A method for improving arc starting stability of a plasma torch
By forming an insulating coating on the cathode of the plasma spray gun, the problem of lateral discharge of the cathode is solved, the arc initiation stability and cathode life are improved, and the operation process is simplified.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA WEAPON SCI ACADEMY NINGBO BRANCH
- Filing Date
- 2026-03-16
- Publication Date
- 2026-06-26
Smart Images
Figure CN122279463A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of plasma spray gun technology, and in particular to a method for improving the arc initiation stability of a plasma spray gun. Background Technology
[0002] Plasma spraying is a thermal spraying technology that uses a high-temperature plasma jet to heat powdered materials to a molten or semi-molten state and then sprays them at high speed onto the treated substrate surface to form a strong coating. The core feature of plasma spraying is the use of a plasma arc as a heat source to spray almost all high-melting-point materials. The plasma arc is formed in a plasma spray gun by ionizing an introduced gas (Ar, He, H2, etc.) through a cathode. In the plasma spray gun, the cathode, acting as the negative electrode, emits electrons after being ignited by high voltage, while the anode, acting as the positive electrode, receives the electron flow from the cathode. The cathode and anode together create a strong electric field that generates the plasma arc, ionizing the gas medium introduced between the electrodes to form a high-temperature plasma arc heat source.
[0003] Therefore, the cathode is the core component in plasma spraying, directly determining the stability of the plasma arc and the success or failure of the spraying process. Furthermore, electrode wear can shorten the service life of the equipment. In plasma spray guns, the cathode is often made of oxygen-free copper. Due to the excellent thermal conductivity of oxygen-free copper, it can quickly remove a large amount of heat through efficient water cooling. In order to enhance the resistance to arc erosion, a tungsten or tungsten alloy bushing is usually embedded in the inner wall of the copper electrode or in the arc attachment area (upstream of the cathode throat). The high melting point of tungsten is used to resist direct arc erosion. As shown in the Chinese utility model patent application number CN201420675768.4 (authorization announcement number CN204224687U), the plasma spraying target nozzle includes a nozzle body, which is an oxygen-free copper nozzle body. The nozzle body has a through hole in the middle, which forms a channel for the spraying material to pass through. The inner wall of the channel is provided with a conductive layer, which is a tungsten layer or a cerium-tungsten alloy layer. The nozzle body is designed in this way to maintain the good thermal conductivity of the nozzle, while the inner wall of the nozzle can withstand the arc erosion at the moment of ignition and the high temperature and high pressure erosion of the plasma.
[0004] However, the high-temperature environment in the plasma spray gun exacerbates electrode wear. Under the combined effects of extreme thermal load, electrical load, and arc erosion, the cathode tip material melts, evaporates, and redeposits, causing a change in the cathode tip shape. Specifically, molten material solidifies on the side of the cathode, forming protrusions. Because the cathode exhibits tip discharge during arc initiation, the area where protrusions form on the cathode side also participates in the discharge, especially in plasma spray guns with multiple cathodes, which need to be at the same plane height for successful arc initiation. The aforementioned phenomenon causes the discharge areas of multiple cathodes to be at different horizontal plane heights, leading to arc initiation failure and causing the plasma spraying control cabinet to generate an error record of "plasma voltage failure." Therefore, further improvements to the cathode of the plasma spray gun are needed to enhance the arc initiation stability of the plasma spray gun. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide a method that can effectively solve the problem of lateral discharge of the cathode and improve the arc initiation stability of the plasma spray gun, in light of the above-mentioned existing technology.
[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problem is as follows: the method for improving the arc initiation stability of a plasma spray gun is characterized by comprising the following steps:
[0007] S1. The coating area of the cathode is sequentially degreased, cleaned and dried. The coating area of the cathode is the outer wall area upstream of the throat of the cathode surface inlaid with tungsten or tungsten alloy.
[0008] S2. Remove oxide scale from the coated area of the cathode after S1 treatment;
[0009] S3. The coated area of the cathode after S2 treatment is sandblasted, that is, sandblasted with fine sand particles at a pressure of 0.2 ~ 0.4 MPa.
