NB/SH/T 0562-2013 Standard Test Method for Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: NB/SH/T 0562—2013
• Chinese name: Standard Test Method for Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature
• English name: Standard test method for determination of yield stress and apparent viscosity of engine oils at low temperature
• Replacement relationship: replaces SH/T 0562—2001 (previous versions: SH/T 0562—1993, SH/T 0562—2001)
• Adoption relationship: modified adoption using the redrafting method of ASTM D4684-08; structural differences see Appendix C
• Publication/implementation: published on 2013-06-08, implemented on 2013-10-01
• Proposed/administrated by: proposed by China Petrochemical Corporation; administrated by the Petroleum Fuels and Lubricants Subcommittee of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280/SC1)
• Drafting organization: Maoming Branch of Sinopec Lubricant Company
• Main drafters: Xu Baoquan, Wu Xian, Jiang Wei, Liang Zhishun, Zhu Xuying

2. Scope of application and non-applicability

• 1.1 specifies the determination method for yield stress and apparent viscosity of engine oils under test temperatures reached by cooling at a controlled rate for at least 45h, finally reaching -10℃–-40℃. Apparent viscosity is determined within the range of shear stress 525Pa and shear rate 0.4s⁻¹–15s⁻¹.
• 1.2 includes two methods, Method A and Method B: Method A combines several devices and can be used for temperature-controlled instruments relying on thermoelectric cooling technology and the latest production direct refrigeration technology; Method B can use the instruments used in Method A, and can also use instruments with methanol circulation refrigeration.
• The precision in Method A of 1.3 is applicable to the determination of yield stress less than 35Pa–210Pa and apparent viscosity in the range of 4300mPa·s–270000mPa·s, but higher yield stresses and apparent viscosities can also be determined.
• 1.4 is applicable to both unused oils and used diesel engine oils and gasoline engine oils (including light and heavy duty engine oils). The applicability to petroleum products other than engine oils has not been determined.
• 1.5 involves certain hazardous materials, operations, and equipment, but it is not intended to address all safety issues associated with this. Users should establish appropriate safety and protective measures before use and determine the applicability of relevant regulatory limitations.

3. Method principle

• Chapter 4 Method summary: Hold at constant temperature at 80℃, then cool at a programmed cooling rate to the final test temperature. Gradually apply a low torque to the rotor shaft until rotation begins, determine the yield stress of the test oil, then apply a higher torque to determine the apparent viscosity of the test oil.
• Chapter 5 Significance and use: When oil cools, its cooling rate and cooling time affect its yield stress and apparent viscosity. In laboratory tests, the oil is slowly cooled within the temperature range where wax crystals precipitate, then relatively quickly cooled to the final test temperature. These laboratory test results can predict failures in actual field due to insufficient pumpability of engine oil. These data providing field engine oil failures are usually tested at -25℃. It is believed that these field failures are caused by the engine oil forming a gel structure, resulting in excessively high yield stress or apparent viscosity, or both.
• 5.2 Temperature cooling curve distribution: For engine oils tested at mild minimum temperatures, see Table A.1 in Appendix A; the temperature cooling curve distribution described in Table A.1 is based on a series of engine oils including engine oils with normal low-temperature fluidity and (requires confirmation against the source standard (source-text extraction)) engine oils (based on PRO viscosity characteristics). For the temperature cooling curve distributions at -35℃ and -40℃, they are based on data from ASTM "Research on Cooling Performance of Modern Advanced Engines". 5.2.2 For test oils at -15℃ or -10℃ test temperatures, see Table A.2 in Appendix A; due to the lack of suitable reference oils, the temperature cooling curve distribution cannot be determined; when using this table at the test temperature of -10℃, the precision of this test method is unknown.

