Yarn Clearing Systems

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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.



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.



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)



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



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

Add this site to your Favourites.

WINDING - 3

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Yarn Clearer Settings



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



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.



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



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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