Dyeing Processes and Methods
This domain tests whether you can choose a machine and a route. The exam expects you to distinguish batch (exhaustion) dyeing from continuous (padding) dyeing and to recognise which fibre form - loose stock, yarn or fabric - each machine handles.
Yarn dyeing
- Hank dyeing - yarn in hanks on poles in a revolving-reel machine; liquor ratio 1:20–1:30; gentle, suited to wool and handloom cotton; labour-intensive and prone to tangling.
- Package dyeing - yarn wound on perforated cones or cheeses, liquor pumped through the package; liquor ratio 1:8–1:10; efficient, but package density (about 0.3–0.4 g/cm³) must be uniform or channels cause uneven shade.
Fabric dyeing
- Jigger - open width, fabric passes repeatedly through a trough between rollers; low liquor ratio; standard for woven cotton sarees, shirting and suiting; unsuitable for knits or crease-sensitive goods.
- Winch - rope form in a high-liquor bath; good for delicate knitwear and synthetics; risk of rope marks and creases.
- Jet and overflow - rope form with low liquor ratio and high circulation.
- Padding - continuous; nip expression typically 60–100% pickup, then steam, bake or thermosol fixation.
Worked example
An order for 20 kg of fine cotton yarn for handloom warps: hank dyeing gives soft, relaxed yarn but high liquor ratio, more water and labour, and tangle risk. Package dyeing is faster and cheaper but can flatten the yarn and produce shade variation if density varies. For a soft handloom feel the hank route is chosen, with a level dyeing recipe, slow temperature rise and salt additions in portions.
Traps
- Recommending a jigger for knitted fabric.
- Ignoring package density when a shade comes out streaky.
- Treating padding pickup as a fixed figure rather than a measured, controlled value.