High velocity plasma torch and method

Abstract

A high velocity plasma spraying method and apparatus, with a preferred plasma pressure in the range of 3 to 10 bar, a preferred plasma enthalpy of 10 kJ / g or more, a preferred plasma enthalpy range of above 10 kJ / g and not more than 20 kJ / g, and a specific power (∑) preferably in the range of 16 kJ / g to 38 kJ / g.

Description

Technical Field

[0001] This disclosure relates to a high-speed plasma spraying method and apparatus. Background Technology

[0002] High-speed processes typically utilize pressurized gas or plasma to generate high-speed subsonic, sonic, and supersonic gas or plasma jets. High-quality coatings can be efficiently produced when the gas jet temperature is high enough to soften or melt the particles being sprayed, and the compressed gas flow velocity is high enough to provide the required density and other coating properties. Different materials require different optimal temperatures and velocities for the sprayed particles to achieve efficient high-quality coating formation. Materials with high melting points and low thermal conductivity (e.g., oxides) may require relatively high gas temperatures and the high heat transfer capacity of the plasma jet to melt or soften the particles sufficiently to form a high-quality coating.

[0003] Heat transfer from gas or plasma to feedstock can be characterized by heat transfer potential (HTP), which is a key parameter determining the ability of plasma to heat particles and the matrix.

[0004] Where λ is the plasma thermal conductivity; T is the plasma temperature. HTP is correlated with plasma enthalpy H and specific power (∑). Plasma enthalpy H, specific power (∑), and thermal efficiency η can be determined by the following formulas: Σ=W / G;H=W·η / G;η=1-Lw / W;W=U·I Where Lw is the power loss conducted to the cooling medium (water); U is the voltage of the plasma nozzle; I is the plasma current; W is the electrical power of the nozzle; and G is the total plasma flow rate, which can be measured in terms of, for example, grams per second (g / s) or kilograms per second (kJ / s). The plasma enthalpy H and specific power ∑ can be easily calculated using these parameters directly measured experimentally. Therefore, plasma enthalpy H and / or specific power ∑ are often used to characterize plasma conditions and further calculate the plasma's HTP and temperature.

[0005] The main high-speed industrial processes can be divided into the following four categories: cold spraying or kinetic energy spraying, warm spraying, HVAF (high-speed gas fuel), HVOF (high-speed oxygen fuel), and plasma-based high-speed processes. Among the first three processes, HVOF can provide the highest HTP value. The main HVOF parameters can be found in Table 1, which is based on data from the paper "Analysis of Potential Improvement of HVOF Based Processes" published by A. Voronetski and V. Belashchenko at ITSC 2006.

[0006] Table 1: Properties of gaseous hydrocarbon fuels when α=1

[0007] In Table 1, T C@0.1 It is the combustion temperature at atmospheric pressure (0.1 MPa); T CC@0.5 The combustion temperature is the combustion temperature at a combustion pressure of 0.5 MPa (≈70 psi); λ is the thermal conductivity of the combustion products; E K =(ρW 2 ) ne (Measured in kg / (m·s²)) is the specific kinetic energy of the combustion products leaving the nozzle; HTP=(λT) CC@0.5 ) ne This is the thermal potential characterizing the efficiency of heat transfer from combustion products to the sprayed particles. The range of available thermal potentials and specific kinetic energies allows the HVOF process to spray high-quality coatings, such as those using certain carbide and metallic raw materials. However, the HTP available for the HVOF process may be insufficient for spraying high-quality coatings, such as those using high-melting-point ceramics and metals.

[0008] The plasma temperature and associated enthalpy transfer ratio (HTP) can be significantly higher than those of gaseous or liquid hydrocarbon fuels listed in Table 1, thus providing a wider operating range and creating more opportunities for high-quality coatings using high-temperature materials. Tables 2 and 3 list some reference plasma data for nitrogen plasma and argon-20% hydrogen plasma at atmospheric pressure. Table 2 shows the performance of nitrogen plasma. Table 3 shows the performance of argon-20% H2 plasma. It should be noted that argon plasma without added H2 or He can only produce plasmas with enthalpy values ​​lower than those shown in Table 3.

[0009] These data are based on plasma data tables published in Thermal Plasmas, Fundamentals and Applications (Volume 1), by Maher I Boulos, Pierre Fauchais, and Emil Pfender, published by Plenum Press.

[0010] Table 2. Some properties of nitrogen plasma at atmospheric pressure

[0011] Table 3. Some properties of argon-20% hydrogen plasma at atmospheric pressure

[0012] It can be seen that when high-temperature materials need to be sprayed, plasma shows greater promise in high-speed thermal spraying processes compared to combustion products. Regarding nitrogen-based plasma, it is worth noting that it can provide significantly higher HTP (High-Temperature Tolerance) than combustion or argon-based plasma spraying processes.

