What is Indigo Dyeing Machine? How Does it Work?
What is Indigo Dyeing Machine? How Does it Work?

What is Natural Indigo Dyeing Machine?

Natural Indigo Dyeing Machine

As the reduced indigo dyeing machine has very little affinity for cotton in spite of the deep shades while dyeing with concentrated vat dye, the result is sufficient fastness. For this reason the cotton warps for Blue Jeans are dyed in 4-6 passages in sheet form. By a passage it means the run of goods through an immersion, vat following by squeezing and an air passage for oxidation of dye stuff . A major part already oxidized dye stuff remains fixed to the material while being processed in the following immersion vat. Only the chemical solution is almost completely replaced by fresh indigo vat. Thus with every subsequent passage the depth of dye penetration increases. After the last air passage the stuff ringed by 2 or 3 ringed trough.

Details in Dyeing & Sizing machine:

  1. Machine Name : Slasher Indigo Dyeing Machine.
  2. Country of origin : West Point, USA.
  3. Model No. : 654
  4. No. of Machine : 01
  5. Creel capacity : 21
  6. Speed of the Machine : 16 meters / minute for Dark Indigo,

: 20  meters / minute for S. Black.

: 23  meters / minute for  Normal Indigo.

  1. Production capacity per day : (21x1320x.95) = 26334 Mts (Considering the product mix 65% Indigo 20% Dark Indigo,15% Sulphur Black.)

Dyes and Chemicals wastage : 1 – 2 %

Szing material wastage           :  2.5%

Pls note : This yarn wastage is already taken in fabric process loss.

Down Time :                                                                                                 

  1. If dyeing route is similar then down time 45 minutes/Dyeing Lot. (Two and Half lot per day)
  2. If dyeing route is different then down time 3 hours (Two time per 7 days)
  3. If dyeing route is same but need to colour change then down time 2 hours (Two time per 15 days).

Indigo Denim Manufacturing Process

Yarn Peperation

Continuous Dyeing





What is Indigo Dyeing Machine Process
Dyeing Machine Process

Continuous dyeing of cotton yarn with Indigo Dyeing Machine

  1. Indigo denim dyeing:

The “Mult-dip” process is by far the only continuous method adopted for indigo yarn dyeing.

The dyeing machineries used for yarn dyeing are divided into two categories namely the rope dyeing range and the slasher dyeing range.

Processing Stages

Rope Dyeing

Ball warping


Re beaming




Finished Fabric.

Slasher Dyeing Process:


Dyeing &Sizing



Finished Fabric.

The main difference between rope dyeing and slasher dyeing is that for rope dyeing and sizeing have to be done separately while in slasher dyeing, the dyeing and sizing can be done simultaneously.

Rope dyeing technique is more popular in the America region. It is suitable for mass production. And because of its possible non stop dyeing advantage, rope dyeing gives better shade consistency.

Indigo Dyeing Machine wetting

In absence of strong demands for deep (dark) dyeing of yarns, they are only pre-wetted by caustic and wetting agent the degree of dyeing depth is influenced in the second trough rinsing is done more or less by strong overflow of cold

Pretreatment process with sulphur black

In general with continuous dyeing no deep (dark) dyeing of yarn is achieved, they are often pre-dyed to a light medium grey-shade with sulphur Black.

The pre-dyeing is done is done at 80ºC/90ºC in the first wetting trough of the continuous processing plant. The second trough is used for rinsing of dye stuff

The yarn is squeezed to 70% to 80% and the rest humidity is immediately passed through the first vat.

The Dyeing Process

The sequence of dyeing for both rope & slaser are very similar, which include the following stages:

Mercerization (Optional)






Finished fabric.


Pre-Scouring has the following functions: wetting out yarn, removing air from yarn and scouring to give cleaner yarn so that a better dyeing can be achieved.

The pre-scouring bath consists of wetting agent, caustic soda and chelating agents. Normally, a minimum of two boxes are required to give satisfactory pretreatment. The first box is the pretreatment with temperature at 85ºC to wet out the yarn. The second

Box is a cold rinsing to coon down and to decrease the yarn.

