ASTM D7279 Standard Test Method for Kinematic Viscosity of Transparent and Opaque Liquids by Automated Houillon Viscometer
10. General Procedure for Kinematic Viscosity
10.1 Set and maintain the automated viscometer bath at the required test temperature.
10.1.1 Thermometers, if used, shall be held in an upright position under the same conditions of immersion as when calibrated.
10.2 Introduce a sufficient volume of sample to the Houillon tube, using a volume delivery device (see 5.1.8) such as a micro-pipette. The specimen volume to be used is a function of the viscometer tube constant (see Fig. 1). Fig. 2 shows the correct specimen levels during a measurement.
NOTE 3 - Use a volume delivery device that is capable of introducing the entire specimen volume in one operation.
10.3 Introduce the specimen into the viscometer tube. Start the measurement sequence.
10.4 The automated viscometer processing system will measure the flow times, calculate the viscosity according to Eq 1, and record the result.
10.5 Start the cleaning sequence (see Section 11).
10.6 Allow the viscometer tube to reach the bath temperature (about 5 min) before performing a new measurement.
NOTE 4 - In some units, the equilibration time required may be much less than 5 min.
11. Cleaning of Viscosity Tubes
11.1 The viscometer tubes are cleaned by vacuuming the specimen residue left in the viscometer tube followed by the use of a solvent to remove any traces of the specimen on the viscometer tube walls. The solvent is then removed by vacuum. Some units use a second solvent for drying the tube. This operation is repeated several times until the viscometer tube is clean. Periodically, the viscometer tube calibration constant should be checked.
11.2 The solvent(s) should have a boiling point appropriate for the bath temperature.
11.2.1 The solvent flow must be sufficient to clean the entire internal section of the viscometer tube. This can be achieved by adjusting the solvent flow(s) and the flow rate using appropriate controls.
11.3 The cleaning of one tube shall not be carried out while a test is being performed in another tube in the same bath.
NOTE 5 - Some multiple tube systems, although not included in the interlaboratory study conducted to obtain the precision and bias of this test method, are designed to clean tubes while other tubes are performing viscosity measurements. Hence, this cleaning does not interfere with the validity of the tests underway in the instrument.
11.4 To ensure good operation, regularly check the viscometer tubes for damage and cleanliness. The latter can be done by checking with the reference oils suitable for the particular tube being used. Use these check oils like regular samples. If the results obtained are different from the certified values of these oils, it is necessary to carry out a more vigorous cleaning of the tubes in question. Non-chromium containing cleaning solution (see 6.2) may have to be used.
11.5 The frequency at which the tubes should be checked using reference oils depends on the frequency with which the tubes are used for measurements.
12. Quality Control/Quality Assurance (QC/QA)
12.1 Confirm proper performance of the instrument and the test procedure by analyzing a QC sample.
12.2 If a suitable QC oil sample is not available, prepare the QC material by replicate analyses of a batch of oil sample and statistically analyze the data to assign a mean value and uncertainty limit to the sample.
12.3 When QC/QA protocols are already established in the testing facility, these may be used when they confirm the reliability of the test result.
12.4 When there is no QC/QA protocol established in the testing facility, Appendix X1 can be used as the QC/QA system. Further guidance can be obtained from Guide D6792.
