Weft bias is caused by the instability of the fabric production process during high temperature setting, for example Cotton cloth can be torn apart by hand, but the natural traces of tearing are not horizontal, but diagonal. This means that the weft bias is more obvious. Generally, fabrics with a slight weft skew are not a big problem and do not affect normal use. For only plaid fabrics, there should be no skew in the warp or weft strips. Otherwise, the loss will be great during production and cutting, and the fabric may even be unable to be cut.
Classification of product weft skew defects
1. Full-width straight weft skew
The characteristic of this type of weft bias is that the weft yarn is basically a straight line, with a slope of about 30° from the horizontal standard. This kind of weft skew is caused by the fabric being dragged forward by tension during the dyeing and finishing process. When the force on the intersection of warp and weft is large, the weft yarn cannot advance horizontally and has a difference in speed or sluggish advancement, resulting in the skew of the weft yarn. There are many reasons why this happens.
The fabrics from the weaving factory are sometimes tight on one side or loose on both sides, which causes wrapping during rope processing, making it difficult to open the width, and it is easy to produce straight weft skew.
Sometimes the blanks from the weaving factory are not cut straight, and when the printing and dyeing factory sews the seams, they are not torn completely, causing the seams to be skewed, and they are not corrected during post-processing. , the degree of distortion is even worse.
When doing open-width processing, the roller surface is uneven; the roller installation is not level; the roller diameters are different and not parallel to each other; the pressure at both ends of the roller is different; The centerline of the machine is not straight, causing the fabric to run in an uneven direction; the installation quality of the machine is poor, and some of the feet are loose; some parts are tilted, and the fabric is stressed unevenly on both sides in the warp direction; the lengths of the cloth mops on both sides of the mercerizing machine are different, resulting in The weft is skewed; the angle between the mopping roller of the cloth feeding edge suction device and the cloth is too small, and the tension on both sides is uneven; bubbles and “water pockets” are locally generated during the open-width rolling process; the guide roller bearings are worn or the probe is worn; the pressure roller on the cloth inspection machine Different pressures on both sides and unequal knife edges of the fabric coding machine will cause weft skew.
The above situation is an abnormal condition of the equipment. If the operation is improper or does not follow the standard system, it will also cause weft skew.
For example: sewing during processing, just for convenience, and tying knots casually; improper operation when entering the open-width roller, causing the fabric to wrinkle or curl; the cloth on the drop roller is uneven; the cloth is fed in Or when unwinding, it tilts east and west or left and right.
Secondly, during rope processing, the tension is uneven, the rollers of the rope washing machine are uneven, and the fabric is unevenly stressed, sometimes loose and sometimes tight, which can easily cause weft skew; the threading heads in the rope machine overlap and the threading The force in the warp direction of the cloth is uneven, too many threads are worn, the cloth body is too tight, and the weft skew is evenly produced. Sometimes the wrapping angle of the cloth in the rope washing machine is too large, the tension is high, and the weft skew is also large; local “”” occurs during rope processing. “Water pockets” cause irregular weft inclination, and the air bubbles “water pockets” produced during desizing are more obvious. When the flat width of the fabric enters the rope shape, the porcelain ring is not centered, and the flat width turns into a rope shape or the rope shape turns into a flat width. Sometimes If the distance is too short, the fabric will be easily wrapped and skewed, and the large J-shaped drop box will have a large arc at the bottom, making it difficult for the fabric to slide and easily compressed, resulting in high tension. Too much will cause difficulty in opening the width and produce weft skew.
2. Full-width arc-shaped latitude
This type of latitude The characteristic is that the weft yarn is arc-shaped or concave and convex. It mainly occurs on the expanding roller of the bending roller. Because there are sometimes small wrinkle strips before the flat width enters the bending roller or the drying cylinder, a bending roller is installed to expand the width and eliminate wrinkles.
While applying an appropriate amount of tension to expand the fabric and eliminate wrinkles, the weft yarn is also stretched into a convex bow shape in the middle. The degree of convex arc is related to factors such as the density and thickness of the fabric, the curvature of the bending roller, and the tension on the fabric on the bending roller.
In addition, on the mercerizing machine and tenter machine, the fabric is clamped by cloth clips and moves forward. After being soaked by hot air, hot light alkali or washed with alkali, the fabric relaxes, causing hysteresis in the middle part of the fabric. , after coming out of the cloth clip, it shows a concave arc-shaped weft. This situation is more likely to occur on thin fabrics.
