What is Twisting?
In the process of yarn production, twisting is essential for both staple fibers (to form continuous yarns) and filaments (to improve processability and compactness). The twist level directly impacts the structure, physical properties of yarns, fabric texture, and garment performance, serving as a key criterion for product grading.
Broad Definition: Twisting refers to any process during spinning where fibrous strands (slivers, yarns, threads, or filaments) are rotated around their axis or axially wrapped to create twist turns, wrapping, interlacing, or networking structures.
What yarns need to twist?
Staple Yarn: Binds overlapping fibers into a continuous yarn, enhancing strength.
Filament Yarn: Creates a compact structure resistant to lateral damage, improves processability, and adds anti-pilling/anti-snagging properties. Strong twists enable unique fabric textures.
Plied Yarn: Enhances uniformity, strength, and physical properties (luster, softness, elasticity).
Fancy Yarn: Produces decorative threads with special visual effects.
Objectives of Twisting
Imparts specific structural forms, physicomechanical properties, and aesthetics to yarns and plied threads.
Requirements for Twisting
1. Optimize strength, elongation, elasticity, softness, luster, and hand feel.
2. Diversify yarn structures.
3. Improve twisting efficiency.
4. Advantages of Twisted Yarns
- Mechanical Performance: High strength, elasticity, and resistance to mechanical stress during dyeing, finishing, and use.
- Spinnability: Adequate fiber length, friction, and cohesion.
- Comfort: Moisture absorption, thermal stability, and chemical resistance (to acids, alkalis, oxidants, etc.) enhance dyeability and wearability.
- Aesthetics: Vibrant dyeability ensures appealing final products.
Mechanism of Twisting
Twisting deforms fibers into helical spirals along the yarn axis, tightly binding the strands and altering their structural and mechanical properties.
Twist Measurement
1. Twist Level
The angular displacement of 360° between two cross-sections of a yarn forms one twist turn, commonly referred to as a single twist. The number of twists per unit length of the yarn is called the twist level.
2. Twist Factor
Twist level alone cannot be used to compare the degree of twisting in yarns of different thicknesses. Under the same twist level, thicker yarns exhibit greater fiber inclination than thinner ones. In practice, the twist factor is often used to represent the twisting intensity of yarns. The twist factor is a relative value that combines linear density (fineness) to indicate the degree of twisting, enabling comparison across yarns of varying thicknesses. It can be calculated using the yarn’s twist and linear density.
3. Twist Direction
Twist direction refers to the inclination of fibers in a single yarn or strands in a plied yarn after twisting. There are two types: S-twist and Z-twist.
S-twist: Fibers or strands slope from the bottom right to the top left, aligning with the middle stroke of the letter "S."
Z-twist: Fibers or strands slope from the bottom left to the top right, aligning with the middle stroke of the letter "Z."
In the production of filament polyester sewing thread & embroidery thread and nylon 66 sewing thread, single yarns typically use S-twist, while plied yarns use Z-twist.
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