4. Reagents and materials (purity / preparation)

• 7.1 Calibration oil: a Newtonian oil with low cloud point, used to calibrate the viscometer cell. Method B uses an oil with apparent viscosity at -20℃ of approximately 30Pa·s (30000cP); Method A uses an oil with apparent viscosity at -25℃ of approximately 60Pa·s (60000cP).
• 7.2 Anhydrous methanol: chemically pure or analytically pure, used as refrigerant. Warning: toxic, flammable.
• 7.3 Anhydrous ethanol: chemically pure or analytically pure, used as refrigerant. Warning: flammable.
• 7.4 Petroleum solvent: n-heptane or similar solvent, chemically pure, no volatile residue. Warning: flammable.
• 7.5 Acetone: analytically pure, no volatile residue. Warning: flammable.
• 3.7 Calibration oil definition: used to determine the viscometer constant of the rotational viscometer cell, through which the apparent viscosity of the test oil can be determined; calibration oil is a Newtonian oil or fluid, commercially available, with (requires confirmation against the source standard (source-text extraction)) properties; viscosity at -20℃ is approximately 30Pa·s (30000cP), or viscosity at -25℃ is approximately 60Pa·s (60000cP).

5. Instruments and equipment

• 6.1 Small rotational viscometer: an instrument consisting of one or more viscometer cells contained in a temperature-controlled metal block with high thermal conductivity. Each viscometer cell contains a calibrated rotor fixture. The top of the rotor shaft should have a crossbar that engages with a locking pin to limit rotor rotation. The rotor rotates about its axis by applying force to a fine thread wound around the rotor shaft.
• 6.1.1 Typical dimensions of small rotational viscometer cell:
  • Rotor diameter 17.06mm ±0.08mm
  • Rotor height 20.00mm ±0.14mm
  • Viscometer cell inner diameter 19.07mm ±0.08mm
  • Shaft radius 3.18mm ±0.13mm
  • Fine thread radius 0.1mm
• 6.1.2 Viscometer cell cover: a cover inserted above the viscometer cell to minimize the air volume circulating to the viscometer cell. The cover is a stepped cylinder with a length of 38mm±1mm, made of a material with low thermal conductivity, such as a thermoplastic with known solvent resistance and suitable for use within the test temperature range of this method, such as acetal copolymer. The upper half has a diameter of 28mm±1mm, and the lower half has a diameter of 19mm, with tolerance ranges consistent with the diameter tolerance of the viscometer cell. The tolerance of the lower half allows the cover to be easily installed into the viscometer cell while preventing the cover from contacting the rotor shaft. The center of this part is drilled with 11mm±1mm, and the cover is split into two halves for easy installation above the cell.
• 6.2 Weights:
  • 6.2.1 Yield stress test: a set consisting of nine weights and a weight rack, each with a mass of 10g±0.1g.
  • 6.2.2 Viscosity test: weight mass 150g±1.0g.
• 6.3 Temperature control system: controls the heater in the metal block of the small rotational viscometer and regulates the flow of coolant to the metal block. The temperature control system should regulate the temperature within the temperature range described in Table A.1 or Table A.2 in Appendix A.
  • 6.3.1 Temperature controller, which is the most critical part of this standard. For the requirements of the controller, see Appendix B.
  • 6.3.2 Temperature cooling curve distribution, for a complete description of the temperature distribution, see Table A.1 and Table A.2 in Appendix A.
• 6.4 Thermometer: used to measure the temperature of the metal block. Two thermometers are required, one with a temperature range of at least 70℃~90℃ and a division value of 1℃; the other with a temperature range of at least -41℃~5℃ (requires confirmation against the source standard (source-text extraction)) and a division value of 0.2℃. Or use other temperature measuring instruments with the same precision and sensitivity, such as digital instruments with built-in resistance temperature detectors (RTD) or thermistor sensors. When using metal-sheathed temperature measuring instruments, be careful to avoid temperature reading deviations caused by the metal sheath. Some metal-armored instruments display temperature readings higher than the actual temperature of the test oil.
• 6.5 Dry gas (dry air or nitrogen): supplement dehydrated dry gas to reduce water vapor condensing above the instrument. After starting the program control, continuously introduce dry gas into the cover; during the measurement phase of the test, interrupt the dry gas and remove the cover.
• 6.6 Locking pin: a device that works with the rotor crossbar to keep the rotor in a state of rotation not exceeding half a turn, in order to prevent premature rotation of the rotor.

