Analysis and Resolution of Vibration Issues in High-Temperature Fire-Rated Axial Flow Fans

Analysis and Resolution of Vibration Issues in High-Temperature Fire-Rated Axial Flow Fans

Mass imbalance in high-temperature fire-rated axial flow fans caused by dust accumulation and angular misalignment can only be resolved through on-site dynamic balancing, although there are some exceptions. Abstract: This paper presents an analysis and resolution of vibration in high-temperature fire-rated axial flow fans caused by the improper use of lubricating oil during maintenance. 1. Vibration in High-Temperature Fire-Rated Axial Flow Fans High-temperature fire-rated axial flow fans exhibit significant vibration following a major overhaul. The vibration spectrum primarily exhibits a typical 1X frequency multiplication pattern caused by mass imbalance. Initially, dynamic balancing was performed to address the simple mass imbalance issue. When the balancing of the motor was doubled during warm-up, the vibration decreased significantly, falling within an acceptable range. However, upon restarting the booster high-temperature fire-fighting axial fan the following day, the maximum vibration value reached 126 μm, exceeding the alarm threshold. Upon retesting and analysing the vibration of the high-temperature fire-rated axial fan, the vibration spectrum was predominantly at 1X frequency. The rotor imbalance did not correspond to the location where the balance had been improved the previous day, and the variation in vibration phase across multiple measurements indicated that the high-temperature fire-rated axial fan had undergone an uneven change in mass. This was not merely a simple issue of mass imbalance. 2. Analysis and Resolution of Vibration in the High-Temperature Fire-Rated Axial Fan During the overhaul, the maintenance tasks for the high-temperature fire-rated axial flow fan included changing the hub oil, measuring blade angles, and sensing and removing dust. Based on the vibration analysis, with the spectrum predominantly at the 1X frequency, misalignment of the high-temperature fire-rated axial flow fan can be ruled out as a cause. It is highly likely that the high-temperature fire-rated axial flow fan will require dust removal again in the near future, and only one blade assembly will be disassembled. No major issues are anticipated during the overhaul. There is no mass imbalance, and the main components of the high-temperature fire-fighting axial flow fan were not overhauled during the maintenance process; no friction was detected during inspection. The vibration spectrum also indicates that there is no friction or wear in the rotating components. Changing the lubricating oil in the hub is an essential part of the high-temperature fire-fighting axial flow fan’s maintenance. According to the manufacturer’s instructions, this high-temperature fire-rated axial flow fan requires a total of 45 litres of lubricating oil. Following feedback from the maintenance supervisor, it was found that the supervisor was unable to ascertain the supply of lubricating oil. Analysis indicates that the bearings are submerged in oil. If the quantity of lubricating oil is insufficient, the rotation of the high-temperature fire-rated axial flow fan causes the distribution of lubricating oil within the central reservoir to become uneven, resulting in mass imbalance and potentially increasing vibration. Furthermore, following operation and rotation, the distribution of lubricating oil within the central reservoir becomes irregular, resulting in unbalanced movement of the high-temperature fire-fighting axial fan and causing irregular fan vibration. 45 litres of lubricating oil were added to the reservoir in the fan hub, and the high-temperature fire-fighting axial fan was started. Analysis of the measured vibration data indicated that the counterweight added the previous day was precisely unbalanced. The counterweight added the previous day was removed, and the fan was restarted. The vibration levels of the high-temperature fire-fighting axial fan returned to pre-maintenance levels, achieving a satisfactory standard. 3. Conclusion The vibration of the high-temperature fire-fighting axial fan was caused by improper maintenance work; the analysis, diagnosis and resolution of the fan’s vibration were circuitous. This case study provides valuable reference for the maintenance and analysis of vibration faults in high-temperature fire-fighting axial fans of the same type.