ASTM D4684 standard test method for determination of yield stress and apparent viscosity of engine oils at low temperature
5. Apparatus
5.1 Mini-Rotary Viscometer - An apparatus that consists of one or more viscometric cells in a temperature-controlled aluminum block. Each cell contains a calibrated rotor-stator set. Rotation of the rotor is achieved by an applied load acting through a string wound around the rotor shaft.
5.1.1 The mini-rotary viscometric cell has the following typical dimensions:
5.2 Temperature Control System - Will regulate the mini-rotary viscometer block temperature in accordance with the temperature limits described in Table X1.1 or Table X1.2.
5.2.1 Temperature Controller - The most critical part of this procedure. A description of the requirements that the controller shall meet are included in Appendix X2.
5.2.2 Temperature Profile - The temperature profile is fully described in Table X1.1 and Table X1.2.
5.3 Thermometers - For measuring the temperature of the block. Two are required, one graduated from at least +70 to 90°C in 1°C subdivisions, the other with a scale from at least -36 to +5°C or -45 to +5°C, in 0.2°C subdivisions. Other thermometric devices of equal accuracy and resolution may be used to calibrate the temperature sensor.
5.4 Refrigeration Device - Consisting of a means of maintaining a coolant (such as methanol) to at least 10°C below the lowest test temperature.
5.5 Circulating System - That will circulate the liquid coolant to the block as needed. Methanol is a suitable coolant. One should observe toxicity and flammability precautions that apply to the use of methanol. The circulating system shall be capable of maintaining test temperature during the test. If methanol is leaking from the system, discontinue the test and repair the leak. (Warning - Methanol is flammable.)
5.6 Chart Recorder - To verify that the correct cooling curve is being followed, it is recommended that a chart recorder be used to monitor the block temperature.
6. Reagents and Materials
6.1 Newtonian Oil - A low cloud-point of approximately 30 Pa•s (30 000 cP) viscosity at -20°C for calibration of the viscometric cells.
6.2 Methanol - Commercial or technical grade of dry methanol is suitable for the cooling bath.
6.3 Oil Solvent - Commercial heptanes or similar solvent that evaporates without leaving a residue is suitable. (Warning - Flammable.)
6.4 Acetone - A technical grade of acetone is suitable provided it does not leave a residue upon evaporation. (Warning - Flammable.)
7. Sampling
7.1 A representative sample of test oil free from suspended solid material and water is necessary to obtain valid viscosity measurements. If the sample in its container is received below the dew-point temperature of the room, allow the sample to warm to room temperature before opening the container.