Developments in High Temperature Silicone Lubrication

Development of High Service Temperature Lubricants

SAE World CongressDetroit, MIApril 2016

Chad Chichester,

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Outline of Presentation

• Siloxane Structures• Relating Structure to Properties and Performance• Results, Model-Guided Design• Future technologies

2014 Dow Corning . All rights reserved

What is Silicone?

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Terminology DefinitionSil icon The silicon atom or silicon metal

Sil oxane Typically a polymer with Si-O-Si repeating backbone (PDMS)

Sil icone Generic term for Si based materials

A Si O Si O Si A

CH3

CH3

CH3

B CH3

CH3

n

m

28.0855

14SiSilicon

Siloxanes: Functionalized groups in organo-silicon chemistry with Si–O–Si backbone

• Strong Bonds: Si-O (460 kJ/mol) vs. C-C (348 kJ/mol)• Long Bonds: Si-O (0.164 nm) vs. C-C (0.153 nm)• Flexible Bonds: Si-O-Si (143º) vs. C-C-C (110º) • Low Steric Hindrance: Unencumbered Oxygen• Low Glass Transition Temperature (148 K)• High Oxidative Stability PDMS (573 K) to PPMS (649 K)• Thermal-Viscous Stability: PDMS (15 kJ/mol) vs. PAO

(30 kJ/mol)• Permanent Shear Stability: Very Low Monomeric

Friction

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CH3

SiH3C

CH3

OSi

OCH3

CH3

SiCH3

CH3

CH3n


= Si = O = C = H

• Viscosity range 0.65 to 1.000.000 cSt• Very High Viscosity Indices• Excellent thermal & oxidative stability• Excellent low temperature flow ability • Low volatility (even low viscosities)• Good plastic and rubber compatibility • High chemical resistance• Insoluble in water

Three Primary Types of Siloxanes• “Standard” Silicones• Dimethyl fluids are usually silica thickened• Poor metal-to-metal lubrication• Excellent Rubber and plastic lubrication

• L Low loads• E Resists moisture, some chemicals• T -50 to 200 oC temperature range• S Low speeds

Dimethyl Silicone

• Usually Lithium thickened• Widest temperature range among siloxanes• Improved metal-to-metal vs. PDMS

• L Low to moderate loads (poor E.P.)• E Resists moisture, oxidation & corrosion• T -70 to 250 oC temperature range• S Moderate speeds

Phenyl-Methyl Silicone

• Usually fluorocarbon-thickened• Excellent chemical resistance• Better load capacity and wear resistance

• L Moderate to high loads• E Harsh chemical and solvent environments• T -40 to 230 oC temperature range• S Slow to Moderate speeds

Fluoro Silicone

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comparison

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SRVok load (N)

4-ball scar (mm)

400N/1hr

DSC, OOT

Visc -35°C

Visc40°C

Visc100°C VI

PAO-6 350 0.822 202 3424 26 5.6 163PDMS 300 SEVERE 286 234 35 16 466PDMS, Formulated 975 1.378 221 141 22 9.7 473Dimethyl+hexyl 2000 0.879 204 x 28 8.3 298PFPE-Y Branched 2000 0.727 500 54450 94 15.1 169Trifluoropropyl 550 1.182 246 36386 159 29.6 228PFPE-Z Linear 600 1.485 500 3591 160 46.3 332

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Model-Based Siloxane Structure DesignFrom Molecule to Tribology

Molecular properties

Rheological properties Tribological parameters

Tribological Properties

• Molecular structure• Molecular mass

distribution

• Volume structure andVolume Pressure Temperature• Viscosity structure andViscosity Pressure Temperature• Pressure viscosity index

• Geometry• Poisson ratio• Young Modulus• Load• Speed

• Asperity friction• Film friction


Further details in SAE Paper 2016-01-0291

Siloxane Structures

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Si O Si OCH3

H3CCH3

CH3

SiCH3

CH3

O Si CH3

CH3

CH3m n

DP

J

QL


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Siloxane StructuresPolydimethylsiloxane: PDMS

Polycyclohexylsiloxane: PCMS

Polyphenylmethylsiloxane: PPMS

CH3

SiH3C

CH3

OSi

OCH3

CH3

SiCH3

CH3

CH3nMw

increasePDMS

PPMS

PCMS

phenyl branch

cyclohexyl branch

dimethyl branch

NEW


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Siloxane StructuresCopolymers and pendant branches

PAMS

PPAMS

Polyphenylhexylsiloxane: PPAMS

Polyalkylmethylsiloxane: PAMS

Polytrifluoropropylsiloxane: PFMS

alkyl branch

phenylalkyl branch

ALLNEW

NEW


Siloxane Is Adaptable To Diverse Applications


CH3

SiH3C

CH3

OSi

OCH3

CH3

SiCH3

CH3

CH3n

PCMS:Cyclohexyl-methyl

PDMS: Dimethyl

PAMS:Alkyl-methyl

Traction Fluids Energy-Efficient Lubricants

Phenyl- / Fluoro- Siloxane Copolymer Lubricants

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F PhThermal stabilityLubricity

Balance of monomer ratio Degree of polymerization

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Film FrictionElastohydrodynamic Non-Conformal contact Hamrock-Dowson

Film thickness depends on:• Entrainment Speed• Contact Load as function of

Applied load Poison ratio of materials Young’s modulus of materials

• Geometry as function of Surface roughness of materials Diameter of moving parts

• Lubricant’s Viscosity as function of its Monomeric friction Radius of gyration Activation energy (temperature

dependence) Pressure viscosity index (pressure

dependence)


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Boundary Friction and WearLubricants were tested using a ball-on-disk machine to determine the effects of molecular structure on boundary friction and wear

Ball = dia. 3/8”: Steel HRC~60Disk = 52100: Steel HRC~35

Fully FloodedLoad = 5kgDisc Speed = 50mm/sEnt. Speed = 25mm/sDuration = 1000 Rev.



