SIST ISO 7146-2:2009

INTERNATIONAL ISO
STANDARD 7146-2
First edition
2008-10-15

Plain bearings — Appearance and
characterization of damage to metallic
hydrodynamic bearings —
Part 2:
Cavitation erosion and its
countermeasures
Paliers lisses — Aspect et caractérisation de l'endommagement des
paliers métalliques à couche lubrifiante fluide —
Partie 2: Érosion de cavitation et sa contre-mesure




Reference number
ISO 7146-2:2008(E)
©
ISO 2008

---------------------- Page: 1 ----------------------
ISO 7146-2:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland

ii © ISO 2008 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 7146-2:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Cavitation erosion. 2
4.1 Mechanism of cavitation erosion . 2
4.2 Classification of cavitation erosion . 4
4.3 General countermeasures against cavitation erosion. 7
5 Five types of cavitation erosion . 8
5.1 General. 8
5.2 Flow cavitation erosion. 8
5.3 Impact cavitation erosion . 11
5.4 Suction cavitation erosion. 12
5.5 Discharge cavitation erosion. 14
5.6 Miscellaneous cavitation erosion (see Figures 17 to 20). 15

© ISO 2008 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 7146-2:2008(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 7146-2 was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 2,
Materials and lubricants, their properties, characteristics, test methods and testing conditions.
This first edition of ISO 7146-2, together with ISO 7146-1, cancels and replaces ISO 7146:1993 the technical
content of which has been technically revised and augmented.
ISO 7146 consists of the following parts, under the general title Plain bearings — Appearance and
characterization of damage to metallic hydrodynamic bearings:
⎯ Part 1: General
⎯ Part 2: Cavitation erosion and its countermeasures

iv © ISO 2008 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 7146-2:2008(E)
Introduction
In practice, damage to a bearing may often be the result of several mechanisms operating simultaneously.
The damage may result from improper assembly or maintenance or from faulty manufacture of the bearing, its
housing or the counterface against which it operates. In some instances, damage may be caused by a design
compromise made in the interests of economy or from unforeseen operating conditions. It is the complex
combination of design, manufacture, assembly, operation, maintenance and possible reconditioning which
often causes difficulty in establishing the primary cause of damage.
In the event of extensive damage or destruction of the bearing, the evidence is likely to be lost, and it will then
be impossible to identify how the damage came about.
In all cases, knowledge of the actual operating conditions of the assembly and the maintenance history is of
the utmost importance.
The classification of bearing damage established in this International Standard is based primarily upon the
features visible on the running surfaces and elsewhere, and consideration of each aspect is required for
reliable determination of the cause of bearing damage.
Since more than one process may cause similar effects on the running surface, a description of appearance
alone is occasionally inadequate in determining the cause of damage. In such cases, the operating conditions
have to be considered.
Cavitation erosion dealt with in ISO 7146-1 is treated in this part of ISO 7146 in more detail.

© ISO 2008 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 7146-2:2008(E)

