A method for coating a manganese-zinc high-conductivity ferrite magnetic ring and the magnetic ring itself.

Abstract

This invention discloses a coating method for a manganese-zinc high-conductivity ferrite magnetic ring and the magnetic ring itself. The coating method includes: substrate pretreatment to expose micropores; gradient preheating to remove moisture; zoned spraying, first electrostatically spraying the outer surface, then spraying the inner wall of the inner cavity; static leveling and stepped curing. This invention overcomes the Faraday cage effect and solves the problem of dead corners in deep cavities by combining internal and external zoned spraying with deep cavity operation; and eliminates pinholes and air gaps with stepped curing, achieving full surface coverage and significantly improving the insulation and withstand voltage performance of the magnetic ring and inductor.

Description

Technical Field

[0001] This invention belongs to the field of magnetic material surface treatment technology, specifically relating to a coating method for a manganese-zinc high-conductivity ferrite magnetic ring and the magnetic ring itself. Background Technology

[0002] Manganese-zinc ferrite magnetic rings are widely used in various electronic circuits due to their high permeability. However, because of their extremely low surface resistivity, insulation failure can easily lead to inter-turn short circuits, and the sharp edges of the magnetic rings pose a risk of cutting the wound enameled wires. Therefore, the surface insulation coating process is a key step in ensuring the electrical performance of the magnetic rings. Electrostatic powder coating is typically used to form an insulating coating on the surface of the magnetic ring to meet the device's withstand voltage insulation and environmental protection requirements.

[0003] However, existing electrostatic spraying processes are prone to charge shielding due to the Faraday cage effect when treating the deep cavities inside magnetic rings, resulting in incomplete coating or uneven coating thickness. Simultaneously, the porous nature of the magnetic ring makes it susceptible to pinholes and bubbles in the coating during high-temperature curing due to the rapid expansion of internal gas. These defects severely weaken the coating's insulation and withstand voltage performance, making it highly susceptible to breakdown and short circuits in the dead corners of the deep cavity, thus failing to meet the requirements of high-reliability applications. Summary of the Invention

[0004] The present invention aims to overcome the defects of the prior art and provide a method for coating manganese-zinc high-conductivity ferrite magnetic rings and the magnetic rings themselves, which solve the problem of spraying dead corners and achieve full surface coverage.

[0005] To address the aforementioned technical problems, this invention provides a method for coating a manganese-zinc high-conductivity ferrite magnetic ring, comprising the following steps: Step 1: The manganese-zinc high-conductivity ferrite magnetic ring substrate is purged with compressed air, ultrasonically cleaned and dried to expose the surface micropores. Step 2: The pretreated manganese-zinc high-conductivity ferrite magnetic ring matrix is ​​subjected to step heating to remove moisture and heat through the core. Step 3: First, electrostatic spraying is performed on the outer surface and end face of the manganese-zinc high-conductivity ferrite magnetic ring substrate, and then the inner wall is sprayed by inserting into the center of the inner hole of the manganese-zinc high-conductivity ferrite magnetic ring substrate. Step 4: Allow the sprayed manganese-zinc high-conductivity ferrite magnetic ring matrix to stand and level, and then perform low-temperature pre-curing and high-temperature complete cross-linking curing in sequence.

[0006] Furthermore, in step 1, after the ultrasonic cleaning and before the drying, a weak acid micro-etching step or an atmospheric pressure air plasma treatment step is also included.

[0007] Furthermore, in step 3, when the spraying distance is shortened to 15cm, an electrostatic spraying method with closed-loop feedback control is adopted, which monitors the tip current in real time and automatically adjusts the voltage, while increasing the sweeping speed by 20-30% and introducing atomized air to assist in adjusting the atomized air pressure.

[0008] Furthermore, in step 3, for the manganese-zinc high-conductivity ferrite magnetic ring substrate with an inner diameter of less than 5 mm, a miniaturized spraying method is used for spraying; during the spraying process, anti-collision and centering control are achieved through a limiting and guiding method.

[0009] Furthermore, before step 4, the method includes detecting the apparent porosity of the manganese-zinc high-conductivity ferrite magnetic ring matrix; if the apparent porosity is greater than 15%, the temperature for low-temperature pre-curing is set to 130-140℃ and the time is set to 30-40 minutes; if the apparent porosity is between 10% and 15%, the temperature for low-temperature pre-curing is set to 140-160℃ and the time is set to 15-30 minutes; if the apparent porosity is less than 10%, the temperature for low-temperature pre-curing is set to 160℃ and the time is set to 15 minutes.

