Welding preheating device for large-size steel structure

Abstract

The invention relates to the technical field of welding, and discloses a large-size steel structure welding preheating device which comprises a turbofan jet, one end of the turbofan jet is an air inlet channel, the other end of the turbofan jet is a rear combustion chamber, the turbofan jet is sleeved with a vortex sleeve, the front end of the air inlet channel is provided with a nitrogen compressor, and one end of the vortex sleeve is provided with a cold air discharge pipe. The cold air discharging pipe and the air inlet channel are located on the same side, and the hot air discharging pipe and the rear combustion chamber are located on the same side. Compared with the prior art, the device has the advantages that the turbofan jet generates high-temperature fuel gas flow, large-flow and high-flow-speed hot gas flow injection is achieved, the preheating range is wider, cold nitrogen is mixed into the gas inlet channel through the nitrogen compressor, the oxygen content of a combustion area is reduced, and the oxidation risk of a preheating area is reduced; the hot gas discharge pipe forms a low-oxygen hot nitrogen layer on the periphery of the high-temperature tail gas, so that oxidation is further inhibited while heat loss is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a large-size steel structure welding preheating device. BACKGROUND

[0002] Preheating of large steel structures before automatic welding is a key process to ensure welding quality, prevent cold cracking and reduce residual stress.

[0003] Due to size limitations, large steel structures are difficult to heat as a whole, and if the overall heating energy is high, local preheating is usually selected. Common preheating methods are electric heating and flame heating. In the electric heating method, an electric heating belt or a resistance heating blanket is covered around the welding area, while in the flame heating method, an oxyacetylene flame or a propane flame is used to sweep and heat the preheating area.

[0004] Currently, the coverage of electric heating belts and resistance heating blankets is limited, and segmented splicing heating is required for super large components (such as bridges and storage tanks), which is prone to temperature gradients, and the heating / cooling rate is limited by the thermal conductivity of the material, making it difficult to adapt to fast welding rhythm.

[0005] The flame heating method may cause oxidation of the base material surface, forming an oxide skin that affects the welding quality, and the flame heat is quickly lost, requiring continuous heating to maintain the temperature, resulting in high energy consumption and cost. SUMMARY

[0006] The technical problem to be solved by the present application is the small coverage and slow heat conduction of the current preheating technology, and the flame heating method is prone to oxidation and heat loss. The present application provides a large-size steel structure welding preheating device.

[0007] To solve the above technical problems, the technical solution provided by the present application is as follows: a large-size steel structure welding preheating device, comprising a turbojet, one end of the turbojet being an air inlet, the other end being a rear combustion chamber, the turbojet being externally sleeved with a vortex sleeve, a nitrogen gas compressor being arranged at the front end of the air inlet, one end of the vortex sleeve being provided with a cold gas discharge pipe, the other end being provided with a hot gas discharge pipe, the cold gas discharge pipe and the air inlet being on the same side, and the hot gas discharge pipe and the rear combustion chamber being on the same side.

[0008] The cold gas discharge pipe and the air inlet end are provided with an air inlet ring, a plurality of guide rods are arranged around the air inlet ring and extend between the cold gas discharge pipe and the air inlet, a baffle ring is slidably arranged on the guide rods, and by sliding, the baffle ring can switch the exhaust direction of the cold gas discharge pipe between exhausting to the outside of the device and exhausting to the air inlet.

[0009] Further, the baffle ring is internally provided with a baffle channel, the baffle ring is externally provided with a flow guide ring, the cold gas discharge pipe is provided with a nitrogen discharge grid, the air inlet is provided with a nitrogen mixing grid, the baffle ring slides towards the rear combustion chamber to connect the cold gas discharge pipe and the nitrogen discharge grid, and the baffle ring slides towards the air inlet to connect the cold gas discharge pipe and the nitrogen mixing grid.

