ISO 3104 Petroleum products - Transparent and opaque liquids - Determination of kinematic viscosity and calculation of dynamic viscosity
8 General procedure for kinematic viscosity determination
8.1 Adjust and maintain the viscometer bath at the required test temperature within the limits given in 6.3, taking account of the conditions given in annex B and of the corrections supplied on the certificates of calibration for the thermometers.

Thermometers shall be held in an upright position under the same conditions of immersion as when calibrated.

NOTE 11 In order to obtain the most reliable temperature measurement, it is recommended that two thermometers with valid calibration certificates be used (see 6.4). They should be viewed with a lens assembly giving approximately x 5 magnification and be arranged to eliminate parallax errors.

8.2 Select a clean, dry, calibrated viscometer having a range covering the estimated kinematic viscosity (that is, a wide capillary for a very viscous liquid and a narrower capillary for a more fluid liquid). The flow time shall not be less than 200 s or the longer time noted in ISO 3105.

NOTE 12 The specific details of operation vary depending on the type of viscometer. The operating instructions for the different types of viscometers listed in table A. are given in ISO 3105.

8.2.1 When the test temperature is below the dew point, affix loosely-packed drying tubes to the open ends of the viscometer. The drying tubes shall fit the design of the viscometer and not restrict the flow of the sample by pressures created in the instrument. Carefully flush the moist room air from the viscometer by applying vacuum to one of the drying tubes. Finally, before placing the viscometer in the bath, draw up the sample into the working capillary and timing bulb and allow to drain back, as an additional safeguard against moisture condensing or freezing on the walls.

8.2.2 Viscometers used for silicone fluids, fluorocarbons and other liquids which are difficult to remove by the use of a cleaning agent shall be reserved for the exclusive use of those fluids, except during their calibration. Subject such viscometers to calibration checks at frequent intervals. The solvent washings from these viscometers shall not be used for the cleaning of other viscometers.

9 Determination of viscosity of transparent liquids
9.1 Charge the viscometer and place in the bath in the manner dictated by the design of the instrument, this operation being in conformity with that employed when the instrument was calibrated. If the sample contains solid particles, filter during charging through a (75 μm) filter (see ISO 3105).

NOTE 13 In general, the viscometers used for transparent liquids are of the type listed in table A.1, types A and B.

9.1.1 With certain products which exhibit "gel-like" behaviour, take care that measurements are made at temperatures sufficiently high for such materials to flow freely, so that similar kinematic viscosity results are obtained in viscometers of different capillary diameter.

9.1.2 Allow the charged viscometer to remain in the bath long enough to reach the test temperature. Where one bath is used to accommodate several viscometers, never add or withdraw a viscometer while any other viscometer is being used to measure flow time.

Because time in the bath will vary for different instruments, for different temperatures and for different kinematic viscosities, establish a safe equilibrium time by trial.

NOTE 14 30 min should be sufficient, except for the highest kinematic viscosities.

9.1.3 Where the design of the viscometer requires it, adjust the volume of the sample to the mark after the sample has reached temperature equilibrium.

9.2 Use suction (if the sample contains no volatile constituents) or pressure to adjust the head level of the test sample to a position in the capillary arm of the instrument approximately 7 mm above the first timing mark, unless any other value is stated in the operating instructions for the viscometer. With the sample flowing freely, measure, in seconds to within 0.1 s (see 6.5), the time required for the meniscus to pass from the first to the second timing mark. If this flow time is less than the specified minimum (see 8.2), select a viscometer with a capillary of smaller diameter and repeat the operation.
9.2.1 Repeat the procedure described in 9.2 to make a second measurement of flow time. Record the result.

9.2.2 If the two measurements agree with the stated determinability figure (see 14.1) for the product, calculate the average of the two measurements and use this value to calculate the kinematic viscosity. If the measurements do not agree, repeat the determination after thorough cleaning and drying of the viscometer and filtering of the sample. Record the result.

10 Determination of viscosity of opaque liquids
10.1 For steam-refined cylinder oils and black lubricating oils, proceed to 10.2 ensuring a thoroughly representative sample is used. For residual fuel oils and similar waxy products, whose kinematic viscosity can be affected by their thermal history, the procedure described in 10.1.1 to 10.1.6 shall be followed to minimize this effect.

NOTE 15 In general, the viscometers used for opaque liquids are of the reverse-flow type listed in table A.1, type C.