[0010] Furthermore, after step 4, an insulation enhancement treatment step is also included: the surface of the coating after high-temperature complete cross-linking and curing is subjected to dry ice blasting micro-sanding or fine sandpaper light surface roughening treatment, followed by chemical activation by wiping with acetone or surfactant, and then a second thin coating and curing.

[0011] Furthermore, the insulating coating material used for the electrostatic spraying and the inner wall spraying includes at least one of epoxy resin powder, epoxy polyester powder, or nylon powder.

[0012] Another aspect of the present invention provides a manganese-zinc high-conductivity ferrite magnetic ring, which is prepared by the insulating coating process of the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to any of the preceding claims.

[0013] Beneficial effects The beneficial effects of this invention are as follows: by setting up substrate pretreatment and gradient preheating, impurities and internal moisture on the substrate surface can be effectively removed, exposing surface micropores and allowing heat penetration into the core, laying the foundation for good adhesion of subsequent coatings and avoiding defects caused by residual moisture or gas during curing; by using a partitioned spraying method that first electrostatically sprays the outer surface and end faces, and then extends into the center of the inner hole for inner wall spraying, the charge shielding problem caused by the Faraday cage effect can be effectively overcome, solving the dead corner problem of incomplete spraying of the deep cavity of the inner wall of the magnetic ring or uneven coating thickness; by using a stepped curing process of static leveling and sequential low-temperature pre-curing and high-temperature complete cross-linking curing, the coating can be fully leveled and the exhaust rate can be reasonably controlled, completely eliminating pinholes and bubbles in the coating caused by the rapid expansion of internal gas due to the porous nature of the magnetic ring, achieving 100% full surface coverage, and significantly improving the insulation withstand voltage performance, coating adhesion and environmental adaptability of the magnetic ring. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the process flow of the method of the present invention. Detailed Implementation

[0015] The technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0016] like Figure 1 As shown, the present invention provides an insulating coating process for the surface of a manganese-zinc high-conductivity ferrite magnetic ring, the overall process of which mainly includes the following four steps: Step 1: Pretreatment of the substrate. The manganese-zinc high-conductivity ferrite magnetic ring substrate is sequentially purged with compressed air, ultrasonically cleaned, and dried. After drying, the surface is subjected to low-temperature plasma activation treatment. The treatment atmosphere is a mixture of oxygen and argon gas, and the treatment time is 15~90 seconds, so as to introduce polar groups into the inner wall of the micropores. Preferably, after ultrasonic cleaning and before drying, a weak acid micro-etching step or an atmospheric pressure air plasma treatment step can be added to further enlarge the micropores and increase the active groups; the low-temperature plasma activation treatment time after drying can be set to 15~30 seconds. Step 2: Gradient preheating. Place the pretreated magnetic ring in a preheating furnace and raise the temperature from room temperature to 80-100℃ at a rate of 2-5℃ / min and hold for 15-25 minutes. Then raise the temperature to 120-140℃ at a rate of 1-3℃ / min and hold for 10-20 minutes, so that the temperature difference between the core and surface of the magnetic ring is ≤5℃. Step 3: Controllable spraying in zones. First, electrostatic spraying is performed on the outer surface and end face of the magnetic ring. The spraying voltage is 50~70kV and the powder supply air pressure is 0.05~0.10MPa. Then, a slender rod-type spray gun is inserted into the central axis of the inner hole of the magnetic ring, keeping the minimum distance between the end of the spray gun and the inner wall at 8~12mm. During the spraying process, the magnetic ring is controlled to rotate around its central axis at a speed of 10~30r / min, while the spray gun moves back and forth at a constant speed of 5~15mm / s along the axial direction to spray the inner wall. The spraying voltage for the inner wall is 30~50kV (lower than the spraying voltage for the outer surface), and the powder supply air pressure is 0.02~0.06MPa. While the inner wall is being sprayed, an ion gas flow is introduced into the inner hole of the magnetic ring at a flow rate of 5-15 L / min to neutralize the static charge accumulated on the inner wall and to help the powder penetrate into the deep cavity area. Step 4: Allow to stand, level, and cure; Vacuum step curing: After spraying, the magnetic ring is allowed to stand at room temperature for 5-10 minutes to level, then placed in a vacuum curing oven. First, a vacuum is drawn to -0.08 to -0.095 MPa, and pre-cured at 100-120°C for 10-15 minutes. Then, the vacuum is released, and the temperature is raised to 180-200°C at a rate of 1-2°C / min under normal pressure and held for 20-30 minutes for complete cross-linking and curing. Finally, it is cooled to room temperature at a rate of ≤3°C / min. Alternatively... Atmospheric pressure adaptive curing: If vacuum pre-curing is not used, the apparent porosity of the magnetic ring matrix can be measured after static leveling. Pre-curing can then be dynamically adjusted directly in an atmospheric pressure curing oven based on the apparent porosity. If the apparent porosity is greater than 15%, the low-temperature pre-curing temperature is set to 130-140℃ and the time to 30-40 minutes; if the apparent porosity is between 10% and 15%, the low-temperature pre-curing temperature is set to 140-160℃ and the time to 15-30 minutes; if the apparent porosity is less than 10%, the low-temperature pre-curing temperature is set to 160℃ and the time to 15 minutes for complete cross-linking curing. Finally, cooling to room temperature is performed at a rate of ≤3℃ / min. These two curing methods are independent and can be used interchangeably.

