Device and method for improving the uniformity of the thickness of the coating on the inner wall of a pipe

Abstract

This invention provides an apparatus and method for improving the uniformity of coating thickness on the inner wall of a pipe fitting. The apparatus includes a working chamber, a gas introduction component, a first power source, an auxiliary anode, and a magnetic field generating mechanism. The gas introduction component has a gas introduction channel with the same inner diameter as the pipe fitting. The auxiliary anode is disposed within the working chamber and coaxial with the gas introduction channel. The magnetic field generating mechanism is disposed outside the working chamber to form an axial magnetic field. When the pipe fitting is fixed to the gas introduction component, the gas introduction channel communicates with the pipe fitting cavity to form a smoothly transitioned and coaxial airflow channel. The auxiliary anode and the pipe fitting together form a cylindrical discharge structure, generating a radial electric field orthogonal to the axial magnetic field within the pipe fitting. This invention improves the uniformity of gas flow field distribution through a smoothly transitioned airflow channel and enhances the uniformity of plasma axial distribution through the synergistic effect of orthogonal electric and magnetic fields, significantly improving the uniformity of coating thickness on the inner wall of the pipe fitting.

Description

Technical Field

[0001] This invention relates to a device and method for improving the uniformity of coating thickness on the inner wall of pipe fittings, belonging to the field of surface engineering technology. Background Technology

[0002] Pipe fittings, as key components of modern infrastructure and industrial systems, are used in diverse fields, including public welfare (building water supply and drainage, urban drinking water systems), urban operations (municipal pipe networks), industrial production (oil and gas transportation), and national defense (gun barrels). However, in actual service, the inner walls of pipe fittings are subjected to the coupled effects of fluid friction, chemical media erosion, and high temperature and pressure, leading to frequent failures such as accelerated wear, corrosion perforation, and oxidation peeling, which seriously affect system reliability and service life. Surface coating technology can simultaneously improve the surface wear resistance, corrosion resistance, and high-temperature oxidation resistance while ensuring that the mechanical properties of the pipe fitting substrate are not damaged, and has become a core means to ensure the long-term stable service of pipe fittings.

[0003] Due to the limited internal space and complex geometry, traditional techniques struggle to achieve uniform preparation of diamond-like carbon (DLC) coatings inside pipes. The DLC thickness uniformity on the inner wall of pipe fittings is generally insufficient, which not only affects the protective effect of the DLC but also directly impacts the service life and safety of the pipe fittings. Existing technologies primarily improve the uniformity of the DLC thickness on the inner wall of pipe fittings by controlling the distribution uniformity of multiple physical coupling fields (such as electric fields, magnetic fields, and gas flow fields). For example, by setting a central anode inside the pipe and optimizing the air intake method and pore distribution of the coaxial gas guide tube, uniform gas distribution within the pipe can be achieved, thereby enabling uniform preparation of the DLC coating. However, for coaxial gas guide tubes with axially hollow, array-type gas distribution structures, the coaxial gas guide tube occupies part of the internal space, directly limiting the range of pipe fitting inner diameters that can be processed. Especially when pipe fitting dimensions change, targeted adjustments to the pore arrangement on the internal coaxial gas guide tube are required, making it difficult to achieve flexible processing capabilities that can quickly adapt to various pipe fitting specifications. Therefore, developing a universal adaptation solution suitable for improving the uniformity of diamond-like carbon coating thickness inside pipes has become one of the key technical challenges that urgently need to be addressed in this field. Summary of the Invention

[0004] To address the problem of insufficient uniformity in the coating thickness of the inner wall of pipe fittings in existing technologies, this invention provides a device and method for improving the uniformity of the coating thickness on the inner wall of pipe fittings. By utilizing a gas introduction component to form a coaxial, smoothly transitioning airflow channel with the pipe fitting, and combining the synergistic effect of a discharge structure based on an auxiliary anode and the pipe fitting with a magnetic field generating mechanism, uniform distribution of the coating thickness on the inner wall of the pipe fitting is achieved.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] A first aspect of the present invention provides an apparatus for improving the uniformity of coating thickness on the inner wall of a pipe fitting, comprising:

[0007] The work area should be large enough to accommodate the pipe fittings to be coated.

[0008] A gas inlet assembly, one end of which is used to connect to a reaction gas source and the other end is used to fix and connect to a pipe fitting. The gas inlet assembly has a gas inlet channel inside, which is used to guide the reaction gas into the inside of the pipe fitting. The gas inlet channel has the same inner diameter as the pipe fitting.

[0009] A first power source and an auxiliary anode, wherein the auxiliary anode is disposed in the working chamber and coaxially arranged with the gas inlet channel, the auxiliary anode is electrically connected to the positive terminal of the first power source and grounded, and the negative terminal of the first power source is used to connect to the pipe fitting;

[0010] A magnetic field generating mechanism is located outside the working chamber and is used to generate an axial magnetic field coaxial with the pipe inside the working chamber.

