Properties of Lubricats and Lubrication

i f b iProperties of Lubricants
and
Lubrication
Mohd Hanif Dewan Senior Engg Lecturer Mohd. Hanif Dewan, Senior Engg. Lecturer,
International Maritime Academy, Bangladesh
3/14/2014 1

Lubricant:Lubricant:
The substances which are used to decrease the force of friction
between the moving parts of machine in contact are known as
Lubricants and the process of decreasing the force of friction
between the moving parts of machine in contact is known as
LubricationLubrication.
Composition of lubricating oils:
Lubricating oil fractions extracted from crude oil are a widely
varying mixture of straight and branched chain paraffinic,
napthenic aromatic hydrocarbons having boiling points rangingnapthenic aromatic hydrocarbons having boiling points ranging
from about 302o to 593oC. Some specialty lubricants may have
boiling point extremes of 177 and 815oC. The choice of grade ofg p g
lubricating oil base is determined by the expected use.
3/14/2014 2
Mohd. Hanif Dewan, Senior Engg. Lecturer,

FRICTION:
When on surface of machinery moves over the anothery
surface, resistance to relative motion of the surfaces
arises. When we look at the solid surface it appears
smooth to naked eye but this smooth surface showssmooth to naked eye , but this smooth surface shows
irregularities of projections and cavities when viewed
under high power microscope.
International Maritime Academy, Bangladesh3/14/2014

Wh h f i l d th itWhen one such surface is placed over another, its
projections fall into the cavities of the other and get
interlocked Due to this interlocking there isinterlocked .Due to this interlocking , there is
resistance to the relative motion of the surfaces.
This is called the frictional forces or frictional
resistance of friction. In due course of motion, the
old projections get broken and deformities arise.
International Maritime Academy, Bangladesh 43/14/2014

So, FRICTION may be defined as the opposing force
that is set up between the surface of contact, whenp
one body moves over the surface of another body.

EFFECT OF FRICTION:
The frictional forces oppose the relative motion between
the moving parts of a machine Therefore extra energythe moving parts of a machine. Therefore extra energy
has to be spent to overcome the friction , which
increases expenses of energy .The friction between
the moving parts of machines also produces heat
which causes damage to the machinery. Thus friction
causes wear and tear of the moving parts of machinerycauses wear and tear of the moving parts of machinery
in contact and due to this cause, the machines lose
their efficiency and become useless.
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FUNCTIONS OF LUBRICANTS:
I. Lubricants avoid the damage of the moving parts of machines
by minimizing the production of heat.
II Lubricants reduce the wear and tear of machinery by keepingII. Lubricants reduce the wear and tear of machinery by keeping
the moving parts of machines apart.
III. Lubricants reduce the maintenance and running cost of
machinemachine.
IV. Lubricants act as the coolant because it reduces the
production of heat between the moving parts of machine in
contactcontact.
V. Lubricants increases the efficiency of machine by reducing the
loss of energy.
VI B i th l b i t th l ti ti f th i tVI. By using the lubricants, the relative motion of the moving parts
of machine becomes smooth and noise level of running
machine reduces.
VII L b i t l t th i tVII. Lubricants also act as the corrosion preventers.
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VIII.Lubricants also act as a seal as in piston. Lubricant
used between piston and walls of the container (cylinder)
prevents the leakage of hot gases produced by theprevents the leakage of hot gases produced by the
internal combustion i.e.it act as seal.
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General capabilities expected from an engine lubricant:
Di i it it t th ld t f i l- Dispersivity or capacity to the cold parts of an engine clean
- Detergency or capacity to keep hot parts of an engine clean
- Thermal strength or capacity to withstand temperature changes
- Anti-oxidant or capacity to resist the action of oxygen
- Anti-wear or capacity to contain wear
- Anti-scuffing or capacity to preserve oil film even in the presence
of high pressures.
- Alkalinity reserve or capacity to neutralise acids formed during
combustion or other sources thereby preventing corrosive wear.
- Demulsibility or capacity to separate contaminants.
- Resistance to hydrolysis or capacity to withstand the action of
water which can affect additives Pumpabilityp y
- Centrifugibility and filterability or capacity to separate insoluble
elements.
- Anti-rust, anti-corrosive and anti-foam are just some of the other, j
properties which protect the metalic object from wear down.
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NORMAL PROPERTIES REQUIRED ARE:NORMAL PROPERTIES REQUIRED ARE:
1. Adequate viscosity at working temperature so that the oil
spreads over the liner surface to provide a tough film which resists
th ti f th i t ithe scrapper action of the piston rings.
2. The oil must provide an effective seal between the rings and
liner.
3. Only a soft deposit must be formed when the oil burns,
4.Alkalintiy level (total base number or TBN) must match the
acidity of the oil being burntacidity of the oil being burnt.
5. Detergent and dispersant properties are required in order to
hold deposits in suspension and thus keep surfaces clean.
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Classification of
LubricantsLubricants
Liquid
Lubricants
Semi Solid
Lubricants
Solid Lubricants
Eg.Mineral Oil,
P t l Oil
Eg. Petroleum
Eg. Graphite,
M l bdPetroleum Oil,
Vegetable Oil etc
g
jellies
Molybdenum
Disulphide etc.

