YARN
MANUFACTURING TECHNOLOGY
All fabrics- except
plastics and non-woven’s- depend upon the use of yarns. A yarn is an assemblage
of fibres that are laid or twisted together to form a continuous strand. Yarns
may be made from either staple fibres or filament fibres. Staple fibres are
twisted into yarns; filament fibres need little or no twist to hold them
together in yarns. The type and length of fiber, the type, ply, and size of
yarns, and the amount of twist given to yarns determine many of the
characteristics of fabrics made from the yarns. For example, fabrics
constructed of spun yarns are less smooth than fabrics constructed of filament
yarns. They also have a lower luster. Cord or rib fabrics contain ply or larger
yarns in the rib direction.
Single Yarns
are made from single filaments or from group of staple or filament fibres
twisted together to form the desired yarn. Monofilament, multifilament and spun
yarns are all single yarns.
Ply Yarns
are made by twisting together two or more single yarns. Each part of the yarn
is called a ply. Most ply yarns are twisted in the opposite direction to
the twist of their component singles. Ply yarns are stronger than their equivalent
single yarns of the same diameter and fibre.
Cord Yarns are ply yarns twisted together. They are seldom used in
conventional fabrics.
Carded yarn:
A yarn produced from fibres that have been carded but not combed.
Carding is a process, which
eliminates fibers too short for inclusion in the spun yarn. The process also
removes dirt and foreign matter still remaining in the fiber mass, and arranges
the fibers into a very thin layer.
Combed yarn: Yarn
produced from fibres that have been carded (or prepared) and combed.
The combing process is an
additional step beyond carding. In this process the fibers are arranged in a
highly parallel form, and additional short fibers are removed, producing high
quality yarns with excellent strength, fineness, and uniformity.
Yarns may be made entirely
of one fibre (homogeneous) and be
classified as such by the name of the fibre used. Or yarns may be a blend of
two or more fibres the names of which are included in the description of the
yarn. Yarns are blended to capitalize on the good qualities of a fibre and to
minimize its weaker qualities by the combining of fibres that complement each
other in the desirable characteristics they provide.
Blended yarns
may be combined or blended in any of these ways:
•by mixing staples fibres
before they are spun
•by combining filament
fibres before adding twist
•by combining simple yarns
of different fibre content into a ply yarn
A combination can also be
achieved by blending two generically different polymers before they are spun.
Elastomeric fibre yarns are
made from rubber or spandex fibres. They differ from stretch yarns that are
made by texturising. Elastomeric yarns may be Covered, Core-spun or bare
elastic yarns.
In addition, Metallic
yarns, Fibrillated or Tape yarns are used in the textile industry.
100% Cotton: The yarn has 100% cotton fiber.
P/C or T/C
: (polyester/cotton or Terelyne/cotton):
Yarn produced by blending cotton and
polyester fibres
CVC: (Chief
value cotton): A blended yarn having
more percentage of cotton as compared to that of polyester. For example, Cotton
: Polyester 70 : 30 or 60 : 40.
Core yarn: Yarn consisting of a central thread surrounded by staple
fibres. The yarn has the strength and elongation of the central thread whilst
exhibiting most of the other characteristics of the surface staple fibres.
Example 1: A sewing thread consisting of
a central synthetic continuous-filament yarn surrounded by cotton fibres.
Example 2: Worsted yarn with bulked-nylon
core, e.g., typically 1/24s worsted count (37 tex
Example 3: A spun yarn from either
natural or man-made fibres incorporating an elastomeric core, These yarns are
normally used in stretch fabrics.
6. yarn count and lot
number
Yarn count: The
'count' of yarn is a numerical expression, which defines its fineness.
Definition given by The Textile Institute says "Count: A number indicating
the mass per unit length or the length per unit mass of yarn."
There are two
types of counting systems-
1.
Direct system: In
a direct yarn counting system the yarn number or count is the weight of a unit
length of yarn. Example: Tex
2.
Indirect system:
In an indirect system the yarn number or count is the number of 'units of
length' per 'unit of weight'. Example: English count (Ne), Metric
count (Nm).
