Test Methods and Precautions
Caustic soda method - Fibres irrigated in 18% caustic
soda are examined under microscope. Based on the ratio of lumen width
to wall thickness, fibres are classified as Mature, Half Mature and
- Balls Sorter-Determines frequency length distribution of
fibres from which mean,CV are etimated. This is a classical method,
time consuming and is not commonly used
- Baer Sorter Determines cumulative fibre length
distribution. Effective length, Mean length and % short fibres are
important parameters determined. Merits-1.Effective length is close to
Grader's staple length 2.Provides accurate estimate of short fibre
content Limitations. 1. Time consuming(2hrs per sample 2. Calls for
considerable operator skill in sampling and preparing the diagram
- Fibrograph - Fibres are randomly clamped at any point
along their length on a comb, the beard thus obtained optically scanned
from which 2.5%, 50% span length, uniformity ratio and short fibre% are
determined. Merits 1. Simulates beard formed by fibres held by back or
front roller nip of a drafting system 2. Very rapid(abou 15 min per
sample 3. Does not depend much upon operator skill
- Effective Length by Baer Sorter = 4 + 2.5% Span length in mm
- Fibre fineness
- Gravimetric method - Fibres are counted either as whole
fibres or after being cut to a finite length and weighed in a sensitive
balance. Time consuming
- Air Flow Methods
- Micronaire Determines rate of flow of air through a
known mass of fibres packed in a cylinder of known dimensions under
constant pressure. This is expressed in mirograms/inch. Micronaire
value is dependent upon not only liner density but also on maturity of
fibres. Micronaire Mc = K/ MH where M = Maturity Ratio H = Fibre weight/unit length and K=constant
- Micromat Fineness and Maturity Tester by SDL- Provides independent estimates of fineness and maturity of cotton
- Arealometer-Determines specific surface area, fineness and maturity of fibres
Mature (M) - L/W <1
Half Mature (HM) - 1 < L/W < 2
Immature (I) - L/W > 2
Mc = (M + .6*H + .4 * I)/100
Mature (N) - L/W < 2
Immature (D) - L/W >or= 2
Maturity Ratio Mr = (N -D)/200 + 0.7
Polarised Microscope Method
Immature - Blue or purple
Mature - Yellow or Green
Fibres dyed in boiling dyebath containing .036g Diphenyl Fast Red 5BL and .084g Chloarantine Fast green in 120g of water
Mature - dyed to red
Immature Dyed to Green
- Pressley - Operates on constant rate of traverse. Rate of
loading increases with traverse and there is risk of overshootin and
overestimation of strength
Pressley Index(PI) = Breaking strength at "0" gauge length in pounds/weight in mg
Pressley Ratio(PR) = Breaking strength at 3mm gauge length in lbs/weight in mgs
Tenacity at"0" gauge length, g/tex = 5.36 * PI
Tenacity at 3mm gauge length,g/tex = 6.8 * PR
Tensile strength in 1000psi = 10.81 * PI
Breaking tenacity, g/tex = Breaking strength in 1000psi *0.496
- Stelometer- operates on constant rate of loading. Generally preferred
Shirley Analyser is the standard equipment used for measrement of trash content. The equipment determines
Denkendorf Mirodust and Trash Analyser
- primary tash consisting of coarse type of trash including seed coats
- Finer trash
- Micro dust larger than 150 microns
- Microdust between 50 and 150 microns. About 200 gms of cotton are used and the test takes about 1hr
enables quick estimation of trash from 25- 30 gms in 12-15min
Neps represent small pin size
entanglements of fibres which detract from appearance of yarn and
fabric. They take up less dye and show up as specks in dyed fabric. In
most cases neps are formed by immature fibres because of their low
rigidity. Sometimes neps are also formed because of seed coat fragments
which provide nucleus for them.
- Manual method - Small pinches of opened fibres are laid on a
black plush board of known area and neps are counted manually. This is
subjective and time consuming.
- Nepotometer - This is a miniature card where fibres are opened into a web and the web is compared against standard boards.
- Shirley Web template - Card web is collected on a black
board on which a template containing 34 circular holes of one square
inch each is laid. Number of holes containing at least one nep is
counted. Assuming a Poisson distribution for nep incidence, Nep level
- Uster AFIS -Opened fibres pass through a sensor. A computer is used to distinguish individual fibres from neps.