6. Recommended operating conditions

• Cooling: cool at a controlled rate for at least 45h (1.1); final test temperature -10℃~-40℃.
• Apparent viscosity measurement conditions: shear stress 525Pa, shear rate 0.4s⁻¹~15s⁻¹ (1.1).
• Method A calibration temperature: -25℃ (9.1.2); Method B calibration temperature: -20℃ (10.1.2).
• Method B pre-test heating: heat the test oil to 80℃±1℃ and hold at constant temperature for 2h (10.2.2.6).
• Method B constant temperature: the test oil in the viscometer cell is held at constant temperature at -20℃±0.2℃ for at least 1h (10.1.2.3).
• Temperature cooling curve distribution: see Table A.1 (-20℃–-40℃), Table A.2 (-10℃–-15℃) in Appendix A; the rated time to reach the test temperature is shown in Table A.3 (-10℃ 45h, -15℃ 47h, -20℃ 45h, -25℃ 47h, -30℃ 49h, -35℃ 51h, -40℃ 53h).
• Table A.1 Test temperature cooling curve distribution table (-20℃~-40℃):
  • Rated 0:20, >20℃~80℃, rate of change (not provided in the available source)
  • 2:00, 80℃~80℃
  • Rated 0:20, 80℃~0℃
  • Rated 0:03, 0℃~-3.0℃
  • Rated 0:07, -3.0℃~-4.0℃, 8.5℃/h
  • rated 0:10, -4.0℃~-5.0℃, 6.0℃/h
  • 6:00, -5.0℃~-8.0℃, 0.5℃/h
  • 36:00, -8.0℃~-20.0℃, 0.33℃/h
  • hold at test temperature -20℃
  • 2:00, -20.0℃~-25.0℃, 2.5℃/h
  • hold at test temperature -25℃
  • 2:00, -25.0℃~-30.0℃, 2.5℃/h
  • hold at test temperature -30℃
  • 2:00, -30.0℃~-35.0℃, 2.5℃/h
  • hold at test temperature -35℃
  • 2:00, -35.0℃~-40.0℃, 2.5℃/h
  • hold at test temperature -40℃
  • Note: If a dual control loop is used, the cold bath temperature should be lower than the corresponding required metal block temperature 5℃, but the bath temperature must not exceed -5℃; the temperature fluctuation should be kept less than ±0.1℃ to improve the precision of viscosity measurement; at the test temperature, complete the determination of yield stress and apparent viscosity within 30min.
• Table A.2 Cooling curve distribution table for test temperature (-10℃~-15℃):
  • rated 0:20, >20℃~80℃
  • 2:00, 80℃~80℃
  • rated 0:20, 80℃~10℃
  • rated 0:03, 10℃~7.0℃
  • rated 0:07, 7.0℃~6.0℃, 8.5℃/h
  • rated 0:10, 6.0℃~5.0℃, 6.0℃/h
  • 6:00, 5.0℃~2.0℃, 0.5℃/h
  • 36:00, 2.0℃~-10.0℃, 0.33℃/h
  • hold at test temperature -10℃
  • 2:00, -10.0℃~-15.0℃, 2.5℃/h
  • hold at test temperature -15℃
  • Permissible temperature difference: ±1.0, ±0.5, ±0.2, ±0.2, ±0.2, ±0.2, ±0.2, ±0.2, ±0.2, ±0.2 (correspondence requires confirmation against the source standard (source-text extraction))
  • Note: If a dual control loop is used, the cold bath temperature should be lower than the corresponding required metal block temperature 5℃, but the bath temperature must not exceed -5℃; the temperature fluctuation should be kept less than ±0.1℃; at the test temperature, complete the determination of yield stress and apparent viscosity within 30min.