[0011] When the tube is fixed to the other end of the gas inlet assembly and electrically connected to the negative terminal of the first power supply, the gas inlet channel communicates with the tube cavity to form a smooth-transitioning and coaxial airflow channel. The auxiliary anode is coaxially disposed inside the tube and together they form a cylindrical discharge structure. The cylindrical discharge structure forms a radial electric field orthogonal to the axial magnetic field inside the tube. The radial electric field is used to ionize the reactive gas passing through the tube to form plasma. The axial magnetic field causes the charged particles in the plasma to move spirally along the axial direction of the tube, guiding the plasma to move along the axial direction of the tube and improving the uniformity of the axial distribution of the plasma.

[0012] The above scheme forms a smooth-transition airflow channel by using a gas inlet component and a coaxial airflow inlet channel with the same inner diameter as the tube. The reactant gas is introduced from one end (end) of the tube through the gas inlet component, rather than from the side wall of the tube or other locations in the vacuum chamber. The reactant gas can flow directionally inside the tube. Moreover, the gas inlet component and the tube have the same inner diameter and are arranged coaxially. This design avoids turbulence or uneven velocity distribution caused by abrupt changes in tube diameter or path when the airflow enters the tube, thereby improving the axial uniformity of the gas flow field distribution inside the tube. At the same time, the cylindrical discharge structure formed by the auxiliary anode and the tube generates a radial electric field. Combined with the axial magnetic field generated by the magnetic field generating mechanism, an orthogonal field environment is formed. The radial electric field ionizes the reactant gas passing through the tube to form plasma, while the axial magnetic field constrains the trajectory of charged particles through the Lorentz force, causing them to move spirally along the axis, limiting the radial diffusion loss of charged particles to the tube wall, and increasing the probability of collision ionization. This results in a high-density, highly uniform plasma distribution inside the tube, ultimately achieving uniform preparation of the coating thickness on the inner wall of the tube.

[0013] A second aspect of the present invention provides a method for improving the uniformity of coating thickness on the inner wall of a pipe fitting, comprising:

[0014] The device for improving the uniformity of coating thickness on the inner wall of the pipe fitting is provided, and the pipe fitting is fixed to the other end of the gas inlet assembly;

[0015] The gas pressure in the working chamber is maintained at a specified pressure, the cylindrical discharge structure forms a radial electric field in the tube, the magnetic field generating mechanism forms an axial magnetic field in the tube, and the reactive gas is introduced into the tube through the gas introduction assembly to form a coating of uniform thickness on the inner wall of the tube.

[0016] This invention utilizes the synergistic effect of multiple physical fields in the device and achieves high-quality and uniform preparation of coatings on the inner wall of pipe fittings through the control of process parameters.

[0017] As a typical implementation, the coating is a diamond-like carbon coating, and the method includes:

[0018] The gas is introduced into the tube and the working chamber via the gas introduction component to maintain the gas pressure in the working chamber at 0.4 Pa to 3.0 Pa. The current of the second power supply is maintained at 1 A to 4 A, the voltage of the first power supply is 400 V to 700 V, the pulse width is 10 μs to 100 μs, and the frequency is 1000 Hz to 2000 Hz, so as to form a diamond-like coating of uniform thickness on the inner wall of the tube.

[0019] Compared with the prior art, the advantages of the present invention include:

[0020] This invention guides the plasma to rearrange itself by constructing an electric field with an auxiliary anode, and restricts the plasma movement by applying an external magnetic field. This can reduce the plasma discharge pressure inside the tube and enhance the plasma discharge intensity inside the tube, thereby obtaining high-density plasma.

[0021] On the one hand, this invention improves the axial mobility of plasma and the axial uniformity of electric field distribution by the synergistic effect of the coaxial electromagnetic coil winding outside the tube and the auxiliary anode inside the tube; on the other hand, it improves the uniformity of gas flow field distribution inside the tube by using the gas inlet method at the tube end, thereby improving the uniformity of diamond-like coating thickness on the inner wall of the tube.

[0022] This invention places an auxiliary anode at the center of the tube, which is connected to the positive terminal of the pulse power supply and grounded. This constitutes a coaxial cylindrical discharge structure with the tube (cathode) and auxiliary anode (grounded) as its core. The presence of the auxiliary anode guides and stabilizes the direction of the electric field lines, making their distribution more uniform in the axial and radial directions of the tube. The coaxial electromagnetic coil winding outside the tube generates an axial magnetic field around the tube. This magnetic field exerts a Lorentz force constraint on charged particles (especially electrons) in the plasma, causing their trajectory to spiral along the direction of the magnetic field lines (axial direction). This greatly limits the radial diffusion loss of electrons to the tube wall, increasing the probability of collisional ionization with gas molecules. Thus, high-density, highly active plasma can be generated and maintained even at lower discharge pressures.

[0023] The synergistic effect of the magnetic and electric fields in this invention significantly enhances the migration capability of plasma (including electrons and ions) along the axial direction of the pipe. This helps to more effectively transport plasma from the generation area to the middle and far end of the pipe, overcoming the problem of plasma concentration at the pipe opening and thinning in the middle in traditional methods.

[0024] The present invention adopts the end-pipe gas inlet method, that is, the reaction gas is introduced from one end (end) of the pipe through the gas guide pipe, rather than from the side wall of the pipe or other positions in the vacuum chamber. Moreover, the gas guide pipe and the pipe are connected by an insulator, and the pipe, the insulator and the gas guide pipe are required to have the same inner diameter and be arranged coaxially. This design ensures the axisymmetry of the flow field when the gas enters the pipe.

