9. Procedure
9.1 Assemble the test apparatus as shown in Fig.1. Set the compressed air temperature to within 0.2°C of the desired test temperature. Set the circulating bath to give a specimen temperature within 0.1°C of the desired test temperature. The required bath temperature setting and time for the specimen to equilibrate can be established for an equipment setup by making trial runs with a thermometer in the oil specimen. For oils with a viscosity at 40°C of less than 9.0 cSt, the test temperature shall be 25°C. For oils with a viscosity at 40°C between 9.0 and 90cSt, the test temperature shall be 50°C. Oils having a viscosity at 40°C greater than 90cSt shall be tested at 75°C.
9.2 Warm approximately 200mL of the oil to be tested in an oven set at a temperature of 10°C higher than the test temperature. Allow the sample to reach the test temperature. This may take about 20min.
9.3 Pour 180 more or less 5mL of the heated sample into the test vessel.
9.4 Allow the sample to equilibrate to the desired test temperature, using the heating-up time previously established (see 9.1) or by directly measuring the temperature.
9.5 Warm the sinker of the balance to the test temperature in an air bath, such as a glass cylinder fitted with a suitable cover situated in the circulating bath. When the sinker has reached the test temperature, immerse it in the sample, taking care that no air bubbles cling to it. Attach the sinker to the beam of the density balance by means of the platinum wire so that the bottom of the sinker is 10 more or less 2mm from the bottom of the test vessel.
NOTE 9 - The sinker can take approximately 20min to reach 50°C or 35min to reach 75°C.
9.6 Allow the density reading to stabilize, read the density from the balance to the nearest 0.1kg/m3, and record it as the initial density.
9.7 Return the sinker to the air bath and replace it with the air inlet tube as shown in Fig.2. After 5min, start the supply of air at a gage pressure of 20kPa at the required temperature. Maintain the pressure and temperature of the air (25, 50, and 75°C) by readjustments, if necessary.
9.8 After 7 more or less 0.1min, shut off the air and immediately start the timer. Quickly remove the inlet tube from the test vessel, and immerse the sinker in the oil/air dispersion. Attach the wire to the beam and maintain a distance of 10 more or less 2mm between the bottom of the sinker and the bottom of the test vessel.
NOTE 10 - In the case of certain oils, which form a considerable volume of oil/air dispersion, the top of the sinker can initially be in foam, and hence, density readings at this time can be in error.
9.9 Record the time, to the nearest 0.1min, for the density to return to the target of 99.8% of the initial density. If the time is greater than 30min, discontinue the test.
NOTE 11 - The test may be run for a longer period of time by agreement between the laboratory and the customer.
NOTE 12 - For some applications, the shape of the air release time curve may be required. This can be implemented by recording the density at intervals, as required.
9.10 Certain oils may lose light components during the air saturation, thus changing their effective density. This will be noted if the time for the density to return to the initial figure is instantaneous. Where air release value information is required for such oils, an air releasing time curve may be drawn. If the loss causes any part of the sinker to be exposed, discontinue the test and repeat, using a sample that is 10 mL larger than previously used.
