- 1. Abubakkar Marwat (05-NTU-05)Yarn Evenness1/19Table of
contents: Introduction Types of irregularity Causes of irregularity
Denoting unevenness or irregularity Types of variations Importance
of yarn evenness Measuring and assessing evenness 1-Visual
examination 2- Gravimetric method 3- Capacitive method 3.1- Uster
evenness tester 4- Mechanical method of roving/sliver evenness
measurement 5- Optical method (Zweigle G580) 6- Pneumatic method 7-
Acoustic method 7.1- Impulse acoustic method Index of
irregularityTextile Testing-II (TS-333)1 1 2 3 4 4 5 5 6 7 7 13 15
15 16 16 18
2. Abubakkar Marwat (05-NTU-05)Yarn Evenness
Introduction:2/19:Non-uniformity in variety of properties exists in
yarns. There can be variation in twist, bulk, strength, elongation,
fineness etc. Yarn evenness deals with the variation in yarn
fineness. This is the property, commonly measured as the variation
in mass per unit length along the yarn, is a basic and important
one, since it can influence so many other properties of the yarn
and fabric made from it. Such variations are inevitable, because
they arise from the fundamental nature of textile fibres and from
their resulting arrangement. The spinner tries to produce a yarn
with the highest possible degree of homogeneity. In this
connection, the evenness of the yarn mass is of the greatest
importance. In order to produce an absolutely regular yarn, all
fibre characteristics would have to be uniformly distributed over
the whole strand (yarn). However, that is ruled out by the
inhomogeneity of the fibre material and by the mechanical
constraints. Accordingly, there are limits to the achievable yarn
evenness. Types of Irregularity::1) Weight per unit length:
Variation in weight per unit length is the basic irregularity in
yarn. All other irregularities are dependent on it. This is because
weight per unit length is proportional to fibre number i.e.; number
of fibres crossing a section of yarn. Variations in fibre number
are the factor influenced by drafting. So any improvement in
drafting or spinning will first reflect in improvement in
variability of weight per unit length. 2) Diameter: Variability in
diameter is important because of its profound influence on
appearance of yarn. Variations in diameter are more easily
perceived by eye. Latest models of evenness testers have therefore
a module for determining diameter variability. Diameter variability
is however caused by weight variability. As twist has tendency to
run into thin place, variability in weight gets exaggerated in
diameter variability. 3) Twist: Twist variation is important
because of its influence on performance of yarn and fabric dye
ability and defects. Soft ends are a major cause of breaks in
weaving preparatory and loom shed. They arise from twist
variations. Soft twisted yarns take more dye and so uneven dyeing
is caused by high twist variation. Weft bars and bands are also
caused by low twisted yarns. Twist variations come from slack
spindle tapes, jammed spindles. A certain amount of variation is
also present along the chase of cop. 4) Strength: Importance of
strength variation is easy to appreciate. Yarn breaks at the
weakest element and so yarns with high strength variability will
result in high breakages in Textile Testing-II (TS-333) 3.
Abubakkar Marwat (05-NTU-05)Yarn Evenness3/19further processes.
Strength variability is partly dependent upon count variability and
partly upon spinning conditions and mechanical defects. 5)
Hairiness: High variation in hairiness leads to streaky warp way
appearance and weft bars in fabric. More light will be reflected
from portions of weft where hairiness is more and this leads weft
bands. High hairiness disturbs warp shed movement in weaving and
results in breaks, stitches and floats. Among other factors, worn
out rings and travelers, vibrating spindles, excessive ballooning
and variation in humidity in spinning room cause variations in
hairiness from bobbin to bobbin 6) Colour: Variations in colour of
yarn cause batch to batch variation in fabric colour, which leads
to rejects. This is particularly critical in cloth marketed to
garment units. Variations in colour of yarn and fabric are caused
by variations in colour of cottons used in mixing. Larger lot sizes
made from a large number of bales help to mitigate this problem.
Checking of cotton and mixing for colour will also minimize large
variations in colour. HVI testing equipments have therefore a
module for checking colour. Causes of irregularity::1) Irregularity
caused by raw material: The natural fibres have variable verities.
They have no true fixed length, fineness, shape of cross-section,
maturity, crimp, etc., which have effect on yarn properties
specially evenness. These variations are due to different rates of
cell development due to changes in environmental conditions
(nutrients, soil, and weather). In man made fibres, variations in
mass/unit length occurs due to changes in polymer viscosity,
roughness of spinneret orifice, variation in extrusion pressure and
rate, filament take-up speed, presence of delustrant or additives,
which can modify the particular shape and fibre surface geometry.