[0013] Several patents disclose different designs and technologies for generating high-pressure, high-velocity plasma to deposit coatings. However, currently only the SG-100 plasma spray gun, initially disclosed in US 3,823,302, equipped with a Mach II anode / nozzle, has been commercialized and can produce relatively high-quality coatings. The SG-100 has also undergone some upgrades, disclosed in patents US 5,444,209 and US 6,897,402. According to the SG-100 Operation Manual (Praxex Surface Technologies, SG-100 Plasma Spray Gun Operation Manual, Manual No.: 05001760) and some other experimental data, the high-speed SG-100 scheme equipped with a Mach-II anode is only suitable for plasma gases composed of argon-helium mixtures. It is reported that the maximum power of the plasma spray gun for the Mach II scheme is 72 kW, the estimated HTP is 4,000 W / m, and the operating enthalpy range is approximately 10 kJ / g-12 kJ / g. This level of HTP, coupled with a maximum spray gun power of 72kW, limits the operating range of the SG-100, and according to the manual, coatings can only be applied at a maximum spray rate of 25g / min. Furthermore, helium is a very expensive gas, which adds another disadvantage to the SG-100.

[0014] Other attempts to develop more efficient high-pressure, high-speed plasma solutions have failed to meet certain practical requirements. For example, US Patent 5,637,242 discloses a high-speed, high-pressure plasma gun operating with nitrogen. This method is very promising because, according to Table 2, nitrogen plasma can meet the requirements for efficient high-speed plasma. However, this publication indicates that the plasma gun can only produce plasma with the following parameters: stagnation enthalpy in the range of 1740 BTU / lb–2904 BTU / lb or 4.04 kJ / g–6.75 kJ / g, corresponding to an HTP range of approximately 790 W / m–4300 W / m; jet temperature between 1794.2 K–3484.9 K; and stagnation pressure of 9.3 ATM–11.8 ATM. It can be seen that the available enthalpy and temperature are lower than those of the plasma produced by SG-100. It can also be seen that its enthalpy and pressure are comparable to those of plasma produced by the HVOF process.

[0015] Based on the above, it can be concluded that nitrogen-based plasmas hold great promise for relatively high-speed applications, which are currently only achievable under low enthalpy conditions below 6.75 kJ / g. For example, high-temperature ceramics and metals may require enthalpy values ​​of approximately 14 kJ / g–15 kJ / g or even higher to melt or soften particles of a specific size within the extremely short residence time associated with supersonic plasmas generated at pressures of 3 bar or higher. It should be noted that a preferred objective of this disclosure is to provide a plasma spray gun and process capable of reliably and efficiently generating N2-based supersonic plasmas with a plasma stagnation pressure of 3 bar or higher and a plasma enthalpy of 10 kJ / g or higher. The high-velocity plasma (HTP) of such plasmas can be greater than 11000 W / m–12000 W / m, which is significantly higher than the HTP of all existing HVOF and high-speed plasma processes. Summary of the Invention

[0016] A method for depositing a coating using a plasma spray gun includes: A plasma spray gun is provided, comprising a cathode module and an anode module. The cathode module has a cathode electrode, and the anode module has an anode electrode. The anode electrode has an anode shaft, an inlet region, and a cylindrical region with a diameter D1. The plasma spray gun generates a plasma arc, and the plasma arc has an anode arc root attachment region located inside the anode. The plasma spray gun further includes a first shaping module (FM1) and a second shaping module (FM2). The first shaping module has a convergent-diffusion nozzle with a throat diameter of Dcr and an outlet diameter of D2. The second shaping module is located downstream of the first shaping module and downstream of the anode arc root attachment region. The second forming module controls one or more parameters of the plasma jet within the second forming module. The inter-electrode module controls the plasma arc channel located between the cathode electrode and the anode electrode, wherein one end of the inter-electrode module is adjacent to the cathode module, the second end is adjacent to the anode module, and a guide plug is provided near the cathode; At least one neutral electrode insert; The plasma spray gun also includes two channels for delivering plasma gas in a total volume G; The plasma spray gun generates a voltage (U) higher than 150V and a current (I) lower than 500A, with a power W = U × I; The raw material is fed into the plasma jet and a coating is deposited on the substrate; The plasma gas includes molecular gas with a volume fraction greater than 50%. The range of W / G is 16kJ / g-38kJ / g; One of the channels for conveying plasma gas includes a first plasma gas channel located between the cathode and the guide plug. The first plasma gas channel is used to convey plasma gas of quantity G1. The plasma gas is guided through a plurality of orifices with a surface area of ​​S1, wherein a swirling flow with a swirling intensity of Vort1 = G1 / S1 is formed. The other channel for transporting plasma gas includes a second plasma gas channel, which is located between the inter-electrode module and the cylindrical region of the anode. This second plasma gas channel is used to transport plasma gas in a quantity of G2. The plasma gas is guided through multiple orifices, the surface area of ​​which is S2, forming a swirling flow with a swirling intensity of Vort2 = G2 / S2; and Among them, the flow rate of G2 is greater than 25 L / min; and Wherein, Vort2 is greater than 0.4 g / (s·mm²).