VISCOSITY:
• It’s a measure of a fluid’s resistance to flow.
• Viscosity of the lubricating oil determines its performance under
operating conditions.
• A low viscosity oil is thin and flows easily .
• A high viscosity oil is thick and flows slowly.
• As oil heats up it becomes moreAs oil heats up it becomes more
viscous (Becomes thin)
• Too low viscosity of the liquid > Lubricant film cannot be maintained
between the moving surfaces > Excessive wear.between the moving surfaces Excessive wear.
• Too high viscosity of the liquid > Excessive friction.
• Selected Lubricant must be proper viscous.
Viscosit is s all e pressed in centipoise or centistoke• Viscosity is usually expressed in centipoise or centistoke.

Viscosity Index :
• It is “Avg. decrease in viscosity of oil per degree rise in temp between
1000F & 2100F.”
• Viscosity of liquids decreases with increasing temperature.
• The rate at which viscosity of a lubricant changes with temperature is
measured by a scale called Viscosity Index.
• Silicones, polyglycol ethers, Diesters or triesters have high Viscosity Index.
Determination of Viscosity Index :
• First the viscosity of the oil under test is determined at 100°F & 210°F.
Let it be U and V respectively.y
• Then viscosity of Pennsylvanian oil is determined. Let it be VH.
• Then viscosity of Gulf oil is determined. Let it be VL
viscosity Index = VL- U x 100
L
Uy L
VL- VH
V.I. = 100 (Pennsylvanian oils.)
V.I. = Zero (Naphthanic-base gulf oils)
Viscosity
Temp
100O 200
H
F
( p g )
Higher the V.I, lesser is the variation of viscosity with change in
temperature.Thus, a good lubricating oil should possess high V.I.
Temp

• Iodine number is the number of Gms equivalent of iodine to amount of ICl
absorbed by 100gm of oil.
• Each oil has its specific Iodine Number.
• So Iodine Number determines the extent of contamination of oil.
• Low Iodine Number is desirable in oils.
Some oils and their Iodine Numbers are given below :
Iodine Number Oil Example
>150 Drying oil Linseed oil, tung oil
100‐150 Semidrying oil Castor oil , Soyabean oil100 150 Semidrying oil Castor oil , Soyabean oil
<100 Non‐Drying oil Coconut oil, Olive oil

• Aniline point is the Min temp at which oil is miscible with equal amt of
aniline
• Aniline Point is a measure of aromatic content of the lubricating oil• Aniline Point is a measure of aromatic content of the lubricating oil.
• Low Aniline Point oil have high aromatic content which attacks rubber
seals.
• Higher Aniline point means low %age of hydrocarbons (desirable).
• Thus Aniline Point is used as an indication of possible deterioration of • Thus Aniline Point is used as an indication of possible deterioration of
rubber sealing etc.
Determination of Aniline Point :
A ili Homogeneous Aniline +
sample oil
(equal)
Heated in Test tube
Homogeneous
solution
Coooled
Cloudiness
The temperature at which separation of the two phases (Aniline + oil) takes place
is the Aniline Point.

• Emulsification is the property of water to get mixed with water
easilyeasily.
• Emulsions can be oil in water emulsion or water in oil emulsion.
• A good lubricating oil should form such an emulsion with water
which breaks easily. This property is called demulsification.which breaks easily. This property is called demulsification.
• The time in seconds in which a given volume of oil and water
separates out in distinct layers is called steam demulsification
number.
• A good lubricating oil should have lower demulsification
number.
• Quicker the oil separates out from the emulsion formed, better
i th l b i ti ilis the lubricating oil.
• In cutting oils the higher the emulsification number, better the
oil is. This is because the emulsion acts as a coolant as well as
a lubricanta lubricant.

• Flash Point is the min temp at which the lubricant vaporizes that ignite for
a momwhen tiny flame is brought near.
• Fire Point is the Min temp at which the lubricant’s vapours burn constantly• Fire Point is the Min temp at which the lubricant s vapours burn constantly
for 5 seconds when tiny flame is brought near.
• Fire point = flashpoint+5 to 400C.
• Both should be higher than the max temp of country (for transportation)Both should be higher than the max temp of country (for transportation)
• If flash point < 140°F = Flammable liquids
And if flash point > 140°F =Combustible liquids.
The flash and fire points are generally determined by
using Pensky-Marten’s apparatus.
•Oil under examination is filled in the oil cup up to the
k d h t d b th i b th b bmark and heated by the air bath by a burner.
•Stirrer is worked b/n tests at a rate of about 1 – 2
rev/sec.
•Heat is applied so as to raise the oil temp by about
5c/min.5c/min.
•The temp at which distinct flash appeared in side the
oil cup is recorded as flashpoint.
•The heating is continued to record the fire point.

• Drop Point is the Temperature
at which grease passes fromg p
the semi-solid to the liquid
state. So, it determines the
upper temp limit for theupper temp limit for the
applicability of grease.
Determination :Determination :
• Beaker is heated.
• Temperature is raised.
• Grease sample passes from aGrease sample passes from a
semi-solid to a fluid state.
• Temp at which its first drop
falls from the opening isfalls from the opening is
recorded as drop-point.

• Cloud Point is the temp at which the lubricant becomes cloudy
or hazy when cooled.
• Pour Point is the temp at which the lubricant just ceases to flow
when cooled.
• Both indicates suitability of lubricant in cold conditions and thusot d cates su tab ty o ub ca t co d co d t o s a d t us
must be low.
• Pour point of wax can be lowered by dewaxing or adding
suitable pour point depressantsuitable pour point depressant.
• Pour point of an oil can be lowered by lowering the viscosity of
the oil which is achieved by removing the viscous constituent of
th ilthe oil.
• Lubricating oils used in capillary feed systems should have low
cloud points, otherwise impurities will clog the capillary.g y
• A high pour point leads to the solidification of the lubricant that
may cause jamming of the machine.

