What does cold stretching refer to during the preparation process of spandex yarn?

In the preparation process of spandex yarn, cold drawing refers to the first stretching of the fiber after spinning is completed and before the fiber is cooled. This step is also called the initial stretch. Specifically, cold drawing occurs after the polymer polyurethane is converted into fiber shape through a spinning machine.

During cold drawing, the fiber is stretched to increase its length and improve its strength. This operation is usually performed in the early stages of fiber formation, when the polyurethane polymer is still in a liquid state and is being expelled from the spinning hole. By stretching the fiber at this early stage, you can increase the orderliness of the molecular chains and improve the strength and stretchability of the fiber.

The name cold drawing comes from the fact that this step occurs before the polyurethane polymer fibers cool down. After cold drawing, the fibers enter a subsequent styling step, also known as hot drawing. During the styling process, the fibers are exposed to higher temperatures and stretched again, causing the molecular chains to rearrange themselves at high temperatures, setting the fiber's final shape.

Cold drawing and setting are key steps in the spandex yarn preparation process. Together, these steps ensure that the spandex yarn has the required elasticity, stretchability and durability. The entire process requires strict process control to ensure that the fibers are properly processed at different stages to meet the performance requirements of the final product.