The term
"Denim" has originated from the city of Nimes in France where
"serge de Nimes" was manufactured. Denim is made from a vat dye, the
Indigo dye, which is applied to cotton fabric in loosely held form in layers.
As far as manufacturing process of denim is concerned, it is similar to
that of Grey fabric up to the process of weaving with the only difference that
in case of Denim Fabric, it is dyed at the stage of sizing where as in case of
Grey Fabric, the decision regarding dyeing stage depends upon the finished
product. The details of each process are given below:
Spinning:
The initial stage of
denim production is Opening and Blending. Opening begins with baled cotton
fiber being separated into small tufts. A blend of cotton fibers is made on
each opening line. These bales are selected using USDA High Volume Instrument
(HVI) data, and PCCA's unique computer blending software produces optimal yarn
strength.
Cotton is delivered by
air suction from the Opening and Blending lines, through additional cleaning
and blending machines, to the Cards. The major functions of Carding are to
remove foreign matter and short fibers, form the cotton into a web and convert
the web into a rope-like form known as a sliver.
The drawing process
produces a single, uniform sliver from six card slivers. The additional
blending, paralleling of fibers and cleaning in this process produces a sliver
for Open End and Ring Spinning. For Ring Spinning, however, the sliver must
pass through an additional process called Roving.
Cotton Fibers are formed
into a yarn by centrifugal action in Open- End Spinning. Individual fibers are
laid down in the groove of a fast spinning rotor and twisted into yarn. After
the cotton fibers are spun into yarn, the yarn is wound into a large
package.
Open End Spinning
The Open End Spinning
Machines have robots on each side which automatically pieces up (repairs broken
ends). On a different track, they have another robot that automatically doffs
(removes full packages) and starts up a new package. The size and quality of
each yarn end are monitored by the Barco Profile System to ensure uniformity.
Ring Spinning
In Ring Spinning, the
spinning frames receive Roving via a transit system from the roving machine.
Yarn is formed from Cotton fibers that
are twisted together after being drafted by passing between three steel rolls
and three rubber rolls. The yarn then is wrapped on a bobbin as it spins on a
spindle by use of a traveler. The relationship between roll speeds, traveler
speeds and spindle speeds controls the amount of twist in the yarn. Ends down
levels and production information are gathered by the Uster Ring Expert System.
The spinning frames automatically doff bobbins full of yarn and send them to
package winding.
ACG also has the capacity
to produce Amsler Open-End yarn, also known as Faux Ring Spun yarn. This
technology enables ACG to impart various slub patterns into an Open-End yarn.
Denim made from this type of yarn has yarn character and surface interest that
cannot be achieved with traditional Open-End yarn.
Fabric Weaving:
a. Grey Yarn on Cones
Normally yarns received
for weaving in cone forms are either from ring spinning or from open end
spinning in single or double fold as required. For weaving, yarn used is
categorised into:
Normally for Weaving,
yarn used as warp should be sufficiently strong to withstand stress and strains
exerted during weaving operations. Hence they are having Count Strength
Product(CSP) and further sized to increase its strength. The weft yarn is
directly used on weaving machines and in some cases, if required, is rewound
also so as to enhance its performance in weaving.
b. Warping on Sectional/
Direct Warping
The warp yarn is
required to be fed into a sheet form to the weaving machines. At warping, the
individual cones are put into the creel (the number of cones depends upon
fabric construction) and yarn from individual cones is pulled together in sheet
form, wound on a barrel called warping beams (for Direct warping) or on weaving
beams (for Sectional Warping). Normally if warp sheet is with patterns of
different coloured yarns it is processed on sectional warping machine.
c. Sizing of yarn in
Set/ Beam to Beam Position
The object of Sizing is
to improve the strength of yarn by chemically binding the fibres with each
other and also improve upon its friction resistance capacity by chemically
coating the surface of yarn/fibres. Further, number of threads in warpers beam
sheet is very less against number of threads required in whole width of fabric.
Hence multiplication of sheets by drawing yarns together from many warp beams
and again making one sheet is also performed on sizing machine. On sizing,
normally, 8-12 % size material on warp thread is applied. This improvement in
strength and frictional resistance characteristic of warp yarn is essential
because during weaving, yarn has to undergo severe strain & stress as well
as frictional operations.
d. Drawing–in
Weaving is basically
interlacement of two sets i.e. warp and weft threads in desired sequence and
pattern. To obtain this interlacement, warp yarn sheet is bifurcated &
opened in the form of two layers/ sheet and weft thread is inserted between so
opened two warp sheets. This operation is called shedding. to perform shedding the
warp yarn needs to be passed through heald eyes of the heald shafts, this
operation is called as drawing-in.
e. Beam Gaiting or
Knotting on Loom
The drawn weavers beams
are fixed on weaving machines, threads are tied and heald shafts are coupled.