[0025] This invention utilizes the coordinated control of the coaxial electromagnetic coil winding outside the tube, the auxiliary anode inside the tube, and the air intake at the end of the tube. It is not limited by the physical space of the inner diameter of the tube and can handle a wide range of inner diameters of tubes. It can also quickly process the inner walls of tubes of different specifications. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a device for improving the uniformity of coating thickness on the inner wall of pipe fittings, provided in a typical embodiment of the present invention.

[0027] Figure 2 These are cross-sectional morphology diagrams of the diamond-like carbon coatings on three specimens in sample A of Example 4 of the present invention;

[0028] Figure 3 These are cross-sectional morphology diagrams of the diamond-like carbon coatings on three specimens in sample B of Example 4 of the present invention;

[0029] Figure 4 These are cross-sectional morphology diagrams of the diamond-like carbon coatings on three specimens in sample C of Example 4 of the present invention;

[0030] Figure 5 This is a comparison diagram of the uniformity of diamond-like carbon coating thickness prepared in Example 4 of the present invention and Comparative Examples 1, 2 and 3. Detailed Implementation

[0031] In view of the shortcomings of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] Example 1

[0034] Please see Figure 1 This embodiment provides a device for improving the uniformity of coating thickness on the inner wall of a pipe, including a working chamber 1, a gas introduction component, a first power supply 7, an auxiliary anode 6, and a magnetic field generating mechanism.

[0035] The chamber 1 is designed to accommodate at least the pipe 2 to be coated. Specifically, the chamber 1 is typically a sealed vacuum chamber that provides the vacuum environment required for coating deposition. Its dimensions are designed according to the specifications of the pipe 2 to ensure that the pipe 2 can be placed coaxially within it.

[0036] One end of the gas inlet assembly is used to connect to the reaction gas source, and the other end is used to fix and connect to the pipe fitting 2. The gas inlet assembly has a gas inlet channel inside, which is used to guide the reaction gas into the interior of the pipe fitting 2. The gas inlet channel has the same inner diameter as the pipe fitting 2.

[0037] Specifically, the gas inlet assembly acts as a bridge connecting the gas source and pipe 2. One of the key improvements in this embodiment is that the inner diameter of the gas inlet channel is designed to be completely consistent with and coaxial with the inner diameter of pipe 2. This design creates a smooth-transitioning and coaxial airflow channel at the connection between pipe 2 and the gas inlet assembly. It should be understood that in the prior art, if the inlet channel and the inner diameter of the pipe are inconsistent, the airflow will generate turbulence or eddies due to the abrupt change in the flow channel cross-section when entering the pipe, resulting in uneven gas velocity distribution in the axial direction of the pipe, and thus causing uneven coating thickness. This embodiment, through the "equal diameter" design, eliminates the abrupt change in the flow channel, allowing the reactive gas to smoothly enter the interior of pipe 2 in a laminar or near-laminar state, thereby ensuring the initial uniformity of the gas flow field in the axial direction and laying the material foundation for the uniform deposition of the subsequent coating.

[0038] The primary power supply 7 and the auxiliary anode 6 are the core components for constructing the discharge environment / radial electric field. The auxiliary anode 6 is located in the working chamber and is coaxially arranged with the gas inlet channel. The auxiliary anode 6 is electrically connected to the positive terminal of the primary power supply 7 and grounded, while the negative terminal of the primary power supply 7 is used to connect to the pipe fitting 2.

[0039] Specifically, when tube 2 is fixed to the other end of the gas inlet assembly and electrically connected to the negative terminal of the first power source 7, tube 2 acts as the cathode, and auxiliary anode 6 acts as the anode, together forming a coaxial cylindrical discharge structure. In this structure, the electric field lines are mainly distributed radially, forming a radial electric field. This radial electric field can ionize the reactant gas passing through tube 2 to form plasma. Compared to traditional point-to-point discharge, this coaxial cylindrical discharge structure can provide a more uniform radial electric field distribution, avoiding the problem of excessively high local plasma density caused by local electric field concentration.

[0040] The magnetic field generating mechanism is located outside the working chamber 1 and is used to generate an axial magnetic field coaxial with the pipe 2 inside the working chamber 1.

[0041] Specifically, the magnetic field generated by the magnetic field generating mechanism is distributed along the axial direction of the tube 2. When the aforementioned radial electric field is formed inside the tube 2, this radial electric field and the axial magnetic field are spatially orthogonal. This orthogonal electric and magnetic field environment exerts specific motion constraints on charged particles (especially electrons). According to the Lorentz force principle, charged particles will undergo helical motion in orthogonal electric and magnetic fields. In this embodiment, the axial magnetic field causes the charged particles in the plasma to helically move along the axial direction of the tube 2. This helical motion greatly increases the mobility of charged particles in the axial direction of the tube and their residence time inside the tube 2, while limiting the radial diffusion loss of charged particles towards the tube wall. This not only improves the ionization efficiency of the gas and the plasma density, but more importantly, it enables the high-density plasma to diffuse uniformly along the axial direction into the depths of the tube, solving the problem of low plasma density and difficult coating deposition deep inside long tubes.

