Neps in cotton are knots closely intertwined by cotton fibers. Large is called & ldquo; filament cluster & rdquo; small is called & ldquo; White Star & rdquo;.
I. Reasons for Neps Formation
Neps are round knots or granular knots formed by entanglement of single or multiple fibers. The reason is that cotton fibers, immature cotton or stiff cotton are agglomerated due to improper treatment in the process of ginning or spinning, and the fundamental reason for neps is the rubbing and rubbing between fibers. Neps can be divided into two categories according to their causes.
The first type is caused by raw materials. Neps formed by raw materials include neps caused by impurities and defects, such as neps formed by fibers attached to cotton seed coat, neps formed by wax adhesion and neps formed during cotton harvesting. Neps quantity is an index for evaluating raw cotton grade. Low grade raw cotton has high impurities and defects, fine fibers and poor maturity, and many neps are formed in the production process. Therefore, the number of neps and impurities spun by different raw materials is incomparable and can not be used as an index to measure the performance of the spinning machine.
The second category is caused by the processing process, including raw cotton roughing, rolling and spinning process. Neps formed by ginning are mainly neps produced by sawtooth ginning machine; neps formed during spinning include neps formed when loosening fibers, friction resistance of fibre passages and neps formed by sticking, winding, blocking and hanging, as well as neps formed by bending hook fibers in drafting process.
At present, there are two ways to loosen fibers (loosening and carding), namely, free loosening and grip loosening. In the process of loosening, the fibers are constantly subjected to axial and radial stresses, resulting in strain, fatigue of some fibers, resulting in the decline of their strength and flexural rigidity, resulting in bending deformation and intertwining to form neps. Free loosening action is gentle, resulting in small deformation and less neps; grip loosening action is intense, resulting in large deformation and more neps. The experiment proves that the neps can be increased by 10% after a free blow and 20% after a grip blow. Therefore, the severe grip on the fibers should be minimized in the process.
The beater of the cleaning machine and the taker-in roller of the carding machine have a strong loosening effect on the holding fibers, which is the main part of the fibers deformation and neps formation. For example, when the taker-in roller combs the cotton rolls held by the cotton sheet and the cotton rollers, the long fibers which are held in the same direction in the cotton roll and the cotton flow are left behind; the disordered, non-uniform and non-grasped fibers are taken away by the taker-in teeth, which is equivalent to the ordered fibers extracted from the disordered cotton bundles, while the disordered fibers in the extraction process are easily drawn, pulled, rubbed and rotated to form. A large number of neps, which is the main part of neps, are mostly loose large neps.
The comber alternately holds and combs both ends of the bundle, producing a small amount of neps and eliminating many neps through noil.
Free combing, such as combing between cylinder and movable cover, fixed cover, doffer or condensate fibers, is easy to detach from needle/tooth when the relative distance between needle/tooth surface is large due to the centrifugal force of fibers on the surface of cylinder card clothing, which is in the gap between cylinder card clothing and adjacent card clothing and loses control and becomes planktonic fibers. Because of the great speed difference between the relative clothing, the plankton fibers are easily rubbed into knots; the number of plankton fibers affects the number of knots formed by rubbing and rubbing.
Friction of the fibre passage makes the edge hairiness of the whisker easy to form neps. Because the fibers roll and friction in the clearing and conveying channels can also make the fibers twist to form neps, so the fibers channel should be smooth and the negative pressure in the conveying pipeline should be increased to ensure smooth and non-blocking cotton flow.
Abnormal phenomena such as sticking, winding, blocking and hanging often cause severe friction, which leads to the formation of neps by twisting and rubbing of fibers. For example, when the cylinder, cover plate and doffer needle/tooth are blunt or with reverse pricking, the fibers can not be transferred smoothly. Some fibers float between the needle/tooth surface and are rubbed by other fibers on the two needle/tooth surface, resulting in more neps. When the distance between taker-in roll and cylinder is too large and the tooth is not smooth, the stripping between taker-in rolls is not good. The return of taker-in roll brings the fibers back to the cotton sheet, and the knot increases obviously by twisting with the cotton whisker. The teeth of cylinder metal card cloth are crushed and rough, the needle/tooth has oil stains and rust spots, and the distance between cylinder and doffer is too large and the transfer rate is low, which will make cylinder twist and increase the knot.
The fibers with poor separation and parallel straightness are easy to entangle and pull into neps during drafting. The main reason for the increase of neps during drafting is the crooked fibers. The fibers that are agglomerated on the surface of Dough's card clothing and grasped at the exposed end are combed by Cylinder. When they come out of the agglomeration area to be stripped by cotton stripping roller, they form a cotton web. The combed end is in front, the grasped end is in back, and the fibers on the card cloth have more back bending hooks. The bending hook part of the fibre is held by Dolph, and the stretching part is exposed outside Dolph's clothing. The stretching part is blown by the air flow formed by Dolph's rotation, which makes some back bending hook fibers become bending hook fibers. The more bending hook fibers, the more neps formed during the stretching process.
