Tampere University of Technology

Global energy consumption due to friction and wear in the mining industry

Citation
Holmberg, K., Kivikytö-Reponen, P., Härkisaari, P., Valtonen, K., & Erdemir, A. (2017). Global energy
consumption due to friction and wear in the mining industry. Tribology International, 115, 116-139.
https://doi.org/10.1016/j.triboint.2017.05.010
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2017

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Peer reviewed version (post-print)

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Tribology International

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10.1016/j.triboint.2017.05.010

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Accepted for publication in Tribology International, 5.5.2017

Global energy consumption due to friction and wear in the mining

industry
Kenneth Holmberga,*, Päivi Kivikytö-Reponena, Pirita Härkisaarib, Kati Valtonenb, Ali Erdemirc,
a
VTT Technical Research Centre of Finland, P.O.Box 1000, FI-02044 VTT, Finalnd
b
Tampere University of Technology, P.O.Box 589, FI-33101 Tampere, Finland
c
Argonne National Laboratory, Argonne, IL 60439, USA
*
Corresponding author. Tel.: +358 40 544 2285; e-mail address: kenneth.holmberg@vtt.fi

Abstract

Calculations on the global energy consumption due to friction and wear in the mineral mining
industry are presented. For the first time, the impact of wear is also included in more detailed
calculations in order to show its enormous tribological and economic impacts on this industry. A
large variety of mining equipment used for the extraction, haulage and beneficiation of underground
mining, surface mining and mineral processing were analysed. Coefficients of friction and wear
rates of moving mechanical assemblies were estimated based on available information in literature
in four general cases: (1) a global average mine in use today, (2) a mine with today’s best
commercial technology, (3) a mine with today’s most advanced technology based upon the
adaptation of the latest R&D achievements, and (4) a mine with best futuristic technology
forecasted in the next 10 years. The following conclusions were reached:

Total energy consumption of global mining activities, including both mineral and rock mining,
is estimated to be 6.2 % of the total global energy consumption. About 40 % of the consumed
energy in mineral mining (equalling to 4.6 EJ annually on global scale) is used for overcoming
friction. In addition, 2 EJ is used to remanufacture and replace worn out parts and reserve and
stock up spare parts and equipment needed due to wear failures. The largest energy consuming
mining actions are grinding (32 %), haulage (24 %), ventilation (9 %) and digging (8 %).
Friction and wear is annually resulting in 970 million tonnes of CO2 emissions worldwide in
mineral mining (accounting for 2.7 % of world CO2 emissions).
The total estimated economic losses resulting from friction and wear in mineral mining are in
total 210,000 million Euros annually distributed as 40 % for overcoming friction, 27 % for
production of replacement parts and spare equipment, 26 % for maintenance work, and 7 % for
lost production.
By taking advantage of new technology for friction reduction and wear protection in mineral
mining equipment, friction and wear losses could potentially be reduced by 15 % in the short
term (10 years) and by 30 % in the long term (20 years). In the short term this would annually
equal worldwide savings of 31,100 million euros, 280 TWh energy consumption and a CO2
emission reduction of 145 million tonnes. In the long term, the annual benefit would be 62,200

1
 million euros, 550 TWh less energy consumption, and a CO2 emission reduction of 290 million
tonnes.

Potential new remedies to reduce friction and wear in mining include the development and uses of
new materials, especially materials with improved strength and hardness properties, more effective
surface treatments, high-performance surface coatings, new lubricants and lubricant additives, and
new designs of moving parts and surfaces of e.g. liners, blades, plates, shields, shovels, jaws,
chambers, tires, seals, bearings, gearboxes, engines, conveyor belts, pumps, fans, hoppers and
feeders.

Keywords: energy, friction, wear, mining

2
1. Introduction

The global energy demand has been increasing steadily since the beginning of last century due to
the growing societal needs and many diverse industrial activities. In the last 40 years, the world’s
energy demand has doubled and in the year 2013, the global final energy consumption increased by
2.3 % from the previous year to around 9,300 Mtoe (equalling to 390 EJ). Even though the
development of renewable energy sources has been increasing, more that 80 % of the total energy
still comes from non-renewable fossil fuels like oil, coal and natural gas, which are the major
contributors to greenhouse gas (GHG) emissions. In 2012, the energy use of the CO2 emitting
energy sources increased by additional 1.4 % from the year before (IEA 2013, 2016; BP2016).

Mining is the search for, extraction, beneficiation, and processing of solid minerals from the earth’s
crust through open-pit mining, strip mining, quarrying and underground excavation. Mining has
been an essential part of human activity for thousands of years to provide raw materials for
improving security and quality of life as well as building the present-day industrial society. Some of
the most important mining activities in our history have been the excavation for iron, gold, silver,
copper, tin, lead, diamonds and coal for many Centuries. Minerals are defined as naturally
occurring, stable at room temperature, represented by a chemical formula, biogenic and have an
ordered atomic or crystalline structure. Even if coal does not by all means fit into the definition of
minerals, the excavation of coal constitutes a major mining activity and hence is included in this
study (US DOE 2002; Darling 2011a,b). Rock excavation from quarry for civil engineering
purposes is in some sources considered as mining because the activities involved are largely very
similar but excluded in our study

In general, a typical mining activity includes breaking, excavation, loading, hauling, transportation
as well as mineral processing to reduce the size of large chunks of mineral containing rocks and to
upgrade the concentration of these minerals by physical or chemical benefication methods. Mines
are found in all parts of the world. The biggest producers of mineral raw materials (excluding
petroleum and natural gas) are China accounting for 33.5 % of the world mineral production, USA
12.0 %, Australia 7.9 %, Russia 7.1%, India 6.4 %, South Africa 4.7 %, Indonesia 4.0 %, Brazil 2.1
% and Canada 2.0 (Reichl et al. 2016). These numbers include production of ferrous metals, non-
ferrous metals, precious metals, industrial minerals and solid mineral fuels like coal and uranium,
but exclude oil and gas. Coal, in the forms of steam coal, coking coal and lignite, is the largest
mining product measured by weight and representing about 60 % of the total mining production.
The second largest mining product is iron representing 11.4 %, and next follows aluminium and
bauxite 3.9 %, salt 2.1 %, sulphur 1.5 %, gypsum 1.2 %, phosphates 1.0 %, manganese 0.14 % and
copper 0.13 % (Reichl et al. 2016).

There are many types and sizes of mines in the world, ranging from small surface quarries to large
industrial underground mines, recovering ores at a depth of some kilometres beneath the surface.
The deepest is a gold mine in South Africa operating at a depth of 4 kilometres (The top ten deepest
2016). Most of the mining operations are surface mines, which include a variety of mines from
large scale coal open-pit mines to small mineral or rock quarries. Still they all include the basic
3
mining processes of drilling, detonating, comminution into manageable size, loading, transportation
and further processing for end-use applications.

The mining activity is globally expanding due to the rapid urbanisation that creates a need for more
metals and minerals in constructions and all kinds of consumer products, despite society’s growing
efforts in recycling and dematerialisation. Another reason for this expansion is that the richest ores
have long been used up so, at present increasing volumes of rock ore excavation is needed to
extract the same amount of pure mineral. The demand for base metals, particularly iron, copper and
aluminium, has been projected to double from 2010 to 2025, largely due to increasing global
urbanisation and industrialization (Albanese and McGagh 2011, Randolph 2011, Norgate and
Haque 2010).

The total amount of energy used in the mining and minerals industry has been estimated to be 4-7%
of the global energy output. The main energy sources are typically about one third electricity, one-
third diesel oil fuel and one-third coal, natural gas and gasoline (Rabago et al. 2001). Largest
amounts of energy are used in rock braking, crushing, grinding, loading, hauling and transportation.
Pumping is also a large energy consumer and in underground mines, ventilation consumes
significant amount of energy as well. Both friction and wear losses associated with the mining
activities have a great influence on energy consumption in mining.

The impact of friction on the global energy consumption has recently been calculated for road
transport by Holmberg et al. (2012a, 2014a,b). They determined that nearly one-third of the fuel’s
energy is spent to overcome friction in passenger cars. The same study advocated that, with the
adaptation of more advanced friction control technologies, parasitic energy losses due to friction in
cars could be reduced by 18% within the next 5 to 10 years, which would result in global fuel
savings of 117,000 million litres annually, and by 61% within the next 15 to 25 years, which would
result in fuel savings of 385,000 million litres annually. These figures equal world-wide economic
savings of 174,000 million euros in the next 5 to 10 years and 576,000 million euros in the next 15
to 25 years. These calculations were based on oil price level 2011. Such a fuel efficiency
improvement in passenger cars would, furthermore, reduce CO2 emission by 290 million and 960
million tons per year, respectively. This should have a significant positive impact on the global
efforts to reduce the greenhouse gas effect and control global warming as overwhelmingly agreed
by the world’s nations at the 2015 Paris Climate Conference (UN 2015).

In another study, Holmberg et al. (2013) carried out similar calculations for one advanced
manufacturing sector represented by paper production. In paper machines 32% of the electrical
energy is used to overcome friction, 36% is used for the paper production and mass transportation
and 32% is other losses. However, in a paper plant, the electrical energy is only 30% of the total
energy consumption because the remaining 70% is process heating by steam. No other industrial
sectors has been analysed in such details with regard to friction effect on energy consumption.

The paper production is by its nature much different from mining and mineral production, where the
handling of heavy rocks and large quantities of solid materials in harsh, dirty and humid conditions
form exceptional challenges. Unlike transportation and manufacturing, in mining, the wear-related

4
energy losses are considerable and wear carries a greater importance as a source for energy
consumption. To the best of our knowledge the impact of wear on energy consumption on industrial
scale has not yet been adequately addressed in the past in any detailed study in the open literature.

Our earlier papers reviewed the global energy consumption due to friction in passenger cars, heavy
duty vehicles and paper machines (Holmberg et al. 2012a, 2013, 2014a). In this study we present
calculations of the global energy consumption due to friction and wear and potential savings
through the adaption of advanced friction and wear optimisation and control technologies in the
mining industry. The focus is on the most energy consuming parts of mining, which is extraction,
transportation and the mineral processing. Oil and gas extraction as well as rock excavation for civil
engineering uses are excluded. Expected changes and trends, such as automation, remote operation,
advanced processing, globalisation and market prices like supercycles (Randolph 2011, Albanese
and McGagh 2001, Norgate and Haque 2010), are not included in the present analyses.

2. Methodology

This work was carried out by a methodology previously developed by Holmberg et al. (2012a,
2014a) for calculation of global impact of friction on transportation. Now it was extended to also
include wear calculations. The methodology is based on the combination of analyses on several
physical phenomena resulting in the energy consumption in mechanical equipment. It includes the
following analyses and calculations:
1. An estimation of the global energy consumption by mining industry.
2. Calculation of the friction, wear and energy losses in three major categories of mining units
(underground mine, surface mine, and mineral processing).
3. Estimation of operational effects in the three mining categories.
4. Estimation of tribocontact-related friction and wear losses today and in the future.
5. Calculation of the global energy consumption today due to friction and wear losses and
potential savings.

The calculations were carried out on the basis of scientific publications, publically available
statistical data and unpublished data received directly from some mine operators (Pyhäsalmi mine
in Finland and Kiruna mine in Sweden) and the authors’ own experience. There are detailed energy
statistics for mining for the U.S.A., Canada and Brazil, and these data were taken as a starting point
for the estimations on a global level (MAC 2005a,b; US DOE 2002, 2007; Brazilian 2014). On
many energy issues in mining, there is no detailed recent data available. Still, it has been relevant to
use also fairly old data because we calculate the energy consumption in global average mines which
we are estimated to have an age of 25 years.

5
3. Energy consumption analyses

3.1 Energy consumption in mining industry globally

The Total Final Consumption (TFC) of energy worldwide was 390 EJ (9,300 Mtoe) in the year
2013 and it was distributed as:
- 29% for industry,
- 27% for transport,
- 35% for domestic, including residential, services, agriculture, forestry etc.,
- 9% for non-energy use, typically as raw materials.

The Total Primary Energy Supply (TPES) was 570 EJ (13,540 Mtoe) and of that was 170 EJ used
by the energy industry for the energy production, 20 EJ was energy transfer and losses, and the rest
forms the Total Final Consumption (IEA 2016).

In the IEA energy statistics, the energy expenditure of mineral mining (as we have defined it above)
is included both in the numbers for mining and quarrying (1.81 EJ) and in the iron and steel (21.44
EJ) categories (IEA Tracking Ind Energy 2007; IEA Energy balances 2013; McLellan 2017). There
are estimations that the mining and minerals industries worldwide use as much as 4 – 7 % of the
total global energy output (Rabago et al. 2001). This would indicate that the mining industry uses
between 16 – 27 EJ annually, but this number may, however, also include rock excavation. The
energy use for mineral mining in USA, excluding oil, gas and rock excavation, was 1.31 EJ in 2007
(US DOE 2007, Tromans 2008). Correlating this to the USA share of world mineral production
results in our estimation that the mineral mining industry uses worldwide about 12 EJ energy
annually. This is our best estimation of global energy use by mining industry, excluding oil, gas
and rock excavation.

In the year 2012, the world minerals production was 10,420 million tonnes in total (excluding oil
and gas) and more than 5,400 million USD by value (Reichl et al. 2016). It includes five main
groups:
1) ferrous metals, 1,600 million tonnes,
2) non-ferrous metals, 355 million tonnes,
3) precious metals, 30,400 tonnes,
4) industrial minerals, 785 million tonnes and
5) coal and other solid fuels, 7,950 million tonnes.

