A method for repairing defects of a ductile cast iron gear case

Abstract

The application relates to a nodular cast iron gear box body defect repair welding method, which comprises the following steps: S1, defect removal: removing rust and oil stains at the bottom corner defect position and the periphery of the box body through an angular grinder, and leaking out metal luster; S2, assembling: spot welding an L-shaped coaming at the bottom corner defect position of the box body; S3, preheating: preheating the bottom corner defect position of the box body by using an oxyacetylene flame; S4, defect site repair welding: according to selected welding process parameters, first welding a transition layer at the bottom corner defect position of the box body, and then filling a surfacing layer between the transition layer and the coaming; S5, post-welding treatment: polishing the welding seam surface to be flush with the original gear box body surface, cleaning the welding seam and surrounding spatters after the welding seam metal cools to room temperature; and S6, flaw detection: performing color flaw detection inspection on the repaired area after 24 hours of welding. The application effectively solves the process problem that cracks or peeling is prone to occur at the fusion zone after the nodular cast iron gear box body is welded, improves the welding quality and production efficiency, and saves the repair cost.

Description

Technical Field

[0001] This invention relates to the field of welding repair technology for ductile iron gearbox housings, and particularly to a method for welding repair of defects in ductile iron gearboxes. Background Technology

[0002] During locomotive maintenance, at the four corners of the base of the cast iron gearbox housing, along the mounting holes, positioning holes, or due to hoisting, disassembly, or other reasons, the base corners are often missing, such as... Figure 1 As shown.

[0003] Traditional welding repair methods use nickel-based welding rods, which are inefficient, expensive, and prone to cracking or peeling in the fusion zone after welding. Therefore, a simple, efficient, and low-cost welding method is needed for the repair of cast iron gearbox housings. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for repairing defects in ductile iron gearboxes by welding. This method effectively solves the problem of cracks or peeling easily occurring in the fusion zone after welding of the ductile iron gearbox body, improves welding quality and production efficiency, and saves repair costs.

[0005] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a method for welding repair of defects in ductile iron gearbox housings, comprising the following steps: S1. Defect removal: Remove rust and oil stains from the bottom corners and surrounding areas of the housing using an angle grinder to reveal the metallic luster. S2. Assembly: Spot weld an L-shaped panel at the bottom corner defect of the box body; S3: Preheating: Preheat the defective area at the bottom corner of the box with an oxyacetylene flame at a temperature of 500℃~600℃. S4: Repair welding of defective areas: According to the selected welding process parameters, first weld a transition layer at the bottom corner defect of the enclosure. The thickness of the transition layer should be 9-11mm. Then, fill the gap between the transition layer and the surrounding plate with a weld overlay layer. S5: Post-weld treatment: Grind the weld surface to be flush with the original gearbox housing surface. Areas with missing material or poor fusion need to be repaired by secondary welding. After completion, use asbestos cloth to insulate the welding area. After the weld metal cools to room temperature, clean the weld and surrounding spatter. S6: Flaw detection: Perform dye penetrant testing on the repaired area 24 hours after welding.

[0006] As a preferred embodiment, in step S2, a groove is provided at the bottom corner defect of the box body to cooperate with both ends of the enclosure.

[0007] As a preferred embodiment, the welding process parameters in step S4 are as follows: Transition layer: Shielded metal arc welding (SMAW) is used; power supply polarity: DC reverse polarity; electrode diameter: 3.2mm; current selection: I = 70-90A; Weld overlay: CO2 gas shielded welding; power supply polarity: DC reverse polarity; welding wire diameter: 1.2mm; current selection: I = 120-140A; voltage selection: U = 19-21V.

[0008] As a preferred option, the transition layer is welded using multi-layer, multi-pass welding, and the interpass temperature is controlled to be no less than 300℃.

[0009] As a preferred option, the welding of the overlay layer is carried out in multiple layers and multiple passes along the inner wall of the enclosure towards the overlay layer, and the interlayer temperature is controlled to be no less than 300°C. After each layer is welded, the interlayer is cleaned to remove oxides and spatter. At the same time, after each layer is welded, the weld is hammered to relieve stress.

[0010] As a preferred option, during transition layer welding, the angle between the welding rod and the weld overlay surface is controlled between 40° and 50°.

[0011] As a preferred option, the angle between the welding wire and the weld overlay surface is controlled between 40° and 50° during welding of the weld overlay layer.

[0012] As a preferred embodiment, the enclosure is made of 2-3mm low-carbon steel plate.

