Wheel/Rail Contact Tribology: Characterising Low Adhesion Mechanisms and Friction ...

185 Pages·2017·31.22 MB·English

08
Fall

Wheel/Rail Contact Tribology:
Characterising Low Adhesion
Mechanisms and Friction Management
Products
Luke Evelyn Buckley-Johnstone
May 2017
Thesis submitted for the Degree of Doctor of Philosophy
Department of Mechanical Engineering
Summary
Friction management and control of adhesion at the wheel/rail interface is vital
for an efficient and cost effective railway network. The understanding of how
the friction management products (grease and friction modifiers) work and
effectively test these products is necessary to improve the performance of a
railway network.
The papers presented concern the effective benchmarking of wayside curve
lubricants (grease) in a twin disc test rig. They compare the effectiveness of
several greases in respect to adhesion, wear protection and retentivity
(number of cycles of adequate lubrication). A new method for assessment of
grease carry down has been trialled in the field. The modified pendulum was
able to detect the difference between a dry and lubricated rail gauge face.
Top of rail friction modifiers (TOR-FMs) have been tested at two different
laboratory test scales. The results showed the difference in operational
behaviour of the chosen TOR-FM when used in a laboratory versus the field.
The ‘wet-rail’ phenomena, where low adhesion as a result of water on the rail
head, has been investigated at two scales of laboratory test and results have
been used to generate a model to predict adhesion coefficients for a range of
water and iron oxide mixtures. The results presented show how the addition of
small amounts of water to a wheel/rail contact can cause reduced adhesion to
‘low/ultra-low’ levels when combined with third body materials (iron oxides,
wear debris etc.).
A novel treatment method to protect the rail head using hydrophobic solutions
was investigated using twin disc and pendulum testing. Tests showed that
these products, when sufficiently diluted, do not reduce friction to dangerous
levels or isolate the vehicle from the track circuit. However, the benefits of use
in the field are questioned.

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Thanks
First and foremost I would like to thanks Professor Roger Lewis who
supported me and made this thesis possible.
For those who helped in every aspect of this piece of work; Dave Butcher
Stephen Lewis, Hiroyuki Suzuki, Matt Harmon, Guiseppe Tronci, Martin
Evans, Klaus Six, Gerald Trummer and Petr Voltr, Apologies to those I have
missed.
To my partner Erin for all her support and guidance without which I would
have been at a loss.
To my family; my pops Nicolas, my mum Barbara (I love and miss you), my
brothers Edward, Jacob and Benedict, my Granddad John, Big John, Judith
and Aphra, my Aunt Mog and Uncle Dick, my Aunt Janet and Uncle Ed, my
Aunt Maureen and Uncle Bruce.
Again, to my pops Jed who raised me and guided me. You are the best.
To my friends Alex Keyte, Liam Power, Greg Kirkham, Stefan Bird, Tom Sara,
Tom Facer, Tim Beech, Rob Wannop, Tom Reeves, Alex Buckman, Emily
Nix, Richard Jeffs, and Jonathan Stephenson. Cheers guys, you are all great
people.

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Table of contents
Summary ......................................................................................................... 2
Thanks ............................................................................................................. 3
1. Introduction ................................................................................................ 8
1.1. Aims and objectives ....................................................................................... 9
1.2. Thesis layout ................................................................................................. 11
2. Literature review ...................................................................................... 12
2.1. Wheel/rail contact ......................................................................................... 12
2.1.1. Contact zones .......................................................................................... 14
2.1.2. Contact pressure ...................................................................................... 15
2.1.3. Friction and creep .................................................................................... 16
2.1.4. Wear ......................................................................................................... 20
2.1.5. Isolation .................................................................................................... 21
2.2. Third body contaminants ............................................................................. 21
2.2.1. Iron oxides ................................................................................................ 22
2.2.2. Leaves ...................................................................................................... 23
2.2.3. Water ........................................................................................................ 24
2.3. Low adhesion ................................................................................................ 25
2.4. Wheel/rail friction management ................................................................... 27
2.4.1. Grease ..................................................................................................... 27
2.4.2. Friction modifiers ...................................................................................... 29
2.5. Tribological testing of the wheel/rail contact ............................................. 31
2.5.1. Contact scaling ......................................................................................... 31
2.5.2. Field testing .............................................................................................. 34
2.5.3. Laboratory testing of the wheel/rail contact .............................................. 35
2.5.4. Full-scale rigs ........................................................................................... 35
2.5.5. Twin disc .................................................................................................. 35
2.5.6. Mini Traction Machines ............................................................................ 36
2.5.7. Pin-on-disc ............................................................................................... 36
2.5.8. Other laboratory tribological test methods ............................................... 37
2.6. Summary ........................................................................................................ 37
2.6.1. Benchmarking of railway grease .............................................................. 38
2.6.2. Friction modifier in the laboratory ............................................................. 38
2.6.3. Low adhesion ........................................................................................... 38
2.6.4. Low adhesion mitigation ........................................................................... 38
2.7. References ..................................................................................................... 40
3. Assessment of railway curve lubricant performance using a twin-disc
tester ............................................................................................................. 47
Abstract ......................................................................................................... 47
3.1. Introduction ................................................................................................... 47
3.2. Test methodology ......................................................................................... 48
3.2.1. Trial tests .................................................................................................. 49
3.3. Results ........................................................................................................... 51
3.3.1. Lubrication starvation tests ...................................................................... 51
3.4. Fully lubricated tests .................................................................................... 54
3.5. Discussion ..................................................................................................... 57
3.6. Conclusions ................................................................................................... 61
3.7. References ..................................................................................................... 62
4. Field trials of a new method for the assessment of gauge face
condition using a modified pendulum test rig .......................................... 63

