Oil low-temperature performance evaluation method based on flow test of dynamic shear rheometer

Abstract

The invention discloses an oil low-temperature performance evaluation method based on a flow test of a dynamic shear rheometer, and by adopting the method, reasonable and accurate viscosity data can be obtained so as to evaluate the low-temperature performance of oil.

Description

Technical Field

[0001] The invention relates to the technical field of oil sample viscosity testing, and in particular to a method for evaluating low-temperature performance of oils based on flow testing using a dynamic shear rheometer. Background Art

[0002] Whether in the construction industry or the road and bridge industry, the use of waterproofing membranes can be seen everywhere. During the use of buildings, diseases are often generated, some of which are related to the quality of waterproofing membranes. Therefore, the performance of waterproofing membranes is particularly important. The raw materials of waterproofing membranes generally include waterproof asphalt, fillers, etc., and the raw materials of waterproof asphalt are composed of base asphalt and oil. Therefore, the performance evaluation of oil plays an important role in improving the performance of waterproofing membranes.

[0003] However, there are relatively few evaluation methods for oil in the existing technology. Therefore, a method for evaluating the low-temperature performance of oil is developed to optimize the selection of raw materials for waterproof membranes and fundamentally improve their performance. This has important significance and great market value for manufacturers and the entire waterproof membrane industry. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for evaluating the low temperature performance of oils based on flow testing using a dynamic shear rheometer, the method comprising the following steps:

[0005] (1) Place the oil to be tested on the test plate of the dynamic shear rheometer;

[0006] (2) Using the general shear rate viscosity program of the dynamic shear rheometer, the torque variation curve of the oil to be tested is measured with temperature, and the low temperature at which the torque does not exceed the limit is obtained from the above variation curve;

[0007] (3) using any temperature among the low temperatures in step (2) as the temperature control temperature of the second Newtonian fluid platform area program, setting the second Newtonian fluid platform area program, measuring the viscosity versus shear rate curve of the oil to be tested, and obtaining the shear rate range of the first Newtonian fluid platform area of ​​the oil to be tested from the above-mentioned change curve;

[0008] (4) taking any shear rate from the shear rate range of step (3), setting the viscosity program of the oil to be tested, obtaining a viscosity versus temperature curve, and obtaining the viscosity at any temperature under the low temperature where the torque does not exceed the limit; and evaluating the low temperature performance of the oil to be tested based on the viscosity.

[0009] According to an embodiment of the present invention, the method further comprises step (5):

[0010] Repeat steps (2)-(4) at least 3 times to obtain at least three sets of viscosity values ​​at any temperature under low temperature where the torque does not exceed the limit, and based on at least three sets of viscosity values ​​at any temperature under low temperature where the torque does not exceed the limit, calculate the coefficient of variation of the viscosity at any temperature, so as to evaluate the low temperature performance of the oil to be tested.

[0011] In the present invention, the oil to be tested has two Newtonian fluid platform areas, namely the first Newtonian fluid platform area and the second Newtonian fluid platform area, and the viscosity of the second Newtonian fluid platform area is lower than the viscosity of the first Newtonian fluid platform area. In the present invention, the Newtonian fluid platform area refers to the Newtonian fluid viscosity remaining constant at different shear rates; it is an approximately horizontal straight line on the relationship diagram between viscosity and shear rate.

[0012] According to the embodiment of the present invention, step (1) is: placing the oil to be tested on the test plate of the dynamic shear rheometer, clicking the Trim Gap program of the dynamic shear rheometer, and waiting for the program to run.

[0013] According to an embodiment of the present invention, step (1) is specifically:

[0014] Use a pipette to squeeze the oil to be tested onto the test plate of the dynamic shear rheometer, and use a scraper to trim the oil to be tested on the test plate, click the Trim Gap program of the dynamic shear rheometer, and wait for the program to run. Preferably, the temperature of the scraper is room temperature.

[0015] In the present invention, since the fluidity of oil is very high, it cannot be prepared into a solid and movable sample at room temperature, so a straw can be used to directly suck the sample and put it between the clamps, thereby solving the problem of sample loading; in general dynamic shear rheometer tests, a scraper will be heated to trim the sample, but oil has good fluidity without heating and melting, therefore, the present invention uses a room temperature scraper to trim the sample, thereby avoiding the influence of a high temperature scraper on the properties of the oil sample and the three-dimensionality of the edge.