[0017] A plasma spray gun, comprising: A cathode module and an anode module, wherein the cathode module has a cathode electrode, the anode module has an anode electrode, the anode electrode has an anode shaft, an inlet region, and a cylindrical region with a diameter of D1, wherein the plasma spray gun generates a plasma arc, and the anode arc root attachment region of the plasma arc is located inside the anode; The plasma spray gun also includes a first shaping module (FM1) and a second shaping module (FM2). The first shaping module has a convergent-diffusion nozzle with a throat diameter of Dcr and an outlet diameter of D2. The second shaping module is located downstream of the first shaping module and downstream of the anode arc root attachment zone. The second forming module controls one or more parameters of the plasma jet within the second forming module; An inter-electrode module controls a plasma arc channel located between the cathode electrode and the anode electrode. One end of the inter-electrode module is adjacent to the cathode module, and the second end of the inter-electrode module is adjacent to the anode module. A guide plug is provided near the cathode. At least one neutral electrode insert; The plasma spray gun also includes two channels for delivering plasma gas in a total volume of G; The plasma spray gun operates under conditions of a voltage (U) higher than 150V and a current (I) lower than 500A, with a power W = U × I; The plasma gas includes molecular gas with a volume fraction greater than 50%. The range of W / G is 16kJ / g-38kJ / g; One of the channels for conveying plasma gas includes a first plasma gas channel located between the cathode and the guide plug. The first plasma gas channel is used to convey plasma gas of quantity G1. The plasma gas is guided through a plurality of orifices with a surface area of ​​S1, wherein a swirling flow with a swirling intensity of Vort1 = G1 / S1 is formed. One of the channels for transporting plasma gas includes a second plasma gas channel, which is located between the inter-electrode module and the cylindrical portion of the anode. This second plasma gas channel is used to transport plasma gas in a quantity of G2. The plasma gas is guided through multiple orifices, the surface area of ​​which is S², forming a swirling flow with an intensity of Vort² = G² / S²; and Among them, the flow rate of G2 is greater than 25 L / min; and Wherein, Vort2 is greater than 0.4 g / (s·mm²). Attached Figure Description

[0018] The features and advantages of the claimed subject matter will become apparent from the following description of embodiments consistent therewith, which should be understood in conjunction with the accompanying drawings, wherein: Figure 1 A schematic diagram of a high-speed plasma system with a supersonic shaping module FM1 is provided; Figure 2 An embodiment of the high-speed plasma spray gun of the present invention is shown; Figure 3 A single-piece anode-FM assembly is shown; Figure 4 A cross-sectional view of the anode-FM assembly after it has been cut into two parts is shown; Figure 5 FM2 with two-stage expansion is shown; and Figure 6 A relatively detailed section of the optimized anode-FM combination is shown, with the cooling system shown in more detail. Detailed Implementation

[0019] As previously stated, this disclosure relates to systems and methods for relatively high-speed plasma spraying and plasma treatment of materials. Preferred systems and methods aim to efficiently generate nitrogen-based plasmas with a nitrogen content of not less than 50%, and their preferred features include one or more of the following: The preferred range of plasma pressure is 3 bar to 10 bar, more preferably 3 bar to 8 bar.

[0020] The plasma enthalpy is preferably 10 kJ / g or higher. The preferred plasma enthalpy range is higher than 10 kJ / g and not exceeding 20 kJ / g.

[0021] The specific power (∑) is in the range of 16 kJ / g to 38 kJ / g.

[0022] Figure 1 A schematic illustration of a plasma system for improvement and optimization in this invention is shown. As shown, the plasma system 2 is generally based on the plasma nozzle 4. The plasma system 2 may include various modules, including a DC power supply module (PS), a control module (CT), a plasma ignition module (IG), and an ignition circuit 16. The control module (CT) controls the flow rate of the plasma gas, the plasma current and voltage, and the sequence of events during plasma startup and shutdown. The ignition module IG may have a high-voltage, high-frequency oscillator. This oscillator can initiate a pilot arc 10 between the cathode 122 and the pilot plug PI. The DC power supply PS can be used to maintain the pilot arc 10. The pilot arc 10 can ionize at least a portion of the gas in the upstream plasma channel 34. The low-resistance path formed by the ionized gas allows the initiation of a main arc 12 in the arc channel 26 between the cathode 122 and the anode module A. After the main arc 12 is established, the switch 14 can be opened, thereby interrupting the pilot arc 10.

[0023] The plasma jet gun 4 itself may include a cathode module CM, an interelectrode insertion module (IEI), an anode module (A), and a plasma jet shaping module FM (including FM1 and FM2). The cathode module CM has at least one cathode 122; the interelectrode insertion module (IEI) is used to extend and stabilize the arc; the plasma jet shaping module FM is located downstream of the anode module A and the anode arc root attachment region 32, and this plasma jet shaping module controls one or more parameters of the plasma jet in its own module. The cathode module may also be equipped with a pressure gauge PG1 for measuring the back pressure in the upstream plasma channel 34. The interelectrode insertion module (IEI) may include a guide insertion module (PI) and at least one neutral interelectrode insertion module (NI).

