11. Procedure for Manual CCS Operation
NOTE 6 - Ensure that the cooling bath is stirred during the operation of the instrument. Failure to do so will permit large gradients in temperature to exist in the cooling bath. These large gradients will affect the sample temperature and reduce the precision of your viscosity measurements.
11.1 Establish the calibration equation or curve (see Section 10). Before any series of determinations, run a minimum of one calibration oil as an overall check on the apparatus and calibration at each temperature of interest. When the drive current for the oil to be used for the calibration check (see Footnote B of Table 1) differs by more than 0.005 A (ampere) from that determined in 10.1.2, reset the current to the value previously determined in 10.1.2; make the observation and correction after 15 s of running. When the viscosity measurement of the calibration oil differs by more than more or less 5 % from its certified value, rerun to confirm this observation. When confirmed, recalibrate as in 10.1.3.
NOTE 7 - The use of blind reference samples (see Note 4) are recommended for an overall check on all performance, at six month intervals.
11.2 Insert test sample from a dropping pipet (eye dropper) into the filling tube. Be certain the test sample fills the gap between the rotor and stator with an excess of liquid above the rotor to fill the cup completely. Turn the rotor by hand to ensure complete wetting of the surface of the stator and rotor while the test sample flows between the rotor and stator. Fill the filling tube fully and insert a rubber stopper in the end of the tube; for viscoelastic samples this stopper will have to be pressed tightly while the motor is turned on (see 11.2.2) to prevent the sample from forcing the stopper out of the tube and allowing the sample to become depleted in the shear area of the viscometric cell. See Annex A1 for a special procedure for highly viscoelastic test samples.
NOTE 8 - The viscosity of some oils can be high enough at room temperature to impede flow into the annulus between the rotor and stator. For oils whose kinematic viscosity at ambient temperature exceeds 100 mm2/s (cSt), warm the sample (not exceeding 50°C) prior to filling the viscometric cell.
11.2.1 Turn the temperature control and coolant flow on, and allow the stator to cool. To ensure optimum control of temperature, see 6.6.1 and 6.6.1.1. Record the time at which the coolant flow is turned on (use a stopwatch or other means of counting by seconds). Attain control temperature within 30 to 60 s for test temperatures down to -20°C and within 60 to 90 s for test temperatures down to -30°C; if not within these limits, replace the cold methanol (see 6.7) or adjust the temperature of the cold methanol. A null reading on the temperature indicator meter and the cyclic controlling of coolant flow indicate that test temperature is reached. Adjust the null meter reset knob so that the null meter reads slightly to the left of zero, such that when the rotor drive is turned on the test temperature will be established with only minimal further temperature adjustment.
11.2.1.1 If the control temperature is reached more slowly than outlined above, replace the cold methanol (see 6.7), or lower the temperature of the cold methanol (see 6.6).
11.2.1.2 If the control temperature is reached more rapidly than outlined above, raise the temperature of the cold methanol in order to obtain satisfactory control.
11.2.2 Turn on the rotor drive 180 more or less 3 s after the coolant flow is turned on.
11.2.3 With the tachometer plugged into the CAL jack, record the speed meter reading immediately after turning on the motor switch. If the indicator rises and then drops rapidly to a position at least 5 % less than the highest reading, there is possible presence of residual solvent in the shear area. This abnormal digital speed meter change or analog meter needle deflection can also occur as a result of poor temperature control (as indicated on the temperature meter) that is most frequently caused by poor thermal contact between the stator thermal well and the thermistor. Terminate the run. Remove the sample and clean as described in 11.3. Repeat the procedure with a fresh sample starting with 11.2.
11.2.4 Record speed indicator meter reading at 60 more or less 5 s from rotor startup, estimating the meter reading to the nearest 1/10 of the smallest meter division for the analog meter, when the digital meter is not being used. Turn off rotor drive and coolant flow.
11.3 Clean the CCS by the following steps:
11.3.1 Circulate warm methanol (35 to 45°C) around the stator during the time of cleaning. Maintain flow of warm methanol until 11.3.2 has been completed. See 11.3.3 for an alternative procedure.
11.3.2 Wash the assembly with petroleum naphtha and finally with acetone (with due care for the flammability of these solvents), using the vacuum to dry the assembly. Turn the rotor several revolutions by hand during final drying with vacuum to ensure that the gap between rotor and stator is clean and dry.
11.3.3 As an alternative to the use of solvents in 11.3.1 and 11.3.2, inject an excess of 30 mL of the next sample to flush the previous sample and fill the cell with the new sample as in 11.2.
11.4 Leave the final sample of a series of runs in the instrument. This will prevent damage if the instrument is accidentally turned on. This final sample can also be used as the sample for the first run after a shutdown period. This allows the electronic components and motor to come up to temperature by operation with a sample already in place. Do not record speed indicator data from this sample upon starting a new set of runs.
