Staple Yarn Preparation: Ginning, Blowroom, Carding, Drawing and Combing

This chapter opens the Engineering Sciences (XE) paper's treatment of Section XE9.2, “Yarn Manufacture, Yarn Structure and Properties”, of XE9 Textile Engineering and Fibre Science, one of the nine optional sections of which a candidate answers any two. It answers the first part of the heading: “Principles of ginning; Principles of opening, cleaning and blending; Working principles of modern blowroom machines; Fundamentals of carding; Conventional vs. modern carding machine; Card setting; Card clothing; Periodic mass variation in card sliver; Card autoleveller; Principles of roller drawing; Roller arrangements in drafting systems; Periodic mass variation in drawn sliver; Drawframe autoleveller; Principles of cotton combing; Combing cycle and mechanisms; Recent developments in combing machine.” It teaches how seed cotton becomes a clean, parallel, even sliver. The numericals are ginning out-turn, cleaning efficiency, draft and doubling, production rates of card and comb, the wavelength of a periodic fault, and autoleveller delay.

1. Ginning: separating lint from seed

Ginning separates the spinnable fibre (lint) from the seed. The yardstick is the ginning out-turn (GOT) = mass of lint ÷ mass of seed cotton × 100. If 100 kg of seed cotton gives 34 kg of lint, GOT = 34 %; the rest is seed, trash and moisture loss. Two principles are used.

GinPrincipleSuited to
Saw ginA seed-cotton roll is held against ribs; saw teeth catch the fibres and drag them through gaps narrower than the seed, which cannot passShort and medium staple; high output
Roller ginA rotating leather or composition roller grips fibres; a fixed knife pins the seed while a reciprocating knife beats it offLong and extra-long staple; gentle on fibre

The saw gin is faster but cuts and tangles more fibre (more short fibre and neps); the roller gin is slow but gentle. Over-drying or over-wet seed cotton hurts both GOT and fibre quality, and many mills add lint cleaners after the gin.

2. Principles of opening, cleaning and blending

Opening reduces large compressed tufts to small ones; cleaning removes trash (leaf, seed-coat, dust) from them; blending mixes bales so that the product is uniform. The three are linked: trash is locked inside tufts, so cleaning can proceed only as far as opening has gone. A beater strikes a tuft held or carried by an air stream; the tuft is flung against grid bars, and heavy trash falls through the gaps while fibres are carried on. Dust is drawn away by suction. Cleaning efficiency is defined as

cleaning efficiency (%) = (trash % in feed − trash % in delivery) ÷ (trash % in feed) × 100.

  • Beater speed and type: a pin or spiked beater opens gently; a blade beater cleans more strongly but damages more. Higher speed and closer settings clean more and also raise fibre breakage and neps.
  • Blending is done by mixing bale-by-bale (bale plucking from many bales at once) and by layering in a hopper or multi-mixer so that fibre properties are averaged. Blend proportion is by mass.
⚠️ Trap
Cleaning efficiency of a machine is not the same as the amount of waste it removes: a machine that throws out much good fibre has a high waste % but poor selectivity. Mills judge a line by cleaning efficiency together with fibre loss and neps added.

3. Modern blowroom machines

A modern blowroom is a chain of machines joined by pneumatic ducts, with gentle action first and stronger action later, so that tufts are already small when the strongest beaters meet them.

Typical modern line
StageFunction
Automatic bale opener (plucker)A travelling head takes thin layers of tufts from many bales; gives bale-wise blending
Metal and heavy-part trapMagnets and detectors protect the card clothing from tramp metal
Mixer or blenderLong-term mixing and a buffer between stages
Pre-cleaner and fine openerBeater and grid cleaning in one or more steps; heavy trash and dust removal
Foreign-matter detector or separatorOptical or sensor detection of coloured or polymer contamination, removed by an air jet
Chute feed to cardsDelivers tufts into a feed chute at each card; the column density sets the card feed and enables levelling

Developments include fewer machines in the line (shorter line means fewer neps), automatic control of waste removal, cleaning intensity set by the amount of trash, and the replacement of the lap by direct chute feeding.