[0016] According to an embodiment of the present invention, in step (2), the general shear rate viscosity procedure refers to the procedure conventionally used by those skilled in the art when testing the viscosity of oils. For example, in the general shear rate viscosity procedure, the temperature during the test is -40 to 100°C, preferably -30 to 60°C, and during the test, the temperature is a range between any two values ​​of -40 to 100°C, and the selection of any two values ​​of -40 to 100°C is a technique known in the art. The shear rate during the test is 0.00001-100,0000s -1 , preferably 0.5-10000s -1 , preferably 1-2000s -1 , more preferably 1-1000s -1, preferably 5-100s -1 ; and the shear rate during the test is 0.00001-100,0000s -1 For any given value, and for 0.00001-100,0000s -1 The selection of any value is a well-known technique in the art. Preferably, the parallel plate material is iron, and preferably, the diameter of the parallel plate material is 20-25 mm.

[0017] According to an embodiment of the present invention, in step (2), the torque does not exceed the limit means that the torque does not exceed 200,000 μN·m. The dynamic shear rheometer provides a torque to the sample to be tested, causing the sample to twist, and accurately records the strain, complex modulus, phase angle and other data during the test. Generally speaking, the lower the temperature, the greater the torque that the dynamic shear rheometer needs to provide. When the torque exceeds the limit of the dynamic shear rheometer, firstly, it will cause damage to the instrument itself, and secondly, the data obtained from the test will also lack credibility. Therefore, the torque of the method of the present invention cannot exceed 200,000 μN·m.

[0018] According to an embodiment of the present invention, in step (2), the low temperature is a temperature range, for example, the low temperature is -10°C to 25°C. Within this temperature range, any temperature is selected as the temperature control temperature of the second Newtonian fluid platform area program. Preferably, within the low temperature range, a lower temperature is selected as the temperature control temperature of the second Newtonian fluid platform area program.

[0019] It is well known in the art that the viscosity of oil is mainly affected by temperature and shear rate. Within a certain temperature range, the viscosity of oil gradually decreases as the shear rate increases.

[0020] like Figure 7 As shown, it is a theoretical relationship diagram of the viscosity and temperature of oils, wherein the curves of the three circles in the lower left figure are enlarged as shown in the upper right figure, wherein from left to right, the first circle represents the first Newtonian fluid platform area of ​​the viscosity of the oil, the second circle is the shear thinning process, and the third circle represents the second Newtonian fluid platform area. Therefore, if you want the viscosity of the oil to be affected only by temperature, you need to find the Newtonian fluid platform area of ​​the oil, and perform viscosity testing within the shear rate range corresponding to the Newtonian fluid platform area to ensure the authenticity and accuracy of the test results. Therefore, the present invention controls the viscosity of the oil to be tested to remain unchanged within a certain shear rate range through the first Newtonian fluid platform area and the second Newtonian fluid platform area of ​​the oil to be tested, so that the viscosity of the oil to be tested is only affected by temperature when evaluating its low temperature performance.

[0021] According to an embodiment of the present invention, in step (3), the setting procedure of the second Newtonian fluid platform area is the same as the general shear rate viscosity procedure of the dynamic shear rheometer in step (2), except that the test temperature and shear rate are different;

[0022] Wherein, the temperature of the setting program of the second Newtonian fluid platform zone in step (3) is any temperature within the low temperature range;

[0023] In step (2), in the general shear rate viscosity program of the dynamic shear rheometer, the temperature during the test is -40 to 100°C;

[0024] In step (2), in the general shear rate viscosity program of the dynamic shear rheometer, the shear rate is a constant value; and in step (3), in the setting program of the second Newtonian fluid platform area, the shear rate is a range value.

[0025] Preferably, in step (3), in the second Newtonian fluid platform region program, the shear rate is 1-1000s -1 , preferably 1-500s -1 , more preferably 1-300s -1 .

[0026] According to an embodiment of the present invention, in step (4), in the viscosity procedure of the oil, the temperature during the test is -15 to 70°C, preferably -15 to 30°C, for example, -15°C, -10°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C or 30°C, and the shear rate during the test is 0.00001-100,0000s -1 , preferably 0.5-10000s -1 , preferably 1-2000s -1 , more preferably 1-1000s -1 , preferably 5-100s -1 Preferably, the parallel plate material is aluminum, and preferably, the diameter of the parallel plate material is 35-45 mm.

