In mechanical equipment such as motors and fans, sliding bearings are very important mechanical components. Sliding bearings mainly bear loads by using the pressure generated by fluid dynamic oil film, and their operating properties determine that they may experience wear. If sliding bearings experience wear, their working efficiency will also decrease. In severe cases, sliding bearings cannot function properly, thereby affecting the normal operation of the entire machinery. This article mainly studies the wear of sliding bearings in the main exhaust fan, providing reference materials for the practical application of sliding bearings.
1. Reasons for wear of sliding bearings in the main exhaust fan
The wear of sliding bearings usually includes scratches, slight wear, or severe wear. According to the actual wear situation of sliding bearings, the main reasons for wear are as follows.
Firstly, the load is too heavy. The main function of sliding bearings is to bear loads, but if the load they bear is too large, the sliding bearings will generate high heat during operation. Continuous high temperatures will reduce the adhesion of the metal, causing the surface material of the sliding bearings to fall off and wear out.
Secondly, foreign objects enter the sliding bearing. During the operation of sliding bearings, if hard foreign objects enter the clearance of the sliding bearings, the hard foreign objects will rub against the surface of the bearings, causing wear on the bearings.
Thirdly, the position of the sliding bearing is improper. Mechanical management personnel did not install the sliding bearings on the centerline during assembly, resulting in bearing misalignment. During operation, one end of the sliding bearings experiences severe friction, and the heat generated by friction causes metal fatigue on the bearing surface, leading to bearing damage.
Fourthly, there is insufficient lubrication of the bearings. Mechanical management personnel did not strictly follow the relevant regulations to lubricate the sliding bearings during maintenance, or made mistakes in lubrication, resulting in insufficient oil supply to the sliding bearings during operation, causing fluid dynamic oil film rupture and resulting in wear, biting, and other situations. In addition, reasons such as oil leakage, poor oil flow, oil pump obstruction, oil network blockage, and pressure reducing valve spring failure may all lead to insufficient oil supply during the operation of sliding bearings. This type of oil interruption fault can also cause wear and failure of sliding bearings.
Fifth, the corrosive effect of acidic substances or cavitation. Sliding bearings need to operate under the action of lubricating oil, but the acidic substances in the lubricating oil have a corrosive effect on the metal, causing the surface material of the sliding bearing to gradually corrode, resulting in local or large parts of the bearing surface material deteriorating. Cavitation refers to the formation and collapse of hollow bubbles in the outer oil, which significantly increases the local pressure and increases the pressure at the local position of the sliding bearing, causing excessive load on the sliding bearing and resulting in wear.
In practical applications, mechanical engineers usually carefully choose the material of bearings to ensure that the sliding bearings are coaxial with the shaft neck during operation, thereby preventing serious damage to the sliding bearings. In general, when mechanical engineers choose the material for sliding bearing bushings, they will choose to use lead based Babbitt alloy. Babbitt alloy has strong corrosion resistance, sintering resistance, and inlay resistance, and its ability to accommodate different shafts is also good, making it an ideal material for sliding bearings. Normally, when sliding bearings begin to wear, the Babbitt alloy layer is usually damaged first. When the experimenters applied the iron spectrum analysis method to analyze the composition of the oil sample, the proportion of Babbitt alloy was significantly higher.
2. Main exhaust fan failure case
The sliding bearing liner of the main exhaust fan studied in this article is made of lead based Babbitt alloy. The power of the motor is 9300kW, the wind pressure is 2000mmH2O, and the exhaust volume is 21000m3/min. Its actual structure is shown in Figure 1. When the mechanical maintenance personnel were maintaining the bearings of the main exhaust fan, they analyzed the composition of the oil sample. However, the direct reading iron spectrum analysis data of the oil sample showed significant differences from the previous inspection data, and the data value increased significantly. The DL value of the large abrasive grain reading significantly increased, and there were more tin and lead elements present.
