ISO 13939:2012

INTERNATIONAL ISO
STANDARD 13939
First edition
2012-08-01
Foil bearings — Guidelines for testing
of the performance of foil journal
bearings — Testing of load capacity,
friction coefficient and lifetime
Paliers-feuilles — Lignes directrices pour les essais de performance
des paliers radiaux à feuilles non lubrifiés — Essais de la capacité de
charge, du coefficient de friction et de la durée de vie
Reference number
ISO 13939:2012(E)
©
ISO 2012

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ISO 13939:2012(E)
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© ISO 2012
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ii © ISO 2012 – All rights reserved

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ISO 13939:2012(E)
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Symbols . 1
2.1 Basic characters — Roman alphabet . 2
2.2 Basic characters — Greek alphabet . 2
2.3 Additional signs — Subscripts . 2
2.4 Additional signs — Superscript (shown on X) . 3
3 Purpose of test . 3
4 Test conditions . 3
4.1 General . 3
4.2 Design of test facility . 3
4.3 Installation of sensors . 3
4.4 Calculation of bearing torque and loads . 5
4.5 Test specimens . 5
5 Test methods . 6
5.1 Principle . 6
5.2 Start-stop test cycle and evaluation of the take-off speed . 6
5.3 Evaluation of static load capacity . 7
5.4 Calculation of non-dimensional static load capacity . 8
5.5 Coefficient of bearing load capacity . 8
6 Clearance and eccentricity ratio . 8
7 Friction coefficient . 9
8 Durability test and lifetime .10
8.1 Test procedure .10
8.2 Determination of lifetime .10
9 Test report .10
Annex A (normative) The configuration of a typical foil journal bearing .12
Annex B (informative) Test report .14
Bibliography .16
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ISO 13939:2012(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 13939 was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7, Special
types of plain bearings.
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ISO 13939:2012(E)
Introduction
Foil bearing is a special type of plain bearing; at the time of publication of this International Standard, no
International Standards on foil bearings exist. This International Standard is an attempt to elaborate a test
method for the basic performance of a foil bearing.
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INTERNATIONAL STANDARD ISO 13939:2012(E)
Foil bearings — Guidelines for testing of the performance
of foil journal bearings — Testing of load capacity, friction
coefficient and lifetime
1 Scope
This International Standard describes a method of comparing the performance test results of foil journal
bearings, which are lubricated by air (gas) and supported by hydrodynamic force generated by the rotation
of the rotating shaft. The test procedure proposed in this International Standard aims to predict and evaluate
the static load capacity, friction coefficient and lifetime of the foil journal bearing, and compare the results with
those occurring under different test conditions, i.e. dimensions of a foil bearing, rotational speed of a shaft,
pressure and humidity of surroundings and so on. The magnitude of the static load capacity can change
according to the test setting, as the test conditions can be changed.
The test method described in this International Standard has the following application coverage:
a) the criterion of the static load capacity is the steady-state, i.e. it is applied in a limited operating condition
with a uniform magnitude, load direction and rotational speed;
b) the evaluation procedure can be applied only if the foil journal bearing is under a uniform rotating inertia at
an arbitrary rotational speed;
c) the dynamic load with a time-variant magnitude and direction is not taken into consideration;
d) for the purposes of this International Standard (these guidelines), the configuration of a typical foil journal
bearing is presented in Annex A.
2 Symbols
For the purposes of this document, the following symbols apply.
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ISO 13939:2012(E)
2.1 Basic characters — Roman alphabet
Table 1 — Symbol — Basic characters — Roman alphabet
Symbol Description Unit
C Clearance, coefficient Micrometres,
Non-dimensional
D Diameter Millimetres
d Diameter Millimetres
e Eccentricity Micrometres
F Force Newton
H Height Millimetres
h
Humidity Percentage
L
Length, lifetime Number of revolutions
p
Pressure Newton per square
millimetre
Ra Surface roughness Micrometres
r
Distance Millimetres
T
Temperature, torque Degrees Celsius, Newton-
metres
t Thickness Millimetres
F Mass, load Newton
w
2.2 Basic characters — Greek alphabet
Table 2 — Symbol — Basic characters — Greek alphabet
Symbol Description Unit
ε
Eccentricity ratio Non-dimensional
μ
Friction coefficient Non-dimensional
ω
Rotational speed Revolutions per minute
2.3 Additional signs — Subscripts
