The spectrum of yarn sliver is mainly used to analyze the causes of various periodic unevenness of yarn sliver, and to eliminate the problems in equipment or technology in time. In mechanical wave analysis, it is necessary to distinguish the fundamental wave from each harmonic wave, in which the harmonic frequency is an integral multiple of the fundamental frequency. Fundamental wave and harmonic wave have their own amplitude and phase. Fundamental wave and harmonic wave can be superimposed into periodic wave of various shapes. The wavelength of synthetic wave is the wavelength of fundamental wave.
1、 Some notes on the application of spectrogram
1.1 draft wave
The drafting wave is the structural difference of each section of sliver caused by the random distribution of fibers, and the highest peak is at 2.5-3.0 times of the average fiber length.
1.2 mechanical wave
Mechanical wave is caused by mechanical defects or faults (such as roller eccentricity, gear missing teeth, tooth surface wear, dirt in rotor, needle cloth defect, etc.) or improper equipment adjustment, which generally occupies one or two adjacent channels.
Credibility of 1.3 waves
In order to ensure the credibility of the test results, the number of measured wavelengths must reach 25, otherwise the test time and sample length should be extended. It should also be noted that if there are abnormal phenomena on the spectrogram, do not rush to analyze or draw a conclusion. The test should be repeated three or four times to confirm that the same phenomenon appears on the spectrum before it can be regarded as credible.
For example, if the test speed is 400m / min and the test time is 1min, then the sample length is 400m, then the mechanical wave with wavelength less than 16m on the spectrogram is credible. When the test time is extended to 5min and the sample length reaches 2000m, the mechanical wave with the wavelength less than 80m is credible.
1.4 "thumb rule" for harmful waves
Periodic irregularity or draft irregularity in yarn, which is reflected in the height of "chimney" or "hill" in spectrogram, will cause adverse effect on fabric appearance in varying degrees. We should not only pay attention to the absolute height P of the "chimney" or "hill", but also compare it with the normal amplitude B at the corresponding position of the spectrum. If the "chimney" occupies two or three channels, the total height P should be accumulated for comparison. The "thumb rule" can be followed, that is, when p > b / 2, the effect on fabric appearance can be considered as serious.
1.5 matters needing attention in spectrum analysis
(1) The difference between the calculated and measured values is within ± 15%. Analysis and calculation is only a means, not an end, and the final conclusion should be confirmed on the basis of analysis and confirmed by field troubleshooting.
(2) Regular sampling should be adopted in daily test, that is, each processing part (each spindle and each eye) of the spinning equipment should be inspected at least once within the specified time. For example, Uster has suggested that the time required to check the whole equipment is 1 week for carding machine, 2 days for comber, 1 day for final drawing frame, 1 month for roving frame and 6 months for ring spinning frame. The sampling plan should be designed scientifically and the key varieties, equipment and processes should be monitored and controlled.
(3) When analyzing the fault, we should make clear the train of thought, pay attention to distinguish individuality and generality; static and dynamic; light load, heavy load; stable or sometimes not.
(4) If necessary, some simulated fault tests can be carried out for comparison and verification, so as to know what it is and why it is. At the same time, in the process of solving problems, from phenomenon to analysis, calculation, to the whole process of troubleshooting, we should make records, constantly summarize and improve.
