ASTM D2603 Test Method for Sonic Shear Stability of Polymer-Containing Oils
7. Calibration of Apparatus
7.1 The reference fluid provides a practical way to define the performance (severity level) of a sonic oscillator unit so that satisfactory comparison can be made between tests run on different days in the same unit and between tests run with different units.
7.2 The decrease in viscosity observed for a given polymer-containing oil on irradiation in an oscillator unit depends on a number of factors; these include sample volume, irradiation time, and oscillator power setting. These parameters can be varied in order to increase or decrease severity of test exposure. Tuning of the oscillator-horn combination is also required in order to assure efficiency of energy coupling between the two units. The procedure described in 7.3 and 7.4 is recommended for establishing a reproducible performance level for a given unit.
7.3 Introduce 30 mL of a reference fluid into the 50-mL Griffin beaker. Immerse the beaker in ice water or in another constant temperature bath until sample fluid level is below the liquid level in the bath. The beaker shall be positioned in a vertical position in the bath. Secure beaker in this position and condition the sample for 10 min before commencing exposure. Immerse the sonic horn into sample fluid until tip is exactly 10 mm below surface of fluid (see Fig. 1). The horn shall be positioned in a vertical position in the fluid and centered in the beaker (a weighted ringstand may be used to support the horn in this position). Irradiate the fluid for 10 min at a preselected power setting. Experience has shown that with some instruments this may require readjustment of the controls during irradiation to maintain the preselected power. Determine the decrease in reference fluid viscosity. Repeat as necessary to determine the proper power setting to produce a viscosity change at 40°C of 15.0 % (+/-0.5 %). Use this power setting for subsequent test runs. Daily recalibration of the apparatus is required because the power setting required to produce a stated viscosity loss will probably vary from day to day. Experience with a given apparatus set will determine whether more frequent calibration is required. Calibration in this manner will assure that repeatable severity levels are established for any predetermined set of test parameters.
7.4 This procedure can be used to establish severity levels appropriate for the requirements of a variety of applications. Once the conditions for a given severity level have been established, it is possible to compare the shear stability of fluids at one or more irradiation times. If calibration at conditions other than 15.0 % +/- 0.5 % decrease of reference fluid viscosity at 40°C are employed, that fact shall be included in the test report.
NOTE 2 - For interlaboratory comparisons, the laboratories should define a common severity level in terms of a specified viscosity loss of the reference fluid occurring in a given irradiation time with a given volume of sample. For example, "the reference fluid should undergo a viscosity loss of 15 % when a 30 mL sample is treated for 10 min".
Alternatively, two or more laboratories can define equivalent operating conditions by a curve of percent viscosity loss of a reference fluid as a function of irradiation time. Power setting and sample size are varied until each laboratory finds a combination that satisfies two or more points on the reference curve. This procedure provides a comparison of the shear stability of an unknown fluid with that of the reference fluid over a range of irradiation times.
