A post-weld rail head grinding method for vertical grinding rail aluminum heat welded joints

Abstract

The application provides a post-weld rail top surface grinding method for vertical grinding rail aluminum hot welding joints; wherein two rails to be welded, the rail 1 with relatively light vertical grinding degree or the new rail, and the rail 2 with relatively serious vertical grinding degree, are aligned in the rail bottom alignment mode before aluminum hot welding; the post-weld grinding method comprises the following steps: I, post-weld joint arching amount measurement, II, determination of the grinding length and depth of the rail 1, III, grinding of the joint and the near-end rail of the rail 1, IV, grinding of the far-end rail of the rail 1, V, determination of the grinding effect of the rail 1 and VI, grinding of the rail 2. The grinding method provides post-weld grinding data support for the aluminum hot welding joints under different vertical grinding conditions, and is of great significance for reducing the operation difficulty, standardizing the on-site operation, improving the post-weld joint quality and the rail tread smoothness.

Description

Technical Field

[0001] This invention belongs to the field of rail welding technology, specifically relating to a method for grinding the top surface of a rail after welding aluminothermic welded joints. Background Technology

[0002] Aluminothermic welding technology for rails is one of the important welding technologies for seamless railway rails. It is applied in jointing, turnouts, locking welding, stress relief on existing lines, emergency rail repair, and routine rail replacement. Its advantages include simple equipment, short operation time, and small space occupation. When repairing damage on existing lines, to adapt to maintenance windows, an insertion welding method is commonly used. This involves sawing off a section of pre-fitted rail at the damaged location and inserting it, then performing aluminothermic welding at both ends to create two new aluminothermic weld joints. With the continuous increase in newly built railway lines and the lengthening of operating time on existing lines in recent years, the number of aluminothermic weld joints has been increasing. Statistics show that in 2022, approximately 200,000 rail damage repairs were performed on existing lines nationwide, of which over 170,000 were aluminothermic welds, dominating the repair work on existing lines.

[0003] Joint grinding is the final step in aluminothermic welding of rails, playing a crucial role in joint quality, service life, and track smoothness. Ren Jinlei et al. designed grinding schemes, including grinding length and depth, for different original joint conditions based on the requirements for straightness and surface unevenness of aluminothermic welded joints when the line design speed v>160km / h. They quantified grinding parameters and reduced unnecessary grinding of the rails. The scheme has been initially applied (Ren Jinlei, Song Hongtu, Gao Songfu. Design of Grinding Scheme for Aluminothermic Welded Joints of High-Speed ​​Railway Rails in "Four Lines and Five Categories" [J]. Railway Technical Supervision, 2021, 49(8): 48-55). This scheme is for post-weld grinding of aluminothermic welded joints of standard profile rails, where there is no wear on the rail treads and working edges on both sides of the joint, and no height difference.

