Aluminothermic welding sand mold riser and preheating test method

Abstract

The invention discloses an aluminothermic welding sand mold riser and a preheating test method, comprising a sand mold profile lower surface for fitting the upper surface of the bottom of a steel rail, a first riser and a second riser symmetrically arranged on the sand mold profile lower surface, the first riser and the second riser are connected and converged inside the sand mold, and the sum of the opening areas of the first riser and the second riser is less than 416mm 2 The aluminothermic welding sand mold riser and preheating test method provided by the present invention reduce the grinding amount and grinding time of the residual riser rod of the joint, avoid biting the rail bottom angle rail parent material in the process of grinding and removing the residual riser rod of the joint, and the preheating test method further verifies that the aluminothermic welding sand mold riser has a good preheating effect, thereby ensuring the mechanical properties of the welded joint.

Description

Technical Field

[0001] The invention relates to the technical field of thermite welding, and more specifically to an armite welding sand mold riser and a preheating test method. Background Art

[0002] Rail aluminothermic welding technology is one of the important welding technologies for rail welding of seamless railway lines. At present, there are three types of aluminothermic welding materials commonly used in China, namely German Thermit welding materials, French QPCJ welding materials and domestic ZTK-Ⅰ welding materials. The welding materials mainly include aluminothermic flux, sand mold, crucible, etc. The cavity surrounded by the rail aluminothermic welding sand mold and the two sections of rails to be welded constitutes a pouring system for molten steel pouring. The sand mold is an important part of the pouring system, in which the sand mold riser is a cavity for storing aluminothermic molten steel. Its main function is to store the metal liquid that needs to be compensated due to volume changes during the solidification of the aluminothermic molten steel to prevent shrinkage defects at the weld ribs.

[0003] In the existing technology, the skylight point of the conventional line currently requires that the maintenance skylight time for double lines should not be less than 120 minutes and for single lines should not be less than 90 minutes. Under this skylight point requirement, the domestic ZTK-1 type welding materials are greatly restricted. The ZTK-1 type sand mold currently used in domestic welding is provided with a sand mold contour lower surface for fitting the upper surface of the rail bottom. The sand mold contour lower surface has a size of 32mm×13mm and an area of ​​416mm 2 A square riser is formed on the outer edge of the square riser after the hot aluminum steel is poured into the square riser. The grinding amount of the joint residual riser rod is large and the grinding is troublesome. In addition, in the process of removing the joint residual riser rod, it is easy to cause the weld bar to be short of meat, thereby biting the rail bottom angle rail parent material.

[0004] Therefore, it is necessary to solve the above problems. Summary of the invention

[0005] In view of this, the purpose of the present invention is to propose an aluminothermic welding sand mold riser and a preheating test method to reduce the grinding amount and grinding time of the residual riser rod of the joint, avoid biting the rail bottom angle rail parent material in the process of grinding and removing the residual riser rod of the joint, and the preheating test method further verifies that the above-mentioned aluminothermic welding sand mold riser has a good preheating effect, thereby ensuring the mechanical properties of the welded joint.

[0006] Based on the above purpose, the present invention provides an aluminothermic welding sand mold riser, comprising a sand mold profile lower surface for fitting the upper surface of the rail bottom, the sand mold profile lower surface is provided with a symmetrically arranged first riser and a second riser, the first riser and the second riser are connected and converged inside the sand mold, and the sum of the opening areas of the first riser and the second riser is less than 416mm2 .

[0007] Optionally, the lower surface of the sand mold contour includes a first side line, a second side line and a horizontal line connected between the first side line and the second side line which are relatively arranged. When the shapes of the first riser and the second riser are both rectangular, the first riser is located on one side of the first side line, and the second riser is located on one side of the second side line. The shortest distance from the first riser to the first side line is 8 mm, and the shortest distance from the second riser to the second side line is 8 mm. The shortest distances from the first riser and the second riser to the horizontal line where the center of the horizontal line is located are both 6 mm. The lengths of the first riser and the second riser are both L1, 8.5 mm ≤ L1 < 16 mm, and the widths are both L2, L2 ≤ 12.5 mm.

