and fibre fineness.

• Mixing different length cottons-No substantial gain in hairiness. Although the hairiness of a yarn could be reduced to some extent by the addition of a longer and finer cotton to the blend. The extent of reduction is not proportional to the percentage of the longer and finer component. This is probably due to the preferential migration of the coarser and shorter component, which has longer protruding ends, from the yarn body. The addition of wastes to the mixing increases the yarn hairiness; the effect of adding comber waste is greater than that of adding soft waste.

• Blending-not a solution to hairiness. The blended yarns are rather more hairy than expected from the hairiness of the components; a result similar to that found in cotton blends. This may be due to the preferential migration of the shorter cotton fibers; a count of the number of protruding ends of both types of fiber shows that there is more cotton fiber ends than expected, although the difference is not very great.

• The number of protruding ends is independent of twist, whereas the number of loops decreases when
the yarn twist increases because of a greater degreee of binding between hte fibres owing to twist.
The number of wild fibres decreases only very slightly with twist because of their position on the
yarn periphery.

• The proportion of fiber ends that protrude from the yarn surface, counted microscopically
has been found to be about 31% of the actual number of ends present in the yarn.

• If the length of the protruding fibre ends as well as that of the loops is considered, the mean
value of the hairiness increases as the cross-sectional area increases and decreases with the length
of the loops. The hairiness is affected by the yarn twist, since an increase in twist tends to shorten
the fibre ends.

• Wild fibres are those for which hte head alone is taken by the twist while the tail is still gripped
by the front drafting rollers.

• Fibre length influences hairiness in the sense that a greater length corresponds to less hairiness.

• Cotton yarns are known to be less hairy than yarns spun from man-made fibres. The possible reason
for this is the prifile of the two fibres.Because of taper, only one end, the heavier root part of the
cotton fibre, tends to come out as a protruding end in a cotton yarn. With man-made fibres, both ends
have an equal probability of showing up as protruding ends.

• If the width of the fibre web in the drafting field is large, the contact and friction with the
bottom roller reduce the ability of the fibres to concentrate themselves and hairiness occurs. This
effect is found more in coarse counts with low TPI. This suggests that the collectors in the
drafting field will reduce yarn hairiness.

• The yarn hairiness definitely depends on the fibres on the outer layer of the yarn that do not
directly adhere to the core. Some of them have an end in the core of the yarn gripped by other fibres,
whereas others, because of the mechanical properties of the fibre(rigidity, shape, etc.) emerge to
the surface. During the twisting of the yarn, other fibres are further displaced from their central
position to the yarn surface.

• Greater the fibre parallelization by the drawframe, lower the yarn hairiness.

• An increase in roving twist results in lower yarn hairiness, because of smaller width of fibre
web in the drafting field.

• The number of fiber ends on the yarn surface remains fairly constant; the number of looped fibers reduces in number and length on increasing twist.

• Combed yarn will have low yarn hairiness, because of the extraction of shorter fibres by the comber.

• Yarn hairiness increases when the roving linear density increases . Yarn spun from double roving
will have more hairiness than the yarn spun from single roving. This is due to the increased number of
fibres in the web and due to higher draft required to spin the same count.
Drafting waves increase hairiness. Irregularity arising from drafting waves increases with increasing draft. Yarn hairiness also may be accepted to increase with yarn irregularity, because fibers protruding from the yarn surface are more numerous at the thickest and least twisted parts of the yarn.
• The yarns produced with condernsers in the drafting field, particularsly if these are situated
in the principal drafting zone, are less hairy than those spun without the use of condensers.

• Higher spindle speed – high hairiness. When yarns are spun at different spindle speed, the centrifugal force acting on fibers in the spinning zone will increase in proportion to the square of the spindle speed, causing the fibers ends as they are emerging from the front rollers to be deflected from the yarn surface to a greater extent. Further, at high spindle speed, the shearing action of the traveller on the yarn is likely to become great enough to partially detach or raise the fibers from the body of the yarn. As against the above factors, at higher spindle speeds the tension in the yarn will increase in proportion to the square of the spindle speed, and consequently more twist will run back to the roller nip, so that it is natural to expect that better binding of the fibers will be achieved. The increase in hairiness noticed in the results suggests that the forces involved in raising fibers from the yarn surface are greater than those tending to incorporate them within the body of the yarn at higher spindle speeds.