[0042] Through the above scheme, this embodiment constructs a physical environment in which a "smooth transition airflow channel" and "orthogonal electric and magnetic fields" work synergistically. The smooth transition of the airflow channel ensures the uniformity of the distribution of the reactive gas, while the orthogonal electric and magnetic fields ensure the uniformity of plasma generation and transport. The synergistic effect of the two ultimately improves the uniformity of the coating thickness on the inner wall of the tube. In addition, the device adopts a coaxial gas inlet method at the tube end, that is, the reactive gas (such as C2H2, Ar) is introduced from one end (end) of the gas inlet component, rather than from the side wall or other positions in the vacuum chamber. Moreover, the gas inlet component and the tube 2 have the same inner diameter and are arranged coaxially. This design ensures the axisymmetry of the flow field when the gas enters the tube.

[0043] It should be noted that the gas inlet component can be fixed directly to the working chamber or fixed through a support to keep the pipe in a designated position and in a fixed state. The specific structure and method of implementation are not limited here.

[0044] Example 2

[0045] Based on Example 1, this example optimizes the specific structure of the device to further improve the uniformity of the coating thickness.

[0046] Specifically, the gas introduction assembly includes a coaxially fixed and connected gas guide tube 5 and an insulating connector 4. The inner diameters of both the gas guide tube 5 and the insulating connector 4 are the same as the inner diameter of the fitting 2. The gas guide tube 5 is used to connect to the reaction gas source, and the insulating connector 4 is used to fix and connect the fitting 2, and to electrically isolate the gas guide tube 5 from the fitting 2.

[0047] It should be understood that during the discharge deposition process, the tube 2 acts as the cathode connected to the negative terminal of the first power supply 7. If the gas guide tube 5 is in direct metal contact with the tube 2, it may cause the gas guide tube 5 to become charged, leading to abnormal discharge or safety hazards. In this embodiment, by setting an insulating connector 4, the gas guide tube 5 and the tube 2 are electrically isolated while ensuring a consistent inner diameter and smooth transition of the airflow channel. This effectively avoids the risk of electrical short circuits and ensures the stability of the discharge process. Preferably, the gas introduction component is set inside the working chamber 1. This integrated design helps reduce external pipeline connections, lowers the risk of gas leakage, and further optimizes the airflow stability in a vacuum environment. Exemplarily, the material of the insulating connector 4 can be alumina, zirconium oxide, boron nitride, quartz, polytetrafluoroethylene, or mica.

[0048] Furthermore, the axial length of the auxiliary anode 6 is designed to be greater than or equal to the axial length of the pipe fitting 2. This design is crucial. If the auxiliary anode 6 is shorter than the pipe fitting 2, the electric field lines will bend and distort in the end region of the pipe fitting 2, resulting in a weakened or uneven distribution of the electric field strength at the end, which in turn causes the end coating thickness to deviate from the design value. By ensuring that the length of the auxiliary anode 6 covers the entire length of the pipe fitting 2, it is ensured that all positions of the pipe fitting 2 in the axial direction are within the range of a uniform radial electric field, eliminating the end effect and thus significantly improving the overall uniformity of the coating in the axial direction.

[0049] Furthermore, the first power supply 7 is preferably a pulsed power supply. Compared with traditional DC power supplies, pulsed power supplies have unique advantages. During pulsed discharge, voltage or current is applied in the form of pulses. During the pulse interval, charged particles in the plasma have time to recombine and diffuse, which helps to suppress the generation of local arc discharge, improve the stability of discharge, and thus obtain a denser and more uniform coating structure.

[0050] In this embodiment, the magnetic field generating mechanism is specifically configured as follows: the magnetic field generating mechanism includes an electromagnetic coil winding 3 and a second power supply 8. The electromagnetic coil winding 3 is wound outside the working chamber 1 and is coaxially arranged with the auxiliary anode 6, and is symmetrically arranged around the central axis of the auxiliary anode 6. Both ends of the electromagnetic coil winding 3 are electrically connected to the second power supply 8.

[0051] This circumferentially symmetrical winding method ensures the generation of a highly axially symmetrical magnetic field within the working chamber 1, preventing plasma from being biased to one side within the tube due to asymmetrical magnetic field distribution. Preferably, the second power supply 8 is a DC power supply, capable of providing a stable and continuous current, thereby generating a stable axial magnetic field. More preferably, the axial length of the electromagnetic coil winding 3 is greater than or equal to the axial length of the tube 2, similar in principle to the length design of the auxiliary anode 6, aiming to ensure that the tube 2 is constrained by a uniform magnetic field along its entire length, preventing plasma escape due to weakening of the end magnetic field. Exemplarily, the electromagnetic coil winding 3 is wound with enameled wire of 1.9 mm diameter, the inner diameter of the electromagnetic coil winding 3 is 160 mm, and the total length of the covered area is 650 mm.

[0052] Regarding the selection of materials and dimensions, the auxiliary anode 6 has a columnar structure, and its materials include, but are not limited to, titanium, tungsten, molybdenum, or stainless steel. These metal materials have good electrical conductivity and resistance to plasma bombardment, which can ensure structural stability during long-term discharge and prevent melting or excessive consumption.

