Flaking due to rolling, fatigue occurs when small pieces of bearing material are split off from the smooth surface of the raceway or the rolling elements. This flaking causes regions with a rough and coarse texture.

Fatigue damage in a loaded zone of a tapered roller bearing inner ring

Flaking damage on the inner ring at the pitch of the tapered roller elements

Flaking and fatigue at a point on the outer ring of a tapered roller bearing

A tapered roller raceway completely damaged as a result of flaking

Dull or cloudy spots appear on the raceway surface along with light wearing. Tiny microscopic cracks are generated downward from these cloudy spots to a depth of 5-10 μm. Small particles of material then peel from the surface with areas of minor flaking starting to occur.

Scoring is surface damage due to accumulated small seizures caused by sliding under improper lubrication or severe operating conditions. Linear damage appears circumferentially on the raceway and roller surfaces. Cycloidal shaped damage on the roller ends and scoring on the rib surface contacting roller ends also occur.

Swirl shaped scuffing and scoring on the ends of a failed taper roller bearing

Smearing is surface damage which occurs from a collection of small seizures between bearing components caused by oil film rupture and/or sliding.

Surface roughening occurs along with melting.

Fracture refers to small pieces which were broken off due to excessive load or shock load acting locally on a roller corner or rib of a raceway ring.

Cracks in the raceway ring and rolling elements. Continued use under this condition leads to larger cracks or fractures

Cage damage includes:

• Cage deformation, Fracture and Wear Fracture of cage pillars
• Deformation of side face
• Wear of pocket surface
• Wear of guide surface

When debris such as small metallic particles is caught in the rolling contact zone, denting occurs on the raceway surface or rolling element surface. Denting can occur at the rolling element pitch interval if there is a shock during the mounting (brinell dents).

Pitting has a dull lustre and appears on the rolling element surface or raceway surface.

Wear is surface deterioration due to sliding friction at the surface of the raceway, rolling elements, roller end faces, rib face, cage pockets, etc.

Wear occurs due to repeated sliding between the two surfaces. Fretting occurs at fitting surface and also at contact area between raceway ring and rolling elements. Fretting corrosion is another term used to describe the reddish brown or black worn particles.

Among the different types of fretting, false brinelling is the occurrence of hollow spots that resemble brinell dents and are due to wear caused by vibration and swaying at the contact points between the rolling elements and raceway.

Creep is the phenomenon in bearings where relative slippage occurs between fitting surfaces and thereby creates a clearance between the surfaces. Creep causes a shiny appearance, occasionally with scoring or wear.

When sudden overheating occurs during rotation, the bearing becomes discoloured. Then, the raceway rings, rolling elements, and cage will soften, melt and deform as damage accumulates.

When electric current passes through a bearing, arcing and burning occur through the thin oil film at points of contact between the raceway and rolling elements. The points of contact are melted locally to form "fluting" or groove-like corrugations which can be seen by the naked eye. Magnification of these grooves reveals crater-like depressions which indicate melting by arcing.

Bearing rust and corrosion are pits on the surface of rings and rolling elements and may occur at the rolling element pitch on the rings or over the entire bearing surfaces.

Straight line scratches on surface of raceways or rolling elements caused during mounting or dismounting of bearing

Discoloration of cages, rolling elements and raceway rings occurs due to their reacting with lubricant at high temperature