Yarn
Yarn is a long continuous length of
interlocked fibers that is suitable
for use in the production of textiles, sewing, crocheting, knitting, weaving, embroidery, or rope making. Thread is a type of
yarn intended for sewing by hand or machine. Spun yarn is made by twisting staple fibers together to make a cohesive thread, or
single. Twisting fibers into yarn in the process called spinning. Spun
yarns may contain a single type of fiber, or be a blend of various types. Yarn
is composed of twisted strands of fiber, which are known as plies when grouped
together. Filament
yarn consists of filament fibers (very long continuous
fibers) either twisted together or only grouped together. Thicker monofilaments are
typically used for industrial purposes rather than fabric production or
decoration. Silk is
a natural filament, and synthetic filament yarns are used to produce silk-like
effects. Texturized yarns are made
by a process of air texturizing filament yarns, which combines multiple
filament yarns into a yarn with some of the characteristics of spun
yarns. The slub effect means
a yarn with thick and thin sections alternating regularly or irregularly.
What Is Spinning?
Spinning is the twisting process where the fiber is drawn out, twisted and
wound onto a bobbin. The yarn issuing from the drafting
rollers pass through a thread-guide, round a traveler that is free to rotate around a ring, and then
onto a tube or bobbin, which is carried on
a spindle, the axis of which passes through the center of the ring. The spindle
is driven (usually at an angular velocity that is either constant or changes
only slowly) and the traveler is dragged around a ring by the loop of yarn
passing around it.
Yarn Manufacturing Process
Yarn
manufacturing is a sequence of processes that convert raw cotton fibers into
yarn suitable for use in various end-products. Some processes are
required to obtain the clean, strong, uniform yarns required in modern textile
markets. Beginning with a dense package of tangled fibers (cotton bale)
containing varying amounts of non-lint materials and unusable fiber (foreign
matter, plant trash, motes, and so on), continuous operations of opening,
blending, mixing, cleaning, carding, drawing, roving, and spinning are performed
to transform the cotton fibers into yarn. Yarn manufacturing produces yarns for
various woven or knitted end-products (e.g., apparel or industrial fabrics) and
for sewing thread and cordage. Yarns are produced with different diameters and
different weights per unit length. While the basic yarn manufacturing process
has remained unchanged for many years, processing speeds, control
technology, and package sizes have increased. Yarn properties and processing
efficiency are related to the properties of the cotton fibers processed.
The end-use properties of the yarn are also a function of processing conditions.
Cultivating and harvesting of Cotton
Cotton is
grown anywhere with long, hot dry summers with plenty of sunshine and low
humidity. Indian cotton, Gossypium arboreum is finer but the staple
is only suitable for hand processing. American cotton, Gossypium hirsutum
produces the longer staple needed for machine production. Planting
is from September to mid-November and the crop is harvested between March and
June. The cotton bolls are
harvested by stripper harvesters and spindle pickers that remove the entire
boll from the plant. The cotton bolls are the seed pod of the cotton plant
attached to each of the thousands of seeds that are fibers about 2.5 cm long.
Ginning
The seed cotton goes into a cotton gin. The
cotton gin separates seeds and removes the "trash" (dirt, stems, and
leaves) from the fiber. In a saw gin, circular saws grab the fiber and pull it
through a grating that is too narrow for the seeds to pass. A roller gin is
used with longer staple cotton. Here, a leather roller captures the cotton. A
knife blade, set close to the roller, detaches the seeds by drawing them
through teeth in circular saws and revolving brushes which clean them
away. The ginned cotton fiber, known as lint, is then compressed into
bales which are about 1.5 m tall and weigh almost 220 kg. Only 33% of the crop
is usable lint. Commercial cotton is priced by quality, and that broadly
relates to the average length of the staple and the variety of the plant.
Longer staple cotton (2½ into 1¼ in) is called Egyptian, medium staple (1¼ into ¾ in) is called American upland, and short-staple (less than ¾ in) is called
Indian. The cottonseed is pressed into cooking oil. The husks and meals
are processed into animal feed and the stems into the paper.
Bale opening and cleaning
Cotton is shipped to mills in
large 500-pound bales. When the cotton comes out of a bale, it is all packed
together and still contains vegetable matter. The bale is open using a machine
with large spikes, called an opener. To fluff up the cotton and
remove the vegetable matter the cotton is sent through a picker or a similar
machine. In a picker, the cotton is beaten with a beater bar to
loosen it up. It is then fed through various rollers, which serve to remove the
vegetable matter. The cotton, aided by fans, then collects on a screen and gets
fed through more rollers till it emerges as a continuous soft fleecy sheet,
known as a lap.
Blending and Mixing
In the spinning process, when various fibers of different or same grades are
kept together then it is called blending.
For example, a yarn produced by using 65% cotton yarn and 35% polyester yarn
then it’s called blending. Blending is based on the movement of important
fiber properties like length, fineness, strength, etc., and quantitatively
proportioning and combining the properties under controlled conditions. In the blending process must be a particular ratio of fibers to mix with each other.
