No Middle Option
.. Or why little has changed over the past 70 years !
Graham Gow
AXEL who ??
Axel Christiernsson International
“the biggest little grease company
nobody’s ever heard of”
Represents almost 20% of west
European grease production (2012)
Recently established presence in USA
“Customised Label™ policy”, i.e. no
AXEL brands
5 manufacturing facilities, Sweden,
the Netherlands, France, 2 x USA
Independent ownership
Growth strategy, expanding into new
geographical areas (Asia ?)
Amazing Grease, art or science ?
Introduction
Ancient Lubrication
”Grease, the final frontier”
”The only remaining part of lubrication technology
where any true exploration remains to be done”
Patricia Todd
New innovative developments ?
More than 70% of all lubricating
greases produced today are
based on Clarence E. Earle´s
patent from the early 1940s
Since then, development has
focussed more on additive
technology than on the thickener
systems themselves
This has led to a commoditisation
of the market
Me too ?
Sticky stuff
Globally local ??
.. a season and a time to every purpose
Clarence E Earle patents on
lithium grease from the
early 1940´s.
AXEL lab documentation
shows a new “paradigm” of
lithium grease technology
beginning in 1948
67 years ago !!
Time for something new ??
Know how, or know why
The final frontier or a sleeping
beauty ?
65 years of polishing the paradigm
Understanding the mechanisms
From know how to know why
From specification to functionality
From EP 2 to ”a good night’s sleep
Introduction
Definition by contents
”A solid to semi fluid product of a thickening
agent in a liquid lubricant. Other ingredients
imparting special properties may be
included.”
ASTM D 288
Grease is a thickened oil not a thick oil!
A multi-phase system ..
.. like a sponge full of water
Annual Book of ASTM Standards, American Society for Testing and Materials
Introduction
Soap
Fiber dimensions:
L = 1-100 µm
ø = 0.01-10 µm
Introduction
Definition by rheology
”A lubricant which under certain loads…
…exhibits the properties of a solid body,
undergoes plastic strain and starts to flow
like a fluid should the load reach the critical
point and regains solid body properties after
the removal of the stress”
V.V. Sinitsyn
Grease is a
non-Newtonian plastic solid!
Sinitsyn, V. V. The choice and Application of Plastic Greases
Introduction
Non-Newtonian fluid
A certain stress is needed for a grease to flow and it is shear
dependent.
Definition by function
“A dynamic energy saving shearable surface separator”
(L. Hamnelid)
DE + 4 S
A material which will keep (bearing) surfaces apart using the
minimum of energy !
A “deforce” if you will !!
So how do greases function ??
Conventional soap based thickeners
(such as lithium 12-HS)
Soap is the most polar component in the grease matrix
Covers the surface with a thin impregnable layer
Prevents additives from doing their job
Poor option ?
So how do we ensure surface avaiability for the active
materials (the ”additives”) ?
Choose better additives ?
We’ve been doing that for more than 60 years !!
More interesting solutions using two opposite ”options”
Either integrate the additives into the thickener
structure ?
”Functional soaps”
Or, choose a non-polar thickener to minimise
competition for the surfaces
”Polymer greases”
Conventional solution = optimise additivation
Like headache pills, additives relieve the
symptoms but do not cure the problem
Limited range of additives available for
grease applications (many are degellants,
others do not work because they do not
reach the surfaces)
Still a poor middle option
New generation of efficient bismuth
additives
Antagonistic or synergistic ?
Important to find the right combination of
chemistries
Perform well in friction reduction
Synthetic lithium complex EPB
Flagship of bismuth additivation
Originally developed for Volvo
Submitted as a candidate for use
in state-of-the-art hub-units for
heavy vehicles.
Extremely low-friction regime
Running temperatures < 100oC
compared to benchmark products
> 160oC
Temperature difference = 60Co !!
Functional soaps
Active components attached to the thickener
structure instead of using liquid additives in the base
oil
Use the polarity of the soap to deliver the ”additives”
to the surfaces where they need to be to be able to
perform as expected
Examples of Functional Soaps
Lithium-calcium
- EP properties inherent from the soap
- Water resistance
- Higher wear
Calcium sulphonate
complex
- EP properties inherent from the soap
- Corrosion inhibition
- Inferior lubrication ability
Lithium-calcium
complex
- Extreme EP properties inherent from the soap
- Corrosion inhibition
(“Alassca”)
- Low friction under heavy loads
Lithium-Bismuth
complex
- EP/AW properties inherent from the soap
- Mechanical stability
- Very low friction and wear
Lithium-bismuth complex
Better high temperature performance
Better friction reduction
Lithium-bismuth complex
Excellent fretting protection
Wind-power prototypes (”Rippel Test”)
Lithium-calcium complex
Extreme load carrying capacity
Best option for open gear lubrication
Without the use of (black) particles !
Facilitates condition monitoring
Meets the current OEM specifications in
everything but content of graphite
No build-up of solids in the gear teeth
Less vibrations
High pressure rheology (GPa)
 Solidification theory
(oil becomes glass under gigaPascal pressures)
 Accurate information on actual
lubrication regime is therefore
paramount for optimal friction
reduction
 The “impacting ball” apparatus
How did we know ?