• Neutralization Point determines Acidity or Alkalinity of oil.
A idit /A id l /A id b i f KOH i d t• Acidity/Acid value/Acid number is mgs of KOH required to
neutralize acid in 1 gm of oil.
• Alkalinity/Base value/Base number is mgs of acid required
to neutralize all bases in 1 gm oil.
• As Neutralization Point of oil increases, age of oil
decreasesdecreases.

• It’s the mgs of KOH required to saponify 1 gm of oil.
S ifi ti i h d l i f E t ith KOH t i• Saponification is hydrolysis of an Easter with KOH to give
alcohol and Na/K salt of acid.
• Mineral oils do not react with KOH and are not saponifiable.
• Vegetable and animal oils have very high saponification
values.
Significance
• Saponification value helps us to ascertain whether the oil
d f i i l t bl ilunder reference is mineral or vegetable oil or a
compounded oil.
• Each oil has its specific Soaponification Number.
Deviation from it indicates the extent of adulteration of oil.

ADDITIVESADDITIVES
Improvements in lubricating oil over the last twenty
years have come about almost entirely from the useyears have come about almost entirely from the use
of additives.
These are added for three main reasons;
1.to protect the lubricant in service by limiting the
h i l h d d t i tichemical change and deterioration
2.To protect the mechanism from harmful
combustion products and malfunctioningcombustion products and malfunctioning
lubricating oil
3.To improve existing physical properties and top g p y p p
create new beneficial characteristics in the oil
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Typical additives are:yp
Barium, calcium, phosphorus, Sulphur, chlorine, zinc, oxidation
inhibitor-increases oil and machinery life, decreases sludge and
varnish on metal parts.varnish on metal parts.
Corrosion inhibitor- protects against chemical attack of alloy
bearings and metal surfacesbearings and metal surfaces.
Antiwear improvers- protects rubbing surfaces operating with this
film boundary lubrication. One such antiwear ( and oxidation
inhibitor) chemical is Zinc dithiophosphate or ZDDPinhibitor) chemical is Zinc dithiophosphate or ZDDP
Detergent- tend to neutralise the deposits before formation under
high temperature and pressure conditions, or as a result of using a
fuel with high sulphur contentfuel with high sulphur content.
Dispersant- used to disperse or suspend the deposits forming
contaminants. Typical dispersants, such as polyesters and
benzlamides are usually clean burning The molecules have abenzlamides, are usually clean burning. The molecules have a
polar charge at one end which attracts and holds the deposits
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Alkaline agents- neutralises acids, htese form the TBN of the oil
and includes additives such as the above dispersants and
detergents. An excess of acid neutralising alkalis are present in thedetergents. An excess of acid neutralising alkalis are present in the
oil and these help to keep parts clean. Failure to keep an oil
alkaline can lead to damage to bearings due to acidic attack as
well as increased liner wearwell as increased liner wear.
Rust inhibitors- protect to form the oxidation of metal component.
Pour point depressants- improves low temperature viscosity
Oiliness agent- reduces friction seizure point and wear ratesOiliness agent- reduces friction seizure point and wear rates
EP additives- increases film strength and load carrying capability
Antifoam agents- prevents stable bubble formation
Viscosity Improvers an additive that improves the viscosity indexViscosity Improvers- an additive that improves the viscosity index
of the oil. I.e. reduces the effect of temerpature of the oil.
Metal deactivators- prevent catalytic effects of metal
Antiseptic bactericideAntiseptic- bactericide.
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LUB OIL ANALYSIS:
Regular testing of crankcase lub oil is important to ensure that
deterioration has not taken place. The results of in service deterioration
could be a reduction in engine protection or actual attack on working
points by corrosive deposits. Oil samples are generally tested every 3 top y p p g y y
4 months depending on the system and experience. Shipboard testing is
taking a rising prominence to allow monitoring of oil condition between
testing.
To ensure good representation care should be taken where the sampleTo ensure good representation, care should be taken where the sample
is drawn
Correct
Main supply line
inlet or outlet from lub oil cooler
Outlet from main lub oil pump
Incorrect
standpipesstandpipes
purifier outlet
purifier direct sump suction
Samples should be drawn over a period of several minutes
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ViscosityViscosity
The viscosity is the most important property of the oil. Oil
of correct viscosity will provide optimum film strength withof correct viscosity will provide optimum film strength with
minimum friction losses and leakage.
The viscosity of a L.O. may fall due to fuel dilution if
running on gas oil, and rise if running on heavy f.o.
Viscosity may also increase due to heavy soot loading if
purifiers and filters not operating efficiently. Oil ageing
caused by oxidation and thermal degradation increases
viscosity.
A simple shipboard test is the Mobil flow stick wherep p
drops of new and used oil are placed in separate
channels on an inclined 'stick'. The rate the oil flows
down the stick is proportional to its viscosity.p p y
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Water contentWater content
Initially determined by 'crackle' test. The
presence of Na and Mg in a 4:1 ratio indicatespresence of Na and Mg in a 4:1 ratio indicates
salt water contamination.
Limits are laid down by the manufacturer but asLimits are laid down by the manufacturer, but as
a rule of thumb a limit of 0.2% should cause
investigation into source and remedial action at