[0004] In practice, during emergency repairs of existing damaged railway lines, it is common to encounter rail welding with vertical wear (wear along the height of the rail): either the existing rails have vertical wear, but the rail used for insertion welding is a new rail; or the existing rails do not have vertical wear, but the rail used for insertion welding is a rail with vertical wear; or both the existing rails and the rails have vertical wear, but the amount of vertical wear differs. The inventor conducted a survey of some railway bureaus in China, and the results show that the wear phenomenon of rails used for insertion welding is currently widespread. Taking the weekly welding plan of a certain engineering section as an example: a total of 96 aluminothermic welds were recorded that week, and the vast majority of the inserted rails used for welding had vertical wear. Among them, the number of welded joints using rails with vertical wear of 1mm was 19, accounting for 20%; the number of welded joints using rails with vertical wear of 2mm was 35, accounting for 36%; and the number of welded joints using rails with vertical wear of 3mm was 28, accounting for 29%. The inventors also investigated the rail sagging situation on some existing railway lines in China. The results showed that rail sagging of 0-5mm was common, with 0-3mm being the most prevalent. The post-weld grinding scheme proposed by Ren Jinlei et al. for aluminothermic welded joints of standard profile rails is clearly not applicable to the prevalent sagging rail welding in practice. Currently, there are almost no specific process specifications for post-weld grinding of sagging rail welded joints within railway bureaus and stations in China, and the process mainly relies on the experience of on-site workers. Due to the diverse nature of sagging rail conditions, post-weld grinding operations are difficult to perform during emergency repairs during track maintenance windows, lack standardized operating methods, and the quality of the welded joints is hard to guarantee. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for grinding the top surface of the rail after welding aluminothermic welded joints in vertical grinding, based on preliminary research data and the requirements of relevant standards and specifications. This method provides post-weld grinding data support for aluminothermic welded joints under different vertical grinding conditions, which is of great significance for reducing operational difficulty, standardizing on-site operations, improving the quality of post-weld joints, and enhancing the smoothness of the rail tread.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A method for grinding the top surface of aluminothermic welded joints of steel rails after welding; wherein the two rails to be welded are, respectively, rail 1 (with relatively less sagging or a new rail) and rail 2 (with relatively more severe sagging), and before aluminothermic welding, rail 1 and rail 2 are aligned by aligning their bottoms; the post-weld grinding method includes the following steps:

[0008] I. Measurement of post-weld joint camber

[0009] Place a 1m notched straightedge on the rail tread, aligning the 0 mark with the center of the weld. Use a feeler gauge or gap gauge to measure the camber a on one side of rail 1, in mm / m.

[0010] II. Determine the grinding length and depth of rail 1.

[0011] If 0 < a ≤ 0.4 mm / m, the grinding depth H of rail 1 is calculated using formula (1)-1, and the grinding length L of rail 1 is calculated using formula (1)-2:

[0012] H = h0 (1) - 1,

[0013]

[0014] If a > 0.4 mm / m, use formula (2)-1 to calculate the grinding depth H of rail 1, and use formula (2)-2 to calculate the grinding length L of rail 1:

[0015] H=h0+Q(a-0.4) (2)-1,

[0016]

[0017] In the above formulas (1)-1, (1)-2, (2)-1 and (2)-2,

[0018] h0 represents the height difference between the rail heads of rail 1 and rail 2 before welding, in mm.

[0019] Q is a constant, Q = 1m.

[0020] a f The target straightness of the joint and near end after grinding of rail 1 is set, in mm / m, and 0.1≤a f ≤0.4mm / m,

[0021] t is the slope of the far end of rail 1, and t = 0.4 mm / m;

[0022] In formulas (1)-2 and (2)-2, The near-end grinding length L of rail 1 近 , or Grinding length L at the far end of rail 1 远 ;

[0023] III. Grinding the joint and the near end of rail 1.

[0024] First, based on the calculated grinding depth H and proximal grinding length L... 近 Mark the near end of the grinding process, and then use a grinder to grind the center of the weld and the near end of rail 1 to the near end of the grinding process.

[0025] IV. Grinding rail 1, far end rail

[0026] First, based on the calculated distal grinding length L... 远Mark the end point of the far end grinding, and then use a grinder to grind from the end point of the near end grinding towards the end point of the far end grinding of rail 1.

[0027] V. Determine the grinding effect of rail 1

[0028] During and after grinding, the straightness of the weld and rail 1 is continuously measured using a 1m straightedge or SRC electronic straightedge until the straightness meets the standard requirements.

[0029] VI. Grinding rail 2

[0030] Rail 2 is polished using conventional methods until it meets the standard requirements for flatness.

[0031] In step I, the actual measured value of the camber a is retained to one decimal place, such as 0.1mm / m, 0.2mm / m, 0.3mm / m, 0.4mm / m, 0.5mm / m, 0.6mm / m, 0.7mm / m, 0.8mm / m, 0.9mm / m, etc.

