Metal powder plasma spraying equipment and process thereof

Abstract

The invention relates to the technical field of plasma spraying, in particular to metal powder plasma spraying equipment which is characterized in that a nozzle is mounted on a spray gun, a powder conveying pipe is mounted at the nozzle, a plurality of gas conveying pipelines are uniformly arranged on the side wall of the spray pipe around the axis of the spray pipe, and an annular pipeline is fixedly mounted on the outer side wall of the spray pipe; the annular pipeline is communicated with the gas conveying pipeline, the annular pipeline is connected with an argon supply system through a flow guide pipe, an annular groove is formed in the end face, located at the outlet, of the spray pipe, and the gas conveying pipeline is communicated with the annular groove. According to the invention, the metal powder is prevented from leaving the plasma flame due to turbulent flow of the mixed gas, so that the spraying phenomenon is avoided, and the utilization rate of the spraying material of the metal powder plasma spraying process is improved on the premise of ensuring that the production efficiency of the metal powder plasma spraying process is not changed. The invention further provides a metal powder plasma spraying process.

Description

Technical Field

[0001] This invention relates to the field of plasma spraying technology, specifically to a metal powder plasma spraying equipment and process. Background Technology

[0002] Plasma spraying is generally used for surface strengthening and modification of materials. Its working principle is as follows: an electric arc is formed at the nozzle by a cathode and anode driven by direct current, heating the powdered coating material to a molten or semi-molten state. Then, a mixture of hydrogen and argon gas ejected from inside the nozzle propels the coating material at high speed onto the pre-treated workpiece surface, forming a firmly adhered surface layer. Hydrogen acts as a reducing agent, helping to improve the quality and performance of the coating. Argon is typically used as an inert gas, providing a stable plasma environment and protecting the spraying process from high-temperature oxidation of the coating material.

[0003] In existing plasma spraying processes, the turbulent flow of the hydrogen and argon gas mixture at the nozzle causes some powder particles to detach from the plasma flame and disperse into the air, resulting in spraying problems. This is particularly problematic with metal powders, as the larger particle diameter makes them more susceptible to impact from the mixed gas and molten liquid flow, leading to particle instability and spraying. This not only wastes spraying material but also poses health risks due to the fibrotic and sensitizing effects of metal powders, harming workers' health and polluting the atmosphere. Therefore, existing plasma spraying processes incorporate suction and filtration devices to remove, inactivate, adsorb, and filter the sprayed powder near the nozzle, preventing harm to workers. However, this method still fails to completely solve the problem of material waste.

[0004] Besides adding a suction filter, another solution is to reduce the flow rate of the hydrogen and argon gas mixture, thereby reducing the impact of turbulence on the metal powder. However, reducing the flow rate of the mixed gas requires a simultaneous reduction in the powder feeding rate, which leads to a decrease in the production efficiency of the plasma spraying process.

[0005] To address this issue, a metal powder plasma spraying equipment and its process are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a metal powder plasma spraying equipment and process, which prevents the metal powder from leaving the plasma flame due to the turbulent flow of the mixed gas during metal powder plasma spraying, thus avoiding the occurrence of spraying phenomenon. In this way, the utilization rate of spraying materials in the metal powder plasma spraying process is improved while ensuring that the production efficiency of the metal powder plasma spraying process remains unchanged.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A metal powder plasma spraying device, comprising:

