Requirements for yarn for knitting
The quality and performance of knitted fabrics depend on the properties of knitted materials, knitted fabric structure and specifications, dyeing and finishing factors. The properties of knitted materials are the main factors that affect the properties of knitted fabrics. The use of knitted fabrics is different, the selection of raw materials is also different. Commonly used fabrics for wearing and decoration are cotton yarn, wool yarn, hemp yarn, silk, viscose yarn, acrylic yarn, polyester yarn, nylon yarn, polypropylene yarn, spandex yarn and new textile materials (such as tencel fiber, differential fiber), etc. : special industrial raw materials are mainly glass fiber, metal wire, arnylon yarn, etc. The composition of raw materials can be pure spun yarn containing only one fiber or blended yarn containing more than two fibers; The structure of the yarn can be short fiber yarn, filament yarn, deformed yarn or yarn with special shape and performance produced by the new spinning process. In addition, the appearance of special-shaped fiber, composite fiber, especially ultra-fine denier fiber, opens up a new way for knitting yarn.
In the process of forming the knitted fabric on the knitting machine, the yarn is subjected to complex mechanical actions, such as stretching, bending, twisting and friction. In order to ensure normal production and product quality, knitting yarn shall meet the following requirements:
1:The yarn should have a certain strength and extensibility
The strength of yarn is an important quality index of knitting yarn. Because yarns are subject to tension and repeated loads during preparation and weaving, knitting yarns must be strong. In addition, in the process of weaving yarn into a circle, it is also more subject to bending and torsion deformation, so it is also required that the knitting yarn has a certain extension, so as to facilitate bending into a circle in the process of weaving and reduce yarn breakage.
2:Yarn should have good softness
The softness of knitting yarn is higher than that of knitting yarn. Because the soft yarn is easy to bend and twist, and make the knitted fabric coil structure uniform, clear and beautiful appearance, but also reduce the yarn break in the weaving process and the damage to the coil parts.
3:yarn should have a certain twist
In general, knitting yarns have less twist than machine yarns. If the twist is too large, the yarn is not easy to be bent and twisted when weaving, which is easy to produce kinks and cause defects, so that the knitting needle is damaged, and will affect the elasticity of the knitted fabric, but also make the coil skew. However, the twist of the yarn must not be too low, because it will affect its strength, increase the break in the weaving, and make the fabric prone to fuzz and pilling. Therefore, the correct choice of twist is an important way to choose the proper yarn.
Twist requirements vary for different uses of knitted fabrics. The sweat cloth is required to be smooth, tight, smooth and clear on the surface. The twist of the yarn can be large, and it can be close to the warp standard for knitting with the same linear density. The yarn twist of outer garment should also be large to enhance crispness and improve pilling. Cotton cloth and elastic cloth are required to feel soft and elastic, and the twist of yarn should be slightly lower. The lower deviation of twist of weft yarn is generally used for weaving with the same linear density. The length of dam should be smaller so as to be easy to pile and to make the filling thick and uniform.
4: the yarn density should be uniform
The uniformity of yarn density, namely the uniformity of yarn stem, is an important quality index of knitting yarn. Even-dry yarn is beneficial to knitting process and guarantee the quality of fabric, so that the coil structure is uniform and the cloth surface is clear. If the yarn has thick node weaving yarn can not pass smoothly, causing yarn break or damage to the parts, and on the cloth surface is easy to form "horizontal", "cloud spot", reduce the quality of knitted fabric; If there are details on the yarn, it is not strong enough here, easy to break, affect the quality of the fabric and reduce the productivity of the machine. Because the knitting machine has a multi-way loop system, it is not only required that the thickness of each yarn is uniform, but also that the difference between the thickness of the yarn should be strictly controlled, otherwise it will form horizontal stripes and shadows on the cloth surface, reducing the quality of the fabric.
5:The yarn should have good hygroscopicity
The ability of yarn to absorb moisture in the air is called hygroscopicity. The hygroscopic capacity of various fibers varies greatly, and the hygroscopic capacity varies with the temperature and humidity of the air. Yarn used for knitting production should have certain hygroscopicity. Under the same relative humidity conditions, good hygroscopic yarn, in addition to its good electrical conductivity, is also conducive to the stability of yarn twist and the improvement of elongation,so that the yarn has a good braiding performance.
6:Yarn should have a good finish and small friction coefficient
Knitting yarn should be as free as possible from impurities and oil stains, and should be smooth. The yarn is not smooth, the wear of the machine parts is severe, easy to damage the machine parts, and the workshop flies, not only affects the health of the workers, but also affects the productivity of the knitting machine and the quality of the fabric.
In addition, in the process of knitting, yarn and a variety of mechanical friction contact for relative sliding, so that the yarn by a certain resistance, resulting in yarn tension. Therefore, the yarn with rough surface or the yarn with too large friction coefficient will produce higher yarn tension when passing through the winding machine, affecting the uniformity of yarn tension, resulting in the unevenness of the coil structure. In order to reduce the friction coefficient of yarn, some antistatic agent and lubricating agent or wax can be added to the surface of yarn.