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Bearing Failure (Part 3): Causes and countermeasures for bearing failure (II)

In Part 2, from among the various types of bearing failure, we explained the characteristics and the typical causes and countermeasures that can be taken for the following types:

  • Flaking
  • Wear and fretting
  • Cracking and chipping
  • Brinelling and nicks
  • Scratching and scuffing



Bearing Failure (Part 2)
In this part, we will explain the characteristics of the other types of bearing failure, their typical causes, and countermeasures that can be taken. Table and image (figure) numbers are the same as in Part 2 for those that are common to both entries, and will continue counting up for items that are new to Part 3.

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Please note that while the JTEKT rolling bearing catalog uses the terms "bearing" and "rolling bearing" interchangeably, this column does not use the term "rolling bearing" as a general rule.

1. Types of bearing failure and where they occur

Table 1 shows the types of bearing failure and where they occur. Please refer back to Part 1 for the names of the various components of the bearing.

Table 1: Types of bearing failure and where they occur

No.

Failure type

Rings and rolling elements

Rings

Cage

Raceway surface and rolling surface

Roller guide surface, cage guide surface, roller end face

Other

Fitting surface

Pocket, guide surface

Rivet

1

Flaking (spalling)

2

Wear

Fretting

3

Cracking

Chipping

4

Brinelling

Nicks

5

Scratching

Scuffing

6

Rust

Corrosion

7

Pear skin (speckles)

Discoloration

8

Smearing

9

Creep

10

Electric pitting

11

Seizure

12

Cage damage

To see the names of all the various bearing components, please see the following:

Bearing Failure (Part 1)

2. Causes and countermeasures for bearing failure

In this part, from among the types of bearing failure listed in Table 1, we will explain the characteristics and the typical causes and countermeasures that can be taken for the following types:

  • Rust and corrosion
  • Pear skin and discoloration
  • Smearing
  • Creep
  • Electric pitting
  • Seizure
  • Cage damage

For a more detailed discussion of the causes and countermeasures, please see the following:

Causes and countermeasures: Ball & Roller Bearings Catalog

Failure examples: Ball & Roller Bearings: Failures, Causes and Countermeasures

1) Rust and corrosion

"Rust" is a film of oxides, or hydroxides, or carbonates formed on a metal surface due to a chemical reaction (see Figures 8 a) and 8 b)). Corrosion is a phenomenon in which a metal surface is eroded by a chemical reaction with an acid or alkaline solution, resulting in oxidation or dissolution.

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Fig. 8 a): Rust [inner and outer ring raceway surfaces and roller rolling surface of a tapered roller bearing]

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Fig. 8 b): Rust [outer ring raceway surface of a double-row cylindrical roller bearing]

Table 9 shows the typical causes of, and countermeasures against, rust and corrosion.

Table 9: Typical rust and corrosion causes and countermeasures

Rust/Corrosion condition

Cause(s)

Countermeasure(s)

Partially or completely covering the bearing surface

・ Improper storage condition
・Dew forming in the air around the bearing

・Improve the bearing storage condition
・Improve the sealing device
・Provide rust-preventative treatment if the bearing is going to be out of operation for a long period of time

Rust and corrosion at the same interval as the rolling element spacing

・Contamination by water or corrosive matter

・Improve the sealing device

2) Pear skin (speckle) and discoloration

"Pear skin" is a phenomenon in which minute brinell marks cover the entire rolling surface, caused by the entry of foreign matter. Pear skin is characterized by a loss of luster and a rolling surface that is rough in appearance, and in extreme cases this is accompanied by discoloration due to heat generation. (See Figure 9 a).)

"Discoloration," meanwhile, is a phenomenon in which the surface color changes because of staining or heat generation during rotation (see Figure 9 b)).

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Fig. 9 a): Pear skin [inner ring raceway surface of a deep groove ball bearing]

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Fig. 9 b): Discoloration [inner and outer ring raceway surfaces and roller rolling surface of a cylindrical roller bearing]

Table 10 shows the typical causes of, and countermeasures against, pear skin and discoloration.