2) Irregularity caused by fibre arrangement: Textile fibres are not
rigid. Their manipulation during conversion into yarn is an
immensely complex combination of mechanical movement which usually
requires some degree of compromise. The desirable results of
relocating large number of fibres at high speed and arranging in
well ordered form tend to be difficult. Fibres assembled into the
form of a twisted strand constitute a yarn. Fibres are not
precisely laid end to end, and gaps are present between them. As a
result of yarns twist, fibres arrange in spiral form in a series of
folds, kinks, and doublings. 3) Effect of fibre behavior: Fibres
shape directly affects yarn regularity. The fibres section,
arrangement of fibre section and space between the fibres will vary
from yarn section to section. Hence the mass of each section will
differ. A thin place in yarn will have lower mass and less
strength. In thin regions, yarn twist tends to be higher since
resistance to deformation is lower. Textile Testing-II (TS-333) 4.
Abubakkar Marwat (05-NTU-05)Yarn Evenness4/194) Inherent
shortcoming of machinery: In many engineering processes the units
from which the final product is assembled are positively controlled
by hand or machine and positioned with only a few thousandths of an
inch tolerance. In spinning it is surprising how often the
individual fibres are only negatively controlled-at times they are
carried forward by air currents or jostled along by surrounding
fibres, or they are held in position by friction and twist. Fibre
manipulation by rollers, aprons, gills, and other machine parts is
hampered by fibre variation, and the machines can only be set to
give the best results within the limitations imposed by the
material. The drafting wave is one example of irregularity due to
the inability of a drafting system to control each fibre. Where
roller drafting is used, the distance from one nip to the other is
greater than the length of the shorter fibres. These short fibres
float in the drafting zone and move forward in an irregular but
cyclical manner which results in the drafted strand having thick
and thin places. The wavelength of this type of irregularity is
about 2-5 times the mean fibre length but it is not necessarily
constant for a particular strand. In addition to a varying
wavelength, the amplitude of the drafting wave is also variable. 5)
Mechanically defective machinery: Since machines even in good
condition produce irregular yarns, it is reasonable to assume that
defective machinery will increase the amount of irregularity. The
implementation of an efficient maintenance system is essential if
the level of irregularity is to be kept within bounds. Machines
drift out of adjustment, bearings become worn, components get
damaged, and lubrication systems clog and dirt works its way into
the mechanism. Faulty rollers (top roller eccentricity) and gear
wheels usually produce periodic variation. Denoting "UNEVENNESS" OR
"IRREGULARITY" ::The mass per unit length variation due to
variation in fibre assembly is generally known as "IRREGULARITY" or
"UNEVENNESS". It is true that the diagram can represent a true
reflection of the mass or weight per unit length variation in a
fibre assembly. For a complete analysis of the quality, however,
the diagram alone is not enough. It is also necessary to have a
numerical value which represents the mass variation. The
mathematical statistics offer 2 methods: 1. The irregularity U%: It
is the percentage mass deviation of unit length of material and is
caused by uneven fibre distribution along the length of the strand.
2. The coefficient of variation C.V.% In handling large quantities
of data statistically, the coefficient of variation (C.V.%) is
commonly used to define variability and is thus well-suited to the
problem of expressing yarn evenness. It is currently probably the
most widely accepted way of quantifying irregularity. It is given
byTextile Testing-II (TS-333) 5. Yarn EvennessAbubakkar Marwat
(05-NTU-05)Coefficient of variation (C.V.%) =S .D avg .value5/19100
where S.D = Standard deviation The irregularity U% is proportional
to the intensity of the mass variations around the mean value The
U% is independent of the evaluating time or tested material length
with homogeneously distributed mass variation. The larger
deviations from the mean value are much more intensively taken into
consideration in the calculation of the coefficient of variation
C.V. %. C.V.% has received more recognition in the modern
statistics than the irregularity value U%. The coefficient of
variation C.V.% can be determined extremely accurately by
electronic means, whereas the calculation of the irregularity U% is
based on an approximation method. It can be considered that if the
fibre assembly required to be tested is normally distributed with
respect to its mass variation, a conversion possibility is
available between the two types of calculations C.V.% = 1.25 x U%
Types of variations: short, medium and long term::Variations in the
fibrous strand are classified according to their wavelength with
respect the fibre length used to form that particular strand. 1)
Short term variation: These variations are of the wave length 1-10
times of fibre length. Amplitude of these variations is greater
than long term variations. These result due to faulty processing at
the last machine. Such variations if excessive produce a fabric of
objectionable appearance. 2) Medium term variations: These
variations are of the wave length 10-100 times the fibre length.