0.5%
Gross contamination can be remedied by placing
the charge in a separate tank and heating to
70oC and circulating through purifier.
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SpectrometrySpectrometry
Indicates the presence of metal element composition and
identifies additive and contaminant levels.
Zinc(Zn),Phosphorus(P)- are components of many oils
such as diesel engine oils, hydraulic oils and gear oils, to
enhance antiwear and over properties of the oilp p
Calcium(Ca)- primarily a component of engine oils,
provides detergency,alkalinity and resistance to
oxidation. Residual fuel engine oils have higher Ca levels
Nickel(Ni)- Bearings, Valves, gear plating, fuel derivative
Barium(Ba)- Multi purpose additive, declining importance
Magnessium(Mg)- as for Ca may also be due to seaMagnessium(Mg) as for Ca, may also be due to sea
water contamination if found in Ratio of 1:4 of Na
Chromium(Cr)- Piston rings, hydraulic actuator cylinders
Manganese(Mn)- Cylinder wearManganese(Mn)- Cylinder wear
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Aluminium(Al)- generally comes from wearing piston skirts,( ) g y g p
levels rise where new piston fitted to old engine. Typically
10ppm, but rises during bedding in. May also indicate the
presence of catylytic fines in residual fuels.
Iron(Fe) Molybdenum(Mo) Chromium(Cr) metals alloyedIron(Fe), Molybdenum(Mo), Chromium(Cr)- metals alloyed
for piston ring etc, a rise in level may indicate ring pack/liner
wear.
Copper(Cu), Lead(Pb) , Tin(Sn), Silver(Ag) - soft metalsCopper(Cu), Lead(Pb) , Tin(Sn), Silver(Ag) soft metals
used in the overlay of shell bearings, and phosphor bronze
gears.Note that high copper content can also occur when
samples are drawn from copper pipes which have not been
flushed as well as gear wearflushed as well as gear wear.
Silicon(Si)- Indicates poor air filtration, possible fuel derivative
Sulphur(S)- May indicate the presence of clay based
(bentonite) greases(bentonite) greases
Sodium(Na)- With Mg indicates the presence of sea water
contamination, possible coolant system and fuel derivative
Vanadium(V)- Usually indicates the presence of fuel oilVanadium(V) Usually indicates the presence of fuel oil
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Alkalinity and acidityAlkalinity and acidity
TBN-TOTAL BASE NUMBER- measure of alkaline additives available
for the neutralisation of acids from combustion products and oxidation.
Level governed by type of fuelLevel governed by type of fuel.
For crosshead engines the TBN will tend to rise due to contamination
by liner lubrication, it should not be allowed to raise more than twice
that of the new charge.
A id th TBN f f h il h ld b t l tAs a guide, the TBN of fresh oil should be at least:
10 x fuel sulphur content (%) for trunk piston engines
(10mgKOH/g)
20 x fuel sulphur content (%) for cyl oil in x-head engines20 x fuel sulphur content (%) for cyl oil in x head engines
(20mgKOH/g)
A simple shipboard go,no-go test is available for measuring the TBN, it
involves the addition of an indicator and acid reagent to a 30ml
sample The quantify of acid reagent added is determined by thesample. The quantify of acid reagent added is determined by the
required level of TBN, for TBN2.5 0.5ml are added, for TBN20 4ml is
added. After three minutes the colour is checked against a chart
Purple:Good level of TBN
Green:Borderline
Yellow:Low level of TBN
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TAN TOTAL ACID NUMBER f i id d tTAN-TOTAL ACID NUMBER-measure of organic acid and strong
acid content of oil. Where SAN is nil, the TAN represents the acidity
in the oil due to both the acids in the additives and the oxidation of
the hydrocarbons in the oil. The TAN of fresh oils varies with oil type,
d t d t li b ith A hi h TAN i di t th t iland tends to climb with age. A high TAN may indicate that an oil
should be changed or freshened by top up. A high TAN may be
accompanied with increased viscosity.
SAN-STRONG ACID NUMBER-indicates the presence of strong,p g,
highly corrosive (inorganic) acids, usually formed from combustion
products. If SAN is not zero the oil should be changed immediately
Oil cleanliness
IC INDEX OF COMBUSTION measures soot loading of oilIC-INDEX OF COMBUSTION-measures soot loading of oil
MD-MERIT OF DISPERSANCY-Ability of an oil to disperse
contaminants, such as soot, wear debris and water and thereby carry
them away from the critical areas. Measured by oil blot test and
h ld t b ll d t f ll b l 50should not be allowed to fall below 50
DP-DEMERIT POINTS- combination of IC and MD: the lower the
value, the healthier is the condition of the oil
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Shipboard water content test
1 Th fl k i fill d t k 'A' ith k1. The flask is filled to mark 'A' with kerosene
2. A capsule of reagent (calcium hydride) is added.
Any water in the kerosene will react with the
calcium hydride and any gas vented off.y y g
3. he container is topped to mark 'B' with sample oil
4. The screw valve and cap are closed.
5. The flask is inverted and shaken
6. After 2 minutes the screw valve is opened. The
hydrogen produced by the reaction between the
reagent and water exerts a pressure which forces
the kerosene through the open valve into thethe kerosene through the open valve into the
graduated cylinder. The amount discharged is
proportional to the water content in the oil sample.
7. If the water content is greater than 1.5% then the
t t h ld b t d thi ti i lltest should be repeated this time using a smaller
sample by filling only to mark 'C'.The second scale
on the graduated cylinder should then be used.
8. If water is detected its type, sea or fresh , shouldyp , ,
then be determined by use of a special reagent the
water
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International Maritime Academy,
Bangladesh