[0010] Further, the cold gas discharge pipe and the air inlet converge inwardly, the rear combustion chamber expands outwardly, the vortex sleeve is internally provided with a vortex ring, and the vortex ring is internally provided with a vortex cavity.

[0011] Further, the nitrogen compressor is provided with a speed reduction tank, the speed reduction tank is provided with a compressed nitrogen pipe, the nitrogen compressor is provided with a nitrogen supply pipe, and the compressed nitrogen pipe is tangentially connected to the vortex cavity.

[0012] Further, the vortex sleeve is externally provided with an electric cylinder, and the electric cylinder is fixedly connected to the baffle ring.

[0013] Further, the turbojet is internally provided with a transmission box, the transmission box is internally provided with a gear box, the gear box is rotatably provided with a variable speed shaft, the variable speed shaft is provided with a second gear, a third gear, a fourth gear and a fifth gear.

[0014] Further, the transmission box is rotatably provided with a gas turbine near the rear combustion chamber, the gas turbine is provided with a first transmission shaft, the first transmission shaft is internally provided with a first gear, and the second gear is engaged with the first gear.

[0015] Further, the transmission box is provided with a starting motor, the starting motor is provided with a ninth gear, and the ninth gear is engaged with the first gear.

[0016] Further, the transmission box is rotatably provided with a first centrifugal impeller near the air inlet, the air inlet is rotatably provided with a duct fan, the nitrogen compressor is internally provided with a second centrifugal impeller, the gear box is rotatably provided with a first output shaft, a second output shaft and a third output shaft, the first output shaft, the second output shaft and the third output shaft are rotatably sleeved from inside to outside, one end of the first output shaft is power-connected with the second centrifugal impeller, the other end of the first output shaft is provided with a sixth gear, one end of the second output shaft is power-connected with the duct fan, the other end of the second output shaft is provided with a seventh gear, one end of the third output shaft is power-connected with the first centrifugal impeller, the other end of the third output shaft is provided with an eighth gear, the sixth gear is engaged with the third gear, the seventh gear is engaged with the fourth gear, and the eighth gear is engaged with the fifth gear.

[0017] Compared with the prior art, the turbojet has the following advantages:

[0018] The turbojet generates a high-temperature gas flow to realize high-flow and high-flow-rate hot gas injection, and the preheating range is wider.

[0019] The hot nitrogen gas sprayed by the hot gas discharge pipe wraps the high-temperature exhaust gas of the turbojet, reducing heat loss.

[0020] By mixing cold nitrogen into the air inlet through the nitrogen compressor, the oxygen content in the combustion zone is reduced, and the risk of oxidation in the preheating area is reduced. The hot gas discharge pipe forms a low-oxygen hot nitrogen layer outside the high-temperature exhaust gas, isolates air from direct contact with the workpiece, and further suppresses oxidation. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a structural schematic diagram of the present application.

[0022] Figure 2 is a structural schematic diagram of the side of the present application.

[0023] Figure 3 is a structural schematic diagram of the present application interfacing with a mechanical arm.

[0024] Figure 4 is a structural schematic diagram of the internal structure of the turbojet of the present application.

[0025] Figure 5 is a structural schematic diagram of the internal structure of the precombustion chamber of the present application.

[0026] Figure 6 is a structural schematic diagram of the gear box of the present application.

[0027] Figure 7 is a structural schematic diagram of the present application when the cold gas discharge pipe is in communication with the nitrogen mixing flow grid.

[0028] Figure 8 is a structural schematic diagram of the baffle ring of the present application.

[0029] Figure 9 is a structural schematic diagram of the present application when the cold gas discharge pipe is in communication with the nitrogen discharge grid.

