Causes and improvements of downtime in the weaving process of yarn-dyed linen fabrics

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Causes and improvements of downtime in the weaving process of yarn-dyed linen fabrics

In recent years, with the improvement of living standards, people have put forward higher requirements for textiles. Yarn-dyed linen products have good moisture absorption, moisture permeability and health care properties, are mildew-proof and moth-proof[1], are comfortable, dry, breathable and light in texture. However, flax yarn has poor elasticity, high hairiness and uneven dryness, making weaving difficult. Domestic linen products are mostly plain and single in color, making it difficult to develop brightly colored products [2-6]. At present, domestic research is conducted on issues such as edge breakage, weft shrinkage, drawing, and weaving defects during the flax weaving process, as well as improvements in flax properties, flax blending processes, and reducing damage to linen fabrics caused by dyeing. There has been progress in the blending, modification and development of high-end products of linen fabrics [9-10], but the research on the weaving process of yarn-dyed linen products is still blank.

This article analyzes the downtime problem of yarn-dyed flax weaving process from the perspectives of flax fiber characteristics, changes in yarn performance after dyeing, machine process, etc., and proposes solutions such as environmental improvement, loom modification, and machine process adjustment to reduce downtime. times to improve weaving efficiency.

1Analysis of causes of downtime

1.1 Effect of yarn properties on weaving

1.1.1 Effect of undyed flax yarn properties on weaving

Flax fiber has high crystallinity and orientation, few amorphous areas, thick fibers, large bending stiffness of a single fiber, lack of natural curl in the fibers, and difficulty in cohesion between fibers [11]. During weaving, flax yarn has many shortcomings such as long and hairy hair, uneven evenness, and poor wear resistance, and is prone to thread breakage and shutdown.

Both cotton and linen are plant fibers, and their chemical composition is mainly cellulose. They have similar properties, have excellent hygroscopicity, are comfortable and breathable, so the performance of linen yarn and cotton yarn are compared. The test environment is standard atmospheric conditions, with a temperature of 25°C and a relative humidity of 65%. The linen yarn and cotton yarn are not dyed or finished. .

When the thread density is almost the same, flax yarn has lower twist, more details, thick spots, and neps, and the yarn’s elongation at break is much lower than that of cotton yarn. Therefore, compared with cotton yarn, flax yarn has smaller elongation at break, poor tensile resistance and evenness, which is not conducive to weaving.

1.1.2 Effect of changes in properties of linen yarn after dyeing on weaving

Yarn-dyed linen fabric breaks through the single style of traditional plain linen fabric, but its weaving is more difficult. The main reason is that the performance indicators of the original linen yarn have changed after dyeing. Select raw flax yarn sample 1# and dyed white, green, blue, and red (sample 2#~5#) four kinds of colored flax yarns to conduct the test under standard atmospheric conditions (temperature 25°C, relative humidity 65%) Performance Testing.

After dyeing, the density of raw flax yarn decreased, especially the 3# green yarn; the twist increased slightly; the breaking elongation and breaking strength increased more, but the degree of improvement was different, among which yarn 4# and yarn The improvement of yarn #5 is small, followed by white yarn #2 and green yarn #3. The moisture regain rate rises and falls. The moisture regain rate of yarn #2~4# increases, and the moisture regain rate of yarn #5 decreases.

The evenness evenness test was conducted on 4 kinds of colored flax yarns and raw flax yarns. The test results are shown in Table 3. The test conditions are: standard atmospheric conditions, yarn test length 400m, test speed 100m/min, time 0.5min.

After the raw flax yarn is dyed, the number of details and slugs of each color linen yarn is reduced, especially for yarn 2#; while the neps change differently, yarns 2# and 3# are reduced, and yarn 4 #, 5# increased; evenness CV value decreased to varying degrees, 4# blue yarn basically did not change, 2

White yarn dropped significantly.

Observing and summarizing the data in Table 2 and Table 3, it is found that the lighter-colored white and green yarns have better performance, and their twist, elongation at break, and evenness are better than those of red and blue yarns. Flax fiber contains high levels of lignin and pectin. These non-cellulosic substances hinder the penetration of dyes into the fiber, making it difficult to react with cellulose [12-13]. It is speculated that lighter-colored dyes are hindered during dyeing. Smaller and less damaging to flax fibers.

