Method for evaluating service life of rubber sealing material and application

Abstract

The invention discloses a method for evaluating the service life of a rubber sealing material and application of the method, and the method comprises the following steps: obtaining the aging time t at a compression set critical value through a compression set rate-aging time curve of the rubber sealing material, and then evaluating the service life of the rubber sealing material through a fitting straight line of the aging time t and thermodynamic temperature. The evaluation method adopted by the invention is simple, the adopted compression set performance is matched with the actual use environment and use condition of the product and is closer to the real service life of the rubber sealing material, and the method adopts multiple groups of samples in the same batch to carry out tests for different times, and adopts a slow heating and cooling method, so that the test efficiency is greatly improved. The actual working environment of the product can be truly simulated, the data accuracy is ensured, and the problem that the test is stopped due to the damage of the sample can be avoided. Detection equipment is simple, personnel operation is convenient, and a reliable basis is provided for safe use of the rubber sealing material.

Description

Technical Field

[0001] The present invention belongs to the technical field of rubber material testing, and particularly relates to a method for evaluating the life of a rubber sealing material and its application. Background Art

[0002] As an important sealing material, rubber is widely used in various fields such as nuclear power, construction, automotive industry, and medical and health. The sealing performance of rubber mainly lies in its high elasticity. However, in the actual application process, rubber will undergo stress relaxation due to long-term pressure, and material aging will occur during long-term operation at high temperature and in a medium. These performance changes will affect the normal use of rubber products. The research on the aging of rubber materials mainly includes natural aging and artificial accelerated aging. Natural aging is the best method for evaluating material failure. However, due to the difficulty in controlling environmental test conditions and the long test cycle, the application of this method is relatively difficult. Therefore, accelerated aging tests have become a research trend. Moreover, with the continuous improvement of the national requirements for project quality, emphasizing the full life cycle of products, project responsibility systems, etc., engineering materials no longer meet the re-inspection requirements for individual key indicators of products. In the application of engineering rubber sealing materials, the service life of products has become an important consideration factor. However, with the update of product standards, specific requirements have been put forward for the theoretical service life of materials, etc., but there is no specific and relatively perfect method for evaluating the accelerated aging life of materials.

[0003] The existing life evaluation methods are to conduct tests on the same specimen with different numbers of test times. Since it may be necessary to test ten times or more at the same temperature to reach the critical value, if the test is damaged due to improper operation by the test personnel during the process or there are defects in the specimen itself and other factors, it may lead to the termination of the test before reaching the critical value. Replacing the specimen will greatly increase the test time; on the other hand, repeatedly testing with the same specimen cannot fully match the actual use environment. Summary of the Invention

[0004] The present invention proposes a method for evaluating the life of a rubber sealing material based on accelerated aging tests. The evaluation method provided by the present invention is closer to the actual use environment of rubber materials. The finally evaluated material life is 104 years, which is very close to the estimated life of 100 years judged by the enterprise according to the product formula design, the saturation of rubber, and the molecular structure of the material.

[0005] One of the purposes of the present invention is to provide a method for evaluating the life of a rubber sealing material, including: obtaining the aging time t at the critical value of the compression set rate through the compression set rate - aging time curve of the rubber sealing material, and then evaluating the life of the rubber sealing material through the fitting straight line of the aging time t and the thermodynamic temperature. The relational expression of the fitting straight line is as shown in formula (1):

[0006] lnt = E / RT + B, Equation (1)

[0007] In Equation (1), t is the aging time corresponding to when the compression set of the rubber sealing material reaches the critical value; E is the activation energy, with the unit of J / mol; R is the gas constant, with a value of 8.314 J / (mol·K); T is the thermodynamic temperature, with the unit of K; B is the constant term, which is the intercept of the fitted line.

[0008] Among them, the compression set - aging time curve of the rubber sealing material is obtained by fitting the compression set measured after aging treatment of the rubber sealing material with slow heating and cooling at a certain rate respectively.