[0009] The system comprises a spray gun, an argon delivery system, a hydrogen delivery system, and a powder delivery pipe. The spray gun is equipped with a nozzle, and the powder delivery pipe is installed at the nozzle for quantitatively delivering metal powder. The nozzle includes a nozzle pipe, a cathode, an anode, and a coolant. The nozzle pipe sprays a mixture of hydrogen and argon gas, as well as a portion of the mixture ionized by an electric arc to form a high-temperature gas at thermal equilibrium. The cathode and anode generate an electric arc. The coolant cools the cathode and anode to ensure continuous operation. An annular blocking device is installed on the nozzle pipe, and the annular blocking device includes a guide pipe and an annular pipe. The nozzle includes multiple gas delivery pipes evenly distributed around its axis on its sidewall. These pipes deliver argon gas to the vicinity of the nozzle outlet. An annular pipe is fixedly installed on the outer sidewall of the nozzle, allowing simultaneous gas delivery to multiple pipes. This annular pipe is connected to the gas delivery pipes and is also connected to an argon gas delivery system via a guide pipe. An annular groove is formed on the nozzle's outlet end face to convert the argon gas from the delivery pipes into a continuous flow. An annular gas wall surrounds the plasma flame, with the depth of the annular groove being a multiple of its width. This ensures the airflow within the output gas wall is laminar, maintaining the shape of the gas wall while preventing interference with the plasma flame. The gas supply pipe connects to the annular groove, and the inner diameter of the annular groove is 5-10 mm larger than the nozzle outlet diameter. Since the plasma flame diffuses after exiting the nozzle outlet, the inner diameter of the annular groove needs to be larger than the nozzle outlet diameter. The difference between the diameter of the annular groove and the nozzle outlet diameter varies from 5-10 mm depending on the flow rate of hydrogen and argon used during spraying. The diameter varies from mm to mm. At the same time, turbulence ensures that the gas wall does not interfere with the plasma flame. The annular groove and the nozzle outlet are on the same plane and parallel to the generatrix. The nozzle is equipped with a sealing device at the end near the outlet. When the spray gun is used to spray other types of spray powder, since the spraying phenomenon of other types of spray powder is weaker than that of metal powder, the value of the wasted spray powder is not proportional to the argon gas. At this time, the annular shielding device can be closed. However, in order to prevent molten powder from entering the annular groove and causing blockage of the annular groove, affecting the next use, the annular groove can be sealed by the sealing device.

[0010] Under the action of the air wall, most of the metal powder cannot leave the plasma flame due to the turbulent flow of the mixed gas. Therefore, most of the metal powder is melted into a coating, which ensures the material utilization rate of the metal powder plasma spraying process. At the same time, the air wall can further isolate the air, prevent the molten metal powder from oxidizing with oxygen in the air, and prevent hydrogen from exploding when it comes into contact with air, thus improving the spraying effect of the metal powder plasma spraying process.

[0011] The annular shielding device can also guide argon gas directly to the nozzle outlet through a pipeline, without the need to open a gas supply pipeline on the nozzle for guidance. This results in a more stable and uniform gas wall, but it increases the size of the spray gun. It is not suitable for spray guns that need to penetrate deep into objects. The choice can be made according to the actual situation.

[0012] Preferably, the sealing device includes a sleeve, a spring, and ball bearings. The sleeve is rotatably mounted on the nozzle. Multiple grooves are evenly distributed around the nozzle axis on the outer wall of the nozzle. Multiple movable grooves corresponding to the grooves are formed on the inner wall of the sleeve. Ball bearings are elastically installed in the movable grooves via the spring. The unstable connection between the ball bearings and the grooves achieves positioning of the sleeve after rotation. A through hole with a diameter equal to the nozzle opening diameter is formed at the end of the sleeve. An annular groove is formed at the outer end of the sleeve. Multiple through holes are formed at the inner end of the sleeve, with both ends of the through holes communicating with the air supply pipe and the annular groove, respectively. The annular groove is positioned on the sleeve to prevent the sleeve from affecting the air wall. An annular movable groove is formed at the inner end of the sleeve. The nozzle has a cylindrical cam at the end near the sleeve, and the cylindrical cam is located in an annular movable groove. The sleeve end has two symmetrical mounting holes communicating with the annular movable groove. A push rod is slidably installed in the mounting holes, and one end of the push rod abuts against the cylindrical cam. The outer end of the sleeve has two symmetrical sliding grooves, and a semi-circular arc baffle is elastically slidably installed in the sliding grooves by a spring. The semi-circular arc baffle and the push rod are engaged by a sliding block. By rotating the sleeve, the push rod engages with the cylindrical cam, and the push rod pushes the semi-circular arc baffles closer and closer to each other, and finally fits together, completely sealing the annular groove. This prevents some molten spray powder from entering the annular groove and solidifying when no argon gas is sprayed out, thus avoiding blockage of the annular groove.

[0013] The sealing device can also use a detachable baffle for sealing, which makes the structure simpler, but reduces the ease of use and the efficiency of adjustment.