[0053] Typically, the diameter of the auxiliary anode 6 ranges from 0.4 mm to 5 mm. Choosing this diameter range requires balancing two factors: if the diameter is too small, although it obstructs the airflow within the pipe less, it is prone to overheating and melting; if the diameter is too large, it will excessively occupy the space within the pipe, hindering airflow and affecting the uniformity of the gas flow field. The diameter range selected in this embodiment ensures the strength of the anode structure while minimizing interference with the flow field within the pipe, making it suitable for processing pipe fittings with different inner diameters.

[0054] Finally, to achieve optimal uniformity, the working chamber 1 is designed as a cylindrical structure, with the working chamber 1, gas inlet assembly, auxiliary anode 6, and electromagnetic coil winding 3 arranged coaxially. More specifically, the working chamber 1 also features an exhaust port, which is coaxially aligned with the working chamber 1, gas inlet assembly, auxiliary anode 6, and electromagnetic coil winding 3. This comprehensive coaxial design ensures the axially symmetrical distribution of the airflow field, electric field, and magnetic field from a macroscopic structural perspective. The airflow flows smoothly along the axis, the electric field is uniformly distributed radially, and the magnetic field is uniformly constrained axially. These three elements work synergistically to construct a highly uniform and stable physical field environment, providing a solid structural guarantee for the preparation of a coating with uniform thickness.

[0055] This invention, through the introduction of a smoothly transitioning airflow channel (composed of a gas guide pipe 5 and an insulating connecting seat 4) with the same inner diameter as the tube 2, ensures that the reactant gas enters the tube with a uniform flow field. Simultaneously, an auxiliary anode 6 is coaxially positioned inside the tube 2, forming a cylindrical discharge structure with the tube as the cathode, generating a radial electric field; and a coaxial electromagnetic coil winding 3 is positioned outside the working chamber 1 to generate an axial magnetic field. The radial electric field and the axial magnetic field are orthogonal within the tube. This synergistic effect of "smooth airflow" and "orthogonal electric and magnetic fields" effectively guides and constrains the plasma to distribute and move uniformly along the tube's axial direction, ultimately achieving a significant improvement in the uniformity of the coating thickness on the inner wall of the tube.

[0056] Example 3

[0057] This embodiment provides a method for improving the uniformity of coating thickness on the inner wall of a pipe fitting. This method is based on the device described in Embodiment 1 or Embodiment 2. By operating the components to work together, a uniform physical field environment is constructed on the inner wall of the pipe fitting, thereby producing a coating with uniform thickness.

[0058] Specifically, the method includes the following steps:

[0059] Step S100: Provide the device for improving the uniformity of coating thickness on the inner wall of the pipe as described in Embodiment 1 or Embodiment 2, and fix the pipe to the other end of the gas inlet assembly.

[0060] In this step, securing the fittings is not merely a simple mechanical connection. Operators must ensure a tight fit between the fittings and the insulating connectors in the gas introduction assembly, guaranteeing both a leak-proof connection to prevent gas leakage and electrical isolation between the fittings and the gas inlet pipe. More importantly, after installation, the fitting's cavity must be precisely aligned with the gas inlet channel and have the same inner diameter, thus forming a "smoothly transitioned and coaxial airflow channel" as described in Example 1. This installation quality directly determines the uniformity of the subsequent airflow distribution.

[0061] In a preferred embodiment, the fittings typically require pretreatment such as cleaning before being fixedly assembled with the gas introduction assembly. For example, the fittings are sequentially ultrasonically cleaned in acetone and anhydrous ethanol for 10-20 minutes, and then dried.

[0062] Step S200: Perform plasma etching cleaning on the pipe fitting.

[0063] In practice, firstly, the working chamber is evacuated using a vacuum pump system to reduce the background vacuum to a low level (e.g., 3×10⁻⁶). -3(Below Pa). Subsequently, inert gas is introduced into the working chamber to maintain the air pressure in the working chamber at 0.3 Pa to 2.0 Pa. At the same time, the cylindrical discharge structure forms a radial electric field inside the tube, and the magnetic field generating mechanism forms an axial magnetic field inside the tube, so as to perform plasma etching and cleaning on the inner wall of the tube.

[0064] Typically, the voltage of the first power supply is 400 V to 1000 V, the pulse width is 10 μs to 100 μs, and the frequency is 500 Hz to 2000 Hz. The current of the second power supply is 1 A to 4 A, and the magnetic field strength of the axial magnetic field is 3 Gs to 12 Gs.

[0065] Specifically, inert gases (such as argon) are ionized under the influence of orthogonal electric and magnetic fields to generate high-energy argon ions. These high-energy ions, accelerated by a radial electric field, bombard the inner wall of the tube, effectively removing oxide layers, oil stains, and adsorbed impurities from the tube surface. This significantly improves the activity of the substrate surface, thereby greatly enhancing the adhesion between the subsequently deposited coating and the substrate. Specifically, the plasma discharge inside the tube can be ignited by adjusting the gas pressure, electric field, and magnetic field parameters. When the system is not equipped with an external magnetic field or the tube diameter is small or large, a high voltage (Paschen curve) is usually required under high pressure to break through the gas ionization threshold and trigger plasma discharge. However, by introducing a specific external magnetic field, the movement path of charged particles is constrained, and the probability of ionization collisions is significantly increased. Under the same gas pressure, the discharge voltage can be significantly reduced to ignite the plasma inside the tube.

