1、BS ISO7146-2:2008ICS 21.100.10NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPlain bearings Appearance andcharacterization ofdamage to metallichydrodynamicbearingsPart 2: Cavitation erosion and itscountermeasuresThis British Standardwas published under theautho
2、rity of the StandardsPolicy and StrategyCommittee on 31 October2008 BSI 2008ISBN 978 0 580 56927 2Amendments/corrigenda issued since publicationDate CommentsBS ISO 7146-2:2008National forewordThis British Standard is the UK implementation of ISO 7146-2:2008.The UK participation in its preparation wa
3、s entrusted to TechnicalCommittee MCE/12, Plain bearings.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct application.Complian
4、ce with a British Standard cannot confer immunityfrom legal obligations.BS ISO 7146-2:2008Reference numberISO 7146-2:2008(E)ISO 2008INTERNATIONAL STANDARD ISO7146-2First edition2008-10-15Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 2: Cavitation ero
5、sion and its countermeasures Paliers lisses Aspect et caractrisation de lendommagement des paliers mtalliques couche lubrifiante fluide Partie 2: rosion de cavitation et sa contre-mesure BS ISO 7146-2:2008ISO 7146-2:2008(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance w
6、ith Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobes licensing
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8、ery care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2008 All rights reserved. Unless otherwise specif
9、ied, no part of this publication may 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 Cas
10、e postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2008 All rights reservedBS ISO 7146-2:2008ISO 7146-2:2008(E) ISO 2008 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Norm
11、ative references . 1 3 Terms and definitions. 1 4 Cavitation erosion. 2 4.1 Mechanism of cavitation erosion 2 4.2 Classification of cavitation erosion 4 4.3 General countermeasures against cavitation erosion 7 5 Five types of cavitation erosion 8 5.1 General. 8 5.2 Flow cavitation erosion 8 5.3 Impa
12、ct cavitation erosion 11 5.4 Suction cavitation erosion. 12 5.5 Discharge cavitation erosion. 14 5.6 Miscellaneous cavitation erosion (see Figures 17 to 20). 15 BS ISO 7146-2:2008ISO 7146-2:2008(E) iv ISO 2008 All rights reservedForeword ISO (the International Organization for Standardization) is a
13、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
14、 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 draft
15、ed 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 Stan
16、dard 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 7146-2 was prepared
17、by Technical Committee ISO/TC 123, Plain bearings, Subcommittee SC 2, Materials and lubricants, their properties, characteristics, test methods and testing conditions. This first edition of ISO 7146-2, together with ISO 7146-1, cancels and replaces ISO 7146:1993 the technical content of which has be
18、en technically revised and augmented. ISO 7146 consists of the following parts, under the general title Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings: Part 1: General Part 2: Cavitation erosion and its countermeasures BS ISO 7146-2:2008ISO 7146-2:2008(E)
19、ISO 2008 All rights reserved vIntroduction In practice, damage to a bearing may often be the result of several mechanisms operating simultaneously. The damage may result from improper assembly or maintenance or from faulty manufacture of the bearing, its housing or the counterface against which it o
20、perates. In some instances, damage may be caused by a design compromise made in the interests of economy or from unforeseen operating conditions. It is the complex combination of design, manufacture, assembly, operation, maintenance and possible reconditioning which often causes difficulty in establ
21、ishing the primary cause of damage. In the event of extensive damage or destruction of the bearing, the evidence is likely to be lost, and it will then be impossible to identify how the damage came about. In all cases, knowledge of the actual operating conditions of the assembly and the maintenance
22、history is of the utmost importance. The classification of bearing damage established in this International Standard is based primarily upon the features visible on the running surfaces and elsewhere, and consideration of each aspect is required for reliable determination of the cause of bearing dam
23、age. Since more than one process may cause similar effects on the running surface, a description of appearance alone is occasionally inadequate in determining the cause of damage. In such cases, the operating conditions have to be considered. Cavitation erosion dealt with in ISO 7146-1 is treated in
24、 this part of ISO 7146 in more detail. BS ISO 7146-2:2008BS ISO 7146-2:2008INTERNATIONAL STANDARD ISO 7146-2:2008(E) ISO 2008 All rights reserved 1Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 2: Cavitation erosion and its countermeasures 1 Scope Thi
25、s part of ISO 7146 defines, describes and classifies the characteristics of damage occurring in service in hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible countermeasures. It assists in understanding the various characteristic forms of damage whi
26、ch may occur. Consideration is restricted to damage which has a well-defined appearance and which can be attributed to particular causes with a high degree of certainty. Various appearances are illustrated with photographs and diagrams. 2 Normative references The following referenced documents are i
27、ndispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 4378-1, Plain bearings Terms, definitions, classification and symbols Part 1: Design,
28、 bearing materials and their properties ISO 4378-2, Plain bearings Terms, definitions, classification and symbols Part 2: Friction and wear ISO 4378-3, Plain bearings Terms, definitions, classification and symbols Part 3: Lubrication ISO 7146-1, Plain bearings Appearance and characterization of dama
29、ge to metallic hydrodynamic bearings Part 1: General 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 4378-1, ISO 4378-2, ISO 4378-3, and ISO 7146-1 apply. BS ISO 7146-2:2008ISO 7146-2:2008(E) 2 ISO 2008 All rights reserved4 Cavitation erosion 4.1 Mec
