The global spinning industry is
currently undergoing big changes, not least towards the use of more modem
and faster spinning machinery and computer system. These high speed machines
require much cleaner raw material, and therefore they constantly challenge
the testing machinery developers to provide faster and more accurate testers
and quality controllers. The techniques described in this article are mainly
related with cotton fibre testing.
In this article, the author has dealt with the following:
Concepts in bale management.
Latest fibre testing instrument.
Principle of fibre testing using HVI.
Advanced fibres information system (AFIS).
Fibre contamination system (FCS).
Integrated indices for fibre
Different methods of maturity
Different methods of fineness
Advantageous of latest fibre
In this, HVI, AFIS & FCT play an
important role, so their principle working method, working time and sample
requirements are given. It gives various new technologies employed in
printing, which will give an idea about the new testing methods and
Machine speeds and settings need to be matched to the properties of the
fibre in process. With the annual production of cotton lint approaching 100
million bales, with spinner's demands & for increasingly high quality,
and with the testing of every bale becoming almost universal in export
mills, cotton testing has never been more important.
The following observations have made the cotton testing an important one.
Raw material typically accounts for
half of the cost of making cotton yarn.
Competitive man-made fibres can be
made to more precise specifications.
Scientific blending, based on
knowledge of each bale, leads to cost & quality effective
Machine speeds and settings need to
be matched to the properties of the fibre in process.
Demands on the yarn quality are
Concepts in bale management
This is based on the categorising of cotton bales according to their
fibre quality characteristics. It includes the measurement of the fibre
characteristics with reference to each individual bale, separation of bales
into classes and lying down of balanced bale mixes based on these classes.
The reason for undertaking this work lies in the fact that there is
sometimes a considerable variation in the fibre characteristics from one
bale to another, even within the same delivery. This variation will result
in the yarn quality variation if the bales are mixed in an uncontrolled
Latest fibre testing instruments
Latest trend in the fibre testing was the developments of a single
instrument in which all the major testing parameters can be tested. The
instruments we discuss in this category are:
High volume instrument (HVI)
Advanced fibre information system (AFIS)
Fibre contamination tester (FCT)
High volume instrument
High volume instrument systems are based on the fibre bundle strength
testing, ie, many fibres are checked at the same time and their average
values determined. Traditional testing using micronaire, pressley,
stelometre, and fibro graph are designed to determine average value for a
large number of fibres, the so called fibre bundle tests. In HVI, the bundle
testing method is automated. Here, the time for testing is less and so the
number of samples that could be processed is increased, quite considerably.
The influence of operator is reduced.
The HVI testing is attractive due to the classing of cotton and the laying
down of a mix in the spinning mill. This HVI testing is suitable for the
extensive quality control of all the bales processed in a spinning mill. The
mill is in a position to determine its own quality level within a certain
operating range. The time for testing per sample is 0.3 minutes. It is best
applied to instituting optimum condition for raw material. About 180 samples
per hour can be tested and that too with only 2 operators.
Principles of fibre testing using HVI
The fibro gram method is preferred while preparing the sample for fibre
length estimation. The sample has to be presented to the measuring zone by
clamping the fibres at a random catch point. Here the fibro sampler is used.
The test specimen obtained using the fibro sampler/comb combination is a
beard of fibres with individual fibres projecting to different length from
the clamping point. In HVI, the strength testing is also done on the same
beard of fibres with individual fibres projecting to different lengths from
the clamping point.
In HVI, strength testing is also done on the same beard of fibres prepared
for length measurement. While using the low volume instrument -- fibro stelo
for strength measurement, the sampling is done on the separate fibre
bundles, of which 15 mm long is prepared after remounting the short fibres
by combing. For micronaire testing, a sample of cotton weighing
approximately 10 grams is used. For colour testing, random mass of fibres
sufficient to cover the test window is used for measurement.
