Roving, Ring Spinning, Doubling and Modern Spinning Systems

This chapter answers the middle part of Section XE9.2, “Yarn Manufacture, Yarn Structure and Properties”, of XE9 Textile Engineering and Fibre Science: “Principles of drafting, twisting, and bobbin building in roving formation; Modern developments in roving machine; Principles of drafting, twisting and cop building in ring spinning; Causes of end breakages; Modern developments in ring spinning machine; Working principles of ring doubler and two-for-one twister; Relationship between single yarn twist and folded yarn twist; Principles of compact, rotor, air-jet, air-vortex, friction, core, wrap and twist-less spinning processes.” It teaches how a sliver is attenuated and twisted into a package, how twist is counted, and how the newer processes insert twist or bind fibres differently. The numericals are twist per metre, twist multiplier and turns per inch, delivery speed from spindle speed, folded-yarn twist, two-for-one spindle speed and rotor-spinning twist.

1. Roving formation: drafting, twisting and bobbin building

The ring frame cannot take a heavy drawframe sliver directly, because its draft is limited, so a roving frame (speed frame) attenuates the sliver by a draft of a few times and adds just enough twist for the roving to be wound and unwound without false drafts. The sliver passes through a double-apron drafting system, then to a rotating flyer, which inserts twist and winds the roving onto a bobbin.

  • Twist: one turn per flyer revolution, so turns per metre = flyer rpm ÷ front-roller delivery speed (m/min). With 1000 rpm and 20 m/min the roving has 50 turns/m. Roving twist is low, since a high twist makes ring-frame drafting hard.
  • Winding: the bobbin turns faster than the flyer (bobbin lead), and the speed difference winds the roving. The winding rpm = delivery speed ÷ (π × current package diameter), so as layers add up the bobbin speed must fall step by step; older frames use cone drums and differentials for this, modern ones use servo drives.
  • Bobbin building: the bobbin rail lifts and reverses after each layer, the traverse shortens each layer to give tapered ends, and the lift per layer is set by the roving diameter (coil pitch), while the rail’s lifting speed falls as the bobbin grows.

Modern developments are individual servo drives on spindles and bobbins (no cone drums), automatic doffing and bobbin transport to the ring frame, electronic control of roving tension, and lightweight top-arm flyers allowing higher speeds.

2. Ring spinning: drafting, twisting and cop building

The roving is drafted in a double-apron system (a break draft then a main draft) several-fold (a high draft), and the strand leaving the front rollers is twisted by the spindle and traveller and wound onto the bobbin. Yarn runs from the front roller through a lappet guide, around the traveller (a small clip moving on the ring) and onto the tube; the yarn drags the traveller around, so the traveller speed lags a little behind the spindle. Each turn of the traveller about the yarn axis inserts one turn of twist, and the difference between spindle and traveller speeds is the winding speed.

Twist (turns per metre) = traveller speed ÷ delivery speed. With a spindle at 15 000 rpm and a traveller lagging by 4 % (14 400 rpm), a twist of 800 turns/m needs a delivery speed of 14 400 ÷ 800 = 18 m/min. Twist is quoted as TPI = α_e × √Ne (α_e is the English twist multiplier), or turns/cm = TM ÷ √tex in the tex system, where TM is the twist multiplier in turns/cm × √tex. Since Ne = 590.5 ÷ tex, TM = 9.57 α_e. For 25 Ne and α_e = 4.2, TPI = 4.2 × 5 = 21.

Cop building: the ring rail moves up and down on a cam or servo path so that the yarn is laid in conical layers of winding and binding coils, with the chase gradually advancing. The cop is built from the bottom up with a tapered shoulder, giving a firm, stable package whose layers do not slough off during unwinding. The yarn tension varies cyclically with the position on the cop and with the build.

⚠️ Trap
Spindle rpm ÷ delivery speed is only the nominal twist. The twist actually inserted is the traveller rpm ÷ delivery speed, a few per cent less. State which convention a question uses before answering.

3. End breakages and modern ring frames

An end break occurs when the tension in the yarn at the point between the front roller and the traveller exceeds the strength at the weakest place. Breaks are therefore tied to both tension and the thin, weak places in the yarn, and are counted per 100 spindle-hours. The tension is affected by spindle speed, traveller weight, ring and traveller condition, balloon shape and the yarn count.

