Poor Renditta and Filament Breaks in a Cooperative Reeling Unit
A cooperative reeling unit processes 800 kg of bivoltine cocoons purchased two days ago from farmers. The cocoons were transported in gunny bags, stored in a godown at 28–30°C, and some have a musky smell and dark patches. Reeling results are renditta 9.8 against a target of 8.0, reelability 62%, average filament breaks 14 per 10,000 m, and raw silk denier 2.8 against a target of 2.2. The reeling water has total hardness 340 mg/L as CaCO3 and pH 8.1; basin temperature is 65°C; reeling speed is high to meet a deadline. The unit wants to blend these cocoons with good cocoons and increase speed further. Advise.
1. Diagnose the main causes of poor renditta and filament breaks from the cocoon, water and reeling parameters.
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The cocoons were kept for two days at 28–30°C in gunny bags, so they were not properly stifled and stored. Pupae continue developing, uric acid and putrefaction cause dark patches and musky smell, and dead or rotten cocoons reduce reelability and raise renditta. Hard water at 340 mg/L and pH 8.1 interfere with sericin softening and increase filament breaks. A basin temperature of 65°C together with high reeling speed adds tension and breaks. Denier 2.8 is coarse, consistent with reeling poor cocoons or using too many cocoons per end. Blending rotten cocoons with good ones will pull down the whole lot, and increasing speed further will worsen breaks.
2. Recommend immediate sorting, stifling or storage, and water-treatment steps.
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Sort the cocoons immediately: remove soft, stained, musky, double and pierced cocoons, and keep only firm, clean cocoons. Stifle promptly at the recommended temperature, usually 80–85°C for a short period or as per the unit standard, then dry to safe moisture. Do not continue storing in gunny bags at 28–30°C. Store in thin layers in a cool, dry, ventilated room and reel as soon as possible. Treat the reeling water: use soft water or a water softener, adjust pH to about 6.5–7.0 with a food-grade acid if needed, and filter suspended matter. Do not blend defective cocoons into a premium lot; reel them separately if at all.
3. Explain how reeling speed and basin temperature should be adjusted, with reasoning.
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Lower the basin temperature to the correct range for the cocoon lot, about 55–60°C, adjusted to cocoon size and sericin, and reduce reeling speed to the standard for bivoltine cocoons. High speed increases filament tension and breaks; overheating makes the filament weak and gummy. Reel a small test lot after sorting and water treatment, measure renditta, reelability and breaks, then set speed and end count. If denier is too coarse, use fewer cocoons per end, but base the end count on cocoon filament size. Train reelers to stop the machine at breaks and join quickly. Maintain a clean basin and replace water regularly. Process the whole 800 kg only after the test lot improves; otherwise sell the defective cocoons for lower-value uses.