Novel laser thermal spraying gun

Abstract

The invention discloses a novel laser thermal spraying gun, and belongs to the technical field of laser additive manufacturing, the novel laser thermal spraying gun comprises a connecting seat, an air knife assembly, an inner nozzle, an outer nozzle, a cooling sleeve cover plate and a cooling sleeve, the outer nozzle comprises a powder feeding body and a Laval pipe, and a diffusion hole is formed in the Laval pipe; the Rafael nozzle accelerates air flow through a gradually-shrinking-gradually-expanding structure, a high-speed and high-temperature jet flow environment is formed, powder is fully preheated and evenly dispersed before reaching a base body, the Rafael pipe and laser spraying are combined, the advantages of the laser cladding technology and the thermal spraying technology are combined, the acceleration effect of Rafael air flow is overlaid, and the thermal spraying effect of the laser cladding technology and the thermal spraying technology is improved. Under the action of high-temperature and high-pressure air flow, the powder is in full contact with a laser heat source in a flying distance long enough through a Laval nozzle, so that the powder and a matrix form metallurgical bonding in a molten state, the bonding strength can be 2-3 times that of traditional thermal spraying, and the powder is suitable for the limited space environment of water erosion protection and repair of the steam turbine blade.

Description

Technical Field

[0001] The present invention relates to the technical fields of laser additive manufacturing, laser cladding and laser thermal spraying, and particularly relates to a novel laser thermal spraying gun. Background Art

[0002] A steam turbine, also known as a steam turbine engine, is a rotary steam power device. High-temperature and high-pressure steam passes through a fixed nozzle to become an accelerated air flow and then jets onto the blades, causing the rotor equipped with the blade row to rotate and perform work externally at the same time. Steam turbines are the main equipment in modern thermal power plants and are also used in the metallurgical industry, chemical industry, and ship power plants. There is a large amount of wet steam in thermal and nuclear power steam turbines. The two-phase flow of wet steam, and the appearance of condensed moisture not only affects the aerodynamic efficiency but also causes blade corrosion. Corrosion damage will lead to blade material loss and shape change, resulting in a decrease in stage efficiency. In severe cases, blade fracture may occur, causing major operating accidents. To solve the corrosion and failure problems of steam turbines, the use of surface modification technology is a very effective method.

[0003] Surface modification technology is widely used in the manufacturing field. It uses various methods, such as surface treatment, surface coating or surface film, surface modification technology and other means, to make the surface of materials or workpieces have specific properties to achieve the optimal combination between the surface and the core materials. This technology can economically and effectively improve product quality and extend service life. Common surface modification technologies include thermal spraying, laser cladding, etc. However, in the actual production process, there are still some problems in the use of these technologies.

[0004] Thermal spraying technology has the advantages of simple operation, fast deposition speed, and strong material adaptability. However, the coating prepared by thermal spraying is mechanically bonded to the substrate, and the coating bonding strength is relatively low, and defects such as voids are easily formed inside the coating. Under harsh working conditions, the service life may be difficult to meet the requirements.

[0005] In the traditional laser cladding process, the distance from the lower end face of the cladding head to the workpiece surface (abbreviated as the working distance) is too short (generally only a few millimeters to more than ten millimeters), and the laser heat input is too large, which easily causes large deformation of the workpiece. When operating in narrow spaces such as the roots of thin-walled parts such as hydro turbine blades, new high-temperature aeroengine and gas turbine blades, the accessibility of the laser head is poor. When small deformation is required and strengthening or remanufacturing is needed, traditional laser cladding technology (including high-speed laser cladding technology) is almost powerless. Summary of the Invention

[0006] The present invention provides a novel laser thermal spraying gun, aiming to solve the problems that the working distance from the laser cladding head to the workpiece in ordinary laser cladding is short, and the laser cladding head itself has a large physical size, making it impossible to successfully prepare coatings in narrow parts such as the turbine rotor and the root of the blade. By combining the laser cladding technology with the thermal spraying technology, the advantages of the thermal spraying technology, such as long working distance and high accessibility in narrow parts, are integrated. At the same time, the laser cladding technology is taken into account, enabling a metallurgical bond to be formed between the prepared coating and the substrate, and the prepared coating has the advantages of high bonding strength and not being easily peeled off.

