A sprocket shaft hoisting device and a hoisting method thereof

Abstract

The present application belongs to the technical field of marine diesel engine manufacturing, and relates to a chain wheel shaft hoisting device and a hoisting method thereof. The present application comprises a connecting flange, the end face of which is provided with multiple groups of bolt holes corresponding to the bolt holes of the end face of chain wheel shafts of different models; the connecting flange is fixedly connected with a small arm, a long arm and a large arm in sequence to form a concave-shaped rigid main body structure; a plurality of lifting lugs are arranged side by side on the upper flange plate of the large arm, and the positions of the lifting lugs are accurately determined based on the calculation of the center of gravity of chain wheel shafts of different models; a reinforcing rib is welded to the inner side of the bending part of the small arm and the long arm and the inner side of the bending part of the long arm and the large arm. During hoisting, the chain wheel shaft is rigidly connected with the connecting flange, and is lifted by selecting the corresponding lifting lug, so that the chain wheel shaft is kept stable and horizontal. The present application solves the problems of difficult control of the center of gravity and easy shaking during hoisting of the chain wheel shaft, and is high in efficiency, safe and reliable, and convenient to operate.

Description

Technical Field

[0001] This invention belongs to the field of marine diesel engine manufacturing technology, and relates to a sprocket shaft hoisting device and its hoisting method. Background Technology

[0002] In the field of marine low-speed diesel engine manufacturing, the installation of sprocket shafts for MAN series main engines, such as the 60, 70, and 80 models, is a critical step in the assembly process. As a core component of the transmission system, the sprocket shaft is heavy, long, and its center of gravity shifts significantly due to random variations, placing extremely high demands on lifting accuracy and safety.

[0003] Currently, the industry commonly uses flexible slings combined with manual adjustments for sprocket shaft hoisting. Operators must rely on experience to repeatedly lift and lower the shaft, visually inspecting and manually adjusting it to find an approximate balance point – a process highly dependent on individual skill. Due to the asymmetrical structure of the sprocket shaft, its center of gravity is not its geometric center, making it extremely difficult to find the balance point through trial and error. This often requires multiple lifting, lowering, and adjustments, making the operation cumbersome and time-consuming. More importantly, the sling binding method has poor stability; the shaft is prone to swaying or even deflection during lifting and movement, posing a safety hazard of slippage. Furthermore, it is difficult to ensure the shaft is precisely aligned with the frame hole, easily leading to installation jamming due to posture deviation. This not only prolongs the installation cycle but may also cause scratches on the journal or frame hole due to forced insertion, affecting the assembly quality of the main unit.

[0004] The existing technology has the following technical problems: First, the slings are flexible connections and cannot provide precise positioning constraints. The sprocket shaft is prone to irregular deflection after lifting, making it difficult to accurately align with the frame holes. This results in repeated shaking and forced insertion during installation, which can easily damage the journal and mating surfaces. Second, due to the lack of a rigid positioning reference, operators need to frequently use pry bars, wooden blocks, and other auxiliary tools to adjust the shaft posture, resulting in high labor intensity and safety hazards such as squeezing and bumping. Third, each lifting operation requires repeated trial lifting, and a single installation usually takes more than 1 hour, which seriously restricts the assembly efficiency of the main unit. Fourth, the sprocket shaft size and center of gravity vary greatly among different models, and the sling method cannot be universalized. Multiple sets of lifting tools or temporary binding schemes need to be prepared for each model, making on-site management complex. Summary of the Invention

[0005] To address the problems of complex operation, unstable installation, poor safety, and low efficiency in existing sprocket shaft hoisting methods, this invention proposes a sprocket shaft hoisting device, comprising: a connecting flange and a forearm connected to the flange end face; the connecting flange end face has several bolt holes corresponding to the bolt holes on the sprocket shaft end face, for rigidly fixing the sprocket shaft to the sprocket shaft end face via its own mounting bolts; one end face of the connecting flange is fixedly connected to one end face of the forearm; the other end of the forearm is fixedly connected to... The device is equipped with a long arm, the other end of which is fixedly connected to a large arm. The forearm, long arm, and large arm form a rigid main structure with a U-shaped bend. The forearm and large arm are located at the two ends of the long arm, respectively. Several lifting lugs are fixedly arranged side by side along the length of the upper flange of the large arm for connecting with the lifting slings. The device is rigidly connected to the sprocket shaft through the connecting flange, which transmits the weight of the sprocket shaft to the forearm, long arm, and large arm. The lifting lugs at different positions are used to balance the center of gravity of the sprocket shaft and the lifting device, so that the sprocket shaft remains horizontal and stable during the lifting process.

