Mechanical pre-shrinking is one of the most effective ways to solve the radial shrinkage of fabrics. According to the plasticity of the fabric under certain temperature and humidity conditions and the high elasticity of natural rubber, through mechanical pre-shrinking finishing, the weft density and diameter of the fabric can be improved. The weaving shrinkage is pre-increased to a certain extent, that is, the fabric is in a relaxed state to reduce the shrinkage rate of the finished product to ensure the dimensional stability of the fabric after it is made into clothing. This is the purpose of pre-shrinking the rubber blanket.

First, the reasons for the shrinkage and deformation of the fabric:
 Fibers with "dry set" deformation cause shrinkage due to internal stress relaxation, but this is not the main reason for fabric shrinkage;
The anisotropic swelling increases the diameter of the yarn, and the travel of the fibers in the yarn around the yarn axis increases, causing the yarn to shrink. This change is 2% to 3.5%, which is still not the main reason for the shrinkage and deformation of the fabric;
The anisotropic swelling effect changes the shrinkage of the fabric before and after wetting, which is the main reason for the shrinkage of the fabric;
Weaving shrinkage: After the yarn is woven, its length is shortened, that is, weaving shrinkage.

Second, the principle of mechanical shrinkage of fabrics:
 When the rubber blanket passes between the guide roller and the pressure roller, it is thinned and elongated, and shrinks back to its original state after leaving, forcing the fabric to shrink synchronously to reduce the shrinkage rate of the fabric;
The technological process of mechanical shrinkage consists of a cloth feeding device, a wetting device, a three-roll blanket compression device and a blanket dryer.

The basic principle of pre-shrinking of rubber blankets: the wetting and expansion of the fabric, the extrusion and deformation of the rubber blanket drive the shrinkage of the fabric, and the drying and shaping of the fabric ensures the shrinkage effect of the fabric.
Wetting and swelling of fabrics: fabrics expand fibers by wetting. Fiber expansion is mainly manifested in the increase of cross-section, while the longitudinal elongation of fibers is very small. The result of fiber expansion must be search deformation in its length direction. In addition, the moisture entering the fiber gap can also have a lubricating effect on the fiber, which is conducive to the further shrinkage of the fiber.
The extrusion deformation of the rubber blanket drives the shrinkage of the fabric: the rubber blanket is deformed by stretching and extrusion during the operation process, and the fabric shrinks with the rubber blanket through contacting the area where the surface of the rubber blanket shrinks, so as to achieve the purpose of pre-shrinking.
Fabric drying and setting: Under normal process conditions, when the fabric leaves the rubber blanket, its shrinkage rate has reached the pre-shrinkage required by the process, but this shrinkage of the fabric is very unstable, so it needs to pass a certain temperature and time. The fabric is treated to maintain the qualitative nature of its shrinkage. The functions of reducing the moisture content of the fabric are: first, to ensure that the fabric meets the processing requirements of the next process; second, to reduce the slippage between fibers to ensure the stability of its shrinkage; third, to promote the shrinkage of the fibers and eliminate the friction between the fibers. Deformation stress, keep shrinkage stable.

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