A method for measuring low temperature viscosity

Abstract

The present invention discloses a method for measuring low-temperature viscosity, and relates to the technical field of lubricating oil detection, evaluation and diagnosis. Before measuring the viscosity of the sample to be tested, the sample to be tested is cooled, and the cooling includes: gradient cooling of the sample to be tested according to the test temperature requirement of the sample to be tested, and then placing the sample to be tested after the gradient cooling on a Brookfield viscometer for testing. The gradient cooling method shortens the cooling time as a whole, and avoids the situation where the sample to be tested is cooled unevenly. It not only realizes the rapid cooling of the sample, improves the cooling efficiency, and effectively shortens the viscosity test time, but also can realize the accurate measurement of the viscosity of the sample to be tested, and reduces the viscosity error of the sample to be tested caused by the measurement method. Objectively, the method error caused by the method itself is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lubricating oil detection, evaluation and diagnosis, and in particular to a method for measuring low-temperature viscosity. Background Art

[0002] In mechanical equipment, lubricating oil mainly plays the role of lubrication and cleaning. The viscosity of lubricating oil at low temperature and low shear rate is very important for the correct operation of many mechanical devices. If the low-temperature viscosity of the oil is too high, it may cause difficulty in starting or increase friction. Therefore, low-temperature viscosity is one of the important indicators and is highly valued.

[0003] At present, the methods used to measure the low-temperature viscosity of gear oil, automatic transmission fluid, and hydraulic oil are mainly GB / T 11145 and ASTM D2983. In the process of the Brookfield viscosity test, there are two main ways to cool the sample. One is to place the sample at the test temperature and keep it at a constant temperature for 16 hours or directly cool it down and keep it at a constant temperature for 16 hours in the set program. The other is to place the sample in a specified air bath to cool for 15.5 hours, and then place it in a constant temperature liquid bath to keep it at a constant temperature for 2 hours. Both methods have the problem of long cooling time.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for measuring low-temperature viscosity to solve the above technical problems.

[0006] The inventors found that rapid cooling will affect the properties of the sample, and there is a situation where the outer wall temperature is lower than the center temperature, which will lead to inaccurate test results. Based on this, the inventors have specially proposed a method of programmed cooling, which has a short cooling time overall and avoids the situation of uneven cooling of the sample to be tested. It not only achieves rapid cooling of the sample, improves cooling efficiency, and effectively shortens the viscosity test time, but also can achieve accurate measurement of the viscosity of the sample to be tested, reducing the viscosity error of the sample to be tested caused by the measurement method. Objectively, the method error caused by the method itself is reduced.

[0007] The present invention is achieved in that:

[0008] The present invention provides a method for measuring low-temperature viscosity, which comprises: cooling a sample to be tested before measuring the viscosity of the sample to be tested, wherein the cooling comprises: performing a program cooling on the sample to be tested to reach a test temperature of the sample to be tested, and then placing the sample to be tested after the program cooling on a Brookfield viscometer for testing.

[0009] The inventors can significantly shorten the cooling time of the sample to be tested by programmed cooling, and the longest time is about 3 hours. Compared with 16 hours in the prior art, the cooling time is at least shortened by more than half. By shortening the cooling time, the detection efficiency is greatly improved.

[0010] By setting cooling baths with different gradients, the sample can be cooled step by step as required. Since the temperature drop in two adjacent cooling baths is smaller, the overall temperature of the liquid can reach equilibrium more quickly, avoiding the difference in sample properties caused by the temperature difference inside and outside the sample, thereby affecting the accuracy of viscosity measurement.

[0011] The above-mentioned Brookfield viscometer is selected from commercially available viscosity measuring instruments, and any instrument that can measure the viscosity of the sample to be tested is acceptable.

[0012] In a preferred embodiment of the present invention, if the test temperature of the sample to be tested is ≥ -12°C, the container containing the sample to be tested is placed in a constant temperature ethanol liquid cooling bath at -12°C to -26°C until the temperature of the sample to be tested reaches the test temperature.

