2023 | 025
Bearing testing and validation to
optimize bearing design for different
engine applications
Engine Component Developments - Tribology

ZHIFENG ZHANG, Miba Precision Components (China)
Co., Ltd.
Sebastian Kirchhammer, Miba Glitelager Austria GmbH
Emil Bakk, Miba Glitelager Austria GmbH
Oliver Feng, Miba Precision Components (China) Co., Ltd.
Hellen Li, Miba Precision Components (China) Co., Ltd.

This paper has been presented and published at the 30th CIMAC World Congress 2023 in Busan,
Korea. The CIMAC Congress is held every three years, each time in a different member country. The
Congress program centres around the presentation of Technical Papers on engine research anddevelopment, application engineering on the original equipment side and engine operation andmaintenance on the end-user side. The themes of the 2023 event included Digitalization &Connectivity for different applications, System Integration & Hybridization, Electrification & Fuel Cells
Development, Emission Reduction Technologies, Conventional and New Fuels, Dual Fuel Engines,
Lubricants, Product Development of Gas and Diesel Engines, Components & Tribology,
Turbochargers, Controls & Automation, Engine Thermondynamis, Simulation Technologies as well as
Basic Research & Advanced Engineering. The copyright of this paper is with CIMAC. For further
information please visit https://www.cimac.com.

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ABSTRACT
Combustion engines are in use over hundred years and have been developed and optimized for highefficiency, economy, long life and to achieve also environmental friendliness. Development is stillgoing on, especially with the focus on alternative fuels with their special combustion and chemical
characteristics. In consequence bearings need high pressure and surface speed capabilities as well as
robustness for dirt, edge loading and different lubrication situations. Certain materials like lead need
to be avoid and especially corrosion resistance is needed for certain fuels and lubricants. In
consequence a manifold of different bearing types were developed for the different applications which,in some cases make a very high effort in production.
To get all these facts in line with economical solutions a special program to identify the necessary
bearing application related capabilities for further investigation in laboratory and to transfer them onbearing test rigs were set up. On-road, off-road, power generation as well as ship propulsion in the
power range from 300 kW to several MW have been considered. Existing and new developed bearing
types have been selected and tested for the variety of applications to proof their applicability.
In the publication the whole program will be explained, transfer of application related performancerequest for different engine sizes in different applications, test candidates will be described, test
equipment will be shown, and the results will show bearing types and modifications to fulfill all
requested specifications and capabilities. Validation and cross reference to field experience will be
explained for test program evaluation as well as for the different bearing designs. Upcoming new
bearing types will be lined up with existing bearing applications based on key performance indicators
to give engine designers the possibility to reference to their own engine experience.

1

INTRODUCTION

For more than a hundred years, the internal
combustion engines have been serving fortransportation, power and shipping and have anenormous installation base. However, some small
size internal combustion engines are being replacedby e-mobilities recently due to CO2 reduction, andthe portion is still growing. Large engines will remain
due to their enormous power density, flexibility indifferent applications and possible green operation
based on alternative fuels a main pillar in power
generation and shipping. Re-fitting of existing
engines gives the opportunity for green operation
also for already existing engines.
All the upcoming changes as for power increase,
reduction of fuel consumption and environmental
demands as alternative fuels will also influenceengine components and need certain development
to adapt bearing materials and types. Additionally,
economic parameters like production processes
and economy of scale need to be addressed.
1.1

Environmental regulations, greenhousegas reduction and engine challenges

In consequence of global warming, greenhouse gas
regulations are entering stage and adding CO2 into
emissions. Example EU target: -55% in 2030 and
CO2 neutral for 2050. IMO cares on global shippingand ECA’s (emission-controlled areas). China alsoannounced the goal that CO2 peak by 2030 and CO2
neutral by 2060. Consequently, further efficiency
increases and to cope with CO2 neutrality
alternative fuels based on hydrogen are underconsideration. A selection of existing and alternative
fuels under consideration for bearing testing arelisted in Table 1.

tendency to form copper complexes, the selectionof materials used in an ammonia-fuelled engine isof the utmost importance.
In addition, all alternative fuels, due to the chemical
structure with high hydrogen, generate significantly
more water from the combustion, compared todiesel fuel. When the water content is accumulatingin the oil to a certain level, the risk for cavitation andtribology will increase.
All engine adaptations for efficiency and new fuelsinteract with the engine component life and stability.
New fuel tank systems and reformers as well as new
after-treatment systems are developed and change
the engine design and the environment of theircomponents. Since the cranktrain including
bearings are one of the core components in theheart of the engine, investigations for safe long-term
operations are necessary. To compensate for thenegative influences of blow-by, a re-formulation of
lubricants may become necessary and will influence
bearing tribology and stability. In consequence
bearing type development and testing needed to beadapted.
1.2

General approach Bearing type testing

The questions which need to be answered indifferent levels of testing are shown Figure 1.

