Lecture for Mtm Manager and Technicians

8/2/2019 Lecture for Mtm Manager and Technicians

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OUT LINEYarn and yarn forms

Classification of yarn

Spun and filament yarns

Ring, rotor and air jet spinning systems

Structure of ring, rotor and air jet spun yarns

Spun yarn characteristics by spinning system

Compact ring spinning

Core yarn spinning

Yarn quality for knitting

New concepts for knitting yarn selection

Yarn twist, irregularity, friction, flexural and torsional rigidity

Major yarn faults contributing 25% to the rejections


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Yarn

An assembly of substantial length and relatively smallcross-section of fibers or filaments with or without twist.

Yarn forms

A number of fibers twisted together (spun yarn);

A number of filaments laid together without twist

A number of filaments laid together with a degree of twist;

A single filament with or without twist (a monofilament); or A narrow strip of material, such as paper, plastic film, or

metal foil, with or without twist, intended for use in a textile

construction


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Yarns

Staple Spun Yarn

As per FiberLength

1. Short staple

(60 mm)

As per YarnConstruction

1. Single

2. Plied

3. Cabled

4. Braided

5. Fancy

As per Spinning SystemRegular

1. Ring Spun Compact

2. Rotor Spun

3. Core spun

4. Air Jet Spun

5. Twistless Spun

6. Friction Spun

7. Wrap Spun

8. Fasciated Spun

Filaments

Monofilament

Multifilament

Intermingled

Textured

Tape

Classification of Yarn


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The yarn consists of staple fibers which are assembled and

bound together by various means to produce the required

characteristics such as strength, handle, appearance etc is

called spun yarn.

The yarn consists of parallel filaments lying close together and

virtually straight running the whole length of yarn. The yarns

with one filament are referred to as monofilaments and those

with more than one as multifilament's.

SPUN YARN

FILAMENT YARN


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RING SPINNING


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ROTOR SPINNING


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AIR JET SPINNING


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A- Image of ring yarn structure (Helically aligned fibers)

B- Image of rotor yarn structure (Surface with the wrapper fibres)

C- Image of vortex air jet yarn structure (Equivalence with ring yarn)

A B C


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COMPACT RING SPINNING


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Filament Core Yarn Spinning


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Elastic Core Yarn Spinning


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Yarn quality refers to whether the yarn meets the minimum

requirements of the knitter.

Yarn unevenness, imperfections (thin, thick and neps), hairiness,

strength, elongation, twist, uniform waxing and appearance are of

much importance.

High fluctuation in yarn quality is an evil for any end-use. It is

better to keep medium level of yarn quality by strict quality control

than achieving high level but without consistency. Hence it isadvisable to fix the standards for different yarn characteristics for

cotton spun yarns for different end uses.

Next slide provide an example to fix quality requirement for knitting

YARN QUALITY


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Yarn CharacteristicRequired value for 30S

Combedother combed counts

Average count 30 ( 29.6 to 30.4) nominal count plus or minus 1.3%

Count C.V% less than 1.5 less than 1.5%

Twist Multiplier 3.5 to 3.6 3.5 to 3.6

TPI C.V% less than 2.5 less than 2.5%

U% 9.2 to 9.8 5 to 10 % Uster Stat . value

-50% thin place / 1000m less than 4 5 to 10 % Uster Stat . value

-30% thin place / 1000m less than 650 5 to 10 % Uster Stat . value

+50% thick place / 1000 m less than 30 5 to 10 % Uster Stat . value

+200 Neps / 1000m less than 50 5 to 10 % Uster Stat . value

Total Imperfection / 1000 m less than 85 5 to 10 % Uster Stat . value

RKM ( tenacity) gms /tex more than 16.5 more than 16.5

RKM C.V% less than 7.5 % 5 to 10 % Uster Stat . value

Elongation % more than 5.5 more than 5.5

Hairiness H 4.0 to 4.5

Hairiness Standard Deviation less than 1.5 25% Uster stat value

Objectionable classimat faults(both short

and long)less than 1 per 100 km less than 1 per 100 km

Total classimat faults less than 150 5 to 10 % Uster Stat . value

H1- thin faults less than 5 per 100 km 5 to 10 % Uster Stat . value

shade variation on cones in UV lamp no shade variation no shade variation

QUALITY STANDARDS FOR COTTON COMBED YARN


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Unevenness It is mass variation within the sample of yarn

Imperfections Thick and thin places have a length equal tothe fiber mean length, while neps are those thick places which

are shorter than 4 mm. Thin and thick places are counted at

sensitivity levels of 50 % and +50 % below and above themean thickness of yarn while neps are counted at sensitivitylevel of + 200 % above the mean thickness.