Such variations do not cause a pattern as it hides into the
adjacent warp yarn. In weft it will appear as a thick line again
hidden by adjacent weft. However excessive variations give the
cloth a streaky appearance. 3) Long term variations: These
variations are of the wave length 100-1000 times the fibre length.
Such variation cause periodic faults known as diamond bars or block
bars in the woven fabric along the weft direction. A weft yarn to
cause a diamond bar pattern must have a long term periodic
variation of wave length less than twice the pick length.
Importance of yarn evenness:: Irregularity can adversely affect
many of the properties of textile materials. The most obvious
consequence of yarn evenness is the variation of strength along the
yarn. If the average mass per unit length of two yarns is equal,
but one yarn is less Textile Testing-II (TS-333) 6. Abubakkar
Marwat (05-NTU-05)Yarn Evenness6/19regular than the other, it is
clear that the more even yarn will be the stronger of the two. The
uneven one should have more thin regions than the even one as a
result of irregularity, since the average linear density is the
same. Thus, an irregular yarn will tend to break more easily during
spinning, winding, weaving, knitting, or any other process where
stress is applied. A second quality-related effect of uneven yarn
is the presence of visible faults on the surface of fabrics. If a
large amount of irregularity is present in the yarn, the variation
in fineness can easily be detected in the finished cloth. The
problem is particularly serious when a fault (i.e. a thick or thin
place) appears at precisely regular intervals along the length of
the yarn. In such cases, fabric construction geometry ensures that
the faults will be located in a pattern that is very clearly
apparent to the eye, and defects such as streaks, stripes, barre,
or other visual groupings develop in the cloth. Such defects are
usually compounded when the fabric is dyed or finished, as a result
of the twist variation accompanying them. Twist tends to be higher
at thin places in a yarn. Thus, at such locations, the penetration
of a dye or finish is likely to be lower than at the thick regions
of lower twist. In consequence, the thicker yarn region will tend
to be deeper in shade than the thinner ones and, if a visual fault
appears in a pattern on the fabric, the pattern will tend to be
emphasized by the presence of colour or by some variation in a
visible property, such as crease-resistance controlled by a finish.
Other fabric properties, such as abrasion or pill-resistance, soil
retention, drape, absorbency, reflectance, or luster, may also be
directly influenced by yarn evenness. Thus, the effects of
irregularity are widespread throughout all areas of the production
and use of textiles, and the topic is an important one in any areas
of the industry. Measuring and Assessing Evenness::1) Visual
examination: Yarn to be examined is wrapped onto a matt black
surface in equally spaced turns. The black boards are then examined
under good lightening conditions using uniform non-directional
light. A.S.T.M. has a series of Cotton Yarn Appearance Standards
which are photographs of different counts with the appearance
classified in four grades. The test yarn is then wound on a
blackboard approximately 9.5 x 5.5 inches with the correct spacing
and compared directly with the corresponding standard. Motorized
wrapping machines are available: the yarn is made to traverse
steadily along the board as it is rotated, thus giving a more even
spacing. It is preferable to use tapered boards for wrapping the
yarn if periodic faults are likely to be present. This is because
the yarn may have a repeating fault of a similar spacing Textile
Testing-II (TS-333) 7. Abubakkar Marwat (05-NTU-05)Yarn
Evenness7/19to that of one wrap of yarn. By chance it may be hidden
behind the board on every turn with a parallel-sided board where as
with a tapered board it will at some point appear on the face. 2)
Gravimetric Method (Cut and weigh method): This is the simplest way
of measuring in mass per unit length of a yarn. The method consists
of cutting consecutive lengths of the yarn and weighing them. For
the method to succeed, however, an accurate way of cutting the yarn
to exactly the same length is required. This is because a small
error in measuring the length will cause an equal error in the
measured weight in addition to any errors in weighing operations.
One way of achieving accurate cutting to length is to wrap the yarn
in around a grooved rod which has a circumference of exactly 2.5 cm
and then to run a razor blade along the groove, leaving the yarn in
equal 2.5 cm lengths. The lengths so produced can then be weighed
on a suitable sensitive balance. If the mass of each consecutive
length of yarn is plotted on a graph as in Fig., a line showing the
mean value can then be drawn on the plot. The scatter of the points
about this line will then give a visual indication of the
unevenness of the yarn. The further, on average, that the
individual points are from the line, the more uneven is the yarn.