Table 10: Typical pear skin and discoloration causes and countermeasures

Discoloration/Pear skin condition

Cause(s)

Countermeasure(s)

Pear skin-like indentation marks on a raceway surface or rolling surface

・Entry of a large amount of tiny particles of foreign matter

・Clean the bearing and the area around it
・Improve the sealing device

Discoloration of the raceway surface, rolling surface, rib surface, or cage guide surface

・The internal clearance is too small
・Improper or insufficient lubricant
・Quality deterioration of lubricant due to aging or other such factors

・Provide a proper internal clearance
・Reexamine the selection of lubricant or lubrication method

3) Smearing

"Smearing" is a phenomenon in which a cluster of tiny seizures cover the rolling contact surface (see Figures 10 a) and 10 b)). Since smearing is caused by high temperature due to friction, the surface of the material usually experiences partial melting, and smeared surfaces usually appear very rough.

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Fig. 10 a): Smearing [inner ring raceway surface of a deep groove ball bearing]

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Fig. 10 b): Smearing [ball surface]

Table 11 shows the typical causes of, and countermeasures against, smearing.

Table 11: Typical smearing causes and countermeasures

Smearing condition

Cause(s)

Countermeasure(s)

Occurring on a raceway surface or rolling surface

・Improper or insufficient lubricant
・Slipping of the rolling elements

・Reexamine the selection of lubricant or lubrication method
・Provide proper preload

4) Creep

"Creep" is a phenomenon in which bearing rings move relative to the shaft or housing (see Figures 11 a) and 11 b)).

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Fig. 11 a): Creep [inner ring bore surface of a double-row cylindrical roller bearing]

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Fig. 11 b): Creep [outer ring outside surface of a deep groove ball bearing]

Table 12 shows the typical causes of, and countermeasures against, creep.

Table 12: Typical creep causes and countermeasures

Creep condition

Cause(s)

Countermeasure(s)

Wear, discoloration, and scuffing caused by slipping on the fitting surfaces

・Insufficient interference
・Insufficient tightening of the sleeve

・Provide greater interference
・Tighten the sleeve as appropriate

5) Electric pitting

"Electric pitting" refers to when an electric current passes through a bearing while in operation, generating sparks between the raceway and rolling elements through a very thin oil film, resulting in melting of the surface metal in this area.

It can result in what is called "pitting" (the emergence of tiny "cavities"; see Figure 12 a)) or in some cases the rolling surface can become corrugated (see Figure 12 b)).

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Fig. 12 a): Electric pitting (pits) [inner ring raceway surface of a cylindrical roller bearing]

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Fig. 12 b): Electric pitting (corrugation) [ball surface and inner ring raceway surface of a deep groove ball bearing]

Table 13 shows the typical causes of, and countermeasures against, electric pitting.

Table 13: Typical electric pitting causes and countermeasures

Electric pitting condition

Cause(s)

対策

Countermeasure(s)

Occurring on a raceway surface or rolling surface

・Sparks generated when electric current passes through a bearing

・Prevent current from passing through the bearing
・Insulate the bearing

6) Seizure

"Seizure" refers to when abnormal heat causes the bearing to partially melt, which leads to either the bearing losing the ability to rotate properly or the rolling or sliding surface becoming extremely rough (see Figures 13 a) and 13 b)).

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Fig. 13 a): Seizure [tapered roller bearing]

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Fig. 13 b): Seizure [cylindrical roller bearing with a rib]

Table 14 shows the typical causes of, and countermeasures against, seizure.

