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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