7. Sampling and sample preparation

• 8.1 Unless otherwise specified, sampling shall be carried out in accordance with GB/T 4756; the test oil shall not contain suspended solid impurities and water. If the temperature of the test oil in the container is below the indoor dew point temperature, the test oil should be heated to room temperature before opening the container for sampling.
• 9.2.1 Preparation of test oil and viscometer cells (Method A): 9.2.1.1 If the viscometer cells (requires confirmation against the source standard (source-text extraction)) are cleaned according to the procedure in 9.2.7; 9.2.1.2 Pour 10mL test oil into clean viscometer cells; all viscometer cells should be equipped with test oil and rotors; if the test oil to be tested is not (requires confirmation against the source standard (source-text extraction)), fill each empty viscometer cell with test oil of the same viscosity grade; 9.2.1.3 Pour test oil into the viscometer cells, carefully place the corresponding rotors, install the center pins, including the empty viscometer cells; 9.2.1.4 Install viscometer cell covers on all viscometer cells, including the empty viscometer cells; 9.2.1.5 Except for the empty viscometer cells, hang a thin thread with a loop of length 700mm on the crossbar at the top of each rotor shaft, pass the other end of the plastic loop thread over the timing wheel, hang a light weight such as a large paper clip on the plastic loop, guide the rotation by hand, wind the thin thread around the rotor shaft, leaving 1080mm (requires confirmation against the source standard (source-text extraction)) of thread end under the timing wheel not wound on the shaft; do not overlap the winding, close the locking pin to prevent rotor rotation. Pass the remaining thin thread (requires confirmation against the source standard (source-text extraction)) through the bearing plate, let it pull on the back of the bearing plate. Repeat this operation until all viscometer cells with test oil that need to be tested are prepared. Note: Before placing the rotor, the thin thread can be pre-wound on the shaft. 9.2.1.6 Place the cover on the viscometer cell. 9.2.1.7 As noted in clause 6.5, pass dry gas into the cover, set the dry gas flow rate to about 1L/h, increase or decrease the flow rate as needed to minimize frost or water vapor condensation around the viscometer cells.
• 10.2.2 Preparation of test oil and viscometer cells (Method B): 10.2.2.1 Remove the nine rotors from the viscometer cells and ensure both the cells and rotors are clean; for cleaning procedure see 10.2.6; 10.2.2.2 Inject 10mL±1.0mL of test oil into each viscometer cell; 10.2.2.3 Place the rotors in their dedicated seats, and install the center pins on them; 10.2.2.4 Hang the thread loop of the 700mm long thin thread on the crossbar at the top of the rotor shaft, wind the thin thread around the rotor shaft, but leave 200mm (requires confirmation against the source standard (source-text extraction)) wound on the shaft; do not overlap the winding; pass the other end of the thin thread over the upper bearing plate so that the crossbar at the top of the rotor shaft faces forward (requires confirmation against the source standard (source-text extraction)); secure the crossbar with the locking pin; if timing manually, the end of the crossbar pointing forward may be colored; 10.2.2.5 As per 10.2.2.3, before placing the rotor, the thin thread may be pre-wound on the shaft; 10.2.2.6 Place the cover on the upper part of the viscometer cell to minimize frost formation on cold metal parts exposed to air; when certain (requires confirmation against the source standard (source-text extraction)) dry gas (such as dry air or nitrogen) is encountered, purge the cover to reduce frost; 10.2.2.7 Start the program control of the cooling curve distribution table, heat the test oil to 80℃±1℃ and hold at constant temperature for 2h to ensure that substances that cannot (requires confirmation against the source standard (source-text extraction)) at room temperature are completely dissolved; 10.2.2.8 After the constant temperature 2h ends, start the cooling cycle, and cool the test oil according to the program-controlled cooling sequence described in 10.2.1.