[0006] According to the sprocket shaft hoisting device described above, the reinforcing ribs are welded and installed on the inner side of the bends between the forearm and the long arm, and on the inner side of the bends between the long arm and the large arm, forming a welded integral structure.

[0007] According to the sprocket shaft hoisting device described above, the forearm, long arm, and boom are all made of H200 steel.

[0008] According to the sprocket shaft hoisting device described above, the bolt holes on the connecting flange include at least three groups of holes distributed circumferentially along its flange surface. The position of each group of holes corresponds one-to-one with the bolt hole position on the end face of at least three different types of sprocket shafts. The bolt holes in each group of holes are distributed at approximately a 120-degree angle on the flange surface of the connecting flange, and the bolt holes in different groups of holes are staggered in the circumferential direction of the flange surface of the connecting flange.

[0009] According to the sprocket shaft hoisting device described above, the flange thickness of the connecting flange is equal to the thickness of the largest shoulder of the sprocket shaft.

[0010] According to the above-described sprocket shaft hoisting device, a total of eight reinforcing ribs are provided. Two ribs are welded to each side of the bend at the forearm and the long arm, and are all set at one end of the forearm, parallel to the end face of the forearm. Two ribs are welded to each side of the bend at the long arm and the upper arm, and are all set at one end of the long arm, parallel to the end face of the long arm. The reinforcing ribs are arranged in groups of four, which respectively enclose one end of the open flange and web of the H200 steel long arm and the upper arm to form a box shape, so that the bend can be transformed from an I-shaped section to a box-shaped section when subjected to bending moment.

[0011] According to the above-described sprocket shaft hoisting device, the boom is 1-1.5 meters long. The welding positions of multiple lifting lugs on the boom correspond to the center of gravity positions of the sprocket shaft and hoisting device after different models are combined. The outer lifting lug is located at the edge of the boom end, and the distance between the inner lifting lug and the middle lifting lug is determined by calculating the center of gravity offset of different models, so that the sprocket shaft and hoisting device remain horizontal when the corresponding lifting lug is selected for hoisting.

[0012] According to the sprocket shaft hoisting device described above, the length of the forearm is 0.2 meters to 0.8 meters; the length of the long arm is 2 meters to 3 meters.

[0013] According to the above-described sprocket shaft hoisting device, the boom, long boom, and main boom are all made of Q355B material H200×200×8×12 steel, with a flange plate thickness of 12mm and a web plate thickness of 8mm. Full penetration bevel welding is used at the bending welds, and the weld grade is Class I. The lifting lugs all adopt EN69-WA0021 standard lifting lugs, with a safe load of 3-8 tons per lug. The axis of the lug hole is parallel to the length direction of the upper flange plate of the main boom, and the center lines of all lug holes are on the same horizontal plane, ensuring that the force direction of the rigging is perpendicular to the length direction of the main boom during hoisting, avoiding additional bending moments. An annular reinforcing plate is also welded between the back of the connecting flange and the end of the boom. The inner hole of the annular reinforcing plate is coaxial with the center hole of the connecting flange, and the outer edge of the annular reinforcing plate is welded to the flange plate and web plate of the boom.

[0014] The lifting method using the sprocket shaft lifting device described above includes the following steps:

[0015] Step S1: Preparing for hoisting and connecting with the equipment;

[0016] The connecting flange is rigidly fixed to the end face of the sprocket shaft using its own mounting bolts, so that the connecting flange and the end face of the sprocket shaft are completely in contact.

[0017] Step S2: Select lifting points and connecting rigging;

[0018] Depending on the model of the machine to be hoisted, select one or more corresponding lifting lugs on the boom and connect the lifting slings to the selected lifting lugs;

[0019] Step S3: Trial lifting and balance adjustment;

[0020] Conduct a trial lift. Lift the sprocket shaft lifting device and the sprocket shaft together to a height of 50-100mm, then pause and observe the overall horizontal status of the sprocket shaft and lifting device, as well as the stress on the rigging. If the whole remains horizontal and the rigging is evenly stressed, continue lifting to the required height. If the whole does not remain horizontal, lower the lifting device, reselect the lifting lug position, and continue until the whole is horizontal and stable after lifting.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. Significantly improves hoisting efficiency and shortens installation time. Traditional hoisting methods require repeated lifting and adjustment of the sling position to find the center of gravity, which takes more than an hour. This invention achieves precise horizontal balance in a single trial lift by rigidly connecting the flange to the sprocket shaft and accurately pre-setting the position of the lifting lugs on the boom based on the center of gravity calculation of different models. This eliminates the tedious process of repeated adjustments and reduces the installation time of a single sprocket shaft to about 20 minutes, improving efficiency by nearly three times.

