Balancing of machines for complete process house :Part-3 Scouring and Bleaching

For this purpose one Pre-treatment Range (PTR) is required.

Machine working speed: 60 m/min, M/c utilization= 80%

Total production per shift (8 hours or 480 min)= (speed x utilization x 480)/100

= (60 x 80 x 480)/100 = 23,040 meter

Total fabric to be pretreated= 50,000/-

23,040 meter fabric treated in 8 hours

50,000 meter…………= (8 x 50,000)/23040 = 17.36 hrs

Balancing of machines for complete process house :Part-1 (Introduction)

•      Machine balancing is a most important part of any process house to run production smoothly.

•      Let us take example of dyeing of 50,000 meter 100% cotton medium weigh quality (150 gsm) fabric to understand this

Process flow:

To start it, let us have following process flow:

Grey cotton fabric------Singeing & Desizing------Scouring------Bleaching-------mercerizing-----dyeing-----finishing----finish folding

Let us have following type of machines to carry out processing of 100% cotton fabric:

•      Singeing cum Desizing

•      Scouring & Bleaching (Pretreatment renage-PTR)

•      Mercerizing

•      Continuous dyeing range (CDR)

•      Softening & Drying on stenter

•      Sanforzing (Zero-zero)

Scouring and cleaning of raw wool:

Wool is composed with Keratine (approx. 33%), Dirt (Aprrox. 26%), Suint (Dry perspiration: 28%), Fat/grease (12%), Burr (Vegetable matter: 2-10%), Mineral matter (aprox. 1%) and Colouring matter (0.5 to 1%).

1. Wool grease can be removed by scouring. These Grease/waxes are comprised of a variety of monocarboxylic, dicarboxylic and hydrocarboxylic acids as well as steroidal alcohols. It has been determined that unscoured wool contains an unoxidized fraction of wool grease and other contaminants that is easily removed and readily recoverable 

2. Suint is usually considered to be a variable composition of water-soluble materials that is readily removed by scouring. 

3. The dirt that is removed from the scoured wool consist of both inorganic and organic materials.

4. Dirt: It is held by adhesive action of suint and wool fat. It removed during the scouring and washing processes.

5. Burrs: It is vegetable fragments consisting of dried grass, straw, sticks etc. These vegetable fragment come on the body of sheep during grazing and scratching the body against bush or tree to relive itching. It is remove using Carbonizing process. Following is the process of removal of Burrs:

i) Wool is resistant to acid. Burr being a vegetable matter is not resistant to acid.

ii) This property is used for the removal of burr.

iii) In this case wool is treated with 5-7% Sulphuric acid for 2 hours followed by hydro-extraction and then drying at 80-90oC for 20-30 minutes. 

iv) Carbonized burr is removed by washing with mechanical agitation.

Technology of bleching:

Bleaching cab be carried out using following three ways:
i) Batch process
ii) Semi-continuous process
iii) Continuous process

Let us discuss these processes one by one:

i) Batch process: 
We can devide batch process in two categories:
a) Fabric bleaching: Kier bleaching, Bleaching in Jigger, Bleaching in winch & Softflow
b) Bleaching of yarn using cabinet and cheese machine

a) Fabric bleaching:

1. Kier Bleaching: Most common process in batch wise process is kier bleaching.  In such process fabric is first desized and then scoured and bleached (Combined process) in kier. Soem time desized and scoured fabric is also taken to kier for bleaching. Hydrogen peroxide is used as bleaching agent. Folling steps may be taken in kier bleaching:

- Loading fabric in kier
- Raisong temperature of bleach liquor slowly to 90-95 degree C with an intermediate holding of 10 minutes at 70-75 degree C to allow any trapped air escape
- Bleaching for about 3 hours  at 90-95 degree C
- Wahing with hot water on rope washing machine

The application of pressure kier can reduce time 1-2 hours as the process temperature is 120 degree C.

After the peroxide bleaching the fabric is thoroghly washed and treated with peroxide killer to remove residual peroxide.

Following recipe may be used for kier bleaching:

Fabric which is desized only:
Hydrogen peroxide (35% Conc.) for desized only: 3-0-5.0 %
Sodium Silicate for desized only: 2.0-3.0 %
Sodium Hydroxide for desized only: 0.6-1.4%
Wetting agent for desized only 0.1-0.2%

Fabric which is desized & Scoured:
Hydrogen peroxide (35% Conc.) for desized & scoured : 1.0-2.0 %
Sodium Silicate for desized & scoured : Not required
Sodium Hydroxide for desized & Scoured: 0.4-0.8%
Wetting agent for desized and scoured: 0.1-0.2%

Scouring Process for Cotton:

It is a process to remove all undesirable impurities especially natural origin like fats, wax, vegetable matter such as seed coat fragments, pectins, protein etc. Scouring process also removes some added impurities (which are not naturally present) such as oil stains, residual sizing material. Scouring process improves absorbency of cotton material. With the improved absorbency, water can transport dyes and chemical within the cotton fibres. Proper scouring is must for uniform dyeing and printing. The main objective of scouring is to  make textile material highly hydrophilic or improve water absorbency.

Mechanism of scouring: Following are main points related to mechanism of scouring:

i) Saponification: The vegetable oil, which is immiscible with water, is glyceride of fatty acids. When such oil are heated with a solution of sodium hydroxide (Caustic soda) in water, the oil splits up into its constituents fatty acid and glycerine. Glycerine is miscible with water easily and the fatty acids reacts with sodium hydroxide present in the solution forming its sodium salt i.e soap which is also soluble in water. Thus oil is removed.

Saponification process

ii) Emulsification: Wax and non saponifiable oils (Non polar) are removed by emulsification as they are immiscible in water (Polar). Normal washing soap  is used as a emulsifying agent which make emulsion of them. Soap generated from the saponification process also act as a emulsifying agent.

The scouring process brings following changes in cotton fibres:

i) Oils and fatty acids are converted into soaps.
ii) Pectins and pectose are converted into soluble salts of pectic acid.
iii) Mineral matters are mostly dissolved or settle down.
iv) Non saponifiable oils are emulsified by the soluble soaps generated from the saponificable oils.
v) Additive dirt's are removed.
vi) Residual sizing materials are broken down into soluble products.