Rock or stone excavation for aggregates and beneficiation from quarries are not included in this
study. Still, it is globally a very large industrial activity with most activities very similar to mineral
mining. This causes sometimes confusion since it is not uncommon that no clear indication is given
if rock excavation is included or not in published studies and calculations on mining. Rock
excavation is the extraction, transportation and processing of rocks for the purpose of civil
engineering. This includes quarrying, tunnelling and general contracting for the construction of
roads and highways, pipelines, rock fill of dams, foundation preparation, ground levelling and

6
demolition. It also includes dimensional stone quarrying, water well drilling and exploration drilling
(Heiniö 1999).

The total amount of mineral ore extracted annually in Finland is about 80 million tonnes while the
total amount of excavated rock used for civil engineering purposes is 90-100 million tonnes
(Paalumäki et al. 2015). In USA, there are about 1000 mines producing industrial minerals and
3,320 quarries producing crushed rocks (Mining Journal online 2014). According to another source,
there was in year 2000 in total 3,453 crushed stone mines out of 13,904 mines totally (US DOE
2002). This would indicate that the industrial rock excavation sector is of the same order of
magnitude as the mineral mining sector. In this study, we have chosen to focus only on mineral
mining and excluded rock excavation since in literature there is more structured information
available on the former but only very few and fragmented reliable data on the latter.

The mineral mining production takes place in both underground and surface mines, and the
upgrading of the mineral is done in mineral processing plants that often are integrated with or in
close connection to the mines (Darling 2011a) . There is no globally collected reliable data of the
number of mines worldwide. Some sources report about 500-750 active mines worldwide (Giancola
2007; Industrial Minerals Directory 2003; Moreno 2002) while other sources estimate up to
125,000 mines and quarries worldwide (Mining Journal 2014) and 13,904 only in USA (US DOE
2002). It is obvious that the big scatter is due to variation in the definitions of mines used. Rock
excavation is most probably included in some numbers and not in the others.

From the ten largest mineral producing countries, we found detailed information about the number
of mines only from two. In the USA there are 13,904 mines (US DOE 2002, NMA 2013). In Brazil
there are 7,054 mines of which 64 are underground mines, 6,978 are surface mines and 12 are
mixed mines (IBRAM 2015). USA represents 12.0 % of the world mineral production and Brazil
2.1 %. An estimation of the total number of mines worldwide based on the USA and Brazilian
numbers and correlating it to their share of world production would result in between 135,000 and
245,000 mines in total worldwide.

In Brazil, the 200 largest mines are listed separately and our assumption is that they represent the
larger industrial mines. This is in the same order as the number of mines reported for Australia
(418), Indonesia (217) and South Africa (113) where the volume of the mining production is of the
same level (IBRAM 2015). By correlating these numbers with the production of minerals we
estimate that there is in total about 150,000 mines and quarries worldwide, including rock mining,
and of those about 5,000 are large industrial mines.

3.2 Energy consuming functional categories in mining

The main operational categories in mining are the following, see Figure 3.2.1 (US DOE 2007, MAC
2005a&b; Norgate and Haque 2010, Will’s 2006, Darling 2011a):
1. Extraction: drilling, blasting, digging, ventilation, and dewatering (pumping).
2. Materials transport and handling: haulage, conveyors, hoisting, and rail transport.
3. Processing: crushing, grinding, and separation.

7
Figure 3.2.1 Main operational categories in mining.

Comminution is the collective term used to describe the progressive reduction in size of “as-mined”
ore, including two main processes, crushing and grinding. The “as-mined” ore consists of both
valuable minerals and non-desirable barren rocks. Explanation and glossary on mining terminology
is found in mining textbooks (Willis 2006, US DOE 2007, Darling 2011).

The strength of the rock has an influence on mining efficiency, equipment wear, and the energy
consumption. On a very general level the strength levels are called hard rock and soft rock but there
are as well more detailed classifications as the Terzhagi rock mass classification (Carter 2011). In
this study, we will use for our calculations these major reference mines: specifically coal, iron, and
copper mines as they represent the largest mineral product groups in mining industry, see Section 1.

The power sources for the mining, transportation and processing equipment are dominated by
electrical motors and diesel engines. The electrical power is more commonly used underground
while diesel engines are most common in surface mining (Chadwick 1992; US DOE 2007).

3.3 Global average mining units and their operating conditions

Based on the analysis in Section 3.1, we choose to further define the following three mining units as
representatives of typical mining activities that occur in most mines:
1) A global average surface mine represented by a coal open-pit mine.
2) A global average underground mine represented by a copper mine.
3) A global average mineral processing unit represented by an iron rock processing mill.

Coal is chosen as the surface mining product because it is by far the largest mining product, iron is
chosen as mineral processing product because it is the second largest mining product and copper is
chosen as underground mining product as a typical representative for the category of non-ferrous
and precious metals.

The technical and operational specifications for the three global average mining units are presented
in Table 3.3.1. Based on available data from some selected large industrial mines Härkisaari (2015)
calculated that the average annual production globally for a coal mine is 10 Mt, for an iron mine 18
Mt, for non-ferrous mines 2 Mt, for precious metals mines 8 t and for industrial metals 3 Mt. The
age of mines varies from seven year to more than 150 years and the average age for mines globally

8
is 45 years while the median is 39 years. The annual production of the three global average mining
units was adjusted to be in harmony with the energy calculations in Section 4.1. The number of
equipment is estimated based on information from literature for surface mines and mineral
processing units (US DOE 2002, Nelson 2011) and based on literature as well as data received from
the Pyhäsalmi mine in Finland for the underground mine.

9
Table 3.3.1. Technical specifications of three defined global average mining units (Komonen 2003;
Leiviskä 2009; Kunttu et al 2010; US DOE 2002; Härkisaari 2015; Tolonen 2015).
Global Average (GA) mining units Mining unit: Mining unit: Mining unit:
GA Underground GA Surface mine GA Mineral
mine processing plant
Process Underground mining Surface mining Mineral processing
Commodity Copper Coal Iron
Age (years) 25 25 25
Annual production (Mt) 4 5 4
Depth (m) 1000 - -
Ore recovery ratio (%) 50 80 -
Availability, stationary equipment (%) 70 70 70
Availability, mobile equipment (%) 30 30 30
OEE Overall Equipment Effectiveness (%) 55 55 55
Annual energy use (TJ) 3840 680 2260
Number of equipment:
Drills, bolters, jumbos 20 4 -
Continuous miners, backhoes - 1 -
Loaders, shovels, scrapers etc. ( *1) 16 12 -
Haul trucks, water trucks 16 35 -
Drag lines - 1 -
Hoists, skips 4 - -
Conveyors 40 - 40
On site crushers 6 - -
Rail transport 1 - -
Water pumps 80 6 40
Ventilation fans 150 - 10
Crushers - - 8
Grinding mills - - 4
Screens, separators, floatation etc. (*2) - - 40
(*1) Includes: Loaders, bucket-wheel excavators, mining shovels, track dozers, scrapers, graders, LHD,
(*2) Includes: Screens, cyclones, separators, pelletizers, filters, thickeners, centrifuges, floatation equipment,

The Overall Equipment Efficiency (OEE, %) is defined as

OEE = availability x performance x quality (3.1)

where availability (%) is the ability of the system to carry out a required task during a given time,
performance (%) is the ratio of the output and nominal production during the operating time and the
quality (%) is the ratio of products that are in the final selling form without defects and ready to be
sold to the customer (Komonen 2009).

3.4 Energy consumption due to friction and wear

3.4.1 Maintenance in mining

Friction between moving parts of industrial machinery consumes energy but may (similarly to
wear) also result in functional problems, failures and machine break down. Such situations cause
machinery downtime and possibly production interruptions, maintenance work and costs for
replacement parts (Vergne 2008). The maintenance cost varies in the different industrial fields due
to the nature of the industrial process, the level of technology used, level of automation, and
maintenance methods used and are typically in the range of 1 to 20% of the annual turnover. The
Finnish Maintenance Society has collected data about maintenance actions and costs in industry
over a long period of years and we have used this information as a starting point for our global

10
estimations of maintenance in mining industry (Komonen 1998a,b, 2003; Leviskä 2009; Kunttu et
al 2010; Paalumäki et al 2015; Tolonen 2015).

In Finnish manufacturing industry in general the maintenance costs were over the years 2005-2009
about 6 % of the turnover, the operational time was 70 %, the overall equipment effectiveness
(OEE) was 70 % and the availability 90 %. The equipment average age was 19 years (Kunttu et al.
2010). In the USA the average utilisation rate in mining 1972-2013 was 87.3 % while it was in
average only 80 % for all industries (Board of Governors 2015). The availability of a haul truck
may be in the rage of 65-85 % depending on the level of maintenance actions and for a shovel, it is
typically 80 % (Bohnet 2001).

In mining, the maintenance costs are higher than in most other industrial sectors. In Finland they
were reported to be 15.2 % of the annual turnover in year 1997 while they were 9.5 % in energy
production, 5.9 % in basic metal industry, 5.3 % in paper- and pulp industry, 3.6 % in chemical and
polymer industry, 2.6 % in food industry, 2.3 % in textile industry, 1.6 % in metal product industry
(Komonen 2003). In reality, the maintenance costs are even higher because several companies
report replacement material costs as operational costs. In deep ore mines, the maintenance costs can
be as high as 32 % of the total operational costs (Brannon et al. 2011).

A study from a Finnish copper underground mine shows that the maintenance cost were 29 % of the
operational costs. More than half (51 %) of the maintenance cost originated from the mineral
processing plant, 41 % from the mining unit, and 8 % from other operations. The maintenance costs
in the mining unit were distributed as 52 % for replacement parts and 48% labour while in the
processing plant, they were 46 % for replacement parts and 54 % was for labour costs (Tolonen
2015).

Our estimation used in this study is that in mining globally:

- the average age of the equipment is 20 years, with frequent wear part replacement,
- the availability in mines is 70 %,
- the typical profit level is 10 – 30 % of the turnover,
- the real maintenance costs including all material and labour costs are 25 % of the turnover,
- half of the total maintenance costs is due to wear, and
- the maintenance costs are distributed as half from replacement part expenses and half are due to
labour costs.

The downtime cost is divided into two parts, the downtime spare equipment cost and the downtime
production loss cost. The downtime when the equipment is not in function due to maintenance
reasons will result in additional costs due to loss of production capacity. The availability in mining
is about 70 % and of this we estimate that half is due to wear of parts and components and the other
half is due to operational disturbances, such as human errors, accidents, strikes etc. This means that
in average the equipment lifetime is reduced by 15 % due to equipment downtime because of wear
related maintenance actions. The logic is that if e.g. equipment has a lifetime of 20 years, it then can
be in operation only 17 years of that time due to 3 years of stand still because of wear related

11
maintenance actions. This means that the mine needs to invest 15 % more in additional capacity to
have other equipment available also during the downtime period.

Some large equipment in mining like e.g., the grinding mills and jumbo drills are critical for the
whole production line. There is typically no spare equipment so in case of breakdown there is an
interruption in the production and wear failures may result in production loss for the downtime
period. Smaller equipment in mining like the haul trucks, pumps, fans, drills etc. are less critical as
there are several of them around and in case one breaks down another can be taken to replace it
from the fleet in service. A third group of equipment is the one in between the two mentioned and
that is consisting of equipment that will cause some reduction in the production in case of
breakdown. We consider in our calculations that the equipment distribution in mining is about
equally divided in these three groups. We estimate that the production loss cost is about 20% of the
maintenance costs (Komonen 1998a,b; Tolonen 2015).

3.4.2 Friction and wear energy indicators

In our previous studies on road vehicles and paper industry, we focused on the effect of friction on
energy consumption (Holmberg et al. 2012a, 2013, 2014a). The calculations were in that sense
straightforward as there is a universal parameter representing friction, the coefficient of friction,
which is the tangential friction force divided by the normal load.

In mining, the wear has a considerable role in energy consumption and thus a tribological study
dealing with energy losses in mining without considering the wear aspect would not be very
representative. The wear issue is, however, more complicated as there is no general parameter
representing wear as in friction. There are parameters like wear rate and wear coefficient which are
frequently used but they cannot be used for all wear situations as e.g. in abrasive, corrosive, and
erosive wear where the sliding counterpart is not well specified. Thus, in the open literature wear is
reported in many forms such as wear coefficient, wear rate, wear volume, wear depth, wear groove
dimensions etc. (Meng and Ludema 1995, Holmberg and Matthews 2009).

In Figure 3.4.2.1, we show how the energy is brought to the machinery or to the production system.
One part of this goes to overcome friction due to shear in lubricated contacts, shear in the top
surface in adhesive sliding contacts and ploughing friction that results from elastic and plastic
deformation of the surfaces. These are all friction mechanisms that can be quantitatively represented
by the coefficient of friction.

Another part of the energy goes to wear related mechanisms and actions. Wear is the removal of
material from the top surface of parts and components by means of deformation, oxidation,
abrasion, fracture, fatigue, crack growth and wear particle generation. This results in energy needed
for the following actions:
1) energy is needed for producing new parts to replace the worn out parts,
2) energy is needed for producing additional equipment capacity to compensate the capacity
loss during equipment downtime and repair and/or maintenance actions due to wear failures.

