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Term Paper of Fluid Mechanics
(MEC207)
Only in Rs. 150Call for purchase09988045377
Topic: What are essential properties of lubricants and types
used in industries?
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Contents:
1.Introduction2.How lubricants work3.Properties and Additives for lubricants4.Types5.Purposes6.Tribological Analysis7.Industrial Uses8.Disposal and Environmental issues9.References
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1. Introduction: Lubricants (sometimes referred to as lube)
The substance used between contact surfaces of moving parts to reduce friction and to
dissipate heat is termed as lubricant. A lubricant may be oil, grease, graphite, or any
substancegas, liquid, semisolid, or solidthat permits free action of mechanical devices
and prevents damage by abrasion and seizing of metal or other components through
unequal expansion caused by heat. In machining processes lubricants may also function as
coolants to forestall heat-caused deformities.The science of friction, lubrication, and surface
wear is called tribology. In addition to industrial applications, lubricants are also used in
cooking (oils and fats are used in frying pans, in baking to prevent food sticking), bio-
medical applications on humans (e.g. lubricants for artificial joints), ultrasound examination,internal examinations for males and females.
2. How Lubricants work:
Solids are materials that have a built-in resistance to changing shape, whereas liquids can
flow. Think of the difference between ice (which just sits there in a lump) and water (which
flows easily as you pour it). If you put a liquid like oil between two solid gears, it will shift
about and change its shape as much as it needs to, cushioning the microscopic bumps
between the gears as they mesh together and reducing the friction between them.
Car engines use thick, syrupy oils for lubrication because these stay liquid at over 300C
(570F)the kind of temperatures engine parts heat up to. Water would quickly evaporate
and turn to steam in those conditions but it also makes metal parts turn rusty, so it's not really
a good choice for a lubricant. Engine parts like a car's gearbox are coated with oil or grease to
reduce friction. Some of these parts are not machined smooth, as you might expect, but
deliberately left a bit rough so that lubricants will cling to them and keep on doing their job.
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Figure 1 Ball bearing
It helps to reduce friction in moving machine parts. There's an outer metal ring fastened to one part of the
machine and an inner metal ring fastened to another part. The two rings are separated by a circular collar (here
colored reddish-brown) with holes inside it. The collar can rotate freely on metal balls that rest in the holes.
Bearings are usually lubricated to keep them running smoothly. Photo courtesy: NASA Glenn Research
Centre (NASA-GRC).
3. Properties:
The lubricant is called upon to limit and control the following:
Friction between the components and metal to metal contact Over heating of the components Wear of the components Corrosion Defects
To accomplish the above functions, a good lubricant shouldposses properties:
Suitable viscosity Oiliness to ensure the adherence of the bearings ,and for loss friction and
wear when the lubrication is in the boundary region, and as a protective
covering against corrosion.
High strength to prevent the metal to metal contact and seizure under heavyload. Should not react with the lubricating surface.
A low pour point to allow the flow of lubricant at low temperature to the oilpump.
No tendency to form deposits by reacting with air, water, fuel or theproducts of combustion
Cleaning ability Non foaming characteristic Non toxic Non flammable Low cost
I. KINEMATIC VISCOSITY:
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Significance & Use: The proper operation of equipment depends on the proper kinematic
viscosity at operating temperature of the oil used for its lubrication.
What it means: Kinematic viscosity is a measure of a liquid's flow under the influence of
gravity. Synthetic lubricants' kinematic viscosity's are midrange, close to neither the high or
low limit. That helps components work their best and helps the lubricants stay in grade.
Dynamic (Absolute) Viscosity = (Force/Area) (Film Thickness/Velocity)
= Kinematic Viscosity Density
II. VISCOSITY INDEX:Significance & Use: Viscosity index indicates how much a lubricant's viscosity will change
according to changes in temperature between 40C (104F) and 100C (212F), which
roughly define the normal temperature range of most operations.
What it means: The smaller a lubricant's viscosity change as a result of temperature change,
the higher that lubricant's viscosity index. High viscosity index lubricants, such as AMSOILproducts, protect better in operations with temperature variations.
III. COLD CRANK SIMULATOR APPARENT VISCOSITY:Significance & Use: Apparent viscosity has been established as a valid predictor of engine-
cranking viscosities at specified low temperatures. Apparent viscosity depends on
temperature and shear rate.
What it means: Cold cranking viscosity affects the start ability of engines and other
equipment in cold temperatures. Low cold cranking viscosities make for easier cold cranking
and more dependable cold temperature starting.
