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All Synthetic OilsAre Not The Same
Dr. T. Tim NadasdiDr. Jim T. Carey
Dr. Angela Galiano-Roth
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Introduction Synthetic lubricating oils have developed a reputation for working in the most extreme conditions. They have been associated with superior performance
thermal and oxidative stability shear stability low temperature performance low frictional properties
The evolution of mineral oil processing has recently led to the introduction of new families of products, marketed as synthetic lubricants
based on severely hydroprocessed mineral oils
This presentation will provide some insight into: fundamental characteristics of these “newer” synthetics compared to traditional synthetic oils effects that these base oils have on finished lubricant/grease performance
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API Basestock Classifications
API Basestock ClassificationPhysical Specifications
Group VI Sulfur % wt. Saturates % wtManufacturing
ProcessI 80-120 >0.03 <90 Conventional (solvent
refining)II 80-120 <0.03 >90 Require
Hydrocracking/dewaxingIII >120 <0.03 >90 Requires severe
Hydrocracking/dewaxingIV >140 0.00 >90 Chemical Synthesis -
PAOV All other synthetics -
esters, polyglycols,phosphate esters...
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Parameter Group I Group II Group III Group IVComparison of Basestock Properties
Oxidation Stability
Volatility
Additive Solvency of basestockLow Temperature capability
Efficiency / Traction
Relative costs 1 1.1-1.2 1.5 4 to 10Viscosity range at 40 deg C (in cSt) Up to 500 Up to 120 Up to 40 Up to 50,000
Direction of arrow indicates improved performance
Generalized Comparison of Base Stock Properties
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Mineral Oil Molecular Make-Up
PresentationSymbol
Chemical Advantage in aLubricant
Disadvantage in aLubricant
Short ChainParaffins
High volatility Low flash Pt.
Medium ChainParaffins
Higher VI Therm. & oxid. stability
Low solvency
Long ChainParaffins
High VI Therm. & oxid. stability
Low solvency Waxy
Aromatics High solvency High viscosity
Poor oxid. stability Low VI
HeteroatomicMolecules (S, N)
Sometimes oxidativestability
Can affect otherproperties (foam,Demuls, oxidation)
Saturated Rings Better low temp. Better solvency Adds some viscosity
Poor oxidativestability
A
H
R
Group I oils are a mixture of many different molecules with different properties R
R
R
H
HH
HHA
A
A
AA
A
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Mineral Oil Group I - Group III Processing
Hydroprocessing
FurtherHydroprocessing
R
R
R
H
HH
HH
A
A
A
AA
AGP I
R
R
RR
RRR
R
GP II
R
R
R
GP III
Polyalphaolephin (PAO)
Viscosity controlled by molecular design
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Basestock Summary
The processes used to manufacture Group II and Group III oils limit their viscosity to ~120 and 40 cSt at 40oC, respectively
Group II and Group III base oils require liquid thickening agents to meet the viscosity requirements of many industrial applications
PAO oils achieve their high viscosity through molecular design and do not require liquid thickening agents for typical industrial applications
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0
50
100
150
200
250
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Year
Cap
acity
(100
0 B
BL/
day)
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Group II
Group I
Total Capacity
86%
14% 29%
71%51%
49%
North American Base Oil Capacity Change
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Market Changes• 1999 ruling by the National Advertising Division of the Better Business Bureau has expanded the meaning of the word synthetic relative to lubricants
• Synthetic base oil compositions may include a variety of base oils that have been chemically altered and when formulated properly deliver the performance standards expected from a “synthetic” lubricant
• GP II, GP III and white oils may fit the new criteria for synthetics
•Increased North American market capacity for GP II & III oils
Practical Result - the meaning of the term synthetic has been expanded and can no longer be just associated with the performance strengths and chemistry of GP IV/V stocks.