Normally
according to mill practice count stands for English count and can be defined as
the number of hanks (1 hank = 840 yards) of yarn weighting 1 lb. The higher the
count number the finer is the yarn. For example, 40 Ne means, 840 X
40 yards of this yarn will weigh 1 lb.
Yarn counts commonly used in BTL
YARN
|
Ratio
|
Available Count
|
||||||||||
100 % Cotton (carded & combed)
|
10/1
|
16/1
|
20/1
|
30/1
|
40/1
|
50/1
|
80/1
|
100/1
|
30/2
|
40/2
|
80/2
|
|
100/2
|
||||||||||||
PC (Poly :Cotton)
|
70:30
60:40
65:35
80:20
|
12.5
|
20/1
|
30/1
|
16/1
|
45/1
|
||||||
Chief value
cotton (CVC)
|
70:30
65:35
80:20
|
30/1
|
38/1
|
45/1
|
26/2
|
|||||||
Polyester/cotton core spun
|
32/2
|
16/1
|
||||||||||
Lycra core spun
|
16+ 70d
|
20+ 70d
|
30+ 70d
|
40+ 70d
|
||||||||
Yarn Lot
Number: This number is the Grey yarn lot number from Padma Textiles Limited.
Yarn with different lot numbers is made from raw material of different sources.
Yarn of same count but different lot numbers can have different inherent
properties that can affect weaving and dyeing.
Yarn twist
can be defined as the spiral turns given to a yarn to hold its constituent
fibres or threads togather.
Twist in yarns brings the
fibres closer together and makes them more compact. Twist is necessary in order
to make yarns from staple fibres. In contrast, fabrics can be made from
filament yarns, which have little or no twist.
The amount or degree of twist is expressed by the
intended end-use of the yarns or in a more technical way as the number of turns
per inch, expressed as the tpi. As the degree of twist is increased, the yarns
become harder, its lustre decreases, its strength increases up to a certain
point of twist, and it becomes shorter in length. Yarns of very high twist are used
to produce the crinkle in true crepe fabrics. Yarns of very low twist are used
in fabrics to be napped.
There are only two directions of yarn twist - clockwise and
counter clockwise. Either direction can be used. Counter-clockwise twist is
known as "S" twist while clockwise is known as "Z" twist.
The direction of twist also affects fabric characteristics and 'Z' twist is the
standard twist used for yarns. 'S' twist is used for special purposes and also
for ply yarns.
Twist factor; twist multiplier: In a yarn, the product of twist level and the square
root of the linear density.
The figure given below describes the essential stages
in converting loose fibres into yarns.
The loose fibre A is brought by carding and combing
into the form of a sliver B in which
the fibres are fairly parallel and without twist. The sliver is then drawn and
simultaneously lightly twisted to give it the necessary strength to give the
finer roving C, and this is then finally
spun into fine yarn D.
Spinning:
The present participle of
the verb 'to spin' used verbally, adjectivally, or as a noun, meaning process
or the processes used in the production of yarns or filaments.
The term may apply to:
(i) The
drafting and, where appropriate, the insertion of twist in natural or staple
man-made fibres to form a yarn;
(ii) The
extrusion of filaments by spiders or silkworms; or
(iii)
The production of filaments from glass, metals, fibre-forming polymers or
ceramics.
In the spinning of man-made filaments,
fibre-forming substances in the plastic or molten state, or in solution, are
forced through the holes of a spinneret or die at a controlled rate. There are
five general methods of spinning man-made filaments i.e. dispersion spinning,
dry spinning, melt spinning, reaction spinning, and wet spinning, but
combinations of these methods may be used.
In the bast and leaf-fibre
industries, the terms 'wet spinning' and 'dry spinning' refer to the spinning
of fibres into yarns in the wet state and in the dry state respectively.
Open-end spinning; break spinning:
A spinning system in which
sliver feedstock is highly drafted, ideally to individual fibre state, and thus
creates an open end or break in the fibre flow. The fibres are subsequently
assembled on the end of a rotating yarn and twisted in. Various techniques are
available for collecting and twisting the fibres into a yarn, the most
noteworthy being rotor spinning and friction spinning.
