Dyeing on an overflow machine, heating and cooling will directly affect the shrinkage of the fiber, resulting in a fold. For thermoplastic fibers such as nylon, once the fold is formed, it will be irreversible. Therefore, when dyeing, special attention should be paid to the need to slowly raise/lower the temperature within 10°C before and after the fiber glass transition temperature, generally at a rate of 1°C/min.
The heating and cooling speed of the dyeing process not only affects the levelness of dyeing, but also restricts the feel of the dyed fabric and the degree of crease on the fabric surface. If the thermal processing temperature is not properly controlled, the surface temperature of the fabric will be heated or cooled, and the fabric surface will be creased due to the thermal shrinkage of the fibers. In the production practice, there have been creases on the cloth surface, sometimes even serious creases, after the operator violated the process regulations and changed the heating and cooling from computer automatic control to manual. Therefore, the dyeing process is strictly in accordance with the computer program, and the slow rise and fall of temperature is not only conducive to level dyeing, but also helps to reduce the crease of the cloth surface. Therefore, it is necessary to strengthen the education of employee craft discipline to control the crease in the dyeing process.