ASTM D5133 low temp, low shear rate, viscosity/temp dependence of lubricants
ASTM D5133 standard test method for Low Temperature, Low Shear Rate, Viscosity/Temperature Dependence of Lubricating Oils Using a Temperature-Scanning Technique
4. Summary of Test Method
4.1 After pre-heating approximately 20 mL of the test oil in a glass stator at 90°C for 1.5 to 2.0 h., the test cell containing the test oil is attached to a suitable viscometer drive module and the test cell immersed in a liquid cold bath and cooled at 1°C/h over the temperature range of -5 to -40°C. Data from the viscometer drive module is collected and fed to a computerized data assimilation program to determine the Gelation Index, Gelation Index temperature, and Critical Pumpability temperature for a selected viscosity such as 30 000 or 40 000 mPa•s (cP).
5. Significance and Use
5.1 Significance of Low-Temperature, Low Shear Rate, Engine Oil rheology - The low-temperature, low-shear viscometric behavior of an engine oil determines whether the oil will flow to the sump inlet screen, then to the oil pump, then to the sites in the engine requiring lubrication in sufficient quantity to prevent engine damage immediately or ultimately after cold temperature starting.
5.1.1 Two forms of flow problems have been identified, flow-limited and air-binding behavior. The first form of flow restriction, flow-limited behavior, is associated with the oil's viscosity; the second, air-binding behavior, is associated with gelation.
5.2 Significance of the Test Method - The temperature-scanning technique employed by this test method was designed to determine the susceptibility of the engine oil to flow-limited and air-binding response to slow cooling conditions by providing continuous information on the rheological condition of the oil over the temperature range of use. In this way, both viscometric and gelation response are obtained in one test.
NOTE 1 - This test method is one of three related to pumpability related problems. Measurement of low-temperature viscosity by the two other pumpability Test Methods D3829 and D4684, hold the sample in a quiescent state and generate the apparent viscosity of the sample at shear rates ranging up to 15 sec(-1) and shear stresses up to 525 Pa at a previously selected temperature. Such difference in test parameters (shear rate, shear stress, sample motion, temperature scanning, and so forth) can lead to differences in the measured apparent viscosity among these test methods with some test oils, particularly when other rheological factors associated with gelation are present. In addition, the three methods differ considerably in cooling rates.
5.3 Gelation Index and Gelation Index Temperature - This test method has been further developed to yield parameters called the Gelation Index and Gelation Index temperature. The first parameter is a measure of the maximum rate of torque increase caused by the rheological response of the oil as the oil is cooled slowly. The second parameter is the temperature at which the Gelation Index occurs.