[0013] In an optional embodiment, if the test temperature of the sample to be tested is ≥ -12°C, no gradient cooling is involved, and the sample to be tested only needs to be placed in a constant temperature ethanol liquid cooling bath environment of -12°C to -26°C.

[0014] For example, if the test temperature of the sample to be tested is -8°C, there is no need for gradient cooling, and the sample to be tested only needs to be placed in a constant temperature ethanol liquid cooling bath environment of -12°C to -26°C (the cooling time is only about 30 minutes). In an optional embodiment, the test temperature of the sample to be tested is -8°C, and the sample to be tested can also be placed in an environment of -10°C, and the cooling time is about 1 hour, which is a longer cooling time.

[0015] The inventors have found that a constant temperature ethanol liquid cooling bath environment of -12°C to -26°C can meet the rapid cooling requirements of most test samples with a test temperature ≥ -12°C. In other embodiments, the temperature of the constant temperature ethanol liquid cooling bath can also adaptively fluctuate by 0.5-1°C according to cooling needs, which is also within the protection scope of the present invention.

[0016] In a preferred embodiment of the present invention, if the test temperature of the sample to be tested is ≥ -12°C, the container containing the sample to be tested is placed in a constant temperature ethanol liquid cooling bath at -18°C until the temperature of the sample to be tested reaches the test temperature.

[0017] In a preferred embodiment of the present invention, if the test temperature of the sample to be tested is -12°C to -26°C, the container containing the sample to be tested is first placed in a constant temperature ethanol liquid cooling bath at -12°C to -26°C until the temperature of the sample to be tested is -12°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath at -27°C to -51°C until the temperature of the sample to be tested reaches the test temperature.

[0018] It should be noted that the above-mentioned close to -12°C includes but is not limited to the temperature of the sample to be tested being -12°C ± 5°C. The inventors have found that setting a temperature gradient of a constant temperature ethanol liquid cooling bath of -12°C to -26°C and -27°C to -51°C can not only meet the needs of rapid cooling of the sample, but also avoid uneven temperature differences between the inside and outside of the sample to be tested to a great extent.

[0019] In a preferred embodiment of the present invention, if the test temperature of the sample to be tested is -27°C to -40°C, the container containing the sample to be tested is first placed in a constant temperature ethanol liquid cooling bath at -12°C to -26°C until the temperature of the sample to be tested is -12°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath at -27°C to -51°C until the temperature of the sample to be tested is -26°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath at -41°C to -60°C until the temperature of the sample to be tested reaches the test temperature.

[0020] It should be noted that the above-mentioned close to -26°C includes but is not limited to the temperature of the sample to be tested being -26°C ± 5°C. The inventors have found that setting a temperature gradient of a constant temperature ethanol liquid cooling bath of -12°C to -26°C, -27°C to -51°C, and -41°C to -60°C can not only meet the needs of rapid cooling of the sample, but also avoid uneven temperature differences between the inside and outside of the sample to be tested to a great extent.

[0021] In a preferred embodiment of the present invention, if the test temperature of the sample to be tested is -41°C to -60°C, the container containing the sample to be tested is first placed in a constant temperature ethanol liquid cooling bath of -12°C to -26°C until the temperature of the sample to be tested is -12°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath of -27°C to -51°C until the temperature of the sample to be tested is -26°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath of -41°C to -60°C until the temperature of the sample to be tested is -40°C±5°C; then the container containing the sample to be tested is transferred to a constant temperature ethanol liquid cooling bath of -61°C to -90°C until the temperature of the sample to be tested reaches the test temperature.

[0022] It should be noted that the above-mentioned close to -40°C includes but is not limited to the temperature of the sample to be tested being -40°C ± 5°C. The inventors have found that setting a temperature gradient of a constant temperature ethanol liquid cooling bath of -12°C to -26°C, -27°C to -51°C, -41°C to -60°C, and -61°C to -90°C can not only meet the needs of rapid cooling of the sample, but also avoid uneven temperature differences between the inside and outside of the sample to be tested to a great extent.

