GB/T 11145-2014 Determination of low-temperature viscosity of lubricants — Brookfield viscometer method

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Incomplete source card: Sections 10, 11, 12, 13, 14 are absent from the available source. Only available content is translated; source completion is pending.

Card type: Test method

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

• Standard number: GB/T 11145—2014
• Chinese full title: Determination of low-temperature viscosity of lubricants — Brookfield viscometer method
• English name: Standard test method for measurement of low-temperature viscosity of lubricants—Brookfield viscometer method
• Replacement relationship: replaces GB/T 11145—1989 "Determination of low-temperature viscosity of vehicle fluid lubricants (Brookfield viscometer method)"
• Adoption relationship: modified adoption by redrafting method of ASTM D2983-09 "Determination of low-temperature viscosity of lubricants (Brookfield viscometer method)"
• Publication/implementation: published on 2014-02-19, implemented on 2014-06-01
• Proposed by/under the jurisdiction of: proposed by China Petrochemical Corporation; under the jurisdiction of the Petroleum Fuels and Lubricants Subcommittee of the China Petroleum Products and Lubricants Standardization Technical Committee (SAC/TC 280/SC 1)
• Drafting organization: Lubricant Research and Development (Beijing) Center of China Petroleum & Chemical Corporation
• Main drafters: Hu Gang, Xia Peng, Li Heran, Li Xuehong, Liang Yanwei
• Previous versions: GB/T 11145—1989
• Main technical changes compared with the 1989 edition (foreword):
  • The standard title was modified;
  • The applicable viscosity range of method A was changed from "1000 mPa·s–1 000 000 mPa·s" to "500 mPa·s–900 000 mPa·s";
  • The applicable temperature range of method A was changed from "-5 ℃~-40 ℃" to "within the low-temperature range permitted by the viscometer";
  • Method A adds the insulated 4B2 spindle, Tannas 4 glass composite spindle and carbon composite spindle, 3 types of spindles (see 5.2.2);
  • Method A adds operating procedures using an air cold bath-constant-temperature liquid bath and a programmed cooling liquid bath [see 5.2.8, 5.4.3 b) and 5.4.3 c)];
  • Method A test tube was changed from "inner diameter 22 mm–23 mm, overall length 128 mm–130 mm, with an annular mark 70 mm from the bottom" to "glass test tube, inner diameter 22.0 mm~22.5 mm, overall length 115 mm±5 mm, with an annular engraved line" (see 5.2.3);
  • Method A sample preparation was changed from "place in a 50 ℃ constant-temperature water bath for 0.5 h" to "for a low-viscosity liquid sample in the test tube, preheat to 50 ℃±3 ℃, hold at constant temperature for 30 min±5 min; for a high-viscosity liquid sample in the test tube, preheat to 90 ℃±3 ℃, hold at constant temperature for 30 min±5 min" [see 5.4.2 c)];
  • Method A unifies the test time limit: "after the viscometer spindle begins to rotate, the test should be completed within 60 s (for samples greater than 150 000 mPa·s, no more than 90 s)" [see 5.4.5 g)3)].
• Technical differences from ASTM D2983-09: adds Chapter 6 method B semiconductor cold bath method and Appendix H; does not adopt the content related to the SimAir test tube.

2. Scope of application and non-applicability

• This standard specifies a test method for determining the low-shear-rate dynamic viscosity of lubricants using a Brookfield viscometer under appropriate torque conditions (Chapter 1).
• Applicable viscosity range: 500 mPa·s~900 000 mPa·s.
• Applicable temperature range: the permitted operating temperature range of the Brookfield viscometer.
• Method application (4.1): lubricants such as automatic transmission fluids, gear oils, hydraulic transmission oils, and industrial and automotive hydraulic oils, for which low-temperature low-shear-rate viscosity is important for the normal operation of related equipment; many lubricant specifications and standards specify the use of this standard for viscosity testing.
• Not applicable: no explicit "not applicable" clause is provided in the available source.