Table 14: Typical seizure causes and countermeasures

Seizure condition

Cause(s)

Countermeasure(s)

Discoloration, distortion, and melting together due to heat

・The internal clearance is too small
・Improper or insufficient lubricant
・Excessive load

・Provide a proper internal clearance
・Reexamine the selection of lubricant or lubrication method
・Reexamine the type of bearing

7) Cage damage

Since cages are made of materials that are relatively less hard, external pressure and contact with other components can easily produce flaws and distortion, and in severe cases chipping and cracking can occur (see Figures 14 a) through 14 e)).

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Fig. 14 a): Cage distortion [cylindrical roller bearing]

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Fig. 14 b): Cage cracking [deep groove ball bearing]

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Fig. 14 c): Cage wear/cracking [tapered roller bearing]

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Fig. 14 d): Cage rust [tapered roller bearing]

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Fig. 14 e): Cage rivet looseness [cylindrical roller bearing]
Table 15 shows the typical causes of, and countermeasures against, cage damage.

Table 15: Typical cage damage causes and countermeasures

Cage damage condition

Cause(s)

Countermeasure(s)

Flaws, distortion, chipping, cracking, and excessive wear in a cage

・Extraordinary vibration, impact, or moment
・Improper or insufficient lubricant
・Improper mounting (misalignment)
・Dents made during mounting

・Reexamine the load conditions

・Reexamine the selection of lubricant or lubrication method
・Minimize the mounting deviation

・Improve mounting

3. Conclusion

1) In "Bearing Failure (Part 3)," from among the various types of bearing failure, we explained the characteristics and the typical causes and countermeasures that can be taken for the following types:

  • Rust and corrosion
  • Pear skin and discoloration
  • Smearing
  • Creep
  • Electric pitting
  • Seizure
  • Cage damage

2) When it comes to determining the cause of bearing failure, the following are all necessary:

  • sufficient knowledge and experience regarding both bearings and lubrication;
  • an awareness of the characteristics of the machine; and
  • a familiarity with the bearing mounting conditions and operating history.

3) In recent years, with machines becoming smaller, lighter, and faster, the need has arisen for bearings to withstand more severer conditions than before. For this reason, you may encounter other types of bearing failure that we were unable to address in these past few entries.

4) If you have any technical questions regarding bearing failure, or opinions/thoughts on these "Bearing Trivia" pages, please feel free to contact us using the following form:

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Related columns:

Bearing Trivia 1st series - What Are Bearings?

What Are Bearings? Let's learn about the basic functions of bearings! Leonardo da Vinci Was the Father of the Bearing!? The amazing history of bearings What's the Structure of the Bearing? The role of the structure and parts in reducing friction What Are the Differences Between Bearings? The various types and special features of bearings The Applications of Bearings I: This is how bearings are used in cars The Applications of Bearings II: This is how bearings are used for machines in industry Bearings Made Using Advanced Materials and Lubricants: Bearings all around you

Bearing Trivia 2nd series - How to Select the Right Bearing

How to Select the Right Bearing (Part 1): The order of priority for selecting bearings, and the types of bearings How to Select the Right Bearing (Part 2): How to decide the bearing arrangement How to Select the Right Bearing (Part 3): Bearing dimensions and service life How to Select the Right Bearing (Part 4): Bearing limiting speed, running accuracy, and fits How to Select the Right Bearing (Part 5): Bearing preload and rigidity How to Select the Right Bearing (Part 6): Bearing lubrication How to Select the Right Bearing (Part 7): Components surrounding the bearing How to Select the Right Bearing (Part 8): Bearing mounting and dismounting

Bearing Trivia 3rd series - Bearing Failure

Bearing Failure (Part 1): "Failure" and "damage"

Bearing Failure (Part 2): Causes and countermeasures for bearing failure (I)

Bearing Failure (Part 3): Causes and countermeasures for bearing failure (II)

Bearing Trivia for Beginner

Bearing Trivia for Beginners: "Fits"
Bearing Trivia for Beginners 2: "Bearing Materials (Part 1: General Information)"

Bearing Trivia for Beginners 3: "Bearing Materials (Part 2: Bearings for Extreme Special Environments)"

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