Since its inception in 1873, denim has been popular with its rough, free and easy, comfortable and durable. With the improvement of living standards, health care textiles have attracted more and more people's attention. Hemp fiber is a natural plant fiber, which has the advantages of anti-mildew and antibacterial, absorbs ultraviolet rays, absorbs moisture quickly, etc., and is used in denim weaving, and the cost of hemp fiber textiles Low, profit margin has become the main point of business chasing; because the characteristics of hemp fiber itself is hard, straight, uneven thickness, so there are many problems in the weaving process, the problem is discussed.
1 raw material selection
The content of hemp fiber in hemp fiber denim in Europe and America must be greater than 55%. Therefore, the raw material cost should be based on the premise of ensuring the style of the fabric, with the lowest linen/cotton blend ratio, and the weft yarn should be selected reasonably. Hemp/cotton denim is generally selected from ramie and cotton blended yarns as warp yarns. Ramie fiber contains the most cellulose in hemp raw materials and contains the least amount of rubber impurities. It is the best raw material for hemp spinning.
2 reasons for the formation of the warp
1.1 and head;
When the warp yarn is broken, the yarn is leaked. This is a common occurrence. On the one hand, the quality of the raw material is poor, it is easy to cause breakage, and on the other hand, the machine and the drainage problem are caused. Warp break joints are often affected by the presence or absence of impurities, defects, and their own softness.
1.2 twisted head;
After cutting the yarn, the hammer is defective or not on the adjacent warp yarn. This is a problem with machines that are caused by the failure of certain parts due to machine wear.
1.3 side and twisted head;
The warp beam is not flush or the warp beam is not aligned. If the warp beam is bad, the strength of the side yarn is too small to cause the warp yarn to be displaced.
1.4 reverse head
Caused by a broken head on the warp beam.
2 warp point prevention method
2.1 Warp quality control
The quality of the warp yarn directly affects the length of the warp, so the quality of the warp yarn must be good. The selection of warp yarns should be kept at a low point, and the higher line density is selected. We choose 84tex (7S), 72tex (8S), 60tex (10S), 50tex (12S), and the quality is based on the industry standard FZ/T32001-1998. Yarn requirements are first class or superior.
2.2 warping machine selection
The warping adopts SGA211 high-speed warping machine, which adopts adjustable double-column disc tensioner, the tension binning is adjustable, the tension is uniform, and the fluctuation is small. The small V-shaped flip type creel is used for collective change, and the efficiency is high. In order to reduce the warp elastic loss, the warp single yarn tension is smaller than the pure cotton denim fabric, that is, the small tension process is adopted, because the surface of the hemp/cotton yarn has many hairiness and long length, and the warping is based on the principle of less the number of warp beams to prevent occurrence. Yarn entanglement, breakage and kinking in the process of dyeing, and twisting and other diseases.
2.3 combination structure
Fabrics should not be used with complex structures to avoid the difficulty of weaving.
2.4 warp tension adjustment
By effectively controlling the tension of the warp yarns, the warp yarn breakage can be minimized. This is achieved by using elastic loads on the loom, rotating the back beam and increasing the length of the free warp yarns;
2.5 warp arrangement control
In order to arrange uniform and well-wound warp beams, a low vehicle speed is adopted, and the tension ring is arranged in front, middle and rear sections. The process parameters are: vehicle speed 300m/mim; pressure of yarn 0.30MPa; warping tension, front section 18cN, middle section 16cN, rear section 14cN.
3 reasons for the formation of latitudinal defects
3.1 The latitude and longitude latitude and longitude latitude and longitude are formed by the weft twisted woven fabric or the woven fabric on the cloth surface, which can be divided into the shed hem point, the large latitude point and the small latitude point. There are many reasons for the formation of weft defects, including fiber and yarn quality, mechanical state and process settings. From the perspective of raw materials, the weft yarn is too large, the free end is seriously untwisted, the surface hairiness is less, and the traction force of the compressed air on the weft yarn is small, resulting in unstable flight of the weft yarn, etc., which is easy to cause weft shrinkage; the weft regain rate is too low. Or the chemical fiber content is too high and easy to ring, which will also cause weft shrinkage; when weaving with low elastic or spandex core yarn, these yarns are too loose and have high resilience, also in the zonal flight The weft shrinkage occurs due to the large deformation and elongation; the neps content of the yarn is too high, and the weft yarn is scraped during the beating process, and the weft is easily caused. The mechanical state is due to the unstable air output of the air compressor, the poor quality of the compressed air, and the instability of the air pressure caused by some pneumatic components. In terms of process setting, the weft insertion is too fast or the weft yarn is obstructed by the hemming and warp yarns, the auxiliary nozzle synchronization time is not coordinated, the machine speed is too high, the sizing quality is not good, and the like, the weft shrinkage point is also caused.
3.2 bad side points
There are two main forms of bad edge defects. One is that the stranded yarn is not twisted to make the edge of the warp yarn fall off, which is related to the rotation speed of the loom and the fabric forming device; the other is the weft yarn. Extra long or too short causes the weft of the side to be wefted, or the weft is short and not broken and the bad side, and mainly occurs at the side of the weft shed. This is because the weft exit side does not clamp the outer end of the weft with the yarn clamp as the main nozzle side, but the weft yarn is controlled by a set of plain yarns plus a set of plain weave. Of course, there are many reasons for the bad edge defects, such as the outer waste side yarns being smashed or the tension between the warp yarns being different, and the ground warp pilling may cause bad edges.