All performance indicators of raw linen yarn have changed after dyeing. The performance indicators of yarns of different colors change in different degrees and directions. The selection of flax yarns of different colors during the weaving process has different effects on weaving, resulting in variable and complex weaving problems.

1.2 The influence of weft insertion mechanism and weaving process on weaving

1.2.1 The impact of weft insertion mechanism on weaving

The weft insertion of yarn is to correctly introduce the weft yarn with a certain length and a certain tension into the shed at a certain speed and within a specified time. Rapier looms are often used in the weaving of yarn-dyed linen fabrics. During weft insertion, since the diameter of the package is larger at the top and smaller at the bottom, the weft yarn has different tension during the unwinding process, which is not conducive to subsequent weaving. The weft feeder can eliminate weft tension, wind and store weft, avoid weft relaxation, and facilitate beat-up and weft cutting. The internal components of the weft feeder that regulate the yarn include brushes, blade tensioners and coaxial tensioners. The blade tensioner is inside and the coaxial tensioner is outside. In the actual use process, enterprises generally use blade tensioners and brushes in consideration of cost, and abandon coaxial tensioners.

The yarn passes through a blade-type tensioner made of two metal sheets in the weft feeder. The tensioner has a slight clamping force on the yarn, which eliminates some of the slack in the yarn after passing through the tensioner.

During the weft insertion process, the roving will push the tensioner apart. If there is a spun yarn later, the tensioner will not be able to clamp the spun yarn immediately due to inertia, resulting in a part of the spun yarn that cannot be eliminated, resulting in a weft yarn with uneven tension, which is not conducive to weaving.

1.2.2 The impact of weaving technology on weaving

Linen yarn has poor elasticity, uneven evenness, and is not resistant to friction. During the weaving process, the warp and weft yarns often break, resulting in machine shutdown. Therefore, the loom needs a shed with a suitable height and reduces the friction of the reed and healds on the warp [14].

The reed swing area is the area most likely to cause downtime. The reed drives the weft yarn into the weaving fell, and the repeated swing of the reed back and forth causes a lot of friction. When the warp and weft yarns are intertwined, due to the buckling of the yarns, the reed width of the loom is often larger than the cloth width of the weaving fell. While the steel reed pushes the newly introduced weft yarn into the fabric fell, it also makes the reed width coincide with the fabric width of the fabric fell. That is, under the action of the steel reed, the fabric width of the fabric fell expands and becomes consistent with the reed width. The reed exerts an expansion force on the warp yarns outside the cloth fell, and the friction between the reed and the edge yarns increases, easily causing yarn breakage.

Improper process preparation of the shed area can easily lead to machine shutdown. The warp stretches when opening, and relaxes when closing. The warp is rubbed at the heddle eye and reed teeth. The height of the shed, the depth of the shed, and the height of the back beam will all have a great impact on the stretching and deformation of the warp [15-17].

Excessive shed will increase the cohesion force of warp yarns to weft yarns, and premature shed closing time will cause excessive friction length of warp and weft yarns. During beating-up, the holding force and friction of the warp and weft yarns will increase, which can easily cause the weft yarns to break. Linen yarn has long hairiness, and yarn-dyed linen is often not sized when weaving, resulting in unclear openings and easy entanglement between yarns. The warp tension on the machine, the position of the drop frame, and the height of the back beam will all have a significant impact on the shedding clarity, the warp elongation at break, and the appearance of the fabric.

2 Solutions to downtime problems

2.1 Relative humidity control of weaving environment

According to weaving production experience, changes in relative humidity have a certain impact on the shutdown rate, which is mainly reflected in the hairiness and elongation at break of the yarn. In a high relative humidity environment, due to the effect of air moisture, the hairiness on the yarn surface is reduced, the shed is clear during weaving, and weaving defects or failures are reduced.

