3. Bleaching in winch and softflow:

The Winch:The winch is one of the oldest dyeing machines knowns. It consists of a tub containing the liquor, and an elliptical winch or reel which is located horizontally above the liquor bath. Numbers of fabric pieces can be treated in this machine simultaneously. Each piece is drawn over the winch, and itstow ends sre sewn together to form an endless rope. The ropes ar kept in the winch machine side by side, separated from each other by rods to prevent them from tangling. During processing, the reel rotates, pulling the ropes out of liquor bath and drpping them back into the bath at opposite side. In this way almost all the fabric is kept inside the liquor bath. A vertical perforated partition is located a few inches from the front of the machine, enclosing the steam pipes, so as to prevent them coming in direct contact with the fabric. The partition also provides a space for adding chemicals in their concentrated solutions form in such a way that they donot come directly in contact of fabric. 

Winch machine is very useful for treatment of light weight fabric and knits as these fabric can easily folded into a rope form without causing damage.  If the fabric is very light weight, it should not be treated in winch as these fabric may float on the liquor bath and tangle.

In winch machine treatment is carried out at higher liquor ratio (MLR::1:20 to 1:50) snf since the tension applied by the pool of the winch is low, the treated fabrics acquire a softer hand. For bleaching of cotton following recipe may be taken:

1. MLR: 1:40

2. Hydrogen peroxide: 3 g/l

3. Sodium silicate: 4g/l

4. Sodium hydroxide: 1 g/l

5. Wetting agent : 0.2 g/l

The above chemicals are added into liquor bath of the winch at around 40 degree C and then temperature is raised to 90-95 degree C over around 45 minutes and maintained for 60 to 120 minutes as per the requirement of whiteness.