ASTM D1092 test method for measuring apparent viscosity of lubricating greases
6. Apparatus
6.1 The assembled pressure viscometer consists of four major divisions, the power system, the hydraulic system, the grease system (described in the annex and shown in Fig. 1), and a bath of optional design. Fig. 2 is a photograph of the first three divisions as commonly used at room temperature. This form of the apparatus can be used with a cylindrical insulated tank 178 mm (7 in.) in diameter and 508 mm (20 in.) deep. The bath medium may be kerosene or alcohol cooled manually with dry ice. Alternatively the grease system, the grease and hydraulic system, or all three major divisions can be built into any liquid or air bath that will cover the temperature range and maintain the grease at test temperature more or less 0.25° C (more or less 0.5°F).
7. Sampling
7.1 A single filling of the grease cylinder requires about 0.223 kg (1/2 lb) of grease which is the minimum size sample.
NOTE 2 - It is possible for an experienced operator to complete the 16 single determinations with a single filling. However, some samples reach the equilibrium pressure slowly, making it advisable to have a sample of several pounds available.
7.2 Generally no special preparation of the sample is necessary.
NOTE 3 - The apparatus works the samples to some extent as they pass through the capillary. Somewhat better precision is obtained if they are previously worked as described in Test Methods D217. Working of some greases may cause aeration.
NOTE 4 - It is desirable to filter some greases through a 60-mesh screen to prevent plugging the No. 8 capillary.
8. Calibration and Standardization
8.1 To calibrate the hydraulic system, remove the grease cylinder and replace it with a needle valve. Select a hydraulic oil of about 2000 cSt (2000 mm2/s) viscosity at the test temperature. Fill the system with hydraulic oil and circulate the oil until it is free of air bubbles. At atmospheric pressure, quickly place a 60-mL Saybolt receiving flask (Test Method D88), under the outlet and start a timer. Determine the delivery time for 60 mL and calculate the flow rate in cubic centimetres per second assuming 1 mL equal to 1 cm3. Repeat this observation at 500, 1000, 1500 psi (3.45, 6.89, 10.4 MPa) and at sufficient pressures above 1500 psi to develop a calibration curve of the type as shown in Fig. 3. The developed curve of the type is used to correct flow rates when grease is dispensed. Repeat the calibration at intervals to determine if wear is changing the pump flow.
8.2 An alternative procedure for the calibration of the hydraulic system is the measurement of the rate of flow of the test grease. To cover the desired range of shear rates, flow rates over an approximate range of pressure are determined. Any suitable means of measuring the rate of grease flow may be used.
