Knitting is divided into two categories: warp knitting and weft knitting. Cotton yarn is mainly used on weft knitting machines. Weft knitting is a weft knitted fabric. The yarn is sent to the loop knitting area of the knitting machine with a certain tension wheel, and is bent into loops and strung together to form a knitted fabric. From a weaving perspective, the yarn count is required to be soft and smooth, with appropriate and uniform twist, a certain strength and elongation at break, uniform evenness, and fewer details. Because the structure of knitted fabrics is relatively loose, there are many gaps between yarns, and uneven raw yarns directly affect the appearance of the fabric, and details are more harmful. There should be less flying flowers.
The main problems currently existing in knitting yarn
The quality and performance of knitted fabrics depend on factors such as the performance of knitted raw materials, the organizational structure and specifications of knitted fabrics, dyeing and finishing. Among them, the performance of knitted raw materials is the main factor affecting the properties of knitted fabrics. Knitted fabrics have different uses and different raw materials. At present, most knitted fabrics for underwear are made of cotton yarn; the raw materials of hosiery products are cotton yarn, wool and chemical fiber; wool sweaters are mainly made of wool, acrylic fiber, acrylic blended yarn, etc.; the main raw materials of knitted outerwear are polyester, nylon, acrylic fiber and blended yarns. Yarns and new textile materials (such as tencel fiber, differentiated fiber, etc.); raw materials for special industries are mainly glass fiber, metal wire, aramid fiber, etc. The raw material components can be pure spinning yarn containing only one fiber or blended yarn with two or more fibers; (such as colorful yarn, slub yarn, knot yarn, core-spun yarn, etc.). In addition, the emergence of new raw materials such as chemical fiber special-shaped fibers, composite fibers, especially ultra-fine denier fibers, has opened up new ways for knitting yarns.
The yarn count tested in the laboratory basically reaches the first-class level. Only carded yarn has neps and impurities exceeding 360, and a few twist coefficients exceed 360. The second is uneven dryness, which is not reflected in the blackboard dryness. The 0.9.1.0 blackboard will have more cloudy shadows on the actual object. This has happened whether it is carded or combed, and even long-staple cotton yarn has appeared. The third is foreign fibers, both carded and combed. Foreign fiber yarn can only be covered by dyeing products. Fourth, neps have white spots and uneven coloring, which is more prominent on carded yarns and uneven coloring on blended yarn fabrics. The fifth is hairiness. Cotton yarn has a lot of hairiness, and there are many floral patterns during weaving. If the floral patterns are rolled in, it is a weaving defect. Bad needles, rough finished fabrics, and cloth surface are hairy and not smooth.
The quality requirements of knitting enterprises on yarn count
Weft knitting machine, more than 100 yarns are fed into the knitting machine at the same time , if there is a slight deviation, it will be exposed on the knitted fabric surface, especially single-sided knitted fabrics, ribs, and double rib fabrics. Due to different organizational structures, the reflection is not obvious. First-class physical inspection is the basic condition, mainly for weaving services. Not only must the rough fabric meet the requirements, but the physical quality of the bare gray fabric after dyeing and finishing is no problem. Both unit strength and twist coefficient can meet the requirements. (1) The twist coefficient should not exceed 340; 2) The yarn count should be uniform; 3) There should be as little foreign fibers as possible; (4) The number of neps and impurities should be small, and there should be no white spots with low coloring rate, and the dyeing uniformity Good, it is best to reach level 4~5; (5) Less hairiness can reduce flying particles during weaving and improve the surface finish of the finished smooth fabric.
During the process of forming knitted fabrics on a knitting machine, the yarn is subjected to complex mechanical effects, such as stretching, bending, torsion, friction, etc. In order to ensure the normal production and product quality, knitting yarn should meet the following requirements:
1. The yarn should have a certain strength and extensibility
The strength of yarn is an important quality indicator of knitting yarn. Since the yarn is subjected to a certain amount of tension and repeated loading during preparation and weaving, the yarn used for knitting must have a certain strength. In addition, the yarn is also subject to bending and torsional deformation during the knitting process, so the knitting yarn is also required to have a certain extensibility to facilitate bending into loops during the knitting process and reduce yarn breakage.