[0014] Preferably, the anode is fixedly installed at one end of the nozzle outlet. Multiple ventilation holes are evenly distributed on the outer wall of the nozzle, and these ventilation holes are connected to an annular pipe. Multiple gas supply pipes, each corresponding to one of the ventilation holes, are provided inside the anode. By providing gas supply pipes to the anode, argon gas can be used to further cool the anode, improving the stability of the metal powder plasma spraying process. Simultaneously, after being heated, the argon gas will not absorb heat from the plasma flame during the subsequent formation of the gas wall, ensuring that the heat from the plasma flame is not dissipated. This ensures that the metal powder can be fully melted by the plasma flame, improving the spraying effect of the metal powder plasma spraying process. The diameter of the gas supply pipe is 1 / 3 of the anode thickness. Setting the gas supply pipe diameter to 1 / 3 of the anode thickness allows for maximum absorption of the heat generated by the anode while ensuring its conductivity.

[0015] Preferably, a transition cone surface is provided between the second through hole and the annular groove. By compressing the argon gas, it moves to both sides along the annular groove after leaving the second through hole, ensuring the uniformity of the argon flow rate throughout the gas wall and further improving the effect of the annular shielding device. The ratio of the projected area of ​​the annular groove along the nozzle axis to the sum of the projected areas of all the second through holes along the nozzle axis is equal to the ratio of the opening sizes at both ends of the transition cone surface. The end with the larger opening of the transition cone surface is connected to the second through hole, and the end with the smaller opening of the transition cone surface is connected to the annular groove. The more gas supply pipes there are, the better the effect of the gas wall. However, too many gas supply pipes will affect the conductivity of the anode, resulting in a worse arc effect generated by the anode and cathode. Therefore, the uniformity of the argon flow rate can be adjusted by the transition cone surface, and the degree of compression of the argon gas can be adjusted according to the ratio of the projected area of ​​the annular groove along the nozzle axis to the sum of the projected areas of all the second through holes along the nozzle axis.

[0016] Preferably, the powder conveying pipe is fitted with a streamlined outer shell. The line connecting the two ends of the streamlined outer shell is parallel to the axis of the annular groove. The end of the streamlined outer shell with the larger radius faces the annular groove. The length of the streamlined outer shell is twice the width of the annular groove, and the distance between the two ends of the streamlined outer shell and the annular groove is equal. In order to avoid the gas wall from affecting the conveying of metal powder, the powder conveying pipe needs to pass through the gas wall. Therefore, in order to reduce the influence of the powder conveying pipe on the gas wall, a streamlined outer shell needs to be fitted on the powder conveying pipe to minimize the resistance to argon gas. At the same time, the gas wall will diffuse to a certain extent after leaving the annular groove. Therefore, the length of the streamlined outer shell is at least twice the width of the annular groove, and its midpoint coincides with the annular groove.

[0017] Preferably, the diameter of the vent hole is 1 mm smaller than the diameter of the gas supply pipe, and the diameter of the gas supply pipe is 1 mm smaller than the diameter of the second through hole. This avoids the argon gas encountering protrusions during flow due to installation inaccuracies, which could lead to a decrease in argon gas kinetic energy and cause argon gas turbulence, affecting the formation of subsequent laminar flow. The relative roughness of the vent hole, gas supply pipe, second through hole, and annular groove is all equal to 0.005. The smaller the roughness of the argon gas flow path, the better the laminar flow effect. The relative roughness is the ratio of the wall roughness to the pipe diameter. When this value is 0.005, the gas laminar flow effect is optimal.

[0018] A metal powder plasma spraying process, comprising the above structure, includes the following steps:

[0019] S1: Before spraying, the operator cleans and treats the surface of the substrate to be sprayed and heats it.

[0020] S2: The operator starts the plasma spraying equipment. The control system first starts the hydrogen and argon gas supply system, and then starts the cathode and anode power supply. The mixed gas of hydrogen and argon drives the electric arc generated between the cathode and anode to be sprayed out from the spray gun nozzle to form a plasma flame. Some of the argon enters the annular shielding device under the action of the guide tube. The annular shielding device makes the argon form a cylindrical gas wall to surround the plasma flame. The robotic arm moves the spray gun close to the area of ​​the substrate that needs to be sprayed.

