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Mar . 22, 2024 12:21 Back to list

Frequent causes of bearing damage Custom Motor Shaft Bearing


A bearing is generally usable up to the end of the rolling fatigue life, but it can also fail earlier due to improper fitting, mounting, lubrication or handling. The main failure modes and their sub-causes are described in the ISO 15243 standard, and are based on the damages visible on the rolling element contact surfaces or on other functional surfaces of the bearings.

 

20*47*14mm 6204-2RS C3 Deep Groove Ball BearingT



These failure modes include:
Fatigue, which can be surface-initiated or sub-surface initiated
Wear, which includes abrasive wear and adhesive wear
Corrosion, which includes moisture corrosion and friction corrosion (with sub-causes fretting corrosion and false brinelling)
Electrical erosion, which includes excessive voltage and current leakage
Plastic deformation, which includes overload, indentation from debris and indentation from handling
Fracture and cracking, which includes forced fracture, fatigue fracture and thermal cracking

Fatigue occurs due to repeated stress on the contact surfaces between the rolling elements and the raceways, and leads to changes in material structure. It is visible as spalling or flaking and is mostly surface initiated, the cause for this type of damage being usually an inadequate lubrication. Sub-surface initiated fatigue is rare and occurs after very long running times. To prevent this type of damage, the grease type and condition as well as the sealing and loading conditions should be checked and adjusted as needed.

Wear occurs when fine foreign material gets into the bearing assembly. Such material can be sand or fine metal particles from grinding or machining, as well as metal particles from gears wear. These foreign particles can cause internal clearance and misalignment, reducing the life of the bearing. A solution for preventing this type of damage is to add seals to the bearing assembly, or to use bearing units with polymer cages. Also, changing the type of grease might help.

Corrosion occurs when water or corrosive agents get inside the bearing units in large quantities. When this happens, the lubricant can no longer provide proper protection, therefore rust forms. Frictional corrosion happens when there are micro movements between the bearing surfaces, under certain conditions, for example when there is movement between a bearing ring and a shaft. This causes small particles to become detached from the surface. When exposed to oxygen, the particles oxidize, leading to bearing damage.

Electrical erosion appears when electric current passes through the bearing. It can be caused by earth return devices which aren’t working properly or by earth connections which are improperly done when welding.

Plastic deformation can be caused by different factors, such as overload as a result of static or shock loads, or indentation from debris or improper handling. Incorrect mounting, blows to the rolling elements, cage or rings, foreign particles that enter the bearing cavity can all cause plastic deformation.

Fracture and cracking can occur when there’s excessive load on the bearing, as a result of improper mounting or handling, or because the bearing size and capacity are not adequate for the application. This type of damage can also manifest as thermal cracking, which occurs in the inner or outer ring when the sliding movement causes high frictional heating.

The table below lists some of the most common conditions you can observe in damaged bearings, as well as the potential causes and the solutions for these types of damage.

 

Observed condition Potential cause of failure Solution
Flaking of the raceway surface Flaking may be caused by excessive load, poor shaft or housing accuracy, poor installation or ingress of foreign objects. If the load is too heavy, use a bearing with a larger capacity. If needed, use an oil with higher viscosity, or improve the lubrication system to form a protective film.
Peeling of the rolling surfaces More likely to occur when lubrication is poor or the surfaces of opposite parts are rough. It may develop into flaking. Control the surface roughness and choose a better lubricant.
Spalling on the ribs or raceway surfaces May be caused by poor mounting, poor lubrication of the rolling elements or discontinuation of the protective film on the contact surfaces due to excessive load. Improve the mounting, correct the load and select an adequate lubricant.
Smearing on the raceway surface The rolling elements slip during the motion and the lubricant doesn't have the right characteristics to prevent slippage. Select a proper lubricant or lubrication system and check the clearance and pre-load.
Raceway surface is worn and dimensions are reduced Poor lubrication, ingress of a foreign object or contamination of lubricant with dirt or foreign objects. Choose a proper lubricant or lubrication system, and improve the sealing efficiency.
Changes in surface colour and finish A matted raceway surface or a discoloured surface may indicate poor lubrication, overheating or accumulation of deteriorated oil. Improve the sealing efficiency and lubrication system, remove the oil with an organic solvent and polish with sandpaper to remove the roughness.
Indentations and hollows in the raceway surface Probably caused by ingress of a solid object or by trapped particles. Remove and keep out foreign objects, check for flakings and improve the handling procedures.
Chipping of the inner ring, outer ring or rolling elements Chipping may be caused by excessive load, poor handling or trapped solid objects. Check and improve the load, and improve the sealing efficiency.
Cracking in the 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 Moisture, ingress of water or corrosive substances, or poor packing and storing conditions. Improve the sealing efficiency, handling and storage.
Seizing of the rings or rolling elements Poor heat dissipation due to poor lubrication or a too small clearance. Excessive load can also be the cause. Improve the dissipation of heat and the lubrication. Check and improve the load.
Fretting of the raceways Too much vibration, a small oscillation angle or poor lubrication. The inner and outer ring should be transported separately, or the lubrication should be improved.
Damage of the cages Excessive load, too high speed or large fluctuation of speed, poor lubrication or high vibration. Improve the load conditions, reduce the vibration and improve the lubrication system.

 

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