SIST ISO 7148-2:2015
Plain bearings - Testing of the tribological behaviour of bearing materials - Part 2: Testing of polymer-based bearing materials
Plain bearings - Testing of the tribological behaviour of bearing materials - Part 2: Testing of polymer-based bearing materials
This part of ISO 7148 specifies tribological tests of polymer-based plain bearing materials under
specified working conditions, i.e. load, sliding velocity and temperature, with and without lubrication.
From the test results, data are obtained which indicate the relative tribological behaviour of metalpolymer
and polymer-polymer rubbing parts.
The purpose of this part of ISO 7148 is to obtain, for polymer material combinations used in plain
bearings, reproducible measured values for friction and wear under specified and exactly-defined test
conditions without lubrication (dry surfaces) and with lubrication (boundary lubrication).
The test results give useful information for practical application only if all parameters of influence are
identical. The more the test conditions deviate from the actual application, the greater the uncertainty
of the applicability of the results.
Paliers lisses - Essai du comportement tribologique des matériaux antifriction - Partie 2: Essai des matériaux pour paliers à base de polymère
Drsni ležaji - Preskušanje materialov za drsne ležaje glede na tribološke lastnosti - 2. del: Preskušanje materialov za ležaje na osnovi polimerov
Ta del standarda ISO 7148 določa preskuse za materiale za ležaje na osnovi polimerov glede na tribološke lastnosti pod določenimi delovnimi pogoji, t. j. obremenitev, drsna hitrost in temperatura, z mazanjem ali brez. Preskusni rezultati zagotavljajo podatke, ki kažejo relativne tribološke lastnosti delov kovina-polimer in polimer-polimer, ki so izpostavljeni drgnjenju.
Namen tega dela standarda ISO 7148 je pridobiti ponovljive izmerjene vrednosti trenja in obrabe kombinacij polimernih materialov pod določenimi in natančno opredeljenimi preskusnimi pogoji brez mazanja (suhe površine) in z mazanjem (mejno mazanje). Preskusni rezultati zagotavljajo uporabne informacije za praktično uporabo samo, če so vsi parametri vpliva enaki. Bolj kot preskusni pogoji odstopajo od dejanske uporabe, večja je negotovost uporabnosti rezultatov.
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INTERNATIONAL ISO
STANDARD 7148-2
Second edition
2012-10-01
Plain bearings — Testing of the
tribological behaviour of bearing
materials —
Part 2:
Testing of polymer-based bearing
materials
Paliers lisses — Essai du comportement tribologique des matériaux
antifriction —
Partie 2: Essai des matériaux pour paliers à base de polymère
Reference number
ISO 7148-2:2012(E)
©
ISO 2012
---------------------- Page: 1 ----------------------
ISO 7148-2:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012
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 2012 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 7148-2:2012(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Symbols, units and abbreviated terms . 1
4 Special features for the tribological testing of polymer-based materials .2
5 Test methods . 5
5.1 General . 5
5.2 Test method A — Pin-on-disc . 5
5.3 Test method B — Block (or pin)-on-ring. 6
5.4 Test method C — Plain bearing-on-shaft . 7
5.5 Test method D — Sphere-on-prism . 7
5.6 Test method E — Rotation under thrust load . 8
6 Test specimens. 9
6.1 Data required. 9
6.2 Polymer-based plain bearing materials (pl). 9
6.3 Materials of mating component . 9
6.4 Dimensions of test specimens . 9
6.5 Preparation of the test specimens .14
7 Test methods and test equipment .15
7.1 General .15
7.2 Test method A — Pin-on-disc .15
7.3 Test method B — Block-on-ring .16
7.4 Test method C — Plain bearing-on-shaft .16
7.5 Test method D — Sphere-on-prism .16
7.6 Test method E — Rotation under thrust load .17
8 Lubrication .17
8.1 General .17
8.2 Dry (dr) .18
8.3 Grease (gr) .18
8.4 Oil (oi) .18
8.5 Solid lubricant (so) .18
9 Designation .18
10 Test conditions .18
10.1 Environmental conditions .18
10.2 Mounting of the test specimens .19
10.3 Test variables .19
11 Test procedure .21
11.1 Running-in .21
11.2 Carrying out the tests .21
12 Analysis .21
12.1 General .21
12.2 Test results.22
Annex A (informative) Test report .23
Bibliography .25
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ISO 7148-2:2012(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 7148-2 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 second edition cancels and replaces the first edition (ISO 7148-2:1999), which has been
technically revised.