GroupExamples of causes
Raw material and preparationShort fibre, neps, low fibre strength; uneven or badly twisted roving; drafting waves
MachineWorn rings or travellers, wrong traveller weight, misaligned spindle or guide, worn aprons, vibration, high spindle speed
AtmosphereVery low humidity gives fly and static; very high humidity gives lapping on rollers
OperationPiecing faults, fly on drafting zone, slack tubes, poor doffing

Modern ring frames have longer machines, individual spindle monitoring and sensors for yarn breaks, servo-driven ring-rail and roller motions, suction-based pneumafil and automatic piecing devices, compact attachments, and automatic doffing with transport of full packages to the winder.

4. Doubling, two-for-one twisting and folded-yarn twist

Doubling (plying, folding) twists two or more single yarns together to make a stronger, more even, more balanced yarn. A ring doubler works like a ring frame: yarn is fed from parallel-wound packages through rollers to a ring-and-traveller package, so twist per metre = traveller speed ÷ delivery speed. A two-for-one twister puts the single-yarn package inside a hollow spindle; the yarn rises through the spindle axis, leaves at the head and balloons around the package. The yarn is twisted once inside the axial path and once in the balloon, so two turns per spindle revolution: twist per metre = 2 N ÷ V. At the same spindle speed it delivers twice the length per revolution of a ring doubler for the same twist, so production is about double. A required fold twist of 600 turns/m at 25 m/min needs N = 600 × 25 ÷ 2 = 7500 rpm.

Single and folded twist. Say the single yarn has twist T_s (turns/m) of one direction (Z) and the fold twist T_f is of the opposite direction (S), with T_f measured per metre of folded yarn and any length change on folding ignored. Each single yarn is wrapped by T_f turns about its own axis, so its residual twist falls to T_s − T_f. If the fold twist is in the same direction, the single twist rises to T_s + T_f. With T_s = 600 Z and T_f = 400 S, the singles keep 200 Z. When the fold twist and single twist torques balance, the yarn is torque-balanced and does not snarl; a fold twist well below the single twist leaves a lively yarn. Folded linear density: n singles of 20 tex give nominally 20 × n tex, shown as R 40 tex (20 tex × 2); in Ne, 1/Ne = Σ(1/Ne_i), so 2/40s means 20 Ne.

5. Compact and rotor spinning

Compact (condensed) spinning adds a condensing zone after the main draft. The flat fibre ribbon coming from the drafting rollers is narrowed on a suction drum or lattice apron with a slot or perforations (aerodynamic or mechanical condensing) before twist is inserted. The spinning triangle that forms at the front-roller nip then becomes small, so fewer edge fibres escape the twist, and the yarn has less hairiness, more strength and elongation, and fewer end breaks than a conventional ring yarn of the same count. The ring-spinning geometry and the twisting are unchanged.

Rotor (open-end) spinning breaks the continuity of the strand. A sliver is fed to an opening roller that combs it into single fibres; an air stream carries them through a transport tube to the inside wall of a fast-turning rotor, where they slide into the groove and form a ring of fibres. The yarn is drawn from the groove through a navel and twisted as the rotor turns, one turn per rotor revolution, so twist (turns/m) = rotor rpm ÷ take-up speed, taking no twist loss. At 90 000 rpm and 900 turns/m the take-up is 100 m/min. The rotor groove doubles many layers of fibre, which evens the yarn, while the trash and the dust fall out of the opening-roller region. The yarn is wound directly onto a cross-wound package, and the roving and rewinding stages are eliminated, but the yarn is limited in fineness (coarse to medium counts) and has wrapper or belt fibres.

6. Air-jet and air-vortex spinning

Both processes make yarn from a drafted sliver without rotating a package. In air-jet spinning the drafted ribbon passes through two nozzles with air swirling in opposite directions. The first jet makes the edge fibres open and wrap around; the second, stronger jet twists the strand; as the strand untwists after the second jet, some edge fibres stay wrapped. The yarn is fasciated: a core of nearly parallel fibres bound by wrapper fibres. In air-vortex spinning a single nozzle forms a vortex at the entrance of a hollow spindle: the drafted ribbon is drawn into the spindle by air, leading ends of the fibres enter and become the core, and the trailing ends are flared open by the vortex and wound around the core. It also has core and wrapper fibres, and a more ring-like, more regular wrapping.

Delivery speeds are several times those of ring spinning, no roving is needed, and the yarn has low hairiness; the cost is lower strength than ring yarn (the core has little twist), with a firmer, more bulky handle. Both suit staple blends, polyester and cotton rich blends, and need a good fibre length and uniformity for the wrapper to form.

⚠️ Trap
In air-jet and air-vortex yarns the twist is not inserted by the revolution of a package or rotor; it is made by the vortex and then partly lost, so ‘turns per metre’ do not describe the structure. The strength comes from wrapper fibres binding a nearly untwisted core.