3. Method principle

• Method A method summary (5.1): after preheating the sample, cool it to room temperature, pour it into a test tube up to the fixed engraved line, fit the stopper onto the test tube, insert the special spindle through the stopper into the sample in the test tube, and secure it to the stopper with the spindle clamp so that the spindle is suspended in the sample. Hold the sample together with the test tube, spindle, stopper and spindle clamp at constant temperature at the test temperature for 16 h, then perform an apparent viscosity test using a Brookfield viscometer. Depending on the viscometer model used for the test, the apparent viscosity of the sample may be read directly from the viscometer or calculated from the dial reading. Method A includes three cooling modes: air cold bath, air cold bath-constant-temperature liquid bath, and programmed cooling liquid bath.
• Method B method summary (6.1): place the sample in a semiconductor cold bath that has reached the test temperature, connect the Brookfield viscometer and spindle, select the spindle speed, and after holding at constant temperature for 2 h, determine the apparent viscosity of the sample.
• Terms (Chapter 3):
  • 3.1 apparent viscosity apparent viscosity: dynamic viscosity determined in accordance with this standard. Note: for non-Newtonian fluid lubricants, the apparent viscosity changes with the Brookfield viscometer spindle speed (shear rate).
  • 3.2 reference viscosity reference viscosity: the viscosity of the reference oil. Note: the reference oil is a Newtonian fluid and has a specific viscosity at several temperature points required by the user.

4. Reagents and materials (purity / preparation)

• 6.3 Reagents and materials (method B):
  • 6.3.1 Reference oil: N27B, N115B; typical viscosity values are given in Appendix C.
  • 6.3.2 Absorbent cotton.
  • 6.3.3 Silk cloth.
  • 6.3.4 Petroleum ether: 60 ℃~90 ℃, analytical reagent.
  • 6.3.5 95% Ethanol: analytical reagent.
• 5.3 Reference oil (method A): regular use of reference oil to calibrate the spindle can improve the accuracy of test results; the corresponding test methods and calibration instructions are provided in Appendix E and Appendix G; reference oil is also used to examine the effect of opening the air cold bath lid on temperature (5.3.3).
• 5.2.10 Blank sample: a liquid with viscosity-temperature properties similar to those of the sample.
• Method A other reagents/materials: not explicitly listed in the available source (other than reference oil and blank sample).