Table 1 Alternative fuels and characteristics
Fuels
Hydrogen
MethanolAmmonia
SAF

Reference to MDO
Energy MJ/ltr Load / Wear
Corrosion8+++ (knock risk)
+
15,7
++
+
11,3
++
++
35
-

Cavitation
+++
++
+++
-

Tank
gas / liquid
liquidgasliquidThe use of alternative fuels also has an impact on
the combustion characteristics in the engine and infact on the performance of the bearings.

Figure 1 Overview of bearing type test and releaselevels with corresponding questions to be answered

With a low ignition temperature, hydrogen tends tospontaneously ignite on hot surfaces or impurities in
the combustion chamber. Due to this, hydrogen
incline higher risks for knocking behaviour.
Furthermore, hydrogen shows a rapid progressionof the flame front.

As you see, bearing type testing and releaseprocess is very complex and contain tasks inlaboratory for example to evaluate corrosion
resistance and long-term stability as well as bearing
test rig tasks to simulate for example start up
behavior or hydrodynamic behavior or a specificbearing design. For the final release a verification
on real engines is necessary to cover all aspects ofoperation.

In the case of ammonia, corrosion resistance can be
an important factor in the design of new engines.
Due to the highly alkaline nature of ammonia and its

Laboratory tests to evaluate tribological behavior,corrosion reactivity and others are standardized toa certain extend. In the Introduction we will focus on

CIMAC Congress 2023, BusanPaper No. 025

Page 1the general criteria as specific load and speed. In
the specific example of the tri-metal bearing we willshow a complete overview including these
additional test procedures, test parameters andexamples.
A typical hydropulsting test rig to evaluate thehydrodynamic performance is shown in Figure 2.

Figure 3 Average and maximum specific unit load ofconrod big end bearings over time for High
Performance and Medium Speed engines
Medium speed engine load increase is lower but inthe same range as the high performance engines
some years ago. Bearing sliding speed haschanged only moderate and need not to beaddressed specifically. But due to necessary fuelflexibility, a high amount of dual fuel engines andretrofit request from customers to cope withenvironmental requests, many more performance
characteristics need to be included in bearing
design and validation.

Figure 2 Hydropulsating bearing test rig
1.3

Bearing performance changes andintroduction to the bearing families

Following the new engine designs also the new
bearing performance demand is changing. Engine
families are classified in Medium Speed Engines for
power generation and marine application and Highpower engines. High power 4-stroke engines with
automotive conrod design are split additionally inperformance and robust. The hydrodynamic
performance is lined up with specific unit load andspeed, the other characterization is donecomparatively in a spider web.
1.3.1

1.3.2

Bearing performance demand for
different engine designs

Additional to the long-term standards, several
characteristics have been added to reflect thechanges in engine design, operation and fuels. The
scale of 1 to 5 in Figure 4 represents performancerequest of the different engine types relatively. 5
indicates highest, 1 indicates lowest demand.

General load and design criteria ofdifferent engine sizes and applications

The change of the design criteria “specific unit load”
for conrod big end bearings is shown to explain theload increase for bearings over time in Figure 3. To
get a clearer picture the graph is split for medium
speed engines and high performance engines.

Figure 4 Overview on bearing performance demandfor different engine designs and applications

CIMAC Congress 2023, BusanPaper No. 025

Page 2

Load and wear demand staid increased according
the engine load but corrosion, cavitation become
more demanding due to fuel flexibility and start /stop performance reflects changes in engine
operation. This performance demand including theupcoming is transferred to the bearing typecharacteristics and are addressed also in thevalidation and verification processes. It can also be
seen, that certain engine designs need similar
performance like the high-performance robust
engines and medium speed engines, which gives
the opportunity to reduce bearing types and designfor economy of scale and in consequence cost
reduction.
Relative hydrodynamic performance and theirapplication areas are given in Figure 5 .