ISO 7148 consists of the following parts, under the general title Plain bearings — Testing of the tribological
behaviour of bearing materials:
— Part 1: Testing of bearing metals
— Part 2: Testing of polymer-based bearing materials
iv © ISO 2012 – All rights reserved
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INTERNATIONAL STANDARD ISO 7148-2:2012(E)
Plain bearings — Testing of the tribological behaviour of
bearing materials —
Part 2:
Testing of polymer-based bearing materials
1 Scope
This part of ISO 7148 specifies tribological tests of polymer-based plain bearing materials under
specified working conditions, i.e. load, sliding velocity and temperature, with and without lubrication.
From the test results, data are obtained which indicate the relative tribological behaviour of metal-
polymer and polymer-polymer rubbing parts.
The purpose of this part of ISO 7148 is to obtain, for polymer material combinations used in plain
bearings, reproducible measured values for friction and wear under specified and exactly-defined test
conditions without lubrication (dry surfaces) and with lubrication (boundary lubrication).
The test results give useful information for practical application only if all parameters of influence are
identical. The more the test conditions deviate from the actual application, the greater the uncertainty
of the applicability of the results.
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 527-2, Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and
extrusion plastics
ISO 527-3, Plastics — Determination of tensile properties — Part 3: Test conditions for films and sheets
ISO 2818, Plastics — Preparation of test specimens by machining
ISO 4385, Plain bearings — Compression testing of metallic bearing materials
ISO 6691, Thermoplastic polymers for plain bearings — Classification and designation
3 Symbols, units and abbreviated terms
See Table 1.
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ISO 7148-2:2012(E)
Table 1 — Symbols, units and abbreviated terms
Symbol Term Unit
A, B, C, D, E Test method -
a Sliding distance km
dr Dry -
Coefficient of friction; ratio between friction force and normal force, i.e.:
F
f
f -
f =
F
n
F Friction force N
f
F Normal force N
n
gr Grease
Coefficient of wear, volumetric wear rate related to the normal force, i.e.:
V w
w v 3
K mm /(N·km)
w
K = =
w
F ×a F
n n
l Linear wear as measured by change in distance mm
w
M Friction moment Nm
f
oi Oil -
p 2
Specific force per unit area (force/projected contact area) N/mm
2
R Compression strength N/mm
d,B
2
R Compression limit 0,2 % N/mm
d0,2
so Solid lubricant
Specimen’s temperature near the sliding surface during testing under steady-
T °C
state conditions
T Ambient temperature °C
amb
T Glass transition temperature °C
g
T Maximum permissible temperature °C
lim
t Test duration h
Ch
U Sliding velocity m/s
3
V Material removed by wear as measured by change in volume mm
W
l
w
Linear wear rate, i.e.; w =
w mm/km
l
l
a
V
w
3
Volumetric wear rate, i.e.: w =
w mm /km
v
v
a
η Lubricant viscosity mPa·s
4 Special features for the tribological testing of polymer-based materials
Polymers have a low thermal conductivity and a low melting temperature, so that heat resulting from
contact friction may lead to partial melting and hence feign wear. Due to the high thermal expansion
of polymers (up to 10 times higher than that of steel) results obtained can be misleading because the
test specimens have expanded under frictional heat. Hence allowance shall be made for the effects of
thermal expansion (change of clearance) and thermal conductivity (melting) when assessing the results.
Where possible the temperature of both test specimens should be controlled.
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ISO 7148-2:2012(E)
Polymers have a glass transition temperature, T , which depends on their chemical structure. At this
g
temperature, their physical properties and their tribological behaviour may change.
Injection-moulded polymer surfaces have different properties from machined surfaces. The test
specimens shall be tested with the same surface conditions as they have in practical application.
Reinforcements and fillers, i.e. fibres, may lead to very strong anisotropy of the material and influence
its wear behaviour depending on fibre orientation. The test specimens should have the same fibre
orientation as in practical application.
In order to avoid stick-slip, the test rig shall be very stiff and shall not be susceptible to vibrations.
The tribological behaviour of polymers depends very strongly on the material combination, which part
moves and which part remains stationary. The test system shall be similar to practical application.
Polymers show wear processes that are different from that of metals. There are not only abrasive
processes with powder-like wear debris, but also adhesive processes with the creation of transfer layers
which may be smooth or rough. Also ploughing wear and melting or plastic deformation is possible.
Therefore, wear cannot be gravimetrically measured in all cases and the wear status shall be judged
after the tests (whether the surfaces are fine- or coarse- grained, scored or plucked out, scaled, melted
or plastically deformed).
Some polymers may show poor repeatability of the results and require repeated testing (i.e. six or more
repetitions).
The preparation and preparatory treatment (e.g. conditioning, storage, cleaning) of the test specimens
can have a high influence on performance.
