ISO 6281:2007
(Main)Plain bearings — Testing under conditions of hydrodynamic and mixed lubrication in test rigs
Plain bearings — Testing under conditions of hydrodynamic and mixed lubrication in test rigs
ISO 6281:2007 establishes guidelines for the testing of lubricated plain journal bearings in test rigs, running under conditions of hydrodynamic or mixed lubrication, during bearing and/or material development. It deals with both static and dynamic loading in solid and multi‑layer journal bearings.
Gleitlager - Prüfung bei Vollschmierung und Mischreibung - Richtlinien
Paliers lisses — Essai des paliers lisses dans les conditions de lubrification hydrodynamique et mixte dans des machines d'essai pour paliers
Drsni ležaji - Preskušanje ležajev na preskuševališču pri hidrodinamičnem mazanju in mešanem trenju - Smernice
General Information
Relations
Buy Standard
Standards Content (Sample)
SLOVENSKI STANDARD
SIST ISO 6281:2008
01-julij-2008
1DGRPHãþD
SIST ISO/TR 6281:2002
'UVQLOHåDML3UHVNXãDQMHOHåDMHYQDSUHVNXãHYDOLãþXSULKLGURGLQDPLþQHP
PD]DQMXLQPHãDQHPWUHQMX6PHUQLFH
Plain bearings - Testing under conditions of hydrodynamic and mixed lubrication in test
rigs
Gleitlager - Prüfung bei Vollschmierung und Mischreibung - Richtlinien
Paliers lisses - Essai des paliers lisses dans les conditions de lubrification
hydrodynamique et mixte dans des machines d'essai pour paliers
Ta slovenski standard je istoveten z: ISO 6281:2007
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO 6281:2008 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
INTERNATIONAL ISO
STANDARD 6281
First edition
2007-06-15
Plain bearings — Testing under
conditions of hydrodynamic and mixed
lubrication in test rigs
Paliers lisses — Essai des paliers lisses dans les conditions de
lubrification hydrodynamique et mixte dans des machines d'essai pour
paliers
Reference number
ISO 6281:2007(E)
©
ISO 2007
---------------------- Page: 2 ----------------------
ISO 6281:2007(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 2007
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 2007 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 6281:2007(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Symbols . 1
3 Test objectives for bearing properties . 2
4 Test rigs . 3
5 Test procedures . 6
6 Testing and test report. 8
Bibliography . 15
© ISO 2007 – All rights reserved iii
---------------------- Page: 4 ----------------------
ISO 6281:2007(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 6281 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 6281 cancels and replaces ISO/TR 6281:1990, of which it constitutes a technical
revision.
iv © ISO 2007 – All rights reserved
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 6281:2007(E)
Plain bearings — Testing under conditions of hydrodynamic
and mixed lubrication in test rigs
1 Scope
This International Standard establishes guidelines for the testing of lubricated plain journal bearings in test rigs,
running under conditions of hydrodynamic or mixed lubrication, during bearing and/or material development. It
deals with both static and dynamic loading in solid and multi-layer journal bearings. It is not applicable to the
testing of dynamic characteristics of lubricant film in journal bearings applied in calculation of vibration and
stability of turbo-rotors. Further details of test procedures will need to be established when carrying out testing
based on these guidelines.
2 Symbols
See Table 1.
Table 1 — Symbols
Symbol Description Unit
a Length of period s
B Bearing width mm
F Bearing load N
F* Bearing load per unit bearing width N/mm
f Coefficient of friction of journal bearing —
t Time s
U Sliding velocity m/s
β Direction of bearing load °
ω Angular velocity rad/s
2
η Dynamic viscosity of lubricant N⋅s/m
© ISO 2007 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 6281:2007(E)
3 Test objectives for bearing properties
The test objectives for plain journal bearing test rigs operating under conditions of hydrodynamic or mixed
lubrication are to obtain information, among others, on the following bearing properties, which can serve as
critical variables when designing and applying the bearing (see ISO 4378):
a) running-in ability;
b) wear resistance;
c) compatibility between bearing and journal materials (resistance to adhesion);
d) embeddability (foreign particles absorption);
e) resistance to journal scoring and abrasion;
f) conformability;
g) deformability (compressive strength);
h) resistance to erosion (cavitation erosion, fluid erosion, particle erosion);
i) static load carrying capacity;
j) dynamic load carrying capacity (fatigue strength);
k) friction characteristics;
l) lubricant flow rate characteristics;
m) temperature increase characteristics.
