Roving tension
Tension refers to the tension acting on the axial direction of the yarn, which is expressed as the tension of the yarn. In the process of roving winding, in order to make the roving smoothly wound on the bobbin, the winding speed of bobbin must be slightly higher than the output speed of front roller, so the yarn will inevitably be tense and produce tension. In the process of yarn advancement, the friction resistance at the sleeve, hollow arm and pressing palm of spindle wing top must be overcome, so the tension of each section of yarn from the front roller to the bobbin is different. The winding tension from the pressing palm to the bobbin is the largest, followed by the hollow arm, and the spinning tension from the front roller to the spindle wing top tube is the smallest.
Roving elongation
When the tension of the sliver is large, the sliver will stretch because of the relative displacement between the inner fibers. The elongation degree can be expressed by the elongation ε.
ε=[(l1-l2)/ l2]×100%
Where: L1 - measured length of bobbin winding / M;
L2 -- calculated length of front roller output / m.
As the spinning section is the formation area of yarn, the twist is small and unstable. Although the tension of the spinning section is the smallest, it is easy to stretch. Therefore, the tension of the spinning section is traditionally called roving tension. The small change of roving tension will sensitively affect the elongation, thus affecting the uneven weight and evenness of roving. Therefore, the roving tension is required to maintain a proper size during spinning, which will not damage the evenness of the output sliver, but also ensure sufficient winding density.
The relationship between roving tension and elongation
The roving tension can be determined by visual observation of the spinning section. If the sliver is tensioned, the tension will be large, the sliver will be loose, and the tension will be small. Visual observation can only be used for qualitative analysis but not for quantitative analysis, so elongation can be used to indirectly reflect roving tension in production.
The factors that affect the relationship between tension change and elongation change are raw materials, spinning varieties, structure and materials of spindle wings, whether to use false twister and structure and materials of false twister, machine section size, winding size, process speed, workshop temperature and humidity, etc. Under the condition of a certain false twist mode and normal temperature and humidity in the workshop, the roving elongation can be used as an indirect method to detect roving tension. At this time, the elongation should be controlled within the range of 1.5% - 2.5%, the maximum should not exceed 3%, and the difference of elongation should be controlled within 1.5%.
In some cases, the change of elongation is not consistent with the change of roving tension, such as:
1) When the tension is normal, increasing the spindle speed, the roving elongation will increase due to the increase of spinning segment jitter. If twist coefficient of roving is increased properly, roving elongation can be reduced.
2) When the temperature and humidity in the workshop are too high, the friction resistance between roving and parts increases, the winding tension increases, the winding diameter decreases, the moisture regain of fibers increases, the cohesion between fibers increases, and the relative slippage caused by bearing certain external forces inevitably decreases, which is reflected in the yarn slack in the spinning section. At this time, the tension increases and the elongation does not necessarily increase.
3) When other conditions are certain, if the false twister is used in the front row, it has no influence on the rule that the tension in the front row is greater than that in the back row, but it has a great influence on the elongation. When the false twister is not installed, the elongation in the front row is greater than that in the back row, and when the false twister is installed, the elongation in the back row is greater than that in the front row.
In the above cases, the corresponding process adjustment shall be made according to the causes of the change of elongation.
Adjustment of roving tension
In general, when the tension of spinning section is too small or too large by visual inspection, or the test elongation exceeds the specified range, the roving tension must be adjusted.
In the intelligent roving frame, the setting parameters can be adjusted, while in the roving frame with forming device, speed change device and tension compensation device, if the tension of small yarn is too large or too small, the starting position of iron gun belt can be adjusted. Move the iron gun belt to the small end of the active iron gun, the speed of the bobbin slows down and the tension decreases. The belt of the iron gun is moved to the big end of the active iron gun, the speed of the bobbin is accelerated, and the tension is increased.
When the tension of big yarn is too large or too small, the forming change gear can be adjusted. When the number of teeth increases, the displacement of belt decreases and the tension increases; when the number of teeth decreases, the displacement of belt increases and the tension of big yarn decreases.
When the tension of small yarn and large yarn is adjusted properly, the tension of middle yarn is also suitable in general. Only when the curve correction of the iron gun is unreasonable, resulting in the large slip rate of the belt in the middle of the iron gun, or the increment of roving diameter layer by layer, or the inconsistent coefficient of the differential device is not equal to zero, the middle yarn tension may exceed the specified range. At this time, the tension compensation can be used to improve the middle yarn tension.
In the processing of chemical fiber, because of the rapid elastic shrinkage of the chemical fiber after being drawn, if the tension of roving is too large, it is easy to produce unexpected drafting, which makes the strip dry worse. Therefore, the spinning tension of the chemical fiber with large resilience should be lower than that of pure cotton when it is pure spinning or blended spinning. In principle, as long as the yarn from the front roller to the top of the spindle wing does not drop, the small tension should be used as far as possible. Generally, when the yarn is full, the tension elongation is negative, and it is appropriate to control the tension elongation within the range of + 1% ～ - 1.5%.
Measures to improve roving elongation
1) The increase of roving elongation caused by the increase of spindle speed is due to the increase of roving jitter from the front roller to the top of spindle wing. The twist coefficient and strength of roving can be increased to reduce the roving elongation.
2) The increase of roving elongation caused by high temperature and humidity is due to the increase of friction resistance at the top of the spindle wing and the pressing palm, which results in the increase of winding tension and the tension of the yarn in the hollow arm of the spindle wing. Can reduce the ingot wing top