[0009] According to the present invention, the evaluation method specifically includes the following steps:

[0010] (1) Make the rubber sealing material to be tested into cylindrical specimens, and place multiple groups of specimens in a compression device for compression respectively;

[0011] (2) Place the compression devices with the compressed specimens in step (1) in an aging oven respectively, and gradually heat up to different temperatures for aging treatment for different times;

[0012] (3) Take out the compression devices in sequence according to the aging time order, put the compression devices into an aging oven with gradually decreasing temperature, keep them at room temperature (23 ± 5°C) after cooling, then take out the specimens from the compression devices and let them stand still, and test the compression set of the specimens at room temperature;

[0013] (4) Make a curve with the compression set of the specimens measured at the same temperature and the aging time, and obtain the aging time t corresponding to when the compression set of the specimens reaches the critical value at the corresponding temperature from this curve;

[0014] (5) Make a graph with the logarithm lnt of the aging time t and the reciprocal of the corresponding thermodynamic temperature and obtain the fitted line of Equation (1), and evaluate the life of the rubber sealing material at a certain temperature through this fitted line.

[0015] According to the present invention, the rubber sealing material contains rubber and additives. Preferably, the rubber is selected from at least one of ethylene - propylene - diene monomer rubber, nitrile rubber, chloroprene rubber, and butyl rubber.

[0016] According to the present invention, the preparation of the cylindrical specimen in step (1) can be completed using common sample preparation equipment. For example, a cylindrical specimen can be obtained by vulcanization in a flat vulcanizer, and the obtained cylindrical specimen is placed on a compression device and compressed with a certain compression ratio. The compression device can be a common compression device. Among them, the compression ratio used for compression is set according to the compression material. According to a preferred embodiment of the present invention, the compression ratio used for compression is 10-25%. Preferably, for rubber sealing materials with a hardness (Shore A hardness) lower than 80, a compression ratio of 25% is selected; for rubber sealing materials with a hardness (Shore A hardness) between 80 and 89, a compression ratio of 15% is selected; and for rubber sealing materials with a hardness (Shore A hardness) greater than or equal to 90, a compression ratio of 10% is selected.

[0017] According to the present invention, the aging treatment in step (2) of the evaluation method for the rubber sealing material can be realized using common aging equipment, such as an aging oven. There are no specific limitations on the aging temperature and aging time used for the aging treatment, and two or more different aging temperatures and aging times can be set according to actual needs. The number of samples for the aging treatment can also be set according to actual needs, and at least two samples are set at different aging temperatures.

[0018] According to a preferred embodiment of the present invention, in step (2):

[0019] The aging treatment uses at least 4 different temperatures, preferably 4-6 different temperatures;

[0020] The temperature for the aging treatment is 50-180°C, for example, it can be any temperature among 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180°C or the temperature between any two of the above numerical ranges; preferably, the temperature for the aging treatment is 60-160°C;

[0021] The heating rate for the temperature increase is 0.5-2.5°C / min. Preferably, when the aging temperature does not exceed 80°C, the heating rate is 0.5-1.2°C / min, and / or when the aging temperature is higher than 80°C, the heating rate is 1.8-2.5°C / min.

[0022] According to a preferred embodiment of the present invention, in step (2):

[0023] The aging treatment uses at least 4 different times, preferably 6-12 different times; more preferably, the longest time for the aging treatment enables the horizontal equivalent stiffness of the sample to reach or exceed the critical value;

[0024] The aging treatment time is 24 to 5000 h, for example, it can be any time among 24, 48, 72, 100, 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000 h or the time between any two of the above numerical ranges; preferably, the aging treatment time is 24 to 3000 h.

[0025] According to a preferred embodiment of the present invention, in the step (2): at least 4 groups of compressed samples are set at different temperatures, preferably 4 to 15 groups.

[0026] According to the present invention, the cooling rate in the step (3) is 0.5 to 2.5 °C / min. Preferably, when the aging temperature does not exceed 80 °C, the cooling rate is 0.5 to 1.2 °C / min, and when the aging temperature is higher than 80 °C, the cooling rate is 1.8 to 2.5 °C / min.

[0027] According to the present invention, the critical value in the step (4) is the compression set rate of the specimen before and after aging; preferably, the critical value is 20 to 60%.