There are two ways of expressing this unevenness: 1. The average
value for all the deviations from the mean is calculated and then
expressed as a percentage of the overall mean (%age mean deviation,
PMD). This is termed U% by the Uster. 2. The standard deviation is
calculated by squaring the deviations from the mean and this is
then expressed as a percentage of the overall mean (CV %). The two
values are related by the following relation: CV % = 1.25 PMD This
method is slow and laborious. Example: Suppose a yarn is cut into
short consecutive lengths (2.5 cm), and then each length weighed:
S.NoWeight X1 2 3 4 5 6 7 8 9 1020 18 19 17 22 21 18 20 19
21X19.5Deviation from Mean (X- X ) 0.5 1.5 0.5 2.5 2.5 1.5 1.5 0.5
0.5 1.5 ( x x) n= 13(X- X )2 0.25 2.25 0.25 6.25 6.25 2.25 2.25
0.25 0.25 2.2525 20x 19.5mg15 Series1 10 5 0 122.5 9 = 22.5Textile
Testing-II (TS-333)23456789 10 8. Yarn EvennessAbubakkar Marwat
(05-NTU-05)8/19 ( x x) Mean Deviation == 13/10 =
1.3nmean.deviationPercentage Mean Deviation (P.M.D) = ( x x)
Standard deviation S.D = S .DCV% = Avg .value1001.58avg .value2n
1=1.3x 100 = 19.5 100= 6.66 %22.5 9 = 1.58 100= 19.5 = 8.10 %
Irregularity in the yarn is 6.66 %. 3) Capacitive method: The
measuring device of an electronic capacitance tester is a parallel
plate capacitor. Under certain conditions, the effect of
introducing a non-conducting material such as a sliver or yarn into
the space between the plates is to change the capacity of the
capacitor, the change being proportional to the weight of material
present. If, therefore, the material is drawn through the capacitor
continuously, the changes in the capacity will follow the variation
in the weight per unit length of the strand, the unit length being
the length of the capacitor. If is necessary to detect the changes
in capacity and to translate them electronically into meter
readings which indicate the coefficient of variation. At the same
time a trace of the variation should be made on a pen recorder if
required. Some of the design problems may be described: 1. Changes
in capacity are linearly related to the weight of material present,
the material thickness should not exceed 40% of the distance
between the capacitor plates. Hence interchangeable capacitors are
necessary to test a range of materials from sliver to fine yarns.
2. The length of the capacitor should be as short as possible so
that the variations in weight are measured over short lengths. 3.
Shape of the cross-section of the tested strand affects the change
in capacity. So it is necessary that the strand maintains its shape
during its passage through the capacitor. 4. The moisture in the
material affects the magnitude of the change in capacity, a higher
moisture content giving a greater change in capacity. 3.1) Uster
evenness tester: Schematic diagram of this capacitance based
evenness tester is shown. Two oscillators A & B have equal
frequencies when there is no material in the measuring capacitor C.
When the two frequencies are superimposed the difference in
frequency is zero. The presence of material (yarn) in the capacitor
causes its capacity to change and so alter the frequency of the
oscillator A. There will then be a difference between the two
frequencies which varies according to the material (strand
thickness) between the capacitor plates. Suitable circuits D
translate these frequency differences into signals which (1) are
indicated on the meter M, (2) drive the pen of the recorder, and
Textile Testing-II (TS-333) 9. Abubakkar Marwat (05-NTU-05)Yarn
Evenness9/19(3) are fed into the integrator which indicates the
average irregularity either as PMD or CV% according to the model
used. The actual tester is illustrated which shows the following
external features: i) the comb of eight measuring capacitors of
different sizes ii) the creel and guides to control the material
iii) the traverse rollers which can control the material speed over
a range from 2-100 yd/min iv) the control switches v) the meter on
the main unit which indicates the momentary variations in the
material vi) the integrator which indicates the P.M.D. or C.V. vii)
the high-speed pen recorder whose chart speed can be varied between
1 & 40 in./min. 3.1.1) Mass evenness, measuring principal: i)
The sensor for measuring the evenness of slivers, rovings or yarns
is a capacitive measuring sensor: ii) A high-frequency electric
field is generated in the sensor slot between a pair of capacitor
plates. If the mass between the capacitor plates changes, the
electrical signal is altered and the output signal of the sensor
changes accordingly. iii) The result is an electrical signal
variation proportional to the mass variation of the test material
passing through. iv) This analog signal is then converted into a
digital signal, stored and processed directly by the USTER TESTER 5
computer. v) The capacitive measuring principle is very reliable
and has good signal stability. With this measuring principle not
only yarns, but also rovings and slivers can be tested. The Uster
is adjusted and balanced after a preliminary warming-up period.
