Roving tension
Tension refers to the tensile force acting on the sliver axial direction, and its expression is the tension of the sliver. During the roving winding process, in order for the roving to be smoothly wound on the bobbin, the winding speed of the bobbin must be slightly higher than the output speed of the front roller, so the sliver must be tensioned and tension is generated. During the advancement of the sliver, it is necessary to overcome the frictional resistance at the sleeve, hollow arm, and palm of the ingot, so the tension of the sliver from the front roller to the bobbin is different. The winding tension from the palm to the bobbin is the largest, followed by the hollow arm, and the spinning tension from the front roller to the top tube of the spindle is the smallest.
Roving elongation
When the tension on the sliver is large, the sliver will be elongated due to the relative displacement between the internal fibers, and the degree of elongation can be expressed by the elongation ε.
Ε = [(l1-l2) / l2] × 100%
Where: l1——The measured length of bobbin winding / m;
L2——The calculated length of the front roller output / m.
Because the spinning section is the sliver formation area, the twist is small and unstable. Although the tension of the spinning section is the smallest, it is the easiest to stretch. Small changes in roving tension will sensitively affect the size of the elongation, which will affect the weight and unevenness of the roving, so the roving tension should be kept at an appropriate size during spinning, which will not damage the uniformity of the output whisker It must also ensure sufficient winding density.
Relationship between roving tension and elongation
The tension of the roving can be determined by visually observing the spinning section. If the sliver is tight, the tension is large, and if the slack is loose, the tension is small. The visual observation is only qualitative analysis and not quantitative analysis, so the elongation can be used to indirectly reflect the roving tension in production.
The factors that affect the relationship between the change in tension and the change in elongation are raw materials, spinning varieties, spindle wing structure and materials, whether to use false twisters and the structure and materials of false twisters, machine cross-sectional size, winding size, process speed, workshop temperature Humidity, etc. When a certain false twisting method is adopted and the temperature and humidity in the workshop are normal, the roving elongation can be used as an indirect method for detecting the roving tension. At this time, the elongation should be controlled in the range of 1.5% to 2.5%, the maximum should not exceed 3%, and the difference in elongation should be controlled within 1.5%.
In some cases, the change in elongation is not consistent with the change in roving tension, such as
1) When the tension is normal, increasing the spindle speed will increase the roving elongation rate due to the increased jitter in the spinning section. If the roving twist factor is increased properly, the roving elongation can be reduced.
2) When the temperature in the workshop is high and the humidity is high, the frictional resistance between the roving and the machine parts increases, the winding tension increases, and the increase in the winding diameter decreases. At the same time, the moisture regain of the fiber increases, and the cohesion between the fibers increases. The relative slip caused by a certain external force is bound to decrease, which is reflected in the spinning section as slack. At this time, the tension increases, and the elongation does not necessarily increase.
3) Under certain conditions, if a false twister is used in the front row, it has no effect on the rule that the front row of the roving tension is greater than the rear row, but it has a great influence on the elongation. In the rear row, when the false twister is installed, the elongation of the rear row is greater than that of the front row.
In the above cases, the corresponding process adjustment should be made according to the cause of the change in elongation.
Roving tension adjustment
Under normal circumstances, when the tension of the spinning section is too small or too large, or the test elongation exceeds the specified range, the roving tension must be adjusted.
In the intelligent roving machine, the setting parameters can be adjusted, while in the roving machine with forming device, speed change device and tension compensation device, the small yarn tension is too large or too small, the starting position of the iron gun belt can be adjusted. Move the iron cannon belt to the small end of the active iron cannon, the bobbin speed slows down and the tension decreases. Move the iron cannon belt to the large end of the active iron cannon, the bobbin speed increases, and the tension increases.
When the tension of the large yarn is too large or too small, the molding conversion gear can be adjusted. As the number of teeth increases, the belt displacement decreases and the tension increases; the number of teeth decreases, the belt displacement increases and the yarn tension decreases.
