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Denim Fabric Weaving – Manufacturing Process, Methods, and technologies

Manufacturing process of Denim Fabrics

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Denim is made from a tightly woven twill in which the weft passes under two or more warp threads. Denim is an indigo-dyed cotton twill fabric in which the weft passes under two or more warp yarns.

Sizing Machine

Textile warp sizing, also known as tape sizing, of Warp yarn, is essential to reduce breakage of the yarn and thus production stops on the weaving machine. On the weaving machine, the warp yarns are subjected to several types of actions i.e., cyclic strain, flexing, abrasion at various loom parts, and inter yarn friction.

With sizing, the strength—abrasion resistance—of the yarn will improve and the hairiness of yarn will decrease. The degree of improvement of strength depends on adhesion force between fibre and size, size penetration, as well as encapsulation of yarn. Different types of water-soluble polymers called textile sizing agents/chemicals such as modified starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and acrylates are used to protect the yarn. Also, wax is added to reduce the abrasiveness of the warp yarns. The type of yarn material (e.g. cotton, polyester, linen) thickness of the yarn and the type of weaving machinery will determine the sizing recipe.

The sizing liquor is applied on warp yarn with a warp sizing machine. After the weaving process the fabric is desized (washed).

Sizing may be done by hand, or in a Sizing machine.

The so prepared beck beams are now sized in a sizing machine preferably with 2 size boxes. The size pick up varies between 8 – 12%. In Europe mainly modified starches with binders are used, whilst in the USA certain low % of PVA is applied in combination with starches by some companies.

Depending on the final finishing process (washed denim) with no filler also CMC gives excellent performance in weaving. Special size mixes for soft denim also can be applied and will be discussed separately. We recommend however not to use PVA for sizing of denim as a surface of denim may show a leather-skinned appearance.

Objectives of Sizing Process

The main objective of the sizing process is given below:

  • To improve the weave ability of warp yarn.
  • To improve the fibre-to-fibre adhesion force in the yarn.
  • To prevent slippage of fibres in the yarn during weaving.
  • To make the yarn twist permanent by applying adhesive film on the yarn surface. The twist in unsized yarn tends to untwist due to rolling action during weaving so that it necessitates to be fixed”.
  • To strengthen the warp yarn.
  • To improve the abrasion resistance of warp yarn.
  • To protect the yarn from being ruptured during passing through drop pin, the eye of heald wire and dent of reed.
  • To reduce the hairiness of warp yarn.
  • To improve the smoothness of warp yarn.
  • To ensure good fabric quality in weaving.
  • To ensure maximum efficiency of the weaving process.
  • To prevent the development of electrostatic charges in the yarn during weaving.

General Sizing Calculations with an example:

The parameters received from warping regarding the set are given below:

  • Total ends = 14640 ends
  • Reed space = 126.20 inches
  • Warp count = 40s
  • Set( warp) length = 5000 metres
  • Sizing waste = 70 metres per set length
  • Actual warp length before sizing = 4930 metres
  • Sized warp length = 5020 metres
  • Warper’s beam = 2200 mm
  • The number of beams = 20.

Now parameters required to size a beam are:

  • Beamwidth = ?
  • Denting order =?
  • Beam width = Reed space (inches) + 20 mm
  • = 126.20 inches + 20 mm
  • = ( 126.20 X 25.4) + 20 mm
  • = ( 3205.48 + 20) mm
  • = 3225. 48 mm ( beam width)

Denting order

This is a very critical calculation in sizing. How to decide the denting order? When we group the warper’s beam s together, and we keep the zig-zag Reed in a downward position and initiate the sizing process, the width of the warp sheet is equal to the width of the warper’s beam.

Now sizer brings the reed in an upward position. The pointed dents of zigzag reed penetrate the warp sheet and the warp and automatically get passed through the dents of the reed. The ends density at both the selvedge and at the remaining sheet vary due to the difference in warper’s beams alignment.

Here sizer needs to correct the denting order at both the selvedge.

Now the question arises, how to find the correct denting order?

The approximate number of dents used  = number of reed stripes X dents per reed stripes

  • = 25 X 60 dent
  • = 1500 dents

Denting order calculation sheet is given below:

The difference in the denting order is corrected by expanding or reducing the width of the zigzag reed.