And
various grades of the same fibers are kept together for manufacturing yarn then it
is called mixing. For example,
yarn is produced by using 40% Indian cotton and 60% Egyptian cotton then it is
called mixing. There is no particular ratio of fibers to mix with each other.
Raw cotton is the prime factor that influences the quality of yarn. The main
technological challenge in any textile process is to convert the high
variability in the characteristics of input fibers to a uniform end product.
This critical task is mainly achieved in the mixing process. The mixing department
in the spinning mill plays a crucial role in the formulation of an appropriate mix
of fibers. Mixing has a significant impact on end-product cost and
quality. A mill can control the total cost of cotton by selecting cotton of the right quality by buying
them at the most appropriate time since cotton prices fluctuate substantially
over the year and by the efficient formulation of mixings for the various counts of
yarn that is being spun.
PORCUPINE OPENER
The
cotton fed by the previous opener is carried forward by the feed lattice. The
sheet of cotton now passes between the pedal and pedal roller. The weight of cotton
fed per unit time is maintained constant by this
pedal feed regulating motion. Pedal roller feeds the
sheet of cotton in between pair of feed roller which is weighted to give
necessary grip on the cotton. 16 circular discs are mounted on the shaft of this
opener. 14 to 18 striker blades are riveted alternatively on each circular disc.
Each striker is bent to a slightly different angle. The compressed sheet of
cotton delivered from the feed roller is heavily beaten by the rapidly
revolving striker of the porcupine beater against the grid bar. Because of this
beating action, the cotton is effectively opened and extracted trash particles
are passed through the spacing of the grid bar. At the end of the grid bar, a stripping rail is provided, this is a metal bar that is set about 1/16 inch
away from the end of the striker. This small clearance between stripping rail
and striker prevents bunches of cotton from being carried
around by the beater.
Step cleaner
Condenser
is employed to feed cotton to the step cleaner. Photo-cell arrangement in the
reserve tower unit monitors the height of reserve fiber and signals stop or
start commands to the proceeding machine. Cotton is fed from the reserve tower
by pair of the feed roller. According to the height of the cotton level, photocell in
the reserve tower of a subsequent machine, drive the feed Roller intermittently
by motorized gear reduction unit. The rapid revolution of 6 beating
cylinders (multiple beaters) and beating of the spikes on cotton against grid
bar centrifugal force and gravity combine effectively to open the cotton and
remove the heavier impurities. Heavier impurities, dust & dirt
particles, short fibers, etc. from the cotton are passed through the spacing of
the bars and are collected outside the grid bar.
Scutching process
Scutching refers to the process of cleaning
cotton of its seeds and other impurities. The first scutching machine was
invented in 1797 but did not come into further mainstream use until after 1808
or 1809, when it was introduced and used in Manchester, England. By 1816, it
had become generally adopted. The scutching machine worked by passing the
cotton through a pair of rollers and then striking it with iron or steel bars
called beater bars or beaters. The beaters, which turn very quickly, strike the
cotton hard and knock the seeds out. This process is done over a series of
parallel bars to allow the seeds to fall through. At the same time, the air
is blown across the bars, which carries the cotton into a cotton chamber.
Carding process
In the carding process, the fibers are separated and then assembled into a loose
strand (sliver or tow). The cotton comes off of the picking machine in laps
and is then taken to carding machines. The carders line up the fibers nicely to
make them easier to spin. The carding machine consists mainly of one big roller
with smaller ones surrounding it. All of the rollers are covered in small
teeth, and as the cotton progresses further on the teeth get finer (i.e. closer
together). The cotton leaves the carding machine in the form of a sliver: a
large rope of fibers.
In a wider sense carding can refer to these four processes:
Willowing-
loosening the fibers;
Lapping-
removing the dust to create a flat sheet or lap of cotton;
Carding-
combing the tangled lap into a thick rope of 1/2 inch in diameter, a sliver;
and
Drawing-
where a drawing frame combines 4 slivers into one, repeated for increased
quality.
Combing process
Combing is
a method for preparing carded fiber for spinning. Combing is divided into linear and
circular combing. The Noble Comb is an example of circular combing. The French
comb is an example of linear combing. The process of combing is accompanied
by gilling a process of
evening out carded or combed top making it suitable for spinning. Combing
separates out short fibers through a rotating ring or rectilinear row of
steel pins. The fibers in the 'top' it produces have been straightened
and lie parallel to each other. When combing wool, the discarded short fibers
are called noils and are ground up into shoddy.
In
general, there are two main systems of preparing fiber for yarn: the worsted system and the woolen system. The worsted system is
defined by the removal of short fibers by combing and top preparation by
gilling. In the woolen system, short fibers are retained, and it may or may not
involve combing.
The circular combing and top comb insertion
are repeated and combed fibers - now called tuft are overlapped. The
overlapping produces some cohesion allowing the tuft then to be twisted to form
a combed sliver. This sliver is weak and unsuitable for spinning. To allow
spinning to take place additional gilling is required to introduce fiber end
irregularity.
