A precise butt welding and assembly method for large marine motor shaft forgings

Abstract

This invention relates to a precise butt joint and welding method for large marine motor shaft forgings that can significantly reduce the weight of the motor shaft (by approximately 55%) and substantially reduce energy consumption during operation, achieving energy saving and efficiency improvement. The method employs an interference fit to achieve precise butt joint positioning. A stop is provided in the connection area for the core and the short shaft. The core is placed with the stop facing upwards. After the core stop meets the set interference, the short shaft is vertically lifted with the shaft head facing upwards and the short shaft stop facing downwards, and placed vertically into the core stop. The heating blanket on the outer circumference of the core is then removed to secure the short shaft stop. Tighten; after the interference fit is completed, add multiple reinforcing ribs at the interface; the short shaft iron core assembly is placed horizontally on the electric roller frame, and welding is carried out in the inner hole. After the welding is completed, the electric heating blanket stops heating but is not removed, and it is allowed to cool slowly; after the inner hole welding is completed, the reinforcing ribs are removed, and the outer circle bevel is machined by machine tool; outer circle welding: the short shaft iron core assembly is placed back on the roller frame, and the outer circle is welded by submerged arc welding. After the welding is completed, it is wrapped with an electric heating blanket and allowed to cool slowly; after the welding is completed, subsequent precision machining and subsequent bolt assembly with the propeller shaft are carried out.

Description

Technical Field

[0001] This invention relates to a precise docking and assembly welding method for large marine motor shaft forgings that can significantly reduce the weight of the motor shaft (weight reduction rate of approximately 55%) and significantly reduce energy consumption during operation, thereby achieving energy saving and efficiency improvement. It belongs to the field of large marine motor shaft forging manufacturing. Background Technology

[0002] Currently, large marine motor shafts are designed using a one-piece forging process, resulting in a solid forging. This has two main disadvantages: firstly, it is heavy and consumes a lot of energy during operation; secondly, it has high manufacturing costs. Summary of the Invention

[0003] Design objective: To overcome the shortcomings of the prior art, this paper proposes a precise butt welding method for large marine motor shaft forgings that can significantly reduce the weight of the motor shaft (weight reduction rate of approximately 55%) and significantly reduce energy consumption during operation, thereby achieving energy saving and efficiency improvement.

[0004] Design Scheme: To achieve the above design objectives, this invention employs a segmented assembly method for the motor shaft, consisting of a propeller shaft, a short shaft, and an iron core. The propeller shaft and iron core are bolted together, while the short shaft and iron core are connected by a combined welding method. Figure 1 The manufacturing difficulties lie in the following aspects: Due to the large size of the short shaft and the iron core, the concentricity after assembly is extremely difficult to control. Conventional stacking and welding splicing methods easily lead to large deviations in straightness after assembly, resulting in uneven wall thickness after the outer diameter is finished. In actual applications, marine motor shafts are high-speed rotating moving parts. If the wall thickness is uneven, it will cause uneven distribution of centrifugal force during high-speed rotation, unstable dynamic balance, and thus reduce the service life of the marine motor shaft, or even cause serious safety accidents. Secondly, the main difficulty in welding is that marine motor shafts are large forgings with a minimum wall thickness of 90mm. Welding the short shaft and the iron core is difficult. If a single-sided bevel welding is used on the outer diameter, there is a risk of incomplete fusion or cracks at the bottom of the inner hole, which will significantly reduce the overall strength of the motor shaft.

