Discussion on Improving the Low Strength and Low Elongation of Nylon 6 Stretch Deformed Yarn

Breaking strength and elongation at break are key physical indicators of nylon 6 stretch textured yarn (DTY), which are mainly affected by factors such as the quality of pre oriented yarn (POY), the running status of DTY after texturing, and the texturing process. Based on experience, in the case where the POY raw material and DTY elasticity process cannot be changed, in order to improve the fracture strength and elongation at break of DTY products, and reduce the coefficient of variation of fracture strength and elongation at break, the key is to adjust without adding elasticity.
Our company built the factory in 1988, and some of the ammunition was not purchased earlier. Recently, it has been found that some DTY machines have low product quality indicators when producing certain specifications of products. For example, in November 2012, when our company's 14 # DTY machine was producing 44.4dtex/12fDTY, there were individual ingot positions with low DTY fracture strength and elongation at break, which could not meet the specified values. At the same time, it caused a large coefficient of variation of the entire batch of wire fracture strength and elongation at break, exceeding the specified range of industry standards, causing product degradation.
Our company's technical personnel have continuously discussed and tested, and finally solved the problem of low DTY fracture strength and elongation through adjustments to the loading system.
1. Testing
1. Test materials
POY precursor: produced by the company, specification is 54dtex/12f, Linear density is 53.53dtex, Linear density deviation rate is -0.87%, and Linear density variation coefficient (CV value) is 0.46%; Breaking strength 4.48cN/dtex, breaking strength CV value 2.03%; Elongation at break 65.1%, elongation at break CV value 2.24%; The evenness of the strip is 0.67% (1/2CV value).
2. Test equipment and instruments
FK6-12 high-speed loading machine, 216 spindle position, manufactured by BAR-MAG company in Germany, FDAME fully automatic tensile tester, produced by Texfecho company in Germany.
YG086 yarn length tester is produced by Laizhou Electronic Instrument Co., Ltd.
3. Test process
The POY raw wire is drawn through 2 rollers and 1 roller, and is then subjected to spindle group friction, hot box shaping, cooling plate cooling, and oil loading on an oil tanker, ultimately packaged into a DTY product. After dismounting, perform fracture strength and elongation at break testing, and adjust and retest ingot positions with low strength and elongation at break. The loading speed is 770m/min, the hot box temperature is 183 ℃, the draft ratio is 1.335, the D/Y is 2.17, and the overfeeding rate is -4.21%.
2. Results and Discussion
1. Product indicators before adjustment
During the routine sampling process, it was found that some samples had low fracture strength and elongation at break, and CV values exceeded the standard values.
To better identify the problem, we conducted a wire drop inspection on all spindle positions of the machine, and found that the strength and elongation of 22 spindle positions were lower than the standard value.
2. POY precursor factor
We analyze that if POY causes low fracture strength and elongation at break of individual DTY ingots, then after replacing POY, there will be significant changes in fracture strength and elongation at break. Otherwise, POY is not the main cause. For this reason, we replaced the high elongation ingot position P0Y with a low strength ingot position, and conducted another wire drop test. We found that the results did not improve, so we can exclude the POY precursor factor. The test results are shown in Table 3.
3. Bombing process factors
This product is a regular product of the company. It has been processed multiple times on other machines and has not encountered such problems. The product has also been recognized by downstream customers, so the possibility of unsuitable technology is extremely low. For the sake of safety, the vehicle will arrange maintenance personnel and electrical and instrument personnel to check and confirm the process parameters of the machine, including measuring the actual temperature of the hot box, friction disc speed, and loading speed. All measured values and set values are in good agreement, indicating that there is no problem with the loading process.
4. Equipment and Silk Road Factors
1. The influence of friction discs and pull rod wire guides
The friction disc is a key component of the friction type twisting deformation process, which applies appropriate radial friction force to the wire rod to rotate and twist it. The longer the friction disc is used, the greater the friction coefficient, the greater the tension of the wire rod, and the greater the relative sliding with the friction disc, causing more serious damage to the wire rod and reducing its strength and elongation.
We found through experiments that the pull rod wire guide has equally significant effects on the strength and elongation of the wire rod. After replacing the friction disc and pull rod wire guide for ingot positions with low strength and elongation, most of the ingot positions returned to normal.
2. The influence of twist arresters
The anti twist device is another key component of the friction type false twist deformation machine, located at the inlet above the hot box. Its function is to generate a friction force that is almost equal to the twisting torque but opposite to the twisting direction, preventing the continued transmission of twist, thereby ensuring the elasticity and strength of DTY.
Our company's 14 # machine adopts a rotary twist stopper. After a period of use, some twist stoppers are prone to inflexible rotation or deformation, resulting in increased friction and damage to the wire, resulting in a decrease in strength and elongation. This time, a test was conducted to replace the anti twist device on the spindle positions that were still not good after replacing the friction disc and spindle group wire guide, and some spindle positions returned to normal.
3. The Influence of the Relative Position of the Twist Stopper and the Pull Rod Wire Guide
The relative position of the anti twist device and the pull rod wire guide has a significant impact on the tension and DTY physical indicators of the wire. The anti twist device is generally located behind the pull rod wire guide. When the wire tension is about 21cN (44.4 dtex/12f varieties), when the positions of the anti twist device and the pull rod wire guide are interchanged, the wire tension decreases to about 17cN, and the strength and elongation of the wire are significantly improved.
3. Conclusion
1. The factors that cause low strength and elongation of DTY include the quality of POY raw silk, texturing process, and the condition of texturing machine equipment. For the large area of low strength and elongation during the processing of new varieties, it is mainly related to the texturing process, and process debugging should be the first step; For the sudden occurrence of low strength and elongation of some ingots in mature processes, the quality of POY raw materials should be checked first. After excluding the quality factors of POY raw materials, the cause should be found from the equipment itself.
2. The wear and deformation of friction discs, pull rod wire guides, and twist arresters are the main factors causing low wire strength and elongation. For long-term use of friction discs, pull rod wire guides, and twist arresters, they should be carefully inspected and replaced regularly.
3. The relative position of the twist arrestor and the pull rod guide has a significant impact on the wire tension and DTY physical indicators. The position of the twist arrestor in front of the pull rod guide is beneficial for reducing the wire tension and improving the product's breaking strength and elongation at break.