Table 3 — Symbol — Additional signs — Subscripts
Subscript Description
a Air (surrounding), average, applied
ah Air in bearing housing
b Bump foil, bearing
f Top foil, friction
fs Top foil surface
h Housing
max Maximum
n Net
r Radial, radius
R Relative
to Take-off
s Steady-state, static
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ISO 13939:2012(E)
2.4 Additional signs — Superscript (shown on X)
Table 4 — Symbol — Additional signs — Superscript
Superscript Description (shown on X)
Non-dimensional value
X
3 Purpose of test
The primary purpose of the test is to measure and evaluate the static load capacity, friction coefficients and
lifetime of the foil journal bearing. These are the primary performance metrics of the foil journal bearing as a
mechanical element with a specific dimension. These are closely related to the performance of the mechanical
systems to which the bearings are applied.
4 Test conditions
4.1 General
In order to compare the static load capacity, the test should be performed after the ambient pressure, temperature
and humidity of the environment in which the bearing operates have reached a state of equilibrium. The bearing
performance is obtained by measuring the bearing torque and the rotational speed of the shaft. In this case, the
take-off speed, at which the shaft floats on the top foil without contact, may be observed. Bearing performance
should be measured and compared at a rotational speed which is higher than the take-off speed.
4.2 Design of test facility
The bearing test facility should be designed to control the relative position of the bearing in relation to the shaft.
The bearing housing may be connected to a separate supporter, such as a spring or springs. Otherwise, a
vibration-proof facility may be applied in order to prevent perturbation, which can have a severe effect on the test
results. Also, excessive friction can have a severe effect on the test results due to misalignment of the bearing.
4.3 Installation of sensors
The equipment to measure the bearing torque and static load capacity of the foil journal bearings may be
installed as shown in Figure 1. Using the measurement system clarified in Figure 1, the bearing torque and
applied load may be measured and calculated as explained in 4.4.
As shown in Figure 2, the displacement sensors are installed at right angles to each other at both ends of
the bearing housing. The displacement of the shaft centre may be observed by measuring and comparing
the values arrived at. The rotational speed of the shaft may be obtained by applying a fast Fourier transform
(FFT) algorithm to the measured displacement data or by the use of a rotational speed meter. A thermocouple
is installed inside the bearing housing to measure the temperatures of surrounding air (gas). To measure the
surface temperature of a top foil, the thermocouple should be welded to the top foil surface.
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ISO 13939:2012(E)
Key
1 applied load
2 cable
3 deadweight housing
4 shaft
5 torque rod
6 pulley
7 load cell
8 counterweight preload
Figure 1 — Measurement system for the bearing torque and applied load
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ISO 13939:2012(E)
Key
1 displacement sensor
2 deadweight housing
3 thermocouple for measuring air temperature
4 thermocouple for measuring top foil surface temperature
5 shaft
6 top foil
Figure 2 — Installation of sensors
4.4 Calculation of bearing torque and loads
The friction force, F, may be measured using a load cell linked to the torque rod installed on the outside of the
housing. Then, the bearing torque, T, generated by the rotation of the shaft is obtained as the product of the
friction force, F, and the distance, r, between the two centres of the housing and load cell, as given by Formula (1):
TF=×  r (1)
where
T is the bearing torque;
F is the friction force;
r is the distance between the housing centre and the sensor-linked location of the torque rod.
The net load, F , exerted on the foil journal bearing, as shown in Figure 1, is obtained by subtracting the
w,n
applied load, F , measured from the load cell installed between the housing and the loading apparatus to the
w,a
mass of the housing, F . Where the load is applied in the lower direction, the net load, F , is obtained by
w,h w,n
adding the mass of the housing, F , to the applied load, F .
w,h w,a
4.5 Test specimens
The housing, bump foil, top foil and shaft comprising the foil journal bearing may be designed and fabricated
according to the purpose of use.
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ISO 13939:2012(E)
5 Test methods
5.1 Principle
To operate and test the foil journal bearing, the take-off speed is measured and the load-carrying capacity
is evaluated after sufficient preheating has taken place. The variables necessary for test and estimation are
presented in the test report (see Annex B).
5.2 Start-stop test cycle and eva
...