Tribology for Energy Conservation, Proceedings of the 24th Leeds-Lyon Symposium on Tribology

523 Pages·1998·21.229 MB·3-576\523

by  D. Dowson, C.M. Taylor, T.H.C. Childs, G. Dalmaz, Y. Berthier, L. Flamand, J.-M. Georges and A.A. Lubrecht (Eds.)

Introduction
The 24th Leeds-Lyon Symposium was held ni London from 4th-6th September 1997, where it
was hosted by the Imperial College of Science, Technology and Medicine. This is the first
occasion on which the meeting has been held neither in Leeds nor Lyon and the change in
venue was brought about by a potential clash of dates with the ts1 World Tribology Congress.
The latter meeting took place from the 8th-12th September and by moving the venue of the
Leeds-Lyon Symposium also to London, it was hoped to minimise the wear, fatigue and stress
of delegates who wished to attend both conferences.
The Institute of Tribology at the University of Leeds and the Laboratoire de Mecanique des
Contacts of the Institut National des Sciences Appliqures de Lyon are most grateful to
Professors Hugh Spikes and Professor Brian Briscoe, who head the Tribology Groups at
Imperial College, for agreeing to have the meeting ni London. The Symposium was, by
necessity, shorter than usual. The meeting addressed the topic of "Tribology for Energy
Conservation" and attracted a wide range of stimulating papers and speakers. Some 051
delegates from nineteen countries attended and about sixty papers were presented in fifteen
sessions.
On the night of Thursday 4th September the Symposium was formally opened with a Keynote
Address presented by Professor Roland Clift, OBE, who spoke to the title "The Role of
Tribology ni Life Cycle Design". This stimulating address was followed by an informal
reception welcoming everybody to Imperial College. At this reception Professor Hugh Spikes
graciously acknowledged the tremendous contribution of Professor Alastair Cameron to
tribology research at Imperial College and the delegates were delighted to add their warm
support and congratulations to Alastair. The sessions of the Symposium covered the topics of
Lubricants, Wear, Friction Reduction, Hydrodynamics, Elastohydrodynamic Lubrication,
Surface Roughness, Manufacturing, Component Life (including Condition Monitoring), and
Automotive aspects. The delegates were particularly pleased to enjoy xis invited lecture
presentations by Professor Wilfrid Bartz, Dr Stefan Korcek, Professor Hugh Spikes, Dr Peter
Dearnley, Mr Mervyn Jones and Professor John Beynon. Once again we are delighted to
record our thanks to the many colleagues who acted ni the role of Chairman or Chairwoman
for the Symposium, and their names are recorded ni this Volume.
On the evening of the 5th September, the Symposium Dinner was held at the Royal Garden
Hotel ni Kensington. This excellent occasion was graced by an after dinner speech by
Professor Sir Hugh Ford, formerly of the Department of Mechanical Engineering at Imperial
College, and we are pleased to acknowledge the support of the following in association with
both the Dinner and the Symposium as a whole:
iv
DePuy International Ltd, Elsevier Science Publishers BV, Kyodo Yushi, Industrial
Lubrication and Tribology (MCB University Press), PCS Instruments, Shell Research
Limited, SKF Engineering & Research Centre BV and Unilever PLC (Research
Engineering, Divisions Appeals Committee).
The final day of the Symposium, Saturday 6th September, coincided with the funeral of Diana,
Princess of Wales, and the cortege, after leaving Kensington Palace, passed close by Imperial
College. The delegates listened to a short address from Professor Duncan Dowson in memory
of Diana, and stood in appropriate .ecnelis
We are sincerely grateful to lla who have helped in the detailed planning and execution of the
Symposium. On this occasion it is our colleagues at Imperial College who have to be
particularly recognised and ni addition to Hugh Spikes and Brian Briscoe we would like to
offer our thanks to Chrissy Stevens, Joyce Burberry, and the Tribology Research students of
Imperial College. Sheila Moore and Cath Goulborn from Leeds, as ever, provided valient
support. However, it is to Dr Philippa Cann that we owe the greatest acknowledgement for
her detailed and careful planning of the Symposium and her generous support of the delegates
ni lla their needs.