Figure5
Relativehydrodynamic
bearing
performance in relation to standard lead bronze trimetal bearing and typical engine applications
1.3.3

1.3.4

Bearing type family characteristics

Referring
to
above
shown
performance
characteristics existing bearing families have beenranked and lined up in a spider web.
Since all bearings have multiple tasks the multilayer design gives the possibility to cover different
performance characteristics in the different layers.
More details can be seen in “Modular Bearing
Design”[1] A certain relation between strength andhardness can be identified for lining and overlays.
Dirt capabilities are evaluated for sensitivity against
small hard particles as dirt shocks or chips to cover
metal residuals in assembly. Long term stability
especially also referring to the fuel flexibility likecorrosion and cavitation needs to be addressed
directly in specific laboratory tests. Start / stop, inconsequence of new operating approaches need tobe addressed in realistic testing scenarios withsimilar tribology.
Basically, load and wear will decide bearing longterm operational performances, start-stop refers tothe bearing performances during the mix friction
condition such as fast start without pre-lube,
emergency relativities bearing capabilities foradaptation and to run in particle involved
environment, corrosion is reflecting bearing
resistance in aggressive lubrication conditions like
acidic oils and, cavitation indicates surface strength
against cavitation attack. The cavitation attack willremove the local bearing materials continuously
therefore will influence the long term perspectives.
An overview over all requested performance criteria
for representative examples out of the different
bearing families is given in Figure 6 andcorresponds with Figure 5.

Performance transfer from engine
application to the test rig

For every application area and performance
characteristic you need a special transfer tolaboratory tests and bearing test programs. Engine
experience need to be incorporated as wellespecially when it comes to relative interpretation.
Since this is a very complex task it is shown as an
example for the multi purpose Tin base Tri-metal
bearing. This tri-metal bearing type was developed
to offer a lead free solution and to replace four
different tin based surface coatings to reduce
production complexity and to achieve economy ofscale in the electroplating shop.

Figure 6 Bearing type family characteristics shownwith representative examples
Due to the different performance offerings of the
bearing types it can be stated, that the bearing type

CIMAC Congress 2023, BusanPaper No. 025

Page 3

and material selection need to be done very
carefully
consideringengineperformance,
application and operation. Nevertheless, a bearing
type concentration need to be done for costconsideration and economy of scale. This can only
be done if engines are understood adequately andtransfer of the performance demand to thevalidation process is made correctly.

2

VALIDATAION EXAMPLE - TRI-METALBEARING FOR HIGH SPEED ROBUSTAND MEDIUMS SPEED ENGINE

These new bearing types have been developed on
basis of several different tin based bearing
technologies and electroplating processes. Bronze
lining and Ni-intermediate layers have been taken
as given. Surface layer has been formulated and thecoating process was developed based on BHW and
Miba technology.
2.1

In order to get adequate tribological properties andto reduce seizure risk when wearing through theoverlay into the high strength copper based lining
materials, Miba selected Sulfides as tribology
improver. Due to the Sulfide phase the welding
characteristics to steel (crankshaft) is dramaticallyreduced. The material offers nearly same
tribological properties as high leaded bronzematerials in seizure load programs. First engine
tests confirmed design targets already in engine
operation. The layer design is same as for leadbronze based bearing types.
2.2

Reference Bearings

Miba03 is a traditional bearing material with PbSn
electroplating overlay and casted CuPb22Sn lining
material and offers a lot of engine and testing
experience. Figure 9 shows the respective crosssection.
Electroplating overlay

Bearing description Miba4B and Miba4C

Nickel Interface

Miba4C is a new bearing types which already has
first positive engine test experiences at thecustomer side. Figure 7 shows a cross section

Lead Bronze

Steel Back

Electroplating overlay
Nickel Interface

Figure 9 cross section of Miba03 material

Lead Bronze

Steel Back

Figure 7 cross section of Miba4C material

It is widely used in High speed and large bore 4stroke engines with good average load
performances and wear resistance. It has
extraordinary dirt resistances when the engine
cleanness is not given. Corrosion and cavitation
resistance is ranked lower due to its sensitivity
against sulphur and softness against cavitation
attack.

As shown a standard build up with steel back, leadbronze lining, intermediate layer of Nickel and thefinal tin based surface coating was selected.
Miba4B, the lead free version is shown in Figure 8.