[0008] Optionally, the lower surface of the sand mold contour includes a first side line and a second side line that are relatively arranged, and a horizontal line connected between the first side line and the second side line. When the first riser and the second riser are both elliptical, the distance from the center of the first riser to the first side line is d1, 12.25mm≤d1≤14.25mm, the distance from the center of the second riser to the second side line is d2, 12.25mm≤d2≤14.25mm, the shortest distance from the center of the first riser and the center of the second riser to the horizontal line where the center of the horizontal line is located is both 12.25mm, the major axis of the first riser and the second riser is a, 12.5mm≤a<16mm, and the minor axis of the first riser and the second riser is b, 8.5mm≤b<12.5mm.

[0009] Optionally, the lower surface of the sand mold contour includes a first side line and a second side line that are relatively arranged, and a horizontal line connected between the first side line and the second side line. When the first riser and the second riser are both circular, the distance from the center of the first riser to the first side line is d3, 12.25mm≤d3≤14.25mm, the distance from the center of the second riser to the second side line is d4, 12.25mm≤d4≤14.25mm, the shortest distances from the center of the first riser and the center of the second riser to the horizontal line where the horizontal center is located are both 12.25mm, and the diameters of the first riser and the second riser are both D, 8.5mm≤D<12.5mm.

[0010] Based on the same inventive concept, the present invention also provides a preheating test method for thermite welding sand mold riser, which tests the armite welding sand mold riser described in any of the above technical solutions, including a preheating simulation test and a preheating test process, wherein the preheating simulation test includes the following steps: Step 1, establish a solid model of the sand mold with the armite welding sand mold riser and the steel rail to be welded according to a ratio of 1:1 and perform fluid domain model mesh division; Step 2, set the combustion temperature and the fluid-solid coupling thermal simulation method; Step 3, set the heating time and enter the iterative calculation; Step 4, analyze the flow field simulation results; Step 5, analyze the preheating simulation results. The preheating test process includes the following steps: Step 1, make a temperature measuring steel rail for the test; Step 2, pre-embed a thermocouple and connect a temperature detector; Step 3, set each preheating parameter, perform a preheating test, and measure the temperature; Step 4, analyze the test results to determine whether they are consistent with the simulated temperature distribution results.

[0011] The invention provides an aluminothermic welding sand mold riser and a preheating test method. The aluminothermic welding sand mold riser comprises a sand mold profile lower surface for fitting the upper surface of the bottom of a steel rail. A symmetrically arranged first riser and a second riser are provided on the sand mold profile lower surface. The symmetrically arranged first riser and the second riser ensure the shrinkage compensation effect when pouring aluminothermic molten steel into the first riser and the second riser. The sum of the opening areas of the first riser and the second riser is set to be less than 416mm. 2 The first riser and the second riser are connected and gathered together inside the sand mold, so that after the thermite steel liquid is poured into the first riser and the second riser, when the residual riser rods of the joint formed on the outer edges of the first riser and the second riser are removed, the grinding amount and grinding time of the residual riser rods of the joint are reduced, thereby avoiding biting of the rail bottom angle steel rail parent material in the process of grinding and removing the residual riser rods of the joint, and the preheating test method further verifies that the above-mentioned thermite welding sand mold riser has a good preheating effect, thereby ensuring the mechanical properties of the welded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, which will help to understand the objects and advantages of the present invention, wherein:

[0013] Figure 1 It is a schematic structural diagram of an aluminothermic welding sand mold riser according to an embodiment of the present invention;

[0014] Figure 2 for Figure 1 Sectional view at AA;

[0015] Figure 3 A front view of an aluminothermic welding sand mold riser according to an embodiment of the present invention;