[0017] This invention effectively overcomes the Faraday cage effect and solves the problem of dead corners in the deep cavity spraying of the inner wall of the magnetic ring by combining two-step electrostatic spraying with deep cavity operation in the inner and outer partitions. At the same time, with the gradient preheating and step curing process, the pinholes and air gaps in the coating are effectively eliminated, achieving 100% full surface coverage and significantly improving the insulation withstand voltage performance, coating adhesion and environmental adaptability of the manganese zinc high-conductivity ferrite magnetic ring.

[0018] Preferably, the manganese-zinc high-conductivity ferrite magnetic ring substrate is subjected to compressed air purging, ultrasonic cleaning, and drying to expose surface micropores. Compressed air purging effectively removes floating dust and loose particles from the surface of the magnetic ring substrate; subsequently, ultrasonic cleaning utilizes the cavitation effect to deeply remove oil and minute impurities from the substrate surface; finally, drying is performed to remove residual moisture and expose the surface micropores of the substrate, providing a good substrate condition for subsequent coating.

[0019] Preferably, in order to further improve the adhesion between the coating and the substrate, in step 1, after the ultrasonic cleaning and before the drying, a weak acid micro-etching step or an atmospheric pressure air plasma treatment step is also included; by introducing the above surface activation step, the deficiency of simple drying in not being able to significantly expand the micropores can be effectively compensated, thereby greatly improving the adhesion of the coating.

[0020] Preferably, when using a weak acid micro-etching step, the cleaned manganese-zinc high-conductivity ferrite magnetic ring substrate can be immersed or sprayed with a weak acid solution. Optionally, the weak acid solution may include dilute acetic acid, dilute citric acid, or a low-concentration inorganic weak acid. The weak acid can produce a slight chemical etching effect on the ferrite surface, thereby effectively expanding the pore size and depth of the surface micropores and forming a richer micro-rough structure.

[0021] Preferably, when using the atmospheric pressure air plasma treatment step, the surface of the magnetic ring substrate can be bombarded using an air plasma generator under atmospheric pressure. The high-energy particles in the plasma can not only further clean the surface, but also break some of the chemical bonds on the surface, generate a large number of free radicals, and significantly increase the number of active groups such as hydroxyl groups on the surface.

[0022] Therefore, through the aforementioned weak acid micro-etching steps or atmospheric pressure air plasma treatment steps, not only are the surface micropores enlarged to form effective mechanical anchors, but the surface also gains more active groups such as hydroxyl groups to provide abundant chemical bonding sites. This synergistic effect of physical-mechanical interlocking and chemical bonding significantly improves the initial adhesion between the subsequent insulating coating and the ferrite substrate, effectively reducing the risk of coating peeling during subsequent processing or long-term use, thereby ensuring the insulation withstand voltage performance and environmental adaptability of the magnetic ring.

[0023] Preferably, after the substrate pretreatment in the first step, gradient preheating is performed. Specifically, the manganese-zinc high-conductivity ferrite magnetic ring substrate is heated in a stepped manner. This gradient preheating method can gradually and fully remove moisture from the interior of the manganese-zinc high-conductivity ferrite magnetic ring substrate and ensure that its core is fully heated through, thereby providing suitable substrate temperature conditions for subsequent coating processes. This helps to improve the initial adhesion of the coating and reduce gas expansion defects during the subsequent curing process.