[0013] The beneficial effects of this application are as follows: 1. This application adopts the method of setting up a surrounding plate, welding the transition layer and the overlay layer according to the selected welding process parameters, and repairing the defects of the gearbox housing by means of preheating before welding, multi-layer and multi-pass welding, controlling the interpass temperature, asbestos cloth insulation, and dye penetrant testing.

[0014] 2. This application uses a welded transition layer, which is welded by shielded metal arc welding. This results in good bonding performance, effectively preventing peeling or cracking while saving expensive welding materials.

[0015] 3. This application uses carbon dioxide gas shielded welding to weld the weld overlay layer, which saves costs, has a fast welding speed, makes it easy to observe the shape of the molten pool, and results in high welding quality.

[0016] 4. By setting up a retaining plate, this application makes the welding operation easier and effectively saves the subsequent shape trimming process, greatly improving work efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the bottom corner defect of the box body in this invention; Figure 2 This is a schematic diagram of the defect at the bottom corner of the box body and the structure of the surrounding panel of the present invention; Figure 3 This is a schematic diagram of the structure of the weld overlay layer of the present invention; Figure 4 This is a schematic diagram of the welding tilt angle structure of the present invention.

[0018] The markings in the diagram are: 1. Gearbox housing, 2. Defect at the bottom corner of the housing, 21. Slot, 3. Enclosure plate, 4. Transition layer, 5. Weld overlay layer, 6. Weld overlay surface, 7. Electric arc. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that, in the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] Please see Figure 1-4 This invention provides a method for welding repair of defects in ductile iron gearbox housings, comprising the following steps: S1. Defect removal: Use an angle grinder to remove rust and oil stains from two defects at the bottom corner of the box and within 30mm of the surrounding area, revealing the metallic luster. S2. Assembly: Spot weld an L-shaped enclosure plate 3 at the bottom corner defect 2 of the box body; S3: Preheating: Preheat the two defects at the bottom corner of the box with an oxyacetylene flame at a temperature of 500℃~600℃. S4: Repair welding of defective areas: According to the selected welding process parameters, first weld the transition layer 4 at the bottom corner defect 2 of the box body. The thickness of the transition layer 4 is 9-11mm. Then, fill and weld the weld overlay layer 5 between the transition layer 4 and the surrounding plate 3. S5: Post-weld treatment: Grind the weld surface to be flush with the original gearbox housing surface. Areas with missing material or poor fusion need to be repaired by secondary welding. After completion, use asbestos cloth to insulate the welding area. After the weld metal cools to room temperature, clean the weld and surrounding spatter. S6: Flaw detection: Perform dye penetrant testing on the repaired area 24 hours after welding.

[0021] In step S2, a groove 21 is provided at the bottom corner defect 2 of the box body to mate with both ends of the surrounding plate 3. Z308 welding rods are used for welding. The shape and dimensions of the surrounding plate 3 are the same as those of the bottom corner defect of the box body. The surrounding plate 3 is made of 2-3mm low-carbon steel plate. It should be noted that any parts not detailed in this application are prior art.

[0022] In step S4, the welding process parameters are as follows: Transition layer 4: Electrode arc welding is used, power supply polarity: DC reverse polarity; electrode diameter 3.2mm; current selection: I = 70-90A; Z308 electrode is used for transition layer 4.

[0023] 5. Overlay layer: CO2 gas shielded welding is used. Power supply polarity: DC reverse polarity; welding wire diameter: 1.2mm; current selection: I = 120-140A; voltage selection: U = 19-21V.

[0024] Specifically, the transition layer 4 is welded using a multi-layer, multi-pass welding method, with each layer being 2-3 mm thick, and the interpass temperature is controlled to be no less than 300℃. The weld overlay layer 5 is welded using a multi-layer, multi-pass welding method, starting from the inner wall of the surrounding plate 3 and moving towards the weld overlay layer 5, with each layer being 2-3 mm thick, and the interpass temperature controlled to be no less than 300℃. After each layer is welded, interpass cleaning is performed to remove oxides and weld spatter. Simultaneously, after each layer is welded, the weld is hammered to relieve stress. In this application, both the transition layer 4 and the weld overlay layer 5 employ multi-layer, multi-pass welding. On the one hand, this effectively heat-treats the previous layer, thereby eliminating welding stress; on the other hand, compared to welding a single pass directly, it significantly reduces welding stress.