[0016] Figure 4It is a flow chart of a preheating simulation test in a preheating test method for a heat welding sand mold riser according to an embodiment of the present invention;

[0017] Figure 5 It is a flow chart of a preheating test process in a preheating test method for a heat welding sand mold riser according to an embodiment of the present invention;

[0018] Figure 6 A mesh diagram of a fluid domain model in a method for preheating a sand mold riser for thermite welding according to an embodiment of the present invention;

[0019] Figure 7 It is a schematic diagram of the simulated end surface temperature distribution result in the preheating test method of thermite welding sand mold riser according to one embodiment of the present invention;

[0020] Figure 8 This is a distribution diagram of the end surface positions of measuring points on the rail to be tested in a method for preheating a sand mold riser for thermite welding according to an embodiment of the present invention.

[0021] Fig. 9 The temperature measurement results at different drill holes on the rail to be tested in the preheating test method of thermite welding sand mold riser in one embodiment of the present invention.

[0022] Description of reference numerals:

[0023] 1: lower surface of sand mold contour; 2: first riser; 3: second riser; 4: first side line; 5: second side line; 6: horizontal line. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the embodiments. The same components are denoted by the same reference numerals. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0025] like Figure 1 and Figure 2 As shown, the aluminothermic welding sand mold riser provided by the present invention comprises a sand mold contour lower surface for fitting the upper surface of the rail bottom, the sand mold contour lower surface is provided with a first riser and a second riser symmetrically arranged, the first riser and the second riser are connected and converged inside the sand mold, and the sum of the opening areas of the first riser and the second riser is less than 416mm 2 .

[0026] It should be noted that: 416mm 2 is the opening area of ​​the square riser in the prior art.

[0027] The invention provides an aluminothermic welding sand mold riser, which comprises a sand mold profile lower surface for fitting the upper surface of the bottom of a steel rail, and a symmetrically arranged first riser and a second riser are provided on the sand mold profile lower surface, and the symmetrically arranged first riser and the second riser ensure the shrinkage compensation effect when pouring aluminothermic molten steel into the first riser and the second riser, and the sum of the opening areas of the first riser and the second riser is set to be less than 416mm 2 The first riser and the second riser are connected and gathered together inside the sand mold, so that after the hot aluminum steel liquid is poured into the first riser and the second riser, when the residual riser rods of the joint formed on the outer edges of the first riser and the second riser are removed, the grinding amount and grinding time of the residual riser rods of the joint are reduced, thereby avoiding biting of the rail bottom angle rail base material in the process of grinding and removing the residual riser rods of the joint.

[0028] like Figures 1 to 3 As shown, the lower surface of the sand mold contour includes a first side line and a second side line that are relatively arranged, and a horizontal line connected between the first side line and the second side line. When the shapes of the first riser and the second riser are both rectangular, the first riser is located on one side of the first side line, and the second riser is located on one side of the second side line. The shortest distance from the first riser to the first side line is 8mm, and the shortest distance from the second riser to the second side line is 8mm. The shortest distances from the first riser and the second riser to the horizontal line where the center of the horizontal line is located are both 6mm. The lengths of the first riser and the second riser are both L1, 8.5mm≤L1<16mm, and the widths are both L2, L2≤12.5mm. In this embodiment, the sum of the opening areas of the first riser and the second riser is not less than 416mm 2 Therefore, after pouring the aluminothermic steel liquid into the first riser and the second riser, when removing the residual riser rods of the joint formed on the outer edges of the first riser and the second riser, the grinding amount and grinding time of the residual riser rods of the joint are reduced, thereby avoiding biting the rail bottom angle rail parent material in the process of grinding and removing the residual riser rods of the joint, and when the shapes of the first riser and the second riser are rectangular, only the existing square sand mold needs to be improved for use, thereby improving the processing and operation convenience of the aluminothermic welding sand mold risers.

