Roling Bearings: Failures, Causes and Countermeasures

1 Koyo . Ball & roller Bearings: Failures, Causes and Countermeasures JT KT. 1 E JTEKT CORPORATION. Rolling Bearings: Failures, Causes and Countermeasures 1. Time of fracture occurrence and Causes _____ 1. 1. bearing Fracture 2. Abnormal operations, their Causes and Countermeasures _____ 2. 1. Types of failure _____ 3. 2. bearing Failure 2. Types of failure and parts in which they occur _____ 3. 3. Failures and Causes _____ 4. 3. Failures, Causes and Countermeasures 1 Flaking, Pitting _____ 5 5 Scratches and Scuffing ___ 9 9 Creep _____ 13. 2 Wear and Fretting _____ 6 6 Rust and Corrosion _____ 10 10 Electric pitting _____ 14. 3 Cracks and Chips _____ 7 7 Pear skin, Discoloration __ 11 11 Seizure _____ 15. 4 Brinelling and Nicks _____ 8 8 Smearing _____ 12 12 Failure of Cage _____ 16. Rolling bearing : Description of each part . Outer ring Cup Outer ring front face Outer ring Tapered) roller Large rib Inner ring back face Ball Cage Inner ring bore surface Pressed cage Guide rib face Inner ring Inner ring raceway surface Inner ring Cone.

2 Raceway groove Inner ring Small rib raceway surface Cage Rolling surface roller small end face Pressed cage . roller large end face Rivet Inner ring front face Outer ring surface Outer ring back face Side surface a Deep groove ball bearing c Tapered roller bearing Outer ring Outer ring Cylindrical roller Center rib Inner ring Inner ring raceway surface Inner ring Inner ring raceway surface Rib Guide rib face roller filling slot Guide rib face Small rib Cage Spherical roller Rolling surface Rolling surface Machined cage with rivet . Cage Rivet roller end face Machined cage roller large end face b Cylindrical roller bearing d Spherical roller bearing Introduction Even when bearings are being used under ideal When bearing failure is found, even if it is insignificant, it conditions, failures of bearings are caused by deterioration is important to investigate the phenomenon to determine of the material due to rolling fatigue.

3 Generally, the service the Causes . At this time, not only the bearing but also the life of bearings is expressed either as a period of time or as shaft, housing, and lubricant used with the bearing should the total number of rotations before the occurrence of be comprehensively investigated, together with the failures in the inner ring, outer ring or rolling element bearing . because of rolling fatigue, due to repeated stress. To judge the Causes of failure, sufficient knowledge and Rolling bearings sometimes fracture earlier than experience in bearings and lubricants and a good expected. The following Causes should be considered; understanding of the characteristics of the equipment are q Inappropriate use of bearings necessary. In addition, consideration of the installation w Faulty installation or improper processing conditions and operational process of the bearing is e Improper lubricant, lubrication method or sealing required.

4 Device Reference Rated service life of rolling bearing r Inappropriate speed and operating temperature Cr p L : Rated service life, 106 rotations t Contamination by foreign matter during installation L P Lh : Rated service life, h y Abnormally heavy load 10 C 6 p Cr : Basic dynamic load rating, N. 60 P . r L . h n P : Dynamic equivalent load rating, N. n : Rotational speed, min-1. p : 3 Ball bearing , 10/3 roller bearing 1. bearing Fracture 1. Time of fracture occurrence and Causes For failure analysis, it is important to accurately For reference, time of fracture occurrence and related determine the time a fracture occurs, because the possible Causes are categorized and listed in Table 1 1. Causes of failure can be limited in according to the time of fracture occurrence. Table 1 1 Time of Breakage Occurrence and Causes Inappropriate Faulty design of shaft, Improper lubricant, Defect in Mis-mounting Defect in sealing device, use of housing or other lubrication method bearings of bearings contamination of water, dust Causes Time of bearings installation aspects or or sealing device or other foreign matters, or fracture occurrence improper processing shortage of lubricant (1) Fracture occurring immediately after bearings were mounted or.

5 Within a short time after mounting (2) Fracture occurring immediately after overhaul . (3) Fracture occurring immediately after lubricant was supplied . (4) Fracture occurring immediately after repair or removal of shaft, . housing or other parts (5) Fracture occurring during normal operation . 1. 2. Abnormal operations, their Causes and Countermeasures Causes and Countermeasures of abnormal operations are categorized and listed in Table 1 2. Table 1 2 Abnormal Operations, their Causes and Countermeasures Abnormal operation Causes Countermeasures (supplementary Countermeasures ). 1. Excessively tight bearing Replace with a new bearing . Correct bearing internal internal clearance clearance and interference.. 2. Creep on bearing ring Replace with a new bearing . Correct interference.. 3. Excessively heavy load Remounting Correct load by adjusting housing.. 4. Improper centering in Remounting Correct centering, or widen mounting clearance.