4. Carding: action, machine, setting and clothing

Carding opens tufts into individual fibres, removes remaining trash, short fibre and neps, partly parallelises fibres and delivers a continuous sliver. The carding action occurs where two wire-covered surfaces move at different speeds with their points facing each other (point-against-point): fibres are held on the slower surface and combed by the faster. The stripping action occurs when the points lean the same way and the faster surface lifts fibres off the slower one; the cylinder strips the taker-in in this way. The slow doffer collects fibres from the fast cylinder as a thin web, which is condensed into the sliver.

A conventional card is a roller-and-clearer or revolving-flat card with a feed lap and slower production. A modern card has a chute feed, extra pre-carding and post-carding segments (stationary flats and carding elements), a wider and faster cylinder, higher doffer speed and autolevelling; it delivers several times the production at equal or better sliver quality. The flats (a slowly moving chain of clothed bars) do most of the carding against the cylinder and carry away flat strips containing short fibre, trash and neps.

  • Card setting is the gauge distance between surfaces, set with feeler gauges: feed plate–taker-in, taker-in–cylinder, cylinder–flats, cylinder–doffer. The settings are only fractions of a millimetre and differ from one pair of surfaces to another. A closer cylinder–flats setting raises carding intensity and neps removal but cuts more fibre and wears the wire faster.
  • Card clothing is the wire on the working surfaces. Flexible clothing is saw-tooth or needle wire set in a fabric foundation (flats, and in older cards cylinder and doffer); metallic clothing is a continuous saw-tooth strip wound on a roller (taker-in, and cylinder and doffer in modern cards). Key parameters: tooth angle (a more acute, aggressive tooth grips fibre firmly but strips poorly), points per unit area (finer fibres need denser, finer wire), tooth depth and height. Sharp, undamaged teeth are essential, so clothing is ground.
🧠 Memory ladder
Remember the arrangement as a ladder: each step from taker-in to cylinder to flats offers finer wire and higher point density, so the fibre is opened progressively and never shocked.

5. Card sliver: periodic variation, autoleveller and production

Periodic mass variation repeats at a fixed length. A mechanical source (an eccentric or bent roller, a worn gear) delivers a fault once per revolution. The material delivered by a faulty roller of diameter d in one revolution is πd long. If the material is further drafted by a draft D between that roller and the delivery, the wavelength in the delivered sliver is

λ = π d × D. Example: a roller of 28 mm diameter with a draft of 6 after it gives λ = π × 28 × 6 ≈ 528 mm. A peak in the spectrogram at that wavelength points at that roller; a broad hill at a wavelength set by the fibre length, not by any roller, is a drafting wave instead, caused by floating fibres.

A card autoleveller corrects the mass of the sliver by changing the draft. In an open-loop system the mass is sensed at the feed (for example the density of the chute column or the feed thickness) and the feed-roller speed is altered after a delay equal to the distance from sensing to correction divided by the material speed; it cannot see its own errors. In a closed-loop system the mass is sensed at the delivery and fed back; it corrects its own drift but acts on material already made. Card levellers correct long and medium wavelengths, not short ones. Production: kg/h = delivery speed (m/min) × sliver tex × 60 ÷ 10⁶ × efficiency; at 120 m/min, 4800 tex and 90 % efficiency this is 31.1 kg/h. Draft = feed tex ÷ delivery tex, ignoring waste.

⚠️ Trap
The wavelength formula uses the draft between the faulty roller and the delivery, not the total draft of the machine. A fault from the front delivery roller itself has no draft after it, so λ = πd.

