Eight-hole coaxial carrier gas powder feeding device and method for atmospheric laminar flow plasma spraying

Abstract

The invention provides an eight-hole coaxial carrier gas powder feeding device and method for atmospheric laminar flow plasma spraying, and the device comprises a powder feeding core which is internally provided with a jet flow cavity, and the cavity wall is provided with eight powder feeding hole channels which are uniformly formed in the circumferential direction of the jet flow cavity at intervals; the jet flow cavity is used for being coaxially communicated with a nozzle of a plasma spray gun so as to allow laminar plasma jet flow to be sprayed in. The periphery of the powder feeding core is sleeved with the premixing component, and a premixing cavity is formed between the premixing component and the powder feeding core; wherein each powder feeding hole channel communicates with the jet flow cavity and the premixing cavity, and the axes of the powder feeding hole channels are close to the spraying direction of the laminar plasma jet flow, so that premixed powder carrying gas enters the jet flow cavity from the premixing cavity through the eight powder feeding hole channels and is mixed with the laminar plasma jet flow sprayed into the jet flow cavity in the direction tending to be coaxial. Through the device provided by the invention, the interference of the powder feeding condition on the laminar flow state of the plasma jet flow is reduced, so that the stable and long-time spraying laminar flow plasma jet flow is generated under the atmospheric condition.

Description

Technical Field

[0001] This application relates to the field of plasma spraying technology, and in particular to an eight-hole coaxial carrier gas powder delivery device and method for atmospheric laminar plasma spraying. Background Technology

[0002] Atmospheric long-flow plasma spraying technology is a novel atmospheric plasma spraying method. This method employs a DC non-transfer arc plasma generator with a special internal channel structure, which can directly obtain plasma jets with lengths varying between 100mm and 1000mm under atmospheric conditions. Under atmospheric conditions, the plasma jet exhibits laminar or quasi-laminar flow characteristics of being "long, straight, and precise," with operating noise levels below 80dB. When using atmospheric plasma spraying technology, it introduces an extremely long heating and acceleration process for the flying powder particles, resulting in lower particle velocity and extremely high particle surface temperature.

[0003] Currently, the commonly used powder feeding system and device is the lateral carrier gas powder feeding device. Since plasma jets have a quasi-laminar flow state, if a traditional lateral carrier gas powder feeding device is used for laminar plasma spraying, the lateral powder feeding will directly interfere with the flow characteristics of the laminar plasma jet, causing the jet length to decrease from a maximum of 0.5m to less than 0.1m, and generating huge noise. This drastically shortens the heating and acceleration process of the flying powder particles, resulting in poor coating quality and the loss of the technical advantages of atmospheric laminar plasma spraying. Summary of the Invention

[0004] To address the aforementioned problems, one objective of this invention is to provide an eight-hole coaxial carrier gas powder feeding device for atmospheric laminar plasma spraying, thereby reducing the interference of powder feeding conditions on the laminar flow state of the plasma jet and thus generating a stable, long-term laminar plasma jet for spraying under atmospheric conditions. A second objective of this invention is to provide a spraying method using the eight-hole coaxial carrier gas powder feeding device for atmospheric laminar plasma spraying.

[0005] To achieve one of its objectives, in a first aspect, the present invention provides an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, the technical solution of which is: An eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, the device comprising: The powder feeding core has a through hole inside to form a jet cavity. Eight powder feeding channels are opened on the wall of the through hole of the powder feeding core. The eight powder feeding channels are evenly spaced along the circumference of the jet cavity. The jet cavity is used to communicate coaxially with the nozzle of the plasma spray gun to allow laminar plasma jet to be sprayed in. A premixing component is fitted around the outer periphery of the powder feeding core and forms a premixing cavity between the powder feeding core and the premixing cavity, which is used to mix the carrier gas and powder evenly. Each of the powder feeding channels is connected to the jet cavity and the premixing cavity, and the axis of the powder feeding channel is close to the injection direction of the laminar plasma jet, so that the premixed powder carrier gas enters the jet cavity from the premixing cavity through the eight powder feeding channels and mixes with the laminar plasma jet injected into the jet cavity in a direction that tends to be coaxial.

[0006] As one of the preferred options, each of the powder feeding channels has a diameter of 1.2 mm to accommodate at least one of metal powder, metal alloy powder, and ceramic powder.

[0007] As one of the preferred embodiments, each of the powder feeding channels is an inclined straight hole, and the inlet communicating with the premixing chamber is closer to the side of the nozzle communicating with the powder feeding core than the outlet communicating with the jet chamber.

[0008] As one preferred embodiment, the inner diameter of the jet cavity gradually increases in the direction away from the nozzle.

[0009] As one of the preferred solutions, the system further includes: the internal through-hole of the premixed component forms a mounting cavity for accommodating the powder feeding core, the mounting cavity including a first mounting area, a second mounting area and a third mounting area with inner diameters arranged from large to small; The outer edge of the powder feeding core, away from the nozzle, is engaged in the first mounting area, while the inner edge, close to the nozzle, is fitted into the third mounting area. The middle portion between the outer and inner edges forms the premixing cavity with the third mounting area.

[0010] As one preferred embodiment, the device further includes: A positioning flange surrounds the outer periphery of the outer edge component of the powder feeding core. The positioning groove is provided at the position where the premixed component encloses and forms the first installation area; The positioning flange is engaged within the positioning groove.

[0011] As one preferred embodiment, the device further includes: A chuck, which is connected to the premixed component and is used to fit around the periphery of the plasma spray gun.