[0021] S3: The control system starts the metal powder conveying system. The metal powder is sprayed out from the coating powder conveying pipe and melted into droplets by the plasma flame. The droplets are atomized into fine droplets under the action of the mixed gas of hydrogen and argon and move towards the substrate. Under the action of the gas wall, the turbulence of the mixed gas cannot push some unmelted particles away from the plasma flame. The fine droplets collide, deform, solidify and accumulate on the surface of the substrate to form a coating. Move the spray gun to spray the substrate surface evenly.

[0022] S4: After the spraying is completed, the operator shuts down all equipment and then performs post-treatment on the coating on the substrate surface.

[0023] Preferably, in step S2, the ratio of metal powder to argon is 1:5-12, and the ratio of argon in the annular shielding device to argon in the mixed gas is 1:4. Since the annular shielding device requires the use of some argon, the argon delivery volume needs to be increased compared to existing metal powder plasma spraying processes. Furthermore, the argon flow rate varies depending on the type of metal powder. In this case, the argon flow rate through the annular shielding device is positively correlated with the required flow rate of the nozzle to ensure that the gas wall prevents the metal powder from leaving the plasma flame. If the ratio of argon to argon in the mixed gas is less than 1:4, the gas wall cannot prevent the metal powder from leaving, resulting in a decrease in the effectiveness of the annular shielding device. If the ratio of argon to argon in the mixed gas is less than 1:4, it will cause argon waste, increasing the production cost of the metal powder plasma spraying process.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. Compared to existing metal powder plasma spraying processes that use suction and filtration devices to remove the sprayed metal powder or reduce the flow rate of the mixed gas to reduce the impact of turbulence on the metal powder, this invention uses an annular shielding device to prevent the metal powder from leaving the plasma flame due to turbulence in the mixed gas during metal powder plasma spraying, thus avoiding the occurrence of spraying phenomena. This improves the utilization rate of the spraying material in the metal powder plasma spraying process while maintaining the same production efficiency.

[0026] 2. The present invention provides a transition cone surface, through which argon gas output by a pressurized gas pipeline moves to both sides along the annular groove after leaving the second through hole, ensuring the uniformity of argon flow at all parts of the gas wall, avoiding the situation where the local flow of the gas wall is too low, which would prevent the metal powder from leaving the negative ion flame, and further improving the effect of the annular shielding device.

[0027] 3. By placing the gas supply pipe inside the anode, the argon gas absorbs the heat generated by the anode, further cooling the anode and ensuring the stability of the metal powder plasma spraying process. At the same time, after being heated, the argon gas will not absorb the heat of the plasma flame when forming the gas wall, and will ensure that the heat of the plasma flame is not lost. This ensures that the metal powder can be fully melted by the plasma flame, improving the spraying effect of the metal powder plasma spraying process. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the overall structure of the nozzle of the present invention;

[0030] Figure 3 for Figure 1 Sectional view of AA;

[0031] Figure 4 This is a front view of the sleeve of the present invention;

[0032] Figure 5 for Figure 4 BB section view;

[0033] Figure 6 for Figure 3 Enlarged view of a section at point C;

[0034] Figure 7 This is a schematic diagram of the semi-circular arc baffle plate in the open state of the present invention;

[0035] Figure 8 for Figure 3 Enlarged view of a section at point D;

[0036] Figure 9 This is a schematic diagram of the streamlined outer shell of the present invention;

[0037] Figure 10 This is a process flow diagram of the present invention.

[0038] In the diagram: 1. Cathode; 2. Anode; 3. Powder conveying pipe; 4. Guide pipe; 5. Annular pipe; 6. Gas conveying pipe; 7. Annular groove; 8. Nozzle; 9. Coolant; 10. Sleeve; 1101. Spring 1; 1102. Spring 2; 12. Groove; 13. Movable groove; 14. Ball bearing; 15. Through hole 1; 16. Through hole 2; 17. Annular movable groove; 18. Cylindrical cam; 19. Mounting hole; 20. Push rod; 21. Semi-circular arc baffle plate; 22. Vent hole; 23. Transition cone surface; 24. Streamlined outer shell; 25. Slide groove. Detailed Implementation

[0039] The following will be combined with the appendix of the present invention. Figures 1 to 10 The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the embodiments of the present invention include, but are not limited to, the embodiments described below. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Please see Figures 1 to 10 This invention provides a metal powder plasma spraying process, the technical solution of which is as follows:

[0041] S1: Before spraying, the operator cleans and treats the surface of the substrate to be sprayed and heats it.