[0029] like Figures 1 to 3As shown, the lower surface of the sand mold contour includes a first side line and a second side line that are relatively arranged, and a horizontal line connected between the first side line and the second side line. When the first riser and the second riser are both elliptical, the distance from the center of the first riser to the first side line is d1, 12.25mm≤d1≤14.25mm, the distance from the center of the second riser to the second side line is d2, 12.25mm≤d2≤14.25mm, and the shortest distance from the center of the first riser and the center of the second riser to the horizontal line where the center of the horizontal line is located is 12.25mm. The major axis of the first riser and the second riser is a, 12.5mm≤a<16mm, and the minor axis of the first riser and the second riser is b, 8.5mm≤b<12.5mm. In this embodiment, the sum of the opening areas of the first riser and the second riser is not less than 416mm 2 Therefore, after the thermite steel liquid is poured into the first riser and the second riser, when the residual riser rods of the joint formed on the outer edges of the first riser and the second riser are removed, the grinding amount and grinding time of the residual riser rods of the joint are reduced, thereby avoiding the rail bottom angle rail base material from being bitten in the process of grinding and removing the residual riser rods of the joint, and when the shapes of the first riser and the second riser are circular, the casting dead angle that may be caused by the sudden change of the geometry of the riser shape is reduced, and the structural stability of the thermite welding sand mold riser is improved.

[0030] like Figures 1 to 3 As shown, the lower surface of the sand mold contour includes a first side line and a second side line that are relatively arranged, and a horizontal line connecting the first side line and the second side line. When the first riser and the second riser are both circular, the distance from the center of the first riser to the first side line is d3, 12.25mm≤d3≤14.25mm, and the distance from the center of the second riser to the second side line is d4, 12.25mm≤d4≤14.25mm. The shortest distance from the center of the first riser and the center of the second riser to the horizontal line where the horizontal center is located is 12.25mm. The diameters of the first riser and the second riser are both D, 8.5mm≤D<12.5mm. In this embodiment, the sum of the opening areas of the first riser and the second riser is less than 416mm. 2 After the thermite steel is poured into the first riser and the second riser, when the residual riser rods of the joint formed on the outer edges of the first riser and the second riser are removed, the grinding amount and grinding time of the residual riser rods of the joint are reduced, thereby avoiding the rail bottom angle rail base material from being bitten in the process of grinding and removing the residual riser rods of the joint, and when the shapes of the first riser and the second riser are circular, the casting dead angle that may be caused by the sudden change of the geometry of the riser shape is reduced, and the circular riser is more convenient for strengthening the test of the preheating effect of the edge, further improving the structural stability of the thermite welding sand mold riser.

[0031] like Figures 1 to 5As shown, based on the same inventive concept, an embodiment of the present invention also provides a preheating test method for thermite welding sand mold riser, which tests the armite welding sand mold riser of any of the aforementioned embodiments, including a preheating simulation test and a preheating test process, wherein the preheating simulation test includes the following steps: Step 1, a solid model of the sand mold with thermite welding sand mold riser and the steel rail to be welded is established in a ratio of 1:1 and the fluid domain model is meshed; Step 2, the combustion temperature and the fluid-solid coupling thermal simulation method are set; Step 3, the heating time is set and the iterative calculation is entered; Step 4, the flow field simulation results are analyzed; Step 5, the preheating simulation results are analyzed. The preheating test process includes the following steps: Step 1, a temperature measuring steel rail for the test is made; Step 2, a thermocouple is embedded and a temperature detector is connected; Step 3, each preheating parameter is set, a preheating test is performed, and the temperature is measured; Step 4, the test results are analyzed to determine whether they are consistent with the simulated temperature distribution results.