[0024] The plasma jet shaping module FM may include two shaping sub-modules FM1 and FM2. Shaping sub-module FM1 may have a high-velocity nozzle (HVN). Typically, HVN 56 can be a convergent-diffusion type nozzle or a de Laval type nozzle, which is widely used to accelerate compressible gases to supersonic speeds by converting the thermal energy of the flow into kinetic energy. HVN 56 may consist of a convergent region 64 and a diffuser region 68, where the convergent region 64 provides a transition from the anode cylindrical portion to a cylindrical throat 66 with a diameter Dcr; the diffuser region 68 is used to accelerate the plasma to supersonic speeds. That is, the diameter Dcr is measured within the throat and between the convergent and diffuser regions.

[0025] Detailed information on the design and characteristics of convergent-diffusion nozzles or Delaware nozzles can be found in numerous books and papers. For example, isentropic flow data tables can be viewed at http: / / www.cchem.berkeley.edu / cbe150a / isentropic_flow.pdf.

[0026] The plasma forming and raw material supply module FM2 can be configured for final forming and controlling the plasma jet, and for introducing material raw materials from the raw material supply module PF into the plasma jet 26 generated by the plasma gun 4. The material raw materials can be in powder form, liquid precursor form, or a suspension of fine powder in a liquid such as ethanol or water. FM2 can be equipped with a pressure gauge PG2 for measuring... Figure 2 The pressure in one of the raw material channels 6 shown is... Figure 2 Spray gun 4 was demonstrated for initial testing and subsequent improvements.

[0027] Cathode module C may have a cathode support 124 with a cathode insert 122, a cathode housing 128, and a cathode vortex distributor 126, which provides a tangential velocity component to the cathode plasma gas G1, thereby forming a region between the cathode 122 and the guide insert 80. Figure 2 The swirling current 130 is shown. The swirling current 130 can propagate downstream along the plasma arc region, thereby stabilizing the arc. The intensity of the swirling current can be characterized by the ratio Vort1 = G1 / S1, where S1 is the surface area of ​​the swirling current orifice G1. Power and water-cooling cables can be connected to connector 142.

[0028] The second plasma gas, or anolyte plasma gas G2, can also be used to generate plasma. Anolyte plasma gas G2 can be supplied through a channel located between the IEI module and the anode module. G2 can also have a tangential component of the gas velocity, providing the same rotational direction as G1, such as... Figure 2As shown, a second vortex or anodic vortex is formed 168. For nitrogen-based plasmas, the anodic erosion rate depends primarily on the plasma current and the efficiency, stability, and frequency of the anodic arc root rotation. The efficiency of the anodic arc root rotation is mainly characterized by the flow rate of G2 and the anodic vortex intensity Vort2 = G2 / S2, where S2 is the surface area of ​​the G2 vortex orifice. Furthermore, this paper also indicates that the total flow rate G = G1 + G2.

[0029] The inter-electrode plug-in (IEI) module may consist of a boot plug-in 80 and one or more neutral plug-ins. Figure 2 Two neutral plugs, 81 and 82, are shown and can be used in this embodiment. The neutral plugs may have cooling channels 210 located radially along the plasma axis 162. Electrical insulation between the neutral plugs and with respect to the ignition plug 80 can be achieved via a set of ceramic rings 88 and sealing O-rings 90.

[0030] The anode module A may consist of an anode housing 48 and an anode-FM assembly 50. The anode portion 55 of the assembly 50 and the upstream portion of FM1 56 may have cooling grooves 164 arranged perpendicular to the plasma axis 162. The anode 55 may also have cooling grooves 166 arranged at an angle to the plasma axis 162, due to limited accessibility to these areas at right angles. The FM2 submodule may have one or more feed channels 6, the diameter of which is df between the inner walls of the feed channels, for conveying and injecting feed into the plasma jet located downstream of the outlet 102 of the feed channel 6 within the gun barrel 28. The inner wall structure of the feed channel 6 is preferably a cylindrical wall structure.

[0031] The spray gun is preferably operated at a power of up to 100kW-120kW with a cooling water flow rate of 35L / min-45L / min or higher, providing an average cooling water flow velocity of 3.2m / sec-4.1m / sec in cooling tanks 164 and 166. If needed, the spray gun can be expanded and operated at, for example, a power level of 200 kW or even higher. Therefore, the spray gun is preferably operated in the range of 75kW to 250kW.

[0032] Figure 3 The anode-FM assembly 50 is shown in more detail. This assembly can be made of copper or a copper alloy. Oxygen-free copper is primarily used for the anode. Assembly 50 can be made of... Figure 3 The anode portion 55, the supersonic high-speed nozzle 56, and the FM2 portion 58 are shown. The anode portion may preferably include an anode inlet region 60 and a cylindrical region 62 with a diameter D1. The anode arc root attachment region 32 may be located inside the anode cylindrical region 62 of the anode portion 55.

