Hidden waves are potential unevenness. It means that due to the short wavelength, the spectrum is not reflected or is not obvious in the previous process and is ignored by the inspector. However, it is more reflected after drafting in the subsequent process. An obvious uneven dryness. Sudden yarn defects caused by hidden waves are extremely harmful and will cause a large area of gray fabric to be degraded. The wavelength of the hidden wave is similar to the wavelength generated by the subsequent process, so it is often mistaken for a mechanical wave caused by problems in the subsequent process. Recently, two hidden waves occurred in the roving process of our factory, which caused unevenness of the yarn and affected the quality of the cloth. However, no mechanical wave was found in the analysis of the roving spectrum, but it was more obvious in the spinning spectrum and was scattered sporadically on the spinning frame.
01 Mechanical waves in spinning yarn caused by roller torsional vibration in roving frame
The mechanical wave spectrum of T/C 65/35 14 tex caused by the torsional vibration of the roller in the roving frame at 20 cm ~ 30 cm is shown in Figure 1.
As can be seen from Figure 1, the spun yarn spectrogram reflects a higher CV value of the spun yarn and more thick spots and details. We repeatedly conducted sampling tests on the spinning frame. This problem was concentrated on the same roving frame. The same spindle roving appeared intermittently on the spinning frame. This phenomenon was not found on the normal roving on the spinning frame, which ruled out the possibility of malfunction of the spinning frame. The spectrogram of the roving was not reflected, and the spectrogram graphics were normal, and the evenness CV value, thick places, and details were normal. After careful inspection of the roving machine, it was found that the machine had replaced the lower apron from another origin after flat car operation. After more than 20 days, the lower rubber ring was seriously adhered to the lower pin and the lower roller.
Remove the lower apron and lower pin. The appendages of the apron attached to the lower pin can only be scraped off with a blade. The roving frame has no record of breakdowns and other drafting components Normal, it is most likely caused by roller torsional vibration. Due to the change of origin of the lower apron of the roving frame, the inner quality of the apron was poor and the surface treatment was improper. After running for a period of time, the lower apron and the bottom roller were seriously adhered to each other, causing torsional vibration of the middle roller. All the aprons of the machine were replaced and samples were repeatedly tested. After the spinning machine spun the yarn, no such mechanical wave was found again.
Generally, the roller in the roving is torsional, and the mechanical wave in the spun yarn spectrum is slightly different from the circumference of the front roller or front rubber roller of the spinning machine (it varies according to the draft multiple of the spun yarn, and the length is 10 cm～50 cm), the mechanical wave wavelength of the spun yarn spectrum of the roving (T/C 14 tex, T/C 28 tex) is between 20 cm and 30 cm, while the mechanical wave wavelength of the spun yarn spectrum caused by the spinning machine failure is 10 cm ~15 cm (see Figure 2).
Defects caused by roller torsional vibration in the roving frame are relatively concentrated on the roving frame, while they are relatively scattered on the spinning frame. The test wave spectrum of the roving of the gauge shows no mechanical waves or draft waves. The causes are:
① The spring swing pin and the lower apron of the roving frame are adhered to the middle roller;
② The lower apron of the roving frame is adhered to Too tight, causing intermittent slight vibrations with high frequency when the middle roller rotates, which is more likely to occur when spinning polyester-cotton blended yarn;
③ Poor gear meshing, especially when pressurized If it is too heavy, the roller load will increase.
The following aspects should be paid attention to regarding roller torsional vibration:
1) The upper and lower aprons of the roving frame cannot be updated at the same time. , it is advisable to match the old with the new. For aprons with a short service life, inspection, cleaning and replacement should be strengthened.
2) The tension of the apron under the roving frame should not be too tight. If the tension of the entire roving frame is too tight, it will cause torsional vibration of the rollers in the entire roving frame.