IV. BORDERLINE PUMPING TEMPERATURE:Significance & Use: Borderline pumping temperature is a measure of the lowest temperature
at which engine oil can be continuously and adequately supplied to the components of an
automotive engine.
What it means: The lower the borderline pumping temperature, the lower the temperature in
which the engine is protected by circulating oil. Synthetic motor oil's extremely low
borderline pumping temperatures assures excellent low temperature protection.
V. POUR POINT:Significance & Use: The test determines the lowest temperature at which oil flows as the jar
is tilted for a prescribed period. The pour point of oil indicates the lowest temperature at
which oil may be used in some applications.
What it means: the lower the pour point, the more useful the lubricant is in cold temperatures.
VI. FLASH AND FIRE POINTSSignificance & Use: Flash point is the lowest temperature at which application of a flame
causes specimen vapours to ignite. Flash point is used to assess the overall hazard of a
material and is used in shipping and safety regulations to define "flammable" and"combustible" materials. Fire point is the lowest temperature at which a specimen sustains
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burning for five seconds.
What it means: Lubricants with high flash and fire points are safer to use and transport than
lubricants with lower ones and have a greater high temperature operating ranges.
VII. NOACK VOLATILITY:Significance & Use: Test determines the evaporation loss of lubricating oils at high
temperature. Evaporation loss is particularly important to motor and cylinder lubrication, due
to the high temperature of these operations and the tendency of evaporative loss to increase in
high temperatures. Significant evaporative loss of oil leads to excessive oil consumption and
destructive changes in oil properties.
What it means: Lubricants with low Noack scores lose less to volatility than lubricants with
high scores. Low-loss oils keep their original protective and performance qualities longer
than high-loss oils do, which keeps oil consumption low and fuel economy and equipment
protection high.
VIII. HIGH TEMPERATURE/HIGH SHEAR VISCOSITY:Significance & Use: Viscosity at the shear rate and temperature of this test is considered
representative of the condition encountered in the bearings of automotive engines in sever
service. Lubricant viscosity in the bearings of automotive engines in severe service is a
critical factor in bearing wear.
What it means: Lubricants with high scores maintain their viscosity in high temperatures after
exposure to high shear. That means they continue to protect engine bearing even after
exposure to sever service conditions.
IX. FOUR BALL WEAR TEST:Significance & Use: Test method determines the relative wear preventive properties of
lubricants in sliding contact under the test conditions. Lubricant comparisons are made by
comparing the average wear scars on three fixed balls made by one ball in rotating contact
with them in baths of the test lubricants.
What it means: The smaller the average wear scar, the better the protection. The Four Ball
Wear Test may be conducted at various levels of severity.
X. Emulsibility, Demulsibility Charateristics:
A highly refined petroleum lubricant resists the tendency to form emulsion mixtures with
water and will generally phase-separate upon standing. However, in pressurized circulating
lubrication systems, the mechanical action of the pump and other components can cause oil
and contaminating water to form an emulsion. Moreover, the system flow rate may be high
enough to prevent sufficient standing time in the reservoir to allow phase separation to occur.
XI. Extreme-Pressure Properties of Lubricants:
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One of the most important attributes of lubricating oil is the ultimate load that can be
sustained without seizure or scoring of the lubricated sliding surfaces. The seizure
condition relates to welding or fusion of metal asperities on the rubbing test pieces, while the
scoring characterizes the nature (furrowed scar) of the seizure.
XII. Foaming Characteristics:A reliable lubricant should release entrained air or other gas and resist foaming. Excessive
foaming is detrimental to the operation of most machinery fluid systems. Foam can fill the
internal spaces such as a separator or reservoir resulting in poor system efficiency or failure;
cause a vapour block in filters resulting in oil starvation; and cause excessive wear of
lubricated parts due to the poor load-carrying ability of entrained gas (air). Excessive foaming
can result in oil loss due to the overflow of the reservoir through vents and create
maintenance problems.
Foaming is attributed to air entrainment due to mechanical
working of the oil during machine operation. In addition, the presence of water and surface
active materials in the oil such as rust preventatives, detergents, etc. can cause foaming.
Foaming may be controlled to some extent with the use of additives. Since these materialscan increase the tendency of the oil to entrain air, the optimum amount of additive for the
oil application must be determined.
XIII. Hydrolytic Stability Characteristics:
A reliable lubricant should resist the tendency to hydrolyze at machinery operating
temperatures when in the presence of water and copper components. Poor hydrolytic stability
gives rise to the formation of acidic by-products and insolubles, which in turn results in
deposits of varnish and sludge and chemical leaching of copper and other machinery metals.
