Test method for evaluating tread pattern groove bottom crack resistance of rubber composition

Abstract

The invention discloses a test method for evaluating tread pattern groove bottom crack resistance of a rubber composition, which comprises the following steps of: preparing an annular solid rubber wheel sample with a groove structure on the surface, mounting the annular solid rubber wheel sample on an LAT100 abrasion tester, selecting a glass disc or a 180-mesh electric corundum millstone, setting a rotation speed, a load and a slippage angle, and testing the abrasion of the rubber composition. Anti-fouling powder is put in a contact area of the sample and the abrasion disc, so that the sample is subjected to a groove bottom crack resistance test in a stress state simulating actual working conditions of the tire; after running for different distances, detecting the bottom of the groove under a microscope, and recording the number and length of cracks at the bottom of the sample groove; and evaluating the groove bottom crack resistance of the rubber composition according to the monitored crack data. According to the invention, the stress borne by the tread groove bottom under the actual use condition of a tire is highly simulated, the tread groove bottom crack resistance of the rubber composition is simply and rapidly evaluated under the laboratory condition, and effective technical support can be provided for research and development of the rubber composition and product improvement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rubber material performance test, in particular to a test method for simulating the resistance of rubber composition to pattern groove bottom cracking under actual working conditions of tires. BACKGROUND

[0002] With the rapid construction of highway network, the express delivery, cold chain transportation, sedan transportation and other transportation industries have developed rapidly and become more and more concentrated, which requires the tire to have an ultra-long driving mileage and durability safety in the whole life cycle. In the use process of load radial tire, in addition to common damage phenomena such as shoulder empty, crown empty, bead burst, etc., there is also pattern groove bottom cracking, the crack is generated from the groove bottom and expands, which causes damage to the cord, seriously threatens the driving safety and shortens the service life of the tire.

[0003] There are many reasons for the pattern groove bottom cracking of the tire, such as too thick or too thin of the base rubber of the tread, unreasonable design of the angle of the pattern groove bottom, poor tear resistance and fatigue resistance of the rubber composition at the pattern groove bottom, etc., and the essence of its occurrence is the multiple effects of cyclic compression / shear / tensile strain, hysteresis heat generation and ozone aging in the air on the rubber composition at the groove bottom during the driving of the tire.

[0004] The current laboratory semi-finished rubber composition test method has limitations. GB / T 13934 flex cracking and crack growth test, compression heat generation ASTM D623, GB / T 1688 tensile fatigue test, ozone aging ASTM D1149 only simulate a single factor, and the sample is a dumbbell / bar / cylindrical sample, which cannot reflect the stress concentration effect at the R angle of the real groove bottom. The invention patent CN114578034 A discloses a method for evaluating tire crown groove bottom cracks. The patent predicts the difficulty of groove bottom crack occurrence by testing the rubber composition swelling degree and Tg. The method is simple and fast, but the test is still limited to the rubber composition test itself, and has nothing to do with the actual stress state of the rubber composition at the groove bottom. The invention patent CN116106037 A discloses a test method for verifying the groove bottom crack resistance of a tire. The patent divides the circumferential circle of the tire groove bottom by equal parts and preforms a crack notch. The change in crack length before and after the indoor machine processing is compared to verify the early groove bottom crack caused by the stress release in the tire. The method considers the stress concentration effect of the rubber composition at the groove bottom, but the stress mode of the finished product drum test is single, the torsion effect under the actual turning working condition of the tire is not considered, and the cost is high. The invention patent CN108287080 A discloses a road test evaluation method for tire groove cracking and extension. The patent measures the length and depth of each groove crack of the tire at different use periods under the premise of positioning the groove crack position of the road test tire. The total number of groove cracks of the tire is obtained at a use period, and the groove cracking and extension of the road test tire are observed and compared. However, the test cost of the method is high, and the test period is long.

