Principle of Soft Flow Dyeing Machine

Textile material can be dyed using batch, continuous or semi continuous process.

Batch processes are the most common method used to dye textile materials. There are three general types of batch dyeing machines:

1. In which fabric is circulated
2. In which dye bath is circulated
3.  In which both the bath and material is circulated.

Jet dyeing is the best example of a machine that circulated both the fabric and the dyebath. Jet dyeing is used for knitted fabrics. For Terry-towels soft flow dyeing is use.

In jet dyeing machine the fabric is transported by a high speed jet of dye liquid.

As seen in the figure, this pressure is created by venturi. A powerful pump circulates the dyed bath through a heat exchanger and the cloth chamber. Cloth guide tube helps in circulation of fabric.

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The vigorous agitation of fabric and dye formulation in the cloth increases the dyeing rate and uniformity. It minimizes creasing as the fabric is not held in any one configuration for very long.  The lower liquor ration allows shorter dye cycles and saves chemicals and energy.

In soft flow dyeing machines the fabric is transported by a stream of dye liquor. However, the transport is 

assisted by a driven lifter reel.

These machines use a jet having lower velocity that that used on conventional jet dyeing machines.

The soft flow machines are more gentle on the fabric than conventional jet machines.

The following are the features of a soft flow U-Type dyeing machine offered by Taxfab:

1. Machine pressure vessel and major wet parts made of stainless steel AISI 316/ 316 L, highly corrosion resistance material.

2. Heavy duty stainless steel centrifugal pump for optional dye liquor circulation. Highly efficient heat exchanger for fast heating and cooling. 

3.  A stainless steel filtering device placed in such a way for easy cleaning. 

4.   A unique design of jet nozzle can provide high discharge of liquore with subsequent pressure to ensure fast movement of fabric transport upto 300 Mtrs / Min., and the speed of fabric can be adjusted, required to desire quality. 

5. A mirror polished fabric transport perforated basket for easy trouble free movement of fabric from back to the front of machine, perforated basket fabricated in such a way that welding part does not come in contact with fabric.

6. For preparing chemical, colour kitchen tank is provided made out of stainless steel 316, with required valves for auto dozing. 

7. All valves is made of investment casting and is of stainless steel 3l6.

8.Electrical control panel with microprocessor to operate the machine is provided with pneumatic control circuits.

9. Magnetic level indicator duly calibrated for correct liquor measurement. 

10.       Take off reel with direct couple geared motor and stainless steel structure 

11. All safety device required for a pressure vessel is incorporated with the machine.

A front view and side of the machine offered by them is as given below:

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Controlling Shade in Indigo Dyeing of Denim

If shade is getting:

Redder- Increase the conc. of Caustic , slightly decrease the conc. of Hydro
Redder, Duller- Increase the con. of hydro
Greener, Paler- decrease the con. of hydro
Greener, duller- Increase the con. of caustic
Bronzing- Increasing the con. of Hydro

Receipes for different shades of Denim

Receipes For Different Shades on Denim


A) Black-on-Black
Black-on-Blue

Recipe

Liquid Sulphast Black= 200 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI = 10 gpl
Soda Ash= 10 gpl

B) Blue-on- Blue

Receipe

Liquid Sulphar Navy Blue = 100 gpl
Liquid Sulphast Black= 50 gpl
Sodium Sulphide= 20 gpl
Sandozol HSI= 10 gpl
Soda Ash= 10 gpl

C) Reactive Series

Receipe

01) Ramazol Turquoise Blue G = 110 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate= 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

D) Ramazol Coffee Brown G

Receipe
01) Coffee Brown G = 100gpl
Urea = 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda= 10 gpl

Ratio of 01) and 02) = 3:1

E) Ramazol Parrot Green

Receipe
01) Ramazol Turquoise Blue G = 90 gpl
Ramazol Yellow FG = 40 gpl
Urea= 100 gpl
Swanic 6L= 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

