What You Should Know About Bearing Failures
Contact Fatigue Failure
Contact fatigue failure refers to failure occurring on bearing working surfaces under alternating stress. Contact fatigue spalling originates beneath the contact surface at the position of maximum alternating shear stress, accompanied by fatigue cracks. The cracks then propagate to the surface and form spalls of various shapes. Pitting or speck spalling appears in dot form, while small sheet-shaped spalling is defined as shallow spalling. As the spalled area expands gradually and extends inward, deep spalling is formed, which serves as the fatigue initiation source of contact fatigue failure.
Wear Failure
Wear failure occurs when continuous relative sliding friction between surfaces abrades metal on working surfaces. Progressive wear gradually damages bearing components, eventually resulting in loss of dimensional accuracy and other associated problems. Wear may alter geometric profiles, increase fitting clearances and change surface topography. It can contaminate lubricants to such an extent that lubrication completely fails, leading to loss of rotational precision or even complete bearing seizure. Wear failure is one of the common failure modes for all types of bearings. It is generally divided into two primary forms: abrasive wear and adhesive wear.
Abrasive wear is triggered when foreign hard particles, rigid contaminants or metal wear debris are squeezed between mating bearing surfaces during relative movement, creating furrow-like scratches on bearing raceways. Hard particles or contaminants may originate inside the main equipment or adjacent components and be carried into the bearing by lubricants.
Adhesive wear arises from uneven stress distribution caused by microscopic asperities or foreign matter on friction surfaces. Under severely degraded lubrication conditions, localized frictional heat leads to surface deformation and micro-welding. In severe cases, surface metal may partially melt. Shear force tears the micro-welded joints from the base material and intensifies plastic deformation. This repeated cycle of adhesion, tearing and re-adhesion forms adhesive wear. Generally, mild adhesive wear is defined as scoring, while severe adhesive wear is referred to as seizure.
Fracture Failure
Bearing fracture failure is mainly caused by two factors: material defects and overload. Overload fracture happens when external loads exceed the material strength limit. It is usually induced by sudden malfunctions of main equipment or improper installation. Defects such as microcracks, shrinkage cavities, pores, large inclusions, overheated microstructure and local burning on bearing components can trigger fracture at defective locations under impact overload or intense vibration, known as defect fracture.
It should be noted that the above defects can be accurately detected via instruments during raw material incoming inspection, forging & heat treatment quality control and machining processes, and relevant control measures must be continuously strengthened. Nevertheless, most bearing fracture failures in practical operation are overload fractures.
Clearance Variation Failure
During operation, external or internal factors alter the original fitting clearance of bearings, reduce precision and even result in seizure. This phenomenon is defined as clearance variation failure.
Major external triggers include excessive interference, improper installation, thermal expansion caused by temperature rise and transient overload. Internal factors cover unstable retained austenite and residual stress.
If bearings are well lubricated and effectively isolated from contaminants and moisture, the oil seals are likely intact. However, it is recommended to inspect bearings and oil seals regularly when opening the bearing housing. Check the condition of oil seals adjacent to bearings to confirm they can prevent hot fluid, corrosive liquid or gas from penetrating along the shaft into the bearing. Worn oil seals shall be replaced promptly.
High temperature is frequently a sign of abnormal bearing operation and also deteriorates internal lubricants. Occasionally, overheating originates from inappropriate lubrication. Long-term bearing operation above 125°C will shorten service life.
Common causes of excessive bearing temperature include insufficient or excessive lubrication, contaminants inside lubricants, overloading, bearing damage, insufficient clearance and high frictional heat generated by oil seals.
Monitor the operating status of running machinery to prevent unplanned equipment shutdown.
Contact fatigue failure refers to failure occurring on bearing working surfaces under alternating stress. Contact fatigue spalling originates beneath the contact surface at the position of maximum alternating shear stress, accompanied by fatigue cracks. The cracks then propagate to the surface and form spalls of various shapes. Pitting or speck spalling appears in dot form, while small sheet-shaped spalling is defined as shallow spalling. As the spalled area expands gradually and extends inward, deep spalling is formed, which serves as the fatigue initiation source of contact fatigue failure.
Wear Failure
Wear failure occurs when continuous relative sliding friction between surfaces abrades metal on working surfaces. Progressive wear gradually damages bearing components, eventually resulting in loss of dimensional accuracy and other associated problems. Wear may alter geometric profiles, increase fitting clearances and change surface topography. It can contaminate lubricants to such an extent that lubrication completely fails, leading to loss of rotational precision or even complete bearing seizure. Wear failure is one of the common failure modes for all types of bearings. It is generally divided into two primary forms: abrasive wear and adhesive wear.
Abrasive wear is triggered when foreign hard particles, rigid contaminants or metal wear debris are squeezed between mating bearing surfaces during relative movement, creating furrow-like scratches on bearing raceways. Hard particles or contaminants may originate inside the main equipment or adjacent components and be carried into the bearing by lubricants.
Adhesive wear arises from uneven stress distribution caused by microscopic asperities or foreign matter on friction surfaces. Under severely degraded lubrication conditions, localized frictional heat leads to surface deformation and micro-welding. In severe cases, surface metal may partially melt. Shear force tears the micro-welded joints from the base material and intensifies plastic deformation. This repeated cycle of adhesion, tearing and re-adhesion forms adhesive wear. Generally, mild adhesive wear is defined as scoring, while severe adhesive wear is referred to as seizure.
Fracture Failure
Bearing fracture failure is mainly caused by two factors: material defects and overload. Overload fracture happens when external loads exceed the material strength limit. It is usually induced by sudden malfunctions of main equipment or improper installation. Defects such as microcracks, shrinkage cavities, pores, large inclusions, overheated microstructure and local burning on bearing components can trigger fracture at defective locations under impact overload or intense vibration, known as defect fracture.
It should be noted that the above defects can be accurately detected via instruments during raw material incoming inspection, forging & heat treatment quality control and machining processes, and relevant control measures must be continuously strengthened. Nevertheless, most bearing fracture failures in practical operation are overload fractures.
Clearance Variation Failure
During operation, external or internal factors alter the original fitting clearance of bearings, reduce precision and even result in seizure. This phenomenon is defined as clearance variation failure.
Major external triggers include excessive interference, improper installation, thermal expansion caused by temperature rise and transient overload. Internal factors cover unstable retained austenite and residual stress.
If bearings are well lubricated and effectively isolated from contaminants and moisture, the oil seals are likely intact. However, it is recommended to inspect bearings and oil seals regularly when opening the bearing housing. Check the condition of oil seals adjacent to bearings to confirm they can prevent hot fluid, corrosive liquid or gas from penetrating along the shaft into the bearing. Worn oil seals shall be replaced promptly.
High temperature is frequently a sign of abnormal bearing operation and also deteriorates internal lubricants. Occasionally, overheating originates from inappropriate lubrication. Long-term bearing operation above 125°C will shorten service life.
Common causes of excessive bearing temperature include insufficient or excessive lubrication, contaminants inside lubricants, overloading, bearing damage, insufficient clearance and high frictional heat generated by oil seals.
Monitor the operating status of running machinery to prevent unplanned equipment shutdown.