[0030] As shown in the figure: 1, turbojet, 2, vortex sleeve, 3, nitrogen compressor, 4, mechanical arm docking tool, 5, side support, 6, electric cylinder, 7, outer duct shell, 8, jet shell, 9, transmission box, 10, combustion chamber, 11, inlet, 12, duct fan, 13, first centrifugal impeller, 14, first natural gas pipeline, 15, deflection blade, 16, gas turbine, 17, afterburner, 18, second natural gas pipeline, 19, flame stabilizer, 20, tail cone, 21, pre-chamber, 22, pilot port, 23, igniter, 24, third natural gas pipeline, 25, air intake pipe, 26, variable speed shaft, 27, second gear, 28, third gear, 29, fourth gear, 30, fifth gear, 31, first output shaft, 32, second output shaft, 33, third output shaft, 34, sixth gear, 35, seventh gear, 36, eighth gear, 37, starting motor, 38, ninth gear, 39, cold air exhaust pipe, 40, inlet ring, 41, guide rod, 42, deflection ring, 43, nitrogen exhaust grid, 44, nitrogen mixing grid, 45, speed reduction tank, 46, vortex ring, 47, vortex chamber, 48, compressed nitrogen pipe, 49, nitrogen supply pipeline, 50, hot gas exhaust pipe, 51, guide ring, 52, gear box, 53, second centrifugal impeller, 54, first transmission shaft, 55, first gear, 56, deflection channel. DETAILED DESCRIPTION

[0031] The application will be further described in detail below with reference to the accompanying drawings.

[0032] The accompanying drawings Figure 1 , the accompanying drawings Figure 2 , and the accompanying drawings Figure 3 , a large-size steel structure welding preheating device, comprising a turbojet 1 and a vortex sleeve 2, the vortex sleeve 2 is sleeved outside the turbojet 1, a mechanical arm docking tool 4 is arranged on the side of the vortex sleeve 2 and can be docked with an automatic mechanical arm, the turbojet 1 is controlled by the mechanical arm to spray high-temperature gas from the nozzle towards the preheating area of the workpiece to preheat, the turbojet 1 belongs to mature prior art, and only the basic principle and structure are described in the application.

[0033] The accompanying drawings Figure 4 , with the direction shown in the figure as the reference, wherein the left side of the picture is front and the right side is rear, the turbojet 1 comprises, from outside to inside, an outer duct shell 7, a jet shell 8 and a transmission box 9, the outer duct shell 7 is provided with an inlet 11 at one end and an afterburner 17 at the other end, a gap through front to back between the outer duct shell 7 and the jet shell 8 is referred to as an outer duct, a gap through front to back between the jet shell 8 and the transmission box 9 is referred to as an inner duct, the outer duct and the inner duct are separated by the jet shell 8 at the junction of the inlet 11 and the outer duct shell 7, the jet shell 8 extends to the front end of the afterburner 17 at the tail end, and the outer duct and the inner duct converge at this position.

[0034] The transmission box 9 is rotatably arranged at one end of the rear combustion chamber 17, and the first centrifugal impeller 13 is rotatably arranged at one end of the air inlet 11. The ducted fan 12 is rotatably arranged in the air inlet 11.

[0035] The combustion chamber 10 is arranged around the outer circle of the tail of the transmission box 9. The annular first natural gas pipeline 14 is arranged in front of the combustion chamber 10. The first natural gas pipeline 14 is provided with a plurality of nozzles extending into the combustion chamber 10. A plurality of igniters 23 are arranged in the combustion chamber 10. The deflection direction of the baffle vane 15 arranged around the tail of the combustion chamber 10 is opposite to that of the gas turbine 16.

[0036] The accompanying drawings are combined Figure 5 The annular second natural gas pipeline 18 and the flame stabilizer 19 are arranged in the rear combustion chamber 17. The second natural gas pipeline 18 is provided with a plurality of nozzles extending in front of the flame stabilizer 19. The tail cone 20 is arranged at the front end of the rear combustion chamber 17. The pre-chamber 21 is arranged inside the tail cone 20. The third natural gas pipeline 24 is arranged at the bottom of the pre-chamber 21. The third natural gas pipeline 24 is further provided with the air induction pipe 25 extending into the outer duct. The pre-chamber 21 is also provided with the igniter 23. The pre-chamber 21 is provided with a plurality of pilot ports 22 in communication with the rear combustion chamber 17.