[0025] Furthermore, instead of a ceramic backing plate or other non-metallic pad, a metal platform is used during welding to prevent the bottom layer from fusing together with the weld metal. Figure 4 As shown, when welding the transition layer 4, the angle between the welding rod and the weld overlay surface is controlled at 40° to 50°. When welding the weld overlay layer 5, the angle between the welding wire and the weld overlay surface is controlled at 40° to 50°, so that the center of the arc 7 is burned on the weld overlay surface 6 3 to 5 mm above the bottom 1, and the molten iron contacts the platform surface by gravity (but does not fuse together).

[0026] Of course, the present invention is not limited to the embodiments described above. Several other embodiments based on the design concept of the present invention are also provided below.

[0027] For example, in other embodiments, unlike the embodiments described above, the thickness of the transition layer 4 in step S4 is 10 mm.

[0028] For example, in other embodiments, unlike the embodiments described above, when welding the weld overlay layer 5, the welding process parameters for the last layer are: carbon dioxide gas shielded welding, power supply polarity: DC reverse polarity; welding wire diameter: 1.2mm; current selection: I = 160-180A; voltage selection: U = 22-24V. The welding process parameters for other layers are: carbon dioxide gas shielded welding, power supply polarity: DC reverse polarity; welding wire diameter: 1.2mm; current selection: I = 120-140A; voltage selection: U = 19-21V.

[0029] For example, in other embodiments, unlike the embodiments described above, the preheating temperature in step S3 is 500°C.

[0030] For example, in other embodiments, unlike the embodiments described above, the preheating temperature in step S3 is 550°C.

[0031] For example, in other embodiments, unlike the embodiments described above, the preheating temperature is 600°C. It should be noted that the above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for welding repair of defects in ductile iron gearbox housings, characterized in that, Includes the following steps: S1. Defect removal: Remove rust and oil stains from the bottom corner defect (2) and surrounding area of ​​the box using an angle grinder to reveal the metallic luster; S2, Assembly: Spot weld an L-shaped enclosure (3) at the bottom corner defect (2) of the box body; S3: Preheating: Preheat the bottom corner defect (2) of the box body with an oxyacetylene flame at a temperature of 500℃~600℃. S4: Repair welding of defective parts: According to the selected welding process parameters, first weld the transition layer (4) at the bottom corner defect (2) of the box body. The thickness of the transition layer (4) is 9-11mm. Then fill the gap between the transition layer (4) and the surrounding plate (3) with a weld overlay layer (5). S5: Post-weld treatment: Grind the weld surface to be flush with the original gearbox housing surface. Areas with missing material or poor fusion need to be repaired by secondary welding. After completion, use asbestos cloth to insulate the welding area. After the weld metal cools to room temperature, clean the weld and surrounding spatter. S6: Flaw detection: Perform dye penetrant testing on the repaired area 24 hours after welding; In step S2, a slot (21) is provided at the bottom corner defect (2) of the box body to match the two ends of the enclosure plate (3), and spot welding is carried out using Z308 welding rod. The enclosure plate (3) is made of 2-3mm low carbon steel plate. In step S4, the welding process parameters are as follows: Transition layer (4): Electrode arc welding is used, power supply polarity: DC reverse polarity; electrode diameter 3.2mm; current selection: I = 70-90A; Z308 electrode is used for transition layer (4); Overlay (5): Carbon dioxide gas shielded welding is used. Power supply polarity: DC reverse polarity; welding wire diameter 1.2mm; current selection: I = 120-140A; voltage selection: U = 19-21V. When welding the transition layer (4), a multi-layer, multi-pass welding method is adopted. The thickness of each layer is 2-3mm, and the interpass temperature is controlled not lower than 300℃. When welding the overlay layer (5), multiple layers and multiple passes are welded from the inner wall of the enclosure plate (3) towards the overlay layer (5). The thickness of each layer is 2-3mm, and the interpass temperature is controlled not lower than 300℃. After each layer is welded, interpass cleaning is carried out to remove oxides and spatter. At the same time, after each layer is welded, the weld is hammered to relieve stress. When welding the transition layer (4), the angle between the welding rod and the weld overlay surface is controlled at 40° to 50°. When welding the weld overlay layer (5), the angle between the welding wire and the weld overlay surface is controlled at 40° to 50°, so that the center of the arc (7) burns on the weld overlay surface (6) 3 to 5 mm above the bottom, and the molten iron contacts the platform surface by gravity but does not fuse together.

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