[0028] The second object of the present invention is to provide a method for evaluating the life of the above rubber sealing material, which is used to evaluate the service life of the rubber sealing material.

[0029] The accelerated aging test of rubber simulates the use environment of rubber materials, quickly obtains data on material failure at high temperature, and obtains the best fitting straight line between the rubber failure time and the aging temperature based on the Arrhenius equation, so as to evaluate the estimated life of the rubber material at the use temperature. The compression set performance of engineering rubber sealing materials is an important performance index during their use, which is consistent with the actual use environment of the product, and the change of its performance directly affects the service life of the product.

[0030] The evaluation method derived by the present invention is simple. The compression set performance adopted is consistent with the actual use environment and actual situation of the product, closer to the true life of the rubber sealing material. Moreover, this method uses multiple groups of specimens of the same batch for different numbers of tests, and at the same time adopts the method of slow temperature rise and fall, which can not only truly simulate the actual working environment of the product, ensure the accuracy of the data, but also avoid the problem of the test being stopped due to specimen damage. The detection equipment is simple and the operation by personnel is convenient, providing a reliable basis for the safe use of rubber sealing materials. Description of the Drawings

[0031] Figure 1 It is the curve of the change of compression set with aging time measured according to Example 1.

[0032] Figure 2It is the linear fitting straight line of lnt and the inverse of temperature made according to Example 1.

[0033] Figure 3 This is the curve of the change of compression permanent deformation versus aging time measured in Example 2.

[0034] Figure 4 It is the linear fitting straight line of lnt and the inverse of temperature made according to Example 2.

[0035] Figure 5 This is the curve of the change of compression permanent deformation versus aging time measured in Example 3.

[0036] Figure 6 It is the linear fitting straight line of lnt and the inverse of temperature made according to Example 3. DETAILED DESCRIPTION

[0037] The present invention provides a method for evaluating the life of a rubber sealing material, which includes obtaining the aging time t at the critical value of the compression permanent deformation rate through the compression permanent deformation rate-aging time curve of the rubber sealing material, and then evaluating the life of the rubber sealing material through the fitting straight line between the aging time t and the thermodynamic temperature. The method specifically includes the following steps:

[0038] (1) Place the rubber sealing material to be tested in a flat vulcanizer and vulcanize it at high temperature into a B-type cylindrical specimen;

[0039] (2) compress multiple groups of specimens at appropriate compression ratios according to the hardness of the specimens and conduct accelerated aging tests at at least four selected temperatures;

[0040] (3) In the accelerated aging test, multiple groups of samples are placed at each temperature. When placing the samples, adjust the program settings of the aging chamber. The aging chamber with a temperature of 80°C or below is heated at a rate of 0.5 to 1.2°C / min. The aging chamber with a temperature of more than 80°C is heated at a rate of 1.8 to 2.5°C / min. The timing starts when the temperature reaches the specified temperature.

[0041] (4) Take out a group of compression devices at regular intervals and place them in a slowly cooling aging box. The aging box with a temperature above 80°C is cooled at a rate of 1.8 to 2.5°C / min, and the aging box with a temperature of 80°C or below is cooled at a rate of 0.5 to 1.2°C / min. After cooling to room temperature, keep the temperature. Then take out the sample from the device and let it stand. After standing for 30 minutes at standard laboratory temperature, perform compression permanent deformation test.

[0042] (5) The compression permanent deformation data of different temperatures and different test cycles were summarized and analyzed, and the compression permanent deformation and aging time curves were drawn using Origin software, and the time when the critical value was reached at different temperatures was obtained: lnt1, lnt2, lnt3, lnt4...lnt n ;

[0043] (6) According to the Arrhenius equation \(K(T)=A\cdot e\) -E / RT , plot the logarithm of the time \(lnt\) to reach the critical value at different aging temperatures against the reciprocal of the corresponding thermodynamic temperature . By plotting each point and then using Origin software to obtain the best-fit straight line \(lnt = E / RT + B\) (where \(t\) is the aging time corresponding to when the compression set of the rubber sealing material reaches the critical value; \(E\) is the activation energy, with the unit of J / mol; \(R\) is the gas constant, with a value of 8.314 J / (mol·K); \(T\) is the thermodynamic temperature, with the unit of K; \(B\) is the constant term), evaluate the estimated life of the rubber sealing material at the service temperature.

