Multistage centrifugal pumps are widely used in chemical, petroleum, food, and other industries. The sliding bearing is one of the key components of a centrifugal pump, commonly known as the bush or bearing liner. The performance of the sliding bearing directly affects the overall operation of the pump. However, as it operates in complex environments, it is susceptible to various influencing factors. The main fault-inducing factors include quality defects, poor lubrication, improper installation, etc. Therefore, Anhui Shengshi Datang will analyze the faults of sliding bearings in multistage centrifugal pumps in this paper and propose corresponding solutions to ensure the normal operation of the equipment.
Fault Analysis and Treatment Methods
1. Bushing Seizure (Wipe Damage)
Fault Causes:
(1) Severe lack of lubricating oil in the lubrication system or bearing housing.
(2) The assembly clearance between the pump shaft journal and the bushing does not meet requirements.
(3) Pump shaft wear, with scratches, bruises, and corrosion on the surface.
(4) Deterioration of lubricating oil, incorrect oil grade, or water ingress into the oil.
Treatment Methods:
(1) Check the lubrication system to ensure sufficient lubricating oil and no leakage.
(2) Check the assembly clearance between the bushing and the journal to ensure it meets technical requirements.
(3) Repair the pump shaft to ensure its roundness, cylindricity, and surface roughness comply with quality standards.
(4) Change the lubricating oil regularly, check and ensure the correct oil grade is used, and keep the lubricating oil clean.
2. Bushing Alloy Spalling or Cracking
Fault Causes:
(1) Bushing quality issues or poor casting.
(2) Improper bushing installation, leading to uneven force distribution.
(3) Poor lubrication, causing overheating due to friction between the bushing and the journal.
Treatment Methods:
(1) Replace with a new bushing, or clean and re-pour/weld the alloy; check for sand holes, blowholes, impurities, debonding, cracks, etc., before installation.
(2) Ensure the bushing is installed correctly and bears load evenly.
(3) Improve lubrication to avoid excessive friction between the bushing and the journal.
3. Bushing Wear
Fault Phenomenon: Scuffing occurs between the bushing and the journal, with scratches, uneven surfaces, alloy layer smearing, and corrosion on the surface.
Fault Causes:
(1) Excessive or insufficient clearance between the bushing and the journal.
(2) Poor lubrication, such as insufficient lubricating oil or deteriorated oil.
(3) Foreign objects entering the bearing clearance.
(4) Pump shaft bending caused by excessive load, shaft material defects, machining errors, etc. When the pump shaft bending exceeds the limit, it directly affects the operation of the sliding bearing, increasing friction loss and vibration.
Treatment Methods:
(1) Adjust the clearance between the bushing and the journal to an appropriate range.
(2) Ensure the lubrication system works properly; replace deteriorated lubricating oil.
(3) Enhance filtration to prevent foreign objects from entering the bearing clearance.
(4) Replace or straighten the pump shaft.
4. High Vibration and Abnormal Noise Due to Improper Operation
Fault Phenomenon: Defects such as bushing looseness, excessive clearance, wear after oil supply interruption, leading to high vibration and noise, caused by improper operation and adjustment.
Fault Causes:
(1) Loosening of the bushing gland bolts.
(2) Improper operation and adjustment, resulting in excessive clearance between the bushing and the journal.
(3) Worsened wear after oil supply interruption, leading to increased vibration and temperature.
(4) Burning or spalling of the bushing alloy layer.
Treatment Methods:
(1) Tighten the bearing housing bushing gland bolts evenly.
(2) Check that the bearing alloy has no spalling, cracks, sand holes, blowholes, etc.; adjust the contact angle between the journal and the bushing to 60°–90°, with a contact area over 80%. Furthermore, adjust the clearance between the bushing and the journal to the appropriate range: top clearance should be (1.5–2)/1000 of the journal diameter, and side clearance should be half of the top clearance.
(3) Check the lubricating oil system; ensure good lubrication and cooling.
(4) Check and repair the burnt bushing alloy layer.
Measures to Prevent Sliding Bearing Failures
In summary, common faults of multistage centrifugal pump bushings are mainly caused by unreasonable design, poor lubrication, clearance exceeding standards, ingress of foreign objects, excessive load, etc., leading to unstable pump operation. Bushing wear will cause increased pump shaft vibration and noise, and in severe cases, can even lead to pump shutdown. To eliminate these faults, the following remedial measures can be taken.
1. Optimize Bearing Design
Optimize the structural design of the sliding bearing to improve its reliability and stability, targeting common faults. For example, use special materials for the bearing liner to increase its wear resistance and fatigue resistance; adopt a combination of hydrodynamic lubrication and hydrostatic/gas static lubrication to improve the bearing's lubrication effect.
2. Ensure Good Lubrication
Regularly check the lubrication condition of the bearing, replace the lubricant promptly, and maintain bearing lubrication. Also, ensure the quality and cleanliness of the lubricant. Meanwhile, reasonably select the type and amount of lubricant based on the actual operating conditions of the equipment.
3. Improve Assembly Quality
Bushing assembly involves dimensions, shape, fit tolerances, etc., to ensure the bushing can be correctly installed in the required position. Adjusting the bushing clearance ensures the fit tolerance between the bushing and the journal is within the specified range, thereby improving the installation quality of the bushing.
After bushing installation is completed, inspection work is necessary to ensure the bushing is installed correctly and the quality is qualified. Through testing, it can be checked whether the bushing is installed correctly, and the installation quality can be judged. In short, improving bushing installation quality requires a comprehensive understanding of bushing assembly knowledge, strict adherence to operating procedures, and working according to relevant dimensions. Through reasonable clearance adjustment and strict inspection, the installation quality of the bushing can meet the specified requirements.
4. Prevent Overload Operation
During pump operation, overload operation should be avoided. Overload operation causes the pump bearings to withstand excessive loads, accelerating bearing wear and fatigue. That is, the pump speed and load should be within a reasonable range to reduce bearing wear and fatigue.
5. Control Pump Operating Temperature
Excessively high pump operating temperature can lead to poor bearing lubrication and accelerated wear. Therefore, measures should be taken to control the pump's operating temperature, such as installing coolers, enhancing ventilation, etc.
6. Regular Inspection and Maintenance
Regularly inspect and maintain the bearings, including cleaning the bearings, replacing the lubricant, and checking the wear condition of the bearings. If bearing faults are found, they should be addressed promptly to prevent fault escalation.
7. Implement Vibration Control Measures
The implementation of vibration control measures is crucial for ensuring normal pump operation. Vibration may occur during pump operation; if not controlled, it can adversely affect the bearings, impacting the pump's service life and stability. Reduce vibration by adding dampers and reinforcing the foundation, among other measures.
8. Select the Appropriate Bearing Type
When selecting a bearing type, comprehensive consideration based on the pump's working conditions and requirements is needed to choose the appropriate bearing type and specification. Many factors need to be considered, including bearing load, speed, environmental conditions, size, and cost. Under the pump's working conditions, horizontal split sleeve bearings (upper and lower halves) are a suitable choice, as they usually offer good lubrication performance and load capacity. At the same time, attention must also be paid to the installation and maintenance of the bearing to ensure its normal operation and extend its service life.
9. Strengthen Employee Training
Operators should strictly follow equipment regulations for operation, avoiding overload operation or unstable speed. Therefore, employee training should be strengthened to improve the skill level of operators.
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