Cooperation with Luleå
The impacting ball apparatus
So where did we go wrong ?
In many cases, it’s the whole grease that lubricates, not the base oil
bleeding out of the matrix (sponge theory)
Grease is therefore not a thickened oil, it’s a thinned down soap !
The soap is the expensive part so we tried to use as little as possible
To achieve this, we used highly polar mineral oils
At high pressures however, the more soap, the lower the friction
At high pressures however, mineral oils give higher friction
Esters are better, and PAOs better still
In addition, we lowered the base oil viscosity for better friction
properties.
At high pressures however, higher viscosity gives lower friction
Friction in the glass phase
For friction reduction in high load applications
(open gears, etc.), a grease should therefore have a
significantly different composition compared to a
conventional multipurpose EP product
It should contain as much soap as possible for any
given consistency
It should have a very heavy (high viscous) base oil
The base oil should preferably be synthetic (PAO)
It should not contain solid materials like graphite
or MoS2
This however is contradictory to most OEM
specifications and makes it difficult to sell
Black blues
A:
AF 1 :
AF 2 :
AF 3
Aluminium complex base grease
Base grease + 4.2% graphite
Base grease + 11.1% graphite
Base grease + 4.2% molybdenum disulphide
Source : Stemplinger et. al.
Polymer thickener
Soap is replaced by a non-ionic (non-polar)
thickener
Improved additive response
Filament forming properties can be designed
to fit purpose
Dramatic improvement in grease life
Significant reduction in friction and wear
Grease ... the intelligent lubricant
” .. lubricating grease is a very intelligent
material; once it’s forced out of the track,
it’s quite happy to stay there where it’s not
being rolled over time and time again”
Philippa Cann
Imperial College
London
Light hearted approach to grease mechanisms
= know-why
Grease mechanisms,
... the point of no return
So how does the grease get back into
the track again ?
An understanding of the
replenishment mechanisms can
contribute greatly to a reduction
in starvation and to a more
efficient film in the contact zone
A better deforce !
Lubricant mechanisms
.. the “wet road” syndrome
Imagine cycling on a wet road
Spray generated behind the wheels
Without a mud flap, the cyclists back
gets very very wet
Similar mechanisms in oil lubricated
contacts
The size of the droplets has a
decisive effect on the efficiency of
the lubricant (P.O. Larsson)
Grease mechanisms,
filament geometry
Now, imagine cycling in sticky glue
instead of rainwater
Long tacky fibres are formed which break
and fall back onto the surface
Similar to pulling “Elastoplast” off your
skin !
Deposited back on the track as a series of
“filaments”
In a roller bearing, any given roller is
separated from the raceway entirely by
what is left behind by the previous
roller !
The “previous” roller
”In a roller
bearing, any
given roller
is separated
from the
raceway by
what is left
behind by
the previous
roller”
Can you see the filaments ?
Laboratory
Aluminium rolling mill
Can you see the filaments ?
Steel mill (cold rolling)
ELGI Gothenburg, April 2009
Alan Begg, senior vice president, SKF Group
Grease life is the key to sustainability
80-90% of all rolling element bearings are grease lubricated
Grease dominates the service life of bearings
Specially formulated low friction greases can contribute to
cutting friction by up to 30% which, in turn, can double the
grease life.
Biodegradability needs to be addressed
2
Long life
8
SKF R0F test rig (10.000 rpm, 120oC)
Standard lithium 12-HS EP 2
(in-house & many competitive products)
500–600 hours
Equivalent polymer based product
(all else equal)
3,500-4,000 hours
i.e. 8 times better !!
Many tests switched off after 4000 hours !!
Reduced lubricant consumption
Extended relubrication intervals
Reliability & dependability
Reduced down-time
Environmental impact
“A good night’s sleep” for the
maintenance manager
Eight times better ??
80-90% of all rolling element bearings are grease lubricated
80-90% of all applications are running at temperatures < 100oC
70% of all lubricating greases are based on lithium technology
Substitute the lithium soap with a polymer
Significant increase in service life (8 times or whatever)
What would that mean in a single end user environment ?
What would that mean on a global scale ?
8
Power generation turbines
(formerly called windmills !)
One of the original targeted applications
Tests in the laboratory had indicated a possible extension of
relubrication intervals somewhere in the region of eight times
longer.
700 kW prototype mill, large spherical roller bearings, low
rotational speed, high axial intermittent loading, low ambient
temperature.
Normal relubrication interval 6 months.
After 3.5 years of trouble free operation (condition monitoring
showed no indications of any problems) the test was terminated.
There was no leakage, no wear and the grease samples looked as if
they had never been used.
And the ingoing base oil viscosity is only 30 mm2/s at 40oC whereas
the current specification stipulates an ISO VG 460 !
8
Steel mill (cold rolling)
8
Test in bearing especially exposed to
emulsion wash out
Normally requires lubrication several
times per shift
After 4 shifts, there was still adequate
lubricant left in the bearing
Filaments clearly obvious
“The best result ever seen”, a good
night’s sleep for the maintenance
manager !