6. Roller drawing and the drawframe

Roller drafting attenuates a strand by passing it between roller pairs whose surface speeds rise in sequence. Draft = V_front ÷ V_back = (feed tex) ÷ (delivered tex), for no loss. A drawing machine usually creates a break draft (small, to prepare fibres) before the main draft. Several slivers are fed together (doubling, n), so delivered tex = n × feed tex ÷ draft. Doubling averages out irregularity: for independent random errors the CV of the doubled sliver falls by √n. A drawframe that uses 6 slivers of 3600 tex at draft 7.5 delivers 6 × 3600 ÷ 7.5 = 2880 tex.

Fibres gripped by neither roller pair are floating fibres; they move erratically and create drafting waves, so the roller setting (nip to nip) is set a little more than the longest fibre in the main zone, and kept small enough that short fibres are still controlled. Pressure bars, aprons or pins add control inside the zone. Common arrangements include three-over-three and four-over-three drawframe drafting with a weighted pressure bar, and double-apron drafting for roving and ring frames. Periodic variation in drawn sliver has the same two origins as in the card: mechanical (λ = πd × D) and drafting waves.

The drawframe autoleveller senses the input sliver mass (usually with a pair of grooved scanning rollers), a controller computes the correction, and a servo motor changes the main-draft speed at the instant the sensed material reaches the draft zone. The time lag is distance ÷ feed speed: with sensing 0.30 m ahead and a sliver speed of 15 m/min the delay is 0.30 ÷ 15 = 0.02 min = 1.2 s. It cures short, medium and long-term errors in the feed; closed-loop sensing on the delivery is used in addition on some machines.

7. Cotton combing

Combing removes short fibres (below a set length), neps and fine trash, and straightens fibres, so the noil is rejected: noil % = noil mass ÷ feed mass × 100. It makes finer, stronger, more even and cleaner yarns from long-staple cotton, at the price of lost fibre and a few extra machines (sliver-lap, ribbon-lap and comber). The cycle in each nip has four main stages.

  • Feeding: the lap is fed forward a small amount per nip (feed per nip, a few millimetres) to the nippers.
  • Nipping and combing: the nippers close on the fibre fringe and the half-lap, a needle-covered segment of the rotating cylinder, combs the protruding fringe, removing short fibres and neps.
  • Detaching and piecing: the nippers open, detaching rollers turn backward to return the previously combed web, which overlaps the new fringe, then turn forward and pull the fringe out; the fibre tails are combed by the top comb as they are drawn through it.
  • Noil removal: the combed-out waste is cleaned from the cylinder by a brush and carried away by air.

Production per hour = nips/min × feed per nip × lap tex × heads × (1 − noil fraction) × 60. For 8 heads, 400 nips/min, feed 5 mm per nip, lap 70 ktex (70 g/m) and noil 16 %: lap fed per head per minute = 400 × 0.005 m × 70 g/m = 140 g, so 1120 g/min for 8 heads, 940.8 g/min of combed sliver, which is 56.4 kg/h at 100 % efficiency. Recent developments are higher nip rates with servo drives, lighter moving masses, automatic lap changing and piecing, and individually adjustable noil settings.

🎯 Why
Raising the noil % raises mean fibre length and lowers short-fibre content, so yarn is stronger and more even; but each extra point of noil is fibre bought and thrown away, so the noil is set by the count and quality being made.

Key takeaways

  • GOT = lint ÷ seed cotton × 100; the roller gin is gentle on long staple, the saw gin is fast and cuts more fibre.
  • Cleaning follows opening; cleaning efficiency = (trash in − trash out) ÷ trash in × 100, and stronger beating adds neps and breaks fibre.
  • Carding action is point-against-point between cylinder and flats; settings and wire get finer toward the flats; a periodic fault has wavelength λ = πd × (draft after the faulty roller).
  • Open-loop levellers sense the input and act after a delay of distance ÷ speed; closed-loop levellers sense the output and correct their own drift.
  • Draft = V_front ÷ V_back; delivered tex = n × feed tex ÷ draft; doubling n independent slivers reduces CV by √n; floating fibres cause drafting waves.
  • Combing removes short fibre, neps and trash through feeding, nipping and combing, detaching and piecing, and noil removal; production = nips/min × feed × lap tex × heads × (1 − noil).

