Textile fabric width control

Introduction

During the manufacturing process, controlling the fabric width is one of the most important indicators. In fact, fabric design has the most direct impact on the finished fabric width. The loom width of the greige fabric, the type of reed used, the fineness of the raw materials, the fabric structure, and the warp and weft density of the greige fabric all directly affect the finished fabric width. Taking polyester woven fabrics as an example, common woven fabrics mainly include: conventional plain weave fabrics, high-twist imitation silk fabrics, stretch fabrics, and staple fiber blended imitation wool fabrics, etc. The dyeing and finishing process also has a significant impact on the fabric width.

Impact of the manufacturing process

Different types of fabrics require different dyeing and finishing processes. The conventional process for flat woven fabrics is as follows: Fabric preparation → Scouring → Dyeing → Post-treatment → Dehydration → Drying → Setting → Inspection. The dyeing and finishing process for high-twist imitation silk fabrics is as follows: Fabric preparation → Pre-shrinking → Pre-setting → Alkali reduction → Washing → Dyeing → Post-treatment → Dehydration and drying → Setting → Inspection. The dyeing and finishing process for elastic fabrics is as follows: Fabric preparation → Open-width scouring → Pre-shrinking → Pre-setting → Dyeing → Post-treatment → Dehydration → Drying → Setting → Inspection. The dyeing and finishing process for blended imitation wool fabrics is as follows: Fabric preparation → Singeing → Pre-shrinking → Pre-setting → Dyeing → Post-treatment → Dehydration → Drying → Setting → Steaming → Inspection. Based on the above processing flows for different varieties, the main processes for dyeing and finishing common polyester woven fabrics include: Fabric preparation, (open-width) scouring, pre-shrinking, pre-setting, alkali reduction, dyeing, post-treatment, dehydration, drying, setting, steaming, and inspection, totaling 12 steps.