F) Ramazol Blue

Receipe
01) Ramazol Black B = 70 gpl
Urea = 100 gpl
Swanic 6L = 10 gpl

02) Sodium Silicate = 250 gpl
Caustic Soda = 10 gpl

Ratio of 01) and 02) = 3:1

Notes on Dyeing of sulphur black on Rope Dyeing Range

1. Process of dyeing of sulphur color:

1st Wash tank: mercerisation by taking 22% NaOH ie. 250 gpl
2nd Wash Tank: Hot Wash
3rd Wash Tank: Cold Wash

2. In 1st and 2nd dye bath take sulphur color 6-8% on the weight of the yarn sheet. Temperature 90 deg. cel. The solution contains the following:

1. solubalised sulphur color: 150 gpl
2. Na2S--> reducing agent: It is added to increase its reducing power
3. Caustinc Soda --> 10 gpl--> reducing agent
4. Wetting agent--> 2gpl
5. Antioxident Sulphide ( Glucose paste--> 5gpl). This is added to prevent the oxidation of of Sulphide solution. It will always remain in reduced form
( Alos if the shade is slightly greyish, one can add tiny tinge of sulpher blue--> 20gpl)

in III, IV and V dye bath--> cold wash
in 6th dye bath. We take H2O2(30%)+Acetic Acid(2:1 by weight). H2O2 acts as an oxidising agent. But as it acts on neutral pH (=7) and after cold bath the solution is slightly alkaline, to make it neutral wil add acetic acid. Acs in alkaline pH, oxidising action of H2O2 will be similar to the bleaching action, which may cause tendering in the fabric.

7th and 8th Dye Bath: Cold Wash

Wash Box Number 4: Here washing is done with detergent and soda ash at 60-70 deg.c

5th and 6th Wash Box: Hot Wash

7th wash Box: Here softner is added at 25 gpl. It is cationic softener with pH 4.5 to 6.5. As during oxidation of sulphur, strength is reduced by 10%. On a yarn sulphur is of two types :
1. Free Sulphur
2. Reacted Sulphur.

The free sulphur will react with moisture in the atmosphere to form:
H2O + S --> H2SO4
Which tenders the yarn. Now at acidic pH reaction is much faster. So we add only a small amount of softener (25 gpl) as against that in indigo which is 100gpl.

3rd Point

Over all during sulphur dyeing and storing, the yarn strength is reduced by 15% as compared to Indigo.

4th point

If ball formation takes place of sulphur dyed warp at loom shed, then we can taken in 4th dye bath little Na2S+Caustic to reduce the free sulphur.

Practical Notes on Rope Dyeing for Indigo Dyed Denim

Practical Considerations in Rope Dyeing for Indigo dyed Denim.

The passage of yarn in rope dyeing is as follows:

Pre-scouring -->hot wash-->cold wash --> Dye baths--> hot wash-->cold wash--> application of softener

lets discuss these processes one by one:

Pre-scouring

1. The objectives of pre-scouring are the removal of wax content from cotton, removal of trapped air from cotton yarn and Making yarn wet

2. This is done at 90 o C

3. We use the following ingredients at pre-scouring stage:

Caustic Soda: Its quantity depends upon the quality of cotton fibres used in the mixing. Generally we take 2-4% of caustic soda. It removes the wax by the action of soapanification.
Wetting agent: It is anionic in nature
Sequestering Agent: Even with the use of water softening, it is very difficult to find the desired softness in water ( about 2-3 ppm) . So we use the agent to make the water soft.

4. Why Trapped Air should be removed. The reason for this can be understood as follows:
In 1 kg of yarn, there is approximately 2 litres of air. 1 litre of air decomposes 1.8 litres of Sodium Hydrosulphide. It will cause uneven dyeing and more consumption of Sodium Hydrosulphide ( hydro).

5. Absorbency of yarn may be checked after scouring.


Hot wash

As some caustic is carried by the yarn after pre-scouring, so hot water is given at 70-800C. If this is not done, this yarn will go into the dye-bath which will change the pH of the dye-bath.

Cold Wash

After hot wash, yarn temperature is more. To bring it back to its room temperature, cold wash is given to it.

