As a flexible material known for its comfort and versatility, knitted fabrics have found wide application in apparel, home décor, and functional protective wear. However, traditional textile fibers tend to be flammable, lack softness, and provide limited insulation, which restricts their broader adoption. Improving the flame-resistant and comfortable properties of textiles has become a focal point in the industry. With the growing emphasis on multi-functional fabrics and aesthetically diverse textiles, both academia and industry are striving to develop materials that combine comfort, flame resistance, and warmth.
Currently, most flame-resistant fabrics are made using either flame-retardant coatings or composite methods. Coated fabrics often become stiff, lose flame resistance after washing, and can degrade from wear. Meanwhile, composite fabrics, although flame-resistant, are generally thicker and less breathable, sacrificing comfort. Compared to woven fabrics, knits are naturally softer and more comfortable, which allows them to be used as either a base layer or an outer garment. Flame-resistant knitted fabrics, created using inherently flame-resistant fibers, offer durable flame protection without additional post-treatment and retain their comfort. However, developing this type of fabric is complex and costly, as high-performance flame-resistant fibers like aramid are expensive and challenging to work with.
Recent developments have led to flame-resistant woven fabrics , primarily using high-performance yarns such as aramid. While these fabrics provide excellent flame resistance, they often lack flexibility and comfort, especially when worn next to the skin. The knitting process for flame-resistant fibers can also be challenging; the high stiffness and tensile strength of flame-resistant fibers increase the difficulty of creating soft and comfortable knitted fabrics. As a result, flame-resistant knit fabrics are relatively rare.
1. Core Knitting Process Design
This project seeks to develop a fabric that integrates flame resistance, anti-static properties, and warmth while providing optimal comfort. To achieve these goals, we selected a double-sided fleece structure. The base yarn is an 11.11 tex flame-resistant polyester filament, while the loop yarn is a blend of 28.00 tex modacrylic, viscose, and aramid (in a 50:35:15 ratio). After initial trials, we defined the primary knitting specifications, which are detailed in Table 1.
2. Process Optimization
2.1. Effects of Loop Length and Sinker Height on Fabric Properties
The flame resistance of a fabric depends on both the combustion properties of the fibers and factors such as fabric structure, thickness, and air content. In weft-knitted fabrics, adjusting the loop length and sinker height (loop height) can influence flame resistance and warmth. This experiment examines the effect of varying these parameters to optimize flame resistance and insulation.
Testing different combinations of loop lengths and sinker heights, we observed that when the base yarn’s loop length was 648 cm, and the sinker height was 2.4 mm, the fabric mass was 385 g/m², which exceeded the project’s weight target. Alternatively, with a base yarn loop length of 698 cm and a sinker height of 2.4 mm, the fabric exhibited a looser structure and a stability deviation of -4.2%, which fell short of the target specifications. This optimization step ensured that the selected loop length and sinker height enhanced both flame resistance and warmth.
2.2. Effects of Fabric Coverage on Flame Resistance
The coverage level of a fabric can impact its flame resistance, particularly when base yarns are polyester filaments, which can form molten droplets during burning. If the coverage is insufficient, the fabric may fail to meet flame-resistance standards. Factors influencing coverage include yarn twist factor, yarn material, sinker cam settings, needle hook shape, and fabric take-up tension.
The take-up tension affects fabric coverage and, consequently, flame resistance. Take-up tension is managed by adjusting the gear ratio in the pull-down mechanism, which controls the yarn position in the needle hook. Through this adjustment, we optimized the loop yarn coverage over the base yarn, minimizing gaps that could compromise flame resistance.
3. Improving the Cleaning System
High-speed circular knitting machines, with their numerous feeding points, produce considerable lint and dust. If not removed promptly, these contaminants can compromise fabric quality and machine performance. Given that the project’s loop yarn is a blend of 28.00 tex modacrylic, viscose, and aramid short fibers, the yarn tends to shed more lint, potentially blocking feeding paths, causing yarn breaks, and creating fabric defects. Improving the cleaning system on circular knitting machines is essential for maintaining quality and efficiency.
While conventional cleaning devices, such as fans and compressed air blowers, are effective in removing lint, they may not be sufficient for short-fiber yarns, as lint buildup can cause frequent yarn breaks. As shown in Figure 2, we enhanced the airflow system by increasing the number of nozzles from four to eight. This new configuration effectively removes dust and lint from critical areas, resulting in cleaner operations. The improvements enabled us to increase the knitting speed from 14 r/min to 18 r/min, significantly boosting production capacity.
By optimizing loop length and sinker height to enhance flame resistance and warmth, and by improving coverage to meet flame-resistance standards, we achieved a stable knitting process that supports the desired properties. The upgraded cleaning system also significantly reduced yarn breaks due to lint buildup, improving operational stability. The enhanced production speed raised the original capacity by 28%, reducing lead times and increasing output.
Post time: Dec-09-2024