[0027] According to an embodiment of the present invention, in step (4), the viscosity at any temperature at the low temperature where the torque does not exceed the limit is evaluated by using the viscosity corresponding to any temperature between -10°C and 0°C. Preferably, the viscosity at -10°C is used to evaluate the low temperature performance of the oil to be tested. In the present invention, the smaller the viscosity at any temperature at the low temperature where the torque does not exceed the limit, the better the low temperature performance of the sample.

[0028] For example, the viscosity at -10℃ refers to the viscosity value of the oil to be tested corresponding to -10℃ on the viscosity-temperature curve.

[0029] According to an embodiment of the present invention, in step (5), the coefficient of variation (denoted as C·V) is the ratio of the standard deviation to the mean, that is, the coefficient of variation C·V=(standard deviation SD / mean value Mean)×100%. The coefficient of variation can eliminate the influence of different units and / or means on the comparison of the degree of variation of two or more data.

[0030] According to an embodiment of the present invention, in step (5), if the coefficient of variation is greater than 15%, the data is abnormal and should be discarded. In the present invention, the smaller the coefficient of variation of the viscosity at any temperature under the low temperature where the torque does not exceed the limit, the better the low temperature performance of the sample.

[0031] According to an embodiment of the present invention, the method for evaluating the low temperature performance of oils comprises the following steps:

[0032] (1) placing the oil 1 to be tested on the test plate of the dynamic shear rheometer;

[0033] (2) using a general shear rate viscosity program of a dynamic shear rheometer, measuring the torque versus temperature curve of the oil to be tested 1, and obtaining the low temperature at which the torque does not exceed the limit from the above curve;

[0034] (3) using any temperature of the low temperature in step (2) as the temperature control temperature of the second Newtonian fluid platform area program, setting the second Newtonian fluid platform area program, measuring the viscosity versus shear rate curve of the oil 1 to be tested, and obtaining the shear rate interval 1 of the first Newtonian fluid platform area of ​​the oil 1 to be tested from the above-mentioned change curve;

[0035] Select at least one different type of oil 2 to be tested, repeat the above steps (1) to (3), and obtain a shear rate interval 2 of the first Newtonian fluid platform region of the oil 2 to be tested;

[0036] According to the shear rate interval 1 and the shear rate interval 2, a common shear rate interval is obtained;

[0037] (4) taking any shear rate from the common shear rate range of step (3), setting the viscosity program of the oil, obtaining a viscosity versus temperature curve, and processing the obtained viscosity data to obtain the viscosity at any temperature under the low temperature at which the torque does not exceed the limit;

[0038] Repeat steps (2)-(4) at least 3 times to obtain at least three sets of viscosity values ​​at any temperature of the low temperature where the torque does not exceed the limit, and based on the three sets of viscosity values ​​at any temperature of the low temperature where the torque does not exceed the limit, calculate the coefficient of variation of the viscosity at any temperature, and the low temperature performance of the tested oil 1, 2, 3... or n can be evaluated respectively.

[0039] According to an embodiment of the present invention, in step (3), the oils to be tested 3, 4, 5, 6, ... n may also be tested to obtain shear rate intervals 3, 4, 5, 6, ... n.

[0040] Beneficial effects of the present invention:

[0041] The method of the present invention can be used to obtain reasonable and accurate viscosity data to evaluate the low-temperature performance of oils.

[0042] The present invention can also test different types of oil samples at the same time, and can also sort the low-temperature performance of these oil samples, and then select oils that are more suitable as raw materials for waterproof membranes, thereby fundamentally improving the performance of waterproof membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The curves of torque variation with temperature of the six oil samples in step 2 of Example 1;

[0044] Figure 2 In the figure, Figure a is a schematic diagram of the Newtonian fluid platform area;

[0045] Figure b is the measured curve of the first Newtonian fluid platform area in Example 1;

[0046] Figure c is the measured curves of the second Newtonian fluid platform region of the six samples in Example 1.

