Neps are an important indicator for yarn quality assessment. The technical requirements for cotton yarn grades not only stipulate the total number of neps and impurities in 1 g of yarn, but also specify the number of neps. Number of grains. The nep content not only affects the appearance quality of yarn and fabric, but also affects the yarn structure and evenness as well as the yarn breakage rate.
Cause of neps
Neps are small round or granular fiber knots formed by a single fiber or multiple fibers arranged and entangled in a disorderly manner. The cause is that cotton fibers, immature cotton or stiff cotton are aggregated due to improper handling during ginning or spinning. The fundamental reason for the formation of neps is the rubbing and friction between fibers. Based on the causes of their formation, neps can be divided into two categories: neps caused by raw materials and neps caused during 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 cotton seed skin, neps formed by the adhesion of cotton wax, and cotton neps. Neps formed during the process, etc. The number of neps is an indicator for evaluating the grade of raw cotton. Low-grade raw cotton has high impurity and defect content, fine fibers, poor maturity, and more neps formed during the production process. Therefore, the number of neps and impurities in yarn spun from different raw materials is incomparable and cannot be used as an indicator to measure the performance of spinning machines.
Neps caused during processing
Neps caused during processing include neps caused during raw cotton roughing, ginning and spinning production. The neps formed by ginning are mainly the neps produced by the sawtooth gin; the neps caused during the spinning process include the neps formed during fiber opening and carding, the friction resistance of the fiber channel and the sticking, entanglement, blocking, Neps formed by hanging, and neps produced by hook fibers during the drafting process.
Neps formed during fiber opening and carding
At present, there are two ways to open and card fibers, namely free loosening and holding loosening. During the process of opening and carding, the fibers are constantly subjected to axial and radial stress to produce strains. Some fibers have fatigue problems, resulting in a decrease in their own strength and bending stiffness, resulting in bending deformation and kinking with each other to form neps. The free loosening effect is gentle, causing small deformation and few neps; the holding loosening effect is violent, causing large deformation and many neps.
The opening and carding effects of the beating hand of the cleaning machine and the licker-in of the carding machine on the held fiber are the main parts that cause fiber deformation and the formation of neps. Most of these neps are large loose neps. The combing machine alternately holds and combs both ends of the cotton bundle, which not only produces a small number of neps, but also eliminates many neps through waste. When carding or condensing fibers between the cylinder and the movable flat plate, fixed flat plate, and doffer, 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 in the gap between the cylinder card clothing and the adjacent card clothing. , lose control and become floating fibers. Because there is a large speed difference between the opposite card clothings, the floating fibers are easily rubbed and formed into knots; the number of floating fibers affects the number of neps formed by rubbing and rubbing.
sticky, entangled,Neps formed by blocking and hanging
Abnormal phenomena such as sticking, entangling, blocking and hanging can easily cause severe friction, which will lead to the twisting and rubbing of fibers to form neps, which are mainly manifested in the following aspects:
(1) When the cylinder, cover plate and doffer card clothing racks are blunt or have counter-thorns, the fibers cannot be transferred smoothly. Some fibers float between the racks and are rubbed by other fibers on the two rack surfaces. Neps will form.
(2) When the distance between the lick-in roller and the cylinder is too large, the surface of the rack will be rough, resulting in poor stripping between the cylinder and the lick-in roller. The lick-in roller will bring the fibers back to the cotton feeding board, and at the same time, the lick-in roller will return to the cotton feeding board. The cotton whiskers are twisted and the neps are significantly increased.
(3) The teeth of the cylinder clothing rack are bruised and rough, the rack has oil stains and rust spots, the distance between the cylinder and the doffer is too large, and the transfer rate is low, which will cause the cylinder to twist around and cause the cotton to be damaged. Knots increase.
Neps formed by the frictional resistance of the fiber channel
Since the rolling friction of the fibers in the cleaning and cotton conveying channels will cause the fibers to twist and form neps, therefore, the fiber channels should be made smooth and clean, and the fiber conveying channels should be improved. Negative pressure in the cotton pipeline to ensure smooth transportation of cotton flow and no blockage.
Neps formed by hook fibers during the drafting process
During the drafting process, fibers with poor separation and parallel straightness in the sliver are easy to get entangled and pulled 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 wire rack, while the straightened part is exposed outside the doffer wire rack. The straightened part will be bent by the airflow formed by the doffer rotation, causing the number of hook fibers to increase. The more neps are formed in the slivers during the drafting process.
Neps formed by other reasons
The cotton clumps, ropes, and unexcluded fiber impurities, short fibers and harmful defects formed during the blowroom process are also easy to cause in the carding process. Converted into neps; neps formed by flying flowers falling on the whiskers; mechanical defects in the equipment, such as worn rubber rings or poor assembly, eccentric spindles, worn wire rings, etc. may also form neps.
The number of neps is one of the important indicators that determines the grade of yarn. To reduce neps, we must first understand neps. We cannot blindly talk about reducing neps and use technical means randomly. We must combine the actual situation of textile enterprises. Depending on the situation, it is only effective to choose effective, direct, and cheap means.
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