Hairiness Hairiness is a measure of the amount of fibresprotruding from the structure of the yarn. The hairiness index H

corresponds to the total length of protruding fibres within the

measurement field of 1cm length of the yarn.


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The practice for the assessment of hosiery yarn quality is on the lines

with the established norms for weaving or for general understanding of

yarn grade rather than anything specific to knitting, except waxing. The

purchase of yarn is based on the general parameters like count, U%,

imperfections, strength, elongation and twist. Most of the knitters test

only the count for setting the GSM of the fabric.

If so, do the knit structure and knitting process have no specific

requirements compared to the weaving! As we know that knit fabrics

and their process requirements are different from weaving. So it is

necessary to think on these lines to improve the quality of knit fabrics

because the quality of the knit fabrics in the future will be defined forvariation in loop parameters at micro level such as loop-to-loop

variation in dimension, geometrical shape of loop and localized

variation in loop density.

So there should be specific system for assessing the yarn quality according to

the requirements of knitting process and knitting fabrics.

NEW CONCEPTS IN KNITTING YARN SELECTION


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An Ideal Loop

AB Loop length, AC & BD Loop arms


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The quality of knitting yarn has to be considered with due

weightage to the new aspects. Uniform loop dimensions (looplength, loop width and loop height), even loop geometrical shape

and controlled localized variation in loop dimensions are very

important to improve the knit structure. Similarly, variation in

GSM, spirality are the problems encountered regularly.

For this, understanding the effects of yarn twist, irregularity,

coefficient of friction, flexural and torsional rigidity are very

important .


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Twist in knitting yarn should be less, a fact known to alltechnologists. Still in a few cases, one finds yarn of higher twist being

preferred on the ground that it performs well in knitting in terms of

lesser yarn breakages. That is true but the benefit is at the cost of

fabric quality.

Knit structures are formed by bending the yarn into a loop andthen interlacing them to create a fabric. The curvature of loop would

be smooth and well defined if the bulkiness of the yarn is higher. The

bulkiness eliminates sharp bending and improves resiliency of the

structure, and these fabrics are expected to stretch easily andrecover during use.

The very purpose of using low twist yarn is to achieve thissmooth curvature to loops and high resiliency to fabric.

YARN Twist


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For obtaining smooth curvature to loop and its uniformity , the yarn

should be uniform in thickness and imperfections should be minimum.The thin place in yarn receives more twist resulting in compact

structure, and thus sharp bends in loop

while thick place receives less twist and forms a large curvature at loop.

The co-efficient of friction at thin places might be higher due toincreased twist, which might be further aggravated by probable low wax

pick-up.

Waxing to cotton knitting yarns is done to reduce the friction from 0.24

to 0.14. If waxing is not uniform, it can definitely change knitting tension

and loop dimensions due to variation in yarn coefficient of friction.

Similarly, uniform moisture in the cones is important, because

coefficient of friction also varies as a function of moisture.

CO-EFFICIENT OF FRICTION

YARN IRREGULARITY


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a) Uniform loop b) Deformed loop


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Flexural and torsional properties of spun yarns depend onbending, torsional, and tensile properties of staple fibres, twist in

yarn, thickness of yarn, compactness and strain energy stored in

yarn, etc. All these parameters can vary from yarn to yarn due to

changes in spinning condition and yarn conditioning afterspinning, though their general properties are more or less same.

The loop dimensions can, therefore, vary when yarns of different

flexural and torsional properties are mixed or if the yarn has

continuous variation in these parameters.

FLEXURAL AND TORSIONAL RIGIDITY


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Unevenness, thin, thick and neps

Stiff yarn - Higher TPI ( holes)

Higher friction

High hairiness variation

Mixed properties of yarn - "Barre"

White specs(immature fibres)

Kitties ( vegetable matters, dust content)

Lower elongation and elasticity

Contamination

Major yarn faults contributing 25% to the rejections


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Cotton-spun yarns for knitting should exhibit good hand orsoftness. This is made easier, because these yarns do not need to be

as strong as weaving yarns and therefore need less twist. This lower

twist leads to softer yarn and fabric.

Yarn torque or liveliness should be at a minimum to help preventexcessive fabric shrinkage, skew, and torque

Good elongation values in the yarn will reduce fabric holes

Good evenness values will prevent machine stops and fabric holes

Thick places in the yarn need to be minimized because they canlead to yarn tension problems, broken needles, and bent latches.

FURTHER POINTS

Lecture for Mtm Manager and Technicians

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