Defect names, causes and remedies for circular knitting, using the terminology defined in ASTM D3990. Causes are ordered roughly by how often they turn out to be responsible.
| Defect | Common causes | Remedies |
|---|---|---|
| Hole An aperture where one or more yarns are broken through. | Knots in yarn, weak or thin places, excessive yarn tension, over-dry yarn, badly set yarn guides, poor lubrication. | Use flat knots, control yarn regularity, re-adjust yarn tension and coulier, reset yarn guides precisely, maintain humidification, use protective filter creels. |
| Drop stitch Randomly appearing holes of varying size where a loop has failed to form. | High yarn tension, over- or under-feed, high fabric take-down tension, clogged eyelets, guides or tension discs, slubs and knots, incorrect dial-to-cylinder gap. | Ensure all needle latches close on the feeding yarn, clear the yarn passage of wax and fluff, correct take-down tension, reset the dial and cylinder gap. |
| Barré Horizontal stripes of uniform or variable width running parallel to the courses, with shaded edges. | Inconsistent fibre properties, yarn count or twist variation between cones, mixed lots, differing knitting tension between feeders, downstream processing variation. | Segregate and verify yarn lots, check count consistency at the creel, equalise feeder tensions, avoid mixing suppliers within a roll. |
| Lycra / elastane break A missing or broken elastane end, leaving a visible line and a loss of stretch. | Low elastane tension, failure of the needle to catch the elastane, damaged elastane guide, end run-out. | Feed elastane to every needle, maintain uniform elastane tension, inspect guides for wear, fit end-break sensors on the creel. |
| Needle line A continuous vertical line along the wale direction. | Bent, broken or worn needle; damaged needle latch; incorrect needle seating in the cylinder. | Replace the damaged needle, verify latch operation across the cylinder, follow a scheduled needle-change programme. |
| Oil line / stain Vertical or irregular oil marks contaminating the fabric. | Over-lubrication, leaking sinker ring or cylinder oiling, poorly directed oil jets, worn seals. | Correct lubrication rate and timing, service seals, redirect oil supply away from the knitting zone. |
| Miss knit / tuck An unintended float or tuck where a loop should have formed. | Incorrect cam setting, worn cams, needle butt damage, wrong needle selection. | Check and reset cam tracks, replace worn cams, inspect needle butts. |
| Slub A thick, short place in the yarn appearing as a lump in the fabric. | Yarn irregularity carried through from spinning, contamination in the fibre. | Improve yarn clearing at winding, tighten incoming yarn quality specification. |
| Snarl A twisted, kinked length of yarn knitted into the fabric. | Excessive yarn twist, insufficient tension between package and feeder. | Set correct twist, maintain adequate yarn tension through the feed path. |
| Spirality Wales leaning away from the vertical, making garments twist after washing. | Residual yarn torque, single-jersey construction, unbalanced twist, high machine speed relative to take-down. | Use twist-balanced or plied yarn, apply appropriate heat setting, control finishing tension. See AATCC 179. |
| Loose course A course knitted with visibly longer loops than its neighbours. | Momentary loss of yarn tension, feeder malfunction, poorly set stitch cam at one feed. | Check the individual feeder, verify tension device operation, reset the stitch cam. |
| Fly / lint contamination Foreign fibre or fluff knitted into the fabric surface. | Airborne lint in the knitting hall, inadequate extraction, poor housekeeping. | Improve suction and filtration, tighten cleaning schedules, control air movement in the hall. |
Read the causes column as a whole and a theme emerges: the overwhelming majority trace back to yarn tension, needle condition or machine setting drift. All three are gradual. None announces itself. Each produces perfectly good fabric until the moment it does not.
That is why detection latency matters more than defect taxonomy. A mill that knows precisely what a drop stitch is, but discovers it four hours later at the inspection table, has four hours of drop stitches.
ASTM D3990, the standard terminology for fabric defects, provides the canonical vocabulary — holes, barré, drop stitches, miss knits, slubs, floats, spirality, streakiness and others. Using its terms avoids ambiguity in buyer correspondence.
Drop stitches and holes are the most frequently reported, largely because both stem from yarn tension problems, which are the most common uncontrolled variable on a knitting floor.
Under the 4-Point System (ASTM D5430) each defect is scored 1 to 4 penalty points by its longest dimension, regardless of type. A hole and a barré band of the same length score identically.
Most surface-visible defects can be, given adequate camera resolution and lighting at the machine. The hardest classes are low-contrast faults on dark fabric and gradual shade variation such as barré, which needs comparison across a wide field of view rather than local detection.
Every remedy in that table is correct and every one is applied after someone notices. Knit-I watches each course as it forms and halts the machine at the fault — so the remedy gets applied to centimetres of fabric instead of hours of it.
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