In some thermoplastics, e.g. polyamides, moisture absorption effects a gradual change in linear
dimensions and modifies their mechanical properties. Environmental parameters should, therefore, be
controlled in the test array. Moisture absorption prohibits gravimetrical measurement of wear.
The more the test conditions deviate from the actual application, the greater is the uncertainty of the
applicability of the results (see Figures 1 and 2).
a) Plain bearing-on-shaft
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ISO 7148-2:2012(E)
b) Linear guidance system
Figure 1 — Simulation of real rubbing contacts
a) Pin-on-disc
b) Block-on-ring
c) Sphere-on-prism
4 © ISO 2012 – All rights reserved
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ISO 7148-2:2012(E)
d) Rotation under thrust load — Sleeve-to-sleeve
e) Rotation under thrust load — Sleeve-to-plate
Figure 2 — Simulation under approximated practical testing conditions and model systems
5 Test methods
5.1 General
Different test methods are provided for tests in accordance with this part of ISO 7148 so that the following
contact geometries are available. The test methods should correspond to the practical application as
closely as possible.
5.2 Test method A — Pin-on-disc
See Figure 3.
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ISO 7148-2:2012(E)
Advantages:
— basic testing of simple test specimens;
— testing of tribological properties;
— no increase of sliding surface area due to wear;
— initial ranking of materials;
— simulation of linear guidance system [see Figure 1b)].
Disadvantages:
— edge of the pin might wipe off lubricant;
— no injection moulding of the pin with fibre reinforced material;
— no injection moulding of the disc because of problems with shrinkage.
Figure 3 — Test method A — Pin-on-disc
5.3 Test method B — Block (or pin)-on-ring
See Figure 4.
Advantages:
— basic testing of simple test specimens;
— testing of tribological properties;
— no increase of sliding surface area due to wear;
— initial ranking of materials;
— with and without lubrication.
Disadvantages:
— no injection moulding of the block because of problems with shrinkage and fibre orientation;
— edge of the block might wipe off lubricant;
— no injection moulding of the disc because of problems with shrinkage.
Figure 4 — Test method B — Block (or pin)-on-ring
6 © ISO 2012 – All rights reserved
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ISO 7148-2:2012(E)
5.4 Test method C — Plain bearing-on-shaft
See Figure 5.
Advantages:
— best simulation of all possible systems;
— testing of original or scaled bearings;
— prediction of practical behaviour;
— with and without lubrication.
Disadvantages:
— long testing time (accelerated testing might cause excessive frictional heating);
— difficult alignment of the test bearing;
— increasing sliding surface area due to wear under boundary lubrication.
Figure 5 — Test method C — Plain bearing-on-shaft
5.5 Test method D — Sphere-on-prism
See Figure 6.
Advantages:
— testing of polymer/polymer or polymer/metal combinations;
— with and without lubrication (test specimen contains reservoir for lubricant);
— testing of lubricant’s interaction with polymers;
— injection-moulded test specimens available;
— self-adjustment of the alignment of the sliding couple;
— increasing sliding surface area due to wear under boundary lubrication.
Disadvantages:
— plastic deformation might affect results;
— increasing sliding surface area due to wear under dry conditions.
Figure 6 — Test method D — Sphere-on-prism
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ISO 7148-2:2012(E)
5.6 Test method E — Rotation under thrust load
See Figure 7.
a) E1 — Sleeve-to-sleeve
b) E2 — Sleeve-to-plate
Figure 7 — Rotation under thrust load
Advantages:
— basic testing of simple specimens;
— injection-moulded test specimens available;
— testing of tribological properties;
— initial ranking of material;
— no increase of sliding surface area due to wear;
— continuous sliding between specimens;
— with and without lubrication.
Disadvantages:
— plastic deformation affects results;
— shrinkage at sliding surface on injection-moulded specimens affects results.
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ISO 7148-2:2012(E)
6 Test specimens
6.1 Data required
For one series of tests, several specimens of one material shall be from the same batch, with uniform
state after conditioning and uniform finish of the sliding surface. Machined and injection-moulded
specimens may create different results because crystallinity can vary with depth from the surface. They
should be tested separately.
As the structural condition of the mating materials constitutes an essential factor as far as the
repeatability of the test results is concerned, the following information is necessary:
a) material specification and composition, including fillers or details of fibre reinforcement (as
specified in ISO 6691);
b) method of manufacture;
c) structure, e.g. density, degree of crystallinity;
d) mechanical material properties, e.g. Shore hardness, 0,2 % compression limit, R (as specified in
d0,2
ISO 4385), compression strength, R ;
d,B
e) state of conditioning, e.g. moisture content;
f) surface condition and surface roughness, Ra, e.g. injection-moulded, machined (as specified in
ISO 2818), turned, ground, lapped, polished, milled.