Practice questions (17)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

  1. Which gin is preferred for long-staple cotton that must be handled gently, and why?

    1. Saw gin, because its teeth draw fibres through ribs at a very high rate, which is why it is the gin for the finest long staple
    2. Roller gin, because it gives the highest ginning out-turn of any gin, whatever the variety of cotton being ginned
    3. Saw gin, because the sawing action straightens and lengthens the fibre, giving the longest and most uniform lint
    4. Roller gin, because a roller grips the fibre while a knife strips off the seed, damaging the fibre less
    Show answer

    Answer: D — Roller gin, because a roller grips the fibre while a knife strips off the seed, damaging the fibre less

    The roller gin handles fibres gently and is used for long and extra-long staple, though it is slower. The saw gin is faster but cuts and tangles more fibre, so it suits short and medium staple; it does not lengthen fibre. Out-turn depends mainly on the cotton variety, not on the gin type being the highest.

  2. Why can a blowroom not remove trash efficiently from large, tightly compressed tufts?

    1. The air stream in the ducts carries trash and tufts at the same speed, so the trash is never separated from fibre
    2. Large tufts are heavier than trash and so fall through the grid bars with it, and these tufts are heavier than the trash
    3. Trash is held inside the tuft, so it can be exposed to the grid bars only after the tuft has been opened
    4. Beaters can act only on tufts that already contain no trash because opening is complete before the blowroom starts
    Show answer

    Answer: C — Trash is held inside the tuft, so it can be exposed to the grid bars only after the tuft has been opened

    Impurities are embedded in the tufts; cleaning needs opening first, which is why opening is progressive. The tempting alternative about weight is wrong: large tufts are retained by the grid, they do not fall through it.

  3. In which arrangement of two wire-covered surfaces does the carding action take place?

    1. The points lean in the same direction and the faster surface lifts fibres off the slower one, so the points of the two surfaces never meet in opposition
    2. A smooth roller presses fibres against a wire-covered surface so that the fibre is simply flattened between them
    3. The surfaces move at exactly equal speeds with no relative motion between points, so fibres are carried round without any combing action
    4. The points face each other, the surfaces move at different speeds and fibres are held on one and combed by the other
    Show answer

    Answer: D — The points face each other, the surfaces move at different speeds and fibres are held on one and combed by the other

    Carding is point-against-point with differing speeds, as between cylinder and flats. The same-direction arrangement described in the first alternative is the stripping action.

  4. The cylinder–flats setting of a card is reduced from a wide to a close gauge, all else unchanged. Which outcome is most likely?

    1. Carding is more intense and neps removal improves, with more fibre breakage and faster wire wear
    2. Fewer neps are removed and the fibre is carded less intensely and the flats strip more of the fibre as short waste
    3. The doffer speed must rise in proportion to the gauge so that no extra fibre breakage can occur
    4. Flat strips become lighter because fewer fibres reach the flats and the wire wears slower than before
    Show answer

    Answer: A — Carding is more intense and neps removal improves, with more fibre breakage and faster wire wear

    A closer gap makes the flats work harder on the fibre fringe, so carding intensity and nep removal rise, at the cost of fibre cutting and wear. Wider settings give the less intense carding named in the first alternative.

  5. Which clothing rule is correct for a card?

    1. A coarser fibre needs a denser clothing with more points per unit area
    2. A finer fibre calls for a finer clothing with more points per unit area
    3. Teeth need not be ground because blunt wire carries fibre more gently
    4. Metallic clothing is limited to the flats of every card
    Show answer

    Answer: B — A finer fibre calls for a finer clothing with more points per unit area

    Finer fibres need finer, denser wire to be held and opened without being crushed. Sharp teeth are essential, so clothing is ground; flats normally carry flexible clothing, while the taker-in and, on modern cards, cylinder and doffer carry metallic clothing.