Sputter overlay
Nickel Interface
Lead Bronze

Electroplating overlay
Nickel Interface
Steel Back
Lead Free Bronze Miba2
Synthec Running in layer
Sputter overlay

Steel Back

Nickel Interface
Lead Bronze

Figure 8 cross section of Miba4B material
Bearing Miba4B is focused on large high speed andmedium speed engines. The layer design is similar
to Miba4C but with a different lead free lining
material.

CIMAC Congress 2023, Busan

Steel Back

Figure 10 Cross section of Miba37(upper) and
Miba61(lower) material
Steel Back

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Page 4

Both Miba37 and Miba61(with Synthec) is AlSn20
Sputter coated bronze bearing with extraordinary
bearing load capability and wear resistance. Figure
10 shows the respective cross sections. Besides
that, cavitation and corrosion resistance are also inoutstanding level due to surface hardness and finegrain. It is widely used in High-Power High-Speedengines as loaded shell in both, conrod and main
bearings configurations. Miba61 has both Sputter
and Synthec Overlay on the top which is Miba’s
USP. With this unique design of the overlay. It canoffer not only the extraordinary loading capability
and wear resistances, but also excellent running inand heavy start stop capabilities. It can contribute
especially when low oil viscosity design and helps
the cranktrain to gain lower friction losses.
2.3

Bearing requirement of the concerned
engines

In general, medium speed engines and high speedengines requirements on the bearing performanceare different. The extraordinary load in high speed
load shells cannot be delivered by a tri-metal
bearing with electroplated overlay so far.
Nevertheless, in certain cases of high performanceengines a tribological robust counter shell or main
bearing design is requested. When analyzing
engine operation, the main difference is sliding
speed. To cope with these applications also andwith the lead free request in future, the program has
been modified to represent the additional
requirements. The specific engine bearing
performance data are compiled in Table 2.
Table 2 bearing performance expectations fordifferent engine applications
Bearing
Performance
Expectation
Load

Table 3 you may find the special designed test
programs which are derived from both typicalmedium speed and high speed engine applications
requirement.
Table 3 Characteristics of bearing test andlaboratory programs
Test Criterion
Engine Type andtest condition, time (h)Load / Wear
Medium speed
75 MPa, 12 m/sec, 15 h
Wear / Fatigue
Medium Speed
75 MPa, 12 m/sec , 70h
Load / Wear
High Speed
75 MPa, 20 m/sec, 15h
Seizure Test
Step Load, 12m/sec
Misalignment
Medium & High Speed
75 MPa, 12 m/sec, 15 hContinuous dirt
Medium & High Speed
75 MPa / 16 m/sec
Corrosion
Medium & High speed
Oil cooking test
Cavitation
Medium and High Speed
Hardness / Ultrasonic

PurposeInterpretation

Wearrobustness

Wall thickness
crackingLong term
wear rate

Wall thickness
crack
propagation

Wearrobustness

Wall thickness
cracking

Tribologicalrobustness

Failure load

Conformability

Load distribution
Seizureinclination

Dirt
sensitivity

Number ofshocksSensitivity
Environment
oil additives
Materialrobustness
cavitation

Layer formation
Thickness ofreaction layer
Hardness
Weight loss

In the listed programs for bearing load and wear
capability are prepared as standard. Besides that,application oriented tests[1], such as misalignment,
continuous dirt, corrosion and cavitation tests arealso performed to mimic the challenges during theengine assembly and operations as close as
possible.

High Speed
EngineMedium Speed
Engine3.2< 95 Mpa< 49 Mpa

Sliding Speed<18 m/s
Average14/s< 15 m/s
Average11m/s

Bearing Life

< 60k hours< 60k hours

Start-Stop< 1k times< 1k times

Dirt resistance
Cavitation
resistance

MediumHigh

Bending test fatigue of the steel back and lining isevaluated at the beginning to design the appropriate
bearing fatigue strength. Then, all other above
described tests are performed for the bearing types,
produced with production processes close to serial
production processes and devices.

MediumMedium3.3

The above given values are transferred to thedifferent test programs shown in the next
paragraphs.

3

TEST SET UP AND PERFORMANCE
CHARACTERISTIC

3.1

Test program setup description

From

CIMAC Congress 2023, Busan

Application related testing results andinterpretation

Fatigue-alternate bending test rig results

The alternative bending bi-metal fatigue isevaluated at room temperature according to a
Wöhler procedure, the specimen is flat and the test
frequency is 25Hz. A crack detection gage isapplied to detect the crack happening at the firstplace and in total 8 samples can be test
simultaneously. The device and the instrumentation
are shown in Figure 11, base results are given in
Figure 12.

