Gear failure index

3.0 Tooth scuffing

Click on photograph to enlarge
	Figure 3a Severe scuffing of an unhardened gear
	Figure 3b Scuffing damage on a gear tooth
	Figure 3c Scuffing damage on the tooth faces of a driven gear showing also the tendency to ridging at the pitch line as the sliding action of the teeth tends to drag the surface material towards the pitch line
	Figure 3d Surface rippling of a hardened and ground pinion
	Figure 3e A case hardened pinion showing crushing and flaking of the case
	Figure 3f Pitch line pitting on a case hardened pinion which has operated at high load and low speed
Main Characteristics	Any pitting of hardened gears is generally a cause for alarm since the problem is unlikely to improve with time. Particularly with case hardened gears if the case is thin or the core material weak the case may be crushed and flake off leaving large pits in the surface. Case hardened gears operating at high loads and low speeds also sometimes show pitting at their pitch lines. This appears to be associated with the reversing surface sliding shear stresses which occur at this position and subject the hardened case to local fatigue failure
Cause	Scuffing damage occurs on gear teeth if they are operated with an inadequate lubricant film between the teeth. High surface temperatures then arise from the frictional heating and local welding and surface dragging and scoring tend to occur. The surface damage is usually more severe on soft gear teeth. With hardened gear teeth the early stages of scuffing damage often show as surface ripples on the operating faces.
Note
Possible Confusion with Other Types of Damage
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