[0005] Therefore, this method 1) adopts an interference fit to achieve precise docking and positioning, with a stop on the iron core and short shaft in the connection area; 2) the iron core is placed with the stop facing upwards, and a heating blanket is wrapped around the outer circle. After the short shaft and the iron core stop meet the set interference, the short shaft is lifted vertically with the shaft head facing upwards and the short shaft stop facing downwards. After being placed vertically on the iron core stop, the heating blanket on the outer circle of the iron core is removed. The iron core stop naturally cools and shrinks, locking the short shaft stop. 3) After the interference fit is completed, add multiple reinforcing ribs at the interface; 4) After the reinforcing ribs are welded, the short shaft core assembly is placed horizontally on the electric roller frame, ready for welding in the inner hole. The bevel depth at the inner hole stop is one-third to two-fifths of the wall thickness, the bevel angle is 45°-62°, and the roller speed is 1 rpm / 20 min to 1 rpm / 30 min; 5) The inner hole welding adopts carbon dioxide gas shielded welding (FCAW), and the inner hole is welded in a full circle. Before welding, a heating blanket is used to wrap the entire reinforcing rib position, with a preheating temperature of 80-100℃. The roller speed is adjusted according to the welding speed of the inner hole, and the inner hole welding position is always kept flat. The interpass temperature during welding is controlled at ≤250℃. After welding, the electric heating blanket is stopped but not removed, and the welding is allowed to cool slowly; 6) After the inner hole welding is completed, the reinforcing ribs are removed. 7) The outer diameter bevel is machined using a machine tool; the bevel depth of the outer hole corresponding to the motor shaft wall thickness is greater than two-thirds of the motor shaft wall thickness, the bevel angle is 55°-72°, and the roller speed is 1 rpm / 10 min~1 rpm / 15 min; 8) Outer diameter welding: the short shaft iron core assembly is placed back on the roller frame, and the outer diameter is welded using submerged arc welding (SAW). Before welding, a heating blanket is used to locally heat the outer diameter bevel position. The preheating temperature is 100℃, and the holding time is 3 hours. The roller speed is adjusted according to the welding speed of the outer diameter, and the welding position is always kept flat. The interlayer temperature during welding is controlled at ≤250℃. After welding, the outer diameter is wrapped with an electric heating blanket and cooled slowly. The machining amount of the outer diameter after welding is uniform, ensuring the uniformity of the wall thickness, so that the dynamic balance of the motor shaft during high-speed rotation meets the requirements. 9) After welding, subsequent finishing and bolt assembly with the propeller shaft are carried out.

[0006] Compared with the prior art, the present invention reduces the weight of the motor shaft by about 55%, thereby significantly reducing energy consumption during operation and achieving the goal of energy saving and efficiency improvement. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of the motor shaft during segmented trial assembly.

[0008] Figure 2 yes Figure 1 Dimensional outline diagram of the joint.

[0009] Figure 3 This is a schematic diagram of the vertical fit between the short shaft and the iron core.

[0010] Figure 4 This is a schematic diagram of the reinforcing ribs.

[0011] Figure 5 This is a schematic diagram of a roller bracket.

[0012] Figure 6 This is a schematic diagram of the inner hole bevel.

[0013] Figure 7 This is a schematic diagram of the outer circle beveling process.

[0014] Figure 8 This is a schematic diagram of the background technology. Detailed Implementation

[0015] See attached document Figure 1-7 A precise butt welding and assembly method for large marine motor shaft forgings.

[0016] 1. Precise alignment and positioning: An interference fit is used to achieve precise alignment. The iron core and short shaft have stop marks in the connection area, with corresponding dimensions (…). Figure 2 ):

[0017] Based on the commonly used dimensions of motor shafts, the dimensions of the stop and the interference fit requirements are shown in Table 1:

[0018] Table 1. Stop dimensions and interference fit

[0019]

[0020] 2. Place the iron core with the stop facing upwards, and wrap the outer circumference with a heating blanket. The heating rate, heating temperature, and holding time for different thicknesses T are shown in Table 2. After the short shaft and the iron core stop meet the interference fit in Table 1, lift the short shaft vertically with the shaft head facing upwards and the short shaft stop facing downwards. Figure 3 After being placed vertically onto the iron core stop, the heating blanket on the outer circle of the iron core is removed. The iron core stop cools and shrinks naturally, clamping the short shaft stop to achieve an interference fit.

[0021] Table 2. Correspondence between wall thickness, heating rate, and heating time

[0022]

[0023] 3. After the interference fit is completed, to ensure the straightness of the short shaft and the iron core after mating, four reinforcing ribs are added at the interface. Figure 4 This also ensures that the overall structure will not deform due to welding stress during the internal hole welding process.

[0024] 4. After the reinforcing ribs are welded, the short shaft core assembly is placed horizontally on the electric roller frame. Figure 5 ), preparing to carry out welding in the inner hole, bevel depth at the inner hole stop, bevel angle diagram ( Figure 6 );

[0025] Table 3 shows the inner hole bevel depth, angle, and roller speed corresponding to the motor shaft wall thickness.

