12. Procedure for Opaque Liquids
12.1 For steam-refined cylinder oils and black lubricating oils, proceed to 12.3 ensuring a thoroughly representative sample is used. The kinematic viscosity of residual fuel oils and similar waxy products can be affected by the previous thermal history and the following procedure described in 12.1.1-12.2.2 shall be followed to minimize this.
12.1.1 In general, the viscometers used for opaque liquids are of the reverse-flow type listed in Table A1.1, C.
12.1.2 Heat in the original container, in an oven, at 60 more or less 2°C for 1h.
12.1.3 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.
12.1.4 Recap the container tightly and shake vigorously for 1min to complete the mixing.
12.1.4.1 With samples of a very waxy nature or oils 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 for ease of stirring and shaking.
12.2 Immediately after completing 12.1.4, pour sufficient sample to fill two viscometers into a 100-mLglass flask and loosely stopper.
12.2.1 Immerse the flask in a bath of boiling water for 30min. (Warning - Exercise care as vigorous boil-over can occur when opaque liquids which contain high levels of water are heated to high temperatures.)
12.2.2 Remove the flask from the bath, stopper tightly, and shake for 60s.
12.3 Two determinations of the kinematic viscosity of the test material are required. For those viscometers that require a complete cleaning after each flow time measurement, two viscometers may be used. A single viscometer in which an immediate, repeat flow time measurement can be made without cleaning may also be used for the two measurements of flow time and calculation of kinematic viscosity. Charge two viscometers 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-µm filter into two viscometers previously placed in the bath. For samples subjected to heat treatment, use a preheated filter to prevent the sample coagulating during the filtration.
12.3.1 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.
12.3.2 After 10min, 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 Specifications D446).
12.3.3 Allow the charged viscometers enough time to reach the test temperature (see 12.3.1). Where one bath is used to accommodate several viscometers, never add or withdraw, or clean a viscometer while any other viscometer is in use for measuring flow time.
12.4 With the sample flowing freely, measure in seconds to within 0.1s, the time required for the advancing ring of contact to pass from the first timing mark to the second. Record the measurement.
12.4.1 In the case of samples requiring heat treatment described in 12.1 through 12.2.1, complete the measurements of flow time within 1 h of completing 12.2.2. Record the measured flow times.
12.5 Calculate kinematic viscosity, v, in mm2/s, from each measured flow time. Regard these as two determined values of kinematic viscosity.
12.5.1 For residual fuel oils, if the two determined values of kinematic viscosity agree within the stated determinability figure (see 17.1.1), use the average of these determined values to calculate the kinematic viscosity result to be reported. Record the result. If the calculated kinematic viscosities do not agree, repeat the measurements of flow times after thorough cleaning and drying of the viscometers and filtering of the sample. If the material or temperature, or both, is not listed in 17.1.1, for temperatures between 15 and 100°C use as an estimate of the determinability 1.0%, and 1.5% for temperatures outside this range; it must be realized that these materials can be non-Newtonian, and can contain solids which can come out of solution as the flow time is being measured.
