How to set the drafting process to control the NEP and lint in the drawing process?
The drafting technology of drawing can be divided into "reverse draft" and "forward draft". Their common point is that they can improve the evenness of the sliver and the fiber straightness, but they have different emphases on the separation and have obvious shortcomings. It is best to achieve the advantages of both and overcome the shortcomings, so that the draft fiber can achieve good control, improve uniformity and fiber straightness.
Draft distribution adopts "reverse draft, large rear area"
First of all, the total draft process uses "reverse draft" to feed 8 slivers together. Increase the total draft multiple of the first track, as long as it is slightly higher than the combined number, and the draft multiple of the last track is slightly lower than the combined number. Secondly, the merging of the first and the last lane is a multiple of the increase in use in the back area, that is, the merging of the first lane is expanded to 1.75-2.10, and the merging of the last lane is expanded to 1.30-1.35. Assuming that the parameters of the three lanes and the second lane are between the first lane and the last lane, it is easy to be larger at this time. The effect will be better if we use the spacing of the back area of the drawing.
The new technology mainly uses "reverse draft", which guarantees the evenness of the sliver, and then uses the increase of the draft multiple in the back area to improve the fiber's straightness, separation and parallelism, to give full play to the advantages of "forward draft", to reduce the level of neps and short fibers as much as possible, and to increase the production speed of the drawing machine at the same time.
In practice, this method is fully applicable to the production of pure cotton varieties, and it can also achieve good results for chemical fiber, wool, hemp, etc.
When the total draft multiple of the first track is higher than the combined number. When the head multiple of "reverse draft" is higher than the union number, it will lead to the deterioration of the whole strip, and with the continuous improvement of the multiple, the degree of deterioration will continue to increase, which is also the main feature of this way. The main treatment of head drawing is fiber straightness, separation and mixing, rather than solving the problem of sliver drying. Through production practice, it has not been found that the overall strip drying is affected by the use of "reverse draft".
The main purpose of increasing the head draft multiple of "reverse draft" is to arrange all drafting tasks at the head, so as to avoid the excessive pressure on the end, and increase the adjustment space of the whole drawing of the end, so as to ensure the completion of all indicators.
The "reverse draft" is used in the total draft distribution, and each drawing is mainly higher than the back draft multiple. The drawing multiple of the first drawing is basically maintained at 1.8-2.1, generally under 22 g / (5 m) of the feeding ration (10 feeds). When the feeding ration is above 22 g / (5 m), the drawing multiple of the back area of the first drawing must be continuously increased, and once the quantitative ratio of the sliver is large in the production process, the drawing of the back area must be enlarged, so as to maintain a good effect.
The purpose of increasing the drawing back draft is to give full play to the advantages of "straight draft", increase the fiber straightness and separation, and avoid neps.
Open "live NEP"
In the process of drawing and drawing, it is not only necessary to straighten the hook of the fiber and undertake the main task of blending. After practical research, it is found that it can also open the "live NEP", which also makes the drawing process become one of the processes that can reduce the NEP of yarn, and has a good space to explore.
The "live NEP" mentioned here is not the real meaning of the NEP. It is a kind of crooked and disordered fiber group in the feeding sliver due to various reasons. If it is not straightened in the drafting process, the fiber group may become a NEP under the action of friction. Therefore, it must be adjusted in the process of merging and drafting to open it into a normal drafting fiber whisker The live neps that fail to open will turn into real neps.
This method is difficult to understand thoroughly through theory, but it has a good effect in production practice. Therefore, in order to reduce the NEP formation in drawing process, the method of increasing the draft after drawing can play a better effect.
With the increase of draft multiple in the rear area, the draft in the main area will be further reduced. Therefore, the middle of the three parallel bars will take the middle value of the first and the last lane, and adopt a larger master, which can also achieve good results.
Generally, neps account for about 20% of all yarn defects.
It is worth noting that to complete the above drafting purpose, we must overcome the major obstacles, mainly because: ① in the case of high speed, the time for the sliver to pass through the two roller spacing is very short, so it must have a relatively large spacing to complete its function; ② because there is a certain angle between the surface roller pattern and the roller bus, so that the fiber will turn to the roller pattern during the drafting process If the gap is not large, neps will be formed easily; ③ if the rear draft is large, there must be a large gap space, otherwise the draft cannot be opened, and it is easy to grow thick, long and thin.
The increase of draft ratio in the rear area is bound to be accompanied by the decrease of draft in the main area. And in practice, it is concluded that the breaking of fiber is not the interval but the multiple of drafting. The breaking long fiber forms a new short fiber, which becomes the hairiness of spinning in the back path. This is also the main reason why some manufacturers can't get rid of their high hairiness and strength. On the previous basis, once the posterior area increases by 0.1-0.2 times, the hairiness will generally decrease by about 20%.
Stabilize and improve evenness of strip
The practice shows that the increase of draft times in the back zone is bound to be accompanied by the decrease of draft times in the main zone, which can optimize the whole process, make the index of the whole strip more stable, the whole curve more smooth and the fluctuation range of the index significantly reduced. Generally, on the basis of the former, the evenness of the strip increases by 2% to 3% once the posterior area increases by 0.1-0.2 times.