[0023] 2. Ensuring lifting safety and eliminating potential hazards. Traditional sling binding methods suffer from poor stability, making the lifting shaft prone to swaying or even slipping, posing significant safety risks. This invention employs a rigid connection, securing the sprocket shaft to the lifting device as a single unit via bolts to the connecting flange and sprocket shaft end face, completely eliminating the possibility of slippage. Simultaneously, reinforcing ribs transform the I-shaped section at the bend into a box-shaped section, significantly improving the main structure's resistance to bending moments and ensuring structural reliability for heavy-duty lifting.

[0024] 3. Improved installation accuracy and guaranteed assembly quality. Traditional sling methods struggle to ensure the shaft is level, leading to jamming and scraping when pushing it into the frame hole. This invention precisely calculates the combined center of gravity and the position of the lifting lugs, ensuring the entire assembly is level after lifting, with the center lines of the lifting lug holes on the same horizontal plane. The rigging force direction is perpendicular, avoiding additional bending moments and allowing the shaft to be pushed in smoothly in an ideal posture. This prevents damage to the journal or frame hole caused by posture deviations, effectively improving the assembly quality of the main unit.

[0025] 4. Reduced operational difficulty and labor intensity. Traditional methods rely on operators to repeatedly try and fail based on experience, which requires high skill levels and is physically demanding. This invention solves the complex center of gravity matching problem during the manufacturing stage through structural design. Operators only need to select the corresponding lifting lugs according to the machine model and connect the rigging, eliminating the need for complex balancing operations. This greatly reduces operational difficulty and skill threshold, while also reducing the physical exertion of operators.

[0026] 5. Achieve multi-purpose functionality and reduce tooling costs. Existing technologies often require multiple lifting devices due to the different center of gravity positions of the sprocket shafts for different machine models. This invention addresses this by providing at least three sets of staggered bolt holes on the connecting flange corresponding to different machine models, and utilizing multiple lifting lugs on the boom to match different centers of gravity. This allows a single lifting device to be compatible with various MAN series 60, 70, and 80 main machine models, avoiding redundant design and manufacturing, effectively reducing tooling management and manufacturing costs, and improving tooling versatility. Attached Figure Description

[0027] Figure 1This is a front view of a structural schematic diagram of a sprocket shaft hoisting device according to the present invention.

[0028] Figure 2 The image shown is a right view of a schematic diagram of a sprocket shaft hoisting device according to the present invention.

[0029] Figure 3 This is a front view of the structural schematic diagram of the connecting flange of a sprocket shaft hoisting device according to the present invention.

[0030] Figure 4 This is a perspective view of the connecting flange of a sprocket shaft hoisting device according to the present invention.

[0031] Figure 5 This is a schematic diagram illustrating the connection and hoisting of a sprocket shaft hoisting device and a sprocket shaft according to the present invention.

[0032] Figure 6 This is a schematic diagram of a sprocket shaft hoisting device according to the present invention, which connects and hoists a sprocket shaft to the main machine for assembly.

[0033] In the diagram: 1-Connecting flange, 2-Forearm, 3-Long arm, 4-Up arm, 5-Lifting lug, 6-Reinforcing rib. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0035] like Figures 1 to 4 As shown: This embodiment of a sprocket shaft hoisting device includes a connecting flange 1, a small arm 2, a long arm 3, a large arm 4, a lifting lug 5, and a reinforcing rib 6. The connecting flange 1 has a disc-shaped structure, and its end face has several bolt holes corresponding to the bolt holes on the end face of the sprocket shafts of different machine models. Specifically, the bolt holes include at least three groups of holes distributed circumferentially along its flange face, and the positions of each group of holes correspond one-to-one with the bolt hole positions on the end face of the sprocket shafts of machines 60, 70, and 80. The bolt holes in each group of holes are distributed at approximately a 120-degree angle on the flange face of the connecting flange 1, and the bolt holes in different groups of holes are staggered in the circumferential direction of the flange face, thereby ensuring that the mounting bolts of different machine models can pass through correspondingly without interference. The flange thickness of the connecting flange 1 is equal to the thickness of the largest diameter shoulder of the sprocket shaft. This structure allows the flange end face to fit evenly with the shoulder during hoisting, avoiding damage to the shaft end mounting holes due to local stress concentration.

