ISO 7148-1:2012 pdf download – Plain bearings —Testing of thetribological behaviour of bearing materials — Part 1: Testing of bearing metals.
7 Test methods and test equipment
The pin, block, sleeve or plate, made of the bearing materials, is pressed with a known normal force, F, against the rotating specimen (disc, ring or sleeve) made from the material of the mating component.
In practice, surfaces with cylindrical surface curvature (journal bearings) are also tested by test method B. If they are multilayer materials, there are two alternatives:
a) adapt the radius a the ring to that of the block (see Figure 2);
b) begin testing with line contact (radius of the block to be larger than the radius of the ring).
The linear wear should not exceed the thickness of the surface bearing material layer. For thin layers, test method A (pin-on-disc) and test method C (thrust rotation) are preferred.
If tests are performed under an other-than-normal atmosphere, use shall be made of either a sufficiently airtight chamber or a high rate of gas flow.
Equipment for the continuous measurement of friction and wear shall be available.
11 grease lubrication Is to he used, the equipment shall be such that sufficient grease is continuously supplied to the sliding track.
Vibrations in the loading mechanism, which can cause undefined variations in the applied normal force, shall be avoided.
8 Lubrication
Oil or grease lubrication shall be used depending on the practical application. The contact surface between the pin, block, sleeve or plate and the disc, ring orsleeve shall be completely filled with lubricant.
When oil lubrication is used, it is preferable for the specimens to be completely immersed in the oil. Spray lubrication may also be used, assuming that the volume of the lubricant supplied is sufficient to ensure that the wear rate is not dependent upon the lubricant flow rate. The oil temperature shall be kept constant.
NOTE Test results can vary widely depending on the lubricant used.
9 Designation
EXAMPI.E The testing of the tribological behaviour of metallic hearing materials according to test method A (pin-on-disc) is designated as follows:
Test ISO 7148-1 -A
10 Test conditions
When testing different material/lubricant combinations comparatively, the method of machining and finishing the pin, block, sleeve or plate (bearing material) and the disc, ring or sleeve (mating material), and the following independent test variables, shall all he kept constant during the test programme:
— Initial surface roughness, Ru, of the specimens;
— normal force, F
— lubricant temperature, TL;
— sliding distance, a;
— sliding velocity, U;
— overlap ratio, KA.
In order to simulate friction and wear in a given plain bearing, realistic values of surface roughness. normal force, oil temperature and a sufficiently long sliding distance should he chosen,
When materials are being evaluated for specific applications, It Is important that the surfaces be typical for that application, and constant for each test.
At prolonged running under conditions of boundary lubrication, the roughness of the mating material surface can change gradually as a result of contact with the bearing material. This, in turn, may lead to change in the wear rate of the bearing material. In evaluating materials for applications in which the plain bearing is expected to run under conditions of boundary lubrication for appreciable periods of time, this can be taken into account by performing a long-term test, measuring the wear volume as a function of the sliding distance, After the test has been completed, the roughness of the mating material surface, Ru, should be measured and given with the test results. A newly prepared surface shall be used for each test.
As far as the normal force. F, is concerned, the most widely accepted compromise is to make the maximum force per unit pin, block or sleeve area equal to the force per unit projected bearing area (specific load) of the practical application.
When comparing material/lubricant combinations in which the bearing materials have different mechanical properties and load capacities, the test may be carried out with values of normal force which generate specific loads (normal force divided by projected contact area) ranging up to one third of the 0.2 % proof stress. R0.2. or one third of the 0,2% compression limit, RdO,Z, (as specified in ISO 4385) at the temperature of the application. In practice, this value is generally considered to be the maximum permissible force per unit projected area for each material in highly loaded plain bearings under boundary lubrication conditions.
For T1,. a temperature corresponding to the highest temperature which is expected to occur in practice shall be chosen. The sliding velocity. U, shall be so low that the system does not reach hydrodynamic conditions.
If the friction and wear behaviour of a bearing material/mating/lubricant combination is to be compared with other combinations without reference to a specific application, the normal torce, Fn, and the lubricant temperature TL (and possibly the surface roughness values Ra) should be varied, preferably. between wide limits.