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

In Part 1, we explained about bearing "breakdown" and "failure".

In this part, we will call bearing visual defects "bearing failure," and we will explain the characteristics of bearing failure, its typical causes, and countermeasures that can be taken.

Bearing Failure (Part 1)

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:

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

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) Flaking (spalling)

"Flaking" refers to the phenomenon in which material flakes from the raceway surface and rolling element surface due to rolling fatigue (see Figures 1 a) and 1 b)). The point at which this phenomenon occurs is the end of the bearing's service life. However, if flaking occurs earlier than expected, this can be considered an abnormality, which requires an investigation regarding the cause and also requires countermeasures to be taken.

Fig. 1 a): Flaking (spalling) [inner ring of a deep groove ball bearing]

Fig. 1 b): Flaking (spalling) [inner ring of a cylindrical roller bearing]

[Reference]

One type of failure caused by rolling fatigue in the material is what is called "pitting."

This phenomenon involves tiny "cavities" with a depth of about 0.1 mm appearing on the raceway surface.

Table 2 shows the typical causes of, and countermeasures against, flaking (spalling).

Table 2: Typical flaking (spalling) causes and countermeasures

Flaking (spalling) condition	Cause(s)	Countermeasure(s)
Occurring on one side of the raceway of a radial bearing	・ Abnormally excessive axial load	・ For the fitting of the housing and the outer ring of the free side bearing, use a clearance fit
Occurring symmetrically along the circumference of the raceway	・Inaccurate housing roundness	・Correct the processing accuracy of the housing bore (take particular care to ensure the processing accuracy for split housings)
Occurring at an angle to the raceway of a radial bearing	・ Improper mounting ・Shaft deflection ・ Inaccuracy of the shaft and housing	・Improve the centering accuracy ・Widen the bearing internal clearance ・ Correct the squareness of the shaft or housing shoulder

2) Wear and fretting

"Wear" occurs most frequently on sliding contact surfaces such as roller end faces and rib faces, cage pocket surfaces, and the guide surfaces of cages and bearing rings (see Figure 2 a)). Note, however, that wear caused by foreign matter or corrosion can affect not only sliding surfaces but also rolling surfaces (see Figure 2 b)).

Fig. 2 a): Wear [end faces of cylindrical rollers]

Fig. 2 b): Wear [outer ring raceway surface of a double-row cylindrical roller bearing]

Table 3 shows the typical causes of, and countermeasures against, wear.

Table 3: Typical wear causes and countermeasures

Wear condition	Cause(s)	Countermeasure(s)
Occurring on a sliding contact surface	・Improper or insufficient lubricant	・ Reexamine the selection of lubricant or lubrication method ・ Improve the sealing device ・ Clean the bearing and the area around it
Occurring on a raceway surface or rolling surface	・Entry of foreign matter ・Improper or insufficient lubricant

"Fretting" refers to the phenomenon in which rust-colored wear particles develop on bearings that are subject to vibration while in a stationary condition (see Figures 3 a) and 3 b)).

Fig. 3 a): Fretting [inner ring bore surface of a tapered roller bearing]

Fig. 3 b): Fretting [outer ring outside surface of a deep groove ball bearing]

Table 4 shows the typical causes of, and countermeasures against, fretting.

Table 4: Typical fretting causes and countermeasures

Fretting condition	Cause(s)	Countermeasure(s)
Rust-colored wear particles on the fitting surfaces	・Insufficient interference	・Provide greater interference ・Apply lubricant to the fitting surface

Since fretting on a raceway surface often looks similar to brinelling, it is sometimes called "false brinelling" (see Figure 4).

Fig. 4: False brinelling [inner ring raceway surface of a deep groove ball bearing]

Table 5 shows the typical causes of, and countermeasures against, false brinelling.

Table 5: Typical false brinelling causes and countermeasures

False brinelling condition	Cause(s)	Countermeasure(s)
False brinelling at the same interval as the rolling element spacing	・ Vibration and oscillation when the bearing is stationary	・Improve the fixing method of the shaft and housing ・Provide preload to the bearing

3) Cracking and chipping

"Cracking" is a collective name for things like splits and fractures. "Chipping," meanwhile, refers to defects that occur in a part of the rib of the bearing ring or in the corner of the roller. (See Figures 5 a) and 5 b).)

Fig. 5 a): Cracking and chipping [outer ring, inner ring, and roller of a spherical roller bearing]

Fig. 5 b): Chipping [outer ring rib of a cylindrical roller bearing]

Table 6 shows the typical causes of, and countermeasures against, cracking and chipping.

Table 6: Typical cracking and chipping causes and countermeasures

Cracking/Chipping condition	Cause(s)	Countermeasure(s)
Cracking of the outer ring or inner ring	・Excessive interference ・Excessive impact load	・Select a proper fit ・Reexamine the load conditions
Chipping on the rib	・ Impact on a rib during mounting ・Excessive impact load in an axial direction	・ Improve the mounting procedure ・Reexamine the load conditions

4) Brinelling and nicks

"Brinelling" is a small surface indentation generated either (i) on the raceway surface through plastic deformation at the contact point between the raceway and rolling elements or (ii) on the rolling surfaces by the entry of foreign matter, when a heavy load is applied while the bearing is stationary or rotating at a low rotation speed (see Figures 6 a) and 6 b)). Nicks are those indentations produced directly by rough handling such as hammering.

Fig. 6 a): Brinelling [outer ring raceway surface of a deep groove ball bearing]

Fig. 6 b): Brinelling [inner ring raceway surface of a tapered roller bearing]

Table 7 shows the typical causes of, and countermeasures against, brinelling and nicks.

Table 7: Typical brinelling and nick causes and countermeasures

Brinelling/Nick condition	Cause(s)	Countermeasure(s)
Brinelling on the raceway at the same interval as the rolling element spacing	・ Impact load during mounting ・Excessive load applied while the bearing is stationary	・ Improve the mounting procedure ・Improve the handling of the machine
Brinelling on a raceway surface or rolling surface	・ Entry of foreign matter	・ Clean the bearing and the area around it ・ Improve the sealing device

Scratching and scuffing

"Scratching" refers to the development of relatively shallow marks caused by sliding contact, in the same direction as the sliding, and they are not accompanied by apparent melting of material (see Figure 7 a)). "Scuffing" refers to marks whose surfaces are partially melted due to higher contact pressure producing a greater heat effect (see Figure 7 b)). In general, you can think of scuffing as a more severe form of scratching.

Fig. 7 a): Scratching [roller rolling surface of a cylindrical roller bearing (scratching in an axial direction)]

Fig. 7 b): Scuffing on a rib surface and roller end face [cylindrical roller bearing with a rib]

Table 8 shows the typical causes of, and countermeasures against, scratching and scuffing.

Table 8: Typical scratching and scuffing causes and countermeasures

Scratching/Scuffing condition	Cause(s)	Countermeasure(s)
Scratching on a raceway surface or rolling surface	・Insufficient lubricant at initial operation ・Careless handling	・Apply lubricant to the raceway and rolling surfaces when mounting ・Improve the mounting procedure
Scuffing on the rib surface and roller end face	・ Improper or insufficient lubricant ・Excessive axial load	・Reexamine the selection of lubricant or lubrication method ・Reexamine the mounting position

Conclusion

1) In "Bearing Failure (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

2) When it comes to determining the cause of bearing breakdown, 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) 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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4) In "Bearing Failure (Part 3)," from among the various types of bearing failure, 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