[0007] The specific technical solution provided by the present invention is as follows: A novel laser thermal spraying gun provided by the present invention, the novel laser thermal spraying gun includes a connecting seat, an air knife assembly fixed on the connecting seat, an inner nozzle fixed on the air knife assembly, an outer nozzle fixed on the inner nozzle, a cooling sleeve cover plate fixed at the lower end of the outer nozzle, and a cooling sleeve tube fixed on the outer nozzle. Among them, a powder feeding channel is formed between the outer nozzle and the inner nozzle, and an inverted conical laser beam cavity is arranged inside the inner nozzle. The outer nozzle includes a powder feeding body that cooperates with the inner nozzle to form the powder feeding channel, and a Laval tube located below the powder feeding body. A diffusion hole is arranged inside the Laval tube, the diffusion hole is communicated with the powder feeding channel, the diffusion hole is communicated with the laser beam cavity, the convergence point of the cross-sectional center line of the powder feeding channel and the cross-sectional center line of the laser beam cavity is located inside the diffusion hole, and the smaller diameter end of the diffusion hole is close to the powder feeding body.

[0008] Optionally, the large end diameter of the diffusion hole is 1.5 times to 3 times the small end diameter of the diffusion hole, and the length of the diffusion hole is 20 mm to 200 mm.

[0009] Optionally, the large end diameter of the diffusion hole is 2 times the small end diameter of the diffusion hole, and the length of the diffusion hole is 130 mm to 160 mm.

[0010] Optionally, the cross-sectional center line of the powder feeding channel and the cross-sectional center line of the laser beam cavity converge at the same point on the central axis of the diffusion hole, and the laser beam cavity and the diffusion hole are coaxially arranged.

[0011] Optionally, the laser beam cavity presents an inverted conical column structure, the taper of the laser beam cavity is 50:88 to 65:88, and the powder feeding channels are uniformly distributed around the annular periphery of the laser beam cavity.

[0012] Optionally, the annular space formed by the splicing of the cooling sleeve tube and the Laval tube is a cooling channel, and the powder feeding body and the Laval tube are integrally formed.

[0013] Optionally, the air knife assembly includes an upper air knife and a lower air knife that are spliced together, and the air knife assembly is located above the laser beam cavity.

[0014] Optionally, the powder feeding channel is a slit-type powder feeding channel, and the convergence points of the longitudinal section centerlines of the slit-type powder feeding channel and the longitudinal section centerline of the laser beam cavity are all on the central axis of the diffusion hole.

[0015] Optionally, the included angle between the longitudinal section centerline of the slit-type powder feeding channel and the longitudinal section centerline of the laser beam cavity is 32° to 40°.

[0016] Optionally, the small end diameter of the laser beam cavity is 6 to 8 mm, and the small end diameter of the diffusion hole is 8 to 10 mm.

[0017] The beneficial effects of the present invention are as follows: The embodiment of the present invention provides a novel laser thermal spraying gun, which includes a connecting seat, an air knife assembly fixed on the connecting seat, an inner nozzle fixed on the air knife assembly, an outer nozzle fixed on the inner nozzle, a cooling sleeve cover plate fixed at the lower end of the outer nozzle, and a cooling sleeve fixed on the outer nozzle. Among them, the outer nozzle includes a powder feeding body that cooperates with the inner nozzle to form the powder feeding channel, and a Laval tube located below the powder feeding body. A diffusion hole is provided inside the Laval tube. The diffusion hole communicates with the powder feeding channel and the laser beam cavity. The convergence point of the cross-section centerlines of the powder feeding channel and the laser beam cavity is located inside the diffusion hole. The smaller diameter end of the diffusion hole is close to the powder feeding body. The Laval nozzle accelerates the air flow through a converging-diverging structure to form a high-speed and high-temperature jet environment, so that the powder is fully preheated and evenly dispersed before reaching the substrate. Combining the Laval tube with laser spraying realizes the combination of the advantages of laser cladding technology and thermal spraying technology. The energy density of laser cladding is high, and with the acceleration effect of the Laval air flow, under the action of high-temperature and high-pressure air flow, through the Laval nozzle, it is in full contact with the laser heat source at a sufficient flight distance, so that the powder forms a metallurgical bond with the substrate in a molten state, and the bonding strength can reach 2 to 3 times that of traditional thermal spraying, which is suitable for the restricted space environment of steam turbine blade water erosion protection and repair. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic structural diagram of a novel laser thermal spraying gun according to an embodiment of the present invention; Figure 2 Isometric view structure diagram of a new type of laser thermal spraying gun according to an embodiment of the present invention; Figure 3 Structure diagram of an upper air knife according to an embodiment of the present invention. Specific implementation manners

[0020] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the scope of protection of the present invention.

[0021] Below will be combined with Figures 1 to 3 A new type of laser thermal spraying gun according to an embodiment of the present invention will be described in detail.