This property is of particular importance for equipment utilizing ester-based lubricating orhydraulic fluids.
ADDITIVES FOR LUBRICANTS:
The lubricating oil should posses all the above properties for the satisfactory engine
performance. The modern lubricants for heavy duty engines are highly refined which
otherwise may produce sludge or suffer a progressive incrase in viscosity. For these reasons ,
the lubricants are seasoned by the addition of certain oil soluble organic compounds
containing inorganic elements such as phosphorus sulphur, AMINE derivatives. METALS
are added to the mineral based lubricating oil to exhibit the desired properties. The oil soluble
organic compounds added to the present day lubricating to impart one or more of the
following characteristics.
Anti-oxidant and anti-corrosive agents Detergent-dispersant Extreme pressure addition power point depression viscosity index improver antifoam agent Oiliness and film-strength agents.
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4. Types of Lubricants used in Industries:
Classification of Lubricants:
Lubricants are classified on the basis of their physical state as follows:
1. Liquid Lubricants or Lubricating Oils2. Semi-Solid Lubricants or greases
3. Solid Lubricants.
1. Liquid Lubricants or Lubricating Oils:
Lubricating oils reduce friction and wear between two moving metallic surfaces by providing
a continuous fluid film in between the surfaces. A good lubricant must have the following
characteristics.a.It must have high boiling point or low vapour pressure.
b.Thermal stability and oxidation resistance must be high.
c.It must also have adequate viscosity for particular operating conditions.
d.The freezing point must be low.
e.It must also have non-corrosive property lubricating oils are further sub classified as:
a. Animal and Vegetable oils
b. Petroleum oils or Mineral oils
c. Blended oils or Additives for lubricating oils
d. Synthetic lubricants
Animal and Vegetable oils: Animal and vegetable oils are glycosides of higher fatty acids.
They have very good oiliness. However, they are costly, undergo oxidation very easily, andhave a tendency to hydrolyze when it contact with moist air or water. These oils undergo
decomposition on heating without distilling, and hence they are fixed oils. They are used as
additives to improve the oiliness of petroleum oils.
Petroleum oils or Mineral oils: They are obtained by fractional distillation of crude
petroleum oils. The length of the hydrocarbon chain varies between C12 to C50. They are
cheap and quite stable under operating conditions. They possess poor oiliness, the oiliness of
which can be improved by the addition of higher molecular weight vegetable or animal oils.
Crude liquid petroleum oil cannot be used as such, because they contain lot of impurities like
wax. Asphalt, colored substances and other oxidisable impurities
Blended oils or Additives for lubricating oils: No single oil serves as the most suitable
lubricant for many of the modern machineries. Specific additives are incorporated intopetroleum oils to improve their characteristics. These oils are to improve their characteristics.
These oils are called blended oils and give desired lubricating properties, required for
particular machinery.
Synthetic lubricants: Mineral oils cannot be used effectively as they tend to get oxidized at
very higher temperatures while wax separation will occur at very low temperatures. so,
synthetic lubricants have been developed, which can meet the severe operating conditions
such as in aircraft engines. The same lubricants may have to be in the temperature range of
-50 0C to 250 0C. Polyglycol ethers, fluoro and chloro hydrocarbons, organophosphates and
silicones are currently used as synthetic lubricants.
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2. Semi-Solid Lubricants or greases: Grease is a semi solid lubricant obtained by
thickening liquid lubricating oil through the addition of a metallic soap. The thickness is
usually sodium or calcium or lithium soap.
Types of grease: a. Soda-base grease
b. Lime-base grease
c. Lithium-soap greased. Barium-soap grease
e. Axle (Resin) grease
3. Solid Lubricants:. Solid lubricants are used where
The operating temperature and load is too high.
Contaminations of lubricating oils or greases by the entry of dust or grit particles are
avoided.
Combustible lubricants must be avoided.
Graphite and Molybdenum disulphide are the widely used solid lubricants.
Graphite: It consists of a multitude of flat plates, which are held together by weak Vander
Waals forces, so the force to shear the crystals paralled to the layers is low. It is used either in
powder form or as suspension. When graphite is dispersed in oil, it is called oil dag andwhen graphite is dispersed in water is called aquadag. It is ineffective at above 370 0C. It
is used for lubricating internal combustion engines.
Molybdenum disulphide: It has a sand-witch like structure in which a layer of molybdenum
atoms lies between two layers of sulphur atoms. The weak Vander Waals forces, acting in
between the layers, can be destroyed easily. MoS2 can also be used as power or dispersions.
It is effective up to 800 0C. It is used in wire-drawing dues.
