Common Slewing Bearing Failures and How to Prevent Them

Slewing bearings are critical components in heavy machinery such as cranes, excavators, wind turbines, and material handling equipment, enabling smooth rotational movement under extreme loads. Despite their robust design, these bearings are susceptible to a range of failures that can lead to costly downtime, unsafe operating conditions, and premature replacement. Understanding the root causes of these failures—and implementing targeted prevention strategies—is essential for maximizing equipment reliability and total cost of ownership. This article examines the most common slewing bearing failure modes experienced across industries and provides actionable prevention guidance, with insights from LYMC, a leading manufacturer known for precision-engineered slewing bearings.

1. Material Spalling and Flaking

Spalling, also referred to as flaking or pitting, is the gradual removal of metal from the raceway surfaces or rolling elements. It is the most frequently reported failure mode in slewing bearings, often resulting in vibration, noise, and eventual seizure.

Root Causes

• Overloading: Excessive static or dynamic loads beyond the bearing’s rated capacity cause subsurface fatigue, initiating cracks that propagate to the surface.
• Inadequate lubrication: Insufficient or degraded grease fails to form a protective elastohydrodynamic film, leading to metal-to-metal contact and accelerated wear.
• Contamination: Hard particles such as sand, dust, or metal debris enter the bearing raceways, acting as abrasives that induce micro-cracking.
• Misalignment: Angular misalignment between the bearing rings concentrates stress on localized areas, promoting early spalling.

Prevention Measures

• Strictly adhere to the manufacturer’s load ratings and avoid shock loads during operation.
• Implement a scheduled relubrication program using high-quality grease appropriate for the operating environment (temperature, moisture, speed).
• Use proper sealing solutions such as labyrinth seals or elastomeric lip seals to keep contaminants out. LYMC bearings feature advanced multi-lip seal designs that provide superior ingress protection.
• Verify alignment during installation with a dial indicator or laser alignment tool; shim as needed to achieve parallelism within 0.1 mm per meter.

2. Cracked Rings or Fractured Raceways

Cracking—whether in the inner ring, outer ring, or rolling elements—is a catastrophic failure that often results in immediate equipment stoppage and potential safety hazards.

Root Causes

• Brinelling: High static impact loads (e.g., during transport or improper lifting) create indentations that act as stress raisers, leading to ring fracture.
• Thermal stress: Rapid temperature changes or uneven heating (e.g., from welding nearby) can cause differential expansion and cracking.
• Hydrogen embrittlement: In corrosive environments, hydrogen atoms diffuse into the steel, reducing toughness and causing sudden fracture.
• Material defects: Inclusions, porosity, or improper heat treatment in inferior bearings create weak points.

Prevention Measures

• Never lift or transport equipment by the slewing bearing; use designated lifting points. LYMC recommends protective shipping brackets that prevent rotation during transit.
• Control welding or cutting operations near the bearing: keep heat sources at least 300 mm away, or use heat shields.
• In corrosive environments, specify bearings with stainless steel or zinc-nickel coating; LYMC offers customized protective coatings for offshore and chemical plant applications.
• Source bearings from reputable manufacturers with ISO 9001 certification and ultrasonic inspection of raw materials. Every LYMC bearing is 100% inspected for internal defects.

3. Excessive Wear and Clearance Increase

Gradual wear of raceways and rolling elements leads to increased internal clearance (axial and radial play), which compromises positioning accuracy, causes vibration, and accelerates further damage.

Root Causes

• Insufficient lubrication frequency: Grease degrades over time; without regular replenishment, the lubricant film breaks down.
• Incorrect grease type: Using grease with wrong base oil viscosity (too low for heavy loads, too high for high speeds) fails to maintain film thickness.
• Fretting corrosion: Micro-motion between the bearing and mounting surfaces in the presence of vibration leads to debris generation.
• Oscillating operation: Bearings that only rotate through a small angle (e.g., in luffing cranes) do not fully distribute grease, leading to localized wear.

Prevention Measures

• Follow the lubrication schedule recommended by LYMC: typically relubricate every 100 operating hours or weekly, whichever comes first. Use the grease quantity formula: Q (grams) = 0.005 × bearing outer diameter (mm) × bearing width (mm).
• Select grease with NLGI grade 2, mineral or synthetic base oil, and EP additives for heavy-load applications.
• For oscillating applications, use a central lubrication system that injects grease when the bearing rotates through its full travel arc at least once per shift.
• Regularly measure internal clearance (with a dial indicator) and compare to the original factory specification; replace when clearance exceeds 1.5 times the initial value.

4. Noise and Vibration Abnormalities

While some noise is inherent during operation, a sudden increase in noise level or the appearance of rhythmic vibration indicates a developing fault. Operators often detect this failure in its early stage.

Root Causes

• Brinelling or denting: Hard impacts create surface irregularities that generate periodic noise each time a rolling element passes over them.
• Loose mounting bolts: Inadequate bolt preload allows relative movement between bearing rings and supporting structure, causing a rumbling sound.
• Worn cage: The rolling element separator (cage) wears over time, leading to element bunching and irregular rotation noise.
• Resonance: The natural frequency of the structure coincides with the bearing’s rotational speed, amplifying vibration.

Prevention Measures

• Perform regular condition monitoring using vibration analysis (accelerometers). Set alarms at 2.5 mm/s RMS; investigate any increase of 1.5x from baseline.
• Torque all mounting bolts to the specified value (e.g., 10.9 grade bolts for M20: 490 Nm) using a calibrated torque wrench; retighten after the first 50 hours of operation.
• Inspect cages during major overhauls. LYMC uses high-strength polyamide or brass cages with optimized pocket geometry to reduce wear.
• If resonance is detected, adjust the operating speed or add tuned mass dampers to shift the natural frequency.

5. Corrosion and Rusting

Corrosion attacks raceways, rolling elements, and sealing surfaces, causing pitting, compromised seals, and ultimately bearing seizure. It is especially prevalent in offshore, chemical, and food processing environments.

Root Causes

• Exposure to water, steam, salt spray, or aggressive chemicals.
• Inadequate grease barrier: standard lithium grease offers minimal corrosion protection.
• Condensation buildup inside the bearing due to temperature cycling (night/day).
• Damage to the protective coating during installation or maintenance.

Prevention Measures

• Use bearings with anti-corrosion treatments: LYMC offers electroless nickel plating, zinc phosphating, or duplex coating (zinc + epoxy paint) depending on the severity of the environment.
• Select grease with excellent corrosion inhibitors (e.g., barium complex or calcium sulfonate thickeners).
• Install breather plugs or pressure equalization valves to allow moisture escape without contaminant entry.
• Perform weekly visual inspections: look for rust trails near seals. If corrosion is detected early, the bearing can be cleaned and regreased; severe cases require replacement.

Conclusion: A Systematic Approach to Prevention

The most effective way to prevent slewing bearing failures is to adopt a comprehensive strategy that combines proper selection, correct installation, regular lubrication, and condition monitoring. Understanding that each failure mode often has multiple contributors—and that addressing one root cause can mitigate several risks—is key. LYMC provides complete technical support, from load calculation tools to on-site installation training, ensuring that your slewing bearings achieve their full design life. By partnering with a manufacturer that prioritizes quality materials, precision manufacturing, and rigorous testing, you minimize the likelihood of premature failure and maximize the return on your equipment investment. For specific failure analysis or to discuss your application’s unique challenges, contact LYMC’s engineering team.