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1、J IS JAPANESE I N D USTR IAL STA N DA R D Translated and Published by Japanese Standards Association Mechanical vibration- Susceptibility and sensitivity of machines to unbalance ICs 21.120.40 Descriptors : vibration, mechanical measurement, rotational motion, rotating electric Reference number : JI
2、S B O911 : 2000 (E) machines, vibration measurement, vibration testing, balancing PROTECTED BY COPYRIGHT 10 s Copyright Japanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/15/2007 00:15:51 MDTNo reproduction or
3、networking permitted without license from IHS -,-,- B O911 : 2000 (IS0 10814 : 1996) Foreword This translation has been made based on the original Japanese Industrial Standard established by the Minister of International Trade and Industry through deliberations at the Japanese Industrial Standards C
4、ommittee according to the proposal of establishing a Japanese Industrial Standard from the Japanese Standards Association (JSA), with a draft of Industrial Standard based on the provision of Clause 1, Article 12 of the Industrial Standardization Law. Date of Establishment: 2000-01-20 Date of Public
5、Notice in Official Gazette: 2000-01-20 Investigated by: Japanese Industrial Standards Committee Divisional Council on Machine Elements JIS B 0911 : 2000, First English edition published in 2002-08 Translated and published by: Japanese Standards Association 4-1 -24, Akasaka, Minato-ku, Tokyo, 107-844
6、0 JAPAN In the event of any doubts arising as to the contents, the original TIS is to be the final authority. O JSA 2002 Ali 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 photoco
7、pying and microfilm, without permission in writing from the publisher. Printed in Japan PROTECTED BY COPYRIGHT Copyright Japanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/15/2007 00:15:51 MDTNo reproduction or
8、 networking permitted without license from IHS -,-,- JAPANESE INDUSTRIAL STANDARD JIS B O911 : 2000 (IS0 10814 : 1996) Mechanical vibration- Susceptibility and sensitivity of machines to unbalance Introduction This Japanese Industrial Standard has been prepared based on the first edition of IS0 1081
9、4 Mechanical vibration-Susceptibility and sensitivity of machines to unbalance published in 1996 without modifying the technical contents. Portions underlined with dots are the matters not stated in the original Interna- tional Standard. Rotor balancing during manufacture (as described in IS0 1940-1
10、 and IS0 11342, for example) is normally sufficient to attain acceptable vibration levels in service if other sources of vibration are absent. There are exceptions, however, where addi- tional balancing during commissioning becomes necessary. Furthermore, after com- missioning, some machines may req
11、uire occasional or even frequent field rebalancing. If the vibration levels are unsatisfactory during commissioning, the reason may be inadequate balancing or assembly errors. Another important cause may be that an assembled machine is especially sensitive to relatively small residual unbalances whi
12、ch are well within normal balance tolerances. If vibration magnitudes are unsatisfactory, the first step often is an attempt to reduce the vibration by field balancing. If high vibration can be reduced by rela- tively small correction masses, high sensitivity to unbalance is indicated. This can aris
13、e, for example, if a resonant speed is close to the normal service speed and the damping in the system is low. A sensitive machine which is also highly susceptible to its unbalance changing, may require frequent rebalancing in situ. This may be caused, for example, by changes in wear, temperature, m
14、ass, stiffness and damping during operation. If the unbalance and other conditions of the machine are essentially constant, occasional trim balancing may be sufficient. Otherwise it may be necessary to modify the machine to change the resonant speed, damping or other parameters. There- fore, there i
15、s a need to consider permissible sensitivity values of the machine. The repeatability of the sensitivity of a machine is influenced by several factors and may change during operation. Some thermal machines, especially those with sleeve bearings, have modal vibration characteristics which vary with c
16、ertain opera- tional parameters such as steam pressure and temperature, partial steam admis- sion or oil temperature. For electrical machines, other parameters such as the excitation current may influence the vibration behaviour. In general, the machine vibration characteristics are influenced by th
17、e design features of the machine, including cou- pling of the rotor and the support conditions including the foundation. It should be noted that the latter may vary with time, for example owing to wear and tear. This Standard is only concerned with once-per-revolution vibration caused by un- balance
