2. Overview
What is lubrication
Regimes of Lubrications
Types of Lubrications
Lubricants
Formulation of Lubricants
Types of Lubrication
Solid Film Lubrication
Self Lubricating Materials
Q & A Session
3. What is lubrication?
Lubrication is the process, or technique employed to
reduce wear of one or both surfaces in close
proximity, and moving relative to each other, by
interposing a substance called lubricant between
the surfaces to carry or to help carry the load
(pressure generated) between the opposing
surfaces.
4. The regimes of lubrication
As the load increases on the contacting surfaces three distinct
situations can be observed with respect to the mode of
lubrication, which are called regimes of lubrication:
Fluid film lubrication is the lubrication regime in which
through viscous forces the load is fully supported by the
lubricant within the space or gap between the parts in motion
relative to one another object.
Hydrostatic lubrication is when an external pressure is
applied to the lubricant in the bearing, to maintain the fluid
lubricant film where it would otherwise be squeezed out.
Hydrodynamic lubrication is where the motion of the
contacting surfaces, and the exact design of the bearing is used
to pump lubricant around the bearing to maintain the lubricating
film
5. Types of Lubrication
Considering the nature of motion between moving or
sliding surfaces, there are different types of
mechanisms by which the lubrication is done. They
are:
Hydrodynamic lubrication or thick film lubrication
Hydrostatic lubrication
Boundary lubrication or thin film lubrication
Extreme pressure lubrication
6. Hydrodynamic Lubrication or
Thick Film Lubrication
Hydrodynamic lubrication is said to exist when the moving
surfaces are separated by the pressure of a continuous
unbroken film or layer of lubrication. In this type of lubrication,
the load is taken completely by the oil film.
Hydrodynamic lubrication depends on the relative speed
between the surfaces, oil viscosity, load, and clearance between
the moving or sliding surfaces.
Application of hydrodynamic lubrication
Delicate instruments.
Light machines like watches, clocks, guns, sewing machines.
Scientific instruments.
7. Hydrostatic Lubrication
Hydrostatic lubrication is essentially a form of
hydrodynamic lubrication in which the metal surfaces
are separated by a complete film of oil, but instead of
being self-generated, the separating pressure is
supplied by an external oil pump.
Hydrostatic lubrication depends on the inlet pressure
of lube oil and clearance between the metal surfaces,
whereas in hydrodynamic lubrication it depends on
the relative speed between the surfaces, oil viscosity,
load on the surfaces, and clearance between the
moving surfaces.
8. Boundary Lubrication or Thin
Film Lubrication
Boundary lubrication exists when the operating condition are
such that it is not possible to establish a full fluid condition,
particularly at low relative speeds between the moving or sliding
surfaces.
The oil film thickness may be reduced to such a degree that
metal to metal contact occurs between the moving surfaces.
The oil film thickness is so small that oiliness becomes
predominant for boundary lubrication.
Boundary lubrication happens when
A shaft starts moving from rest.
The speed is very low.
The load is very high.
Viscosity of the lubricant is too low.
9. Extreme Pressure Lubrication
When the moving or sliding surfaces are under very
high pressure and speed, a high local temperature is
attained. Under such condition, liquid lubricant fails
to stick to the moving parts and may decompose and
even vaporize.
To meet this extreme pressure condition, special
additives are added to the minerals oils. These are
called “extreme pressure lubrication.”
Additives are organic compounds like chlorine (as in
chlorinated esters), sulphur (as in sulphurized oils),
and phosphorus (as in tricresyl phosphate).
10. What is lubricant?
A lubricant is a substance introduced to reduce
friction between surfaces in mutual contact, which
ultimately reduces the heat generated when the
surfaces moves. The property of reducing friction is
known as lubricity.
Lubricants are generally composed of a majority of
base oil plus a variety of additives to impart
desirable characteristics.
Lubricants perform the following key functions:
Keep moving parts apart, Reduce friction, Transfer
heat, Carry away contaminants & debris, Transmit
power
11. Formulation
Typically lubricants contain 90% base oil (most often
petroleum fractions, called mineral oils) and less than
10% additives. Vegetable oils or synthetic liquids
such as hydrogenated polyolefins, esters, silicones,
fluorocarbons and many others are sometimes used
as base oils.
Non-liquid lubricants include grease, powders (dry
graphite, PTFE, molybdenum disulfide, tungsten
disulfide, etc.)
Dry lubricants such as graphite, molybdenum
disulfide and tungsten disulfide also offer lubrication
at temperatures (up to 350 °C)
12. Types of Lubricants
Solid lubricants possess lamellar structure
preventing direct contact between the sliding
surfaces even at high loads.
Graphite and molybdenum disulfide particles are
common Solid lubricants. Boron nitride, tungsten
disulfide and polytetrafluorethylene (PTFE) are
other solid lubricants.
Solid lubricants are mainly used as additives to oils
and greases. Solid lubricants are also used in form
of dry powder or as constituents of coatings.
13. Types of Lubricants
Semi-fluid lubricants (greases) are produced by emulsifying
oils or fats with metallic soap and water at 400-600°F (204-
316°C).
Typical mineral oil base grease is vaseline.
Grease properties are determined by a type of oil (mineral,
synthetic, vegetable, animal fat), type of soap (lithium, sodium,
calcium, etc. salts of long-chained fatty acids) and additives
(extra pressure, corrosion protection, anti-oxidation, etc.).
Semi-fluid lubricants (greases) are used in variety applications
where fluid oil is not applicable and where thick lubrication film
is required: lubrication of roller bearings in railway car wheels,
rolling mill bearings, steam turbines, spindles, jet engine
bearings and other various machinery bearings.
14. Types of Lubricants
Fluid lubricants (Oils) Mineral fluid lubricants are
based on mineral oils. Mineral oils (petroleum oils)
are products of refining crude oil. There are three
types of mineral oil: paraffinic, naphtenic and
aromatic.
Paraffinic oils are produced either by hydrocracking
or solvent extraction process.
Naphtenic oils are produced from crude oil distillates.
Aromatic oils are products of refining process in
manufacture of paraffinic oils.
15. General properties of
Lubricants
A good lubricant generally possesses the following
characteristics:
high boiling point and low freezing point (in order to
stay liquid within a wide range of temperature)
high viscosity index
thermal stability
hydraulic stability
corrosion prevention
high resistance to oxidation.
16. Solid Film Lubricants
These materials are characterized as dry film or solid
film lubricants.
These materials may be applied to a surface in the
form of an additive to a fluid lubricant, or in a pure
form, and may also be added or alloyed into the
surface when the component is being manufactured.
The more common types of materials include the
following:
Molybdenum disulfide (MoS2),Polytetrafluoroethylene
(PTFE),Graphite, Boron nitride, Talc, Calcium fluoride,
Cerium fluoride, Tungsten disulfide
17. Self-Lubricating Composites
Self-lubricating composites have been available for a
long time and are used rather extensively by industry
to combat friction and wear in a variety of sliding,
rolling, and rotating bearing applications.
They are generally prepared by dispersing
appropriate amounts of a self-lubricating solid (as
fillers, preferably in powder form) with a polymer,
metal, or ceramic matrix.
Examples are Ti, TiN, TiC, Pb, PbO, ZnO, Sb2O3