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Abstract ................................................................................................................. 63
4.1. Introduction ................................................................................................... 63
4.2. Apparatus ...................................................................................................... 64
4.2.1. Methodology ............................................................................................. 66
4.3. Study A: Field-testing on the Severn Valley Railway using a pendulum
tester with a modified foot .................................................................................. 67
4.3.1. Site information ........................................................................................ 67
4.4. Study B: Field-testing of angled pendulum in Stockholm, Sweden. ........ 69
4.4.1. Site information ........................................................................................ 69
4.5. Results ........................................................................................................... 70
4.5.1. Results – Study A ..................................................................................... 70
4.5.2. Results – Study B ..................................................................................... 71
4.6. Discussion ..................................................................................................... 71
4.6.1. Study A ..................................................................................................... 71
4.6.2. Study B ..................................................................................................... 72
4.7. Conclusions ................................................................................................... 73
4.8. References ..................................................................................................... 74
5. Assessment of friction modifiers performance using two different
laboratory test-rigs ...................................................................................... 75
Abstract ................................................................................................................. 75
5.1. Introduction ................................................................................................... 75
5.2. Literature review ........................................................................................... 77
5.3. Test methodology ......................................................................................... 78
5.3.1. Study A ..................................................................................................... 78
5.3.2. Study B ..................................................................................................... 79
5.4. Results ........................................................................................................... 79
5.5. Conclusions ................................................................................................... 82
5.5.1. Study A ..................................................................................................... 82
5.5.2. Study B ..................................................................................................... 83
5.6. References ..................................................................................................... 83
6. Assessing the impact of small amounts of water and iron oxides on
adhesion in the wheel/rail interface using High Pressure Torsion testing
....................................................................................................................... 85
Abstract ................................................................................................................. 85
6.1. Introduction ................................................................................................... 85
6.2. Water quantification ...................................................................................... 87
6.2.1. Apparatus ................................................................................................. 87
6.2.2. Methodology ............................................................................................. 87
6.3. High Pressure Torsion testing ..................................................................... 88
6.3.1. Apparatus ................................................................................................. 88
6.3.2. Methodology ............................................................................................. 90
6.3.3. Test conditions ......................................................................................... 92
6.4. Results ........................................................................................................... 92
6.5. Low Adhesion Model .................................................................................... 95
6.6. Discussion ..................................................................................................... 98
6.7. Conclusions ................................................................................................... 99
6.8. Acknowledgements .................................................................................... 100
6.9. References. .................................................................................................. 100
7. Full-scale testing of low adhesion effects with small amounts of water
in the wheel/rail interface .......................................................................... 102
Abstract ............................................................................................................... 102
7.1. Introduction ................................................................................................. 102
7.2. Experimental details ................................................................................... 104

