Main factors affecting yarn strength
Main factors affecting yarn strength
1. Definition of yarn strength
An indicator of the tensile force a yarn can withstand. There are absolute strength and relative strength.
Absolute strength (breaking strength): It is the external force that the yarn can withstand when stretched to break. There are ① single yarn strength, ② strand strength, ③ strand yarn strength, etc. The unit is Newton, gram-force, kilogram-force, or pound-force.
Relative strengths include: ① breaking strength ② specific strength ③ breaking length ④ quality index
Breaking strength: The external force that the yarn can withstand per unit cross-sectional area when the yarn is stretched to break. The unit is Newton/mm2, kilogram force/mm2;
Specific strength: The external force that the unit fineness of the yarn can withstand when the yarn is stretched to break. The units are Newton/tex, gram/tex, gram/denier;
Breaking length: It is the length when the weight of the yarn is equal to its breaking strength. The unit is kilometers.
In the metric series of yarn fineness, it is equal to the product of the strength P (gram force) of a single yarn or strand and its metric count divided by 1000;
In the Tex series, it is equal to the ratio of the strength P (gram force) of a single yarn or strand to its Tex, that is, the specific strength;
Quality index: An index indicating the relative strength of yarn.
When the yarn fineness is measured in British systems, it is equal to the product of the yarn strength (pound force) and the British count of its single yarn; when the yarn fineness is measured in Tex, it is equal to the yarn strength Pl (kg force) and its single yarn count. 1000 times the Tex Quotient.
2. Main factors affecting yarn strength
A) Fiber properties:
The higher the fiber strength, the finer the fineness, and the longer the length, the higher the yarn strength.
The natural twist of cotton fibers and the curl of wool and chemical fibers will increase the cohesion between fibers when the yarn twist is not large, thereby increasing the yarn strength.
Short lint content has a great influence on yarn strength. Among cotton yarns, the short staple rate below 16 mm increases by 1%, and the strength of cotton yarn decreases by 1 to 2%.
B)Yarn structure:
The fibers transfer in and out of the yarn radius direction: there is a lot of internal and external transfer and the yarn strength can be increased when the structure is uniform; when the fibers are arranged in layers and there are many folds, buckling, and hooks, the yarn strength is reduced;
Yarn twist: Below the critical twist, the yarn strength increases as the twist increases. After exceeding the critical twist, the yarn strength decreases as the twist increases.
Yarn uniformity: yarn strength unevenness
Thick places, small details, and neps in the yarn: pure cotton yarn is prone to breakage at small details and large neps; polyester-cotton yarn is prone to breakage at thick places and inflection points of thick details.
Mixing uniformity: Fibers of different types and properties are evenly mixed vertically and horizontally.
C)Spinning method:
Yarns spun with different spinning methods have obvious differences in strength due to different structures.
The strength of thick air-spun yarn is about 5-10% lower than that of ring-spun yarn of the same size, but the fineness of air-spun yarn is uniform and the weak points are not lower than ring-spun yarn.
The strength of electrospinning yarn is similar to that of air-spun yarn.
Self-twisting yarn: In-phase self-twisting yarn has very low strength due to the existence of twist-free areas on the yarn; out-of-phase self-twisting yarn has higher strength due to staggering the twist-free areas on the yarn. The strength of the twisted self-twisted yarn is further improved due to the reasonable distribution of twist.
D) Blending ratio:
In two-component blended yarn (T/C), when the blending ratio of one component (T) gradually increases from zero, the strength of the blended yarn generally decreases gradually. After reaching a low value, if this component (T) continues to increase ), the yarn strength gradually increases. The greater the difference in elongation at break between the two blended fibers, the more obvious this dip in strength will be.
E) Atmospheric temperature and humidity:
As the temperature increases, the yarn strength decreases; as the relative humidity increases, the yarn moisture regain increases, the strength of cotton and linen yarns increases, and the strength of wool and man-made fiber yarns decreases. Therefore, the strength test should be carried out after equilibrium under the specified standard state (temperature 20°C, relative temperature 65%), otherwise the measured strength must be corrected for temperature and moisture regain. eisCNEyS
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