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Classification of yarn neps and analysis of their formation reasons

Update:21-01-2021
Summary:

Nep is an important indicator of yarn quality assessmen […]

Nep is an important indicator of yarn quality assessment. The technical requirements for grade of cotton yarn not only specify the total number of neps and impurities in 1 g yarn, but also specify the number of neps. The amount of neps not only affects the appearance quality of yarns and fabrics, but also affects the yarn structure and evenness of yarns and the rate of spun yarn breakage.
Causes of neps
Neps are round knots or granular fiber knots formed by a single fiber or multiple fibers randomly arranged and entangled. The cause of formation is that cotton fibers, immature cotton or rigid cotton are assembled due to poor handling during ginning or spinning. The root cause of neps is the twisting and rubbing between fibers. From the reason of its formation, neps can be divided into two categories: neps caused by raw materials and neps caused during processing.
Neps caused by raw materials
The neps formed by raw materials include neps caused by impurities and defects, such as neps formed by fibers attached to cottonseed hides, neps formed by adhesion of cotton wax, and neps formed during cotton harvesting. The number of neps is an index for evaluating the grade of raw cotton. Low-grade raw cotton has high content of impurities, defects, fine fibers, poor maturity, and many neps formed during the production process. Therefore, the amount of neps and impurities spun from different raw materials is incomparable and cannot be used as an index to measure the performance of the spinning machine.
Nep caused during processing
The neps caused during processing include the neps caused by raw cotton rough processing ginning and spinning production. The neps formed by ginning are mainly the neps produced by the sawtooth gin; the neps caused by the spinning process include the neps formed during fiber opening and carding, the frictional resistance of the fiber channel and the sticking, entanglement, blocking, The neps formed by hanging, and the neps generated by the hook fiber during the drafting process.


Neps formed when fibers are opened and combed
At present, there are two ways to open and card fibers, namely, free release and grip release. In the process of opening and carding, the fibers are constantly subjected to axial and radial stress to produce strain. Some fibers have fatigue problems, resulting in their own strength and flexural rigidity decrease, bending deformation and mutual kinking to form neps. Free release is gentle, causing small deformation and less neps; grip release is intense, causing large deformation and more neps.
The opening and carding action of the beater of the cleaning machine and the licker roller of the carding machine on the holding fiber are the main parts that produce fiber deformation and form neps. Most of the neps are loose large neps. The combing machine holds and combs the two ends of the cotton tuft alternately, which not only produces a small amount of neps, but also eliminates many neps through the noil. When the cylinder and the movable cover plate, the fixed cover plate, and the doffer are combed or condensed fibers, due to the large centrifugal force on the surface of the cylinder card clothing, the fibers are easy to detach when the gap is large, and they are in the gap between the cylinder card clothing and the adjacent clothing , Out of control, become floating fibers. Due to the large speed difference between the relative card clothings, the floating fibers are susceptible to rubbing and forming knots; the number of floating fibers affects the number of neps formed by rubbing and rubbing.
Neps formed by sticking, entanglement, blocking and hanging
Abnormal phenomena such as sticking, entanglement, blocking, hanging, etc., can easily cause violent friction, which can cause fibers to twist and rub to form neps, which are mainly manifested in the following aspects:
(1) When the racks of cylinder, cover and doffer card clothing are blunt or have back thorns, the fibers cannot be transferred smoothly. Some fibers float between the racks and are twisted by other fibers on the two rack surfaces. Neps will form.
(2) When the licker roller-cylinder gap is too large, the surface of the rack is rough, resulting in poor stripping between the licker roller and the licker roller. In turn, the neps increase significantly.
(3) Cylinder card clothing rack tooth parts are scratched, rough, the rack has oily rust spots, and the cylinder-doffer gauge is too large and the transfer rate is low, which will cause the cylinder to circulate and increase the neps.


Nep formed by the frictional resistance of the fiber channel
Since the tumbling and friction of the fibers in the cleaning and cotton conveying channels will cause the fibers to twist and form neps, the fiber channels should be smooth and the negative pressure in the cotton conveying pipeline should be increased to ensure that the cotton flow is smooth and not blocked.
Neps formed by hook fibers during drafting
During the drafting process, the fibers with poor separation and parallel straightness in the strands are easy to entangle and draw into neps. Among them, hook fiber is the main reason for the increase of neps during drafting. During drafting, the hook part of the fiber is held by the doffer clothing rack, and the straight part is exposed outside the doffer clothing rack. The straight part will be bent by the airflow formed by the rotation of the doffer, making the hook fiber more. The more neps are formed during the drafting process.
Other causes of neps
The cotton masses, ropes, and unremoved fiber impurities, short fibers and harmful defects formed during the opening and cleaning process are also easily converted into neps in the carding process; the neps formed by flying flowers on the sliver ; The equipment has mechanical defects, such as abrasion or poor assembly of the apron, eccentric spindle, and wear of the traveler may also form neps.
The number of neps is one of the most important indicators to determine the grade of yarn. To reduce the neps, the first is to understand the neps. You should not blindly say to reduce the neps and use technical methods. It should be combined with the actual situation of the textile enterprise. The most effective, direct, and cheapest method is useful.

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