It also a common practice where at this stage optional Sulphur bottoming application is done.


The desired depth of Indigo on the yarn is mainly achieved by the number of dip. In general, the lower the dye bath concentration (2-4 g/l) as more dips are required, the better the fastness, and the vice versa. For a full Navy shade of about 2% pick up (based on Indigo grain), an initial dye bath will  balance itself until it is able to pick up 2% dye.

The reduce Indigo Dyeing Machine solution cannot be prepared directly in the dye baths. Its because it will take much higher quantity in caustic and hydrosulphite, and much longer tome to reduce the Indigo when the concentration of Indigo dyeing is a continuous exhaust dyeing process, a replenishing of dye and chemicals are necessary during dyeing. As a result, preparation of concentrated stock vat is necessarsy for the initial dye bath and the replenishment.

Indigo dyeing is generally carried out at room temperature, although dyeing at higher temperature has a better leveling effect. High temperature will deteriorate the reduction condition of the dye bath at much faster rate. As a result, a higher consumption of caustic and hydro.

In order to produce a consistent dyeing, control over the dye concentration, redox potential and the alkalinity of the dye bath is absolutely necessary.

Indigo Dyeing Machine
Indigo Dyeing Machine

Control during dyeing

  1. Hydrosulphite or ORP value

The content can either be checked by a vatometer, range from 1.5-2.5 g/l, or by direct titration method. The control can further be confirmed by measurement of the redox potential of the dye means of an ORP meter range from 730mv-860mv is common.

  1. Caustic soda or pH value

The content can be checked either by titration with HCl or by pH meter, generally pH ranges from 11.5-12.5.

  1. Dye concentration in dye bath

It can be checked by means of leuco solution is oxidized and the transmittance at λ max is measured. The reading can be converted into concentration in g/l by comparing with a calibration curve plot from known dye concentration.

The control figure varies from range to range, so one must establish their own set of control data.

Normal running speed is 20-25 yds/min (18-22 m/mim).

The longer   the dipping time, the better will be the penetration and the lesser will be the ring dyeing effect. Dipping time varies from 6-30seconds. The common is 20-30 sec. However, the dipping time should not exceed 60 sec. It is because there is an adverse effect where the Indigo Dyeing Machine fixed on the yarn may be redused back into the dye bath.

However, for super dark shade, beside mercerization of yarns at the pretreatment stage, bottom or topping with Sulphur Black is also a common practice further; there is a newer practice by controlling the pH with the additional of buffer to give significant ring effect which enhances darker shade.


The wet pick up affects the dyeing fastness to a very great extent. Higher squeeze pressure gives lower wet pick up and results in lesser surface colour and better penetration.

Rope dyeing and Looptex units have squeeze pressure from 5-10 Newtons, which can give a wet pick up as low as 60% while for slasher dyeing range have inferior fastness property than the rope dyeing range.

Hardness of the squeezing rollers should be approximately 70-75ºShore. If the squeezing rollers are too hard, slippage will occur and results in uneven yarn tension. If they are too soft, they will groove easily and results in shading.

Maintaining in a smooth surface of the squeezing roller is important. Normally the surface should be ground twice per year. When applying pressure to the squeezing mangle, make sure the mangle is not bended. Otherwise, shading will result.


In between dipping, airing is necessary to oxidize the dyed yarn. Usually, airing time varies from 60-120 sec, and 90 sec is common. Try to avoid long airing time, as this will create unnecessary high tension on the yarn and make the subsequent processes difficult.


Most dye ranges are equipped with2-3 rinse boxes. Cold rinsing is generally sufficient. For rope dyeing, the last box is used for applying re-beaming aid.


Sufficient drying capacity should be provided, otherwise high range speed cannot be achieved. Insufficient drying or unevenly dried yarn will result in weak size pick up in the case of slasher and poor re-beaming in case of rope dyeing.

Preparation of stock vat, chemicals, dye bath

Preparation of stock vat

Since the dyeing is a wet on wet process, to limit the excess amount of liquid feeding into the dyeing system, it is always advisable to make up the stock vat as concentrated as possible.

