Fundamentals of Lubricants

Automotive & Industrial Lubrication & Lubricants

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Introduction of Participants

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Safety Talk

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Fundamentals of Lubricants

SEHAM MANSOUR4

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Session ContentsDuring this session we will discuss:Principles of lubricationLubrication regimes (conditions)Factors that influence lubricant choiceBasic lubricant properties

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Session Objective To appreciate the importance of lubrication and how the lubricant protects the equipment being lubricated.6

What is Lubrication? The dictionary defines lubrication as the application of some oily or greasy substance (called lubricant) in order to diminish friction. Although this is a valid definition, it fails to realize all that lubrication actually achieves. 7

Machines need lubricationThree major elementsBearingsGearsCylinders and their pistons

Othersflexible couplingschainswire ropes

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All machines, no matter how complex, can be broken down into basic mechanical elements that require lubrication. The three major elements are: Bearings These may be plain or rolling element types. Special forms of bearing surfaces are cams and cam followers, slide and guides. Gears Cylinders and their pistons.

Other basic elements of machines that require lubrication are flexible couplings, chains and wire ropes.

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Friction

Friction is the resistance to motion of one surface relative to another

Generate heat Promote wear Waste power Increase maintenance cost9

In order to lubricate and thus protect the machines, we have to reduce the friction between moving surfaces as friction generates heat, promotes wear, wastes power and increases maintenance cost.

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Energy Consumed by Friction

30% to 50% of energy generated10

It is reported that between one-third to half of the energy generated is consumed by friction. Therefore, reducing friction consequently reducing wear will make huge savings in terms of longer equipment life, less down time and maintenance cost, reduced production loss and increased machine output.

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Friction

Two types of Friction

Solid Friction Fluid Friction11

Lubricant is used to minimize friction as friction cannot be eliminated.

There are two types of friction: Solid Friction Fluid Friction

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Friction12

When two metal surfaces move against each other, they experience friction.

The seemingly smooth metal surfaces examined under microscope ...

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Solid Friction

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they are not smooth at all; there are peaks and valleys on the surfaces. The rougher the surface, the greater the friction and this is called solid friction.

When two metal surfaces moving relatively against each other without lubrication, a lot of heat and pressure will be generated thus causing the high points or asperites on the two surfaces to weld together and then tear apart making the surfaces rougher. This surface damage is called wear.

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Fluid Friction

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In order to reduce the friction between the metal blocks, we need to introduce a low friction substance to separate the two surfaces. The substance used is called lubricant. The lubricant forms a film between the two surfaces and allows them to slide easily over one another, without surface-to-surface contact.

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Definition of Lubrication

Solid Friction lubricant Fluid Friction

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Definition of LUBRICATION is to convert a solid friction into a fluid friction by using a lubricant, as fluid friction is a lot smaller than solid friction.

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Solid Friction vs Fluid Friction

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Fluid Friction

To better understand fluid friction, just imagine a pack of cards and each card represents one oil molecule. Top layer adheres to the moving surface and moves along. This moving layer drags the layer below it with a slightly reduced speed which, in turn, drags another layer beneath it with more reduced speed and so forth until the speed reduced to zero at the bottom layer which adheres to the stationary surface.17

To better understand fluid friction, just imagine a pack of cards and each card represents one oil molecule. Top layer adheres to the moving surface and moves along. This moving layer drags the layer below it with a slightly reduced speed which, in turn, drags another layer beneath it with more reduced speed and so forth until the speed reduced to zero at the bottom layer which adheres to the stationary surface.So, you can imagine as oil layers slip pass each other they create a little friction which is a lot less than the friction created by two metal surfaces rubbing against each other. This fluid friction within the oil is directly related to a very important property called Viscosity.

