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YARN FAULTS AND CLEARING:
It is still not possible to produce a yarn without faults for various reasons. Stickiness of cotton
can contribute to the formation of thick and thin places. Fly liberation in Ringframe department is
one of the major reasons for short faults in the yarn because of the fly gets spun into the yarn.
Hence it is not possible to have fault free yarn from ringspinning, it is necessary to have yarn
monitoring system in the last production process of the spinning mill. As physical principle for
electronic yarn clearing the capacitive and the optical principle have established. Both principles
have their advantages in specific applications.
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Depending upon the rawmaterial, the machiery set up, production and process parameters,
there are about 20 to 100 faults over a length of 100 km yarn which do not correspond to the
deisred appearance of the yarn. This means that the yarn exhibits a yarn fault every 1 to 5 km.
These faults are thick and thin faults, foregin fibres and diry places in the yarn.
The yarn faults which go into the woven or knitted fabric can be removed at very high costs or
can not be removed at all. Therefore the yarn processing industry demands a fault free yarn.
The difference between frequent yarn faults and seldom occuring yarn faults are mainly given
by the mass or diameter deviation and size. These faults are monitored by classimat or clearer
installation on winding.
Each yarn contains, here and there, places which deviate to quite a considerable extent from
the normal yarn corss-section. These can be short thick places, long thin places , long thick
places or even spinners doubles. Eventhough such events seldom occur, they represent a
potential disturbance in the appearance of the fabric or can negatively influnece subsequent
processing of the yarn.
Short thick places are those faults which are not longer than approximately 8 cms, but have a
cross-sectional size approx. twice that of the yarn. These faults are relatively frequent in all spun
yarns. To an extent they are the result of the rawmaterial ( vegetable matter, non-seprated
fibres, etc). To a much larger extent, these faults are produced in the spinning section of the
mill and are the result of spun in fly. Short thick places are easily determinable in the yarn. In
many cases, they cause disturbances in subsequent processing. Once they reach a certain
size( cross-section and length) , and in each case accoridng to the type of yarn and its
application, short thick place fults can considerably affect the appearance of the finished
product.
Long thick places are much more seldom-occuring than the short thick places and usually
have a length longer than 40cms. In some cases, their length can even reach many meters.
Their cross sectional size approx. + 40% to +100% and more with respect of the mean cross-
section of the yarn. Long thick places will affect the fabric apperance. Faults like spinners
doubles are difficult to determine in the yarn, with the naked eye. On the other hand, they can
produce quite fatal results in the finished product. A spinners double in the warp or in yarn for circular knitting can downgrade hundreds of meters of woven , or knitted fabric.
Thin places occur in two length groups. Short thin places are known as imperfections, and
have a length approx. three times the mean staple length of the fibre. Their frequency is
dependent on the rawmaterial and the setting of the drafting element. They are too frequent in
the yarn to be extracted by means of the electronic yarn clearing.
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Long thin places have lengths of approx. 40cms and longer and a cross-sectional decrease
with respect to the mean yarn cross-section of approx.30 to 70%. They are relatively seldom-
occuring in short staple yarns, but much more frequently-occuring in long staple yarns. Long
thin faults are difficult to determine in the yarn by means of the naked eye. Their effect in the
finished product however, can be extremely serious.
The quite extensive application of electronic yarn clearing has set new quality standards
with respect to the number of faults in spun yarns.
It is therefore necessary to evolve a method of yarn fault classification before clearing the faults
in winding. The most important aspect is certainly the determination of the fault dimensions of
cross-sectional size and length. With such a cross-section and length classification and by
means of the correct choice of the class limits, the characteristic dimensions of the various fault
types can be taken into consideration, then a classification system will result which is suitable
primarily for satisfying the requirements of yarn clearing and yet allows, to quite a large extent,
for a selection of the various types of faults.
The yarn faults are classified according to their length and cross-sectional size, and this in 23
classes.