Material MW Density VI Friction Wear [g/cm3] 30oC 125oC 30oC 125oC 30oC 125oC [mm]

PDMS A 1760 0.885 9 3 410 169 91 0.032 0.012 0.26 2.28PDMS B 3270 0.927 19 5 458 244 138 0.03 0.078 0.25 2.20PDMS C 6090 0.942 46 13 457 303 200 0.023 0.009 0.28 2.67PDMS D 9930 0.945 109 27 409 318 206 0.019 0.007 0.27 2.39PDMS E 19900 0.953 276 73 440 229 222 0.013 0.029 0.28 2.24PDMS F 32000 0.966 979 241 475 180 184 0.018 0.006 0.27 2.27PPMS 10A 8180 0.976 95 22 399 419 239 0.023 0.039 0.28 2.35PPMS 10B 26600 0.991 450 109 443 247 226 0.014 0.014 0.29 2.52PPMS 50 2690 1.054 120 16 285 245 0.028 0.029 0.21 0.92PPMS 90 1990 1.074 441 22 191 307 0.018 0.037 0.10 0.40A30-8 9630 0.908 100 18 333 350 199 0.02 0.008 0.21 2.39A30-12 8510 0.921 139 20 313 587 189 0.021 0.016 0.11 0.49A100-8 24000 0.934 998 108 335 651 304 0.016 0.025 0.08 0.25A100-12 29900 0.906 1438 120 314 757 267 0.022 0.014 0.07 0.28A8-8 14500 0.966 192 43 402 288 144 0.022 0.043 0.29 2.81A8-12 15300 0.958 216 40 360 255 217 0.016 0.01 0.27 2.69A30-16 10500 0.908 193 22 306 448 201 0.012 0.019 0.12 0.44A100-8/12 31400 0.886 600 75 326 526 191 0.024 0.009 0.08 0.25PA100 279000 0.977 0.29 2.19PA30 9230 1.026 67 17 411 411 207 0.017 0.008 0.14 0.44PCMS 50 2820 1.022 739 41 280 538 0.018 0.039 0.14 0.49PCMS 90 2090 1744 0.045 0.032 0.13 0.40FMS 100 3240 1.248 296 20 211 1348 324 0.013 0.024 0.11 0.42PAO 2 433 0.782 7 1 118 0.021 0.007 0.12 0.46PAO 4 757 0.804 29 3 137 321 78 0.022 0.012 0.11 0.60PAO 6 956 0.814 48 4 162 473 80 0.022 0.011 0.10 0.30PAO 8 1090 0.813 77 6 165 561 125 0.018 0.011 0.10 0.29PAO 10 1260 0.823 126 6 109 628 132 0.019 0.012 0.10 0.57

BoundaryViscosity [cSt]

EHL Film Thickness [nm] pure rolling

EHL Friction 50 % S/R

Newtonian and Non-Newtonian Siloxanes


PPMS 90 (90% Phenyl) A100-12 (100% Dodecyl)

Ring branches (PPMS and PCMS) show nearly Newtonian nature High aryl and cycloalkyl content causes high pressure-viscosity PPMS 90: High monomeric friction allows a relatively low molecular mass (Mw=1990

g/mol) to build viscosity, so shear thinning is low

Linear branches may exhibit temporary shear-thinning Low to high alkyl branch length causes low pressure-viscosity coeff. A100-12: Low monomeric friction requires a relatively high molecular mass

(Mw=29900 g/mol) to build viscosity, so shear thinning is high

EHD Friction Increases With Cyclic Branch Content


PPMS:Phenyl-methyl PCMS:Cyclohexyl-methyl

Friction at 398 K and Σ=0.5

Cyclohexyl siloxanes have greater thermal stability of performanceFriction at 303 K and Σ=0.5

Comparison with Existing Technologies


Thermal Stability

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Properties of Ph/F copolymer neat fluids

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Wear resistance of neat copolymer fluids

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DIN 51350

SRV measurement results

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Wear resistance improvements by additives

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Copolymer grease properties

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Applications of Siloxanes as Lubricants

Dimethyl Silicone

• Overrunning clutch• Clutch release bearing• Bearings operating at low temperatures

Phenyl-Methyl Silicone

• Potential applications: High temperature bearings

Fluoro Silicone

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Phenyl-Fluoro

Silicone

• Chemical mixers and pumps• O-rings or gaskets exposed to aggressive chemicals• Brake compressor• Plug Valves• Circuit Breakers

• O-ring&valve lubricants• Damping grease• Plastic gears• Break Caliper

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Future Research Opportunities


Si O Si OCH3

H3CCH3

CH3

SiCH3

CH3

O Si CH3

CH3

CH3m n

DP

J

QL

Other types of chemical structures

Mixtures Functional groups Additives

Selected fluids from this work exhibit the following properties: Additive compatibility Miscibility with Hydrocarbons Special High Temperature

Summary

• Silicones stand out synthetic fluids for their exceptional thermal stability and temperature-viscosity indices

• Newly synthesized siloxanes are examples of the tribological potential beyond currently use of silicones– Temporary shear thinning Polyalkylmethyl siloxanes– High traction Polycyclohexylmethylsiloxanes– High temperature Ph/F co-polymers

• Flexible structure of new Ph/F copolymers allows design of fluids with high termal stability and improved wear resistance

• Their additive acceptance offers additional possibilities for lubricant formulation

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Thank you!

Developments in High Temperature Silicone Lubrication

Engineering

Transcript of Developments in High Temperature Silicone Lubrication