D445_11 (17a)

Charge the viscometer in the manner dictated by the design of the instrument. This operation being in conformity with that employed when the instrument was calibrated. If the sample is thought or known to contain fibers or solid particles, filter through a 75 unit of measure screen, either prior to or during charging. See Specifications D446. To minimize the potential of particles passing through the filter from aggregating, it is recommended that the time lapse between filtering and charging be kept to a minimum. In general, the viscometers used for transparent liquids are of the type listed in table A 1.1 of the written standard, A and B. With certain products which exhibit gel-like behavior, exercise care that flow time measurements are made at sufficiently high temperatures for such materials to flow freely, so that similar kinematic viscosity results are obtained in viscometers of different capillary diameters. Allow the charged viscometer to remain in the bath long enough to reach the test temperature. Where one bath is used to accommodate several viscometers, never add or withdraw, or clean the viscometer, while any other viscometer is in use for measuring a flow time. Because this time will vary for different instruments, for different temperatures, and for different kinematic viscosities, establish a safe equilibrium time by trial. 30 minutes should be sufficient, except for the highest kinematic viscosities. Where the design of the viscometer requires it, adjust the volume of the sample to the mark after the sample has reached temperature equilibrium. Use suction if the sample contains no volatile constituents or pressure to adjust the head level of the test sample to a position in the capillary arm of the instrument, about 7 millimeters above the first timing mark, unless any other value is stated in the operating instructions for the viscometer. With the sample flowing freely, measure in seconds to within 0.1 second the time required for the meniscus to pass from the first to the second timing mark. If this flow time is less than the specified minimum, see 10.2 of the written standard. Select a viscometer with a capillary of smaller diameter, and repeat the operation. Repeat the procedure described in 11.2 of the written standard to make a second measurement of flow time. Record both measurements. From the two measurements of flow time, calculate two determined values of kinematic viscosity. Reference section 11.2.3 and 11.2.4 of the written standard for information on determining values of kinematic viscosity. Verify that the calibration constant for the viscometer being used is appropriate for the temperature at which the measurement is being made. Refer to the viscometer calibration certificate for more details. In this particular case, the viscometer tube calibration constant, C, equals 0.01512 millimeters squared per second squared. Using the flow time measurement from test number 1, 226.44 seconds, calculate the kinematic viscosity determination using the following equation. Nu equals 226.44 seconds times 0.01512 millimeters squared per second squared equals 3.424 millimeters squared per second. Calculate the second kinematic viscosity determination using the flow time measurement from test number 2, 226.75 seconds. Nu equals to 226.75 seconds times 0.01512 millimeters squared per second squared equals 3.428 millimeters squared per second. Determine the difference between the two kinematic viscosity results. Average kinematic viscosity determination number 1 and 2. Use the determine ability calculation for gas oils from section 17.1.1. 0.0013 times y plus 1, where y is the average of determined values being compared. 0.0013 times 3.426 millimeters squared per second plus 1 equals 0.005754 millimeters squared per second. Because the difference between the two kinematic viscosity determinations, 0.004, is less than the calculated determined ability, 0.005754, the measurement is considered to meet ASTM D445 determined ability. Therefore, report the kinematic viscosity result as the average of the 2 determined values, 3.426 millimeters squared per second, rounded to 4 significant figures as per section 15.1 of the written standard.