30、hanism of cavitation erosion Cavitation erosion is a form of damage to the surface of a solid body in liquid caused by implosion (violent inward collapse) of cavities or vapour bubbles. When the static pressure in the liquid is decreased under the vapour pressure of the liquid at a given temperature
31、, evaporation occurs and bubbles of vapour are generated in the liquid. This phenomenon is called “cavitation”. When these cavities encounter higher pressure, because they have flowed to a place of higher pressure or the pressure at the place of cavitation has increased in the meantime, they condens
32、e instantaneously and implode, causing a very high and local pressure and high temperature in the liquid. It can lead, after repeated implosion, to “cavitation erosion” of the surface of the solid body near the place of implosion. Because of the high intensity of cavity implosion, chemical reaction
33、“cavitation corrosion” can take place. The damage may also occur together with “fluid erosion” and “cavitation corrosion”. A phenomenon known as the “micro-Diesel-effect”, where the imploding cavities release electrical charge, is also detected in plain bearing oil. When a bearing surface is eroded
34、by cavitation, first the colour of the surface changes slightly due to roughening. Then small pores form, and cracks initiate on the surface, especially at grain boundaries. These cracks with sharp edges are spread first on the surface and then deepen according to the properties of the underlying ma
35、terial (see Figure 1). The cracks are joined together leading to break-out and wash-away of small particles of bearing materials. When the damage is caused solely by collapsing cavities, the attacked areas show a rough texture. Metallurgical section often shows signs of local work-hardening and fati
36、gue cracking due to hammer blows caused by cavity collapse. But if particles are trapped in the damage pockets, the surface can be eroded and exhibits a smooth and polished appearance. The place of cavitation erosion is usually limited locally and spreads seldom to a broader region. The cavitation e
37、rosion usually appears in the unloaded areas of the bearing. The occurrence of cavitation erosion depends on many factors as given in the following: journal speed, specific bearing load, dynamic load pattern (especially time rate of load variation), motion of journal center, bearing vibration, beari
38、ng clearance, size and geometry of bearing clearance space, edge form and location of oil hole, groove and pocket, existence and position of the drilling in journal, bearing material, especially its hardness, elastic modulus, toughness, fatigue strength and corrosion resistance, oil supply pressure,
39、 oil constituent and its vapor pressure, oil viscosity, oil temperature, air and water content and contamination of oil, etc. BS ISO 7146-2:2008ISO 7146-2:2008(E) ISO 2008 All rights reserved 3a) view under magnification b) cross-section under magnification Key 1 sliding surface 3 bonding area 2 bea
40、ring metal (tin-based) 4 steel backing Figure 1 (continued) BS ISO 7146-2:2008ISO 7146-2:2008(E) 4 ISO 2008 All rights reservedc) cross-section under higher magnification Key 1 sliding surface 2 bearing metal (tin-based) 3 bonding area 4 steel backing Figure 1 Sliding surface with cavitation erosion
41、 4.2 Classification of cavitation erosion Though cavitation erosion occurs in plain bearings of various machines, that in bearings of internal combustion engines has been studied most intensively and has attracted increasing attention as engine performance has increased. For engine bearings, cavitat
42、ion erosion has been classified into types 1 to 4 by the mechanism of cavity creation. However, this classification may also be applied to other kinds of machines, provided that the characteristic flow conditions are similar. Examples of characteristic appearances and mechanisms of four types of cav
43、itation erosion in journal bearings are given in Figures 2 and 3. Besides these four types, there are some kinds of cavitation erosion which may not always be easy to identify. These are classified as type 5, miscellaneous. (See Table 1.) Table 1 Cavitation erosion classification Type number Cavitat
44、ion erosion classification 1 Flow 2 Impact 3 Suction 4 Discharge 5 Miscellaneous BS ISO 7146-2:2008ISO 7146-2:2008(E) ISO 2008 All rights reserved 5Types 1 and 2 take place both under static and dynamic bearing load, whereas types 3 and 4 only under dynamic bearing load. a) cavitation erosion type 1
45、: flow b) cavitation erosion type 2: impact c) cavitation erosion type 3: suction d) cavitation erosion type 4: discharge Key U direction of journal rotation Figure 2 Examples of the characteristic appearance of four types of cavitation erosion in journal bearings BS ISO 7146-2:2008ISO 7146-2:2008(E
46、) 6 ISO 2008 All rights reserveda) cavitation erosion type 1: flow b) cavitation erosion type 2: impact d 1) oil is discharged into groove in both directions d 2) depression occurs as the discharged oil flows further due to inertia c) cavitation erosion type 3: suction d) cavitation erosion type 4:d
47、ischarge Key 1 cavities in oil 2 oil flow 3 partial oil groove 4 oil column U direction of journal rotation v velocity of journal center aContinuous oil flow. bOil flow abruptly stopped. cOil inflow stopped, but oil column flows further by inertia, causing depression. Figure 3 Mechanisms of four typ
48、es of cavitation erosion in journal bearings BS ISO 7146-2:2008ISO 7146-2:2008(E) ISO 2008 All rights reserved 74.3 General countermeasures against cavitation erosion 4.3.1 As general countermeasures against cavitation erosion, some of the following steps may be recommended, depending on the type or
49、 mechanism of cavitation erosion that has taken place. 4.3.2 Modify the oil flow in bearing and passage by: a) making the oil flow as continuously and smoothly as possible, with minimal interruption; b) avoiding sharp edges and discontinuous surfaces and providing a larger chamfer or radius at the edge of oil holes, grooves and pockets; c) avoiding or reducing projection and relief on the bearing surface. 4.3.3 Increase the oil supply pressure. 4.3.4 Reduce the bearing clearance. 4
