A method for measuring the tensile properties of high hardness vulcanized rubber

Abstract

The application discloses a high-hardness vulcanized rubber tensile property determination method and belongs to the technical field of analysis. For the rubber with the hardness after vulcanization exceeding 70 Shore A hardness or 70 international hardness value, the size of the test sample is adjusted according to the hardness of the rubber after vulcanization, including the width, length and thickness of the sample, the sample is cut into a strip-shaped sample with the width of 8mm, 10mm or 12mm, the thickness of 2mm and the length of 200mm, so that the tensile strength, elongation at break and 300% modulus of the sample can truly represent the physical properties of the rubber, and the problem that the rubber with a large hardness value cannot truly represent the physical properties (strength, elongation and modulus) of the rubber due to the too small tensile strength and too fast breaking is solved.

Description

Technical Field

[0001] This invention belongs to the field of analytical technology, specifically relating to a method for determining the tensile properties of high-hardness vulcanized rubber. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The tensile properties of vulcanized rubber are among the most important aspects of rubber mechanical property testing and are also one of the effective methods for assessing the vulcanization performance of rubber products. Currently, the tensile properties of vulcanized rubber are mainly tested according to GB / T 528-2009, using dumbbell or ring specimens as specified in the standard to determine tensile strength, elongation at break, and 300% elongation at a given point. However, in actual production, some vulcanized rubbers with high hardness, such as rubbers with a hardness exceeding 70 Shore A or 70 international hardness after vulcanization, are encountered. When using dumbbell or ring specimens as specified in the standard for tensile testing, the vulcanized rubber is too hard to prepare samples, and its tensile strength is too low, resulting in rapid fracture. Consequently, the test results for tensile strength, elongation at break, and 300% elongation at a given point cannot accurately characterize the physical properties (strength, elongation, and 300% elongation at a given point). Therefore, there is an urgent need for a method that can accurately test the tensile properties of high-hardness vulcanized rubber. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for determining the tensile properties of high-hardness vulcanized rubber. This invention uses strip-shaped samples to determine the tensile stress-strain properties of vulcanized rubber with high hardness, which is very simple, fast, and has high reproducibility, thus improving the accuracy of the test.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for determining the tensile properties of high-hardness vulcanized rubber, comprising the following steps:

[0007] (1) Prepare the compound rubber according to the test rubber design formula and vulcanize it to obtain vulcanized test pieces;

[0008] (2) Based on the different hardness of the vulcanized rubber compound, the vulcanized test piece is cut into strip samples of different widths using a cutting knife; wherein the correspondence between the international hardness and the width of the strip sample is as follows: international hardness IRHD is 70 and above, the width of the strip sample is 8mm-12mm, the thickness of the strip sample is 2mm±0.2mm, and the length of the strip sample is ≥200mm.

[0009] (3) Fix the strip specimen into the fixture of the tensile testing machine. After clamping and fixing the specimen, start the test and record the tensile strength, tensile elongation and constant elongation stress data.

[0010] In some embodiments of the present invention, in order to further improve the accuracy of the tensile property test of high-hardness vulcanized rubber, the correspondence between international hardness and the width of the strip specimen is shown in the table below.

[0011] 70-80 8mm±0.1mm 80-85 10mm±0.1mm 85 and above 12mm±0.1mm

[0012] In some embodiments of the present invention, the minimum storage time for vulcanized samples is 16 hours, and the maximum should not exceed 4 weeks. Meanwhile, comparative evaluation tests should be conducted within the same time intervals whenever possible.

[0013] In some embodiments of the present invention, the storage is a light-protected storage, and the vulcanized test pieces are conditioned at standard temperature (without humidity control) for at least 3 hours before being cut into samples, according to GB / T2941. During storage, heat insulation can also be provided to protect the samples as completely as possible from external influences that could damage them during the time interval between vulcanization and testing.

[0014] In some embodiments of the present invention, strip-shaped samples are cut parallel to the calendering direction of the vulcanized rubber.

[0015] In some embodiments of the present invention, when a tensile testing machine is used for testing, the test conditions are: tensile speed 50mm / min-300mm / min, initial clamp distance 25mm-100mm, preload 0.5-1N, and tensile speed 20-50mm / min under preload.

[0016] In some embodiments of the present invention, at least five specimens are prepared for each test, and tensile strength, tensile elongation, and stress at a given elongation are recorded. The final result is the average value of the five specimens.

[0017] In some embodiments of the present invention, if the sample breaks at the original clamping point, the test result is discarded and another sample is taken for repeated testing.

[0018] In some embodiments of the present invention, the tensile strength T is calculated according to the formula and expressed in MPa:

[0019]

[0020] F m : The maximum force recorded, in Newtons (N);

[0021] W: Width of the sample, in millimeters (mm);

[0022] t: Thickness of the test length portion, in millimeters (mm).

[0023] In some embodiments of the present invention, the elongation at break E b Calculate using the following formula, expressed as a percentage:

[0024]

[0025] L0: Initial test length, in millimeters (mm);

[0026] L b : The test length at which the fracture occurred, in millimeters (mm).