12
Relevant data in a unified form as needed for the calculation of the energy parameters related to
wear is not available today so this approach is beyond the scope of our study and current state-of-
practice. For that reason, we have chosen another approach: that is to calculate the costs related to
these energy parameters. This is easier because now we have relevant data available from the
industry. It is a common practice largely in industry to follow the maintenance share of the turnover
by monitoring the costs for spare parts, maintenance work, and downtime. This is often done both
for single machines and for whole systems. In addition, we also calculate the production loss costs
at downtime due to wear failure. Thus all kind of wear failures as they are categorised in industrial
environment are included in the calculations.

Figure 3.4.2.1 Energy break down in tribological contacts

In the calculations, we consider both energy consumed and related costs. One of these is estimated
based on detailed analysis and the others converted from the former. The following parameters are
used and converted:
- Energy consumption Joule => Euro
- Material replacement Kg => Euro => Joule
- Maintenance labour Euro
- Downtime, spare equipment Euro => Joule
- Downtime, production loss Euro

3.5 Energy loss sources in mining

Energy in mining is needed to carry out the excavation of the minerals, its transportation and its
processing to an intermediate product for the market. The main mining operational categories were
presented in Section 3.2.

13
Typical equipment used for the various actions in both surface and underground mining and mineral
processing is shown in Figure 3.5.1. In this study we analyse the main energy consuming mining
equipment using equipment categories introduced in previous studies (Heiniö 1999; US DOE 2002;
MAC 2005a,b; US DOE 2007; Norgate & Haque 2010; Härkisaari 2015).

Figure 3.5.1. Underground and surface mining actions and examples of typical equipment used
(Härkisaari 2015, US DOD 2007; US DOE 2002).

The energy used in mining is dominated by two sources, electrical power and diesel fuel. In
addition coal and natural gas, and to a minor extent also gasoline and wind power are used. Diesel
fuel is traditionally and still today much used energy source in surface mining because of the
mobility, high efficiency and flexibility of diesel engines. Electrical power is extensively used in
underground mining because it does not produce emissions or exhaust gas. Electrical power is the
main source for power in mineral processing plants for crushing and grinding operations, as well as
for ventilation systems and water pumping, where the machinery is stationary (Chadwick 1992,
Smith 1994, US DOE 2002, US DOE 2007, Albanese and McGagh 2011, Errah 2011, LKAB
Annual report 2013, Paalumäki 2015).

The energy consumed in U.S. for mining industry comes from 34 % diesel, 32 % electricity, 22 %
natural gas, 10 % coal and 2 % gasoline. Materials handling was in average the largest energy
consumer (42 %) followed by processing (39 %) and extraction (19%). Diesel fuel is mostly used in
material handling to 87 % (US DOE 2002, US DOE 2007). Typical breakdown of energy
consumption in single mining equipment and machines is reported in (US DOE 2002).

14
3.5.1 Rock drilling machines

In rock drilling, a drilling equipment is used to open a cylindrical hole for exploration, blasting, or
tunnelling. Drilling equipment includes diamond drills, rotary drills, percussion drills, drill boom
jumbos and explosive loader trucks. The drills are run mainly by electricity or diesel power or to a
minor extent by compressed air. The number of drilling machines per mine is typically 2-6
depending on the mine production capacity (Heiniö 1999, US DOE 2007, Norgate & Haque 2010,
Rostami 2011, Rostami & Hambley 2011, Vergne 2008, McCarthy 2011, Paalumäki 2015).

3.5.2 Excavation machines

Excavation or digging is done to make a pass into or through, or to remove material from the earth’s
surface. The goal of digging is to extract as much valuable material as possible and reduce the
amount of unwanted materials. Digging equipment includes hydraulic shovels, cable shovels,
continuous mining machines, long wall mining machines and drag lines (US DOE 2007, Busfield
2011, Humphrey & Wagner 2011, Paalumäki 2015).

3.5.3 Draglines, skips and hoists

Draglines are used in sites of flat geology for transporting load (usually overburden) to a dump
point. They are very productive, comparatively low in operating cost and labour requirement and
extremely robust with long lifetimes. A drag line can operate from 50 m above and 65 m below its
working level, with a bucket of 125 m2 it has a capacity of moving 30-35 million cubic meters per
year (Humphrey & Wagner 2011, Paalumäki 2015). Similar hoisting systems can be used also in
underground applications by using skips to carry the primary crushed rock to the surface. The skip
is powered by an electric motor and one hoist can carry about 20-40 tonnes (Vergne 2008, Tiley
2011, Härkisaari 2015).

3.5.4 Haul trucks and loaders

The main part of all material moving operations in mines is carried out by loaders and haul trucks
because of their great flexibility and efficiency. In surface mines, the rocks are typically excavated
by shovels, excavators or front-end loaders and loaded on a dump truck for haulage to the
processing plants. The wheel loaders have typically a capacity of 50 to 90 tonnes, the shovel units
and excavators 200 to 250 tonnes and off-road dump trucks 150 to 300 tonnes. Similar haul trucks
are used in both underground and surface mining. In underground mining, however, the
circumstances create some limitations and adapted applications are used especially in relation to
size, exhaust, road quality and cycle effectivity (Smith 1994, Blackwell 1999, US DOE 2007,
Norgate & Haque 2010, Albanese & McGagh 2011, Humphrey & Wagner 2011, Berkhimer 2011,
McCarthy 2011, Härkisaari 2015, Paalumäki 2015).

Main part of the equipment used in haulage and transfer of material in mining is powered by diesel
engines. In general, diesel fuel powers rubber tire or track vehicles that deliver material in batches,
while electricity powers continuous delivery systems such as conveyors and slurry lines (Chadwick

15
1992, US DOE 2007). Main energy consumers are the engine, the tires or chains and the
transmissions.

3.5.5 Conveyor belt systems

Conveyor belt systems are an alternative to haul trucks for transporting ore from one process to
another on flat areas and high-angle conveyor systems for uphill hauls. Their popularity have
increased in the last decades because they are more cost efficient and require less labour costs. The
length of a conveyor system can vary from some meters to 20 kilometres (Nordell 1999). Belt
conveyors conserve energy because they are driven by electric motors with an efficiency of near
95% and their payload-to-dead load ratio is approximately 4:1. By comparison, the efficiency of the
diesel engine in a haulage truck does not exceed 40% and a truck’s payload-to-dead load ratio is no
better than 1½:1 (Vergne 2008,). A conveyor system is on the other hand more fixed and can
transport well fragmented material but cannot take as-mined blasted material, unlike haul trucks.
(Nordell 1999, Jansen 2008, Albanese & McGagh 2011, Brown 2011, Humphrey & Wagner 2011,
Paalumäki 2015). Much friction is generated and hence energy is consumed by the huge number of
bearings and wear is also considerable to reduce lifetime of the bearings, the idling rolls and the
belts.

3.5.6 Rail transportation

The traditional transport option for long distance and fairly horizontal transportation, including
mine to port transport, is by rail. Even if haul trucks have taken a dominating role there is a new
interest in rail transport. This is due to new possibilities offered by alternative fuels, hybrid diesel-
electric locomotives, energy storing at braking, autonomous train operation, low emissions and low
level of energy use (Randolph 2011, Paalumäki 2015).

3.5.7 Crushers

Crushing is the process to reduce the size of as-mined material into coarse particles, typically
coarser than 5 mm, to a level that grinding can be carried out. Crushing is accomplished by
compression of the ore against rigid surfaces, or by impact against surfaces in a rigidly constrained
motion path. It is usually a dry process and is performed in several stages. Crushing plants include
primary, secondary and tertiary crushers. Primary crushers include jaw crushers and gyratory
crushers. Secondary and tertiary crushers include cone crushers, Rhodax crushers, impact crushers,
and rotary coal breakers.

Crushing machines are normally powered by electric motors and their efficiency is often very low,
normally less than 10 %. The problem lies in the fact that most of the energy input in a crushing or
grinding machine is absorbed by the machine itself, and only a small fraction of the total energy is
available for breaking the material (Wills & Napier-Munn 2006, US DOE 2007, Vergne 2008,
Norgate & Haque 2010, Albanese & McGagh 2011, Brown 2011, Utley 2011, Mosher 2011,
Legendre & Zevenhoven 2014, Paalumäki 2015).

16
3.5.8 Grinding machines

Grinding is the process of reducing the size of material into fine particles, typically below 0.1 mm
(Will’s and Napier 2006; Mosher 2011). Grinding is performed in rotating cylindrical steel vessels.
It is accomplished by abrasion and impact of the ore by free motion of unconnected media such as
rods, balls or pebbles. It is usually performed wet to provide a slurry feed to the concentration
process, although dry grinding has some limited applications.

Grinding mills are classified into two types, tumbling mills and stirred mills. In tumbling mills, the
mill shell is rotated and motion is imparted to the charge via the mill shell. The grinding media may
be steel rods, balls or the rock itself. In stirred mills, the mill shell has a vertical or horizontal
orientation and is stationary and motion is imparted to the charge by the movement of an internal
stirrer. There is a large variety of mill types in grinding plants such as semi-autogenous grinding
mills (SAG), rod, ball and tube mills, discharge mills, vibratory mills, centrifugal mills, tower mills,
stirred mills, roller mills, high pressure grinding roll mills etc. They are normally powered by
electric motors and their efficiency can be very low, even as low as 1% has been reported for a ball
mill (Fuerstenau et al 2002, Wills & Napier-Munn 2006, US DOE 2007, Tromans 2008, Vergne
2008, Norgate & Haque 2010, Albanese & McGagh 2011, Mosher 2011, Paalumäki 2015).

3.5.9 Separators, machines for concentration and final processing

Separation of mineral material is to a large part carried out by physical separations, where the
valuable materials are separated from undesired substances based on the physical properties of the
materials. A wide variety of equipment is used for separation processes, the largest energy-
consuming methods amongst these being centrifugal separation for coal mining, and floatation for
metals and minerals mining. Other equipment types are e.g. screens, cyclones, jigging devices, and
magnetic and electrostatic separators.

Centrifuges are spinning baskets designed to receive solid-liquid slurries and remove the liquid.
Floatation machines isolate valuable ore from non-valuable substances by chemical reagents to
bond to the valuable product and make them air-avid and water-repellent. In iron ore mining,
screening is the most common separation method. It is used to separate the ore into lump and fines
streams, while magnetic separation is used to separate magnetite from barren rock. Final processing
includes actions that further prepare the ore to yield the desired product in its purest and most
valuable form. These actions include e.g. roasting, smelting, refining. These processes require
relatively much less energy (Cohen 1983, Wills & Napier-Munn 2006, US DOE 2007, Vergne
2008, Norgate & Haque 2010, Flintoff & Kuehl 2011, Kawatra 2011).

3.5.10 Compressed air systems

Compressed air is used extensively in mining to drive pneumatic systems such as air motors,
actuators, instrumentation, and pneumatic tools. It can also be used to cool and clean components or
parts and to blow off waste material (Vergne 2008, Hooper 2011, Paalumäki 2015).

17
3.5.11 Dewatering, pumping

Dewatering is the process of pumping water from the mine workings. The sources of water in
mining are e.g. inflow of rain water, inflow of ground water, leakage from sea, lakes, rivers or
dams, mine service water, drainage from hydraulic backfill or hydraulic mining. In mineral
processing most separation processes involve the use of substantial quantities of water. The
pumping systems in mining are always large energy consumers (Cochen 1983, Will’s 2006, US
DOE 2007, Vergne 2008, Peppers 2011, McCarthy and Dorricott 2011, Richards 2011, Paalumäki
2015).

3.5.12 Ventilation

Good ventilation is needed in underground mining to bring fresh air to the underground workers
while removing stale and contaminated air from the mine and also for cooling work areas in deep
underground mines. The electric power required for the ventilation system for a mine is one of the
major components of the total electric power consumption and may be even as much as 40%
(Chadwick 1982, Mukka 2002, Vergne 2008, Halim & Kerai 2013, Paalumäki 2015).

4. Calculation of energy consumption in mining

4.1 Energy consumption breakdown in the global average mining units

Based on our analysis in Section 3 we make the following estimation as input data for our
calculations:
- 12 EJ/a is the global energy consumption of mineral mining industry,
- 150,000 is the total number of mines and quarries (this number includes rock excavation),
- 5,000 of all mines are large industrial mines while the rest are smaller mines and quarries,
- 5,000 large industrial mines worldwide use 80% of all energy in mining industry = 9.6 EJ/a,
- 15% of the large industrial mines are underground mines,
- 85% of the large industrial mines are surface mines,
- 1,700 large mineral processing units worldwide estimated from the assumption that there are
2-4 times more mines than mineral processing units,

Our estimation that the 5,000 large industrial mines use 80% of all energy used in mining may seem
high compared to their small number of all mines. Here we have considered that the number of all
mines worldwide also includes some mines taken out of use, many mines that are used only
occasionally depending on market prices or used only very limited in time. Our estimation
correlates fairly well when we compare it to average annual energy use considering energy
consumption per tonne ore produced and recovering ratio from the Canadian mining report (MAC
2005a,b).

Typically 30-50% of the energy in mining goes to mineral processing. The energy intensity for
surface mining is 5-10 kW/t and for underground mining 20-50 kW/t, which means that it is about

18
four to five times more for underground mining (Cochen 1983, NMA 2013, Rabago et al. 2001, US
DOE 2002, MAC 2005a,b; US DOE 2007, Norgate & Haque 2010, Albanese et al. 2011, Nelson
2011). According to another source, the energy intensity in surface mining is 25 kWh/t and in
underground mining 180kWh/t (Batterham & Goodes 2007). The ore and coal production in US is
10 times higher in surface mining than underground (Nelson 2011). We conclude that the annual
mining production is about seven times bigger in surface mines but their energy intensity is about
seven times smaller compared to underground mines, which means that both surface mining and
underground mining use about the same amount of energy annually worldwide.

