1、 ISO 2012 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 feuilles non lubrifis Essais de la capacit de charge, du coeff
2、icient de friction et de la dure de vie INTERNATIONAL STANDARD ISO 13939 First edition 2012-08-01 Reference number ISO 13939:2012(E) ISO 13939:2012(E) ii ISO 2012 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2012 All rights reserved. Unless otherwise specified, no part of this publication ma
3、y 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 ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel.
4、 + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ISO 13939:2012(E) ISO 2012 All rights reserved iii 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 .
5、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 Prin
6、ciple . 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
7、 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 ISO 13939:2012(E) Foreword ISO (the International Organization for Standardizat
8、ion) 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 r
9、epresented 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
10、 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 Internat
11、ional 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
12、prepared by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 7, Special types of plain bearings. iv ISO 2012 All rights reserved 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
13、Standards on foil bearings exist. This International Standard is an attempt to elaborate a test method for the basic performance of a foil bearing. ISO 2012 All rights reserved v Foil bearings Guidelines for testing of the performance of foil journal bearings Testing of load capacity, friction coeff
14、icient 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 In
15、ternational 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 humidi
16、ty 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 th
17、e 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 wit
18、h 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. INTE
19、RNATIONAL STANDARD ISO 13939:2012(E) ISO 2012 All rights reserved 1 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 Eccen
20、tricity 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 w Mas
21、s, load Newton 2.2 Basic characters Greek alphabet Table 2 Symbol Basic characters Greek alphabet Symbol Description Unit Eccentricity ratio Non-dimensional Friction coefficient Non-dimensional Rotational speed Revolutions per minute 2.3 Additional signs Subscripts Table 3 Symbol Additional signs Su
22、bscripts 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 2 ISO 2012 All rights reserved ISO 13939:2012(E) 2.4
23、 Additional signs Superscript (shown on X) Table 4 Symbol Additional signs Superscript Superscript Description (shown on X) X Non-dimensional value 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 jo
24、urnal 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 stat
25、ic 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
26、 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 contro
27、l 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,
28、 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 clari
29、fied 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
30、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
31、of surrounding air (gas). To measure the surface temperature of a top foil, the thermocouple should be welded to the top foil surface. ISO 2012 All rights reserved 3 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 Fi
32、gure 1 Measurement system for the bearing torque and applied load 4 ISO 2012 All rights reserved 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 Install
33、ation 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
34、, 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 w,n , exerted on th
35、e foil journal bearing, as shown in Figure 1, is obtained by subtracting the applied load, F w,a , measured from the load cell installed between the housing and the loading apparatus to the mass of the housing, F w,h . Where the load is applied in the lower direction, the net load, F w,n , is obtain
36、ed by adding the mass of the housing, F w,h , to the applied load, F 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. ISO 2012 All rights reserved 5 ISO 13939:2012(E) 5 Test methods
37、 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 cyc
38、le and evaluation of the take-off speed Using an electric motor or a turbine operated by a high-pressure air supply system, rotate the shaft and then the foil journal bearing starts to operate. Once the shaft begins its rotation, the bearing torque should be measured as the speed of rotation is grad
39、ually increased. Figure 3 shows a typical example of variation in bearing torque, which is measured with the rotational speed of the shaft from the start-stop test. As the rotational speed increases, the bearing torque increases suddenly at a certain rotational speed and then decreases to maintain t
40、he steady-state condition with a relatively constant torque value. As the bearing torque decreases to meet its steady value, the rotational speed is determined as the take-off speed of the foil journal bearing and should be recorded in the test report (see Annex B). As the rotational speed decreases
41、 to zero, the bearing torque suddenly rises again and then decreases. Figure 3 Rotational speed versus bearing torque 6 ISO 2012 All rights reserved ISO 13939:2012(E) The following processes comprise a single start-stop test cycle. a) Firstly, the load for the start-stop test should be determined an
42、d applied. Where selecting a load to evaluate the load capacity and lifetime of the bearing, the loading value exerted on the actual rotating system should be applied. Otherwise, the initial applied load, F w , for a start-stop test may be calculated as follows, as a rule of thumb, then applied load
43、, F w,a , may be evaluated by the test process in 5.3. FCLdd w ( )( ) (2) where C is the coefficient of foil bearing load capacity, i.e. equal to 2 000; L is the axial length of top foil, in millimetres (mm); d is the shaft diameter, in millimetres (mm); is the shaft rotational speed, in thousands o
44、f revolutions per minute (r/min). b) After the shaft reaches the take-off speed, the state should continue for 15 s, and then the power to the motor should be shut off to maintain a stopped state for 5 s. c) This process is defined as a start-stop test. In the start-stop test, the rotational speed,
45、the accumulated number of shaft rotations, the bearing torque, the temperature inside the housing and the top foil surface are observed. 5.3 Evaluation of static load capacity The static load capacity, F w,s , is the maximum steady load which may be delivered by a foil bearing in a steady- state con
46、dition. The following is the process to determine the static load capacity. a) The rotational speed of the shaft is controlled to a given test speed, for example the speed of the actual foil bearing; measurement shall not take place before thermal equilibrium is reached, as measured using a thermoco
47、uple installed inside the bearing housing. The test speed should have a margin from the take-off speed to guarantee stable running of the bearing system. b) After increasing the rotational speed by about 10 % of the test speed to provide the foil bearing with higher load capacity, apply the initial
48、load, F w . Then, the rotational speed should return to the test speed. In this state, the rotational speed and the bearing torque should be observed for 5 min to estimate whether the air film or bearing rupture. Whenever a foil bearing has a film of air between the shaft and top foil, it demonstrat
49、es smooth rotation without any problems. Where unnecessary contacts develop between the shaft and top foil, it creates unstable vibrations. In this case, be sure to move to process (d) or this can lead to a sudden adhesion in a few seconds. c) If no failure is generated, the rotational speed should be increased by about 10 % of the test speed, a load of 1 N should be added and the rotational speed should be decreased to the test speed. Then, the bearing should be