[0033] The supersonic nozzle 56 may include a convergence region 64 and a diffusion region 68. The convergence region 64 provides a transition from the anode cylindrical portion to a throat or critical region 66 with a diameter Dcr; the diffusion region 68 has an outlet 136 and can accelerate the plasma to supersonic speeds. Preferably, the throat diameter Dcr is 4 mm or higher. A preferred range for Dcr is 0.4 W. 0.5 Up to 0.6 W 0.5 Where W is the electrical power, expressed in kW; Dcr is expressed in mm. The kW unit is not included in this formula; it is only a base value. Therefore, for a spray gun power of 100kW, the preferred Dcr diameter is 4mm to 6mm; for W=200kW, the preferred Dcr is 5.6mm to 8.4mm. The nozzle outlet diameter is denoted as D2. The preferred diameter D2 should be 1.05 to 1.5 times the Dcr value. The anode cylindrical portion 62 and the supersonic nozzle (HVN) 56 used in the experiment have the following dimensions: D1=8mm; α1=400. The Dcr value is between 4mm and 6mm.

[0034] The upstream cylindrical portion 70 of FM2 can be located upstream of the feed channel 6 and the outlet of the diffusion zone 68 with a diameter of D2. The cylindrical portion 70 can be used to minimize the diffusion component of the plasma velocity before injecting the feed into the plasma. However, the cylindrical portion 70 will slightly reduce the thermal efficiency of the nozzle. Therefore, when thermal efficiency is more important than the radial component of the plasma velocity, the cylindrical portion 70 can be minimized or eliminated.

[0035] FM2 may also have a cylindrical barrel 28 located downstream of the raw material channel 6. The barrel 28 has a diameter of D2 and a length of approximately 6mm–40mm. The barrel 28 may also have other diameters and lengths determined by process requirements and available raw materials.

[0036] The initial experiments used nitrogen-based plasma gas, preferably at a pressure of 3–8 bar. The cathode gas flow rate G1 ranged from 110 slpm to 220 slpm. The current was 200 A–500 A, and the voltage was up to 310 V. The anode plasma gas flow rate G2 was a nitrogen-argon mixture with different N2 / Ar ratios. The G2 flow rate ranged from 0.55 g / s to 2.2 g / s. The total surface area of ​​the anode vortex orifice was S2 = 1.4 mm²–1.7 mm². Therefore, the anode vortex intensity Vort2 = G2 / S2 was approximately in the range of 0.3 g / (sec·mm²)–1.5 g / (sec·mm²), while the maximum Vort2 value disclosed in patent US 9,150,949 was 0.4.

[0037] Considering several drawbacks that render the spray gun solution unsuitable for practical industrial applications, modifications and improvements to the process and hardware are necessary. The following process changes and upgrades can be considered and disclosed: Anodic corrosion Excessive erosion was observed in the anode portion 55 during the initial experiments. The degree of erosion was significantly higher than that observed during spraying tests at atmospheric pressure. When the G2 flow rate was below 25 L / min, a highly eroded and re-solidified area was particularly observed in the annular region 118 inside the anode, associated with the anode arc root adhesion zone. Figure 4 The region 118 is shown as a cross-section of the anode-FM assembly 50, which was cut into two parts less than an hour after the experiment began.

[0038] Such intense erosion not only leads to an extremely short anode life but also causes molten copper to splash, contaminating the coating, which is generally unacceptable. Anode erosion intensifies with increasing plasma gas pressure and decreases with increasing anode plasma gas flow rate and Vort2 intensity. Studies have found that conditions with a G2 flow rate above 25 L / min and a vortex intensity above 0.4 g / (sec·mm2) are more conducive to providing relatively more efficient rotation in the anode arc root attachment zone and achieving acceptable anode erosion. Therefore, the G2 flow rate can be set in the range of above 25 L / min to 150 L / min, with a preferred range of 35 L / min to 75 L / min. The preferred range for Vort2 is greater than 0.40 g / (sec·mm2). 2 And not exceeding 1.0 g / (sec·mm) 2 Within these preferred ranges of G2 and Vort2, the expected and preferred specific power ∑ can be achieved, ranging from 16 kJ / g to 33 kJ / g. It is also noteworthy that, unexpectedly, at these preferred G2 and Vort2 values, the tangential component of the plasma jet velocity detected downstream of FM1 is relatively insignificant.

[0039] The requirements for enhanced G2 flow rate and intensity Vort2 can be explained as follows: For nitrogen plasma at atmospheric pressure and a current of 400A-500A, the heat flux Qp from the plasma to the plasma channel wall (including the anode wall of plasma channel 132 inside the anode) can be roughly estimated to be approximately 1.5·10⁻⁶. 4 kW / m² to 3.0·10 4 The specific value for the kW / m² level depends on the spray gun power and efficiency. Meanwhile, for the same plasma, without applying an anode vortex to rotate the arc, the estimated heat flux Qa from the anode arc root attachment region to the anode wall can reach 1.5·10⁻⁶. 5 kW / m² to 2.0·10 5 The value of kW / m², or even higher. It should be noted that 1.5·10 5 kW / m² to 2.0·10 5kW / m² is estimated as the maximum heat flux that can be handled even with advanced cooling water arrangements (Thermal Plasmas, Fundamentals and Applications, Vol. 1, Maher I Boulos, Pierre Fauchais, and Emil Pfender, Plenum Publishing, p. 13). Therefore, even at atmospheric pressure, anodic swirl and associated arc rotation are required to rotate the anode root attachment region and distribute heat along a ring-shaped area associated with the rotating anode root attachment region inside the anode, thereby extending the service life of the spray gun operating with nitrogen-based plasma. Patent US 9,150,949 discloses that an anode swirl intensity Vort² in the range of 0.1 g / (s·mm²)–0.4 g / (s·mm²) at atmospheric pressure is sufficient to achieve a relatively low level of anode erosion.