[0022] Refer to Figure 1 、 Figure 2 And Figure 3 As shown, a new type of laser thermal spraying gun provided by an embodiment of the present invention includes a connection seat 1, an air knife assembly 2 fixed on the connection seat 1, an inner nozzle 3 fixed on the air knife assembly 2, an outer nozzle 4 fixed on the inner nozzle 3, a cooling sleeve cover plate 5 fixed at the lower end of the outer nozzle 4, and a cooling sleeve 6 fixed on the outer nozzle 4. Among them, the connection seat 1 is used to fix the new type of laser thermal spraying gun according to the embodiment of the present invention to other components. For example, the new type of laser thermal spraying gun according to the embodiment of the present invention is fixed on a laser cladding device or a laser spraying and melting equipment through the connection seat 1.

[0023] Refer to Figure 1 、 Figure 2 And Figure 3As shown in the figure, a powder feeding channel 7 is formed between the outer nozzle 4 and the inner nozzle 3, that is, a powder feeding channel 7 is arranged at the joint surface of the outer nozzle 4 and the inner nozzle 3. The powder feeding channel 7 is a slit-type powder feeding channel. The convergence points of the longitudinal section center lines of the slit-type powder feeding channel and the longitudinal section center line of the laser beam cavity 8 are all on the central axis of the diffusion hole 9. Using the slit-type powder feeding channel can ensure that the powder ejected through the powder feeding channel converges in the direction where the laser beam cavity 8 is located. Furthermore, a coating with uniform thickness and excellent surface quality can be formed on the substrate surface. Inside the inner nozzle 3, there is a laser beam cavity 8 with an inverted conical structure. The laser beam cavity 8 presents an inverted conical column structure. The taper of the laser beam cavity 8 is 50:88 - 65:88. The powder feeding channels 7 are evenly distributed around the annular periphery of the laser beam cavity 8. The cross-section center line of the powder feeding channel 7 and the cross-section center line of the laser beam cavity 8 converge at the same point on the central axis of the diffusion hole 9. The laser beam cavity 8 and the diffusion hole 9 are coaxially arranged, that is, the intersection points between the central axes of all the powder feeding channels 7 and the central plane of the laser beam cavity form a cake-like structure in the same horizontal plane. Furthermore, a powder cake coating can be formed at the convergence point of the light beam in the laser beam cavity, and the powder cake formed at the outlet of the powder feeding cavity has a certain diameter. Thus, it can converge with the laser beam above the diffusion hole 9, making the laser beam contact the powder cake before reaching the diffusion hole 9. This ensures that most of the energy of the laser beam entering the diffusion hole is used to heat and melt and accelerate the powder particles in flight, avoiding the substrate from being overheated and significantly reducing the dilution rate, reducing the substrate deformation amount and the dilution rate, and can greatly improve the powder utilization rate and processing efficiency, ensuring that the effective components of the coating are not affected by the substrate material, thereby improving the corrosion and wear resistance of the coating.

[0024] Reference Figure 1 、 Figure 2 and Figure 3 As shown in the figure, the outer nozzle 4 includes a powder feeding body 41 that cooperates with the inner nozzle 3 to form the powder feeding channel 7, and a Venturi tube 42 located below the powder feeding body 41. The inside of the Venturi tube 42 is set as the diffusion hole 9. The diffusion hole 9 is communicated with the powder feeding channel 7, and the diffusion hole 9 is communicated with the laser beam cavity 8. The convergence point of the cross-section center line of the powder feeding channel 7 and the cross-section center line of the laser beam cavity 8 is located inside the diffusion hole 9. Further, the cross-section center line of the powder feeding channel 7 and the cross-section center line of the laser beam cavity 8 converge at the same point on the central axis of the diffusion hole 9, that is, the cross-section center line of the powder feeding channel 7 and the cross-section center line of the laser beam cavity 8 converge on the central axis of the diffusion hole 9. Furthermore, most of the energy of the laser beam entering the diffusion hole is used to heat and melt and accelerate the powder particles in flight, avoiding the substrate from being overheated and significantly reducing the dilution rate, reducing the substrate deformation amount and the dilution rate, and can greatly improve the powder utilization rate and processing efficiency, ensuring that the effective components of the coating are not affected by the substrate material, thereby improving the corrosion and wear resistance of the coating.