[0010] S4. Apply insulating material to the coated area of the cathode after S3 treatment, and cure it in a drying oven to form an insulating coating on the coated area of the cathode.
[0011] Furthermore, in step S1, the coating area of the cathode undergoes degreasing, cleaning, and drying sequentially as follows: First, the coating area of the cathode is immersed in a degreasing solution for ultrasonic cleaning for 2-12 minutes. Then, the ultrasonically cleaned cathode is rinsed with pure water until no degreasing solution residue remains on the surface. Finally, the cathode is placed in a drying oven for drying. Degreasing, cleaning, and drying the coating area of the cathode increases adhesion. If the coating area of the cathode has an oil film, this film will hinder direct contact between the insulating coating and the coating area of the cathode, leading to peeling, blistering, or poor adhesion of the insulating coating. Degreasing ensures a more thorough removal of the oil film from the coating area of the cathode, and rinsing with pure water removes any residue from the degreasing solution. Drying removes the moisture from the degreasing and cleaning processes, facilitating subsequent cathode processing.
[0012] Furthermore, in step S2, the oxide scale removal process on the coated area of the cathode after treatment S1 involves sequentially polishing with 400-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper. Oxide scale hinders direct contact between the insulating coating and the coated area of the cathode, thus affecting the bonding effect between the insulating coating and the cathode. Mechanical polishing is a more effective way to remove oxide scale. Moreover, using sandpaper of different grits for sequential polishing not only achieves the best balance between efficiency and quality but also minimizes damage to the cathode.
[0013] Furthermore, the roughness of the coated area of the cathode after the S3 sandblasting treatment is 0.4~1.6μm. The sandblasting treatment of S3 creates a uniform roughness in the coated area of the cathode, increasing the bonding strength between the insulating coating and the coated area of the cathode, allowing the insulating coating to adhere more firmly to the coated area of the cathode; and the cathode needs to undergo coating treatment as soon as possible after sandblasting to avoid oxidation caused by prolonged exposure to the atmosphere.
[0014] Furthermore, in step S4, the coating treatment of the cathode after treatment S3 using insulating material is as follows: First, the cathode after treatment S3 is placed on a workbench and clamped. Then, a brush is used to apply the insulating material evenly to the coating area of the cathode in the same direction for the first time. A second coat is then applied in a direction perpendicular to the first coat direction, and this process is repeated until the coating is complete. Finally, the cathode is placed in a drying oven to cure and form an insulating coating. This coating treatment improves the uniformity of the insulating coating; specifically, the perpendicularity of the brushing direction enhances the uniformity of the insulating coating.
[0015] Furthermore, the insulating material in S4 is polyimide, polytetrafluoroethylene, or polyetheretherketone.
[0016] Furthermore, the substrate of the cathode coating area in S1 is tungsten or a tungsten alloy. The high melting point of tungsten is utilized to resist arc erosion.
[0017] Furthermore, the thickness of the insulating coating in S4 is 1~10μm. Too thin an insulating coating will affect its effectiveness, while too thick a coating will affect assembly accuracy.
[0018] Compared with the prior art, the advantages of this invention are as follows: This method can form an insulating coating on the coating area of the cathode in a plasma spray gun. By performing degreasing, cleaning, drying, oxide scale removal, and sandblasting on the coating area of the cathode, the insulating coating can adhere more firmly to the coating area of the cathode. This insulating coating can prevent lateral discharge of the cathode during the arc ignition stage of the plasma spray gun, resulting in a higher success rate of arc ignition and thus improving the stability of arc ignition, which is beneficial to extending the service life of the cathode. In addition, this method has the advantages of process repeatability and simple operation, making it convenient for operators to carry out actual operations. Attached Figure Description
[0019] Figure 1 This is a flowchart of the present invention;
[0020] Figure 2 This is a schematic diagram of the structure of an embodiment of the present invention; Detailed Implementation
[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0022] Example 1
[0023] The method for improving the arc initiation stability of a plasma spray gun in this embodiment includes the following steps:
[0024] S1. The coated area 1 of the cathode is sequentially degreased, cleaned, and dried. First, the coated area 1 is immersed in a degreasing solution for ultrasonic cleaning for 2 minutes. Then, the ultrasonically cleaned cathode is rinsed with pure water until no degreasing solution residue remains on the surface. Finally, the cathode is placed in a drying oven for drying. The coated area 1 of the cathode is the outer wall region upstream of the throat of the tungsten or tungsten alloy embedded in the cathode. Figure 2 As shown.