Types of Lubrication
C id i th t f ti b t iConsidering the nature of motion between moving or
sliding surfaces, there are different types of mechanisms
by which the lubrication is done They are:by which the lubrication is done. They are:
1. Hydrodynamic lubrication or thick film lubrication
2. Hydrostatic lubricationy
3. Boundary lubrication or thin film lubrication
4. Extreme pressure lubrication
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1. Hydrodynamic Lubrication or Thick Film Lubrication
Hydrodynamic lubrication is said to exist when the
moving surfaces are separated by the pressure of a
i b k fil l f l b i i hicontinuous unbroken film or layer of lubrication. In this
type of lubrication, the load is taken completely by the oil
filmfilm.
The basis of hydrodynamic lubrication is the formation of
an oil wedge. When the journal rotates, it creates an oil g j ,
taper or wedge between the two surfaces, and the
pressure build up with the oil film supports the load.
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Hydrodynamic lubrication depends on:
relative speed between the surfaces,
‐ oil viscosity,
‐ load, andload, and
clearance between the moving or sliding surfaces.
In hydrodynamic lubrication the lube oil film thickness is greater
than outlet pressure at the inlet increases quickly remains fairlythan outlet, pressure at the inlet increases quickly, remains fairly
steady having a maximum value a little to the outside of the
bearing center line, and then decreases quickly to zero at the
outlet.
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Application of hydrodynamic lubrication
Delicate instruments.
fScientific instruments.
Large plain bearings like pedestal bearings, main bearing of diesel
engines.g
Fig: Hydrodynamic Lubrication3/14/2014 37

Hydrodynamic LubricationHydrodynamic Lubrication
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Elastohydrodynamic,
This is the type of lubrication used with rollingThis is the type of lubrication used with rolling
element bearings. To clarify, the material of the
running surface deforms under high pressure as theg g p
rolling element passes over it. The oil wedge forms
in this deformation.
(i) Deformation and increased viscosity with
pressure are involved
(ii) Frictional coefficient = 0 05(ii) Frictional coefficient = 0.05
(iii) film thickness less than Hydrodynamic
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2. Hydrostatic Lubrication:
Hydrostatic lubrication is essentially a form of hydrodynamic
l b i ti i hi h th t l f t d blubrication 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
hydrodynamic lubrication it depends on the relative speedhydrodynamic lubrication it depends on the relative speed
between the surfaces, oil viscosity, load on the surfaces, and
clearance between the moving surfaces.
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Example: the cross head pin bearing or gudgeon pin bearing
in two stroke engines employs this hydrostatic lubrication
mechanism. In the cross head bearing, the load is very high
and the motion is not continuous as the bearing oscillation isa d t e ot o s ot co t uous as t e bea g osc at o s
fairly short. Thus hydrodynamic lubrication cannot be
achieved. Under such conditions, hydrostatic lubrication offers
the advantagethe advantage.
Hydrostatic Lubrication
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3 Boundary Lubrication or Thin Film Lubrication3. 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,
ti l l t l l ti d b t th iparticularly at low relative speeds between the moving or
sliding surfaces.
The oil film thickness may be reduced to such a degreey g
that metal to metal contact occurs between the moving
urfaces. The oil film thickness is so small that oiliness
becomes predominant for boundary lubricationbecomes predominant for boundary lubrication.
Boundary lubrication happens when,
•A shaft starts moving from rest.
Th d i l•The speed is very low.
•The load is very high.
•Viscosity of the lubricant is too low.y
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Examples for boundary lubrication:
Guide and guide shoe in two stroke engine.
Lubrication of the journal bearing in diesel engines (mainly duringLubrication of the journal bearing in diesel engines (mainly during
starting and stopping of engine).
Piston rings and when cylinder liner is at TDC and BDC position
h th i t di ti h d if th l ti d iwhen the piston direction changes and if the relative speed is very
slow.
Boundary Lubrication
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A thin lubricant should have high viscosity indexA thin lubricant should have high viscosity index,
good resistance to heat and oxidation, good
oiliness and low pour point.
Velocity

4. 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 maycondition, 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.” These additives form on the
metal surfaces more durable films capable of withstanding high loads
and high temperature. Additives are organic compounds like chlorine g p g p
(as in chlorinated esters), sulphur (as in sulphurized oils), and
phosphorus (as in tricresyl phosphate).
The Extreme pressure Additives are the organic compounds
possessing the active radicals or groups such as chlorine, sulphur ,
phosphorus etc. These compounds react with metallic surfaces at
high temperature to form metallic chlorides.
3/14/2014 45

Extreme Pressure Lubrication
sulphides or phosphides which can form surface layers
on the moving or sliding metallic surfaces and act as
good lubricantsgood lubricants.

Stresses on Lube oilStresses on Lube oil
The main stresses experienced by Lube oils in diesel engines operating
on heavy fuel oils are expressed as follows
A id St C d b l h i d id ti id Thi l d tAcid Stress‐ Caused by sulphuric and oxidation acids. This leads to
increased corrosive wear, deposits, reduced Base Number and shorter oil
life.Rapid depletion of the BN is the clearest sign of oil stress
h l/ d h d b l d l dThermal/Oxidative stress‐This caused by elevated temperatures leading
to increased rates of thermal/oxidative breakdown of lubricant and fuel.
This leads to increased levels of deposits, sludges, corrosive wear of
bearing material, oil thickening and reduced oil life. In addition deposits
on the under crown side of the piston can lead to increased hot corosion
on the piston.
Asphaltene Stress‐This caused by fuel contamination of the lube oil and
can lead to increased levels of deposits, sludges, lacquers, oil thickening
and reduced oil life. In addition deposits on the under crown side of the
piston can lead to increased hot corosion on the piston
3/14/2014 47

