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1. Preface
As the core rotary load-bearing component of construction machinery, lifting equipment and wind power equipment, slewing bearings serve as the “joint hub” of mechanical equipment. Their operational stability directly affects equipment working efficiency, service life and construction safety. Abnormal noise, vibration, overheating, oil leakage and jamming are the five core failure precursors of slewing bearings during operation. Due to ambiguous diagnostic standards, most operation and maintenance personnel either conduct excessive maintenance on minor faults or delay the disposal of severe faults, resulting in increased maintenance costs and potential safety hazards.
Based on universal industrial technical standards, this paper systematically analyzes the normal operating conditions, abnormal symptoms and accurate diagnosis methods of the five types of faults, clarifies the critical criteria for maintenance, repair and scrapping, and provides a simplified operation and maintenance decision-making process. It serves as a standardized technical basis for daily equipment inspection, fault disposal and parts replacement.
2. General Guidelines for Fault Diagnosis
All judgment parameters specified in this manual comply with ISO 10816-3 mechanical vibration standards and universal industrial manufacturing and operation & maintenance specifications for slewing bearings. The manual is applicable to ball-type and roller-type general slewing bearings and covers the operation and maintenance scenarios of rotary mechanisms for conventional construction machinery and lifting equipment.
3. Accurate Diagnosis and Disposal Standards for Five Major Fault Precursors
Precursor 1: Abnormal Operating Noise (Acoustic Fault Precursor)
1. Normal Operating Condition: During no-load rotation of the equipment, only uniform and gentle rolling “rustling” sound of steel balls can be heard, without periodic abnormal noise or miscellaneous sound, and the volume remains stable without fluctuation.
2. Abnormal Fault Symptoms: Irregular “clicking” or “creaking” friction and jamming sounds, or continuous periodic howling and sharp friction noises occur during operation, which are significantly aggravated under load conditions.
3. Accurate Diagnosis Key Points
① Mounting Plane Inspection: Use a 0.02mm feeler gauge to fully detect the equipment mounting reference plane. If the flatness error exceeds 0.1mm/m, uneven stress on the slewing bearing will cause abnormal noise, and the mounting plane shall be ground and leveled.
② Lubrication Condition Verification: Stop the equipment and manually rotate the bearing body. Excessive rotation resistance and dry jamming indicate insufficient lubrication. Standard lubrication cycle: replenish grease every 100 operating hours for ball-type slewing bearings and every 50 operating hours for roller-type slewing bearings.
③ Raceway Foreign Matter Inspection: Disassemble the end seal strip to visually inspect the internal condition of the raceway. If contaminants such as iron filings and sand exist, thoroughly clean the raceway and replace the seal accessories with new ones.
4. Critical Criteria for Maintenance & Scrapping
Maintainable: Abnormal noise caused by mounting plane deviation, slight bolt misalignment, insufficient lubrication or minor impurities can be completely eliminated after leveling, grease replenishment and cleaning, restoring normal operation.
Mandatory Scrapping: Abnormal noise is accompanied by surface peeling and wear of the raceway with a peeling depth greater than 0.5mm, or the deformation and wear rate of rolling elements exceeds 5%. Permanent structural damage occurs, and the operational accuracy and safety cannot be guaranteed after repair.
Precursor 2: Operating Vibration (Mechanical Fault Precursor)
1. Normal Operating Condition: Under low-speed no-load and load operating conditions, the equipment vibration value is ≤ 0.1mm/s (in compliance with ISO 10816-3 standard), without jitter or periodic impact.
2. Abnormal Fault Symptoms: The no-load vibration value exceeds 0.3mm/s. Obvious periodic impact, body jitter and rotary shaking occur during load operation, which greatly reduces operational stability.
3. Accurate Diagnosis Key Points
① Gear Meshing Inspection: Adopt the red lead powder coating method to detect the gear meshing condition. If the gear tooth contact spot coverage is less than 60%, it is judged as gear gap deviation, and the meshing gap shall be precisely adjusted.
② Fastening Bolt Re-inspection: Re-tighten all mounting bolts at 110% of the design standard torque, and immediately tighten any loose bolts with insufficient torque evenly.
③ Dynamic Fault Detection: Simulate the actual load condition of the equipment on a special test bench for dynamic balance test to accurately locate core fault points such as eccentricity and meshing deviation.
4. Critical Criteria for Maintenance & Scrapping
Maintainable: Vibration faults caused by gear meshing misalignment, bolt looseness, mounting eccentricity and other assembly and commissioning problems can be eliminated after adjustment, tightening and calibration, with the vibration value returning to the standard range.
Mandatory Scrapping: Long-term vibration causes crack and deformation of the gear ring, or the raceway ellipticity error exceeds 0.02mm, resulting in irreversible structural deformation that cannot be repaired by commissioning.
Precursor 3: Abnormal Temperature Rise (Thermodynamic Fault Precursor)
1. Normal Operating Condition: After continuous equipment operation, the temperature rise of the slewing bearing is ≤ 35℃ (based on ambient temperature), without local overheating or abnormal heat generation.
2. Abnormal Fault Symptoms: Local hot spots on the bearing exceed 80℃, or the temperature rises sharply in a short time, accompanied by overheating and peculiar smell.