3. Suspended angle weft skew
The characteristic of this type of weft skew is that one side of the fabric has normal weft and the other side is skewed. Reasons: One corner of the fabric is stressed; or one corner of the guide roller or drying cylinder is fouled; or the cloth on the exit roller moves towards one side, causing it to be too thick; or when entering multiple rollers, one corner becomes too thick. The edges are severely curled, which is mainly caused by the large pressure difference between the left and right sides of the roller. This kind of weft skew is difficult to correct, so weft adjustment can only be carried out alternately with stenter or special pressure rollers.
4. Local weft skew fixed on a certain part of the textile
The characteristic of this type of weft skew is local Regularly shaped latitudes. Cause: Mainly because there is dirt accumulated on the cloth guide roller, such as yarn strips wrapped around it; or there are wrinkles before the fabric enters the roller, causing inconsistent tension. Because the dirt or wrinkles on the guide roller are fixed, the location and shape of the fabric where the weft is skewed are also relatively fixed.
5. Intricate weft bias without regular shape
The fabric is made up of unit components or machines on the open-width machine. The primary latitudinal tilt caused by the platform is basically regular or regular in shape, and its position is fixed. If the weft is not adjusted in time or is improperly adjusted, and some abnormal components of the machine in the next process are affected, the accumulation of weft skew will occur, forming intricate and different shapes of weft skew. However, this type of latitudinal tilt is rare.
Measures to prevent and control latitude skew
The occurrence of latitude skew is multi-faceted, and measures to prevent latitude skew should also be taken from multiple aspects.
1. In terms of equipment
The rollers, guide rollers and drying cylinders on the open-width equipment must be in good condition, that is, the rollers The cylinder installation should be flat, the parallelism between the rollers should be flat, and the left and right sides of the roller pressure should be flat. The centerline of the installation equipment must be straight and the bottom fasteners must be firm. The pins, sleeves and chains of mercerizing machines, shaping machines, tenter machines and other machines must be checked and replaced regularly to ensure that the cloth clips or needle plates on both sides rotate at the same speed. The upper and lower guide rollers that adjust the speed between each unit of the open-width machine should be kept level.
The rope-shaped cloth guide porcelain ring should be adjusted so that the cloth bundle is centered. To reduce the tension of the single machine of the rope machine, use a mobile distribution gear position to make the rear end of the cloth threading a flat end, etc., and control the number of threading threads. To reduce the tension in the synchronous rotation of the rope-like cloth washing machine, the operating line must be straight. Single-head rope-like equipment can be loosely synchronously driven by light guides. In order to prevent the cloth from being pressed when it comes out of the large J-shaped box, the concave weft skew can be expanded by several bending rollers; when the mercerizing machine produces a concave weft skew, a pair of arcs can be installed after the mercerizing machine comes out of the cloth clip. Shaped weft straightening device, a smooth small roller with an active overspeed of 10% is installed under the cloth, and a square rubber bending roller is pressed on the cloth. The center of the bow-shaped protrusion is pressed at the center of the cloth, depending on the degree of concave weft skew on the cloth surface. Adjust the pressure of the upper arc-shaped rubber bending roller so that the concave weft yarn in the middle part can be adjusted evenly. Generally, the arc can be adjusted by 5 to 6 cm. When the convex weft runs obliquely on the bending roller, turn the convex shape over in the opposite direction to straighten the weft, but the degree of weft straightening is limited, and at the same time, wrinkles must be prevented.
The air nozzle of the hot air tenter is changed from a vertical form to an oblique air nozzle. When the wind speed is 12-15m/s, the angle between the air nozzle and the cloth surface is 15°-20°, so that the wind moves along the direction of the cloth. Blowing air can improve the arc weft caused by the hot air tenter itself.
2. In terms of operation
The seam should be straight, the needle density should be moderate, and it is required to tear the head as much as possible For back seams, the seam head weft inclination is less than 0.5%. Rope-like fabrics cannot be knotted and run, and the ends must be sewn with a sewing machine. When the rope processing ends at the bottom of the fabric pile pool, the fabric must be rolled dry without excessive water. It is necessary to eliminate “water pockets” during rope processing, especially during desizing.
The thickness of the roller wrapping cloth should be even. During processing, it is necessary to avoid fibers and yarns wrapping around the roller and causing weft skew. During open-width processing, attention should be paid to preventing edge curling and wrinkles. The force on both sides of the electric edge suction device should be even, and the cloth feeding angle should be larger. The machine should be flat and upright when calibrating cloth.
3. Strengthen the quality inspection system
Technicians of each vehicle must be responsible and responsible for each machine The quality of processed products is checked by ourselves, and if weft deviation is found, the weft is adjusted in a timely manner.
4. Strengthen the management of weft straightening devices
The photoelectric weft straightening device must be well maintained and inspected regularly. Light source, mechanical execution, regular replacement of electronic circuit boards, extending the service life of photoelectric probes, etc. </p