[0012] As one preferred embodiment, the device further includes: The air inlet is used to connect to the supply equipment; The powder delivery pipe is connected to the air inlet and the premixing chamber respectively, and is used to deliver the powder and the carrier gas into the premixing chamber.

[0013] To achieve the second objective, the present invention provides a spraying method for an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, the method comprising the following steps: The coaxial carrier gas powder delivery device provided in the first aspect of the present invention is assembled onto the plasma spray gun so that the jet cavity is coaxially connected with the nozzle of the plasma spray gun. Select a base material and fix the base material using a fixing clamping device; Turn on the plasma equipment, set the spraying parameters, and control the plasma spray gun to generate a laminar plasma jet with a jet length of 100mm-1000mm under atmospheric conditions. Turn on the coaxial carrier gas powder delivery device, and send the powder and carrier gas into the premixing chamber to mix evenly. The premixed powder-carrying gas enters the jet chamber from the premixing chamber through eight powder delivery channels and mixes with the laminar plasma jet injected into the jet chamber in a direction that tends to be coaxial. The robot arm is controlled to move the plasma spray gun, and the laminar flow plasma jet with eight-hole coaxial carrier gas is used to spray the powder onto the surface of the substrate material to obtain powder coatings with different structures.

[0014] As one of the preferred embodiments, the utilization rate of the powder is not less than 90%, and the jet length of the ejected laminar plasma jet is not less than 0.3m; the powder coating includes a metal coating, and the bonding strength between the metal coating and the substrate material is greater than 40MPa.

[0015] Compared with the prior art, this application has the following advantages: The eight-hole coaxial laminar flow carrier gas powder delivery device provided in this application embodiment can largely avoid the influence of the laminar flow state of the atmospheric laminar plasma jet, and does not affect the heating and acceleration process of powder particles. Simultaneously, the powder delivery device is coaxial with the mainstream direction of the plasma jet, and the carrier gas flow rate can be adjusted between 1.5 SLPM and 3.5 SLPM, achieving a powder utilization rate of over 90%, significantly improving powder delivery efficiency and refining the powder heating and acceleration trajectory. Furthermore, the disturbance-free powder delivery results in a minimum apparent length of 0.3 m for the plasma jet. When using this device to prepare metal coatings, a metal coating with a bonding strength greater than 40 MPa can be obtained.

[0016] The method and the device described above have the same advantages over the prior art, and will not be repeated here. Attached Figure Description

[0017] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a perspective view of an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying according to an embodiment of this application; Figure 2 This is a front view of an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying according to an embodiment of this application; Figure 3 This is a side view of an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying according to an embodiment of this application; Figure 4 This is a side cross-sectional view of an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying according to an embodiment of this application; Figure 5 This is a flowchart illustrating the steps of a spraying method using an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, as described in one embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 1. Powder feeder; 11. Jet chamber; 12. Powder feed channel; 2. Premixing component; 3. Premixing chamber; 4. Chuck; 5. Positioning flange; 6. Air inlet; 7. Powder feed pipe. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that the gas flow states in atmospheric plasma spraying are turbulent and laminar, respectively. Currently, commonly used plasma spray guns use turbulent gas, with powder feeding methods including unidirectional or bidirectional internal powder feeding. Under atmospheric conditions, another working form of DC non-transfer arc plasma jets is long laminar plasma, characterized by its length (long jet length), straightness (small axial physical gradient), and precision (concentrated beam). It possesses excellent stability, controllability, low noise, small airflow pulsation, minimal cold air entrainment, and slow axial energy decay, making it completely different from traditional atmospheric plasma spraying technology. This technology, through the aerodynamic design of a special internal channel structure of the plasma generator, reduces the influence of the cold air boundary layer on the arc root motion, greatly limiting the re-breakdown and re-extinction modes of the arc root, causing the anode arc root to tend to be in a steady-state attachment process. Ultimately, it can achieve a smaller exit Reynolds number and turbulent kinetic energy, generating plasma jets of different lengths (100-1000 mm) under atmospheric conditions.

[0022] Atmospheric laminar plasma spraying technology provides ceramic powder particles with an ultra-long acceleration process, resulting in a large amount of vapor-deposited quasi-columnar yttrium-based ceramic coating through prolonged heating. This is characterized by low flight speed and ultra-high particle surface temperature. The alumina and YSZ particles used exhibit very high surface temperatures within a spraying distance of 50-350 mm, with results even approaching the theoretical limit of 4773 K measured by the DPV-2000 temperature measurement system. At a spraying distance of 500 mm, the particle surface temperature is between 2100-2300 K, and alumina particles with a surface temperature of around 2500 K can still be detected at this distance.

[0023] The extremely long heating process imparts a high temperature to the particles. For high-melting-point ceramic particles, it can significantly increase the particle temperature. However, for metal alloy coatings, the particles are heated to an overheated and molten state by the long laminar plasma jet. The liquid overheated metal in the plasma jet will directly interfere with the laminar plasma flow characteristics, causing the plasma jet to be reduced from a maximum of 0.5m to less than 0.1m and generating huge noise. This drastically shortens the heating and acceleration process of the flying powder particles, resulting in poor coating quality and the loss of the technical advantages of atmospheric laminar plasma spraying.

[0024] In addition, side-mounted powder feeding devices are commonly used for atmospheric plasma spraying. Side-mounted powder feeding refers to the method of feeding auxiliary gas and powder from the side of the nozzle during plasma spraying. During side-mounted powder feeding, the powder is delivered from the powder feeder through the powder feeding pipe 7 to the powder feeding nozzle on the side of the spray gun. The powder feeding gas carries the powder into the plasma arc, where it is rapidly heated to a molten or semi-molten state. The powder then impacts the pre-treated substrate surface at high speed with the plasma stream, forming a coating.