8. Analytical procedure

Method A

• 9.1 Calibration and standardization
  • 9.1.1 Calibration of temperature sensor: For instruments where the temperature sensor is not permanently attached to the temperature controller, when the temperature sensor is installed on the temperature controller, calibrate the temperature sensor in the control metal block.
    • 9.1.1.1 The displayed temperature of the sensor should be verified with the reference thermometer noted in clause 6.4, at least at three temperature points.
    • 9.1.1.2 During verification, inject 10mL of typical test oil into each viscometer cell, with the rotor and viscometer cell cover in place. The viscometer cell cover should not be used for instruments with direct refrigeration (see 6.1.2).
    • 9.1.1.3 When establishing the calibration curve between the temperature sensor and the temperature controller, the temperature sensor should be calibrated, and the temperature should be measured at least every 5℃, including -5℃ and the lowest test temperature. For each verification temperature, measure at least twice, with each observation at least 10min apart. If an instrument with an independent temperature controller is used, see B.1 in Appendix B. Note: All temperatures in this standard refer to actual temperatures and not necessarily displayed temperatures.
  • 9.1.2 Calibration of viscometer cells: At -25℃, perform two tests with calibration oil to calibrate the calibration constant of each viscometer cell.
    • 9.1.2.1 Each viscometer cell shall be calibrated (requires confirmation against the source standard (source-text extraction)) times; the calibration constant can be calculated from the average of the times measured for three rotations of the rotor. When two viscometer cell calibrations are performed consecutively, new calibration oil shall be used for the second test, and the instrument shall be cleaned before each test. Note: Once a complete set of viscometer cells has been calibrated, subsequent verifications that meet the requirements of 9.1.11 may be performed as a single determination.
    • 9.1.2.2 Use the same weight of mass 150g for calibration and viscosity measurement. If both weights have a mass of 150g±0.1g, different weights may be used for calibration and apparent viscosity measurement.
  • 9.1.3 Prepare the viscometer cells according to the procedure in 9.2.1 and enter the calibration test stage. Note: Before inserting the rotor into the viscometer cell (requires confirmation against the source standard (source-text extraction)) the rotor, ensure that the rotor shaft is straight and the rotor surface is smooth, free from dents, scratches and other defects. For thermoelectric cooling instruments (requires confirmation against the source standard (source-text extraction)) the umbrella support point, ensure that this point is sharp and located at the center of the rotor shaft. If these conditions are not met, the rotor should be repaired or replaced.
  • 9.1.4 Use the instrument to (requires confirmation against the source standard (source-text extraction)) the calibration curve, or select the temperature cooling curve given in GB/T 9171. As the test temperature of the calibration oil, follow the instrument's use (requires confirmation against the source standard (source-text extraction)) and start the cooling curve program. Note: Using the temperature calibration (requires confirmation against the source standard (source-text extraction)) line, the determination of two viscometer cell constants can be completed within one day.
  • 9.1.5 Place the thermometer in the thermometer insertion hole. Each measurement is at the same position. It should be ensured that the thermometer has been in the thermometer insertion hole for at least (requires confirmation against the source standard (source-text extraction)) 1 (requires confirmation against the source standard (source-text extraction)) before the end of the test.
  • 9.1.6 After completing the temperature cooling curve, check whether the final test temperature is within ±0.1℃ of the required calibration temperature. The temperature controller is independently verified with a thermometer in the sleeve.
  • 9.1.7 Starting from the leftmost viscometer cell, test each viscometer cell in sequence according to the following steps.
    • 9.1.7.1 Turn the timing wheel so that the timing wheel is aligned with the rotor of the viscometer cell to be tested.
    • 9.1.7.2 Hang the thin thread on the timing wheel.
    • 9.1.7.3 Hang the weight rack on the plastic loop and add 10g weight (total mass 20g).
    • 9.1.7.4 Locking pin.
    • 9.1.7.5 When the crossbar disengages from the locking pin and starts to rotate, prevent closing the locking pin to limit rotor rotation to no more than half a turn.