[0044] The evaluation method adopted in the present invention is simple. The compression set performance adopted is consistent with the actual service environment and usage of the product, and is closer to the true life of the rubber sealing material.

[0045] The following specifically describes the present invention in combination with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0046] The test instruments and test conditions adopted in the embodiments are as follows:

[0047] The accelerated aging test is carried out in accordance with the provisions of GB / T 3512-2014.

[0048] The compression set test is carried out in accordance with GB / T 7759.1-2015 "Vulcanized rubber or thermoplastic rubber - Determination of compression set - Part 1: At normal and high temperatures".

[0049] The hardness test is carried out in accordance with GB / T531.1-2008 "Vulcanized rubber or thermoplastic rubber - Methods for the determination of indentation hardness - Part 1: Durometer method (Shore hardness)".

[0050] Example 1:

[0051] (1) Put the commercially available ethylene propylene diene monomer (EPDM) rubber sealing material into a flat vulcanizer for high-temperature vulcanization into a B-type cylindrical specimen; place the specimens in a compression device for compression respectively. The hardness of the specimens (Shore A hardness) is 63, and the specimen compression ratio is set to 25%;

[0052] (2) Place the compression device in aging boxes at 70°C, 80°C, 90°C, and 100°C respectively. Adjust the program settings of the aging boxes when placing them. The aging boxes at 70°C and 80°C are heated at a rate of 1°C / min, and the aging boxes at 90°C and 100°C are heated at a rate of 2°C / min. When the temperature reaches the specified temperature, start timing to conduct accelerated aging tests on 12 groups of samples;

[0053] (3) In the accelerated aging test, the samples were aged for 24 h, 72 h, 168 h, 312 h, 528 h, 648 h, 816 h, 960 h, 1296 h, 1824 h, and 2496 h, respectively, and then the compression device was taken out and placed in a slowly cooling aging box. The aging boxes at 90 ° C and 100 ° C were cooled at a rate of 2 ° C / min, and the aging boxes at 70 ° C and 80 ° C were cooled at a rate of 1 ° C / min. After cooling to room temperature, they were kept warm for 1 hour, and then the samples were taken out of the device and allowed to stand. After standing for 30 minutes at standard laboratory temperature, the compression permanent deformation test was carried out (the test results are shown in Table 1);

[0054] Table 1 Aging test data at different temperatures and different aging times in Example 1

[0055]

[0056] (4) The compression permanent deformation data of different temperatures and different test cycles were summarized and analyzed, and the curves of compression permanent deformation and aging time lnt were drawn using Origin software (such as Figure 1 ), and the time for the sample to reach 50% of the critical value at 70℃, 80℃, 90℃, and 100℃ were 2540h, 898h, 347h, and 154h, respectively.

[0057] (5) The logarithm of the time to reach the critical value at different aging temperatures, lnt, and the reciprocal of the corresponding thermodynamic temperature Plot each point and then use Origin software to find the best fitting line y = 1.1905x-26.895 (where y represents lnt, x represents T is the thermodynamic temperature), and the estimated life of the rubber material at room temperature is 68 years. In actual use, the service life of the rubber sealing material can be further evaluated in combination with environmental factors, and it needs to be divided by a safety factor of 2 (Li Yusong et al. Test on the aging resistance of polymer water-stopping materials (I) [J]. Aging and Application of Synthetic Materials, 2000, (04): 19-26.), so the estimated life is 34 years.