In addition, the cotton balls, yarns, impurities, staple fibers and harmful defects formed during the opening and cleaning process are easily converted into neps in the carding process. Neps formed by flying flowers falling on the sliver, mechanical defects, such as wear and tear of aprons or poor assembly, and eccentricity of spindlesThe wear and tear of travellers may also cause neps.
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2. The Method of Eliminating Neps
Through noil removal and carding to loosen neps, opening and clearing noil, carding belly noil, flange flower and Combing Noil are the main areas to eliminate neps; carding can effectively eliminate fiber entanglement and reduce neps; through careful carding of cylinder and flange, some loose neps are broken down into single fibers and large neps are broken down into single fibers or small neps; at the same time, short fibers are also increased. 。
Measures to reduce neps
By loosening, carding and drawing the fibers into orderly single fibers, neps will be gradually removed, and neps will inevitably be produced. However, neps should be reduced as much as possible and more neps should be removed. There are many reasons for Neps formation. It should be considered systematically to make the spinning components and equipment in good condition. Rational configuration of process parameters is the guarantee. Good mechanical condition and reasonable process design can significantly reduce neps.
Carding process combs fiber bundles into single fibers, which will inevitably add many new neps; and the fine carding of Cylinder-cover can also break loose neps into fine neps or single fibers; therefore, carding is the key process to produce, remove and carding neps. Because neps and impurities in sliver directly affect yarn neps and fabric defects, as well as the movement of fibers in drawing, coarsening and fine processes, and the normal movement of travellers in twisting and winding of spinning yarns, resulting in evenness and yarn defects, it is necessary to control and reduce the number of neps and impurities in sliver and improve carding quality as an effective way to reduce neps.
The key to reduce neps in sliver is to achieve “ fine flat car, tight gauge, sharp needle/tooth; realize strong carding, control float, reduce rubbing, rubbing, less generation, more exclusion of ”; and uuuuuuuuuu That is fine paperback machine, special repair, ensure boarding process, improve static and dynamic balance, roundness and flatness of cover needle surface of cylinder, taker-in roller and doffer, and maintain close and accurate carding separation distance, which is the basis. It is the key to select high quality card clothing and grind needles in time to make the needle/teeth of Carding Clothing sharp, smooth and intact, and to improve the ability of grasping, holding, carding and transferring fibers. Achieving a tight gap and sharp needle/tooth can improve carding quality, control fibre float and reduce rubbing knot; improve fiber straightening parallelism and reduce neps in drafting process; between cylinder and taker-in, the tight gap can increase the transfer of fibre bundles to cylinder on taker-in roll, and reduce the return of taker-in to the cotton board and the feeding layer rubbing into knot. Close interval between cylinder and doffer can increase doffer transfer rate and reduce return load on cylinder, thus reducing load between cylinder and cover, improving one-time carding ability between cylinder and cover, and reducing neps. At the same time, the loose neps in the cotton flow are more combed and eliminated by carefully combing between the cylinder and the cover plate to reduce the neps.
Card clothing is the key to improve carding quality. Card clothing is the core component to improve output and quality and reduce neps in carding process. Its tooth shape, manufacturing quality, specification matching, sharpness and abrasion resistance directly affect yarn quality. Using high-quality sharp card clothing can significantly reduce neps. The new card rack has the characteristics of short, shallow, sharp, thin, dense and small. It has strong carding ability and meticulous carding. It improves the ability of carding fibers and combing neps. The fiber transfers well and reduces the neps formed by rubbing planktonic fibers. The test shows that the NEP content of sliver decreases by 2%-60% after the application of the new card clothing, the straightening parallelism and separation degree of the fibers in sliver are increased, the neps produced in the drafting process of the later process are reduced, and the yarn neps are reduced.
With the prolongation of the service life of the card clothing, its wear becomes more and more serious, the tip of the tooth becomes blunt and not sharp, the needle/tooth is not smooth because of the rolling injury, and the neps increase. It is one of the important measures to control neps to regularly test and analyze the performance of clothing by gun, to reasonably determine the period of needle grinding and replacement, to keep needle/tooth sharp, and to grind needles or change clothing in time.