[0037] The high-pressure gas generated by the combustion of the fuel mixed with air in the combustion chamber 10 drives the gas turbine 16 to rotate after being guided by the baffle vane 15. The rotating power of the gas turbine 16 is transmitted to the first centrifugal impeller 13 and the ducted fan 12 through the transmission box 9. The ducted fan 12 rotates to suck air from the air inlet 11 and discharge it to the outer duct and the inner duct at the same time. The first centrifugal impeller 13 compresses the air in the outer duct and discharges it to the combustion chamber 10 to mix with the fuel for combustion. The gas after passing through the gas turbine 16 enters the rear combustion chamber 17 and mixes with the airflow from the outer duct.

[0038] At the same time, the air induction pipe 25 mixes part of the airflow in the outer duct with the fuel and sends it into the pre-chamber 21. The igniter 23 ignites the fuel in the pre-chamber 21. The flame generated by the combustion is injected into the rear combustion chamber 17 through the pilot port 22 and re-ignites the mixture in the rear combustion chamber 17. The mixture burned in the rear combustion chamber 17 forms a stable combustion area after passing through the flame stabilizer 19, continuously igniting the newly entered mixture in the rear combustion chamber 17. When a stable combustion environment is formed in the rear combustion chamber 17, the fuel can be stopped from being fed into the pre-chamber 21.

[0039] The high-temperature gas stream generated by the above method can be continuously sprayed out of the afterburner 17, and the spraying of high-temperature gas near the welding area can be used for local preheating of large welding workpieces. Since natural gas is relatively easy to obtain and transport, and is also easy to mix with air for combustion, the application selects natural gas as the fuel.

[0040] The drawings will be described in conjunction with the Figure 7 The nitrogen compressor 3 is arranged at the front end of the air inlet channel 11, one end of the vortex sleeve 2 is arranged as a cold gas discharge pipe 39, and the other end is arranged as a hot gas discharge pipe 50. The cold gas discharge pipe 39 is on the same side as the air inlet channel 11, and the hot gas discharge pipe 50 is on the same side as the afterburner 17. The cold gas discharge pipe 39 converges inwardly, and the afterburner 17 expands toward the inner wall of the hot gas discharge pipe 50. The vortex sleeve 2 is provided with a vortex ring 46 in the middle part. The vortex ring 46 is internally provided with a vortex cavity 47, which is a ring-shaped groove structure. One end of the vortex cavity 47 is in communication with the inside of the vortex sleeve 2, and the communication position is close to the hot gas discharge pipe 50. The communication position between the vortex cavity 47 and the inside of the vortex sleeve 2 converges inwardly, and the other end expands outwardly.

[0041] The drawings will be described in conjunction with the Figure 7 The outlet of the nitrogen compressor 3 is in communication with a speed reduction tank 45, and the end of the speed reduction tank 45 is provided with a compressed nitrogen pipe 48 which is tangentially communicated with the vortex cavity 47. The communication position between the compressed nitrogen pipe 48 and the vortex cavity 47 is close to the cold gas discharge pipe 39. The inlet of the nitrogen compressor 3 is connected with a nitrogen supply pipe 49.