  • Warping for slasher sheet dying and sizing

Direct warping for slasher sheet dying and sizing

Warp yarns run along the length of fabric and weft yarns go across the width of the fabric. Warping is the preparation of yarn to weave fabric. It is the transfer of many yarns from the creel of single packages to a beam. The yarns will form a parallel sheet of yarn wound onto the beam.

Warping for slasher sheet dying and sizing

Productivity in Direct Warping

Warping means winding the yarn in a particular beam at a uniform tension and yarn are stay parallel. The productivity of warping depends on various parameter such as how many numbers of creel how many actual creels used and also depends on the running time of the warping machine. If the machine is run with greater efficiency, then it possible to make the required number of beams asset wise and usually use as much as 320 or 346 to make a beam of 22000 m or 11000m length and also requirement wise beam.

In the direct warping machine, we observed how much time to make a beam of the required length to collect data.

Details Information about direct warping

Sl. No Cone Length (m) Count Total Warp Length (m)
D1 22,000 7.2 RSL 11,000
D2 11,000 7RsL 9,250
D3 23,200 7.2RsL 22,000
D4 21,000 12 RSL+12R 17,500
D5 18,000 12 OE + 9 OES 16,250

Slasher Dyeing and Sizing Machine

Indigo dyeing and sizing machine (Dyeing section of the machine)

It is a continuous process that combines dyeing & sizing in a single operation. Slasher dyeing warp yarns are repeatedly passed in warp beam form through several baths of indigo (Indigo is a blue Vet dye) before being sized and wound for weaving.

Flow Chart of Indigo Dyeing in Slasher Dyeing Machine

Production of weavers beams

The patented Benninger trough is a closed trough with a yarn inlet and outlet. Both inlet and outlet are equipped with an oxygen trap. The trough is split into two compartments. The yarn passes first the dipping and wetting compartment with a passage length of 6.6m, then through the flexible squeeze rollers before entering the penetration chamber with a passage length of 6 m. Both compartments are, during the indigo dying process, flooded with 98% pure nitrogen.

The nitrogen flow is regulated by adjusting a flow valve. The nitrogen flow volume per trough is approximately 50 – 70 L/min. The dye liquid volume per trough is 360 I at the level of the overflow weir. Additionally, to the 360, L in the trough is approximately 70 L in the overflow compartment, which results in a total dye liquid volume of 430 L per trough.

Indigo Dye Liquid Circulation flow schematic

Each trough is filled by a centrifugal pump. The pumps have a capacity ‘of 80 L /min. In this case, the dye liquid exchange rate per trough is every 4.5 min. This exchange frequency is only possible due to the oxygen-free atmosphere in the dye troughs. The dye liquid backflow is achieved by the slightly lower level in the mixing tank in comparison to the theoretical level in the dye troughs. The total indigo volume required for a 6-trough dyeing range is 3600 I (including mixing tank), which is substantially less in comparison to conventional slasher dyeing ranges with 8000 to 12000.

Indigo Dye Liquid Circulation flow schematic

Difference between Rope dying V/S slasher dyeing

Rope Dyeing Sheet Dyeing
There is an opportunity at re-beaming to repair broken ds No such opportunity
More than one slasher sets can be dyed at one time Only one slasher set may be dyed at one time
Possible to mix yarns of different colours – one can get denim stripes at re-beaming Not possible
No need to start and stop the machine each set, so shade matches perfectly Need to start/stop the machine. Difficult to achieve the target shade until hundreds of meters of yarn have been run.

When the slasher dyeing machine slows down at the end of each yarn set, the wash down shade will be altered

A large number of yarns are difficult to open at re-beaming – not very suitable for lighter weight yarn Advantageous for lighter weight fabrics > 16s
No extra ends Extra ends