The Editors would once again like to acknowledge the role of the international referees who
reviewed the papers appearing ni this Volume of Proceedings and also to record their thanks to
the Publishers who have continued to provide proceedings with a high quality of presentation.
The Leeds-Lyon series of tribology meetings has now covered an extensive range of topics as
indicated below.
.1 'Cavitation and Related Phenomena in Lubrication' Leeds 1974
.2 'Superlaminar Flow ni Beatings' Lyon 1975
.3 'The Wear of Non-Metallic Materials' Leeds 1976
.4 'Surface Roughness Effects in Lubrication' Lyon 1977
.5 'Elastohydrodynamic Lubrication and Related Topics' Leeds 1978
.6 'Thermal Effects ni Tribology' Lyon 1979
.7 'Friction and Traction' Leeds 1980
.8 'The Running-In Process in Tribology' Lyon 1891
.9 'The Tribology of Reciprocating Engines' Leeds 1982
.01 2qumerical and Experimental Methods Applied to Tribology' Lyon 3891
.11 ~/lixed Lubrication and Lubricated Wear' Leeds 1984
.21 'Global Studies of Mechanisms and Local Analyses of
Surface Distress Phenomena' Lyon 1985
iiv
.31 'Fluid Film Lubrication - Osborne Reynolds Centenary' Leeds 1986
.41 'Interface Dynamics' Lyon 1987
.51 'Tribological Design of Machine Elements' Leeds 1988
.61 'Mechanics of Coatings' Lyon 1989
.71 'Vehicle Tribology' Leeds 1990
.81 'Wear Particles : From the Cradle to the Grave' Lyon 1991
.91 'Thin Films in Tribology' Leeds 1992
20. 'Dissipative Processes in Tribology' Lyon 1993
21. 'Lubricants and Lub no~tac~ Leeds 1994
I .° ° !
22. 'The Third Body Concept: Interpretation of Tribological
Phenomena' Lyon 1995
'Elastohydrodynamics - '96' Leeds 1996
23.
24. 'Tribology for Energy Conservation' London 1997
We are looking forward to the next Leeds-Lyon Symposium on Tribology, which on this
occasion will be held in Lyon. The meeting will address the topic "Lubrication at the Frontier •
The role of the interface and surface layers in the thin film and boundary regime" and will be
held from 8th - 1 l th September, 1998. We look forward to giving a warm welcome both to
old friends and to new delegates to the meeting.
Tribology for Energy Conservation / .D Dowson et .la (Editors)
© 1998 Elsevier Science B.V. All fights reserved.
A Role for Tribology in Life Cycle Design
Roland Clift
Centre for Environmental Strategy
University of Surrey, Guildford, Surrey GU2 5XH
Life cycle thinking is an approach to assessing the full environmental implications of a product or, more gen-
erally, of the benefit or service which it delivers. This contribution outlines how the life cycle approach could
be used to identify the potential significance of developments in tribology. Extending service life, and facili-
tating disassembly and re-use of materials, emerge as being at least as important as improving lubrication.
.1 BACKGROUND 2. LIFE CYCLE DESIGN
Life Cycle thinking- sometimes known as the 1.2 Life Cycle tnemssessA
"cradle-to-grave" approach - has become a cen- The procedure for carrying out a Life Cycle
tral feature of modern environmental manage- Assessment (LCA) has been formalised Ill as
ment and of the developments which underlie the comprising the following phases:
protean concept of Sustainable Development. Goal Definition dna Scoping: The purpose of
The basic idea is simple enough (and is closely the study is defined in such a way that the eco-
related to Life Cycle Costing): it is not sumcient, nomic systems to be compared can be specified in
in assessing the environmental performance of a sufficient detail. An important feature is definition
product, merely to look at its use; it is necessary of the lanoitcnuF Unit; i.e. the common basis on
to ask where the materials come from, what ener- which alternatives are compared. Following the
gy and other resources are used to make the prod- emphasis on Clean Technology noted above, the
uct; and what happens to it after use. Functional Unit should be defined in terms of the
Life Cycle Assessment is the formalised service delivered rather than the product itself.
approach to carrying out such an analysis e.g. -1 Possible system boundaries are shown
.3 Incorporating life cycle thinking into product schematically in Figure .1 Following the Life
or process design has led to the approach known Cycle approach, the economic system must be
as Design for the Environment e.g. 4-5. When defined to include extraction and all subsequent
the thinking moves on from the material product processing of primary resources (system boundary
to environmentally-efficient ways to provide ser- 2) rather than merely concentrating on final pro-
vices or benefits, it leads into the idea of Clean cessing or manufacturing (system boundary l).