Rotor spinning:
A method of open-end
spinning which uses a rotor (a high-speed centrifuge) to collect individual fibres into a yarn. The fibres on
entering a rapidly rotating rotor are distributed around its circumference and
temporarily held there by centrifugal force. The yarn is withdrawn from the
rotor wall and, because of the rotation, twist is generated.
Friction spinning:
A method of open-end
spinning which uses the external surface of two rotating rollers to collect and
twist individual fibres into a yarn. At least one of the rollers is perforated
so that air can be drawn through its surface to facilitate fibre collection.
The twisting occurs near the nip of the rollers and, because of the relatively
large difference between the yam and roller diameters, high yarn rotational
speeds are achieved by the friction between the roller surface and the yarns.
Air-jet Spinning:
A system of staple-fibre
spinning which utilizes air to apply the twisting couple to the yarn during its
formation. The air is blown through small holes arranged tangentially to the
yarn surface and this causes the yarn to rotate. The majority of systems using
this technique produce fasciated yarns, but by using two air jets operating in
opposing twist directions it is possible to produce yarns with more controlled
properties but of more complex structure.
Centrifugal spinning:
A method of man-made fibre
production in which the molten or dissolved polymer is thrown centrifugally in
fibre form from the edge of a surface rotating at high speed.
The term is also used to
describe a method of yarn formation involving a rotating cylindrical container,
in which, the yarn passes down a central guide tube and is then carried by
centrifugal force to the inside of a rotating cylindrical container.
Dispersion spinning:
A process in which the
polymers that tend to an infusible, insoluble, and generally intractable
character (e.g., polytetrafluoroethylene) are dispersed as fine particles in a
carrier such as sodium alginate or sodium xanthate solutions. These permit
extrusion into fibres, after which the dispersed polymer is caused to coalesce
by a heating process, the carrier being removed either by heating or by a
dissolving process.
Draw-spinning:
A process for spinning
partially or highly oriented filaments in which the orientation is introduced
prior to the first forwarding or collecting device.
Dry spinning (man-made fibre production):
The spinning process
involving conversion of a dissolved polymer into filaments by extrusion and
evaporation of the solvent from the extrudate.
Flash spinning:
A modification of the
accepted dry-spinning method in which a solution of a polymer is extruded at a
temperature well above the boiling point of the solvent such that on emerging
from the spinneret evaporation occurs so rapidly that the individual filaments
are disrupted into a highly fibrillar form.
Flyer spinning:
A spinning system in which
yarn passes through a revolving flyer leg guide on to the package. The yarn is
wound-on by making the flyer and spinning package rotate at slightly different
speeds.
Melt spinning (man-made fibre production):
The spinning process
involving conversion of a molten polymer into filaments by extrusion and
subsequent cooling of the extrudate.
Reaction spinning (man-made-fibre production):
A process in which
polymerization is achieved during the extrusion of reactants through a
spinneret system.
Ring spinning:
A spinning system in which
twist is inserted in a yarn by using a revolving traveller. The yarn is wound
on since the rotational speed of the package is greater than that of the
traveller.
Wet spinning (man-made-fibre production):
The spinning process
involving conversion of a dissolved polymer into filaments by extrusion into a
coagulating liquid.
The extrusion may be
directly into the coagulating liquid or through a small air-gap. In the latter
case it may be known as dry-jet wet spinning or air-gap wet spinning.
The conventional cotton spinning system essentially
includes the following processing stages:
Blowroom
(opning/cleaning): The bales of raw
fibres are opened, cleaned and blended, then formed into laps.
Carding (and
Combing): The laps of fibre are
formed into fleece and then card slivers (rope-like strands). For higher grade
and finer yarns, the combing process is continued with the removal of short
fibres and neps.
Drawing: Several slivers are combined and drawn out into a
longer, thinner strand, i.e. sliver.
Roving (for
ring spinning): This process is to
draw out the sliver into an even finer strand (roving) and twist it slightly.
