End breakage per 1000 spindles is one of the important economic and technical indexes in spinning production, which reflects the comprehensive effect of the whole spinning production technology system. Reducing yarn end breakage rate can not only reduce the cost of cotton, improve the efficiency of spinning frame and unit yield, but also is one of the important ways for cotton spinning enterprises to expand the stand, reduce labor and improve economic efficiency. The technical management of reducing yarn breakage is closely related to the improvement of cotton yarn quality, such as improving cotton yarn strength, improving yarn evenness, reducing thin and thick spots, and reducing yarn defects. According to the production practice for many years, the causes and solutions of spinning end breakage are summarized, analyzed and discussed for reference.
1. Basic Approaches to Reducing Yarn Breakage in Spinning During the spinning process
A yarn break occurs when the spinning tension exceeds the strength of the yarn; this is the essence of yarn breakage. The average values of these two must ensure that the yarn strength is greater than the spinning tension for normal spinning to occur. Here, the term 'yarn strength' collectively refers to the dynamic strength of the spinning segment, the ballooning segment, and the winding segment; similarly, 'spinning tension' is also dynamic, encompassing the spinning segment tension, ballooning tension, and winding tension. Spinning tension and yarn strength are fluctuating variables. A break occurs when the peak value of spinning tension exceeds the minimum instantaneous value of yarn strength. Therefore, the basic approaches to reducing yarn breakage involve, on one hand, lowering the peak value of spinning tension and minimizing tension fluctuations, and on the other hand, increasing the minimum value of yarn strength and reducing the fluctuation in yarn strength.
2.Reducing the Maximum Value and Fluctuation of Spinning Tension
2.1 Factors Affecting the Fluctuation of Spinning Tension .
(1) The instability of high-speed running of the band. When the diameter of the spindle is 22 mm and the spindle speed is 20,000 r/min, the linear speed of the band can reach up to 1382.3 m/min. Since the band drives the spindle through friction, it directly affects the stability of the spindle speed. Therefore, the quality and operating state of the band have a significant impact on the fluctuation of spinning tension.
(2) The instability of high-speed rotation of the spindle. The high-speed rotation of the spindle is the source of power for spinning tension and ballooning. Defects such as uneven spindle speed, vibration, and up-and-down movement affect the stability of spinning tension.
(3) Poor quality of bobbins. Winding in spinning is achieved through the bobbin. If the bobbin quality is poor, issues such as bobbin shaking, up-and-down movement, and poor synchronization between the bobbin and the spindle will affect the stability of spinning tension.
(4) The influence of ring and traveler. The ring and traveler operate under high speed, high pressure, and high temperature during spinning. With a 42 mm diameter ring and spindle speeds between 16,000 r/min and 20,000 r/min, the linear speed of the traveler can reach 35.2 m/s to 44 m/s, generating temperatures above 300°C. Tests have shown that for an 18.2 tex cotton yarn at the bottom of the tube forming a large diameter, the contact pressure is 243 cN. Assuming that the instantaneous contact area of the traveler on the ring is 0.1 mm² during the run-in period of the traveler, the contact pressure is 24.3 MPa, which is 1.34 times the maximum limit value of 18.1 MPa specified for aircraft engine crankshaft bearing surfaces. The traveler rotates on the ring under special conditions of high speed, high temperature, and high pressure, which has a significant negative effect on the stability of spinning tension. The reasonable selection and matching of rings and travelers have a significant impact on the variation of spinning tension.
(5) Poor concentricity of the spindle, ring, and guide hook, which increases the likelihood of swinging, tilting, and wedging of the traveler in the space of the ring, leading to tension fluctuations.
(6) The spinning balloon causes the yarn inside the guide hook to swing laterally within a certain width. If the swinging area is not horizontal, it will cause the balloon to be unstable or affect the stability of spinning tension.
(7) An inclined selvedge plate can easily cause a spinning balloon and collision with the selvedge plate, leading to unstable spinning tension.
(8) Worn traveler cleaners with burrs or an excessive gap between the traveler and the cleaner can prevent effective removal of fly waste wrapped around the traveler, causing unstable spinning tension that tends to increase.
(9) Vibration and jolting during the lifting and lowering of the ring rail can also cause unstable spinning tension.
(10) Fly waste entering the spinning balloon or unreasonable distribution of air conditioning outlets in the spinning environment, along with airflow disturbances, can cause fluctuations in spinning tension.