6.2 Polymer-based plain bearing materials (pl)
These may be made by moulding, injection moulding or by cutting bar or tube to length or by machining all
over from semi-finished materials or by cutting from injection-moulded or laminated (composite) plates.
If fibre-reinforced polymers are to be tested, the fibres shall lie in the same direction in the test as in the
final product, e.g. parallel or perpendicular to the sliding surface.
6.3 Materials of mating component
All metallic and polymer-based materials may be considered as mating materials. The choice should be
the same as in practical application. In technical applications, all systems are possible, e.g. gear box of
aluminium with injection-moulded gears and shafts of polyoxymethylene (POM). The mating materials
shall have the same sliding couple, e.g. rotating POM disc or ball on fixed pin or prism out of aluminium.
In this case, the reverse combination POM pin on aluminium disc leads to errors in evaluation.
6.4 Dimensions of test specimens
6.4.1 General
If dimensions other than those described as follows are used, the results might not be comparable due
to the effects of transfer films and heat dissipation.
6.4.2 Disc
The disc shall have the following preferred dimensions:
— outside diameter: 110 mm;
— inside diameter: 60 mm;
— radius of the sliding track: (51,5 ± 0,2) mm;
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ISO 7148-2:2012(E)
— width: 10 mm.
The basic form of the disc is identical to the ring of deep groove ball thrust bearings on the shaft side.
6.4.3 Ring
The ring shall preferably have an outside diameter of 40 mm and a width corresponding at least to the
width of the block.
6.4.4 Pin
The pin shall preferably have a diameter of 3 mm for injection-moulded materials. For fibre-reinforced
materials, a larger diameter is preferred.
If a pin with a diameter greater than 7 mm is used, the radius of the sliding track has to be reduced or
the disc diameter increased. Means shall be provided for preventing rotation of the pin.
The free length of the pin shall not exceed 2 mm. Due to its dimensions, it is possible to make the 3 mm
diameter polymer pin out of a standard tension bar in accordance with ISO 527-3 or ISO 527-2. This
allows the correlation of wear and strength tests.
6.4.5 Block
The preferred basic dimensions of the block should be 10 mm × 10 mm × 20 mm. If a suitably large
component is not available, the block may, as an exception, be used with a length of 10 mm. The roughness
of the block depends on the machining conditions, e.g. milling or turning. The radius of the rubbing surface
of the block should be a minimum of 1,001 times the radius of the ring. If the maximum radius exceeds
1,003 times the radius of the ring (line contact), the running-in period can be unduly prolonged (see 11.1).
6.4.6 Sphere
The sphere shall preferably have a diameter of 12,7 mm. Thermoplastics may be injection-moulded (see
Figure 8). Spheres made out of metals are commercially available (balls for ball bearings or valves).
10 © ISO 2012 – All rights reserved
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ISO 7148-2:2012(E)
Dimensions in millimetres
Key
1 six-flat mount with cylindrical hole
2 gate position
Figure 8 — Example of an injection-moulded sphere
6.4.7 Prism
The prism has a preferred special shape. If injection-moulded, the prism specimen shall have a uniform
wall thickness (2 mm) and metallic support (see Figure 9) in order to avoid deformation. Alternatively,
cut plates may be fitted into a special mount (see Figure 10).
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ISO 7148-2:2012(E)
Dimensions in millimetres
Key
1 metal stiffening
2 gate position
Figure 9 — Example of an injection-moulded prism
Key
1 metal holder
2 machined plate
Figure 10 — Example of machined plates, inserted in a metallic holder
12 © ISO 2012 – All rights reserved
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ISO 7148-2:2012(E)
6.4.8 Plain bearing
The plain bearing bush may be made by machining or by injection moulding. Depending on the test
equipment used, it is possible to use plain bearings with different inside diameters, the preferred inside
diameters being 20 mm, 5 mm or 1 mm, the latter being used for special applications, the width/diameter
ratio being 0,75 or 1.
The diameter, bearing clearance, wall thickness and type of bearing used (bush or half bearing) shall be
indicated in the test report. Smaller plain bearings should have a flange in order to allow to fix them in the
mount (see Figure 11). The sliding surface area shall lie within the cylindrical part of the plain bearing.
Key
1 flange
2 sliding surface
Figure 11 — Example of an injection-moulded plain bearing with step and chamfer in the bore
6.4.9 Shaft
The shaft piece used for the test shall be made with a circular run-out tolerance 1 μm maximum and a
circularity of not more than 5 μm. Irrespective of the test equipment used, it shall be ensured that the
test specimens (test bush and shaft) mounted in the test equipment have a maximum angular deviation
of 0,05° prior to the test and in the absence of a normal force. The diameter of the shaft (i.e. the bearing
clearance) shall be sufficient to allow for thermal expansion of the bush (risk of bore closure leading
to seizure) and depends on the wall thickness, temperature of operation and material properties. The
(cold) diametral clearance may vary from 0,003 times to 0,01 times the shaft diameter, being kept as
small as possible consistent with avoiding seizure.