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Page 5

High Speed
Engines

Medium Speed
Engines

Unit load

75Mpa

75Mpa

Sliding speed

20m/s

12m/s

Oil specification

SAE10

SAE10

The unit load is 75Mpa, bearing surface sliding
speed is 12m/s, oil specification is SAE10 and theoil inlet temperature is 110 °C. The wear
performance and load capability are measured in
the bearing main loaded area. And the results arecalculated as the average value at the bearingedges and the center of the bearing main loaded
area.

20m/s

Figure 11 Test device and test set up with wire strain
gaugesTestingParameters

Figure 13 Wear test rig result break in
Figure 12 fatigue test result on bronze-basedmaterials
As reference, especially for medium speed engines
also Miba 15 is shown as reference. From the test
result as 2 shown that we can conclude that:
1. Traditional lead based copper material
CuPb22Sn2 (Miba01) has advantages in termsof lifetime against AlSn25 (Miba 15)
2. Miba new generation of lead free material
INNOalloy (Miba2C) has even stronger fatigue
strength compared to traditional leaded bronzematerial and is in similar range as the existinghigh strength lining (Miba49) used in truck
applications.
3.3.1

As testing result Figure 13 shows that Miba4C
material shows an improved wear resistanceagainst traditional Miba03 electroplated bearing.
Miba37 is best of the performer in terms of the wear,
Miba61 has certain fluctuation because of theSynthec overlay on the top is designed as runningin layer therefore may have wear rate variations
from test to test. And in general, it is believed thatthe first 15 hours is the typical period for the bearing
material break in.
When the Miba4C is testing under 75Mpa with
20m/s sliding speed, we see that in orange column
as Figure 13 shown that it has the comparable wear
resistance capability compared to 12m/s.

Wear test result – break in

The wear test parameters were differentiated forhigh load and high speed and medium load medium
speed engines, please refer to Table 4 for thedifferent parameter settings for the applications.
Table 4 testing parameters setting for different
applications

CIMAC Congress 2023, BusanPaper No. 025

Page 6

3.3.2

Wear test rig result- long term

The test procedure, loads and speed, as well as
the oil condition remains as the same as the shortterm wear test. However, the test endurance isextended to 55 hours after the break in total withintermediate inspection after 15 hours to separate
long term wear rate from break in wear. Long term
wear is then shown in Figure 14 for the different
bearing types.

All tri-metal bearings showed very similar
performance as Figure 15 tells us. Althoughsmearing can be detected on the shown tri-metal
picture, but the bearing is full functional. In
comparison Miba 37, the sputter bearing shows aslightly higher wear rate due to it AlSn20 overlay
which tends to release tin under mixed friction
conditions. An additional polymer layer applied as
emergency lubricant in Miba61 improves the sputter
bearing to the best bearing type available.
3.3.4

Static Seizure Load test rig result

In this test program, the bearing seizure load will beidentified in case of high temperature and limited oil
supply to the main loaded area. The oil is SAE10
and the oil inlet temperature is 120°C to accelerate
the test. The oil supplement volume is 1,75L/min,sliding speed is 12m/s in which high energy inintroduced and the bearing is loaded starting from
2,85Mpa until seizure happens.
Figure 14 wear test results – long term
Both of Miba4C and Miba4B has significant
reduction on the wear rate and shows excellent
long-term wear resistance characteristics compared
to traditional electroplating bearing Miba03. Miba4C
is very close to Miba61 in terms of wear rate. Of
course, the Miba61 has the same level wear ratecompared to Miba37 after the Synthec overlay is
gone.
3.3.3

Start Stop test rig result

Figure 16 static seizure load test rig result

This program is designed to verify bearing materials
behavior under mix friction or even boundary
lubrication conditions. Start up procedure from a
mid size high speed, high performance engine wasmodelled, therefore the test look quite different toautomotive application test. Result interpretation isdone via the average wear rate at bearing ends andcenterline position of the main loaded area. Test
unit load is continuously set to 2.4Mpa and thesliding speed ramps under given load from 0 to 2m/s
within 1800 cycles. The oil in use is SAE10 with an
inlet temperature of 120°C.