5. Purposes:
Keep moving parts apart:
Lubricants are typically used to separate moving parts in a system. This has the benefit of
reducing friction and surface fatigue together with reduced heat generation, operating noise
and vibrations. Lubricants achieve this by several ways. The most common is by forming a
physical barrier i.e. a thin layer of lubricant separates the moving parts. This is termed
hydrodynamic lubrication. In cases of high surface pressures or temperatures the fluid film is
much thinner and some of the forces are transmitted between the surfaces through
Reduce friction:
Typically the lubricant-to-surface friction is much less than surface-to-surface friction in a
system without any lubrication. Thus use of a lubricant reduces the overall system friction.
Reduced friction has the benefit of reducing heat generation and reduced formation of wear
particles as well as improved efficiency. Lubricants may contain additives known as friction
modifiers that chemically bind to metal surfaces to reduce surface friction even when there is
insufficient bulk lubricant present for hydrodynamic lubrication, e.g. protecting the valve
train in a car engine at start-up.
Transfer heat:
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Both gas and liquid lubricants can transfer heat. However, liquid lubricants are much more
effective on account of their high specific heat capacity. Typically the liquid lubricant is
constantly circulated to and from a cooler part of the system, although lubricants may be used
to warm as well as to cool when a regulated temperature is required. This circulating flow
also determines the amount of heat that is carried away in any given unit of time. High flow
systems can carry away a lot of heat and have the additional benefit of reducing the thermal
stress on the lubricant. Thus lower cost liquid lubricants may be used. The primary drawback
is that high flows typically require larger sumps and bigger cooling units. A secondary
drawback is that a high flow system that relies on the flow rate to protect the lubricant from
thermal stress is susceptible to catastrophic failure during sudden system shut downs. An
automotive oil-cooled turbocharger is a typical example. Turbochargers get red hot during
operation and the oil that is cooling them only survives as its residence time in the system is
very short i.e. high flow rate. If the system is shut down suddenly (pulling into a service area
after a high speed drive and stopping the engine) the oil that is in the turbo charger
immediately oxidizes and will clog the oil ways with deposits. Over time these deposits can
completely block the oil ways, reducing the cooling with the result that the turbo charger
experiences total failure typically with seized bearings. Non-flowing lubricants such as
greases & pastes are not effective at heat transfer although they do contribute by reducing the
generation of heat in the first place.
Carry away contaminants and debris:
Lubricant circulation systems have the benefit of carrying away internally generated debris
and external contaminants that get introduced into the system to a filter where they can be
removed. Lubricants for machines that regularly generate debris or contaminants such as
automotive engines typically contain detergent and dispersant additives to assist in debris and
contaminant transport to the filter and removal. Over time the filter will get clogged and
require cleaning or replacement, hence the recommendation to change a car's oil filter at the
same time as changing the oil. In closed systems such as gear boxes the filter may be
supplemented by a magnet to attract any iron fines that get created. It is apparent that in a
circulatory system the oil will only be as clean as the filter can make it, thus it is unfortunate
that there are no industry standards by which consumers can readily assess the filtering ability
of various automotive filters. Poor filtration significantly reduces the life of the machine
(engine) as well as making the system inefficient.
Transmit power
Lubricants known as hydraulic fluid are used as the working fluid in hydrostatic power
transmission. Hydraulic fluids comprise a large portion of all lubricants produced in the
world. The automatic transmission's torque converter is another important application for
power transmission with lubricants.
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Protect against wear:
Lubricants prevent wear by keeping the moving parts apart. Lubricants may also contain anti-
wear or extreme pressure additives to boost their performance against wear and fatigue.
Prevent corrosion:
Good quality lubricants are typically formulated with additives that form chemical bonds
with surfaces to prevent corrosion and rust.
Seal for gases:
Lubricants will occupy the clearance between moving parts through the capillary force, thus
sealing the clearance. This effect can be used to seal pistons and shafts.
6. Tribological Analysis:The study of wear in mechanical systems is part of a scientific discipline called tribology
(triboto rub in Greek).Wear in mechanical systems is the result of tribological action, and
is defined as the progressive loss of substance from the surface of a solid body due to contact
and relative motion with a solid, liquid, or gaseous body. Tribological analysis of a machine
leads to identification of types of tribological actions in the machine and thereforeidentification of possible wear modes and their severity. This information combined with
identification of internal and external contamination sources is used to develop sampling and
detection procedures of monitoring and diagnostic purposes.
Figure 2 Causes of bearing failures.