5. Apparatus and equipment

• 5.2.1 Brookfield viscometer: dial-reading type LVT or digital display type. It should be ensured that the viscometer is in good working condition before use, and the viscometer head and spindle should be regularly calibrated using reference oil (see Appendix E).
• 5.2.2 Viscometer spindle: Brookfield viscometer 1 steel spindle (only for air cold bath), insulated 4B2 spindle, Tannas 4 glass composite spindle or carbon composite spindle (can be used for air cold bath, air cold bath-constant-temperature liquid bath and programmed cooling liquid bath), respectively shown in Figure 1 as A, B, C and D. Spindle inspection procedure:
  • a) When using the 4B2 spindle, first confirm whether the steel parts at both ends of the spindle are firmly connected to the insulating part in the middle; the steel part on either side of the insulating column may be gently turned, and there should be no relative rotation.
  • b) Check the eccentricity of the spindle after connection to the Brookfield viscometer at least once every three months. When the eccentricity exceeds 1 mm, the spindle should be recalibrated. Damaged or bent spindles should not be used.
  • c) Appropriate measures are recommended for storing spindles; composite spindles should not be soaked in cleaning solvent for too long.
  • Note: using the 4 steel spindle in a liquid bath causes low test results due to metal heat transfer. When the test temperature is lower and the sample viscosity is higher, the low test results are more obvious.
• 5.2.3 Test tube: glass test tube, inner diameter 22.0 mm~22.5 mm, overall length 115 mm±5 mm, with an annular engraved line.
• 5.2.4 Test tube stopper: an insulating stopper installed at the mouth of the test tube (see Figure 2). The hole in the center of the test tube stopper is used to pass the spindle through, and the hole diameter should be such that the spindle does not contact the hole wall when rotating. The test tube stopper should be installed on the test tube so that it rises a certain height above the rim of the test tube, so that during cooling of the sample the spindle maintains an appropriate immersion depth [see 5.4.2 g)].
• 5.2.5 Spindle clamp: a clamp or spacer placed on top of the test tube stopper to secure the spindle, as shown in Figure 2. During cooling of the sample, the spindle maintains an appropriate immersion depth.
• 5.2.6 Test tube holder: made of cork (see Figure 3), used for transferring and testing the sample when using an air cold bath, and also used to keep the sample temperature unchanged when transferring the sample from the air cold bath to the constant-temperature liquid bath when using an air cold bath-constant-temperature liquid bath. The see-through windows on opposite sides of the test tube holder wall can help the operator adjust the immersion depth of the spindle.
• 5.2.7 Air cold bath: a compressor-refrigerated cabinet with air circulation, a turntable and a sample rack, with a temperature control range of 5 ℃–-40 ℃ and a temperature control accuracy of ±0.3 ℃. Before the air cold bath lid is fully opened, it should be possible to shut off the air circulation and turntable. Use the sample rack to secure the test tubes on the turntable; the turntable is driven by a motor, and the turntable speed is 3 r/min–5 r/min. To reduce the effect of air convection on temperature when opening the air cold bath lid, it is recommended that the air cold bath be equipped with an inner lid with an operating hole, through which the operation of placing the sample into the test tube holder is completed.
• 5.2.8 Liquid bath: compressor-refrigerated liquid bath, including constant-temperature liquid bath and programmed cooling liquid bath, with a temperature control accuracy of ±0.1 ℃. Liquid bath types include:
  • a) Constant-temperature liquid bath: used for the air cold bath-constant-temperature liquid bath cooling method, that is, after the sample is cooled in the air cold bath for 15.5 h, the sample is transferred to a constant-temperature liquid bath at the same temperature to continue cooling.
  • b) Programmed cooling liquid bath: cool at the cooling rate in Appendix F, simulating the cooling process of the sample in the air cold bath.
  • Note: Using a liquid bath in the measurement stage can reduce the influence of the environment on the sample temperature, and the apparent viscosity value obtained is more accurate.
• 5.2.9 Thermometer: a calibrated thermometer with a scale division of 0.1 ℃; the thermometer meets the technical requirements of GB/T 514—2005, see Table 1.
  • Table 1 Thermometers meeting GB/T 514—2005: temperature range -45 ℃–-35 ℃ corresponds to thermometer number GB-22; -35 ℃–-25 ℃ corresponds to GB-23; -25 ℃–-15 ℃ corresponds to GB-24; -15 ℃–-5 ℃ corresponds to GB! (number requires confirmation (source-text extraction)).
• 5.2.10 Blank sample: a liquid with viscosity-temperature properties similar to those of the sample. After inserting the thermometer into the blank sample, place the blank sample together with the sample into the air cold bath. Monitor the temperature change of the sample in the air cold bath to understand the effect of opening the air cold bath cover on the sample temperature.
• 6.2 Instruments and equipment (Method B):
  • 6.2.1 Brookfield viscometer: dial reading LVT type.
  • 6.2.2 LVT type 4 spindle: same as A in Figure 1.
  • 6.2.3 Semiconductor cold bath: technical conditions and operating parameters are given in Appendix H.
  • 6.2.4 Thermometer: low-temperature mercury-thallium thermometer, 0 ℃~60 ℃, with a scale division of 0.1 ℃.
  • 6.2.5 Test tube: ground-mouth flat-bottom glass, inner diameter 22 mm–23 mm, overall length 128 mm–130 mm, wall thickness 1.0 mm~1.5 mm, with a ring-shaped mark at 70 mm from the bottom (see Figure 4).
  • 6.2.6 Sleeve: ground-mouth flat-bottom glass, inner diameter 44 mm–45 mm, overall length 138 mm–140 mm (see Figure 4).
  • 6.2.7 Constant-temperature water bath.