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Lubrication Conditions Full FilmHydrodynamicElasto-hydrodynamic Boundary (thin film)Mixed Solid Film

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Three commonly used terms to describe lubrication regimes that occur in the machine: Hydrodynamic lubrication Boundary lubrication Solid Film lubrication18

Hydrodynamic Lubrication

Hydrodynamic lubrication occurs when two surfaces in sliding motion (relative to each other) are fully separated by a film of fluid.19

Fluid film or hydrodynamic lubrication is the most desirable form of lubrication since the film is thick enough to completely separate the load-carrying surfaces and, thus prevent metal-to-metal contact.

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Elasto-hydrodynamic Lubrication

Elasto-hydrodynamic lubrication is similar but occurs when the surfaces are in a rolling motion (relative to each other).20

This diagram provides an example of how operating conditions can produce a Elasto-hydrodynamic lubrication condition. The film layer in elastohydrodynamic conditions is much thinner than that of hydrodynamic lubrication, and the pressure on the film is greater such as ball and rolling element bearings . It is called elasto-hydrodynamic because the film elastically deforms the rolling surface to lubricate it.

Here we have a shaft rotating in a bearing. Immediately after start-up, friction is momentarily high and the shaft tends to climb up the right side of the bearing. As the shaft gains more speed, more oil is drawn into the wedge, a higher fluid pressure is developed and the shaft is lifted and pushed to the left. At full speed, the shaft is supported on a thick oil film and the converging wedge has moved right under the journal, thus achieving a hydrodynamic lubrication.

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Boundary (Thin Film) Lubrication

Boundary lubrication is found where there are frequent starts and stops, and where shock-loading conditions are present.21

Thin films occur when it is not possible to completely maintain full film and some contact between the surfaces happens. This may be due to excessive loads and/or low speed, such as during the start-up of bearings (as shown on previous slide) etc.In order for full-film conditions to be met, the lubricating film must be thicker than the length of the asperities. This type of lubrication protects surfaces the most effectively and is the most desired. Some oils have extreme-pressure (EP) or anti-wear (AW) additives to help protect surfaces in the event that full films cannot be achieved due to speed, load or other factors. These additives cling to metal surfaces and form a sacrificial layer that protects the metal from wear. Boundary lubrication occurs when the two surfaces are contacting in such a way that only the EP or AW layer is all that is protecting them. This is not ideal, as it causes high friction, heat and other undesirable effects.21

Mixed Film Mixed lubrication is a cross between boundary and hydrodynamic lubrication. While the bulk of the surfaces are separated by a lubricating layer, the asperities still make contact with each other. This is where the additives again come into play.

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mixed lubrication regime deals with the condition when the speed is low, the load is high or the temperature is sufficiently large to significantly reduce lubricant viscosity when any of these conditions occur, the tallest asperities of the bounding surfaces will protrude through the film and occasionally come in contact.22

Stribeck Curve

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igure illustrates, according to Stribecks equation, that as the viscosity or speed increases, the lubricant film increases, which in turn reduces friction at least up to the point that boundary lubrication is overcome and any further increases in viscosity and/or speed results in fluid friction and energy losses. But increasing load reduces the lubricant film.23

Solid Film (Dry Film) Various materials that protect interacting surfaces after the fluid film is lost have been either discovered or created. These materials may be applied to a surface in the form of an additive to a fluid lubricant, or in a pure form, and may also be added or alloyed into the surface when the component is being manufactured.

These materials are characterized as dry film or solid film lubricants. Moly, graphite and Teflon are the most commonly recognized by practitioners of machinery lubrication.24

Solid films are used to provide lubrication when it is not practical to effectively separate mating surfaces by fluid or thin films (boundary lubrication).The solid lubricating film is formed when a low friction solid lubricant such as molybdenum disulfide is suspended in a carrier and applied in the manner of a normal lubricant. The carrier may be a grease or a solvent which evaporates, leaving the solid film more or less bonded permanently to the metal surface to provide extra cushioning effects. There are no chemical reactions are involved here.