INDIGO DYEING

1. Indigo is not a perfect vat color. It may be called a trash vat color. The constant of substantivity for other colors is 30, for indigo it is only 2.7. So there is a need of 5 to 6 dye baths and make the use of multi-dip and multi-nip facility to increase the penetration.
2. The dyeing is done at room temperature as indigo belongs to Ik class of vat dyes, where dyeing is done at room temperature and oxidation is done by air only and not by chemicals. If oxidizing agents are used, they will cause stripping of colors.

3. Indigo is not soluble in water. So it is reduced with Sodium Hydrosulphide. Then caustic soda is added to make sodium salt of vat colors to make it soluble. To reduce 1 kg of Indigo, 700 gms of sodium hydrosulphide is required. However some extra SHS needs to be taken to avoid some decomposition of SHS.

Practically it is prepared in the following sequence

-Take indigo
-Add caustic
-Then reducing agent

4. When caustic is added to indigo, it is an exothermic reaction. It is allowed to cool down, then before sending it to feeder, sodium hydro-sulphide is added. Reducing agent is not added first as it will be decomposed first, so consumption of it will increase. It is also not advisable to take solubalised vat, as offered by some companies due to the following reasons:

a. If it is used after 6 months, there will be a decomposition of sod. Hydrosulphide. It will become partially soluble. Then to make it soluble again, more SHS has to be added.
b. Transportation is difficult
c. Cost is more

5. Feeding System

Rat of flow of yarn is given by

((No of ropes x no of ends x speed of machine)/ count x 1.693 x 1000)

in kg of yarn / minute

So we can determine the rate of feed of indigo. It is very important that replenishment of indigo is there as any variation will result in the change of shade and also if level is more, there is a problem of over-flow.

6. If total capacity of dye bath for example is 15000 litres, then circulation must be 3 times the volume. If it is less then there are 100% chances of getting a lighter shade.

7. Core and ring dyeing effect
This effect is obtained by multidip-multinip facility

8. pH of the Dye bath should be kept in between 10.5-11.5. At this pH , sodium salt of Indigo is mono phenolic form. At this form, the strike rate of dye is very high. So after washing, there will be a better dye effect. At pH 11.5 to 11.7, at this affinity is less, so dye effect will be less prominent.

pH is controlled by the addition of caustic soda.

9. Testing of Hydro

TOTAL HYDRO
We take 10 ml of indio with SHS in 30-35 ml of water. It is set for one minute and shaken. As air will decompose SHS. So vacuum created will fetch the water from above. If 3 ml of water is required, then concentration of hydro is 3 gpl. As a thumb rule, concentration of total hydro should be min. 1.5 gpl.

REDUCED HYDRO

It is the hydro that is used for the reduction of Indigo. It should be around 0.7 ( 1000 kg of Indigo needs 700 kg of hydro to reduce it). For testing we take 10 ml of dye solution and 30 ml of water and 5-6 drops of 40% formaldehyde and shake it for one minute. The water that goes gives the readings of the reduced hydro.

Total Hydro- Reduced Hydro = free hydro

If Total hydro is min. 1.5 gm/lit. then free hydro must be min. 0.5 gms/ litre which acts as buffer

10. Also hydro reduction capacity is measured by mV meter which measures the Redox Potential.

It should be around 760-800

Through the day, the redox potential should be +- 20 mV of the norm. If it is more then the process control is a failure.

Caustic--> It is around 0.4 to 0.5 times the hydro used.

Washing
Rubbing fastness of indigo is very important. On a scale of (1-4), it is 2. Washing is done to improve the rubbing fastness.

Wash at 60 deg.--> Wash at 60 deg.--> Wash at room temperature--> wash with softener

Why Softener:

1. The rope is going to be opened at Long Chain Beamer. It the softener is not used, opening will be hampered.

2. It is generally 1.2% of the weight of the yarn. It is a cationic softener. It is always having pH in the range of 4 to 55. Softening is done at room temperature. If high temperature is used there is always some chance of tendering of yarn.

3. Concept of Buffer pH is given by Virkler USA, they say by addition of this, there is 40% less consumption of Indigo for same shade depth.

4. Metering Consumption

If solution is of 900 litres
10% Indigo-->90 litres
Hydro--> 90*.7 = 63 kg
Caustic--> 63*0.445= 28 kg.