We summarise that the energy consumption for mining globally is distributed as:
- 30% or 3.6 EJ for surface mining,
- 30% or 3.6 EJ for underground mining, and
- 40% or 4.8 EJ for mineral processing.

And further we calculate that the global annual energy consumption in the 5000 large industrial
mines is:
- 2.88 EJ in 750 underground mines,
- 2.88 EJ in 4250 surface mines and
- 3.84 EJ in 1700 processing plants.

Now we can calculate the annual energy consumption of our previously defined global average
mining units that represent an average of the large industrial mines and it is:
- 3,840 TJ/a (1.07 TWh/a) for the global average underground copper mine, with a
production rate of 4 Mt/a,
- 680 TJ/a (0.19 TWh/a) for the global average surface coal mine, with a production rate of
5 Mt/a, and
- 2,260 TJ/a (0.63 TWh/a) for the global average iron processing plant, with a production
capacity of 4 Mt/a.

The total energy used in mining industry is consumed by the different mining operational categories
as shown in Figures 4.1.1 and 4.1.2. The energy consumption distribution for mining actions is
based on data from (Cochen 1983, MAC 2005a, US DOE 2002, MAC 2005b, Willi’s 2006, US
DOE 2007, Tromans 2008, Norgate & Haque 2010, Härkäsaari 2015).

19
Figure 4.1.1 Share in percentage of the global energy consumption in mining (=12 EJ) in total and
according to mining operational categories.

Figure 4.1.2 Global energy consumption in mining (=12 EJ) according to mining operational
categories.

4.2 Friction and wear vs energy and economic losses

The friction losses are related both to lubricated and dry contacts in mobile and stationary
equipment like engines, gears, transmissions and tires in mining vehicles; electrical motors,
transmissions, hydraulics and rollers in stationary mineral processing machines; and hydraulic and
ventilation systems. We carried out three case studies where the friction and wear losses were
analysed and calculated in detail (Härkisaari 2015). The three cases are a mobile jaw crusher, a
grinding mill, and a haul truck, see Figure 4.2.1. They represent three typical equipment categories
in mining. The jaw crusher represents a rock demolition equipment used on site, the grinding mill is
a large and the most energy consuming equipment in mineral processing, and the haul truck
represents a very common mobile vehicle used in material transportation.

20
Figure 4.2.1 Three case studies were carried out for detailed energy and cost analysis: a mobile jaw
crusher, an off-highway haul truck and a grinding mill.

The breakdown of the energy use in the three cases studied are shown in Figures 4.2.2, 4.2.3 and
4.2.4.

Figure 4.2.2 The energy distribution in a diesel powered mobile jaw crusher typically used in iron
ore crushing (weight 50 tons).

21
Figure 4.2.3 The energy distribution in an electrically powered autogenous grinding mill typically
used in primary milling of iron ore (mill diameter x length = 6 x 6 m).

Figure 4.2.4 The energy distribution in a diesel driven off-highway rigid frame 90 tons haul truck
used in mining.

The energy used for brakes in the haul truck is considered equal to the energy used to accelerate the
vehicle and thus it represents the energy of inertia to overcome when moving the vehicle.

The distribution of friction losses according to the various lubrication mechanisms in both mobile
and stationary equipment was estimated for both diesel and electric powered machines by using
previous friction analysis and applying them to mining conditions; see Table 4.2.1 (Holmberg
2012a, 2014a).

22
Table 4.2.1 Friction and energy losses in main components as part of the total friction losses.
Mobile mining Stationary mining machinery
vehicle
Lubrication Diesel engine, Diesel engine, Electrical motor,
mechanisms e.g. haul truck e.g. jaw crusher e.g. grinding
mill
% % %
Friction of total 51 30 32
energy input

Engine / motor 16 30 38
- valve train ML 15 15
- bearings, seals HD 30 30
- piston assembly 45 45
HD squeeze 40 40
EHDS 40 40
ML 10 10
BL 10 10
- pumping, hydraulic VL 10 10
Transmission 12 27
- gears EHDSR 55 55
- bearings EHDR 20 20
- viscous losses VL 20 20
- seals, forks ML 5 5
Hydraulics VL 12 20 -
Tyres RF 33 - -
Braking 27 - -
(~acceleration)
Dry sliding & rolling - 23 62
Friction total 100 100 100

HD = hydrodynamic lubrication EHD = elasto-hydrodynamic lubrication

ML = mixed lubrication EHDS = elasto-hydrodynamic sliding
BL = boundary lubrication EHDR = elasto-hydrodynamic rolling
RF = rolling friction EHDSR = elasto-hydrodynamic sliding/rolling
VL = viscous losses

The results of the analysis of friction losses is summarised in Table 4.2.2. In the conversions we
have used global average prices 2014 which were 0.7 €/l for diesel fuel, 0.06 €/kWh (=> 1 MJ costs
0.0166 Euro) for electric power and 6 €/hour for maintenance work.

23
Table 4.2.2 Summary of annual friction losses in three case studies (Härkisaari 2015).
Operation Tribo- Annual Annual Friction loss Energy loss Energy loss
category operational energy use from total due to due to
use energy friction friction
Unit - h l & TJ % l & TJ €/a
Jaw crusher CAW 5,700 8.2 (TJ) 30 2.46 (TJ) 40,800
Grinding mill AEW 7,000 126 (TJ) 32 40 (TJ) 664,000
Haul truck LW 4,800 1,220,000 (l) 51 622,200 (l) 435,600

The results of the wear loss calculations is in Table 4.2.3 and both friction and wear losses are
summarised in Table 4.2.4.

Table 4.2.3 Summary of annual wear losses in three case studies (Härkisaari 2015)

Operation Tribo- Wear part Maintenance Maintenance Total

category replacement labour labour
Unit - € h € €
Jaw crusher CAW 90,500 500 3,000 93,500
Grinding mill AEW 800,000 750 4,500 804,500
Haul truck LW 64,500 1,150 6,900 71,400

Table 4.2.4 Annual costs of friction and wear vs the estimated purchase price in three case studies
(Härkisaari 2015)

Operation Tribo- Purchase Annual cost Friction Wear loss Wear and
category price of friction loss of of purchase friction /
and wear purchase price new device
price
Unit - € € % % %
Jaw crusher CAW 1,000,000 134,300 4 9 13
Grinding mill AEW 5,000,000 1,468,500 13 16 29
Haul truck LW 1,500,000 506,800 29 5 34

From Table 4.2.4 we can observe one interesting feature when comparing costs for friction and
wear as percentage of purchase price. The costs for friction and wear losses are of the same level in
the grinding mill (13% and 16%), the costs for friction losses are six times higher than for wear
losses in the haul truck (29 % and 5 %), and the friction loss costs are about half of the wear loss
costs for the jaw crusher (4 % and 9 %). Based on this, we divide all the mining equipment in three
tribocategories as illustrated in Figure 4.2.5:

- crushing abrasive wear, CAW, where severe abrasive wear, due to the forced stone
crushing and severe impact actions, is dominating; represented by the jaw crusher and also
including other crushers, drills, bolters and jumbos,

24
 - abrasive erosive wear, AEW, where moderate abrasive wear, resulting from free falling or
moving collisions of rock material, is typical; represented by the grinding mill and also
including the various digging equipment like loaders, excavators, shovels, dozers, scrapers,
graders, LHD, backhoes and continuous miners, pumps, conveyors, skips, and 50% of
separation equipment, and
- lubricated wear, LW, where lubricated contacts are dominating; represented by the haul
truck and including all trucks and also hoists, drag lines, fans, railway and 50% of
separation equipment like screens, cyclones, separators, pelletizers, filters, thickeners,
centrifuges and floatation equipment.

Figure 4.2.5 Annual costs for friction and wear in mining equipment is divided in three
tribocategories: crushing abrasive wear dominated (CAW), abrasive erosive wear dominated
(AEW), and lubricated wear dominated (LW).

The ratio of friction costs / wear costs is according to Table 4.2.4 for CAW 1 : 2.25, for AEW 1.2 :
1 and for LW 5.8 : 1. We use in this study the following ratios for the friction to wear costs:

- Crushing abrasive wear (CAW) = 1:2

- Abrasive erosive wear (AIW) = 1:1
- Lubricated wear (LW) = 6:1

4.3 Calculations of friction and wear energy losses and costs

Based on available global statistics found on web and considering that the largest mining activities
are found in China, USA, Australia, India and Russia, we have considered to use the following
prices and global average values in our calculations:
- 0.7 €/litre as price for diesel fuel,
- 0.06 €/kWh as price for electricity, and
- 6 €/hour as price for maintenance work.

25
One litre diesel fuel has an energy content of 35.9 MJ. The price of one GJ diesel fuel is thus 19.5
€. From above, the price of electricity for one GJ is 16.7 €. In our calculations below, we use as the
global average energy price, 1 GJ = 18 € or 1 TJ = 18 k€.

The annual friction and wear losses for the three global average (GA) mining units as shown in
Table 4.3.1 were calculated as follows:
1. the total energy use for the GA underground mining, surface mining and mineral processing
plants is taken from Section 4.1 calculations, and the distribution of the energy consumption
for the various mining actions is according to Figure 4.1.2 and reduced to 80 % for the large
industrial mines,
2. the mining actions are classified in three tribocategories as described in Section 4.2 and
shown in Figure 4.2.1, and the number of units are as calculated in Section 4.1,
3. the friction losses for each mining action is calculated as part of the total energy
consumption based on data from Table 4.2.2 for the representative case study:
a. 30 % friction losses for CAW, represented by the jaw crusher
b. 32 % friction losses for AEW, represented by the grinding mill, and
c. 51 % friction losses for LW, represented by the haul truck.
4. the friction energy losses in TJ is converted to energy costs in Euro (1 TJ = 18 k€)
5. based on the ratio for friction and wear costs in the three case studies in Section 4.2, we
calculate the wear-related costs from the friction costs by using the ratios:
a. CAW friction/wear cost ratio = 1 : 2
b. AEW friction/wear cost ratio = 1 : 1
c. LW friction/wear cost ratio = 6 : 1
6. the energy used to manufacture the failed machine components and tools are calculated from
their value in Euro (step 5) using the following price, energy for prime value and energy
after processing value (Cranta Design – CES Selector 2015):
a. Steel: 0.44 €/kg – 33 MJ/kg – 65 MJ/kg
b. Steel, wear parts: 1.2 €/kg – 30 MJ/kg – 50 MJ/kg
c. Rubber: 3.6 €/kg – 115 MJ/kg – 135 MJ/kg
d. Drill tool: 95 €/kg - 1370 MJ/kg – 1385 MJ/kg
resulting in 1 k€ = 0.035 TJ for wear parts and 1 € = 0.05 TJ for whole equipment
7. we have in §3.4.1 estimated that the maintenance labour costs are half of total maintenance
costs, and the cost for the wear parts is the other half,
8. from Section 3.4.1 we know that the downtime due to wear reduces the equipment
availability with 15% and we assume an average lifetime (AL) of 20 years for the mining
equipment, we also assume that half of downtime is covered with spare equipment,
9. form Section 4.2 Table 4.2.4 we get that the ratio of annual friction and wear costs (FWC) /
purchase price (PP) (=equipment replacement value), is:
a. 0.13 for CAW represented by jaw crusher,
b. 0.29 for AEW represented by grinding mill, and
c. 0.33 for LW represented by haul truck.
10. Based on step 8 and 9 we now calculate the downtime spare equipment cost (DSEC) from
the equation:
DSEC = 0.15 x PP / AL x 2 = 0.15 x FWC / AL x (FWC/PP ratio) x 2 (4.1)

26
 11. the energy used to produce the replacement equipment is calculated from the downtime
costs in similar way as for the replacement components previously (step 6) but now
estimated for the whole equipment by using the conversion 1 € = 0.05 TJ,
12. the production loss costs are estimated to be 25 % of the total maintenance costs, and the
mining equipment is estimated to be distributed equally in the three criticality levels, as
described in §3.4.1:
a. high criticality level are equipment like: grinding mills, hoists,
b. average criticality level are equipment like: conveyers, pumps, crushers, separators,
feeders, drills,
c. low level are most other equipment like: trucks, fans, loaders, excavators, scrapers,
etc.
we assume that half of the downtime is due to total stop in production resulting in loss of
profit and calculate that the average production loss cost due to friction and wear = (total
maintenance costs) * 0.25 / 2
13. finally we sum up the total downtime costs, energy consumption and total costs for each GA
unit.

The main results of current global energy consumption in mining are presented in Tables 4.3.1 and
4.3.2.