[0036] One end face of the flange of connecting flange 1 is fixedly connected to one end face of the forearm 2 by welding. The other end of the forearm 2 is fixedly connected to the long arm 3, and the other end of the long arm 3 is fixedly connected to the boom 4. The forearm 2, long arm 3, and boom 4 together form a rigid main structure with a U-shaped bend, where the forearm 2 and boom 4 are located at opposite ends of the long arm 3. The length of the forearm 2 is preferably 0.2-0.8 meters; in this embodiment, it is 0.4 meters. This length ensures sufficient wrench operating space at the connecting flange 1 and optimizes the overall center of gravity balance. The length of the long arm 3 is preferably 2-3 meters; in this embodiment, it is 2.3 meters. This height ensures that after the sprocket shaft is hoisted into place, the long arm 3 is close to the frame, meeting the assembly space requirements. The length of the boom 4 is 1-1.5 meters; in this embodiment, it is 1.2 meters, providing sufficient length space for the arrangement of the lifting lugs 5 to match the center of gravity offset of different machine models. The forearm 2, long arm 3, and boom 4 are all made of Q355B H200×200×8×12 steel, with a flange plate thickness of 12mm and a web plate thickness of 8mm. Full penetration groove welding is used at the bending welds, with a weld grade of Class I, ensuring the main structure has extremely high rigidity and load-bearing capacity.

[0037] Three lifting lugs 5 are fixedly installed side-by-side along the length of the upper flange plate of the boom 4 for connection with the lifting slings. All lifting lugs 5 conform to the EN69-WA0021 standard, with a safe load capacity of 3-8 tons per lug 5. The welding positions of the multiple lifting lugs 5 on the boom 4 correspond to the center of gravity positions of the sprocket shafts and lifting devices of different aircraft models (60, 70, and 80). The outer lifting lug is located at the end edge of the boom 4, and the distance between the inner and middle lifting lugs is calculated based on the center of gravity offset of different aircraft models. The axis of the lifting lug hole of the lifting lug 5 is parallel to the length of the upper flange plate of the boom 4, and the center lines of all lifting lug holes are on the same horizontal plane, ensuring that the force direction of the slings is perpendicular to the length of the boom 4 during lifting, thus avoiding additional bending moments.

[0038] To improve the structural strength at the bends, reinforcing ribs 6 are welded to the inner sides of the bends between the forearm 2 and the long arm 3, and between the long arm 3 and the upper arm 4, forming a welded integral structure. Eight reinforcing ribs 6 are provided in total. Two are welded to each side of the bend between the forearm 2 and the long arm 3, all located at one end of the forearm 2 and parallel to its end face; two are welded to each side of the bend between the long arm 3 and the upper arm 4, all located at one end of the long arm 3 and parallel to its end face. The reinforcing ribs 6 are arranged in groups of four, respectively, to enclose one end of the open flange of the long arm 3 and the upper arm 4 of the H200 steel section with the web, forming a box shape. This transforms the I-shaped section into a U-shaped section at the bend under bending moment, effectively resisting bending and torsional deformation and preventing local buckling of the web or flange.

[0039] To further enhance the strength of the connection between the connecting flange 1 and the forearm 2, an annular reinforcing plate is welded between the back of the connecting flange 1 and the end of the forearm 2. The inner hole of the annular reinforcing plate is coaxial with the center hole of the connecting flange 1, and the outer edge of the annular reinforcing plate is welded to the flange plate and web plate of the forearm 2, effectively dispersing the concentrated stress transmitted from the connecting flange 1 to the forearm 2 during hoisting.

[0040] like Figure 5 , Figure 6 As shown: Taking the installation of the sprocket shaft of a MAN 80 main engine as an example, the hoisting method of the present invention will be described in detail:

[0041] Step 1: Pre-hoisting preparations and connection with the equipment;

[0042] First, provide technical instructions to the operators, clarifying the weight, length, and corresponding lifting point positions of the sprocket shaft to be lifted. Inspect all components of the lifting device for integrity, ensuring no cracks in the welds and no deformation of the lifting lug 5. Place the lifting device flat on the wooden blocks and use a crane to lift the sprocket shaft and slowly approach the connecting flange 1. Based on the model of the 80 machine sprocket shaft, select the corresponding bolt hole group on the connecting flange 1. Take the three mounting bolts that come with the sprocket shaft and thread them sequentially through the bolt holes on the connecting flange 1 and screw them into the bolt holes on the end face of the sprocket shaft. Tighten the bolts in sequence, reaching half of the standard torque, ensuring a complete and seamless fit between the connecting flange 1 and the end face of the sprocket shaft, achieving a rigid and fixed connection.