[0027] In some embodiments of the present invention, the constant tensile stress Se is calculated according to the following formula, expressed in MPa:

[0028]

[0029] F e : The force recorded at a given stress, in Newtons (mm);

[0030] W: Width of the sample, in millimeters (mm);

[0031] t: Thickness of the test length portion, in millimeters (mm).

[0032] The beneficial effects of this invention are as follows:

[0033] This invention discloses a method for determining the tensile properties of high-hardness vulcanized rubber. Depending on the hardness of the vulcanized rubber compound, samples of different widths are cut using a cutting tool. The widths can be 8mm ± 0.1mm, 10mm ± 0.1mm, or 12mm ± 0.1mm, with a thickness of 2mm ± 0.2mm and a length of approximately 200mm (100mm for testing). At least five samples are prepared. A tensile testing machine is then used to perform tensile tests at an appropriate speed. This invention solves the problem that when using dumbbell or ring samples (as per GB / T 528-2009) for tensile testing of high-hardness rubber compounds, the tensile strength, elongation at break, and 300% elongation results are insufficient to accurately represent the physical properties (strength, elongation, and 300% elongation) due to insufficient tensile strength and rapid fracture. This invention proposes a strip-based tensile testing method to determine the tensile stress-strain properties of high-hardness vulcanized rubber. The method is simple and quick, and the sample width can be adjusted according to the hardness, expanding the applicability of tensile strength, elongation at break, and 300% elongation. Furthermore, the method of this invention is simple and easy to implement, with high reproducibility, improving the accuracy of testing and effectively solving the problem that GB / T 528-2009 cannot accurately reflect the tensile properties of rubber compounds with high hardness. In actual production, the formula, mixing process, and vulcanization process can be adjusted based on the tensile property test results to ensure the stability of rubber quality. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 This is a diagram showing the shape of the strip-shaped sample of the present invention;

[0036] Figure 2 The tensile stress-strain curve of the strip-shaped specimen in Embodiment 2 of the present invention;

[0037] Figure 3 The tensile stress-strain curve is shown for the type 1 dumbbell-shaped specimen of Comparative Example 1 of this invention. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] Example 1

[0040] (1) Sample:

[0041] The optimal vulcanization conditions (time, temperature, and pressure) for the rubber compound should be selected based on its rheological properties. The minimum storage time for vulcanized samples is 16 hours, and the maximum should not exceed 4 weeks. During this storage period, the samples should be stored away from light, and before cutting them, they should be conditioned at the standard temperature for at least 3 hours according to GB / T 2941.

[0042] Based on the different hardness of the vulcanized rubber compound, and according to the corresponding relationship in Table 1, cut samples of different widths with a cutter. The widths can be 8mm±0.1mm, 10mm±0.1mm, and 12mm±0.1mm, respectively; the thickness is 2mm±0.2mm; and the length is approximately 200mm (of which 100mm is used for testing). Before stretching, the sample length at both ends of the clamp should be 100mm. At least five samples should be cut, and the strip samples should be cut parallel to the calendering direction of the vulcanized rubber.

[0043] Table 1. Correspondence between international hardness and specimen width

[0044] 70-80 8mm±0.1mm 80-85 10mm±0.1mm 85 and above 12mm±0.1mm

[0045] Specimen thickness measurement: Measure the thickness using a thickness gauge at the center and 25mm from both ends of the valid test specimen. Take the median of the three values ​​as the thickness result. The difference between the maximum and minimum values ​​and the median value should not exceed ±0.1mm. Specimen width measurement: Measure the width of the valid test specimen using a digital vernier caliper at the center and 25mm from both ends of the center. Take the median of the three values ​​as the sample width, accurate to 0.05mm.

[0046] (2) Experimental procedure:

[0047] Tensile testing machine software settings: tensile speed 300 mm / min, initial clamp distance 100 mm, preload 0.5-1 N, tensile speed under preload 20-50 mm / min. Adjust clamp distance L = 100 mm ± 0.2 mm, clamp and fix the specimen, start the test, and record tensile strength, tensile elongation, and stress at a given elongation. The final result is the average of 5 specimens. If the specimen breaks outside the initial clamp, discard the test result and repeat the test with another specimen.

[0048] (3) Result expression

[0049] Tensile strength T is calculated according to the formula and expressed in MPa:

[0050]

[0051] F m : The maximum force recorded, in Newtons (N);

[0052] W: Width of the sample, in millimeters (mm);

[0053] t: Thickness of the test length portion, in millimeters (mm).

[0054] Elongation at break E b Calculate using the following formula, expressed as a percentage:

[0055]

[0056] L0: Initial test length, in millimeters (mm);

[0057] L b : The test length at which the fracture occurred, in millimeters (mm).

[0058] Constant tensile stress S e Calculate using the following formula, expressed in MPa:

[0059]

[0060] F e : The force recorded at a given stress, in Newtons (N);

[0061] W: Width of the sample, in millimeters (mm);

[0062] t: Thickness of the test length portion, in millimeters (mm).