7. Friction, core, wrap and twistless spinning

Friction spinning: opened fibres are fed into the wedge between two perforated drums turning in the same direction; suction holds them there while the drums, rolling the strand between them, twist it. Taking no slip, the strand’s surface speed equals the drum surface speed, so the strand turns at V_drum ÷ (π d) and the twist in turns per metre is (D ÷ d) × N_drum ÷ V_delivery in the ideal case (D drum diameter, d strand diameter, N_drum drum rpm). Very high twist insertion rates give high delivery speeds, with coarse yarn counts and a core-sheath structure when a filament or sliver core is fed (the core is covered by friction-twisted staple fibre).

  • Core spinning: a continuous filament (for example polyester, or a stretched elastane) is fed at the nip of the front rollers of a ring frame and the staple sheath is twisted around it. The product combines the strength or elasticity of the core with the handle of the sheath, as in sewing thread and stretch fabrics.
  • Wrap (hollow-spindle) spinning: a drafted, untwisted strand passes through a hollow spindle that carries a filament or yarn package; the spindle wraps the filament around the strand, so wraps per metre = spindle rpm ÷ delivery speed (at 6000 rpm and 30 m/min, 200 wraps/m). The core stays parallel and only the wrap holds it.
  • Twist-less spinning: the fibre strand is bonded, not twisted, by an adhesive (a water-soluble binder), or by melting low-melt fibres or by entanglement. It is made at high speed but the strength depends on the bond, which changes with moisture and heat.
ProcessTwist or binding mechanism
Ring, compactTrue twist by traveller; one turn per traveller revolution
RotorTrue twist from rotor rotation; open-end
Air-jet, air-vortexWrapper fibres bind a nearly parallel core
FrictionTwist from two rolling drums; core-sheath possible
Wrap, coreFilament wrap on untwisted core; or filament core with staple sheath

Key takeaways

  • Roving twist = flyer rpm ÷ delivery speed; the winding speed difference is bobbin rpm − flyer rpm, and bobbin speed falls as the package grows.
  • Ring twist = traveller rpm ÷ delivery speed, and TPI = α_e × √Ne with TM = 9.57 α_e; winding = spindle − traveller speed.
  • End breaks occur when tension exceeds the strength of the weakest place; speed, traveller, preparation faults and humidity all act.
  • A two-for-one twister gives two turns per spindle revolution (twist = 2N ÷ V); with fold twist opposite to single twist the singles keep T_s − T_f.
  • Compact spinning shrinks the spinning triangle for less hairiness; rotor spinning twists by rotor rotation, with twist = rotor rpm ÷ take-up speed.
  • Air-jet and air-vortex yarns are fasciated; friction yarns are core-sheath; wrap yarns need a wrapper on a parallel core; twist-less yarns are bonded.

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. Why is only a small amount of twist given to roving?

    1. To give enough cohesion for winding and handling while leaving the strand easy to draft on the ring frame
    2. To give the roving its final strength, so that the ring frame can omit drafting, leaving only a final twist to be inserted there
    3. Because a high twist would make the bobbin run slower than the flyer, which would stop the bobbin from winding the roving at all
    4. Because the flyer cannot revolve faster than the delivery roller, so a large twist can never be inserted on a roving frame
    Show answer

    Answer: A — To give enough cohesion for winding and handling while leaving the strand easy to draft on the ring frame

    The roving needs just enough twist to be wound and unwound without false drafts, yet must still be drafted by the ring frame, which a high twist would prevent. The roving is not the final yarn and is drafted heavily afterwards.

  2. On a roving frame with a bobbin that leads the flyer, what must happen to the bobbin speed as the package diameter grows, for a fixed delivery speed?

    1. It must rise, to keep the roving under tension
    2. It must fall, since the winding rpm falls as the diameter rises
    3. It must stay constant, because twist depends only on the flyer
    4. It must equal the flyer speed, so that no winding occurs
    Show answer

    Answer: B — It must fall, since the winding rpm falls as the diameter rises

    Winding rpm = delivery speed ÷ (π × package diameter), and bobbin speed = flyer speed + winding rpm. A larger diameter needs fewer winding revolutions per minute, so the bobbin speed falls. Equal bobbin and flyer speeds would mean no winding at all.