[0025] In the process of lateral carrier gas powder feeding, parameters such as carrier gas flow rate, powder feeding rate, and spraying distance can improve the uniformity of plasma sprayed coatings, including powder distribution uniformity, coating thickness uniformity, coating structure uniformity, and coating bonding strength uniformity. Lateral carrier gas is essentially a highly vertical crossflow, which is detrimental to the axial transport of powder. Although lateral carrier gas crossflow powder feeding has advantages in thermal spraying (especially plasma / flame spraying) such as simple structure and flexible adjustment, publicly available experiments and field data have revealed its inherent shortcomings, manifested in the following aspects: 1. The carrier gas must be at room temperature, as its density differs from that of high-temperature plasma by tens of times. The lateral carrier gas is typically a metal tube with a diameter of 2mm-4mm. When added to the thermal plasma, the spatial dispersion of the powder is extremely low, with a powder utilization rate of no more than 50%. This drastically increases the overall turbulence of the system, making it difficult to maintain the laminar flow state of the plasma jet. Therefore, although the carrier gas flow rate for lateral powder delivery can reach 1.5SLPM-2.5SLPM, both the carrier gas and the powder have a significant impact on various processes in plasma spraying.

[0026] 2. After the carrier gas cuts into the main flame at high speed from a vertical side, it can only "entrain" the powder in the local shear layer. As a result, a hollow cone distribution with a sparse center and a dense edge is formed. The concentration gradient along the injection direction is large, which leads to a fluctuation of more than ±25% in the powder flux per unit area and a poor uniformity of coating thickness.

[0027] 3. Some metal or ceramic particles have high inertia and are thrown towards the wall before they can penetrate to the center of the flame.

[0028] 4. A cold carrier gas (usually room temperature Ar or N2) cuts into a 10000K plasma arc at a speed of 80m / s-150m / s, instantly forming a local low-temperature layer on the injection side. Numerical simulations show that the temperature in this region can drop sharply by 2000K-3000K, resulting in "two-state" particles where the low-melting-point phase has vaporized and the high-melting-point phase has not yet melted through, ultimately increasing the porosity of the coating by 1.5-2 times.

[0029] 5. Side spray guns can only achieve effective deposition on the side of carrier gas injection. When the robot changes the scanning direction (such as 180° rotation), the powder beam is "blocked" outside the workpiece by the flame flow, and the instantaneous deposition efficiency drops by more than 40%.

[0030] 6. The high-speed transverse jet forms a periodic vortex street (Strouhal number ≈ 0.2) at the torch tube outlet, inducing plasma arc voltage fluctuations of ±8V; arc root drift causes instantaneous deviation of spraying power of ±6%, and local "unmelted black areas" or "over-melted nodules" appear in the coating, affecting the bonding strength.

[0031] In summary, the numerous limitations of lateral carrier gas powder delivery devices make it difficult to maintain a stable laminar flow state of the plasma jet under atmospheric conditions for extended periods. Furthermore, they cannot generate ultra-long jets (jets with a length of only 0.1m), thus hindering the reduction of flame length and powder heating time and preventing the full realization of the advantages of long-flow laminar plasma spraying. Especially when using laminar plasma methods to spray metal alloy coatings, the longer jet provides excellent heating to the metal alloy particles, causing them to be in a superheated, molten state. These superheated particles disrupt the laminar flow, and the use of a lateral carrier gas powder delivery system further complicates the process, making it impossible to maintain a stable laminar flow state of the plasma jet under atmospheric conditions for extended periods, resulting in an ultra-long jet with a length of only 0.1m.

[0032] Therefore, how to enable plasma spray guns to maintain a stable laminar flow state for a long time in an atmospheric environment, and how to use laminar flow plasma spraying to coat metal alloy coatings, so as to give full play to the advantages of long-term atmospheric laminar flow plasma spraying, has become an urgent technical problem to be solved.

[0033] In view of this, refer to Figures 1-4 As shown, Figures 1-4 These are, respectively, a perspective view, a front view, a side view, and a side sectional view of an eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying. Figures 1-4 As shown, the present invention provides an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying. The device includes: a powder delivery core 1 with a through hole forming a jet cavity 11 inside, and eight powder delivery channels 12 are formed on the through hole wall of the powder delivery core 1. The eight powder delivery channels 12 are evenly spaced along the circumference of the jet cavity 11. The jet cavity 11 is used to coaxially communicate with the nozzle of the plasma spray gun to allow the laminar plasma jet to be sprayed in; a premixing component 2 is fitted on the outer periphery of the powder delivery core 1 and forms a premixing cavity 3 between the premixing component 2 and the powder delivery core 1. The premixing cavity 3 is used to mix the carrier gas and powder evenly. Each powder feeding channel 12 is connected to the jet cavity 11 and the premixing cavity 3 respectively, and the axis of the powder feeding channel 12 is close to the injection direction of the laminar plasma jet, so that the premixed powder carrier gas enters the jet cavity 11 from the premixing cavity 3 through the powder feeding channel 12 and mixes with the laminar plasma jet injected into the jet cavity 11 in a direction that tends to be coaxial.