Of these bearing properties, the first group, a) to h), depends primarily on the mechanical and tribological
properties of sliding materials under specified conditions. The second group, i) to m), depends primarily on
hydrodynamic variables, and therefore also on
⎯ viscosity as a function of temperature, pressure and shear rate,
⎯ energy dissipation in the lubricant film (shear heating and heat dissipation), and
⎯ elastic and thermal deformation of the bearing and journal, and hence change of lubricant film thickness
(thermo-elastohydrodynamic lubrication).
The determination of these bearing properties, or test objectives, requires lubrication conditions that can
involve boundary, mixed or hydrodynamic lubrication — the three modes of lubrication regime. In certain
cases, a repeated, time-dependent change between mixed and hydrodynamic lubrication can be required.
NOTE Specific test methods may not yet exist for all of the above-mentioned bearing properties.
Figure 1 depicts the typical relation between the dimensionless number, ηU/F*, and the coefficient, f, of friction
of the journal bearing, where η, U and F* denote dynamic viscosity of the lubricant, sliding velocity and
bearing load per unit bearing width (F* = F/B), respectively. It shows the three regimes of boundary, mixed
and hydrodynamic lubrication and qualitatively indicates the dependence between these important parameters.
2 © ISO 2007 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 6281:2007(E)
Key
1 boundary lubrication
2 mixed lubrication
3 hydrodynamic lubrication
Figure 1 — Three modes of lubrication regime
4 Test rigs
4.1 General recommendations
It is often more practical and efficient to investigate the bearing in a test rig than in an actual application. The
design of the bearing test rig should be such as to simulate as far as possible all the relevant characteristic
parameters (geometric, dynamic, hydrodynamic, thermal, thermodynamic, etc.) of the actual application.
In addition, the following is recommended for the test rig.
a) Simple mechanical construction.
b) Simple dismantling and assembly procedures for the test objects; with well-defined positioning of the
bearing and housing; preferably it should be possible to inspect the test bearing in situ. In addition, the
test rig should be equipped with an emergency stop mechanism, both for safety reasons and to allow the
inspection of the sliding surface before the onset of catastrophic damage.
c) Well-defined dimensions for the test bearing.
d) High dimensional stability with little shaft deflection. The test rig should be as rigid as possible, with a high
natural frequency. In special cases, however, it may be necessary to vary the dimensional stability or the
shaft deflection in order to simulate the operating condition of the actual application.
e) Appropriate lubricant supply condition. When the lubricant flow within the bearing clearance has to be
simulated exactly, the circumferential and axial position of the lubricant supply in the test rig should be the
same as in the actual application.
f) Well-defined and experimentally verifiable lubrication conditions.
g) The regime of laminar or turbulent flow should be the same in the test rig and in the actual application.
h) The rig should replicate as far as possible the temperature and stress range that can occur in practice.
i) Appropriate measuring techniques or equipment should be employed.
© ISO 2007 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 6281:2007(E)
4.2 Generic types of test rig
Generic types of test rig for plain journal bearings are shown in Figures 2 and 3. Figure 2 a) and b) depict the
rotational motion of the journal, where a combination of both is also possible. In practice, many more patterns
of journal motion other than rotation may occur, such as inclination, bending, axial, conical and their
combinations. In addition, the bearing itself can rotate or oscillate or even move in space instead of, or
together with, the journal, as with a crank-pin bearing. In any case, the relative motion of the journal to the
bearing has to be known (measurable) exactly. However, constant rotational speed of journal and the parallel
movement of journal to bearing are the simplest and most preferable for testing.
Figure 3 shows patterns of the bearing load. In the case of statically loaded journal bearing [Figure 3 a)], the
magnitude, F, and the direction, β, of the bearing load are constant. In a special case of dynamically loaded
bearing, F is constant, but β increases or decreases with time [Figure 3 b)]. In the general case of dynamically
loaded bearing [Figure 3 c)], both or at least one of F and β change periodically, while the remaining variable
can be constant. The periodic form of F (also β) is then arbitrary, such as sinusoidal with or without constant
offset, curving steeply up and downwards, as, for example, in engine bearing loading.