[0066] Step S300, coating preparation.

[0067] In specific operation, a radial electric field is formed inside the tube by a cylindrical discharge structure, and an axial magnetic field is formed inside the tube by a magnetic field generating mechanism. Reactive gas is introduced into the tube through a gas introduction component to form a coating of uniform thickness on the inner wall of the tube.

[0068] Specifically, the preparation of a uniform coating requires the establishment of a uniform physical field. The operator turns on the first power supply, creating a potential difference between the auxiliary anode 6 and the tube 2. Since the auxiliary anode 6 is coaxially positioned inside the tube 2, the two together form a cylindrical discharge structure, thereby generating a radially distributed electric field within the tube 2. Simultaneously, the second power supply 8 is turned on, supplying power to the electromagnetic coil winding 3 outside the working chamber 1. The energized electromagnetic coil winding 3 generates a magnetic field, which penetrates the working chamber wall and enters the tube 2, forming a magnetic field distributed along the axial direction of the tube 2. At this point, an electromagnetic environment with orthogonal radial electric and axial magnetic fields is established inside the tube 2. As mentioned earlier, this orthogonal electric and magnetic field environment effectively constrains the trajectory of charged particles, improving the plasma density and axial distribution uniformity.

[0069] The reactive gas is introduced from the end via a gas inlet assembly. Since the gas inlet channel has the same inner diameter as pipe 2 and a smooth transition, the reactive gas can enter the pipe interior at a uniform flow rate, avoiding turbulence caused by abrupt changes in the flow channel. Under the influence of a radial electric field, the reactive gas is ionized to form plasma. The active particles in the plasma, guided by orthogonal electric and magnetic fields, spiral along the pipe axis and distribute uniformly, ultimately depositing a coating on the inner wall surface of the pipe. Due to the synergistic homogenizing effect of the gas flow field, electric field, and magnetic field, the deposition rate of the coating at various positions along the pipe axis tends to be consistent, thus ensuring the uniformity of the coating thickness.

[0070] For example, when the coating is a diamond-like carbon coating, the air pressure in the working chamber is maintained at 0.4 Pa to 3.0 Pa, the current of the second power supply is maintained at 1 A to 4 A, the voltage of the first power supply is 400 V to 700 V, the pulse width is 10 μs to 100 μs, and the frequency is 1000 Hz to 2000 Hz, and this is continued for 30 min to 120 min, so as to form a diamond-like carbon coating of uniform thickness on the inner wall of the tube.

[0071] Regarding the selection of the reaction gas, this embodiment provides several implementation methods. The reaction gas can be high-purity acetylene (C2H2), a mixture of high-purity acetylene (C2H2) and high-purity argon, a mixture of high-purity acetylene (C2H2) and high-purity nitrogen (N2), or a mixture of high-purity acetylene (C2H2) and hexamethyldisiloxane (HMDSO).

[0072] After the coating is prepared, the tube is cooled to room temperature under vacuum and then removed from the working chamber.

[0073] Example 4

[0074] To verify the significant effect of the device and method provided by this invention in improving the uniformity of coating thickness on the inner wall of pipe fittings, this invention provides a detailed description of the technical solution based on specific experimental data. This invention selected three different specifications of pipe fittings as samples, labeled Sample A, Sample B, and Sample C, and set up corresponding comparative proportions for comparative testing. Three test pieces 9-1, 9-2, and 9-3 were respectively set at different axial positions on the inner wall of each sample (e.g., inlet end, middle, and end).

[0075] Specifically, Sample A uses a 316L stainless steel pipe with an inner diameter of 40 mm and a length of 300 mm, and the auxiliary anode 6 is a titanium rod with a diameter of 5 mm; Sample B uses a 316L stainless steel pipe with an inner diameter of 30 mm and a length of 300 mm, and the auxiliary anode 6 is a tungsten rod with a diameter of 3 mm; Sample C uses a 316L stainless steel pipe with an inner diameter of 10 mm and a length of 200 mm, and the auxiliary anode 6 is a tungsten wire with a diameter of 0.4 mm. The selection of the material and diameter of the auxiliary anode 6 conforms to the parameter range defined in the claims of this invention, aiming to verify the adaptability of this parameter range to pipes of different sizes.

[0076] The experimental steps are as follows:

[0077] First, each sample is pretreated.

[0078] The sample was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes in sequence, dried, and then installed in the device described in Example 2. During installation, it is essential to ensure that the gas inlet channel of the gas inlet assembly is the same as the inner diameter of the sample and coaxially connected to form a smooth transition gas flow channel.

[0079] Subsequently, a plasma etching and cleaning step is performed.

