Destructive Pitting; Flake Pitting (Large-Area Flank Fractures) - Rotax 915 i A Series Maintenance Manual

DESTRUCTIVE PITTING

Features:
Extensive flank fractures, generally occurring as
zones of pitting. The bottom of the fracture generally
has a mussel-shaped structure. The total pitting area
can be so great that the running smoothness is no-
ticeably affected and/or the remaining flank area
which still bears the load is rapidly destroyed by wear
etc.
Causes:
Pitting is attributable to the fatigue of the material
due to combined stresses from compression and
sliding. They are triggered when the material
strength is exceeded locally. Essential influences on
pit strength are: oil viscosity and oil temperature.
Conclusion:
Pitting of up to 5% of the flank area is permissible if
the individual flank fractures do not exceed a size
(greatest longitudinal extent) of 0.5 mm. Otherwise
the gear set must be replaced.
ATTENTION
The whole gear set must always be replaced.
Dog hubs or drive gears must not be replaced
individually.
Figure 6.48: Magnification approx. 5x.
Pitted area in the dedendum flank region of a spur gear.
Effectivity: 915 i A Series
Edition 0/Rev. 1
BRP-Rotax
MAINTENANCE MANUAL HEAVY
Figure 6.49: Magnification approx. 1.5x.
Pit formation in the dedendum region of a spur gear
tooth system
FLAKE PITTING (LARGE-AREA FLANK
FRACTURES)
See the following figures.
Features:
A large-area, triangular flank fracture emanating from
a micropitting zone or a fine line of pits in the tooth
dedendum. The fracture area has a relatively con-
stant depth. Further cracks can run obliquely over
the flank from the fracture. The damage sometimes
extends into the addendum region, which results in
breakage of the tooth tip.
ATTENTION
If flake pitting is found, the gear set must be
replaced.
Max. permissible pitting or flake pitting. See
tive pitting.
ATTENTION
The whole gear set must always be replaced.
Gears must not be replaced individually.
Destruc-
72–10–00
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June 01 2019