Foil bearings — Performance testing of foil thrust bearings — Testing of static load capacity, bearing torque, friction coefficient and lifetime

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.

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Status
Published
Publication Date
06-Jan-2019
Current Stage
6060 - International Standard published
Start Date
07-Jan-2019
Completion Date
07-Jan-2019
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ISO 22423:2019 - Foil bearings -- Performance testing of foil thrust bearings -- Testing of static load capacity, bearing torque, friction coefficient and lifetime
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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 22423:2019(E)
ISO 2019
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ISO 22423:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 22423:2019(E)
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

© ISO 2019 – All rights reserved iii
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ISO 22423:2019(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

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

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.org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7,

Special types of plain bearings.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
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ISO 22423:2019(E)
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

speed limits (where d is the mean diameter of bearing and n is the rotation rate) on rolling bearings.

© ISO 2019 – All rights reserved v
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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
© ISO 2019 – All rights reserved 1
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ISO 22423:2019(E)
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
r Distance, radius Millimetre
T Temperature Degrees Celsius
t Thickness Millimetre
2 © ISO 2019 – All rights reserved
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ISO 22423:2019(E)
4.2 Basic characters — Greek alphabet
Table 2 — Symbol — Basic characters — Greek alphabet
Symbol Description Unit
µ Friction coefficient Non-dimensional
ω Rotational speed r/min
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 bearing as a mechanical element with specific dimensions. They are closely related to the

performance of the mechanical systems in which foil thrust bearings are used.
6 Test conditions
6.1 General

The static load capacity of a foil thrust bearing should be tested, 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 determined by measuring the bearing torque and the rotational speed of

the shaft. The take-off speed, which is the speed at which the runner floats on the top foil without

making contact, should be determined. The bearing performance should be measured and compared at

a rotational speed that is higher than the take-off speed.
© ISO 2019 – All rights reserved 3
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ISO 22423:
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