DIN ISO 7146-2-2015 Plain bearings - Appearance and characterization of damage to metallic hydrodynamic bearings - Part 2 Cavitation erosion and its countermeasures (ISO 7146-2 200.pdf

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1、December 2015 English price group 13No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 21.100.10!%I“2385688www.din.deD

2、IN ISO 7146-2Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 2: Cavitation erosion and its countermeasures (ISO 7146-2:2008),English translation of DIN ISO 7146-2:2015-12Gleitlager Erscheinungsbild und Charakterisierung von Schden an lgeschmierten meta

3、llischen Gleitlagern Teil 2: Kavitationsschden und Gegenmanahmen (ISO 7146-2:2008),Englische bersetzung von DIN ISO 7146-2:2015-12Paliers lisses Aspect et caractrisation de lendommagement des paliers mtalliques couche lubrifiante fluide Partie 2: rosion de cavitation et sa contre-mesure (ISO 7146-2:

4、2008),Traduction anglaise de DIN ISO 7146-2:2015-12www.beuth.deDocument comprises 23 pagesDTranslation by DIN-Sprachendienst.In case of doubt, the German-language original shall be considered authoritative.11.15 Contents Page National foreword 3 Introduction 5 1 Scope . 6 2 Normative references . 6

5、3 Terms and definitions. 6 4 Cavitation erosion. 7 4.1 Mechanism of cavitation erosion 7 4.2 Classification of cavitation erosion 9 4.3 General countermeasures against cavitation erosion 12 5 Five types of cavitation erosion 13 5.1 General. 13 5.2 Flow cavitation erosion 13 5.3 Impact cavitation ero

6、sion 16 5.4 Suction cavitation erosion. 17 5.5 Discharge cavitation erosion. 19 5.6 Miscellaneous cavitation erosion (see Figures 17 to 20). 20 A comma is used as the decimal marker. DIN ISO 7146-2:2015-12 2National Annex NA (informative) Bibliography4 National foreword This document (ISO 7146-2:200

7、8) has been prepared by Technical Committee ISO/TC 123 “Plain bearings” (Secretariat: JISC, Japan), Subcommittee SC 2 “Materials and lubricants, their properties, characteristics, test methods and testing conditions”. The responsible German body involved in its preparation was DIN-Normenausschuss Wl

8、z- und Gleitlager (DIN Standards Committee Rolling Bearings and Plain Bearings), Working Committee NA 118-02-02 AA Werkstoffe, Schmierung, Prfung. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. DIN shall not be held responsible f

9、or identifying any or all such patent rights. The DIN Standards corresponding to the International Standards referred to in this document are as follows: ISO 4378-1 DIN ISO 4378-1 ISO 4378-2 DIN ISO 4378-2 ISO 4378-3 DIN ISO 4378-3 ISO 7146-1 DIN ISO 7146-1 DIN ISO 7146-2:2015-12 3 National Annex NA

10、 (informative) Bibliography DIN ISO 4378-1, Plain bearings Terms, definitions, classification and symbols Part 1: Design, bearing materials and their properties DIN ISO 4378-2, Plain bearings Terms, definitions, classification and symbols Part 2: Friction and wear DIN ISO 4378-3, Plain bearings Term

11、s, definitions, classification and symbols Part 3: Lubrication DIN ISO 7146-1, Plain bearings Appearance and characterization of damage to metallic hydrodynamic bearings Part 1: General DIN ISO 7146-2:2015-12 4 Introduction In practice, damage to a bearing may often be the result of several mechanis

12、ms 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 operates. In some instances, damage may be caused by a design compromise made in the interests of economy or from unfore

13、seen operating conditions. It is the complex combination of design, manufacture, assembly, operation, maintenance and possible reconditioning 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 lik

14、ely 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 history is of the utmost importance. The classification of bearing damage established in this International Standard is

15、 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 damage. Since more than one process may cause similar effects on the running surface, a description of appearance alone is

