ISO 6281-2020 pdf free download – Plain bearings — Testing under conditions of hydrodynamic and mixed lubrication in test rigs.
6 Test rigs
6.1 General recommendations
lt is often more practicaland efficient to investigate the bearing in a testrig than in an actual application.The design of the bearing test rig should be such as to simulate as far as possible all the relevantcharacteristic parameters (e.g. geometric, dynamic, hydrodynamic, thermal, and thermodynamic] ofthe actual application.
In addition, the following is recommended for the test rig.a) A simple mechanical construction.
b) Simple dismantling and assembly procedures for the test objects; with well-defined positioning
of the bearing and housing; preferably it should be possible to inspect the test bearing in situ.ln addition, the test rig should be equipped with an emergency stop mechanism, both for safetyreasons and to allow the inspection of the sliding surface before the onset of catastrophic damage.)A well-defined dimensions for the test bearing.
d) A high dimensional stability with little shaft deflection. The test rig should be as rigid as possible,
with a high natural frequency.In special cases, however, it can be necessary to vary the dimensionalstability or the shaft deflection in order to simulate the operating condition of the actual application.e) An appropriate lubricant supply condition.When the lubricant flow within the bearing clearance
needs to be simulated exactly, the circumferential and axial position of the lubricant supply in thetest rig should be the same as in the actual application.
f)Well-defined and experimentally verifiable lubrication conditions.
g) The regime of laminar or turbulent flow should be the same in the test rig and in the actual
application.
h) The rig should replicate as far as possible the temperature and stress range that can occur in
practice.
i)Appropriate measuring techniques or equipment should be employed.6.2Generic types of test rig
Generic types of test rig for plain journal bearings are shown in Figure 2 and Figure 3.Figure 2 a) andFigure 2 b) depict the rotational motion of the journal, where a combination of both is also possible.ln practice, many more patterns of journal motion other than rotation can occur, such as inclination,bending, axial, conical and their combinations. In addition, the bearing itself can rotate, oscilate oreven move in space instead of, or together with, the journal, as with a crank-pin bearing.In any case, therelative motion of the journal to the bearing shall be known(measurable) exactly. However, constantrotational speed of journal and the parallel movement of journal to bearing are the simplest and mostpreferable for testing.
Figure 3 shows patterns of the bearing load.ln the case of statically loaded journal bearing [Figure 3 a)J,the magnitude,F, and the direction, B, of the bearing load are constant.In a special case of dynamicallyloaded bearing,F is constant, but $ increases or decreases with time[Figure 3 b)].In the general case ofdynamically loaded bearing [Figure 3 c)], both or at least one of F and $ change(s) with time, while theremaining variable can be constant.The change of form of F(also 3) is then arbitrary, such as sinusoidalwith or without constant offset, curving steeply up and downwards, as, for example, in engine bearingloading.
With regard to the loading of the test bearing, it is often more practical to load the test bearing directlysupported by the journal [Figure 4 a)], than to load the test bearing indirectly through the journal[Figure 4 b)J].For static loading, a dead weight system,with or without lever, or hydraulic or pneumaticactuation can be used.For dynamic loading, a rotating or vibrating mass system, with or without lever,an electromagnetic exciter, and hydraulic actuation, can be applied.Dynamic loading by means of amass fixed to the journal seems to be simple, but the amplitude of the bearing load is then determinedprimarily by the rotational speed of the journal. Therefore, it is not easy to change the load amplitudeindependently of the rotational speed. Furthermore, the magnitude and direction of the bearingload shall be precisely measured, and it is important to let the journal move freely inside the bearingclearance without hindrance from the loading mechanism.
Besides such bearing test rigs operating under hydrodynamic or mixed lubrication, as described above,many other kinds of test apparatus and test methods may be used to investigate the tribological ormechanical properties of bearing materials,including coefficient of friction，mechanical strength,hardness, elasticity, plasticity and bond strength. The study of the tribological properties of boundaryfilms has also led to the development of other test apparatus and methods; these are, however, outsidethe scope of this document (see IS0 4384-1, ISO 4384-2,IS0 4385,ISO 7148-1,ISO 7148-2,ISO 7905-2,ISo 7905-3, and lSO 7905-4).
NOTE The testing of the resistance to corrosion of bearing materials by the lubricant is the subject ofISO 10129.ISO 6281 pdf download.