Yarn Manufacturing / Spinning
The exam checks the spinning sequence and the purpose of each machine, plus the arithmetic that spinners use daily: draft, doubling, resultant count, twist and production rate. Definitions of sliver, roving and yarn, and the difference between carded and combed routes, are frequent short-answer items.
Process sequence and objectives
- Blow room: opening, cleaning, mixing and lap or chute feed formation.
- Carding: individualises fibres, removes neps, trash and short fibre, delivers card sliver.
- Draw frame: drafting plus doubling for levelness and parallelisation, removes hooks.
- Comber: removes short fibre as noil (typically 12–18%) for fine, strong counts.
- Speed frame: drafts sliver to roving and adds protective twist.
- Ring frame: final draft, twist insertion and winding on bobbins.
Key relations
- Draft = feed mass per unit length ÷ delivery mass per unit length; total draft is the product of individual machine drafts.
- Resultant count after doubling and drafting is found by combining hank and doubling values.
- Cotton twist: TPI = twist multiplier × √Ne; TM is roughly 3.5–4.0 for knitting, 4.0–4.8 for warp.
- Rotor (open-end) spinning reaches very high rotor speeds, gives 3–5 times ring production, but yarn is weaker and suited to coarser counts.
Worked example
Find TPI for 30s cotton at TM 4.2. TPI = 4.2 × √30 = 4.2 × 5.477 = 23.0 turns per inch. Per metre: 23.0 × 39.37 ≈ 906 turns/m. The reasoning: the twist multiplier is constant for a given feel, so twist rises with the square root of the count.
Traps
- Using tex where the formula demands Ne - the √Ne form is for the indirect cotton count.
- Omitting the square root and multiplying TM by count directly.
- Saying combing removes long fibres; it removes short ones as noil.
- Confusing card sliver hank with drawn sliver hank when computing draft.