[0040] It is known that in the steady-state heat transfer equation, the heat flux is proportional to the 0.8th power of δ, where δ is the gas density and is proportional to the gas pressure (e.g., George P. Sutton, *Rocket Propulsion Elements*, 6th edition, pp. 97-98). Therefore, the heat flux Qp can be estimated as Qp ~ P. p 0.8 Where Pp represents the plasma pressure. Therefore, it can be noted that at a plasma pressure of 5 bar, Qp can reach approximately 5.4 × 10⁻⁶. 4 kW / m² to 10.8·10 4 At a plasma pressure of 8 bar, the Qp can reach 8.0·10 kW / m². 4 kW / m² to 15.8·10 4 At a plasma pressure of 10 bar, the Qp can reach 9.5·10 kW / m². 4 kW / m² up to 19.0·10 4 kW / m². These values ​​explain why, at plasma pressures above 8 bar, even though the anolyte swirl provides efficient arc rotation, thus significantly reducing the Qa input in the total heat flux, the anolyte still exhibits increased erosion values.

[0041] Powder buildup inside the barrel It has been determined that employing a stepped expansion structure within the second forming module FM2 downstream of the nozzle can reduce powder accumulation within the forming module. See also Figure 5The first stepped expansion section 140, located downstream of D2, preferably has a diameter D3 that is 1.05 to 1.3 times the value of D2. The second stepped expansion section 76, located downstream of the first stepped expansion section, preferably has a diameter D4 that is 1.1 to 1.5 times the value of D3. The D4 / D3 ratio is preferably in the range of 1.15 to 1.3. It should be noted that the first stepped expansion section 140 generates a relatively low-pressure zone in the raw material injection area, which also helps to achieve stable raw material delivery, including small-sized powders (10 micrometers or less in diameter).

[0042] Therefore, it can be understood that the plasma ejected from FM1 travels at supersonic speeds. However, it should be understood that the plasma ejected from FM2 can travel at supersonic or subsonic speeds.

[0043] The shortest distance L2 between the inner wall 104 of the raw material channel and the step 140 is 0.3 mm to 2.5 mm. This shortest distance is... Figure 5 The designation is 134. The shortest distance L3 between the raw material channel wall 106 and the step 76 can also be L3 ranging from 0.3mm to 2.5mm. This shortest distance L3 is... Figure 5 It is marked with 138.

[0044] Multiple tests conducted under varying plasma pressures demonstrated that Step 140 generates a stable vacuum pressure in the feed injection zone. Within all tested operating parameters, the measured vacuum pressures ranged from 7 inches of mercury to 17 inches of mercury (0.23 bar to 0.57 bar). The vacuum pressure remained remarkably stable for each set of test parameters.

[0045] Barrel extension and anode-FM cooling For different coatings applied using different raw materials, barrels of varying lengths 28 can be selected. In this case, it is more advantageous to separate the FM2 section 58 from the anode-FM assembly. Figure 6 The scheme is illustrated. In this design, the FM2 module is now a separate component 108, which may partially include a cylindrical downstream nozzle section 70, two-stage stepped expansion sections 76 and 140, a feed channel 6, and a barrel 28.

[0046] The anode 55 assembly with convergent-diffusion nozzle 56 can serve as another independent component 110, which withstands higher temperatures and associated heat fluxes compared to FM2. Therefore, radial cooling channels 184 and quasi-radial cooling channels 186-1 and 186-2 can be used more effectively for cooling the independent component 110 compared to the axial cooling channels 114 and 116 used for cooling FM2 108. Notably, the radial and quasi-radial cooling channels allow the radial cooling channels to be closer to the plasma wall when needed, thereby improving the cooling conditions of component 110.

[0047] Figure 6 A water-cooling channel for cooling components 110 and 108 is also shown integrated into a 100kW-120kW spray gun, with a water flow rate Qw of approximately 35L / min-45L / min and a maximum water pressure Pw of 250psi (approximately 17 bar). This water flow rate is sufficient to cool the aforementioned 120kW spray gun when the thermal efficiency of the spray gun can be as low as 50%. In this case, the inlet and outlet water temperature difference can be 20°C. Choosing Pw=17 bar or lower can be interpreted as the maximum rated pressure of the main components of the industrial water / power hose used for plasma spraying being 250psi. Higher rated pressures significantly reduce hose flexibility and may result in limited movement and excessive loads on robots and manipulators used for coating deposition. It should be noted that by using appropriately sized hoses and fittings, a water flow rate of 35L / min-45L / min can be achieved at a water pressure of 17 bar or lower with the disclosed spray gun. However, higher pressure configurations can still be used if required.