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7.2.1. Test apparatus ....................................................................................... 104
7.2.2. Methodology ........................................................................................... 107
7.2.3. Test conditions ....................................................................................... 109
7.3. Results ......................................................................................................... 111
7.4. Discussion ................................................................................................... 113
7.5. Conclusions ................................................................................................. 115
7.6. Acknowledgements .................................................................................. 115
7.7. References ................................................................................................... 116
8. Wheel-Rail creep force model for predicting water induced low
adhesion phenomena ................................................................................ 117
Abstract ............................................................................................................... 117
8.1. Introduction ................................................................................................. 117
8.2. Literature review ......................................................................................... 118
8.2.1. Influence of water on adhesion .............................................................. 118
8.2.2. Existing creep force models taking the effect of water into account ...... 119
8.3. Tram experiments wheel test rig ............................................................... 120
8.4. WILAC model ............................................................................................... 122
8.4.1. Creep force calculation .......................................................................... 122
8.4.2. Linear regression models ....................................................................... 123
8.4.3. Blending between conditions ................................................................. 124
8.5. Model parameterisation and validation .................................................... 125
8.6. Discussion ................................................................................................... 128
8.7. Conclusions ................................................................................................. 129
8.8. Acknowledgements .................................................................................... 130
8.9. References ................................................................................................... 130
9. Investigation of the isolation and frictional properties of hydrophobic
products on the rail head, when used to combat low adhesion ............ 132
Abstract ............................................................................................................... 132
9.1. Introduction ................................................................................................. 132
9.2. Test methodology ....................................................................................... 133
9.2.1. Twin disc test ......................................................................................... 133
9.2.2. Pendulum test ........................................................................................ 134
9.3. Results ......................................................................................................... 136
9.3.1. Twin disc results ..................................................................................... 136
9.3.2. Pendulum results ................................................................................... 140
9.4. Discussion ................................................................................................... 144
9.4.1. Twin disc testing ..................................................................................... 144
9.4.2. Pendulum Testing .................................................................................. 145
9.5. Conclusions ................................................................................................. 146
9.6. References ................................................................................................... 147
10. Discussion ............................................................................................ 148
10.1. Adhesion measurements with third body materials .............................. 148
10.2. Benchmarking of applied products ......................................................... 149
10.2.1. Grease ................................................................................................. 149
10.2.2. Friction modifiers .................................................................................. 150
10.3. Low adhesion ............................................................................................ 151
10.4. Hydrophobic products .............................................................................. 152
10.5. References ................................................................................................. 152
11. Conclusions .......................................................................................... 154
11.1. Bench marking of applied products ........................................................ 154
11.2. Low adhesion ............................................................................................ 155
11.3. Novel friction management solutions ..................................................... 156

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11.4. Adhesion measurements ......................................................................... 156
12. Future work ........................................................................................... 158
12.1. Test methods ............................................................................................. 158
12.1.1. Benchmarking of applied products ....................................................... 158
12.1.2. Grease ................................................................................................. 158
12.1.3. Friction modifiers .................................................................................. 158
12.2. Low adhesion ............................................................................................ 159
12.3. Novel solutions ......................................................................................... 159
13. Appendix A ........................................................................................... 161
13.1. Additional HTP results .............................................................................. 161
14. Appendix B ........................................................................................... 162
14.1. Paper 5: Full-scale tram wheel rig test results ....................................... 162

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1. Introduction
Increasing demands on the United Kingdom’s (UK) rail network, as well as
those worldwide, have led to more pressure on the infrastructure to deliver
consistent and safe transport. To meet these demands, a more predictable
network must be created by extending maintenance intervals, increasing
component life (particularly of rail and wheels), reducing energy consumption,
reducing acceleration and braking distances whilst improving reliability. These
goals can be achieved by improving one component of a railway system: the
wheel/rail contact.
Since the 1970s, the new passenger type vehicles that have been introduced
on the UK network have increased in weight per meter (Network Rail, 2011).
All forces that are required to start, stop and steer trains are transmitted
through the contact patch formed by a steel-wheel on a steel-rail, which is
roughly the size a coin (1 cm2) (Lewis, 2006a). The contact is highly variable
and depends on many factors such as wheel/rail profile, vehicle type (weight)
and curve radii creating highly variable conditions of contact. All damage,
instantaneous or gradual, to the wheel/rail is related to this open tribological-
system.
Rail transport is more energy efficient and has lower CO emissions than the
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road alternatives for both passenger and freight transportation. This can be
attributed to the low energy required at the contact interface between the
wheel and rail when compared to a rubber tyre on a Tarmac road. However,
unlike rubber tyres, which are able to maintain contact with the road surface
through the tyre’s tread, this contact can be easily affected by the introduction
of a small amount contaminant.
It is the control of this tribological system that can be used to manage the
wheel/rail contact. This can be done through the design of wheel/rail profiles,
material selection and introduction of third body materials (grease, sand,
friction modifiers) to control friction. The control of friction can be used to
reduce wear, increase tractive/adhesive forces in braking and acceleration,
reduce noise and control rolling contact fatigue (RCF). As this is an open
system, a number of unwanted or uncontrollable factors can have a
considerable affect. For example, oil on the top of rail may cause a wheel
slide during braking.
Contaminants that are found in a wheel/rail contact have been previously
grouped into three categories: climatic, operational and transported bodies
(Descartes, 2005). Climatic bodies include water and leaves. Operational
bodies include lubricating oils, sand and ballast material. Transported bodies
include any products that are carried on freight. Additionally, Descartes has
separated the ‘natural’ contaminants arising from the wheel rolling over the
rail, such as consistently present wear debris (Descartes, 2008). These
contaminants form the third body layer on the rail head and can be both
advantageous and detrimental in the management of the railway (Lewis,
2012).
Friction management is a part of a whole systems approach to the systematic
management of the wheel/rail interface. This approach to managing the
wheel/rail contact includes the materials of the wheel and rails, the vehicle
dynamics and the contact mechanics as visualized in Figure 1(Kalousek,
1996).

