A rolling contact wear test method for wheel-rail materials

Abstract

The present invention provides a wheel-rail material rolling contact wear test method, comprising the following steps: (1) processing a wheel material or a rail material to be tested into a test sample, and processing a material to be tested in conjunction with the wheel material or the rail material to be tested into a ring-shaped companion sample; (2) installing the test sample on the main shaft of a testing machine, and installing the companion sample on the slave shaft of the testing machine; starting the machine, applying radial pressure, setting the rotation speeds of the main shaft and the slave shaft, wherein the rotation speed of the main shaft is greater than the rotation speed of the slave shaft, and the slip rate of the two is any value in the range of 0 to 10%, and performing a wear test in a dry state; (3) starting a fan or an air nozzle to blow air to cool the friction interface; (4) observing the real-time friction coefficient between the samples, and after the friction coefficient is stable, continuing to rotate the samples for at least 50,000 revolutions, and then stopping the test; (5) measuring the mass of the test sample, calculating the mass wear before and after the test, and performing surface observation.

Description

Technical Field

[0001] The invention belongs to the field of testing technology, and in particular relates to a test method for measuring the surface wear of wheel and rail materials. Background Art

[0002] Wear is the phenomenon that when two surfaces are in contact and in relative motion, the material is gradually lost from the surface, resulting in surface damage. Wear is the most important form of damage that restricts the service life of railway wheels and rails. When the train is running, there is relative rolling and slight sliding (called creep) between the wheel and rail interface at the same time. The relative rolling and sliding motion and frictional contact between the wheel and rail are the direct causes of wear. Under different axle loads, speeds and curve radii, the contact stress and creep rate between the wheel and rail vary greatly; therefore, when the train is actually running, the wear phenomenon between the wheel and rail is complex and changeable.

[0003] A large number of tests and simulation studies have been carried out at home and abroad on the wear characteristics of wheel-rail materials. Field tests and full-size wheel-rail test benches have high test costs, long cycles, and it is difficult to control influencing variables. Although numerical simulation methods can reveal the wear laws of wheels and rails under different working conditions, it is difficult to simulate complex contact conditions and wear evolution processes. Therefore, it is of great significance to develop a small-scale wear test method that can simulate wheel-rail contact conditions, control test costs, and easily observe the wear surface.

[0004] The current "Metallic Materials Wear Test Method Test Ring-Test Block Sliding Wear Test" (GB / T12444-2006) stipulates that the test samples shall be processed into circular wear specimens ("test rings") and block wear specimens ("test blocks") of specified shapes and sizes, and then the test blocks shall be in contact with the test rings of specified rotation speed and subjected to a certain test force. After the specified number of revolutions, the volume wear of the test block (the volume lost by the test specimen after the wear test) shall be calculated by the wear scar width, and the mass wear of the test ring (the mass lost by the test specimen after the wear test) shall be determined by weighing. In this test method, the wear form of the "test ring-test block" contact is a pure sliding condition, which cannot simulate the rolling and sliding contact form when the railway wheel contacts the rail.

[0005] The obsolete "Metal Wear Test Method MM Wear Test" (GB / T 12444.1-1990) stipulates the method for measuring rolling and sliding composite wear: both test samples are processed into circular ring samples of specified shape and size, and the two ring samples are fixed on the testing machine up and down to make uniform contact; the upper and lower samples are driven by the shaft to rotate, and the shaft speed of the lower sample is (400±10)r / min or (200±10)r / min, and the corresponding shaft speed of the upper sample is 360r / min or 180r / min. The main problems of this test method in actual operation are: 1. The slip rate (the difference between the rolling speed of the lower sample and the rolling speed of the upper sample, and the percentage of the ratio of the rolling speed of the lower sample) and the speed setting do not match. In this method, the fixed slip is 10%, and the speed has only two gears, high and low; under this parameter setting, the rolling and sliding contact conditions of the sample are limited, and the fatigue wear behavior of the wheel-rail under medium and low slip cannot be simulated. 2. No cooling treatment is performed in the dry test. The accumulated friction heat between the wheel-rail specimens will have an adverse effect on the wear process: the accumulation of surface oxides caused by high temperature will change the contact conditions and wear mechanism, and even cause the microstructure evolution of the surface material of the contact interface, thus affecting the test results. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a rolling contact wear test method for wheel-rail materials, so that the wear of wheel-rail materials under rolling and sliding contact conditions can be simulated in the laboratory, and the wear resistance of wheel-rail materials with different compositions and processes can be studied and compared.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A wheel-rail material rolling contact wear test method comprises the following steps:

[0009] (1) Processing a wheel material or rail material to be tested into a test sample, wherein the test sample has an annular body and an axial boss along the outer wall of the body; processing a material to be tested in conjunction with the wheel material or rail material to be tested into an annular companion sample, wherein the axial thickness of the companion sample is greater than the width of the axial boss of the test sample;

[0010] (2) installing the test sample on the main shaft of the testing machine, and installing the companion sample on the slave shaft of the testing machine, so that the boss of the test sample contacts the companion sample; starting the machine, applying radial pressure, setting the rotation speeds of the main shaft and the slave shaft, wherein the rotation speed of the main shaft is greater than or equal to the rotation speed of the slave shaft, and the slip rate of the two is any value within the range of 0 to 10%, and conducting a wear test in a dry state;

[0011] (3) Start the fan or air nozzle to blow air to cool the friction interface;

[0012] (4) Observe the real-time friction coefficient between the specimens. After the friction coefficient stabilizes, continue to rotate the specimens for at least 50,000 revolutions, and then stop the test;

[0013] (5) Determine the mass of the test sample, calculate the mass wear before and after the test, and perform surface observation.

[0014] The shapes and relative positions of the test sample and the accompanying sample are Figure 1 In the figure, the body of the test sample is labeled 1, and the boss of the test sample is labeled 2; the boss 2 and the companion sample 3 form parallel rolling contact.

[0015] When the test sample is a wheel, the accompanying sample can be a rail; vice versa. In addition, the accompanying sample can also be ordinary steel with a hardness similar to that of the test sample, but the material of the accompanying sample must be uniform.

[0016] Preferably, in step (1), the test sample and the accompanying sample should be subjected to a hardness test on the circumference of the end face, with at least three measuring points set, and the hardness difference should not exceed ±2HRC to ensure the material uniformity of the sample.

[0017] Preferably, in step (2), the testing machine is a dual-motor testing machine with a stepless speed regulation function.

[0018] In step (2), the slip rate is selected according to the test simulation conditions. When the test needs to simulate the working conditions of the combination of wheel-rail adhesive wear and surface fatigue wear, a lower slip rate of 0-2% should be selected; when the working conditions of the combination of surface fatigue wear and abrasive wear need to be simulated, an intermediate slip rate of 2-6% can be selected; when the working conditions dominated by abrasive wear need to be simulated, a higher slip rate of 6-10% should be selected. When conducting comparative and optimization tests on different materials or processes, the slip rates in different test groups should be kept fixed and the same.

[0019] Preferably, in step (4), when the friction coefficient fluctuation between the samples is observed to be stable within ±0.05 for more than 1000 revolutions in real time, it is determined that the friction coefficient has reached stability.

[0020] Compared with the prior art, the method of the present invention has the following beneficial effects: the use of a dual-motor testing machine with stepless speed regulation function can achieve 0-10% arbitrary slip configuration to meet the requirements of different simulated working conditions. The cooling by fan or air nozzle can significantly reduce the temperature of the contact interface of the sample, maintain a stable wear state, and the simulation effect is closer to the actual application of railway wheels and rails.

[0021] The present invention can be used to simulate the wear of wheel-rail materials under rolling-sliding contact conditions in the laboratory, and to conduct comparative tests on the wear resistance of wheel-rail materials with different compositions and processes, and the test results are closer to actual railway applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 Schematic diagram of the shape, size and relative position of the test sample and the accompanying sample of the present invention, the unit of the size in the figure is mm.

[0024] I: test specimen; II: companion specimen; 1: body of the test specimen; 2: boss of the test specimen.

[0025] Figure 2 The following are photos of the test sample and the accompanying sample after the wear test according to the test method of the present invention is completed in Example 1; wherein:

[0026] A (left) shows the photo of the test sample processed from the ER8 wheel rim after the test;

[0027] B (right) shows a photograph of a test specimen made from the rail head of U71MnG rail after testing.

[0028] Figure 3 The following are photos of the test sample and the accompanying sample after the wear test according to the test method of the present invention is completed in Example 2; wherein:

[0029] A (left) shows the photo of the test sample processed from the ER8 wheel rim after the test;

[0030] B (right) shows a photograph of a test specimen made from the rail head of U71MnG rail after testing.

[0031] Figure 4 This is a schematic diagram of the shape, size and relative position of the test sample and the accompanying sample in Comparative Example 1, where the unit of the dimensions in the figure is mm.