6.4.10 Sleeve
The sleeve may be made by machining or injection moulding. The preferred basic dimensions of the
sleeve are shown in Figure 12.
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ISO 7148-2:2012(E)
Dimensions in millimetres
Figure 12 — Dimensions of sleeve
6.4.11 Plate
The plate may be made by machining or injection moulding. The preferred basic dimensions of the sleeve
are shown in Figure 13.
Dimensions in millimetres
t = 2 to 5
Figure 13 — Dimensions of plate
6.5 Preparation of the test specimens
The preparation applies to bearing materials and mating materials.
Immediately prior to the test, a cleaning procedure shall be carried out in order to avoid influences on
the sliding behaviour which can result from remainders of the cutting solutions and other substances
that could possibly have been used in the manufacture of the test specimens.
After the cleaning procedure has been completed, the test specimens shall not be touched on the sliding
surfaces, which are to be in contact with each other, neither by hand nor with any tool.
14 © ISO 2012 – All rights reserved
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ISO 7148-2:2012(E)
The following cleaning procedures shall be carried out.
— Brush loose particles from the test s
...
SLOVENSKI STANDARD
SIST ISO 7148-2:2015
01-marec-2015
1DGRPHãþD
SIST ISO 7148-2:2002
Drsni ležaji - Preskušanje materialov za drsne ležaje glede na tribološke lastnosti -
2. del: Preskušanje materialov za ležaje na osnovi polimerov
Plain bearings - Testing of the tribological behaviour of bearing materials - Part 2:
Testing of polymer-based bearing materials
Paliers lisses - Essai du comportement tribologique des matériaux antifriction - Partie 2:
Essai des matériaux pour paliers à base de polymère
Ta slovenski standard je istoveten z: ISO 7148-2:2012
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO 7148-2:2015 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 7148-2:2015
---------------------- Page: 2 ----------------------
SIST ISO 7148-2:2015
INTERNATIONAL ISO
STANDARD 7148-2
Second edition
2012-10-01
Plain bearings — Testing of the
tribological behaviour of bearing
materials —
Part 2:
Testing of polymer-based bearing
materials
Paliers lisses — Essai du comportement tribologique des matériaux
antifriction —
Partie 2: Essai des matériaux pour paliers à base de polymère
Reference number
ISO 7148-2:2012(E)
©
ISO 2012
---------------------- Page: 3 ----------------------
SIST ISO 7148-2:2015
ISO 7148-2:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012
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 2012 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 7148-2:2015
ISO 7148-2:2012(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Symbols, units and abbreviated terms . 1
4 Special features for the tribological testing of polymer-based materials .2
5 Test methods . 5
5.1 General . 5
5.2 Test method A — Pin-on-disc . 5
5.3 Test method B — Block (or pin)-on-ring. 6
5.4 Test method C — Plain bearing-on-shaft . 7
5.5 Test method D — Sphere-on-prism . 7
5.6 Test method E — Rotation under thrust load . 8
6 Test specimens. 9
6.1 Data required. 9
6.2 Polymer-based plain bearing materials (pl). 9
6.3 Materials of mating component . 9
6.4 Dimensions of test specimens . 9
6.5 Preparation of the test specimens .14
7 Test methods and test equipment .15
7.1 General .15
7.2 Test method A — Pin-on-disc .15
7.3 Test method B — Block-on-ring .16
7.4 Test method C — Plain bearing-on-shaft .16
7.5 Test method D — Sphere-on-prism .16
7.6 Test method E — Rotation under thrust load .17
8 Lubrication .17
8.1 General .17
8.2 Dry (dr) .18
8.3 Grease (gr) .18
8.4 Oil (oi) .18
8.5 Solid lubricant (so) .18
9 Designation .18
10 Test conditions .18
10.1 Environmental conditions .18
10.2 Mounting of the test specimens .19
10.3 Test variables .19
11 Test procedure .21
11.1 Running-in .21
11.2 Carrying out the tests .21
12 Analysis .21
12.1 General .21
12.2 Test results.22
Annex A (informative) Test report .23
Bibliography .25
© ISO 2012 – All rights reserved iii
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SIST ISO 7148-2:2015
ISO 7148-2:2012(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 7148-2 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 second edition cancels and replaces the first edition (ISO 7148-2:1999), which has been
technically revised.