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Definition of Lubrication With a better understanding of this process, it should be easier to define what lubrication actually is. It is a process of either separating surfaces or protecting them in a manner to reduce friction, heat, wear and energy consumption. This can be accomplished by using oils, greases, gases or other fluids.25

In equipment that handles gases of various kinds, it is often desirable to lubricate the sliding surfaces with gas in order to simplify the apparatus and reduce contamination to and from the lubricant. The list of gases used in this manner is extensive and includes air, steam, industrial gases, and liquid-metal vapours.25

Functions of LubricantLubricating film between moving surfacesAct as a coolantRemove contaminantsHydraulic mediumBoundary lubricationlubricant can no longer form fluid filmRust & corrosion protectionResistance to deposit formation26

A lubricant should have all following functions: forms a lubricating film between two moving surfaces to minimize friction acts as a coolant to remove heat generated in the system carries away contaminants (lubricant being replaced) acts as a hydraulic medium in a hydraulic system provide protection against boundary condition provide protection against rust & corrosion resist deposit formation

The first four properties can be provided by base oils, but the last three will require the assistance of additives.

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Selection of LubricantTemperature of operationSpeedLoadOil change intervalOperating conditions and possible contaminantsMethod of lubricant applicationSize, type and materials of elements to be lubricated27

Wherever possible, follow the recommendations of the equipment manufacturer. If the manufacturers recommendations are not available, a lubrication engineer will take into consideration all above essential factors before making the recommendations.

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ViscosityInternal resistance to flow

Selection of viscosity depends onSpeedLoadTemperature28

Viscosity is used to measure if the oil is thin or thick-bodied. The thicker the oil the higher the resistance and harder to flow.

In day to day example, we can see that honey flows much slower than water because it is thicker in body or more viscous.

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Viscosity

The resistance of Oil to flowHigh viscosityLow viscosity

Changes with the temperature Significantly reduced when temperature increases.Viscosity characteristics29

Speed

The faster a shaft rotates in a bearing, the thicker the developing oil wedge will become. Therefore, for high speed applications we need a light-bodied oil (low viscosity oil) and, conversely, for low speed applications an oil with heavy body (high viscosity) is required.30

The faster a shaft rotates in a bearing, the thicker the developing oil wedge will become. Therefore, for high speed applications we need a light-bodied oil (low viscosity oil) and, conversely, for low speed applications an oil with heavy body (high viscosity) is required.

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Load

A lightly-loaded application will operate with a lighter-bodied oil (low viscosity oil) than a heavily loaded one, as a lesser load-carrying lubricating film is required.31

A lightly-loaded application will operate with a lighter-bodied oil (low viscosity oil) than a heavily loaded one, as a lesser load-carrying lubricating film is required.

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Temperature

Viscosity is dramatically influenced by temperature, as shown in the following diagram illustrating an experiment conducted on the same oil but at varying temperatures.At low temperature, oil does not flow as freely as at high temperature. It is, therefore, very important to indicate the temperature at which the viscosity was determined when reporting a viscosity.32

Viscosity is dramatically influenced by temperature, as shown in the following diagram illustrating an experiment conducted on the same oil but at varying temperatures.

At low temperature, oil does not flow as freely as at high temperature. It is, therefore, very important to indicate the temperature at which the viscosity was determined when reporting a viscosity.32

Types of ViscosityDynamic ViscositymPa.s (milli Pascal.second)low temperature (SAE W grade oil)

Kinematic Viscositymm2/s40 C100C33

Dynamic viscosity is used to measure low temperature viscosities. At low temperature, if the engine oil is too thick then the starter motor will not produce enough power to turn the crankshaft to start the engine. So, dynamic viscosity is used to measure the ability of the engine to crank at certain viscosity and Cold Cranking Simulator (CCS) is the test method used .There are other test methods used to measure low temperature viscosities. For example, Brookefield viscometer is used to measure low temperature viscosities of transmission fluids and tractor fluids.

