Neps in Carding: Major Defect in Yarn Manufacturing
Dept. of Textile Technology
Sarvajanik College of Engineering & Technology, Surat, India
Textile terms and definitions define a `Nep’ as a small knot of entangled fibers that usually comprises dead or immature fibers.
Neps in cotton continue to be a major problem in the cotton yarn manufacturing process. The two main factors affecting nep formation are fiber characteristics and mechanical processing. The mechanical processes affecting neps formation include ginning, opening and blending, carding, combing, drawing and spinning.
Neps are associated with poor yarn and ultimately with poor fabric appearance and have an effect on yarn uniformity and dyeing quality.
Neps in the raw material can be classified as mechanical neps or biological neps. Mechanical neps are those made up of only fibrous material containing at least five or more fibers.
Neps containing foreign material such as seed coat fragments, leaf or stem materials were designated as biological neps.
A third category of neps found on the surface of the dyed fabrics was named pancake type neps. This type of nep appears as light or white spots in the finished fabric.
Ginning conditions that influence nep formation are the ginning process itself, the amount of lint cleaning, heat history and the amount of energy input into the individual fiber. In one study, it was found that ginning using three tower driers and two lint cleaners significantly increased the amount of card web neps compared with one lint cleaner and without using heat for drying.
Carding both generates and removes neps. Carding is the most significant process where significant decrease in the level of neps can take place.
It was also observed that with finer cottons, increasing the card licker-in speed increased the card web neps.
A closer flat-cylinder setting, on the other hand, reduced the web neps. It was also found a good correlation exists between the card web neps and the yarn neps.
Hence trials are to be concluded based on critical nep size reduction. The number of neps above critical nep size shall be eliminated in carding by optimizing setting, grinding frequency, wire condition/replacement, suction, process parameters, etc.
It is to be noted that neps below critical nep size will not influence yarn quality/fabric appearance significantly. This analysis and controlling / minimizing of critical nep size is highly significant for yarn dyeing quality requirements.
It is also advisable that any trials/R&D study should be concluded based on knitted fabric appearance/critical nep size in carding to impress / delight yarn buyers by manufacturing premium yarn quality.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.