[0032] In the above grinding method, the two rails to be welded are classified as rail 1 and rail 2 according to their relative degree of sag. Rail 1 is the rail with less sag or is newer, while rail 2 has a more severe sag. Therefore, after aluminothermic welding using the rail bottom alignment method, there is a height difference between rail 1 and rail 2 on both sides of the joint tread surface, with rail 1 being higher than rail 2. Figure 4 As shown.

[0033] Preferably, in steps III and IV, a contour grinder or a circumferential grinder is used for grinding.

[0034] Preferably, in steps V and VI, the standard is TB / T 1632.1-2014 "Rail Welding Part 1: General Technical Conditions".

[0035] The specific requirements in the above standard are: No low joints should appear within a 1m length of the working surface of the rail head of the welded rail joint. When the design speed of the line v≤160km / h, 0.1≤a1≤0.4, 0≤b1≤0.3 or 0≤b2≤0.3. (a1 represents the straightness of the top surface of the rail head, b1 and b2 represent the straightness of the working side edges, where a positive value for b1 indicates a wider gauge, and a positive value for b2 indicates a smaller gauge; the unit is mm / m). The grinding depth of the base material should preferably be less than 0.5mm. After the welded joint has been finished, the surface unevenness of the rail head within a 1m range centered on the weld should meet the following requirement: no greater than 0.2mm in any 200mm section.

[0036] As a preferred embodiment, in step II, when h0 = 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm or 6mm, and 0.1mm / m ≤ a ≤ 0.9mm / m, the grinding length and depth of rail 1 are determined according to Table 1 below; otherwise, the grinding length and depth of rail 1 are calculated according to formulas (1)-1 and (1)-2, or formulas (2)-1 and (2)-2:

[0037] Table 1 Quick Reference Table for Vertical Grinding of Steel Rails

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] When the total grinding length exceeds half the length of rail 1 due to excessive height difference, it is advisable to pre-assemble or prefabricate rails with small height difference before welding.

[0047] In this manual, "existing line" refers to a concept relative to newly built lines, namely, railway lines that bear a certain amount of traffic and load. Existing lines are in operation, and maintenance time is limited. "Wearing rails" refers to standard profile rails that, after a period of service, exhibit wear along the vertical direction on the rail head tread.

[0048] In this specification, "aluminothermic welding" refers to a method of welding two rail sections together by mixing aluminum powder, iron oxide powder, and ferroalloys in a certain proportion to form an aluminothermic welding flux, igniting it with a high-temperature match to produce molten steel and slag, and then pouring the molten steel into a mold. Aluminothermic welding is also known as cast welding. The main steps of aluminothermic welding are generally: preparation, drying the rails, rust and dirt removal, rail alignment, sand mold installation, clamp installation, sealing the mold, preheating, crucible flux preparation, reaction casting, mold removal, slag removal, and grinding. The grinding method described in this invention is the final step in the aluminothermic welding process.

[0049] The term "joint grinding" or "joint grinding" refers to the use of a grinding machine to repair the aluminothermic welded joint and the steel rail base material on both sides so that its surface quality meets the standard requirements.

[0050] In this manual, the terms "near end" or "far end" for rails refer to those relative to the weld center. Rails closer to the weld center are considered "near end," while those farther away are considered "far end." Attached Figure Description

[0051] The present invention will be further described below with reference to the accompanying drawings.

[0052] Figure 1 The image shows rails 1 and 2 aligned with their bottom edges in Example 1. A: A 3D view of the aligned rails, and B: A photograph of the actual object.

[0053] Figure 2 The photo shows the installation of the sand mold after rails 1 and 2 are aligned in Example 1.

[0054] Figure 3 The photograph shows the welded head rail bottom in Embodiment 1 after welding.

[0055] Figure 4 The photograph shows the macroscopic state of the weld head tread after the aluminothermic welding butt push-off is completed in Example 1.