[0080] The air pressure in Studio 1 was reduced to 3×10. -3 Below Pa, high-purity argon gas with a flow rate of 50 sccm is introduced to maintain the gas pressure at 0.8 Pa (samples A and B) or 1.5 Pa (sample C). The first power supply 7 and the second power supply 8 are turned on. The voltage of the first power supply 7 is set to 700 V, the pulse width is 10 μs, and the frequency is 1000 Hz. The current of the second power supply 8 is set to 2 A. The inner wall of the sample is etched and cleaned for 20 minutes to remove the surface oxide layer and contaminants and improve the coating adhesion.

[0081] After etching and cleaning, a diamond-like carbon coating is deposited.

[0082] A mixture of high-purity argon and high-purity acetylene at a flow rate ratio of 1:4 was introduced into chamber 1 as the reaction gas. The gas pressure in chamber 1 was maintained at 3.0 Pa (samples A and B) or 4.0 Pa (sample C). The current of the second power supply 8 was kept at 1 A, and the voltage of the first power supply 7 was adjusted to 650 V (samples A and B) or 700 V (sample C), with a pulse width of 10 μs and a frequency of 1000 Hz. The deposition time was 90 minutes.

[0083] After deposition, the sample was cooled to room temperature under vacuum and removed. Three specimens (9-1, 9-2, and 9-3) from the inner wall of the sample were taken out, and the thickness of the diamond-like carbon (DLC) coating was measured. The cross-sectional morphology of the coating was observed and the thickness was measured using a scanning electron microscope (SEM). The uniformity of the DLC coating thickness in the same direction was also calculated.

[0084] The formula for calculating thickness uniformity is:

[0085] ;

[0086] In the formula: d max d represents the maximum thickness of the diamond-like carbon coating in the same direction within the tube; min This represents the minimum thickness of the diamond-like carbon coating in the same direction within the tube; d average This represents the average thickness of the diamond-like coating in the same direction within the tube.

[0087] Figure 2 , Figure 3 , Figure 4 The figures show cross-sectional morphology images of the diamond-like carbon coatings on the inner walls of three samples: Sample A, Sample B, and Sample C. The figures clearly demonstrate a dense coating structure and good adhesion to the substrate.

[0088] Specific measurement results show that: the coating thicknesses on the three specimens on the inner wall of sample A are 2.20 μm, 2.35 μm, and 2.05 μm, respectively, with a calculated axial thickness uniformity of 86%; the coating thicknesses at three locations on the inner wall of sample B are 1.65 μm, 1.70 μm, and 1.45 μm, respectively, with an axial thickness uniformity of 84%; and the coating thicknesses at three locations on the inner wall of sample C are 960 nm, 1144 nm, and 893 nm, respectively, with an axial thickness uniformity of 75%.

[0089] To further highlight the key role of the feature that "the airflow introduction channel and the inner diameter of the pipe are the same and coaxial" in the technical solution of this invention, this embodiment also sets up three comparative examples. Comparative examples 1, 2, and 3 correspond to the specifications of samples A, B, and C, respectively, but the difference is that the coaxial gas introduction component in embodiment 2 is not used in the comparative examples, that is, a smooth transition and coaxial airflow channel is not formed. Instead, an air inlet is set coaxially at one end of the working chamber for direct air intake (the insulating connecting seat 4 and the air guide pipe 5 are omitted). The rest of the device structure and process parameters are the same as those in the embodiment.

[0090] like Figure 5 The figure shows a comparison of the uniformity of diamond-like carbon coating thickness prepared in the experimental examples and comparative examples. The uniformity of coating thickness in Comparative Example 1 is only 68%, in Comparative Example 2 it is 66%, and in Comparative Example 3 it is 58%.

[0091] A comparison reveals that the coating thickness uniformity of the embodiment of this invention is significantly higher than that of the comparative example. The reason for this is that in the comparative example, due to the mismatch between the air inlet channel and the inner diameter of the pipe, and the need to maintain coaxial proximity, the airflow experiences turbulence or eddies upon entering the pipe due to abrupt changes in the flow channel cross-section. This results in uneven velocity and concentration distribution of the reactant gas along the axial direction of the pipe, leading to uneven plasma density distribution and ultimately a significant decrease in coating thickness uniformity. In contrast, this invention, by setting an airflow inlet channel with the same inner diameter as the pipe, creates a smooth-transition airflow environment, eliminating turbulent disturbances at the inlet and ensuring axial uniformity of the gas flow field. Simultaneously, the orthogonal electric and magnetic fields generated by the auxiliary anode and the electromagnetic coil winding effectively constrain the plasma distribution, thereby achieving a significant improvement in coating thickness uniformity.