Various Factors of Lubricating Oil:g
OXIDATION
‐ Oxidation degrades the lube oil producing sludges, varnishes and
resins Presence of moisture and some metals particularly copperresins. Presence of moisture, and some metals particularly copper
tend to act as a catalyst. Once oxidation starts, deterioration of the
properties of the oil is rapid.
‐ Oxidation reduces its effectiveness as a lubricant. Oxidation will
also cause deposits which can block passage ways and coat working
parts. The rate of oxidation will depend upon temperature, the p p p p ,
higher the temperature the more rapid the rate. Anti oxidants are
available which reduce the rate, also additional properties can be
achieved by the use of additivesachieved by the use of additives.
3/14/2014 48

‐‐ Most of the chemicals found in an oil will react more or less with
oxygen, The effects of this oxidation is always undesirable. Hence, a
major objective of the refining process of a mineral oil is to remove j j g p
those hydrocarbons i.e. the aromatics, the small amount of
unsaturates together with molecules containing sulphur, oxygen and
nitrogennitrogen.
‐ The use of anti‐oxidants make a slightly better balance although
there usefulness is limited.
Tin based white metal is susceptible to hardening as an oxide layers‐ Tin based white metal is susceptible to hardening as an oxide layers
from on the surface. These tin oxides are a grey‐black in appearance
and are extremely hard. There formation reduces the bearing
l h id l i hi k h h i i l hi lclearance as the oxide layer is thicker than the original white metal
material from which it formed. The oxide has a lower coefficient of
friction than the original white metal but it will cause problems if it
brakes up as fragments will become embedded edge on in the white
metal and can score the pin. .
3/14/2014 49

Emulsification
‐ This occurs due to water contamination; also, contamination with
grease, fatty oils, varnish, paint and rust preventers containing fatty
products can also promote emulsification.
- The presence of an emulsion can be detected by a general
cloudiness of the sample. Salt water emulsifies very easily and
should be avoided.
- Water entrained in the oil supplied to a journal bearing can lead
to loss of oil wedge, rub and failure.
Fresh water contamination whilst not in itself dangerous can lead
to rusting. The iron oxides catalyses the oil to form sludge's. Theg y g
additives in the oil can leach out to change the water into an
electrolyte.
- Salt water contamination is very serious as it causes tin oxidey
corrosion, and also leads to electrochemical attack on the tin
matrix in the white metal. The sea water act as then electrolyte.
A major problem of water within a lub oil is where the mix enters aA major problem of water within a lub oil is where the mix enters a
bearing, here it is possible for the water to be adiabatically heated
causing it to flash off collapsing the oil wedge.3/14/2014 50

THERMAL DEGRADATION:
Under high temperatures an oil is liable to thermal degradation
which causes discoloration and changes the viscosity. Additives
cannot change an oils susceptibility to this degradation.cannot change an oils susceptibility to this degradation.
RECHARGING
When recharging no more than 10 % of the working charge shouldWhen recharging no more than 10 % of the working charge should
be topped up due to heavy sludgeing that can occur due to the
heavy precipitation of the sludge.
EP ADDITIVE OILS
Can assist in healing of damaged gear surfaces but should be used
as a temporary measure only due to risk of side effects.as a temporary measure only due to risk of side effects.
3/14/2014 51

Contamination of Lube oil in Diesel Engine:Contamination of Lube oil in Diesel Engine:
Water
Water from,
1 bil '1.bilge's
2.Jackets
3.Sea via coolers
4.leaky seals or washing in purifiers
5.Condensation
Problems caused by water contamination,Problems caused by water contamination,
•Water leads to corrosion especially if there is sulphur
present due to fuel contamination
forms emulsions which are not capable of withstanding•forms emulsions which are not capable of withstanding
high loads
•removes water soluble additives when centrifuged out
•leads to possible bacterial attack
3/14/2014 52

Fuel
May be heavy residual or light diesel/gas oil and can be sourced toMay be heavy residual or light diesel/gas oil and can be sourced to
faulty to cylinder combustion or faulty seals on fuel p/ps.
Problems
Increases viscosity for hfo reduces viscosity for D O- Increases viscosity for hfo, reduces viscosity for D.O.
- Reduces flashpoint
- Introduces impurities such as sulphur
Dil t l b il h i l titi- Dilutes lub oil when in large quantities.
Solid impurities
b f th li d b ti ti l l fcarbon from the cylinder combustion process, particularly of
importance with trunk piston engines but also for crosshead engines
with inefficient diaphragm. The carbon can lead to restrictions and
f f Sblockages of oil ways causing bearing failure. Straight mineral oils
hold 1% carbon in suspension, dispersant oils hold about 5%.
3/14/2014 53

Bacterial attack:
Certain bacteria will attack oil but water must be present TheCertain bacteria will attack oil but water must be present. The
bacteria may exist in a dormant state in the oil but water is
required if they are to reproduce.. The bacteria digest the oil
causing breakdown emulsions to be formed, acidity
increases, dead bacteria block filters and corrosive films form
on working surfaces.on working surfaces.
In summary their must be three essential conditions for
microbiological growth;
1 There must be a source of carbon present in the oil1. There must be a source of carbon- present in the oil
2. There must be some bacteria or fungal spores present-
these are almost universally present in the atmosphere.
3. There must be free water present.
3/14/2014 54

