Welding process of track joint

Abstract

The invention relates to a welding process for a rail joint. The welding process comprises the following steps: S1, welding for the first time; s2, slotting the surface of the welding seam; s3, welding for the second time; s4, repairing and cutting after welding; according to the welding process, after a splicing seam formed by butt joint of rail square steel base metal serves as a first groove to be welded for the first time, a notch is formed in the top face of a first welding seam, second welding is conducted on the notch to form a second welding seam, and a fusion line of the first welding seam and the base metal is covered with the second welding seam; two welding process parameters and the sizes of a splicing seam and a notch are optimally designed, so that cost increase, deformation and residual stress generation caused by transition welding or performance deterioration caused by insufficient welding are effectively avoided, the hardness and tensile strength of a welding seam are ensured, and the welding quality is improved through detection. The surface hardness, the impact resistance and the tensile strength of a rail joint formed by welding are higher than those of a square steel base material, and the effect is excellent and remarkable.

Description

Technical Field

[0001] This invention relates to the field of rail welding technology, and more particularly to a welding process for rail joints. Background Technology

[0002] The rails of a rail-mounted gantry crane are constructed from spliced ​​square steel bars. During manufacturing, adjacent square steel bars are typically butted together to form a narrow joint, which is then used as a bevel for welding. For example, Chinese invention patent CN110860768B discloses a welding process between the rail-mounted gantry crane's main beam and the square steel rails. In this process, a steel backing is placed at the butt joint of the square steel rails. Preheating to 80-120℃ is performed before welding. Manual arc welding and welding rods are used to weld the butt joint ends of the rails, with the interpass temperature controlled at 100-120℃. After welding, the rail weld is treated by hammering. The steel backing is removed, and the excess weld height is ground away to ensure a smooth transition and a consistent shape between the joint and the square steel rail. However, when this welding process was used to weld the square steel rails, performance testing revealed a decrease in surface hardness, falling below the hardness of the base material, and the tensile strength also failed to meet the standard of not being lower than the tensile strength of the base steel.

[0003] Therefore, this invention proposes a welding process for track joints to solve the above problems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a welding process for a rail joint that improves the surface hardness and tensile strength of the weld, so as to meet the requirements that the surface hardness of the weld is not lower than that of the base material and the tensile strength of the weld is not lower than that of the base material.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is: a welding process for a track joint, the innovation of which is: including the following steps: S1. First welding: The square steel base material of the track is butted to form a splice with a gap of d1, and a steel backing plate is placed under the splice. Then, the splice is used as the first bevel for the first welding. The first welding is carried out by manual arc welding and welding rod. The first weld is formed in the splice. The first weld includes a root weld layer, a filler weld layer and a cover weld layer formed from bottom to top. The root weld layer and the cover weld layer are both single-layer multi-pass welding, and the filler weld layer is multi-layer multi-pass welding. S2. Grooving on the weld surface: A groove with a width of d2 and a depth of h is formed along the length of the rail square steel base material at the top surface of the first weld. The two ends of the groove extend to the upper surface of the rail square steel base material. S3. Second welding: The groove is used as the second bevel for the second welding. The second welding is done by manual arc welding and welding rod. The second weld is formed in the groove. The second weld is made by single-layer multi-pass welding. The second weld and the first weld are combined to form a T-shaped weld. S4. Post-weld repair: The second weld is treated by hammering. After treatment, the steel backing plate is cut off, and the part of the T-shaped weld that protrudes from the rail square steel base is ground off to make the T-shaped weld consistent with the shape of the rail square steel base and smoothly transition.

[0006] Furthermore, the minimum preheating temperature during the first welding is 120°C, the maximum interpass temperature is 168°C, and the welding heat input is 1.51~2.71 kJ / mm. The welding conditions for the root pass are: welding current 170A, voltage 27~28V, welding speed 80~120mm / min; The welding conditions for the filler layer are: welding current 169~170A, voltage 28~29V, welding speed 90~130mm / min; The welding conditions for the cover weld layer are: welding current 169A, voltage 28~29V, welding speed 130~150mm / min.

[0007] Furthermore, the minimum preheating temperature for the second welding is 85°C, the maximum interpass temperature is 150°C, and the welding heat input is 1.46~2.12kJ / mm; the welding conditions for the second welding are welding current 180A, voltage 29V, and welding speed 140~150mm / min.

