cojinetebearings

Bearing Failures, Their Causes and Preventive Measures

Type Bearing Failure and Damage Damage Posibble Causes Preventive Measures

Flaking

Flaking is damage where material is removed in flakes from a surface layer of the bearing raceways or rolling elements due to rolling fatigue. This failure mode is generally attributed to the approaching end of bearing service life. However, if flaking occurs at early stages of bearing service life, it is necessary to determine causes and adopt preventive measures. Flaking occurring at an initial stage. Too small internal clearance
Improper or insufficient lubricant
Excessive loading
Rust
Provide proper internal clearance.
Select proper lubricating method or lubricant.
Flaking on one side of radial bearing raceway An excessively large axial load Fitting between outer ring on the free side and housing should be changed to clearance fit.
Symmetrical flaking along circumference of raceway Inaccurate housing roundness Correct machining accuracy of housing bore. (Especially for split housings, care should be taken on ensure machining accuracy.)
Slanted flaking on the radial ball bearing raceway. Flaking occurring near the edge of the raceway or rolling contact surface of roller bearing. Improper mounting Correct centering
Shaft deflection Widen bearing internal clearance
Misalignment of the shaft and housing Correct squareness of shaft or housing shoulder.

Pitting

Pitting is damage in which small holes 0.1mm in depth are generated on the raceway surface by rolling fatigue Flaking on the raceway surface at the same interval as rolling element spacing. Heavy impact load during mounting Improve mounting procedure
Damage on a cylindrical roller bearing or tapered roller bearing caused when they are mounted
Rust gathered while out of operation Provide rust prevention treatment before long cessation of operation

Cracking Chipping

Crackings include slight crackings, splitting and fracture. Chippings are a type of failure occuring at certain part of a bearing ring rib or corner of a roller. Cracking in outer ring or inner ring Excessive interference Select proper fit
Excessive fillet on shaft or housing Adjust fillet on shaft or in the housing to smaller than that of the bearing chamfer dimension
Heavy impact load
Advanced flaking or seizure Re-examine load conditions
Cracking on rolling elements Heavy impact load Improve mounting and handling procedure
Advanced flaking Re-examine load conditions
Cracking on the rib Impact on rib during mounting Improve mounting procedure
Re-examine load conditions

Brinelling Nicks

Brinelling is a small surface indentation generated either on the raceway through plastic deformation at the contact point between the raceway and rolling elements or on the rolling surfaces from insertion of foreign matter, when heavy load is applied while the bearing is stationary or rotating at a low rotation speed. Nicks are those indentations produced directly by rough handling such as hammering. Brinelling on the raceway or rolling contact surface Entry of foreign matter Clean bearing and it's peripheral parts
Impact load during mounting Improve sealing devices
Brinelling on the raceway surface at the same interval as the rollong element spacing Excessive load applied while bearing is stationary Change mounting procedure
Improve machine handling
Nicks on the raceway or rolling contact surface Careless handling Improve mounting and handling procedure

Pear skin Discolor

Pear skin is damage in which minute Brinell marks cover the entire rolling surface, caused by contamination. This is characterized by loss of luster and a rolling surface that is rough in appearance. In extreme cases, it is accompanied by discoloration due to heat generation. This phenomena is also commonly called frosting. Color change caused by rust and corrosion is generally separate from this phenomenon. Indentation similar to pear skin on the raceway and rolling contact surface. Entry of minute foreign matter Clean the bearing and it's surrounding parts
Improve sealing device
Discoloration of raceway, surface rolling contact surface, rib face, and cage riding land. Too small bearing internal clearance
Improper or insufficient lubricant
Deterioration of lubricant due to aging, etc
Provide proper internal clearance
Select proper lubricating method and lubricant type

Scratch

Scuffing

Scratches are relatively shallow marks generated by sliding contact, in the same direction as the sliding. This is not accompanied by apparent melting of material. Scuffing refers to surface marks, which are partially melted duo to higher contact pressure and therefore a greater heat effect. Generally, scuffing may be regarded as an advanced case of scratched. Scratches on raceway or rolling contact surface  Insufficient lubricant during start-up Apply lubricant to the raceway and rolling contact surface when mounting
Careless handling Improve mounting procedure
Scuffing on rib face and roller end face Improper or insufficient lubricant
Improper mounting
Excessive axial load
Select proper lubricating method or lubricant.
Correct centering of axial direction

Smearing

Smearing is damage in which clusters of minute seizures cover the rolling contact surface. Since smearing is caused by high temperature duo to friction, the surface of the material usually melts partially; and the smeared surface appear very rough in many cases. Smearing on raceway or rolling contact surface Improper or insufficient lubricant Select proper lubricating method or lubricant
Slipping of the rolling elements. This occurs duo to the breakdown of lubricant film when an abnormal self-rotation causes slip of the rolling elements on the raceway. Provide proper preload

Rust Corrosion

Rust is a film of oxides, or hydroxides, or carbonates formed on o metal surface due to chemaical reaction. Corrosion is damage in which a metal surface is eroded by acid or alkali solutions through a chemical reaction(electrochemical reaction such as chemical combination and battery formation); resulting in oxidation.It often occurs when sulfur or chloride contained in the lubricant additives is dissolved at high temperature. It can also occur when water becomes entrapped in the lubricant. Rust partially or completely covering the bearing surface  Improper storage condition Bearing should be stored in dry area
Improve sealing devices
Condensation in atmosphere Provide a preservative oil treatment before long cessation of operation.
Rust and corrosion at the same interval as rolling element spacing Contamination by water or corrosive matter Improve sealing devices

Wear

Normally, wear on bearings is observed on sliding contact surfaces such as roller end faces and rib faces, cage pockets, and cage ribbing lands. However, wear caused by foreign material and corrosion can affect not only sliding surfaces but also rolling surfaces. Wear on contact surfaces(roller end faces, rib faces, rib faces, cage pockets) Improper or insufficient lubricant Select proper lubricating method or lubricant.
Improve sealing devices.
Wear on raceways and rolling contact surfaces  Entry of contaminants Clean the bearing and surrounding application component parts and housing
Improper or insufficient lubricant Select proper lubricating method or lubricant.
Improve sealing devices.

Fretting Corrosion

Fretting occurs to bearings which are subject to vibration while in a stationary condition or which are exposed to slight axial movements. It is characterized by rust-colored wear particles. Fretting damage on the rotating ring is usually a clear indication of improper fit. Since fretting on the raceways often appears similar to brinelling, it is sometimes call "false brinelling". Rust-colored wear particles generated on the fitting surface (fretting corrosion) Insufficient interference fit Provide greater interference fit
Apply lubricant to the fitting surfaces.
Brinelling on the raceway surface at the same interval as rolling element spacing (false brinelling) Vibration and oscillation when bearings are stationary Improve fixing method of the shaft and housing
Provide preload to bearing

Seizure

Seizure is damage caused by excessive heating in bearings. Discoloration, distortion and melting together of bearing components Too small internal clearance Provide proper internal clearance
Improper or insufficient lubricant Select proper lubricating method or lubricant
Excessive load Re-examine bearing type
Review maintenance & relubrication schedule

 

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