[0042] The nitrogen compressor 3 compresses the externally provided nitrogen and then introduces it into the vortex cavity 47. Since the direction of the compressed nitrogen pipe 48 is tangential to the vortex cavity 47, the nitrogen forms a vortex after entering the vortex cavity 47. The rotating nitrogen flow in the vortex cavity 47 moves axially to the direction of the hot gas discharge pipe 50 while rotating under the constraint of the contour of the vortex cavity 47 and enters the internal cavity of the vortex sleeve 2. In the process of moving to the hot gas discharge pipe 50, the gas flow close to the outer channel shell 7 is blocked by the outwardly expanding wall surface of the afterburner 17 and moves reversely, while the nitrogen flow close to the inner wall surface of the vortex sleeve 2 is not blocked and normally discharges outwardly through the hot gas discharge pipe 50. The reversely moving inner layer flow enters the cold gas discharge pipe 39 and discharges. Since the gas tangentially enters the vortex sleeve 2, the outer layer flow rotates at high speed close to the pipe wall due to centrifugal force, the inner layer flow converges to the central low pressure area with low rotating speed. On this basis, the axial movement directions of the inside and outside gas flows are opposite, so that friction is generated between the inside and outside gas flows. The kinetic energy of the outside gas flow is converted into heat energy through viscous friction, and the temperature rises to 100-130℃. The inner layer flow loses kinetic energy and adiabatic expansion, and the temperature drops to -10~-50℃. Finally, the hot nitrogen gas flow is blown out of the hot gas discharge pipe 50, and the cold nitrogen gas flow is blown out of the cold gas discharge pipe 39.

[0043] The drawings will be described in conjunction with the Figure 7 ,Figure 8 and attached Figure 9 The cold gas discharge pipe 39 is provided with an air inlet ring 40 at the end of the air inlet channel 11, and a plurality of guide rods 41 are arranged around the air inlet ring 40 and extend between the cold gas discharge pipe 39 and the air inlet channel 11, a baffle ring 42 is slidably arranged on the guide rods 41, the middle of the baffle ring 42 is provided with an inwardly-retracted baffle passage 56, and the end of the baffle ring 42 is provided with an outwardly-expanded flow guide ring 51. The cold gas discharge pipe 39 is provided with a nitrogen discharge grid 43 around it, and the air inlet channel 11 is provided with a nitrogen mixing grid 44 around it. The baffle ring 42 slides towards the rear combustion chamber 17, and the baffle passage 56 communicates the inside of the cold gas discharge pipe 39 with the nitrogen discharge grid 43. The baffle ring 42 slides towards the air inlet channel 11, and the flow guide ring 51 communicates the inside of the cold gas discharge pipe 39 with the nitrogen mixing grid 44.

[0044] By changing the position of the baffle ring 42, the discharge direction of the cold gas discharge pipe 39 can be controlled. When discharging through the nitrogen discharge grid 43, the cold nitrogen flow is directly discharged to the outside. When discharging through the nitrogen mixing grid 44, the cold nitrogen flow enters the air inlet channel 11 and mixes with air, and is sucked into the turbojet 1. When the baffle ring 42 is in an intermediate position between the above two situations, the cold nitrogen flow can be guided to the nitrogen discharge grid 43 and the nitrogen mixing grid 44 at the same time. The outer part of the vortex sleeve 2 is provided with a side support 5, and the side support 5 is provided with an electric cylinder 6. The free end of the electric cylinder 6 is fixedly connected with the baffle ring 42. The position of the baffle ring 42 is controlled by the extension and retraction of the free end of the electric cylinder 6. By accurately controlling the baffle ring 42, the flow rate of the cold nitrogen entering the nitrogen discharge grid 43 and the nitrogen mixing grid 44 can be adjusted, achieving the effect of flow rate adjustment.

[0045] In the case where the air sucked into the turbojet 1 is mixed with the additional nitrogen provided by the vortex sleeve 2, the oxygen content involved in the combustion of the combustion chamber 10 and the rear combustion chamber 17 will be reduced, thereby reducing the oxygen content in the final jet flow of the turbojet 1, to a certain extent, reducing the degree of oxidation of the local preheating area of the workpiece. At the same time, since the temperature of the nitrogen entering the air inlet channel 11 is relatively low, the effect of pre-cooling the air intake of the turbojet 1 is achieved, making the air flow density sucked into the turbojet 1 larger, and the volume of the exhaust gas after combustion and expansion larger, which can improve the power of the gas turbine 16, optimize the efficiency of the turbojet 1, and avoid the formation of rich oil combustion in the turbojet 1 by real-time adjustment of the position of the baffle ring 42 through the electric cylinder 6 to avoid excessive nitrogen entering.

