ASTM D1478 test method for low-temperature torque of ball bearing grease
9. Calculation and Report
9.1 Depending on the dynamometer scale calibration, calculate and report starting and running torques in g•cm to three significant figures using the appropriate equation, as follows:
9.1.1 For a scale calibrated in grams:
torque = 6.50 x scale reading
9.1.2 For a scale calibrated in pounds:
torque = 2950 x scale reading
9.1.3 For a scale calibrated in Newtons:
torque = 663 x scale reading
9.2 To convert torque in g•cm to torque in mN•m, multiply by 0.0981 and round to three significant figures.
10. Precision and Bias
10.1 Precision - The precision of this test method was not obtained in accordance with currently accepted guidelines (for example, Committee D-2 Research Report RR: D02-1007, Manual on Determining Precision Data for ASTM Methods on Petroleum Products and Lubricants).
10.1.1 Alternative A:
10.1.1.1 Low-temperature torque results derived from cooperative testing using this procedure show appreciable scatter. In general, the data were found to conform to Weibull probability distributions, rather than the "normal" distributions around which ASTM statements of repeatability and reproducibility are formulated. Weibull parameters such as Slope, L10, and L50 have been used to describe the test data.
10.1.1.2 Precision may be judged from Fig. 6 and Fig. 7, Weibull plots for starting and running torques, respectively, and from the calculated Weibull parameters in Table 1. Precision may also be judged from the range for the center 50 % of the reported test results.
10.1.1.3 Replicate testing is essential when using this procedure, since appreciable scatter in test results can be expected.
10.1.2 Alternative B:
10.1.2.1 The following criteria should be used in judging the acceptability of results (95 % confidence). These calculations are based on logarithmic data transformations.
10.1.2.2 Repeatability - Duplicate results by the same operator should be considered suspect if they differ by more than the following amounts:
Starting torque: 34 % of their mean
Torque after 60 min: 78 % of their mean
10.1.2.3 Reproducibility - The results submitted by each of two laboratories should be considered suspect if they differ by more than the following amounts:
Starting torque: 79 % of their mean
Torque after 60 min: 132 % of their mean
10.2 Bias - Bias cannot be determined in this test method because the value of the torque can be defined only in terms of the test method.
11. Keywords
11.1 ball bearing grease; ball bearing torque; low-temperature torque; lubricating grease; torque