Table 4.3.1 Energy loss and costs due to friction and wear in a global average underground mine,
surface mine and mineral processing unit.
Mine 1990 Number Total Friction Wear replacment Maintenence
Downtime Wear Total friction and
of mines energy parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit TJ TJ kEuro TJ kEuro kEuro TJ kEuro kEuro TJ kEuro TJ kEuro
Calc step 2 1 3 4 6 5 7 11 8,9,10 11,12 13 13 13 13

GA underground 750 3638 1614 29046 469 13408 13408 32 646 3352 502 30815 2115 59861
Crushing wear CAW 534 160 2886 5772 250
Abr impact wear AIW 683 218 3932 3932 102
Lubricated wear LW 2421 1235 22228 3705 295

GA surface mine 4250 671 290 5227 83 2383 2383 5 103 596 89 5464 379 10691
Crushing wear CAW 43 13 231 461 20
Abr impact wear AIW 227 73 1307 1307 34
Lubricated wear LW 402 205 3689 615 49

GA processing plant 1700 2259 742 13348 477 13632 13632 20 405 3408 497 31076 1239 44424
Crushing wear CAW 226 68 1220 2440 106
Abr impact wear AIW 1911 611 11005 11005 285
Lubricated wear LW 122 62 1123 187 15

Table 4.3.2 Energy loss and costs due to friction and wear worldwide in underground mining,
surface mining and mineral processing.
Mine 1990 Friction Wear replacment Maintenence Downtime Wear Total friction and
parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit PJ MEuro PJ MEuro MEuro PJ MEuro MEuro PJ kEuro PJ MEuro
Underground mining 1513 27230 440 12570 12570 30 606 3143 470 28889 1983 56119
Surface mining 1543 27766 443 12659 12659 27 545 3165 470 29028 2013 56794
Mineral processing 1576 28364 1014 28967 28967 43 861 7242 1057 66037 2633 94402
4631 83361 1897 54197 54197 101 2012 13549 1997 123954 6629 207315

27
4.4 Emissions and summary of analysis

A study on energy and greenhouse gas impacts of mining and mineral processing showed that
loading and hauling make the largest contribution to the total greenhouse gas emissions for mining
and processing of iron ore and bauxite. In the case of copper ore, the crushing and grinding makes
the largest contribution of greenhouse gases in the production of copper ore (Northgate et al 2010).
A potential of reducing the CO2 emissions by 40 Mt in the USA and by 6 Mt in the North-East
Russia region has been shown (US DOE 2007, Keikkala et al 2007).

We calculate the CO2 emissions related to friction and wear directly from the energy consumption.
We use the estimation of Rabago et al. (2001) that in mining 1/3 of the energy requirement is met
by electricity, 1/3 by diesel fuel, and 1/3 by coal, natural gas and gasoline. The calculated emissions
for Mine 1990 are shown in Table 5.2.1.

A summary of the calculation process and the sources for the data used is shown in the flowchart in
Figure 4.4.1. It summarises that 2015 the impact of friction and wear was resulting in 6.6 EJ energy
consumption, 970 million tonnes CO2 emissions, and 210,000 million economical costs in the
mineral mining industry worldwide.

Fig. 4.4.1 Flow chart for calculations of global impact of friction and wear on mineral mining
industry

28
5. Trends in friction and wear reduction and potential savings
5.1 Tribocontact friction and wear losses today and in future

The basic friction and wear mechanisms have been extensively studied and are described in the
tribological literature (Bhushan 1999, Sethuramiah 2003, Stachowiack et al 2005, Blau 2009, Totten
2006, 2012). There is a good understanding of how various contacts can be classified and what level
of frictional losses and wear rates they typically represent. However, not so much of the literature is
especially focusing on machines and vehicles working under mining conditions. The tribological
mechanisms have some special features in mining industry and that is especially the very heavy
loading conditions and the very dusty and often also humid environment. In this study we have
estimated the coefficients of friction and the wear rates in various tribocontacts based on published
data in the literature and adjusted them to better suit the mining conditions.

Friction and wear levels for different tribocontacts in four types of global average mines were
separately estimated: the typical 25-year-old mine in use today (designated hereafter as “Mine
1990”), a mine that represents a combination of today’s most advanced commercial tribological
solutions (“Com 2015”), a mine that represents the best tribological solutions demonstrated in
research laboratories today (“Lab 2015”), and a mine that reflects estimations by the best experts in
the field of what is possible to achieve in the future after about 10 years extensive R&D work
(“Mine 2025”).

The coefficients of friction and the relative wear level based on the above classifications are given
in Table 5.1.1 and 5.1.2 and shown in Fig. 5.1.1 and 5.1.2. The references in the tables relate mainly
to the friction and wear values for Com 2015 and Lab 2015, while the friction values for Mine 1990
and Mine 2025 are estimates by the authors based on available present information and their own
experience. Potential technical solutions for friction and wear reduction are discussed in Section 6.

Table 5.1.1 presents friction coefficients for common tribological contacts. Friction can be reduced
and controlled by advanced technological solutions. The friction estimates in Table 5.1.1 are based
on commercial oil lubrication for Mine 1990 and Com 2015 and on a new kind of lubrication,
sometimes non-petroleum-based (e.g., a water-based lubricant such as polyalkylene glycol) for Lab
2015 and Mine 2025.

Viscous losses in transmission systems are due to shear and churning of oil in the transmission case.
Part of the energy losses in engine systems, pumping and hydraulic systems are related to viscous
losses. Viscous losses are included in this analysis because, even if they are not directly friction
losses, they can be reduced by tribological solutions with lower viscosity lubricants and thus also
lower viscous losses.

In table 5.1.1, we have used as starting point the values estimated for heavy duty vehicles reported
previously (Holmberg et al 2014a) and modified them for mobile equipment in mining conditions
especially considering the much harsher and dusty conditions in the following ways:

29
 - the friction in lubricated contacts is estimated to be 50% higher for Mine 1990 and Com
2015 and three times higher for Lab 2015 and Mine 2025 compared to heavy duty road
vehicles because of the more contaminated conditions, higher loads, and lower speeds used,
- the tire rolling friction is estimated to be 0.035 in modern mines (Com 2015) because of the
more rigid tire design and the rougher surfaced roads in mines (NRC 2006, Wicaksana
2011), and
- the viscosity used is estimated to be thicker in some mining equipment and the change to
lower viscosity oils is more unlikely due to thicker lubricant film requirement from dusty
conditions and occasional heavy impact loading.

Table 5.1.1 Tribological contact performance for the chosen four types of mines (Thompson &
Vissner 2003, Wetherelt & Wielen 2011, Thompson & Visser 2003, Wicaksana et al. 2011, NRC
2006, Holmberg et al. 2014a, Coal Age 2015).
Contact types acting as friction sources Coefficients of friction
Mine 1990 Com 2015 Lab 2015 Mine 2025
Boundary lubrication (BL) 0.2 0.15 0.03 0.015
Mixed lubrication (ML) 0.15 0.08 0.03 0.015
HD lubrication (HD) 0.04 0.015 0.006 0.003
EHD sliding (EHDS) 0.12 0.06 0.03 0.015
EHD sliding-rolling (EHDSR) 0.09 0.05 0.015 0.003
EHD rolling (EHDR) 0.015 0.003 0.003 0.002
Tire rolling (TR) 0.05 0.035 0.025 0.02
Resistance to viscous shear (VL), (cSt at 80ºC) 40 30 25 20

In Table 5.1.2 we have used the previously introduced classification of typical wear conditions in
mining industry: forced crushing abrasive wear dominated, free movement abrasive erosive wear
dominated, and lubricated wear dominated. Due to the complexity of the wear process there is no
universal physically based unit, like coefficient of friction, that can be used to reflect prevailing
wear conditions. Thus we express the improved lower wear conditions as relative wear reduction in
percentage as compared with the level of Mine 1990. The improvements in wear resistance were
estimated based on data collected in Section 6.

30
Table 5.1.2 Estimated relative friction and wear rate reduction trends and possibilities in mining
machines and equipment over the period 1990 to 2025 (based on references given in section 6).
Relative friction and wear reduction
Contact conditions from Mine from Mine from Mine
1990 to 1990 to 1990 to Mine
Com 2015 Lab 2015 2025
% % %
Friction reduction
- crushing abrasive wear dominating, CAW 20 40 50
- abrasive erosive wear dominating, AEW 20 40 50
- lubricated wear dominating, LW 40 80 90
Wear reduction
- crushing abrasive wear dominating, CAW 40 60 70
- abrasive erosive wear dominating, AEW 50 75 85
- lubricated wear dominating, LW 30 40 50

Figure 5.1.1 Trends in friction reduction by new tribological solutions for different lubrication and
contact conditions in mining applications.

31
Figure 5.1.2 Trends in wear reduction by new tribological solutions for different contact severity
levels in mining applications.

In the estimations above, we have considered that in the global average mine (i.e, Mine 1990) the
machines and equipment components are not all that old but have partly been replaced by newer
and more modern ones during the maintenance actions. The average lifetime for mining machines
and devices is about 20 years and the average age is about 12 years. Considering that some parts
have been renewed at maintenance then the average age of components in function is about 8-10
years, excluding the “wear parts” that are replaced more frequently.

5.2 Potential savings

The energy, costs and emissions were calculated for Com 2015, Lab 2015 and Mine 2025 in the
same way as previously for Mine 1990 in Section 4.3 but now including the reductions in friction
and improvements in wear resistance estimated in Section 5.1. The results are shown in Table 5.2.1.

32
Table 5.2.1 Global annual energy consumption, costs and emissions due to friction and wear in
mineral mining and calculated reduced values if new technical solutions would be implemented in
full extent in all mines worldwide.

Energy losses Costs Emissions

friction wear total friction wear total friction wear total
Unit PJ PJ PJ MEuro MEuro MEuro MtCO2 MtCO2 MtCO2
Mine 1990
Underground mining 1513 470 1983 27230 28889 56119 221 69 290
Surface mining 1543 470 2013 27766 29028 56794 225 69 294
Mineral processing 1576 1057 2633 28364 66037 94401 230 154 384
Mining total 4632 1997 6629 83360 123954 207314 676 292 968
Com 2015
Underground mining 555 283 838 12561 17325 29886 81 41 122
Surface mining 724 271 995 13043 16625 29668 106 40 145
Mineral processing 880 556 1436 15839 34498 50337 128 81 210
Mining total 2160 1110 3270 41442 68448 109890 315 162 477
Lab 2015
Underground mining 317 193 510 5706 11894 17600 46 28 75
Surface mining 349 174 523 6289 10756 17045 51 25 76
Mineral processing 636 306 942 11453 18856 30309 93 45 138
Mining total 1303 673 1976 23448 41506 64954 190 98 288
Mine 2015
Underground mining 209 145 354 3765 8964 12729 31 21 52
Surface mining 240 126 366 4309 7810 12119 35 18 53
Mineral processing 524 199 723 9432 12123 21555 77 29 106
Mining total 973 470 1443 17505 28897 46402 142 69 211

It is not realistic to think that new energy, cost and emission reducing tribological solutions can be
very quickly implemented in the mining industry worldwide. The reason is the great number of
mines, the great number and variety of owners that are not well organised worldwide and the
conservative attitude to implementing new technology in many parts of the mining industry and in
many countries. Here is a great difference with e.g. the heavy duty vehicle sector in transportation
where the fleet owners are well organised and the manufacturers are in the forefront of
implementing new technology.

We estimate that a large scale implementation of existing technology and development of new
advanced solutions could have the effect that energy, cost and emission would be reduced to more
than half of the difference between Mine 1990 and Com 2015 (15 %) during the time range of 10
years and to more than the level of Com 2015 (30 %) during the time range of 20 years. Tables
5.2.2 and 5.2.3 show the potential savings based on this estimation.

33
Table 5.2.2 Potential global annual energy savings, and costs and emission reductions by
implementing new technology on short term (10 years) and long term (20 years).

Energy losses Costs Emissions

friction wear total friction wear total friction wear total
Unit PJ PJ PJ Meuro Meuor Meuor MtCO2 MtCO2 MtCO2
Short term (10 years, 15 %)
Underground mining 227 71 297 4085 4333 8418 33 10 43
Surface mining 231 71 302 4165 4354 8519 34 10 44
Mineral processing 236 159 395 4255 9906 14160 35 23 58
Mining total 695 300 994 12504 18593 31097 101 44 145
Long term (20 years, 30 %)
Underground mining 454 141 595 8169 8667 16836 66 21 87
Surface mining 463 141 604 8330 8708 17038 68 21 88
Mineral processing 473 317 790 8509 19811 28320 69 46 115
Mining total 1390 599 1989 25008 37186 62194 203 87 290

Table 5.2.3 Potential energy and cost savings, and emission reduction by new tribological
technology on short term (10 years) and by country estimated based on their share of the global
mineral raw material production (Reihel 2016).

Production of mineral Energy savings Cost savings CO2 emission

raw materials (TJ/a) (million euro/a) reduction
(excluding petrol and (million tonnes/a)
gas)
World (100%) 995,000 31,100 145
China (33.5 %) 335,000 10,400 48.6
USA (12.0 %) 120,000 3,730 17.4
Australia (7.9 %) 78,600 2,420 11.5
Russia (7.1 %) 70,600 2,210 10.3
India (6.4 %) 63,700 1,990 9.3
South Africa (4.7 %) 46,800 1,240 6.8
Indonesia (4.0 %) 40,000 1,300 5.8
Brazil (2.1 %) 20,900 650 3.0
Canada (2.0 %) 20,000 620 2.9
Finland (0.02 %) 200 6.2 0.03

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6. Means of reducing wear, friction and energy use in mining

In this section, we present some new technical solutions that can be implemented to achieve friction
and wear reductions in mining equipment. The examples mainly describes what we have named
“today’s best solution on the laboratory level” (Lab 2015). Some of the new solutions for friction
and wear reduction can be directly implemented by the users to existing machines. Such are the
changes to new type of engine lubricant, lubricant additives and tires with new materials and new
design as well as frequently replaced wear parts. On the other hand, many of the new friction and
wear reducing solutions need re-design or replacement of existing components, like the introduction
of new materials, surface treatments, coatings and textured components or new design solutions.
This kind of improvements need to be introduced by the machine producers and will come out on
the market, when the new products are launched.