Timely grinding of the heel toe surface of the cover plate can keep the proper Heel Toe difference (0.56 mm) so as to reduce the overall distance between the needle surface of the cover plate and the cylinder, strengthen carding and reduce the knot formed by the rubbing of planktonic fibers between the needle surface. Good results can be achieved. At present, the heel toe surface of carding machine cover in many cotton spinning mills has been severely worn and the heel toe difference is large, which makes the technological separation between cylinder and cover plate smaller. In fact, the gap between cylinder and cover plate needle surface is larger, which fails to achieve tight separation and strong carding, so the carding neps increase. In some factories, the chain of cover plate has been worn and lengthened, and the distance between cylinder and cover plate is easy to change and inaccurate, thus affecting carding quality and increasing neps. For these factories, timely grinding the heel toe surface of the cover plate and changing the chain are effective measures to reduce neps.
Carding machine without additional combing parts can properly increase the front and rear fixed cover with suction device to improve carding quality, eliminate fine dust and reduce neps. Reasonable control of tummy noil, cover pattern and combed noil can eliminate neps and reduce yarn neps. Reversal of the cover or increase the running speed of the cover can effectively reduce neps.
According to the characteristics of raw cotton, technological parameters should be selected, such as fine fibers, poor maturity, low speed and soft loosening, not using three-wing blades and porcupine fighters, using three-wing comb needle with low speed, taker-in roller and doffer with low speed.Controlling the speed ratio of taker-in roll to cylinder; low speed ratio, more neps; high speed ratio, less neps; pure cotton should be controlled at about 1:2.
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IV. Detection methods and changes of Neps
In China's cotton textile enterprises, at present, most manufacturers use traditional hand-feeling visual method to detect neps and impurities in semi-finished products and finished products of various textile processes; a few manufacturers use AFlS single fiber testing system to detect. Visual neps are defined as round nodules or granular nodules formed by one or more fibers, or white stars. They are placed on the black glass plate after the test sample is loosened manually in the fibre laboratory. Using the light projected above, the black glass plate can not be regarded as a NEP by loose white dots. This NEP is a group of fibers twisted together by many fibers in order to be recognized by the eye. A large NEP may also be decomposed into several small neps. The test results depend on the eye of the tester. The diameter of a single fiber is nearly 20 /& mu; m, and the diameter of neps formed by a single fiber is nearly 60 /& mu; M. Due to the limitation of human eye resolution, many objective neps can not be visually detected. The weight of neps varies greatly among individual neps. The test reports that the weight of Neps in raw sliver is only 1.4% of the weight of Neps in cotton roll and large cotton roll.
AFIS single fiber testing system defines neps as non-single fibers whose projection diameter exceeds the prescribed value (100 μ m). Neps formed by two fibers, which are not easily recognized by the naked eye, can be detected. Such neps are much smaller than those visually measured, so that the size of neps can be measured, reflecting the true situation of neps.
Because there are different definitions and testing methods for neps, one NEP can be measured by AFlS as many neps. Therefore, the number of neps measured by AFlS is very small, and the number of neps measured by AFlS is very large, which makes the number of neps tested very different. Because the NEP data measured by different methods are incomparable, the NEP data must indicate the test method.
Because the raw materials, equipment and technology of each factory are different, neps are produced in different ways. Current literature reports suggest that the changes of neps detected by the two methods are different; the number of neps detected by eye detection method increases with the increase of processing procedures; neps detected by AFIS single fiber testing system decreases with the increase of processing procedures; the results of the two trends are opposite.
We think from the production of neps, we do not consider the exclusion and wrapping or covering, the size of neps and whether they can be detected, neps in fibers increase with the increase of processing procedures. The ideal result is to reduce neps. Neps removal should be strengthened so as to gradually increase the number of Neps in the cleaning process and produce a large number of Neps in the carding process. However, more neps are removed than produced, resulting in a decrease in sliver neps (more combed products are prepared, less combed slivers are produced than excluded), increase in coarsening and roving, and increase in spinning due to package coverage. The number of neps is more than that of neps, and the surface neps of yarns measured by visual method are reduced.
Recently, there has been a great controversy about the change of Neps in carding process reported in the literature.Some scholars believe that carding is the main process to produce neps, and sliver neps increase more than 10 times than cotton roll neps; others believe that carding is the main process to reduce neps, which can reduce the number of feeding neps by nearly 80%. We believe that the key to increase or decrease neps in carding process is carding quality; carding is normal, less production and more exclusion, then sliver neps decrease; If carding is abnormal, more neps will be produced and less neps will be eliminated, which will result in more neps in sliver.
V. Concluding remarks
Neps are mainly produced by cotton fibers in the process of ginning and carding. Holding loosening is the main part of neps. The key to increase or decrease neps is carding quality, and the core is card clothing. The change of neps has only an ideal trend, but no fixed rule. In actual production, it varies with the performance of raw materials and spinning machines.
