What is yarn?
Yarn: It is a general term for yarn and thread. It is a thin, soft and continuous strip made of textile fibers with a certain strength, including single yarn. and strands.
Single yarn: It is made from short fibers through spinning processing, so that the short fibers or filaments are arranged in the axial direction and twisted.
Strands: composed of two or two The above single yarns are combined and twisted, and their strength and wear resistance are better than those of single yarns. At the same time, the strands can also be combined and twisted in a certain way to obtain multi-twisted strands.
What is twisting?
If one end of the whisker is held and the other end is turned, yarn can be formed. This process is called twisting.
For short fibers, twisting is The necessary means to make fiber strips into yarns. Before twisting, it is generally necessary to condense the loose fibers into fiber strips. After twisting, the outer fibers of the fiber are squeezed into the inner layer to generate centripetal pressure, so that the slivers are along the length of the fiber. Get friction.
For filament yarns and strands, twisting can form a tight structure that is not easily damaged by lateral external forces. Twisting can also form deformed yarns and Fancy thread. The amount of twisting and the direction of twisting not only affect the feel and appearance of the fabric, but also affect the intrinsic quality of the fabric.
After the sliver is twisted, its outer fiber will produce an inclined spiral twist, the fiber will twist and deform, and the yarn sliver will tightly embrace, changing the overall properties of the fiber. Structural morphology and mechanical and physical properties. (As shown in the picture below)
When to yarn When the strip has a wrapping angle, the fibers will exert centripetal pressure on the yarn strip. The larger the wrapping angle, the greater the centripetal pressure. Due to the existence of centripetal pressure, the outer layer of fibers is squeezed into the inner layer, which increases the tightness of the yarn and the friction between the fibers, thus changing the structural form of the yarn and its physical and mechanical properties. This is twisting. The essence of yarn.
Evaluation of yarn twist degree:
Twist direction/twist degree/twist coefficient/twist shrinkage
01
Twist direction: indicates the direction of twisting
The twist direction refers to the inclined direction of the fibers in the single yarn or the single yarn in the strand after the yarn is twisted. It is divided into two types: Z twist and S twist.
After twisting, the twist direction of the yarn From the lower right corner to the upper left corner, the tilt direction is consistent with the middle of “S”, it is called S twist or smooth twist; the twist direction of the yarn is from the lower left corner to the upper right corner, and the tilt direction is consistent with the middle of “Z”, it is called Z Twist or backhand twist. Generally, single yarns often use Z twist, and strands use S twist.
The twist direction of the strands is represented by the twist direction of the strands. For example, if the single yarn is Z-twisted, the first twist is S-twist, and the second-twist is Z-twist, the twist direction is represented by ZSZ.
The twist direction of the yarn has a great influence on the appearance and feel of the fabric. The twist direction of the warp and weft yarns can be used to match the fabric structure to create the appearance and feel. Fabrics of various styles.
02
Twist: the number of twists per unit length of the yarn
The two cross-sections of the yarn produce an angular displacement of 360°, which becomes a twist, that is, usually Said turn around.
my country’s cotton yarn adopts special number system twist, which is expressed by the number of twists within 10 cm yarn length; combed wool yarn and chemical fiber filament use Metric count system twist is expressed in the number of twists per meter; in addition, there is also the imperial count system twist expressed in the number of twists per inch.
Twist affects the strength, rigidity and flexibility, elasticity and shrinkage of yarn. As the twist of the yarn increases, its strength increases, but the twist cannot exceed a certain value, otherwise its strength will decrease. This certain value is called the critical twist of the yarn. Yarns of different raw materials have different critical twists. Generally, under the premise of meeting the strength requirements, the smaller the twist of the yarn, the better, because the increase of twist will make the yarn feel harder, the elasticity decreases, and the shrinkage increases. This is why filament yarns generally try not to twist or twist as little as possible. Because of the twist.
03
Twist measurement method
Twist testing methods commonly used in my country include direct counting method and untwisting and twisting method. Short fiber and strand tests generally use the direct counting method, whileThe yarn adopts the untwisting and twisting method. In addition, there are secondary and triple untwisting and twisting methods, slipping method, etc.
Direct counting method
Under a certain tension, clamp the two ends of the yarn of known length, fix one end and press the other end The untwisting direction rotates around the axis until the single yarn or single yarn in the strand or the single fiber in the multifilament is completely parallel. The number of untwisted twists is the twist within the length of the yarn sample.
Untwisting and twisting method
Clamp the known yarn under a certain tension At both ends of the length, one end is fixed, and the other end rotates around the axis in the untwisting direction. Measure the number of twists when it returns to the starting length after untwisting and reverse twisting. The number of twists is within the length of the yarn sample. twice the twist.
04
Twist coefficient: relative value of twist degree
Twist cannot be used for comparison The degree of twisting of different thickness yarns, because with the same twist, the fiber tilt of thick yarns is greater than that of thin yarns. In actual production, the twist coefficient is often used to express the degree of twist of the yarn. The twist coefficient is a relative value that combines linear density to express the twist degree of yarn, and can be used to compare the twist degree of yarns of different thicknesses. The twist coefficient can be calculated based on the twist of the yarn and the linear density of the yarn.
Twist coefficient is a combined linear density expression of yarn The relative value of the degree of twist can be used to compare the degree of twist of yarns of different thicknesses. The larger the value, the greater the degree of twist.
05
Twist coefficient: relative value of twist degree
After twisting, Due to the tilt of the fibers, the length of the yarn is shortened and twist shrinkage occurs. The size of twist shrinkage is usually expressed by the twist shrinkage ratio, that is, the difference in yarn length before and after twisting accounts for the percentage of the length before twisting.
The twist rate affects the linear density and twist of the spun yarn, and must be considered in the design of spinning and twisting processes. The twist shrinkage of cotton yarn is generally 2%~3%. The size of the twist shrinkage is not only related to the twist coefficient, but also related to factors such as spinning tension, workshop temperature and humidity, and yarn thickness.
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