ASTM D2983 for low-temperature viscosity of lubricants by Brookfield viscometer
ASTM D2983 standard test method for low-temperature viscosity of lubricants measured by Brookfield Viscometer
9. RPM Selection
9.1 Because many lubricant fluids are non-Newtonian at low temperatures, the rpm selected for a measurement can strongly influence the resultant viscosity (see Appendix X1). For this reason, Table 1 lists the viscosity range for each rpm.
9.2 If an expected apparent viscosity is known, use the highest rpm corresponding to the known viscosity range. Table 1 must be used in selecting the appropriate rpm. Table 1 also provides the multiplication factor for viscometers without a viscosity readout or if the older analog viscometer is used. Simply multiply the torque display or the dial reading by the number provided for the speed selections used. Make certain that the torque value (or dial reading) is as close to mid-range as possible (that is, 50).
9.3 If the expected viscosity range of the sample is unknown, a first sample must be used to determine the highest rpm that gives an acceptable viscometer reading. This is accomplished by increasing speed in steps from 0.6 to 60 rpm. The second sample is then run at the previously determined speed and only this result is reported.
10. Calculation
10.1 For viscometers without direct viscosity readout, calculate the viscosity at the test temperature of the test oil or reference oil as shown in Table 1.
10.2 The shear stress and shear rate at the surface of the Brookfield spindle may be estimated by the procedure in Appendix X3.
11. Report
11.1 A routine report includes the apparent viscosity, the test temperature, and the test rpm. RPM data are needed to ensure that different laboratories use the same shear rates.
11.2 In cases where this test method is used for reference testing, a full report of the Newtonian reference fluid, its reference viscosity, its apparent viscosity, and its test rpm must accompany the test fluid data of 9.3. Reference fluid data are needed to ensure that different laboratories run at the same temperature, shear rate, and viscometric conditions.
12. Precision and Bias
12.1 Statement of Precision:
12.1.1 Repeatability - The difference between successive test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, and in the normal and correct operation of the test method, exceed the values indicated below only in one case in 20.
Repeatability = 3.79 (X/1000)<1.7>
where:
X = the apparent viscosity, in mPa•s.
12.1.1.1 For Example Only - the following shows the repeatability at several viscosities:
20 000 mPa•s: 616 mPa•s 100 000 mPa•s: 9 520 mPa•s
50 000 mPa•s: 2 930 mPa•s 200 000 mPa•s: 30 930 mPa•s
12.1.2 Reproducibility - The difference between two single and independent results, obtained by different operators working in different laboratories on identical test material would, in the long run, and in the normal and correct operation of the test method, exceed the values indicated below only in one case in 20.
Reproducibility = 11.34 (X/1000)<1.7>
where
X = the apparent viscosity, in mPa•s.
12.1.2.1 For Example Only - the following table shows the reproducibility at several viscosities:
20 000 mPa•s: 1 850 mPa•s 100 000 mPa•s
28 560 mPa•s
50 000 mPa•s: 8 790 mPa•s 200 000 mPa•s
92 790 mPa•s
12.1.3 No information can be presented on the bias of the procedure in Test Method D2983 for measuring viscosity because no material having an accepted reference value is available.
12.2 General Considerations:
12.2.1 The interlaboratory study for the above precision statement was made on two groups of samples. For viscosities within the range of 500 to 1700 mPa.s, 6 hydraulic oils were evaluated in ten laboratories. For viscosities within the range of 17 000 to 200 000 mPa.s, 8 formulated oils were tested in eleven laboratories.
12.2.2 All laboratories utilized Brookfield viscometers for analysis.
