How do carding and drawing decide whether the yarn is even?

What happens

Cotton reaches the spinning mill as compressed tufts. The carding machine separates them into individual fibres between wire-covered rollers set fractions of a millimetre apart. It removes most remaining trash and neps (tiny fibre knots), roughly aligns the fibres and forms sliver: a soft, untwisted rope. Drawing then runs several slivers together through roller pairs turning progressively faster, stretching them into one strand: thick and thin spots average out and fibres straighten. An autoleveller measures the sliver continuously and adjusts the stretch to keep its weight constant. For finer, smoother yarns, combing removes short fibres and more neps.

Why it matters

1. Neps that pass the card end up in the fabric. Immature-fibre neps take little dye and show as white specks, found only once dyeing costs are spent.
2. Machine differences can leave stripes in fabric. Cotton Incorporated lists card-to-card differences in trash removal, and poor blending through finisher drawing, as causes of barré (repeating stripes).
3. Repeating unevenness in sliver shows in fabric: variations of about 1–50 cm cause a moiré pattern; those over 5 m can cause cross-stripes (Uster Technologies patent).
4. Fibres under about 12 mm slip through drafting rollers in small bundles, a major cause of thick places in yarn. Uster found combing them out reduces thick places.

Best practice

• Service card wire by measurement, not the calendar: test every card’s sliver for neps weekly, as Uster advises, and grind only above a set limit. Nep levels rise faster after each grind.uster.com↗ (opens in a new tab)
• Work to a maintenance schedule. Cotton Incorporated advises checking all card wire and settings every 600 operating hours, and keeping the card room at about 24–29 °C and 40–60% relative humidity.cottoninc.com↗ (opens in a new tab)
• Autolevel and monitor the final drawing stage. Trützschler calls precise levelling in the last draw-frame passage ‘decisive’ for yarn quality; Rieter’s monitor stops the frame automatically when sliver thickness leaves set limits.truetzschler.com↗ (opens in a new tab)rieter.com↗ (opens in a new tab)
• Renew draw-frame wear parts in time. Rieter expects roller covers, belts and clearers to last 1–3 years; in one mill, renewal cut sliver unevenness by 8% and yarn imperfections by 14%.rieter.com↗ (opens in a new tab)
• When combing, match noil (the waste removed) to the incoming fibre and state whether yarn is fully or partially combed. With the same cotton, 16% noil gives better yarn than 10%.cottonworks.com↗ (opens in a new tab)

The terms

Sliver

A soft, untwisted rope of loosely aligned fibres made by carding and drawing.

Nep

A tiny knot of tangled fibres, often immature, that can show as a speck.

Noil

Short fibres, neps and trash removed by the comber, given as a percentage.

Autoleveller

A device that measures sliver and adjusts the stretch to keep its weight constant.

Barré

Unwanted repeating bars or stripes across a fabric.

Sources

1. USDA ARS, Agricultural Research (May 1997): Neps (opens in a new tab)agresearchmag.ars.usda.gov
2. Cotton Incorporated TRI 1002: Barré (opens in a new tab)cottoninc.com
3. US Patent 5,671,061 (assigned to Uster Technologies AG): periodic mass variations in sliver and yarn (opens in a new tab)patents.google.com
4. Uster Technologies SE-636: Process control in spinning (opens in a new tab)uster.com
5. Cotton Incorporated TRI 1008: Quality Carding (opens in a new tab)cottoninc.com
6. Trützschler: Autoleveller draw frame TD 10 (opens in a new tab)truetzschler.com
7. Rieter: Draw frame RSB-D 27 (Rieter Quality Monitor) (opens in a new tab)rieter.com
8. Rieter: Draw frame mini kit improves sliver and yarn quality (case study) (opens in a new tab)rieter.com
9. CottonWorks: Textile Yarns (opens in a new tab)cottonworks.com
10. Trützschler blog: The Trützschler card TC 19i, the first intelligent card (opens in a new tab)blog.truetzschler.com