[0043] Step 2: Select lifting points and connecting rigging;

[0044] Based on the preliminary calculations of the center of gravity of the 80-ton sprocket shaft and lifting device assembly, the center of gravity is determined to be located between the second and third lifting lugs on the boom 4. The second and third lifting lugs 5 are selected as lifting points, i.e., two-point lifting. Two slings with a rated load of not less than 2 tons are connected at one end to the selected lifting lug 5 and the other end to the crane hook. Ensure the slings are free of tangling and that the direction of force is perpendicular to the length of the boom 4.

[0045] Step 3: Trial lifting and balance adjustment;

[0046] Operate the overhead crane to slowly lift the sprocket shaft. When the sprocket shaft lifting device and the entire sprocket shaft are approximately 50-100mm off the ground, stop lifting. At this point, the operator observes the horizontal status of the shaft and the entire lifting device. Upon inspection, the entire structure is in a good horizontal position, the slings are evenly stressed, and there are no abnormal deformations or noises. If the entire structure is not horizontal at this point, it should be lowered, and the lifting lug 5 combination should be reselected according to the direction of tilt until the entire structure reaches a horizontal state during a test lift. In this embodiment, due to precise pre-calculation, balance is achieved on the first test lift.

[0047] Step Four: Formal Lifting and Installation;

[0048] After a trial lift confirms everything is correct, continue lifting until the center height of the sprocket shaft aligns with the center height of the main frame hole. Operators climb the ladder and, through manual fine-tuning and jogging of the crane, precisely adjust the axial position of the sprocket shaft to align the shaft end with the frame hole. Because the entire assembly remains level, the shaft can be smoothly and slowly pushed into the frame hole, with slight up-and-down movement during insertion to assist in positioning. Once the shaft passes through the sprocket and reaches the opposite shaft seat, initial positioning is complete.

[0049] Step 5: Disassemble the hoisting equipment;

[0050] After initial installation and positioning, use a wrench to remove the three mounting bolts connecting flange 1 to the sprocket shaft end face. During disassembly, operate slowly to prevent slight wobbling of the lifting device due to stress release during bolt removal, and avoid any impact. Then, smoothly lift the lifting device away. Finally, insert the two large bolts in the center of the sprocket shaft into the shaft center, install the corresponding nuts, and tighten them to the specified torque. The sprocket shaft installation is now complete.

[0051] Through the above steps, the entire installation process takes only about 20 minutes, which is significantly shorter than the traditional sling installation method that usually takes more than 1 hour. The process is also safe and stable.

[0052] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sprocket shaft hoisting device, characterized in that, include: A connecting flange (1) and a small arm (2) connected to its flange end face; the connecting flange (1) has several bolt holes on its end face corresponding to the bolt holes on the sprocket shaft end face, for rigid fixed connection with the sprocket shaft end face through its own mounting bolts; one end face of the connecting flange (1) is fixedly connected to one end face of the small arm (2); a long arm (3) is fixedly connected to the other end of the small arm (2), and a large arm (4) is fixedly connected to the other end of the long arm (3); the small arm (2), the long arm (3) and the large arm (4) A rigid main structure with a U-shaped bend is formed; the forearm (2) and the upper arm (4) are located at the two ends of the long arm (3); several lifting lugs (5) are fixedly arranged in parallel along the length direction on the upper flange plate surface of the upper arm (4) for connecting with the lifting slings; the sling shaft is rigidly connected to the connecting flange (1) to transmit the gravity of the sling shaft to the forearm (2), the long arm (3), and the upper arm (4), and the lifting lugs (5) at different positions are selected to balance the center of gravity of the sling shaft and the lifting device, so that the sling shaft is horizontal and stable during the lifting process.

2. The sprocket shaft hoisting device according to claim 1, characterized in that, The reinforcing rib (6) is welded to the inside of the bend between the forearm (2) and the long arm (3) and the inside of the bend between the long arm (3) and the upper arm (4).

3. The sprocket shaft hoisting device according to claim 1, characterized in that, The forearm (2), long arm (3), and upper arm (4) are all made of H200 steel.