  3. In ring spinning, what produces the winding of yarn onto the tube?

    1. The traveller turning faster than the spindle by dragging the yarn round the ring
    2. The lappet guide rotating about the ring and so carries the yarn onto the tube
    3. The difference between the spindle speed and the traveller speed
    4. The front roller turning faster than the spindle and so pulls the yarn onto the tube
    Show answer

    Answer: C — The difference between the spindle speed and the traveller speed

    The traveller is dragged by the yarn and lags the spindle; the speed difference equals the winding revolutions per minute. The traveller never leads the spindle, and the lappet guide does not rotate about the ring.

  4. Other things being equal, what is the usual effect of raising the spindle speed on a ring frame on the end-breakage rate, and the main reason?

    1. It falls, because the yarn is wound faster and spends less time under load and so the tension in the yarn falls
    2. It falls, because the traveller wears out less when it moves faster while the yarn tension is also lower
    3. It is unchanged, since the twist depends only on the roving and so no tension change can arise
    4. It rises, because the balloon and traveller tensions rise so that more weak places fail
    Show answer

    Answer: D — It rises, because the balloon and traveller tensions rise so that more weak places fail

    Higher speed raises the tension in the yarn path (more drag from the air and the traveller), so more weak places exceed their strength and breaks rise. Lower breakage at high speed would require a stronger yarn, not a faster winding.

  5. A ring doubler and a two-for-one twister run at the same spindle speed N (take the traveller speed of the ring doubler equal to N). Both must insert the same folded-yarn twist. How does the delivery speed of the two-for-one twister compare with that of the ring doubler?

    1. Half, because it inserts half as many turns per revolution
    2. The same, because both have the same spindle speed
    3. Four times, because twist depends on the square of the number of turns
    4. Twice, because it inserts two turns per spindle revolution
    Show answer

    Answer: D — Twice, because it inserts two turns per spindle revolution

    Twist = turns per minute ÷ delivery speed. The ring doubler gives N turns per minute and the two-for-one twister gives 2N, so for the same twist the two-for-one delivery speed is twice as large. The twist is not proportional to the square of the turns.

  6. Single yarns of Z twist are folded with an S fold twist, and the folding is done without any change of length. What happens to the twist in each single yarn?

    1. It increases by the fold twist
    2. It is unchanged, since twist is a property of the fibres
    3. It decreases by the fold twist, so some twist is removed
    4. It doubles, since two singles are present
    Show answer

    Answer: C — It decreases by the fold twist, so some twist is removed

    The opposite-sense fold twist untwists the singles by T_f turns per metre, leaving T_s − T_f. Adding is what happens when the fold twist is in the same direction as the single twist.

  7. What is the main reason a compact ring yarn has less hairiness than a conventional ring yarn of the same count?

    1. The condensing zone narrows the fibre ribbon, so the spinning triangle is much smaller and fewer edge fibres escape
    2. The twist is removed after the front rollers, and the strand is then wound onto a bare tube, so the hairs cannot stand out
    3. The fibres are cut shorter before spinning, leaving a bare, untwisted strand with no wrapping at the surface
    4. The yarn is wrapped by filament in a hollow spindle, and the filament covers the surface fibres
    Show answer

    Answer: A — The condensing zone narrows the fibre ribbon, so the spinning triangle is much smaller and fewer edge fibres escape

    Condensing narrows the ribbon before twisting, so a small triangle forms and fewer fibres are left uncaptured at the edges. Twist is inserted exactly as in ring spinning; no wrap or cutting is involved.

  8. Which feature of rotor spinning chiefly explains its good short-term evenness?

    1. Fibres are drafted by a long roller system with aprons and carried through to a compact winding
    2. The yarn is wrapped by a filament, which makes its strength exceed that of any staple yarn
    3. The sliver is combed into single fibres and many layers of them are laid in the rotor groove (doubling)
    4. Twist is inserted by two rolling drums, and the drums also draft the sliver into single fibres
    Show answer

    Answer: C — The sliver is combed into single fibres and many layers of them are laid in the rotor groove (doubling)

    Single fibres collected in the groove and doubled many times average out the irregularity. Long roller drafting is a feature of ring spinning, and filament wrap and rolling drums belong to other processes.

  9. Which description fits an air-jet spun yarn?

    1. A uniformly twisted structure with every fibre in a helix
    2. A core of nearly parallel fibres bound by wrapper fibres
    3. A continuous filament core covered with staple fibre by friction
    4. Fibres held together only by a water-soluble adhesive
    Show answer

    Answer: B — A core of nearly parallel fibres bound by wrapper fibres

    Air-jet yarn is fasciated: the vortex wraps edge fibres around a nearly untwisted core. A fully helical structure is the ring yarn, filament-covered staple is a core or friction yarn, and adhesive bonding is twist-less spinning.

