Blended Edge Main Bearings

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This Is a HeadlineThis is a subheadlineBlended Edge Main Bearings





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





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

5



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

6



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

7







MAN Diesel & Turbo

Teglholmsgade 41

2450 Copenhagen SV, Denmark

Phone +45 33 85 11 00

Fax +45 33 85 10 30

[email protected]

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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Blended Edge Main Bearings