[0005] Therefore, the present application aims to provide a test method with groove geometric characteristics and high simulation of dynamic compression and shear stress to simulate the actual working condition of the tire, so as to evaluate the performance of the rubber composition in resisting the groove bottom crack of the tire from the semi-finished product. SUMMARY

[0006] In view of the above problems existing in the prior art, the present application provides a test method for evaluating the resistance of rubber composition to tire groove bottom crack, which can simply and quickly evaluate the resistance of rubber composition to tire groove bottom crack under laboratory conditions, and provide effective technical support for the research and development of rubber composition and product improvement.

[0007] The purpose of the present application is achieved in the following manner: a test method for evaluating the resistance of rubber composition to tire groove bottom crack, comprising the following steps, (1) preparing a rubber composition sample, wherein the sample is an annular solid rubber wheel with a groove structure on the surface; (2) The sample is installed on the LAT100 abrasion tester installation shaft, the abrasion disc is selected as a glass disc or a 180-mesh electric corundum disc, the rotation speed of the abrasion disc is 15-30 km / h, a load of 60N-120N is applied to the sample, the sliding angle between the sample and the rotation direction of the abrasion disc is kept at 15°-30°, the anti-fouling powder is put into the contact area between the sample and the abrasion disc, the feeding speed of the anti-fouling powder is 0 (3) After running for different distances, the groove bottom is detected under a microscope, and the number and length of the sample groove bottom cracks are recorded; (4) The resistance to groove bottom cracking performance of the rubber composition is evaluated according to the monitored crack data.

[0008] The inner diameter of the annular solid rubber wheel with a groove structure on the surface is 35 mm±1mm, the outer diameter is 84 mm±1mm, and the thickness is 19 mm±0.5mm; the groove structure is a U-shaped groove, the groove bottom angle is 90°±3°, the groove width is 5 mm±1mm, and the groove depth is 6 mm±1mm.

[0009] The abrasion disc is selected as a glass disc, the rotation speed of the abrasion disc is 20 km / h, a load of 100N is applied to the sample, and the sliding angle between the sample and the rotation direction of the abrasion disc is 20°.

[0010] The anti-fouling powder is a mixture of magnesium oxide and aluminum oxide, the volume ratio is 1:3, and the particle size is 120 mesh.

[0011] The feeding speed of the anti-fouling powder is 80 g / min.

[0012] The running distances are 5 km, 10 km, 15 km, 20 km, 25 km, 30 km, and 35 km in seven stages.

[0013] The groove bottom crack evaluation standard is divided into six levels, (1) Level 0: The groove bottom is intact without cracks; (2) Level 1: The groove bottom crack is a pinprick point, the number is 1, and the length is less than 0.5 mm; (3) Level 2: The groove bottom crack is a pinprick point, the number is 2-3; (4) Level 3: The number of pinprick points of the groove bottom crack exceeds 3, one or more pinprick points expand into obvious cracks, which can be seen to be obviously larger, and the length is greater than 0.5 mm; (5) Level 4: The crack expands from a point to a line, and the length is less than or equal to 5 mm; (6) Level 5: The crack expands from a point to a line, and the length is greater than 5 mm.

[0014] Compared with the prior art, the application simulates the stress on the groove bottom of a tire in actual use by preparing an annular solid rubber wheel sample with a groove structure on the surface, and evaluates the resistance of the rubber composition to groove bottom cracks under laboratory conditions, thereby providing effective technical support for the research and development of rubber compositions and product improvement. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a structural schematic diagram of the annular solid rubber wheel sample with a groove structure on the surface.

[0016] Figure 2 is a physical diagram of the annular solid rubber wheel sample with a groove structure on the surface.

[0017] Figure 3 is a device diagram of the LAT100 abrasion tester.

[0018] Figure 4 is a diagram of the groove bottom cracks of each grade observed under a body microscope.

[0019] Figure 5 is a schematic diagram of a tire loading scheme for a road test vehicle. DETAILED DESCRIPTION

[0020] The application will be further described below in conjunction with the drawings and specific examples. It should be understood that these examples are only used to illustrate the application and are not used to limit the scope of the application, and after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope defined by the application.