[0034] Specifically, the plasma spray gun in a plasma spraying system generates a plasma jet. The tungsten electrode (cathode) and nozzle (anode) of the spray gun are connected to the negative and positive terminals of the power supply, respectively. A high-frequency spark ignites an electric arc, ionizing the working gas (such as Ar or N2) supplied to the spray gun into a plasma jet under the action of the arc. This device is a powder feeding device optimized for plasma spraying equipment that generates long laminar flow plasma jets, and is suitable for different laminar flow spraying systems such as DC non-transfer arc plasma spray guns and annular plasma nozzles. For example, the applicable plasma spraying equipment has a rated power of 30kW, a stable output power of 25kW-26kW, an air flow rate of 7L / min-15L / min, and a highly controllable plasma jet length of 100m-400mm, which varies regularly according to the air flow rate and output power. The ambient noise during operation is below 80dB, the outlet temperature is 11000K, the outlet velocity is 1300m / s, and it maintains an ultra-long high-temperature zone. The laminar plasma jet generated by the spray gun has significant characteristics of being ultra-long, stable, and concentrated.

[0035] To achieve uninterrupted powder feeding, the powder feeding device is assembled with the nozzle of the spray gun, and the jet cavity 11 inside the powder feeding core 1 is connected to the nozzle. The jet cavity 11 is coaxial with the jet center of the nozzle, so that the laminar plasma jet is horizontally sprayed from the central laminar jet zone of the nozzle to the jet cavity 11, and horizontally passes through the jet cavity 11, and is sprayed from the outlet of the jet cavity 11 to the external matrix material.

[0036] A major improvement in this embodiment is the presence of eight evenly distributed powder feeding channels 12 on the powder feeding core 1, ensuring that the powder-carrying gas is dispersed into the jet cavity 11 from all sides. Since the powder-carrying gas is fed into the jet cavity 11 through the powder feeding channels 12 and mixed with the laminar plasma jet, the shape of the powder feeding channels 12 determines the transport path of the powder-carrying gas. In this embodiment, the powder feeding channels 12 are inclined towards the injection direction close to the laminar plasma jet, thus the angle between the central axis of the powder feeding channels 12 and the main jet axis is relatively small.

[0037] As a specific explanation of this embodiment, the injection direction of the laminar plasma jet in the eight-hole coaxial carrier gas powder delivery device is relative to the jet cavity 11. Specifically, the laminar plasma jet is injected from the central jet area of ​​the nozzle into the inlet of the jet cavity 11, passes horizontally along the jet cavity 11, and finally exits from the outlet of the jet cavity 11 onto the external matrix material. Therefore, the injection direction in this embodiment specifically refers to the direction in which the jet enters the jet cavity 11 from the nozzle; that is, the side closer to the nozzle is the injection end of the jet, and the side farther from the nozzle is the exit end. The axis of the powder delivery channel 12 is closer to the injection direction, meaning that each powder delivery channel 12 extends obliquely from the through-hole wall towards the side where the nozzle is located, thereby maintaining a small angle with the injection direction of the laminar plasma jet. Therefore, by making the powder carrier gas enter the laminar plasma jet in a coaxial manner in the jet direction, the reverse or vertical impact of the powder carrier gas flow into the main jet is avoided, the degree of disturbance is reduced, and the plasma jet is kept in a laminar or quasi-laminar state.

[0038] In some embodiments, the jet cavity 11 may be cylindrical, tapered, expanding, or other shapes, with its diameter ranging from the nozzle design of the spray gun to match different spray gun nozzles. Preferably, the inner diameter of the jet cavity 11 gradually increases in the direction away from the nozzle. In this embodiment, the inner diameter of the jet cavity 11 gradually increases from the inlet to the outlet, forming a conical shape with openings at both ends. The narrow opening communicates with the nozzle, while the flared opening faces outward.

[0039] Another significant advancement in this embodiment lies in the design of a premixing component 2 to premix the powder and carrier gas. The premixing component 2 is fitted onto the powder feeding core 1 to form a premixing cavity 3, ensuring uniform mixing of the carrier gas and powder before they enter the powder feeding channel 12. This also reduces the initial velocity of the interrupted airflow, further minimizing its impact on the laminar plasma main jet. For example, the premixing component 2 can be a shell with an inner diameter larger than the outer diameter of the powder feeding core 1, fitted around the outer periphery of the powder feeding core 1. The premixing cavity 3 can be designed as an annular cavity, formed by the outer wall of the powder feeding core 1 and the inner wall of the premixing component 2.

[0040] Notably, through systematic experimental verification, this invention has revealed that the number of powder feeding channels 12 significantly impacts jet stability, coating quality stability, and powder utilization. Through multiple spraying tests and flow field simulation analysis, this invention demonstrates that eight powder feeding channels 12 are uniformly arranged circumferentially along the through-holes, achieving spatial uniform distribution of the powder flow within the flame and precise, stable control of the powder feeding process. This fundamentally improves the coating quality, consistency, and production efficiency.

[0041] Powder is injected from a single nozzle, forming a concentrated "powder bundle" in the high-temperature flame. This results in a "Gaussian distribution" of the coating cross-section (thick in the middle and thin at the edges), and inconsistent heating and acceleration of powder particles at the center and periphery of the flame, potentially leading to unmelted particles or pores within the coating. The eight-hole powder feeder 1 precisely divides a single powder stream into eight independent, fine powder streams within the feeder, simultaneously injecting them into the flame through eight small holes (symmetrically distributed in a ring) surrounding the nozzle. The powder is injected across the entire annular cross-section of the flame, rather than at a central point. This allows for more efficient utilization of the flame's energy and momentum, and more uniform heating and acceleration of the powder particles. The resulting coating exhibits a highly uniform thickness across the entire scan width, eliminating the phenomenon of being thicker in the middle and thinner at the edges. Simultaneously, the particles melt uniformly, resulting in a denser coating with significantly reduced porosity.