[0032] In one embodiment of the present invention, first, a ZTK-I sand mold with a size of 32 mm × 13 mm and an area of ​​416 mm is prepared in the prior art. 2 After pouring the hot aluminum steel into the square riser, a joint residual riser rod is formed on the outer edge of the square riser. The joint residual riser rod is polished, and the average polishing amount is 11787mm 3 , the grinding time is 553s, and overflow flash is generated after different joints are welded at the square riser. The grinding time of overflow flash varies greatly, with the shortest grinding time being 301s, the longest grinding time being 601s, and the average grinding time being 447s; then, the sand mold with a riser for thermite welding sand mold is preheated and simulated by numerical simulation software. The first riser and the second riser are two rectangular risers with a size of 8.5mm×12.5mm. The thickness of the interval between the first riser and the second riser at the opening is 18mm. The sand mold is preheated and simulated by numerical simulation software to observe the temperature state of each part of the end face of the rail to be welded. A 1:1 solid model of the sand mold with a riser for thermite welding sand mold and the rail to be welded is established by three-dimensional software, and the fluid domain model is meshed as follows: Figure 6 The model uses 60kg / m rails and ZTK-1N sand molds, with a 30mm gap between two rails and a 50mm distance between the outlet end of the preheater and the top of the rail. Figure 7 As shown, there are 32 gas outlets, each with a diameter of 1.1 mm, which is consistent with the special preheater for thermite welding in the prior art. Finally, a preheating temperature measurement test is carried out. Since thermite welding uses an oxygen-propane mixed gas, the flame heating after combustion cannot directly measure the end surface temperature of the rail. Therefore, the internal temperature of the rail at a certain distance from the end surface can only be measured by drilling. Before the test, the rail to be tested is drilled in advance, with a total of 12 holes. The end surface position distribution of the measurement points is shown in the figure. Figure 8As shown in the figure, the hole is 5mm away from the end face of the rail, and the thermocouple is inserted into the hole for temperature measurement. The temperature measurement range of the K-type thermocouple used in this test is -200℃-1200℃, and the temperature acquisition instrument collects the temperature step of 1s. After the preheating is completed, the collected temperature is exported for result analysis; in the preheating test, the preheater is 50mm away from the top surface of the rail, and the rail has a 30mm reserved rail gap. The top surface of the rail head is used as the standard. The oxygen pressure for preheating is 0.3MPa, and the propane pressure is 0.1MPa. The temperature measurement results are plotted as shown in the figure. Fig. 9 As shown by Fig. 9 It can be seen that during the preheating process, the overall temperature distribution results are as follows: with the increase of preheating time, the temperature of each measuring point on the rail end surface gradually increases, among which the rail head is slightly lower than other parts such as the rail waist, and the temperature distribution of each part of the rail end surface is relatively uniform, which is basically the same as the temperature distribution state and temperature results of the simulation results.

[0033] Combining the characteristics of ZTK-Ⅰ type aluminothermic welding operation process with the results of this preheating test, the temperature distribution of each part of the end surface at three time nodes with preheating time of 210s, 240s and 270s was selected for summary analysis. The average temperature of points 1-4 was taken as the rail head temperature, the average temperature of points 5-8 was taken as the rail waist temperature, and the average temperature of points 9-12 was taken as the rail bottom temperature. The results are shown in Table 1.

[0034] Table 1 Preheating temperature results

[0035]

[0036]

[0037] It can be seen from Table 1 that as the preheating time increases, the end surface temperature rises basically evenly. When the preheating time is 210s, 240s, and 270s, the average end surface temperature meets the standard requirements: the preheating temperature should be 700-1000℃.

[0038] Since good preheating is an important part of ensuring the mechanical properties of the joint, welding tests were carried out under different preheating time conditions. After welding, the grinding amount was measured and calculated, the grinding time was recorded, and the mechanical properties test of the joint was carried out. Tests with different preheating time: ZTK-1 type aluminothermic welding material was used, the flux model was T3, and 60kg / m U75V rails were used for the test. The welding tools included a special preheating device, a fixture device, an alignment device, etc. The welding test used the same parameters as the preheating test. The three groups of preheating time parameters of 210s, 240s, and 270s that met the requirements in the preheating test were selected, and three welding joints were welded for each. After the welding joint was completed, the mold was removed after 6min30s, and the nodule was pushed after 8min30s. After pushing the nodule, the riser rod was removed, the grinding amount was calculated, and the grinding time and other data were recorded. Table 2 shows the riser grinding amount under different preheating times.

