Factors affecting the quality of sanding and finishing
There are many factors affecting the quality of sanding and the relationship is complex. Such as the tissue specifications of the fabric, processing technology, the size of the abrasive grains on the grinding roller (sand mesh number), the rotation speed of the sanding roller, the gap between the fabric and the sanding roller, the wrapping angle, the on-machine tension of the fabric and the moisture content of the fabric, etc. All will affect the sanding effect. In addition, the mechanical properties of fabrics will also undergo corresponding changes after sanding, such as increased softness, decreased breaking strength and tearing strength, etc. The most prominent one is the contradiction between the sanding effect and the decrease in fabric strength.
1. Requirements for semi-finished products of sanded fabrics
The quality of pre-treatment directly affects the sanding effect and fabric feel, so desizing is required Clean and scouring thoroughly, the weight loss rate should be controlled at 1%-2% (consistent before and after); the cloth surface should be smooth to avoid wrinkles, needle-free clips, and cloth clip marks; the requirements for gray fabrics are higher, and the roving neps should be less; dyeing Uniform and consistent, no color difference between left, center, right, front and back, front and back.
It is best to roll the fabric into a large roll before sanding to ensure that the fabric is flat and the rolling tension should not be too high to avoid seam marks; if the fabric box falls, you need to use Drying and sanding machine to remove creases. Softening treatment is required before sanding, which can reduce the friction coefficient between fibers (reduce the cohesion between fibers) and facilitate the formation of fuzz on the fiber surface during sanding. Guangdong Innovation Fine Chemical Raising Softener SD-3175 can be used. High-temperature setting should be avoided before sanding, otherwise the fabric will become tight and hard, resulting in difficulty in raising. If there are wrinkles on the cloth surface, a drying and grinding machine or low-temperature setting can be used.
When processing dark varieties, due to the gradient of dye concentration between the surface layer and the inner layer of the fabric, once the flatness of the fabric surface is poor and there are many thick warps, thick wefts and neps, the fabric warp will After sanding, white spots will appear on the convex areas. Therefore, the process of grinding first and then dyeing can be used for dark-colored varieties, which is beneficial to the bright color of the suede surface, with small color difference between the front and back sides, making it easy to check the shade, and can prevent the piles of different colors from raising when they are then sanded after dyeing. Contaminate each other. For medium and light-colored varieties, the process of dyeing first and then grinding can be used, such as blended fabrics and fabrics with adhesion tendencies. The raising process should be carried out after dyeing, otherwise the fabric will easily cause difficulty due to sticking during the dyeing process. Eliminates wrinkles and is not conducive to leveling.
2. The impact of fabric weave specifications and requirements for sanding mesh count
Different fabric weave specifications have different sanding process conditions. During sanding, the weft yarn is grinded by the abrasive grains at 90°, while the warp yarn is only subjected to the balancing effect of the abrasive grains at 180°, so the damage to the breaking strength of the weft yarn is relatively greater than that of the warp yarn.
If the warp and weft yarn densities of the plain weave fabric are close, the probability of the warp and weft being ground during sanding is equal. Since the abrasive grains cause great wear on the weft yarns, it is advisable to use finer grained abrasive grains. At the same time, the tension of the fabric should be small, so that the contact with the sanding roller is lighter; if the warp density of the plain fabric is higher than the weft density, its grinding effect will be smaller, and the contact opportunities between the weft yarn and the abrasive grains will be less, and better grinding results will be obtained. To achieve the velvet effect, coarser abrasive grains should be used.
The disadvantage of plain weave fabric is that the interweaving points are easily exposed; the structure of satin fabric is relatively loose and prone to lint and snagging; the twill fabric is prone to produce a sense of yin and yang due to uneven warp and weft. The yarn twist and density will also affect the sanding effect. Fabrics with high twist and high density are difficult to sand; thin fabrics will cause strong damage and cause weft movement; medium-thick fabrics have many exposed points in the weft direction and have better sanding effects (even and dense fluff). Therefore, for fabrics with different tissue specifications and yarn count densities, sanding leather with different mesh numbers should be selected to ensure the sanding quality.