Measurement of different parameters using HVI & LVI
Both the high volume instrument and the low volume instrument use an
optical principle of determination of fibre length. A narrow rectangular
beam of light is allowed to fall on the specimen beard. The attenuation of
light through the specimen at different areas of the beard is measured and
used to obtain the different span length values. In the HVI, the tip of the
beard is scanned first and scanning gradually proceeds towards the clamp
while in the LVI, the beard is scanned in the opposite direction. In both
the instruments, the span length values are obtained by actual measurement.
In the LVI, the fibrostelo is used. This module uses the pendulum lever
principle of loading the specimen to estimate the fibre strength
characteristics. A random sample of cotton fibres is prepared, short fibres
being removed by combing so that all the fibres in the test specimen extend
all the way through the jaws.
Breaking tenacity in g/tex = (breaking load in kg/sample weight in mg.) ×
HVI 9000 Strength Measurement
HVI uses the "Constant rate of elongation" principle while testing
the fibre sample. The available conventional methods of strength measurement
are slow and are not compatible to be used with the HVI. The main hindering
factor is the measurement of weight of the test specimen, which is necessary
to estimate the tenacity of the sample. Expression of the breaking strength
in terms of tenacity is important to make easy comparison between specimens
of varying fineness.
The problem is overcome in the HVl 9000 by positioning the jaws and breaking
the fibres at a constant "Amount" location across the beard. By
breaking the fibres at a constant amount location, it is made sure that the
samples are broken with a constant number of fibres between the jaws.
Therefore, raw data strength is directly proportional to the force to break
the fibres. The raw data so obtained are then adjusted to desired levels by
testing samples of designated values. In order to make the estimation of the
specimen linear density accurate enough, a micronaire correction factor is
normally introduced so that the strength values are not affected by
variations in micronaire.
The micronaire module of HVI 9000 and the low volume fineness tester use
the airflow method to estimate the fineness value of cotton. A sample of
known weight is compressed in a cylinder to known volume and subjected to an
air current at a known pressure. The rate of airflow through this porous
plug of fibre is taken to be a measure of the fineness of cotton.
The number of fibres in a given weight of cotton will be more in the case of
finer fibres than in the case of finer fibres than in the case of coarser
fibres. If air is blown through these samples, the plug containing finer
fibres will be found to offer a greater resistance than the plug with
coarser fibres. This is due to the fact that the total surface area in the
case of the former will be greater than the latter and hence the drag on the
air flowing past will be more. This differentiating factor is made use of to
indirectly measure the fineness of cotton.
The instrument operates as follows. The chamber lid is closed, a piston at
the chamber bottom compresses the fibre to a fixed and known volume. A
regulated stream of air is then forced through the sample and the pressure
drop across the sample is applied to a differential pressure transducer. The
transducer outputs an analog signal voltage proportional to the pressure
This analogue voltage is applied to an analogue to digital converter, which
outputs a digital signal representing the voltage. Cotton with known
fineness values is tested and the voltages obtained are used to obtain the
calibration curve, which is used for all subsequent testing to display the
The fineness is expressed in the form of a parameter called the micronaire
value, which is defined as the weight of one inch of the fibre in
micrograms. Maturity of cotton also influences the micronaire value.
The HVI colour module utilises optical measuring principles to define
colour. The colour module has a photodiode, which collects the reflected
light from the sample. The photodiode output is converted into meaningful
signals using signal conditioners. The illumination of the sample is done
with the help of two lamps connected in parallel. Light from the lamps is
reflected from the surface of a cotton sample on the test window. The
reflected light is diffused and transmitted to the Rd and +b photodiode.
These two signals are conditioned to provide two output voltages, which are
proportional to the intensity of light falling on the respective
photodiodes. These voltages are converted to digital signals from which the
computer derives Rd and +b readings to be displayed on the screen.
HVI callbration principles
HVI uses a unique calibration principle by which routine calibration is
performed by presenting samples bf known value to the instrument, which then
makes adjustment to the raw instrument values, obtained so that measurements
will agree with the calibration cotton designated values. The general
principle by which this calibration is done involves a simple, two-point
In actual practice, raw values from the instrument will not match exactly
with the designated values due to the variety of reasons including component
ageing, atmospheric conditions and other sources of calibration drift. In
such cases, the computer software makes adjustments to the raw data by using
regression analysis. For the calibration of length, strength and micronaire,
ICC cotton can be used while the calibration of colour has to be performed
using the standard colour tiles supplied along with the instrument.
