ASTM D6186 Test Method for Oxidation Induction Time of Lubricating Oils
ASTM D6186 Standard Test Method for Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry (PDSC)
8. Procedure
8.1 Before starting a test, the control thermocouple calibration shall be conducted at the test temperature (either 210, 180, 155, or 130°C) according to 7.2.1 and 7.2.2. When the test temperature is not known, conduct the calibration at 210°C.
8.2 Weigh 3.0 +/- 0.2 mg of oil into a new sample pan. Spread the sample evenly upon the flat portion. Do not spill any of the sample into the trough portion of the pan. A flat bottom pan can be used if the sample is placed upon a 0.5 cm diameter circle in the center of the pan.
8.3 Place the uncovered pan containing the sample onto the platform of the cell according to the PDSC manufacturer's instructions for placing the sample pan. Place a new empty pan of the same configuration onto the cell platform according to the PDSC manufacturer's instructions for placing the reference pan. Close the cell and the pressure release valve.
8.4 Beginning at ambient temperature (approximately 22°C), program the sample temperature to increase at a rate of 100°C/min to the test temperature.
8.5 Allow the sample to equilibrate at the test temperature for 2 min.
8.6 Open the oxygen valve and slowly pressurize the cell to 3.5 +/- 0.2 MPa (500 +/- 25 psig). This requires approximately 2 min to reach maximum pressure. Measure the oxidation induction time from the time when the oxygen valve is opened.
8.7 As soon as the pressure has equilibrated, check the cell purge rate and adjust and maintain at 100 +/- 10 mL/min with the outlet valve.
8.8 After a duration of 120 min from the time when the oxygen valve was opened, close the oxygen valve and slowly release the cell pressure by opening the cell pressure release valve. In the case of a sample for which the approximate oxidation induction time is known, the test can be stopped after the oxidation exotherm has occurred.
8.9 Plot the thermal curve and measure the extrapolated onset time for the oxidation exotherm. Report this time, to the nearest one minute, as the oxidation induction time for the sample. If more than one oxidation exotherm is observed, report the oxidation induction time for the largest exotherm.
NOTE 6 - A typical thermal curve is shown in Fig. 3.
8.10 If the induction time is less than 10 min, rerun the test at the next lower temperature, starting at 8.2. Allow the cell to cool to ambient temperature before running the test at the next lower temperature.