Table 1 shows the technical parameters of various brushed fabrics produced by a printing and dyeing factory for reference. Table 2 shows the parameters of single-sided plain weave pure polyester produced by a silk and satin dyeing factory
Table 1 The mesh number of sand leather selected for fabrics with different weave specifications
Table 2 The mesh number of abrasive leather selected for different fabric densities
Since the fabric relies on the sharp edges of abrasive grains to cut fibers to produce fluff, under the same conditions, different particle sizes The abrasive grains have a great influence on the sanding effect. The abrasive particles are coarse, the hair is long and fast, but the drop is strong; the particles are fine, the hair is short and dense, the hand feels good, and the drop is small. Therefore, light and thin fabrics should use high mesh sand leather; thick and thick fabrics should use low mesh sand leather.
3. The influence of balance between grinding roller speed and fabric running speed
4. The influence of fabric tension and the degree of contact between the fabric and the grinding roller
The fabric tension indicates the tightness of the fabric in contact with the grinding roller, and the degree of contact indicates the degree of contact between the fabric and the sanding roller. The size of the covering angle when the roller is in contact has a great influence on the sanding effect and strength of the fabric. If the contact area between the fabric and the grinding roller is large, the covering angle will be large, the tension will be large, and the sanding effect will be good, but the strength drop will be greater; otherwise, the effect will be poor and the strength drop will be small.
The total arc length (covering angle) of the pressure roller contact of the sanding roller is 150mm~170mm, 0~3 grids are unloaded, and 3~10 grids are the loaded working part. Each grid represents 25mm arc length. Therefore, it should be based onn=””>Reasons: The semi-finished product feels hard, the cloth surface has poor penetration effect, the tension is small, the vehicle speed is fast, the old sand leather has been used for too long, the DC motor speed is unstable and the cloth is damp.
Solution: notify the pre-processing repair or apply softener, tighten the chain shaft tension, slow down, increase the pressure, replace with new sandpaper and fully dry the cloth surface.
07 Grinding Willow
Causes: The seams of the sandpaper overlap, the sandpaper rotates in the same direction, threads are wrapped around the grinding roller, and the sandpaper joints are marked or damaged.
Solution: Re-tighten the sandpaper, change the direction of rotation of the sandpaper, adjust left and right, and clean the threads on the grinding roller.
08 Left, middle and right hair difference
Cause: the left and right cloth pressing rollers are unbalanced, the sandpaper has been used for a long time, and the sand grains in the edges have different degrees of wear .
Solution: Adjust the balance roller to make the left and right balance consistent, and replace with new sand leather to solve the problem of the gap between the two sides when changing from narrow to wide.
09 Poor strength
Cause: The fabric is thin, the sandpaper mesh is low, the strength is high, the pressure is high, and the vehicle speed is slow.
Solution: Replace high-grit sandpaper, relax tension, reduce pressure, and increase speed.
10 Uneven sanding
Causes: In addition to improper pre-treatment, the main reason is that the tension and pressure on the left and right sides of the cloth are inconsistent, and the fabric and abrasive belt The left and right gaps are of different sizes, the sand grains on the abrasive belt are uneven, and the moisture in the abrasive belt reduces the sharpness of the local abrasive grains.
Solution: Strengthen pre-treatment to achieve even cooking: adjust the left and right tension of the cloth and the pressure of the cloth pressing roller to make it uniform: use a precision tape measure to correct the gap between the fabric and the abrasive belt; sand The belt should be stored in a ventilated and dry place to avoid moisture.
11 sanding gear
Cause: the wrapping angle is too small; the tension of the cloth in and out is inappropriate.
Solution: Adjust the wrapping angle and the tension of the cloth in and out.
12 worn holes
Cause: There are raised yarn ends or yarn knots on the cloth surface, and the gap between the cloth inlet and the abrasive belt is too small , the cloth is wrinkled and curled when feeding.
Solution: Choose a fabric that is flat and has few yarn ends or knots. Adjust the gap between the cloth feed roller and the gauze belt. The fabric feed should be smooth and without curling edges.
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