Figure
 1:
  Visualisation
 of
 a
 systematic
 approach
 to
 wheel/rail
 interface

management
 (Kalousek,
 1996).

“Friction modifiers” is a broad term used in the railway industry to describe
products that are designed to be used to treat rail heads to reduce energy
consumption and suppress noise by controlling the friction at the wheel/rail
interface (Stock, 2016).
1.1. Aims and objectives
The objective of this thesis is to explore the effects that third body materials
have on the tribological system of the wheel-rail contact. Four different third
body materials have been investigated separately and are each dealt with
individually. The broad theme between all conducted experiments has been
how to best select appropriate tribological test methods to investigate
behaviour of specific third bodies; what the applicable tribological
performance data needed to be gathered is and how this information can be
used to inform railway operators in the selection of appropriate course of
action for wheel/rail interface management.
Laboratory and field-testing of applied products (grease and friction modifiers)
were carried out to help better understand and improve product selection.
1. Wayside greases
The currently standards for railway grease do not require tests that accurately
represent the conditions the grease will be subjected to in the field. It is
necessary to select an appropriate test method that can analyse the key
tribological features for wheel/rail gauge corner contact. Experiments have
been completed using a twin disc test set-up to compare the performance of
several commercially available greases. This is used to define a standardize

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laboratory test methodology able to differentiate between several
commercially available products.
Additionally, grease performance in the field is poorly quantified.
Measurements of rail profile change can be readily made over multiple site
visits and wear can be monitored to give a grease performance over time.
However, these measurements give no information on whether grease is
present on the rail at the time. The aim was to develop a device to improve
the measurement of grease performance in the field over the current visual
inspection through gauge corner friction measurements.
2. Top of rail friction modifiers
The aim was to design a test methodology to examine the frictional
development of a top of rail friction modifier (TOR-FM) (a product designed to
give intermediate friction levels at tread contact) when subjected to repeated
axle passes. The performance requirements of a TOR-FM require an
intermediate friction level to be sustained on the railhead for multiple train
passes and understanding how these product develop in the laboratory is
critical to informing their use in the field.
The objective is to measure and understand the effects that test scale has on
the performance of a TOR-FM using a full-scale wheel/rail test stand and a
scaled wheel/rail contact in a twin disc test rig.
3. Water and iron oxides
The aim was to develop experiments to investigate the hypothesis that water,
in combination with iron oxides, can severely reduce adhesion between the
wheel/rail and to understand and define the conditions that promote adhesion
reduction to define possible mitigation options.
Laboratory test of oxide water mixtures in a highly controllable laboratory High
Pressure Torsion (HPT) rig recently commissioned at the University of
Sheffield. The tests compared adhesion between wheel/rail specimens in the
presence of different ratios of water-iron oxide mixtures. Results were used to
better understand the shearing process of these mixtures and an adhesion
model developed.
Using the information from HPT tests and the adhesion model a set of full-
scale tests were defined and conducted. This allowed adhesion measurement
on a fully representative wheel/rail contact. Water flow rates were varied to
investigate these water and iron oxide mixtures.
In parallel a wheel/rail adhesion model was developed using the test data and
a paper detailing this is included for clarity and context.
4. Hydrophobic solutions
Finally, an investigation into alternative solutions to mitigate against low
adhesion using hydrophobic solutions to treat the rail head has been
completed. Two sets of tribological test set-ups have been used to investigate
adhesion and adhesion change over time.

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