Combing the fibers removes the short fibers
and arranges the fiber in a flat bundle, with all the fibers going the same
direction. This preparation is commonly used to spin a worsted yarn. Woolen
yarns cannot be spun from fiber prepared with combs, instead, the fiber must
be carded.
Cotton is combed when it is to be used for quality fabric with high thread
counts.
Draw Frame
Production
costs of draw frame are less than 3% of total yarn cost. But it has a great
influence on yarn quality, especially on evenness. The draw frame is the definitive
compensation point for eliminating errors. High-performance draw frames
currently produce over 400 kg of sliver per hour at each delivery. The main objective
of the Draw Frame is Equalizing. One of the main tasks of the draw frame is
improving evenness over the short, medium, and – especially – long term.
Parallelizing To obtain optimal value for strength in the yarn
characteristics, the fibers must be arranged parallel in the fiber strand. It
is mainly the draw frame‘s task to create this parallel arrangement. It
fulfills this task through the draft since every drafting step leads to
the straightening of the fibers. Blending In addition to the equalizing effect,
doubling also provides a degree of compensation for raw material variations by
blending, which occurs simultaneously. Dust removal Dust is steadily becoming a
greater problem both in processing and for the personnel involved. It is
therefore important to remove dust to the greatest practical extent at every
possible point within the overall process.
Ring frame
The Ring frame is credited
to John Thorp in Rhode Island in 1828/9 and developed by Mr. Jencks of Pawtucket, Rhode Island,
who Richard Marsden names as the inventor.
The wage cost per spindle is higher for ring spinning. In the states, where
the cotton staple was cheap, the additional labor costs of running mules could be
absorbed, but Lancashire had to pay shipping costs. The critical factor was the
availability of labor, when skilled labor was scarce then the ring became
advantageous. This had always been so in New England, and when it
became so in Lancashire, ring frames started to be adopted. A ring frame was constructed
from cast iron and later pressed steel. On each side of the frame are the spindles, above them are draughting (drafting) rollers and on top is a creel loaded with bobbins of roving. The roving (unspun
thread) passes downwards from the bobbins to the draughting rollers. Here the
back roller steadied the incoming thread, while the front rollers rotated
faster, pulling the roving out and making the fibers more parallel. The rollers
are individually adjustable, originally through levers and weights.
The attenuated roving now
passes through a thread guide that
is adjusted to be centered above the spindle. Thread guides are on a thread rail
which allows them to be hinged out of the way for doffing or piecing a broken
thread. The attenuated roving passes down to the spindle assembly, where it is
threaded through a small D ring
called the traveler. The traveler moves along the ring. It is this that gives the ring
frame its name. From here the thread is attached to the existing thread on the
spindle.
Doffing
Doffing is
a separate process. An attendant winds down the ring rails to the bottom. The
machine stops. The thread guides are hinged up. The completed bobbin coils are
removed from the spindles. The new bobbin tube is placed on the spindle
trapping the thread between it and the cup in the wharf of the spindle, the
thread guides are lowered and the machine restarted. Now all the processes are
done automatically. The yarn is taken to a cone winder. Currently, machines are
manufactured by Rieter (Switzerland), Toyota (Japan), Zinser, Suessen,
(Germany) and Marzoli (Italy). The Rieter compact K45 system has 1632 spindles,
while Toyota has a machine with 1824 spindles. All require controlled
atmospheric conditions.
Yarn Measurement System
A. Cotton Counts: Refers to the thickness of the cotton yarn where 840 yards of
yarns weigh 1 pound (0.45 kg). 10 count cotton means that 8,400 yards
(7,700 m) of yarn weighs 1 pound (0.45 kg). This is coarser than 40
count cotton where 40x840 yards are needed. In the United Kingdom, Counts to
40s are coarse (Oldham Counts), 40 to 80s are medium counts and above 80 is a
fine count. In the United States, one to 20s is coarse counts.
B. Hank: A length of 7 leas or 840 yards (the worsted hank is only 560
yd)
C. Thread: A length of 54 in (the circumference of a warp beam)
D. Bundle: Usually 10 lb
E. Lea: A length of 80 threads or 120 yards
F. Denier: this is an alternative method. It is defined as a number that
is equivalent to the weight in grams of 9000m of a single yarn. 15 denier is
finer than 30 deniers.
G. Tex: is the weight in grams of 1 km of yarn.
Yarn Marketing System
At
present yarn marketing becomes a vital factor for the spinners having huge
competitions with local and international markets. The market climate remained
to fluctuate with international raw cotton prices again setting record
highs. On the other hand, supply and demand fundamentals became still more
bullish during the months of 2010-2011. In the present volatile yarn market, a proper marketing strategy has to be adopted for the sake of industries. These
policies have already been implemented in yarn marketing by Dr. Engr. Md. Saiful
Islam. He told information is business that is not only available but also open
while he was asked about his success of yarn marketing at his office. We can
easily be benefited from the information around us.
Conclusion
Yarn
making is a very important portion of the textile manufacturing industry.
First, step yarn making and finally finish garments.
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