All the bearings can survive from 40Mpa which isenough for the standard application needs as
indicated by Figure 16. All the electroplated bearing
materials, Miba03, Miba4C and Miba4B show
excellent seizure resistance. Miba37 and Miba61
has relative lower seizure resistance due to it’s hardoverlay and of course please notice that the oil
supplement to the bearing loaded area is limited
due to static load characteristics.
3.3.5

Dynamic Seizure Load test rig result

The dynamic load step program is to identify theseizure load in case of high temperature. The oil is
SAE10 and the oil inlet temperature is 120°C toaccelerate the test. The oil supplement volume is
1,75L/min, sliding speed is 12m/s in which highenergy is introduced and the bearing is loaded
starting from 2,85Mpa with 50Hz dynamic loadincreasing until seizure happens.

Figure 15 start stop test rig result and bearing
appearance

CIMAC Congress 2023, BusanPaper No. 025

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➔ A continuous test part with particles of max.
25µm. If the bearing pass this first part thebearing is suitable to run in an engine withstandard cleanliness. Particles are kept in theoil system for the whole test procedure.

Figure 17 Dynamic seizure load test rig result
All the bearings can survive from 80Mpa which isenough for the standard application needs. All the
bearing materials show performance significantly
above the application needs as Figure 17 shown.
3.3.6➔ In the second part robustness against particles
smaller than the clearance (max. size 40µm) is
tested. An increasing amount of dirt starting with
0,03g up to 0,15 g is applied in 5 shock. Highrobustness for dirt coming from combustion or
cleaning residuals can be stated for the bearing
failing during this test sequence.
➔ Extreme robustness against mechanicaldamages by particles is tested in part 3. Particle
size with 80µm is much bigger than the bearing
clearance and will scratch into overlay andlining.

Dirt resistance test rig result

This test program is designed to identify the bearing
material’s robustness against hard particle shocks.
The test bearing has a diameter of 48 mm and awidth of 12mm. 75 MPa specific unit load at
16m/sec is applied in an environment with SAE10
oil at 110°C. The hard silicate particles[1] are shot
directly in the oil feed line in via a revolving device
shown in Figure 18 together with some dirt
example.

The bearing needs not only a good local resistancebut also an extreme tribological behavior towithstand. 8 shocks from 0,18 g to 0,39 g areapplied.

Figure 19 dirt resistance test rig result

Figure 18 Dirt revolver – dirt (Silicates with extreme
hardness) is filled in the chambers according
specification starting in the second chamber.
The test is segmented in three parts:

CIMAC Congress 2023, Busan

The test result shown by Figure 19 gives theindication that Miba4C, Miba4B and Miba03 havethe best performance against the dirt, Miba03
material survived from all the 13 shocks andMiba4C, Miba4B is almost there. Miba37 andMiba61 are above 2 and they are capable for the
standard application requirement. In the high speed
and medium speed applications, that quite often theengines are failed by insufficient cleanness at theearly stage of the operation due to difficulties ofburrs removal and clean during the machining andassembly. Miba4C gives the bearing an excellent
resistance and robustness on the deburrs therefore
has better chance to survive from the cleanness
issues.

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Page 8

3.3.7

Misalignment / conformability test rig
resultLocal overloading is quite frequently happening
during the engine running in phase when there is
misalignment of the housing or pin or blending of thepin or the deformation of the housing during thefiring. The bearing system can either adpapt anddistribute the load on a wider area quickly or fail by
seizure. Our misalignment test is designed to
identify this adaptation capabilities in case of loacal
overloading. Especially the sensitivity against edge
loading is shown comparatively for different bearing
types by the survival rate. Additionally overlay life
under the extraordinary load conditions is indicatedby average runtime under full load and shows thelong term operational risk.
An inclination of 40 µm within bearing length of 34
mm is applied on the bearing running under 75Mpa
unit load and 12m/s sliding speed. SAE10 oil andthe inlet temperature of 110°C reduce the oil film
thickness in addition and accelerate the test.
Bearing appearance after test is shown in figure in
18 and shows the local behavior of the bearing.
Miba 03

Miba 4C

Miba 6K

Figure 21 misalignment test rig result
Bearing type Miba4B, Miba4C and Miba61 adapt
quickly by local wear and all bearings survived.
Miba37 and Miba03 showed less robustness
against edge loading. If the sputter bearing Miba 37
is optimized with a Polymer running in layer
conformability is on highest level and long term
performance becomes extraordinary since thesputter layer is not worn off.
3.3.8

Corrosion and Cavitation test rig result

The static oil cooking test is a procedure to verify
the oil-material-compatibility of various bearing
materials. It was developed in times when HFO
entered the market and afterwards it was adapted
to represents engine operation with special gaseous
fuels. Additional tests are initiated and developed
now to represent the new alternative fuels.
For the test representing medium speed and lower
loaded high speed engines, the reactions between
the bearing materials and additives used in gas
engine oils are observed. For an accelerated test
result, the conditions are chosen to be 160°C for
150 hours. To determine the corrosion behavior, thecontent of bounded sulfur on the bearing surface ismeasured and related to the bearing surface byusing SEM EDX.

