2. Dow Corning INTERNAL
Basic Theory of Lubrication
Transport of a stone statue (600kN) in Egypt 1880 B.C. by 172 slaves. The lubrication engineer is using a
liquid (olive oil) to reduce friction wood/wood.(friction coefficient of wood against wood is u 0.25 to
0.5). Ball bearings AD40 lake Nimi Rome. 3500BC wheels
4. Dow Corning INTERNAL
What is Tribology?
Jost 1966 Tribos Greek word : Rubbing
Tribology : Science of Rubbing :
science and engg of interacting
surfaces in relative motion……
The study and application of
friction ,
wear , and
lubrication
6. Dow Corning INTERNAL
Why study Tribology?
1.0 to 1.4% GNP of any country is lost in wear and tear
of the machinery parts.
- Germany: yearly losses caused by friction and
wear of nearly 20 Billions Euros
- USA: yearly losses of 100 Billions Euros
.
-Methodologies help us to diagnose the wear and to
prescribe appropriate solution ….thus saving large
sums of money and leading to conservation of
material, energy and environment.
7. Dow Corning INTERNAL
• Friction: Mechanical resistance against
a relative moving of two surfaces
• Wear : Material losses out of a solid
body in consequence of
tribological stress
• Lubrication : Prevention of surface contact
during the relative motion for
wear prevention
Tribology Terminologies : Friction,
Wear and Lubrication
9. Dow Corning INTERNAL
F
FN
tangential force Friction
force
Ff
W
Applied Force F > Frictional force Ff
F α Ff
F = µ Ff
Action
Reaction
Mathematical expression : Friction
11. Dow Corning INTERNAL
Types of Friction
Static Friction- A
body’s resistance to
move when
stationary
•Dynamic Friction- A body’s
resistance to move when
moving
12. Dow Corning INTERNAL
Rolling Friction- A body’s
resistance to roll when
rolling
•Fluid Friction-A body’s
resistance to move through a
fluid
Types of Friction …..Contd…
13. Dow Corning INTERNAL
F
FN
Friction
force
Ff
W
Coefficient of Friction(μ) is defined as:
F = µ Ff
μ＝F/Ff or W/Ff
W= Applied Load (load expereinced)
Ff= Friction Force (load exerted)
Mathematical Expression : Coefficient
of Friction
14. Dow Corning INTERNAL
Coefficient of Static Friction (μｓ):
Coefficient of friction at the sliding motion is just started.
Coefficient of Kinetic Friction (μｋ) :
Coefficient of friction during the sliding motion.
μｓ ≧ μｋ
Coefficient of Static Friction and Kinetic
Friction
15. Dow Corning INTERNAL
1) Friction force(Static/Kinetic) is directory
proportional to Perpendicular Load,
is not related to Apparent Contact Area.
2) Kinetic Friction is not related to Sliding Speed.
3) Static Friction Force is Larger than Kinetic Friction
Force.
1) And 2) : Coulomb Amontons Law
Some important facts on Friction
17. Dow Corning INTERNAL
Calculate the coefficient of friction for the first slide if the
Load of the statue is 600000N and there are 172 slaves who
Are putting a force of 800N?
18. Dow Corning INTERNAL
1. Direct Contact. 2. Initiation of Internal-
Destruction.
3. Formation of Broken
Element.
5. Formation of Wear-
Particles.
6. Break Away.
4. Promotion.
Wear and its Mechanism
20. Dow Corning INTERNAL
Abrasive Wear due to hard particles
or hard protuberances forced against
and moving along a solid surface.
21. Dow Corning INTERNAL
Adhesive Wear due to localized bonding
between contacting solid surfaces leading to
material transfer between the two surfaces or the
loss from either surface.
Adhesive wear of threaded flanks
23. Dow Corning INTERNAL
Erosive Wear due to mechanical
interaction between that surface and a
fluid, a multi-component fluid, or
impinging liquid or solid particles
24. Dow Corning INTERNAL
Corrosive Wear is deterioration of
useful properties in a material due to
reactions with its environment
e.g….Acid Etching
27. Dow Corning INTERNAL
Lubrication
Lubrication - the use of ANY material between contact
surfaces of moving parts to reduce........Friction
thereby reducing
Heat
Wear
Noise , heat, power etc
28. Dow Corning INTERNAL
Lubrication Regimes/Situations
How Lubricants Work
Hydrodynamic Lubrication
Boundary Lubrication
Mixed Lubrication
29. Dow Corning INTERNAL
+ Fluid Friction: The sliding surfaces are separated
by a lubricant.
h>10-5cm: Fluid friction
h10-4-10-6cm and l>4 : Elastic fluid friction
+ Dry Friction: The sliding surfaces are in direct contact.
+ Mixed Friction: The region of transition from lubricated
to dry friction, both type of friction occur
simultaneously.
+ Boundary Friction: The case of mixed friction in the region
of transition to dry friction.
30Å I.