4. The sprocket shaft hoisting device according to claim 1, characterized in that, The bolt holes on the connecting flange (1) include at least 3 groups of holes distributed circumferentially along its flange surface. The position of each group of holes corresponds one-to-one with the bolt hole position on the end face of at least 3 different machine models of sprocket shafts. The bolt holes in each group of holes are distributed at approximately a 120-degree angle on the flange surface of the connecting flange (1), and the bolt holes between different groups of holes are staggered in the circumferential direction of the flange surface of the connecting flange (1).

5. The sprocket shaft hoisting device according to claim 1, characterized in that, The flange thickness of the connecting flange (1) is equal to the diameter of the sprocket shaft and the thickness of the maximum shoulder.

6. The sprocket shaft hoisting device according to claim 3, characterized in that, The reinforcing ribs (6) are provided in eight pieces. Two pieces are welded on each side of the bend of the forearm (2) and the long arm (3), and are set at one end of the forearm (2) and parallel to the end face of the forearm (2). Two pieces are welded on each side of the bend of the long arm (3) and the upper arm (4), and are set at one end of the long arm (3) and parallel to the end face of the long arm (3). The reinforcing ribs (6) are arranged in groups of four, which respectively enclose the open flange of one end of the long arm (3) and the web of the H200 steel to form a box shape, so that the bend can be transformed from an I-shaped section to a box-shaped section when subjected to bending moment.

7. The sprocket shaft hoisting device according to claim 1, characterized in that, The boom (4) is 1-1.5 meters long. The welding positions of multiple lifting lugs (5) on the boom (4) correspond to the center of gravity positions of the sprocket shaft and the lifting device after different models are combined. The outer lifting lug is located at the edge of the end of the boom (4). The distance between the inner lifting lug and the middle lifting lug is determined according to the center of gravity offset of different models, so that when the corresponding lifting lug (5) is selected for lifting, the sprocket shaft and the lifting device remain horizontal as a whole.

8. The sprocket shaft hoisting device according to claim 1, characterized in that, The length of the forearm (2) is 0.2 m to 0.8 m; the length of the long arm (3) is 2 m to 3 m.

9. A sprocket shaft hoisting device according to claim 1, characterized in that, The forearm (2), long arm (3), and boom (4) are all made of H200×200×8×12 steel of Q355B material. The flange plate thickness is 12mm and the web plate thickness is 8mm. Full penetration groove welding is used at the bending welding point, and the weld grade is Grade 1. The lifting lugs (5) are all made of EN69-WA0021 standard lifting lugs. The safe load of each lifting lug (5) is 3-8 tons. The axis of the lifting lug hole of the lifting lug (5) is parallel to the length direction of the upper flange plate of the boom (4), and the center line of each lifting lug hole is on the same horizontal plane to ensure that the force direction of the rigging is perpendicular to the length direction of the boom (4) during lifting, and to avoid generating additional bending moment. An annular reinforcing plate is also welded between the back of the connecting flange (1) and the end of the forearm (2). The inner hole of the annular reinforcing plate is coaxial with the center hole of the connecting flange (1), and the outer edge of the annular reinforcing plate is welded to the flange plate and web plate of the forearm (2).

10. A lifting method using the sprocket shaft lifting device according to claim 1, characterized in that, Includes the following steps: Step S1: Preparing for hoisting and connecting with the equipment; The connecting flange (1) is rigidly fixed to the end face of the sprocket shaft by the mounting bolts of the sprocket shaft itself, so that the connecting flange (1) and the end face of the sprocket shaft are completely in contact; Step S2: Select lifting points and connecting rigging; According to the model of the machine to be hoisted, select one or more corresponding lifting lugs (5) on the boom (4) and connect the lifting slings to the selected lifting lugs (5); Step S3: Trial lifting and balance adjustment; Perform a trial lift. Lift the sprocket shaft lifting device and the sprocket shaft together to a height of 50-100mm and then pause. Observe the overall horizontal status of the sprocket shaft and the lifting device and the stress on the rigging. If the whole remains horizontal and the rigging is evenly stressed, continue lifting to the required height. If the whole does not remain horizontal, lower the lifting device and reselect the position of the lifting lug (5) until the whole is in a horizontal and stable state after lifting. Step S4: Formal lifting and installation; Slowly lift the horizontal sprocket shaft to the corresponding position of the main frame hole, and push the sprocket shaft smoothly into place along the axial direction to complete the initial installation and positioning of the sprocket shaft; Step S5: Disassemble the hoisting device; Remove the mounting bolts between the connecting flange (1) and the end face of the sprocket shaft, and lift the hoisting device away smoothly.

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