[0025] S2. Remove the oxide scale from the coated area 1 of the cathode after S1 treatment. That is, select 400-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper to grind and polish the coated area 1 of the cathode after S1 treatment in turn to remove the oxide scale on the surface of the coated area 1 of the cathode.
[0026] S3. The coated area 1 of the cathode after S2 is subjected to sandblasting treatment, that is, fine quartz sand is used for sandblasting at a pressure of 0.2MPa, so that the roughness of the coated area 1 of the cathode after sandblasting treatment is 0.4μm.
[0027] S4. Apply insulating material to the coating area 1 of the cathode after S3 treatment. First, place the cathode after S3 treatment on the workbench and clamp it. Then, use a brush to apply polyimide slurry to the coating area 1 of the cathode. First, apply the slurry evenly in the same direction. Then, apply the slurry in a direction perpendicular to the first application direction. Repeat this step until the coating is finished. Finally, place the cathode in a drying oven to dry and form an insulating coating on the coating area 1 of the cathode. The thickness of the insulating coating is 1μm.
[0028] TriplexPro processed by the method in Example 1 TM The -200 model plasma spray gun continuously ignited the arc 60 times without any "plasma voltage failure" error record.
[0029] Example 2
[0030] The method for improving the arc initiation stability of a plasma spray gun in this embodiment includes the following steps:
[0031] S1. The coated area 1 of the cathode is sequentially degreased, cleaned, and dried. First, the coated area 1 is immersed in a degreasing solution for ultrasonic cleaning for 6 minutes. Then, the ultrasonically cleaned cathode is rinsed with pure water until no degreasing solution residue remains on the surface. Finally, the cathode is placed in a drying oven for drying. The coated area 1 of the cathode is the outer wall region upstream of the throat of the tungsten or tungsten alloy embedded in the cathode. Figure 2 As shown.
[0032] S2. Remove the oxide scale from the coated area 1 of the cathode after S1 treatment. That is, select 400-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper to grind and polish the coated area 1 of the cathode after S1 treatment in turn to remove the oxide scale on the surface of the coated area 1 of the cathode.
[0033] S3. The coated area 1 of the cathode after S2 is subjected to sandblasting treatment, that is, fine quartz sand is used for sandblasting at a pressure of 0.3MPa, so that the roughness of the coated area 1 of the cathode after sandblasting treatment is 1.4μm.
[0034] S4. Apply insulating material to the coating area 1 of the cathode after S3 treatment. First, place the cathode after S3 treatment on the workbench and clamp it. Then, use a brush to apply polytetrafluoroethylene slurry to the coating area 1 of the cathode. First, apply the slurry evenly in the same direction. Then, apply the slurry in a direction perpendicular to the first application direction. Repeat this step until the coating is finished. Finally, place the cathode in a drying oven to dry and form an insulating coating on the coating area 1 of the cathode. The thickness of the insulating coating is 6μm.
[0035] TriplexPro processed by the method in Example 2 TM The -200 model plasma spray gun continuously ignited the arc 60 times without any "plasma voltage failure" error record.