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Dynamic Viscosity

Rotational viscometers measure dynamic viscosity. A rotor is immersed in the oil. The torque required to rotate it at a given speed, or the speed achieved for a given torque is measured. This provides an indication of an oils viscosity. The thicker the oil, the greater the torque required to turn the rotor or the slower the rotor turns.

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Rotational viscometers measure dynamic viscosity. A rotor is immersed in the oil. The torque required to rotate it at a given speed, or the speed achieved for a given torque is measured. This provides an indication of an oils viscosity. The thicker the oil, the greater the torque required to turn the rotor or the slower the rotor turns.

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The Brookfield Viscometer

The Brookfield viscometer is a device commonly used for the low temperature measurement of transmission fluids and tractor fluids.The rotating spindle is immersed in the cooled oil sample (e.g. down to -55C for a 70W transmission oil). The speed of rotation is selected and the torque reading is a measure of the apparent (or dynamic) viscosity.

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The Brookfield viscometer is a device commonly used for the low temperature measurement of transmission fluids and tractor fluids.The rotating spindle is immersed in the cooled oil sample (e.g. down to -55C for a 70W transmission oil). The speed of rotation is selected and the torque reading is a measure of the apparent (or dynamic) viscosity.

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Cold Cranking Simulator

During the late 1950s, a viscometer was developed. It was called the Cold Cranking Simulator (CCS). An electric motor is used to apply a relatively constant torque to the rotor and the speed of rotation is related to the viscosity. By using this method we can assign a W designation to the oil. For example, oils which do not exceed a specified viscosity at -5C are designated as 25W whereas oils which do not exceed a specified viscosity at -30C are designated as 0W.36

During the late 1950s, a viscometer was developed. It was called the Cold Cranking Simulator (CCS). Its purpose was to try and find a correlation between oil viscosity at low temperatures and the ability of the engine to crank. Because if the oil is too thick then the starter motor will not produce enough power to turn the crankshaft and so the engine will not start. An electric motor is used to apply a relatively constant torque to the rotor and the speed of rotation is related to the viscosity.

By using this method we can assign a W designation to the oil. For example, oils which do not exceed a specified viscosity at -5C are designated as 25W whereas oils which do not exceed a specified viscosity at -30C are designated as 0W.36

Kinematic Viscosity

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The Kinematic viscometer is normally used to measure viscosity at 40C and 100C. The viscosity is measured by timing an oil to pass two points of a narrow capillary tube. This time is then multiplied by a constant (based on the tube size) to give the viscosity.

The viscosity obtained at 100C is used to define the summer or non-W grades of motor oil.Viscosity at 40 C is used to define industrial oils as most industrial equipment operate at around this temperature.

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ViscosityWhat would happen if we have two different types of oils of the same viscosity at a given temperature and we heat these oils up separately?38

They will thin out but probably by a different amount. This phenomenon is caused by another important property called Viscosity Index.

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Viscosity Index (VI)

The resistance of oil viscosity to change with temperaturehigh number, less changelow number, more change39

Viscosity Index (VI) is a number indicating the effect of temperature on the viscosity.The higher the VI, the less viscosity change by temperature, vice versa, the lower the VI, the larger viscosity change with temperature.

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Viscosity Index

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Multigrade oils have higher VI than monograde ones, VI for multigrades is approximately 120 ~ 180, and for monogrades approximately 95 ~ 110.Therefore, multigrade oils are more resistant to viscosity change by temperature than monograde oils. This is because multigrade oils have special additive called Viscosity Index Improver which minimizes change in viscosity by temperature.

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Why Do Oils Have Different VIs?Type of crude oil used paraffins (higher VI) naphthenes aromatics41

These variations in VI are due to different types of crude oils used and the severity of the solvent refining process.Generally, paraffinic crude oils have higher VIs than naphthenic and aromatic crude oils.

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Why Do Oils Have Different VIs?Type of crude oil used paraffins (higher VI) naphthenes aromaticsSeverity of refining time, temperature (solvent refining) pressure, temperature (hydrotreating) Minimum 95 VI42

The severity of the refining process used in the manufacture of the base oil has significant effect on the VI of the base oil produced.