    • 9.1.7.6 Remove the weight rack and 10g weight from the plastic loop.
    • 9.1.7.7 Hang 150g weight on the plastic loop.
    • 9.1.7.8 Open the locking pin, and start timing as soon as the rotor is released.
    • 9.1.7.9 Measure the time for the rotor to make three rotations (the instrument can time automatically).
    • 9.1.7.10 After three rotations, close the locking pin and remove the weight from the plastic loop.
    • 9.1.7.11 Record the time for three rotations and the viscometer cell number.
    • 9.1.7.12 Repeat 9.1.7.1~9.1.7.11 for the remaining viscometer cells in numerical order.
  • 9.1.8 Repeat 9.1.3~9.1.8 to obtain a second set of calibration data.
  • 9.1.9 Use formula (8) and formula (9) to calculate the calibration constant C for each viscometer cell (formula content requires confirmation against the source standard (source-text extraction)).
  • 9.1.11 Whether the measured calibration constant (requires confirmation against the source standard (source-text extraction)) deviates from the average calibration constant of all viscometer cells by more than 4%, and whether the difference between (requires confirmation against the source standard (source-text extraction)) and (requires confirmation against the source standard (source-text extraction)) of any viscometer cell deviates from the average by more than 4%; if so, the obtained results are questionable. If it does not meet the standard requirements, then check whether the rotor is damaged, perform necessary repairs or replacement, and then recalibrate according to the above steps.
  • 9.1.12 If the deviation between the controller temperature and the thermometer-corrected value is greater than 0.1℃, use the procedure in B.2 of Appendix B to help determine the cause and make corrections.
• 9.2 Test Procedure
  • 9.2.2 Select the cooling curve according to the test temperature, and start the test program according to the instrument user guide. Table A.3 lists the time required to reach a specific test temperature.
  • 9.2.3 Ensure that before the end of the test temperature, the thermometer has been in the thermometer well for at least 1 (requires confirmation against the source standard (source-text extraction)). All temperature measurements shall use the same thermometer well, and the position shall be the same as that used during calibration.
  • 9.2.4 At the end of cooling, check the time-temperature chart to ensure that the time-temperature curve distribution (requires confirmation against the source standard (source-text extraction)) is within the difference range, and that the test temperature of the thermometer well (requires confirmation against the source standard (source-text extraction)) is within ±0.2℃ of the test temperature. These two checks (requires confirmation against the source standard (source-text extraction)) may (requires confirmation against the source standard (source-text extraction)) be automatically completed by the control software configured in the instrument, and the final temperature (requires confirmation against the source standard (source-text extraction)) shall be separately verified by the instrument. If, in two consecutive runs (requires confirmation against the source standard (source-text extraction)), the deviation between the measured final temperature and the expected test temperature (requires confirmation against the source standard (source-text extraction)) is greater than 0.1℃, the sensor shall be recalibrated according to 9.1.1.
  • 9.2.5 If the temperature curve is within the deviation range, the measurement may continue; if it exceeds the deviation range, terminate this measurement and recalibrate according to 9.1.1.
  • 9.2.6 Determination of yield stress and apparent viscosity:
    • 9.2.6.1 Remove the cover from (requires confirmation against the source standard (source-text extraction)) and begin the determination.
    • 9.2.6.2 Determination of yield stress: starting from the leftmost viscometer cell, skip the viscometer cells that do not need to be measured, and perform the following steps on the viscometer cells in sequence:
      • 9.2.6.2.1 Turn the timing wheel so that the timing wheel is aligned with the rotor of the viscometer cell to be tested.
      • 9.2.6.2.2 Remove the fine wire from the upper bearing (requires confirmation against the source standard (source-text extraction)) and hang it on the timing wheel.
      • 9.2.6.2.3 Hang (requires confirmation against the source standard (source-text extraction)) onto the plastic ring.
      • 9.2.6.2.4 For instruments with automatic (requires confirmation against the source standard (source-text extraction)) function, start timing, then release the locking pin; for instruments with manual timing, start timing immediately after the locking pin is opened.
