©INFINEUM INTERNATIONAL LIMITED 2019. All Rights Reserved. Performance you can rely on. ©INFINEUM INTERNATIONAL LIMITED 2019. All Rights Reserved. InfineumInsight.com/Learn Viscosity and Viscosity Modifiers 1
©INFINEUM INTERNATIONAL LIMITED 2019. All Rights Reserved.
Performance you can rely on.
© INFINEUM INTERNATIONAL LIMITED 2019. All Rights Reserved.
InfineumInsight.com/Learn
Viscosity and Viscosity Modifiers
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Base Oil 60-90%
5-15%
5-25%
Viscosity Modifier& flow improver
‘Finished Oil’
Additive PackageLubricantCommercially
available product
Balance of Additives, VM and Base Oil
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Why do we need Viscosity Modifiers?
-30oC
+90oC
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Agenda
03Learn how oils are classified as multigrade
under SAE J300
02Understand why we use viscosity modifiers
and how they work
01 Origins of viscosity
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What is Viscosity?
AREA = A
• Viscosity = shear stress (Newton’s Law)
shear rate• Temperature dependent
• Resistance to flow of a fluid• ‘Thickness’ of a fluid
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What is Viscosity?
Two key types of viscosity:
Kinematic viscosity• Measured under low shear
i.e. gravity
• mm2/s or cSt
Dynamic viscosity• Measured under high shear
environments
• mPa⋅s or cP
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Viscosity of Materials
100 000cP
1cP
0.5cP
Different materials have different viscosities
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Molecular Origins of Viscosity
Flow direction
Molecules interact with surface
Molecules interact with each other
The interacting forces between the layers of molecules creates resistance to flow, giving rise to viscosity
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Viscosity Index
Viscosity Index (VI) defines the viscosity relationship with temperature:
• Low VI oils viscosity change significantly with temperature
• High VI oils viscosity changes much less with temperature
30
120 VI
50
0
100
150
0 VI
200
250
5040 60 70 80
Temperature (°C)
90 110100
300K
ine
mat
ic V
isco
sity
(mm
2/s
)
Same at 100ºC
120 VI
100 VI
0 VI
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What is the Optimal Viscosity?
I II III
Boundary MixedHydrodynamic
Stribeck Curve
Too Thick Too Thin
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Log (speed)
Boundary
Mixed
Hydrodynamic
Fric
tio
n c
oef
fici
ent
Right Viscosity
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What is the Optimal Viscosity?
I II III
Boundary MixedHydrodynamic
Stribeck Curve
Too Thick Too Thin
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Log (speed)
Boundary
Mixed
Hydrodynamic
Fric
tio
n c
oef
fici
ent
Viscous drag energy losses
Right Viscosity
Catastrophic wear
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Viscosity Modifiers
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Viscosity Modifiers
Used in majority of engine oils and many transmission oils
Viscosity Modifiers (VM) are used to reduce influence of temperature on the viscosity of lubricants• Also known as Viscosity Index
Improvers
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Viscosity Modifiers
• Increase viscosity proportionally to the volume that the polymer occupies
• Volume of Viscosity Modifier in solution is dependent on medium it is in, temperature and pressure
• Polymeric in structure
• Occupy large volumes in solution
Many factors will affect how much volume the polymer occupies in space, and therefore how much viscosity it adds
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Function of Viscosity Modifiers
Log
(vis
cosi
ty)
Temperature
Oil A SAE 30
Cold Starting Engine operation
Too thick
Too thin
Oil B SAE 5W
Base oil viscosity has strong temperature dependence
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Function of Viscosity Modifiers
Log
(vis
cosi
ty)
Temperature
Oil A SAE 30
Cold Starting Engine operation
Too thick
Too thin
Oil B SAE 5W
Adding VM reduces temperature dependence, giving protection at higher temperatures, whilst being pumpable at lower temperatures
Oil B + VM = SAE 5W-30 Just Right
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Key Terms
Thickening Efficiency
ShearStability
Shear Stability IndexThickening Efficiency
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Thickening Efficiency
Oil C Oil D
Thickening Efficiency (TE) is amount of viscosity increase per 1% polymer
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Shear-Thinning Temporary & Permanent Viscosity Loss
Non-Reversible
Stationary polymer coil in oil solution
Temporary Viscosity Loss
Orientation of coil under shear forces
Smaller cross-section gives less thickening which equals lower viscosity
Rupture of coil under shear forces
Lower molecular weight gives less thickening which equals lower viscosity
Permanent Viscosity Loss
Non –ReversibleReversible
Applied shear force
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Shear Stability Index (SSI)
SSI depends on polymer chemistry, molecular geometry and molecular weight
• Larger polymers have a greater chance of experiencing permanent viscosity loss
The higher the SSI the more permanent viscosity loss upon oil shearing