ISO 7148 consists of the following parts, under the general title Plain bearings — Testing of the tribological
behaviour of bearing materials:
— Part 1: Testing of bearing metals
— Part 2: Testing of polymer-based bearing materials
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SIST ISO 7148-2:2015
INTERNATIONAL STANDARD ISO 7148-2:2012(E)
Plain bearings — Testing of the tribological behaviour of
bearing materials —
Part 2:
Testing of polymer-based bearing materials
1 Scope
This part of ISO 7148 specifies tribological tests of polymer-based plain bearing materials under
specified working conditions, i.e. load, sliding velocity and temperature, with and without lubrication.
From the test results, data are obtained which indicate the relative tribological behaviour of metal-
polymer and polymer-polymer rubbing parts.
The purpose of this part of ISO 7148 is to obtain, for polymer material combinations used in plain
bearings, reproducible measured values for friction and wear under specified and exactly-defined test
conditions without lubrication (dry surfaces) and with lubrication (boundary lubrication).
The test results give useful information for practical application only if all parameters of influence are
identical. The more the test conditions deviate from the actual application, the greater the uncertainty
of the applicability of the results.
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 527-2, Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and
extrusion plastics
ISO 527-3, Plastics — Determination of tensile properties — Part 3: Test conditions for films and sheets
ISO 2818, Plastics — Preparation of test specimens by machining
ISO 4385, Plain bearings — Compression testing of metallic bearing materials
ISO 6691, Thermoplastic polymers for plain bearings — Classification and designation
3 Symbols, units and abbreviated terms
See Table 1.
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Table 1 — Symbols, units and abbreviated terms
Symbol Term Unit
A, B, C, D, E Test method -
a Sliding distance km
dr Dry -
Coefficient of friction; ratio between friction force and normal force, i.e.:
F
f
f -
f =
F
n
F Friction force N
f
F Normal force N
n
gr Grease
Coefficient of wear, volumetric wear rate related to the normal force, i.e.:
V w
w v 3
K mm /(N·km)
w
K = =
w
F ×a F
n n
l Linear wear as measured by change in distance mm
w
M Friction moment Nm
f
oi Oil -
p 2
Specific force per unit area (force/projected contact area) N/mm
2
R Compression strength N/mm
d,B
2
R Compression limit 0,2 % N/mm
d0,2
so Solid lubricant
Specimen’s temperature near the sliding surface during testing under steady-
T °C
state conditions
T Ambient temperature °C
amb
T Glass transition temperature °C
g
T Maximum permissible temperature °C
lim
t Test duration h
Ch
U Sliding velocity m/s
3
V Material removed by wear as measured by change in volume mm
W
l
w
Linear wear rate, i.e.; w =
w mm/km
l
l
a
V
w
3
Volumetric wear rate, i.e.: w =
w mm /km
v
v
a
η Lubricant viscosity mPa·s
4 Special features for the tribological testing of polymer-based materials
Polymers have a low thermal conductivity and a low melting temperature, so that heat resulting from
contact friction may lead to partial melting and hence feign wear. Due to the high thermal expansion
of polymers (up to 10 times higher than that of steel) results obtained can be misleading because the
test specimens have expanded under frictional heat. Hence allowance shall be made for the effects of
thermal expansion (change of clearance) and thermal conductivity (melting) when assessing the results.
Where possible the temperature of both test specimens should be controlled.
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Polymers have a glass transition temperature, T , which depends on their chemical structure. At this
g
temperature, their physical properties and their tribological behaviour may change.
Injection-moulded polymer surfaces have different properties from machined surfaces. The test
specimens shall be tested with the same surface conditions as they have in practical application.
Reinforcements and fillers, i.e. fibres, may lead to very strong anisotropy of the material and influence
its wear behaviour depending on fibre orientation. The test specimens should have the same fibre
orientation as in practical application.
In order to avoid stick-slip, the test rig shall be very stiff and shall not be susceptible to vibrations.
The tribological behaviour of polymers depends very strongly on the material combination, which part
moves and which part remains stationary. The test system shall be similar to practical application.
Polymers show wear processes that are different from that of metals. There are not only abrasive
processes with powder-like wear debris, but also adhesive processes with the creation of transfer layers
which may be smooth or rough. Also ploughing wear and melting or plastic deformation is possible.
Therefore, wear cannot be gravimetrically measured in all cases and the wear status shall be judged
after the tests (whether the surfaces are fine- or coarse- grained, scored or plucked out, scaled, melted
or plastically deformed).
Some polymers may show poor repeatability of the results and require repeated testing (i.e. six or more
repetitions).
The preparation and preparatory treatment (e.g. conditioning, storage, cleaning) of the test specimens
can have a high influence on performance.