[0042] S2: The operator starts the plasma spraying equipment. The control system first starts the hydrogen and argon gas supply system, and then starts the power supply of cathode 1 and anode 2. The mixed gas of hydrogen and argon drives the electric arc generated between cathode 1 and anode 2 to be sprayed out from the spray gun nozzle 8 to form a plasma flame. Some of the argon gas enters the annular shielding device under the action of the guide pipe 4. The annular shielding device makes the argon gas form a cylindrical gas wall to surround the plasma flame. The robotic arm moves the spray gun close to the area of ​​the substrate that needs to be sprayed.

[0043] S3: The control system starts the metal powder conveying system. The metal powder is sprayed out from the coating powder conveying pipe 3 and melted into droplets by the plasma flame. The droplets are atomized into fine droplets under the action of the mixed gas of hydrogen and argon and move towards the substrate. Under the action of the gas wall, the turbulence of the mixed gas cannot push some unmelted particles away from the plasma flame. The fine droplets collide, deform, solidify and accumulate on the surface of the substrate to form a coating. Move the spray gun to spray the substrate surface evenly.

[0044] S4: After the spraying is completed, the operator shuts down all equipment and then performs post-treatment on the coating on the substrate surface.

[0045] refer to Figures 1 to 3In S2, the argon gas entering the annular pipe 5 from the drainage pipe will fill the annular pipe 5 and enter the gas supply pipe 6 of the anode 2 through the vent 22. The argon gas in the gas supply pipe will enter the transition cone surface 23 through the through hole 2 16. Since the ratio of the projected area of ​​the annular groove 7 along the axis of the nozzle 8 to the sum of the projected areas of all the through holes 2 16 along the axis of the nozzle 8 is equal to the ratio of the opening sizes at both ends of the transition cone surface 23, it is ensured that the flow rate of argon gas entering the annular groove 7 and the flow rate of argon gas entering the annular groove 7 are equal. Moreover, the opening of the transition cone surface 23 away from the through hole 2 16 is smaller. Therefore, the argon gas will be squeezed by the transition cone surface 23 after it moves away from the through hole 2 16. Since the argon gas moves along the annular groove 7 to both sides of the through hole 2 16 in a depressurized state, the argon gas will fill the annular groove 7, making the argon gas flow rate at each point of the annular groove 7 basically equal. This ensures that the shielding and limiting effect of the gas wall on the plasma flame in each direction is the same, further reducing the spraying problem and improving the material utilization rate of the metal powder plasma spraying process. Since both the gas wall and the plasma flame diffuse to some extent after leaving the nozzle, this invention sets the inner diameter of the annular groove 7 to be 5-10 mm larger than the outlet diameter of the nozzle 8. If the difference between the inner diameter of the annular groove 7 and the outlet diameter of the nozzle 8 is less than 5 mm, the gas wall and the plasma flame will interfere with each other, affecting the flight of metal powder and fine droplets, resulting in more severe spraying. If the difference between the inner diameter of the annular groove 7 and the outlet diameter of the nozzle 8 is greater than 10 mm, the metal powder intercepted by the gas wall will be far from the plasma flame and cannot be melted into fine droplets in a short time, resulting in a decrease in coating quality. After the cathode 1 and anode 2 are activated, an electric arc will be generated between the cathode 1 and anode 2. When the mixed gas of hydrogen and argon passes through the electric arc, the hydrogen will undergo an ionization reaction with the electric arc, producing free electrons, ions, and unionized atoms, reaching a thermal equilibrium state of 15000℃, forming a plasma flame. The plasma flame at the nozzle 8 outlet will rapidly heat up the anode 2 and cathode 1. However, the materials used in the existing anode 2 and cathode 1 need to operate stably at a suitable temperature. Therefore, it is necessary to circulate coolant 9 through the cathode 1 and anode 2 to cool them down. Argon gas passing through the gas pipeline 6 can further assist the anode 2 in cooling down.