[0024] Preferably, electrostatic spraying is first performed on the outer surface and end face of the manganese-zinc high-conductivity ferrite magnetic ring substrate. By prioritizing the spraying of the outer surface and end face, an insulating protective layer can be initially established on the outside of the magnetic ring, and a process basis can be provided for the subsequent inner wall spraying.

[0025] Preferably, when performing electrostatic spraying on the outer surface and end face, the spraying distance can be controlled at around 15cm to effectively reduce the Faraday cage effect. However, at this distance, electrostatic arcing is easily triggered or the coating becomes excessively thick in some areas. Therefore, this application adopts an electrostatic spraying method with closed-loop feedback control. This method can monitor the tip current in real time and automatically adjust the output voltage according to the monitored current changes, thereby avoiding the risk of electrostatic arcing at a shorter distance.

[0026] Preferably, while employing the aforementioned closed-loop feedback control method, a servo system can be used to increase the sweeping speed by 20-30%, and atomized air can be introduced to assist in adjusting the atomization pressure. By increasing the sweeping speed, excessive powder deposition in certain areas can be avoided, preventing localized over-thickness of the coating. By introducing atomized air to adjust the atomization pressure, the atomization effect and flight trajectory of the insulating coating material can be optimized. Thus, while effectively overcoming the phenomenon of exposed substrate in dead zones and reducing the Faraday cage effect, the risk of electrostatic arcing and the problem of excessively thick localized coatings are precisely avoided, ensuring the uniformity of coating thickness and the safety of the process.

[0027] Preferably, in the partitioned spraying step 3, the outer surface and end faces of the manganese-zinc high-conductivity ferrite magnetic ring substrate are first electrostatically sprayed, and then the inner wall is sprayed by extending into the center of the inner hole of the manganese-zinc high-conductivity ferrite magnetic ring substrate. This two-step electrostatic spraying method, with internal and external partitions, effectively overcomes the Faraday cage effect in the deep cavity, solves the problem of dead zones in the deep cavity spraying of the magnetic ring's inner wall, and achieves 100% full surface coverage.

[0028] Preferably, for small manganese-zinc high-conductivity ferrite magnetic ring substrates with an inner diameter of less than 5 mm, a miniaturized spraying method can be used for inner wall spraying. By using a miniaturized spraying tool adapted to the narrow inner space of the small magnetic ring, the atomization effect of the insulating coating material and the coverage range within the deep cavity can be optimized.

[0029] Preferably, to ensure the stability and safety of the spraying tool when operating inside the deep cavity, a limiting and guiding method can be used to achieve anti-collision and centering control. Optionally, the limiting and guiding component can be made of a material with self-lubricating and low coefficient of friction properties. Further optionally, the outer diameter of the limiting and guiding component can be designed to be smaller than the inner diameter of the manganese-zinc high-conductivity ferrite magnetic ring substrate.

[0030] The limiting and guiding components ensure that the spraying tool remains centered within the inner hole without making direct contact with the inner wall, achieving precise centering control. This not only effectively prevents the spraying tool from scratching the inner wall of the magnetic ring or causing physical defects in the coating during movement and spraying, but also ensures the uniformity and integrity of the coating inside the deep cavity, thereby significantly improving the quality and reliability of the insulating coating on the inner wall of the small magnetic ring.

[0031] Preferably, after the partitioned spraying in step 3 is completed, a fourth step is performed: static leveling and stepped curing. Specifically, the sprayed manganese-zinc high-conductivity ferrite magnetic ring substrate is statically leveled, allowing the insulating coating material powder on the surface to be evenly distributed and initially adhered under the action of gravity and surface tension. Then, low-temperature pre-curing and high-temperature complete cross-linking curing are performed sequentially.

[0032] Preferably, when using atmospheric pressure adaptive curing, before the stepped curing stage in the fourth step, a step of detecting the apparent porosity of the manganese-zinc high-conductivity ferrite magnetic ring matrix is ​​included. It should be noted that for small-sized magnetic rings, samples from the same batch can be used for apparent porosity testing to avoid contamination or damage to the magnetic ring matrix. Since the internal pore structure of manganese-zinc high-conductivity ferrite magnetic ring matrices prepared by different batches or different molding processes often varies, detecting the apparent porosity can provide accurate data support for subsequent curing processes, enabling personalized customization of process parameters.