Two other factors which encourage the growth of bacteria:
1. A slight acidity in the water (pH 5 or 6) and
2. A slightly raised temperature (20 to 40oC) which can lead to2. A slightly raised temperature (20 to 40 C) which can lead to
rapid growth.
Biocide additives are available but they are not always compatible
with other desired additives and can lead to large organicwith other desired additives and can lead to large organic
blockages if treated in the machinery. The best solution is to avoid
the presence of water. If mild attack takes place the oil may be
heated in the renovating tank to above 90oC for 24hrs before being
returned to the sump via the centrifugal separator. For a severe
attack the only solution is complete replacement of the charge y p p g
followed by sterilization of the system. It may be noted that on
replenishment the bacteria may be present in a dormant state in
the new chargethe new charge.
3/14/2014 55

LUBRICATION FEATURES OF A LARGE DIESEL ENGINELUBRICATION FEATURES OF A LARGE DIESEL ENGINE
• In some engines such as long and super long stroke engines, the
piston is not directly connected to the crank pin via a connectingpiston is not directly connected to the crank pin via a connecting
rod.
• The piston has a piston rod extending from the bottom of theThe piston has a piston rod extending from the bottom of the
piston.
• The piston rod is then connected to the connecting rod at the
h d b icrosshead bearing.
• The crosshead bearing has a to and fro motion and therefore a
continuous hydrodynamic film cannot formcontinuous hydrodynamic film cannot form.
• Therefore oil has to be pumped to the crosshead bearing at a
predetermined pressure in order to take the loads of compression
56
and combustion.
• The crosshead is connected to the crank pin via a connecting rod.3/14/2014

Piston
Piston rod
Piston rings
Piston skirt
Pl tf ti li d Piston rod
Stuffing box
Platform separating cylinder
from crank case
Crosshead, crosshead
bearing (reciprocating)
Connecting rod
Oil pumped at
a certain
pressure
Crank pin, bottom end
bearing (rotatory motion)
Journal journal bearing
57
Journal, journal bearing
(rotatory motion)
Web
3/14/2014

Problems caused by stuffing box leakage oil enteringProblems caused by stuffing box leakage oil entering
crankcase:
Low speed engines are particularly at risk from crankcase
l b i t t i ti d b li d il d i t thlubricant contamination caused by cylinder oil drainage past the
piston rod gland and combustion products. This can lead to
severe damage of engine crankcase components and reduction
of life of oil which is normally expected to last the lifetime.
There has been a general increase in the viscosity and Base
number of crankcase oils over recent years particularly fory p y
engines built since the early 1980's. Increased alkalinity, viscosity
and insolubles, fuel derived elements such as vanadium and oil
additive derived elements such as calcium, suggest that theadditive derived elements such as calcium, suggest that the
contamination is from the cylinder oil drainage.
Deterioration of the crankcase oil has led to the expensive
necessity of replacing up to 50% of the sump this is particularlynecessity of replacing up to 50% of the sump, this is particularly
of concern as it is often only a temporary measure.
3/14/2014 58

Four causes are put forward:Four causes are put forward:
1. New crankcase oil contaminated with new cylinder oil-unlikely
2. Cylinder oil drainings being recycled and returned to the sump-very
likely as it is a common practice to purify oil leaking through the gland,y p p y g g g ,
tests done on this purified oil found high amounts of insolubles.
3. Leakage past rod gland- very likely, high pressure scavenge air can
blow cylinder oil and dirt past the top scrapper ring and sealing ringsy p p pp g g g
into the piston rod drain tank, and even possibly directly into the sump.
A problem that worsens with age and wear.
4. Leakage of exhaust valve lubrication system-unlikely
The most likely cause for contamination is leakage past the
piston rod. It is seen that maintenance of the stuffing box is of the
utmost importance. Tell tales and drainage lines should be proved free
and use of oil drained from the uppermost drain should not be allowed
even after purification due to the high level of contamination which can
destroy the properties of the oil in the sump.
3/14/2014 59

Cylinder liner lubricationCylinder liner lubrication
The type of Cyl. Lub oil required will depend upon the cylinder
conditions and the engine design e.g crosshead or trunk piston.
Ho e er the propert req irements are basicall the same b t illHowever, the property requirements are basically the same but will
vary in degree depending upon the fuel and operating conditions.
In some engines, lubricating oil in the cylinder is different from the oil
supplied to the other bearings.
The cylinder oil contains additives to withstand the high temperatures
and contaminants from combustion products.
The oil is slightly basic in nature to counter the acids formed from
combustioncombustion.
Scraper rings spread the oil over the liner surface.
Lub. oil is usually injected between the two scraper rings.
Oil is injected at a predetermined period during the downward stroke.O s jected at a p edete ed pe od du g t e do a d st o e
Before starting, oil is pumped into the liner by manual priming
methods.
After starting, the oil pump is driven by the engine through a cam
shaft
60
shaft.
3/14/2014

CYLINDER LUB OIL PROPERTIESCYLINDER LUB OIL PROPERTIES
Normal properties required are:
1 adequate viscosity at working temperature so that the oil1. adequate viscosity at working temperature so that the oil
spreads over the liner surface to provide a tough film which
resists the scraper action of the piston rings
2. the oil must provide an effective seal between the rings and
liliner
3. only a soft deposit must be formed when the oil burns
4. alkalinity level (total base number or TBN) must match the
acidity of the oil being burntacidity of the oil being burnt
5. detergent and dispersant properties are required in order to hold
deposits in suspension and thus keep surfaces clean
Behaviour depends upon the temperature of the liner, piston crown
d i t i TBN d d t l l li k d Thiand piston rings. TBN and detergency are closely linked. This can
have an adverse effect when running on lighter fuels with lower
sulphur content for any period of time. Coke deposits are can
increase.
3/14/2014 61