• Higher draft before ring frame-less hairiness. There is a gradual reduction of hairiness with increase in draft. In other word, as the fiber parallelization increases hairiness decreases. Reversing the card sliver before the first drawing head causes a reduction in hairiness, the effect being similar to that resulting from the inclusion of an extra passage of drawing.

• Smaller roving package-less hairiness. Yarn hairiness decreases with decrease in roving (doff) size, and yarn spun from front row of roving bobbins is more hairy and variable as compare to that spun from back row of rowing bobbins. It may be noted that though the trends are consistent yet the differences are non-significant:

• The spinning tension has a considerable influence on the yarn hairiness. The smaller the tension,
the greater the hairiness. This is the reason why heavier travellers result in low yarn hairiness.
If the traveller is too heavy also , yarn hairiness will increase.

• Spindle eccentricity leads to an increase in hairiness. Small eccentricities influence hairiness
relatively little, but, from 0.5 mm onwards, the hairiness increases almost exponentially with eccentricity.

• The increase in hairiness due to spindle eccentricity, will be influenced by the diameter of ring,
dia of bobbin, the shape of the traveller,the yarn tension, etc.

• Yarn hairiness will increase if the thread guide or lappet hook is not centred properly.
Heavier traveler- less hairiness. The reduced hairiness of yarns at higher traveller weights can be explained by the combined effect of tension and twist distribution in the yarn at the time of spinning. The spindle speed remains constant, but the tension in the yarn will increase with increasing traveller weight, and better binding of the fibers would be expected.
Parallel fibers-less hairiness. The improvement of yarn quality on combing is mainly ascribed to the reduction in the number of short fiber improvement in length characteristics, and fiber parallelization. There is a marked difference in hairiness of the carded yarn and the combed yarns, even with a comber loss of only 5%, but the effect on hairiness of increasing the percentage of comber waste is less marked. Combing even at low percentage waste causes a marked drop in hairiness relative to that of the carded yarn. In the case of combed cotton yarns the average value of hairiness decreases with increase in count, whereas in the case of polyester/ viscose blend yarns the hairiness increases with increase in count. In the case of polyester/ cotton blend yarns trend is not clear.

• Flat and round travellers do not influence yarn hairiness, but a greater degree of hairiness was
observed with elliptical travellers and anti-wedge rings.

• Traveller wear obviously influences hairiness because of the greater abrasion on the yarn.
Yarn hairiness increases with the life of the traveller.

• Bigger the ring diameter, lower the yarn hairiness.

• Yarn spun in a dry atmosphere is more hairy.

• Hairiness variation between spindles is very detrimental. Because these variation can lead to
shade or appearance variaion in the cloth.

• The variation in hairiness within bobbin can be reduced considerably by the use of heavy travellers
alone or by balloon-control rings with travellers of normal weight. In both the cases yarn is prevented
from rubbing against the separators.

• Yarn hairiness is caused by protruding ends, by the presence of a majority of fibre tails.
This suggests that these tails will become heads on unwinding and that friction to which the
yarn is subjected will tend to increase their length. It is therefore logical that a yarn should be more
hairy after winding.

• Repeated windings in the cone widning machine will increase the yarn hairiness and after three
or four rewindings, the yarn hairiness remain same for cotton yarns.

• Winding speed influences yarn hairiness, but the most important increase in hairiness is produced
by the act of winding itself.

• Because of winding, the number of short hairs increases more rapidly thatn the number of long hairs.

• In two-for-one twisters (TFO), more hairiness is produced because, twist is imparted in two steps.
Yarn hairiness also depends upon the TFO speed, because it principally affects the shortest fibre ends.

• Hairiness varitions in the weft yarn will result in weft bars.

