This document summarizes research on friction modifiers and lubricity additives for industrial lubricants. Testing showed that polymeric additives reduced friction and wear in neat metalworking fluids, hydraulic fluids, and industrial gear oils compared to conventional additives. However, some polymeric additives caused hydraulic fluids and gear oils to emulsify water, preventing their use. The best performing additives were formulation-dependent and provided both friction reduction and demulsification properties.
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Friction Modifiers and Lubricity Additives
• A lubricity additive (LA) is a generic description for an additive added to a lubricant
formulation to perform one or more specific tasks, such as, reduced wear, prevent
metal-metal welding, to lower torque or to control friction
• A friction modifier is used to control friction, which may mean reducing the
coefficient of friction to very low levels or it may mean controlling friction between
specific values
• Ordinarily a formulator needs to chose one or more additives that are designed to
perform one or more of these tasks
• e.g. FMs to reduce friction, extreme pressure (EP) additives to prevent
welding, ZDDP for anti-wear protection
• The new FMs presented today have the capability to provide extremely low
coefficient of friction whilst significantly reducing wear
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New Friction Modifiers
• Organic (C, H, O)
• Metal Free
• Free from Phosphorus, Sulphur and Chlorine
• Examples of polymeric and non-polymeric
• Tailored to specific applications
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Models of a conventional FM GMO vs polymeric HPLA
Green = non polar - oil soluble, Yellow = polar – attractive to metal
surfaces
Conventional and Polymeric Friction
Modifiers
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• Reduce the torque required for form tapping to provide
greater energy efficiency
• Reduce wear to increase tool life
• Multi-metal applications
Aim
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Neat Metalworking Fluids
• Group I mineral oils used as the base fluid
• Polymeric High Performance Lubricity Additive (HPLA)
added at 8% and 16% for demonstration purposes
• HPLA can be used at lower treat-rates but will be
dependent upon the application (base oil, formulation,
metals to be machined, metalworking operation e.g.
drilling, broaching, deformation, etc)
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Form Tapping
• Form tapping measured using a Microtap instrument
- Aluminium Al 6061
- Hard Steel 1018
• Tests Conducted:
• 8% and 16% polymeric HPLA added to base oil and compared to:
- Gp I base oil alone
- Gp I base oil + 10% conventional ester (TMP Trioleate)
- Gp I base oil + 7.5% HPLA + 0.5% phosphate ester
• 10% polymeric HPLA in base oil compared to:
- Gp I base oil + 10% high viscosity ester (commercial products)
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Micro-tapping Machine
• Records torque required to tap pre-formed holes
• The results are reported as the maximum torque required
6mm form tapping
• HSS tap
• torque limit 700 Ncm
• speed = 600 – 800 rpm
• tap depth = 0.5 inch / 13 mm
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Form Tapping (6mm) – Aluminium 6061
HPLA vs. commercial high viscosity esters:
comparable performance
0
20
40
60
80
100
120
140
160
Base Oil (ISO 32 - 68) Base Oil + 10% Ester (ISO
46)
Base Oil + 10% HPLA Base Oil + 10% Comp A Base Oil + 10% Comp B
TorqueNcm
-13 %
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-10 %
fail fail
Paul Bonner – OilDoc Conference & Exhibition 2013
Form Tapping (6mm) – Hard Steel (1018)
HPLA vs. commercial high viscosity esters:
10% improvement over A, B fails
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Summary for Neat MWFs
• HPLA outperforms conventional esters in the form tapping of Al 6061
(5 – 7% less torque)
• HPLA outperforms conventional esters in the form tapping of mild steel and 1018
hard steel (up to 23% less torque)
• HPLA outperforms high viscosity esters in form tapping of hard steel by 10% over
commercial sample A, with commercial sample B failing the test
• Provides excellent wear protection and can act synergistically with phosphate
ester
• Forms stable films, especially at higher temperatures and can provide a very
dramatic reduction in frictional characteristics of mineral oil based neat oils
• HPLAs are also extremely effective in ester base fluids
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• Reduce friction of the fully formulated oil to:
• lower the operating temperature of the oil and reduce wear
