Neps are an important indicator of yarn quality assessment. The technical requirements for the grade of cotton yarn not only specify the total number of neps and impurities in 1 g of yarn, but also specify the number of neps. The amount of neps not only affects the appearance quality of the yarn and fabric, but also affects the yarn structure and evenness and the yarn breakage rate.
Causes of Neps
Neps are circular nodules or granular fiber knots formed by the disorderly arrangement and entanglement of single or multiple fibers. The cause is that cotton fibers, immature cotton or stiff cotton are assembled due to poor handling during ginning or spinning. The root cause of neps is the rubbing and rubbing between fibers. From the perspective of its formation reasons, neps can be divided into two categories: neps caused by raw materials and neps caused by processing.
Neps caused by raw materials
Neps formed by raw materials include neps caused by impurities and defects, such as neps formed by fibers attached to the cottonseed skin, neps formed by cotton wax adhesion, and neps formed in the process of cotton collection. The number of neps is an indicator for evaluating the grade of raw cotton. The raw cotton of low grade has high content of impurities and defects, fine fibers and poor maturity, and there are many neps formed in the production process. Therefore, the amount of neps and impurities spun by different raw materials is incomparable and cannot be used as an indicator to measure the performance of the spinning machine.
Neps from processing
Neps from processing include neps from raw cotton roughing, ginning and spinning. The neps formed by ginning are mainly those produced by the sawtooth gin; the neps caused by the spinning process, including the neps formed during fiber opening and carding, the frictional resistance of the fiber channel and the sticking, entanglement, blocking, The neps formed by hooking and the neps produced by the hook fibers during the drafting process.
Neps formed during fiber opening and carding
At present, there are two ways to open and comb fibers, namely free release and grip release. During the process of opening and carding, the fibers are continuously subjected to axial and radial stress to generate strain, and some fibers have fatigue problems, resulting in a decrease in their own strength and bending stiffness, resulting in bending deformation and kinking each other to form neps. The free loosening effect is soft, polyethylene wax emulsion, resulting in small deformation and less neps; the grip loosening effect is severe, causing large deformation and many neps.
The opening and combing of the holding fibers by the beater of the cleaning machine and the licker-in of the carding machine are the main parts of the fiber deformation and the formation of neps. Most of the neps are loose large neps. The comber alternately holds and combs both ends of the cotton bundle, which not only produces a small amount of neps, but also eliminates many neps through noils. When the cylinder and the movable cover, the fixed cover, the doffer are carded or the fibers are aggregated, due to the large centrifugal force of the fibers on the surface of the cylinder card clothing, the fibers are easy to detach when the distance is large, and they are located in the gap between the cylinder card clothing and the adjacent card clothing. , out of control and become planktonic fibers. Due to the large speed difference between the opposite card clothings, the floating fibers are easily rubbed into knots; the number of floating fibers affects the number of neps formed by rubbing and rubbing.
Neps formed by sticking, tangling, blocking and hanging
Abnormal phenomena such as sticking, tangling, blocking, and hanging can easily cause severe friction, which leads to the formation of neps by fiber rubbing and rubbing, mainly in the following aspects:
①When the cylinder, cover and doffer clothing racks are blunt or have reverse thorns, the fibers cannot be transferred smoothly, and some fibers float between the racks and are rubbed by other fibers on the surfaces of the two racks. Neps.
②When the gap between the licker-in and the cylinder is too large, the surface of the rack is rough, resulting in poor peeling between the cylinder and the licker-in. Significantly increased neps.
③The tooth portion of the cylinder card clothing rack is crushed and rough, the rack has oil stains and rust spots, and the cylinder-dolph gap is too large, and the transfer rate is low, which will cause the cylinder to wrap around, resulting in an increase in neps.
Neps formed by frictional resistance of fiber channels
Because the tumbling friction of the fibers in the cleaning and cotton conveying channels will cause the fibers to twist and form neps, therefore, the fiber channel should be smooth and clean, and the negative pressure in the cotton conveying pipeline should be increased to ensure smooth and unblocked cotton flow.
Neps formed by hook fibers during drafting
During the drafting process, fibers with poor separation and parallel straightness in the sliver are easily entangled and drawn 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 card clothing rack, and the straight part is exposed outside the doffer card clothing rack. The more neps the sliver forms during the drafting process.
Neps from other causes
The cotton balls, ropes and unremoved fibrous impurities, short fibers and harmful defects formed during the process of opening and cleaning are also easily converted into neps in the carding process; neps formed by flying flowers falling on the sliver ; There are mechanical defects in the equipment, such as wear or poor assembly of the rubber ring, eccentric spindle, wear of the traveler, etc. may also form neps.
The number of neps is one of the most important indicators to determine the yarn grade. To reduce the neps, the first thing is to understand the neps. You can’t blindly say that you can reduce the neps and use technical means. The most effective, most direct, and cheapest means, that is useful.
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