[0063] Example 2

[0064] Tensile properties were tested using three vulcanizates, A, B, and C, with different hardness values. The formulations of vulcanizates A, B, and C are shown in Table 2.

[0065] Table 2 Formulations of vulcanizates A, B, and C

[0066] Natural rubber 100 100 100 Carbon black N220 53 60 65 stearic acid 3.5 3.5 3.5 Zinc oxide 2 2 2 Plasticizer A 1 1 1 Plasticizer B 0.3 0.3 0.3 Protective wax 1 1 1 Accelerator NS 1 1 1 sulfur 1.5 1.5 1.5 total 163.3 170.3 175.3

[0067] The hardness of vulcanizate A was tested to be IRHD 70-80. It was cut into strips 8mm wide, 2mm thick, and 200mm long according to the method in Example 1, and tensile tests were performed. The test results are shown in Table 3, and the tensile stress-strain curves are as follows: Figure 2 As shown.

[0068] The hardness of vulcanizate B is IRHD 80-85. It was cut into strips 10mm wide, 2mm thick, and 200mm long according to the method in Example 1, and tensile tests were performed. The test results are shown in Table 3, and the tensile stress-strain curves are as follows: Figure 2 As shown.

[0069] The hardness of vulcanizate C is above the international hardness IRHD 85. It was cut into strips 12mm wide, 2mm thick, and 200mm long according to the method in Example 1, and tensile tests were performed. The test results are shown in Table 3, and the tensile stress-strain curves are as follows: Figure 2 As shown.

[0070] Comparative Example 1

[0071] The three rubber compounds in Example 2 were cut into type 1 dumbbell-shaped specimens according to the method in GB / T 528-2009 and then subjected to tensile tests. The test results are shown in Table 3, and the tensile stress-strain curves are as follows. Figure 3 As shown.

[0072] Table 3. Tensile property test results of high-hardness vulcanized rubber

[0073]

[0074] analyze:

[0075] The stability of the data was assessed by comparing the data range. Table 2 shows that the detection method of this invention has high reproducibility and higher detection accuracy. This is due to two main reasons. First, the unique shapes of dumbbell and ring specimens make them prone to structural damage during preparation, easily resulting in serrations at the edges and inaccurate tensile test results. In contrast, the strip-shaped specimen of this invention is simple to prepare, avoiding structural damage and ensuring accurate tensile test results. Second, the specimen width can be adjusted appropriately according to different hardness levels, ensuring a wider range of applicability.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the tensile properties of high-hardness vulcanized rubber, characterized in that, Includes the following steps: (1) According to the test formula of the test rubber, prepare the compound rubber and vulcanize it to obtain vulcanized test pieces; (2) Based on the different hardness of the vulcanized rubber compound, the vulcanized test piece is cut into strips of different widths using a cutting knife; the correspondence between the international hardness and the width of the strip is as follows: the international hardness IRHD is 70 and above, the width of the strip is 8 mm-12 mm, the thickness of the strip is 2 mm ± 0.2 mm, and the length of the strip is ≥ 200 mm. (3) Fix the strip specimen into the clamp of the tensile testing machine. After clamping and fixing the specimen, start the test and record the tensile strength, tensile elongation and constant elongation stress data. The relationship between international hardness and the width of bar specimens is shown in the table above. When using a tensile testing machine, the test conditions are: tensile speed 50 mm / min - 300 mm / min, initial clamping distance 25 mm - 100 mm, preload 0.5 - 1 N, and tensile speed 20 - 50 mm / min under preload.

2. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, The minimum storage time for vulcanized samples is 16 hours, and the maximum should not exceed 4 weeks.

3. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 2, characterized in that, The storage is to avoid light. Before cutting the vulcanized test pieces into samples, they should be conditioned at the standard temperature for at least 3 hours in accordance with the provisions of GB / T 2941.

4. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, Cut strip-shaped samples parallel to the calendering direction of the vulcanized rubber.

5. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, At least five specimens were prepared for each test, and the tensile strength, tensile elongation, and stress at a given elongation were recorded. The final result was the average of the five specimens.

6. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 5, characterized in that, If the specimen breaks at the original clamping point, the test results are discarded, and another specimen is taken for repeated testing.

7. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, Tensile strength T is calculated according to the formula and expressed in MPa: F m : The maximum force recorded, in Newtons; W: Width of the sample, in millimeters; t: Thickness of the test length portion, in millimeters.

8. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, Elongation at break E b Calculate using the following formula, expressed as a percentage: L0: Initial test length, in millimeters; L b : The test length at fracture, in millimeters.

9. The method for determining the tensile properties of high-hardness vulcanized rubber as described in claim 1, characterized in that, The constant tensile stress Se is calculated using the following formula, expressed in MPa: F e : The force recorded at a given stress, measured in Newtons; W: Width of the sample, in millimeters; t: Thickness of the test length portion, in millimeters.

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