Figure 20 Bearing appearance after test
The bearing appearance after test as Figure 20
show severe edge loading and how bearings copewith this extraordinary load condition. The standard
tri-metal bearing wear in a more limited area incomparison to the new Miba4C, which is also
indicated by a lower survival rate. The polymer
bearing cope with extraordinary robustness andload capability which is shown by the reduced wear
and adapted area. Results are summaries in Figure
21.

Group1

Group2

Figure 22 Corrosion result relatively
From Figure 22 we can see 2 specific groups ofbearing types engaged in Sulfur reaction. The
electroplated overlays of Tri-metal bearings

CIMAC Congress 2023, BusanPaper No. 025

Page 9(Group1) Miba 03, Miba 4B and Miba 4C, which
need copper to improve wear stability show morereactivity. Additives containing sulfur mainly reactwith copper by forming CuS on the bearing surface.
Field experience with given Tin base overlays havealready confirmed good performance when it comesto wear – corrosion in medium speed engines.
The overlay compositions for Sputter as Miba 37
and Polymer bearings like Miba 61 show nearly noreactivity.
The cavitation test occurs on material surfaces thatare exposed to intense ultrasonic cavitation. Pleaserefer to “New developed and standard bearing types
focused on gas engines” [3]for the testing details.
This is a fast method of measuring the erosion
resistance of a material or coating to intense stressand other erosion factors. By operating conditionsof 200W and 10 minutes it provides a quantitative
measurement of weight loss.

and the blow-by of unburned fuel), can influence theservice life of the bearing. Therefore, it is of utmost
importance to select the right oil material
combinations for the application.
To discover and quantify possible chemicalinteractions between the bearing materials used
and the engine oils, in new and aged condition,
special test methods based on static oil material
compatibility tests were developed. These arebased on a combination of the ASTM D130 and
VDMA 24570 standards. For the testing procedurematerial stripes (pure metals and bearing material
compounds) are immersed in the new or aged oil attemperatures between 60°C up to 180°C. The used
coupons are weighed in constant time intervals toevaluate the weight loss and the optical appearance
as indicator of sensitivities to corrosion.
In order to understand the processes of oil ageingin the engine and its effects on the bearing material,
Miba is currently designing a test setup for artificial
oil ageing. For this purpose, oil samples are aged
under the influence of different combustion products
and alternative fuels. In combination with thepreviously described static oil material compatibility
tests and trials on the tribometer, the effects ofdifferent conditions and fuels on the bearing
performance can be evaluated.

Figure 23 Cavitation test result
Based on test result Figure 23, Miba37 shows very
low cavitation due to its high hardness of the
sputtered AlSn20 overlay. Miba03, Miba4B and
Miba4C have higher material loss in the cavitation
test, caused by the reduced hardness, compared toMiba37. The polymer layer of Miba61 wears out
after a short time in the test, the wear slows down
considerably in the case of the sputtered layer
below.
3.3.9

Oil Material Compatibility TestingWith the accelerated transition from conventional
diesel engines to alternative fuel systems, it is very
important for a bearing solution provider to keep an
eye on the entire engine system from combustion to
the use of engine oil types.
Especially the choice of engine oil can play adecisive role in the longevity and performance of aplain bearing. The selection of the wrong additive
packages on the one hand and the corresponding
oil ageing with alternative fuels on the other hand(also in connection with the combustion products

CIMAC Congress 2023, Busan

Figure 24 Schematic representation of artificial
aging on a laboratory scale
The main goal of the oil ageing and oil material
compatibility tests is to reproduce results from thefield in a laboratory scale and to bring these findings
into the test rigs, together with external partners anduniversities. This can help to develop new materials
and technologies for future applications.
3.3.10 Result and interpretation
A result interpretation is performed as overview
based on the spider web diagram as overview inFigure 25. Please note, that the applications rank
from medium speed to high speed highPaper No. 025

Page 10performance engines and may differ, when looking
only into one application spectrum.

