During elastic band production, pre-shrinkage is a critical step in controlling shrinkage in finished products. Its core goal is to release internal fiber stress through physical or chemical means, ensuring dimensional stability during subsequent use. This process requires comprehensive control based on material properties, process parameters, and equipment conditions. Its implementation involves fiber pretreatment, weaving process optimization, heat setting, wet shrinkage technology, mechanical shrinkage, post-finishing enhancement, and quality inspection systems.
Fiber pre-treatment is a fundamental step in pre-shrinkage. Natural fibers such as cotton and linen require washing or steam treatment to eliminate initial stress, while synthetic fibers such as polyester and spandex require heat stretching or chemical relaxers to reduce molecular chain rigidity. Temperature and humidity must be strictly controlled during the pre-treatment phase to avoid excessive fiber damage or residual stress, providing a stable base material for subsequent weaving.
Optimizing the weaving process directly impacts the initial structural stability of elastic bands. Adjusting the warp and weft density and weave structure can reduce fiber buckling and stress concentration during weaving. For example, using a weave with longer floats and a higher number of weave cycles can increase fabric porosity, improving air permeability and dimensional stability. Furthermore, weaving tension is adjusted in sections, thickening the base to resist bending moments and thinning the top to conserve material, further balancing elasticity and shrinkage.
Heat setting is the core step in pre-shrinking. Using a drying room, drying drum, or infrared equipment, precisely controlled heating temperature and time rearrange and stabilize the fiber molecular chains. During dry heat pre-shrinking, uniform temperature distribution is crucial to avoid localized overheating that can cause fiber embrittlement. After heat setting, the fiber's elastic recovery and dimensional stability are significantly improved, effectively reducing shrinkage and deformation during subsequent use.
Wet shrinking techniques are suitable for specific fiber types. For materials such as beautiful silk and woven cotton and linen, soaking or spraying the fabric with water allows water molecules to fully penetrate the fiber, promoting moisture absorption and shrinkage. Worsted wool should be ironed at approximately 160°C, while woolen wool should be covered with a damp cloth and ironed at 180°C until slightly dry. Wet shrinking can eliminate internal stresses in the fiber caused by drying, but the moisture content and drying speed must be strictly controlled to prevent excessive shrinkage and wrinkling.
Mechanical shrinking achieves dimensional stability through external forces. A shrinking machine compresses the woven elastic bands to simulate the stresses experienced in actual use, allowing the fibers to shrink in advance. Mechanical shrinking requires a combination of tension control and pressure regulation to ensure uniform shrinkage distribution and avoid localized over-compression that can lead to loss of elasticity.
Post-shrinking is a complementary step. Coating or impregnation creates a protective layer on the elastic band surface, limiting fiber movement and further enhancing dimensional stability. The choice of post-shrinking agent must balance environmental performance and durability to avoid negatively impacting the material's elasticity.
Quality testing is performed throughout the shrinking process. Tensile testing assesses elastic recovery, dimensional measurement is used to measure shrinkage, and visual inspection is used to verify surface flatness. This testing data is fed back into production, forming a closed-loop control system to ensure that each batch of elastic bands meets shrinkage standards.
Elastic band shrinking requires a coordinated effort of fiber pretreatment, weaving optimization, heat setting, wet shrinkage, mechanical shrinkage, finishing, and quality testing to effectively control shrinkage. This process not only relies on equipment precision and process parameters, but also requires a deep understanding of material properties and usage scenarios in order to produce high-quality elastic bands with stable dimensions and lasting elasticity.