[0032] I: test specimen; II: companion specimen; 1: body of the test specimen; 2: boss of the test specimen.

[0033] Figure 5 These are photos of the test sample before and after the wear test of Comparative Example 1; wherein:

[0034] A (left) shows the photo of the test sample processed from the ER8 wheel rim before the test;

[0035] B (right) shows a photograph of a test sample made from an ER8 wheel rim after testing.

[0036] Figure 6 Shown are photos of actual wheel-rail wear, where:

[0037] A (left) shows a photo of a wheel;

[0038] B (right) shows a photograph of a rail. DETAILED DESCRIPTION

[0039] The present invention is described below with reference to specific examples. It will be appreciated by those skilled in the art that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention in any way.

[0040] The experimental methods in the following examples are all conventional methods unless otherwise specified. The raw materials, reagents, etc. used in the following examples are all commercially available products unless otherwise specified. The purchase of some equipment is as follows:

[0041] Wear tester: GPM-30A friction and wear tester produced by Jinan Yihua Tribology Testing Technology Co., Ltd.

[0042] Example 1 Rolling contact wear test of wheel-rail material simulating abrasive wear conditions of wheel-rail side wear

[0043] (1) The ER8 wheel rim is processed into the test specimen, and the U71MnG rail head is processed into the companion specimen. Both the test specimen and the companion specimen are annular specimens with rolling contact cylindrical surfaces. The shapes and dimensions are shown in Figure 1 The specific dimensions are: outer diameter 60mm, inner diameter 30mm, thickness 10mm, boss width 5mm, wheel upper rail lower, see Figure 1 The hardness uniformity test was conducted on the test sample and the accompanying sample, and the hardness results obtained at the three test points met the requirement of ±2HRC. The test sample and the accompanying sample were cleaned and dried in a drying oven for more than 1 hour before being weighed.

[0044] (2) A dual-motor testing machine with stepless speed regulation is used. The test sample and the accompanying sample are installed on two rotating shafts, wherein the test sample is fixed on the main shaft and the accompanying sample is fixed on the slave shaft, the test sample is on the top and the accompanying sample is on the bottom, so that the boss of the test sample contacts the accompanying sample, so that the two sample cylindrical surfaces form parallel rolling contact, and the air nozzle is fixedly aligned with the sample contact interface. Start the machine, start from the pure rolling condition, and gradually adjust the motor speed and radial pressure to make the main shaft motor speed reach 500r / min, the slave shaft speed 450r / min, the slip rate is controlled to 10%, and the radial load reaches 2000N.

[0045] (3) Turn on the air nozzle to blow air to cool the friction interface.

[0046] (4) As the rolling cycles accumulate, the friction coefficient gradually increases and stabilizes at μ = 0.5 ± 0.05 for more than 1,000 turns. The friction coefficient is considered to be stable. After about 100,000 turns (3 hours), the test is stopped.

[0047] (5) Turn off the testing machine and air jet equipment, remove the test sample and accompanying sample, clean them again, dry them in a drying oven for more than 1 hour, weigh them, observe the surface, and calculate the mass wear. Photos of the test sample and accompanying sample after the test Figure 2 .

[0048] Take another ER8 wheel rim and U71MnG rail head and repeat the above operation twice. The wear results of the three groups are shown in Table 1.

[0049] Table 1 Wheel-rail sample quality wear results

[0050]

[0051] Example 2 Rolling contact wear test of wheel-rail material simulating combined working conditions of surface fatigue wear and abrasive wear

[0052] (1) The test materials, test equipment, specimen size, pre-test treatment, and test installation requirements are the same as those in Example 1.

[0053] (2) Starting from the pure rolling condition, gradually adjust the motor speed and radial pressure so that the spindle motor speed reaches 500 r / min, the slave shaft speed reaches 480 r / min, the slip rate is controlled to 4%, and the radial load reaches 2000 N.

[0054] (3) Turn on the fan to blow air to cool the friction interface.

[0055] (4) As the rolling cycles accumulate, the friction coefficient gradually increases and stabilizes at μ = 0.5 ± 0.05 for more than 1,000 turns. The friction coefficient is considered to be stable. After about 100,000 turns (3 hours), the test is stopped.

[0056] (5) Turn off the testing machine and fan, remove the test sample and accompanying sample, clean them again, dry them in a drying oven for more than 1 hour, weigh them, observe the surface, and calculate the mass wear. See the photos of the test sample and accompanying sample after the test. Figure 3 .

[0057] Take another ER8 wheel rim and U71MnG rail head and repeat the above operation twice. The wear results of the three groups are shown in Table 2.

