ASTM D6895 Standard Test Method for Rotational Viscosity of Heavy Duty Diesel Drain Oils at 100°C
12. Procedure
12.1 Run the procedure in accordance with the instrument geometry requirements and the manufacturers' recommendations to obtain shear stress versus shear rate data in the ranges of 0.1 to 10 Pa and 10 to 300 s(-1). The order of steps is as follows:
12.1.1 Load sample.
12.1.2 Equilibrate at 100°C (minimum 5 min, maximum 10 min).
12.1.3 Preshear sample at 10 s(-1) for 30 s.
12.1.4 Stop preshear.
12.1.5 Preheat sample at 100°C for 10 min.
12.1.6 Run increasing stress or rate sweep for duration of approximately 10 min to generate data of shear stress, shear rate and viscosity followed immediately by the next step. The run time will vary somewhat among different instruments and procedures. Times as low as 2 min and as high as 20 min have been utilized successfully to run this test method.
12.1.7 Run decreasing stress or rate sweep for duration of approximately 10 min to generate data of shear stress, shear rate, and viscosity.
12.1.8 Clean sample from instrument in accordance with the manufacturers' instructions. Cone and plate systems shall be rinsed with a suitable solvent followed by wiping with a rag or towel.
13. Calculation or Interpretation of Results
13.1 Analyze the increasing and decreasing sweeps separately.
13.2 Import the shear stress (Pa), shear rate (s(-1)) and viscosity (mPa·s) into a spreadsheet program. This calculation may be done with a calculator. Delete data below the noise limit as determined in 10.3.
13.3 Calculate two additional columns for ln (shear rate) and ln (shear stress). See Appendix X1 for sample calculation.
13.4 Plot the ln stress versus ln rate columns as a scatter plot with ln rate on the x-axis.
13.5 Fit a least squares linear regression to the data plot. Obtain the equation of the line. This line follows Eq 2. There is no criterion for correlation coefficient of candidate oils. See Appendix X1 for sample calculation.
13.6 Obtain the slope of the line, c which is the rate index, to three decimal places and the intercept as ln b to four decimal places.
13.7 Calculate the viscosity at 100 s(-1) by interpolation between two data points spanning 100 s(-1) as follows:
VIS100 = VIS1 + D(100 - T1)
where:
D = ((VIS2 - VIS1)/(T2 - T1)),
VIS2 and T2 = viscosity and shear rate respectively at the first data point above 100 s(-1), and
VIS1 and T1 = viscosity and shear rate respectively at the first data point below 100 s(-1).