6. Recommended operating conditions

• Method A Cooling method (5.1 Note): air cold bath, air cold bath-constant-temperature liquid bath, programmed cooling liquid bath.
• Air cold bath (5.2.7): temperature control range 5 ℃–-40 ℃, temperature control accuracy ±0.3 ℃; turntable speed 3 r/min–5 r/min.
• Liquid bath (5.2.8): temperature control accuracy ±0.1 ℃.
• Constant-temperature time (5.1): the sample together with the test tube, spindle, stopper, and spindle clamp is held at the test temperature for 16 h.
• Air cold bath-constant-temperature liquid bath (5.4.3 b)): cool in the air cold bath for 15.5 h, transfer to a constant-temperature liquid bath at the same temperature to continue cooling for 0.5 h; the constant-temperature liquid bath is held at the test temperature for at least 2 h or more.
• Programmed cooling liquid bath (5.4.3 c)): cool the sample for 16 h.
• Sample preheating (5.4.2 c)): liquid samples of low viscosity in the test tube are preheated to 50 ℃±3 ℃ and held at constant temperature for 30 min±5 min; liquid samples of high viscosity are preheated to 90 ℃±3 ℃ and held at constant temperature for 30 min±5 min. Reference oils do not need to be preheated.
• Test time limit (5.4.5 g)3)): after the viscometer spindle starts rotating, the test should be completed within 60 s (for samples with viscosity greater than 150 000 mPa·s, no more than 90 s).
• Method B (6.1): measure after holding at constant temperature for 2 h; 6.5.1 b) hold at constant temperature for 2 h, during the constant-temperature process adjust the refrigerating instrument current so that the digital thermometer display value is controlled within the preset temperature ±0.4 ℃, hold at constant temperature for 0.5 h; 6.5.2 c) hold at the test temperature for 2 h, during the constant-temperature period control the digital thermometer display value within the test temperature ±0.4 ℃.
• Method B Sample preparation (6.5.2 a)): add the sample to the ring-shaped mark of the test tube (about 27 mL), insert the cork stopper, place in a 50 ℃ constant-temperature water bath for 0.5 h, after removal wipe the outer wall dry, place in a test tube rack, and cool at room temperature for 0.5 h.
• Method B Observation time: see Table 4 (spindle speed 0.6 r/min maximum observation time 5 min; 1.5 r/min 3 min; 3.0 r/min 3 min; 6.0 r/min 2 min; 12.0 r/min 1 min; 30.0 r/min 0.5 min; 60.0 r/min 0.5 min; the maximum spindle speeds are respectively 3, 4.5, 9, 12, 12, 15, 30 r/min).

7. Sampling and sample preparation

• 5.4.2 Method A Sample preparation:
  • a) Two test specimens should be measured for each sample (see the note to this clause and 7.3), using duplicate parallel samples. Note: During the test, when adjusting the spindle speed, the sample will be heated and its temperature will rise, affecting the test result. When using the air cold bath and test tube holder to transfer samples, the first test specimen is used to determine the optimum spindle speed, and the result measured for the second test specimen at that spindle speed is used as the test result to be reported. This is not required when using a liquid bath for the test.
  • b) After fully shaking the sample uniformly, pour the sample into the test tube up to the mark. The reference oil and blank sample are added in the same way.
  • c) Preheating: liquid samples of low viscosity are preheated to 50 ℃±3 ℃ and held at constant temperature for 30 min±5 min; liquid samples of high viscosity are preheated to 90 ℃±3 ℃ and held at constant temperature for 30 min±5 min. Note: The purpose of preheating the sample is to eliminate the effect on the result of the internal structure formed by the sample before the test. Samples with higher viscosity require a higher preheating temperature and a longer preheating time. Reference oils do not need to be preheated.
  • d) During preheating, the test tube should be covered (using aluminum foil or a rubber sleeve, etc.) to protect the sample.
  • e) After preheating is completed, the sample is cooled to room temperature (25 ℃±5 ℃), and the cover is opened.
  • f) Fit the test tube with a test tube stopper, and secure the spindle with the spindle clamp, see Figure 2.
  • g) Adjust the depth to which the spindle immersion mark is immersed so that it is slightly below the sample liquid level, leaving space for the sample to contract after cooling.
• 6.5.2 a) Method B Sample preparation: a new sample must be used for each test. Add the sample to the ring-shaped mark of the test tube (about 27 mL), and insert the cork stopper. Place in a 50 ℃ constant-temperature water bath for 0.5 h, after removal wipe the outer wall dry, place in a test tube rack, and cool at room temperature for 0.5 h. Replace with a perforated test tube stopper, insert the spindle, position it with the spindle clamp, and then place it in the semiconductor cold bath at the test temperature.
• Sampling: no independent sampling clause is provided in the available source.