With regard to the loading of the test bearing, it is often more practical to load the test bearing directly
supported by the journal [Figure 4 a)], than to load the test bearing indirectly through the journal [Figure 4 b)].
For static loading, a dead weight system, with or without lever, or hydraulic or pneumatic actuation can be
used. For dynamic loading, a rotating or vibrating mass system, with or without lever, an electromagnetic
exciter, hydraulic actuation, etc., can be applied. Dynamic loading by means of a mass fixed to the journal
seems to be simple, but the amplitude of the bearing load is then determined primarily by the rotational speed
of the journal. Therefore, it is not easy to change the load amplitude independently of the rotational speed.
Furthermore, the magnitude and direction of the bearing load have to be precisely measured, and it is
important to let the journal move freely inside the bearing clearance without hindrance from the loading
mechanism.
Besides such bearing test rigs operating under hydrodynamic or mixed lubrication, as described above, many
other kinds of test apparatus and test methods may be used to investigate the tribological or mechanical
properties of bearing materials, including coefficient of friction, mechanical strength, hardness, elasticity,
plasticity and bond strength. The study of the tribological properties of boundary films has also led to the
development of other test apparatus and methods; these are, however, outside the scope of this International
Standard (see ISO 4384-1, ISO 4384-2, ISO 4385, ISO 7148-1, ISO 7148-2, ISO 7905-2, ISO 7905-3 and
ISO 7905-4).
NOTE The testing of the resistance to corrosion of bearing materials by the lubricant is the subject of ISO 10129.
a) Rotation b) Oscillation
Figure 2 — Rotational motion of journal
4 © ISO 2007 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 6281:2007(E)
a) Static load
b) Dynamic load (rotating load)
c) Dynamic load (arbitrary pattern)
Key
a length of period
F bearing load
β direction of bearing load
t time
ω angular velocity
Figure 3 — Examples of bearing load patterns
© ISO 2007 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 6281:2007(E)
a) Load on bearing b) Load on journal
Key
F bearing load
ω angular velocity
1 test bearing
2 journal
Figure 4 — Two modes of load application
5 Test procedures
The actual test procedure depends on the property to be determined. It is important to establish the test
conditions in order to ensure that test results obtained on test rigs are applicable in practice and that results
obtained on different test rigs are mutually compatible.
In the following, guidelines or examples of test procedures for obtaining the bearing properties according to
Clause 3, a) to m), are described together with the evaluation of the results. Bearing properties a) to h)
depend primarily on mechanical and tribological characteristics of the bearing material itself, and in some
cases, may be determined qualitatively by proper material testing. However, they can be evaluated
quantitatively only by testing in bearing test rig. When stepwise increase or decrease of bearing load or
severity of operating condition is prescribed, thermal equilibrium must be achieved in the test object at each
step to assure reproducibility of the results. During the test, it is important to be aware of the eventual change
of the test object itself, even under seemingly constant operating conditions, through wear, foreign particles
embedding, diffusion, chemical reaction, lubricant degradation, etc. This should be verified and documented in
the test report.
a) Running-in ability
1) 2)
The change of surface topography, roughness, friction torque, wear rate or wear intensity of the
bearing, or the temperature of the lubricant and/or bearing should be measured from the initial state of the
sliding surfaces under the specified operating condition. From the characteristic change of these variables
with time, the completion of running-in process can be detected. The shorter the time until running-in is
completed, the higher the running-in ability.
1) Ratio of wear extent to the time interval during which it has developed.
2) Ratio of wear extent to the specified distance on which wear developed or to the volume of the work done.
6 © ISO 2007 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 6281:2007(E)
b) Wear resistance
The severity of the operating condition of the bearing should be increased until wear occurs. Wear can be
mechanical or mechano-chemical in nature. The former can be adhesive wear, seizure, scoring or
scratching, abrasion, fatigue wear, spalling, cavitation wear, erosive wear or fretting wear. The latter can
be oxidative wear, fretting corrosion or electro-erosive wear. The more severe the operating condition
under which wear begins to occur and the smaller the wear rate and/or the wear intensity, the higher the
wear resistance.
c) Compatibility between bearing and journal material (resistance to adhesion)
The frictional torque and/or the temperature of the lubricant and bearing should be measured during the
stepwise increase in the severity of the operating condition (i.e. increase in inlet lubricant temperature,
specific bearing load, sliding velocity), and the occurrence of adhesion should be detected. The more
severe the operating condition under which the adhesion begins to occur, or the less the sliding surface
suffers adhesion damage, the higher the compatibility and the resistance to adhesion.