2.2 Technical Measures to Stabilize Spinning Tension
2.2.1 Spindle System The spindle tip and bottom bearing.
Spindle rod, and upper bearing should not be worn; spindle rotation should not shake or bounce vertically; the spindle foot should not be slightly warm or vibrate; regularly inspect and calibrate the spindle rod and spindle disc for eccentricity and bending; the band should have normal length and tension, without frayed edges or twists, free from oil stains and fiber buildup, and not in contact with the edges of the spindle disc or rolling disc; joints should not be thick or hard, and operation should not jump; the surface and bearing of the band disc should not be worn, bearings should be cleaned regularly without hardened oil dirt, and rotation should not jump or wobble; the top of the bobbin should not have burrs or damage, the upper eye of the bobbin should fit tightly with the upper taper of the spindle rod to ensure synchronous rotation of the spindle and bobbin; there should be a slight gap between the lower mouth of the bobbin and the lower bell of the spindle; there should be no yarn scraps between the bobbin and the spindle; the bobbin should not shake, move up and down, or jump during rotation.
2.2.2 Ring, Traveler, and Ballooning System
(1) The ring should be free of rust spots, and the upper edge and traveler track should be free of burrs.
(2) The service cycle of traditional rings should be adjusted according to wear, using planetary polishing machines to refinish rings and employing high-quality abrasives and solutions while paying attention to refinishing methods to improve refinishing quality.
(3) The height of the ring board should be maintained in a straight line throughout the machine, whether at small or full bobbin stages; the ring board should be level left to right and front to back; the ring fastened to the ring board should not be loose or tilted; lifting and lowering of the ring board should not vibrate or jolt.
(4) Select and adjust the weight of the traveler based on factors such as yarn strength, ring condition, spindle speed, traveler linear speed, balloon shape, break distribution, humidity fluctuations, and yarn hairiness count.
(5) Establish proper traveler replacement cycles based on the number of breaks and hairiness count, and diligently execute them to prevent missed traveler changes.
(6) Carefully calibrate spindle levelness; meticulously align the centers of the spindle, ring, and guide hook both statically and dynamically; for spindles repositioned after adjustment, recalibrate dynamic alignment at both small and full bobbin stages; for newly adjusted guide hook positions, recalibrate dynamic alignment at both small and full bobbin stages.
(7) The guide hook should not be worn or loose; regardless of bobbin size, the guide hook should remain level.
(8) The selvedge plate should not have burrs, and when installed between two spindles, it should not be skewed or loose.
(9) The traveler cleaner should have a reasonable design and accurate manufacturing; cleaners should not be loose or have burrs, and the gap should be kept minimal.
(10) The spinning balloon should not be skewed; if caused by an unlevel inner side of the guide hook, replace the guide hook immediately. The spinning balloon should be stable without vibration; at full bobbin stage, the balloon should have a slight circular arc shape. The balloon should not touch the bobbin head or selvedge plate.
(11) Regularly inspect the flatness of the ring's upper surface and the roundness deviation of its inner hole, ensuring they do not exceed 0.05 mm; the actual depth of the ring's traveler track on the inside should not be less than the designed depth.
(12) In operational management, maintain cleanliness of components involved in drafting and twisting and winding.
3.Increasing the Minimum Value of Yarn Strength and Reducing Strength Fluctuation
Increasing the minimum value of yarn strength and reducing single-strength CV% is a systematic project involving many factors. Each factor could be a topic in itself, with plenty of academic theories and practical experiences available for our learning and exchange. Below are only the main factors briefly described.
3.1 Blending and Mixing Cotton The length, grade, fineness, strength, maturity, short fiber content, moisture regain, neps, and other defects of cotton fibers are all related to the strength of the yarn. Blending should complement the physical and mechanical properties of different cotton batches to maximize their benefits. Mixing is the thorough and even distribution of fibers from various batches. A higher concentration of fibers within the cotton yarn cross-section that contribute to strength results in greater strength at that point, whereas areas with fewer such fibers are weaker and more prone to form weak links in the yarn. Blending and matching batches should be done frequently and in small quantities to prevent fluctuations in the average physical and mechanical properties of mixed cotton, which could lead to fluctuations in yarn strength. Mixing is equally important as blending. The following tasks should be carefully executed: the cotton bale arrangement chart should be established by the quality management department; cotton bales should be stored upright, with high stacking and gap filling, and loose fibers should not be placed on top of the bales; returned cotton should be packed and arranged according to the bale arrangement chart after processing; the bottom layer of cotton bales should not be exposed due to some bales being used up, and the remaining unfinished bales should not be dispersed and wedged into the gaps between bales.
