Knit fabric Defect

knit fabric defects due to problems in:

• Yarn quality
• Knitting machine settings
• Machine parts (needle, sinker, cam)
• Process handling
• Dyeing and finishing

1) Yarn dust / lint specks

• Looks like: Tiny dark/grey specks scattered (more visible on light shades).
• Causes: Fly from spinning/knitting room, poor housekeeping, high hairiness.
• Impact: Dirty appearance, reject risk on pale hues.
• Prevention: Air filtration, lint extraction at feeders, compact spinning/low hairiness, frequent machine cleaning.

2) Slubs / thick‑and‑thin / neps

• Looks like: Intermittent thick bars or small knots; barre after dyeing.
• Causes: Count variation, carding/combing faults, rotor deposits.
• Impact: Streaks, uneven shade, pilling risk.
• Prevention: Yarn evenness control (Uster), autoleveller, yarn clearer limits tuned, supplier gating.

3) Foreign fibre contamination (PP, dyed fibers, seed coat)

• Looks like: Colored or white fibers embedded; “peppery” look.
• Causes: Contaminated cotton, packing materials, bale mix.
• Impact: Spot defects after dyeing; buyer claims in whites/pastels.
• Prevention: Cotton sorting, vision systems, yarn clearer FF detectors, black‑bag ban on floor.

4) Oil/grease stain 

• Looks like: Local dark patches; halos post‑dye.
• Causes: Lube leaks, dirty ring frames, cone handling.
• Prevention: Preventive maintenance (PM), food‑grade knitting oil, clean trolleys; quarantine stained packages.

5) Elastane (Lycra) faults

• Types: Lycra missing (no stretch bands), Lycra out (exposed on face), overfeed/underfeed bands.
• Causes: Broken elastane, feeder slippage, wrong draft/overfeed %, yarn path friction.
• Impact: Stripe bands, growth issues, uneven recovery.
• Prevention: Interlacing quality, constant overfeed (±1%), clean ceramic guides, tension closed‑loop, elastane quality check (tenacity/elongation).

Knitting‑Stage Defects

6) Holes

• Looks like: Pinholes to large holes; often with ladder (run).
• Causes: Broken/missing needles, sharp sinkers, fabric take‑down spike, hard knots.
• Prevention: Needle audit per hours, knot quality (≤3 knots/1000 m), tension alarms, yarn fault clearer stop‑marks allowed but controlled.

7) Drop stitch / ladder / run

• Looks like: Vertical line of missed loops.
• Causes: Missed clearing height, worn needle hook, low loop length with high tension, selector mis‑hit.
• Prevention: Set clearing height, replace worn parts, stabilize loop length (CV% < 1.5), selector calibration.

8) Set‑up mark / start‑up crease

• Looks like: Horizontal band at roll start or after stops.
• Causes: Take‑down/compaction not stabilized, tension transients.
• Prevention: Scrap first few meters, gradual ramp on restart, standard start‑up SOP.

9) Loop mark / press‑off / tucking defects

• Looks like: Irregular loops or stitch formation, “bird’s‑eye” specks.
• Causes: Incorrect cam/tuck timing, high yarn friction, variable feed.
• Prevention: Cam timing verification, guide polishing, constant feed via positive feeders.

10) Barre (horizontal stripiness)

• Looks like: Repeating shade bands around circumference.
• Causes: Yarn lot mixing, feeder tension variation, needle wear distribution, cylinder out‑of‑round, variable stitch length by feeder.
• Prevention: Same yarn batch/lot per roll, feeder‑wise loop length mapping, rotate cylinder elements, SPC on loop length (per feeder trend).

11) Spirality / skew (single jersey)

• Looks like: Wale angle deviates from vertical; side seam twist in garments.
• Causes: Yarn twist bias vs machine direction, stitch length too tight/loose, high take‑down.
• Prevention: Balanced yarn twist, optimized stitch length, relaxation and compaction; test according to AATCC 199/179.

12) Needle lines / vertical lines

• Looks like: Fine continuous vertical streak.
• Causes: Damaged individual needle/sinker track, bent jack, dirty trick.
• Prevention: Replace suspect needles in groups; routine trick cleaning.

13) Feeder line / stripe

• Looks like: Narrow circumferential band at one or more feeders.
• Causes: Off‑spec cone, tension change, elastane draft change on one feeder.
• Prevention: Swap feeder positions during trials, cone pairing strategy, feeder tension calibration.

14) Tension bands / take‑down variation

• Looks like: Alternating tight/loose bands horizontally.
• Causes: Inconsistent take‑down speed/pressure, brake issues on take‑up.
• Prevention: Closed‑loop take‑down, check drive belts, pressure roll cleaning.

15) Yarn out (missing yarn / end out)

• Looks like: Thin horizontal line (for weft feeders) or structural gap.
• Causes: Cone run‑out, yarn break with failed stop.
• Prevention: Yarn break sensors/stop motion sensitivity, cone change SOP.

16) Mis‑plating (plated jersey)

• Looks like: Face/back yarns swapped; random flecks of back yarn on face.
• Causes: Incorrect yarn path heights, feeder mis‑set, overfeed mismatch.
• Prevention: Set plating spacing precisely, synchronized feeds, regular plating checks.

17) Puckering at stitch

• Looks like: Corrugated texture longitudinally.
• Causes: Too low loop length, high yarn tension, moisture‑set yarn memory.
• Prevention: Increase loop length, relax greige before finishing.

18) Snag (knits)

• Looks like: Pulled loop on surface; sometimes “fisheye”.
• Causes: Sharp machine parts, handling damage, Velcro contact.
• Prevention: Deburr machine paths, fabric protective handling, test snagging resistance (ASTM D3939).

