Comprehensive Explanation of Bearing Failures
Bearing failures frequently occur during operation. The key lies in accurate fault diagnosis and proper troubleshooting. Below is a detailed introduction to the causes and solutions of common bearing failures.
01 Excessively High Bearing Temperature
A certain temperature rise at the bearing mounting position is acceptable during equipment operation. Under normal conditions, the housing should not feel hot when touched by hand; otherwise, the bearing temperature is excessive.
Causes of overheating:
Substandard or deteriorated lubricating oil; excessively high oil viscosity; overly tight assembly of mechanical components (insufficient clearance); excessively fitted bearing; creep of bearing raceway on the shaft or housing; overload; fracture of bearing cage or rolling elements.
02 Bearing Noise
Slight running noise is permissible for rolling bearings. Loud noise, abnormal sound or knocking noise indicates bearing faults.
Causes of noise generation in rolling bearings:
(1) Wear of mating surfaces between bearing inner and outer rings. Such wear destroys the fit between bearing and housing, bearing and shaft, leading to axis offset and abnormal noise during high-speed shaft operation. Bearing fatigue causes surface metal spalling, increasing radial clearance and triggering abnormal noise.
(2) Insufficient lubrication resulting in dry friction, as well as bearing breakage will produce abnormal sound.
(3) After bearing wear and loosening, loose or damaged cages will also cause abnormal noise and bearing damage.
When disassembling and inspecting rolling bearings, bearing faults and root causes can be judged according to damage conditions.
03 Metal Spalling on Raceway Surfaces
The rolling elements and raceways of inner and outer rings bear periodic fluctuating loads, generating periodically varying contact stress.
Causes of metal spalling on raceways:
Fatigue spalling occurs on the working surfaces of rolling elements or inner/outer raceways after a certain number of stress cycles. Excessive bearing load accelerates fatigue. In addition, improper bearing installation and shaft bending can also lead to raceway spalling. Fatigue spalling of bearing raceways reduces shaft operating accuracy and causes mechanical vibration and noise.
04 Bearing Burn
Burned bearings exhibit temper discoloration on raceways and rolling elements.
Causes of burning:
Insufficient lubrication, substandard or deteriorated lubricating oil, and excessively tight bearing fitting.
05 Plastic Deformation
Uneven pits appear on the contact surfaces between bearing raceways and rollers, indicating plastic deformation.
Causes of plastic deformation:
Under heavy static load or impact load, local stress on working surfaces exceeds the yield strength of materials. This phenomenon commonly occurs in low-speed rotating bearings.
06 Bearing Race Cracking
Causes of race cracking:
Excessively tight bearing fit, loose inner or outer ring, deformation of housing parts, poor machining quality of bearing mounting surfaces.
07 Cage Fracture
Causes of cage fracture:
Insufficient lubrication, broken rolling elements, skewed raceways.
In such cases, service and lubrication conditions shall be checked, and cage selection shall be re-evaluated.
08 Adhesion of Cage Metal to Rolling Elements
Causes:
Rolling elements jammed inside the cage or insufficient lubrication.
09 Severe Wear of Raceway
Causes:
Foreign matter entering the raceway, insufficient lubricating oil or improper lubricant grade.
10 Lubrication Failure
Discoloration (blue or brown) of raceways and rollers serves as a sign of lubrication failure, followed by wear of raceways, rollers and cages, which eventually leads to overheating and severe failure. The early feature is slight glass-like scratches on raceway surfaces.
Normal operation of rolling bearings relies on a sound oil film between components. Lubrication failure is usually caused by inadequate lubrication, improper lubrication (too much, too little, overly thick or thin lubricant) and ineffective lubrication (incorrect lubrication method, oil cutoff, overdue oil replacement).
11 Bearing Corrosion
Signs include reddish-brown areas on raceways, rollers, cages or other positions; the color is rust brown in the early stage and usually black in later stages.
Causes: Contact with corrosive fluids and gases. In severe cases, corrosion leads to premature fatigue failure of bearings.
Solution: Eliminate corrosive media and adopt sealed bearings whenever possible.
12 Bearing Misalignment (Uneven Load)
Sign of misalignment: The wear marks formed by balls on raceways are not parallel to the raceway edges. Severe misalignment causes abnormal temperature rise of bearings and bearing housings as well as ball wear on cages. Different bearing types have different allowable misalignment values. Generally, self-aligning bearings deliver the best misalignment tolerance. For other bearing types, misalignment resistance can be improved by optimizing raceway geometry.
13 Loose Bearing Fit
Loose fit triggers relative movement between mating components. Sustained slight relative movement generates wear, commonly referred to as creep.
This wear produces abrasive particles that oxidize into characteristic brown powder, aggravating abrasion and looseness.
