ASTM D5481 Standard Test Method for Measuring Apparent Viscosity at High-Temperature and High-Shear Rate by Multicell Capillary Viscometer
10. Procedure
10.1 Bring the viscometer to the test temperature and allow test temperature to stabilize for at least 30 min. Because the viscometer uses only a small amount of electrical power, it may be desirable to leave the viscometer at test temperature unless use is not anticipated for an extended period of time.
10.2 Flush the previous sample with 4 to 6 mL of the new test sample. Open the plug valve. (Warning - Always keep the plug valve closed except when charging or adjusting the volume of sample; NEVER turn on the pressure with the plug valve open.) Insert a 4 to 6-mL test sample, and close the plug valve. Turn on the pressure (it is not necessary to adjust the pressure from the previous run) until the flush sample has passed through the capillary to waste. It is not necessary to achieve temperature equilibrium since no time measurement is being made. Turn off the pressure.
10.3 Charge a 9 to 11-mL test sample into the viscometric cell by opening the plug valve, inserting the test sample, and then closing the plug valve.
10.4 Repeat 10.2 and 10.3 for each of the viscometric cells.
10.5 Allow 15 min for the test sample to attain 150 +/- 0.1°C.
10.6 After temperature equilibrium has been established, ensure that the plug valve is closed on each cell and make measurement of efflux time and pressure as follows:
10.6.1 From the calibration of the viscometric cell and the expected viscosity of the sample (if known), estimate the required pressure to achieve the nominal flow time, t o (see 9.1.1). Table 2 provides a guide for setting pressure if the SAE viscosity grade is known. Adjust the pressure in the ballast tank to this value within +/- 1 %; allow approximately 10 s for this pressure to stabilize.
10.6.2 Reset the timer to zero.
10.6.3 Open the plug valve and withdraw excess sample by vacuum through the filling tube until no more liquid is being withdrawn. Immediately close plug valve and immediately proceed to 10.6.4.
10.6.4 Turn on the run switch for the viscometric cell. Read and record the pressure approximately 10 s after turning on the pressure switch.
10.6.5 When the timer has stopped (indicating that the measurement has been completed), turn off the pressure switch, and record the flow time. It may be necessary to adjust the indicator meter of the timer during the course of a test to ensure clear "start" and "end" signals.
10.6.6 Repeat 10.6.1 through 10.6.5 for each cell.
11. Calculation of Results
11.1 Using the calibration equation, calculate the viscosity in mPa•s and the apparent shear rate at the wall in s(−1) for each cell. If the apparent shear rate at the wall is not within +/- 5 % of 1.4 x 10(6)s(−1), recalculate the pressure required and make a second determination in the same or a different cell.
11.2 In some instances, it can only be necessary to determine that the viscosity of the test sample exceeds a specified viscosity. When the exact viscosity of the test sample is not required, the pressure for the cell can be calculated from the calibration using the specified viscosity and flow time, to. If the measured flow time for the test sample exceeds to, then the viscosity must exceed the specified viscosity.