Several points are noticeable:Textile Testing-II (TS-333) 10.
Abubakkar Marwat (05-NTU-05)Yarn Evenness10/193.1.2) Material
speed: In yarns, drafting wave variations have a wavelength of
about 2-2.5 times the mean fibre length. So the testing speed must
be chosen so that frequency of these fluctuations lies within the
capacity of the recording pen to follow them. For example, with a
yarn speed of 50 yd/min and a drafting wavelength of about 3 the
pen must be capable of responding accurately to 10
fluctuations/sec. The recorder of Uster can cope up with a yarn
speed of 100 yd/min. 3.1.3) Chart speed and chart contraction: The
yarn speed & chart speed ratio, i.e. the chart contraction, is
chosen to suit the type of variation being examined. For short term
variation a ratio of 8-20 is recommended. For medium term variation
a ratio of 40-160 is recommended. For long term variation a ratio
of 200-1000 is recommended. 3.1.4) Choice of measuring capacitor:
In order to achieve a change in capacity which is linearly related
to the amount of material between the capacitor plates the
thickness of the material relative to the size of the capacitor
must not exceed certain limits. In the Uster instruction manual a
Table states which capacitor in the comb must be used for the
different hanks and counts. 3.1.5) The imperfection indicator: The
introduction of the imperfection indicator in place of the Hy-Lo
offers the quality control department greater opportunities for
detailed analysis of faults in yarns. Signals from the main units
are fed to the imperfection indicator which simultaneously measures
neps, thick and thin places. A count of all three types of fault is
made and the results shown of separate counters. It is possible to
adjust the sensitivity of the system so that a chosen size of fault
is counted and smaller faults ignored. In 1964, a new set of Uster
yarn standards were introduced, the yarn parameters considered
being evenness, neps, thick places and thin places. Yarns spun from
staple fibres contain "IMPERFECTIONS. They are also referred to as
frequently occurring yarn faults. Neps-a fault length of 1mm having
cross-section 200 % of the average valueTextile Testing-II (TS-333)
11. Abubakkar Marwat (05-NTU-05)Yarn Evenness11/19Thick place-a
fault length of approximately the fibre staple length having a
cross-section of 50 % more than the average value Fig:USTER TESTER
5allows the following sensitivity thresholds for thick places:
+35%/+50%/+70%/+100%. Every time the selected limit is exceeded, a
thick place is counted.Thin place-a fault length of approximately
the fibre staple length, having a crosssection approx. 50 % less
than the average valueThe reasons for these different types of
faults are due to raw material or improper preparation process. A
reliable analysis of these imperfections will provide some
reference to the quality of the raw material used. Imperfection
indicator record imperfections at different sensitivity
levels:Textile Testing-II (TS-333) 12. Abubakkar Marwat
(05-NTU-05)Yarn Evenness12/19Thin place -30% : yarn cross section
is only 70% of yarn mean value -40% : yarn cross section is only
60% of yarn mean value -50% : yarn cross section is only 50% of
yarn mean value -60% : yarn cross section is only 40% of yarn mean
value Thick place +35% : the cross section at thick place is 135%
of yarn mean value +50% : the cross section at thick place is 150%
of yarn mean value +70% : the cross section at thick place is 170%
of yarn mean value +100%: the cross section at thick place is 200%
of yarn mean value Neps 400%: the cross section at the nep is 500%
of the yarn mean value 280%: the cross section at the nep is 380%
of the yarn mean value 200%: the cross section at the nep is 200%
of the yarn mean value 140%: the cross section at the nep is 140%
of the yarn mean value Thick places and thin places which overstep
the minimum actuating sensitivity of +35% and -30% , respectively,
correspond to their length to approximately the mean fibre length.