If looseness expands to obvious movement of inner or outer rings, mounting surfaces (bore, outer diameter and side faces) will suffer wear and heat generation, resulting in noise and shaking.
01 Excessively High Bearing Temperature
A certain temperature rise at the bearing mounting position is acceptable during equipment operation. Under normal conditions, the housing should not feel hot when touched by hand; otherwise, the bearing temperature is excessive.
Causes of overheating:
Substandard or deteriorated lubricating oil; excessively high oil viscosity; overly tight assembly of mechanical components (insufficient clearance); excessively fitted bearing; creep of bearing raceway on the shaft or housing; overload; fracture of bearing cage or rolling elements.
02 Bearing Noise
Slight running noise is permissible for rolling bearings. Loud noise, abnormal sound or knocking noise indicates bearing faults.
Causes of noise generation in rolling bearings:
(1) Wear of mating surfaces between bearing inner and outer rings. Such wear destroys the fit between bearing and housing, bearing and shaft, leading to axis offset and abnormal noise during high-speed shaft operation. Bearing fatigue causes surface metal spalling, increasing radial clearance and triggering abnormal noise.
(2) Insufficient lubrication resulting in dry friction, as well as bearing breakage will produce abnormal sound.
(3) After bearing wear and loosening, loose or damaged cages will also cause abnormal noise and bearing damage.
When disassembling and inspecting rolling bearings, bearing faults and root causes can be judged according to damage conditions.
03 Metal Spalling on Raceway Surfaces
The rolling elements and raceways of inner and outer rings bear periodic fluctuating loads, generating periodically varying contact stress.
Causes of metal spalling on raceways:
Fatigue spalling occurs on the working surfaces of rolling elements or inner/outer raceways after a certain number of stress cycles. Excessive bearing load accelerates fatigue. In addition, improper bearing installation and shaft bending can also lead to raceway spalling. Fatigue spalling of bearing raceways reduces shaft operating accuracy and causes mechanical vibration and noise.
04 Bearing Burn
Burned bearings exhibit temper discoloration on raceways and rolling elements.
Causes of burning:
Insufficient lubrication, substandard or deteriorated lubricating oil, and excessively tight bearing fitting.
05 Plastic Deformation
Uneven pits appear on the contact surfaces between bearing raceways and rollers, indicating plastic deformation.
Causes of plastic deformation:
Under heavy static load or impact load, local stress on working surfaces exceeds the yield strength of materials. This phenomenon commonly occurs in low-speed rotating bearings.
06 Bearing Race Cracking
Causes of race cracking:
Excessively tight bearing fit, loose inner or outer ring, deformation of housing parts, poor machining quality of bearing mounting surfaces.
07 Cage Fracture
Causes of cage fracture:
Insufficient lubrication, broken rolling elements, skewed raceways.
In such cases, service and lubrication conditions shall be checked, and cage selection shall be re-evaluated.
08 Adhesion of Cage Metal to Rolling Elements
Causes:
Rolling elements jammed inside the cage or insufficient lubrication.
09 Severe Wear of Raceway
Causes:
Foreign matter entering the raceway, insufficient lubricating oil or improper lubricant grade.
10 Lubrication Failure
Discoloration (blue or brown) of raceways and rollers serves as a sign of lubrication failure, followed by wear of raceways, rollers and cages, which eventually leads to overheating and severe failure. The early feature is slight glass-like scratches on raceway surfaces.
Normal operation of rolling bearings relies on a sound oil film between components. Lubrication failure is usually caused by inadequate lubrication, improper lubrication (too much, too little, overly thick or thin lubricant) and ineffective lubrication (incorrect lubrication method, oil cutoff, overdue oil replacement).
11 Bearing Corrosion
Signs include reddish-brown areas on raceways, rollers, cages or other positions; the color is rust brown in the early stage and usually black in later stages.
Causes: Contact with corrosive fluids and gases. In severe cases, corrosion leads to premature fatigue failure of bearings.
Solution: Eliminate corrosive media and adopt sealed bearings whenever possible.
12 Bearing Misalignment (Uneven Load)
Sign of misalignment: The wear marks formed by balls on raceways are not parallel to the raceway edges. Severe misalignment causes abnormal temperature rise of bearings and bearing housings as well as ball wear on cages. Different bearing types have different allowable misalignment values. Generally, self-aligning bearings deliver the best misalignment tolerance. For other bearing types, misalignment resistance can be improved by optimizing raceway geometry.
13 Loose Bearing Fit
Loose fit triggers relative movement between mating components. Sustained slight relative movement generates wear, commonly referred to as creep.
This wear produces abrasive particles that oxidize into characteristic brown powder, aggravating abrasion and looseness.
If looseness expands to obvious movement of inner or outer rings, mounting surfaces (bore, outer diameter and side faces) will suffer wear and heat generation, resulting in noise and shaking.