Figure 26 overview of the Miba4C in one of thecustomer engines after 3000 hours operation in thefield
The bearing is in perfect condition with smoothening
in the main loaded area and no sign of material
fatigue and excessive wear is observed.

Figure 25 Bearing type families characteristics
The difference between tri-metal and highperforming sputter bearing can be identified easily.
Tri - metal bearings with extraordinary good
tribological performance for misalignment, dirt andstarvation conditions competes with extraordinaryhydrodynamic performance of sputter bearings. In
many cases of the large bore engines when theengine cleanness or bearing adjacent parts quality
is not given, therefore the bearing emergency
character really matters. As a consequence, trimetal
bearings
withhighertribological
performances in terms of robustness and operation
safety against the particles, misalignment and oil
starvation are much more preferred instead of the
sputter bearings. In addition, sputter bearings havesize limitations due to constrains from the coatingmachinery. Nevertheless, the new tri – metal
bearings have extended their application area byimproving load and cavitation against standard tri –metal lead bronze bearing and do not have size
limitations.

4

FIELD EXPERIENCES

The Miba4C bearing material already has lots ofsuccess running experiences in both high speed
and medium speed engines with more thanthousands of hours. An example of a medium speedengine after 3,000 hours of operation is given in
Figure 26.

Figure 27 cross section at the main loaded area
When looking deeper by metallurgical cross section
shown in Figure 27, perfect microstructure on bothelectroplating overlay and lining material is found,no sign of Sn depletion and lead aggregation can befound, meanwhile the remaining thickness of theoverlay is still in good value and we see that thebearing wear resistance is strong.
A deeper insight view into the Miba4C overlay
structure and condition is given in Figure 28. Basedon a cross section prepared by our adapted ION
beam milling device further details become visible.

Loaded Area

Reference Area

Figure 28 Ion beam polishing cross section
investigation

CIMAC Congress 2023, BusanPaper No. 025

Page 11

The reference area shows a structure similar to a 6 REFERENCES AND BIBLIOGRAPHY
new one. When looking on the loaded area we seea homogenized and smoothened structure withimproved tribological properties and good wear
[1] Aufischer, R.2013.Modular Bearing Design toresistance.
Cope with the New Engine Designs
Demanding High Performance, Lead Free
5 SUMMARY AND OUTLOOKSolutions and Robustness, ICEF 2013,
The Miba inhouse bearing test is a specialized
Dearborn, Michigan, USA 2013
bearing performance validation approach fordifferent applications by recognizing the application [2] Forstner, C and Mairhofer, G. 2007.
Applciation oriented bearing testing, CIMAC
demands and transferring the demands to bearing
2007, Vienna, 246
rig test parameters and settings.
[3]

Rumpf, T.2001.New developed and Standard
Bearing Types Focussed on Gas Engines,
CIMAC 2001

Paper No. 025

Page 12During the new bearing material development, in
considering the bearing type portfolio management,that to use one bearing material type to serve morethan one engine application is possible. With the
newly developed Miba 4B and Miba4C bearing
material, we are now in a good position from one
hand to reduce the portfolio complexity andincrease the economical scale and consequently
reduce the cost, which means that Miba03, MibaZ1,
MibaT6, BHW87 will be replaced by Miba4C, fromanother hand Miba4C can be used in both highspeed robust application and medium speed
applications. And the influences on bearing by the
new or alternative fuels, such as ammonia,
methanol, H2, etc., is very well combined.
Besides that, local production of the Miba4C with
the SnSbCu electroplating overlay in Miba bearing
plant at Suzhou industrial park, China is alreadyplanned. Once it is fully implemented, we are more
flexible to serve the local customers in engine
development or special requirements.
At last but not the least, it is an upgrading approach
therefore the test rig parameters, settings arealways adapting to the new demands from thetechnology and the market.
As conclusion it can be drawn that:⚫

Application related bearing testing isrepresenting different applications with theircharacteristics⚫

One Bearing type can serve more than one
engine application when considering it from the
beginning and develop accordingly⚫

New/alternative fuels need more attention in
future. Especially bearing long term stability
may become more important when considering
cavitation
andcorrosion.
Additional
investigation in alignment with field experience
will become necessary

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