6.1 Wear reduction in critical parts subject to crushing abrasive wear

Material wear resistance is a system property, which is a combination of mechanical properties,

microstructure of the material and the wear environment including abrasive material, contact
mechanism, load or impact energy, moisture and temperature. Severe abrasive and impact wear
conditions with forced crushing wear (which was defined earlier in section 4.2) as crushing abrasive
wear (CAW), occur typically in various types of crushers, bolters, drills and jumbos. This means
high-stress abrasive or impact-abrasive wear resulting from direct rock contact. The large range of
properties of the mined ores, minerals and rocks makes the material selection for different mines
very challenging (Chattopadhyay 2001, Sare 2001, Scott 2006, Rostami 2011, Bruce 2012, Ratia
2014, Tolonen 2015).

6.1.1. Rock crushing

In mining operations, the selected process including crushing and grinding, depend on the mined
ore and the mineral. Jaw crushers are mostly used as primary or secondary crushers for hard
minerals. Gyratory crushers are selected for higher capacity and horizontal impactors for feed with
lower hardness. For the final crushing stage, cone crushers, vertical shaft impactors (VSI), and high
pressure grinding rolls (HPGR) are typical options [Metso 2016].

In wear parts of jaw, cone, and gyratory crushers, austenitic high-manganese steels have been the
conventional materials for decades. The strain hardening ability combined with high toughness and
ductility makes them a cost effective choice [Lindroos 2015]. The work hardened layer may be up
to 15 mm deep with hardness of up to 600 HV. However, the hardenability also limits its use in
crushing of softer materials and other applications with lower loads. Hard metals with high abrasion
resistance, but lower ductility are used when high impact resistance is not needed. Rubbers are used
in sieves and in conveyer belts, where their high hardness-elasticity ratio outperforms steels.

35
A change from low hardness martensitic wear resistant steel with hardness of 460 HB, commonly
used in old mining components, to high harness martensitic steel with 530 HB hardness reduced the
wear with 20 – 30 % in crushing conditions (Ratia et al. 2013).

There are many studies, where the wear performance of manganese steels has been examined
[Lindroos 2015, Yue 2014, Erdakov 2014, Lindqvist 2005]. A 20 % increase in the wear life just by
optimizing the manufacturing process of the wear parts has been reported [Erdakov2014]. The wear
resistance of tool steels with large, hard carbides may be double compared to manganese steels and
even five times higher with hard metals [Siitonen 2009]. Powder metallurgical tool steels and metal
matrix composites (MMC) have been investigated for cone crusher applications [Kivikytö-Reponen
2009]. The lowest wear rates were gained with tool steel reinforced with recycled and crushed
WC/Co hard metal.

White cast irons have high hardness, but they are much less ductile than manganese steels. They are
still potential materials for some applications like e.g. for vertical shaft impactors. In a laboratory
study with hammer-mill type high-stress impact wear device, white cast iron wear resistance was of
the same level with powder metallurgical metal matrix composites [Osara 2001].

Fe–Cr–B are iron-based alloys with wear-resistant eutectic borides M2B forming a network
structure. In a crusher hammer test with dolomite, Fe–8Cr–2B alloy with 850 HV hardness had
150–180 % times higher service life than Mn13Cr2 high manganese steel [Yue 2014]. These kinds
of low alloyed steels have also potential for crusher applications.

6.1.2 Rock drilling

The drill bits consist of steel base with hard buttons on the drill face. Quench and tempering steels
are used as base material due to good toughness and strength, reasonable high wear resistance and
fatigue strength, and dimensional stability when hardened [Plinninger 2002, Ovarock 2008,
Rostami & Hambley 2011]. The drill buttons are typically made of cemented carbides e.g. WC-Co
that is a hard and tough material for repeated high energy impacts against hard rock in rotary
percussive drilling. In rotary crushing drilling, the drill bit is rotated against the rock and thus the
method is typically used for relatively softer rock materials [Beste 2004].

Fine grained hard metals result in improved wear resistance compared with wear parts of
conventional materials (Nordgren 2015). The alternative sintering processes, like field assisted
sintering, spark plasma sintering and pulsed electric current sintering, make it possible to produce
very fine structures. Moreover, the abrasive wear resistance of cemented carbides can be
significantly increased by diamond coatings or diamond inserts. Diamond coatings can be deposited
on rock drilling bits using the hot flame method [Alahelisten 1995], PVD, or CVD coatings [Liu
2005]. Polycrystalline diamond compacts (PDC) are mainly used for cutters in softer rocks [Li
2001]. Diamond inserts are also used in percussive drilling. The polycrystalline diamond inserts are
reported to drill even ten times deeper (Element Six 2016).

36
6.2 Wear reduction in wear parts targeted to free movement abrasive wear

Moderate wear conditions with wear resulting from free falling or moving rock material, earlier
defined in section 4.2 as abrasive erosive wear (AEW), occur typically in grinding mills, and in
digging equipment like loaders, excavators, shovels, dozers, scrapers, graders, LHD, backhoes, and
in continuous miners, pumps, conveyors, hoppers, shakers, skips, and in separation equipment in
mineral processing like screens, cyclones, separators, pelletizers, filters, thickeners, centrifuges and
floatation equipment. The wear parts include components such as linings, grinding media, side
plates, shields, and nozzles (Lynch 2015, Taylor et al. 2015). The dominating wear mechanism is
low-stress scratching abrasion and erosion where the abrasive particle remains intact as it moves
freely across the wear surface (Hawk 2001).

The wear parts in moderate abrasive wear solutions are mainly steels and cast irons, ceramics, and
polymers, such as elastomers or composite structures. A wide range of materials is used to resist
wear in the comminution processes (Durman, 1988). The comminution media is often manganese
steels containing additional alloying elements, such as Cr, Ni and Mo. Low alloy, low carbon steels
are recommended for rough grinding only, where metallic contamination is not a problem. The
austenitic stainless steels are typically only used in acid media or when requiring non-magnetic
balls, owing to their high cost. The Ni–Cr cast irons are also used as grinding media. Chromium
carbides are harder than iron carbides and therefore more wear resistant, and also play a major role
in wear resistance in corrosive environments (Aldrich 2013). The material selection is depending on
the mineral process e.g., the movement type of the mineral particles. Ductile behaving materials
commonly show a peak of erosion rate at small impact angles, while the brittle materials often show
maximum wear behaviour for normal incidence (Finnie 1995, Chattopadhyay 2001, Sare et al.
2001, Jones 2011, Bruce 2012, Levchenko 2013).

Bionic research has given inspiration to develop surfaces with improved erosive and impact wear
resistance by topographical surface design. The solutions used by nature are e.g. microtextures,
such a bumps and grooves, and surface curvature on desert scorpions (Han et al 2012,2017) and
directional windward surface ring features on desert plants (Han et al 2013a,b).

Steel and iron. Wear resistant steels, chromium-molybdenum steel alloys, tool steels, work
hardening steels and white cast iron are widely used in mineral processing. There are several
microstructural ways to improve strength, toughness and as consequence the wear resistance of
materials by e.g., work hardening, boundary strengthening, solid-solution strengthening, particle
hardening, two phase aggregates, ductile binder phase, and extrinsic crack-tip shielding mechanism.
Work hardening steels require operation conditions, where surface hardening occurs, therefore they
are not the best solutions for moderate wear conditions (Clark & Llewellyn 2001, Ojala et al 2014).

Carbide free bainitic steels have shown good abrasive and erosive wear performance with 35 - 80
% lower wear and five times longer lifetime compared to the standard quenched and tempered steel
(Vuorinen et al. 2016). An improvement in decreased wear rate of 43 % was measured for
hypereutectic white iron compared to the standard high chrome eutectic white iron (Llewellyn & al
2004, Walker & Robbie 2013). Wear resistance improvements of more than one order of magnitude

37
was measured for overlay welded high chromium white iron in comparison with the quenched and
tempered low alloyed carbon steel in laboratory drum testing (Allebert et al. 2015).
An upgrade of concrete mixer material from mild steel of 130 HV to quenched and tempered
martensitic steel of 680 HV increased lifetime by a factor of 7 in sliding wear and by a factor of 3 in
high-angle mild impact wear. A hardness level of more than 400 HV was needed for significant
increase in lifetime followed by a clear relationship between hardness and wear (Jungedal 2012).
Similar results have been reported in wear tests simulating various mining conditions (Dommarco et
al 2001, Rendon & Olsson 2009, Parent & Li 2013, Walker & Robbie 2013, Allebert et al 2015,
Wang et al 2016).

Ceramics are very hard and have a very good resistance to sliding wear. However, often they are
too brittle in many mineral processing applications, where the certain level of toughness is required.
In order to achieve the higher strength and toughness of metallic materials, refinement of the
microstructure or composite structures have been developed (Curry & Clermont 2016).

Composites, hard coatings and microstructure tailoring. In order to achieve the higher strength
and toughness of metallic materials, refinement of the microstructure or composite structures have
been developed (Berns 2003). Promising solutions for wear reduction are the composites, either
metal/ceramic composites or elastomeric/ceramic composites. One solution is the so-called “double
dispersion” type of structure in metal matrix composites, where hardmetals improve fracture
toughness and bending strength simultaneously. An increase of the hard particle size in the material
microstructure simultaneously raises the fracture toughness and hence the abrasive wear resistance.
The bending strength will decrease, because the crack length caused by fracturing hard particle
increases. When coarse hard particles are dispersed in the metal matrix, the ‘long cracks’ are
eliminated (Berns 2003).

The use of new material solutions resulted in a five times wear life improvement in semi-
autogenous grinding mills compared to normally used manganese steel (Siitonen 2009). The erosion
resistance of a hard internal surface of an AISI 1045 steel pipe was more than five times better than
that of AISI 1020 steel, which represents the standard, non-hardened, carbon steel line pipe material
in slurry handling (Clark 2001). A three times lifetime improvement was achieved by the use of
chrome white cast irons compared to the conventional grades in slurry pump service (Llewellyn
2004). By replacing the whole pumping systems, the lifetime of the pumps was reported to increase
over 70 % and the energy savings were up to 30 % (Metso Showroom 2013).

Elastomer wear parts and rubber-like wear parts are used in several applications in mineral
processing industry (Metso 2016). However, changes in wear environment, the presence of certain
metallic ions, or the increase in temperature can all lead to rapid failure. For natural rubber such
problematic environments are oils, greases and solvents (Sare 2001). It is well known that
mechanical properties of the polymers are highly affected by the chemical composition and
exposure to UV light (Rattanasom 2009, Darestani Farahani 2006, Busca 2010).

The best performing natural rubber showed a 14 times improved relative erosion resistance in SiC
slurry compared to AISI 10 18 steel and over 2 times improvement compared to chromium white

38
iron and WC/NiBSi PTA W overlay in conditions relevant for piping and tubular components such
as pumps, valves and cyclones (Jones 2011). WC-3.3%Co performed extremely good in the same
test, 59 times better relative wear resistance compared to AOSO1018 steel (Jones 2011).

Generally the wear resistance is a trade-off of wear part price, life-time, functionality and
recyclability. The new business models e.g. shearing or leasing may introduce new possibilities for
new innovations, that earlier were considered to be too expensive for specific wear parts.

6.3 Wear and friction reduction in lubricated contacts in mining machines

Wear conditions when lubricated contacts are dominating (LW) are found in all of the mining
trucks and in hoists, drag lines, fans, railway and some separation equipment like screens, cyclones,
separators, pelletizers, filters, thickeners, centrifuges and floatation equipment. Common for all
machines and equipment working in mining is the dusty environment and rough loading conditions,
sometimes combined with space constrains and humidity. Although the machines themselves are
associated with mining, their elements are ubiquitous. It is their size, configuration, and operating
conditions that are challenging (Scott 2006). Wear and friction mechanisms in lubricated conditions
and new tribological solutions have been reviewed by Sethuramiah (2003) and Cha and Erdemir
(2015) and means for friction reduction in heavy duty vehicles like trucks and buses were reported
by Holmberg et al (2014a).

Considering the severe contact conditions involving dust and dirt accumulation in lubricating oils;
the components used in mining operations must have high hardness, strength and toughness in order
to combat wear and maintain low friction. Various hardfacing treatments based on plasma spray
processes may provide a relatively thick and hard surface layer that can resist wear. Alternatively,
ultra-fast boriding and nitriding treatments can also be considered as they produce fairly thick (100-
200 micrometer) and hard boride and nitride layers on top of a thick diffusion layer (Kartal et al
2010). Carburising can also help but the hardness of the treated layer may not be high enough to
counteract the very abrasive nature of contaminated oils. Carburizing may serve as a hard transition
layer for ultra-hard coating that may be produced on the affected surfaces by CVD and PVD
processes.

6.3.1 Surface treatment and microstructural material design

Considerable improvements in wear resistance of lubricated components have been achieved over
the last decades by improving the surface properties of the components. This has been possible
partly by improved material processing methods resulting in higher quality materials free from
defects, contaminations and inhomogeneity. The near surface material layers have been developed
to better resist the loading cycles by optimising the microstructures, often resulting in harder and
more wear resistant surfaces. The development of rolling contact bearings is in the forefront of this
development and a good example (Scherge 2003b, Glaeser 2012, Jahanmir 2012, Kotzalas 2012,
Chang 2012, Scharf 2012, Bosman 2010,2011, Chen et al 2015). In the following, we will mention
only few recent examples.

