Knitting requires higher evenness (that is, the evenness of yarn thickness), good softness, certain strength, extensibility and twist (yarn twist is relatively low). During the process of forming knitted fabric on the knitting machine, the yarn will be subject to complex mechanical actions, such as stretching, bending, twisting, friction, etc.
In order to ensure normal production and product quality, knitting yarn shall meet the following requirements:
1. Yarn should have certain strength and elongation
Yarn strength is an important quality index of knitting yarn. As the yarn is subjected to certain tension and repeated load during preparation and weaving, the knitting yarn must have certain strength.
In addition, the yarn is also subject to bending and torsion deformation in the process of knitting into loops. Therefore, the knitting yarn is required to have certain extensibility to facilitate the knitting process of bending into loops and reduce yarn breakage.
2. Yarn should have good softness
The softness of knitting yarn is higher than that of woven yarn. Because the soft yarn is easy to bend and twist, the loop structure in the knitted fabric is uniform, the appearance is clear and beautiful, and the yarn breakage and damage to the loop forming parts during weaving can be reduced.
3. The yarn 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 flexibility of the yarn will be poor. It is not easy to be bent and twisted during weaving, and it is also easy to produce kinks, which will cause weaving defects and damage the knitting needle; In addition, the yarn with excessive twist will affect the elasticity of the knitted fabric and cause the coil to skew.
However, the twist of knitting yarn should not be too low, otherwise it will affect its strength, increase the end breakage during weaving, and the yarn is loose, making the fabric easy to pile and pilling, and reducing the wearing performance of the knitted fabric.
Therefore, the correct selection of twist is an important way to select yarn reasonably. The twist requirements of knitted fabrics vary with different uses.
The undershirt cloth shall be smooth, compact, smooth and clean, with clear lines, and the twist of yarn shall be larger, which can be close to the warp yarn standard for weaving with the same linear density. The twist of the yarn for outerwear should be larger to enhance the straightness and improve the pilling phenomenon.
Cotton wool cloth and elastic cloth shall be soft and elastic, and the twist of yarn shall be slightly lower. Generally, the lower twist deviation of weft yarn for weaving with the same linear density is adopted. Yarn used for raising knitted fabric requires less twist in order to facilitate the drawing and make the pile thickness even.
In addition, the twist varies with the linear density of the yarn.
4. The linear density of yarn shall be uniform and the yarn defects shall be few
Yarn linear density uniformity, that is, yarn evenness, is an important quality index of knitting yarn.
The yarn with even evenness is beneficial to knitting process and fabric quality, making the loop structure even and the cloth surface clear. If there are thick knots on the yarn, the knitting will not pass smoothly, causing yarn breakage or damage to the machine parts, and it is easy to form "stripes" and "cloud spots" on the cloth surface, reducing the quality of knitted fabrics; If there are details on the yarn, the strength here is insufficient and the end is easy to break, which affects the quality of the fabric and reduces the productivity of the machine.
Because there are multiple loop forming systems on the knitting machine that feed yarn into the loop at the same time, it is not only required that the yarn thickness of each loop be uniform, but also that the yarn thickness difference between each loop should be strictly controlled, otherwise the defects such as horizontal stripes and shadows will be formed on the fabric surface, reducing the fabric quality.
