Continuous Bleaching Process with CBR Bleaching Machine

Posted by Default on December 27, 2018 in

Bleaching process: 
Bleaching is a process by which the natural coloring matter and any other colouring matter is removed from natural fiberswhich are responsible for diminishing the fabric whiteness. However for light and medium shades or when fiber brightness is important, bleaching becomes an essential operation before dyeing or printing. With regard to man-made fibers, which are generally ‘white’, manufacturing process sequences can cause a slight discolouration that sometimes cannot be accepted as ‘full’ white. In such cases bleaching is the only resort. 

The natural colouring matter can be destroyed by oxidation or by reduction or a combination of both. 

List of oxidizing bleaching agent: 

• Chlorine (Cl₂)
• Hydrogen peroxide (H₂O₂)
• Sodium peroxide (Na₂O₂)
• Potassium persulphate (K₂S₂O₈)
• Hypochlorous acid (HOCl)
• Potassium permanganate (KMnO₄)
• Perborates (KBO₄)
• Ozone (O₃)

List of reducing bleaching agent:

• Sulphur dioxide (SO₂)
• Sodium sulphite (Na₂SO₃)
• Sodium hydrosulphite (Na₂S₂O₄)
• Sulphurous acid (H₂SO₃)
• Bisulphites (NaHSO₃)

Importance of continuous pretreatment processes: 

In continues bleaching range it combines the pre-treatment processes of textiles like scouring and bleaching in the machine itself. This minimizes energy consumption and reduces number of operations. 

Bleaching of cotton with Hydrogen peroxide (H₂O₂): 

H₂O₂ → H₂O + [O]

H₂O₂ ↔ H⁺ + HO₂^-………..1

HO₂^- → OH^- + [O]………...2 (Nascent oxygen or bleaching agent released)

H₂O₂ + NaOH → NaHO₂ + H₂O……………3         (Saponification)

NaHO₂ ↔ Na⁺ + HO₂^- ……….4

2H₂O₂ → 2H₂O + O₂↑………..5

Process flowchart of CBR bleaching machine: 

Batch 
↓ 
Entry J-scray 
↓ 
Padding unit 
↓ 
Steamer 
↓ 
Hot wash (95°c) 
↓ 
Hot wash (95°c) 
↓ 
Hot wash (95°C) 
↓ 
Acetic acid wash 
↓ 
Vertical drying chamber 1 
↓ 
Vertical drying chamber 2 
↓ 
Exit J-scray 
↓ 
Batching

Important information about CBR bleaching machine:

• Speed of the machine: 70 m/min
• Length of machine: 280 m
• Pick up% : 100%
• pH maintained of the liquor: 10-12
• Capacity of minute trough: 50 L
• Chemical brand used: IGSURF

Fig: CBR bleaching machine

CBR Recipe: 

Sl.No	Chemicals used	Chemicals name	Quantity (ml/kg)
1	Hydrogen peroxide	H2O2	18-25
2	Caustic(360 gpl)	NaOH	35-40
3	Wetting agent	36CL	4-5
4	Stabilizer	3115PS	1/4th of peroxide
5	Sequestering agent	3120CI	3-4

Calculation : 
Dosing per minute: (Speed x GLM x Dosing) / 1000, 
where, GSM x 100= GLM (gram linear meter) 

Working procedure CBR machine: 

1. Cloth is taken from the batch through the guiders and guide rollers into the J-scray using a beatter roller to remove any crease in the fabric. From which it is taken into the padding unit with the help of bow rollers to prevent from formation of crease in the fabric. 

2. The fabric is immersed in the liquor using an immersion roller. It has a pipe attached to it through which it maintains the level of liquor from minute trough, which has a holding capacity of 50L. It receives the liquor from the tank using sensors. 

3. The fabric is then passed into the steamer using a squeezer known as optimax roller. Unlike desizing machine it has double bed where the fabric in the upper part is arranged in a double S threading. 

4. The dwell time varies from 10min for yarn dyed fabric to 15min for bleached fabric. The temperature is maintained at 95°c-97°c. The temperature at lower compartment of steamer is slightly less to avoid formation of cloud. 

5. The fabric is then passed through a metallic guider to washing chamber having water holding capacity of 1000L. 

6. After three consecutive hot wash at 95°c, the fabric is washed with acetic acid to neutralize the fabric and passed to the two VDR ( Vertical drying range) having temperature of 120°c to dry the fabric. 

7. From where it is taken through the guiders and guide rollers to the winding roller and finally batching is done.