Lubrication of gear in Tribology

1. GAZIANTEP UNIVERSITY
NATURAL AND APPLIED SCIENCE INSTITUTE
MECHANICAL ENGINEERING
CONSTRUCTION AND MANUFACTURING DIVISION
ME 560 TRIBOLOGY
PROJECT OF GEAR LUBRICATION
REVIEWED BY ASST.PROF.DR.ABDULLAH AKPOLAT
SUBMITTED BY: BAHADIR KARBA

2. GEAR LUBRICATION

3. INTRODUCTION TO GEAR
The use of gears for power
transmission dates back
several hundred years.
Before the age of iron and
steel, gears consisted of
circular wooden wheels
with wooden pegs fastened
to the rims to serve as
teeth.

4. The power used
in operating these mechanisms was
provided either by
man,animal,wateror wind.
Wear was not too much
of a problem with the crude
wood-tooth gears, but later, when
cast iron gears came into usage,
some form of lubrication
became necessary; lubrication also
reduced some of the noise.

5. In those early days it was known that a
greasy material would reduce noise.Animal fats
or plants were about the only lubricants available,
so They were used.
They served the purpose satisfactorily
because speeds and loads were low and mechanical
wear on the teeth was not too serious.
Broken teeth could be replaced without too much
trouble
.

6. However, by the time the steam engine was
invented, gears were made of iron, which would
withstand greater loads and speeds. Later, as
the machine age continued to develop, gears of
greater precision were required.

7. Types of gear lubrication
There are three gear lubrication methods in
general use:
(1) Grease lubrication.
(2) Splash lubrication (oil bath method).
(3) Forced oil circulation lubrication.

8. There is no single best lubricant and method.
Choice depends upon to the Gear speed
At low speed, grease lubrication is a good choice.
For medium and high speeds, splash lubrication
and forced oil circulation lubrication are more
appropriate, but there are exceptions.
*Sometimes, for maintenance reasons, a grease
lubricant is used even with high speed.

9. Ranges of tangential speed (m-s) for spur gears and
bevel gears

10. Ranges of sliding speed (m-s) for worm wheels

11. Grease lubrication can be applied in low speed /
low load applications, however, it is important
to apply grease periodically, especially for gears
of the open-type usage.
Since lubricants diminish or become depleted in
the long term, periodic checks for oil change or
refilling is necessary

12. Usage of lubricants under improper conditions cause
damage to gear teeth.
When using gears at high speed / heavy load, care
should be taken in selecting the right type of
lubricant; quantity and methods.
The proper selection of lubricant is especially
important.

13. (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:
– Choosing a lubricant with suitable cone
penetration.
A lubricant with good fluidity is especially
effective in an enclosed system.
– Not suitable for use under high load and
continuous operation.

14. – Proper quantity of
grease
There must be sufficient
grease to do the job.
However, too much
grease can be harmful,
particularly in an
enclosed system.
Excess grease will cause
agitation, viscous drag
and result in power loss.

15. (2) Splash Lubrication (Oil Bath Method)
Splash lubrication is used with an enclosed
system.
It needs at least 3m/s tangential speed to be
effective.
However, splash lubrication has several
problems, two of them being oil level and
temperature limitation

18. 1. Oil level
There will be excess agitation loss if the oil level
is too high.
On the other hand, there will not be effective
lubrication or ability to cool the gears if the
level is too low.
This problem may be countered by raising the
static level of lubricant in an oil pan.

20. 2. Temperature limitation
The temperature of a gear system may rise
because of friction loss due to gears, bearings
and lubricant agitation.
Rising temperature may cause one or more of the
following problems:
– Lower viscosity of lubricant
– Accelerated degradation of lubricant
– Deformation of housing, gears and shafts
– Decreased backlash

21. (3) Forced Oil Circulation Lubrication
Forced oil circulation lubrication applies
lubricant to the contact portion of the teeth
by means of an oil pump.
There are drop, spray and oil mist methods of
application

22. Drop Method
An oil pump is used to suck-up the lubricant and
then directly drop it on the contact portion of
the gears via a delivery pipe

24. Spray Method
An oil pump is used to
spray the lubricant
directly on the
contact area of the
gears

25. Spray Method
High speed industrial gearboxes are lubricated
through spray lubrication.
These units often have spray lubrication
provided through the use of nozzles, with oil
circulating at a pressure of 0.7 bar.
Extra care must be taken to ensure the oil
reaches the contacting surfaces.

26. Spray system

27. Oil Mist Method
Lubricant is mixed with compressed air to form
an oil mist that is sprayed against the contact
region of the gears.
It is especially suitable for high-speed gearing

29. Oil tank, pump, filter, piping and other devices are
needed in the forced oil lubrication system.
Therefore, it is used only for special high-speed
or large gear box applications.
By filtering and cooling the circulating lubricant,
the right viscosity and cleanliness can be
maintained.
This is considered to be the best way to lubricate
gears.

30. The purpose of lubricating gears is as
follows:
1. Promote sliding between teeth to reduce
the coefficient of friction μ.
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

31. Basic function of lubrication
reduce friction between surfaces in mutual
contact, which ultimately reduces the heat
generated when the surfaces move.
heating or cooling the surfaces

32. Types of gear oils
Rust and oxidation preventive gear oils:
Rust and oxidation preventive (R&O) oils are mainly
mineral base.
They contain Rust and oxidation inhibitors. The
viscosity of R&O oils according to the iso grading
system is between 32 to 320

33. Compounded gear oils
Compounded oils are mineral base.
They contain rust and oxidation inhibitors,
demulsifiers and up to 10% of fatty oils for
better lubricity.
Compounded oils are used mainly in worm
gears.
The viscosity of compounded oils according to
the ISO grading system is between 460 to
1000

34. Extreme Pressure (EP) gear oils
EP oils may be either mineral or synthetic base.
They contain EP additives, rust and oxidation
inhibitors, anti foaming –agents and
demulsifiers .
The viscosity of EP oils according to the ISO
grading system is between 68 to 1500.

35. SYNTHETIC GEAR OIL
Synthetic gear oils may be based on
polyalphaolefins (PAO), esters oils or
polyglycols .
They may contain EP additives, rust and
oxidation inhibitors, anti-foaming agents and
demulsifiers.

36. The viscosity of synthetic oils according to the
ISO grading system is between 32 to 6800.
Synthetic gear oils are used for gears
operating under extreme conditions:
very low or very high temperatures, high
pressures.