d) Embeddability (foreign particles absorption)
Foreign particles of known hard material (i.e. hardness, quantity and size) should be mixed with the
lubricant, and the quantity and depth to which the foreign particles have embedded into the bearing
surface in a specified time, together with the grade of damage of the journal surface, should be measured
under the specified operating condition. The larger the quantity and the greater the depth to which the
foreign particles have embedded, or the less the damage of the journal surface by the foreign particles,
the higher the embeddability.
e) Resistance to journal scoring and abrasion
The severity of the operating cond
...
INTERNATIONAL ISO
STANDARD 6281
First edition
2007-06-15
Plain bearings — Testing under
conditions of hydrodynamic and mixed
lubrication in test rigs
Paliers lisses — Essai des paliers lisses dans les conditions de
lubrification hydrodynamique et mixte dans des machines d'essai pour
paliers
Reference number
ISO 6281:2007(E)
©
ISO 2007
---------------------- Page: 1 ----------------------
ISO 6281:2007(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 2007
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 2007 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 6281:2007(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Symbols . 1
3 Test objectives for bearing properties . 2
4 Test rigs . 3
5 Test procedures . 6
6 Testing and test report. 8
Bibliography . 15
© ISO 2007 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 6281:2007(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 6281 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 6281 cancels and replaces ISO/TR 6281:1990, of which it constitutes a technical
revision.
iv © ISO 2007 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 6281:2007(E)
Plain bearings — Testing under conditions of hydrodynamic
and mixed lubrication in test rigs
1 Scope
This International Standard establishes guidelines for the testing of lubricated plain journal bearings in test rigs,
running under conditions of hydrodynamic or mixed lubrication, during bearing and/or material development. It
deals with both static and dynamic loading in solid and multi-layer journal bearings. It is not applicable to the
testing of dynamic characteristics of lubricant film in journal bearings applied in calculation of vibration and
stability of turbo-rotors. Further details of test procedures will need to be established when carrying out testing
based on these guidelines.
2 Symbols
See Table 1.
Table 1 — Symbols
Symbol Description Unit
a Length of period s
B Bearing width mm
F Bearing load N
F* Bearing load per unit bearing width N/mm
f Coefficient of friction of journal bearing —
t Time s
U Sliding velocity m/s
β Direction of bearing load °
ω Angular velocity rad/s
2
η Dynamic viscosity of lubricant N⋅s/m
© ISO 2007 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 6281:2007(E)
3 Test objectives for bearing properties
The test objectives for plain journal bearing test rigs operating under conditions of hydrodynamic or mixed
lubrication are to obtain information, among others, on the following bearing properties, which can serve as
critical variables when designing and applying the bearing (see ISO 4378):
a) running-in ability;
b) wear resistance;
c) compatibility between bearing and journal materials (resistance to adhesion);
d) embeddability (foreign particles absorption);
e) resistance to journal scoring and abrasion;
f) conformability;
g) deformability (compressive strength);
h) resistance to erosion (cavitation erosion, fluid erosion, particle erosion);
i) static load carrying capacity;
j) dynamic load carrying capacity (fatigue strength);
k) friction characteristics;
l) lubricant flow rate characteristics;
m) temperature increase characteristics.
Of these bearing properties, the first group, a) to h), depends primarily on the mechanical and tribological
properties of sliding materials under specified conditions. The second group, i) to m), depends primarily on
hydrodynamic variables, and therefore also on
⎯ viscosity as a function of temperature, pressure and shear rate,
⎯ energy dissipation in the lubricant film (shear heating and heat dissipation), and
⎯ elastic and thermal deformation of the bearing and journal, and hence change of lubricant film thickness
(thermo-elastohydrodynamic lubrication).
The determination of these bearing properties, or test objectives, requires lubrication conditions that can
involve boundary, mixed or hydrodynamic lubrication — the three modes of lubrication regime. In certain
cases, a repeated, time-dependent change between mixed and hydrodynamic lubrication can be required.
NOTE Specific test methods may not yet exist for all of the above-mentioned bearing properties.
