Mechanical wave is due to defects or faults in spinning machinery (such as roller eccentricity, gear missing teeth, tooth surface wear, cots, aprons rotate poorly etc.) resulting in periodic irregularities on the yarn strip, which is reflected in the spectrum as a "chimney" shape. Roving with mechanical wave causes yarn evenness to decline and even fabric surface to produce strip shadow, and product quality to deteriorate. Therefore, in production, great attention should be paid to the generation of mechanical wave, and the causes of various mechanical waves should be studied in depth, so as to eliminate faults in time and ensure product quality.
There are two kinds of mechanical waves in roving process: one is caused by the problems of mechanical transmission parts in roving process, which is called general mechanical waves; the other is spurious waves in roving process, which can be divided into three kinds: spurious twist effect wave of roving, variable period wave of roving and twist effect wave of roving.
Analysis method of mechanical wave in roving process
1) Mechanical waves have a fixed wavelength and are often accompanied by harmonics. Comparing with the spectrogram, we can find out the fundamental wave. If there is a multiple relationship between the wavelengths, there will be harmonics. Generally, the analysis begins with the mechanical wave of the maximum wavelength. In the analysis of a series of mechanical wave spectra, the unevenness curve can be used to determine the fundamental wave length quickly. The combination of the two can make up for each other's advantages and disadvantages, and then the analysis can be carried out.
2) Judging mechanical waves. The periodic yarn irregularity is reflected in the height of "chimney" on the spectrogram, and the harmful wave can be judged by comparing the height of "chimney" with the corresponding normal spectrogram amplitude. When the protrusion height is greater than half of the normal spectrum amplitude, it is harmful wave; when the protrusion height is less than half of the normal spectrum amplitude, it is not considered. When a double-column mechanical wave occurs, the two heights should be added together, then compared with the normal spectral height, and then consider whether it is necessary to analyze and solve it.
3) Whether it belongs to spurious wave or not is judged according to the position of the wavelength. After eliminating the spurious wave, the reason of producing mechanical wave is found out. It should be noted that some mechanical waves are not necessarily false waves and need to be tested and judged.
4) The location of mechanical wave is determined by comparing the occurrence wavelength with the calculated mechanical wave of each component.
5) Handling problems or testing and validation of replacement spare parts.
Problems to be noticed in mechanical wave analysis
1) It is not advisable to rush to a conclusion with an abnormal spectrogram, but to repeat the experiment for 2-3 times. When the same problem occurs on the spectrogram, it can be confirmed, and then the analysis can be carried out.
2) The calculated wavelength value does not need to correspond strictly with the measured value, and the allowable difference should be no more than 15%. Because there is slip in the actual drafting process, the drafting ratio is smaller than the set value, that is, the measured wavelength is smaller; the unexpected drafting in the spinning process will make the measured wavelength larger.
3) pay attention to comprehensive analysis and cross process analysis. When multiple vehicles have the same fault, the problem does not necessarily occur in this process, but may also occur in the previous process. For example, in the production process, two R 9.8 tex roving samples were sampled and tested at a speed of 50 m/min, and the testing time was 2.5 min. Mechanical waves of about 1 m appeared on the multi-test spectrogram. This fault was not caused by the roving process, but by the last drawing process.
4) In the process of analysis, simulation tests should be carried out when necessary to verify the comparison. There is a mechanical wave in the sliver about 14 cm before the end drawing process. After 7.44 times drafting of the roving, there is a mechanical wave at 7.44 x 14 cm_1 m of the roving spectrum, as shown in Fig. 1. After changing the drawing roller, the testing sliver spectrum is normal, and the mechanical wave disappears at 1m of the roving test spectrum, as shown in Fig. 2.
There are many methods to analyze the position of mechanical wave in roving process. The fundamental wave length can be determined and analyzed quickly by means of irregularity curve. It should be noted that when analyzing the position of mechanical wave by means of spectrogram, there is not a strict one-to-one correspondence with the measured wavelength, and there exists a certain range of allowable errors, so it can only narrow the scope of fault detection for special roving machine. In the analysis of mechanical wave, we should pay attention to the possibility of multiple faults and the same performance. We should observe, analyze and follow up the test and verification. We should accumulate experience constantly in practice so as to achieve the goal of stabilizing yarn quality, so as to avoid the decline of fabric quality and improve the economic benefits of enterprises.