[0033] Preferably, the parameters of the low-temperature pre-curing (performed at ambient pressure) are dynamically adjusted based on the detected apparent porosity. Specifically, if the apparent porosity is greater than 15%, it indicates that the magnetic ring matrix has many pores and a high gas content. In this case, the low-temperature pre-curing temperature is set to 130-140℃ and the time is set to 30-40 minutes. If the apparent porosity is between 10% and 15%, the low-temperature pre-curing temperature is set to 140-160℃ and the time is set to 15-30 minutes. If the apparent porosity is less than 10%, it indicates that the magnetic ring matrix is ​​relatively dense and has a low gas content. In this case, the low-temperature pre-curing temperature is set to 160℃ and the time is set to 15 minutes.

[0034] All the above pre-curing was carried out under normal pressure, and the subsequent high-temperature full cross-linking curing parameters were the same as those of the vacuum step curing method (180~200℃, 20~30 minutes).

[0035] By dynamically adjusting the pre-curing parameters based on the apparent porosity, the exhaust rate of the gas inside the magnetic ring substrate can be matched with the gelation rate of the surface insulating coating. When the apparent porosity is high, a lower pre-curing temperature and a longer pre-curing time can delay the gelation and skinning process on the coating surface, allowing sufficient time for the internal gas to escape smoothly. When the apparent porosity is low, a higher pre-curing temperature and a shorter pre-curing time can accelerate coating gelation and improve production efficiency. Therefore, this dynamic adjustment mechanism can effectively reduce pinholes and bubbles in the coating caused by rapid expansion of internal gas, significantly improving the coating's density and insulation withstand voltage performance.

[0036] Preferably, after the low-temperature pre-curing is completed, the high-temperature complete cross-linking curing is performed. The temperature of the high-temperature complete cross-linking curing is usually higher than the temperature of the low-temperature pre-curing, for example, it can be set to 180-220℃, and the time can be set to 60-120 minutes. In this invention, the high-temperature complete cross-linking curing parameters are uniformly adopted as 180~200℃ and 20~30 minutes to avoid the adverse effects of excessively long high temperatures on the magnetic properties of ferrite. Thus, through high-temperature complete cross-linking curing, the resin molecules in the insulating coating material undergo a full cross-linking reaction, forming a dense and robust three-dimensional network structure, thereby further improving the adhesion between the coating and the manganese-zinc high-conductivity ferrite magnetic ring matrix, and endowing the coating with excellent mechanical strength, environmental aging resistance, and highly reliable electrical insulation properties.

[0037] Preferably, after step 4, an insulation enhancement treatment step is also included: the surface of the coating after high-temperature complete cross-linking and curing is subjected to dry ice blasting micro-sanding or fine sandpaper light surface roughening treatment, followed by chemical activation by wiping with acetone or surfactant, and then a second thin coating and curing.

[0038] The above-mentioned insulation enhancement treatment steps can effectively overcome the problem of decreased interlayer adhesion caused by complete surface cross-linking after the first curing. Specifically, through the synergistic effect of physical roughening and chemical activation, unreacted groups inside the coating can be exposed, thereby ensuring strong chemical cross-linking and mechanical interlocking between the secondary coating formed by the second thin coating and the first coating, significantly improving the interlayer adhesion, density, and voltage resistance reliability of the overall insulation coating.

[0039] Preferably, the dry ice blasting micro-polishing uses dry ice particles as the abrasive, which are accelerated and blasted onto the coating surface by a high-pressure airflow. Optionally, the particle size of the dry ice particles is 0.1mm-3mm, and the blasting pressure is 0.2MPa-0.8MPa. Thus, by utilizing the micro-explosion effect and low-temperature embrittlement effect of dry ice impact, uniform micro-polishing of the surface is achieved without damaging the overall structure of the coating and the magnetic ring substrate, removing surface powder and weak boundary layers.

[0040] Preferably, in the light surface roughening treatment with fine sandpaper, the mesh size of the sandpaper used can be selected as 800-2000 mesh, and more preferably 1000-1500 mesh. This allows for the formation of micro-scratches of suitable depth on the coating surface, increasing the surface area and providing sufficient physical anchors for the mechanical bonding of the subsequent secondary thin coating.

[0041] Preferably, the chemical activation using acetone or surfactant wiping specifically includes: using a lint-free cloth soaked in acetone or surfactant solution to evenly wipe the roughened coating surface, followed by natural evaporation or low-temperature drying. Optionally, the surfactant includes nonionic surfactants or anionic surfactants. This effectively removes residual dust and impurities from the surface, while the slight swelling effect of the solvent further exposes the active groups (such as hydroxyl and epoxy groups) in the polymer chain segments, increasing surface energy and improving the wettability of the secondary coating.