The impact of the processing process

1. Fabric Preparation: The main tasks of the fabric preparation process are embroidery, hemming, and weighing. While the length of time the rolled greige fabric is left after unwinding does affect fabric shrinkage, this effect is weak. For warp-stretch fabrics, weft-stretch fabrics, and biaxial stretch fabrics, excessively long storage time after unwinding will increase fabric shrinkage. The shrinkage of the greige fabric width in weft-stretch fabrics directly affects the finished fabric width. The shrinkage of the warp yarns in warp-stretch fabrics leads to increased crimping of the weft yarns, ultimately resulting in a narrower weft width. The pressure on the upper and lower layers of fabric on the fabric cart after preparation is different. Whether it is stretch fabric or high-twist fabric, if the greige fabric is subjected to uneven external influences during the release of internal stress after unwinding, it will lead to uneven changes in the fabric width of the entire batch, ultimately resulting in inconsistent fabric width after preshrinking or setting, causing adverse effects on subsequent processing. For polyester woven high-twist fabrics, especially stretch fabrics, the storage time after unwinding and preparing the batch should not be too long. Excessive storage time will lead to inconsistent fabric width after preshrinking, significantly impacting subsequent processes.
2. Scouring: Scouring includes rope scouring and open-width scouring. Rope scouring is the pretreatment of ordinary polyester woven fabrics, the purpose of which is to remove impurities from the fabric without affecting the processing quality of subsequent processes. The heating rate, maximum process temperature, auxiliary agent concentration, and holding time are the most important process parameters in the pretreatment process. In a wet and hot state, polyester, as a thermoplastic fiber, will always undergo changes. The higher the temperature and the faster the heating rate, the more pronounced these changes will be. To reduce these changes, the pretreatment temperature will not exceed the glass transition temperature of the polyester fiber. Therefore, rope scouring has little effect on the finished fabric width of ordinary flat polyester woven fabrics. For stretch fabrics, especially weft-stretch and biaxial stretch fabrics, open-width scouring is required to effectively control the shrinkage of the greige fabric width. Open-width scouring needs to be performed in an open-width scouring machine. The multiple open-width scouring tanks in the open-width scouring machine can provide different scouring temperatures. Cold water is used first, followed by warm water; open-width scouring is performed while continuously expanding the fabric width, allowing the fabric width of the weft-stretch fabric to shrink uniformly by more than 20% after processing. Slow and uniform shrinkage is the basis and key to maintaining a flat finished fabric surface. Open-width scouring at low temperatures is a simple and effective process route for achieving slow and uniform shrinkage of polyester stretch fabrics. Scouring wide-width plain weave stretch fabrics using an open-width scouring machine can eliminate internal stress in the greige fabric under relatively mild wet-heat conditions, reducing the chance of wrinkles appearing on the fabric surface during subsequent processing. Excessive width shrinkage indicates that the open-width scouring speed is too fast. For weft-stretch (double-stretch) greige fabric with an initial width of 210cm, the width after processing is generally around 180cm (including the selvage). If the width after scouring is greater than 160cm, it indicates that the open-width scouring speed is too fast.
3. Preshrinking: This is performed in rope form in the dyeing vat. The preshrinking temperature is higher than the scouring temperature but lower than the dyeing temperature. Preshrinking is a pretreatment under high-temperature wet-heat conditions. In addition to removing sizing agents, oils, stains, and other impurities from the fabric, the high-temperature wet-heat processing aims to eliminate internal stress in the fabric as much as possible and allow the fabric width to shrink gradually. Under high-temperature wet-heat conditions, areas with high crystallinity within the fiber tend to become disoriented, while areas with low crystallinity tend to become oriented. The orientation and disorientation phenomena occurring within the thermoplastic fibers cause the overall orientation of the fabric to become more balanced, and the internal stress formed during the manufacturing and storage of the fabric is released. The final result is increased dimensional stability of the fabric, a flatter fabric surface, and a more stable width. Preshrinking of polyester woven fabrics is similar to mercerization of cotton fabrics. During the preshrinking process, the warp tension comes from the dyeing vat nozzle, resulting in greater tension in the warp direction and relatively less tension in the weft direction. During preshrinking, the weft yarns are shorter, and the number of warp yarns each weft yarn wraps around is only equal to the number of warp ends in the fabric. The number of weft yarns that each warp yarn wraps around is equal to the weft density of the fabric multiplied by the length of the fabric piece. Therefore, the resistance encountered by the warp yarns during preshrinking is far greater than that of the weft yarns. At the same time, the warp yarns become more difficult to shrink under the tension of the nozzles, ultimately leading to greater weft shrinkage than warp shrinkage in non-elastic polyester woven fabrics after preshrinking. When thermoplastic fibers shrink under high temperature and humidity, the thickened weft yarns will cause the warp yarns wrapped around them to become shorter overall; similarly, the warp yarns will also cause the weft yarns to become shorter overall. The mutually influencing yarns, after the preshrinking process, cause the fabric’s width and length to become more reasonable. Understanding the shrinkage of greige fabrics with different twists, raw materials, and structures during weaving and dyeing and finishing processes is the basis for rationally designing the finished fabric width. During preshrinking, the greater the nozzle tension, the more pronounced the fabric width shrinkage. A ​​nozzle diameter that is too small affects the smooth passage of the fabric through the nozzle, easily causing fabric damage and resulting in uneven fabric shrinkage. If the nozzle diameter is too large and the nozzle tension is adjusted too high, fabrics without selvage structures are prone to edge fraying. After the fabric frays at the edges, subsequent processing and finished product shaping become difficult. Although increasing the fabric temperature in the tank can improve the fabric edge fraying phenomenon, excessively high water temperature in the tank during preshrinking can also easily lead to uneven preshrinking of the greige fabric. Segmented heating, with holding times at different heating stages, is the main way to extend the process time and moderate the process conditions during the preshrinking of high-twist fabrics. Extending the time and moderating the conditions will make the fabric preshrinking effect more significant. Uniform shrinkage, dimensional stability, and a flat fabric surface are the main quality indicators of preshrinking. Sometimes, high-twist fabrics have excessively wide widths after preshrinking, and the fabric surface shows splitting, which are all caused by improper preshrinking process design. If a segmented heating preshrinking process is used, consider appropriately reducing the nozzle tension and the fabric circulation speed to increase the immersion time of the fabric in the preshrinking liquid in the tank. The fabric shrinks in a high-temperature, humid, and relaxed state, which is conducive to increasing the preshrinking effect. 4. Presetting Presetting is performed on a setting machine. For polyester woven fabrics, presetting is a continuation of preshrinking, with the same objective. The former is carried out under wet heat conditions, while the latter is carried out under dry heat conditions. The results of slow preshrinking under wet heat conditions require consolidation and reinforcement through presetting under dry heat conditions. During presetting, temperature, width, tension, and speed are the main process parameters. The presetting temperature is slightly higher than the finished product setting temperature, which is beneficial for the dimensional stability of the fabric after presetting. The presetting width should be slightly smaller than the finished product width. During setting, the greater the warp tension and the wider the width, the flatter the fabric surface. Increasing the warp tension increases the chance of the warp yarns being straightened, and the weft yarns become more tortuous, thus tending to reduce the width. The speed depends not only on the length of the drying chamber but also on the fabric thickness, raw material properties, and organizational structure.
   The presetting width is determined based on the preshrinking width, the flatness of the fabric surface before presetting, and the finished product setting width. The adjustment range of the presetting width should not be too large, and the fluctuation of the setting temperature should not be too large; otherwise, after weight reduction and dyeing, the width of the fabrics in the same batch before finished product setting will differ too much, making finished product setting impossible.
4. Alkali Reduction The purpose of weight reduction is to make the high-twist polyester filaments thinner. The thinner yarns will have reduced rigidity, and the space for movement between the yarns will increase, resulting in improved fabric feel. After alkali reduction, the fabric becomes softer, and the width will slightly increase. The increased width is most closely related to the raw materials and organizational structure, generally increasing by about 1 cm. The phenomenon of fabric width widening is more pronounced after high-temperature weight reduction in the dyeing vat. Washing after weight reduction and before dyeing has no effect on the fabric width.
5. Dyeing Similar to preshrinking, the dyeing process is also carried out under high-temperature wet heat conditions. The difference is that the dyeing temperature is higher than the preshrinking temperature, representing the second wet heat setting of the fabric. After the first wet heat setting during preshrinking and the first dry heat setting during presetting, the fabric width is basically stable. Although the dyeing temperature is about 10℃ higher than the pre-shrinking temperature, the polyester fibers, after being heat-set at high temperature, exhibit a characteristic during dyeing where the fabric width increases slightly, usually by about 1 cm compared to the predetermined width.