Advanced Fibre Information System (AFIS)
Advanced Fibre Information System is based on the single fibre testing.
There are two modules here, one for testing the number of neps and the size
of neps, while the other one is used for testing the length and the
diameter. Both modules can be applied separately or together.
With the introduction of AFIS, it is possible to determine the average
properties for a sample, and also the variation from the fibre to fibre. The
information content in the AFIS is more. The spinning mill is dependant on
the AFIS testing method, to achieve the optimum conditions with the
available raw material and processing machinery. The AFIS-N module is dealt
here and it is basically used for counting the number of neps and the size
of neps. The testing time per sample is 3 min in AFIS-N module.
This system is quick, purpose oriented and reproducible counting of neps in
raw material and at all process stages of short staple spinning mill. It is
thus possible, based on forecasts supervisory measures and early warning
information to practically eliminate subsequent complaints with respect to
finished product. The lab personnel is freed from the time consuming,
delicate and unpopular, proceeding of nep counting. Personnel turnover and
job rotation no more affects the results of the nep counting. The personnel
responsible for quality can now at least deal with the unpopular neps in a
more purpose-oriented manner than ever before.
AFIS -Working principle
Advanced Fibre Information System (AFIS)
Source: International Textile Centre
A fibre sample of approximately 500 mg is inserted between the feed
roller and the feed plate of the AFIS-N instrument Opening rollers open the
fibre assembly and separate off the fibres, neps, trash and dust. The trash
particles and dust are suctioned off to extraction. On their way through the
transportation and acceleration channels, the fibres and neps pass through
the optical sensor, which determines the number and size of the neps.
The corresponding impulses are converted into electrical signals, which are
then transmitted to a microcomputer for evaluation purposes. According to
these analyses, a distinction is made between the single fibres and the neps.
The statistical data are calculated and printed out through a printer. The
measuring process can be controlled through a PC-keyboard and a screen.
It can be evidenced that the results are provided very quickly using the
AFIS measurement method and this with reference to approximately the same
weight of sample material. This to be particularly the case when one
compares the AFIS-N method with the frequently- used manual/ visual ASTM
method. The savings are 150 with raw cotton and 1:25 with draw frame sliver.
Fibre Contamination System (FCT)
The FCT system is used for testing stickiness, neps, trash and seed coat
fragments. The sample in the form of bundle is fed into a self-cleaning,
micro carding device integrated in the FCT, to produce about 10 m of
transparent web in order to expose the impurities and contaminants in the
best way possible. An area of 1 sq m per sample is tested.
Firstly, the web is analysed by a machine vision system for the presence of
trash, neps and seed coat fragments and then they are pressed between the 2
stickiness crush rollers in the same manner as with the crush rolls of the
commercial cards. The cotton web removed by the vacuum is then deposited on
the stickiness crush rollers. They are examined by a laser signal analysis
system for determining the stickiness content. Time taken for one sample is
The advantages are:
Major contaminants like stickiness,
seed coat neps and fibre neps are also considered as parameters for
Evaluation of performance of the
precleaning systems such as cards, comber etc, for determination of
their optimum operational setting and efficiency are done.
Integrated indices of fibre quality
If a versatile measure of cotton quality can be quantified and
universally accepted, it would be enormously valuable in both technical and
commercial applications. Numbers of different cottons, such as bales in a
warehouse, are much easier to compare if each has one descriptive number
rather than several. A single-figure index should meet the following
It is based on common HVI results,
and should not require purchase of additional instruments.
It reflects a balance between market
forces and technical considerations.
Is, as often happens, more or fewer
properties than usual are tested, the estimate is unbiased, ie for
average cottons the premium or discount (p/d) is unchanged.