8. Analytical procedure

Method A

• 5.4.1 Prepare the air cold bath:
  • a) Set the expected test temperature of the air cold bath.
  • b) Turn off the turntable, then install the turntable in the operating position, pour the blank sample into the test tube up to the mark, and install the thermometer.
  • c) Place the blank sample at the center position of the sample rack to monitor the final temperature and cooling rate of the sample in the air cold bath.
  • d) Close the air cold bath cover and turn on air circulation. Observe the blank sample temperature and record it at regular intervals. If reading the thermometer is difficult, it is permissible to use a digital thermometer of the same accuracy level instead.
  • e) Adjust the set temperature of the air cold bath so that the blank sample temperature reaches and stabilizes at the test temperature; at this time, the displayed temperature of the air cold bath (which is not necessarily completely consistent with the blank sample temperature) will serve as the set temperature for that test temperature.
  • f) If the temperature is adjusted, the air cold bath should be re-stabilized; the specific stabilization time depends on the performance of the air cold bath, and the blank sample temperature should be kept stable for at least 1 h or more. Do not adjust the set temperature of the air cold bath during the sample cooling process. To test the apparent viscosity at multiple temperatures, the corresponding set temperatures of the air cold bath should be determined in advance using the blank sample.
• 5.4.3 Cool the sample:
  • a) Use the air cold bath to cool the sample: 1) place the sample on the sample rack, place the same reference oil at both the start and end positions, and place the blank sample at the center of the sample rack; 2) place a sufficient number of test tube holders in the air cold bath to cool together with the sample; the placement of the test tube holders should not affect the cooling of the sample by the cold air in the air cold bath; close the air cold bath cover and turn on the turntable and air circulation; 3) cool the sample and test tube holders for 16 h.
  • b) Cool the sample using an air cold bath and a constant-temperature liquid bath: 1) The sample is cooled in the air cold bath according to 5.4.3 a) 1) and 5.4.3 a) 2) for 15.5 h, while adjusting the constant-temperature liquid bath temperature to the test temperature, and keeping the constant-temperature liquid bath at the test temperature for at least 2 h or more; 2) Use the cooled test tube holder to rapidly transfer the sample from the air cold bath to the liquid bath, and continue cooling for 0.5 h.
  • c) Cool the sample using a programmed cooling liquid bath: 1) At room temperature, place the preheated sample in the specified position in the programmed cooling liquid bath, and set the programmed cooling liquid bath test temperature; 2) Begin cooling, and cool the sample for 16 h. Note: Use a thermometer to measure the bath temperature near the sample, accurate to ±0.1 ℃, to examine the sample cooling rate and test temperature.
• 5.4.4 Prepare the Brookfield viscometer:
  • a) Adjust the Brookfield viscometer to be vertical, so that the bubble on the viscometer is at the center position.
  • b) Turn on the Brookfield viscometer, and with the spindle not connected, zero the viscometer. A digital-display Brookfield viscometer can automatically zero.
  • c) When using a digital-display Brookfield viscometer, select the spindle setting according to the spindle type, and immediately press the spindle selection key to store it after selection. Note: If the spindle selection key is pressed by mistake, the Brookfield viscometer will default to selecting the most recently used spindle within 2 s, resulting in an incorrect spindle selection.
  • d) A digital-display Brookfield viscometer can directly read the apparent viscosity value, and can also read the dial reading value.
• 5.4.5 Test the viscosity of the sample:
  • a) Complete the cooling of the sample according to 5.4.3.
  • b) Complete the preparation of the Brookfield viscometer according to 5.4.4.