[0058] Table 2 Wheel-rail sample quality wear results

[0059]

[0060] Comparative Example 1

[0061] (1) The test materials, pre-test treatment and test installation requirements are the same as those in Examples 1 and 2;

[0062] (2) The test equipment is the same model as in the examples, but the design of the rotating shaft fixture is different. Therefore, the size of the test sample and the accompanying sample is slightly different. The width is 20 mm, but the contact area of ​​the test sample and the accompanying sample is the same. For details, see Figure 4 .

[0063] (3) Starting from the pure rolling condition, gradually adjust the motor speed and radial pressure so that the spindle motor speed reaches 500 r / min, the slave shaft speed reaches 495 r / min, the slip rate is controlled to 1%, and the vertical load reaches 2000 N.

[0064] (4) During the test, the wheel-rail specimens were placed in an open room temperature environment without any cooling treatment.

[0065] (5) As the rolling cycles accumulate, the friction coefficient gradually increases and stabilizes at μ = 0.5 ± 0.05 for more than 1,000 turns. The friction coefficient is considered to be stable. After about 100,000 turns (3 hours), the test is stopped.

[0066] (6) Turn off the testing machine, remove the wheel-rail sample, clean it again, dry it in a drying oven for more than 1 hour, weigh it, observe its surface, calculate the mass wear, and take photos of the test sample before and after the test. Figure 5 .

[0067] Take another ER8 wheel rim and U71MnG rail head and repeat the above operation twice. The wear results of the three groups are shown in Table 3.

[0068] Table 3 Wheel-rail sample quality wear results

[0069]

[0070] Comparing the photos of the test samples in Examples 1 and 2 and Comparative Example 1 after the test, it can be seen that in the test using fans or compressed air cooling measures in the embodiments, the surface of the wheel-rail sample presents a furrow shape ( Figure 2 ) or surface peeling morphology ( Figure 3 ), but they all maintained a silvery white color and the contact surface was relatively smooth. In the comparative test, no cooling treatment was taken, and a large amount of dark brown oxidation products accumulated on the surface of the wheel sample, which is consistent with the actual wheel-rail wear surface (see Figure 6 ) are very different; the wear mode change caused by oxides introduces unstable factors, resulting in large differences in the wear amount of the tested wheel samples in the repeated test groups (Table 3), while the repeatability of the wear results of the three groups of tests in the embodiment is good, indicating that the test method of the present invention is stable, can better simulate the actual wear conditions, and the test results are highly credible.

Claims

1. A rolling contact wear test method for wheel-rail materials, comprising the following steps: (1) Processing the wheel material or rail material to be tested into a test specimen, wherein the test specimen has an annular main body and an axial boss along the outer wall of the main body; processing the material to be tested in conjunction with the wheel material or rail material to be tested into an annular companion specimen, wherein the axial thickness of the companion specimen is greater than the width of the axial boss of the test specimen; (2) Install the test specimen on the main shaft of the testing machine, and install the companion specimen on the slave shaft of the testing machine, so that the boss of the test specimen contacts the companion specimen; start the machine, apply radial pressure, set the speed of the main shaft and the slave shaft, wherein the speed of the main shaft is greater than or equal to the speed of the slave shaft, and the slip rate of the two is any value in the range of 0 to 10%, and conduct a wear test in a dry state; in, The testing machine is a dual-motor testing machine with stepless speed regulation function; The slip rate is selected according to the test simulation conditions; when the test needs to simulate the working conditions of the combination of wheel-rail adhesive wear and surface fatigue wear, the slip rate is 0-2%; when the working conditions of the combination of surface fatigue wear and abrasive wear are simulated, the slip rate is 2-6%; when the working conditions dominated by abrasive wear are simulated, the slip rate is 6-10%; (3) Start the fan or air nozzle to blow air to cool the friction interface; (4) Observe the real-time friction coefficient between the specimens. After the friction coefficient stabilizes, continue to rotate the specimens for at least 50,000 revolutions, and then stop the test. Among them, when the friction coefficient fluctuation between the samples is observed to be stable within ±0.05 for more than 1000 revolutions in real time, the friction coefficient is determined to be stable; (5) Determine the mass of the test sample, calculate the mass wear before and after the test, and conduct surface observation.

2. The wheel-rail material rolling contact wear test method according to claim 1, characterized in that: In step (1), the test specimen and the companion specimen shall be subjected to a hardness test on the circumference of the end face, with at least three measuring points set, and the hardness difference shall not exceed ±2HRC.

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