Technology e.g. .6 Further development into Similarly, it is necessary to follow material prod-
systematic use and re-use of artefacts and materi- ucts to the end of their use within the human econ-
als leads to the way of thinking which has become omy; i.e. to follow them through re-use, recycling
known as Industrial Ecology e.g. .7 and waste management to the point at which they
This paper attempts to introduce some pre- become inert residues or dispersed emissions.
liminary suggestions on how life cycle thinking yrotnevnI Analysis: This phase, usually the
can inform developments in tribology, and how most time-consuming part of an LCA, requires all
tribology could contribute to life cycle design. the inputs to and emissions from the economic
Figure I: System Boundaries
! " " " " " " " " " " " " " " " 1
I
I
1
' E
/ ........ I I ...........
W i" ............. I Extraction ,q Energy C Conversion W
l IILII . . . . . . . I _
, M
!
i
~, ' i ...... Material l..,. E
W I IIII I Purification ! TM D( '"'"'"'""'"'"'"'"" '"'"'"'"" '"' '""
| iiiii ,r i II ......
!
1 r" " " " " " - - 1
I I e
t i II i~
W "~ ' ' ' ' ' i ...............M.a.n.u.f.ac.t.u.r ing ~ ..., ' ' .... ~ .......
",, , | /i iiiI Process
| I |L. IJII II ...........
I I
! , M
W
"~ ', USE..,.,....~ "'
!
! elcyceR
,
, M
, ~
' Disposal or
W ' gnilcyceR ~
,
I
I
Q
m ~ m w e ~ w ~ ~ ~ m. wee ma ~ ee m e ~ ma ~ ~ ee ~ ,ma m m m u w I ~ ~ g m ~ ~ |
1. Manufacture Process 2. Life Cycle
M - Material flow E - Energy W - Waste and emission
Table I: Environmental Impact Themes approach is still a matter for debate.
Interpretation: The results of the LCA are
Resource Depletion: Abiotic resources finally used, for example to select alternative prod-
Energy ucts or to identify parts of the economic system
+ Water + Land with disproportionately large environmental
impact (see below). There have been attempts to
Environmental Impacts: Global warming reduce the various environmental impacts to a sin-
Ozone depletion gle scalar environmental score - a process known
Human toxicity as Valuation- but there is no general agreement on
A q uat ic/terrest ria!
whether or how this can be carried out.
ecotoxicity
Acidification 2.2 Life Cycle Design
Photochemical Use of the general LCA approach in product
oxidant creation design has become known as Design for the
Nutrification Environment ,4 .5 The designer is presented with
information on the environmental impacts associ-
ated with different materials and components, to
system to be defined and quantified. This enable selection to balance performance require-
amounts to carrying out material and energy bal- ments with environmental efficiency. Following
ances over the extended system 2 in Figure I but the life cycle approach, the design should ideally
including more detail, particularly on trace emis- extend to re-use of the product. This leads to a
sions of toxic species, than si normally required for concern to minimise the number of different mate-
process analysis. The full Inventory Table may rials used, and to design products for ease of dis-
include hundreds of individual species. The full set mantling and material separation.
of inputs and emissions are termed the "environ- The challenges in developing Design for the
mental burdens" or "environmental interven- Environment as a tool which can be widely used
tions" for the economic system providing the include simplifying the vast mass of data describ-
Functional Unit. ing the life cycle impacts of alternative materials
Impact Assessment: The level of detail con- and components ,8 .9 In spite of the problems
tained in the Inventory Table si usually such that inherent in Valuation, this usually requires some
some simplification or aggregation is needed attempt to compare options on the basis of a very
before the results can be usefully interpreted. Of small number of environmental indicators.