[0042] Because the powder is uniformly fed into the effective area of ​​the flame, it avoids the situation where powder "escapes" from the edge of the flame and is not captured by the substrate. More powder is effectively used to build the coating, reducing waste. The eight-hole powder feed core 1 allows for a higher powder feed rate, and the powder is more widely distributed in the flame, avoiding the risk of powder particles colliding with each other, cooling, and clogging the nozzle in the center of the flame. The system can use a higher powder feed rate without reducing coating quality, thereby accelerating the coating deposition rate and improving production efficiency.

[0043] The eight-hole design of the eight-hole powder feeder core 1 reduces powder pulsation and fluctuations during the conveying process. The eight channels distribute the powder flow, making each stream more stable. Even with minor fluctuations in the powder-feeding carrier gas, the combined effect of the eight channels significantly reduces their impact on the overall powder distribution within the flame compared to a single powder stream. This results in a wider process window and extremely high coating quality consistency across batch-produced parts.

[0044] Uniform powder distribution means that heat is transferred to the substrate more evenly, avoiding localized overheating. This helps reduce coating cracking or warping caused by thermal stress. Each powder particle has a greater probability of receiving optimal heat and kinetic energy, improving the melting quality of the particles and reducing defects such as unmelted particles and oxide inclusions in the coating, thereby enhancing the coating's bonding strength and overall performance (such as corrosion resistance and wear resistance).

[0045] For R&D and process optimization, the eight-hole powder feeder 1 offers greater flexibility. Operators can obtain high-quality coatings within a wider range of power and powder feed rate parameters, making process debugging and optimization easier. It is suitable for atmospheric plasma spraying, and can spray ceramics (such as yttrium oxide-stabilized zirconia YSZ thermal barrier coating), metal alloys, etc. It is also suitable for supersonic flame spraying, and can spray high-performance metal ceramics and alloy coatings such as tungsten carbide-based (WC-Co) and nickel-based alloys.

[0046] It can be seen that the eight-hole coaxial carrier gas powder delivery device can control the gas composition entrained in the plasma jet in the atmospheric environment and effectively prevent the external airflow from disturbing the plasma jet, maintain the ultra-long heating and acceleration process of particles in the plasma jet, and give full play to the performance advantages of atmospheric laminar plasma spraying technology.

[0047] In summary, the eight-hole coaxial laminar flow carrier gas powder delivery device proposed in this patent can largely avoid the influence of the laminar flow state of the atmospheric laminar plasma jet, and does not affect the heating and acceleration process of powder particles. Simultaneously, the powder delivery device is coaxial with the mainstream direction of the plasma jet, and the carrier gas flow rate can be adjusted between 1.5 SLPM and 3.5 SLPM, achieving a powder utilization rate of over 90%, significantly improving powder delivery efficiency and refining the powder heating and acceleration trajectory. Furthermore, the interference-free powder delivery ensures a minimum apparent length of 0.3 m for the plasma jet, enabling the preparation of metal coatings with a bonding strength greater than 40 MPa. The technical advantages of the eight-hole powder delivery core 1 make it particularly suitable for high-requirement thermal spraying scenarios, such as aerospace (high-temperature protective coating for engine blades), precision machinery (wear-resistant coatings for bearings and molds), new energy (conductive coatings for fuel cell bipolar plates), and chemical industry (corrosion-resistant coatings for pipelines and storage tanks).

[0048] Preferably, the diameter of each powder feeding channel 12 is 1.2 mm to accommodate at least one of metal powder, metal alloy powder, and ceramic powder. In this embodiment, each hole has a diameter of 1.2 mm. This hole size was determined through multiple sets of powder flow rate and powder particle size adaptation experiments, allowing for the continuous transport of standard plasma-sprayed metal or ceramic powder. This hole size not only ensures uniform injection of the powder-carrying gas flow into the jet cavity 11 but also achieves stable powder feeding rates and coaxial jet mixing characteristics under different powder systems, further improving powder utilization and coating density. This invention, by designing appropriate powder feeding hole diameters and the number of channels, utilizes eight coaxial powder feeding holes to reduce the interference of powder feeding conditions on the laminar flow state of the plasma jet, generating a stable, long-duration laminar plasma jet under atmospheric conditions, with a jet length exceeding 0.5 m, achieving sufficient particle heating. Using this carrier gas powder feeding device, a laminar plasma spray gun can stably prepare high-quality YSZ coatings on different substrates.

[0049] In other embodiments, the aperture of the powder feeding channel 12 can be appropriately adjusted according to the powder particle size range and the carrier gas flow rate.

[0050] Furthermore, in the configuration where the axis of the powder feeding channel 12 is closer to the injection direction of the laminar plasma jet, each powder feeding channel 12 is an inclined straight hole, and the inlet communicating with the premixing chamber 3 is closer to the side communicating with the nozzle of the powder feeding core 1 than the outlet communicating with the jet chamber 11. Each powder feeding channel 12 is a straight through hole, with the inlet of each powder feeding channel 12 located on the outer wall of the powder feeding core 1 and communicating with the premixing chamber 3, and the outlet opening on the inner wall of the powder feeding core 1, i.e., on the cavity wall of the jet chamber 11. The inlet of the powder feeding channel 12 is closer to the nozzle than the outlet, and the powder carrier gas delivered by the powder feeding channel 12 has a small inclination angle with the laminar plasma jet on the side closer to the nozzle. After the carrier gas and powder are fully mixed in the premixing chamber 3, the injection direction of the powder gas flow tends to be parallel to the direction of the plasma jet, and then merges with the laminar plasma jet injected from the nozzle in the same direction.

