Common causes of bearing damage

A bearing is generally usable until the end of its fatigue life, but it can also fail earlier due to improper mounting, fit, lubrication or handling. The main failure modes and their underlying causes are described in ISO 15243 and are based on visible damage to surfaces in contact with the rolling element or to other functional surfaces of bearings.

These failure modes include:
Fatigue, which can appear on the surface or below the surface
Wear, including abrasive and adhesive wear
Corrosion, including corrosion from moisture and friction (including vibration corrosion and pitting)
Electrical erosion, including excessive voltage and current leakage
Plastic deformation, especially due to overloading, nicks, debris, and fingerprints from handling
Fracture and cracking, including force fracture, fatigue failure, and thermal cracking

Fatigue is due to repeated stresses on the contact surfaces between rolling elements and raceways and leads to changes in the structure of the materials. It appears as flaking or crumbling and manifests itself mainly on the surface. The cause of this type of damage is usually inadequate lubrication. Fatigue below the surface is rare and occurs after very long operating times. To avoid this type of damage, the type and condition of the grease as well as the tightness and load conditions should be checked and adjusted as necessary.

Wear occurs when foreign objects enter the bearing assembly. It can be sand or fine metal particles from grinding or machining, as well as metal particles from the wear of gears. These foreign objects can cause internal play and misalignment, thereby reducing bearing life. One solution to avoid this type of damage is to add seals to the bearing assembly or to use bearing assemblies with polymer cages. A change in the type of fat can also help.

Corrosion occurs when water or corrosive agents get inside bearing units in large quantities. When this happens, the lubricant is no longer able to provide adequate protection, and rust forms. Friction corrosion occurs when there are micro-movements between the surfaces of the bearing, under certain conditions, for example, when there is movement between a bearing race and a shaft. Small particles are then detached from the surface. When exposed to oxygen, the particles oxidize, leading to bearing damage.

Electric erosion appears when an electric current passes through the bearing. It can be caused by improperly functioning ground return devices or by improperly grounded grounds during welding.

Plastic deformation can be caused by various factors, such as overloading from static loads or jolts, or from nicks caused by debris or improper handling. Improper installation knocks on the rolling elements, the cage or the rings or even foreign bodies that enter the bearing cavity can cause plastic deformation.

Fracture and cracking may occur from the excessive load on the bearing, from improper mounting or handling, or from inadequate bearing size and capacity for the application. This type of damage can also manifest as thermal cracking, which occurs in the inner or outer ring when the sliding motion causes high frictional heat.

The table below describes some of the most common problems you may observe with damaged bearings, along with the causes and potential solutions to these types of damage.

Observed problem	Potential cause of failure	Solution
Crumbling of the road surface	Chipping can be caused by excessive load, imprecision of the shaft or cage, improper installation or ingress of foreign objects.	If the load is too heavy, use a bearing with a larger capacity. If necessary, use an oil with a higher viscosity, or improve the lubrication system to form a protective film.
Chipping of rolling surfaces	More likely to occur when lubrication is poor or the surfaces of opposing parts are rough. Chipping can lead to chipping.	Check the roughness of the surface and choose a better lubricant.
Chipping on ribs or path surfaces	It May be caused by improper fastening, improper lubrication of the rolling elements, or the removal of the protective film on the mating surfaces due to excessive load.	Improve the fixation, correct the load, and select a suitable lubricant.
Dirt on the road surface	The rolling elements slide during movement and the lubricant does not have the required characteristics to prevent this sliding.	Select an appropriate lubricant or lubrication system and check the clearance and preload.
The running surface is worn and the dimensions are reduced	Poor lubrication, penetration of a foreign object or contamination of the lubricant with dust or foreign objects.	Choose an appropriate lubricant or lubrication system and improve the seal.
Changes in color and the finish on the surface	A frosted or discolored surface may indicate poor lubrication, overheating, or the buildup of degraded oil.	Improve sealing and lubrication system, remove the oil with an organic solvent, and polish with sandpaper to remove roughness.
Cavities and marks on the road surface	Probably due to the penetration of a solid object or trapped particles.	Remove and store foreign objects out of reach, check for chipping and optimize handling procedures.
Chipping of the inner, outer ring, or rolling elements	Chipping can be caused by excessive load, improper handling, or trapped solid objects.	Check and improve the load, and optimize the seal.
Cracks in rings or rolling elements	Excessive load, impact, or overheating. A loose fit could also be the cause.	Examine and improve the load and correct the fit.
Rust or corrosion of the rings or rolling elements	Humidity, infiltration of water or corrosive substances, or poor packaging and storage conditions.	Improve sealing, handling, and storage.
Seizure of rings or rolling elements	Poor heat dissipation due to poor lubrication or too little clearance. Excessive load can also be the cause.	Improve heat dissipation and lubrication. Check and improve the load.
Wear of paths	Too much vibration, a small angle of oscillation, or poor lubrication.	The outer and inner rings must be transported separately, or the lubrication must be improved.
Damaged cages	Excessive load, too high speed or large variations in speed, poor lubrication, or strong vibrations.	Improve load conditions, reduce vibrations, and improve the lubrication system.

 

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