  6. What distinguishes an open-loop autoleveller from a closed-loop one?

    1. The open-loop type senses the delivered sliver and so corrects its own mechanical drift and corrects the error before the material reaches the draft point
    2. The closed-loop type senses the input and must wait for a time delay before correcting because the output cannot be measured once it is delivered
    3. The open-loop type senses the input and times its correction for the sensed material, but cannot detect its own errors
    4. Both types sense the same point; only the actuator differs and, in both, the delay is always zero
    Show answer

    Answer: C — The open-loop type senses the input and times its correction for the sensed material, but cannot detect its own errors

    Open loop measures before the correction point and therefore needs a timed delay; because the output is not checked, errors it makes itself go unnoticed. Closed loop measures the output and feeds back, so it detects its own drift but corrects material already delivered.

  7. What is the main effect of setting the roller gap in a drafting zone smaller than the length of the longest fibres, other things equal?

    1. Fibres are gripped by both roller pairs at once, so they break or the rollers slip, spoiling drafting
    2. All fibres become floating fibres and drafting waves disappear because the gap is exactly the fibre length
    3. The draft is reduced in proportion to the gap because the total draft always falls with the gap
    4. Only the short fibres are removed from the strand while all the rest of the fibre is retained
    Show answer

    Answer: A — Fibres are gripped by both roller pairs at once, so they break or the rollers slip, spoiling drafting

    A fibre longer than the gap is held at both ends, one pair holding it back while the other pulls it forward, so it breaks or slips. Floating fibres are the opposite problem and occur when the gap is too wide.

  8. Increasing the noil percentage in combing generally has which combined effect on the combed sliver?

    1. Mean fibre length falls and short-fibre content rises
    2. Neps increase because more fibre is combed
    3. Both mean length and short-fibre content stay fixed, only the lap tex changes
    4. Mean fibre length rises and short-fibre content falls
    Show answer

    Answer: D — Mean fibre length rises and short-fibre content falls

    Noil is rich in short fibre and neps, so removing more of it raises mean length and lowers short-fibre content, giving a stronger, more even yarn at a higher cost. Neps fall, not rise, with more combing.

  9. A drawframe autoleveller senses the sliver 0.30 m before the point where the main-draft speed is changed. The sliver moves at 15 m/min in that stretch. After how long must the speed change be applied to a sensed thick place so that it acts on that very place?

    1. 0.2 s
    2. 1.2 s
    3. 12 s
    4. 0.45 s
    Show answer

    Answer: B — 1.2 s

    Delay = distance ÷ speed = 0.30 m ÷ (15 m/min) = 0.02 min = 1.2 s. Using 15 m/s instead of 15 m/min gives 0.02 s; stopping at 0.02 min without converting, or slipping by a factor of ten, gives the other wrong values.

  10. Which of the following statements about ginning, opening, cleaning and blending are correct?

    1. Ginning out-turn is the lint mass divided by the seed-cotton mass, expressed as a percentage
    2. Grid bars let heavy trash fall out while the fibre tufts are carried on
    3. A stronger beating always improves yarn quality, since it only removes trash
    4. Plucking from many bales at once gives bale-to-bale blending
    Show answer

    Answer: A — Ginning out-turn is the lint mass divided by the seed-cotton mass, expressed as a percentage; B — Grid bars let heavy trash fall out while the fibre tufts are carried on; D — Plucking from many bales at once gives bale-to-bale blending

    The statements on out-turn, grid bars and multi-bale plucking are correct. Stronger beating also breaks fibre, makes neps and adds short fibre, so the statement that it always improves quality is wrong.