[0046] refer to Figure 4This invention employs four gas delivery pipes 6. The more gas delivery pipes 6 there are, the higher the uniformity and stability of the gas wall, and the better the cooling effect on the anode 2. However, the impact of the gas delivery pipes 6 on the resistance and conductivity of the anode 2 needs to be considered to avoid a decrease in the arc energy generated by the cathode 1 and anode 2, leading to a drop in the temperature of the high-temperature gas after the ionization of the mixed gas and the arc, thus preventing the melting of the metal powder. Setting the diameter of the gas delivery pipes 6 to 1 / 3 of the thickness of the anode 2 maximizes the absorption of heat generated by the anode 2 while ensuring its conductivity. If the ratio of the gas delivery pipe 6 to the thickness of the anode 2 is greater than 1 / 3, the conductivity of the anode 2 will deteriorate, and the arc generated by the anode 2 and cathode 1 will not be able to fully ionize the mixed gas, resulting in insufficient melting of the metal powder. If the ratio of the gas delivery pipe 6 to the thickness of the anode 2 is less than 1 / 3, the auxiliary cooling effect of argon on the anode 2 will decrease.

[0047] refer to Figure 1 When metal powder falls from the powder delivery pipe 3 to the through-hole 15, it is melted into droplets by the plasma flame and atomized into fine droplets under the action of the mixed gas. These droplets then travel at speeds exceeding 200 m / s, colliding with the substrate surface, deforming, solidifying, and accumulating to form a coating. Due to the turbulent state of the mixed gas, the flight trajectory of some metal powder under the influence of the mixed gas is not parallel to the jet direction of the plasma flame, causing the metal powder to move away from the plasma flame. After moving a short distance, this portion of metal powder encounters an argon gas wall, preventing it from continuing to move away from the plasma flame and guiding its flight trajectory to be parallel to the jet direction of the plasma flame. This ensures that most of the metal powder is fully melted by the plasma flame and forms a coating, improving the utilization rate of the coating material in the metal powder plasma spraying process. Simultaneously, the argon gas wall further isolates the fine droplets from contact with air, preventing oxidation and improving the spraying effect of the metal powder plasma spraying process. Furthermore, after the gas wall is heated by the anode 2, the temperature difference between it and the plasma flame can be reduced, preventing the gas wall from absorbing a large amount of heat from the plasma flame. This ensures that the metal powder can be fully melted, further improving the spraying effect of the metal powder plasma spraying process.

[0048] To prevent the gas wall from affecting the falling metal powder, the powder delivery pipe 3 needs to pass through the gas wall. Therefore, the powder delivery pipe 3 will obstruct part of the gas wall, affecting its formation. Thus, this invention mounts a streamlined outer shell 24 onto the powder delivery pipe 3 to minimize resistance to the argon gas, ensuring the stability and integrity of the gas wall. Simultaneously, the gas wall will diffuse to some extent after leaving the annular groove 7. Therefore, the length of the streamlined outer shell 24 is at least twice the width of the annular groove 7, and its midpoint coincides with the annular groove 7. If the streamlined outer shell 24 is less than twice the width of the annular groove 7, part of the gas wall will contact the powder delivery pipe 3, leading to gas wall instability. If the streamlined outer shell 24 is greater than twice the width of the annular groove 7, it will not have a negative impact on the gas wall, but it will increase the production cost of the streamlined outer shell 24.

[0049] In another embodiment, a pipe can be opened inside the nozzle 8 to transport the metal powder, thereby avoiding the influence of the air wall and ensuring the integrity and stability of the air wall. However, such a pipe must be designed in a curved shape, which can easily lead to powder blockage, and maintenance is difficult after the powder is blocked.