[0048] More specifically, the cooling water passage of the disclosed spray gun operates as follows: Water is supplied from the IEI module (not shown) to the water distributor 120, and then flows into tanks 184 and 186. After the water cooling tanks, the water flows to distribution section 120-1, where the cooling water is redirected by the water distributor 120 and then guided to tank 186-2 and distribution section 120-2. Water flows out from distribution section 120-2, flows to distribution section 120-4, and then from distribution section 120-4 flows into axial cooling channel 114 (only one is shown in the figure) to cool FM2. Once the water flow reaches portion 112-1 of the annular water flow distributor 112, the cooling water enters the return axial water channel 116 and flows through portion 120-5 of distributor 120 into the outlet pipe (not shown), which is connected to the main water pipe from / to the water pump (not shown).

[0049] The water flow velocity Vw (e.g., m / s) in the anode tank depends on the total surface area Sw (e.g., square meters) and the water flow rate Qw (e.g., cubic meters / s). The water flow velocity (m / s) is Vw = Qw / Sw. In a single-piece anode-FM design, the water flow rate Qw flows through... Figure 2 All cooling tanks 164 and 168 shown have a total cross-sectional surface area of ​​approximately 180 mm². Therefore, for flow rates of 35 L / min–45 L / min, a water flow velocity of approximately 3.2 m / s–4.1 m / s can be provided.

[0050] for Figure 6In the preferred embodiment shown, all water flows through three channels 184 and 186-1. The total cross-sectional area S1 of these channels is approximately S1 = 65 mm². Therefore, the water flow velocity in channels 184 and 186 is approximately 9 m / s–12 m / s, which is about three times the water flow velocity in a one-piece design without water diversion via distributor 120. After diversion occurs in section 120-1 of distributor 120, all water flow can pass through channel 186-2 with a total cross-sectional area S2 of approximately S2 = 60 mm², thereby increasing the flow velocity by 8%. It should be noted that distributor 120 can be slightly modified to achieve three or more water diversions in the anode cooling channel, thereby increasing the water flow velocity and improving the anode cooling conditions when needed. However, it should be noted that excessive water diversion will increase the hydraulic resistance of the spray gun and require higher water pressure.

[0051] also, Figure 6 The advanced water cooling circuit shown above can be further considered as sequentially water cooling each region of the anodizing module 110 using two sets of tanks. The first set of tanks preferably includes tank 184 and tank 186-1. Its total cooling surface area S1 is preferably S1 = 65 mm² = 65.10 mm. -4 m². At approximately 100kW-120kW of spray gun power, the corresponding water flow rate is approximately 35L / min-45L / min (i.e., 5.8·10). -4 m 3 / s to 7.5·10 -4 m 3 / s), the cooling water flow velocity in the first set of tanks can be estimated as Vw=9m / s-12m / s.

[0052] The preferred total cooling surface area of ​​the second set of tanks 186-2 is S2 = 60 mm² = 60·10 -4 m², and can provide higher water flow rates.

[0053] This preferred increase in cooling water flow rate and the associated improvement in cooling conditions of the anode forming module 110 are considered sufficient to enable the spray gun to operate reliably at a higher specific power ∑ = W / G, up to a maximum of 38 kJ / g. This higher plasma power can then benefit from an even higher cooling water flow rate.

[0054] For example, when a longer barrel is required to allow for a relatively long residence time of the sprayed particles, a higher specific power is preferred. However, an extended barrel longer than 10 mm can lead to higher heat loss, resulting in a relatively low plasma heat transfer potential and enthalpy. In this case, it is envisioned that a W / G ratio in the range of 33 J / g–38 kJ / g can compensate for the additional heat loss and the decrease in plasma heat transfer potential and enthalpy.

[0055] It should be noted that the heat load of the anodizing module 110 is preferably significantly higher than that of other areas and components of the disclosed plasma spray gun. Therefore, without further improvements to the spray gun's cooling conditions, a specific power of up to 38 kJ / g or within the range of 16 kJ / g to 38 kJ / g can be reliably generated. Therefore, the aforementioned additional preferred cooling is preferably limited to the anodizing module 110.