  • c) Prepare to test the air cold bath sample: 1) Record the blank sample temperature; the blank sample temperature should be within the range of the test temperature ±0.3 ℃; 2) Turn off the turntable and air circulation until they stop completely; 3) Open the air cold bath cover, place the sample into the test tube holder that was cooled together, and remove it from the air cold bath, removing only one sample at a time; 4) Immediately close the air cold bath cover, and reopen the turntable and air circulation; 5) Transfer the removed sample together with the test tube holder under the viscometer; 6) Align the spindle and the viscometer drive shaft in a straight line, screw the spindle nut directly onto the drive shaft thread, and avoid disturbing the sample with the spindle during the connection process; 7) Remove the spindle clamp; 8) Observe the spindle height through the viewing window on the test tube holder, and adjust the knob on the viscometer stand until the spindle immersion mark (see Figure 1) is level with the sample meniscus. A cold light source (flashlight or diode) may be used to transmit light through the viewing window on the opposite side of the test tube holder to observe the position of the spindle immersion mark; 9) The spindle should pass through the center of the test tube stopper hole, and during the test, the spindle should not contact the test tube stopper.
  • d) Prepare to test the air cold bath and constant-temperature liquid bath sample: 1) After the sample is cooled in the air cold bath according to 5.4.3 b) 1) for 15.5 h, record the blank sample temperature; the deviation of the blank sample temperature from the test temperature should be no greater than ±0.3 ℃; 2) Use the cooled test tube holder to rapidly transfer the sample from the air cold bath to the liquid bath, and continue cooling for 0.5 h; 3) Use a thermometer to measure the bath temperature near the test tube. If the temperature exceeds the test temperature by ±0.1 ℃, but is within ±0.3 ℃, adjust the liquid bath to the test temperature ±0.1 ℃ and continue constant temperature for 0.5 h before starting the test; if the temperature exceeds ±0.3 ℃, adjust the liquid bath temperature and retest; 4) The sample cooling time should not exceed 18 h; 5) Move the viscometer above the test tube; 6) Align the spindle and the viscometer drive shaft in a straight line, screw the spindle nut directly onto the drive shaft thread, and avoid disturbing the sample with the spindle during the connection process; 7) Remove the spindle clamp; 8) Adjust the knob on the viscometer stand until the spindle immersion mark is level with the sample meniscus; 9) The spindle should pass through the center of the test tube stopper hole, and during the test, the spindle should not contact the test tube stopper.
  • e) Prepare to test the programmed cooling liquid bath sample: 1) After the sample test tube is immersed for 15 h, use a thermometer to measure the bath temperature near the test tube. If the temperature exceeds the test temperature by ±0.1 ℃, but is within ±0.3 ℃, adjust the liquid bath to the test temperature ±0.1 ℃ and continue constant temperature for 1 h before starting the test; if the temperature exceeds ±0.3 ℃, adjust the liquid bath temperature and retest; 2) The sample cooling time should not exceed 18 h; 3) Move the viscometer above the test tube; 4) Operate according to 5.4.5 d) 6) to 5.4.5 d) 9).
  • f) Read the viscometer reading: 1) Select the optimal spindle speed according to Chapter 7, and adjust the viscometer spindle speed; 2) Confirm again that the spindle immersion mark is consistent with the sample meniscus, start the viscometer motor; for a dial-reading viscometer, read only the dial reading; for a digital-display viscometer, read both the apparent viscosity and the dial scale reading value; 3) When using an air cold bath, the sample should begin testing within 30 s after leaving the air cold bath. According to 5.4.2 a), use duplicate samples for cooling; the first sample is used to determine the optimal spindle speed, and the result measured with the second sample at that spindle speed is used as the reported test result.
  • g) Determination of apparent viscosity: 1) When using a calibrated spindle, the apparent viscosity of the sample is the product of the calibration viscosity calculation coefficient in Appendix E and the dial reading. For measuring oils with relatively low viscosity such as hydraulic oil, a calibrated spindle should be used; 2) When using an uncalibrated spindle, the apparent viscosity of the sample is the product of the viscosity calculation coefficient in Table 2 and the dial reading. If a digital-display viscometer is used, the apparent viscosity value can be read directly; 3) After the viscometer spindle begins to rotate, the test should be completed within 60 s (for samples with viscosity greater than 150 000 mPa·s, no more than 90 s). When a digital-display viscometer directly reads viscosity, report the maximum viscosity reading within the test time; 4) At the same time, record the apparent viscosity (mPa·s), spindle speed (r/min), and test temperature (℃).

