Barré in Deep-Navy Cotton Knit Fabric: Maturity, Micronaire and Bale Laydown
A knitting yarn spinner supplies 30 Ne (20 tex) combed cotton single jersey yarn to a dyehouse. Over three months the customer reports barré-faint longitudinal streaks-in deep reactive-dyed navy fabric. The mill buys three cotton growths and currently opens bales from all lots in a random 1:1:1 pattern. HVI data are: Lot A micronaire 3.8, maturity ratio 0.82, neps 210 count/g, short-fibre index 12.4%; Lot B micronaire 4.2, maturity 0.86, neps 140, SFI 9.8%; Lot C micronaire 4.9, maturity 0.91, neps 95, SFI 8.1%. Mean fibre lengths are 27, 29 and 30 mm. Stock is 60 bales of A, 40 of B and 20 of C. Carding and combing settings are unchanged, but comber noil has been cut from 15% to 12% to improve yield. The customer threatens a claim and asks for a corrective action plan with evidence, not assurances.
1. Using the data, explain the most likely cause of barré and why micronaire alone is an unsafe sorting parameter for this mill.
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Barré is a longitudinal colour difference, so the primary suspect is differential dye uptake along the yarn, not a dyehouse machine fault. In cotton, maturity controls the cellulose fraction and the amount of amorphous cellulose: immature fibres (low maturity ratio, thick lumen, thin wall) absorb reactive dye more heavily and appear darker, and they also form neps that show as dark specks or streaks. Lot A combines micronaire 3.8 with maturity 0.82, neps 210/g and SFI 12.4%; that is a fine but immature, neppy cotton. Lot C is micronaire 4.9 with maturity 0.91: coarse but mature. Their dyeing behaviour is therefore different even though both are “cotton.”
Micronaire is a combined measure of fineness and maturity. A low micronaire can mean a fine mature cotton or a coarse immature cotton; a high micronaire can mean coarse mature or fine immature. Sorting only by micronaire can place A and C in the same laydown, where the maturity spread is 0.09 and the neps spread is more than 2:1. The random 1:1:1 laydown therefore mixes fibres with different dye uptake and different nep levels, producing barré. Cutting comber noil from 15% to 12% compounds the problem by allowing more short fibre and neps through. The evidence required is an AFIS maturity and nep test by lot, plus a dye-uptake or K/S test on yarn from each lot; the corrective action must begin with laydown segregation, not with a shade addition at the dyehouse.
2. Propose a bale laydown for this mill and state the numerical sorting and laydown rules you would enforce. Show calculations and acknowledge any target you cannot meet.
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An average micronaire target of 4.2 is not sufficient, because it can be met while the maturity spread remains unacceptable. A workable rule is: within one laydown, micronaire range ≤0.4, maturity-ratio range ≤0.05, neps ≤150 count/g, and no bale from a growth with a maturity ratio more than 0.05 from the laydown mean. Use 20–24 bales and open them in a fixed pattern.
Test the obvious 2:2:1 mix: 8 bales of A, 8 of B, 4 of C. Mean micronaire = (8×3.8 + 8×4.2 + 4×4.9)/20 = (30.4 + 33.6 + 19.6)/20 = 83.6/20 = 4.18. Mean maturity = (8×0.82 + 8×0.86 + 4×0.91)/20 = (6.56 + 6.88 + 3.64)/20 = 17.08/20 = 0.854. The average looks correct, but the range is 0.82–0.91 = 0.09, which fails the 0.05 rule. This is exactly the trap: averaging hides the dye-uptake spread.
A compliant 20-bale mix of A and B is 10 A + 10 B: micronaire = (38 + 42)/20 = 4.0; maturity = (8.2 + 8.6)/20 = 0.84; range 0.04. A compliant B/C mix is 15 B + 5 C: micronaire = (63 + 24.5)/20 = 4.375; maturity = (12.9 + 4.55)/20 = 0.8725; range 0.05. I would not force 4.2 by adding C to A. For deep navy, run B-rich or B/C laydowns and reserve A for a separate, fully segregated lot after restoring noil and passing a dye-uptake trial. If the customer insists on 4.2, achieve it with B/C, not by averaging across the maturity gap.
3. What additional measurement would you request to separate maturity from fineness, and what process changes would reduce neps without giving up the entire yield gain?
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Request an AFIS-MDI (maturity/diameter) or equivalent maturity-and-fineness test on every bale, backed by a Shirley FMT or sodium hydroxide swelling test for verification. Micronaire alone cannot separate the two properties. AFIS-MDI reports maturity ratio and fineness independently, and the same instrument gives nep count and short-fibre content; that gives the mill the evidence it needs to reject or segregate bales before opening.
On process, restore comber noil to at least 14–15% for the navy quality, then recover yield elsewhere: reduce card production rate, set card flats and wire correctly, avoid recirculating noil, and control the combing draft. A 3% noil increase on 120 t/month is about 3.6 t of fibre; at $1.80/kg that is about $6,480/month, which is likely less than a barré claim, dye reprocessing and customer loss. Run a trial beam with 14% and 15% noil and measure AFIS neps and yarn neps; accept the lowest noil level that brings yarn neps into the baseline range. Do not simply restore 15% and leave the carding settings unchanged, because the neps may originate at the card rather than the comber.