Conventional testing involves
considerable time and results are not available in time for cotton
selection and mixing preparation. High volume Instument(HVI) have
speeded up testing substantially and testing of a cotton is completed
in about 2-4 minutes. Bale wise testing of cootons is possible and
bales with substandard characteristics can be weeded out.HVI determines
Upper half mean length or 2.5 and 50% span lengths, uniformity index or
ratio, Micronaire and bundle strength. Optional attachments for
estimating trash level by optical scanning and colour of cotton and
moisture level are available. In Micronaire test HVI requires an
approximate weighment of cotton. As an option Macromat which measures
both fineness and maturity can be incorporated in HVI. HVI, though
rapid, has certain limitations in terms of accuracy of results. These
include in case of
- Fibre Length
Fibre breakages occur during comb
preparation on HVI as this is done at high speed. Such breakages are
more with harsh, entangled cottons. This results in lower estimates of
fibre length. Breakages are also higher with card sliver compared to
comber sliver.Over estimation of fibre fractionation is therefore found
- Bundle Strength
- HVI works on constant rate of extension while stelometer works on
constant rate of loading. Further, time for break is much lower in HVI
to speed up testing.
- A randomly clamped beard is used is used in stelometer and
fibres are combed to remove short fibres. So all fibres are gripped by
both jaws. In HVI, fibre bundle is not combed to remove short fibres
before clamping. All fibres are therefore not clamped by both jaws.
- The mass of broken specimen is weighed in a balance in
stelometer while in HVI indirect estimate of mass (by optical means) is
obtained. The state of crimp in the fibre affects the estimated mass.
a result, significant differences are found in bundle strength values
by HVI and conventional testing. HVI does not give true results for
material at different stages of spinning.
Fibre samles are opened into individual fibres by an opening roller and passed on to different modules for measuring
- fibre Length
- Fibre Fineness
- Nep content
Nep measurement is the most useful
part of this instument. A computer distinguishes individual fibres from
neps. Seed coat neps are separately assessed. A good correlation is
claimed between neps measured with AFIS and neps in yarn by Uster
imperfection tester. A second sensor measures trash and dust.
Man made fibre Filament and Yarn
Staple length determines the strength of yarn and optimum twist factor.
Extra long staple fibres require a lower twist factor and enable higher
spindle speeds. At the same time, they are more prone to nep generation
and result in inferior yarn appearance. In the case of cut staple
fibres, fibre length is measured by laying the fibre on a glass plate
smeared with oil to enable straightening of fibre. Length of fibre is
measured on a scale. Roughly about 10-15 fibres are thus tested and
average determined. In the case of variable staple fibre and synthetic
tops used in worsted spinning system, automatic fibre diagram machine
by SDL or WIRA is used. Cut square method is used to draw a tuft of
fibres from the sliver and tuft is passed between the plates of
capacitor. A measure is thus obtained of number of fibres in the tuft
from the base to tip, from which cumulative fibre distribution is
obtained. The measurement is fully automated and the fibre diagram
together with results of mean length, upper half mean and CV are
Fineness determines the count to which the fibre can be spun. It also
determines the strength, evenness and imperfections of yarn and also
the end breaks in spinning. Fibre fineness is determined
gravimetrically or by vibroscope.
About 25 fibres are cut to a specified length under tension by means of
a template and weighed in a sensitive balance from which weight per
unit length is determined. The method is time consuming.
The fibre, held between two clamps, is tensioned by a pre determined
weight and subjected to transverse vibrations at variable frequency.
The frequency at which maximum amplitude is obtained, which is
resonance frequency, is determined, from which fineness is determined.
Vibromat by Textechno Herbertstein and Vibroscop by Lenzing are based
on this principle. The equipment is fully automatic and fibre fineness
and CV are displayed.
Fibre strength determines the strength of yarn and fibre elongation
determines yarn elongation. Single fibre testing is normally done.
Fibre is clamped preferably pneumatically between two jaws at a
predetermined tension. Lower jaw is traversed at a constant rate while
upper jaw is attached to a sensitive load cell of 50-100cN capacity.
The load extension curve, breaking load, elongation, work of rupture
and modulus are determined and displayed. Facility is also offered in
some instruments to carry out tests under liquid. Fafegraph and Favimat
by Textechno Herbert stein and Lenzing are some commonly used
instruments. Bundle strength in stelometer is not recommended because
of fibre slippage under the jaws.
Crimp is an imprtant property that determines processing behaviour in
carding, drafting and fault incidences in yarn. Crimp frequency,
amplitude, crimp stability,crimp elongation, decrimping point are some
of the important properties that determine crimp. Crimp frequency and
amplitude may be determined by projecting a magnified image of fibre on
screen. Opto electronic sensor is used in some equipments to provide
digital representation of fibre held between two clamps at very low
tension. Tensile tests using an extremely sensitive force measuring
system enables the measurement of the curve of crimp force vs
elongation, crimp extension, decrimping point and crimp stability.
