Dyeing Department

The dyeing cycle starts with gradual infusion of the dye liquor from the dye tank into the main tank which is half filled with water. After the dosing of the dye liquor that happens over 30 minutes, the rest of water is added into the main tank in order to fulfill the total volume.

The density of the yarn wound on to the perforated packages is extremely important. There is an optimum value that must be maintained both above and below which there can be uneven dyeing. Higher package densities can also enhance the chances of breakdown of the main pump due to excess of pressure during dye liquor movements. The yarn package density on the perforated package is typically kept between 0.30-0.35 kg per cubic metre.

Like in case of fabric dyeing, the evenness of the shade is as important in yarn dyeing too. Two factors affect the shade evenness in case of yarn dyeing more than the others. One of them is the in-to-out and out-to-in movement and their ratio; a faulty ratio can result in deeper shades in the layers towards the centre of the yarn packages and lighter shades at the periphery layers. The other factor is dyeing package density, as described above.

In most of the mills, colours for dyeing are weighed manually. The weighing must be accurate, since a slight variation can magnify itself at a larger scale while dyeing. The electronic weighing machine must therefore be calibrated frequently. Many mills have shifted to digitally controlled colour dispensers in order to achieve higher accuracy and lab-to-bulk reproducibility.