      • 9.2.6.2.5 Observe whether the rotation of the rotor (requires confirmation against the source standard (source-text extraction)) exceeds 3mm (3mm approximately twice the diameter of the crossbar). Another method is to rotate the timing wheel (requires confirmation against the source standard (source-text extraction)) by (requires confirmation against the source standard (source-text extraction)) equivalent to the rotating shaft rotating 3mm.
      • 9.2.6.2.6 Some instruments have an electric (requires confirmation against the source standard (source-text extraction)) (requires confirmation against the source standard (source-text extraction)) motion sensing device; one of these types may be selected as the observation method.
      • 9.2.6.2.7 As described in 9.2.6.2.5, if it is observed that the rotor rotates more than 3mm within 15s, remove the weight hanger of 10g from the plastic ring and operate according to 9.2.6.3.
      • 9.2.6.2.8 If, according to 9.2.6.2.5, it is observed that the rotor rotates less than 3mm within 15s, stop timing, lift the weight hanger, and add 10g weights. Note: Because weights have been added to the weight hanger, it is necessary to hang weights on the weight hanger, restart timing, do not use the locking pin, and determine the yield stress. Some instruments may use software, but ensure that the mass used is consistent with the mass required by the program.
      • 9.2.6.2.9 Carefully add the added weights to the weight hanger and start timing.
      • 9.2.6.2.10 Repeat the steps of 9.2.6.2.8 and 9.2.6.2.9 until the accumulated weights cause the rotor to rotate. At this point, remove all weights from the plastic ring.
      • 9.2.6.2.11 If no rotation is observed when the total weight reaches 100g, record the yield stress >350Pa and proceed according to 9.2.6.3.
    • 9.2.6.3 Determination of apparent viscosity:
      • 9.2.6.3.1 Gently hang a weight of mass 150g onto the plastic ring.
      • 9.2.6.3.2 Slightly lift the locking pin; if the 150g weight can cause the rotor to rotate, immediately close the locking pin and let the rotor continue to rotate until the crossbar contacts the locking pin and stops the rotation. If no rotation is observed, terminate the test and proceed according to 9.2.6.3.7. Note: There have been cases where the yield stress exceeded the applied stress of 150g.
      • 9.2.6.3.3 When using an instrument with an automatic timing function, start timing, release the locking pin, and perform the apparent viscosity determination. If timing manually, start timing immediately when the locking pin is opened.
      • 9.2.6.3.4 Starting from the release point, stop timing after the rotor has rotated 3 turns. When the time for one turn is greater than 60s, record only the time for one turn. Note: The time for three turns may be timed automatically.
      • 9.2.6.3.5 After completing three turns (or one turn if the time for one turn is greater than 60s), remove the weight from the plastic ring.
      • 9.2.6.3.6 Record the time for three turns (or one turn) and the number of turns, and calculate the apparent viscosity according to clause 9.3.
      • 9.2.6.3.7 If no rotation occurs after using the 150g weight, record that the test oil is "too viscous to measure" (TVTM).
      • 9.2.6.3.8 Repeat the operations of 9.2.6.2~9.2.6.3.7 to determine the remaining viscometer cells.
  • 9.2.7 Cleaning:
    • 9.2.7.1 After all viscometer cells have been tested, clean the viscometer cells. Set the instrument to heat up and heat the viscometer cells to room temperature or higher, but it is recommended not to exceed 55℃.
    • 9.2.7.2 When the required cleaning temperature is reached: 9.2.7.2.1 For instruments without movable viscometer cells, remove the fine wire, rotor, and viscometer cover, and clean according to 9.2.7.3; 9.2.7.2.2 For instruments with movable viscometer cells, the movable viscometer cells may be removed and cleaned independently according to 9.2.7.3, or the instrument may be cleaned according to 9.2.7.3 below.
    • 9.2.7.3 Clean the viscometer cell: 9.2.7.3.1 Use a vacuum tube to extract the oil sample from the viscometer cell; 9.2.7.3.2 Rinse the viscometer cell with a suitable solvent at least 3 times, using at least about 15mL of solvent each time, and finally rinse once with acetone; 9.2.7.3.3 Use dry air to purge or preferably use a vacuum tube to remove residual solvent. Warning: If air purging is used, ensure that the air is clean and free of oil, water, and other impurities, because these may remain in the viscometer cell, and indoor air may be contaminated.
    • 9.2.7.4 Clean the rotor with a suitable solvent and blow it dry.