Figure 1 depicts the typical relation between the dimensionless number, ηU/F*, and the coefficient, f, of friction
of the journal bearing, where η, U and F* denote dynamic viscosity of the lubricant, sliding velocity and
bearing load per unit bearing width (F* = F/B), respectively. It shows the three regimes of boundary, mixed
and hydrodynamic lubrication and qualitatively indicates the dependence between these important parameters.
2 © ISO 2007 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 6281:2007(E)
Key
1 boundary lubrication
2 mixed lubrication
3 hydrodynamic lubrication
Figure 1 — Three modes of lubrication regime
4 Test rigs
4.1 General recommendations
It is often more practical and efficient to investigate the bearing in a test rig than in an actual application. The
design of the bearing test rig should be such as to simulate as far as possible all the relevant characteristic
parameters (geometric, dynamic, hydrodynamic, thermal, thermodynamic, etc.) of the actual application.
In addition, the following is recommended for the test rig.
a) Simple mechanical construction.
b) Simple dismantling and assembly procedures for the test objects; with well-defined positioning of the
bearing and housing; preferably it should be possible to inspect the test bearing in situ. In addition, the
test rig should be equipped with an emergency stop mechanism, both for safety reasons and to allow the
inspection of the sliding surface before the onset of catastrophic damage.
c) Well-defined dimensions for the test bearing.
d) High dimensional stability with little shaft deflection. The test rig should be as rigid as possible, with a high
natural frequency. In special cases, however, it may be necessary to vary the dimensional stability or the
shaft deflection in order to simulate the operating condition of the actual application.
e) Appropriate lubricant supply condition. When the lubricant flow within the bearing clearance has to be
simulated exactly, the circumferential and axial position of the lubricant supply in the test rig should be the
same as in the actual application.
f) Well-defined and experimentally verifiable lubrication conditions.
g) The regime of laminar or turbulent flow should be the same in the test rig and in the actual application.
h) The rig should replicate as far as possible the temperature and stress range that can occur in practice.
i) Appropriate measuring techniques or equipment should be employed.
© ISO 2007 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 6281:2007(E)
4.2 Generic types of test rig
Generic types of test rig for plain journal bearings are shown in Figures 2 and 3. Figure 2 a) and b) depict the
rotational motion of the journal, where a combination of both is also possible. In practice, many more patterns
of journal motion other than rotation may occur, such as inclination, bending, axial, conical and their
combinations. In addition, the bearing itself can rotate or oscillate or even move in space instead of, or
together with, the journal, as with a crank-pin bearing. In any case, the relative motion of the journal to the
bearing has to be known (measurable) exactly. However, constant rotational speed of journal and the parallel
movement of journal to bearing are the simplest and most preferable for testing.
Figure 3 shows patterns of the bearing load. In the case of statically loaded journal bearing [Figure 3 a)], the
magnitude, F, and the direction, β, of the bearing load are constant. In a special case of dynamically loaded
bearing, F is constant, but β increases or decreases with time [Figure 3 b)]. In the general case of dynamically
loaded bearing [Figure 3 c)], both or at least one of F and β change periodically, while the remaining variable
can be constant. The periodic form of F (also β) is then arbitrary, such as sinusoidal with or without constant
offset, curving steeply up and downwards, as, for example, in engine bearing loading.
With regard to the loading of the test bearing, it is often more practical to load the test bearing directly
supported by the journal [Figure 4 a)], than to load the test bearing indirectly through the journal [Figure 4 b)].
For static loading, a dead weight system, with or without lever, or hydraulic or pneumatic actuation can be
used. For dynamic loading, a rotating or vibrating mass system, with or without lever, an electromagnetic
exciter, hydraulic actuation, etc., can be applied. Dynamic loading by means of a mass fixed to the journal
seems to be simple, but the amplitude of the bearing load is then determined primarily by the rotational speed
of the journal. Therefore, it is not easy to change the load amplitude independently of the rotational speed.
Furthermore, the magnitude and direction of the bearing load have to be precisely measured, and it is
important to let the journal move freely inside the bearing clearance without hindrance from the loading
mechanism.
Besides such bearing test rigs operating under hydrodynamic or mixed lubrication, as described above, many
other kinds of test apparatus and test methods may be used to investigate the tribological or mechanical
properties of bearing materials, including coefficient of friction, mechanical strength, hardness, elasticity,
plasticity and bond strength. The study of the tribological properties of boundary films has also led to the
development of other test apparatus and methods; these are, however, outside the scope of this International
Standard (see ISO 4384-1, ISO 4384-2, ISO 4385, ISO 7148-1, ISO 7148-2, ISO 7905-2, ISO 7905-3 and
ISO 7905-4).