In some thermoplastics, e.g. polyamides, moisture absorption effects a gradual change in linear
dimensions and modifies their mechanical properties. Environmental parameters should, therefore, be
controlled in the test array. Moisture absorption prohibits gravimetrical measurement of wear.
The more the test conditions deviate from the actual application, the greater is the uncertainty of the
applicability of the results (see Figures 1 and 2).
a) Plain bearing-on-shaft
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b) Linear guidance system
Figure 1 — Simulation of real rubbing contacts
a) Pin-on-disc
b) Block-on-ring
c) Sphere-on-prism
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d) Rotation under thrust load — Sleeve-to-sleeve
e) Rotation under thrust load — Sleeve-to-plate
Figure 2 — Simulation under approximated practical testing conditions and model systems
5 Test methods
5.1 General
Different test methods are provided for tests in accordance with this part of ISO 7148 so that the following
contact geometries are available. The test methods should correspond to the practical application as
closely as possible.
5.2 Test method A — Pin-on-disc
See Figure 3.
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Advantages:
— basic testing of simple test specimens;
— testing of tribological properties;
— no increase of sliding surface area due to wear;
— initial ranking of materials;
— simulation of linear guidance system [see Figure 1b)].
Disadvantages:
— edge of the pin might wipe off lubricant;
— no injection moulding of the pin with fibre reinforced material;
— no injection moulding of the disc because of problems with shrinkage.
Figure 3 — Test method A — Pin-on-disc
5.3 Test method B — Block (or pin)-on-ring
See Figure 4.
Advantages:
— basic testing of simple test specimens;
— testing of tribological properties;
— no increase of sliding surface area due to wear;
— initial ranking of materials;
— with and without lubrication.
Disadvantages:
— no injection moulding of the block because of problems with shrinkage and fibre orientation;
— edge of the block might wipe off lubricant;
— no injection moulding of the disc because of problems with shrinkage.
Figure 4 — Test method B — Block (or pin)-on-ring
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5.4 Test method C — Plain bearing-on-shaft
See Figure 5.
Advantages:
— best simulation of all possible systems;
— testing of original or scaled bearings;
— prediction of practical behaviour;
— with and without lubrication.
Disadvantages:
— long testing time (accelerated testing might cause excessive frictional heating);
— difficult alignment of the test bearing;
— increasing sliding surface area due to wear under boundary lubrication.
Figure 5 — Test method C — Plain bearing-on-shaft
5.5 Test method D — Sphere-on-prism
See Figure 6.
Advantages:
— testing of polymer/polymer or polymer/metal combinations;
— with and without lubrication (test specimen contains reservoir for lubricant);
— testing of lubricant’s interaction with polymers;
— injection-moulded test specimens available;
— self-adjustment of the alignment of the sliding couple;
— increasing sliding surface area due to wear under boundary lubrication.
Disadvantages:
— plastic deformation might affect results;
— increasing sliding surface area due to wear under dry conditions.
Figure 6 — Test method D — Sphere-on-prism
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5.6 Test method E — Rotation under thrust load
See Figure 7.
a) E1 — Sleeve-to-sleeve
b) E2 — Sleeve-to-plate
Figure 7 — Rotation under thrust load
Advantages:
— basic testing of simple specimens;
— injection-moulded test specimens available;
— testing of tribological properties;
— initial ranking of material;
— no increase of sliding surface area due to wear;
— continuous sliding between specimens;
— with and without lubrication.
Disadvantages:
— plastic deformation affects results;
— shrinkage at sliding surface on injection-moulded specimens affects results.
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6 Test specimens
6.1 Data required
For one series of tests, several specimens of one material shall be from the same batch, with uniform
state after conditioning and uniform finish of the sliding surface. Machined and injection-moulded
specimens may create different results because crystallinity can vary with depth from the surface. They
should be tested separately.
As the structural condition of the mating materials constitutes an essential factor as far as the
repeatability of the test results is concerned, the following information is necessary:
a) material specification and composition, including fillers or details of fibre reinforcement (as
specified in ISO 6691);
b) method of manufacture;
c) structure, e.g. density, degree of crystallinity;
d) mechanical material properties, e.g. Shore hardness, 0,2 % compression limit, R (as specified in
d0,2
ISO 4385), compression strength, R ;
d,B
e) state of conditioning, e.g. moisture content;
f) surface condition and surface roughness, Ra, e.g. injection-moulded, machined (as specified in
ISO 2818), turned, ground, lapped, polished, milled.
6.2 Polymer-based plain bearing materials (pl)
These may be made by moulding, injection moulding or by cutting bar or tube to length or by machining all
over from semi-finished materials or by cutting from injection-moulded or laminated (composite) plates.