[0039] Table 2 Riser grinding amount at different preheating times

[0040]

[0041] It can be seen from the data in Table 2 that when the preheating time is 210s, the post-weld riser grinding amount is 4817mm 3 , it is calculated that the amount of riser grinding after welding of the original ZTK-1 sand mold is reduced by 59%; the preheating time is 240s and 270s. After welding, the amount of riser grinding after welding joint is relatively close, which are 5454mm3 and 5596mm3 respectively. It is calculated that the amount of riser grinding after welding of the original ZTK-1 sand mold is reduced by 54% and 53%.

[0042] The static bending strength of thermite welded joints is an important indicator that affects the service effect of the joints. Therefore, the static bending strength test was carried out on the welded joints under various welding processes using the ZTK-1N sand mold. Static bending performance at different preheating times: The test used a YAW-3000J rail static bending pressure testing machine. The static bending test support was 1m, the weld was centered, the weld center was subjected to concentrated load, and the joint was loaded until it broke. Among the three joints welded with each set of preheating time parameters, two rail heads were under compression and one rail head was under tension. A total of nine rail joints were tested and the results are shown in Table 3.

[0043] Table 3 Results of static bending test of joints with different preheating time

[0044]

[0045] The fracture morphology after static bending was observed with the naked eye and a magnifying glass, and no excessive defects were found in the 9 joints. TB / T 1632.3-2019 stipulates that the aluminum thermite welded joints of 60kg / m, 980MPa grade rails should meet the following requirements: rail head compression F ≥ 1300kN, fmax ≥ 10mm, rail head tension F ≥ 1200kN, fmax ≥ 10mm. The results show that the static bending results of each joint meet the standard requirements, and the static bending value increases with the increase of preheating time.

[0046] Combined with the grinding amount of the post-weld joint, the analysis shows that when the preheating time is 210s, the grinding amount and grinding time are the shortest, and the static bending value of the post-weld joint is the lowest, which is close to the standard requirements; when the preheating time is 240s, the grinding amount and grinding time are somewhat increased compared with 210s, and the static bending value of the post-weld joint is greatly improved; when the preheating time is 270s, the static bending value of the post-weld joint is the largest, but at this time the grinding amount is also the largest, and the grinding time is the longest, which is not conducive to the on-site skylight operation. Considering the grinding time of the post-weld joint riser and overflow flash and the static bending strength of the joint, the preheating time should be 240s.

[0047] The tensile strength of thermite welded joint is an important indicator that affects the service effect of the joint. The welding test was carried out using a welding process with a preheating time of 240s. One joint was welded, numbered H10 (9 specimens were selected during the test). According to TB / T1632.1-2014, tensile specimens were taken from the H10 joint for testing, and the tensile strength was recorded respectively. The average tensile strength Rm of the 9 specimens was taken as the test result. The test results are shown in Table 4.

[0048] Table 4 Tensile test results

[0049]

[0050] The results show that when the preheating time is 240s, the tensile strength of the joint meets the standard requirements.