[0047] Figure 3 The viscosity of the six oil samples in step 4 of Example 1 is changed with temperature (Figure a) and the viscosity bar graph at -10°C (Figure b);

[0048] Figure 4 The bar graph is a -10°C viscosity coefficient of variation of the six oil samples obtained in step 4 of Example 1;

[0049] Figure 5 This is a colored block diagram comparing the viscosity at -10°C of Example 1 in Test Example 1 with the performance of the oil obtained from the actual investigation of the waterproof asphalt production company;

[0050] Figure 6 This is a colored block diagram comparing the -10°C viscosity variation coefficient of Example 1 in Test Example 2 with the performance of the oil obtained from an actual survey of a waterproof asphalt production company.

[0051] Figure 7 This is the theoretical relationship diagram between oil viscosity and temperature. DETAILED DESCRIPTION

[0052] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0053] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0054] Example 1

[0055] The present invention provides a method for evaluating the low-temperature performance of oils based on a flow test (Flow) of a dynamic shear rheometer. The viscosity curves of six oil samples, namely Grease-2#, Grease-3#, Wax Oil-3, Wax Oil-minus 2, Wax Oil-minus 3 and Wax Oil-minus 4, are measured. The test results will be compared with the performance of the oils obtained from an actual survey of a waterproof asphalt production company.

[0056] The specific steps of the low temperature performance evaluation method of oil are:

[0057] 1. Test equipment preparation: six small aluminum cans containing different oil samples, at least six straws and a room temperature scraper that comes with the instrument;

[0058] Replace the 40mm parallel plate, press the button to raise the upper parallel plate, reserve space for sample placement, use a straw to absorb grease-2# and squeeze it out on the lower parallel plate, click Trim Gap on the computer and use a room temperature scraper to trim the oil sample;

[0059] 2. The first step of the three-step method: Set up and run the viscosity program of the general shear rate (in the viscosity program of the general shear rate, the test temperature is -30~60℃ (such as Figure 1 The shear rate during the test was 20 s -1 During the test, the parallel plate material used is iron, preferably, the diameter of the parallel plate material is 20-25mm). After completion, the curve of the torque change of Grease-2# with temperature is obtained. The curve of the torque change of Grease-2# with temperature is as follows: Figure 1 As shown;

[0060] Repeat steps 1 and 2 to test the torque-temperature curves of Grease-3#, Wax Oil-3#, Wax Oil-minus 2, Wax Oil-minus 3 and Wax Oil-minus 4 respectively. The torque-temperature curves are as follows: Figure 1 As shown;

[0061] According to the above data on the change of torque with temperature, a low temperature (i.e. -10°C) at which the torque does not exceed the limit (i.e. 200,000 μN·m) is selected as the temperature control temperature of the second Newtonian fluid platform zone program in the second step of the three-step method; Figure 1 As shown, at -10°C, the torques of Grease-2#, Grease-3#, Wax Oil-3, Wax Oil-minus 2, Wax Oil-minus 3 and Wax Oil-minus 4 did not exceed 200,000 μN·m. Therefore, -10°C was taken as the low temperature at which the torque did not exceed the limit (i.e., 200,000 μN·m).

[0062] 3. Step 2 of the three-step method: Take another sample of Grease-2#, set the temperature control temperature of the second Newtonian fluid platform area program to -10°C, set the relevant program of the second Newtonian fluid platform area (same as the program for the test of Grease-2# above, but set the shear rate during the test to (10-100s -1 ), the viscosity variation curve of the oil to be tested with shear rate is measured, and the viscosity variation curve of Grease-2# with shear rate is obtained. The viscosity variation curve of Grease-2# with shear rate is as follows: Figure 2 As shown;

[0063] Repeat step 5 to test the viscosity variation curves of grease-3#, wax oil-3#, wax oil-minus 2#, wax oil-minus 3# and wax oil-minus 4# respectively. The variation curves are as follows: Figure 2 As shown;

[0064] From the above viscosity versus shear rate curve, find the second Newtonian fluid platform area of ​​Grease-2#, and find the corresponding shear rate range, which is the range of the shear rate of Grease-2# in the third step of the three-step method; Figure 2 It can be seen that the shear rate range of the first Newtonian fluid platform area of ​​Grease-2#, Grease-3#, Wax Oil-3#, Wax Oil-minus 2, Wax Oil-minus 3 and Wax Oil-minus 4 is 10-100 (1 / s). In this shear rate range (i.e. 10-100 (1 / s)), the viscosity is a constant. That is, in this shear rate range (10-100 1 / s), the shear rate will not affect the viscosity of the oil, and the control variable.

