The fabric shrinks and deforms during the dyeing and finishing process
During the weaving and dyeing and finishing processes, the fabric usually undergoes strong mechanical tension in the warp direction, causing weft cleavage in the fabric. An unstable state of amplitude contraction and meridional elongation.
After the fabric is padded, the length will shrink to varying degrees, and subsequent shrinkage will continue to occur after washing again. If clothes are made from this kind of fabric, once washed, the clothes will be deformed due to shrinkage of the fabric, causing great losses to consumers.
The best solution is to reduce mechanical tension during processing and choose tension-free loose mechanical processing. However, in a series of processes from spinning, weaving to printing and dyeing, , it is also unrealistic to fully meet this requirement.
Improving fabric shrinkage measures
Currently Measures taken: In the final process of dyeing and finishing, try to give the warp yarns of the fabric a chance to retract, so as to restore the balanced bending state of the yarns and achieve the purpose of reducing shrinkage in the future.
So it is a task of great economic significance to make the fabric stable in shape and not deformed through mechanical action. This finishing method is called mechanical pre-shrinking finishing, and the equipment it uses is a pre-shrinking machine (or anti-shrinking machine).
The main reasons for fabric shrinkage
1. The main reason is that the warp and weft yarns are subject to different tensions during the processing process, resulting in differences in the bending degrees of the warp and weft yarns. After being soaked and dried in a free state, the curved shape of the warp and weft yarns will automatically return to the original shape. The equilibrium state, the so-called weaving shrinkage adjustment effect, results in the shrinkage phenomenon.
2. The anisotropic expansion of the fiber when it is soaked, that is, the length and diameter of the fiber both increase, but the increase in diameter is greater than the increase in length. many. For example, the diameter of cotton fiber increases by 14% after being soaked, but the length only increases by 1.1% to 1.2%. Therefore, after the fabric is soaked, the fibers in the fabric become thicker due to expansion, but the length does not increase much, and the yarn must follow the The fibers thicken and increase in diameter.
3. The warp and weft yarns are wrapped around each other in the fabric. If the diameter of the weft yarns increases, the length of the warp yarns must increase to maintain the In the state of wrapping the weft yarn, the length of the warp yarn cannot grow without increasing external force, so the distance between the weft yarns is bound to be tightened, that is, the density of the weft yarns increases, resulting in warp shrinkage of the fabric. The same phenomenon occurs with weft yarns.
4. When the fabric dries naturally, the fibers lose their expanded form and the yarn returns to its original thickness. However, due to the frictional resistance between the yarns, the yarn is limited of free movement, the fabric remains in its contracted shape. Therefore, after the fabric is soaked and allowed to dry naturally, the area of the fabric often shrinks, the thickness increases, and the surface becomes uneven. Although the anisotropic expansion of fibers is one of the causes of fabric shrinkage, it accounts for a small percentage. Therefore, the main cause of shrinkage of cellulose fiber fabrics is the weaving shrinkage adjustment function.
5. The shrinkage rate of the fabric has a great relationship with the tissue structure of the fabric and the characteristics of the fibers. For example, fabrics such as khaki and poplin whose warp density is much higher than the weft density have much smaller shrinkage in the weft direction than in the warp direction. Although viscose and cotton are both cellulose fibers, due to the loose structure of viscose fiber and its large wet expansion rate, it is easy to be stretched, especially in the wet state. Therefore, the shrinkage rate of viscose fabric is greater than that of cotton fabric. Even using mechanical pre-shrinking and trimming methods cannot solve the shrinkage problem. Generally, chemical cross-linking method has to be used to change the characteristics of viscose fibers, thereby solving the shortcoming of excessive shrinkage of viscose fabrics.
Mechanism of mechanical shrinkage finishing
Fabric shrinkage finishing The purpose 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 quality requirements of garment processing.
Mechanical shrinking treatment uses a compressible rubber blanket to carry the fabric for shrinking. When the rubber blanket is curled under force, the outer arc elongates and the inner arc contracts. If it is bent in the opposite direction, the originally elongated side becomes contracted, and the contracted side elongates. During the pre-shrinking process, the fabric with a certain humidity runs close to the rubber blanket, passing through the compression zone, from the outer arc of the rubber blanket to the inner arc, that is, from the stretching part to the shrinking part, because the fabric is clamped by the rubber blanket and the pressure roller. It is held without being allowed to slide. As the rubber blanket recovers and shrinks, it is compressed, resulting in a certain shrinkage.��. The fabric feeding tension is too small, the fabric 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., etc., all 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.
Latitude and oblique. The causes include incorrect cloth feeding position, uneven cloth guide roller, and uneven pressure on both sides of the cloth feeding roller. 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.
The fallen cloth is wet. Caused by excessive moisture in the fabric during processing. 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.
Insufficient shrinkage. The pre-shrinking effect is not good and the dimensional stability is poor. 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.
Narrow door width. Due to the pre-shrinking process, the door width before preshrinking is insufficient, or the fabric feeding tension is too high during preshrinking, resulting in the door width becoming narrower after the fabric is preshrunk. 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