[0023] In a preferred embodiment of the present invention, the sample to be tested is preheated before the gradient cooling, and then cooled to room temperature for the gradient cooling. Room temperature refers to 25°C ± 5°C.

[0024] The above-mentioned preheating step is used for the sample to be tested with a relatively high viscosity. In other embodiments, the sample to be tested may be a solid or semi-solid sample at room temperature. In order to more accurately measure the viscosity of the sample to be tested with a relatively high viscosity, a preheating treatment may be performed. In other embodiments, the preheating step may not be provided and cooling may be performed directly.

[0025] In a preferred embodiment of the present invention, the temperature of the preheated sample is 30° C. to 50° C. to ensure that the sample can flow evenly and reduce sampling errors caused by uneven samples.

[0026] In a preferred embodiment of the present invention, the preheating is constant temperature preheating, and the constant temperature preheating time is 30min±5min.

[0027] In a preferred embodiment of the present invention, the sample to be tested is lubricating oil. Lubricating oil includes but is not limited to liquid or semi-solid lubricants used in various types of automobiles and mechanical equipment to reduce friction and protect machinery and processed parts. Its functions may include but are not limited to: lubrication, auxiliary cooling, rust prevention, cleaning, sealing and buffering.

[0028] The present invention has the following beneficial effects:

[0029] The present invention provides a method for measuring low-temperature viscosity. By using a program cooling method, the cooling time is shortened as a whole, and the uneven cooling of the sample to be tested is avoided. The method not only realizes the rapid cooling of the sample, improves the cooling efficiency, and effectively shortens the viscosity test time, but also can realize the accurate measurement of the viscosity of the sample to be tested, and reduces the viscosity error of the sample to be tested caused by the measurement method. Objectively, the method error caused by the method itself is reduced. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0031] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0032] Example 1

[0033] This embodiment provides a method for measuring low-temperature viscosity. The sample to be tested in this embodiment is the Kaineng standard material N115B low-temperature viscosity oil, and the test temperature is -12.2°C. The method includes the following steps in sequence:

[0034] (1) Sampling: Shake the sample vigorously for 30 seconds and pour 25 mL of the sample into the test tube at the scale line.

[0035] (2) Gradient cooling: Place the test tube in a -18°C ethanol liquid cooling bath (Shanghai Boli SYP1016) and keep the temperature constant until the sample temperature reaches the specified temperature. The cooling bath is an ethanol liquid cooling bath.

[0036] (3) Sample testing: Place the sample in a Cannon fully automatic low-temperature Brookfield viscometer for viscosity testing.

[0037] Example 2

[0038] This embodiment provides a method for measuring low temperature viscosity. The sample to be tested in this embodiment is N115B low temperature viscosity oil, and its test temperature is -17.8°C. The method includes the following steps performed in sequence:

[0039] (1) Sampling: Shake the sample vigorously for 30 seconds and pour 25 mL of the sample into the test tube at the scale line.

[0040] (2) Perform gradient cooling: Place the test tube in a -18°C ethanol liquid cooling bath and keep the temperature constant until the sample temperature is -12°C. Move the test tube to a -33°C ethanol liquid cooling bath and keep the temperature constant until the sample temperature reaches the specified temperature. The above cooling bath is an ethanol liquid cooling bath.

[0041] (3) Sample testing: Place the sample in a Brookfield viscometer to test the viscosity.

[0042] Example 3

[0043] This embodiment provides a method for measuring low temperature viscosity. The sample to be tested in this embodiment is N115B low temperature viscosity oil, and its test temperature is -30°C. The method includes the following steps performed in sequence:

[0044] (1) Sampling: Shake the sample vigorously for 30 seconds and pour 25 mL of the sample into the test tube at the scale line.