Method B

• 6.4 Preparation work:
  • 6.4.1 Turn on the power switch of the constant-temperature water bath, and keep the temperature constant at 50 ℃. Connect the refrigeration system of the semiconductor cold bath.
  • 6.4.2 Calibrate the viscometer: a) To ensure the reliability of the apparent viscosity measurement, the viscometer should be regularly calibrated with reference oils. There are two types of reference oils, N27B and N115B. The different standard viscosity values of each reference oil are shown in Appendix C; b) The precision of calibrating the viscometer with reference oils is shown in Table 3.
  • Table 3 Precision of calibrating the viscometer with reference oils: spindle speed 1.5 r/min allowable deviation (dial reading) ±5.0; 3.0 r/min ±4.5; 6.0 r/min ±1.0; 12.0 r/min ±4.0; 30.0 r/min ±3.5; 60.0 r/min ±3.5. (Note: 6.0 r/min corresponds to ±1.0, suspected to be source-text extraction, a doubtful point, requires confirmation against the source standard (source-text extraction))
• 6.5.1 Adjust the semiconductor cold bath temperature:
  • a) Fill the spaces between the test tube and the sleeve, and between the sleeve and the cold bath wall, with 95% ethanol. Remove the test tube, and put a cork on the test tube. Connect the water circuit and electrical circuit of the refrigeration instrument, and set the preset temperature of the cold bath to slightly below the test temperature.
  • b) Put an oil sample with a lower pour point (slightly below the ring mark) into the test tube as a simulated sample, insert a low-temperature mercury-thallium thermometer with a test tube stopper, so that the mercury bulb is at the position corresponding to the spindle in the sample. Place the test tube into the sleeve in the cold bath, and keep the temperature constant for 2 h. During the constant-temperature process, adjust the current of the refrigeration instrument so that the displayed value of the digital thermometer is controlled within ±0.4 ℃ of the preset temperature, and observe the temperature of the simulated sample. If the simulated sample does not match the test temperature, adjust the preset temperature of the cold bath until the temperature of the simulated sample is consistent with the test temperature. Keep the temperature constant for 0.5 h.
• 6.5.2 Determine apparent viscosity:
  • a) Use a new sample for each test. Add the sample to the ring mark of the test tube (about 27 mL), and stopper it well with a cork. Place it in a constant-temperature water bath at 50 ℃ for 0.5 h. After removal, wipe the outer wall dry, place it in a test tube rack, and cool at room temperature for 0.5 h. Replace with a perforated test tube stopper, insert the spindle, position it with the spindle clamp, and then place it in the semiconductor cold bath at the test temperature. Move the viscometer above the test tube, adjust it to a horizontal position, and connect the spindle. With the aid of a cold light source (flashlight or diode) on the back side of the cold bath observation hole, adjust the spindle immersion depth so that the spindle immersion mark is level with the liquid surface, and make the spindle centered in the test tube stopper hole.
  • b) According to the relationship between the viscosity range and spindle speed provided in Table 2, select the spindle speed. Press down the clutch lever of the viscometer, start the viscometer motor, and gently release the clutch lever. When the “0” position of the viscometer dial reading is within the observation window, press down the clutch lever, turn off the motor, then release the clutch lever, and observe whether the pointer can quickly return to the “0” position. If the pointer can move freely, it indicates that the viscometer installation and adjustment are normal. Record the start time of constant temperature.
  • c) Keep the temperature constant at the test temperature for 2 h. During the constant-temperature period, control the displayed value of the digital thermometer within ±0.4 ℃ of the test temperature. If there is a deviation, adjust the current of the semiconductor cold bath.
  • d) After reaching the constant-temperature time, adjust the spindle depth again so that the spindle immersion mark is level with the sample liquid surface. Then press down the clutch lever, start the viscometer motor, and gently release the clutch lever. When the pointer stabilizes at a certain position on the dial or reaches the maximum observation time specified in Table 4, read and record the dial reading.
  • e) If the product of the dial reading and the viscosity calculation coefficient is not within the viscosity range given in Table 2, then keep at constant temperature for 10 min, and reselect the spindle speed for measurement.
  • f) In order to read the dial reading at a higher spindle speed, when the pointer enters the observation window, immediately press down the clutch lever, and at the same time turn off the motor, read the dial reading, then gently release the clutch lever.
  • g) After the measurement is completed, raise the viscometer and remove the spindle. Move the viscometer away, take out the test tube containing the sample, and place it in a constant-temperature water bath at 50 ℃. After the sample temperature rises again, take out the spindle, place it in a beaker containing petroleum ether, use tweezers to hold absorbent cotton and scrub it twice, then wipe it dry with silk cloth and set aside for use. Note: Maintaining an appropriate immersion depth of the spindle is very necessary for obtaining good repeatability and reproducibility. Data show that if the sample meniscus changes up and down by 1.2 mm, the apparent viscosity will produce an error of 2%.

