In the twisting production of high strength filament polyester or nylon sewing thread, a common phenomenon exists: to pursue high output and the resulting high profits, higher twisting speeds are often set to gain competitiveness in product pricing.
This poses risks to the production of high-quality filament sewing threads. There is a close and complex relationship between the twisting speed of high strength filament sewing threads and their strength-elongation indicators as well as twist uniformity. In general, under the premise of ensuring quality, there exists an optimal range of twisting speeds. If the speed is too high or too low, it will adversely affect the strength-elongation indicators.
Twisting Filament Polyester Hyosung 210DX3 Sewing Thread
I. Mechanism of the Impact of Twisting Speed on Strength-Elongation Indicators
1. Impact on Strength
Positive Effect (within a certain range): Appropriate speed can make the twisting process faster and more uniform. The fiber cohesion is effectively and consistently enhanced, which helps the strength reach or approach the theoretical maximum.
Negative Effect (when the speed is too high):
● Tension Fluctuations and Irregularities: At excessively high speeds, the inertial and centrifugal forces during yarn unwinding, drafting, and winding increase sharply, leading to severe and hard-to-control yarn tension fluctuations. Irregular tension directly causes twist unevenness, increases weak spots, thereby reducing the average strength and increasing the strength unevenness CV%.
● Increased Hairiness and Fiber Damage: At high speeds, friction and impact between the yarn guide, ring, and traveler intensify. This not only produces more hairiness but may also directly damage the individual filaments of the high-strength filament, causing "internal damage" and resulting in strength loss.
● Risk of Thermal Damage: High-speed friction between the traveler and ring generates significant heat. If the speed is too high, heat accumulation may cause localized heating of the thread (especially for thermoplastic fibers like polyester and nylon), leading to melting or thermal aging, which severely reduces strength.
2. Impact on Elongation
Moderate Speed: The twist is uniform and stable, and the elongation remains at a stable and appropriate level.
Excessively High Speed: Large tension fluctuations lead to some sections having too much or too little twist. Sections with excessive twist may exhibit abnormally high elongation, while sections with insufficient twist may have low elongation, increasing the elongation unevenness; If high speed causes thermal or physical damage to the fibers, their inherent breaking elongation will decrease, leading to a reduction in the overall elongation of the sewing thread.
3. Twist Irregularity (CV%)
Too Low Speed: The machine runs stably, and the unevenness is low.
Too High Speed: Spindle vibration intensifies, the balloon shape becomes unstable, and yarn tension fluctuations increase, resulting in greater variation in the number of twists per unit length, i.e., an increase in twist unevenness.
4. Breakage Rate
Too Low Speed: The breakage rate is extremely low.
Too High Speed: Due to the combined effects of hairiness, tension, thermal damage, and other factors, the breakage rate increases exponentially.
II. Comprehensive Relationship: Finding the "Optimal Speed Window"
In actual production, what we pursue is not the singular highest speed, but the highest efficiency under the premise of ensuring product quality (strength-elongation indicators, twist uniformity, appearance, etc.). This forms the concept of an "optimal speed window."
III. Interaction of Other Influencing Factors with Speed
Speed does not act independently; it is closely related to other process parameters:
1. Filament Raw Material
Number of Filaments and Fineness: The thicker the yarn bundle and the greater the number of filaments, the greater the twisting resistance, the more pronounced the instability at high speeds, and the corresponding optimal speed is lower.
Oil Content and Performance: Good spinning oil can reduce friction and static electricity, allowing relatively higher speeds.
2. Twist Level
High twist itself requires more twisting work, placing a greater load on the equipment. Pursuing high speed under high twist conditions carries higher risks, and the deterioration of strength-elongation indicators will be more evident.
3. Twisting Equipment and Special Parts
Equipment Type: Modern direct twisting machines can withstand higher speeds than traditional ring spinning machines.
Ring and Traveler: Their material, shape, and combination directly determine the maximum allowable speed and friction heat generation. Using high-quality ceramic or composite-coated parts can widen the optimal speed window.
Tension Control System: Advanced and stable tension devices are key to maintaining quality at high speeds.
Conclusion and Production Recommendations
1. Core Relationship: The relationship between twisting speed and strength-elongation indicators is an inverted U-shaped curve. There is an optimal speed range that maximizes the strength-elongation indicators. Deviating from this range, whether in strength or elongation uniformity, will lead to deterioration.
2. Quality First: Blindly pursuing high speed comes at the cost of sacrificing product strength-elongation indicators and uniformity, ultimately leading to quality issues for downstream users (garment, bag factories), such as skipped stitches, thread breakage, and insufficient seam strength.
3. Systematic Optimization: Determining the optimal speed is a systematic project. It requires Design of Experiments (DOE) to systematically test breaking strength, breaking elongation, strength CV%, elongation CV%, hairiness index, and breakage rate at different speeds under specific equipment, raw materials, and twist levels, thereby finding the most cost-effective process solution.
4. Monitoring and Maintenance: In high-speed production, it is essential to strengthen the inspection and replacement cycle management of key parts (such as travelers) and continuously monitor yarn tension to ensure the stability of the production process.
In short, for high strength filament polyester or nylon 66 sewing thread twisting process, a "stable and appropriate speed" is far more capable of ensuring their core strength-elongation performance than an "extremely high speed."
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