1 Purpose of pre-shrinking finishing
The purpose of fabric pre-shrinking finishing is to pre-shrink the fabric to a certain amount in the warp and weft directions, thereby reducing the shrinkage of the final product and meeting the needs of the garment. Processing quality requirements.
During the dyeing and finishing process, the fabric is subjected to tension in the warp direction, and the buckling wave height in the warp direction is reduced, resulting in elongation. When hydrophilic fiber fabrics are soaked in water, the fibers swell and the diameters of the warp and weft yarns increase, thereby increasing the buckling wave height of the warp yarns and shortening the length of the fabric, causing shrinkage. The percentage of the length shortened to the original length is called shrinkage.
The finishing process of using physical methods to reduce the shrinkage of fabrics after being immersed in water to reduce shrinkage is also called mechanical pre-shrinking finishing. Mechanical preshrinking is to wet the fabric by spraying steam or spray first, and then apply mechanical extrusion in the warp direction to increase the buckling wave height, and then dry it through loose drying. The shrinkage rate of pre-shrunk cotton can be reduced to less than 1%, and due to the mutual extrusion and rubbing between fibers and yarns, the softness of the fabric’s hand will also be improved.
Wool fabrics can be relaxed and pre-shrunk. After the fabric is padded with warm water or sprayed with steam, it is slowly dried in a relaxed state to make the fabric Contraction occurs in both the warp and weft directions.
2 Mechanical pre-shrinking treatment
Mechanical pre-shrinking treatment can be used A compressed rubber blanket carries the fabric for preshrinking.
Usually, the fabric is properly moistened (10% to 15%) and heated before the machine, so that the fiber becomes softer and has greater plasticity. It is also used in Before wetting (after singeing finishing), it should be penetrated with light pulp or foam sizing and dried in a drying cylinder to strengthen pre-shrinkage control and improve pre-shrinkage effect.
When the fabric is pre-shrunk by the rubber blanket, it is first pre-dried to remove part of the moisture. After leaving the machine, it is dried and ironed by a tension-free blanket dryer to eliminate compression shrinkage. Wrinkles caused by excessive shrinkage for a plumper feel and soft shine.
3 Operation points
During the processing, it must be on the fabric Make shrinkage monitoring marks, check and verify fabric pre-shrinkage, and make timely adjustments if problems are found to ensure stable shrinkage.
During the operation of preshrinking equipment, personnel operation management and equipment management must be strengthened to prevent the occurrence of defects. At the same time, it is necessary to master the solutions to defects to reduce the defect rate. .
4 Problems and solutions
Prone to pre-shrunk finishing Problems: fish scale spots, warp wrinkles, wrinkles, weft skew, wet fabric drop, insufficient shrinkage, narrow door width, etc.
1. Fish scale spots
Due to the aging of the rubber blanket and the fabric Caused by uneven pre-shrinkage, the defective and aged rubber or felt must be ground or replaced.
2. Warp wrinkles
Due to the fabric before shrinking It is caused by excessive warp tension when wrinkles have been applied or when the fabric is fed into the shrinking machine. In the pre-processing process, attention should be paid to preventing the occurrence of warp wrinkles. That is, during pre-shrinking, the stretch cloth frame can be relaxed to reduce the warp tension to solve the problem of warp wrinkles.
3. Wrinkling
The cloth feeding tension is too small and the cloth The surface is too loose, the pressure on the left and right sides of the cloth roller is unequal, the edges of the gray fabric are too loose or the edges on both sides are unevenly tight, etc., which can cause wrinkles. The adjustable stretch frame can increase the cloth feeding tension, and the cloth feeding roller can be adjusted to maintain uniform pressure on both sides.
4. Weft skew
The reason is incorrect position of cloth feeding , The cloth guide roller is uneven, and the pressure on both sides of the cloth feeding roller is uneven. During processing, the cloth feeding position should be adjusted to ensure that the cloth guide roller is straight, and the pressure should be adjusted to make the pressure at both ends of the cloth feeding roller uniform.
5. The cloth is wet
Due to the fabric being processed during Caused by excessive moisture. Therefore, during the pre-shrinking process, the spray volume and operating speed must be controlled, and the vehicle speed can be reduced so that the drop cloth can be fully dried.
6. Insufficient shrinkage
The pre-shrinking effect is not good. Poor dimensional stability. This is caused by reasons such as the position of the pressure roller being too high, the temperature of the pressure roller being too low, the pressure of the cloth feeding roller being insufficient, and the tension of the cloth entering and exiting being too high. The position of the pressure roller can be appropriately lowered, the spray moisture supply can be controlled, the steam pressure of the pressure roller can be increased, the pressure of the cloth feeding roller can be increased, and the cloth tension in and out can be reduced.
7. Narrow door width
Due to pre-processing, The door width before shrinking is insufficient, or the fabric feeding tension is too high during preshrinking, causing the door width of the fabric to become narrower after preshrinking. In the previous processing steps, the process must be strictly followed to ensure that the width of the incoming fabric meets the requirements; at the same time, during the pre-shrinking process, attention should be paid to appropriately reducing the fabric feeding tension. </p