In solvent refining, the amount of time allowed for the solvent to extract the lower VI aromatics out of the oil, and the temperatures used to do this, are factors that influence the degree or severity of refining. By reducing the refining time and temperature, refineries can increase yield and, hence, profits, but the final product has a lower VI. In hydrogen refining (hydrotreating), pressure and temperature conditions can be varied to produce (with the aid of catalysts), higher VI base oils. In either case, as the most severely refined base oils are produced with reduced refinery yield, they are more expensive for oil companies to purchase. Most oil companies set a minimum VI specification (generally 95 VI) as one safeguard to quality of base oils.

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VI Improver Molecule

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Multigrade oil has high VI (Viscosity Index) because it has VII (Viscosity Index Improver) to boost the viscosity index.

VI Improver molecules are long and big and provide thickening power to the oil.

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Expansion of VI Improver

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VI improver is not readily soluble at low temperatures,the molecules curl up in ball shapes. But, as temperature increases, the molecules become more soluble ...When the temperature is low, the VI improver molecule curls up in a ball and, so, does not produce such an obstacle to the flow of the oil around it and the oil flows freely.However, when the oil is heated up, the VI improver molecules expand and...

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VI Improver

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they hinder the movement of the oil molecules, thus the thickening effects.

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ClassificationsWhy do we need classification?indicate applicationdefine oil qualitycommon technical languagereduce errors46

Service classifications are designed to: Allow user to correctly select products which satisfy the lubrication requirements of their equipment. Define oil quality for given application Provide common technical language to avoid misuse of product Reduce lubrication errors and thus provide more protection for the customer.

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Viscosity ClassificationsSAE (Society of Automotive Engineers)

Engine Oils47

Viscosity is the most important property of an engine oil and SAE has established classifications defining different viscosity grade engine oils.

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SAE Viscosity Grades - Engine Oils

WinterSummer48

In this system, there are winter (W) grade and non-winter oils which does not have any suffix. The winter oil describes viscosity at low or sub-zero temperatures whereas summer oil describes viscosity at 100C.For examples, SAE 15W is a winter engine oil and SAE 40 is a summer oil.48

Viscosity Classes of OilViscosity Classes at low Temperatures(-35C to -20 C)

5W10W15W

0W

Winter Grade oils49

Viscosity of Classes of OilViscosity Classes at high Temperatures (100 C)

20

30

40Summer Grade oils50

Engine Oil Classification

Cold GradeDefined by the W = Winter

Warm Grade SAE 15W- 40

SAE xxW yyMultigrade LubricantEx. : Transmission Syn FE 75W-90SAE xxW ou SAE yyMonograde LubricantEx. : Rubia S 10W

The Higher the number , the more viscous is the lubricant

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Engine Oil Classification: Rubia D20W 50

Winter Grade

60

50

40

30

20Starting TSummer GradeThe higher the summer grade, the higher temperature the oil can accept. (protects the engine at high temperature) -30c

-25c

-20c

-15c

-10c

-5c 0W

5W

10W

15W

20W

25W

SAE J300The lower the winter grade the lower temperatures are accepted by the oil(easy start at low temperature)52

Viscosity Grades for Engine Oils (SAE J300)

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Above table describes the maximum low temperature and minimum 100C viscosities for Winter grade oils. Also sets out the minimum and maximum viscosity requirements for different grades of summer oils.

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Monogrades and Multigrades Monograde : SAE 15W, SAE 40 etc.Multigrade : SAE 15W-40 SAE 5W-30 etc.54

If an oil is designed to meet only one viscosity specifications, it is called monograde oil e.g. SAE 15W, SAE 40 etc.

But, if an oil is designed to meet both high and low temperature viscosity requirements, it is called multigrade oil e.g SAE 15W-40.This means the oil meets the SAE 15W winter viscosity specifications as well as summer SAE 40 viscosity specification (i.e. the requirement of viscosity @ 100C).