Hairiness Testing of Yarns
Hairiness of yarns has been discussed for many years,but it always remained a fuzzy subject. With the advent of compact yarns and their low hairiness compared to conventional yarns,the issue of measuring hairiness and the proper interpretation of the values has become important again.Generally speaking,long hairs are undesirable, while short hairs are desirable (see picture ). The picture shown below just give a visual impression of undesirable and desirable hairiness at the edge of a cops.
Figure:

RING YARN COMPACT YARN:

There are two major manufacturers of hairiness testing equipment on the market,and both have their advantages and disadvantages. Some detail is given below.
USTER
USTER is the leading manufacturer of textile testing equipment. The USTER hairiness H is defined as follows .
H =total length (measured in centimeters) of all the hairs within one centimeter of yarn .
(The hairiness value given by the tester at the end of the test is the average of all these values measured, that is,if 400 m have been measured,it is the average of 40,000 individual values) . The hairiness H is an average value,giving no indication of the distribution of the length of the hairs. Let us see an example
0.1cm 0.2cm 0.3cm 0.4cm 0.5cm 0.6cm 0.7cm 0.8cm 0.9cm 1.0cm total
yarn 1 100 50 30 10 5 6 0 2 1 0 398
yarn 2 50 10 11 5 10 0 5 10 0 11 398

Both yarns would have the same hairiness index H, even though yarn is more desirable,as it has more short hairs and less long hairs,compared to yarn 2.
This example shows that the hairiness H suppresses information,as all averages do. Two yarns with a similar value H might have vastly different distributions of the length of the individual hairs.
The equipment allows to evaluate the variation of the value H along the length of the yarn. The "sh value "is given, but the correlation to the CV of hairiness is somehow not obvious.A spectrogram may be obtained.
2.ZWEIGLE
Zweigle is a somewhat less well known manufacturer of yarn testing equipment. Unlike USTER,the Zweigle does not give averages. The number of hairs of different lengths are counted separately, and these values are displayed on the equipment. In addition, the S3 value is given,which is defined as follows:
S3 =Sum (number of hairs 3 mm and longer)
In the above example,the yarns would have different S3 values:
S3yarn 1 =2 .
S3yarn 2 =4 .
A clear indication that yarn 2 is "more hairy "than yarn 1. The CV value of hairiness is given a histogram (graphical representation of the distribution of the hairiness) is given.
The USTER H value only gives an average,which is of limited use when analyzing the hairiness of the yarn.The Zweigle testing equipment gives the complete distributionof the different lengths of the hairs. The S3 value distinguishes between long and short hairiness, which is more informative than the H value.

YARN CONDITIONING FOR SPINNING

YARN CONDITIONING

Why conditioning is required?

Moisture in atmosphere has a great impact on the physical properties of textile fibres and yarns.Relative humidity and temperature will decide the amount of moisure in the atmosphere. High relative humidity in different departments of spinning is not desirable. It will result in major problems. But on the otherhand, a high degree of moisture improves the physical properties of yarn. Moreover it helps the yarn to attain the standard moisture regain value of the fibre. Yarns sold with lower moisture content than the standard value will result in monetary loss. Therefore the aim of CONDITIONING is to provide an economical device for supplying the necessary moisture in a short time, in order to achieve a lasting improvement in quality.

In these days there is a dramatic change in the production level of weaving and knitting machines, because of the sophisticated manufacturing techniques. Yarn quality required to run on these machines is extremely high. In order to satisfy these demands without altering the rawmaterial, it was decided to make use of the physical properties inherent in the cotton fibres. Cotton fibre is hygroscopic material and has the ability to absorb water in the form of steam. It is quite evident that the hygroscopic property of cotton fibres depends on the relative humidity. The higher the humidity, more the moisture abosrption. The increase in the relative atmospheric humidity causes a rise in the moisture content of the cotton fibre, following an S-shaped curve.

