Poor unwinding performance of DTY packages has been a problem that has plagued polyester filament manufacturers in recent years. Poor unwinding performance cannot be reflected in various existing test indicators. However, it will cause yarn breakage during weaving processing and uneven fabric surface, seriously affecting weaving efficiency and product quality.
01 Causes of poor DTY unwinding
1. Influence of raw material quality
For the unwinding performance of DTY packages, the impact of POY quality is crucial. Its impact is in the following aspects:
(1) Physical indicators: POY has low strength elongation, high unevenness, high evenness, especially the elongation difference between POY packages at different spindle positions is greater than 10%, and the Ubbelohde CV is greater than 1.5% and uneven oiling .
(2) Appearance: POY bobbin has wool, trip wire, and inside the bobbin there are sandwich wool, stacked silk, etc. caused by floating silk.
The above-mentioned quality defects of POY can cause the single filaments of the DTY yarn to break or the single filaments to loosen and lack cohesion during the post-processing process, causing the yarns at different levels of the DTY bobbin to become entangled with each other and unable to unwind smoothly.
The causes of these POY quality defects can be divided into three aspects: the influence of slice or melt quality, the influence of process conditions and the influence of equipment. In terms of slice and melt quality, the main reasons are high moisture content (greater than 0.005%), uneven viscosity, large fluctuations, etc., which cause floating yarn, broken ends or uneven quality of POY single filament during spinning. The main impact of the process is poor component assembly type and poor assembly quality, resulting in poor component filtration effect. The spinning temperature is too high or too low, and the side-blowing wind speed fluctuates more than 0.05m/s, which results in poor cooling effect of the filament and uneven single filaments of the filament. The spinning speed is too high, causing the filament to break during over-stretching or causing weakness in the single filament.
Uneven oiling causes the single filaments to loosen, causing the filaments to break and form serious filaments during post-processing. Improper setting of forming parameters will cause overlap or trip wires on the POY package, which will affect post-processing. In terms of equipment, one is that the process requirements cannot be met due to faults or limitations. For example, the slice drying device cannot make the moisture content of the slices after drying less than 0.003% to meet the spinning requirements, causing spinning difficulties, and filaments are produced due to damage to the holes and surfaces of the spinneret plate. etc.; secondly, the yarn guide, friction roller, and forming mechanism are worn due to long-term use, causing damage to the yarn or poor forming, which affects the smooth progress of post-processing.
2. Influence of post-processing technology
The influence of process parameters on the unwinding performance of the filament yarn is mainly manifested in that the post-processing speed is too high, the draw ratio is too large, the speed ratio is poor, the temperature of the heating box is set too high, and the overfeed setting is poor. These will cause DTY end breakage and increased yarn downgrading rate, making it difficult to unwind the yarn. Improper setting of forming parameters results in uneven bobbin hardness, resulting in trip wires, overlapping wires, and excessive forming angle, which adversely affects the smooth unwinding of the yarn in the DTY bobbin.
3. Influence of post-processing equipment
The impact of the equipment is mainly concentrated on the aging and damage of the yarn guide, damage to the twisting apron or friction plate, scaling on the surface of the heater and cooling plate, or damage to the surface during cleaning. The above factors can cause the yarn to deteriorate. The strip is damaged or the single filament is loose when passing through the above devices, resulting in poor unwinding of the strip.
4. Winding oil agent
The effect of winding oil on unwinding is that the winding oil cannot maintain good cohesion of DTY filaments, causing the individual filaments to loosen and generate static electricity during high-speed unwinding, causing the filaments to tangle with each other, thereby damaging the filaments. The unwinding of the strip has an effect.
02 Methods to improve DTY unwinding performance
1. Improve the spinnability and monofilament uniformity of POY
POY spinning should pay attention to the setting of drying and spinning process conditions, the consistency and stability of the side blowing system, the assembly quality of components, the quality of filter materials and whether the spinneret is damaged, and the uniformity of POY oiling, giving POY Good physical properties, reducing the differences between monofilaments and spindle positions. The POY elongation difference between different spindle positions should be less than 6% to 8%, and the Ubbelohde CV should be less than 1% to ensure that POY does not produce lint during post-processing. Regularly check the damage condition of the yarn guide to ensure the quality of the POY package forming package and the good unwinding performance of POY.
2. Adjust the processing parameters of DTY
On the premise of ensuring other quality indicators, milder processing parameters should be used for post-processing. In the specific setting of the process, the production status and various quality indicators of POY should be considered. On the one hand, the post-processing speed should be appropriately reduced, the drawing ratio should be reduced, and the temperature of the heating box should be appropriately reduced. Generally, the temperature of the first hot box should not exceed 205°C. The temperature of the second hot box does not exceed 170°C to reduce processing tension. The processing tension ratio should not be higher than 1.2, so as to cover up the quality defects of POY as much as possible without making the defects more prominent. On the other hand, the package forming parameters that have a great impact on the unwinding performance of the filament should be adjusted. The package forming parameters mainly affect the hardness of the package, trip wires, stacked wires, forming angle and package taper angle, etc. In terms of the design of the forming parameters of the DTY package, the package hardness of the package should be increased as much as possible to maintain the consistency of the package hardness. The package hardness of the package has a very obvious impact on the unwinding performance of the filament. Table 1 lists the package hardness. Effect of loading hardness on unwinding performance.
Although the hardness of the package increases, it will weaken the package.The winding performance has been greatly improved, but the increase in package hardness is also limited in terms of technology. As the tension increases, it will have a greater impact on other quality indicators such as wool fiber downgrading rate and dyeing uniformity, and it is easy to cause snagging on the DTY bobbin. Therefore, it is necessary to increase the package hardness of the bobbin while ensuring various quality indicators.
The selection of forming angle and package taper angle is also very important. Generally, the forming angle should not be greater than 16°. In terms of the selection of the package taper angle, the smaller the taper angle is, the better the unwinding performance of the DTY package will be. However, if the taper angle is too small, it will increase production consumption. Based on comprehensive considerations, 75° is appropriate.
3. Strengthen inspection of post-processing equipment
Regularly check the components of the equipment including yarn guides, twisting components, roller aprons (rubber rollers), surfaces of the heating box and cooling plate, rollers and friction roller surfaces. If any damaged components are found, replace them in time.
4.Choose the appropriate winding oil agent
A good winding oil should make the filaments have good cohesion. When unwinding, the filaments will not loosen and stick to each other. This requires the winding oil to have good permeability and antistatic properties, and a good viscosity. Moderate and good uniformity makes the filament oiling moderate and ensures the normal unwinding of the filament.
03 Summary
From the above analysis, it can be seen that the unwinding performance of the bobbin is related to many factors such as raw materials, equipment, and technology. Improving the unwinding performance of the yarn requires comprehensive management of these influencing factors.
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