6 Mounting 5. Defect in bearing Replace with a new bearing . Take proper Countermeasures , after inspecting the Causes .. 6. Improper volume of lubricant Correct lubricant volume. Increase in temperature 7. Improper lubricant Change to proper lubricant. 8. Improper lubrication method Correct lubrication method by remounting or replacement with new parts. 9. Oil seal Correct interference by installing new seal or changing seal Excessive interference type. Shortage of lubricant Supply lubricant. Improper oil seal Correct oil seal type or sealing method. 10. Abnormal contact with Remounting or modify parts. labyrinth seal or other parts 1. Flaws including scratches, Repair bearings or replace with new ones. Care should be brinelling, etc. taken in handling Noise at uniform 2. Electric pitting bearings.. Repair bearings or replace with new ones. Prevent electricity Excessively loud noise or foreign noise from passing through bearings by modifying their design.

7 Intervals 3. Cracking of inner or outer Replace with a new bearing . s . ring 4. Flaking of raceway surface Replace with a new bearing . 5. Receway surface roughened Repair bearings or replace with new ones. s . by foreign matter metallic noise 1. Excessively narrow internal Replace with a new bearing or widen internal clearance. Noise at nonuniform High-pitched clearance 2. Shortage of lubricant Supply lubricant. 3. Sliding of rolling element Change to proper lubricant or decrease operational clearance. 1. Contamination by foreign Change to proper lubricant. s . matter 2. Contact with another rolling Remounting or modify parts. part 3. Flaw or flaking on rolling Replace with a new bearing . intervals element 4. Wear of cage Replace with a new bearing . 1. Contamination by foreign Change to proper lubricant. matter s . Excessively high vibration 2. Excessively wide clearance Remounting bearing or replace with a new one.

8 3. Flaw on raceway surface or Replace with a new bearing . rolling contact surface 1. Improper mounting Remounting Widen internal clearance. Care should be taken Excessively large with centering.. 2. Improper sealing device Remounting Reduce interference of oil seal.. rotational torque 3. Improper lubricant Decrease lubricant volume. Care should be taken not to supply an excessive amount of lubricant.. 2. 2. bearing Failure 1. Types of failure Defects in the appearance of bearings are referred to as assigning a general term to each type of failure, then bearing failures. Table 2 1 describes bearing failures, first adding more detailed classifications. Table 2 1 bearing Failure bearing failures Main cause (reference). Failures Failure details Rolling fatigue Flaking, Pitting Unavoidable Wear Wear, Fretting Fracture Cracks, Chips Flaw Brinelling, Nicks, Scratches, Scuffing Improper handling Rust Rust, Corrosion Seizure Seizure, Discoloration, Smearing Improper lubrication Creep Creep Improper fitting Electric pitting Electric pitting Passage of electricity 2.

9 Types of failure and parts in which they occur Table 2 2 describes bearing failures, parts where they occur, and standards for judging the failures. Table 2 2 bearing Failures, Parts in which they Occur, and Standards for Judging Failures bearing ring, Rolling element bearing ring Cage roller guide surface bearing failure Raceway surface Pocket surface Cage guide surface Others Fitting surface Rivet Rolling surface Guide surface roller end face Flaking, Pitting . Wear . Fretting . Cracks . Chips . Brinelling . Nicks . Scratches . Scuffing . Rust . Corrosion . Pear skin . Discoloration . Smearing . Creep . Electric pitting . Seizure . Failure of cage . Notes : In principle, not reusable. : Reusable in accordance with seriousnes of failure, by repairing or meeting required conditions. : No failure of this part. 3. 3. Failures and Causes Table 2 3 describes failures and Causes . For further detail, refer to Section "3.

10 Failures, Causes and Countermeasures " . Table 2 3 Failures and Causes Failure Cause Sketches of failures Circumference on one side Excessive axial load Fig. 1 . Symmetrical flaking on each side Inclined mounting, or shaft or housing not in the shape of a circle Fig. 2 . Flaking Flaking on one side or flaking in the form Distortion of shaft, insufficient centering, of an oblique line on raceway surface of bearings not installed on shaft at the correct Flaking along circumference on one side. bearing ring on fixed side Fig. 3 angle (Deep Groove Ball bearing ). Partial flaking on thrust bearing Eccentric mounting Flaking found on part only Contamination by foreign matter s , flaws, initial stage of flaking Scratches, Scuffing Scuffing on roller end face and guide rib Excessive axial load, improper lubrication face Symmetrical flaking on each side. Fig. 4 (Tapered roller bearing ). Scraches on raceway surface Grease of too high viscosity, excessive acceleration in starting Scratches on raceway surface oh thrust Sliding of rolling element caused by centrifugal bearing force during rotation Cracks or chips of rolling element Improper bearing material, excessive impact too wide internal clearance of cylindrical roller Flaking in the form of an oblique line.