Cylinder liner
Compression rings
Scraper rings
Oil i j i
p g
Oil injection passage
Piston
Injection points
Cylinder oil
pump/lubricator
Handle
62
Camshaft
3/14/2014

Trunk type engine (no piston rod)‐
Splash type lubricationSplash type lubrication
Piston ringsCylinder liner Piston rings
Gudgeon pin
y
Oil is picked up by the webs
while rotating, and splashed
onto the piston and liner
Crank pin, bottom end
bearing (rotatory
motion)
Connecting rod
Journal, journal bearingJournal, journal bearing
(rotatory motion)
Web extension
63
Web
Web extension
Oil
3/14/2014

Piston rod
CROSSHEAD
LUBRICATION
Telescopic pipes (one
moves inside the
other)
Movement of crossheadOil supply
Crosshead
bearing
Movement of bearing
Connecting rodStationary pipe
64
Connecting rody p p
3/14/2014

Journal bearing
Journal
Bearing
Oil supply
The journal bearing may undergo hydrodynamic lubrication
or a combination of hydrodynamic and hydrostatic (externally
pressurized) lubricationpressurized) lubrication.
The oil supply may be from any one or number of positions,
depending on the design.
65
p g g
3/14/2014

Distribution within a journal bearing
If the maximum radial clearance is Cr
then Cr = e + Hm
where e is the eccentricity between the shaft
and bearing centre line and Hm is the minimumand bearing centre line and Hm is the minimum
clearance (oil film thickness)
an eccentricity factor can be calculated from
n = e / Cr
Factors involved with the eccentricity factor n
are:
minimum oil film thickness,
journal attitude angle- journal attitude angle,
pressure distribution,
peak pressure angle,
friction,friction,
horsepower loss and
oil flow through the loaded region.
The latter three determine the temperature of
the bearing which for high speed bearings can
be a limiting factor.
3/14/2014 66

Oil passage between bearings in a unit
TRUNK TYPE ENGINE
Gudgeon pin
k
Connecting rod
Web
Crank pin
JournalOil passage
(drilled)
673/14/2014

Lubrication systemLubrication system
• TG‐ Temperature gauge
• PG‐ Pressure gauge
ENGINE Shaft
TG PG
Bearings
Cooler
PG
PG
TG
Storage tank Pump
Filter
PG
68
68
Filter
3/14/2014

Engine sump
ENGINE Shaft Bearing
C ti f
Storage tank/sumpPump
Connection for
filling the tank
• The storage tank usually forms the bottom-most compartment of the engine.
strainer
• It is also sometimes known as the sump.
• Oil from the sump is usually transported to the bearings by an engine driven
pump or an independently electric motor driven pump that transports the oil top p p y p p p
the journal bearings.
• Through passages drilled in the crank shaft and webs, it is transported to the
crank pin.
69
p
• Usually a strainer is provided on the suction side of the pump to prevent large
contaminant particles from damaging the pump and bearings.
3/14/2014

Oil cooler‐ tube and shell type
Oil in
TG
TG
TG
PG
Water in Water out
Oil out
TG
PG PG
PG
Oil out
• In this case, cooling water flows through the tubes.
• Oil flows in the shell around the tubes and passes the heat to the water• Oil flows in the shell around the tubes and passes the heat to the water.
• The in/out temperatures of the oil and water are to be monitored.
• Oil pressure is always kept above water pressure to prevent water
70
contamination of oil
• However, if there is a leak oil is lost and the sump level is therefore to be
monitored regularly3/14/2014

Engine lubrication system
Some adverse situations:
• TG- Temperature gauge
• PG- Pressure gauge
Some adverse situations:
•Oil inlet pressure to engine LOW
•Oil outlet temperature from engine HIGH
ENGINE Shaft
TG PG
•Oil outlet temperature from cooler HIGH
Cooler
Bearings
PG
TG
PG
TG
71
71
Storage tank Pump
Filter
3/14/2014

Properties ideal for bearings:
1 Soluble for high speed fluid film hydrodynamic1. Soluble for high speed fluid film hydrodynamic
lubrication, hence, low viscosity with reduced oil film
friction.
2. moderate bearing loads
3. improved heat transfer behavior
4. corrosion protection
5. cooling
6 low friction6. low friction
7. good low temperature viscosity
8. good high temperature viscosity8. good high temperature viscosity
3/14/2014 72

PROPERTIES IDEAL FOR GEAR CASE:
• high film strength to prevent metal to metal contact.
H hi h i i dh i i lidi dHence, high viscosity adhesive to resist sliding and
centrifugal forces
• corrosion protectionp
• cooling
• reduces friction
• good low tempo viscosity• good low tempo viscosity
• good high tempo viscosity The thicker the oil film the
greater the cushioning against shocks. Also less tendency
f it f ti b h d li ti i kfor pit formation by hydraulic action in cracks,
• sound damping properties with cushioning effects
• antifoam propertiesp p
3/14/2014 73

Turbine oilTurbine oil
Compromise between above two requirements
1. Generally a good quality refined mineral oil derived
f ff i b t k d ith ifrom paraffanic base stock used with various
additives including EP additives for highly loaded
gearing.
2. Anti-foaming properties important
3/14/2014 74

Properties of Lubricats and Lubrication

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