[0051] As a specific illustration of this embodiment, the system further includes: a through-hole in the premixing component 2 forming a mounting cavity for accommodating the powder feeding core 1, the mounting cavity including a first mounting area, a second mounting area, and a third mounting area with inner diameters decreasing from large to small; the outer edge portion of the powder feeding core 1 away from the nozzle is engaged in the first mounting area, the inner edge portion near the nozzle is fitted in the third mounting area, and the middle portion located between the outer edge portion and the inner edge portion forms a premixing cavity 3 with the third mounting area. Exemplarily, the premixing component 2 is a shell with an internal through-hole, the outer wall surface of the shell is stepped, the inner wall surface is stepped and fits against the outer wall surface of the powder feeding core 1, and the longitudinal cross-section of both the shell and the powder feeding core 1 is annular. One end of the annular shell is connected to the plasma spray gun via a chuck 4, so that the powder feeding device fits against the outside of the plasma nozzle. The chuck 4 is an annular chuck 4, integrally formed with the end face of the shell. A circular chuck 4 is fixed to the outside of the spray gun with a certain outer diameter, which can be adjusted from 40mm to 70mm, allowing the plasma robot to maintain overall stability at a maximum swing speed of 1.5m / s. Because this device uses coaxial powder feeding, the robot can be programmed along any path, and the spray gun can achieve effective deposition in all scanning directions.

[0052] The mounting cavity extends axially through the outer shell. When the powder feeding core 1 is placed inside the mounting cavity, both end faces of the powder feeding core 1 are flush with both end faces of the outer shell. Based on the nozzle direction, the mounting cavity is divided into a first mounting area, a second mounting area, and a third mounting area from back to front, with the inner diameters of the three areas decreasing in size. The outer diameter of the rear end (outer edge) of the powder feeding core 1 matches the inner diameter of the first mounting area, allowing it to fit snugly within the first mounting area; the outer diameter of the front end (inner edge) of the powder feeding core 1 matches the inner diameter of the third mounting area, allowing it to fit snugly within the third mounting area; the outer diameter of the middle portion of the powder feeding core 1 is smaller than the inner diameter of the second mounting area, with a gap between them, thus forming an annular premixing cavity 3.

[0053] The outer surface of the middle section extends in an arc shape from the rear end to the front end, until its outer diameter is the same as the inner diameter of the cavity in the third mounting area. Therefore, the multi-stage stepped mounting cavity achieves precise positioning and stable assembly of the powder feeding core 1, aligning it with the center of the nozzle. Furthermore, the snap-fit ​​structure allows for quick replacement of the powder feeding core 1, adapting to different materials or orifice designs.

[0054] Preferably, a positioning flange 5 is provided on the outer edge of the powder feeding core 1, and a positioning groove is provided on the housing that surrounds the first mounting area. The positioning flange 5 is engaged with the positioning groove. When the powder feeding core 1 is engaged with the mounting cavity of the housing, the positioning groove and the positioning flange 5 further tighten the connection between the two. Figure 4 As shown, the positioning groove is located in the first mounting area near the second mounting area.

[0055] Therefore, the multi-stage stepped mounting cavity achieves precise positioning and stable assembly of the powder feeding core 1, aligning it with the center of the nozzle. Furthermore, the snap-fit ​​structure allows for quick replacement of the powder feeding core 1, adapting to different materials or orifice designs.

[0056] Furthermore, the powder feeding channel 12 falls into the second installation area, with the inlet located at the front end of the second installation area and the outlet located at the rear end of the second installation area.

[0057] In another embodiment, the device further includes: an air inlet 6 for connecting to a supply device; and a powder delivery pipe 7, connected to both the air inlet 6 and the premixing chamber 3, for delivering powder and carrier gas into the premixing chamber 3. In this embodiment, the air inlet 6 can use nitrogen, argon, or a mixed gas, with an inlet diameter of 4mm-8mm, and is connected using a standard quick-connect fitting. The powder delivery pipe 7 is a straight pipe and can be made of stainless steel, high-temperature alloy, or other materials. The powder delivery pipe 7 connects to a gas cylinder via the air inlet 6 and is also connected to a powder feeder, allowing it to deliver carrier gas and powder into the premixing chamber 3.

[0058] Correspondingly, regarding the second aspect, please refer to Figure 5 As shown, Figure 5 This is a flowchart illustrating the steps of a tail gas treatment method based on full-temperature-range synergistic optimization. The present invention also provides a spraying method using an eight-hole coaxial carrier gas powder feeding device for atmospheric laminar plasma spraying, utilizing the eight-hole coaxial carrier gas powder feeding device for atmospheric laminar plasma spraying provided in the first aspect of the present invention for spraying. The method includes the following steps: S1. Assemble the coaxial carrier gas powder delivery device described above onto the plasma spray gun, so that the jet cavity 11 is coaxially connected with the nozzle of the plasma spray gun.

[0059] S2. Select the base material and fix it using a clamping device.

[0060] S3. Turn on the plasma equipment, set the spraying parameters, and control the plasma spray gun to generate a laminar plasma jet with a jet length of 100mm-1000mm under atmospheric conditions.

[0061] S4. Turn on the coaxial carrier gas powder feeding device, and send the powder and carrier gas into the premixing chamber 3 to mix evenly. The premixed powder-carrying gas enters the jet chamber 11 from the premixing chamber 3 through the eight powder feeding channels 12, and mixes with the laminar plasma jet injected into the jet chamber 11 in a direction that tends to be coaxial.