If fibre-reinforced polymers are to be tested, the fibres shall lie in the same direction in the test as in the
final product, e.g. parallel or perpendicular to the sliding surface.
6.3 Materials of mating component
All metallic and polymer-based materials may be considered as mating materials. The choice should be
the same as in practical application. In technical applications, all systems are possible, e.g. gear box of
aluminium with injection-moulded gears and shafts of polyoxymethylene (POM). The mating materials
shall have the same sliding couple, e.g. rotating POM disc or ball on fixed pin or prism out of aluminium.
In this case, the reverse combination POM pin on aluminium disc leads to errors in evaluation.
6.4 Dimensions of test specimens
6.4.1 General
If dimensions other than those described as follows are used, the results might not be comparable due
to the effects of transfer films and heat dissipation.
6.4.2 Disc
The disc shall have the following preferred dimensions:
— outside diameter: 110 mm;
— inside diameter: 60 mm;
— radius of the sliding track: (51,5 ± 0,2) mm;
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— width: 10 mm.
The basic form of the disc is identical to the ring of deep groove ball thrust bearings on the shaft side.
6.4.3 Ring
The ring shall preferably have an outside diameter of 40 mm and a width corresponding at least to the
width of the block.
6.4.4 Pin
The pin shall preferably have a diameter of 3 mm for injection-moulded materials. For fibre-reinforced
materials, a larger diameter is preferred.
If a pin with a diameter greater than 7 mm is used, the radius of the sliding track has to be reduced or
the disc diameter increased. Means shall be provided for preventing rotation of the pin.
The free length of the pin shall not exceed 2 mm. Due to its dimensions, it is possible to make the 3 mm
diameter polymer pin out of a standard tension bar in accordance with ISO 527-3 or ISO 527-2. This
allows the correlation of wear and strength tests.
6.4.5 Block
The preferred basic dimensions of the block should be 10 mm × 10 mm × 20 mm. If a suitably large
component is not available, the block may, as an exception, be used with a length of 10 mm. The roughness
of the block depends on the machining conditions, e.g. milling or turning. The radius of the rubbing surface
of the block should be a minimum of 1,001 times the radius of the ring. If the maximum radius exceeds
1,003 times the radius of the ring (line contact), the running-in period can be unduly prolonged (see 11.1).
6.4.6 Sphere
The sphere shall preferably have a diameter of 12,7 mm. Thermoplastics may be injection-moulded (see
Figure 8). Spheres made out of metals are commercially available (balls for ball bearings or valves).
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Dimensions in millimetres
Key
1 six-flat mount with cylindrical hole
2 gate position
Figure 8 — Example of an injection-moulded sphere
6.4.7 Prism
The prism has a preferred special shape. If injection-moulded, the prism specimen shall have a uniform
wall thickness (2 mm) and metallic support (see Figure 9) in order to avoid deformation. Alternatively,
cut plates may be fitted into a special mount (see Figure 10).
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Dimensions in millimetres
Key
1 metal stiffening
2 gate position
Figure 9 — Example of an injection-moulded prism
Key
1 metal holder
2 machined plate
Figure 10 — Example of machined plates, inserted in a metallic holder
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6.4.8 Plain bearing
The plain bearing bush may be made by machining or by injection moulding. Depending on the test
equipment used, it is possible to use plain bearings with different inside diameters, the preferred inside
diameters being 20 mm, 5 mm or 1 mm, the latter being used for special applications, the width/diameter
ratio being 0,75 or 1.
The diameter, bearing clearance, wall thickness and type of bearing used (bush or half bearing) shall be
indicated in the test report. Smaller plain bearings should have a flange in order to allow to fix them in the
mount (see Figure 11). The sliding surface area shall lie within the cylindrical part of the plain bearing.
Key
1 flange
2 sliding surface
Figure 11 — Example of an injection-moulded plain bearing with step and chamfer in the bore
6.4.9 Shaft
The shaft piece used for the test shall be made with a circular run-out tolerance 1 μm maximum and a
circularity of not more than 5 μm. Irrespective of the test equipment used, it shall be ensured that the
test specimens (test bush and shaft) mounted in the test equipment have a maximum angular deviation
of 0,05° prior to the test and in the absence of a normal force. The diameter of the shaft (i.e. the bearing
clearance) shall be sufficient to allow for thermal expansion of the bush (risk of bore closure leading
to seizure) and depends on the wall thickness, temperature of operation and material properties. The
(cold) diametral clearance may vary from 0,003 times to 0,01 times the shaft diameter, being kept as
small as possible consistent with avoiding seizure.
6.4.10 Sleeve
The sleeve may be made by machining or
...
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