Finalization is the main process of finishing. Through the mechanical action of the setting machine and the antishrinking, softening and hardening effects of chemical reagents, knitted fabrics can achieve certain shrinkage, density and hand feel, and achieve the appearance effect of uniform door width, smooth lines and clear lines.
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Purpose of finalization
The purpose of heat setting mainly includes the following four aspects:
1. Eliminate the internal stress produced by the fiber during the stretching process, relax the macromolecules to a certain extent, and improve the shape stability (dimensional stability) of the fiber. The shape stability can be measured by the remaining shrinkage rate of the fiber in boiling water (boiling water shrinkage rate). The smaller the boiling water shrinkage, the less the size of the fiber is likely to change when it is subjected to damp heat treatment (such as dyeing or washing) during processing and taking;
2. Further improve the physical mechanical properties of the fiber, such as improving the crystallinity, elasticity, knot strength, abrasion resistance, etc. of the fiber, and fixing the curl (for short fibers) or twist (for filaments);
3. Improve the dyeing performance of the fiber;
4. Remove the moisture brought by the fiber during the stretching and oiling process, so that the fiber can meet the moisture content requirements of the finished product, and avoid the possibility of yellowing of the fiber due to the non drying of the oil agent and long-term storage.
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Three elements of tenter shaping
1. Temperature
Temperature is the most important factor affecting the quality of heat setting.
Because the degree to which the original wrinkles are eliminated, the improvement of the surface smoothness, the dimensional thermal stability and other wearing properties of the fabric after heat setting are closely related to the heat setting temperature.
2. Time
Setting time is another main process condition of heat setting. After the fabric enters the heating zone, the time required for heating and setting can be divided into the following parts:
Heating time: the time required to heat the fabric surface to the setting temperature after the fabric enters the heating area.
Heat penetration time: after the fabric surface reaches the setting temperature, the heat penetration time required to make the fibers in the inner and outer parts of the fabric have the same setting temperature.
Molecular adjustment time: the time required to adjust the molecules in the fiber according to the setting conditions after the fabric reaches the setting temperature.
Cooling time: the time required for the fabric to be cooled after leaving the drying room to fix the size of the fabric.
The setting time usually refers to the time required for the first three items, not including the fourth item. If the first item is regarded as a preheating effect, the setting time only refers to the time required for the second and third items, that is, the time required for thermal penetration and molecular adjustment.
The time required for heating and thermal penetration depends on the performance of the heat source, the weight per unit area of the fabric, the thermal conductivity of the fiber, and the moisture content of the fabric.
3. Tension
The tension of the fabric in the heat setting process has a certain impact on the setting quality, including the dimensional thermal stability, strength and elongation at break of the fabric.
The thermal stability of the warp dimension increases with the increase of the warp overfeed, while the thermal stability of the weft dimension decreases with the increase of the door width stretching.
The average single yarn strength of the fabric after setting is slightly higher than that of the fabric without setting, and the change in weft direction is more obvious than that in warp direction.
After setting, the breaking elongation of the fabric decreases in the weft direction with the increase of the elongation, and increases in the warp direction with the increase of the overfeed.