10.1.1 Heat the sample in its original container, in an oven, at 60°C +/- 2°C for 1 h.

10.1.2 Thoroughly stir the sample with a suitable rod of sufficient length to reach the bottom of the container. Continue stirring until there is no sludge or wax adhering to the rod.

10.1.3 Recap the container tightly and shake vigorously for 1 min to complete the mixing.

NOTE 16 With samples of a very waxy nature or samples of high kinematic viscosity, it may be necessary to increase the heating temperature above 60°C to achieve proper mixing. The sample should be sufficiently fluid after heating for ease of stirring and shaking.

10.1.4 Immediately thereafter pour sufficient sample to fill two viscometers into a 100 ml glass flask and loosely stopper the flask.

10.1.5 Immerse the flask in a bath of boiling water for 30 min.

NOTE 17 Care should be taken, as vigorous boil-over may occur when opaque liquids which contain high levels of water are heated to high temperatures.

10.1.6 Remove the flask from the bath, stopper tightly and shake for 1 min.

10.2 Charge two viscometers and place in the bath in the manner dictated by the design of the instrument. For example, for the cross-arm or the BS U-tube viscometers for opaque liquids, filter the sample through a 75 pm filter into two viscometers previously placed in the bath. For samples subjected to heat pretreatment (10.1) use a preheated filter to prevent the sample coagulating during the filtration.

NOTE 18 Viscometers which are charged before being inserted into the bath may need to be preheated in an oven prior to charging the sample. This is to ensure that the sample will not be cooled below test temperature.

10.2.1 After 10 min in the bath, adjust the volume of the sample (where the design of the viscometer requires) to coincide with the filling marks as in the viscometer specifications (see ISO 3105).

10.2.2 Allow the charged viscometers enough time in the bath to reach the test temperature. (See note 14.) Where one bath is used to accommodate several viscometers, never add or withdraw a viscometer while any other viscometer is being used to measure flow time.

10.3 With the sample flowing freely, measure, to the nearest 0.1 s (see 6.5) the time required for the advancing ring of contact to pass from the first timing mark to the second. Record the result.

In the case of samples requiring heat pretreatment (10.1), complete the determinations within 1 h of completing the pretreatment.

10.4 Calculate the mean kinematic viscosity, v, in mm2/s, from the two determinations.

For residual fuel oils, if the two measurements agree within the stated determinability figure (see 14.1), calculate the average of the two measurements and use this value to calculate the kinematic viscosity to be reported. If the measurements do not agree, repeat the determination after thorough cleaning and drying of the viscometer and filtering of the sample. Record the result.

NOTE 19 For other opaque liquids, no precision data is available.

11 Cleaning of the viscometer
11.1 Between successive determinations, clean the viscometer thoroughly by several rinsings with the sample solvent (5.2), followed by the drying solvent (5.3). Dry the tube by passing a slow stream of filtered dry air through the viscometer for 2 min or until the last trace of solvent is removed.

11.2 Periodically clean the viscometer with the cleaning solution (CAUTION - see 5.1) for several hours to remove residual traces of organic deposits, rinse thoroughly with water (5.4) and drying solvent (5.3), and dry with filtered dry air or a vacuum line. Remove any inorganic deposits with hydrochloric acid treatment before the use of cleaning solution, particularly if the presence of barium salts is suspected.

11.3 Alkaline cleaning solutions shall not be used, as changes in the viscometer calibration may occur.

12 Calculation
12.1 Calculate the kinematic viscosity, v, from the measured flow time, t, and the viscometer constant, C, by means of the following equation:
v = C x t
where
V is the kinematic viscosity, in square millimetres per second;
C is the calibration constant of the viscometer, in square millimetres per second squared [mm2/s2];
t is the mean flow time, in seconds.

12.2 Calculate the dynamic viscosity, η, from the calculated kinematic viscosity, v, and the density, ρ, by means of the following equation:
η = v x ρ x 10(-3)
where
η is the dynamic viscosity, in millipascal seconds;
ρ is the density, in kilograms per cubic metre, at the same temperature used for the determination of the kinematic viscosity;
v is the kinematic viscosity, in square millimetres per second.

NOTE 20 The density of the sample may be determined by an appropriate method such as ISO 3675, and corrected to the temperature of determination by means of ISO 91-1.