The next step(s)
Since grease life is perceived as the key to sustainability, there are
greases already available today which can significantly contribute to a
better future
There are greases already available which can reduce friction under
heavy loads
There are greases already available which offer reduced friction,
reduced temperatures and increased bearing life
The next step is to combine these technologies
Yet another step is to engage a new mindset and to innovate !
Generation III, long life, low friction version
Polymer/bismuth thickener :
Hi-Lo polarity thickener
Contains compatibility “bridge” between “unlike” substances
“Functional” polymer thickener
Extended service life at elevated temperatures
(SKF R0F/10,000 rpm/150oC : L10 1233h, L50 2797h)
Dropping point 240oC
Excellent mechanical stability
Future equivalent to polyurea-type products
24
Generation III, long life, low friction version
Coefficient of traction less than 50% compared to benchmark products !
0,12
Traction Coeffcient
0,10
0,08
Measurements made in an
MTM2 EHL apparatus at YKI
Stockholm
0,06
0,04
Acinol 152 EP
Axellence 152 EP
NOION 632 EPB
NOION 5215
Lab 2909
0,02
0,00
0
10
20
30
Slide/Roll ratio
40
50
60
Energy savings project
Volvo Powertrain, Skövde, Sweden
Paint shop where 25 circulation fans
evacuate the air
OEM recommendation to lubricate the flue
fan bearings with a high quality state-ofthe-art lithium complex grease
Volvo specification 97720
Base oil viscosity 210 mm2/s at 40oC
Full film ? .. or not ?
Full film lubrication is not the most advantageous
regime for friction in roller bearings !
Causes the rollers to slide and wobble on the
lubricant
Can lead to extensive wear in terms of smearing
and flaking of the raceway
Confirmed by practical problems experienced in
the actual flue gas fan bearings
Best result is achieved when all the bearing
components have the same linear speed and that
requires a certain (small) amount of surface
contact (the rollers should roll, not slide !)
Film thickness calculations
Conventional calculations are based only
on the fluid oil to establish the required
level of base oil ”kinematic” viscosity
These are however only valid for
Newtonian behaviour
By adding a new parameter, the elastic
modulus, the contribution of the thickener
system (and the ”filaments”) can now be
established.
Method developed by AXEL tribologist,
Kenneth Forsberg
A new perspective
Conclusion of re-calculation was to reduce
the base oil viscosity by a factor of 4-5
Rollers and rotating ring should
theoretically have the same linear speed
In addition, less internal friction creating
lower temperatures and a smoother
operation
First ”new” product chosen was a
synthetic (PAO) lithium complex product,
base oil viscosity now 46 mm2/s at 40oC
First field trials
Monitoring of roller bearing temperature
and vibrations
Significant reduction in temperature
(20-30 Co)
Removal of unneccesary friction
Rapid drop in vibration
Remaining vibration from particle
deposition on the fan blades
After six months, the bearings were still
in prime condition (normal maintenance
interval = 1 month)
Modern Materials
Volvo at the forefront of innovation
Interested in new technologies
Lithium complex thickener replaced by polymer (all else
equal)
Bearing temperature in the flue gas fans reduced by an
additional 10 Co down to an operating temperature of
60oC
Test rig simulation (SKF R2F), comparing the polymer
grease with the original Volvo 97720 grease, measuring
parameters affecting the ”total frictional moment” (M),
shows possible energy savings in the region of 36%
And, according to our new film thickness calculations
with the polymer grease, the optimum base oil viscosity
should be 8 mm2/s at 40oC
To be continued .....
Can you see the filaments ?
Volvo Powertrain, flue gas bearings
In reality
Volvo Powertrain have measured the energy
savings achieved over a considerable period of
time, representing some 10% improvement
.. which translates into economic savings (i.e.
reduced maintenance costs) of some 200.000 SEK
per year
In one single paint shop
What does that mean for the whole plant ?
What does that mean on a much wider (national
or global) scale ?
A very large number
What next ... nano-particles ??
Earlier attempts to introduce nano-particles into grease
did not show increased performance
Theory is that they ”disappear” into the thickener
system and are not avaiable at the metal surfaces
Different in polymer thickened products
By adding friction modifiers and nano-particles to our
commercial polymer grease, tests in the SRV show
much lower friction and wear
50% reduction in the coefficient of friction compared to
the commercial polymer grease (already excellent in
friction properties as previously demonstrated by Volvo
Powertrain)
Nano-WS2 in grease structures
Effective especially in non-ionic greases (surface availability)
Synergistic with friction modifiers
50% lower friction
Less wear
Already available technologies
The implementation of
modern tribology offers
substantial savings in
wear, energy and not least,
money
”new materials and new
technologies are cascading
upon the world but their
tribological benefits are
often not recognised by
potential users”
Peter Jost,
World Tribology Congress
2013, Turin
Friction is a selling tool .. So why not use it to make a profit ?
graham.gow@axelch.com