[0046] On this basis, the hot gas discharge pipe 50 discharges hot nitrogen in the same direction as the turbojet 1. Since the structure of the hot gas discharge pipe 50 is annular, a layer of hot nitrogen can be finally wrapped around the periphery of the high-temperature exhaust gas discharged by the turbojet 1, to a certain extent, reducing the direct mixing of normal temperature air with high-temperature exhaust gas, avoiding the increase of oxygen content in the final jet flow to the workpiece, and reducing heat exchange with air, avoiding heat loss, and improving preheating temperature.

[0047] Combining the attached Figure 6 , the turbojet 1 is internally provided with a transmission box 9, the transmission box 9 is internally provided with a gear box 52, the gear box 52 is rotatably provided with a variable speed shaft 26 at the top, and the variable speed shaft 26 is respectively provided with a second gear 27, a third gear 28, a fourth gear 29 and a fifth gear 30.

[0048] The gas turbine 16 is provided with a first transmission shaft 54, the first transmission shaft 54 extends into the gear box 52 and is provided with a first gear 55, and the second gear 27 is engaged with the first gear 55.

[0049] The nitrogen compressor 3 is internally provided with a second centrifugal impeller 53, the gear box 52 is rotatably provided with a first output shaft 31, a second output shaft 32 and a third output shaft 33, the first output shaft 31, the second output shaft 32 and the third output shaft 33 are rotatably sleeved from inside to outside, one end of the first output shaft 31 is power connected with the second centrifugal impeller 53, the other end is provided with a sixth gear 34, one end of the second output shaft 32 is power connected with the ducted fan 12, the other end is provided with a seventh gear 35, one end of the third output shaft 33 is power connected with the first centrifugal impeller 13, the other end is provided with an eighth gear 36, wherein the sixth gear 34 is engaged with the third gear 28, the seventh gear 35 is engaged with the fourth gear 29, and the eighth gear 36 is engaged with the fifth gear 30.

[0050] Through the above transmission mode, the gas turbine 16 can drive the ducted fan 12 and the first centrifugal impeller 13 at the same time, and also drive the second centrifugal impeller 53 in the nitrogen compressor 3.

[0051] The bottom of the transmission box 9 is provided with a starting motor 37, the output end of the starting motor 37 is provided with a ninth gear 38, the ninth gear 38 is engaged with the first gear 55, and the device is started by the starting motor 37.

[0052] The above describes the present application and its embodiments, which is not limited, and the actual structure is not limited. In general, if a person skilled in the art is inspired, without departing from the purpose of the present application, without creative design, similar structure and embodiments of the technical solution should belong to the protection scope of the present application.

Claims

1. A large-size steel structure welding preheating device, comprising a turbofan jet (1), one end of the turbofan jet (1) being an air intake (11) and the other end being an afterburner (17), characterized in that: The turbofan jet (1) is fitted with a vortex sleeve (2) on the outside. A nitrogen compressor (3) is installed at the front end of the air intake (11). One end of the vortex sleeve (2) is set as a cold gas exhaust pipe (39) and the other end is set as a hot gas exhaust pipe (50). The cold gas exhaust pipe (39) is on the same side as the air intake (11), and the hot gas exhaust pipe (50) is on the same side as the rear combustion chamber (17). An intake ring (40) is provided at the end of the cold air exhaust pipe (39) and the intake duct (11). Multiple guide rods (41) are arranged around the intake ring (40) and extend between the cold air exhaust pipe (39) and the intake duct (11). A baffle ring (42) is slidably arranged on the guide rod (41). The baffle ring (42) can switch the exhaust direction of the cold air exhaust pipe (39) between exhausting to the outside of the device and exhausting to the intake duct (11) by sliding.