[0050] Because argon gas needs to pass through multiple sections of pipe—vent hole 22, gas delivery pipe 6, and through hole 16—from the annular pipe 5 through the annular groove 7, to avoid installation errors that could cause argon gas to be blocked by protrusions along its path, resulting in a decrease in argon gas kinetic energy and turbulence, thus affecting the formation of subsequent laminar flow, this invention increases the diameter of vent hole 22, gas delivery pipe 6, and through hole 16 by 1 mm sequentially. This reduces the installation difficulty of anode 2 and sleeve 10, and ensures that each subsequent pipe completely encompasses the previous one, thereby guaranteeing stable argon gas flow. The smaller the roughness of the argon gas flow path, the better the laminar flow effect. Relative roughness is the ratio of wall roughness to pipe diameter; the optimal laminar flow effect is achieved when this value is 0.005. The laminar flow effect of the gas wall deteriorates as this value increases.

[0051] refer to Figure 6 and Figure 7When plasma spraying other types of powder coatings, the powder dispersion is weaker compared to metal powders, and the wasted powder is not proportional to the value of the argon gas. In this case, the annular shielding device can be closed. Rotate the sleeve 10 so that the ball bearing 14 disengages from the spring 1101 in the groove 12 and fully enters the movable groove 13. During the rotation of the sleeve 10, the push rod 20 gradually moves away from the cathode 1 under the action of the cylindrical cam 18. The push rod 20, through its cooperation with the inclined slider of the semi-circular shielding plate 21, changes the transmission direction by 90°, thereby driving the semi-circular shielding plate 21 to move the spring 1102 closer to each other. When the movable groove 13 aligns with the next groove 12, the spring 1101 pushes the ball bearing 14 into the groove 12, completing the self-locking fixation. At this point, the push rod 20 moves to its limit position under the action of the cylindrical cam 18, and the two semi-circular baffles 21 fit perfectly together, completely sealing the annular groove 7. This prevents molten powder from entering the annular groove 7 after argon gas is no longer ejected, causing blockage and affecting subsequent use. An elastic material can be installed on the contact surface of the semi-circular baffles 21 to reduce the installation precision of the semi-circular baffles 21, push rod 20, and cylindrical cam 18.

[0052] Although various embodiments of the present invention have been listed and described, it will be understood by those skilled in the art that many changes, modifications, substitutions and alterations can be made to the state and components of these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A metal powder plasma spraying equipment, characterized in that, The system includes a spray gun, an argon delivery system, a hydrogen delivery system, and a powder delivery pipe (3). A nozzle is mounted on the spray gun, and a powder delivery pipe (3) is installed at the nozzle. The nozzle includes a spray pipe (8), a cathode (1), an anode (2), and a coolant (9). An annular blocking device is mounted on the spray pipe (8), which includes a guide pipe (4), an annular pipe (5), a gas delivery pipe (6), and an annular groove (7). Multiple gas delivery pipes (6) are evenly distributed around the axis of the spray pipe (8) on its sidewall. An annular pipe (5) is fixedly installed on the outer wall. The annular pipe (5) is connected to the gas supply pipe (6). The annular pipe (5) is connected to the argon gas delivery system through the guide pipe (4). An annular groove (7) is opened on the end face of the nozzle (8) at the outlet. The depth of the annular groove (7) is 4 times the width of the annular groove (7). The gas supply pipe (6) is connected to the annular groove (7). The inner diameter of the annular groove (7) is 5-10 mm larger than the outlet diameter of the nozzle (8). A sealing device is installed at the end of the nozzle (8) near the outlet.

2. The metal powder plasma spraying equipment according to claim 1, characterized in that: The sealing device includes a sleeve (10), a spring (1101), and ball bearings (14). The sleeve (10) is rotatably mounted on the nozzle (8). Multiple grooves (12) are evenly distributed around the axis of the nozzle (8) on the outer side wall of the nozzle (8). Multiple movable grooves (13) corresponding to the grooves (12) are provided on the inner side wall of the sleeve (10). Ball bearings (14) are elastically installed in the movable grooves (13) through the spring (1101). A through hole (15) with a diameter equal to the opening diameter of the nozzle (8) is provided at the end of the sleeve (10). An annular groove (7) is provided at the outer end of the sleeve (10). Multiple through holes (16) are provided at the inner end of the sleeve (10), and the two ends of the through holes (16) are respectively connected to the air supply pipe (6) and the annular groove (15). The sleeve (10) is connected to the groove (7). An annular movable groove (17) is provided at the inner end of the sleeve (10). A cylindrical cam (18) is provided at the end of the nozzle (8) near the sleeve (10). The cylindrical cam (18) is located in the annular movable groove (17). Two mounting holes (19) communicating with the annular movable groove (17) are symmetrically provided at the end of the sleeve (10). A push rod (20) is slidably installed in the mounting hole (19). One end of the push rod (20) abuts against the cylindrical cam (18). Two sliding grooves (25) are symmetrically provided at the outer end of the sleeve (10). A semi-circular baffle plate (21) is elastically slidably installed in the sliding groove (25) by a spring (1102). The semi-circular baffle plate (21) and the push rod (20) are connected by a sliding block.