During the preparation of the stock vat, there are certain points which need to be observed. First, the vatting temperature should be about 40-45ºC. Second, stirring is to be kept to the minimum, as unnecessary stirring will introduce oxygen into the stock vat and affect the stability of the reduced vat. Third, volume and concentration of the stock vat must be kept constant for every stock vat batch, for the constant volume and concentration will ensure a consistent replenishing amount.

A typical vatting procedure is as follows:

  1. a) Make a mark on stock vat tank so that the volume is easily maintained by watching the level.
  2. b) Add require amount of dye.
  3. c) Add requires amount of NaOH, 50% liquid is preferred, as it generates lesser heat.
  4. d) Add require amount of auxiliaries, chelating agent, wetting and dispersing agent. This is optional as both our paste and grain already have a certain amount of auxiliaries built in.
  5. e) Add water to half the volume of stock vat. Stir for 5 min until the mass in the smooth slurry.

Dyes and Chemical:

  1. Vat dyes (indigo)
  2. Sulpher dyes (Black, Yellow, Green)
  3. Caustic
  4. Primasol
  5. Triplex
  6. Setamol
  7. Hydeose
  8. Sodium stone
  9. Common salt
  10. Sobitol
  11. Rucowet
  12. ASD
  13. Peroxide
  14. Acetic Acid
  15. Starch
  16. Size-ca
  17. PVA
  18. Wax
  19. Etc

Dyeing Recipe:

2% shade for indigo (blue) dyeing


  • Caustic soda : 5 g/l
  • Wetting agent : 5 g/l
  • Squesting agent : 2 g/l


  • Vat (indigo) : 2%
  • Reducing agent (Hydro) : 4%
  • Caustic : 90 g/l
  • wetting : .25%

Sizing:  (for 650 Lts)

  • Starch                        : 75 kg
  • PVA : 20 kg
  • Size CA : 20 kg
  • Wax : 5 kg
  • water : 470 lts

Dyeing Recipe:

2% shade for Blue Black dyeing

Hard Bottoming

  • Sulphur Black : 45 g/l
  • Sodium Sulphide : 67.75 g/l
  • Caustic soda : 10 g/l
  • Wetting agent : 5 g/l
  • Squesting agent : 2 g/l
  • Dispersing agent : 3g/l


  • Vat (indigo) : 2%
  • Reducing agent (Hydro) : 4%
  • Caustic : 90 g/l
  • Wetting : .25%

Sizing:  (for 650 Lts)

  • Starch                        : 75 kg
  • PVA : 20 kg
  • Size CA : 20 kg
  • Wax : 5 kg
  • Water : 470 lts

Dyeing Recipe:

Sulphur Black dyeing

Hard Bottoming

  • Caustic soda : 40 g/l
  • Wetting agent : 5 g/l
  • Squesting agent : 2 g/l


  • Sulphur Black : 7%
  • Sodium Sulphide : 10.5%
  • Caustic soda : 20 g/l
  • Wetting agent : 5 g/l
  • Squesting agent : 3 g/l
  • Dispersing agent : 2g/l

Sizing:  (for 650 Lts)

  • Starch                        : 75 kg
  • PVA : 20 kg
  • Size CA : 20 kg
  • Wax : 5 kg
  • Water : 470 lts


Natural Indigo Dyeing Machine -Sizing is a process where sizing is done to prepare the warp to with stand the weaving operation by binding together the fabric in the yarn to increase its strength by covering yarn with a thin film of size when binds the protruding fibre obtain smooth surface

  • To improve abrasion resistance of the yarn
  • To reduce hairiness of yarn to obtain smooth surface
  • To reduce generation of static charge for polyester blend yarn.
  • To improve breaking strength of cellulose yarn from Indigo Dyeing Machine
Written By – Farid Ahmed, General Manager, Knit Dyeing Textile Ltd. Epz, Savar, Dhaka

About Engr. Kh. Mashiur Rahman

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