Notes for: Gear Systems – A Tribological Review
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Paper discusses gear lubrication
Three types of lubricated conditions:
o Boundary – when gears start or stop
o Mixed – as gearing transitions to full operating speed
o Full film – when gearing approaches and reaches full speed
At high-pressure Hertzian regions, the lubricant is essentially a rigid solid
Types of oil used as gear lubricants:
o Inhibited oil
o Extreme pressure oils
o Chemically active additives
o Compounded oil
o Open gear compounds – “heavily bodied” lubricants intended for use with large
gears @ slow speeds and heavy loads (contain additives that prevent them from
being thrown off or squeezed out of the contact region)
o Greases
Higher viscosity is better, but excessive heat and power loss from frictional effects must
be considered
Lubricant application methods:
o Splash lubricating systems
o Pressure-fed lubrication systems
Lubricated gears have a very different set of failure modes, due to wear (adhesion,
abrasion) and Hertzian fatigue (pitting, other effects) instead of the classic fracture and
bending failure modes that are experienced for non-lubricated gears