FIG: CLASSIMAT FAULTS:
y The cross-sectional deviations are given +% or -% values. i.e theupper limit, respectively , lower
limit with respect to the mean yarn fault cross-section is measure in %. The fault length is
measured in cms.
FIG: YARN CLEARING CONCEPT OF USTER QUANTUM CLEARER
N - NEPS
S- SHORT FAULTS
L-LONG FAULTS
CCP - COARSE COUNTS
CCM-FINE COUNTS
The classes and their limits are set out according to the following:
y Short thick place faults: 16 classes with the limits, 0.1 cm, 2cm, 4cm, and 8cm for the lengths
and +100%, +150%,+250%, and +400% for the cross-sectional sizes are provided. The classes
are indicated A1...D4. The classes A4, B4,C4,D4 contain all those faults, according to their
length, whose cross-sectional size oversteps +400%.
y spinners doubles: This refers to a class (with the indication E) for faults whose length oversteps
8cms and whose cross-sectional size oversteps +100 ( open to the right and upwards)
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y Long thick place faults and thick ends: The long thin place faults are contained in 4 classes with
the limits 8 cms and 32 cms for the lengths, and -30% , -45% and -75% for the cross-sectional
sizes. The classes are designated H1.....I2. The classes I1 and I2 are open to the right. i.e they
contain all those thin places having a size between -30 and -45%, respetively, -45% and -75%
and whose lengths are longer than 32 cms. The classification of the shorter thin places is of no
advantage in the analysis of the seldom-occuring faults.
FIG: A DIAGRAM FROM LOEPFE YARN CLEARER MANUAL
Types of Electronic Yarn Clearers
Electronic Yarn Clearers available in the market are principally of two types ±capacitive and
optical. Clearers working on the capacitive principle have µ mass¶as the reference for performing
its functions while optical clearers function with µ diameter¶ as the reference. Both have their
merits and demerits and are equally popular in the textile industry. Besides the above basic
difference in measuring principle, the basis of functioning of both the types of clearers are
similar if not exactly same. Since most of the other textile measurements like, U% / CV%, thick
and thin places etc., in various departments take into account mass as the reference parameter,
the functioning of the capacitive clearer is explained in some detail in the following sections.
Functioning Principle
The yarn is measured in a measuring field constituted by a set of parallely placed capacitor
plates. When the yarn passes through this measuring field (between the capacitor plates), an
electrical signal is produced which is proportional to the change in mass per unit length of the
yarn. This signal is amplified and fed to the evaluation channels of the yarn clearing installation.
The number and type of evaluation channels available are dependent on the sophistication and
features of the model of the clearer in use. Each of the channels reacts to the signals for the
corresponding type of yarn fault. When the mass per unit length of the yarn exceeds the
threshold limit set for the channel, the cutting device of the yarn clearer cuts the yarn.