the various approaches to this problem, the so- Furthermore, whereas various options for re-
called problem-oriented approach is the most wide- use should ideally be considered at the design
yl used ,2 .3 Each environmental intervention in stage, this is rarely done in practice. One of the
the Inventory Table is assessed for its contribution principal reasons is that the used artefact will be
to a set of distinct environmental impacts, sum- returned at the end of its service life at some
marised in Table .1 These cover both resource unknown future time, so that possible uses for the
depletion and the effect of emissions. Because the recovered materials may be difficult to predict.
location of many of the processes forming the eco- However, the introduction of "Take-back legisla-
nomic system is unspecified, environmental tion" (which basically requires a supplier to accept
impacts are expressed as potential contributions the responsibility for end-of-life products) will
to specific impact categories. In the case of gen- demand more attention to re-use.
uinely global impacts- global warming and ozone
depletion - this lack of geographical definition 2.3 Environmental dna Economic Performance
presents no problem. However, for more local The inputs to Life Cycle Design are the accu-
impacts, such as toxicity and nutrification (disrup- mulated environmental burdens and impacts
tion of natural ecosystems, for example by algal along the material supply chain to the point of use.
growth in lakes and rivers), the validity of this This si sometimes termed the environmental tuck-
sack of a material or a product. It is of interest to the picture, the overall energy requirements for
examine how the rucksack builds up along the maintenance and repair of farm vehicles over their
supply chain. It is also informative to relate the service life are of order 02 to 40 MJ/kg.
accumulation of burdens to the accumulation of A curve with the form of Figure 2 is significant
added value, an idea which has been developed for a number of reasons. It suggests that primary
within Unilever 10 where it is termed Overall commodities are undervalued in proportion to
Business Impact Assessment (OBIA). their environmental significance. It shows one of
Preliminary (and as yet unpublished) analysis the reasons why many large companies are trying
of a few materials and sectors suggests the kind of to "reposition" their businesses along the supply
behaviour shown schematically in Figure .2 The chain. It shows why material recycling can be envi-
"curve" describing the supply chain is convex; i.e. ronmentally beneficial but appear to be uneco-
primary extraction and processing are associated nomic: recycling avoids the early stages in the
with environmental impacts which are dispropor- material supply chain where environmental
tionate to the economic value of these steps. The impact si disproportionate to economic activity.
lowest environmental impacts per economic value Figure 2 also has a bearing on the role of tri-
added arise at the later stages in the supply chain. bology, which will now be outlined for the specific
A specific example is the energy used in making cases of road and farm vehicles.
and maintaining vehicles, an example which si
particularly relevant to this symposium and which
is explored in more detail below. The energy used 3. TRIBOLOGY IN A LIFE CYCLE CONTEXT
in producing steel is in the range 33 to 36 MJ/kg
,11 where the lower figure corresponds to a well- 3.1 Efficiency of Use and Service Life
developed recovery and recycling system in which Throughout this Symposium, the emphasis si
"leakage" of steel from the economy is kept small. on the role of tribology in reducing friction in
The energy used in forming and assembling farm machinery or in extending a machine's service life,
vehicles si typically 31 to 51 MJ/kg .11 To extend with fewer contributions on improving processing
Figure :2 Accumulated Environmental Burdens along the Supply Chain
USE
LATNEMNORIVNE i
NEDRUB
.Ae-i 4
ADDED EULAV
e.g. .1 RESOURCE EXTRACTION .2 PROCESSING AND REFINING
.3 FORMING .4 ASSEMBLY
efficiency and very little evident attention to re-use aerodynamic drag, and manufacture and disposal
or recycling. The question naturally arises of account for 20% of the total energy use over the life
whether this emphasis is appropriate and this indi- cycle, then 10% reduction in machine friction
cates a role for life cycle thinking in prioritising reduces life cycle energy consumption by 4%. The
developments in tribology. The following observa- same overall energy saving can be achieved by
tions are based on considering overall energy use, extending service life by about 30%. The tribology
as a "proxy" for depletion of abiotic energy community is better equipped than this author to
sources, because energy use will in most cases assess whether %01 reduction in friction or 30%
dominate over the other environmental impacts in extension in service life is the more achievable.