NOTE The testing of the resistance to corrosion of bearing materials by the lubricant is the subject of ISO 10129.
a) Rotation b) Oscillation
Figure 2 — Rotational motion of journal
4 © ISO 2007 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 6281:2007(E)
a) Static load
b) Dynamic load (rotating load)
c) Dynamic load (arbitrary pattern)
Key
a length of period
F bearing load
β direction of bearing load
t time
ω angular velocity
Figure 3 — Examples of bearing load patterns
© ISO 2007 – All rights reserved 5
---------------------- Page: 9 ----------------------
ISO 6281:2007(E)
a) Load on bearing b) Load on journal
Key
F bearing load
ω angular velocity
1 test bearing
2 journal
Figure 4 — Two modes of load application
5 Test procedures
The actual test procedure depends on the property to be determined. It is important to establish the test
conditions in order to ensure that test results obtained on test rigs are applicable in practice and that results
obtained on different test rigs are mutually compatible.
In the following, guidelines or examples of test procedures for obtaining the bearing properties according to
Clause 3, a) to m), are described together with the evaluation of the results. Bearing properties a) to h)
depend primarily on mechanical and tribological characteristics of the bearing material itself, and in some
cases, may be determined qualitatively by proper material testing. However, they can be evaluated
quantitatively only by testing in bearing test rig. When stepwise increase or decrease of bearing load or
severity of operating condition is prescribed, thermal equilibrium must be achieved in the test object at each
step to assure reproducibility of the results. During the test, it is important to be aware of the eventual change
of the test object itself, even under seemingly constant operating conditions, through wear, foreign particles
embedding, diffusion, chemical reaction, lubricant degradation, etc. This should be verified and documented in
the test report.
a) Running-in ability
1) 2)
The change of surface topography, roughness, friction torque, wear rate or wear intensity of the
bearing, or the temperature of the lubricant and/or bearing should be measured from the initial state of the
sliding surfaces under the specified operating condition. From the characteristic change of these variables
with time, the completion of running-in process can be detected. The shorter the time until running-in is
completed, the higher the running-in ability.
1) Ratio of wear extent to the time interval during which it has developed.
2) Ratio of wear extent to the specified distance on which wear developed or to the volume of the work done.
6 © ISO 2007 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 6281:2007(E)
b) Wear resistance
The severity of the operating condition of the bearing should be increased until wear occurs. Wear can be
mechanical or mechano-chemical in nature. The former can be adhesive wear, seizure, scoring or
scratching, abrasion, fatigue wear, spalling, cavitation wear, erosive wear or fretting wear. The latter can
be oxidative wear, fretting corrosion or electro-erosive wear. The more severe the operating condition
under which wear begins to occur and the smaller the wear rate and/or the wear intensity, the higher the
wear resistance.
c) Compatibility between bearing and journal material (resistance to adhesion)
The frictional torque and/or the temperature of the lubricant and bearing should be measured during the
stepwise increase in the severity of the operating condition (i.e. increase in inlet lubricant temperature,
specific bearing load, sliding velocity), and the occurrence of adhesion should be detected. The more
severe the operating condition under which the adhesion begins to occur, or the less the sliding surface
suffers adhesion damage, the higher the compatibility and the resistance to adhesion.
d) Embeddability (foreign particles absorption)
Foreign particles of known hard material (i.e. hardness, quantity and size) should be mixed with the
lubricant, and the quantity and depth to which the foreign particles have embedded into the bearing
surface in a specified time, together with the grade of damage of the journal surface, should be measured
under the specified operating condition. The larger the quantity and the greater the depth to which the
foreign particles have embedded, or the less the damage of the journal surface by the foreign particles,
the higher the embeddability.
e) Resistance to journal scoring and abrasion
The severity of the operating condition of the bearing should be increased stepwise and the occurrence of
the journal scoring (severe scratches) or abrasion verified. The more severe the operating condition
under which the damage begins to occur, and the less the scoring and abrasion caused to the journal (or
the smaller the wear rate and the wear intensity), the higher the resistance to journal scoring and
abrasion.
f) Conformability
The bearing load should be increased stepwise under a specifi
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