Yarn Manufacture: Ginning, Opening, Carding, Drawing, Combing, Roving and Spinning
What the exam tests
The yarn manufacture domain follows the fibre from kapas to ring bobbin. Expect questions on the purpose of each machine, the correct order of the sequence, and one calculation - gin turnout, draft or twist.
Ginning and the blow room
- Saw gin (short and medium staple, high output) versus roller gin (long staple, preserves fibre length).
- Gin turnout % = (mass of lint / mass of seed cotton) × 100; Indian cotton is typically 33–35%.
- The blow room opens tufts, removes trash and dust and blends. Beaters (Hollander, Porcupine, Kirschner) are judged by cleaning efficiency - trash content before versus after.
Carding to spinning
- Carding individualises fibres, removes neps and trash, and delivers a sliver in a can; it sets fibre direction for all later drafting.
- Drawing doubles 6–8 slivers and drafts about 6–8, improving evenness and parallelisation.
- Combing removes short fibre as noil (roughly 8–25%) and is used only for fine, strong yarns.
- Roving (simplex) drafts the drawn sliver into a fine, lightly twisted package that survives winding.
- Ring spinning drafts, twists and winds in one operation; rotor (open-end) spinning is faster but gives lower yarn strength.
Worked example
Find the twist per inch of a 40s cotton yarn with twist multiplier 4.0. TPI = TM × √Ne = 4.0 × √40 = 4.0 × 6.32 = 25.3. A higher TM gives a harder, stronger but less soft yarn.
Traps
Confusing the duties of carding and combing; writing that combing increases sliver weight; forgetting that doubling with an equal draft leaves the count unchanged while improving evenness; mixing ring and rotor economics.