Spinning: The roving is drawn out (drafted) into yarn with
twist for strength and onto bobbins or tubes.
Twisting/
Winding: For plying two or more yarns
together, and rewinding the yarn-bobbins onto cheese or cones.
Blending:
A process or processes
concerned primarily with efficient mixing of various lots of fibres. Blending
is normally carried out to mix fibres, which may be of different physical
properties, market values, or colours.
Process overview:
The long continuous
filament fibers can't be used for blending because they're too long and too
difficult to handle. Also, natural fibers, such as wool and cotton, with which
many manufactured fibers are blended, are very short. Therefore, before
blending, manufactured fibers are first cut into short fibers, called staple
fibers. The staple fibers can more easily be twisted with the shorter natural
fibers, or with staple fibers of another manufactured fiber.
Staple fibers are created
by extruding many conitinuous filaments of specific denier from the spinneret
and collecting them in a large bundle called a "tow". A tow may
contain over a million continuous filaments. The tow bundle is then crimped, in
much the same way a curling iron is used to crimp a woman's hair, and is then
mechanically cut into staple fibers, usually ranging in length from 1 to 6-1/2
inches, depending how they are to be used.
Purposes of Blending:
Blending of different
fibers is done to enhance the performance and improve the aesthetic qualities
of the fabric. Fibers are selected and blended in certain proportions so the
fabric will retain the best characteristics of each fiber. Blending can be done
with either natural or manufactured fibers, in a variety of combinations and
percentages.
For example, polyester is
the most blended manufactured fiber. Polyester fiber is strong, resists
shrinkage, stretching and wrinkles, is abrasion resistant and is easily
washable. Blends of 50 to 65% polyester with cotton provides a minimum care
fabric used in a variety of shirts, slacks, dresses, blouses, sportswear and
many home fashion items A 50/50 polyester/acrylic blend is used for slacks,
sportswear and dresses. And, blends of polyester (45 to 55%) and worsted wool
creates a fabric which retains the beautiful drape and feel of 100% wool, while
the polyester adds durability and resistance to wrinkles.
Yarns used to create other
than comparatively smooth textures in fabrics may be achieved by the following
methods:
Modification in the spinning process of single yarns:
Various textures that
results from modifications in the spinning process of simple yarns are
identified by such terms as:
•Boucle yarn is one of the most widely used fancy yarns. It is
characterized by an effect yarn forming tight loops that project from the body
of the yarn at regular intervals.
•Slub yarns are made by varying the tension of yarn twist at regular
intervals to produce soft, thick elongated low twist areas (slub).
•Snarl yarn is made by twisting at one time two or more yarns held
at different tension. The effect yarn forms alternating unclosed loops along
both sides of the core yarn.
•Spiral or Corkscrew yarn is made by twisting together two yarns of
different thickness and twist, one soft and heavy and the other fine. The heavy
yarn is fed faster than the fine yarn and winds around it in a spiral
formation.
Modification of Thermoplastic filament yarns:
Variations in texture can
be done by application of heat to the thermoplastic yarns by texturization or
crimping. Texturization is the process by which filaments are distorted
to impart crimp, curl, coil and loop structures along their length to achieve
bulk, stretch and absorbency.
In texturization process, untextured
yarns are heated to plastic condition after it was distorted by texturing
element (spindle, gear, knife etc.). Then they are cooled to retain the
required shape. Textured yarns are basically three types:
•Bulk yarn - Mainly Gear crimping, Stuffer box and Air Jet methods
are used to produce these yarns of increased bulk but minimum stretch. These
processes can increase bulk from 100 to 300 percent. They are used as carpet
yarns and in sweater fabrics. The resultant fabrics are usually soft with some
degree of bulk and warmth but are light in weight.
•Stretch yarn - False twist and Edge crimping method is used to
produce this type of yarns having 300 to 500 percent elongation. In the first
method, the yarn is twisted, heat-set, and untwisted to get a coiled yarn. In
the second method, the hot filaments are drawn over a knifelike edge, which
flattens one side and causes the yarn to curl. They are used in swimsuits,
lingerie, stockings, one-sized garments where a form-fitting resilience without
pressure is required.