Medium length or long thick and thin places are to be considered as
mean value variations and are not counted by the instrument. The
standard sensitive levels are as follows Thin place : -50% Thick
place : +50% Neps : 200% ( 280% for open-end yarns) Neps can be
divided, fundamentally, into two categories: -raw material neps
-processing nepsThe raw material neps in cotton yarn are primarily
the result of vegetable matter and immature fibres in the raw
material. The influence of the raw material with wool and synthetic
fibres in terms of nep production is negligible. Processing neps
are produced at ginning and also in cotton, woolen and worsted
carding. Their fabrication is influenced by the type of card
clothing, the setting of the card flats, workers and strippers, and
by the production speeds used. 3.1.6) Uster yarn standards:
Advances in spinning technology and improvements in quality control
systems, have demanded standards on the quality of the yarns rather
than the characteristics of the intermediate products. Yarns from
all over the world were sampled and tested, the results analyzed
and the standards prepared. The representation of the standards is
in graphical form. Charts for combed and carded cotton, blends and
worsted-spun yarns are available, but for the purpose of
explanation we shall consider the charts for combed cotton
yarns.Textile Testing-II (TS-333) 13. Abubakkar Marwat
(05-NTU-05)Yarn EvennessTextile Testing-II (TS-333)13/19 14.
Abubakkar Marwat (05-NTU-05)Yarn Evenness14/19In figure 1, the yarn
count is on the logarithmic horizontal scale and the C.V.
percentage on the vertical scale. Suppose the yarn considered is a
40s (15 tex). Locating the 40 position on the count scale we travel
vertically until meet the 50% line; reading across to the vertical
scale we read off the value C.V. 16.2%. This means that of all the
40s combed yarns spun, 50% of them will have a C.V. of 16.2 or
worse, and 50% of them better (lower) than 16.2%. The spinning
technologist can therefore compare his own product with the
products of other spinners. If our own 40s combed yarn has a C.V.
of 13.2% we would be amongst the spinners of good quality yarns as
the intercept on the 5% line corresponds to a C.V. of 13.5%. In
other words, only one spinner in twenty spins 40s combed are evenly
as ourselves. Standard charts for thick and thin places, and neps,
are similarly constructed, the example shown in fig.2 being the nep
count chart. For our 40s combed cotton yarn the number of neps per
1000 m, for the 50% line, is 54. (On the carded yarn chart the
corresponding value for 40s is about 600) 3.1.7) Extreme
imperfections: With the selector switch set to Extreme
Imperfections the thick place, which are more than double the
average cross-section, can be counted. For worsted spinners two
limits have been fixed, +33% and 100% and the two counters register
the number of times that these limits have been exceeded. 4)
Mechanical method of sliver/roving evenness measurement: Principle
of mechanical method of evenness testing is compression of fibrous
strand. Wool Industries Research Association has developed W.I.R.A
sliver, roving levelness tester. It can provide a continuous record
of the test performed. Main features of the tester: Positively
driven roller R1, with a rectangular groove Negatively driven top
roller which has flange type shape and can be positioned into the
groove of roller R1 R2 is mounted on an arm (lever) which is
pivoted at P Recording pen and graph paper Test procedure: In order
to check different types of materials several pair of rollers is
available. For example, rollers with groove width of 1/32, 1/16,
1/8 and 1/4 . Suitable pair of rollers are mounted at the equipment
Magnification lever system is adjusted to get adequate pen movement
Pen movement can be adjusted from 20 times to 400 times of the top
roller up & down movement to get properly magnified trace Pen
to and fro movement is adjusted to get a trace between trace
paperTextile Testing-II (TS-333)11 2 inches on the 15. Abubakkar
Marwat (05-NTU-05)Yarn Evenness15/19Material speed to chart speed
can be varied from the gear box for material to chart speed ratio
of 2 to 100 of material speed inches/minIt is possible to derive
the co-efficient of variation by measuring the height of the chart
at large number of points, and carrying out the statistical
calculation. Assessment of result: The irregularity trace obtained
from the mechanical tester (WIRA) is recorded on chart paper having
30 divisions, each 1/10 inches wide. Redraw trace will be centered
at line 15 following procedure is adopted to determine standard
deviation and CV%of mass. Step1 = choose centre line at 15 Step2 =
mark two lines 16, 18 above centre line and two lines at 12, 14
below centre line Step3 = mark distance a,b,c on a plain paper and
measure sum up distance (a+b+c) for line 18, 16, 14, & 12.
Step4 = record sum up lengths in table form Step5 = in this trace
70 inches sliver had been checked to obtain 7 inches trace
calculate % length of trace on each line for line 18: 0.88/70 x 100
= 12.6 Subtract 12.6 form 100 for length = 100-12.6 = 87.4 Step6 =
prepare a sheet of probability paper by marking from
12,13,14,15,16,17,18 on vertical side. Mark horizontal scale (in
%age) for the worked out length % plotted. Step7 = draw the best
straight line through the plotted points Step8 = from straight line
read ordinate against values of horizontal line of 15.9%, 5%, and
84.1%. These ordinates would be 11.95%, 14.72%, 17.47% for this
mentioned test. Step9 = work out standard deviation S.D = max.