that can result from a reduction in viscosity of the hydraulic
fluid at operating temperature
• Provide greater wear protection to low viscosity oils
• Increase energy efficiency through the use of lower viscosity
hydraulic fluids
Aim
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Hydraulic Fluids
• Group II mineral oil used as base fluid
• Two commercial additive packages evaluated
• Gp II base oil + additive packs top treated with 1% polymeric
HPLA
• Coefficient of friction tested using MTM machine
• Demulsification tested in 1:1 water over 30 minutes using ASTM
D1401-02
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Demulsification test
• Hydraulic fluids are required to pass a demulsification test ASTM
D1401-02 to meet specifications. This is due to the likelihood of
some water being entrained during use
• If a hydraulic fluid becomes emulsified then cavitation is likely
which causes a decrease in efficiency and high wear
• A 1:1 (40 ml) water : oil was mixed by paddle stirrer at 1500 rpm
for 5 minutes and then observed
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Summary for Hydraulic Fluids
• HPLA provides extremely low coefficient of friction to
the hydraulic fluids formulated using Gp II base oil and
two commercial additive packs
• However, HPLA causes the hydraulic fluid to emulsify
water
• A re-design of the friction modifier is required to
maintain the outstanding low friction profile whilst
improving demulsification
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Industrial Gear Oils
• Base fluid used was PAO/ester blend (ISO 320)
• A commercial additive package was used as a reference add
pack
• The base oil plus add package was top treated with a polymeric
HPLA (at 1%) and two different non polymeric HPLAs (at 2%)
• Coefficient of friction determined using the Mini-traction machine
• Demulsification tested in 1:1 water over 30 minutes using ASTM
D1401-02
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• Due to the higher viscosity of the IGO formulation the MTM had to
be run at higher loads and temperatures than used for the
metalworking fluids and hydraulic fluids in order to obtain a
Stribeck curve covering both mixed and boundary lubrication
regimes
Coefficient of Friction by MTM
Parameter Standard Values Modified IGO Values
Load 36 N 75 N
Ball / disk size ¾ “ on 46 mm disk ½ “ on 32 mm disk
Temperature 100C 150C
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IGO – MTM Results Non-Polymeric HPLA
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.01 0.1 1 10
COEF
Speed m/s
PAO/Ester ISO 320
Commercial Addpack in PAO/Ester
Commercial Addpack with 2 %
nonpolymeric HPLA 1 in PAO/Ester
Commercial Addpack with 2 %
nonpolymeric HPLA 2 in PAO/Ester
Commercial Addpack with 1%
polymeric HPLA in PAO/Ester
• Two non-polymeric HPLAs were tested and gave a good
reduction in friction compared to the commercial addpack alone
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Summary of IGO
• Polymeric HPLA showed no improvement in frictional performance compared to
the commercial additive pack
• Both non-polymeric HPLA 1 and HPLA 2 showed a significant reduction in
coefficient of friction over the commercial additive pack
• Non-polymeric HPLA 1 failed the demulsification test whilst HPLA 2 passed
• The structure of the friction modifier is critical to get both reduced friction and
excellent demulsification properties in a PAO/ester based formulation
• The performance of the friction modifier is likely to be dependent upon the base oil
and the additives in a given formulation and further work to understanding their
mutual interactions will be required, which may require new FMs tailored
specifically for unique base oil / additive pack combinations
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Conclusion
• It has been shown that both polymeric and non-polymeric HPLA are effective in
reducing friction in neat MWF, hydraulic fluids and industrial gear oils
• Polymeric HPLA reduces torque in neat MWF by 7% in aluminium and 20% in
hard steel vs. conventional esters and 10% vs. commercially available high
viscosity esters. Wear is also reduced and synergy seen with phosphate esters
• Polymeric HPLA reduces friction in a hydraulic fluid additive pack but does not
have the required demulsification properties
• Non-polymeric HPLA was found to reduce friction in an industrial gear oil additive
pack whilst not negatively affecting demulsibility properties of the formulated
lubricant
• For each application the properties of the base oil and the specifications
demanded for the application dictate different novel lubricity additive / friction
modifier molecules
