T-225
SECTION 20 LUBRICATION OF GEARS
The purpose of lubricating gears is as follows:
1. Promote sliding between teeth to reduce the coefficient of friction (m ).
2. Limit the temperature rise caused by rolling and sliding friction.
To avoid difficulties such as tooth wear and premature failure, the correct lubricant
must be chosen.
20.1 Methods Of Lubrication
There are three gear lubrication methods in general use:
1. Grease lubrication.
2. Splash lubrication (oil bath method).
3. Forced oil circulation lubrication.
There is no single best lubricant and method. Choice depends upon tangential speed
(m/s) and rotating speed (rpm). At low speed, grease lubrication is a good choice. For
medium and high speeds, splash lubrication and forced circulation lubrication are more
appropriate, but there are exceptions. Sometimes, for maintenance reasons, a grease
lubricant is used even with high speed. Table 20-1 presents lubricants, methods and their
applicable ranges of speed.
Table 20-1(A) Ranges of Tangential Speed (m/s) for Spur and Bevel Gears
Table 20-1(B) Ranges of Sliding Speed (m/s) for Worm Gears
The following is a brief discussion of the three lubrication methods.
20.1.1 Grease Lubrication
Grease lubrication is suitable for any gear system that is open or enclosed, so long as
it runs at low speed. There are three major points regarding grease:
1. Choosing a lubricant with suitable viscosity.
A lubricant with good fluidity is especially effective in an enclosed system.
2. Not suitable for use under high load and continuous operation.
The cooling effect of grease is not as good as lubricating oil. So it may become a
problem with temperature rise under high load and continuous operating conditions.
No.
Lubrication
Range of Tangential Speed (m/s)
0
5
10
15
20
25
I
I
I
I
I
I
Grease Lubrication
Splash Lubrication
Forced Circulation Lubrication
1
2
3
F–––––––––––––––––E
F––––––––––––––––––––––––––––––––E
F–––––––––––––––––––––––––––––––––––––––––––
No.
Lubrication
Range of Sliding Speed (m/s)
0
5
10
15
20
25
I
I
I
I
I
I
Grease Lubrication
Splash Lubrication
Forced Circulation Lubrication
1
2
3
F––––––––E
F––––––––––––––––––––E
F–––––––––––––––––––––––––––––––––––––––––––––––––-–––––––––