3.2 Opening and Cleaning Cotton Opening and cleaning transforms cotton chunks into smaller tufts, creating favorable conditions for carding to separate the tufts into individual fibers. Care must be taken to avoid damaging the fibers and increasing nep formation; opening and cleaning should focus on removing heavy and large impurities, but it's crucial to prevent the breakage of impurities, which could complicate the removal of fine and light impurities during carding, hence early removal is essential. The process should be gentle and open up the cotton instead of beating it, feed continuously and uniformly at a thin rate, improve the operational efficiency of each machine, and ensure early and careful removal of impurities. For traditional opening and cleaning machines, it's necessary to reduce the longitudinal and lateral irregularity of the cotton sliver. Compared to the matched cotton, the growth rate of short fibers (<16 mm) should be controlled between -1% and +1%, and the growth rate of neps should be kept below 80%, aiming even lower. Since neps formed during the cleaning process may break down into short fibers during carding, reducing the work of removing short fibers in the carding sliver becomes more challenging. Generally, the operational efficiency of automatic waste cotton grabbers should be above 95%; the interconnection of each machine in the opening and cleaning unit should be sensitive, and the operational efficiency of each machine before the forming machine should meet the above requirements; the angle teeth of the curtain rods in each cotton box should not have hooks, broken nails should not have sharp edges, and the evener roller or cotton conveying roller should not wrap or reverse the fibers; the combing needles, saw blades, and saw teeth of various beaters should not have hooks, reverse fibers, or wrap; the trash grid and dust bars should have smooth and flat surfaces without hooks or clogs; the inner surface of the conveying duct should be smooth, not hooky or leaky, and the pneumatic conveying should be unobstructed.
3.3 Carding Carding aims to separate the tufts into individual fibers, resolve entangled fibers, and remove neps and impurities from the fiber bundles while preventing damage to the fibers that could increase short fiber content. Short fibers can negatively affect the strength, hairiness, yarn evenness, yarn defects, nep count, and details or thick places of the cotton yarn. The core of the carding process is to properly handle the relationship between carding intensity, carding strength, and transfer. The carding elements should achieve "seven sharp points," meaning that the pins of the seven carding elements-the licker-in, pre-carding plate, fixed flat, movable flat, front fixed flat, tin plate, and doffer-should all be sharp, smooth, durable, and accurately spaced. The accuracy of the flatness of the carding elements is fundamental for implementing precise spacing, and the sharpness and smoothness of the carding elements are essential for good carding and transfer. The licker-in is the main part where fibers are damaged. With proper "seven sharp points" implementation, high-speed ratio between the tin plate and licker-in, and increased transfer process, as well as close spacing and strong carding process between the tin plate and movable flat, significant improvements can be achieved in reducing short fiber increase in carding slivers and enhancing yarn strength. For example, under a condition of 12.7% short fiber content (<16 mm) in the matched cotton, increasing the speed ratio between the tin plate and licker-in from 2.3:1 to 2.5:1 and enlarging the gap between the licker-in and feeding plate from 0.46 mm to 0.52 mm resulted in a reduction of short fiber content in the sliver from 17.5% to 15.8%, in the refined sliver from 8.14% to 6.62%, and in the coarse yarn with short fibers <12.5 mm from 3.65% to 3.39%. The evenness CV of the 14.6 tex yarn decreased from 13.51% to 13.29%, and the evenness CV of the 18.2 tex yarn decreased from 12.20% to 12.10%, with an increase in strength from 272.3 cN to 276.7 cN. The carding process should also focus on the following management tasks: keeping original records of the wrapping and usage of carding elements, the amount of fiber processed by carding machines to provide a basis for timely replacement of carding elements; regularly testing the "seven sharp points" of carding elements and keeping records; recording the co-grinding and re-grinding quality of carding elements; regularly testing the short fiber content, neps, and impurities of the input cotton layer and sliver after the same machine, analyzing statistically to identify underperforming machines for maintenance; controlling the increase rate of short fibers in the sliver compared to mixed cotton between 3% and 5%; strengthening operational management, improving the level of damage prevention by operators, correctly using equipment, and preventing damage to needles.
3.4 Drawing The drawing process is crucial for improving fiber parallelization and ensuring normal spinning tension, which significantly affects yarn strength. It has a considerable impact on the weight unevenness of fine yarn and the formation of long-detail defects. The main technical measures include:
(1) For varieties with significant fluctuations in sliver weight, changing the combination of drawing from 6×8 to 8×8 can improve the effect and reduce the end weight unevenness.