Ordinate value min. ordinate value/2 Textile Testing-II (TS-333)
16. Abubakkar Marwat (05-NTU-05)Yarn Evenness16/1917.47 11.95 2 = =
2.76 Step10 = work out co-efficient of variation of mass CV% =
S.D/mean chart height x 100 2.76= 46.72 = 5.9 % 5) Optical method
(Zweigle G580): This instrument uses optical method of determining
the yarn diameter and its variation. In the instrument an infra-red
transmitter and two identical receivers are arranged as shown in
Fig. the yarn passes at speed through one of the beams, blocking a
portion of the light to the measuring receiver. The intensity of
this beam is compared with that measured by Reference the reference
receiver and from the receiver difference in intensities a measure
of yarn diameter is obtained. The optical method measures the
variations in diameter of a yarn and not in its mass. For a
constant level of twist in Receiver the yarn the mass of a given
length is related to its diameter by the equation: Absolute Mass =
CD2 where C = constant, Infra-red yarn dia. light D = diameter of
yarn YarnHowever, in practice the twist level throughout a yarn is
not constant. Therefore the imperfections recorded by this
instrument differ in nature from those recorded by instruments that
measure mass variation. Advantages: it is very accurate like human
eye. Because of the way yarn evenness is measured, this method is
not affected by moisture content or fibre blend variations in the
yarn. Disadvantage: twist through the yarn is not same thereby
changing the diameter and hence results are not very accurate. 6)
Pneumatic Method: In this method the yarn to be tested is passed
through a narrow tube, into which a stream of air is being forced.
The air flow rate is then measured, usually by pressure change or
some associated phenomenon. In theory, the air-flow in an empty
tube is impeded, as yarn is inserted, by an amount related in some
way to the mass of material present in the yarn. Clearly, careful
calibration is a necessary procedure in using equipment of this
type and the relationship may not necessarily be a linear one. In
addition, the effects of such factors as temperature and
atmospheric pressure, as well as relative humidity, will have to be
controlled more carefully than usual.Textile Testing-II (TS-333)
17. Abubakkar Marwat (05-NTU-05)Yarn Evenness17/196.1) Procedure:
Two air streams are directed towards each other, and a bundle of
filaments is guided to meet the resulting jet at right angles. The
filaments are directed towards the stream of higher intensity,
which thus causes pressure fluctuations in both, and these changes
are measured in the stream of lower intensity to generate a signal
proportional to the mass of yarn interfering with air-flow. The
method is still relatively untried and unproved. 7) Acoustic
Method: Sound waves are used to measure the evenness of yarn. Yarn
is moved through a sound field between a sound generator and a pick
up device. Time taken for sound waves to move across the gap is
measured electronically. Transit time of sound is dependent upon
the weight of yarn in the gap. 7.1) Impulse Acoustic Method: A new
method was elaborated to determine the inner (transversal)
unevenness of multifilament chemical yarns and its defectiveness in
the yarns cross-section by means of the impulse-acoustic
spectrograms, both separately and in combination with an analysis
of the full stretching diagram. This method was applied for
different chemical yarns. There are no other methods of obtaining
such information, including all the standard testing methods
currently used. 7.1.1) Principles of the new impulse acoustic
method of yarn control: The impulse-acoustic emissionrecording
method is based on stretching the untwisted multifilament
structures (parallel fibres or bundles of filaments) and
accumulating the filaments deformation energy to rupture step by
step the structural elements, i.e. the separate filaments. The
deformation energy of every stretched filament comes free at
rupture, and gives returning impulses owing to the contraction
process. Therefore, at the moment of rupture, the energy of
contraction is transformed into to the energy of acoustic
oscillation. These impulses, their intensity, arrangement etc. are
recorded, and produce the acoustic spectrum, which is the picture
of deformation and the multi-element material destruction (of the
multifilament yarn) at the time of its deformation. It therefore
represents the picture of distribution of the yarn rupture. The
impulse-acoustic spectrum is shown in the coordinates of
deformation/impulse intensity. Textile Testing-II (TS-333) 18.