[0065] 4. Step 3 of the three-step method: In the common shear rate range (i.e. 35-45s -1 ) to select a shear rate (the shear rate during the test is 35-45s -1 Any value between 0 and 1 is acceptable), and the improved viscosity program is run (in the improved viscosity program, the test temperature is in the low temperature range, i.e., -10°C to 30°C; during the test, the parallel plate material used is iron, and preferably, the diameter of the parallel plate material is 20-25mm), and the viscosity curves of the six oil samples varying with temperature are obtained. The viscosity curves are shown in FIG. Figure 3 As shown in a, the viscosity at -10°C is recorded respectively. Steps 2-7 are repeated again to obtain three sets of viscosity versus temperature curves, and the viscosity at -10°C is recorded respectively.

[0066] The above three sets of viscosity data were processed to obtain the average viscosity of the six groups of samples at -10℃ (such as Figure 3 b), and based on the -10°C viscosity, the coefficient of variation of the viscosity of each group of samples was calculated. Figure 4 As shown, the low temperature performance of the sample can be evaluated. The smaller the coefficient of variation, the better the uniformity of the oil and the better the compatibility with other raw materials of waterproof asphalt.

[0067] Here, coefficient of variation C·V=(standard deviation SD / mean value Mean)×100%.

[0068] from Figure 3 (b) and Figure 4 It can be seen that at -10°C, the low temperature performance of the oils from best to worst is: wax oil-3, grease-2#, wax oil-minus three, wax oil-minus two, grease-3#, wax oil-minus four. When evaluating the low temperature performance, the present invention uses viscosity as the main evaluation index, and the coefficient of variation as an auxiliary evaluation index.

[0069] Test Example 1

[0070] In order to evaluate whether the method of the present invention can play a guiding role in actual production, the viscosity results at -10°C in Example 1 are compared with the performance of the oil obtained from an actual investigation of a waterproof asphalt production company. The results of the oil performance investigation (i.e., the company's actual production experience) are: wax oil-3> wax oil-minus 2> wax oil-minus 3, wax oil-minus 4> grease-2#, grease-3#. The comparison results are as follows: Figure 5 As shown in the left figure. Compared with the test results of Example 1, the results show that the -10°C viscosity ranking is roughly consistent with the ranking obtained from the actual investigation of waterproof asphalt production companies.

[0071] Test Example 2

[0072] In order to further evaluate whether the method of the present invention can meet the actual production needs, the results of the viscosity variation coefficient at -10°C in Example 1 are compared with the performance of the oil obtained from the actual investigation of the waterproof asphalt production company. The investigation results are the same as those of Test Example 1. The comparison results are as follows: Figure 6 The results show that the coefficient of variation of viscosity at -10°C is small, and the three-step method of the present invention also has high accuracy in practical application.

[0073] The above is an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the low temperature performance of oils based on flow testing using a dynamic shear rheometer, characterized in that: The method comprises the following steps: (1) Place the oil to be tested on the test plate of the dynamic shear rheometer; (2) Using the general shear rate viscosity program of the dynamic shear rheometer, the torque variation curve of the oil to be tested is measured with temperature, and the low temperature at which the torque does not exceed the limit is obtained from the above variation curve; (3) using any temperature among the low temperatures in step (2) as the temperature control temperature of the second Newtonian fluid platform area program, setting the second Newtonian fluid platform area program, measuring the viscosity versus shear rate curve of the oil to be tested, and obtaining the shear rate range of the first Newtonian fluid platform area of ​​the oil to be tested from the above-mentioned change curve; (4) taking any shear rate from the shear rate range of step (3), setting the viscosity program of the oil to be tested, obtaining a viscosity versus temperature curve, and obtaining the viscosity at any temperature under the low temperature where the torque does not exceed the limit; and evaluating the low temperature performance of the oil to be tested based on the viscosity.

2. The method according to claim 1, characterized in that The method further comprises step (5): Repeat steps (2)-(4) at least 3 times to obtain at least three sets of viscosity values ​​at any temperature under low temperature where the torque does not exceed the limit, and based on at least three sets of viscosity values ​​at any temperature under low temperature where the torque does not exceed the limit, calculate the coefficient of variation of the viscosity at any temperature, so as to evaluate the low temperature performance of the oil to be tested.