1. Motor 2. Couplings 3. Fan
Figure 1 Sliding bearing of main exhaust fan
There are fewer sliding abrasive particles on the analyzed iron spectrum plate, while more non-ferrous metal particles are deposited along the entire length of the analyzed iron spectrum plate, about 10-20 μ m. These particles are randomly arranged on the analyzed iron spectrum plate according to the direction of magnetic lines, presenting as a granular and non smooth mass on the surface. The substance has a deep color and can absorb most of the light. When polarized light is used to irradiate the substance, there is no scintillation light on the surface of the substance, indicating that the substance is not black iron oxide.
These wear particles are mainly Babbitt alloy in the sliding bearing liner, which suggests that there is wear on the bearing liner, and it is caused by inadequate lubrication. Mechanical maintenance personnel have issued relevant warnings. When the mechanical maintenance personnel conducted the oil sample inspection of the main exhaust fan bearing, they also analyzed the vibration situation, and the vibration situation analysis results did not show any abnormal conditions. All vibration parameters were normal, which resulted in the wear situation not being dealt with in a timely manner.
One month later, the mechanical maintenance personnel conducted another inspection on the oil sample of the main exhaust fan oil bearing. The experimental test results were consistent with the previous test results. The Babbitt alloy content in the oil sample was high and there was melting. Some Babbitt alloy abrasive surfaces had already formed a spherical shape, indicating that the wear of the sliding bearing was still developing. It is recommended to stop the machine for maintenance and carefully analyze the damage to the bearing and other components.
Afterwards, the mechanical maintenance personnel dismantled the bearing shells of the main exhaust fan. The four sample points shown in Figure 1 were all worn, and the degree of wear varied. The sliding bearing liner was scratched, and some surface metal fell off. After replacing the sliding bearing with a new bearing shell, its operation returned to normal.
The case of this study mainly applied oil sample analysis method to predict mechanical faults, and the application value of oil sample analysis method in early mechanical fault prediction is higher than vibration analysis. The main reason is that the main exhaust fan does not have very obvious faults, and its various devices and parts are in normal working condition, without obvious vibration abnormalities. Therefore, oil sample analysis method should be used for early fault prediction to reduce the occurrence of adverse events such as severe wear and bite. If the iron spectrum analysis technology is not applied in this inspection, and only vibration analysis is relied on for fault diagnosis, the sliding bearing Z will eventually bite due to severe wear, and the bearing will fail, causing the entire unit to shut down.
3. Discussion on Ferrographic Analysis Technology
In mechanical equipment, sliding bearings are commonly used, but they are prone to wear and tear. In practical applications, the iron spectrum analysis method can be used to monitor and analyze the composition of oil samples, thereby timely detecting abnormal situations and facilitating mechanical maintenance personnel to troubleshoot in a timely manner. Although vibration analysis can also effectively detect mechanical operation faults, the troubleshooting of wear faults is difficult, and in the early stages of sliding bearing wear, its working state is still normal, and wear does not affect the normal operation of other parts. Therefore, the overall vibration parameters of the machinery may be within the normal parameter range, making it impossible to effectively predict obstacles.
Unlike vibration analysis methods, ferrography analysis can effectively detect a large number of abrasive particles, providing scientific basis for early troubleshooting. However, in practical applications, due to the high sensitivity of ferrography to ferromagnetic substances, but the slow response to non-magnetic substances, if the amount of non-magnetic substances is not large, ferrography analysis may fail. From this, it can be seen that the application difficulty of ferrography analysis in predicting wear faults of sliding bearings is relatively high. In this regard, enterprises should actively strengthen their research on fault prediction technology, carefully study the causes of wear and tear of the main exhaust sliding bearings, accumulate experience, and propose effective measures to prevent the occurrence of faults, thereby reducing the occurrence of sliding bearing failures, minimizing economic losses caused by faults, and improving the economic efficiency of enterprises.
4. Conclusion
Sliding bearings are an important component of the main exhaust fan, and their operating status directly affects the overall efficiency of the machinery. From a theoretical perspective, the use of ferrography analysis can effectively predict the wear of sliding bearings, providing maintenance personnel with inspection basis and thus maintaining the normal operation of machinery. However, the practical application of ferrography analysis is difficult, and enterprises should strengthen their research on ferrography analysis technology, accumulate more experience in mechanical fault prediction and handling, improve mechanical work efficiency, and lay a good foundation for the development of enterprises.
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