[0026] Table 3 Design Parameters for Inner Hole Bevel

[0027]

[0028] 5. Inner hole welding: The inner hole is welded by carbon dioxide gas shielded welding (FCAW). The entire circumference of the inner hole is welded. Before welding, a heating blanket is used to wrap the entire circumference of the reinforcing rib. The preheating temperature is 80-100℃. The roller speed is adjusted according to the welding speed of the inner hole. The inner hole welding position is always kept flat. The interpass temperature is controlled at ≤250℃ during welding. After welding, the heating blanket is stopped but not removed. The hole is cooled slowly. For welding materials and welding parameters, please refer to Table 4 and Table 5.

[0029] Table 4. Materials for Welding Internal Holes

[0030]

[0031] Table 5 Internal Hole Welding Parameters

[0032]

[0033] 6. After the inner hole welding is completed, remove the reinforcing ribs and machine the outer circle bevel using a machine tool. (See diagram for bevel machining depth.) Figure 7 );

[0034] Table 6 shows the bevel depth, angle, and roller speed corresponding to the motor shaft wall thickness.

[0035] Table 6 Design Parameters for Outer Circular Bevel

[0036]

[0037] 7. Outer circle welding: Reposition the short shaft iron core assembly onto the roller frame. Weld the outer circle using submerged arc welding (SAW). Before welding, use a heating blanket to locally heat the bevel position of the outer circle. The preheating temperature is 100℃ and the holding time is 3 hours. The roller speed is adjusted according to the welding speed of the outer circle. Always keep the welding position flat. The interlayer temperature during welding is controlled at ≤250℃. After welding, wrap with an electric heating blanket and cool slowly. For welding materials and welding parameters, please refer to Table 7 and Table 8.

[0038] Table 7 Material List for Outer Circle Welding

[0039]

[0040] Table 8 External Circle Welding Parameters

[0041]

[0042] 8. After welding is completed, subsequent precision machining and bolt assembly with the propeller shaft are carried out.

[0043] It should be understood that although the above embodiments provide a relatively detailed textual description of the design concept of the present invention, these textual descriptions are merely simple textual descriptions of the design concept of the present invention, and not limitations on the design concept of the present invention. Any combination, addition, or modification that does not exceed the design concept of the present invention falls within the protection scope of the present invention.

Claims

1. A method for precise butt welding and assembly of large marine motor shaft forgings, characterized by: 1) An interference fit is used to achieve precise docking and positioning, and the iron core and short shaft are equipped with a stop in the connection area; 2) Place the iron core with the stop facing upwards, wrap the outer circle with a heating blanket, and after the short shaft and the iron core stop meet the set interference, lift the short shaft vertically with the shaft head facing upwards and the short shaft stop facing downwards, and place it vertically on the iron core stop. Then remove the heating blanket on the outer circle of the iron core. The iron core stop will cool and shrink naturally, and clamp the short shaft stop. 3) After the interference fit is completed, add multiple reinforcing ribs at the interface; 4) After the reinforcing ribs are welded, the short shaft iron core assembly is placed horizontally on the electric roller frame, ready to carry out welding in the inner hole. The bevel depth at the inner hole stop is one-third to two-fifths of the wall thickness, the bevel angle is 45°-62°, and the roller speed is 1 revolution / 20min to 1 revolution / 30min. 5) The inner hole welding adopts carbon dioxide gas shielded welding. The inner hole is welded around the entire circumference. Before welding, a heating blanket is used to wrap the reinforcing ribs around the entire circumference. The preheating temperature is 80-100℃. The roller speed is adjusted according to the welding speed of the inner hole. The inner hole welding position is always kept flat. The interlayer temperature during welding is controlled at ≤250℃. After welding is completed, the heating blanket is stopped but not removed. The hole is allowed to cool slowly. 6) After the inner hole welding is completed, remove the reinforcing ribs and machine the outer circle bevel using a machine tool; 7) The bevel depth of the outer hole corresponding to the motor shaft wall thickness is greater than two-thirds of the motor shaft wall thickness, the bevel angle is 55°-72°, and the roller speed is 1 rpm / 10 min to 1 rpm / 15 min; 8) Outer circle welding: Reposition the short shaft iron core assembly onto the roller frame. Weld the outer circle using submerged arc welding (SAW). Before welding, use a heating blanket to locally heat the bevel position of the outer circle. The preheating temperature is 100℃ and the holding time is 3 hours. Adjust the roller speed according to the welding speed of the outer circle. Always keep the welding position flat. Control the interlayer temperature during welding to ≤250℃. After welding, wrap with an electric heating blanket and cool slowly. 9) After welding is completed, subsequent finishing and bolt assembly with the propeller shaft are carried out.

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