Wet Processing / Dyeing‑Linked Defects (show on dyed/finished goods)

19) Shade variation (roll‑to‑roll / within roll)

• Causes: GSM/thickness changes, residual oils/waxes, relax state differences, liquor ratio and temp gradients.
• Prevention: Pre‑relax, scour quality (saponification index), batch planning by GSM/lot, SOP for load/MLR.

20) Patchy / mottled dyeing

• Looks like: Cloudy areas; “frosty” melange on solids.
• Causes: Greige contamination, poor leveling, temperature shocks, elastane exposure.
• Prevention: Effective scouring + chelation, temperature ramp controls, appropriate leveling agents, protect elastane (<130 °C unless stabilized).

21) Barre after dye

• Amplified by: Yarn variability; different cotton maturity; elastane feeding bands.
• Control: Yarn gating, robust lab dips across multiple cones, cylinder/feeder mapping.

22) Tailing / crease marks

• Looks like: Long diagonal/rope marks.
• Causes: Rope twist imbalance in jet/winch, low liquor turbulence, overloading.
• Prevention: Rope length optimization, untwisting devices, lower loading, anti‑crease.

23) Oil stains after dye

• Causes: Knitting oil not scoured, machine leaks.
• Prevention: Emulsifying scours, oil type compatible with scour chemistry, PM to stop leaks.

24) Uneven compaction marks / width variation

• Looks like: Bands of different GSM/width.
• Causes: Compactor felt wear, pressure/temp non‑uniform, uneven overfeed.
• Prevention: Felt life tracking, cross‑width temp mapping, overfeed control.

25) Excessive shrinkage / growth

• Causes: Inadequate relaxation/compaction; elastane damage.
• Prevention: Relax tumble → compaction; set overfeed; validate against ISO 6330/AATCC 135.

26) Skew after finishing

• Causes: Stenter chain speed mismatch, uneven tentering, yarn torque release.
• Prevention: Chain synchronization, overfeed balance, heat‑set (for blends).

Appearance / Surface Defects (finishing & handling)

27) Hairiness / fuzz

• Causes: Short fibre yarns, abrasive finishing, brushing carryover.
• Control: Compact yarns, enzyme/bio‑polish, shear/singe (where applicable).

28) Pilling (surface pills)

• Causes: Fibre migration and abrasion; blending with short staples; loose structures.
• Control: Enzyme/bio‑polish on cotton, tighter stitch density, anti‑pilling finishes, choose fibres with longer staple/low hairiness.
• Assess: ISO 12945‑2 / ASTM D4970 (Grade target ≥ 3–4).

29) Press shine / glazing

• Looks like: Glossy lanes.
• Causes: Over‑pressing, hot calendar contact on cellulosics.
• Prevention: Lower temperature/pressure, add matting softener, use felt side.

30) Width bowing / wavy edges

• Causes: Unequal stenter tentering, selvedge over‑dry.
• Prevention: Edge pin/clip balancing, moisture profile control.

31) Contamination after finishing

• Types: Handling stains, solvent drips, rust from frames.
• Control: Clean conveyors/rollers, stainless hardware, covered storage.

Structural / Construction Defects

32) Fabric holes at tuck or transfer (rib/interlock/jacquard)

• Causes: Transfer needle failure, wrong cam for yarn count.
• Prevention: Needle selection quality, yarn count vs gauge matrix adherence.

33) GSM variation (across or along)

• Causes: Variable stitch length, take‑down drift, compaction changes.
• Prevention: SPC on loop length, frequent GSM checks per feeder & after compactor, closed‑loop take‑down.

34) Width variation / barre across width

• Causes: Differential shrinkage, moisture gradient, compactor nip wear.
• Prevention: Moisture pre‑equilibration, nip maintenance, cross‑width thermal profiling.

Inspection & Acceptance (Practical)

4‑Point System (knits)

• Assign points per defect size/length:
  1 point: ≤ 3″ (≤ 75 mm)
  2 points: >3″–6″ (75–150 mm)
  3 points: >6″–9″ (150–230 mm)
  4 points: >9″ (>230 mm) or any hole
• Max allowed: Buyer‑specific (e.g., ≤ 28 points per 100 yd² or ≤ 30 points per 100 m²).
• Zero tolerance: Holes, foreign fiber in whites, continuous barre.

Inline controls

• Roll‑start scrap, feeder‑wise loop length log, thermal/width log at stenter/compactor, dye house RFT board.

Root‑Cause Map (quick reference)

SOP Snippets (you can paste into your QC manual)

Knitting start‑up SOP

1. Load lot with matched cones by feeder.
2. Set loop length; record per feeder.
3. Run 20–30 m scrap; check GSM/width/appearance.
4. Approve and start bulk with hourly loop‑length audits.

Greige to dye SOP

1. Relax (24 h for cotton jersey on trolley; avoid stacking heavy).
2. Inspect and grade using 4‑Point; segregate critical defects.
3. Batch by GSM ±3%, width ±1 cm, yarn lot same; mark roll IDs.

Finishing SOP

1. Pre‑wet to even moisture; set tenter/compactor recipe.
2. Width & skew set; overfeed control; felt condition check.
3. Verify shrinkage/spirality samples every 2,000 m.

Test Methods to Quantify Risks (recommended)

• Pilling: ISO 12945‑2 / ASTM D4970
• Bursting strength (knits): ISO 13938‑2 / ASTM D3786
• Dimensional change: ISO 6330 / AATCC 135
• Skew/spirality: AATCC 199 / AATCC 179
• Snagging: ASTM D3939
• Air permeability: ASTM D737 / ISO 9237