ASTM D3336 Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures
10. Results
10.1 The lubricant is considered to have failed when any one of the following conditions occurs:
10.1.1 Spindle input power increases to a value of 300 % above the steady state condition at test temperature.
10.1.2 An increase in temperature at the test bearing of 15°C (27°F) over the test temperature during any portion of a cycle. Ignore any temperature rise that takes place within 30 min after reaching test temperature after daily start-up.
10.1.3 There is loading of the test bearing or belt slippage at start up or during the test cycle.
11. Precision and Bias
11.1 The precision of this test is not known to have been obtained in accordance with currently accepted guidelines (for example, see Committee D-2 Research Report "Manual on Determining Precision Data for ASTM Methods on Petroleum Products and Lubricants").
11.2 Grease life data generated in two separate cooperative testing programs show appreciable scatter and follow Weibull distributions rather than normal distributions. Statistical parameters such as repeatability and reproducibility are therefore not appropriate. Weibull parameters such as slope, L10, L50 and Lc better describe the distribution of test data.
11.2.1 Precision may be judged from Weibull plots of the test data, shown in Fig. 4 and Fig. 5, and from calculated Weibull parameters, summarized in Table 1 (90 % confidence limits are shown in parentheses). Precision may also be judged from the mean and range for the center 50 % of results reported, also summarized in Table 1.
11.3 Replicate testing is essential when using this procedure since appreciable scatter in grease life results can be expected.
11.4 Bias - The procedure for measuring life of lubricating greases in ball bearings at elevated temperatures has no bias because the value of performance life in ball bearings at elevated temperature can be defined only in terms of a test method.
12. Keywords
12.1 ball bearing; grease; life
