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Term Paper of Fluid Mechanics

(MEC207)

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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.
http://www.explainthatstuff.com/water.htmlhttp://www.explainthatstuff.com/water.html


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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.
http://en.wikipedia.org/wiki/Heat_capacityhttp://en.wikipedia.org/wiki/Turbochargerhttp://en.wikipedia.org/wiki/Bearing_(mechanical)http://en.wikipedia.org/wiki/Hydraulic_fluidhttp://en.wikipedia.org/wiki/Working_fluidhttp://en.wikipedia.org/wiki/Automatic_transmissionhttp://en.wikipedia.org/wiki/Torque_converterhttp://en.wikipedia.org/wiki/Torque_converterhttp://en.wikipedia.org/wiki/Automatic_transmissionhttp://en.wikipedia.org/wiki/Working_fluidhttp://en.wikipedia.org/wiki/Hydraulic_fluidhttp://en.wikipedia.org/wiki/Bearing_(mechanical)http://en.wikipedia.org/wiki/Turbochargerhttp://en.wikipedia.org/wiki/Heat_capacity


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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
http://en.wikipedia.org/wiki/Gas_compressorhttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Piston_enginehttp://en.wikipedia.org/wiki/Piston_enginehttp://en.wikipedia.org/wiki/Crankcasehttp://en.wikipedia.org/wiki/Recyclinghttp://en.wikipedia.org/wiki/Burninghttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Landfillhttp://en.wikipedia.org/wiki/Burninghttp://en.wikipedia.org/wiki/Recyclinghttp://en.wikipedia.org/wiki/Crankcasehttp://en.wikipedia.org/wiki/Piston_enginehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Gas_compressor


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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_oil


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http://www.unicornoil.com/Lub_intro.htm http://www.weareoil.com/technical_properties_of_lubricant.htm http://en.wikipedia.org/wiki/Lubricant
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