[0021] Different tire tread rubber compositions were used as the comparative example, example 1, example 2, example 3 and example 4, respectively, and the specific compositions of the tire tread rubber compositions are shown in Table 1 below.

[0022] Table 1 The comparative example and the examples all used a two-stage mixing process, and the specific process was as follows: The first-stage masterbatch BR was carried out in a Banbury internal mixer, and the mixing process was as follows: rubber was pressurized for 1 min (rotational speed 80 rpm), the weight was lifted, carbon black, white carbon black, active agent, etc. were added, and pressurization was carried out for 1.5 min (rotational speed 80 rpm), the weight was lifted / pressurized for 1 min (rotational speed 80 rpm), and the rubber was discharged; The second-stage vulcanized rubber mixing was carried out on an open mill, and the first-stage mixed rubber was added with oil-extended sulfur, accelerator, etc., and the rubber was kneaded and sheeted.

[0023] The mixed vulcanized rubber was vulcanized in a mold, and the vulcanization conditions were 151℃×30min, pressure 30MPa, to obtain aFigure 1 、 Figure 2 The surface of the annular solid rubber wheel sample provided with the U-shaped groove structure is set as shown in the table. The inner diameter of the annular solid rubber wheel provided with the groove structure is 35 mm, the outer diameter is 84 mm, the thickness is 19.5 mm, the groove structure is a U-shaped groove, the groove bottom angle is 90°, the groove width is 5 mm, and the groove depth is 6 mm. The sample is placed at room temperature for 24 hours.

[0024] As shown in Figure 3 , the annular solid rubber wheel sample provided with the U-shaped groove structure is installed on the LAT100 abrasion tester installation shaft, the abrasion disc is selected as a glass sand disc, the rotation speed of the abrasion disc is set as 20 km / h, 100 N load is applied to the sample, the slip angle a of the sample and the rotation direction of the abrasion disc is set as 20°, the anti-fouling powder feeding speed is set as 80 g / min, and the running distance is set as seven stages of 5 km, 10 km, 15 km, 20 km, 25 km, 30 km and 35 km.

[0025] The sample is tested according to the set test conditions. The sample is tested on both the front and back surfaces at each stage. After each stage is completed, the number and length of the groove bottom cracks are detected and recorded under the body microscope, and the groove bottom crack resistance of the rubber composition is evaluated.

[0026] When evaluating the groove bottom crack resistance of the rubber composition, the groove bottom crack evaluation standard can be used, which is as follows: (1) Grade 0: The groove bottom is intact without cracks; (2) Grade 1: The groove bottom crack is a pinprick with 1 crack and a length of less than 0.5 mm; (3) Grade 2: The groove bottom crack is a pinprick with 2-3 cracks; (4) Grade 3: The number of pinpricks on the groove bottom exceeds 3, and one or more pinpricks expand into obvious cracks, which can be seen to be significantly larger, with a length of greater than 0.5 mm; (5) Grade 4: The crack expands from a point to a line with a length of less than or equal to 5 mm; (6) Grade 5: The crack expands from a point to a line with a length of greater than 5 mm.

[0027] The test results of the comparative examples and examples 1-4 are judged, and the judgment levels are shown in Table 2.

[0028] Table 2 In Table 2 above, the smaller the level, the better the performance of the tire pattern groove bottom crack resistance, and the smaller the crack level change, the better the tire pattern groove bottom crack resistance. As Figure 4 a-e respectively correspond to the schematic diagrams of the groove bottom 1-5 grade cracks observed under the body microscope.

[0029] Using the rubber composition of Example 4 as the tire tread, a 12R22.5 tire was trial-produced, and a road test was carried out in a certain area in Henan. The above comparative example and Example 4 were cross-comparatively installed on the vehicle to ensure the consistency of the road conditions and driving behavior. Two vehicles (heavy-duty tractors) were used for the road test, and 22 tires were installed on each vehicle. The comparative example tires and the Example 4 tires were cross-installed on each vehicle. The specific installation scheme is shown in Table 1. Figure 5 After 100,000 kilometers of road test, it was observed that the comparative example tires all had groove bottom cracks, and the Example 4 tires were all intact without groove bottom cracks.