Table I. Energy use is also the most relevant con- It is recognised that the service life of passen-
cern in the context of this Symposium. ger vehicles may not be limited by wear; it also
For road vehicles - principally cars for passen- depends on technological developments or, more
ger transport- it is generally accepted that energy simply, fashion. This suggests a different role for
consumption during use si much greater than dur- surface engineering, introduced below.
ing manufacture and disposal, which account for
up to 20% of the life cycle energy consumption of 3.2 nA :elpmaxE larutlucirgA Machinery
a car. Thus, for this case at least, attention to eW now turn from the familiar example of pas-
reducing frictional losses in service is appropriate. senger cars to another type of vehicle, that used in
However, bearing in mind that a large propor- farming. A recent European study 11 has consid-
tion of the energy consumption in use is accounted ered the specific case of farming to produce bread-
for by aerodynamic drag and therefore not affected making wheat. The estimates for abiotic energy
by reducing machine friction, it si clear that extend- inputs (i.e. not including sunlight!) are sum-
ing service life also has a significant role. As a rough marised in Table .2 Three agricultural scenarios
estimate, if half the energy in use si dissipated by were considered:
Table 2: Life Cycle Energy stupnI rof Wheat noitcudorP 191
gnimraF :soiranecS A - Conventional Intensive Cultivation :
B- Integrated Cultivation
C- "Organic" Cultivation i
B C
:metsyS Grain yield (tonne/ha)
Protein content (%) 8 6 4
21 11 21
ill illl i~
ygrenE :stupnI Mineral fertilisers 14,900 6,900
(M J/ha) Organic fertilisers 1,200
Pesticides 1,500 730
Fuel 7,200 5,800 6,000
• Vehicles 3,700 2,500 4,100
~ Other !,600 1,400 2,600
i TOTAL 28,000 000,71 14,000
% of Total Energy
Input associated
with machines:
Fuel 26 34 43
Vehicle manufacture and maintenance 31 51 29
Ratio (Vehicle/Fuel) 15.0 0.43 0.68
, ,
A. Conventional intensive cultivation, charac- reduce fuel use si therefore limited.
terised by relatively large inputs of agrochemi- The energy used in making and maintaining
cals to maximise grain yield per hectare under farm vehicles breaks down very roughly as 50%
cultivation; consumed in producing materials (such as steel -
.B "Integrated" farming, which uses multiple see above), 20% in manufacturing the machines
cropping and different crop rotation patterns and 30% in repair and maintenance. On the basis
to reduce agrochemical inputs; of these estimates, it appears that the best scope
C. "Organic" farming, which uses no agrochemi- for applying developments in tribology lies in
ca! inputs but relies instead on fertilisation by reducing the need for repair and maintenance and
nitrogen-fixing crops and by animal manure. in extending service life. Furthermore, the life of
an agricultural machine is limited by failure, not
The three scenarios examined in the study by by fashion.
Audsley et al 1 I are not directly comparable, but The numerical values in Table 2 are specific to
they are broadly representative of these three certain types of agricultural equipment 11.
farming patterns. However, it is likely that the qualitative conclu-
Table 2 summarises the estimates for the life sions will also apply to other types of industrial
cycle energy inputs. The high consumption of equipment, specifically to that used in mining and
non-renewable energy by the agricultural sector si quarrying.
emphasised by these figures, which underline con-
cerns over the sustainability of current approaches 3.3 Use and Re-use
to farming. Per tonne of wheat, "integrated" The importance of re-using materials and com-
farming appears to have the smallest energy input. ponents and of maximising service life has been
However, scenario B produces a grain with lower emphasised several times. There is an interesting
protein content, which has to be blended with question as to whether comparison on a proper
high-protein imported wheat, so that the compar- life cycle basis would inform the comparison
ison is more complex than the simple figures in between recyclable metal and non-recyclable
Table 2. ceramic machinery.