In order to explore the changes in elongation at break of flax yarn under different relative humidity, the yarn was placed in a constant temperature and humidity chamber for 24 hours before the test, and then placed in a climate box with adjustable relative humidity. The relative humidity was 55%, 65%, 75%, 85%, the placement time is 6h. The yarn was subjected to a constant-speed tensile test after humidity control and balance, and the test temperature was 25°C [18-19].

Colored linen yarns have higher elongation at break in environments with higher relative humidity. When the relative humidity is below 75%, the yarn elongation at break increases significantly; when the relative humidity exceeds 75%, the yarn elongation at break increases slightly. In order to ensure high weaving efficiency, the yarn-dyed linen fabric weaving environment should maintain high humidity for a long time. Considering issues such as cost efficiency, the optimal relative humidity in the yarn-dyed linen weaving workshop is about 75%.

2.2 Weaving adjustment

2.2.1 Improvement of weft insertion mechanism and selection of looms

The tensioner of the traditional weft feeder is composed of multiple straight plastic brushes, which are not wear-resistant and have poor yarn shielding properties, so they are not suitable for weaving yarn-dyed linen fabrics. As shown in Figure 4, the LAMELLA tensioner is composed of multiple S-shaped stainless steel sheets. It has strong wear resistance and high yarn shielding. The drawn yarn tension is uniform, which is conducive to weaving. However, the LAMELLA tensioner also has shortcomings such as the yarn is easy to cut when threading, adjustment and processing are difficult, and the machine is easy to break, so the LAMELLA tensioner was replaced with an S-FLEX tensioner. As shown in Figure 5, the S-FLEX tensioner is bowl-shaped and is fixed by 6 springs on the outside. Like the LAMELLA tensioner, the S-FLEX tensioner is not affected by uneven flax yarn thickness, but the effect is slightly worse than the LAMELLA tensioner. The advantage is that it is easy to adjust and process and is not easily damaged.

The distance between the weft feeding rapier head and the first track piece is preferably 110~115mm, and the end distance of the rapier head is preferably 60~70mm. The gaps between various gears should be small. Excessive stroke can easily damage the rapier head. The sword head and sword belt (including ribs) must be polished repeatedly with sandpaper, and there should be no bulges or steps at the intersection of the two. Properly adjusting the clamping force of the weft sword and reducing the tension of the weft sword on the weft yarn can reduce downtime caused by yarn clamping failure during the weaving process.

The R9000 rapier loom is used to weave yarn-dyed linen fabrics. In addition to the characteristics of high shuttleless loom speed, high degree of automation and high production efficiency, its active weft insertion method has strong variety adaptability and can adapt to the weft insertion of various types of yarns. Compared with other looms, the R9000 rapier loom is more suitable for multi-color weft insertion and can produce products with various styles and patterns of 12-color weft insertion. The positive rapier drive can handle yarns with difficult weft insertion. Weft insertion.

2.2.2 Adjustment of the machine process

According to the previous analysis, weaving problems mainly occur at the shed. Improper warp yarn tension, warp drop frame position, back beam height, and opening size will cause poor yarn weaving results, frequent machine downtime, and affect the efficiency of the loom.

In the actual production process of the factory, the weaving speed of yarn-dyed linen fabric is about 350r/min, and the loom efficiency is 60%. In this paper, machine tension, leveling time, rear beam height, and opening amount are used as test factors, which are recorded as ABCD respectively. Each factor is taken at 3 levels to conduct a 4-factor and 3-level orthogonal test.

The number of 100,000 weft stoppages in test 5# is the least, 36.7 times, so the optimal machine process combination is A2B2C2D3. The process parameters of the machine are: warp tension 23cN, leveling time 340°, back beam height 1, and opening amount 24°.

The above process configuration effectively reduces the downtime caused by yarn weaving, and the loom efficiency is increased to more than 70%.

3 Conclusion

Yarn-dyed linen fabric has excellent properties, but the elongation at break of colored linen is low, and there are differences in the performance of different colored linen yarns, resulting in frequent shutdowns during the weaving process. After increasing the relative humidity of the weaving environment to 75%, replacing the tensioner with an S-FLEX tensioner, adjusting the sword head clamping force, adjusting the warp tension to 23cN, the hedging time to 340°, the back beam height to 1, and the opening amount to 24°, the weaving efficiency has been significantly improved.