[0045] (2) Gradual cooling: Place the test tube in a -18°C ethanol liquid cooling bath, and keep the temperature constant until the sample temperature is -12°C. Move the test tube to a -33°C ethanol liquid cooling bath, and keep the temperature constant until the sample temperature reaches close to -26°C. Then move the test tube to a -50°C ethanol liquid cooling bath, and keep the temperature constant until the sample temperature reaches the specified temperature. The above cooling bath is an ethanol liquid cooling bath.

[0046] (3) Sample testing: Place the sample in a Brookfield viscometer to test the viscosity.

[0047] Example 4

[0048] This embodiment provides a method for measuring low temperature viscosity. The sample to be tested in this embodiment is N115B low temperature viscosity oil, and its test temperature is -50°C. The method includes the following steps performed in sequence:

[0049] (1) Sampling: Shake the sample vigorously for 30 seconds and pour 25 mL of the sample into the test tube at the scale line.

[0050] (2) Perform gradient cooling: Place the test tube in a -18°C ethanol liquid cooling bath, and keep the temperature constant until the temperature of the sample to be tested is -12°C. Move the test tube to a -33°C ethanol liquid cooling bath, and keep the temperature constant until the temperature of the sample to be tested reaches close to -26°C. Then move the test tube to an ethanol liquid cooling bath maintained at -51°C, and keep the temperature constant until the temperature of the sample to be tested is -40°C. Move the test tube to an ethanol liquid cooling bath maintained at -69°C, and keep the temperature constant until the sample temperature reaches the specified temperature. The above cooling bath is an ethanol liquid cooling bath.

[0051] (3) Sample testing: Place the sample in a Brookfield viscometer to test the viscosity.

[0052] Experimental Example 1

[0053] In this experimental example, Kleinberg viscosity standard solutions N115B and N27B were selected to verify the accuracy of the low-temperature viscosity measurement method.

[0054] (1) Take four clean samples of the two standard solutions and pour them into test tubes at the scale line, about 25 mL, and plug the test tubes with corks containing thermometers.

[0055] (2) Move the above 8 test tubes (4 portions for each standard solution) to a -18°C ethanol liquid cooling bath and maintain the temperature until the sample temperature reaches -12.2°C. Record the total cooling time from room temperature to -12.2°C. After the cooling is completed, take 1 portion of each N115B and N27B and test the Brookfield viscosity on a Brookfield viscometer.

[0056] (3) Take the other 6 cooled test tubes from step (2) and move them to an ethanol liquid cooling bath maintained at -33°C, and keep the temperature constant until the sample temperature reaches -17.8°C. The total cooling time from room temperature to -17.8°C is recorded. Take one portion of N115B and one portion of N27B respectively to perform Brookfield viscosity tests on a Brookfield viscometer.

[0057] (4) The other four test tubes cooled in step (3) are further cooled until the sample temperature reaches -23.3°C, and the total cooling time from room temperature to -23.3°C is recorded. One portion of N115B and one portion of N27B are respectively taken for Brookfield viscosity test.

[0058] (5) Take the other two cooled test tubes from step (3) and move them to a -51°C ethanol liquid cooling bath until the sample temperature reaches -34.4°C. Record the total cooling time from room temperature to -34.4°C. Take one portion of each of N115B and N27B for the Brookfield viscosity test.

[0059] (6) The two test tubes in step (5) are further cooled and kept constant until the sample temperature reaches -40°C. The total cooling time from room temperature to -40°C is recorded. One portion of N115B and one portion of N27B are respectively taken for Brookfield viscosity test.

[0060] The cooling time at different temperatures in this experimental example is shown in Table 1. It can be seen from Table 1 that the gradient cooling can quickly reach the temperature required for the test. The time in the table is the total time required to reduce to a specific temperature.

[0061] Table 1 Total cooling time at different temperatures

[0062]

[0063]

[0064] An air bath cooling method was used for the control experiment.