10 - 50Å II.
l = 1 to 4
l < 1
l =
Thickness of fluid layer
Roughness of surface
I. : Boundary lubrication Layer
II. : Oxide Layer
h : Distance between surfaces.
h
State of Friction
30. Dow Corning INTERNAL
Lubricated by gas.
Gas bearing.
0.001>μ>0.0001
6
Fluid friction.
Friction force is viscosity of fluid.
0.01>μ>0.001
5
Transition or Mixed state of 3 and 5.
Mixed friction.
0.1>μ>0.01
4
Covered by absorbed organic
molecules . Generally exists.
1>μ>0.1
3
Thoroughly cleaned surface, Under
dry air.
10>μ>1
2
Perfectly cleaned surface, Under
high vacuum.
μ>10
1
Condition
Coefficient of Friction
Coulomb Amontons Law is valid at phase 2 and 3.
Coefficient of friction vs Surface
Condition
31. Dow Corning INTERNAL
Striebeck Curve
ηN/P
N: Rotational Speed
η: Viscosity
P: Load
Coefficient of Friction is
Proportional to
Viscosity and
Rotational Speed
Inverse Proportional to
Load
ηN/P
Coefficient of Friction
vs
33. Dow Corning INTERNAL
Type Composition
Grease Base oil, Thickener, Additives, Solid lubricants
Oil Base oil, Additives
Paste Base oil, Additives, Solid lubricants
Anti Friction Coating Binder, Solvent, Additives, Solid lubricants
Dispersion Base oil, Additives, Solid lubricants
Powder Solid lubricants
Type of Lubricants
34. Dow Corning INTERNAL
The function of the Lubricants is
to keep the friction between sliding parts at a low,
to prevent the wear,
to remove the heat of friction,
to remove wear particles from the load carrying zone,
to prevent the penetration of foreign matter
into the lubrication clearance.
The Function of the Lubricants
35. Dow Corning INTERNAL
MOLYKOTE SPECIALTY
LUBRICANTS
• MOLYKOTE is a Brand name of specialty lubricants
of Dow Corning.
• MOLYKOTE specialty lubricants provide solution to
customer’s problem for lubrication.
36. Dow Corning INTERNAL
Philosophy of MOLYKOTE® Greases
• All our greases are
Special Lubricants
• We sell
Problem Solving Greases
• For special applications
High Temperature Extreme Pressure
Lifetime Lubrication Aggressive Environment
41. Dow Corning INTERNAL
IMPORTANT INFORMATION FROM CUSTOMERS
(Let’s meet with design people)
• What is the problem? (Customer’s test result)
• What is the application? –Where, Why
•What is operating condition? – LETS :
Load/Environment/Temperature/Speed,Materials,etc
• What is the requirement?
• What is the current product?
• How much is the potential?
• When is the time limit?
(Customer’s commercialization schedule)
44. Dow Corning INTERNAL
Lubricating Oils & modified Lube oils
:Dispersions
Oils – are used for gearbox, compressor, vacuum pumps, hydraulics, chains,
etc.
Dispersions – are oils with solid lubricants added in it like gear oil additive,
chain oil dispersion, etc.
Dispersions
Oils > 90 % Additives + solid Lubricants
2-10%
Solid lubricants are either molybedenum disulphide or Graphite or
PTFE or ZnS.
50. Dow Corning INTERNAL
Different Frictional States during Lubrication
and suitable Lubricants
Pastes, Solid Lubricants
Anti-Friction-Coatings
Greases < (2m/s),
Oils
Greases with solid lubs
Dispersions
51. Dow Corning INTERNAL
Terms: Dn Value
Dn Value
– Bore size* of bearing in mm times RPM
– Example: 2” ID bearing @ 5000 RPM
• 2” X 2.54 X 10 = 50.8 mm
• Dn = 50.8 mm X 5000 RPM = 254,000
– * Root diameter is used outside the Americas
53. Dow Corning INTERNAL
Hydrodynamic Lubrication
High rotation speed at relatively low bearing loads
results in hydrodynamic friction.
Characterized by stable squeeze film (oil film) between
the rubbing surfaces.
No contact between the surfaces occurs in
hydrodynamic lubrication.
In hydrodynamic lubrication the coefficient of friction
drops due fall in viscosity of the lubricant with
consequent decrease of the temperature. The system
corrects itself. Thus hydrodynamic lubrication is
stable.
55. Dow Corning INTERNAL
Boundary Lubrication
A constant contact between surface points
(microasperities).
Characterized by high coefficient of friction (energy
loss), increased wear, possibility of seizure between
the bearing and journal materials , non-uniform
distribution of the bearing load (localized pressure
peaks).
Very severe engine bearing failures are caused by
boundary lubrication.
Conditions for boundary lubrication observed at low
speed friction (engine start and shutdown) and high
loads.
Extreme pressure (EP) additives in the lubricant
prevent seizure conditions caused by direct metal-to-
metal contact between the parts in the boundary
lubrication regime.