Nature and quantum of spinfinish has critical influence on performance
of fibre. Lap licking, cylinder loading and roller lapping are often
traced to improper spinfinish.Spinfinish is traditionally estimated by
extraction with a solvent like carbon tetrachloride or benzene on
Soxhlet's apparatus. This is time consuming though accurate. ALFA 200
by Lenzing and Rapid extraction apparatus by SDL are rapid methods for
One of the problems encountered with synthetic fibres is generation of
static electricity. static generation is a cause for lap licking,
cylinder loading, web falling incidices and coiler chokeup in carding
and roller lapping in drawframe to ringframe. High hairiness in yarn,
fabric defects like stitches and floats are also attributed static
electricity. Sparking may take place due to static in synthetic
carpets. Accurate instruments are available for estimating the amount
static charge and half decay time. Half decay time denotes the time
taken for static charge to come down to half its level.
Abnormalities in fibre
Presence of extraneous agglomerations on the surface of fibre, fused
and undrawn fibres, overlength fibres are some of the abnormalities in
fibre. Projectina is useful in to detect such abnormalities in fibre.
Baer sorter can be used for estimating over length fibres.
Filaments and Yarns
Draw force is an important property in POY yarns. It determines the
performance of yarns and fabric defects like weft bars. From
measurement of draw force variations in molecular orientation,
shrinkage and dyeing chareteristics of the material can be assessed.
Testing of draw force under dynamic conditions has the merit of high
speed testing and continuous recording of variations in draw force.
crimp force or crimp rigidity of textured yarns and shrinkage force of
flat and textured yarns are also important quality characterics that
determine in fault incidence in fabric. For measuring draw force, the
yarn is passed between two godets at high speed. The measuring roll of
force measuring system senses the yarn in between the two godets. Below
the measuring system, the yarn is heated by a heating system to high
temperature. There is usually facility to run the tester either with
constant extension or contraction for continuous measurement of yarn
tension, or with constant tension for continuous measurement of
extension or contraction.
The yarn is run at constant extension and draw force is continuously measured and recorded.
Overfeed is kept between two godets to determine shrinkage.The test is
carried out at low speed and high temperature to determine shrinkage.
Alternatively the yarn is tested at high speed and low yarn temperature
to determine crimp contraction or crimp rigidity.
Shrinkage is tested by running yarn at high yarn temperature
Broken filaments arise from disturbances in process, unsatisfactory
manufacturing conditions and ineffective process control. Broken
filaments on running threads are determined by sensor consisting of
optical and infra red emitter and transmitter.
Breaking load, elongation and work of rupture are some of the important
characterics of filaments and staple fibre yarns. Lea and single thread
strength are the commonly used measures of yarn strength.
Single thread strength
Tensile testers may be classified as
Constant rate of loading type
Constant rate of elongation
Constant rate of traverse
Constant rate of loading
Rate of loading of yarn is constant in these instruments throughout the
test period. Inclined plane testers belong to this category. Though
this system of loading has many merits, this type of tester is not used
now a days.
Constant rate of Elongation
This is most popular system these days. Tensile testers using a range
of sensitive load cells are used for determining breaking load and load
elongation curve of yarn. The yarn is held between two jaws with upper
jaw connected to load cell and lower jaw traversed downwards at a
constant rate of traverse. Insertion of a new specimen into the clamps
and clamping of the specimen at a pre determined tension are done
automatically. Automatic package changers( with upto 20 packages) are
also provided with the tester so that after a prescribed number of
tests are caried from a package, the package is automatically changed
to a new package and insertion of new yarn to the clamps is
automatically done. A series of high resolution load cells enable
testing of yarn with strength between 100cN to 1000cN. Software is
provided for determining mean, maximum, minimum, S.D., CV, Confidence
limits and a host of other useful information. A high resolution opto
electronic sensor measures the elongation of yarn.
Constant rate of traverse
Pendulam type testers belong to this category. These have become obsolete because of long operting time and higher errors.
Factors affecting strength
Gauge length has considerable influence on strength. With increase in
gauge length, strength will decrease because of increased chances of
occurrence of more weak places and the weak place being weaker. So
gauge length has to be standardised. Normally 50 cm gauge length is
used except in POY yarns. In the case POY yarns, 20cm gauge length is
used because of the high elongation of these yarns.
Rate of loading or elongation
Rate of loading or elongation inf;uences test results. With increase in
rate of loading or elongation, time for break decreases and a higher
strength will be obtained. Rate of loading or elongation is usually
adjusted so that time for break is around 20sec.
Regular calibration of equpiment is essential to avoid erroneous results.
Calibration is done by hanging standard weights from upper clamp.