  11. Which statements about periodic mass variation and drafting are correct?

    1. A fault from an eccentric roller repeats at a wavelength proportional to its circumference and to the draft after it
    2. Floating fibres cause drafting waves whose wavelength is related to the fibre length, not to a roller circumference
    3. Doubling four independent random slivers leaves the CV unchanged
    4. A fault of the front delivery roller itself is stretched by the total draft of the machine
    Show answer

    Answer: A — A fault from an eccentric roller repeats at a wavelength proportional to its circumference and to the draft after it; B — Floating fibres cause drafting waves whose wavelength is related to the fibre length, not to a roller circumference

    Mechanical faults give λ = πd × D and drafting waves track fibre length. Doubling n independent slivers lowers the CV by √n, so four slivers halve it. The front delivery roller has no draft after it, so its fault stays at πd.

  12. In the cotton combing cycle, which statements are correct?

    1. The half-lap of needles combs the fibre fringe while the nippers hold it
    2. The top comb combs the tail ends of fibres as the fringe is drawn out during detaching
    3. The noil consists chiefly of the longest fibres, which the nippers hold back
    4. The detaching rollers only turn forward and never reverse
    Show answer

    Answer: A — The half-lap of needles combs the fibre fringe while the nippers hold it; B — The top comb combs the tail ends of fibres as the fringe is drawn out during detaching

    Combing happens on the fringe held by the nippers, and the top comb treats the rear ends during detaching. Noil is made of short fibres and neps, and the detaching rollers do reverse to return the web for piecing.

  13. A card delivers sliver at 120 m/min. The sliver is 4800 tex (g/km). Take the card’s running efficiency as 90 %. The production is ____ kg/h (answer to one decimal place).

    Numerical answer — type the value.

    Show answer

    Answer: 31.1

    Delivered length per hour = 120 × 60 = 7200 m = 7.2 km. Mass = 7.2 km × 4800 g/km = 34 560 g = 34.56 kg at 100 %. At 90 %: 34.56 × 0.9 = 31.104, so 31.1 kg/h.

  14. Six slivers of 3600 tex are fed to a drawframe whose total draft is 7.5. Ignoring waste, the delivered sliver is ____ tex.

    Numerical answer — type the value.

    Show answer

    Answer: 2880

    Delivered tex = n × feed tex ÷ draft = 6 × 3600 ÷ 7.5 = 21 600 ÷ 7.5 = 2880 tex. Forgetting the doubling (3600 ÷ 7.5 = 480) is the usual slip.

  15. The back roller of a drafting system has a diameter of 28 mm and has a bent journal that causes one periodic fault per revolution. The total draft between this roller and the delivery is 6. The fault wavelength in the delivered strand is ____ mm (nearest whole number; use π = 3.1416).

    Numerical answer — type the value.

    Show answer

    Answer: 528

    Material delivered per revolution = π × 28 = 87.96 mm. After the draft of 6 it is stretched to 87.96 × 6 = 527.8 mm, which is 528 mm.

  16. A comber has 8 heads and runs at 400 nips per minute. Each nip feeds 5 mm of a lap of 70 ktex (70 g per metre). Noil is 16 % of the feed mass. At 100 % efficiency the combed-sliver production is ____ kg/h (answer to one decimal place).

    Numerical answer — type the value.

    Show answer

    Answer: 56.4

    Lap fed per head per minute = 400 × 0.005 m = 2 m, which is 2 × 70 = 140 g. Eight heads: 1120 g/min. Combed sliver = 1120 × 0.84 = 940.8 g/min = 56 448 g/h = 56.4 kg/h.

  17. In a blowroom stage the feed contains 4.0 % trash and the delivered material contains 2.5 % trash. Using cleaning efficiency (%) = (trash % in feed − trash % in delivery) ÷ trash % in feed × 100, the cleaning efficiency is ____ %.

    Numerical answer — type the value.

    Show answer

    Answer: 37.5

    (4.0 − 2.5) ÷ 4.0 × 100 = 1.5 ÷ 4.0 × 100 = 37.5 %. Dividing by the delivery trash instead gives 60 %, a common slip.