18、; however it should be recognized that unbalance is not the only cause of once- per-revolution vibration. PROTECTED BY COPYRIGHT Copyright Japanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/15/2007 00:15:51 MDT
19、No reproduction or networking permitted without license from IHS -,-,- 2 B O911 : 2000 (IS0 10814 : 1996) 1 Scope 1 . 1 This Standard defines methods for determining machine vibration sensitivity to unbalance and provides evaluation guidelines as a function of the proximity of relevant resonant spee
20、ds to the service speed. It includes a classification of certain machines in groups associated with the sus- ceptibility to a change in unbalance. This Standard also makes recommendations on how to apply the numerical sensitivity values in some particular cases. 1 . 2 Machines are classified into th
21、ree types in clause 4, and sensitivity values assigned to different groups of machines are shown in clause 5. The sensitivity values should be used on simple machine systems, preferably with rotors having only one reso- nant speed over the entire service speed range. They may also be used for machin
22、es that have more resonant speeds in the service speed range if the resonant speeds are widely separated (e.g. more than 20 % spaced). The proposed sensitivity values are not intended to serve as acceptance specifi- cations for any machine group but rather to give indications of how to avoid gross d
23、eficiencies as well as exaggerated or unattainable requirements. They may also serve as a basis for more involved investigations, for example, when in special cases a more exact determination of the required sensitivity is necessary. If due regard is paid to the proposed values, satisfactory running
24、 conditions can be expected in most cases. The consideration of these values alone does not guarantee that a given magni- tude of vibration in service is not exceeded. Many other sources of vibration can occur which are not the subject of this Standard. 2 Normative references The following standards
25、 contain provisions which, through reference in this Standard, constitute provisions of this Standard. If the indication of the year of publication is given to these referred standards, only the edition of indicated year constitutes the provision of this Standard but the revision and amend- ment mad
26、e thereafter are not applied. IS0 1925 : 1990 Mechanical vibration-Balancing-Vocabulary IS0 2041 : 1990 Vibration and shock-Vocabulary 3 Definitions For the purposes of this Standard, the definitions given in IS0 1925 and IS0 2041 and the following definitions apply. 3 . 1 having a significant chang
27、e of unbalance over a certain period of operation. susceptibility to unbalance An indication of the likelihood of a machine 3 . 2 to a change in unbalance. sensitivity to unbalance A measure of the vibration response of a machine Note : It is usually numerically expressed in the two ways shown in 3
28、. 2 . 1 and 3 . 2 . 2 below. 3 . 2 . 1 local sensitivity Ratio of the magnitude of the change of the displacement or velocity vector in a specified measuring plane to the magnitude of a change in the unbalance in a specified plane in the rotor at a specified speed. PROTECTED BY COPYRIGHT Copyright J
29、apanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/15/2007 00:15:51 MDTNo reproduction or networking permitted without license from IHS -,-,- 3 B O911 : 2000 (IS0 10814 : 1996) In technical terms, the local sens
30、itivity can be expressed as: where AlSkl is the change in once-per-revolution vibration in plane A l C 1 is the change in trial unbalance attached to plane r in Note : The local sensitivity is frequently referred to as the “influence coeffi- cient”. It is a dimensional quantity. k; the rotor (or cha
31、nge in trial unbalance set). 3 . 2 . 2 modal sensitivity, M, Ratio of the change of the modal displacement vec- tor to a change of the modal eccentricity (modal unbalance divided by modal mass). It is a non-dimensional quantity. In practical determinations of modal sensitivity, care should be taken
32、to extract the relevant modal components. Modal sensitivity for excitation of the machine by unbalance for mode n can be shown to be: (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . where i 2 is the rotational speed; ccr, is the nth undamped resonant speed; Cn is the damping ra
33、tio of the nth mode. Under conditions where the rotational speed equals a resonant speed, M, becomes approximately 1/(2 it is influenced only by the level of damping in the system. Modal sensitivity is sometimes referred to as the vibration magnifi- cation factor for mode n. Note : 4 Machine suscept