Lea strength test is common in staple fibre and cotton yarns. The yarn
is wound on a wrap reel of 54inch circumferance for 80 wraps to prepare
a lea of 120 yards length. The lea is tested for strength in a pendulam
type of tester in olden days. Now a days a load cell is used in place
of pendulam to measure strength. Load cell is attached to the top jaw.
Lea strength has the merit of larger sampling length. It also takes
into account variability in the yarn and so can give a better
indication of the performance of yarn at later stages.
The yarn is seldom extended upto breaking point. It is more often
subjected to repeated loads of small value. So performance of material
under cyclic loading may give better information about durability. The
specimen is loaded upto a certain load or elongation and brought back
to its original level. This action is repeated cyclically a number of
times till the specimen breaks. Number of cycles of loading withstood
by specimen, is taken as a measure of its strength. Alternately, the
specimen is tested for strength after a known number of cycles of
Count of the yarn is determined along with the lea test by weighing the
broken leas. Auto sorter is used to determine mean, minimum, maximum,
S.D., CV, Confidence limits and other statistics from count tests of
leas from within and from different packages. The instrument consists
of an electronic balance to measure the weight of leas. This is
equipped with a software for determining the various statistics. Some
manufacturers like Textechno Herberstein have developed an instrument
'Autocount' for automatically determining count. This consists of drive
rollers which withdraw a known length of yarn from a package and
deposit it on an electronic balance for weighing and estimating count
and related statistics.
Irregularity is an imprtant quality characteristic of staple fibre and
cotton yarns. It determines the appearance of yarn and fabric, feel of
fabric, performance of yarn in further processes and the strength
realisation of fibre in yarn. Irregularity is commonly measured by
capacitance type irregulaity tester. Uster Eveness tester is the widely
used instrument for measuring irregulariy. The yarn is passed between
two capcitance plates at a constant speed. The capacitance of the
condenser varies according to weight per unit length of yarn. The
variations in capacitance are converted into voltage and amplified. A
continuous record of variations is obtained. Instantaneous values of
Mean Deviation%(U%) or Coefficient of variation(CV%) of the variations
is computed by an integrator and displayed. A number Condenser slots of
different sizes are used for tesing slivers, rovings and yarns as per
their count. Apart from short term variation, the instrument has also
facility for determining medium term term variations and variance
length curve of the yarn.
This is an attachment for determining the extreme places. Thick places,
Thin places, Neps, each of 4 categories based on their size, are
measured by the instrument.
Spectrogrpah carries out a fourier analysis of mass variations in the
material and displays a curve showing the amplitude of different
wavelengths present in the material. This is useful to detect the
presence of periodic irregularities and their wavelength in the
material. Periodic irregulaities are a source of weft bars and warp way
dects in woven and knitted fabrics. Spectrograph is a useful aid in
minimising periodicities caused by mechanical faults in machinery.
Precautions in testing
Conditioning of material to test room is important, when test room
humidity varies considerably from manufacturing room. One hour in the
case of yarns and 2-3 hours in the case of rovings of conditioning
would be adequate. The bobbins should be laid in such a way that
moisture enters from all sides to ensure uniform conditioning. In the
case of sliver, uniform conditioning may take several days. So it is
recommended that testing be carried out immediately after the material
is brought to testing room, after removing a few top layers of sliver.
Material speed has to be standardised. With increase in material speed, irregulaity will increase.Condenser slot size.
Condenser slot size
This should be properly chosen. It is advisable to use a slot that gives a lower material to air space.
Regular calibration has to be carried out to ensure accuracy.
- Entanglement Tester.
Presence of entanglements affects the performance of textured yarns.
Traditionally, this done by piercing the yarn with a needle and pulling
it through the yarn till it encounters a compaction. The distance
covered by needle is then measured. This is however a time consuming
test and has been rplaced by automatic testers. Here the piercing unit
is automatically inserted into the yarn and the yarn advances at a
speed adjustable as required with its tension being measured. As soon
the piercing unit encounters a compaction, the tension in yarn
increases and at preselected tension levels, the length between two
compction points is determined and displayed. In addition, soft
entanglement points are determined.
Friction is an important property particularly in filaments and sewing
threads. The yarn is taken around a guide at constant speed and the
tension in the yarn before and after passing over the guide is measured
by a sensitive electronic tension meter. Coeffcient of friction is
estimated from the two tension values.
Maintenance of moisture to the standard level is important in yarn
packages before they are packed, weighed and sold. If moisture level is
lower than standard by even 0.5%, considerable losses will be incurred
by mills beacause of wrong invoicing. Moisture is measured in the whole
package by a non contacting electrode senser which passes a harmless
electromagnetic field through the package. The high dielectric constant
of water enables the estimation of moisture content.