3. Accurate Diagnosis Key Points
① Heat Source Location: Scan the overall bearing with an infrared thermal imager to accurately locate local overheating areas and check for local excessive friction caused by long-term eccentric load and uneven stress.
② Grease Inspection: Sample and detect the viscosity and oxidation degree of in-service grease. Completely remove old grease and replace with new special grease if the grease is black, thin, caked or aged and invalid.
③ Heat Dissipation System Inspection: Ensure the heat sink is free of dust and oil blockages, and the cooling fan operates at rated speed to meet heat dissipation requirements.
4. Critical Criteria for Maintenance & Scrapping
Maintainable: Abnormal temperature caused only by aging, insufficient grease or poor heat dissipation can be eliminated after grease replacement and heat dissipation system cleaning, restoring the standard temperature rise.
Mandatory Scrapping: High-temperature friction causes blue oxidation burning layers on the raceway surface, or the hardness of the raceway and rolling elements decreases by more than HRC 5 degrees. The metal structural performance is damaged with risks of fracture and jamming.
Precursor 4: Seal Leakage (Sealing System Fault Precursor)
1. Normal Operating Condition: Only a uniform thin oil film (for lubrication and protection) exists at the seal interface, without oil seepage, dripping or grease overflow.
2. Abnormal Fault Symptoms: Linear grease outflow and continuous oil seepage and dripping occur at the seal position, or the seal strip is aged, hardened, cracked and fallen off, resulting in sealing failure.
3. Accurate Diagnosis Key Points
① Seal Structure Maintenance: Slight wear of single-lip seals can be partially repaired for reuse; double-lip seals with damage, cracking or aging shall be completely replaced instead of being repaired.
② Sealing Pressure Test: Inject 0.2MPa air pressure into the seal cavity after maintenance. Qualified sealing is confirmed if no pressure relief or leakage occurs after 5 minutes of pressure holding.
③ Working Condition Adaptation Optimization: For harsh working conditions with heavy dust, sand and open-air exposure, priority shall be given to adopting enhanced seals with dust scrapers to prevent impurity intrusion.
4. Critical Criteria for Maintenance & Scrapping
Maintainable: Only the seal parts are aged and damaged without damage to the raceway and rolling elements. The overall sealing performance meets the standard after seal replacement and sealing test.
Mandatory Scrapping: Long-term leakage causes raceway rusting and oxidation with a rust area exceeding 10%, or dry friction due to oil shortage leads to jamming and severe wear of rolling elements.
Precursor 5: Jamming and Functional Failure (Ultimate Structural Fault)
1. Normal Operating Condition: The equipment operates smoothly with a rotation speed fluctuation ≤ 5% and qualified rotation accuracy, featuring smooth start and stop without jamming.
2. Abnormal Fault Symptoms: The slewing bearing operates unsmoothly with jamming during start and stop. In severe cases, it is completely locked with total loss of rotation accuracy and fails to operate normally.
3. Accurate Diagnosis Key Points
① Gear Damage Detection: Inspect the condition of gear rings and teeth. Scrapping is mandatory if more than 3 teeth are broken or chipped.
② Raceway Accuracy Detection: Use a laser profiler to scan raceway wear and peeling. Peeling and depression depth greater than 1mm indicates irreparable damage.
③ Load Condition Verification: Bearings operating under 150% overload of the design rated load for a long time suffer from overall structural fatigue damage, which requires downgrade evaluation or direct scrapping.
4. Critical Criteria for Maintenance & Scrapping
Maintainable: Jamming is only caused by external foreign matter intrusion and minor impurity blockage. The rotation function and operational accuracy can be fully restored after thorough foreign matter removal.
Mandatory Scrapping: Functional failure is accompanied by overall structural deformation, large-area raceway peeling and multi-tooth fracture, or the remaining service life of the equipment is less than 500 hours. Repair is economically unviable and poses potential safety hazards.
4. 3-Step Decision-Making Process for Operation & Maintenance
To quickly and accurately determine fault disposal schemes and unify operation and maintenance standards, the following three-step decision-making process can be adopted:
1. Symptom Positioning: Classify equipment fault types and lock core fault causes according to the above five fault precursors.
2. Data Comparison: Compare the measured parameters such as vibration, temperature, wear and deformation with equipment design standards and industrial standards to confirm fault levels.
3. Cost Judgment: Prioritize repair if the total maintenance cost is lower than 30% of the price of a new part; adopt direct scrapping and replacement if the maintenance cost is excessive or structural damage is severe.
5. Operation & Maintenance Summary and Preventive Suggestions
Most slewing bearing failures are caused by inadequate daily inspection, untimely lubrication, overload operation and seal failure. Compared with post-fault maintenance and replacement, regular preventive maintenance can greatly extend equipment service life and reduce operation and maintenance costs.
It is recommended to conduct a comprehensive special inspection every 500 operating hours, and adopt intelligent monitoring equipment such as vibration and temperature sensors to realize early fault warning. Adhere to the principle of “repair when repairable, scrap when necessary”. When repair is economically unviable or the equipment has potential structural safety hazards, timely scrapping and replacement shall be implemented to avoid operation with faults and ensure safe and stable equipment operation.