Plain bearings — Appearance and characterization of damage
to metallic hydrodynamic bearings —
Part 2:
Cavitation erosion and its countermeasures
1 Scope
This part of ISO 7146 defines, describes and classifies the characteristics of damage occurring in service in
hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible
countermeasures. It assists in understanding the various characteristic forms of damage which may occur.
Consideration is restricted to damage which has a well-defined appearance and which can be attributed to
particular causes with a high degree of certainty. Various appearances are illustrated with photographs and
diagrams.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 4378-1, Plain bearings — Terms, definitions, classification and symbols — Part 1: Design, bearing
materials and their properties
ISO 4378-2, Plain bearings — Terms, definitions, classification and symbols — Part 2: Friction and wear
ISO 4378-3, Plain bearings — Terms, definitions, classification and symbols — Part 3: Lubrication
ISO 7146-1, Plain bearings — Appearance and characterization of damage to metallic hydrodynamic
bearings — Part 1: General
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4378-1, ISO 4378-2, ISO 4378-3,
and ISO 7146-1 apply.
© ISO 2008 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 7146-2:2008(E)
4 Cavitation erosion
4.1 Mechanism of cavitation erosion
Cavitation erosion is a form of damage to the surface of a solid body in liquid caused by implosion (violent
inward collapse) of cavities or vapour bubbles. When the static pressure in the liquid is decreased under the
vapour pressure of the liquid at a given temperature, evaporation occurs and bubbles of vapour are generated
in the liquid. This phenomenon is called “cavitation”. When these cavities encounter higher pressure, because
they have flowed to a place of higher pressure or the pressure at the place of cavitation has increased in the
meantime, they condense instantaneously and implode, causing a very high and local pressure and high
temperature in the liquid. It can lead, after repeated implosion, to “cavitation erosion” of the surface of the solid
body near the place of implosion.
Because of the high intensity of cavity implosion, chemical reaction “cavitation corrosion” can take place. The
damage may also occur together with “fluid erosion” and “cavitation corrosion”. A phenomenon known as the
“micro-Diesel-effect”, where the imploding cavities release electrical charge, is also detected in plain bearing
oil.
When a bearing surface is eroded by cavitation, first the colour of the surface changes slightly due to
roughening. Then small pores form, and cracks initiate on the surface, especially at grain boundaries. These
cracks with sharp edges are spread first on the surface and then deepen according to the properties of the
underlying material (see Figure 1). The cracks are joined together leading to break-out and wash-away of
small particles of bearing materials.
When the damage is caused solely by collapsing cavities, the attacked areas show a rough texture.
Metallurgical section often shows signs of local work-hardening and fatigue cracking due to hammer blows
caused by cavity collapse. But if particles are trapped in the damage pockets, the surface can be eroded and
exhibits a smooth and polished appearance. The place of cavitation erosion is usually limited locally and
spreads seldom to a broader region. The cavitation erosion usually appears in the unloaded areas of the
bearing.
The occurrence of cavitation erosion depends on many factors as given in the following: journal speed,
specific bearing load, dynamic load pattern (especially time rate of load variation), motion of journal center,
bearing vibration, bearing clearance, size and geometry of bearing clearance space, edge form and location of
oil hole, groove and pocket, existence and position of the drilling in journal, bearing material, especially its
hardness, elastic modulus, toughness, fatigue strength and corrosion resistance, oil supply pressure, oil
constituent and its vapor pressure, oil viscosity, oil temperature, air and water content and contamination of oil,
etc.
2 © ISO 2008 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 7146-2:2008(E)

a)  view under magnification

b)  cross-section under magnification
Key
1 sliding surface 3 bonding area
2 bearing metal (tin-based) 4 steel backing
Figure 1 (continued)
© ISO 2008 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 7146-2:2008(E)

c)  cross-section under higher magnification
Key
1 sliding surface
2 bearing metal (tin-based)
3 bonding area
4 steel backing
Figure 1 — Sliding surface with cavitation erosion
4.2 Classification of cavitation erosion
Though cavitation erosion occurs in plain bearings of various machines, that in bearings of internal
combustion engines has been studied most intensively and has attracted increasing attention as engine
performance has increased. For engine bearings, cavitation erosion has been classified into types 1 to 4 by
the mechanism of cavity creation. However, this classification may also be applied to other kinds of machines,
provided that the characteristic flow conditions are similar. Examples of characteristic appearances and
mechanisms of four types of cavitation erosion in journal bearings are given in Figures 2 and 3. Besides these
four types, there are some kinds of cavitation erosion which may not always be easy to identify
...

