Bleaching in Jet and Soft flow dyeing machine: In a jet dyeing machine, a very efficient contact between the liquor and the fabric is established since both are in constant movement. This improved effective treatment and also reduce the treatment time. Jet dyeing machine is similar to winch in that the fabric is circulated through the liquor/dye bath in the rope form. However, in a jet, the transportation of the fabric occurs by circulating the liquor through a venturi jet, instead of the mechanical pull of the reel in a winch. (The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe.) The fabric is pulled out of the main dyeing chamber by means of a high speed flow of dye-liqour that passes through the venture opening. The venture tube has a narrowed passage through which the pumped dye-liquor is forced to move much faster. The jet flow of the dye-liquor formed causes a suction that forces the fabric to pass through the jet tube that lead back into main chamber. Although jet dyeing machine is mainly used for dyeing of Polyester fabric at higher temperature (around 130^oC) with material to liquor ratio ( MLR) 1:5 to 1:10. Because it has high speed in which the fabric moves, creases changes their positions rapidly and there is not enough time to set them in one location. Therefore, creasing is minimal.

Advantages of Jet Dyeing Machine:

The jet dyeing machine is very useful for dyeing polyester fabric. However it can be used for bleaching of cotton fabric also. Following are the main advantages of jet dyeing machine: 

1. Low consumption of water
2. Short dyeing time
3. Can be easily operated at high temperatures and pressure
4. Comparatively low material to liquor ratios, typically ranges between 1:4 and 1:20
5. Fabrics are handled carefully and gently

The next development in the jet dyeing machine is a soft flow dyeing machine.

Soft Flow Dyeing Machine:

Soft flow dyeing machine is very useful for dyeing delicate fabrics like knits. In the soft flow dyeing machine water is used for keeping the fabric in circulation. The conception difference of this equipment from a conventional jets that operates with a hydraulic system is that the fabric rope is kept circulating during the whole processing cycle (right from loading to unloading). There is no stopping of liquor or fabric circulation for usual drain and fill steps. The principle working behind the technique is very unique. There is a system for fresh water to enter the vessel via a heat exchanger to a special interchange zone. At the same time the contaminated liquor is allowed channel out through a drain without any sort of contact with the fabric or for that matter the new bath in the machine.

Key Features of Soft flow Dyeing Machine:

       1.   Significant savings in processing time

       2.   Savings in water

       3.   Excellent separation of different streams results in optimum heat recovery              and a distinct possibility of further use or a dedicated treatment

Following recipe can be taken for bleaching cotton fabric in soft flow dyeing machine:

Hydrogen peroxide (50% concentration):  2-4%

Sodium carbonate: 0.5-1.5%

Caustic flakes: 0.5-1.0%

Sodium silicate: 1.5-4.0%

Wetting agent: 0.2-0.5%

Sequestering agent: 0.02-0.05%

Detergent: 0.5-1.0%

The process parameters are given below:

MLR: 1:4 to 1:5

Temperature: 90-95^oC

Time: 2-4 hours

pH value: 10.3-10.8