[0025] ReferenceFigure 1 , Figure 2 and Figure 3 As shown in Figure 1 , Figure 2 and Figure 3 , the smaller diameter end of the diffusion hole 9 is close to the powder feeding body 41, ensuring that the powder particles entering through the powder feeding channel are fully mixed with the laser beam in the diffusion hole and then enter the Laval tube. The large end diameter of the diffusion hole 9 is 1.5 to 3 times the small end diameter of the diffusion hole 9, and the length of the diffusion hole 9 is 20 mm to 200 mm. The powder particles entering the interior of the diffusion hole 9 form a Venturi effect inside the diffusion hole, accelerating the air flow and evenly dispersing the powder, thereby improving the spraying coverage efficiency.

[0026] In the embodiment of the present invention, the powder particles are sent into the laser beam through the powder feeding channel 7 in the middle, and high-pressure gas fed from the left (forming an air knife to prevent dust and the like from contaminating the laser protection lens) is superimposed. Under the action of high-temperature and high-pressure air flow, through the Laval nozzle (diffusion hole 9), the powder particles are in full contact with the laser heat source at a sufficient flight distance. By combining the laser and thermal spraying technologies, under the action of the Laval tube, the powder particles are further accelerated to form a supersonic droplet jet out of the nozzle, and on the workpiece surface 20 - 200 mm away from the outlet, a coating is gradually accumulated. By optimizing different process parameters such as laser power and scanning speed, the substrate part can be partially melted, so as to flexibly control the formation of a metallurgical bond between the coating and the substrate, control the heat input, and thus control the substrate deformation within a reasonable range. Furthermore, by combining the advantages of the laser cladding technology and the thermal spraying technology, it can be widely applied to the coating preparation on the surfaces of complex-structured parts such as steam turbine blades.

[0027] Furthermore, in the embodiment of the present invention, the large end diameter of the diffusion hole 9 is 2 times the small end diameter of the diffusion hole 9, and the length of the diffusion hole 9 is 130 mm to 160 mm. Such a setting can ensure that a good Venturi effect is formed in the diffusion hole 9. Then, through the powder feeding channel 7 in the middle, the powder particles are sent into the laser beam, and high-pressure gas fed from the left (forming an air knife to prevent dust and the like from contaminating the laser protection lens) is superimposed. Under the action of high-temperature and high-pressure air flow, through the Venturi effect of the diffusion hole 9, the powder particles are further accelerated. The powder particles are in full contact with the laser heat source at a sufficient flight distance. By combining the laser and thermal spraying technologies, under the Venturi effect of the Laval tube, the powder particles are further accelerated to form a supersonic droplet jet out of the nozzle, and on the workpiece surface 20 - 200 mm away from the outlet, a metallurgical bond coating with uniform texture and reliability is gradually accumulated.

[0028] Reference Figure 1 , Figure 2 and Figure 3As shown, the annular space formed by the cooling sleeve 6 and the Rafale tube 42 is a cooling channel 10. The powder delivery body 41 and the Rafale tube 42 are integrally formed. A low-temperature coolant (such as a water-ethylene glycol mixture) is passed through the cooling channel 10 to remove the heat generated by the reaction between the high-temperature laser and the powder particles, and prevent the nozzle and the Rafale tube 42 from being ablated due to excessive temperature. The air knife assembly 2 includes an upper air knife and a lower air knife spliced together. The air knife assembly 2 is located above the laser beam cavity 8, and forms a laminar airflow through compressed air to stabilize the powder delivery path, and prevent the powder entering the powder delivery channel from forming dust and other pollutants to the laser protection lens, such as Figure 3 As shown, the upper air knife and the lower air knife have the same structure. The upper air knife and the lower air knife are spliced together to form a laminar airflow that is more stable and reliable, and has a better blocking effect on the dust formed by the powder entering the powder feeding channel, and can better prevent the powder entering the powder feeding channel from forming dust and polluting the laser protection lens.

[0029] refer to Figure 1 , Figure 2 , Figure 3 As shown, the angle between the center line of the longitudinal section of the slit powder feeding channel and the center line of the longitudinal section of the laser beam cavity is 32°~40°, the small end diameter of the laser beam cavity is 6~8mm, and the small end diameter of the diffusion hole is 8~10mm. At this angle, the action time between the laser beam and the powder cake is the longest, the powder utilization rate is the highest, the laser utilization rate is the highest, and the metallurgical bonding strength of the coating is the highest. In addition, with the Venturi effect of the Lafarge tube below, it is fully in contact with the laser heat source at a sufficiently long flight distance. Under the premise of taking into account laser cladding and particle powder acceleration, the powder particles are accelerated and melted to form supersonic droplets that are ejected out of the nozzle. On the workpiece surface 20-200 mm away from the outlet, a uniform and reliable metallurgical bonding coating is gradually accumulated.