2. The large-size steel structure welding preheating device according to claim 1, characterized in that: The deflector ring (42) has an inward deflector channel (56) in the middle and an outward guide ring (51) at the end of the deflector ring (42). The cold air exhaust pipe (39) is surrounded by a nitrogen exhaust grille (43), and the intake duct (11) is surrounded by a nitrogen mixing grille (44). The deflector ring (42) slides toward the rear combustion chamber (17) so that the deflector channel (56) connects the inside of the cold air exhaust pipe (39) with the nitrogen exhaust grille (43). The deflector ring (42) slides toward the intake duct (11) so that the guide ring (51) connects the inside of the cold air exhaust pipe (39) with the nitrogen mixing grille (44).

3. The large-size steel structure welding preheating device according to claim 1, characterized in that: The cold air exhaust pipe (39) and the air intake (11) converge inward, and the rear combustion chamber (17) expands towards the inner wall of the hot air exhaust pipe (50). The vortex sleeve (2) is provided with a vortex ring (46) in the middle, and the vortex ring (46) is provided with a vortex cavity (47) inside.

4. The large-size steel structure welding preheating device according to claim 3, characterized in that: The outlet of the nitrogen compressor (3) is connected to a deceleration tank (45), and the end of the deceleration tank (45) is provided with a compressed nitrogen pipe (48) which is tangentially connected to the vortex chamber (47). The inlet of the nitrogen compressor (3) is connected to a nitrogen supply pipe (49).

5. The large-size steel structure welding preheating device according to claim 2, characterized in that: An electric cylinder (6) is mounted on the outside of the vortex sleeve (2), and the free end of the electric cylinder (6) is fixedly connected to the deflector ring (42).

6. The large-size steel structure welding preheating device according to claim 1, characterized in that: The turbofan jet (1) consists of an outer bypass casing (7), a jet casing (8), and a transmission box (9) from the outside to the inside. A first centrifugal impeller (13) is rotatably mounted on one end of the transmission box (9) near the intake duct (11). A bypass fan (12) is rotatably mounted inside the intake duct (11). A second centrifugal impeller (53) is mounted inside the nitrogen compressor (3). A gearbox (52) is mounted inside the transmission box (9). A first output shaft (31) and a second output shaft (32) are rotatably mounted in the center of the gearbox (52). The first output shaft (31), the second output shaft (32) and the third output shaft (33) are rotated and sleeved from the inside to the outside. One end of the first output shaft (31) is powered by the second centrifugal impeller (53), and the other end is provided with the sixth gear (34). One end of the second output shaft (32) is powered by the ducted fan (12), and the other end is provided with the seventh gear (35). One end of the third output shaft (33) is powered by the first centrifugal impeller (13), and the other end is provided with the eighth gear (36).

7. The large-size steel structure welding preheating device according to claim 6, characterized in that: The gearbox (52) has a gearbox shaft (26) rotatably mounted on its top. The gearbox shaft (26) is provided with a second gear (27), a third gear (28), a fourth gear (29) and a fifth gear (30) in sequence. The third gear (28) meshes with the sixth gear (34), the fourth gear (29) meshes with the seventh gear (35), and the fifth gear (30) meshes with the eighth gear (36).

8. The large-size steel structure welding preheating device according to claim 7, characterized in that: The transmission box (9) has a gas turbine (16) rotatably mounted near the rear combustion chamber (17). The gas turbine (16) has a first drive shaft (54), which extends into the gearbox (52) and has a first gear (55). The first gear (55) meshes with a second gear (27).

9. The large-size steel structure welding preheating device according to claim 8, characterized in that: The bottom of the transmission box (9) is provided with a starter motor (37), and the output end of the starter motor (37) is provided with a ninth gear (38), which meshes with the first gear (55).

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