[0042] Preferably, the coating material used in the secondary thin coating is the same as or similar to the insulating coating material used in the third step. The coating thickness of the secondary thin coating is controlled between 5μm and 20μm, and can be selected as 8μm to 15μm. Thus, without significantly increasing the overall size and weight of the magnetic ring, it further fills in any microscopic pinholes or defects that may exist in the first coating, achieving a significant increase in insulation performance.

[0043] Preferably, the insulating coating material used for the electrostatic spraying and the inner wall spraying includes at least one of epoxy resin powder, epoxy polyester powder, or nylon powder. Optionally, the insulating coating material is epoxy resin powder or epoxy polyester powder. Therefore, the above-mentioned insulating coating material has excellent electrical insulation properties, mechanical strength, and chemical corrosion resistance, and can form a dense insulating protective layer on the surface of the magnetic ring, meeting high voltage resistance and environmental protection requirements. Simultaneously, it has good adhesion to the manganese-zinc ferrite matrix, ensuring that the coating is not easily peeled off under complex working conditions.

[0044] In another embodiment of this application, a manganese-zinc high-conductivity ferrite magnetic ring is proposed, which is prepared using the insulating coating process described in any of the above embodiments. The manganese-zinc high-conductivity ferrite magnetic ring includes a magnetic ring substrate and an insulating coating covering the surface of the magnetic ring substrate. Due to the aforementioned zoned spraying and curing processes, the insulating coating achieves uniform coverage on the outer surface, end face, and deep cavity of the magnetic ring substrate, effectively overcoming the Faraday cage effect and completely eliminating pinholes and air gaps in the coating. Therefore, the manganese-zinc high-conductivity ferrite magnetic ring achieves 100% full-surface insulation coverage, significantly improving insulation withstand voltage performance, coating adhesion, and environmental adaptability. It can effectively avoid breakdown short circuits in deep cavity dead corners, meeting the requirements of high-reliability applications.

[0045] Test methods Inner wall dead angle coverage: A high-resolution industrial endoscope is used to penetrate deep into the inner hole of the magnetic ring to observe the coating coverage in the deep cavity and dead angle areas of the inner wall. The percentage of the effective coverage area to the total area of ​​the inner wall is calculated using image analysis software.

[0046] Coating thickness uniformity: Using a high-precision coating thickness gauge, the coating thickness at multiple test points on the outer surface, end face and inner wall of the magnetic ring is measured respectively. The range of thickness at all test points (the difference between the maximum and minimum values) is calculated. The smaller the range, the better the thickness uniformity.

[0047] Pinhole rate: The surface of the cured magnetic ring coating is scanned using a high-voltage electric spark pinhole detector to record the number of pinholes that have been broken down by electric sparks, and the result is converted into the pinhole rate per unit area (pinholes / cm²).

[0048] Breakdown voltage (insulation withstand voltage): Using a withstand voltage tester, a gradually increasing AC voltage is applied between the outer and inner surfaces of the magnetic ring, and the voltage value (kV) at the moment when the coating breaks down is recorded. Each sample is tested 5 times and the average value is taken.

[0049] Example 1 Manganese-zinc high-conductivity ferrite magnetic rings with an inner diameter of 4 mm and an initial apparent porosity of 18% were prepared.

[0050] Step 1: Pretreatment of the substrate; The magnetic ring substrate is purged with compressed air and ultrasonically cleaned, followed by weak acid micro-etching to expand the surface micropores, and finally dried; After drying, it is subjected to low-temperature plasma activation treatment (oxygen + argon, treatment time 45 seconds).

[0051] Step 2: Gradient preheating; The pretreated magnetic ring substrate is heated in a stepped manner to remove moisture and heat through the core.

[0052] Step 3: Sectional spraying; first, electrostatic spraying is performed on the outer surface and end faces of the magnetic ring substrate; then, a miniaturized spraying method is used to extend into the center of the inner hole for inner wall spraying. During the spraying process, anti-collision and centering control are achieved through a limiting and guiding method. The insulating coating material is epoxy resin powder.

[0053] Step 4: Static leveling and curing; Vacuum step curing: After static leveling, evacuate to -0.09MPa, pre-cur at 110℃ for 12 minutes, release the vacuum, heat to 190℃ at normal pressure for 25 minutes, and then cool.

