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 initial processes of denim manufacturing consist of the regular activities of opening and blending of cotton fibers.
Carding is done to remove any foreign matter and the short fibers so that cotton takes the form of a web which is then converted into a rope-like form, the sliver. Then drawing process produces a single, uniform sliver from a number of carded slivers. Yarn is then spun through Open-End Spinning or Ring Spinning. Roving is also carried on, if the spinning has to be done through Ring Spinning.
Generally, denim fabric are 3/1 warp-faced twill fabric made from a yarn dyed warp and an undyed weft yarn. Normally dyed and Grey ring or open- end yarns are used in warp and weft respectively. Traditionally speaking, the warp yarn is indigo dyed.
Warp Preparation - Dyeing and Sizing Processes
are indigo dyed and sized with the help of two methods.
(i) Threads from several back beams are combined to form a warp sheet and dyed and sized on the same machine.
(ii) Threads, about 350-400 in number are formed into ropes. 12-14 ropes run adjacent to each other through the continuous dyeing unit. After dyeing, the ropes are dried on drying cylinders and then collected in a can. After that, a worker's beam is prepared. Sizing is then done in the conventional manner.
There are various dyeing and sizing processes, which can be classified into four categories.
Continuous Indigo-Rope dyeing and sizing
- Continuous Indigo-Rope dyeing and sizing.
- Continuous Indigo dyeing and sizing.
- Indigo-back beam dyeing and sizing.
- Continuous dyeing and sizing.
The yarn coming out from the ring frames is wound into cheeses or cones and then placed on the ball warper on which 350-400 threads are formed into a rope and are cross wound to a ball in accordance with the length of warp beam. During this process, lease bands are inserted at particular intervals as they are required for further processing on Long Chain Beamer. Based on the size of the rope dyeing plant, 12-24 ropes, at a time, are dyed, oxidized, dried and placed in large containers. These ropes are then opened on the Long Chain Beamer through tension roll and expansion comb and wound on to a back beam. Back beams are then sized and the sized warp is then woven. This system is commonly used in the US.
Continuous Indigo dyeing and sizing:
In this process, back beams are processed on the dyeing/ sizing machine instead of ropes. The warp is dyed, oxidized, dried and sized at a one go. Although this process is less cumbersome, the risk of individual thread breakage is greater than dyeing in rope form. This method is commonly used in the European countries.
Indigo-back beam dyeing and sizing
Dyeing and sizing is done in two stages in this method. In the first stage, back beams are dyed, oxidized, dried and wound on a batch roll. The batch roll is then sized, dried and wound on a weaver's beam.
Continuous dyeing and sizing
Although glass is hard and rigid yet it can be transformed into fine, translucent and flexible Glass Fiber, commonly known as fiberglass. It is very glossy in appearance and feels like silk. There are two methods for glass fiber manufacturing, Continuous Filament Process and Staple Fiber Process. Apart from being glossy and flexible, glass fiber is also heat resistant. Due to its many qualities, this fiber is widely used for home furnishings, apparels and many other industrial purposes. It's really very interesting to know about the whole process of Glass Fiber Manufacturing.
The weaving process interlaces the warp, which are the length-wise indigo dyed yarn and the filling, which are the natural-colored cross-wise yarn. The warp thread is in the form of sheet. The weft thread is inserted between two layers of warp sheets by means of a suitable carrier, such as Shuttle, Projectile, Rapier, Air current, Water current, etc. The selection of carrier depends upon the type of weaving machinery
used. The two different technologies available for weaving machines are - Conventional Shuttle Weaving System which is done by Ordinary Looms or Automatic Looms; and the Shuttle less Weaving System which is done by Airjet, Waterjet, Rapier, or a Projectile weaving machine.
The Conventional Shuttle loom
results in lesser production due to slow speed and excessive wear and tear of machinery. As such, now denim is generally woven through Shuttle less Weaving System namely, Airjet looms, rapier looms
or projectile looms.
The final woven fabric, wound on a cloth roll, is taken out from weaving machines at particular intervals and checked on inspection machines so that any possible weaving fault can be detected. In this quality control exercise, wherever any fault is seen, corrective measures are taken then and there only. The woven Denim Fabrics then goes through various finishing processes, such as brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing eliminate impurities and help to even the surface of denim fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking manages its dimensional stability.
The standard width denim fabrics is then sent for making up. In this process, the fabric is cut into the desired width according to the size required. The made- up denim fabric is then thoroughly checked for defects such as weaving defects, uneven dyeing, bleaching and dyeing defects, oil stains, or patches. After inspection, the final product is categorized quality-wise. The fault less fabrics are sent to the packaging department while the defective ones are sent for further corrections.