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Content
Introduction .................................................................................................5
Blended Edge Design ...................................................................................6
Elastohydrodynamic (EHD) Simulations .........................................................6
Blended Edge Positions ...............................................................................7
Spare Part Bearings .....................................................................................7
Lower Oil Groove Removal ...........................................................................7
Conclusion ...................................................................................................7
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Blended Edge Main Bearings 5
Blended Edge Main Bearings
Introduction
The blended edge (BE) design was in-
troduced on thin shell white metal main
bearings to better cope with crankshaft
inclinations and thereby increase its re-
sistance towards edge fatigue failures.
The blended edge design is the cor-
responding thin shell feature as for the
thick shell flex-edge design in MC en-
gines. The BE design was introduced in
2004 and has since that time success-
fully been used for new engines. Today,
the BE white metal bearing is featured
in the S46, S50, S60, S65, S70, S80,
K80, S90, K90 and K98 engine series.
Occasionally, bearings fail without any
clear root cause, but for example in-
dications of small imperfections of the
journal geometry could be found. In
such cases, a BE bearing could be thesolution, depending on the actual fail-
ure type. Fig. 1 shows a typical edge
orientated fatigue failure of the white
metal lining, and Fig. 2 shows the re-
placed blended edge bearing in good
condition after more than 7,000 running
hours.
Fig. 1: Typical fatigue damage to a white metal main bearing. The damage has in this case occurred at
the lower port side aft position. This bearing is of the plain design (i.e. no BE). The damage was detected
after 1,300 running hours
Fig. 2: Blended edge bearing that replaced the bearing in Fig. 1. This photo was taken after more than
7,000 running hours. No traces of fatigue failures can be seen
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Blended Edge Main Bearings6
Blended Edge Design
The blended edge design consists of
a smooth radius that allows the main
bearing shaft to incline without risking
touching the bearing edge or causing
high oil film pressure near the edge.
The blended edge is described by two
dimensions, its length and its depth.
The actual values depend on engine
size and configuration. Fig. 3 shows an
example of a blended edge.
With a good blended edge design, the
high edge load can be reduced and
distributed over a larger area, thus
resulting in a decreased max. oil film
pressure and increased safety against
edge fatigue failure.
Elastohydrodynamic (EHD)
SimulationsFor more than a decade, MAN Diesel
& Turbo has developed advanced soft-
ware to perform evaluation of bearing
performance. With continuous invest-
ment in computer hardware, we can
now simulate all main bearings with
different parameters. This makes it
possible to optimise the main bearing
design. Figs 4 and 5 show EHD simu-
lations of main bearings without and
with BE. With the BE design, the max.
oil film pressure is decreased by 40%,
and the minimum oil film thickness is
increased several times to a level that
provides good safety margin.
Fig. 3: Blended edge, dimensions given in mm
Fig. 4: Max. oil film pressure. The red colour indicates high oil film pressure. The figure to the left is a
plain bearing and the figure to the right i s a blended edge bearing
Port
Aft
Plain bearing Blended edge bearing
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Blended Edge Main Bearings 7
Blended Edge Positions
Each main bearing in an engine is
subjected to an individual load and in-
clination orbit. The optimum blended
edge positions can only be determined
through EHD simulations. Such simula-
tions have been performed on all en-
gines, where blended edge bearings
are specified. For easy recognition by
the crew, the blended edge bearing
shells are marked “BE” type. When
the blended edge bearings were in-
troduced, only a few positions were
specified as BE. However, over time
our experience of BE bearings has in-
creased, and we are today more likely
to use blended edge bearings in more
positions. In a few engines, BE is even
specified in all positions, since this hasproven to be an improvement of the
bearing performance.
Spare Part Bearings
The trade off with blended edge bear-
ings is its decreased bearing load ca-
pacity when the inclinations are small
and the bearing force is very high. In
such positions, “straight” cylindrical ge-
ometry bearings are the better choice,
and if blended edge bearings are spec-
ified elsewhere in the same engine, it
must be equipped with both plain and
blended edge spare parts. If an engine
is delivered with a BE spare part bear-
ing only, BE bearings can be used in all
main bearing positions.
Lower Oil Groove Removal
The oil groove feeds and distributes oil
into the bearing, but it also decreases
the bearing area. On engines with
high horizontal load, the combination
of blended edge and lower oil groove
causes poor fluid film conditions, see
Fig. 6. The influence of the lower oil
groove for the oil supply is marginal
and it is therefore considered better to
remove the lower oil groove to improve
the horizontal bearing load capacity.
This design change was implemented
in 2009 with good results.
Conclusion
The blended edge design provides im-
proved distribution of edge pressure
and in certain positions increases the
minimum oil film thickness by more than
100%. This dramatically decreases the
risk of main bearing edge fatigue failure.
Port
Plain bearing Blended edge bearing
Fig. 5: Min. oil film thickness. The red colour indicates low oil film thickness. The figure to the left is a plain bearing and the figure to the right i s a blended edge bearing
Fig. 6: Lower oil groove is highlighted with dashed
boxes
Aft
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MAN Diesel & Turbo
Teglholmsgade 41
2450 Copenhagen SV, Denmark
Phone +45 33 85 11 00
Fax +45 33 85 10 30
info-cph@mandieselturbo.com
www.mandieselturbo.com
MAN Diesel & Turbo – a member of the MAN Group
All data provided in this document is non-binding. This data serves informational
purposes only and is especially not guaranteed in any way. Depending on the
subsequent specific individual projects, the relevant data may be subject to
changes and will be assessed and determined individually for each project. This
will depend on the particular characteristics of each individual project, especially
specific site and operational conditions. Copyright © MAN Diesel & Turbo.
5510-0113-01ppr May 2014 Printed in Denmark
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