SLOVENSKI STANDARD
SIST ISO/DIS 7146-2:2008
01-julij-2008
'UVQLOHåDML7HNRþLQVNLVORMNRYLQVNLKOHåDMHY,]UD]LLQ]QDþLOQRVWLSRãNRGE
GHO.DYLWDFLMVNHSRãNRGEHLQXNUHSL]DQMLKRYRSUHSUHþHYDQMH
Plain bearings - Appearance and characterization of damage to metallic hydrodynamic
bearings - Part 2: Cavitation erosion and its countermeasures
Paliers lisses - Aspect et caractérisation de l'endommagement des paliers métalliques à
couche lubrifiante fluide - Partie 2: Érosion de cavitation et sa contre-mesure
Ta slovenski standard je istoveten z: ISO/FDIS 7146-2
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO/DIS 7146-2:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 7146-2
ISO/TC 123/SC 2 Secretariat: DIN
Voting begins on: Voting terminates on:
2006-12-21 2007-05-21
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION • МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ • ORGANISATION INTERNATIONALE DE NORMALISATION
Fluid film metallic plain bearings — Description and
characterization of damage —
Part 2:
Cavitation erosion and its countermeasures
Paliers lisses métalliques à couche lubrifiante fluide — Description et caractérisation des détériorations —
Partie 2: Érosion de cavitation et sa contre-mesure
(Revision of ISO 7146:1993)
ICS 21.100.10

In accordance with the provisions of Council Resolution 15/1993 this document is circulated in
the English language only.
Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué
en version anglaise seulement.
To expedite distribution, this document is circulated as received from the committee secretariat.
ISO Central Secretariat work of editing and text composition will be undertaken at publication
stage.
Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du
secrétariat du comité. Le travail de rédaction et de composition de texte sera effectué au
Secrétariat central de l'ISO au stade de publication.
THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE
REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.
© International Organization for Standardization, 2006

---------------------- Page: 2 ----------------------
ISO/DIS 7146-2
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
Copyright notice
This ISO document is a Draft International Standard and is copyright-protected by ISO. Except as permitted
under the applicable laws of the user's country, neither this ISO draft nor any extract from it may be
reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying,
recording or otherwise, without prior written permission being secured.
Requests for permission to reproduce should be addressed to either ISO at the address below or ISO's
member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Reproduction may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
©
ii ISO 2006 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/DIS 7146-2
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Cavitation erosion .2
4.1 Mechanism of cavitation erosion.2
4.2 Classification of cavitation erosion.5
4.3 General countermeasures against cavitation erosion .5
5 Five types of cavitation erosion.7
5.1 General .7
5.2 Flow cavitation erosion.8
5.3 Impact cavitation erosion .10
5.4 Suction cavitation erosion .12
5.5 Discharge cavitation erosion .14
5.6 Miscellaneous cavitation erosion (see Figures 17 to 20).15

© ISO 2006 – All rights reserved iii

---------------------- Page: 4 ----------------------
ISO/DIS 7146-2
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the Inter-
national Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an Interna-
tional Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 7146-2 was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 2, Mate-
rials and lubricants, their properties, characteristics, test methods and testing conditions.
ISO 7146 consists of the following parts, under the general title Plain bearings — Fluid film metallic bearings
— Terms and characteristics of damage:
⎯ Part 1: General
⎯ Part 2: Cavitation erosion and its countermeasures
iv © ISO 2006 – All rights reserved

---------------------- Page: 5 ----------------------
ISO/DIS 7146-2
Introduction
In practice, damage to a bearing may often be the result of several mechanisms operating simultaneously.
The damage may result from improper assembly or maintenance or from faulty manufacture of the bearing, its
housing or the counterface against which it operates. In some instances, damage may be caused by a design
compromise made in the interests of economy or from unforeseen operating conditions. It is the complex
combination of design, manufacture, assembly, operation, maintenance and possible reconditioning which
often causes difficulty in establishing the primary cause of damage.
In the event of extensive damage or destruction of the bearing, the evidence is likely to be lost, and it will then
be impossible to identify how the damage came about.
In all cases, knowledge of the actual operating conditions of the assembly and the maintenance history is of
the utmost importance.
The classification of bearing damage established in this International Standard is based primarily upon the
features visible on the running surfaces and elsewhere, and consideration of each aspect is required for reli-
able determination of the cause of bearing damage.
Since more than one process may cause similar effects on the running surface, a description of appearance
alone is occasionally inadequate in determining the cause of damage. In such cases, the operating conditions
have to be considered.
Cavitation erosion dealt with in ISO 7146-1 is treated in this ISO 7146-2 in more details.