Difference between Slasher and Rope Dyeing

Comparison on Slasher Dyeing Rope Dyeing
Required space Less More
Mercerizing Easy Difficult
Manpower Less More
Dye bath Less capacity More
Broken end repairing Not possible In rope dyeing, there is a possibility to repair broken and LCB (Long-chain Beamer)
Flexibility Flexibility to produce denim in different colours and small quantities Less flexible, difficult to change colours
Set change Machines should start and stop at the time of set change. Hence shade matching is not easier until hundreds of meters of yarn run. No need to start and stop the machine at the time of set change. Hence shade matching is easier.
Extra ends Extra ends required No extra ends
Different colour mixing Not possible Possible to mix ends of different colours. One can get stripe design at re-beaming.
Count range Advantages for lighter yarn. Can use Ne 1-30 without a major change Large numbers of yarns are difficult to open at re-beaming. Hence it is not suitable for fine yarn. Can use Ne 1-16 without major change. In the latest machines, an even higher yarn count can be dyed.
Rear characteristics of the fabric Less thin/thick and knot points High thin/thick and knot points
Dye dipping time for effective dye result <= 14s (standard 30 – 14s regulated by speed) <= 21s (standard 15 – 21s regulated by speed)
Production capacity Approx. 9 to 11 millimetres in case of normal capacity. Approx. 10 to 22 millimetres in case of double capacity 12 ropes = 9 to 11.5 millimetres

14 ropes = 18 to 23 millimetres

Ropes = 27 to 34.5 millimetres

Cost The cost of production is lesser compared to rope dyeing Cost production is more compared to sheet dyeing

Denim Weaving Processes

  • Drawing-in/warp tying process
  • Yarn flow
  • Basic weaving motions

Denim is traditionally made from 100% cotton, so the very first stage of production is to take the raw cotton fibre and turn it into yarn that can be woven into fabric. Cotton is fed into a machine that pulls and twists the fibres into yarn. The tighter the twist, the stronger the yarn will be, although tighter yarns take longer to manufacture making them more costly to produce.

Cotton yarn comes in a variety of sizes ranging from quite fine yarn, suited to chambray and lighter denim weaves, to heavier, thicker yarns ideal for jeans and jackets. When choosing a yarn size, the higher the number, the finer it is.

Usually, the fabric mill will weave yarns of the same size but can combine different sizes to create a fabric with a rougher texture. However, it’s not recommended to weave vastly different sized yarns, as this can create a surface that is too uneven and compromise the integrity of the fabric.

Contemporary denim yarns may also include spandex to create a cotton/spandex blend. This creates more stretch in the raw denim fabric and is popular with stretch denim jeans. Just like 100% cotton yarn, the cotton/spandex yarn is numbered, with higher numbers indicating greater stretch. This step is where the denim fabric is woven to the specifications of the customer. Appropriate size and colour of warp yarn is loaded onto the weaving machine, known as a loom. The smaller rolls of weft thread are loaded to the side of the loom, where they run across the warp threads to create a twill weave.

Drawing-In & Warp Tying

When a new denim style is put on a weaving machine, it is necessary to draw or insert the warp yarns through various elements, including the stop motion devices, weave design control devices, and a filling beat-up device.

Each end of yarn must have its own individual drop wire and heddle and be inserted into the correct dent in the reed. This procedure can be done manually or automatically on drawing-in machines. Of course, manual drawing-in is much more time-consuming. When the same end count and the draw are to follow on a loom with a depleted warp, then a full beam of yarn can be tied to the yarns of the old beam. This can be done by a tying-in machine, which automatically selects an end of yarn from the old beam and ties it to the appropriate end on the new beam.

Yarn Flow

Warp yarns are fed from the loom beam and pass over a whip roll or rollers, which help to control variation in yarn tension during weaving. The yarns are then directed through drop wires, heddles, and a comb-like device called a reed. The spaces between the reed wires across the width of the reed are called dents. Each reed will have a specific number of dents per inch — 12 to 18 for most denim and denim-type fabrics. The reed number and the number of warp ends to determine the woven width of the fabric.

The weft yarn is left undyed in its natural off-white colour. Once it’s woven across the coloured warp threads, it can mostly be seen on the underneath of the denim, giving blue jeans that signature “white” appearance on the inside, while the outside is indigo blue.

Modern looms produce standard denim around 57”-58” (145cm) wide, while stretch denim is a little narrower at 52”-54” (135cm) to help minimize shrinkage. Older machines were narrower again at 28”-30” (71cm-76cm) wide, but could create selvedge denim with edges that would not fray, resulting in less wastage off the roll.

During the weaving process, factory staff inspect the yarn and fabric to make sure there are no obvious knots or defects in the denim.

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  1. Balaji Selvaraj says


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