There are two main reasons why the fabric width increases after reduction and dyeing. One is that the fabric continuously circulates within the equipment, and this circulation process is a mechanical softening process. After the yarn softens, the sliding between the yarns becomes easier than before the pre-setting, causing the fabric to widen slightly. The other reason is that the new stresses imposed on the fabric during the pre-shrinking and pre-setting processes are released under wet and hot conditions, causing the fabric to widen slightly.

7. Post-treatment: For ordinary fabrics, high-twist fabrics, and staple fiber imitation wool fabrics, the reduction cleaning and color fixing processes after dyeing have no effect on the fabric width. For elastic fabrics, especially weft-stretch fabrics made of blended materials, when cellulose fibers are dyed with sulfur dyes and then oxidized with an oxidizing agent for color development, or when cellulose fibers are dyed with reactive dyes and then fixed with soda ash, the process conditions should not be too harsh, and the process time should not be too long. Otherwise, excessive damage to the spandex elasticity will cause the fabric width to increase excessively, ultimately leading to an excessively wide finished fabric and the loss of weft elasticity.
8. Dehydration, Opening, and Drying: Dehydration and opening after pre-shrinking and dyeing have little effect on the pre-setting itself. “Opening” here refers to using equipment or manual methods to flatten the rope-like fabric without entanglement, facilitating drying or setting. Although the water content after dehydration affects drying efficiency, some varieties, if dehydrated too much, will develop new creases and other defects on the fabric surface. In most cases, to improve processing efficiency, the conventional types of polyester woven fabrics mentioned earlier can be directly pre-set after opening, eliminating the drying process. As long as the length of the drying chamber of the setting machine is long enough, the pre-setting effect of the fabric can be fully guaranteed. Dehydration, opening, and drying after dyeing have little effect on the fabric width.
   Although loose drying equipment and tension drying equipment have a certain impact on the fabric width after drying, this impact occurs after dyeing and is far less significant than the impact of finished product setting on the fabric width. Some fabrics with special textures, such as bark crepe and pearl linen, require loose drying after dewatering and opening to maintain their surface texture. Most polyester woven fabrics can be directly heat-set after opening.
9. Finished Product Setting: The finished product setting of ordinary flat polyester woven fabrics has the greatest impact on dimensional stability. Whether it’s ordinary fabrics, high-twist fabrics, wool-like staple fiber fabrics, or stretch fabrics, the finished product width should be based on the fabric’s width before setting. Although increasing the warp tension during fabric setting helps to narrow the finished product width, it is impossible to significantly narrow the width of a fabric that is too wide after dyeing through finished product setting. Similarly, it is impossible to significantly increase the width of a fabric that is too narrow after dyeing through finished product setting, even by greatly reducing the warp tension during finished product setting.

Concunction

The tension adjustment during finished fabric setting is more important than the warp tension adjustment during fabric preparation. Adjusting the warp tension during finished fabric setting by adjusting the tension bar, fabric tensioner, spreader roller, and overfeed device at the front end of the setting machine can affect not only the fabric weight and hand feel, but also the finished fabric width. After pre-shrinking on a rubber blanket pre-shrinking machine, the width of T/C fabrics will increase moderately. After steaming of wool-like fabrics, the width will also widen slightly. For imitation denim fabrics with viscose staple fiber as warp and elastic weft, the width will also widen after washing. Pin-frame stenter machines are beneficial in maintaining the warp tension of the fabric during finished fabric setting; this tension includes both positive stretching tension and negative pre-shrinking tension. Clip-type stenter machines are less effective in this regard than pin-frame stenter machines.
The final fabric width does not depend on the finished fabric setting width, but on the characteristics of the fabric itself and the entire dyeing and finishing process. With reasonable design and careful processing, the final fabric width will fully reflect the characteristics of the fabric itself, and the width size will be stable.

Related Article

Contract us