Claims

1. A method for depositing a coating using a plasma spray gun, comprising: A plasma spray gun is provided, comprising a cathode module and an anode module. The cathode module has a cathode electrode, and the anode module has an anode electrode. The anode electrode has an anode shaft, an inlet region, and a cylindrical region with a diameter D1. The plasma spray gun generates a plasma arc, and the plasma arc has an anode arc root attachment region located inside the anode. The plasma spray gun further includes a first shaping module (FM1) and a second shaping module (FM2). The first shaping module has a convergent-diffusion nozzle with a throat diameter of Dcr and an outlet diameter of D2. The second shaping module is located downstream of the first shaping module and downstream of the anode arc root attachment region. The second forming module controls one or more parameters of the plasma jet within the second forming module. The inter-electrode module controls the plasma arc channel located between the cathode electrode and the anode electrode, wherein one end of the inter-electrode module is adjacent to the cathode module, the second end is adjacent to the anode module, and a guide plug is provided near the cathode; At least one neutral electrode insert; The plasma spray gun also includes two channels for delivering plasma gas in a total volume G; The plasma spray gun generates a voltage (U) higher than 150V and a current (I) lower than 500A, with a power W = U × I; The raw material is fed into the plasma jet and a coating is deposited on the substrate; The plasma gas includes molecular gas with a volume fraction greater than 50%. The range of W / G is 16kJ / g-38kJ / g; One of the channels for transporting plasma gas includes a first plasma gas channel located between the cathode and the guide plug. The first plasma gas channel is used to transport plasma gas of quantity G1. The plasma gas is guided through a plurality of orifices with a surface area of ​​S1, wherein a swirling flow with a swirling intensity of Vort1 = G1 / S1 is formed. The other channel for transporting plasma gas includes a second plasma gas channel, which is located between the inter-electrode module and the cylindrical region of the anode. This second plasma gas channel is used to transport plasma gas in a quantity of G2. The plasma gas is guided through multiple orifices, the surface area of ​​which is S2, forming a swirling flow with a swirling intensity of Vort2 = G2 / S2; and Among them, the flow rate of G2 is greater than 25 L / min; and Wherein, Vort2 is greater than 0.4 g / (s·mm²).

2. The method according to claim 1, wherein, The plasma pressure is 3 bar to 8 bar.

3. The method according to claim 1, wherein, The value of Vort2 is in the range of 0.40 g / (s·mm²) to 0.60 g / (s·mm²).

4. The method according to claim 1, wherein, G2 is in the range of 35 L / min to 75 L / min.

5. The method according to claim 1, wherein, The diameter Dcr of the throat is 0.4 W. 0.5 Up to 0.6 W 0.5 Where Dcr is measured in mm.

6. The method according to claim 1, wherein, The outlet diameter D2 of the convergent-diffusion nozzle is 1.05 to 1.5 times the Dcr value.

7. The method according to claim 1, wherein, The second forming module has a first stepped expansion section with a diameter of D3.

8. The method according to claim 7, wherein, D3 is 1.05 to 1.3 times the value of D2.

9. The method according to claim 1, wherein, The second forming module has a second stepped expansion section with a diameter of D4.

10. The method according to claim 9, wherein, The value of D4 is 1.1 to 1.5 times that of D3.

11. The method according to claim 7, wherein, The shortest distance between the inner wall of the raw material channel and the first stepped expansion section is L2, where L2 = 0.3 mm to 2.5 mm.

12. The method according to claim 9, wherein, The shortest distance between the inner wall of the raw material channel and the second stepped expansion section is L2, where L2 = 0.3 mm to 2.5 mm.

13. A plasma spray gun, comprising: A cathode module and an anode module, wherein the cathode module has a cathode electrode, the anode module has an anode electrode, the anode electrode has an anode shaft, an inlet region, and a cylindrical region with a diameter of D1, wherein the plasma spray gun generates a plasma arc, and the anode arc root attachment region of the plasma arc is located inside the anode; The plasma spray gun also includes a first shaping module (FM1) and a second shaping module (FM2). The first shaping module has a convergent-diffusion nozzle with a throat diameter of Dcr and an outlet diameter of D2. The second shaping module is located downstream of the first shaping module and downstream of the anode arc root attachment zone. The second forming module controls one or more parameters of the plasma jet within the second forming module; An inter-electrode module is used to control the plasma arc channel located between the cathode electrode and the anode electrode, wherein one end of the inter-electrode module is adjacent to the cathode module, the second end of the inter-electrode module is adjacent to the anode module, and a guide plug is provided near the cathode; At least one neutral electrode insert; The plasma spray gun also includes two channels for delivering plasma gas in a total volume of G; The plasma spray gun operates under conditions of a voltage (U) higher than 150V and a current (I) lower than 500A, with a power W = U × I; The plasma gas includes molecular gas with a volume fraction greater than 50%. The range of W / G is 16kJ / g-38kJ / g; One of the channels for transporting plasma gas includes a first plasma gas channel located between the cathode and the guide plug. The first plasma gas channel is used to transport plasma gas of quantity G1. The plasma gas is guided through a plurality of orifices with a surface area of ​​S1, wherein a swirling flow with a swirling intensity of Vort1 = G1 / S1 is formed. One of the channels for transporting plasma gas includes a second plasma gas channel, which is located between the inter-electrode module and the cylindrical portion of the anode. This second plasma gas channel is used to transport plasma gas in a quantity of G2. The plasma gas is guided through multiple orifices, the surface area of ​​which is S², forming a swirling flow with an intensity of Vort² = G² / S²; and Among them, the flow rate of G2 is greater than 25 L / min; and Wherein, Vort2 is greater than 0.4 g / (s·mm²).

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