[0062] S5. Control the robotic arm to move the plasma spray gun, and use an eight-hole coaxial carrier gas powder delivery laminar flow plasma jet to spray onto the surface of the substrate material to obtain powder coatings with different structures.

[0063] This method relies on three core control units: a plasma control unit, a powder feeding control unit, and a motion control unit. These three units can be centrally coordinated through a main control system to achieve synchronous coordination of plasma jet generation, powder supply, and spraying path. The plasma control unit controls the spraying parameters of the plasma equipment, including arc current, voltage, and working gas flow rate. For example, when the plasma equipment is turned on, a mixture of nitrogen and argon working gas is used, with a rated output power of 30kW, a stable output power of 25kW-26kW, and a gas flow rate of 7L / min-15L / min. By adjusting different gas flow rates and output power, long laminar plasma jets with jet lengths between 100mm and 1000mm can be obtained under atmospheric conditions. The powder feeding control unit controls the powder feeding parameters of the coaxial carrier gas powder feeding device, including carrier gas flow rate and powder feeding rate. After selecting the carrier gas and powder type, the powder feeding control unit is activated to divide the ceramic powder into eight fine streams and uniformly feed them into the laminar plasma jet. The motion control unit controls the motion parameters of the robotic arm, including spraying distance, spraying speed, spraying angle, scanning step distance, number of scans, and scanning path. It adjusts the working range between the substrate material and the plasma jet, controls the distance between the jet and the substrate, and the speed and interval of the jet on the substrate surface, thus effectively controlling the substrate temperature during the spraying process. The robotic arm controls the long laminar flow plasma jet ejected from the spray gun to reciprocate on the workpiece surface at a certain speed and interval. By controlling different spraying distances, powder feed rates, and substrate temperatures, coatings with different structures can be obtained.

[0064] This invention's spraying method employs an eight-hole coaxial carrier gas powder feeding structure, achieving coaxial mixing and stable entrainment of powder and laminar plasma jet, thus avoiding the disruption of the jet flow field caused by traditional lateral powder feeding. According to experimental results, the powder utilization rate is ≥90%, and applicable powder types include metal powders, ceramic powders, and composite powders. Under powder feeding rates of 3g / min-30g / min, and within a spraying distance of 1500mm-400mm, the maximum acceleration can reach 150m / s-250m / s. The bonding strength between the metal coating obtained by spraying with metal powder and the substrate material is greater than 40MPa. Thus, under atmospheric laminar plasma spraying conditions, this powder feeding device significantly extends the powder heating and acceleration path, improving powder utilization and coating bonding strength. Experiments demonstrate that metal or ceramic coatings prepared using this method exhibit high density, uniform thickness, and strong adhesion, with a surface quality significantly superior to traditional powder feeding processes.

[0065] The following two specific examples further illustrate the embodiments of the present invention.

[0066] Example 1: Nickel-based superalloy K465 alloy has high resistance to creep and fatigue and high temperature resistance, and is usually used as stationary blades of propellers.

[0067] A method for spraying a YSZ coating onto the surface of high-temperature alloy K456 using an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying: S11. Prepare high-temperature alloy K456 material and fix it to the base temperature control unit using a fixing clamping device.

[0068] S12. Sandblast the substrate surface, and then use supersonic flame to spray the NiCrAlY bonding layer with a thickness of 100µm-150µm.

[0069] S13. YSZ powder with a particle size of 37µm-69µm is used, and the powder feeding rate is 3g / min-4g / min.

[0070] S14. Activate the plasma control device and the coaxial carrier gas powder delivery device. Using the plasma control device, adjust the working gas to nitrogen and argon at a volume ratio of 7:3, operating current of 160A, and output power of 25kW-26kW to generate a laminar plasma jet. Utilize the coaxial carrier gas powder delivery device to feed the YSZ powder and carrier gas into the premixing chamber 3 for uniform mixing. The premixed carrier gas then enters the jet chamber 11 from the premixing chamber 3 through eight powder delivery channels 12, mixing with the laminar plasma jet in a coaxial direction.

[0071] S15. Select a spraying distance of 250mm, a scanning speed of 0.4m / s, and an interval of 4mm. Control the robotic arm to spray the high-temperature alloy K456 surface 10 times to obtain a coating with a thickness of more than 200µm.

[0072] S16. First, turn off the powder feeding control unit, then turn off the plasma control unit, and finally turn off the plasma generator circulating water device.

[0073] S17. Wait for the substrate temperature control unit to lower the sample temperature to room temperature, remove the sample, and obtain a YSZ coating with a certain vertical crack structure.

[0074] Example 2: DZ640M is a cobalt-based precipitation-hardening, directionally solidified columnar superalloy with an operating temperature below 1040℃. This alloy has a stable microstructure and excellent resistance to thermal fatigue, oxidation, and hot corrosion. It also exhibits good overall properties such as creep resistance, endurance, and fatigue resistance. Its main products include directionally solidified castings such as turbine guide vanes.

[0075] A method for spraying a YSZ coating onto the surface of a DZ640M using an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying: S21. Prepare DZ640M material and fix it to the substrate temperature control unit using a fixing clamping device.

[0076] S22. The substrate surface is sandblasted, and then the NiCrAlY adhesive layer is sprayed using a supersonic flame to a thickness of 100µm-150µm.

[0077] S23. Use YSZ powder with a particle size of 37µm-69µm and a powder feeding rate of 3g / min-4g / min.