9. Qualitative and Quantitative and Calculation Formulas

• Table 2 Viscosity Calculation Coefficient Table:
  • Spindle speed 0.6 r/min, viscosity calculation coefficient 10000, viscosity range 400 000~1 000 000 mPa·s;
  • 1.5 r/min, 4000, 200 000~400 000 mPa·s;
  • 3.0 r/min, 2000, 100 000~200 000 mPa·s;
  • 6.0 r/min, 1000, 50 000~100 000 mPa·s;
  • 12.0 r/min, 500, 20 000~50 000 mPa·s;
  • 30.0 r/min, 200, 9 800~20 000 mPa·s;
  • 60.0 r/min, 100, 1 500~9 800 mPa·s;
  • 120.0 r/min, 50, 250~1 500 mPa·s.
  • Note: The spindle speed of a digital-display Brookfield viscometer can reach 120 r/min, and the maximum spindle speed of a dial-scale viscometer is 60 r/min.
• 5.4.5 g) Apparent viscosity calculation: when using a calibrated spindle, the apparent viscosity is the product of the calibration viscosity calculation coefficient in Appendix E and the dial reading; when using an uncalibrated spindle, the apparent viscosity is the product of the viscosity calculation coefficient in Table 2 and the dial reading; a digital-display viscometer can directly read the apparent viscosity value.
• 8.1 Calculation: according to the readings of 5.4.5 and 6.5.2 d), calculate the apparent viscosity of the sample or reference oil at the test temperature according to 5.4.5 g). (In the original text 8.1, “6.6.2 d)” is suspected to be source-text extraction doubtful point, requires confirmation against the source standard (source-text extraction))
• 8.2 Appendix I provides a method for calculating the shear stress and shear rate on the test surface of the Brookfield viscometer spindle.
• Appendix I Shear stress and shear rate:
  • I.2 Shear stress calculation: τ=1.253×M (I.1), where τ is the shear stress, in pascals (Pa); M is the dial reading; 1.253 is a constant determined by the spindle dimensions and the viscometer spring constant.
  • I.3 Shear rate calculation: S=0.2156×rpm (I.2), where S is the shear rate, in reciprocal seconds (s⁻¹); rpm is the spindle speed, in revolutions per minute (r/min); 0.2156 is a constant determined by the spindle radius and the inner diameter of the test tube (in a test tube with inner diameter 22.25 mm, the shear rate on spindle No. 4).
• Appendix E Calibration coefficient calculation and use:
  • E.6.1 Use the least squares method to perform linear regression on the dial reading and spindle speed; an example is shown in Figure E.1. a) In Figure E.1, the correlation coefficient (R) between the dial reading and spindle speed is >0.999; b) In Figure E.1, the intercept of the straight-line dial scale is 0.0993, reflecting that the systematic error caused by mechanical friction of the viscometer is within an acceptable range. If the intercept is greater than or equal to 2, it indicates that there is a problem with the viscometer and it needs to be cleaned or repaired.
  • E.6.2 The calibration coefficient is obtained by dividing the known reference oil viscosity by the slope of the regression line. In Figure E.1, the calculated calibration coefficient is 6474.
  • E.6.3 The calibration coefficient obtained by this method is related only to the spindle and is independent of test temperature, viscosity, and rotational speed.
  • E.6.4 The viscosity of the sample is the calibration coefficient multiplied by the dial reading divided by the spindle speed. As shown in Figure E.1, the viscosity of the sample is: 6474×36.4÷12.0≈19 600.
  • E.6.5 The calibration coefficient is also used to check whether the temperature of a liquid bath or air cooling bath is accurate.
• Appendix G Calculation of test temperature from the apparent viscosity of a Newtonian reference oil:
  • G.3.1 The apparent viscosity is the product of the dial reading and the calibration viscosity calculation coefficient.
  • G.3.2 On the reference oil label, select the viscosities at temperatures adjacent to both sides of the test temperature; the temperatures are T₁ and T₂, and the corresponding viscosities are η₁ and η₂, respectively.
  • G.3.3 Substitute T₁, η₁ and T₂, η₂ into formula (G.1), respectively, to determine A and B: lglg (η+0.7) = A-BlgT (G.1), where T is temperature, in kelvins (K); η is viscosity, in millipascal seconds (mPa·s).
  • G.3.4 Substitute the reference oil viscosity η measured at the test temperature (T₀) into formula (G.1) to calculate the temperature T.
  • G.3.5 Calculate ΔT according to formula (G.2): ΔT=T-T₀ (G.2), where T is the calculated test temperature, in kelvins (K); T₀ is the actual test temperature, in kelvins (K).
  • G.4 Example: Set the test temperature to -30 ℃ (243.15 K); at a rotational speed of 60 r/min, the observed dial reading is 65; at a rotational speed of 60 r/min, the calibration viscosity coefficient is 104; the apparent viscosity is 6 760 mPa·s; it is known that at a temperature of -28.9 ℃, the reference oil viscosity is 5300 mPa·s; it is known that at a temperature of -34.4 ℃, the reference oil viscosity is 12 750 mPa·s; according to formula (G.1), A is calculated to be 9.445 14, and B is 23.476 18; according to formula (G.1), the test temperature is calculated to be -30.5 ℃ (243.65 K); according to formula (G.2), ΔT is calculated to be 0.5 ℃.
  • G.5 Explanation: In the example, the calculated test temperature deviates from the set temperature by 0.5 ℃, which is greater than 0.3 ℃. The possible reasons are temperature control, the test system, the spindle