[0008] Furthermore, d1 is 20~25mm.

[0009] Furthermore, d2 is 5 to 6 times d1.

[0010] Furthermore, h is 2~3 mm.

[0011] The advantages of this invention are: The welding process of this invention uses the joint formed by butt welding of the square steel base material of the track as the first bevel for the first welding. Then, a groove is opened on the top surface of the first weld, and a second welding is performed on the groove to form a second weld, covering the fusion line between the first weld and the base material. By optimizing the design of the two welding process parameters and the dimensions of the joint and groove, the increased cost, deformation and residual stress caused by over-welding or the performance degradation caused by insufficient welding are effectively avoided. The hardness and tensile strength of the weld are guaranteed. Through testing, the surface hardness, impact resistance and tensile strength of the rail joint formed by welding are higher than those of the square steel base material, and the effect is excellent and significant. Attached Figure Description

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0013] Figure 1 This is a schematic diagram of the joint formed by butt welding of the track square steel base material according to the present invention.

[0014] Figure 2 This is a schematic diagram of the weld bead distribution of the first weld seam of the present invention.

[0015] Figure 3 This is a schematic diagram of the groove being opened at the top surface of the first weld in accordance with the present invention.

[0016] Figure 4 This is a schematic diagram of the weld bead distribution of the second weld seam in this invention.

[0017] Figure 5 This is a schematic diagram of the test location during the hardness test of this invention. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] Example This embodiment provides a welding process for a rail joint, including the following steps: S1. First welding: Butt weld the square steel base material 1 of the track to form a splice with a gap d1 of 23mm, and place a steel backing plate 2 under the splice. Figure 1 As shown, the first weld is then performed using the joint as the first bevel. The first weld is performed using manual arc welding and welding rods, forming the first weld 3 within the joint, as shown. Figure 2 As shown, the first weld seam includes a root pass, a fill pass, and a cover pass formed sequentially from bottom to top. The root pass and the cover pass are both single-layer multi-pass welds, while the fill pass is multi-layer multi-pass welded.

[0020] The track square steel base material is 30Mn2 alloy steel with a tensile strength of 830-840MPa, an energy absorption value (20℃) of 28~33J, and a surface hardness of 248~256HB; the steel liner plate is made of Q355B steel plate with a thickness of 8mm; the welding rod grade is CHE857 with a diameter of 4mm, the minimum preheating temperature for the first welding is 120℃, the maximum interpass temperature is 168℃, and the welding heat input is 1.51~2.71kJ / mm.

[0021] The welding conditions for the root pass, fill pass, and cap pass are shown in Table 1.

[0022] Table 1 Welding condition parameters for root pass, filler pass, and cap pass. S2. Grooving on the weld surface: A groove 4 with a width d2 of 120mm and a depth h of 2mm is formed along the length of the track square steel base material at the top surface of the first weld 3. The two ends of the groove 4 extend to the upper surface of the track square steel base material, such as... Figure 3 As shown; S3. Second Welding: The groove 4 is used as the second bevel for the second welding. The second welding is performed using manual arc welding and welding rods, forming a second weld within the groove 4. Figure 4 As shown, the second weld is a single-layer multi-pass weld, and the second weld and the first weld together form a T-shaped weld; The same welding rods were used for the second welding. The minimum preheating temperature for the second welding was 85℃, the maximum interpass temperature was 150℃, and the welding heat input was 1.46~2.12kJ / mm. The welding conditions for the second welding are shown in Table 2.

[0023] Table 2 Welding condition parameters for the second weld S4. Post-weld repair: The second weld is treated by hammering. After treatment, the steel backing plate is cut off, and the part of the T-shaped weld that protrudes from the rail square steel base material is ground off to make the T-shaped weld consistent with the shape of the rail square steel base material and smoothly transition. The welding is completed to form the rail joint.

[0024] After the welded rail joints passed the flaw detection test, samples were taken from the rail joints for tensile, impact, and hardness tests. The test results are shown in Tables 3, 4, and 5, respectively. The sampling locations for the hardness tests are shown in Tables 3, 4, and 5. Figure 5 .