[0051] The present invention provides an aluminothermic welding sand mold riser and a preheating test method. The aluminothermic welding sand mold riser comprises a sand mold profile lower surface for fitting the upper surface of the bottom of a steel rail. A symmetrically arranged first riser and a second riser are provided on the sand mold profile lower surface. The symmetrically arranged first riser and the second riser ensure the shrinkage compensation effect when pouring aluminothermic molten steel into the first riser and the second riser. The sum of the opening areas of the first riser and the second riser is set to be less than 416 mm2, and the first riser and the second riser are connected and gathered together inside the sand mold. Therefore, after pouring the aluminothermic molten steel into the first riser and the second riser, when removing the joint residual riser rod formed on the outer edges of the first riser and the second riser, the grinding amount and grinding time of the joint residual riser rod are reduced, thereby avoiding biting of the rail bottom angle steel rail base material in the process of grinding and removing the joint residual riser rod. In addition, the preheating test method further verifies that the aluminothermic welding sand mold riser has a good preheating effect, thereby ensuring the mechanical properties of the welded joint.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heat welding sand mold riser, characterized in that: The invention comprises a lower surface of a sand mold profile for fitting the upper surface of the bottom of a steel rail, wherein a first riser and a second riser are symmetrically arranged on the lower surface of the sand mold profile, wherein the first riser and the second riser are connected and converged inside the sand mold, and the sum of the opening areas of the first riser and the second riser is less than 416 mm 2 .

2. The aluminothermic welding sand mold riser according to claim 1, characterized in that: The lower surface of the sand mold contour includes a first side line, a second side line and a horizontal line connected between the first side line and the second side line which are arranged opposite to each other. When the shapes of the first riser and the second riser are both rectangular, the first riser is located on one side of the first side line, and the second riser is located on one side of the second side line. The shortest distance from the first riser to the first side line is 8 mm, and the shortest distance from the second riser to the second side line is 8 mm. The shortest distances from the first riser and the second riser to the horizontal line where the center of the horizontal line is located are both 6 mm. The lengths of the first riser and the second riser are both L1, 8.5 mm ≤ L1 < 16 mm, and the widths are both L2, L2 ≤ 12.5 mm.

3. The aluminothermic welding sand mold riser according to claim 1, characterized in that: The lower surface of the sand mold contour includes a first side line, a second side line and a horizontal line connected between the first side line and the second side line which are arranged opposite to each other. When the first riser and the second riser are both elliptical, the distance from the center of the first riser to the first side line is d1, 12.25mm≤d1≤14.25mm, the distance from the center of the second riser to the second side line is d2, 12.25mm≤d2≤14.25mm, the shortest distance from the center of the first riser and the center of the second riser to the horizontal line where the center of the horizontal line is located is 12.25mm, the major axis of the first riser and the second riser is a, 12.5mm≤a<16mm, and the minor axis of the first riser and the second riser is b, 8.5mm≤b<12.5mm.

4. The aluminothermic welding sand mold riser according to claim 1, characterized in that: The lower surface of the sand mold contour includes a first side line, a second side line and a horizontal line connected between the first side line and the second side line. When the first riser and the second riser are both circular, the distance from the center of the first riser to the first side line is d3, 12.25mm≤d3≤14.25mm, the distance from the center of the second riser to the second side line is d4, 12.25mm≤d4≤14.25mm, the shortest distances from the center of the first riser and the center of the second riser to the horizontal line where the center of the horizontal line is located are both 12.25mm, and the diameters of the first riser and the second riser are both D, 8.5mm≤D<12.5mm.

5. A method for preheating aluminothermic welding sand mold riser, for testing the aluminothermic welding sand mold riser according to any one of claims 1 to 4, characterized in that: It includes a preheating simulation test and a preheating test process, and the preheating simulation test includes the following steps: Step 1: Establish a solid model of the sand mold with the aluminothermic welding sand mold riser and the rail to be welded at a ratio of 1:1 and perform mesh division of the fluid domain model; Step 2: Setting the combustion temperature and fluid-solid coupling thermal simulation method; Step 3: Set the heating time and enter iterative calculation; Step 4: Analyze the flow field simulation results; Step 5: Analyze the preheating simulation results; The preheating test process comprises the following steps: Step 1: Make a temperature measuring rail for testing; Step 2: Pre-embed the thermocouple and connect the temperature detector; Step 3: Set various preheating parameters, conduct preheating test, and measure the temperature; Step 4: Analyze the test results to determine whether they are consistent with the simulated temperature distribution results.

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