[0054] Example 2 Manganese-zinc high-conductivity ferrite magnetic rings with an inner diameter of 10 mm and an initial apparent porosity of 8% were prepared.

[0055] Step 1: Pretreatment of the substrate; The magnetic ring substrate is purged with compressed air and ultrasonically cleaned (without weak acid etching), and then dried and subjected to low-temperature plasma activation treatment (60 seconds).

[0056] Step 2: Gradient preheating; The pretreated magnetic ring substrate is heated in a stepped manner to remove moisture and heat through the core.

[0057] Step 3: Zoned spraying; First, electrostatic spraying is performed on the outer surface and end face of the magnetic ring substrate; then, the inner wall is sprayed by extending into the center of the inner hole; the insulating coating material is epoxy polyester powder.

[0058] Step 4: Static leveling and stepped curing; Adaptive curing at ambient pressure: The apparent porosity was found to be 8% (less than 10%). After static leveling, pre-curing was performed at ambient pressure according to dynamic parameters (160℃, 15 minutes), and then the temperature was increased to 190℃ for curing for 25 minutes.

[0059] Example 3 Manganese-zinc high-conductivity ferrite magnetic rings with an inner diameter of 15 mm and an initial apparent porosity of 16% were prepared.

[0060] Step 1: Pretreatment of the substrate; The magnetic ring substrate is purged with compressed air and ultrasonically cleaned, followed by weak acid micro-etching to enlarge the surface micropores, and then dried; After drying, it is subjected to low-temperature plasma activation treatment (30 seconds).

[0061] Step 2: Gradient preheating; The pretreated magnetic ring substrate is heated in a stepped manner to remove moisture and heat through the core.

[0062] Step 3: Sectional spraying; first, electrostatic spraying is performed on the outer surface and end faces of the magnetic ring substrate; then, the coating is applied to the inner wall of the inner hole. Nylon powder is used as the insulating coating material.

[0063] Step 4: Static leveling and step curing; Vacuum step curing is used: After static leveling, vacuum is drawn to -0.09MPa, pre-curing is performed at 110℃ for 12 minutes, the vacuum is released, and the temperature is raised to 190℃ at normal pressure for 25 minutes for curing, followed by cooling.

[0064] Comparative Example 1 The difference from Example 1 is that: a traditional single external electrostatic spraying process is used, without extending into the inner hole for inner wall spraying; and porosity testing is not performed during the curing stage, and a uniform 150°C pre-curing for 20 minutes is used, followed by high-temperature complete cross-linking curing.

[0065] Comparative Example 2 The difference from Example 2 is that a vacuum dip coating process (alternative solution) is used instead of partitioned electrostatic spraying, and the pressure difference is used to allow the insulating varnish to penetrate into the deep cavity and inner hole; and porosity testing is not performed during the curing stage, and a uniform pre-curing at 150°C for 20 minutes is used, followed by high-temperature complete cross-linking curing.

[0066] The performance of the manganese-zinc high-conductivity ferrite magnetic rings prepared in Examples 1-3 and Comparative Examples 1-2 were tested according to the above test methods.

[0067] A comparison of Examples 1-3 with Comparative Example 1 shows that: Comparative Example 1 uses traditional single external electrostatic spraying, which results in charge shielding due to the Faraday cage effect, leading to an inner wall dead-angle coverage of only 42.0%, a coating thickness variation as high as 48 μm, and a high risk of breakdown short circuits in the deep cavity of the inner wall, with a breakdown voltage of only 1.2 kV. In contrast, Examples 1-3, through a two-step electrostatic spraying process combining inner and outer sections with deep cavity operations, effectively overcome the Faraday cage effect, achieving an inner wall dead-angle coverage of over 99%, significantly reducing the coating thickness variation to 12-15 μm, and achieving 100% full surface coverage.

[0068] A comparison of Examples 1-3 with Comparative Examples 1 and 2 reveals that: Comparative Examples 1 and 2 did not dynamically adjust the porosity, and uniformly used fixed pre-curing parameters, leading to a rapid expansion of the gas inside the magnetic ring. The pinhole rates of Comparative Examples 1 and 2 were as high as 15 pinholes / cm² and 6 pinholes / cm², respectively, severely weakening the insulation withstand voltage performance. In contrast, Examples 1 and 3 used a vacuum step-curing method, fundamentally avoiding pinholes caused by gas expansion; Example 2 used atmospheric pressure adaptive curing, dynamically adjusting the pre-curing parameters according to the apparent porosity (8% apparent porosity corresponds to 160℃ / 15 minutes), ensuring that the exhaust rate matched the coating gelation rate, resulting in a pinhole rate of 0 and a breakdown voltage of over 5.8kV.