[0030] An embodiment of the present invention provides a new type of laser thermal spraying gun, which includes a connection seat, an air knife assembly fixed on the connection seat, an inner nozzle fixed on the air knife assembly, an outer nozzle fixed on the inner nozzle, a cooling sleeve cover plate fixed at the lower end of the outer nozzle, and a cooling sleeve fixed on the outer nozzle. Among them, the outer nozzle includes a powder feeding body that cooperates with the inner nozzle to form the powder feeding channel, and a Laval tube located below the powder feeding body. Diffusion holes are provided inside the Laval tube. The diffusion holes are communicated with the powder feeding channel and the laser beam cavity. The convergence point of the cross-sectional center line of the powder feeding channel and the cross-sectional center line of the laser beam cavity is located inside the diffusion holes. The smaller diameter end of the diffusion holes is close to the powder feeding body. The Laval nozzle accelerates the air flow through a converging-diverging structure to form a high-speed and high-temperature jet environment, so that the powder is fully preheated and evenly dispersed before reaching the substrate. By combining the Laval tube with laser spraying, the advantages of laser cladding technology and thermal spraying technology are combined. The energy density of laser cladding is high. With the acceleration effect of the Laval air flow, under the action of high-temperature and high-pressure air flow, through the Laval nozzle, it is in full contact with the laser heat source at a sufficient flight distance, so that the powder forms a metallurgical bond with the substrate in a molten state, and the bonding strength can reach 2 to 3 times that of traditional thermal spraying, which is suitable for the restricted space environment of steam turbine blade water erosion protection and repair.

[0031] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A novel laser thermal spraying gun, characterized in that, The novel laser thermal spraying gun includes a connecting seat, an air knife assembly fixed on the connecting seat, an inner nozzle fixed on the air knife assembly, an outer nozzle fixed on the inner nozzle, a cooling sleeve cover plate fixed at the lower end of the outer nozzle, and a cooling sleeve pipe fixed on the outer nozzle. Among them, a powder feeding channel is formed between the outer nozzle and the inner nozzle. An inverted conical laser beam cavity is arranged inside the inner nozzle. The outer nozzle includes a powder feeding body that cooperates with the inner nozzle to form the powder feeding channel, and a Laval tube located below the powder feeding body. A diffusion hole is arranged inside the Laval tube. The diffusion hole communicates with the powder feeding channel and the laser beam cavity. The convergence point of the cross-sectional center line of the powder feeding channel and the cross-sectional center line of the laser beam cavity is located inside the diffusion hole. The smaller diameter end of the diffusion hole is close to the powder feeding body.

2. The novel laser thermal spraying gun according to claim 1, wherein The large end diameter of the diffusion hole is 1.5 to 3 times the small end diameter of the diffusion hole, and the length of the diffusion hole is 20 mm to 200 mm.

3. The novel laser thermal spraying gun according to claim 2, wherein The large end diameter of the diffusion hole is 2 times the small end diameter of the diffusion hole, and the length of the diffusion hole is 130 mm to 160 mm.

4. The novel laser thermal spraying gun according to claim 1, characterized in that, The cross-sectional center line of the powder feeding channel and the cross-sectional center line of the laser beam cavity converge at the same point on the central axis of the diffusion hole, and the laser beam cavity and the diffusion hole are coaxially arranged.

5. The novel laser thermal spraying gun according to claim 2, characterized in that, The laser beam cavity presents an inverted conical column structure, the taper of the laser beam cavity is 50:88 to 65:88, and the powder feeding channels are evenly distributed around the ring of the laser beam cavity.

6. The novel laser thermal spraying gun according to claim 2, characterized in that, The annular space formed by the splicing of the cooling sleeve pipe and the Laval tube is a cooling channel, and the powder feeding body and the Laval tube are integrally formed.

7. The novel laser thermal spraying gun according to claim 2, wherein, The air knife assembly includes an upper air knife and a lower air knife that are spliced with each other, and the air knife assembly is located above the laser beam cavity.

8. The novel laser thermal spraying gun according to claim 2, wherein, The powder feeding channel is a slit-type powder feeding channel, and the convergence points of the longitudinal section center line of the slit-type powder feeding channel and the longitudinal section center line of the laser beam cavity are all on the central axis of the diffusion hole.

9. The novel laser thermal spraying gun according to claim 8, characterized in that, The included angle between the longitudinal section center line of the slit-type powder feeding channel and the longitudinal section center line of the laser beam cavity is 32° to 40°.

10. The novel laser thermal spraying gun according to claim 8, characterized in that, The small end diameter of the laser beam cavity is 6 to 8 mm, and the small end diameter of the diffusion hole is 8 to 10 mm.

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