The aspect of these figures which is of concern It was noted above that an important part of
here si the role of agricultural machinery. Table 2 Design for the Environment lies in minimising the
gives estimates for total energy use associated with number of different materials used in a product,
fuel (taking a life cycle view and allowing for ener- and in designing so that a machine can be disas-
gy used in extracting and processing the fuels) and sembled easily and the materials separated- a kind
with manufacture and maintenance of the farm of "reverse engineering". This could represent an
vehicles. These represent a surprisingly large frac- important role for surface engineering. At present,
tion of the total energy input, from nearly 40% in materials are most commonly selected for their
scenario A to over 70% in scenario C. Thus Table bulk properties, with any relevant surface proper-
2 shows that there si scope for applying tribology ties treated as inherent properties of the material.
in the unglamorous world of cereal farming. If surface properties could be separated from bulk
Furthermore, the relative importance of fuel properties, then the contribution of developments
efficiency compared with vehicle manufacturing in tribology to making human life sustainable in
and maintenance is quite different from the case of its industrialised form could be very great.
passenger cars" the ratio of energy used in making
and maintaining farm vehicles to energy used as
fuel is here in the range 0.43 to 0.68, compared 4. CONCLUSIONS
with up to 0.25 for passenger cars. These figures
relate to machines where aerodynamic drag si neg- Life cycle assessment needs to be deployed to
ligible, so that much of the fuel use goes into doing identify the potential significance of developments
mechanical work (e.g. on the soil in ploughing). in tribology, and hence to prioritise effort. Even
The scope for developments in lubrication to for passenger vehicles, extending service life is
potentially at least as important as improving Life Cycle Assessment of Products,
lubrication. The case for concentrating on extend- University of Leiden (CML), 1992.
ing service life si even stronger for industrial .4 G.A. Keoleian and D. Menerey, Life Cycle
machines. In the longer term, use of surface engi- Design Guidance Manual- Environmental
neering to reduce the number of different materi- Requirements and the Product System, US
als used and to improve their recyclability through Environmental Protection Agency,
reducing contamination with other materials has Cincinatti, 1993.
great potential. .5 S.J. Cowell, .S Hodgson and R. Clift, A
Manager's Introduction to Product Design
and the Environment, The Environment
ACKNOWLEDGEMENTS Council, London, 1997.
.6 R. Clift, .J Chem. Tech. and Biotech., 62
I am grateful to Professor Brian Briscoe for (1995) 321.
persisting in encouraging me to produce this con- .7 T.E. Graedel and B.R. Allenby, Industrial
tribution, and to Dr Sarah Cowell for her work on Ecology, Prentice Hall, Englewood Cliffs,
the life cycle assessment of agricultural machinery. .6991
.8 M. Goodekoop, The Eco-indicator 95- Final
Report, NOH report 9523, Netherlands
REFERENCES Ministry of Housing, Spatial Hanning and
Environment, Amersfoort, 1995.
.1 E Consoli, .D Allen, .I Boustead, .J Fava, .W .9 H. Wenzel (ed.), Environmental Assessment
Franklin, A.A. Jensen, N. de Oude, R. in Product Development - 5 case stories,
Parrish, R. Perriman, .D Postlethwaite, .B Danish Environmental Protection Agency,
Quay, .J Seguin and .B Vigon, Guidelines for Copenhagen, 1995.
Life-Cycle Assessment: A 'Code of Practice', .01 A.P. Taylor and D. Postlethwaite, Overall
SETAC, Brussels and Pensacola, 1993. Business Impact Assessment (OBIA), 4th
.2 L.-G. Lindfors, K. Christiansen, L. Hoffman, SETAC Symposium on LCA Case Studies,
.Y Virtanen, .V Juntilla, O.-J. Hanssen, A. Brussels, 1996.
Ronning, .T Ekvall and G. Finnveden, Nordic I1. ~E Auds!ey, .S A!ber, R. Clift, .S Cowell, E
Guidelines on Life-Cycle Assessment, Nordic Crettaz, G. Gaillard, .J Hausheer, O. Jolliet,
Council of Ministers, Copenhagen, .5991 R. Kleijn, .B M ortensen, D. Pearse, E. Roger,
.3 R. Heijungs, J.B. Guin6e, G. Huppes, R.M. H. Teulon, .B Weidema and H. van Zeits,
Lankreijer, H.A. Udo de Haes, A. Wegener Harmonisation of Environmental Life Cycle
S!eeswijk, A.M.M. Ansems, P.G. Eggels, R. Assessment for Agriculture, Report for DG
van Duin and H.P. de Goede, Environmental VI no. AIR3-CT94-2028, 1997.