ISO 22423:2019

INTERNATIONAL ISO
STANDARD 22423
First edition
2019-01
Foil bearings — Performance testing
of foil thrust bearings — Testing of
static load capacity, bearing torque,
friction coefficient and lifetime
Reference number
©
ISO 2019
© ISO 2019
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
4.1 Basic characters — Roman alphabet . 2
4.2 Basic characters — Greek alphabet . 3
4.3 Additional signs — Subscripts . 3
5 Purpose of test . 3
6 Test conditions . 3
6.1 General . 3
6.2 Design of test apparatus . 4
6.3 Installation of sensors. 4
6.4 Test specimens . 4
7 Test methods . 5
7.1 Principle . 5
7.2 Start–stop test cycle and evaluation of the take-off speed . 5
7.3 Calculation of bearing torque and load . 7
7.4 Determination of static load capacity . 7
7.5 Evaluation of static load capacity per unit area. 8
8 Friction coefficient. 8
9 Durability test and lifetime . 8
9.1 Test procedure . 8
9.2 Determination of lifetime . 9
10 Test report . 9
Annex A (informative) Configuration of a typical foil thrust bearing .10
Annex B (informative) Test report .12
Bibliography .13
Foreword
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electrotechnical standardization.
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This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7,
Special types of plain bearings.
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iv © ISO 2019 – All rights reserved

Introduction
Design improvements commonly required for rotating machines such as turbines, generators,
compressors and pumps include increases in speed and decreases in size. Foil bearings in
turbomachinery operate by generating a self-acting air (or gas) film between surfaces in relative
motion. A gap between a rotating shaft or runner and a foil surface compresses a gaseous lubricant to
an elevated pressure, separating the relatively moving surfaces and providing a load-carrying capacity.
The use of the surrounding air (or gas) as the bearing lubricant eliminates the need for an auxiliary
lubrication system to deliver conventional oil lubricants. This permits drastic reductions in the weight,
complexity and maintenance costs of foil bearing-supported turbomachines, in comparison to their
rolling bearing-supported counterparts. It also permits higher shaft speeds by removing the n × d
m
speed limits (where d is the mean diameter of bearing and n is the rotation rate) on rolling bearings.
m
INTERNATIONAL STANDARD ISO 22423:2019(E)
Foil bearings — Performance testing of foil thrust bearings
— Testing of static load capacity, bearing torque, friction
coefficient and lifetime
1 Scope
This document specifies the method for comparing performance evaluation results for a foil thrust
bearing that supports load with aerodynamic force generated by the rotation of a driving shaft and
lubricates using air, not lubricating oil. The test procedure explained in this document measures and
evaluates the static load capacity, bearing torque, friction coefficient and lifetime of the foil thrust
bearing and compares the test results to those for different test conditions. The measured static load
capacity can be varied depending on the capabilities of the test device used.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
thrust runner
runner
circular disc connected to the rotating shaft and facing the surface of the top foil
Note 1 to entry: The surfaces of the thrust runner should be machined smoothly enough to form the air film
between the runner and the top foil.
3.2
take-off
stage aimed to secure the distance between the thrust runner (3.1) and the top foil by developing an
aerodynamic pressure between them
3.3
clearance
shortest distance between the thrust runner (3.1) and the top foil
3.4
bearing torque
torque value developed by rotational friction between the thrust runner (3.1) and the top foil
Note 1 to entry: The measurement of the bearing torque is as described in 7.3.
3.5
load
load capacity
weight that can be delivered by a bearing under steady-state conditions
3.6
initial load
load (3.5) exerted on the rotating system in the beginning
Note 1 to entry: It should be lower than the static load capacity and the load at which the lifetime of the bearing is
determined, as explained in 7.4 and 9.2.
3.7
reference load
load (3.5) expected to be supported by a bearing
Note 1 to entry: The calculation of the reference load is given in 7.2.
3.8
static load capacity
maximum load (3.5) value of a bearing in static state
Note 1 to entry: The measurement of the static load capacity is explained in 7.4.
3.9
friction coefficient
flow resistance caused by rotational friction between the thrust runner (3.1) and the top foil
Note 1 to entry: The measurement of the friction coefficient is described in Clause 8.
3.10
lifetime of bearing
total number of start–stop test cycles of the foil thrust bearing at which the coating layer disappears
Note 1 to entry: The measurement of the lifetime of bearing follows Clause 9.
4 Symbols
For the purposes of this document, the following symbols apply.
4.1 Basic characters — Roman alphabet
Table 1 — Symbol — Basic characters — Roman alphabet
Symbol Description Units
A Area Square millimetre
F Force, load Newton
H Height Millimetre
h Humidity Percentage
L Lifetime Number of start-stop cycles
M Torque Newton-millimetre
R Surface roughness Millimetre
a
r Distance, radius Millimetre
T Temperature Degrees Celsius
t Thickness Millimetre
2 © ISO 2019 – All rights reserved

4.2 Basic characters — Greek alphabet
Table 2 — Symbol — Basic characters — Greek alphabet
Symbol Description Unit
a
µ Friction coefficient Non-dimensional
ω Rotational speed r/min
a
The symbol f is also commonly used and accepted.
4.3 Additional signs — Subscripts
Table 3 — Symbol — Additional signs — Subscripts
Subscription Description
a Air (surrounding), average, applied
b Bump foil, bearing
f Top foil, friction
fs Top foil surface
i Inner
inc Increment
max Maximum
n Net
o Outer
r Radial, radius, runner, reference
R Relative
to Take-off
s Steady-state, static
u Upper
ua Unit area
w Working
5 Purpose of test
The primary purpose of the test is to measure and evaluate the static load capacity, bearing torque,
friction coefficients and lifetime of a foil thrust bearing. These are the primary performance metrics of
a foil thrust beari
...