34、ibility classification 4.1 Type I : Low susceptibility Machines of this type have a low likelihood of experiencing significant unbalance changes during operation. Typically, they have large rotor masses in comparison to the support housing and operate in a clean environment, have negligible wear and
35、 exhibit minimal rotor distortion caused by temperature changes. Examples : Paper machine rolls, printing rolls and high-speed vacuum pumps. PROTECTED BY COPYRIGHT Copyright Japanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not
36、for Resale, 03/15/2007 00:15:51 MDTNo reproduction or networking permitted without license from IHS -,-,- 4 B O911 : 2000 (IS0 10814 : 1996) Modal sensitivity range A: Very low sensitivity 4 . 2 Machines of this type have a moderate likelihood of experiencing significant unbalance changes during ope
37、ration, such as rotors in an environment with large temperature changes and/or moderate wear. Pumps in clean media, electric armatures, gas and steam turbines, small turbo generators for industrial applications and turbo com- pressors. Type II : Moderate susceptibility Examples : Expected running co
38、nditions Very smooth resonant speed; difficult to detect 4 . 3 Machines of this type have a high likelihood of experiencing significant unbalance changes during operation, such as blowers running in deposit producing environments, pumps operating in sludge, rotors with high wear or running in corros
39、ive environments. Type III : High susceptibility Examples : Centrifuges, fans, screw conveyors and hammer mills. C: Moderate sensitivity D: High sensitivity 5 Modal sensitivity values Acceptable, moderate and slightly unsteady vibrations Sensitive to unbalance; regular field balancing may be require
40、d 5.1 Modal sensitivity ranges A to E In figures 1 to 3, modal sensitivity is clas- sified for service speeds below and above a resonant speed of the machine system. The range limits are chosen in such a way that, close to a resonant speed, the mag- nification factor is constant. The curves in figur
41、es 1 to 3 are derived from equation (2). The range limits depend on the type of machine in the susceptibility classifica- tion (the damping ratio being lower, in the same sensitivity range, for type III than for type I machines). Generally, for the sensitivity ranges below, the corresponding running
42、 conditions given in table 1 can be expected. Examples of how to use figures 1 to 3 are given in annex B. Table 1 I I B: Low sensitivity I Smooth, low and stable vibrations I E: Very high sensitivity I Too sensitive to unbalance; to be avoided I 5 . 2 Characteristics of modal sensitivity 5 . 2 . 1 W
43、hile range A will theoretically appear to be the most desirable, consider- ations of cost and feasibility may often make it necessary to operate with higher modal sensitivities. 5 . 2 . 2 For high-performance machines (e.g. those that have a short period between planned maintenance cycles), it may b
44、e permissible to allow higher values of modal sensitivity. PROTECTED BY COPYRIGHT Copyright Japanese Standards Association Provided by IHS under license with JSALicensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/15/2007 00:15:51 MDTNo reproduction or networking permitted without
45、 license from IHS -,-,- 5 B O911 : 2000 (IS0 10814 : 1996) 5 . 2 . 3 For machines for which field balancing is not practical or not economical, smaller values of modal sensitivity may have to be selected. 5.2.4 Consideration of the sensitivity does not always give sufficient assurance that, at all p
46、arts of the machine, vibration limits are not exceeded (see clauses 7 and 8). 5 . 3 Accelerating rotors Higher values of the modal sensitivity are permissible for machines which, in service, always accelerate rapidly through all resonant speeds because steady-state response has insufficient time to
47、develop. Machines which are only started and stopped infrequently may also be acceptable with higher values of modal sensitivity. Figure 4 illustrates, for a single degree of freedom system, the reduction in the modal sensitivity as a function of the rotational acceleration. However, for most practi
48、cal acceleration rates, this effect is small and can be neglected. Such a reduction in the modal sensitivity may be calculated using Figure 4 before referring to figures 1 to 3 (as these figures are only applicable for slowly accelerat- ing rotors), taking the following points into account: a) passi
49、ng through a resonant speed is assumed to happen with constant rotational acceleration; b) the modal sensitivity shall be tested (where possible) under steady-state condi- tions as close to the resonant speed as possible; the maximum amplitudes during rapid acceleration or deceleration will occur at rotor speeds different from the resona