3. The method according to claim 1 or 2, characterized in that: In step (2), the general shear rate viscosity procedure refers to the procedure commonly used by those skilled in the art when testing the viscosity of oils. For example, in the general shear rate viscosity procedure, the temperature during the test is -40 to 100°C, and during the test, the temperature is in the range of any two values ​​between -40 and 100°C, and the shear rate during the test is 0.00001-100,0000s -1 , and the shear rate during the test is 0.00001-100,0000s -1 Any certain value.

4. The method according to any one of claims 1 to 3, characterized in that: In step (2), the torque not exceeding the limit means that the torque does not exceed 200,000 μN.m. Preferably, in step (2), the cryogenic temperature is a temperature range, for example, the cryogenic temperature is -10°C to 25°C.

5. The method according to any one of claims 1 to 4, characterized in that: In step (3), the setting procedure of the second Newtonian fluid platform area is the same as the general shear rate viscosity procedure of the dynamic shear rheometer in step (2), except that the test temperature and shear rate are different; Wherein, the temperature of the setting program of the second Newtonian fluid platform zone in step (3) is any temperature within the low temperature range; In step (2), in the general shear rate viscosity program of the dynamic shear rheometer, the temperature during the test is -40 to 100°C; In step (2), in the general shear rate viscosity program of the dynamic shear rheometer, the shear rate is a constant value; and in step (3), in the setting program of the second Newtonian fluid platform area, the shear rate is a range value. Preferably, in step (3), in the second Newtonian fluid platform region program, the shear rate is 1-1000s -1 , preferably 1-500s -1 , more preferably 1-300s -1 .

6. The method according to any one of claims 1 to 5, characterized in that: In step (4), in the viscosity test procedure of the oil, the temperature during the test is -15 to 70°C, and the shear rate during the test is 0.00001 to 100,0000s -1 .

7. The method according to any one of claims 1 to 6, characterized in that: The test temperature in the viscosity procedure of the oil in step (4) is lower than the test temperature in the viscosity procedure of the general shear rate in step (2).

8. The method according to any one of claims 1 to 7, characterized in that: In step (4), the viscosity at any temperature at the low temperature where the torque does not exceed the limit is used to evaluate the low temperature performance of the oil to be tested.

9. The method according to any one of claims 1 to 8, characterized in that: In step (5), the coefficient of variation (denoted as C·V) is the ratio of the standard deviation to the mean, that is, coefficient of variation C·V=(standard deviation SD / mean value Mean)×100%.

10. The method according to any one of claims 1 to 9, characterized in that: The method for evaluating the low temperature performance of oils comprises the following steps: (1) placing the oil 1 to be tested on the test plate of the dynamic shear rheometer; (2) using a general shear rate viscosity program of a dynamic shear rheometer, measuring the torque versus temperature curve of the oil to be tested 1, and obtaining the low temperature at which the torque does not exceed the limit from the above curve; (3) using any temperature among the low temperatures in step (2) as the temperature control temperature of the second Newtonian fluid platform area program, setting the second Newtonian fluid platform area program, measuring the viscosity versus shear rate curve of the oil 1 to be tested, and obtaining the shear rate interval 1 of the first Newtonian fluid platform area of ​​the oil 1 to be tested from the above-mentioned change curve; Select at least one different type of oil 2 to be tested, repeat the above steps (1) to (3), and obtain a shear rate interval 2 of the first Newtonian fluid platform region of the oil 2 to be tested; According to the shear rate interval 1 and the shear rate interval 2, a common shear rate interval is obtained; (4) taking any shear rate from the common shear rate range of step (3), setting the viscosity program of the oil, obtaining a viscosity versus temperature curve, and processing the obtained viscosity data to obtain the viscosity at any temperature under the low temperature at which the torque does not exceed the limit; Repeat steps (2)-(4) at least 3 times to obtain at least three sets of viscosity values ​​at any temperature of the low temperature where the torque does not exceed the limit, and based on the three sets of viscosity values ​​at any temperature of the low temperature where the torque does not exceed the limit, calculate the coefficient of variation of the viscosity at any temperature, and the low temperature performance of the tested oil 1, 2, 3... or n can be evaluated respectively.

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