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Let’s Look at 3 “Synthetic” Gear Oils
All 3 oils are considered synthetic hydrocarbons
The difference in the oils is in the blend of PAO, Polyisobutylene (PIB) and Group III base stocks
All other additives in the oils are the same
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Three Synthetic Gear Oils
1. The same commercial premium gear oil additive package in all oils2. The same commercially available ester in all oils
The oils differ ONLY in their base stock composition
Oil A Oil B Oil CHydrocarbon Type PAO PAO/PIB GP III/PIB
Viscosity ISO 460 ISO 460 ISO 460Viscosity Index 164 150 145
PAO 88 51Polyisobutylene (PIB) 37 37Group III Oil 51Gear Oil Additive Package1 2 2 2Ester2 10 10 10
Total 100 100 100
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Test Regiment
Bulk Oil Oxidation Test- This test is run for 24 hours at 375oF. Air is bubbled though the test oilwhich contains a metal catalyst. Viscosity increase and TAN are measured.
Worm Gear Test- This test involves running oils in a worm gear at various loads. It is run for48hrs during which time the oil temperature and gear box efficiency aremonitored. The used oil is tested for shear stablity (viscosity loss) and wearmetals.
Test Method Relation to Lubricant PerformancePour Point ASTM D97 In general, lower pour points indicate better low
temperature performance
Brookfield Visc ASTM D5133 Related to flowability and pumpability of oil at lower temperatures
Bulk Oil Oxidation See Below Estimation of oxidation stability and oil lifeWorm Gear Test See Below Shows lubricant performance in a real worm gear box
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Low Temperature Results - Pour Point
Even with PPD concentration optimized for lowest pour point, Oil C still has a pour point that is 9oC higher than PAO or PAO/PIB blends
Oil A(PAO)
Oil B(PAO/PIB)
Oil C(GP III/PIB)
Oil C+ PPD
-35
-30
-25
-20
-15
-10
-5
01 2 3 4
Deg
ree
Cel
sius
-33 oC
-24 oC
-18 oC
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0
100,000
200,000
300,000
400,000
500,000
600,000
-10 -20 -30
Temperature oC
Visc
osity
in c
P
Oil A(PAO)
Oil B(PAO/PIB)
Oil C(GP III/PIB)
Low Temperature Results - Brookfield Viscosity
Oil A shows significantly better flow characteristics at lower temperatures
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Bulk Oil Oxidation Results
Both TAN and viscosity increase indicate that Oil C undergoes the highest oxidation
0
5
10
15
20
25
% Change in Viscosity 7 7 23Change in TAN (mgKOH/g)
0.4 2.6 3.2
Oil A(PAO)
Oil B(PAO/PIB)
Oil C(GP III/PIB)
Visc
osity
Cha
nge
(%)
TAN
Cha
nge
(mg
KO
H/g
)
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Testing in a Worm Gear BoxWorm Gear
(Steel)
Bearings(Steel)
Driven Gear(Cu/Sn alloy)
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Gear Box Efficiency (%)
Oil A (PAO) has an average efficiency benefit of 6% over Oil C (GP III/PIB)
7071727374757677787980
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hours
Oil A(PAO)
Oil B(PAO/PIB)
Oil C(GP III/PIB)
Effic
ienc
y (%
)Worm Gear Test Results
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Sump Temperature (oF)
165170175180185190195200205210215
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hours
Tem
pera
ture
(o F)
Oil A(PAO)
Oil BPAO/PIB)
Oil CGpIII/PIB)
Oil A Oil B Oil CHydrocarbon Type PAO PAO/PIB GpIII/PIB
Viscosity Change - 1.8% - 4.8% - 5.9%Cu, ppm 70 320 1100Sn, ppm 25 42 160Fe, ppm 1 2 8
Used Oil Data
Worm Gear Test Results
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Oil Summary Group II oils are limited to ~120 cSt and Group III to ~40cStGroup II and Group III base oils require “thickening” agents to meet the viscosity requirements of many industrial applicationsSynthetic industrial lubricants made with Group II/III oils MAY have different performance properties than lubricants made with PAO aloneSelection of synthetic lubricants should focus on product performance, application requirements, and field experienceAll synthetics ARE NOT the same
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Considerations for Greases
Performance differences seen in oils will likely translate to greases
Need to understand grease lubrication regimes and determine which type of synthetic oil will perform best in the intended application
Different types of synthetic oils will likely interact differently with grease thickeners
Effect on bleed rate?Effect on shear stability?Effect on thickener reaction?Effect on low temperature properties?