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Textile Technology :: "Spinning"y HOMEPAGE
Recommended Textile spinning Articlesy COTTON MIXING y BLOWROOM PROCESS y CARDING PROCESS y THEORY OF CARDING y CARD CLOTHING y Open End Spinning y RING FRAME y RINGS AND TRAVELLER y COM-4 AND ELITE SPINNING
y WINDING y YARN CONDITIONING
Process Parametersy PROCESS PARAMETERS IN BLOWROOM y PROCESS PARAMETERS IN CARDING y PROCESS PARAMETERS IN COMBING y PROCESS PARAMETERS IN DRAW FRAME y PROCESS PARAMETERS IN SPEED FRAME y PROCESS PARAMETERS IN RING SPININING y CONSTANTS AND CALCULATIONs y Technological value of cotton fibre
Used (pre-owned) Textile Machinery Dealersy Asia y Europe y North America
ELECTRICAL DEPARTMENTy ELECTRICITY y INDUCTION MOTOR y POWER FACTOR
Humidification in spinning milly HUMIDIFICATION
y COMPRESSED AIR
Most popular Textile Articlesy DRAWING PROCESS y AUTOLEVELLING y COMBING PROCESS y SPEED FRAME
YAR N Q UALITY ASSURANCE y FIBRE TESTING-1
FIBRE TESTING-2
5/12/2018 Yarn Clearing Systems - slidepdf.com
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y COTTON FIBRECOTTON FIBRE-1
y EFFECT OF COTTON PREPARATION ON HVI AND AFIS y HVI-FIBER TESTING y COTTON LENGTH PROPERTIES y EFFECT OF FIBER LENGTH ON YARN QUALITY
y PROCESSING STICKY COTTON Polyester manuf acturing
y POLYESTER FIBRE
YAR N TESTING y YARN TESTING y YARN EVENNESS-1 y YARN EVENNESS-2 y YARN HAIRINESS y STUDIES ON YARN HAIRINESS BY MR.KAMATCHI SUNDARAM- VOLTAS, INDIA y BARRE IN FABRIC y BARRE CONTROL y YARN REQUIREMENT FOR KNITTING
LINEAR PROGRAMMING y PRODUCT MIX USING LP FOR A SPINNING MILL y TEXTILE COSTING y FACTORS AFFECTING OVERALL CONTRIBUTION- CASE STUDY USING LP
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Yarn Clearer Settings
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The yarn clearer has to be provided with certain basic information in order to obtain the
expected results in terms of clearing objectionable faults. The following are some of them -
a. Clearing Limit:
The clearing limit defines the threshold level for the yarn faults, beyond which the cutter is
activated to remove the yarn fault. The clearing limit consists of two setting parameters -
Sensitivity and Reference Length.
i. Sensitivity - This determines the activating limit for the fault cross sectional size.
ii. Reference Length ± This defines the length of the yarn over which the fault cross ± section is
to be measured. Both the above parameters can be set within a wide range of limits depending
on specific yarn clearing requirements. Here, it is worth mentioning that the µ reference length¶
may be lower or higher than the actual µ fault length¶. For a yarn fault to be cut, the mean value
of the yarn fault cross-section has to overstep the set sensitivity for the set reference length.
b. Yarn Count :
The setting of the yarn count provides a clearer with the basic information on the mean value of
the material being processed to which the clearer compares the instantaneous yarn signals for
identifying the seriousness of a fault.
c. Material Number :
Besides the yarn count there are certain other factors which influence the capacitance signal
from the measuring field like type of fibre (Polyester / Cotton / Viscose etc.) and environmental
conditions like relative humidity. These factors are taken into consideration in the µ Material
Number¶ . The material number values for different materials are provided in Table.
Table :material number
7.5 cotton, wool, viscost8.5 very damp material (80%Rh)
6.5 very dry material(50% RH)
6 natural silk 7 very damp material
5 very dry material
5.5acetate, acrylonitrile
polyamide
50 to 80% RH
50 to 80% RH
4.5 polypropylene, poly
ethylene50 to 80% RH
3.5 polyester 50 to 80%RH
2.5 polyvinyl chloride 50 to 80% RH
From the values given in the table it could be seen that, for water absorbent fibres like cotton,
the Material Number is changed by 1 for a 15% change in Relative Humidity. A reduction in
material number results in a more sensitive setting causing higher fault removal. For blended
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yarns, the material number is formed from the sum of the percentage components of the blend.
For instance, when a 67/33 Polyester / Cotton blend is run at an RH of 65%, the Material umber
should be set at (0.67 * 3.5) + (0.33 * 7.5) = 4.8.
d.Winding Speed:
The setting of the winding speed is also very critical for accurate removal of faults. It is
recommended that, instead of the machine speed, the delivery speed be set by actual
calculation after running the yarn for 2-3 minutes and checking the length of yarn delivered.