3. The metal powder plasma spraying equipment according to claim 2, characterized in that: The anode (2) is fixedly installed at one end of the air outlet of the nozzle (8). Multiple air vents (22) are evenly opened on the outer wall of the nozzle (8). The air vents (22) are connected to the annular pipe (5). Multiple gas supply pipes (6) are opened inside the anode (2) that correspond one-to-one with the air vents (22). The diameter of the gas supply pipe (6) is one-third of the thickness of the anode (2).

4. The metal powder plasma spraying equipment according to claim 2, characterized in that: A transition cone surface (23) is provided between the second through hole (16) and the annular groove (7). The ratio of the projected area of ​​the annular groove (7) along the axis of the nozzle (8) to the sum of the projected areas of all the second through holes (16) along the axis of the nozzle (8) is equal to the ratio of the opening sizes at both ends of the transition cone surface (23). The larger opening end of the transition cone surface (23) is connected to the second through hole (16), and the smaller opening end of the transition cone surface (23) is connected to the annular groove (7).

5. The metal powder plasma spraying equipment according to claim 2, characterized in that: The powder conveying pipe (3) is fitted with a streamlined outer shell (24). The line connecting the two ends of the streamlined outer shell (24) is parallel to the axis of the annular groove (7). The end of the streamlined outer shell (24) with the larger radius faces the annular groove (7). The length of the streamlined outer shell (24) is twice the width of the annular groove (7), and the distance between the two ends of the streamlined outer shell (24) and the annular groove (7) is equal.

6. The metal powder plasma spraying equipment according to claim 3, characterized in that: The diameter of the vent (22) is 1 mm smaller than the diameter of the gas pipeline (6), the diameter of the gas pipeline (6) is 1 mm smaller than the diameter of the second through hole (16), and the relative roughness of the vent (22), the gas pipeline (6), the second through hole (16), and the annular groove (7) is all equal to 0.

005.

7. A metal powder plasma spraying process, comprising the metal powder plasma spraying equipment described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1: Before spraying, the operator cleans and treats the surface of the substrate to be sprayed and heats it. S2: The operator starts the plasma spraying equipment. The control system first starts the hydrogen and argon gas supply system, and then starts the cathode (1) and anode (2) power supply. The mixed gas of hydrogen and argon drives the electric arc generated between the cathode (1) and anode (2) to be sprayed out from the spray gun nozzle (8) to form a plasma flame. Some of the argon enters the annular shielding device under the action of the guide pipe (4). The annular shielding device makes the argon form a cylindrical gas wall to surround the plasma flame. The robotic arm moves the spray gun closer to the area of ​​the substrate that needs to be sprayed. S3: The control system starts the metal powder conveying system. The metal powder is sprayed out from the coating powder conveying pipe (3) and melted into droplets by the plasma flame. The droplets are atomized into fine droplets under the action of the mixed gas of hydrogen and argon and move towards the substrate. Under the action of the gas wall, the turbulence of the mixed gas cannot knock some unmelted particles away from the plasma flame. The fine droplets collide, deform, solidify and accumulate on the surface of the substrate to form a coating. Move the spray gun to spray the substrate surface evenly. S4: After the spraying is completed, the operator shuts down all equipment and then performs post-treatment on the coating on the substrate surface.

8. The metal powder plasma spraying process according to claim 7, characterized in that: In step S2, the ratio of metal powder to argon is 1:5-12, and the ratio of argon in the annular shielding device to argon in the mixed gas is 1:4.

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