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Damage to Bearings, and its Causes and Remedies

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15. Damage to Bearings, and its Causes and Remedies

Inappropriate handling or use of bearings often results in damage and a shortened life. This section highlights the common causes of trouble and preventative remedies.

Damage	Damage Symptoms	Cause	Remedy
Flaking	Flaking over the entire circumference on one side of the raceway	Abnormal axial load	Use clearance fit for the outer ring of the non-fixed bearing
	Ball-pitch flaking on the raceway	Impact load during mounting	Carefully mount the bearing
	Ball-pitch flaking on the raceway	Rust generated during downtime	Apply rust-proof treatment when a long downtime is scheduled
	Premature flaking on the raceway surface and ball surface (Figure 1)	Excessive load	Ensure proper load condition
		Insufficient clearance	Ensure proper clearance and fitting
		Poor lubrication	Use the correct amount of appropriate lubricant
		Poor mounting	Check the accuracy of the shaft and housing, as well as the mounting method
		Rust	Store and handle with care
	Flaking inclined toward the raceway (Figure 2)	Poor mounting and shaft alignment (centering)	Mount and align (center) the bearings properly
		Shaft deflection	Select a bearing with a large clearance
		Poor accuracy of shaft and housing	Adjust the perpendicularity of the shaft and housing
	Flaking at the symmetric position of the raceway	Poor housing accuracy	Adjust the accuracy on the surface of the housing bore diameter
Indentation	Ball-pitch indentations or dents on the raceway (Figure 3)	Impact load during mounting or when dropped	Handle with care
	Ball-pitch indentations or dents on the raceway (Figure 3)	Excessive load when the bearing is stopped or during low-speed rotation	Check the static load
	Indentation on the raceway and ball surface	Intrusion of sand, metallic dust, etc.	Clean the shaft and housing, and check the sealing device
Seizure	Discoloration of raceway and ball surface	Excessive load	Ensure proper clearance and fitting
		Insufficient clearance	Ensure proper clearance
		Poor lubrication	Use the correct amount of appropriate lubricant
		Poor mounting	Check the mounting method and relevant components
Smearing	Softening and adhesion to raceway and ball surface (Figure 4)	Poor lubrication	Use the correct amount of appropriate lubricant
Smearing		Sliding of balls	Apply proper preload
Electrolytic corrosion	Corrugated electrolytic corrosion of the raceway (Figure 5)	Sparking resulting from an electric current passing through the bearing	Ground and/or insulate the bearing
Breakage	Cracked or chipped raceway surface (Figure 6)	Excessive impact load	Apply appropriate load conditions
		Excessive interference	Ensure proper fitting
		Developed flaking or seizure	Adjust the shaft and sleeve
	Cracked or chipped balls	Excessive impact load	Check the mounting method and load condition
	Cracked or chipped balls	Excessive clearance during use	Check the fitting and bearing clearance
	Broken cage (Figure 7)	Moment load	Handle with care
		Impact due to high-speed and high-acceleration rotation	Check the rotation conditions
		Inappropriate lubrication	Check the lubricant and lubrication methods
		Foreign matter has become entangled	Improve the sealing device
Galling	Galling on the raceway and ball surface (Figure 8)	Inappropriate lubrication (solid grease or insufficient grease)	Refill with an appropriate amount of soft grease
Galling	Galling on the raceway and ball surface (Figure 8)	Heavy acceleration at the start of use (ball slippage)	Avoid sudden acceleration
Wear	Abnormal wear of raceway, balls, and cage (Figure 9)	Intrusion of foreign matter	Improve the sealing device
		Rust	Store and handle with care
		Poor lubrication	Use the correct amount of appropriate lubricant
	Galling wear on the fitting surface: creep (Figure 10)	Insufficient interference	Ensure proper fitting
	Galling wear on the fitting surface: creep (Figure 10)	Insufficient sleeve fastening	Fasten the sleeve appropriately
	Red wear on the fitting surface: fretting (Figure 11)	Small clearance on fitting surface	Increase interference
	Ball-pitch fretting on the raceway: false brinelling	Vibrations when the bearing is not used, such as during transportation	Fix the shaft and housing
	Ball-pitch fretting on the raceway: false brinelling	Rocking movement with a small amplitude	Use oil as lubricant, and apply preload
Rust and corrosion	Rust on the bearing surface and/or within the bearing	Poor storage conditions	Store and handle with care
	Rust on the bearing surface and/or within the bearing	Condensation of moisture contained in air	Store and handle with care
	Rust on fitting surface (Figure 12)	Fretting	Increase interference
	Rust on fitting surface (Figure 12)	Variable load	Apply oil on the fitting surface
	Corrosion	Intrusion of acid, alkali, or gas	Check the sealing device
	Corrosion	Chemical action of lubricant	Check the lubricant