Shear Stability Index (SSI) measure of permanent loss of viscosity due to added polymer
• 30 cycles in Kurt Orbahnshear test
• SSI usually measured in a reference oil that represents polymer behavior in SAE 15W-40 grade
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Typical Shear Rates
Shear Rate, sec-1
25
20
15
10
5
0102 103 104 105 106 107
Vis
cosi
ty, m
Pa-s
Idle HighwayRedline
Non-ReversibleShear-Thinning
Oil pump
Pouring oil
Journal bearing
Piston rings
Valve train
There are different shear environments within the engine
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Shear Rate and Shear-thinning
103102 104 105
Shear Rate (sec-1)
107106
Vis
cosi
ty(m
Pa-s
)
5
0
10
15
VMThickening
Other additives
Base Stocks
Low shear viscosity of engine oil,eg pouring oil
High shear viscosity of engine oil.eg Ring Zone,Bearings, Valve Train Shear Rate
Temporaryviscosity loss
Every VM experiences temporary viscosity loss in the oil
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Viscosity Modifier Chemistry
Ethylene-Propylene Co-polymer (OCP)
Polymethacrylate:(PMA)
VM polymers can have different chemistries
PMA
o o oo ooR R R
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Viscosity Modifier Chemistry
Hydrogenated Styrene-Diene:Star Polymer
Hydrogenated Styrene-Diene:Linear Polymer
HSD linear polymers form flexible micelles in solution, whereas star polymers are permanent micelles
Diblock HSD
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Performance Comparison TE vs SSITh
icke
nin
g Ef
fici
ency
0 10 20 30 40 50 60
SSI
Semi-CrystallineOCP
AmorphousOCP
PMA
Hydrogenated Styrene-DieneStar Polymers
Hydrogenated Styrene-DieneLinear Polymers
Factors that need to be considered when selecting VM:
• Cost to achieve required thickening (Cost vs. TE)
• Shear Thinning Properties• Low Temperature Properties• Other performance
harms/credits• Soot handling• Deposit control• Oxidative stability
Higher is better
Lower is better Selection of appropriate VM is
a balance of TE and SSI for your application
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Pour Point Depressants
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Pour Point Depressants
Types:
• Polymethacrylates (PMA)
• Fumarate Vinyl Acetates (FVA)
Break up regularity of wax crystals
• Prevent large crystal sheets from forming
• Encourage small crystals - easier flow
• Minimize low-temperature viscosity
Pour Point Depressants
• Commonly referred to as PPDs
• Also know as Lube Oil Flow Improvers (LOFIs)
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Wax crystal modification by PPD
+ PPD
• Wax crystals can cause most serious type of engine problem
• Engines can start but oil does not flow, leading to catastrophic engine failure
PPDs are needed to stop wax crystals forming at low temperatures
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SAE Viscosity Grades
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Typical Shear Rates
Shear Rate (sec-1)
25
20
15
10
5
0102 103 104 105 106 107
Vis
cosi
ty (
mPa
-s)
Idle HighwayRedline
Non-ReversibleShear-Thinning
Oil pump
Pouring oil
Journal bearing
Piston rings
Valve train
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Viscosity Measurement Methods
KV HTHS
MRV CCS
High temp
Low temp
High shearLow shear
Cold starting
Cold pumping
Oil consumption
Wear / Fuel economy
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SAE J300 Engine Oil Viscosity Grades
6200 at -35°C6600 at -30°C7000 at -25°C7000 at -20°C9500 at -15°C
13000 at -10°C–––––––––
0W5W
10W15W20W25W81216203040405060
SAEGrade
CCSmPa-s, Max
––––––
<6.1<7.1<8.2<9.3
<12.5<16.3<16.3<21.9<26.1
60 000 at -40°C60 000 at -35°C60 000 at -30°C60 000 at -25°C60 000 at -20°C60 000 at -15°C
–––––––––
MRVmPa-s, Maxw/ No Yield
Stress Min
KinematicViscositymm2/s
Max
––––––
1.72.02.32.62.9
3.5(1)
3.7(2)
3.73.7
HTHS@ 106 Sec-1
mPa-s, Min
3.83.84.15.65.69.34.05.06.16.99.3
12.512.516.321.9
(1) For 0W, 5W, 10W Multigrades – Changed from 2.9 in 11/2007
(2) For 15W, 20W, 25W Multigrades and SAE 40 Grade33
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SAE J300 Engine Oil Viscosity Grades
Correct• SAE 10W-30
• Labeling • Must label as the lowest ‘W’ grade
• An oil that meets 5W also meets 10W, 15W, etc.
• Oils with VM must be labeled as multigrades• Care needs to be taken with CCS and HTHS
labelling as there’s overlap between the SAE grades
Incorrect• 10W-30• SAE 10W/30• SAE 10W30• SAE 10w-30
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Summary
Viscosity is a measure of a fluid’s resistance to flow
It depends strongly on temperature
Viscosity modifiers in lubricants:
Used to reduce the influence of temperature on lubricant viscosity
Protect engine at higher temperatures, whilst allowing flow at cooler temperatures
Chemical structure and molecular weight affect performance, which is a careful balance of thickening efficiency and shear stability index
Oil formulators must consider which VM will be most appropriate for their application
Viscosity grades are defined by SAE J300
“Oils which are formulated with polymeric viscosity index improvers for the purpose of making them multiviscosity-grade products are non-Newtonian and must be labelled with the appropriate multiviscosity grade ”
Source: SAE J300
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