[0056] Figure 5 The diagram shown is a schematic of measuring the amount of camber in the welded joint after welding using a notched straightedge in Example 1.

[0057] Figure 6 The diagram shown is a schematic of grinding the weld and rail 1 in Example 1, where A: grinding is performed using an end face grinder, and B: grinding is performed using a circumferential surface grinder.

[0058] Figure 7 The diagram shown is a schematic of the rail after grinding in Example 1. The broken line segment at the top represents the overall trend of the rail tread: point -1 is the grinding end point on one side of rail 2, point 0 is the weld center, point 1 is the grinding end point near the end of rail 1, and point 2 is the grinding end point far from the end of rail 1.

[0059] Figure 8 The photos show the two rails on both sides centered on the weld head after grinding in Example 1. A: A photo taken from an oblique side, and B: A photo taken directly facing the weld.

[0060] In the above figures, 1: track 1; 2: track 2. Detailed Implementation

[0061] The present invention will be described below with reference to specific embodiments. Those skilled in the art will understand that these embodiments are for illustrative purposes only and do not limit the scope of the invention in any way.

[0062] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products.

[0063] In the following embodiments, ZTK-1 type aluminothermic welding material (Beijing CRRC New Material Technology Co., Ltd.) was used, with flux type T3. Both sections of rail being welded were 60kg / m U71Mn H steel rails, one being a new rail (rail 1) and the other a ground rail (rail 2). The height differences between rail 1 and rail 2 were 3mm, 6mm, and 9mm, respectively. Welding tools included a dedicated preheating device, sand mold clamps, alignment equipment, rail saw, buttress remover, and grinder.

[0064] All welding process parameters follow the specifications in the aluminothermic welding operation manual provided by the manufacturer, with a rail gap of 28-30mm reserved. Using a rail base alignment method, there is no difference in profile between the two ends of the rail to be welded in the height direction; therefore, standard profile sand molds can be used for welding.

[0065] During rail alignment, using the rail base as a reference, adjust the camber of both rails to 1.5–2 mm / m. The specific method is as follows: Place a 1m straightedge at the rail base corner, with the 0 mark at the center of the rail gap. Use a specialized rail alignment device such as an A-frame, wedges, or rail lifter to adjust the height of both rails. During adjustment, use a feeler gauge or gap gauge to measure the camber until the set value is met.

[0066] After the rails are aligned, the sand mold is installed. The preheater support is placed at one end of rail 1, with a height of 50mm. The preheating gas pressure is 0.3MPa for oxygen and 0.1MPa for propane. The preheater height is 50mm, and the preheating time is 4 minutes. After pouring, the mold is removed after 6 minutes and 30 seconds, and the lumps are pushed out after 8 minutes and 30 seconds. After welding, there is a height difference between the base material on both sides of the joint tread.

[0067] Example 1: Grinding method for the top surface of rails 1 and 2 after aluminothermic welding with a height difference of 3mm.

[0068] During aluminothermic welding, rails 1 and 2 are aligned with their bases. See the completed 3D model and physical image. Figure 1 After the rails are aligned, install the clamping sand mold, such as... Figure 2 As shown. From Figure 2 It can be seen that after using the standard profile sand mold for mounting, although the rail head tread of rail 2 (vertical ground rail) is generally lower than that of rail 1 (new rail), the sand mold does not tilt, and the rail bottom fits well with the base plate. The welded joint rail bottom looks like... Figure 3 As shown, no overflow burrs were generated at the bottom of the welded joint. Figure 4 As shown, after welding, there is a height difference between rail 1 and rail 2 on both sides of the welded joint tread surface, with rail 1 being higher and rail 2 lower. Post-weld grinding should be performed according to the following steps.

[0069] I. Measurement of post-weld joint camber

[0070] like Figure 5 As shown, a 1m notched straightedge is placed on the rail tread, with the 0 mark aligned with the center of the weld. The camber a on one side of rail 1 is measured to be 0.4mm / m using a feeler gauge or gap gauge.