Setting a higher speed than the actual is likely to result in higher number of cuts. Similarly a
lower speed setting relative to the actual causes less cuts with some faults escaping without
being cut. In most of the modern day clearers, the count, material number and speeds are
monitored and automatically corrected during actual running of the yarn.
Fault Channels:
The various fault channels available in a latest generation yarn clearer are as follows:
1. Short Thick places
2. Long Thick Places
3. Long Thin Places
4. Neps
5. Count
6. Splice
The availability of one or more of the above channels is dependent on the type of the yarn
clearer. Most of the modern clearers have the above channels. Besides detection of the various
types of faults, with latest clearers, it is also possible to detect concentration of faults in a
specific length of yarn by means of alarms(cluster faults).
Contamination Clearing:
Detection of contamination in normal yarn has become a requirement in recent times due to the
demands by yarn buyers abroad. Therefore, some of the optical yarn clearers have an
additional channel to detect the contamination in yarn. This is mostly used while clearing cotton
yarn. The various facilities available in the yarn clearers nowadays enable precise setting and
removal of all objectionable faults while at the same time ensure a reasonably high level of productivity.
SPLICING:
A high degree of yarn quality is impossible through knot, as the knot itself is objectionable due
to its physical dimension, appearance and problems during downstream processes. The knots
are responsible for 30 to 60% of stoppages in weaving.
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Splicing is the ultimate method to eliminate yarn faults and problems of knots and piecing. It
is universally acceptable and functionally reliable. This is in spite of the fact that the tensile
strength of the yarn with knot is superior to that of yarn with splice. Splicing is a technique of
joining two yarn ends by intermingling the constituent fibres so that the joint is not significantly
different in appearance and mechanical properties with respect to the parent yarn. The
effectiveness of splicing is primarily dependent on the tensile strength and physical appearance.
Splicing satisfies the demand for knot free yarn joining: no thickening of the thread or only
slight increase in its normal diameter, no great mass variation, visibly unobjectionable, no
mechanical obstruction, high breaking strength close to that of the basic yarn under both static
and dynamic loading, almost equal elasticity in the joint and basic yarn. No extraneous material
is used and hence the dye affinity is unchanged at the joint. In addition, splicing enables a
higher degree of yarn clearing to be obtained on the electronic yarn clearer.
Splicing technology has grown so rapidly in the recent past that automatic knotters on modern
high speed winding machine are a thing of the past. Many techniques for splicing have been
developed such as Electrostatic splicing, Mechanical splicing and Pneumatic splicing. Among
them, pneumatic splicing is the most popular. Other methods have inherent drawbacks like
limited fields of application, high cost of manufacturing, maintenance and operations, improper
structure and properties of yarn produced.
Pneumatic Splicing
The first generation of splicing systems operated with just one stage without proceeding to
trimming. The yarn ends were fed into the splicing chamber and pieced together in one
operation. Short fibres, highly twisted and fine yarns could not be joined satisfactorily with such
method. Latest methods of splicing process consist of two operations. During the first stage, the
ends are untwisted, to achieve a near parallel arrangement of fibres. In a second operation the
prepared ends are laid and twisted together.
Principle of Pneumatic Splicing
The splicing consists of untwisting and later re-twisting two yarn ends using air blast, i.e., first
the yarn is opened, the fibres intermingled and later twisted in the same direction as that of theparent yarn. Splicing proceeds in two stages with two different air blasts of different intensity.
The first air blast untwists and causes opening of the free ends. The untwisted fibres are then
intermingled and twisted in the same direction as that of parent yarn by another air blast
Structure of Splice
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Analysis of the longitudinal and transverse studies revealed that the structure of the splice
comprises of three distinct regions/elements brought by wrapping, twisting and tucking /
intermingling.
Wrapping :
The tail end of each yarn strand is tapered and terminates with few fibres. The tail end makes a
good wrapping of several turns and thus prevents fraying of the splice. The fibres of the twisting
yarn embrace the body of the yarn and thus acts as a belt. This in turn gives appearance to the
splice.
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