1、BS ISO 7146-2:2008 ICS 21.100.10 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BRITISH STANDARD Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 2: Cavitation erosion and its countermeasuresThis British Standard was published un
2、der the authority of the Standards Policy and Strategy Committee on 31 October 2008 BSI 2008 ISBN 978 0 580 56927 2 Amendments/corrigenda issued since publication Date Comments BS ISO 7146-2:2008 National foreword This British Standard is the UK implementation of ISO 7146-2:2008. The UK participatio
3、n in its preparation was entrusted to Technical Committee MCE/12, Plain bearings. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its
4、correct application. Compliance with a British Standard cannot confer immunity from legal obligations.BS ISO 7146-2:2008Reference number ISO 7146-2:2008(E) ISO 2008INTERNATIONAL STANDARD ISO 7146-2 First edition 2008-10-15 Plain bearings Appearance and characterization of damage to metallic hydrodyn
5、amic bearings Part 2: Cavitation erosion 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 7146-2:2008 ISO 7146-2:2008(E) PDF disclaimer This PDF file may contai
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8、eters were optimized for printing. Every 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 rig
9、hts 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 photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of th
10、e requester. ISO copyright office Case 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 7146-2:2008 ISO 7146-2:2008(E) ISO 2008 All rights reserved iii Contents Page Forewo
11、rd iv Introduction v 1 Scope . 1 2 Normative 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
12、 5.2 Flow cavitation erosion 8 5.3 Impact 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 7146-2:2008 ISO 7146-2:2008(E) iv ISO 2008 All rights reservedForeword ISO (the International
13、 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 committee has been est
14、ablished has the right to be represented 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 standardiz
15、ation. International Standards 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 voti
16、ng. Publication as an International 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
17、 patent rights. ISO 7146-2 was prepared 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 7146:19
18、93 the technical content of which has been 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 countermeasur
19、es BS ISO 7146-2:2008 ISO 7146-2:2008(E) ISO 2008 All rights reserved v Introduction 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 hou
20、sing or the counterface against which it operates. 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 reconditioni
21、ng which often causes difficulty in establishing 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 condi
22、tions of the assembly and the maintenance 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
23、 determination of the cause of bearing damage. 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 eros
24、ion dealt with in ISO 7146-1 is treated in this part of ISO 7146 in more detail. BS ISO 7146-2:2008BS ISO 7146-2:2008 INTERNATIONAL STANDARD ISO 7146-2:2008(E) ISO 2008 All rights reserved 1 Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 2: Cavitation
25、 erosion and its countermeasures 1 Scope This 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 th
26、e various characteristic forms of damage which 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 referen
27、ces The following referenced documents are indispensable 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
28、, classification and symbols Part 1: Design, 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 bear
29、ings Appearance and characterization of damage 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 7146-2:2008 ISO 7146-2:2008(E) 2 ISO 2008 Al
30、l rights reserved4 Cavitation erosion 4.1 Mechanism 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
31、pressure of the liquid at a given temperature, 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 cavitatio
32、n has increased in the meantime, they condense 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 inte
33、nsity of cavity implosion, chemical reaction “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 b
34、earing oil. When a bearing surface is eroded 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 acc
35、ording to the properties of the underlying material (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
36、 shows signs of local work-hardening and fatigue 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
37、 seldom to a broader region. The cavitation erosion 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), motio
38、n of journal center, bearing vibration, bearing 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 a
39、nd corrosion resistance, oil supply pressure, oil constituent and its vapor pressure, oil viscosity, oil temperature, air and water content and contamination of oil, etc. BS ISO 7146-2:2008 ISO 7146-2:2008(E) ISO 2008 All rights reserved 3a) view under magnification b) cross-section under magnificat
40、ion Key 1 sliding surface 3 bonding area 2 bearing metal (tin-based) 4 steel backing Figure 1 (continued) BS ISO 7146-2:2008 ISO 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 F
41、igure 1 Sliding surface with cavitation erosion 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 performa
42、nce has increased. For engine bearings, cavitation 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
43、appearances and mechanisms of four types of cavitation 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 Cavita
44、tion erosion classification Type number Cavitation erosion classification 1 Flow 2 Impact 3 Suction 4 Discharge 5 Miscellaneous BS ISO 7146-2:2008 ISO 7146-2:2008(E) ISO 2008 All rights reserved 5 Types 1 and 2 take place both under static and dynamic bearing load, whereas types 3 and 4 only under d
45、ynamic bearing load. a) cavitation erosion type 1: 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 jou
46、rnal bearings BS ISO 7146-2:2008 ISO 7146-2:2008(E) 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 eros
47、ion type 3: suction d) cavitation erosion type 4:discharge 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, c
48、ausing depression. Figure 3 Mechanisms of four types of cavitation erosion in journal bearings BS ISO 7146-2:2008 ISO 7146-2:2008(E) ISO 2008 All rights reserved 7 4.3 General countermeasures against cavitation erosion 4.3.1 As general countermeasures against cavitation erosion, some of the followin
49、g steps may be recommended, depending on the type or 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 pres