  10. Which of the following are recognised contributors to end breakages in ring spinning?

    1. Uneven roving, which leaves thin places in the yarn
    2. A worn or wrongly chosen traveller, which changes the tension
    3. Fly and lapping on the drafting rollers in dry or very humid conditions
    4. A perfectly even yarn whose strength exceeds the tension everywhere
    Show answer

    Answer: A — Uneven roving, which leaves thin places in the yarn; B — A worn or wrongly chosen traveller, which changes the tension; C — Fly and lapping on the drafting rollers in dry or very humid conditions

    Thin places, a worn or wrong traveller and fly or lapping all lower the strength or raise the tension, so they cause breaks. A yarn that is everywhere stronger than the peak tension does not break.

  11. Which statements about unconventional spinning systems are correct?

    1. Rotor spinning is an open-end process in which fibres are collected in a groove and the yarn is twisted by the rotor rotation
    2. A core-spun yarn has a filament core covered by a staple sheath
    3. Wrap spinning wraps a filament round an untwisted core using a hollow spindle
    4. Air-jet spinning needs a rotating package to insert twist
    Show answer

    Answer: A — Rotor spinning is an open-end process in which fibres are collected in a groove and the yarn is twisted by the rotor rotation; B — A core-spun yarn has a filament core covered by a staple sheath; C — Wrap spinning wraps a filament round an untwisted core using a hollow spindle

    The descriptions of rotor, core-spun and wrap yarns are standard. Air-jet spinning uses air vortices and needs no rotating package.

  12. A single yarn has 600 turns/m of Z twist and is folded with 400 turns/m of fold twist (per metre of folded yarn, length change on folding ignored). Which statements are correct?

    1. With S fold twist, each single retains 200 turns/m of Z twist
    2. With Z fold twist, each single carries 1000 turns/m
    3. With S fold twist, each single carries 1000 turns/m of Z twist
    4. With Z fold twist, each single retains 200 turns/m
    Show answer

    Answer: A — With S fold twist, each single retains 200 turns/m of Z twist; B — With Z fold twist, each single carries 1000 turns/m

    A fold twist opposite to the single twist subtracts (600 − 400 = 200) and one in the same sense adds (600 + 400 = 1000). The statements that swap these two cases are wrong.

  13. A ring-frame spindle runs at 15 000 rpm, and the traveller lags the spindle by 4 % of the spindle speed. A twist of 800 turns per metre is required, taking twist = traveller rpm ÷ delivery speed. The front-roller delivery speed must be ____ m/min.

    Numerical answer — type the value.

    Show answer

    Answer: 18

    Traveller speed = 15 000 × 0.96 = 14 400 rpm. Delivery speed = 14 400 ÷ 800 = 18 m/min. Using the spindle speed instead gives 18.75, which ignores the lag.

  14. A yarn of 25 Ne is spun with an English twist multiplier α_e = 4.2, defined by TPI = α_e × √Ne. The twist is ____ turns per inch.

    Numerical answer — type the value.

    Show answer

    Answer: 21

    √25 = 5, so TPI = 4.2 × 5 = 21 turns per inch.

  15. A Z-twist single yarn has 600 turns/m. It is folded with a fold twist of 400 turns per metre of folded yarn in the S direction. Ignoring any change of length on folding, the residual Z twist in each single yarn is ____ turns/m.

    Numerical answer — type the value.

    Show answer

    Answer: 200

    Opposite-sense fold twist removes T_f from each single: 600 − 400 = 200 turns/m of Z twist remain. Adding the two (1000) is the answer for a fold twist in the same direction.

  16. A two-for-one twister must insert a fold twist of 600 turns per metre while the yarn is taken up at 25 m/min. Taking two turns per spindle revolution and no loss, the spindle speed required is ____ rpm.

    Numerical answer — type the value.

    Show answer

    Answer: 7500

    Twist = 2N ÷ V, so N = twist × V ÷ 2 = 600 × 25 ÷ 2 = 7500 rpm. A ring doubler would need 15 000 rpm for the same twist and speed.

  17. In a rotor-spinning unit the twist (turns per metre) equals the rotor rpm divided by the take-up speed in m/min (no twist loss). The rotor runs at 90 000 rpm and the yarn needs 900 turns per metre. The take-up speed is ____ m/min.

    Numerical answer — type the value.

    Show answer

    Answer: 100

    Take-up speed = rotor rpm ÷ twist = 90 000 ÷ 900 = 100 m/min.