[0069] Furthermore, Example 1, targeting small magnetic rings with an inner diameter of less than 5 mm, employs a miniaturized spraying method combined with a limiting and guiding mechanism. This not only achieves precise spraying inside the deep cavity but also avoids scratching the inner wall with the spraying tool, further ensuring the uniformity and integrity of the inner wall coating. In summary, the insulating coating process provided by this invention significantly improves the insulation withstand voltage performance, coating adhesion, and environmental adaptability of the magnetic ring, meeting the requirements of high-reliability application scenarios.

Claims

1. A method for insulating coating the surface of a manganese-zinc high-conductivity ferrite magnetic ring, characterized in that, Includes the following steps: Step 1: The manganese-zinc high-conductivity ferrite magnetic ring substrate is purged with compressed air, ultrasonically cleaned and dried to expose the surface micropores. Step 2: The pretreated manganese-zinc high-conductivity ferrite magnetic ring matrix is ​​subjected to step heating to remove moisture and heat through the core. Step 3: First, electrostatic spraying is performed on the outer surface and end face of the manganese-zinc high-conductivity ferrite magnetic ring substrate, and then the inner wall is sprayed by inserting into the center of the inner hole of the manganese-zinc high-conductivity ferrite magnetic ring substrate. Step 4: After spraying, the manganese-zinc high-conductivity ferrite magnetic ring matrix is ​​allowed to stand and level, and then low-temperature pre-curing and high-temperature complete cross-linking curing are performed in sequence. The low-temperature pre-curing process employs vacuum step curing. After static leveling, a vacuum is applied to -0.08 to -0.095 MPa, and pre-curing is performed at 100 to 120°C for 10 to 15 minutes, followed by vacuum release. Alternatively, ambient pressure adaptive curing is used. Under ambient pressure, the apparent porosity of the manganese-zinc high-conductivity ferrite magnetic ring matrix is ​​first measured. If the apparent porosity is greater than 15%, the low-temperature pre-curing temperature is set to 130-140°C and the time to 30-40 minutes. If the apparent porosity is between 10% and 15%, the low-temperature pre-curing temperature is set to 140-160°C and the time to 15-30 minutes. If the apparent porosity is less than 10%, the low-temperature pre-curing temperature is set to 160°C and the time to 15 minutes.

2. The insulating coating process for the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to claim 1, characterized in that, In step 1, after ultrasonic cleaning and before drying, a weak acid micro-etching step or an atmospheric pressure air plasma treatment step is also included.

3. The insulating coating process for the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to claim 1, characterized in that, In step 3, an electrostatic spraying method with closed-loop feedback control is adopted, which monitors the tip current in real time and automatically adjusts the voltage. At the same time, the sweeping speed is increased by 20-30%, and atomized air is introduced to assist in adjusting the atomized air pressure.

4. The insulating coating process for the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to claim 1, characterized in that, In step 3, for the manganese-zinc high-conductivity ferrite magnetic ring substrate with an inner diameter of less than 5 mm, a miniaturized spraying method is used for spraying; during the spraying process, anti-collision and centering control are achieved through a limiting and guiding method.

5. The insulating coating process for the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to claim 1, characterized in that, Following step 4, an insulation enhancement treatment step is also included: dry ice blasting micro-polishing or fine sandpaper light surface roughening treatment is performed on the surface of the coating after high-temperature complete cross-linking and curing. The dry ice blasting micro-polishing uses dry ice particles with a particle size of 0.1mm-3mm and a blasting pressure of 0.2MPa-0.8MPa. The fine sandpaper used for the light surface roughening treatment has a mesh size of 800-2000. Subsequently, chemical activation is performed by wiping with acetone or surfactant, followed by a second thin coating and curing.

6. The insulating coating process for the surface of the manganese-zinc high-conductivity ferrite magnetic ring according to claim 1, characterized in that, The insulating coating material used for the electrostatic spraying and the inner wall spraying includes at least one of epoxy resin powder, epoxy polyester powder, or nylon powder.

7. A manganese-zinc high-conductivity ferrite magnetic ring, characterized in that, It is prepared by the insulating coating process on the surface of the manganese-zinc high-conductivity ferrite magnetic ring as described in any one of claims 1-6.

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