Paper Making Machine Maintenance

With the development of science and technology, the structure of paper machines has been continuously optimized. The traditional inspection methods of Paper Machine equipment (mainly referring to the inspection of listening sticks) and the methods of relying on experience to judge equipment failure can no longer meet the maintenance requirements of modern paper machines. Especially after the appearance of paper machines with an annual output of 200,000 tons, or even 400,000 to 800,000 tons, paper machine equipment maintenance personnel's judgment requirements on the accuracy of equipment failures have been further improved, and equipment fault diagnosis technology just meets this demand. One of its major advantages is that it can make accurate judgments on equipment failures, and can use this as a basis to make optimal formulations for equipment maintenance and repair strategies.

Due to its own characteristics, the mechanical structure will inevitably generate vibration during operation. When the operating conditions of the equipment do not change, its vibration will remain at a relatively stable level. When the equipment fails, such as bearing damage, gear collapse, dynamic imbalance, etc., its vibration will inevitably change. If you can find the vibration source that changes the vibration status of the equipment and analyze it, you can determine the cause of the equipment failure.

However, in the actual vibration data detection, the vibration signal (vibration time-domain signal) collected by the sensor is a comprehensive reflection of equipment vibration. It contains not only the vibration signal generated during the normal operation of the device, but also the vibration signal generated due to the failure of the device, as well as other interference signals such as noise. If the collected vibration signals are directly analyzed, it will be difficult to determine the source of the fault and affect the accuracy of the fault judgment. The Fourier transform transforms the analysis of complex time-domain signals into simple frequency-domain signal analysis. Through the analysis of the failure frequency, the cause of equipment failure can be determined, so that targeted maintenance and repair strategies can be adopted for the failed equipment.

Application of equipment fault diagnosis technology

During the routine inspection, the equipment inspector found that the vibration of the second press ZL roller gear box in the press section was abnormal. Due to the complicated structure of the equipment, the inspector could not determine the specific cause of the abnormal vibration. In order to determine the cause of the vibration of the ZL roller, the vibration data of the gear box was collected. Through the analysis of the spectrogram, the vibration at a frequency of 97.55 Hz behaves abnormally, and multiple harmonics based on this frequency also appear (Figure 2).

The failure frequency of each type of bearing can be calculated by the bearing model. The specific data is shown in Table 1. It can be seen from the comparison of the data in Table 1 that the fault frequency in the spectrum diagram is caused by the fault of the inner ring of bearing 1 in the gear box. The vibration caused by the failure of the inner ring also stimulates the 6 × frequency of the inner ring failure frequency, indicating that the bearing inner ring failure is very serious. Based on the diagnosis results, the workshop arranged the shutdown of the paper machine in a timely manner and carried out targeted maintenance on the gear box. The inspection found that the inner ring of bearing 1 (bearing on the inner side) was severely damaged (figure 3), consistent with the diagnosis. The cause of the damage is the blockage of the bearing lubricating oil pipe in the gear box, which leads to the lack of oil and damage to the bearing.