Method B

• 10.1 Calibration and Standardization
  • 10.1.1 When using a temperature controller (requires confirmation against the source standard (source-text extraction)), apply (requires confirmation against the source standard (source-text extraction)) thermometer verification, verifying at least (requires confirmation against the source standard (source-text extraction)) temperature points. The temperature shall be measured at least every 5℃, and a calibration curve shall be established between the temperature sensor and the temperature controller. Note: In this test method, (requires confirmation against the source standard (source-text extraction)) the actual temperature rather than necessarily the displayed temperature.
  • 10.1.2 At -20℃, calibrate each viscometer cell (viscometer cell constant) according to (requires confirmation against the source standard (source-text extraction)) calibration oil of known viscosity.
    • 10.1.2.1 Operate according to 10.2.2~10. (requires confirmation against the source standard (source-text extraction)).
    • 10.1.2.2 Start the temperature controller, and within (requires confirmation against the source standard (source-text extraction)) time, cool the temperature of the small rotational viscometer metal block to -20℃, then begin the test.
    • 10.1.2.3 The test oil in the viscometer cell shall be kept at -20℃±0.2℃ for at least 1h. If necessary, fine-tune the temperature to maintain this test temperature.
    • 10.1.2.4 At the end of the constant temperature period, record the test temperature and remove the cover.
    • 10.1.2.5 Operate according to 10.2.3.1~10.2. (requires confirmation against the source standard (source-text extraction)).
    • 10.1.2.6 Continue according to 10.2.4.
    • 10.1.2.7 In order from left to right, for each viscometer cell (requires confirmation against the source standard (source-text extraction)).
    • 10.1.2.8 Repeat steps 10.1.2.5 and 10.1.2.6 for each viscometer cell.
    • 10.1.2.9 Calculate using formula (12): C=η₀/T (12). Where: η₀ (requires confirmation against the source standard (source-text extraction)); C (requires confirmation against the source standard (source-text extraction)); T (requires confirmation against the source standard (source-text extraction)). The viscometer cell constant with one 150g weight attached, mPa; the time for the rotor to rotate three turns, s.
    • 10.1.2.10 If the calibration constant of any viscometer cell is higher or lower than the average of the others by 10%, then there may be a problem with the rotor or the operation. Check whether the rotor is damaged, perform necessary repairs or replacement, and then recalibrate.
  • 10.1.3 If the deviation between the controller temperature and the calibrated value of the thermometer is greater than the allowable deviation value, use B.2 in Appendix B to help identify the cause.
• 10.2 Test Procedure
  • 10.2.1 According to (requires confirmation against the source standard (source-text extraction)) listed in Tables A.1 and A.2 of Appendix A, use a program to control the temperature controller to control the temperature of the small rotational viscometer metal block. The program-controlled temperature is the temperature in Tables A.1 and A.2 of Appendix A plus the appropriate temperature correction coefficient determined in 10.1.1. Table A.3 in Appendix A gives the specified time to reach the designated test temperature.
  • 10.2.2 Preparation of test oil and viscometer cell (see Method B part in Section 7 Sampling and Test Specimen Preparation).
  • 10.2.2.8 After the program-controlled cooling ends, use a thermometer rather than a temperature controller accurately calibrated by temperature (requires confirmation against the source standard (source-text extraction)) to measure the metal block temperature. The temperature at the end of the program-controlled cooling should be within ±0.2℃ of the expected test temperature. If the metal block temperature is within this range, the determination of yield stress and apparent viscosity shall be completed within 30min after the end of the program-controlled cooling, see 10.2.3.
    • 10.2.2.8.1 If the final temperature (requires confirmation against the source standard (source-text extraction)) is expected to be higher than the temperature by 0.2℃~0.5℃, adjust the temperature controller so that the metal block temperature reaches the corrected test temperature, and during the measurement (requires confirmation against the source standard (source-text extraction)) hold at that temperature for 30min. The entire temperature correction time should not exceed 1h. For any data obtained by this method, the test result (requires confirmation against the source standard (source-text extraction)) then the result is invalid.
    • 10.2.2.8.2 If the final temperature is below 0.2℃ or above 0.5℃, then the preselected test temperature is invalid. If the test result is only for reference, the yield stress and apparent viscosity may be determined without further temperature adjustment; the result is at the actual temperature rather than the preselected temperature (requires confirmation against the source standard (source-text extraction)); the test result is for reference only.
    • 10.2.2.9 If the final temperature described in 10.2.2.8 has both positive and negative deviations exceeding 0.2℃, it is judged as a failure; before starting another measurement, refer to the operation in B.2 of Appendix B.
    • 10.2.2.10 For model CMRV-4 and newer models, if the program reports that the cooling curve is out of tolerance, the instrument operation should be thoroughly checked for correctness. Ratio