•Modified Stretch yarns - They are between the above two in stretch
properties (about 10 to 15 percent). They are made in basically the same manner
as stretch yarns except for a final step of heat-setting the yarn after the
untwisting step.
Yarns made from Bicomponent Fibres:
Bicomponent fibres are
composed of two different polymers joined physically in a single filament. The
components can be joined side by side or in a sheath-core structure. Due to
chemical differences of the components each shrinks to a different degree when
exposed to certain conditions such as heat or moisture. The difference in
shrinkage causes a pulling of the yarn into a crimped conformation creating
bulk and texture.
Defects present in yarn
can be classified in to five categories:
1)
Count variation: Variation in diameter along the length of yarn beyond acceptable
range.
2)
Unevenness or irregularity: it is mass variation per unit length (cm). This fault
is expressed as U% or CV% and evenness tester is used to measure it.
3)
Frequently occurring faults: These are the faults that occur in range of the 10 to
5000 times per 1000 m of yarn. Yarns spun from staple fibres contain
imperfections, which can be subdivided into three groups:
Thin places: Cross
sectional size -30% to -60% of normal yarn with fault length of 4 to 25 mm.
Thick places: Cross
sectional size +30% to +100% of normal yarn with fault length of 4 to 25 mm.
Neps: Cross sectional
size +140% to +400% of normal yarn with fault length of 1 mm. Neps are defined
as small tight balls of entangled fibres on linear textile strands.
4)
Seldom occurring faults: These are the thick and thin places in yarn which
occur so seldom that for their determination at least 100,000 m of yarn must be
tested. This faults may be classified into the following classes:
A.
Short thick
places: 1 to 8 cm and above +100%
B.
Long thick
places: Above 8 cm and above +45%
C.
Long thin places:
Above 8 cm and less than -30%
5)
Periodic faults: If any fault repeats after a certain length/time then the fault is
called periodic or systematic fault.
6)
Hairiness:
This is the measure for the protruding fibres from the yarn body.
7)
Lot mixing: Some times yarn lot can be mixed at the stages of
spinning process as well as in the preparatory section of weaving/knitting
mill. This type of mixing causes severe problem in subsequent processes.
The important yarn tests
are given below:
1)
Determination of
Yarn Count
2)
Determination of
Yarn Evenness
3)
Tensile Strength
Testing
4)
Twist Testing
5)
Abrasion
resistance
Determination
of Yarn Count:
To determine the yarn count
of a sample, it is needed to measure the length and weight of the sample. The
equipment used for this purpose are Wrap reel and Analytical balance or Knowles
balance or Quadrant balance etc. Beesley's balance can be used to get the yarn
count directly from the balance. When yarn specimen supplied is not sufficient
to perform the tests on the above methods, Beesley's balance can be used to
examine the yarn count with reliability.
Determination of Yarn Evenness:
The surface irregularity of
yarn is of particular importance in relation to processing properties, as even
with a well maintained mean count, the appearance of the fabric can sometimes
be affected considerably. Yarn evenness is assessed basically by deriving
either the variation along the length of a yarn in the mass per unit length (or
number of fibres per cross-section) or the variation in diameter. Visual
evaluation and electronic methods are used for this purpose.
Tensile Strength Testing:
Particular importance is
often attached to the tensile strength attained in a single or folded yarn of
particular type and composition. Yarn extension also plays a considerable role
in the processing of the yarn and in the end-use properties of the fabric
produced.
The range of instruments
which are available for testing the strength of yarns is quite wide e.g. Single
-thread testers operating on the principles of pendulum lever, inclined plane,
Strained gauge, and Constant-tension hank testers of the pendulum lever or
Ballistic type. Some of these instruments are relatively simple, some
complicated, some have recording devices, and some are automatic. The choice of
the best type to use is often difficult. Strength testing deals with the
finding of load-elongation curve or stress-strain curve and breaking point or
stress etc.
Twist Testing:
Generally, the Twist tester
is used to determine the number of twist per unit length or tpi manually.