[0092] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A device for improving the uniformity of coating thickness on the inner wall of pipe fittings, characterized in that, include: The working chamber (1) can at least accommodate the pipe (2) to be coated. A gas inlet assembly, one end of which is used to connect to a reaction gas source and the other end is used to fix and connect to a pipe fitting (2). The gas inlet assembly has a gas inlet channel inside and is used to guide the reaction gas into the pipe fitting (2). The gas inlet channel has the same inner diameter as the pipe fitting (2). A first power source (7) and an auxiliary anode (6), wherein the auxiliary anode (6) is disposed in the working chamber (1) and coaxially disposed with the gas inlet channel, the auxiliary anode (6) is electrically connected to the positive terminal of the first power source (7) and grounded, and the negative terminal of the first power source (7) is used to connect to the pipe fitting (2). A magnetic field generating mechanism is located outside the working chamber (1) and is used to generate an axial magnetic field coaxial with the pipe fitting (2) inside the working chamber (1); When the tube (2) is fixed to the other end of the gas inlet assembly and electrically connected to the negative terminal of the first power supply (7), the gas inlet channel communicates with the cavity of the tube (2) to form a smooth transition of the inner wall and a coaxial airflow channel. The auxiliary anode (6) is coaxially arranged inside the tube (2) and together they form a cylindrical discharge structure. The cylindrical discharge structure forms a radial electric field orthogonal to the axial magnetic field inside the tube (2). The radial electric field is used to ionize the reaction gas passing through the tube (2) to form plasma. The axial magnetic field causes the charged particles in the plasma to move spirally along the axial direction of the tube (2), guiding the plasma to move along the axial direction of the tube (2) and tend to be uniformly distributed.

2. The device for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 1, characterized in that: The gas introduction assembly includes a coaxially fixed and connected gas guide tube (5) and an insulating connector (4). The inner diameters of the gas guide tube (5) and the insulating connector (4) are the same as the inner diameter of the fitting (2). The gas guide tube (5) is used to connect to the reaction gas source, and the insulating connector (4) is used to fix the connection to the fitting (2) and electrically isolate the gas guide tube (5) from the fitting (2). Preferably, the gas introduction component is disposed within the working chamber (1).

3. The device for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 1, characterized in that: The axial length of the auxiliary anode (6) is greater than or equal to the axial length of the pipe fitting (2); And / or, the first power supply (7) is a pulse power supply.

4. The device for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 1, characterized in that: The magnetic field generating mechanism includes an electromagnetic coil winding (3) and a second power source (8). The electromagnetic coil winding (3) is wound around the outside of the working chamber (1). The electromagnetic coil winding (3) is coaxially arranged with the auxiliary anode (6) and is arranged symmetrically around the central axis of the auxiliary anode (6). The two ends of the electromagnetic coil winding (3) are electrically connected to the second power source (8). Preferably, the second power supply (8) is a DC power supply; Preferably, the axial length of the electromagnetic coil winding (3) is greater than or equal to the axial length of the pipe fitting (2).

5. The device for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 1 or 4, characterized in that: The auxiliary anode (6) has a columnar structure; and / or the material of the auxiliary anode (6) includes titanium, tungsten, molybdenum or stainless steel; and / or the diameter of the auxiliary anode (6) is 0.4 mm to 5 mm.

6. The device for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 4, characterized in that: The working chamber (1) is a cylindrical structure, and the working chamber (1), the gas inlet component, the auxiliary anode (6), and the electromagnetic coil winding (3) are coaxially arranged.

7. A method for improving the uniformity of coating thickness on the inner wall of pipe fittings, characterized in that, include: Provide an apparatus for improving the uniformity of coating thickness on the inner wall of a pipe as described in any one of claims 1-6, and fix the pipe (2) to the other end of the gas inlet assembly; The gas pressure in the working chamber (1) is maintained at a specified pressure, the cylindrical discharge structure forms a radial electric field in the tube (2), the magnetic field generating mechanism forms an axial magnetic field in the tube (2), and the reaction gas is introduced into the tube (2) through the gas introduction assembly to form a coating of uniform thickness on the inner wall of the tube (2).

8. The method for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 7, characterized in that, Also includes: First, the tube (2) is subjected to plasma etching cleaning, and then a coating is formed on the inner wall of the tube (2); Preferably, the method for plasma etching cleaning of the pipe fitting (2) includes: First, adjust the air pressure in the working chamber (1) to 3×10. -3 Below Pa, inert gas is introduced into the working chamber (1) to maintain the gas pressure in the working chamber (1) at 0.3 Pa to 2.0 Pa, so that the cylindrical discharge structure forms a radial electric field in the tube (2) and the magnetic field generating mechanism forms an axial magnetic field in the tube (2) to perform plasma etching cleaning on the inner wall of the tube (2); wherein the voltage of the first power supply (7) is 400 V to 1000 V, the pulse width is 10 μs to 100 μs, the frequency is 500 Hz to 2000 Hz, the current of the second power supply (8) is 1 A to 4 A, and the magnetic field strength of the axial magnetic field is 3 Gs to 12 Gs.

9. The method for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 7, characterized in that, The coating is a diamond-like carbon coating, and the method includes: The gas is introduced into the tube (2) and the working chamber (1) via the gas introduction component, and the gas pressure in the working chamber (1) is maintained at 0.4 Pa to 3.0 Pa. The current of the second power supply (8) is maintained at 1 A to 4 A, and the voltage of the first power supply (7) is 400 V to 700 V, the pulse width is 10 μs to 100 μs, and the frequency is 1000 Hz to 2000 Hz, so as to form a diamond-like coating of uniform thickness on the inner wall of the tube (2).

10. The method for improving the uniformity of coating thickness on the inner wall of pipe fittings according to claim 7 or 9, characterized in that, The working gas is high-purity acetylene, or a mixture of high-purity acetylene and high-purity argon, or a mixture of high-purity acetylene and high-purity nitrogen, or a mixture of high-purity acetylene and hexamethyldisiloxane.

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