© ISO 2006 – All rights reserved v

---------------------- Page: 6 ----------------------
DRAFT INTERNATIONAL STANDARD ISO/DIS 7146-2

Fluid film metallic plain bearings — Description and
characterization of damage —
Part 2:
Cavitation erosion and its countermeasures
1 Scope
This part of ISO 7146 defines, describes and classifies the characteristics of damage occurring in service in
hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible counter-
measures. It will assist in understanding of the various characteristic damages which may occur.
For the purpose of this International Standard, the term “damage to plain bearings” or “bearing damage” in-
cludes all changes in appearance occurring on the bearing surface during operation that adversely affect the
performance of the bearing.
Consideration is restricted to damages which have a well-defined appearance and which can be attributed to
particular causes with a high degree of certainty. Various appearances are illustrated with photographs and
diagrams.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated refer-
ences, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO 4378-1:1997, Plain bearings — Terms, definitions and classification — Part 1: Design, bearing materials
and their properties
ISO 4378-2:1983, Plain bearings — Terms, definitions and classification — Part 2: Friction and wear
ISO 4378-3:1983, Plain bearings — Terms, definitions and classification — Part 3: Lubrication
ISO 7146-1:xxxx, Plain bearings — Fluid film metallic bearings — Terms and characteristics of damage —
Part 1: General
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4378-1, ISO 4378-2 and ISO 4378-3
apply.
© ISO 2006 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO/DIS 7146-2
4 Cavitation erosion
4.1 Mechanism of cavitation erosion
Cavitation erosion is a damage of surface of a solid body in liquid caused by implosion (violent inward col-
lapse) of cavities or vaporous bubbles. When the static pressure in the liquid is decreased under the vapor
pressure of the liquid at a given temperature, evaporation occurs and vaporous bubbles are generated in the
liquid. This phenomenon is called “cavitation”. When these cavities encounter higher pressure because they
have flowed to a place of higher pressure or the pressure at the place of cavitation has increased in the mean-
time, they condense instantaneously and implode, causing a very high and local pressure and high tempera-
ture in the liquid. It can lead, after repeated implosion, to a “cavitation erosion” on the surface of the solid body
near the place of implosion.

a) View at magnification: x 1
2 © ISO 2006 – All rights reserved

---------------------- Page: 8 ----------------------
ISO/DIS 7146-2

b) Cross-section at magnification: x 45 (etched)
Key
1 Sliding surface
2 Bearing metal (tin-based)
3 Bonding area
4 Steel backing
© ISO 2006 – All rights reserved 3

---------------------- Page: 9 ----------------------
ISO/DIS 7146-2

c) Cross-section at magnification: x 100 (unetched)
Key
1 Sliding surface
Figure 1 — Sliding surface with cavitation erosion
Because of high intensity of cavity implosion, chemical reaction “cavitation corrosion” can take place. The
damages may also occur together with “fluid erosion” and “cavitation corrosion” interacting each other. A phe-
nomenon called “Micro-Diesel-effect”, where the imploding cavities make lightning is also detected in the oil of
plain bearing.
When a bearing surface is attacked by cavitation erosion, the color of the surface changes first slightly by
roughening. Then small pores are formed and cracks are initiated on the surface, especially at grain bounda-
ries. These cracks with sharp edges are spread first on the surface and then deepen according to the proper-
ties of underlying material (see Figure 1). The cracks are joined together leading to break-out and wash-away
of small particles of bearing materials.
When the damage is caused solely by collapsing cavities, the attacked areas show a rough texture. Metallur-
gical section shows often signs of local work-hardening and fatigue cracking due to hammer blows caused by
cavity collapse. But if particles are trapped in the damage pockets, the surface can be eroded and exhibits
smooth and polished appearance. The place of cavitation erosion is usually limited locally and spreads sel-
dom to a broader region. The cavitation erosion usually appears in the unloaded areas of the bearing.
The occurrence of cavitation erosion depends on many factors as given in the following: journal speed, spe-
cific bearing load, dynam
...