(2) Reducing the CV value of mature sliver weight. This involves focusing on controlling the weight of raw sliver; appropriately increasing the number of semi-mature sliver weight inspections; conducting weight inspections three times per shift and controlling the weight CV for each inspection; when the weight CV exceeds the standard, promptly trace the analysis to determine whether it is caused by differences in input cotton weight or defects such as rubber rollers or pressure application mechanisms, broken ends or missing stops, or excessive suction in the drafting mechanism, and take targeted measures; maintaining stable temperature and humidity control.
(3) Preventing long detail defects in the drawing process caused by poor factors in the drawing process. Long detail defects spun through drawing, rough spinning, and fine spinning with about 7.5 times drafting and 40 times spinning cannot be resolved in the rough spinning and fine spinning processes. Therefore, the drawing process should eliminate long detail defects before reducing the CV of mature sliver. This involves whether the process design is reasonable, whether the drafting elements and pressure application mechanisms are functioning normally, whether operational management and machine cleaning are satisfactory.
(4) Properly configuring the drafting process to improve fiber parallelization. Based on experience: the back zone drafting of the head drawing should be 1.75 times, and the front zone drafting should be within 3.5 times; the back zone drafting of the tail drawing should be around 1.25 times, with corresponding front zone drafting of 6.5 to 7 times, increasing the number of fibers entering the front zone and thereby increasing the drafting force. Special attention should be paid to whether the front roller gripping force is greater than the drafting force to prevent the critical state where the gripping force is equal to or greater than the maximum drafting force. When fluctuations occur in the weight or structure of the input cotton sliver causing long detail defects in fine yarn and long coarse yarn defects, it is advisable to appropriately increase the back zone drafting multiple or roller spacing, which is a passive method to reduce drafting force. If conditions allow, increasing the gripping force is a more rational approach.
(5) Eliminating mechanical waves in drawing. Mechanical waves in the drawing process may not necessarily worsen the evenness CV of fine yarn, but after several times of high multiple drafting, they can form long sections of coarse and fine details. If the cotton yarn weight is lighter than the yarn segment and overlaps with the uneven details, it will cause a strength weak ring in the cotton yarn. Therefore, it is essential to prevent mature sliver from generating mechanical waves. Additionally, the following management tasks should be carried out: regularly inspecting the sensitivity of broken end and missing stop mechanisms, with operators repairing any found issues promptly; enhancing operational management, improving operator skill levels, strictly prohibiting misfeeding, ensuring proper wrapping of cotton bales, avoiding overlapping input cotton layers, clearing defective products such as light sliver, keeping the workplace clean to prevent contamination, measuring mature sliver evenness CV daily or per shift for each machine, servicing machines with mechanical wave and deteriorating evenness CV promptly, addressing issues with machine parts and processes that commonly cause defects, prohibiting operators from cutting rubber rollers with knives or improper handling that damages them, having dedicated personnel regularly check the operation of rubber rollers and bearings, and providing operators with special cleaning agents to remove cotton wax and melted oil stains on rubber rollers.
4.Other Work to Reduce Yarn Breakage .
In addition to focusing on reducing spinning tension and increasing yarn strength, other aspects should be considered to reduce yarn breakage:
(1) Increase the moisture regain rate of roving to above 7.5% to ensure normal production of fine yarn. If this affects the normal production of roving, efforts should be made in terms of process, equipment, and operation to alleviate the issue.
(2) Maintain the relative humidity of fine yarn between 55% and 60%, ensuring that the moisture regain rate of fine yarn is slightly lower than that of roving, keeping the roving in a drying state during fine yarn production.
(3) Ensure a good yarn breakage cotton suction system with a 100% qualification rate for suction. The suction ducts should not leak air, hang fibers, or clog, and the air valves should not leak, maintaining good vacuum levels.
(4) Ensure proper installation of the suction flute pipes, normal rotation of the top rollers, and regular cleaning. The doffer should promptly clear the accumulated flowers in the suction box.
(5) Strengthen operational management, diligently follow operating procedures, keep the machine clean, and reduce the impact of flying flowers, short fibers, and dust in the environment on yarn breakage.
Through the analysis of spinning principles, it is believed that the essence of yarn breakage is that the maximum value of spinning tension is greater than the minimum value of yarn strength. Therefore, reducing yarn breakage should mainly focus on lowering the maximum value of spinning tension to reduce tension fluctuations and improving the minimum value of yarn strength to reduce strength fluctuations. Reducing yarn breakage is a broad, complex, meticulous, and comprehensive systematic project that is closely related to the enterprise's equipment, processes, operations, raw materials, temperature, and humidity, as well as other basic management work and quality improvement measures. A holistic and integrated approach should be taken, adhering to meticulousness and continuous improvement in all technical and managerial tasks to achieve effective results.