[0071] II. Determine the grinding length and depth of rail 1.

[0072] Because the measured value of a = 0.4 mm / m, a is set as follows: f =0.4mm / m, the grinding depth H of rail 1 is calculated using formula (1)-1, and the grinding length L of rail 1 is calculated using formula (1)-2:

[0073] H = h0 (1) - 1,

[0074]

[0075] Where h0 is the height difference between the rail heads of rail 1 and rail 2 before welding, in mm; here h0 = 3 mm.

[0076] Q is a constant, Q = 1m;

[0077] a f The target joint and near-end straightness after grinding of rail 1 are specified, in mm / m; here a f =0.4mm / m,

[0078] t is the slope of the far end of rail 1, and t = 0.4 mm / m;

[0079] In formula (1)-2, The near-end grinding length L of rail 1 近 , Grinding length L at the far end of rail 1 远 ;

[0080] Calculations show that H = 3 mm and L 近 =1m, L 远 =7.5m, total grinding length L=8.5mm.

[0081] Referring to Table 1, we can quickly determine: H = 3mm, L 近 =1m, L 远 =7.5m, total grinding length L=8.5mm.

[0082] III. Grinding the joint and the near end of rail 1.

[0083] First, based on the calculated grinding depth H and proximal grinding length L... 近 Mark the end point of the polishing process at the proximal end, and then... Figure 6 The center of the weld and the near end of rail 1 are ground using a profile grinder or a peripheral grinder to the near end of the grinding.

[0084] IV. Grinding rail 1, far end rail

[0085] First, based on the calculated distal grinding length L... 远 Mark the end point of the grinding process, and then use a profile grinder or a peripheral grinder to grind from the near end point of the grinding process to the far end point of the grinding process.

[0086] V. Determine the polishing effect

[0087] During and after grinding, the straightness of the weld and rail 1 is continuously measured using a 1m straightedge or SRC electronic straightedge until the requirements are met.

[0088] VI. Grinding of Rail 2

[0089] Rail 2 is polished using conventional methods until it meets the standard requirements for flatness.

[0090] A schematic diagram of the rail after grinding and the overall trend of the rail tread surface are shown below. Figure 7 After grinding, the steel rails on both sides centered on the weld joint are visible. Figure 8 As shown in the photo. Figure 7 As shown, the rail as a whole exhibits a certain amount of camber on both sides of the weld. On the rail 1 (new rail) side, the rail transitions from the far end to the near end of the grinding endpoint with a certain slope. Figure 8 The results show that rails 1 and 2 are straight after grinding.

[0091] Example 2: Grinding method for the top surface of rails 1 and 2 after aluminothermic welding with a height difference of 6mm.

[0092] Post-weld grinding was performed following the same steps as in Example 1, except that in step I, the camber a on one side of rail 1 was measured to be 0.3 mm / m, and a was set to... f =0.3mm / m, calculated using formulas (1)-1 and (1)-2, H = 6mm, L 近 =1mm, L 远 =15mm, total grinding length L=16mm. The same grinding parameters can also be quickly obtained by referring to Table 1.

[0093] Example 3: Grinding method for the top surface of rails 1 and 2 after aluminothermic welding with a height difference of 9mm.

[0094] The post-weld grinding was performed following the same steps as in Example 1, except that in step I, the camber a on one side of the measuring rail 1 was set to 0.5 mm / m. f =0.4mm / m, using formulas (2)-1 and (2)-2:

[0095] H=h0+Q(a-0.4) (2)-1,

[0096]

[0097] Where h0 is the height difference between the rail heads of rail 1 and rail 2 before welding, in mm; here h0 = 9 mm.