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Wear results in producingwear particles and in changes in the material and geometry of the
tribologically stressed surface layers of the components forming a tribological pair, that is,
two components that are in contact with each other. Normally wear is unwanted; however, in
certain circumstances, for example, during running-in, wear may be beneficial. A typical
example of a tribological pair is a pair of gears in which tribological action occurs on the
meshing surfaces. Elements of a tribological pair may be in direct contact (e.g., not lubricatedgears) or contact between these surfaces may be via interfacing medium (e.g., lubricant) that
modifies interaction between the elements of a tribological pair. The body and counterbody
are members of a wear couple where wear is of particular importance. The interface medium
may have a wear reducing effect (e.g., lubricant) or wear increasing effect (e.g., dust). The
environment may also play a major role in the wear process. The external operating variables
that act on the elements of the tribological system form the operating variables of the
tribological system. Thewear characteristics describe the nature of material loss that occurs
through the action of the operating variables. Tribological action requires both contact
between the wearing couple and relative velocity between elements of the couple. External
actions on the element, for example, bending or shear are not considered to be tribological
actions.
Figure 3 Tribological actions
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Figure 4 Tribological Parameters
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Figure 5 Contact Areas between surfaces (dry friction)
7. Industrial Uses:
1. Hydraulic oils2. Air compressor oils3. Gas Compressor oils4. Gear oils5. Bearing and circulating system oils6. Refrigerator compressor oils7. Steam and gas turbine oils8. Aviation9.
Gas turbine engine oils
10.Piston engine oils11.Marine12.Crosshead cylinder oils13.Crosshead Crankcase oils14.Trunk piston engine oils15.Stern tube lubricants
8. Disposal and Environmental issues:
Figure 6 the Waste Hierarchy
It is estimated that 40% of all lubricants are released into the
environment. Disposal: Recycling, burning, landfill and discharge into water may achieve
disposal of used lubricant. Burning the lubricant as fuel, typically to generate electricity is
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also governed by regulations mainly on account of the relatively high level of additives
present. Burning generates both airborne pollutants and ash rich in toxic materials, mainly
heavy metal compounds. Thus lubricant burning takes place in specialized facilities that have
incorporated special scrubbers to remove airborne pollutants and have access to landfill sites
with permits to handle the toxic ash. Unfortunately, most lubricant that ends up directly in the
environment is due to general public discharging it onto the ground, into drains and directly
into landfills as trash. Other direct contamination sources include runoff from roadways,
accidental spillages, natural or man-made disasters and pipeline leakages. Improvement in
filtration technologies and processes has now made recycling a viable option (with rising
price of base stock and crude oil). Typically various filtration systems remove particulates,
additives and oxidation products and recover the base oil. The oil may get refined during the
process. This base oil is then treated much the same as virgin base oil however there is
considerable reluctance to use recycled oils as they are generally considered inferior.
Basestock fractionally vacuum distilled from used lubricants has superior properties to all
natural oils, but cost effectiveness depends on many factors. Used lubricant may also be used
as refinery feedstock to become part of crude oil. Again there is considerable reluctance to
this use as the additives, soot and wear metals will seriously poison/deactivate the critical
catalysts in the process. Cost prohibits carrying out both filtration (soot, additives removal)
and re-refining (distilling, isomerisation, hydrocrack, etc.) however the primary hindrance to
recycling still remains the collection of fluids as refineries need continuous supply in
amounts measured in cisterns, rail tanks. Occasionally, unused lubricant requires disposal.The best course of action in such situations is to return it to the manufacturer where it can be
processed as a part of fresh batches. Environment: Lubricants both fresh and used can cause
considerable damage to the environment mainly due to their high potential of serious water
pollution. Further the additives typically contained in lubricant can be toxic to flora and
fauna. In used fluids the oxidation products can be toxic as well. Lubricant persistence in the
environment largely depends upon the base fluid, however if very toxic additives are used
they may negatively affect the persistence. Lanolin lubricants are non-toxic making them the
environmental alternative which is safe for both users and the environment.
9. References:
Lubrication and Maintenance of industrial Machinery ;Author: Robert M.Gresham and George E. Totten; (Society of Tribologists and Lubrication
Engineers); ISBN-13: 978-1-4200-8935-6
http://en.wikipedia.org/wiki/Crude_oilhttp://en.wikipedia.org/wiki/Distillinghttp://en.wikipedia.org/wiki/Lanolinhttp://en.wikipedia.org/wiki/Lanolinhttp://en.wikipedia.org/wiki/Distillinghttp://en.wikipedia.org/wiki/Crude_oil7/30/2019 Term Paper of Fluid
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