[0036] Example 3
[0037] The method for improving the arc initiation stability of a plasma spray gun in this embodiment includes the following steps:
[0038] S1. The coated area 1 of the cathode is sequentially degreased, cleaned, and dried. First, the coated area 1 is immersed in a degreasing solution for ultrasonic cleaning for 12 minutes. Then, the ultrasonically cleaned cathode is rinsed with pure water until no degreasing solution residue remains on the surface. Finally, the cathode is placed in a drying oven for drying. The coated area 1 of the cathode is the outer wall region upstream of the throat of the tungsten or tungsten alloy embedded in the cathode. Figure 2 As shown.
[0039] S2. Remove the oxide scale from the coated area 1 of the cathode after S1 treatment. That is, select 400-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper to grind and polish the coated area 1 of the cathode after S1 treatment in turn to remove the oxide scale on the surface of the coated area 1 of the cathode.
[0040] S3. The coated area 1 of the cathode after S2 is subjected to sandblasting treatment, that is, fine quartz sand is used for sandblasting at a pressure of 0.4MPa, so that the roughness of the coated area 1 of the cathode after sandblasting treatment is 1.6μm.
[0041] S4. Apply insulating material to the coating area 1 of the cathode after S3 treatment. First, place the cathode after S3 treatment on the workbench and clamp it. Then, use a brush to apply polyether ether ketone slurry to the coating area 1 of the cathode. First, apply the slurry evenly in the same direction. Then, apply the slurry in a direction perpendicular to the first application direction. Repeat this step until the coating is finished. Finally, place the cathode in a drying oven to dry and form an insulating coating on the coating area 1 of the cathode. The thickness of the insulating coating is 10 μm.
[0042] TriplexPro processed using the method in Example 3 TM The -200 model plasma spray gun continuously ignited the arc 60 times without any "plasma voltage failure" error record.
[0043] All the above embodiments are merely preferred embodiments of the present invention. The application of the methods in all embodiments is not limited to plasma spray guns; other electrode materials with cathode discharge capabilities can also be used.
Claims
1. A method for improving the arc initiation stability of a plasma spray gun, characterized in that, Includes the following steps: S1. The coating area of the cathode is sequentially degreased, cleaned and dried. The coating area of the cathode is the outer wall area upstream of the throat of the cathode surface inlaid with tungsten or tungsten alloy. S2. Remove oxide scale from the coated area of the cathode after S1 treatment; S3. The coated area of the cathode after S2 treatment is sandblasted, that is, sandblasted with fine sand particles at a pressure of 0.2 ~ 0.4 MPa. S4. Apply insulating material to the coated area of the cathode after S3 treatment, and cure it in a drying oven to form an insulating coating on the coated area of the cathode.
2. The method according to claim 1, characterized in that: In step S1, the coating area of the cathode is sequentially degreased, cleaned, and dried as follows: First, the coating area of the cathode is immersed in degreasing solution for ultrasonic cleaning for 2-12 minutes. Then, the cathode after ultrasonic cleaning is rinsed with pure water until there is no residual degreasing solution on the surface. Finally, the cathode is placed in a drying oven for drying.
3. The method according to claim 1, characterized in that: The oxide scale removal process for the coated area of the cathode after S1 in S2 is performed by sequentially polishing with 400-mesh, 1000-mesh, 1500-mesh, and 2000-mesh sandpaper.
4. The method according to claim 1, characterized in that: The roughness of the coated area of the cathode after the S3 sandblasting treatment is 0.4~1.6μm.
5. The method according to claim 1, characterized in that: The process of coating the cathode area after S3 with insulating material in S4 is as follows: First, the cathode after S3 is placed on the workbench and clamped. Then, a brush is used to apply the insulating material to the cathode area in the same direction for the first time. Then, a second time, the material is applied in a direction perpendicular to the first application direction. This process is repeated until the coating is finished. Finally, the cathode is placed in a drying oven to cure and form an insulating coating.
6. The method according to claim 1, characterized in that: The insulating material in S4 is polyimide, polytetrafluoroethylene, or polyetheretherketone.
7. The method according to claim 1, characterized in that: The substrate of the cathode coating area in S1 is tungsten or a tungsten alloy.
8. The method according to claim 1, characterized in that: The thickness of the insulating coating in S4 is 1~10μm.