Abrasion resistance:
Abrasion resistance is the
ability of a fibre to withstand the rubbing or abrasion it gets in everyday
use. This property of yarn plays an important part in its processing e.g. it
determines the friction occurring on thread guides. A measurement of abrasion
resistance is the number of cycles required to break the test specimen at a
given initial tension.
Classimat is a system,
which can detect seldom-occurring faults of yarn. Yarn clearer that are used
with automatic winders will detect only the large defects that may adversely
effect the quality of finished products. In contrast, classimat system can
evaluate all defects i.e. small defects as well as large ones in the yarn
produced on spinning frames. Measurement should be made for more than 100 Km,
200 Km to 300 Km if possible, and their results must be calculated for every
100 Km.
Classimat defect classification:
Length classes:
A:
shorter than 1 cm
B:
1 to 2 cm
C:
2 to 4 cm
D:
4 to 8 cm
E:
longer than 8 cm
F
and H: 8 to 32 cm
G
and I: longer than 32 cm
Cross-section classes:
1. +100% to +150%
2. +150% to +250%
3. +250% to 400%
4. Over +400%
E:
Over +100%
F
and G: +45% to +100%
H1
and I1: -30% to -45%
H2
and I2: -45% to -75%
|
|||||||||||||||||
Fault
Cross-sectional size
|
|||||||||||||||||
A4
|
B4
|
C4
|
D4
|
||||||||||||||
+400%
|
|||||||||||||||||
A3
|
B3
|
C3
|
D3
|
||||||||||||||
+250%
|
|||||||||||||||||
A2
|
B2
|
C2
|
D2
|
E
|
|||||||||||||
+150%
|
|||||||||||||||||
A1
|
B1
|
C1
|
D1
|
||||||||||||||
+100%
|
|||||||||||||||||
F
|
G
|
||||||||||||||||
+45%
|
|||||||||||||||||
-30%
|
|||||||||||||||||
H1
|
I1
|
||||||||||||||||
-45%
|
|||||||||||||||||
H2
|
I2
|
||||||||||||||||
-75%
|
|||||||||||||||||
0.1
|
1
|
2
|
4
|
8
|
32
|
cm
|
|||||||||||
Fault length
|
|||||||||||||||||
The Uster Classimat system
thus evaluates 23 classes of various cross sectional size and length. Within
each length class a cumulative counting is undertaken i.e. an indication of,
for instance-
B1 = Sum of the counting in
the classes B1 + B2 + B3 + B4
B2 = Sum of the counting in
the classes B2 + B3 + B4
B3 = Sum of the counting in
the classes B3 + B4
B4 = Sum of the counting in
the class B4
The same is valid for the
length classes A, C and D.
Furthermore, H1 = Sum of
the counting in the classes H1 + H2
I1 = Sum of the counting in the classes I1 + I2
In this way, only with A4,
B4, C4, D4, E, F, G, H2 and I2 will the faults be indicated which are actually
counted in the respective classes. With other classes, the indicated fault
figures refer to cumulative values.
With Classimat, the mean
value is determined over a length approx. 150 m of yarn and this mean value
serves as the reference point for the fault cross-sectional size. A fault is
therefore classified in the cross-sectional class 3 if its cross-section
oversteps the yarn mean value by 250% but has not reached the limit of +400%.
(Refer to Annex 1)
The Electronic yarn clearer
(EYC) can detect the fault length and cross-section of yarn passed through its
channels and according to set ranges its clearer clears the yarn. Different
channels and their set range are given below:
1.
Nep channel: Set
for short very thick defect and set range is +100% to +500%
2.
S channel: Set
for short thick defect and set range is +50% to +300%, 1 to 10 cm
3.
L channel: Set
for long thick defect and set range is +10% to +200%, 10 to 200 cm
4.
T channel: Set
for long thin defect and set range is -10% to -80%, 10 to 200 cm
5.
C channel: Set
for delivery yarn count and set range is ±5% to ±80%,
12.8 m
6.
Splice channel:
Set for splice quality
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