39
The group of Mattias Scherge has in a series of studies investigated the ultra-low wear taking place
in properly lubricated sliding contacts typical for engines, transmissions, motors etc. They showed
that even under low wear conditions, morphology, crystalline arrangements, and chemical bonds of
the surface and subsurface are modified significantly and considerable plastic deformation occurs
up to a depth of 1 m (Scherge 2003a,b, Shakhvorostov 2007). The tribological conditions lead to
complex and strongly inhomogeneous layered structures. A combination of nano-crystalline top
layer and a work-hardened subsurface was found to have high wear resistance and low friction. In
lubricated tests they showed how proper heat treatment of an AlSi11Cu3 disk in sliding contact
with a 100Cr6 pin resulted in a reduction of wear by one order of magnitude and a drop in friction
coefficient from 0.04 to 0.01 (Linsler 2015). Further improvement of the wear resistance was
achieved by implementing an optimal running-in corridor (Scherge 2015).

The wire to roller contact in industrial cranes and hoists is boundary lubricated and the wear is
dominated by plastic flow of the top surface and microscale fatigue. Real contact simulating twin-
disc tests showed that an advanced partially chilled ductile cast iron roller material could
considerably improve the tribological performance compared to the present state-of-art material, a
non-hardened cast iron (GJS600-10) roller. The coefficient of friction decreased from 0.05 to 0.005
and the wear rate by two orders of magnitude (Oksanen 2015, FIMECC 2014).

6.3.2 Thin surface coatings

There are many lubricated contacts where surface coatings can improve the efficiency,
performance, and durability in engines, drive trains and transmissions. The main tribocontacts
resulting in friction losses are typically the piston ring and cylinder liners, gears, bearings, valves,
and cam and follower contacts.

Research on low-friction and low-wear coatings has been extensive, because the traditional
lubrication techniques cannot in many cases alone meet the increasingly more demanding
operational conditions of modern mechanical systems. New advanced techniques for physical and
chemical vapor deposition (PVD and CVD) plasma, and thermal spraying methods, etc., have made
it possible to deposit engine components with coatings with good reliability and cost effectively
(Holmberg et al 2009, Erdemir 2005,Donnet et al 2004, Jacobson 2012, Scharf 2012, Doll &
Matthews 2012, Davies 2001,2004, Cha & Erdemir 2015). The tribological performance and
durability of such coatings have been further improved by using advanced computer codes and
finite element modelling (Holmberg et al 2005, 2007, 2012b, 2014c,d).

Low-friction coatings such as diamond-like carbon, MoS2, etc., can drastically reduce the friction
coefficients of dry and lubricated sliding contacts by more than 90% [Holmberg et al 2009]. Such
huge reductions are typically for boundary-lubricated regimes, where direct metal-to-metal contacts
occur In HD and EHD regimes, there are very few asperity contacts, and shearing takes place within
the fluid film itself. The use of hard and low-friction coatings, have been reported to increase as
much as ten-fold the fatigue lifetime in rolling contacts, reduce bearing wear by seven-fold and
increase gear lifetime by three-fold [Holmberg et al 2009, Doll 2011].

40
The development of diamond-like carbon (DLC) coatings has been of great interest in recent years,
since they provide the best overall and robust friction and wear performance under lubricated and
dry conditions (Erdemir et al 2006, Kano 2006, Podgornik et al 2005, Gåhlin et al 2001, Ronkainen
2016, Kalin 2013). Some engine components are nowadays coated with DLC and used in actual
cars and trucks (Donnet & Erdemir 2008, Cha&Erdemir 2015). Other hard and low-friction
materials and coatings developed for improved friction and wear performance in engine
components include Cr-N, TiN, Ni-SiC, MoS2, WC/Co, AlTiN, W-C:H, MoN-Cu composite
coatings along with TiN, TiC, or TiB2 particles embedded in ceramic matrices, and various
nanostructured and nano-layered coatings (Tung 2004, Merlo 2003, Holmberg et al 2005, Enomoto
1998, Lampe 2003, Canter 2009, Cook et al 2010, Farley et al 2010, Erdemir et al. 2016).

6.3.3 Thick composite coatings

There is a range of techniques to deposit thick wear resistant coatings, such as welded overlays,
thermal spraying, cladding, electroplating and thermoreactive deposition. Thermal spray coatings is
a family of thick hard composite coatings with good wear resistance in the thickness rage of about
0.1-50 mm. Generally, the wear resistance of the coatings increases with their density and cohesive
strength. Composite structures with carbide particles embedded in an often metallic matrix with
higher elasticity and toughness provides good wear protection. A porous surface structure can be
beneficial in lubricated sliding contacts as the oil pockets in pores can improve the lubrication and
avoid starvation.

Thermal spray coatings has been used successfully to reduce wear in e.g. powertrain components,
cylinder bore and piston rings, crank and transmission shafts, valves, clutches, disc brakes, pumps,
turbine and compressor shafts, bearing journals, thrust collars, seals, axles, pins, rollers in
conveyors and hydraulic cylinders. Popular coatings to provide wear resistance are e.g. WC/Co,
WC/Ni, WC/CoCr, CrC/NiCr and Co-Cr-Si-Mo alloys (Davis 2001, 2004).

Advanced thermal spray technology was used to coat the cylinder surface of aluminium and
magnesium engines with wear resistant metal matrix composite coatings with residual porosity
values of about 2 % and resulted in 30 % reduction in friction and 2 – 4 % decrease in fuel
consumption (Gerard 2006). Mo and CrC based thermal spray coatings could considerably improve
the tribological performance compared to the present state-of-art material solution, a non-hardened
cast iron (GJS600-10) roller, in twin-disc tests simulating the real contact of wire against roller in
industrial cranes. The coefficient of friction decreased from 0.05 to 0.002 and the wear rate by two
orders of magnitude (FIMECC 2014). Thermally sprayed WC-CoCr coated hydraulic cylinders
were compared to the state-of-art hard chrome plated cylinders in lubricated tribotesting and the
WC-CoCr cylinders showed 20 % reduced friction, considerably lower wear and reduced hydraulic
leakage (Castro et al 2014).

6.3.4 Surface texturing

The roughness and surface topography have a remarkable influence on friction, wear, and fatigue
life performance in tribological components. Researchers have been concerned about formation of
deep scratches and larger dimples on sliding surfaces that result in higher friction and wear.

41
However, lately it has become clear that when prepared properly, dimples, grooves, and protrusions
can have very beneficial effects even at the nanoscale (Al-Azizi et al 2013), although the underlying
mechanisms become very complex (Johansson 2012).

Recent reports have shown that micro- and nano-scale dimples created by laser beams or
lithographic techniques can considerably improve the friction and wear performance under
lubricated conditions (Andersson et al 2007, Etsion 2012, Ronkainen 2016). Laser surface texturing
of piston rings has reduced fuel consumption of engines by as much as 4% (Kovalchenko et al
2004, Klingerman et al 2005, Etsion et al 2009, Wang 2010, Ryk 2006). Fine particle shot-peening
of surfaces produces a topography with micro-dimples which was found to reduce friction in
lubricated contacts by up to 50% (Ishida et al 2009). A laboratory test showed considerable
reduction in hydrodynamic friction by applying hydrodynamically tailored textures on cylinder liner
surfaces in heavy duty diesel engines (Johansson 2012).

6.3.5 Lubricants and nanotechnology based additives

The sliding or rolling surface contacts in engines are lubricated by oils. The lubricants contain a
range of anti-friction, anti-wear, and extreme pressure additives for the formation of a chemical
boundary film that supresses wear damages. Our analysis showed that viscous losses and shear in
hydrodynamic contacts result in significant energy losses. If the lubricant viscosity is further
reduced while the low friction and wear protection functions are maintained, a very large energy
saving in engines could be achieved.

Optimised bearing design based on boundary slippage technology can reduce the bearing friction as
much as 60 % (Zhang 2014, 2016). A potential alternative to mineral oils and synthetic-based
hydrocarbon oils are the polyalkylene glycol (PAG)-based lubricants today considered for engine
lubrication (Cuthbert et al 2016). They have a lower viscosity and better environmental
compatibility and have for that reason been the object of several studies [Van Voorst 2000]. Work
by Green et al. [Green et al 2011] shows a reduction in fuel consumption of a single-unit truck of
1.3% to 2.1%, depending on which driving cycles are applied, when changing from “mainstream”
lubricants in the engine, gearbox, and rear axle to lower viscosity oils.

It has turned out to be very difficult to reach friction coefficients below 0.04 in boundary lubricated
sliding conditions by using the traditional oils and additives, such as the well-established mineral or
synthetic oils with typical anti-friction, anti-wear, and extreme pressure (EP) additives containing
sulphur, chlorine, and phosphorous. New research shows that, with different types of additives in
combination with low-friction coatings like DLC, it is possible to achieve much lower friction.

The use of the friction modifier additive glycerol mono-oleate (GMO) in a polyalphaolefin (PAO)
oil resulted in a friction coefficient of 0.05 in sliding DLC coated contact. The same material
combination resulted in a considerable friction reduction to a coefficient of friction of 0.005 when
lubricated by pure glycerol [Martin 2009, Barros Bouchet 2010, Martin 2010]. This friction is about
one-tenth of what today can be achieved with the best engine lubricants. In hydrodynamic
lubrication has similar levels of friction reductions been achieved by the use of organic friction

42
modifiers [Choo et al 2007] or by liquid crystal mesogenic fluids [Amann 2010]. Using a series of
novel additives, Li et al. [2013] report coefficients of friction as low as 0.001 under liquid-
lubricated sliding surfaces.

The use of ionic liquids and nanomaterials as anti-friction and anti-wear additives in lubrication is
another interesting and potential technology. Ionic liquids are highly polar, because they consist of
many types of anions and cations, while conventional oil consist of relatively inert hydrocarbon
molecules [Minami 2009, Somers et al 2013]. The viscosity of ionic liquids can controlled largely
from 50 to 1500 cP at 23 °C and some ammonium-based ionic liquids have shown a very low
friction coefficient down to 0.06. Friction reduction of 20 to 35 % and wear reduction of 45 to 55 %
has been reported [Qu et al 2006, 2009a,b].

Laboratory-scale experiments have shown considerable reductions in friction and wear of sliding
surfaces by the use of nanomaterials as low friction and anti-wear additives. They are typically
carbon-based and include nano-diamonds, onion-like carbons, carbon nano-tubes, graphene, and
graphite. Some inorganic fullerenes of transition metal dichalcogenides, (e.g. MoS2 and WS2) and
metallic, polymeric, boron-based nanoparticles, and Sb doped SnO2 have been considered as well
[Martin et al 2008, Kalin 2012,2013, Ge et al 2015].

6.3.6 Reduced contamination in tribocontacts

The heavy dust and contamination rich environment often in combination with high humidity is
most challenging for all mining equipment and results in increased wear and higher friction. A
major source of machine failure in mining is due to solid contaminants. When dust particles have
the possibility to enter tribological contacts relying on very thin lubricant films like in EHL and
boundary lubrication they cause scratches and indents in the sliding surfaces. This results in
increased wear and reduced lifetime (Ioannides & Jacobson 1989, Scott 2006, Ioannides 2012).
Contamination critical lubricated components are e.g. bearings, gears, seals, wire ropes, hydraulic
systems and components in engines and electrical motors.

Filtration is an effective way of removing solid contaminants from the lubrication system. However,
even though effective filtration often is available it can be expensive and thus there is a trade-off
compared to regular filtering and component replacement. Due to the very large amount of solid
contaminants in mining environment it is often necessary with a by-pass valve, which ensures that
the filter cannot cut off the lubricant supply completely when clogged. An external by-pass filtering
system in the form of a mobile cart is a good solution.

Seals are used both to keep the lubricant escaping from the tribocontacts and to prevent
contaminants from entering into the mechanical system. The contacting surfaces in dynamic seals
typically operate in the boundary or hydrodynamic lubrication regime and are thus also critical for
contamination (Lai 2012, Flitney 2012). When extra sealing in mining is needed, often a design
with two or more seals fitted in series is used. Magnetohydrodynamic sealing by ferrofluids offers
an advanced solution to avoid leakage and hinder entry of non-metallic contaminants (Eitel 2005).

43
An important issue is the selection of viscosity level in thin lubricant film sliding contacts. This is
an optimisation task between two conflicting requirements. On one hand it is beneficial to have a
thicker oil film that allows hard contaminant particles without causing surface scratching. On the
other hand it is beneficial to use low viscosity lubricants, as discussed above, resulting in lower
shear and reduced friction. Monitoring of real contaminant particle sizes and calculations of film
thickness in tribocontacts form a tool for optimal design with regard to both energy consumption
and wear life.

It is good to favour grease lubrication in mining compared to oil lubrication, when possible, as the
grease also has the ability to capture contaminant particles and hinder them from entering into
heavily loaded contacts. An example of a special design for mining environment is the design of a
nonseizure bearing for conveyer idler rollers (Scott 2006).