Different methods of maturity
The notion that micronaire is a
measure of fineness still appears frequently. Double compression airflow
Polarised light analysis.
Causticaire, ie, micronaire of
conditioned specimens before and after soaking in concentrated caustic
Near infrared spectrometry.
Image analysis of both longitudinal Includes/IncImages and cross sections was applied
successfully to the measurement of maturity; less exactly when the minimum
projected width was used. In general image analysis can measure the mean and
distribution of several fibre transverse dimensions:
The apparent fibre diameter, a
nebulous concept in a fibre having such a non circular shape, but a
useful measure of micronaire, ribbon width is a better term in most
The other properties are more apparent
when cross sections are made:
Martin radius, the mean of 8
equidistant radii from the centre of gravity.
Total cross sectional area,
including both fibre wall and the hollow lumen.
Cross sectional area of fibre wall
an exact measure of linear density and considered along with the above
area, a measure of maturity.
Perimetre, nearly a constant for a
given variety regardless of the degree of thickening and perhaps the
best available measure of standard linear density.
Degree of thickening, usually defined as
the cross sectional area divided by the area of a circle having the same
perimetre as the fibre. A double compression instrument, where estimates of
linear density and maturity depend on small differences between airflow
properties measured at two level of compression. It showed the effect of
varying sample mass necessary for automated HVI lines and found drift in the
micromat rather than the step changes of earlier models.
Different methods of fineness
Direct measurements of mass divided by length, the later is the limiting
factor in accuracy; this has been developed by image analysis, where it is
commonly expressed as cross-sectional wall area. Measurement of resistance
to airflow, by single or double compression
Advantages of latest fibre testing
The results are practically
independently of the operator.
The tests are based on the large
volume of samples and so they are more significant.
The results are summarised and are
The raw material data is utilised in
the best manner.
As a result of the fibre material,
the problems can be predicted and corrective measures taken before such
problems can occur.
Attempts are being made to express fibre quality by a single index. As
the number of properties tested in HV lines continues to increase, so too,
does the average person's confusion about the meaning of results.
- Cannot tell readers the relative
importance of properties for their own circumstances.
- Do not distinguish fully between the different measures of the same
property, such as uniformity index and uniformity ratio.
- Do not address the diversity of ways of measuring some properties, such as
maturity or stickiness, and the different results obtained from different
instruments or techniques.
- FCT is used at the gin as a quality controller and immediate cotton
The traditional test of counting neps is
so labor intensive and subjective that it invites innovation; the first step
alone, is to prepare a card web, for which few laboratories have the
machinery. A major response has been the development of the NEP module, AFIS-N,
of the Advanced Fibre Information System.
As the fibres are separated aerodynamically then passed across a photocell,
the electro-optical sensor distinguishes the wave forms of single fibres,
trash and neps. Whether the sugar is metabolic or entomological and whether
the secretion is from white fly or aphids matters little to the person
trying to process sticky cotton.
Model liquid chromatography makes it
possible to separate characterise and quantify the sugars. The sensitivity
of rotor spinning to accumulations of trash and dust are led to the
development of more sensitive instruments for testing small impurities in
sliver. The AFIS apparatus lends itself to measurement of trash, dust and
neps from lint through the roving stages and provides the entire size
The above discussion gives an idea about
main latest fibre testing techniques using HVI, AFIS, FCT and this concludes
that one can achieve higher accuracy with least time in this system. Fibre
testing is an important part in the final product, so it is clear one can
achieve great quality with accurate testing techniques, which were discussed
in this paper. Apart from this, various methods are also included which will
give proper results in fibre testing.
When considering from economical point, it advisable to use medium volume
instruments (MVI) & low volume instrument (LVI) to achieve the same
quality with medium cost. With present depression in textile field, it is
essential to achieve good quality raw material by good testing techniques
and achieve good growth in textile field. It is essential in this
competitive global market survival with this latest fibre testing
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Note: For detailed version of this
article please refer the print version of The Indian Textile Journal April
Kumaraguru College of Technology,