Abubakkar Marwat (05-NTU-05)Yarn Evenness18/19 The impulse acoustic
spectrum consists of a series of separate impulses located at the
axis of elongation or the time of deformation. Great differences
exist among the acoustic spectra of various yarns. The spectra
differ in the impulse intensities and their positions in relation
to the elongation. These data give an excellent reflection of
individual filaments breaking arrangements. Higher unevenness and
defectiveness of yarn correspond to a broader width of the
spectrum. The intensity and position of the first impulse, or a
small group of impulses, give information about more defective
filaments. It is necessary to stress that the information concerned
with the first impulse is perceived only by the impulseacoustic
method. This information cannot be perceived in a standard
stretching diagram such as that commonly carried out by
dynamometric tests (loaddeformation curve). At present, together
with the impulse-acoustic tests, a traditional load-deformation
diagram is also recorded, as it was established that the best
information and interpretation of the test results can be obtained
by combination of the impulseacoustic spectrum with the full
deformation diagram (up to the point of the yarn rupture). The
acoustic spectrum and the full stress-strain curve both permit
every impulse coordinate to be found. 7.1.2) Equipment for tests:
The testing device for the impulse-acoustic method consists of a
low noise and vibration level electronic dynamometer with an
additional acoustic system. A scheme of the testing device is shown
in Fig. 3. The FPZ-10/1 Tiratest testing machine (dynamometer) from
Thringisches Prfmaschinenwerk GmbH (Germany) was applied for our
research. The measuring system includes standard deformation and
load sensors and an additional acoustic measuring chain composed of
a sensor, amplifier, and amplitude detector. The acoustic
piezo-sensor is placed on the dynamometer clamp, as shown in Fig.
4. Every filament break while stretching the yarn gives an acoustic
returning impulse which is registered by the measuring system. The
form of the acoustic signal is shown in Textile Testing-II
(TS-333)Figure.4. Clamp; scheme of sensor position; 1 - sensor, 2
clamp, 3 rod, 4 connecting cable, 5 yarn.Figure 5. Form of acoustic
impulse corresponding to single filament rupture; U amplitude of
signal, t time. 19. Abubakkar Marwat (05-NTU-05)Yarn
Evenness19/19Figure 5. All signals from the three sensors are sent
to an analogue-digital transformer, and next to a computer for
registration, processing and indication. The resulting information
includes the impulse-acoustic spectrum combined with the full
stretching diagram stored in the computer memory and visible on the
monitor. According to the constant amplification factor, the height
of each amplitude is proportional to the energy impulse returning
from the filament ends. In this way, all the impulses of filament
breaks as well as the full stretching diagram are reordered
(Fig.6).It should be stressed that an appropriate sensitivity and
minimal response time of the electronic system recording every
impulse are necessary to separate each acoustic impulse while
testing yarns consisting of a high number of filaments. Standard
and special software were applied to analyze the test results.
7.1.3) Sample preparation & testing procedure: The yarn samples
are initially untwisted to zero twist; in this manner the bundle of
parallel filaments is prepared. To fix the yarns, its ends are
glued between two pieces of paper (with polyvinyl acetate glue, or
another with a short drying time). The samples are conditioned at
standard conditions (relative air humidity of 65 2% and temperature
of 20 2 ). The velocity of the clamp movement guarantees obtaining
a time to sample break of 20 2 sec. If another procedure was
necessary it would be used. The clamping length is within the range
of 30 mm to 100 mm. This length should be correlated with the
friction forces between filaments. If the friction between
filaments is high, a short length is necessary. However, the best
length for standard tests is 100 mm. The number of tests for one
kind of sample should be 5 (or 10 in the case of filaments of high
unevenness). Index of Irregularity::Index of irregularity (I) is
the measure used to find out the extent to which actual
irregularity deviates from that due to random. Index of
Irregularity=CVa/CVr where CVa is actual measured irregularity. A
higher value means that there is more scope for improving the
processes. Table below shows how irregularity due to random
arrangement and Index of irregularity vary with count. Count 20
card 30 card 40 combed 60 combed 100 combedCVr 7.7 9.26 10.5 12.5
15.2CVa 17 17.5 14 15.5 18I 2.20 1.88 1.33 1.24 1.18It will be seen
that while Irregularity due to random arrangement increases Index
of irregularity reduces with increase in count. CVr reduces from
yarn to roving and further from roving to yarn because of the
increase in number of fibres in cross-section. Index of
irregularity on the other hand increases from yarn to roving and
then from roving to yarn. Typical results are given in Table below:
Material Yarn 20s Roving 1Ne Drawing sliver Yarn 100s Roving 100s
(2.8) Ne Drawing sliver(100s) 0.19NeTextile Testing-II (TS-333)CVr
7.7 1.7 0.6 15.2 2.54 0.66CVa 17 6 4 18 5 2.5I 2.20 3.52 6.68 1.18
1.96 3.79