Flaking

Flaking

(Figure 1)

Poor mounting

Poor mounting

(Figure 2)

Indentation

Indentation

(Figure 3)

Smearing

Smearing

(Figure 4)

Electrolytic corrosion

Electrolytic corrosion

(Figure 5)

Crack

Crack

(Figure 6)

Broken cage

Broken cage

(Figure 7)

Galling

Galling

(Figure 8)

Ball scratches

Ball scratches

(Figure 9)

External creep

External creep

(Figure 10)

Fretting

Fretting

(Figure 11)

Rust

Rust

(Figure 12)

Rolling Tracks and How Load is Applied

When a bearing rotates with a load applied, the rolling contact between the balls and the bearing rings will generate rolling tracks on the raceway surface of both inner and outer rings. The outline of rolling tracks and how the load is applied can be roughly summarized as shown in the eight figures below. Most of the damage to bearings at an early stage is caused by factors such as unexpected excessive load and mounting errors. Disassembling the bearing and looking at their rolling tracks will enable you to estimate the amount and direction of the load applied as well as the rotating rings, which will provide you with a clue on how to set appropriate load conditions.

Unidirectional radial load (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is observed at the center of the raceway over the entire circumference. The track has an even width throughout.
Outer ring:	The rolling track is observed at the center of the raceway. The track is widest in the radial load direction, while it becomes narrower the farther it is from the load direction.

Unidirectional radial/axial loads (combined load) (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is deflected to the axial load direction, and is observed over the entire circumference of the raceway surface. The track has an even width throughout.
Outer ring:	The rolling track is deflected to and is widest in the axial load direction. This may be observed either over the entire circumference, or just in some parts discontinuously.

Unidirectional radial load (Inner ring: static, and outer ring: rotational)

Inner ring:	The rolling track is observed at the center of the raceway. The track gets widest in the radial load direction, while it becomes narrower the farther it is from the load direction.
Outer ring:	The rolling track is observed at the center of the raceway over the entire circumference. The track has an even width throughout.

Moment load (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is observed at the center of the raceway over the entire circumference. The track has an even width throughout.
Outer ring:	The rolling track is inclined diagonally with a fluctuating width.

Unidirectional radial load with radial preload (or negative operating clearance) (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is observed at the center of the raceway over the entire circumference. The track has an even width throughout.
Outer ring:	The rolling track can be observed at the center of the raceway either over the entire circumference, or just in some parts discontinuously. The track is widest in the radial load direction.

Axial load and moment load (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is deflected to the axial load direction, and is observed over the entire circumference of the raceway surface. The track has an even width throughout.
Outer ring:	The rolling track is deflected to the axial load direction and is inclined diagonally, and is observed over the entire circumference of the raceway surface. The track has an even width throughout.

Unidirectional axial load (Inner ring: rotational, and/or outer ring: rotational)

Inner ring:	The rolling track is deflected to the axial load direction, and is observed over the entire circumference of the raceway surface. The track has an even width throughout.
Outer ring:	The rolling track is deflected to the axial load direction, and is observed over the entire circumference of the raceway surface. The track has an even width throughout.

When the outer ring is deformed to oval shape (Inner ring: rotational, and outer ring: static)

Inner ring:	The rolling track is observed at the center of the raceway over the entire circumference. The track has an even width throughout.
Outer ring:	The rolling track is widest where the raceway is compressed. The length in the circumferential direction changes depending on the amount of deformation and the bearing’s initial radial internal clearance.

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