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Viscosity ClassificationsSAEEngine oilsSAEAutomotive gear oils55

There is another SAE viscosity classification for automotive gear oils and this is covered in SAE J306 55

Axle & Manual Transmission Lubricants (SAE J306)

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Although the numbers used in SAE gear oil viscosity classifications are significantly higher than those used in the engine oil classifications, they do not differ too much in the actual viscosities. For examples, an SAE 10W engine oil is similar in viscosity to an SAE 70W gear oil, an SAE 50 engine oil is similar in viscosity to an SAE 90 gear oil.

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Different Viscosity Systems - Relationship

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As can be seen that at same temperature, an ISO 32 grade industrial oil has about the same viscosity as 70W gear oil and 10W engine oil.

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Viscosity ClassificationsSAEEngine OilsSAEAutomotive gear oilsISOIndustrial Oils58

We have so far considered Automotive classifications. The major Industrial oil viscosity classifications is the ISO (International Standards Organization).

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ISO Viscosity Grades for Industrial Oils

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The actual ISO viscosity grades extend from ISO VG 2 at the lighter end to ISO VG 1500 at the heavier end.

The numbers used to represent the viscosity grades are the mid-point viscosity of a minimum and maximum viscosity limit determined at 40C. An oil with a viscosity which falls in the range 28.8 to 35.3 mm/s at 40C is known as an ISO VG 32 oil.

By contrast, you will recall that the kinematic viscosities for engine oils in the SAE system are specified at 100C, not 40C. Because industrial oils generally operate at temperatures which are closer to 40C than 100C, the ISO VG system defines viscosity limits at 40C.

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Pour PointThe lowest temperature at which the lubricant can still flow.

The pour point is defined by several equivalent standard test methods: NFT 60105, ASTM D 97, ISO 3016.

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ASTM ColorColor variations can be caused by :Differences in crude oilsViscosityMethod and degree of treatment during refiningAdditivesColour has little significant on the quality of the oil.Colour only has significance when staining or discoloration may be undesirable.Darkening of the oil may be caused by :Oxidation or Chemical changeMixture with a darker oil

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Rust Prevention Characteristic

High performance additives in lubricants helps retain lubricant film on the metal surface and prevent it to get exposed with water or atmospheric oxygen.

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Oxidation InhibitionLikened to rusting of iron and steel.Effects of oxidation on the lubricating oil. Darkens in colour Increases in viscosity Becomes acidic Precipitates sludge and lacquer Factors Affecting Oxidation. Temperature Surface exposure to oxygen Catalytic effect of metal

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Why Change the Oil?

UNDESIRABLE CHANGES IN THE LUBRICANT

INCREASE IN VISCOSITY INCREASE IN ACIDITY (formation of corrosive oxygenated compounds) FORMATION OF DEPOSITS, VARNISH AND SLUDGE

OXIDATION DETERMINES THE SERVICE LIFE OF A LUBRICANT

OXIDATION OF THE OIL IN SERVICE

OXYGEN

CATALYSTS(IRON, COPPER)

TEMPERATURE

TIME

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Elemental Analysis

Atomic Absorption Spectrometer (AAS)

Inductive Coupled Plasma Spectrometer (ICP)Calcium, Magnesium and Zinc Contents (ppm/mass%)65

Elemental AnalysisX-Ray Fluorescence Spectrometer (XRF)Calcium, Magnesium and Zinc Contents (ppm/mass%)

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Acid and Base Numbers

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Foam Characteristics

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Cu Corrosion Test

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Rust Prevention Test

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Flash Point

Cleavland Open Cup (COC)Penske Martin Closed Cup (PMCC)71

Demulsibility Test

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Air Release Value Test

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FT-IR Spectrometer (for IR Scan)

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Water Content

Karl Fisher TitratorVisual Crackle Test75

Density

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