[0058] Embodiment 2:

[0059] (1) Place the commercially available ethylene propylene diene monomer (EPDM) rubber sealing material in a flat vulcanizer and cure it at high temperature into a B-shaped cylindrical specimen; place the specimens in a compression device respectively for compression. The hardness of the specimens (Shore A hardness) is 64, and the compression ratio of the specimens is set at 25%;

[0060] (2) Place the compression devices into aging ovens at 80°C, 90°C, 100°C, and 110°C respectively. When placing, adjust the program settings of the aging ovens. The aging oven at 80°C heats up at a rate of 1°C / min, and the aging ovens at 90°C, 100°C, and 110°C heat up at a rate of 2°C / min. After heating up to the specified temperature, start timing and conduct an accelerated aging test on 12 groups of specimens;

[0061] (3) In the accelerated aging test, after the specimens are aged for 24h, 48h, 72h, 168h, 312h, 528h, 816h, 1296h, 1824h, 2496h, and 2832h respectively, take out the compression devices and place them in an aging oven with slow cooling. The aging ovens at 90°C, 100°C, and 110°C cool down at a rate of 2°C / min, and the aging oven at 80°C cools down at a rate of 1°C / min. After cooling down to room temperature, keep it warm for 1h, then take out the specimens from the device and let them stand still. After standing for 30min at standard laboratory temperature, conduct a compression set test (the test results are shown in Table 2);

[0062] Table 2 Aging test data at different temperatures and different aging times in Example 2

[0063]

[0064] (4) Summarize and analyze the compression set data at different temperatures and different test cycles, and use Origin software to plot the curves of compression set versus aging time lnt (such as Figure 1 ), and obtain that the times for the specimens to reach the critical value of 50% at 80°C, 90°C, 100°C, and 110°C are 2515h, 992h, 441h, and 206h respectively;

[0065] (5) Plot the logarithm lnt of the time to reach the critical value at different aging temperatures against the reciprocal of the corresponding thermodynamic temperature , and by plotting each point and then using Origin software to obtain the best fitting straight line y = 1.1293x - 24.164 (where y represents lnt and x represents T is the thermodynamic temperature), evaluate the estimated life of the rubber material at room temperature to be 133.05 years. In the actual use process, the service life of the rubber sealing material can be further evaluated by combining environmental impact factors. It is necessary to divide by a safety factor of 2, so the estimated life is 67 years.

[0066] Example 3:

[0067] (1) placing commercially available EPDM rubber sealing materials in a flat vulcanizer and vulcanizing them at high temperature into B-type cylindrical specimens; placing the specimens in compression devices for compression, the specimen hardness (Shore A hardness) is 62, and the specimen compression rate is set to 25%;

[0068] (2) The compression device was placed in aging boxes at 90°C, 100°C, 110°C, and 120°C respectively. The program settings of the aging boxes were adjusted when the compression device was placed in the aging boxes. The temperature of each aging box was increased at a rate of 2°C / min. When the temperature reached the specified temperature, the timing was started to conduct accelerated aging tests on 12 groups of samples.

[0069] (3) In the accelerated aging test, the samples were aged for 24 h, 48 h, 72 h, 168 h, 336 h, 408 h, 648 h, 984 h, 1320 h, 1512 h, and 1848 h, respectively. The compression device was taken out and placed in a slowly cooling aging box. Each aging box was cooled at a rate of 2 °C / min. After reaching room temperature, it was kept warm for 1 h. The samples were then taken out of the device and allowed to stand for 30 min at standard laboratory temperature before the compression permanent deformation test was performed (the test results are shown in Table 3);

[0070] (4) The compression permanent deformation data of different temperatures and different test cycles were summarized and analyzed, and the curves of compression permanent deformation and aging time lnt were drawn using Origin software (such as Figure 1 ), and the time for the sample to reach 50% of the critical value at 90°C, 100°C, 110°C, and 120°C was 1737h, 742h, 351h, and 167h, respectively;

[0071] (5) The logarithm of the time to reach the critical value at different aging temperatures, lnt, and the reciprocal of the corresponding thermodynamic temperature Plot each point and then use Origin software to find the best fitting straight line y = 1.1181x-23.337 (where y represents lnt, x represents T is the thermodynamic temperature), and the estimated life of the rubber material at room temperature is 208 years. In actual use, the service life of the rubber sealing material can be further evaluated in combination with environmental factors. It needs to be divided by a safety factor of 2, so the estimated life is 104 years.