This operation is called Beam Gaiting. If undrawn warp threads are directly
knotted to the threads of finished beams, it is called Knotting. These
operations are essential because normally weavers beam can carry only certain
length of warp sheet on it and when so woven, whole length is converted to the
fabric by weaving machine. Further warp length is required to be fed which can
be done by knotting or gaiting other beams on weaving machine.
f. Weaving
As stated earlier,
weaving is interlacing two sets of yarn and making fabric. One set is called
warp thread which is in sheet form, the other one is called weft thread which
is inserted between two layers of warp sheet by means of a suitable carrier
i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending
upon the type of the weaving machines. The different types of technologies
available for weaving machines are briefly explained as below:
- Conventional Shuttle Weaving
System by Ordinary Looms or Automatic Looms.
- Shuttle less Weaving System by
Airjet /Waterjet/Rapier/Projectile
Shuttle loom is a
conventional Technology with much less production on account of slow speed and
excessive wear and tear of machinery. This shuttle loom technology has now
become obsolete. Denim is woven through Shuttle less Weaving System by using 96
ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile
looms. These looms are distinguished by weft insertion method, which is briefly
discussed hereunder.
Airjet Looms
These types of looms
adopt the latest development in Weaving Technology where weft insertion is done
with the help of compressed air. A very high weft insertion rate up to 1800
metre per minute is achieved. Compared to rapier and projectile looms, these
looms are less versatile but are economical and are used in mass textile
production unit like denim.
Finishing:
a. Grey Fabric
The finally woven fabric
or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out
from weaving machines at certain intervals and checked on inspection machines
for possibilities of any weaving fault. If such faults are seen anywhere in
fabric during inspection, certain corrective steps are taken at weaving,
warping, sizing, etc so that they can be minimised in subsequent product. This
is a quality control exercise.
b. Denim Fabric
Denim Fabrics woven of
100% cotton would be very strong and durable. Traditionally Blue Denim is
warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in
a solid colour and weft left un-dyed. The look and quality of the Denim Fabric
shall improve after dyeing, the process of which differs from plant to plant.
Normally the process of dyeing dictates the technology of Denim manufacturing.
The dyeing for Denim
Fabric happens at the sizing stage. Generally there are two most popular
methods of dyeing Denim Fabric. They are:
A company can adopt any
of the methods. In countries like India Sheet Dyeing Method is commonly used
for manufacture of its Denim Fabrics, which has following advantages over Rope
Dyeing Method:
- The technology is less capital
intensive.
- The technology is a proven one.
- The cost of production is
lower.
- The process time is lower.
- The Sheet Dyeing machines are
very easy to operate.
The only defect in Sheet
dyeing is that their is a problem of center to selvedge shade variation.
c. Sheet Dyeing Process
This process eliminates
a few intermediate processes of the rope dyeing. The yarn sheet is washed with
chemicals such as caustic and washing soda and after squeezing the excess
water; the yarn sheet is allowed to pass through Dyeing Troughs one time for
oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed
again with fresh water for two-three times and finalIy squeezed before allowing
it to pass through six drying cylinders. The dyed yarn enters the starching
device and sizing is done. After sizing, the sized warp beam goes for weaving.
After weaving, the woven Denim Fabrics goes for various finishing processes
consisting of brushing, singeing, washing, impregnation for dressing and
drying. Brushing and singeing should eliminate impurities and help to even the
surface of the fabric. Dressing regulates the hand and rigidity of the fabric
while compressive shrinking regulates its dimensional stability.
Even today Denim Fabric
without Indigo Dyeing is not called authentic Denim. Initially when Denim
Fabric entered the fashion market, Denim manufacturers were using Natural
Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo
Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers
still prefer the latter and attract premium after branding them “Natural Dye
Used”.
d. Making-Up
Weaving of fabrics on
such multi sizes is not economical, hence a standard width fabrics is then sent
to making up. Fabrics are cut into the desired width as per size required on
this machine. Denim Fabric and Grey Fabric are thoroughly checked for various
types of defects such as:
- Weaving Defects
- Uneven Dyeing
- Bleaching and Dyeing Defect
- Oil Stain
- Patches
Here the final product
is categorised quality-wise. The products then found okay are segregated and
sent to packaging department whereas defective ones are sent for correction.
After inspection, the sets are wrapped with polythene covers and sent for
despatch as per buyer’s specifications.
Dispatch:
Rolls and sets so formed
and packed as per buyers’ requirements are then sent for final despatches.