The relative humidity in turn affects the properties of the fibre via the moisture content of the cotton fibre. The fibre strength and elasticity increase proportionately with the increase in humidity. If the water content of the cotton fibre is increased the fibre is able to swell, resulting in increased fibre to fibre friction in the twisted yarn structure. This positive alteration in the properties of the fibre will again have a positive effect on the strength and elasticity of the yarn.

CONTEXXOR CONDITIONING PROCESS BY XORELLA:

The standard conventional steaming treatment for yarn is chiefly used for twist setting to avoid snarling in further processing. It does not result in lasting improvement in yarn quality. The steaming process may fail to ensure even distribution of the moisture, especially on cross-wound bobbins(cheeses) with medium to high compactness. The thermal conditioning process of the yarn according to the CONTEXXOR process developed by XORELLA is a new type of system for supplying the yarn package.

The absence of Vacuum in conventional conditioning chambers, prevents homogeneous penetration. The outer layers of the package are also too moist and the transition from moist to dry yarn gives rise to substantial variations in downstream processing of the package, both with regard to friction data and strength.

Since the moisture is applied superficially in the wet steam zone or by misting with water jets, it has a tendency to become re-adjusted immediately to the ambient humidity level owing to the large surface area. Equipment of this king also prevents the optimum flow of goods and takes up too much space.

PRINCIPLE OF WORKING:

Thermal conditioning uses low-temperature saturated steam in vacuum. With the vacuum principle and indirect steam, the yarn is treated very gently in an absolutely saturated steam atmosphere. The vacuum first removes the air pockets from the yarn package to ensure accelerated steam penetration and also removes the atmospheric oxygen in order to prevent oxidation. The conditioning process makes use of the physical properties of saturated steam or wet steam (100% moisture in gas-state). The yarn is uniformly moistened by the gas. The great advantage of this process is that the moisture in the form of gas is very finely distributed throughout the yarn package and does not cling to the yarn in the form of drops. This is achieved in any cross-wound bobbins, whether the yarn packages are packed on open pallets or in cardboard boxes.

pic: XORELLA CONDITIONING SYSTEM

• ADVANTAGES OF CONTEXXOR PROCESS:
• saturated steam throughout the process
• even penetration of steam and distribution of moister
• lowest energy consumption with XORELLA ECO-SYSTEM
• short process time
• absolute saturated steam atmosphere of 50 degree C to 150 degreees C.
• no additional boiler required, the steam is generated in the system
• minimum energy consumption(approx. 25 KWh for 1000 kgs of yarn)No tube buckling in case of mad-made yarns
• treatment of all natural yarns, blends, synthetics and microfibre yarns.
• low installation and maintenance cost
• preheating for trollys and plastic tubes to avoid drops (Wool)
• standardize sizes
• length up to 20 meters (66 feet) and max. temperature deviation of 1°C
• various loading and unloading facilities
• no contamination of the treated packages
• energy recovery option offered by indirect heating system using steam or hot water
• no special location required, the systems can be operated next to the production machines.

BENEFITS ACHIEVED OUT OF CONDITIONING:

FOR KNITTING:

The treatment temperature for knitting yarn is held below the melting point of the wax. Temperatures for unwaxed

yarn are coordinated to the compatibility fo each individual type of yarn

• Upto 20% greater efficiency due to a reduction in the unwinding tension
• fewer needle breaks
• uniform moisture content and friction values
• regular stitch formation
• no change in size of finished articles
• no extra dampening required
• free from electrostatic
• less fly hence less problems. It helps if the yarn is running on a closer gauge machines

NOTE: Please note that the wax applied should be able to withstand min 60 degree centigrade. If low quality wax is used, it will result in major problem. Conditioning should be done at 55 to 60 degree centigrade.

FOR WEAVING:

• upto 15% fewer yarn breaks due to greater elongation
• less fly, resulting in a better weaving quality
• increased strength
• increased take-up of size, enhanced level of efficiency in the weaving plant
• softer fabrics

Pic: improved strength Pic: improved elongation

FOR TWISTING:

Conditioning and fixing of the twist at the same time in a single process.

FOR DYEING:

• no streaks
• better dye affinity

Pic: dye pick up of conditioned and unconditoned yarn