[0065] (1) Select the Kaineng standard solutions N115B and N27B with different viscosities, take another clean sample, shake the sample, and pour the sample into the test tube to the mark. It should be noted that in other embodiments, the liquid sample with higher viscosity in the test tube needs to be preheated to 30°C to 50°C and kept at a constant temperature for 30min±5min. After the preheating is completed, the sample is cooled to room temperature (25°C±5°C).

[0066] Place the sample in an air cooling bath and cool it for 15.5 hours. At the same time, adjust the temperature of the thermostatic liquid bath to the test temperature (the test temperatures of N115B standard substances are -12.2°C, -17.8°C, -23.3°C, and -28.9°C; the test temperatures of N27B standard substances are -28.9°C, -34.4°C, and -40°C), and keep the thermostatic liquid bath at the test temperature for at least 2 hours. Use a cooled test tube holder to quickly transfer the sample from the air cooling bath to the ethanol liquid cooling bath and continue cooling for 0.5 hours.

[0067] The sample was placed in a Brookfield viscometer for testing. The test results are shown in Tables 2 and 3.

[0068] Table 2 Effect of cooling method on Brookfield viscosity of N115B standard material at different temperatures

[0069]

[0070] Table 3 Effect of cooling method on Brookfield viscosity of N27B standard material at different temperatures

[0071]

[0072] From the data in Table 2 and Table 3, it can be seen that for different standard substances at different test temperatures, the difference in test results between gradient cooling and air bath cooling is not significant. That is, from the above test results, it can be seen that the present invention can use gradient cooling to cool the sample with high accuracy.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made 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 measuring low temperature viscosity, characterized in that: It includes: The lubricating oil is cooled before the viscosity of the lubricating oil is measured, and the cooling includes: gradually cooling the lubricating oil to reach the test temperature of the lubricating oil, and then placing the lubricating oil after program cooling on a Brookfield viscometer for testing; if the test temperature of the lubricating oil is ≥-12°C, placing the container containing the lubricating oil in a constant temperature ethanol liquid cooling bath at -12°C to -26°C until the temperature of the lubricating oil reaches the test temperature; If the test temperature of the lubricating oil is -12℃~-26℃, first place the container containing the lubricating oil in a constant temperature ethanol liquid cooling bath at -12℃~-26℃ until the temperature of the lubricating oil is -12℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath at -27℃~-51℃ until the temperature of the lubricating oil reaches the test temperature; If the test temperature of the lubricating oil is -27℃~-40℃, first place the container containing the lubricating oil in a constant temperature ethanol liquid cooling bath at -12℃~-26℃ until the temperature of the lubricating oil is -12℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath at -27℃~-51℃ until the temperature of the lubricating oil is -26℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath at -41℃~-60℃ until the temperature of the lubricating oil reaches the test temperature; If the test temperature of the lubricating oil is -41℃~-60℃, first place the container containing the lubricating oil in a constant temperature ethanol liquid cooling bath of -12℃~-26℃, until the temperature of the lubricating oil is -12℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath of -27℃~-51℃, until the temperature of the lubricating oil is -26℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath of -41℃~-60℃, until the temperature of the lubricating oil is -40℃±5℃; then transfer the container containing the lubricating oil to a constant temperature ethanol liquid cooling bath of -61℃~-90℃, until the temperature of the lubricating oil reaches the test temperature.

2. The method for measuring low temperature viscosity according to claim 1, characterized in that: If the test temperature of the lubricating oil is ≥ -12°C, place the container containing the lubricating oil in a constant temperature ethanol liquid cooling bath at -18°C until the temperature of the lubricating oil reaches the test temperature.

3. The method for measuring low temperature viscosity according to any one of claims 1 to 2, characterized in that: Before the programmed cooling is performed, the sample to be tested is preheated and then cooled to room temperature for gradient cooling.

4. The method for measuring low temperature viscosity according to claim 3, characterized in that: The temperature of the sample after preheating is 30-50°C.

5. The method for measuring low temperature viscosity according to claim 4, characterized in that: The preheating is constant temperature preheating, and the constant temperature preheating time is 30min±5min.

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