3) The gear meshing must be appropriate, especially the gears of the middle and rear roller shaft heads, and the keys, pins, and grooves should be used in combination.
4) Strengthen the refueling management of the front gear, and the lubricating oil label must be correct to avoid gear wear.
5) Pay attention to the difference in temperature and humidity. For products containing a lot of polyester, especially pure polyester products, the drafting force is large and improper temperature and humidity can easily cause roller torsional vibration.
02 Mechanical waves of spinning caused by scratches on the front rubber roller of the roving frame
T/C 65/35 13 tex roving front rubber roller The scratches cause the spun yarn to form a mountain-shaped draft wave at 15 cm to 60 cm, as shown in Figure 3.
Sampling from cloth samples and spinning machines was analyzed with a Uster evenness analyzer. There are mountain-shaped draft waves of 15 cm to 60 cm. The entire roving with yarn defects on the spinning frame has this draft wave. Spun yarn spun with normal roving on the same spindle does not have such draft waves. According to actual measurements of the yarn, the regular evenness wavelength is 3.3 m to 3.5 m, and the slub length is 12 cm to 15 cm. This should be a yarn defect caused by the roving process. On the two fixed roving frames we found that the front rubber rollers were seriously scratched. A comparative test was conducted on the scratched cot on the same spindle of roving and spun yarn. The spectrogram of the spun yarn spun by the scratched cot was consistent with the spectrum of the fabric sample and the sample taken on the spinning machine. Generally, if the rubber roller in front of the roving is scratched, the mechanical wave in the spun yarn spectrum is obvious, the roving spectrum is not obvious, and the spun yarn spectrum has draft waves at 15 cm to 60 cm.
It has been repeatedly verified that it is caused by scratches on the rubber roller in front of the roving, that is, the scratched area (concave) causes the fiber speed change point to shift.��Caused by forward and backward movement. If you only make the roving spectrum chart, you cannot analyze the root cause of the roving machine failure.
The hidden wave caused by the scratch of the rubber roller in front of the roving is different from the hidden wave caused by the torsional vibration of the middle and back rollers:
① If the back roller Caused by torsional vibration, change the total draft from 6.9 times to 6.0 times;
② If the middle roller is torsional, change the draft ratio in the rear area from 1.3l times to 1.38 times. After changing the total draft The position of the mechanical wave behind the spun yarn spectrogram of the spun yarn does not move significantly at multiples and draft times in the back zone, and is still between 15 cm and 60 cm. Therefore, it can be ruled out that the torsional vibration of the middle and back rollers is caused, which is generally caused by the rubber roller in front of the roving.
In view of the problem of serious scratches on the rubber roller, the rubber roller used in the roving process should pay attention to:
1) The hardness of the rubber roller should be At Shore A between 80 and 84 degrees, the rubber roller sleeve difference must be within 0.05 mm before getting on the car, and the pressure must be released after parking for more than 4 hours.
2) Check the status of rubber rollers every day and replace any problematic rubber rollers immediately.
3) The rubber roller ages (sometimes the paint falls off), especially the chemical fiber blended and pure spinning. Due to its high oil content, the surface hardness of the rubber roller increases, and the elastic grip of the jaws increases. The holding force is weakened. When the drafting force is large, the jaws will move regularly during the drafting process, which may cause this kind of failure.
4) Impurities and debris embedded in the roving frame rollers (especially the middle roller) and cotton collector may also cause mountain-shaped draft waves to appear in the spun yarn spectrum, forming regular bars. Uneven drying.
03 Conclusion
Roving frame roller torsional vibration, gear installation is poor, gear wear clearance is too large , poor roller groove (pitch), rubber roller scratches, dents and other undesirable factors will produce hidden waves, which may not be reflected in the roving spectrum. It will only be obvious in the fine yarn spectrum, and it is easy to be detected. Neglecting it will lead to large areas of uneven dryness. Therefore, we must strengthen daily basic work and take precautions before they happen. </p