2. The yarn should have good softness
The softness of knitting yarn is higher than that of weaving yarn. Because soft yarn is easy to bend and twist, it can make the loop structure in knitted fabrics uniform and clear and beautiful in appearance. It can also reduce yarn breakage and damage to knitting machine parts during the weaving process.
3. The thread should have a certain twist
Generally speaking, the twist of knitting yarn is lower than that of woven yarn. . If the twist is too large, the softness of the yarn will be poor, and it will be difficult to bend and twist during weaving. It will also easily produce kinks, causing weaving defects and damaging the knitting needles. In addition, the yarn with too much twist will affect the elasticity of the knitted fabric. , causing the coil to skew. However, the twist of the knitting yarn cannot be too low, otherwise it will affect its strength, increase breakage during weaving, and make the yarn bulky, making the fabric prone to pilling and reducing the wearing performance of the knitted fabric. Therefore, the correct selection of twist is an important way to rationally select yarn. Knitted fabrics have different uses and different twist requirements.
Jersey cloth requires smoothness, tightness, smooth surface, and clear texture. The twist of the yarn should be larger, which can be close to the same linear density woven warp standard. The twist of the yarn used for outerwear should be larger to enhance the stiffness and improve the pilling phenomenon. Cotton fabrics and stretch fabrics are required to feel soft and elastic, and the twist of the yarn should be slightly lower. Generally, the lower deviation of the twist of the weft yarn used for weaving with the same linear density is used. The yarn used for fleece knitted fabrics is to facilitate brushing and make the pile thickness uniform, and the twist requirement is smaller.
AnotherThe amount of external twist also varies with the linear density of the yarn.
4. The linear density of the yarn should be uniform and the yarn defects should be few.
The uniformity of the yarn linear density is the yarn dryness. The uniformity is an important quality indicator of knitting yarn. Uniform yarn is beneficial to knitting processing and ensures fabric quality, making the loop structure uniform and the cloth surface clear. If there are thick spots on the yarn, the knitting will not be able to pass smoothly, causing yarn breakage or damage to the machine parts, and “horizontal stripes” and “cloud spots” will easily form on the cloth surface, which will reduce the quality of the knitted fabric; if there are thick spots on the yarn Details, the strength is insufficient here and ends are easy to break, affecting the quality of the fabric and reducing machine productivity. Because there are multiple loop-forming systems on the knitting machine that feed yarn into loops at the same time, not only is the yarn thickness of each loop required to be uniform, but the difference in yarn thickness between each loop must also be strictly controlled, otherwise horizontal stripes will be formed on the cloth. Defects such as shadows reduce fabric quality.
5. Yarn should have good hygroscopicity
The ability of yarn to absorb moisture in the air is called hygroscopicity. The moisture absorption capabilities of various fibers vary greatly, and the amount of moisture absorbed varies with the temperature and humidity of the air. Yarn used in knitting production should have certain hygroscopicity. Under the same relative humidity conditions, yarns with good hygroscopicity, in addition to their better electrical conductivity, are also conducive to the stability of the yarn twist and improvement of extensibility, so that the yarn has good weaving performance.
6. The yarn should have good smoothness and a small friction coefficient
Knitting yarn should be as free from impurities and Oil stains, etc., and should be smooth. Unsmooth yarns cause severe wear and tear on machine parts and are easy to damage machine parts. There are also many flying flowers in the workshop, which not only affects the health of workers, but also affects the productivity of knitting machines and the quality of fabrics.
In addition, during the knitting process, the yarn has to come into frictional contact with various machine parts and slide relative to each other, causing the yarn to encounter a certain resistance, thereby generating yarn tension. Therefore, yarns with rough surfaces or yarns with excessive friction coefficients will generate higher yarn tension when passing through the knitting machine, affecting the uniformity of the yarn tension, thus causing uneven coil structures. In order to reduce the friction coefficient of the yarn, the surface of the yarn can be treated with antistatic agents and lubricants or waxes.
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