When the tension of the small yarn and the large yarn is adjusted properly, the tension of the middle yarn is generally appropriate. Only when the correction of the iron gun curve is unreasonable, resulting in a large belt slip rate in the middle of the iron gun, or the roving diameter is increased in different layers, or the differential device inconsistency coefficient is not equal to zero, the yarn tension may exceed the specified range. Tension compensation is used to improve the yarn tension.
When processing chemical fiber, due to the rapid elastic shrinkage of the chemical fiber after being drawn, if the tension of the roving is too large, it is easy to produce unexpected drawing, which will deteriorate the sliver. Therefore, in the case of pure or blended chemical fibers, the spinning tension should be lower than that of pure cotton spinning. In principle, as long as the yarn from the front roller to the top of the spindle does not fall, use as little tension as possible. In general, the tension elongation is negative when the yarn is full, and the tension elongation is preferably within the range of + 1% to -1.5%.
Measures to improve excessive elongation of roving
1) The increase in roving elongation caused by the increase in spindle speed is due to the increased jitter of the roving from the front roller to the top of the spindle wing. The twist factor of the roving can be appropriately increased and the strength of the roving can be increased to reduce the elongation of the roving.
2) The increase in roving elongation caused by high temperature and high humidity is due to the increased frictional resistance at the tip of the spindle and the pressure palm, which causes the winding tension and the tension of the sliver in the hollow arm of the spindle to increase. . The number of roving winding turns at the tip of the spindle and the pressing palm can be reduced to reduce the tension on the two sections of yarn. If the requirements are still not met, the twist of the roving can be increased and the roving strength can be increased to reduce the elongation of the roving. When the latter measure is taken, the drafting device of the spinning frame must have sufficient pressure to prevent the drafting from becoming hard.
Measures to reduce the difference of roving elongation
1) Difference in elongation between tables
Uneven temperature and humidity in the workshop and chaotic process between the machines can cause excessive differences in elongation between machines. Therefore, the setting parameters of each machine and the number of teeth of the conversion gear should be unified. On the roving machine with iron gun stepless speed change device, the tension of the iron gun belt should be consistent. For individual machines whose elongation exceeds the specified, the starting position of the iron gun belt can be adjusted and the forming gear can be changed to make it stretch. The rate is controlled within the specified range.
2) Elongation difference between front and rear rows
Because the distance from the top of the front row of ingot wings to the front roller is greater than that of the rear row, the jitter and twisting of the front row are more serious, so that the elongation of the front row is greater than that of the rear row. In order to reduce this difference, the following measures can be taken: ① Make the front row of yarns wrap around 3/4 turns on the top of the spindle, or 3 turns on the pressure palm, and the rear row of yarns wrap around 1/4 turn on the top of the spindle, Or around the pressure palm for 2 turns, so that the winding tension in the front row increases and the spinning tension decreases, which not only reduces the elongation of the sliver above the tip of the spindle, but also increases the winding diameter of each layer of bobbin. Less, to reduce the linear velocity of the winding, thereby reducing the elongation of the front row of rovings. ②When feeding with a large sliver can, the rear row of slivers is accidentally drawn large, and the rear row of spindles is supplied; the front row of slivers is accidentally drawn small, and the front row of spindles is supplied to reduce the difference in elongation of the front and rear rovings . ③ Adjust the specifications of the front and rear false twisters.
3) Difference in elongation between ingot and ingot
This difference is mainly caused by the abnormality of spindle, spindle and bobbin. For example, the bending of individual spindles and the unbalance of the arms of individual spindles cause the spindle to sway; the arc of the palm is inconsistent, and the pressure of the yarn is different so that the winding diameter of the bobbin is different; the outer diameter of the bobbin is different, resulting in the winding linear speed Different; the inner bore of individual bobbins is worn too much and swaying; the hollow arm channel of individual spindle wings is not smooth, and the friction resistance increases, causing the roving to elongate. The above reasons can increase the difference in elongation between the ingot and the ingot. In order to reduce this difference, the maintenance of spindles and spindles should be strengthened, and the outer diameter of the bobbin should be consistent. If the inner bore of the bobbin is worn too much, it should be replaced immediately.