3.3 double weft point
There are two complete or incomplete weft yarns combined to destroy the ups and downs of the plain weave fabric, which is called double weft point, and its formation causes two types of broken weft and bad weft. Most of the double weft defects are caused by weft breaking, and most of the weft yarn ends after wefting are close to the side of the shed. The closer to the edge of the cloth, the more concentrated it is within 40cm of the edge of the cloth. A small part is on the main nozzle side. The reason is also multi-faceted. For example, if the quality of the original yarn cannot meet the requirements of the jet weft insertion, the twist is low, the single strength is low or the detail is large, and the breaking strength is lower than the traction force of the jet stream to the weft yarn during the weft insertion process, and the breakage may occur. The weft causes a weft or double weft. During the weft insertion process, the traction force of the airflow on the weft yarn is too large, and the single strength of the original yarn may cause the weft to form a double weft point; after the weft insertion occurs, the weft detector misjudges, or only one weft detector, the weft yarn If it is blown off, it may not find the weft and the double weft appears. In addition, the operator does not operate properly, and the bad latitude to be taken out is not taken out, which is also a cause of double weft defects. Poor winding of the weaving shaft, loosening and sinking, or low warp sizing rate, poor coating effect and many hairiness, etc., can cause the warp opening to be unclear, so that the weft yarn is blocked, which may lead to poor latitude and double weft.ç–µ ;; scissors are not installed in the best position or the blade is not sharp, cut continuous weft, it is also easy to form double weft points. 3.4 driving traces
Driving marks are common fabric defects in the production process of air jet looms, including driving weft, dense roads and shrinking waves. The main reason for this is the creep and slack characteristics of fabrics and warp yarns. When the loom is parked, both the fabric and the warp are subjected to a large tension on the machine. At this time, the reed is separated from the weaving, and the weaving will deviate from the corresponding position during normal weaving. The length of time varies. When driving, if the position of the weaving mouth is not handled properly, driving marks will be generated.
4 latitudinal control measures
4.1 Loom process adjustment
Weft flight conditions should be given priority. If the opening amount is increased, the height of the heald frame should be as close as possible to ensure that the upper warp yarn is tangent to the upper edge of the profiled weir. The side yarn should be worn inside the l and 2 heald frames, and the shed should be matched with the ground shed (ie the upper and lower warp yarns are in the same plane when the shed is full), because the weft enters and flies out, It is the use of a side shed. This measure can prevent weft, bad edges and double weft points.
4.2 Raw yarn quality control
The quality of the weft yarn, especially its strip and drafting ratio, must be strictly checked to avoid the occurrence of weft shrinkage. When the weaving width is 1650 mm and the drafting ratio is 3.5 times or less, the drawing force is easily satisfied, and when it is more than 3.5 times, the weft is likely to be deviated.
4.3 Weft state adjustment
Under the premise of ensuring the proper storage of the weft feeder, the weft unwinding tension should be as small as possible, and observe whether the length of the waste edge on the fabric is the same. Use weft brakes to reduce the peak tension of the weft. The distance between the two main nozzles is such that the weft arrival time is the earliest. This can prevent double weft and weft shrinkage.
4.4 Selection of stretching nozzle
Use a straight-pull nozzle to add a stop in front of the profiled cymbal, or add a thin iron clip on the stopper to increase the stretching effect. Vertical jet or suction type stretching nozzles can also be used, and the comparative suction effect is better, the variety adaptability is strong, and the bad edge defects are small. Minimize the static airflow and reduce damage to the weft. Use a gripper to prevent the main nozzle weft from retracting the bad edges.
4.5 Auxiliary nozzle setting
The arrangement of the auxiliary nozzles should use the same spacing as much as possible to prevent turbulence. The injection interval and pressure of the nozzle should be appropriate. Observe the flight curve and try to be a straight line, and the arrival time should be stable. This measure can prevent double weft, bad edge and weft point.
4.6 Adjusting the distance of the weft detector
The distance of the weft detector should be appropriate. The first weft detector should be separated from the side yarn by a certain distance (generally l0mm) to prevent damage and mishandling of the warp yarn as a weft yarn. In the case where there is no hundred feet, the sensitivity or level value of the second weft detector is lowered, and the distance between the two weft detectors can be appropriately lengthened to 160 mm to reduce the false detection. This measure is beneficial to the prevention of driving marks.
4.7 Prevention of driving marks
The prevention and control of driving marks is a complicated process, which can adjust the height, depth, opening time, opening size and height of the heald frame of the back beam; it can also use the control of the weaving mouth, the warp beam reverse or forward rotation, and the air beating. Due to the uncertainty of the position of the heald frame during downtime and shutdown, the adjustment process becomes difficult and the effect is not good. In practice, the use of the inverter's stepless declination first wefting force plus a latitude start method can solve the problem of driving marks. In addition, improve the operation level of the driver, keep the equipment clean and working condition, and make the equipment efficiency above 96%, which can meet the quality requirements well.
5 Conclusion
Denim has been popular since its inception and has continued to innovate. In the current situation of returning to nature, hemp fiber is used in denim weaving due to its natural characteristics, anti-mildew and antibacterial, absorption of ultraviolet light, fast moisture absorption, etc., and has low cost and large profit margin. There are also many problems with marijuana stretch denim. We can only improve the quality and expand the market through continuous innovation.
references
[1] Mei Ziqiang. Denim and denim clothing practical manual (M). Beijing: China Textile Press, 2000.
[2] Zheng Xiuzhi, Liu Peimin. Woven fabric structure and design (M). Beijing: Textile Industry Press, 1992.
[3] Gao Weidong, Rong Ruiping, Xu Shanqing. Now weaving process and equipment (M). Beijing: China Textile Press, 2000.
[4] Yu Chongwen, Zhang Yuanming, Jiang Fanchang. Ramie yarn production process and quality control (M). Shanghai: China Textile University Press, 1998.
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