[0098] Q is a constant, Q = 1m;

[0099] a f The target joint and near-end straightness after grinding of rail 1 are specified, in mm / m; here a f =0.4mm / m,

[0100] t is the slope of the far end of rail 1, and t = 0.4 mm / m;

[0101] The near-end grinding length L of rail 1 近 , Grinding length L at the far end of rail 1 远 .

[0102] Calculate H = 9.1 mm, L 近 =1.25m, L 远 =22.75m, total grinding length L=24mm.

[0103] Because the height difference h0 between rail 1 and rail 2 is 9mm, which exceeds the range listed in Table 1, the grinding parameters can only be calculated using formulas.

[0104] In summary, this invention provides a method for grinding the top surface of the rail after welding aluminothermic welded joints in vertical grinding. This method provides post-weld grinding data support for aluminothermic welded joints under different vertical grinding conditions, which is of great significance for reducing operational difficulty, standardizing on-site operations, improving the quality of post-weld joints, and improving the smoothness of the rail tread.

Claims

1. A method for grinding the top surface of aluminothermic welded joints of steel rails after welding; wherein the two rails to be welded are designated as rail 1 (relatively less worn or new) and rail 2 (relatively more worn); before aluminothermic welding, rail 1 and rail 2 are aligned by aligning their bottoms; the grinding method includes the following steps: I. Measurement of post-weld joint camber Place a 1 m notched straightedge on the rail tread, aligning the 0 mark with the center of the weld. Use a feeler gauge or gap gauge to measure the camber a on one side of rail 1, in mm / m. II. Determine the grinding length and depth of rail 1. If 0 < a ≤ 0.4 mm / m, the grinding depth H of rail 1 is calculated using formula (1)-1, and the grinding length L of rail 1 is calculated using formula (1)-2: （1）-1， （1）-2； If a > 0.4 mm / m, the grinding depth H of rail 1 is calculated using formula (2)-1, and the grinding length L of rail 1 is calculated using formula (2)-2: （2）-1， （2）-2； In the above formulas (1)-1, (1)-2, (2)-1 and (2)-2, h0 represents the height difference between the rail heads of rail 1 and rail 2 before welding, in mm. Q is a constant, Q = 1m a f The target straightness of the joint and near end after grinding of rail 1 is set, in mm / m, and 0.1≤a f ≤0.4 mm / m, t is the slope of the far end of rail 1, and t = 0.4 mm / m; In the formulas (1)-2 and (2)-2, The near-end grinding length of rail 1 , Grinding length of the far end of rail 1 ; III. Grinding the joint and the near end of rail 1. First, based on the calculated grinding depth H and proximal grinding length... Mark the near end of the grinding process, and then use a grinder to grind the center of the weld and the near end of rail 1 to the near end of the grinding process. IV. Grinding rail 1, far end rail First, based on the calculated distal grinding length... Mark the end point of the far end grinding, and then use a grinder to grind from the end point of the near end grinding towards the end point of the far end grinding of rail 1. V. Determine the grinding effect of rail 1 During and after grinding, the straightness of the weld and rail 1 is continuously measured using a 1 m straightedge or SRC electronic straightedge until the straightness meets the standard requirements. VI. Grinding rail 2 Rail 2 is polished using conventional methods until it meets the standard requirements for flatness.

2. The polishing method according to claim 1, characterized in that, In steps III and IV, a contour grinder or a circumferential grinder is used for grinding.

3. The polishing method according to claim 1 or 2, characterized in that, In steps V and VI, the standard is TB / T 1632.1-2014 "Rail Welding Part 1: General Technical Conditions".

4. The polishing method according to claim 1, characterized in that, In step II, when h0 = 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm or 6mm, and 0.1mm / m ≤ a ≤ 0.9mm / m, the grinding length and depth of rail 1 are determined according to the following table; otherwise, the grinding length and depth of rail 1 are calculated according to formulas (1)-1 and (1)-2, or formulas (2)-1 and (2)-2: 。

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