[0072] Table 3 Aging test data at different temperatures and different aging times in Example 3

[0073]

Claims

1. A method for evaluating the life of a rubber sealing material, comprising: The step of obtaining the aging time t at the critical value of the compression permanent deformation rate through the compression permanent deformation rate-aging time curve of the rubber sealing material, and then evaluating the life of the rubber sealing material through the fitting straight line of the aging time t and the thermodynamic temperature, wherein the relationship of the fitting straight line is as shown in formula (1): lnt=E / RT+B Formula (1) In formula (1), t is the aging time corresponding to when the compression permanent deformation of the rubber sealing material reaches the critical value; E is the activation energy, the unit is J / mol; R is the gas constant, the value is 8.314 J / (mol·K); T is the thermodynamic temperature, the unit is K; B is the constant term.

2. The evaluation method according to claim 1, characterized in that: The evaluation method specifically comprises the following steps: (1) The rubber sealing material to be tested is made into cylindrical specimens, and multiple groups of specimens are placed in a compression device for compression; (2) placing the compression devices with the compression samples in step (1) in aging boxes respectively, gradually heating them to different temperatures and performing aging treatments for different times; (3) Take out the compression devices in the order of aging time, put them into an aging box with gradually decreasing temperature, keep them warm after they reach room temperature, then take out the samples from the compression devices and let them stand, and test the compression permanent deformation rate of the samples at room temperature; (4) A curve is prepared by measuring the compression permanent deformation rate and aging time of the sample at the same temperature, and the aging time t corresponding to the critical value of the compression permanent deformation rate of the sample at the corresponding temperature is obtained from the curve; (5) The logarithm of the aging time t, lnt, and the reciprocal of the corresponding thermodynamic temperature A graph is drawn and a fitting straight line of formula (1) is obtained, and the life of the rubber sealing material at a certain temperature is evaluated by the fitting straight line.

3. The evaluation method according to claim 1 or 2, characterized in that: The rubber sealing material comprises rubber and additives. Preferably, the rubber is selected from at least one of EPDM rubber, nitrile rubber, chloroprene rubber and butyl rubber.

4. The evaluation method according to claim 2, characterized in that: In the step (1): The compression rate used in the compression is 10-25%. Preferably, the compression rate of rubber sealing materials with a hardness lower than 80 is 25%, the compression rate of rubber sealing materials with a hardness of 80-89 is 15%, and the compression rate of rubber sealing materials with a hardness greater than or equal to 90 is 10%.

5. The evaluation method according to claim 2, characterized in that: In the step (2): The aging treatment uses at least 4 different temperatures, preferably 4 to 6 different temperatures; and / or, The temperature of the aging treatment is 50 to 180° C., preferably 60 to 160° C.; and / or, The heating rate of the heating is 0.5-2.5°C / min. Preferably, when the aging temperature does not exceed 80°C, the heating rate is 0.5-1.2°C / min, and / or when the aging temperature is higher than 80°C, the heating rate is 1.8-2.5°C / min.

6. The evaluation method according to claim 2, characterized in that: In the step (2): The aging treatment is performed for at least 4 different times, preferably 6 to 12 different times; and / or, The aging treatment time is 24 to 5000 hours, preferably 24 to 3000 hours.

7. The evaluation method according to claim 2, characterized in that: In the step (2), at least 4 groups of support samples are set at different temperatures, preferably 4 to 15 groups.

8. The evaluation method according to claim 2, characterized in that: The cooling rate in step (3) is 0.5-2.5°C / min. Preferably, when the aging temperature does not exceed 80°C, the cooling rate is 0.5-1.2°C / min, and / or when the aging temperature is higher than 80°C, the cooling rate is 1.8-2.5°C / min.

9. The evaluation method according to claim 2, characterized in that: The critical value in step (4) is the compression permanent deformation rate of the sample before and after aging; preferably, the critical value is 20-60%.

10. A method for evaluating the service life of a rubber sealing material according to any one of claims 1 to 9, used for evaluating the service life of a rubber sealing material.

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