[0078] S24. Activate the plasma control device and the coaxial carrier gas powder delivery device. Using the plasma control device, adjust the working gas to nitrogen and argon at a volume ratio of 7:3, operating current of 160A, and output power of 25kW-26kW to generate a laminar plasma jet. Utilize the coaxial carrier gas powder delivery device to feed the YSZ powder and carrier gas into the premixing chamber 3 for uniform mixing. The premixed carrier gas then enters the jet chamber 11 from the premixing chamber 3 through eight powder delivery channels 12, mixing with the laminar plasma jet in a coaxial direction.

[0079] S25. Select a spraying distance of 250mm, a scanning speed of 0.4m / s, and an interval of 4mm. Control the robotic arm to spray the DZ640M surface 10 times in a cycle to obtain a coating with a thickness of more than 200µm.

[0080] S26. First, turn off the powder feeding control unit, then turn off the plasma control unit, and finally turn off the plasma generator circulating water device.

[0081] S27. Wait for the substrate temperature control unit to lower the sample temperature to room temperature, remove the sample, and obtain a YSZ coating with a certain vertical crack structure.

[0082] It should be noted that, for the method embodiments, the embodiments of this application are not limited to the described order of actions, because according to the embodiments of this application, some steps may be performed in other orders or simultaneously.

[0083] The above method embodiments are basically similar to the system embodiments, so the description is relatively simple. For relevant details, please refer to the description of the system embodiments.

[0084] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0085] It should also be noted that, in this document, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations, nor should they be construed as indicating or implying relative importance. Moreover, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device.

Claims

1. An eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, characterized in that, The device includes: The powder feeding core has a through hole inside to form a jet cavity. Eight powder feeding channels are opened on the wall of the through hole of the powder feeding core. The eight powder feeding channels are evenly spaced along the circumference of the jet cavity. The jet cavity is used to communicate coaxially with the nozzle of the plasma spray gun to allow laminar plasma jet to be sprayed in. A premixing component is fitted around the outer periphery of the powder feeding core and forms a premixing cavity between the powder feeding core and the premixing cavity, which is used to mix the carrier gas and powder evenly. Each of the powder feeding channels is connected to the jet cavity and the premixing cavity, and the axis of the powder feeding channel is close to the injection direction of the laminar plasma jet, so that the premixed powder carrier gas enters the jet cavity from the premixing cavity through the eight powder feeding channels and mixes with the laminar plasma jet injected into the jet cavity in a direction that tends to be coaxial.

2. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 1, characterized in that, Each of the powder feeding channels has a diameter of 1.2 mm to accommodate at least one of metal powder, metal alloy powder, and ceramic powder.

3. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 1, characterized in that, Each of the powder feeding channels is an inclined straight hole, and the inlet communicating with the premixing chamber is closer to the side of the nozzle communicating with the powder feeding core than the outlet communicating with the jet chamber.

4. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 1, characterized in that, The inner diameter of the jet cavity gradually increases in the direction away from the nozzle.

5. An eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to any one of claims 1-4, characterized in that, The system also includes: the internal through-hole of the premixed component forms a mounting cavity for accommodating the powder feeding core, the mounting cavity including a first mounting area, a second mounting area and a third mounting area with inner diameters arranged from large to small; The outer edge of the powder feeding core, away from the nozzle, is engaged in the first mounting area, while the inner edge, close to the nozzle, is fitted into the third mounting area. The middle portion between the outer and inner edges forms the premixing cavity with the third mounting area.

6. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 5, characterized in that, The device further includes: A positioning flange surrounds the outer periphery of the outer edge component of the powder feeding core. The positioning groove is provided at the position where the premixed component encloses and forms the first installation area; The positioning flange is engaged within the positioning groove.

7. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 1, characterized in that, The device further includes: A chuck, which is connected to the premixed component and is used to fit around the periphery of the plasma spray gun.

8. The eight-hole coaxial carrier gas powder delivery device for laminar plasma spraying according to claim 1, characterized in that, The device further includes: The air inlet is used to connect to the supply equipment; The powder delivery pipe is connected to the air inlet and the premixing chamber respectively, and is used to deliver the powder and the carrier gas into the premixing chamber.

9. A spraying method using an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying, characterized in that, The method includes the following steps: The coaxial carrier gas powder delivery device as described in any one of claims 1-8 is assembled onto the plasma spray gun, so that the jet cavity is coaxially connected with the nozzle of the plasma spray gun. Select a base material and fix the base material using a fixing clamping device; Turn on the plasma equipment, set the spraying parameters, and control the plasma spray gun to generate a laminar plasma jet with a jet length of 100mm-1000mm under atmospheric conditions. Turn on the coaxial carrier gas powder delivery device, and send the powder and carrier gas into the premixing chamber to mix evenly. The premixed powder-carrying gas enters the jet chamber from the premixing chamber through eight powder delivery channels and mixes with the laminar plasma jet injected into the jet chamber in a direction that tends to be coaxial. The robot arm is controlled to move the plasma spray gun, and the laminar flow plasma jet with eight-hole coaxial carrier gas is used to spray the powder onto the surface of the substrate material to obtain powder coatings with different structures.

10. The spraying method of an eight-hole coaxial carrier gas powder delivery device for atmospheric laminar plasma spraying according to claim 9, characterized in that, The utilization rate of the powder is not less than 90%, and the jet length of the ejected laminar plasma jet is not less than 0.3m; the powder coating includes a metal coating, and the bonding strength between the metal coating and the substrate material is greater than 40MPa.

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