16、 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 this part of ISO 7146 in more detail. Plain bearings Appearance and characterization of damage to metallic hydrodynami

17、c bearings Part 2: Cavitation erosion and its countermeasures DIN ISO 7146-2:2015-12 5 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 po

18、ssible countermeasures. It assists in understanding the 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 illustra

19、ted with photographs and diagrams. 2 Normative references 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)

20、applies. ISO 4378-1, Plain bearings Terms, definitions, 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

21、and symbols Part 3: Lubrication ISO 7146-1, Plain bearings 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 appl

22、y. DIN ISO 7146-2:2015-12 6 4 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

23、the vapour 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 o

24、f cavitation 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 th

25、e high intensity 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

26、 in plain bearing 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

27、 deepen according 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 se

28、ction often 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

29、and spreads 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 variat

30、ion), motion 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

31、 strength and corrosion resistance, oil supply pressure, oil constituent and its vapor pressure, oil viscosity, oil temperature, air and water content and contamination of oil, etc. DIN ISO 7146-2:2015-12 7 a) view under magnification b) cross-section under magnification Key 1 sliding surface 3 bond

32、ing area 2 bearing metal (tin-based) 4 steel backing Figure 1 (continued) DIN ISO 7146-2:2015-12 8 c) 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 4.2 Classification of cavit

33、ation 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, cavitation erosion has been classif

34、ied 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 cavitation erosion in journal b

35、earings 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 Cavitation erosion classification 1

36、 Flow 2 Impact 3 Suction 4 Discharge 5 Miscellaneous DIN ISO 7146-2:2015-12 9 Types 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: flow b) cavitation erosion type 2: impact c) cavitation erosion type

37、 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 DIN ISO 7146-2:2015-12 10 a) cavitation erosion type 1: flow b) cavitation erosion type 2: impact d 1) oi

38、l 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:discharge Key 1 cavities in oil 2 oil flow 3 partial oil groove 4 oil column U direction of journal rotation v v

39、elocity 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 types of cavitation erosion in journal bearings DIN ISO 7146-2:2015-12 11 4.3 General countermeasures against cavi

40、tation erosion 4.3.1 As general countermeasures against cavitation erosion, some of the following 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 s

41、moothly 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

42、.4 Reduce the bearing clearance. 4.3.5 Select appropriate bearing material with increased: a) resistance tin is more resistant than lead, tin-based alloys are more resistant than lead-based alloys, and aluminium alloy (with less tin content) is more resistant than lead bronze; b) hardness, toughness

43、 and fatigue strength; c) homogeneity, freedom from slag and soft material, etc. 4.3.6 Make the bearing surface smooth and free of pores and crevices. 4.3.7 Maintain the oil free from water, dust and dirt, which act as nuclei for cavitation. 4.3.8 Minimize oil temperature and/or maximize oil viscosi

44、ty, which measures are usually favourable to minimizing erosion. 4.3.9 Inclusion of air bubbles in oil reduces cavitation erosion, but this countermeasure is not recommended, as it promotes oil degradation and viscosity reduction. 4.3.10 If steps 4.3.2 to 4.3.9 do not help, relax the operating condi

45、tions, by: a) reducing the journal speed; b) reducing the specific bearing load; c) changing the dynamic load pattern; d) reducing the vibration of bearing housing. DIN ISO 7146-2:2015-12 12 5 Five types of cavitation erosion 5.1 General For four types of cavitation erosion, typical damage appearanc

46、e, possible causes, possible countermeasures and typical examples are given in the following (see Figures 2 and 3). General countermeasures are specified in 4.3. This clause gives some possible additional concrete countermeasures. In addition, some examples for miscellaneous cavitation erosion are given. 5.2 Flow cavitation erosion 5.2.1 Typical damage appearance The bearing surface material has been removed or eroded locally. The depth of damage is often limited to the alloy layer or the overlay. In extreme cases, however, the damage can