[0030] Through the market verification of the examples and the provided test method for evaluating the resistance of the rubber composition to tire groove bottom cracks, it can be seen that the present application can highly simulate the stress state of the rubber composition in the groove bottom under the actual use conditions of the tire, and can provide effective technical support for the research and development and product improvement of the rubber composition. The tires made of the rubber composition with a crack level of 0 grade tested by the method of the present application do not need further road test, and the rubber composition with a crack level greater than or equal to 1 grade does not need further road test, which reduces the test cost and shortens the product development time.

[0031] The above is only a preferred embodiment of the present application, and it should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present application, and these should be considered as the protection scope of the present application.

Claims

1. A test method for evaluating the resistance of a rubber composition to tire groove bottom cracking, characterized in that: The method comprises the following steps, (1) preparing a rubber composition sample, which is an annular solid rubber wheel with a groove structure on the surface; (2) installing the sample on a LAT100 abrasion tester installation shaft, selecting a glass disc or a 180-mesh electric corundum disc as the abrasion disc, rotating the abrasion disc at a speed of 15-30 km / h, applying a load of 60 N-120 N to the sample, maintaining a slip angle of 15°-30° between the sample and the rotating direction of the abrasion disc, and feeding the anti-fouling powder to the contact area between the sample and the abrasion disc at a feeding speed of 0 (3) detecting the groove bottom under a microscope after running for different distances, and recording the number and length of the groove bottom cracks of the sample; (4) evaluating the groove bottom crack resistance of the rubber composition according to the monitored crack data.

2. The test method for evaluating the resistance of a rubber composition to tire groove crack according to claim 1, characterized in that: The annular solid rubber wheel with a groove structure on the surface has an inner diameter of 35 mm±1 mm, an outer diameter of 84 mm±1 mm, and a thickness of 19 mm±0.5 mm; the groove structure is a U-shaped groove, the groove bottom angle is 90°±3°, the groove width is 5 mm±1 mm, and the groove depth is 6 mm±1 mm.

3. The test method for evaluating the resistance of a rubber composition to tire groove crack according to claim 1, characterized in that: The abrasion disc is selected as a glass disc, the rotating speed of the abrasion disc is 20 km / h, a load of 100 N is applied to the sample, and the slip angle between the sample and the rotating direction of the abrasion disc is 20°.

4. The test method for evaluating the resistance of a rubber composition to tire groove crack of claim 1, characterized in that: The anti-fouling powder is a mixture of magnesium oxide and aluminum oxide, the volume ratio is 1:3, and the particle size is 120 mesh.

5. The test method for evaluating the resistance of a rubber composition to tire groove crack of claim 1, characterized in that: The anti-fouling powder feeding speed is 80 g / min.

6. The test method for evaluating the resistance of a rubber composition to tire groove crack of claim 1, characterized in that: The running distances are 5 km, 10 km, 15 km, 20 km, 25 km, 30 km, and 35 km.

7. The test method for evaluating the resistance of a rubber composition to tire groove crack of claim 1, characterized in that: The groove bottom crack resistance of the rubber composition is evaluated according to the groove bottom crack evaluation standard, which is divided into six levels, (1) Level 0: the groove bottom is intact without cracks; (2) Level 1: the groove bottom crack is a pinhole with a size of 1, a number of 1, and a length of less than 0.5 mm; (3) Level 2: the groove bottom crack is a pinhole with a size of 2-3; (4) Level 3: the number of pinholes on the groove bottom exceeds 3, one or more pinholes expand into obvious cracks, which can be seen to be obviously larger, and the length is greater than 0.5 mm; (5) Level 4: the crack expands from a point to a line with a length of less than or equal to 5 mm; (6) Level 5: the crack expands from a point to a line with a length of greater than 5 mm.

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