[0025] Table 3 Tensile test results of the examples Table 4 Impact Test Results of Examples Table 5 Hardness test results of the examples In this embodiment, the welding process involves first welding the joint formed by butt welding of the square steel base material of the track as the first bevel. Then, a groove is opened on the top surface of the first weld, and a second weld is formed at the groove, covering the fusion line between the first weld and the base material. By optimizing the design of the two welding process parameters and the dimensions of the joint and groove, the increased cost, deformation, and residual stress caused by over-welding or the performance degradation caused by insufficient welding are effectively avoided. The hardness and tensile strength of the weld are guaranteed. Through testing, the surface hardness, impact resistance, and tensile strength of the rail joint formed by welding are all higher than those of the square steel base material, and the effect is excellent and significant.

[0026] Comparative Example This comparative example uses the same rail square steel base material, welding rods, and steel liner plate as Example 1 to complete the rail joint welding. The welding process includes the following steps: The track square steel base materials are butt-jointed to form a splice with a gap d1 of 23mm. A steel backing plate is placed under the splice. Then, welding is performed using the splice as a bevel. Welding is carried out using manual arc welding and welding rods. The weld is formed within the splice and includes a root pass, a fill pass, and a cap pass, formed sequentially from bottom to top. The root pass and cap pass are both single-layer multi-pass welds, while the fill pass is multi-layer multi-pass welded. The minimum preheating temperature, maximum interpass temperature, welding heat input, and welding conditions for the root pass, fill pass, and cap pass within the weld are the same as in Example 1. After welding, the weld is treated by hammering. After treatment, the steel backing plate is cut off, and the part of the weld protruding from the track square steel base material is ground off to make the weld consistent with the shape of the track square steel base material and have a smooth transition.

[0027] The hardness and tensile strength of the rail joints obtained in this comparative example were tested, and the test results are shown in Tables 6 and 7.

[0028] Table 6 Comparative tensile test results Table 7 Comparative Hardness Test Results The test results in Tables 6 and 7 show that when only one welding is performed at the joint, the hardness and tensile strength of the track joint are lower than those of the base material, and thus cannot meet the performance requirements.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A welding process for a rail joint, characterized in that: Includes the following steps: S1. First welding: The square steel base material of the track is butted to form a splice with a gap of d1, and a steel backing plate is placed under the splice. Then, the splice is used as the first bevel for the first welding. The first welding is carried out by manual arc welding and welding rod. The first weld is formed in the splice. The first weld includes a root weld layer, a filler weld layer and a cover weld layer formed from bottom to top. The root weld layer and the cover weld layer are both single-layer multi-pass welding, and the filler weld layer is multi-layer multi-pass welding. S2. Grooving on the weld surface: A groove with a width of d2 and a depth of h is formed along the length of the rail square steel base material at the top surface of the first weld. The two ends of the groove extend to the upper surface of the rail square steel base material. S3. Second welding: The groove is used as the second bevel for the second welding. The second welding is done by manual arc welding and welding rod. The second weld is formed in the groove. The second weld is made by single-layer multi-pass welding. The second weld and the first weld are combined to form a T-shaped weld. S4. Post-weld repair: The second weld is treated by hammering. After treatment, the steel backing plate is cut off, and the part of the T-shaped weld that protrudes from the rail square steel base is ground off to make the T-shaped weld consistent with the shape of the rail square steel base and smoothly transition.

2. The welding process for the track joint according to claim 1, characterized in that: The minimum preheating temperature for the first welding is 120°C, the maximum interpass temperature is 168°C, and the welding heat input is 1.51~2.71 kJ / mm. The welding conditions for the root pass are: welding current 170A, voltage 27~28V, welding speed 80~120mm / min; The welding conditions for the filler layer are: welding current 169~170A, voltage 28~29V, welding speed 90~130mm / min; The welding conditions for the cover weld layer are: welding current 169A, voltage 28~29V, welding speed 130~150mm / min.

3. The welding process for the track joint according to claim 1, characterized in that: The minimum preheating temperature for the second welding is 85℃, the maximum interpass temperature is 150℃, and the welding heat input is 1.46~2.12kJ / mm. The welding conditions for the second welding are welding current 180A, voltage 29V, and welding speed 140~150mm / min.

4. The welding process for the track joint according to claim 1, characterized in that: The value of d1 is 20~25mm.

5. The welding process for the track joint according to claim 4, characterized in that: The d2 is 5 to 6 times that of the d1.

6. The welding process for the track joint according to claim 1, characterized in that: The value of h is 2~3 mm.

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