6.3.7 Tires

There has been much development on road vehicle tire material and design during the last five
decades but a large part of that is not in the open literature. However, new technologies could be
used for considerable improvement of tire materials, tread designs, weight reduction, optimized
pressure monitoring, and new maintenance technologies [Zhao et al 2013, NRC 2006, Leduc 2009].

In mining, mobile vehicles like haul trucks, loaders, shovels etc. the tire wear is a major concern.
The material is typically fibre reinforced rubber. The wear behaviour of haul truck tires is not well
understood. Factors affecting the tire wear are the load on the tires, driving speed, driving style,
road conditions as well as tire properties and tire maintenance. The main reason for rubber wear is
scrubbing in different forms. Scrubbing occurs at acceleration, braking and when the tire slides. The
wear depth of a haul truck tire can be even as much as 10 mm/month. The operational lifetime of
haul truck tires in an underground mine would be typically 2000 service hours or 5 months
(Woodman & Cutler 2002, Carter 2007, Parreira & Meech 2012, Härkisaari 2015).

6.4 Crusher and grinding mill design

Today, the driving forces for mineral handling equipment design, solutions and optimization are
typically reduction of energy losses and increase of production volumes. Furthermore, the design
has an effect on dematerialization, low impact of materials, cleaner productions, longer lifetime
through improved wear performance, but also through disassembly and remanufacturing.

Wear is the primary target in cases when it may cause catastrophic increase of costs or loss of
production volumes. Below we give some examples of how wear can be reduced by new equipment
design solutions.

The geometry of liners and also other wear parts has been optimised in relation to the final product
performance. When liners are worn and the geometry is changed, the shape of the cavity is changed.
There have been extensive studies and predictions of the worn geometry of wear parts in crushing

44
environments (Lindqvist 2005). A new crusher chamber design and the introduction of new wear
resistant materials in a primary gyratory crusher resulted in reduced energy consumption of 28 %
(Hämäläinen 2013).

It has been observed that mills underperform over a significant part of the liner life, typically10–25
% of the liner life in the beginning and 5–10 % in the end (Yahyaei 2015). New methods have been
proposed for improved liner design resulting in a predicted 3.7 % increase in throughput per annum
(Toor 2013, Yahyaei 2015). Computational modelling is often used as a tool for improved design.
An optimum liner design depends on liner geometries, material, processed mineral, and the process
conditions. In modelling optimisation for improved design the focus has been on mill performance
in order to control the energy intensive mineral process, especially grinding. A variety of control
approaches for process simulation such as ore size reduction and mineral separation processes were
reviewed by (Hodouin 2001). Discrete element modeling simulations have been used to calculate
impact energy spectrum, collision rates and frequency of balls in a large industrial grinding mill
(Herbst 2004, Powell 2011). The combined use of computational fluid dynamics and discrete
element modelling has provided valuable insights on changes in the operating variables, and
component wear behavior (Lichter 2007).

7. Discussion

7.1 Confidence in used method, data and sources

In this study we used a methodology for calculating global impact of friction and wear on mining
industry similar to what we used previously to calculate impact of friction for passenger cars, buses,
trucks and paper machines. The accuracy of the calculations depends on the accuracy of the data
that we could extract from open sources. In many cases we have found good statistical data to use
but there have also been cases of lack of reliable data that were needed. In such cases we have used
estimations based on our best expert understanding. We have all the way through the calculation
process crosschecked our results with data from available sources and made corrections
accordingly. Thus we are convinced that the results from the calculations are in the right order of
magnitude and show the relevant trends even if the absolute values should not be considered as
precise.

In this mining study we had problems with finding good global data on topics like the number of
mines, number of large industrial mines, number of mineral processing units, energy consumption
in mines and processing units, wear data from mines, maintenance data, etc. However, we found
some detailed studies carried out in USA, Canada, Finland, Brazil (Komonen 1998a, 2003, 2009;
DOE 2002, 2007, MAC 2005 a,b, IBRAM 2015, Tolonen 2015) and based on these it was possible
to estimate the global data used in our calculations.

45
7.2 Comparison with state-of-art

To the best of our knowledge no similar studies on global impact of friction and wear in mining has
previously been carried out. However, there are a few studies that used a somewhat similar
approach in calculations of energy consumption on national scale. In the USA study (US DOE
2007) average energy consumption of mining equipment was calculated and savings were estimated
for four cases: current, best practice, practical minimum and theoretical minimum. Here is a
similarity in thinking with the four cases we have calculated: Mine 1990, Com 2015, Lab 2015 and
Mine 2025. In the Canadian studies (MAC 2005a,b) costs and energy use of the functional
categories in underground and open-pit gold, copper, lead, iron and oil sand mines, which are
relevant for Canada, and potential savings were estimated. The results from these studies are
broadly in line with our calculations.

The big potential of energy saving especially in some of the very energy consuming parts of mining
and mineral processing, such as especially grinding, hauling, ventilation and digging, is shown in
our study and similarly in some other studies based on different methods for energy consumption
estimation (Rabago et al 2001, Sare et al 2001, MAC 2005a,b, Keikkala et al 2007, US DOE 2007,
Norgate & Haque 2010).

One unique feature in this study is that for the first time we calculate both the impact of friction and
wear in one industrial sector. It shows that in mining the impact of wear is about half of the impact
of friction with regards to energy consumption and CO2 emissions and even larger than the impact
of friction with regards to costs. This should not be directly generalised for other industrial sectors
since mining is an extremely heavy and rough activity with much wear. The maintenance costs are
of the level of one fifth of the turnover in mining while it is often below 5% in other sectors.
Anyway, we can conclude that globally the impact of wear on energy consumption, costs and
emissions is of the same order of magnitude as the impact of friction. Still the impact of friction
seems to be higher and the impact of wear is perhaps only half of that.

7.3 Role of rock mining

Some of the data for mining that is available is confusing because of the various definitions used on
what all is included in mining. We have restricted our study to mineral mining, including bauxite
which in some data is excluded, and excluding excavation of petrol and gas. With this definition, it
has been possible to find fairly good statistical data on the mining activity structure, energy
consumption, equipment and costs. We have excluded rock mining because there is not at all
similar good statistical data available on that. However, the rock mining activity is to our
understanding about of the same volume as mineral mining globally and the equipment and energy
consumption structure very much the same. Thus, a first estimate of the impact of friction and wear
in the whole mining sector, now including also rock mining, would be to double using the results
from mineral mining.

46
8. Conclusions

We have studied the global energy consumption due to friction and wear in the mining industry and
the following can be concluded:

Total energy consumption of global mining activities, including both mineral and rock mining,
is estimated to be 6.2 % of the total global energy consumption. About 38 % of the consumed
energy in mineral mining (equalling to 4.6 EJ annually on global scale) is used for overcoming
friction. In addition 2 EJ is used to remanufacture and replace worn out parts and reserve spare
parts and equipment needed due to wear failures. The largest energy consuming mining actions
are grinding (32 %), haulage (24 %), ventilation (9 %) and digging (8 %).
Friction and wear is annually resulting in 970 million tonnes of CO2 emissions worldwide in
mineral mining (2.7 % of world CO2 emissions).
The total estimated economic losses resulting from friction and wear in mineral mining are in
total 210,000 million Euro annually distributed as 40 % for overcoming friction, 27 % for
production of replacement parts and spare equipment, 26 % for maintenance work, and 7 % for
lost production.
By taking advantage of new technology for friction reduction and wear protection in mineral
mining equipment, friction and wear losses could potentially be reduced by 15 % in the short
term (10 years) and by 30 % in the long term (20 years). In the short term, this would annually
equal worldwide savings of 31,100 million euros, 280 TWh energy consumption and a CO2
emission reduction of 145 million tonnes. In the long term, the annual benefit would be 62,200
million euros, 550 TWh energy consumption, and a CO2 emission reduction of 290 million
tonnes.

Potential new remedies to reduce friction and wear in mining include the use of new materials,
materials with improved strength and hardness properties, more effective surface treatments, high
performance surface coatings, new lubricants and lubricant additives, and new designs of moving
parts and surfaces of e.g. liners, blades, plates, shields, shovels, jaws, chambers, tires, seals,
bearings, gearboxes, engines, conveyor belts, pumps, fans, hoppers and feeders.

Acknowledgements

We want to acknowledge Kari Komonen and Seppo Tolonen, Finland, for their most valuable
contributions with expertise on maintenance and mining.

This study has been carried out as part of the Finnish joint industrial consortium strategic research
action coordinated by DIMECC Ltd within the program on Breakthrough Materials called BSA in
the O’DIGS Project. We gratefully acknowledge the financial support of Tekes, the Finnish
Technology Agency, the participating companies, and VTT Technical Research Centre of Finland.
Additional support was provided by the U.S. Department of Energy, Basic Energy Sciences, Office
of Energy Efficiency and Renewable Energy, under contract DE-AC02-06CH11357.

47
Appendix A1 Friction and wear loss & costs globally (all mines = 12 EJ)
Mine 1990 Friction Wear replacment Maintenence Downtime Wear Total friction and
parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit PJ MEuro PJ MEuro MEuro PJ MEuro MEuro PJ kEuro PJ MEuro
Underground mining 1513 27230 440 12570 12570 30 606 3143 470 28889 1983 56119
Surface mining 1543 27766 443 12659 12659 27 545 3165 470 29028 2013 56794
Mineral processing 1576 28364 1014 28967 28967 43 861 7242 1057 66037 2633 94402
4631 83361 1897 54197 54197 101 2012 13549 1997 123954 6629 207315

Com 2015 Friction Wear replacment Maintenence Downtime Wear Total friction and
parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit PJ MEuro PJ MEuro MEuro PJ MEuro MEuro PJ kEuro PJ MEuro
Underground mining 979 17617 263 7528 7528 19 388 1882 283 17325 1262 34942
Surface mining 1016 18293 253 7234 7234 17 347 1809 271 16625 1287 34918
Mineral processing 1234 22214 528 15082 15082 28 562 3771 556 34498 1790 56712
3229 58124 1045 29845 29845 65 1297 7461 1109 68448 4339 126571

Lab 2015 Friction Wear replacment Maintenence Downtime Wear Total friction and
parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit PJ MEuro PJ MEuro MEuro PJ MEuro MEuro PJ kEuro PJ MEuro
Underground mining 445 8003 182 5188 5188 11 221 1297 193 11894 637 19897
Surface mining 490 8820 164 4695 4695 10 193 1174 174 10756 664 19575
Mineral processing 892 16064 288 8216 8216 19 371 2054 306 18856 1199 34920
1827 32887 633 18098 18098 39 785 4525 673 41506 2500 74393

Mine 2015 Friction Wear replacment Maintenence Downtime Wear Total friction and
parts labour spare equipment prod loss total total wear
Parameter energy cost energy cost cost energy cost cost energy cost energy cost
Unit PJ MEuro PJ MEuro MEuro PJ MEuro MEuro PJ kEuro PJ MEuro
Underground mining 293 5280 137 3913 3913 8 160 978 145 8964 438 14244
Surface mining 336 6043 119 3410 3410 7 138 852 126 7810 462 13854
Mineral processing 735 13227 184 5262 5262 14 284 1315 198 12123 933 25351
1364 24550 440 12585 12585 29 582 3146 470 28897 1833 53448
48
Appendix A2
Conversion factors

Energy conversions
1 kWh = 3.6 MJ
1 Mtoe = 41 868 TJ
1 kWh = 0.06 Euro as global average 2014
1 hour labour = 6 Euro salary cost as global average 2014
Diesel fuel conversions
1 litre = 0.832 kg
1 MJ = 0.028 l
1l = 35.9 MJ
1 kg = 43.1 MJ
1 kg => 3.16 kg CO2 emission
1l => 2.63 kg CO2 emission
1 liter = 0.7 Euro as global average 2014
Energy to emission conversions
1 PJ diesel oil => 0.07364 MtCO2
1 PJ coal => 0.2278 MtCO2
1 PJ gas => 0.1361 MtCO2
1 PJ mining average => 0.146 MtCO2

49
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Figure captions

Figure 3.2.1 Main operational categories in mining.

Figure 3.4.2.1 Energy break down in tribological contacts

Figure 3.5.1. Underground and surface mining actions and examples of typical equipment used
(Härkisaari 2015, US DOD 2007; US DOE 2002).

Figure 4.1.1 Share in percentage of the global energy consumption in mining (=12 EJ) in total and
according to mining operational categories.

Figure 4.1.2 Global energy consumption in mining (=12 EJ) according to mining operational
categories.

Figure 4.2.1 Three case studies were carried out for detailed energy and cost analysis: a mobile jaw
crusher, an off-highway haul truck and a grinding mill.

Figure 4.2.2 The energy distribution in a diesel powered mobile jaw crusher typically used in iron
ore crushing (weight 50 tons).

Figure 4.2.3 The energy distribution in an electrically powered autogenous grinding mill typically
used in primary milling of iron ore (mill diameter x length = 6 x 6 m).

Figure 4.2.4 The energy distribution in an diesel driven off-highway rigid frame 90 tons haul truck
used in mining.

Figure 4.2.5 Annual costs for friction and wear in mining equipment is divided in three
tribocategories: crushing abrasive wear dominated (CAW), abrasive erosive wear dominated
(AEW), and lubricated wear dominated (LW).

Figure 4.4.1 Flow chart for calculations of global impact of friction and wear on mineral mining
industry

Figure 5.1.1 Trends in wear reduction by new tribological solutions for different contact severity
levels in mining applications.

Figure 5.1.2 Trends in wear reduction by new tribological solutions for different contact severity
levels in mining applications.

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