Vehicle-mounted cold-pressing integrally-formed inductor and preparation method thereof

Abstract

This invention discloses a cold-pressed integral molded inductor for automotive applications and its preparation method, relating to the field of automotive inductor technology. The method includes the following steps: mixing and stirring metal alloy powder and modified phosphating solution; after phosphating and drying, a passivation powder is obtained; the passivation powder and coating solution are stirred in a solvent to form a slurry; the slurry is spray-granulated; and the granulated powder is cold-pressed to form an integral molded inductor. This invention, focusing on the uniform coating of the granulated powder, uses spray drying granulation instead of the traditional stirring-coating-extrusion granulation method. This not only shortens the process flow but also yields uniformly coated powder, and the particle size distribution of the granulated powder is controllable, significantly improving its flowability.

Description

Technical Field

[0001] This invention relates to the field of automotive inductor technology, and in particular to an automotive cold-pressed integral molded inductor and its preparation method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Molded inductors are made by embedding metal alloy powder into a coil and pressing it. The powder used in the industry for molded inductors generally involves processes such as passivation of iron-based raw powder, resin coating, granulation and drying, and mixing in a release agent to obtain granulated powder for molding. One problem hindering the production of molded inductors is the inability to eliminate internal cracks, such as… Figure 1 As shown in the diagram, extensive experiments revealed that internal cracks in integrated inductors often occur during the baking and curing stage. This is because the difference in thermal expansion coefficients between the copper wire and the magnetic powder core leads to internal cracking. Complete resin curing requires time for cross-linking, so the bonding force between the granulated powder particles at this stage is insufficient to resist the thermal expansion force of the copper wire. Furthermore, the density of the central column in the integrated inductor is lower than that of the edge magnets, making this area weaker and prone to cracking. Cracks not only affect the inductor's magnetic properties but also reduce its reliability. Therefore, addressing internal cracking in integrated inductors is crucial. Changing the molding process, such as using prefabricated T-cores or E-cores, increases the magnetic powder core density at the central column location, reducing the risk of cracking. However, this process has low production efficiency and requires hot pressing, significantly increasing production costs.

[0004] In summary, how to solve the problem of internal cracks in integrally molded inductors at a low cost has become an urgent problem to be solved by existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an inductor for vehicle-mounted cold-pressed integral molding and its preparation method. From the perspective of uniform granulation powder coating, the invention adopts spray drying granulation to replace the traditional stirring coating-extrusion granulation method. This not only shortens the process flow but also obtains uniformly coated powder, and the particle size distribution of the granulated powder is controllable, greatly improving its flowability.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] The first aspect of this invention provides a method for fabricating a vehicle-mounted cold-pressed integrally molded inductor, comprising the following steps:

[0008] Metal alloy powder and modified phosphating solution are mixed and stirred, and after phosphating and drying, passivation powder is obtained.

[0009] The passivation powder and coating liquid are stirred in a solvent to form a slurry, and the slurry is then spray-granulated.

[0010] The granulated powder is cold-pressed into a molded inductor.

[0011] Furthermore, the modified phosphating solution is prepared by mixing phosphoric acid, zirconium dihydrogen phosphate, zirconium nitrate, and anhydrous ethanol.

[0012] Furthermore, the mass percentage content of zirconium nitrate and phosphoric acid is 0.1%–0.5% and 0.5%–1.0%, respectively.

[0013] Furthermore, during the phosphating process, the phosphating temperature is 25℃~60℃, the time is 1 hour, and the drying temperature is 80℃~120℃.

[0014] Furthermore, the coating liquid includes bisphenol-modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, and silane coupling agent.

[0015] Furthermore, the mass percentages of modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, and silane coupling agent are 0.1%–0.5%, 1%–2%, 1%–2%, and 0.1%–0.2%, respectively.

[0016] Furthermore, an explosion-proof closed-loop centrifugal spray granulation system is used for the spray granulation process. The explosion-proof closed-loop centrifugal spray granulation system operates in a closed environment, using inert gas N2 as the drying medium and circulation carrier. The drying tower is under positive pressure and maintains predetermined inlet air temperature, outlet air temperature, and rotation speed.

[0017] Furthermore, the conditions for spray granulation are: inlet air temperature 120℃~150℃, outlet air temperature 80℃~95℃, rotation speed 4000rpm~7000rpm, and drying tower pressure 0.1MPa~0.2MPa.

[0018] Furthermore, during the cold pressing process, the pressing pressure is 500MPa to 800MPa.

[0019] The second aspect of the present invention provides an automotive cold-pressed integral molded inductor, which is manufactured using the preparation method of the automotive cold-pressed integral molded inductor described in the first aspect.

[0020] The above one or more technical solutions have the following beneficial effects:

[0021] This invention discloses a vehicle-mounted cold-pressed integral molding inductor and its preparation method, using soft magnetic alloy powder containing Zr. 4+Phosphating solutions are used to phosphate the surface of metal magnetic powder, increasing interparticle resistance and reducing eddy current losses by generating an inorganic phosphate layer. To overcome the poor high-temperature resistance of passivation layers formed by single-phosphoric acid, this invention designs a modified phosphate solution with high-temperature resistance for passivating alloy powder. This modified phosphate solution contains zirconium dihydrogen phosphate, zirconium nitrate, or a mixture thereof. The weakly acidic solution containing nitrates enhances its oxidation capacity, which is beneficial for powder surface passivation. 4+ Salt layer can improve the high-temperature stability of passivation layer.

[0022] This invention forms a high-temperature resistant and stable passivation layer on the surface of alloy powder particles through a passivation step, which can increase the resistance of the powder and reduce powder loss.

[0023] This invention employs a secondary resin coating method that differs from traditional stirring methods, utilizing explosion-proof spray drying granulation equipment for resin coating. The secondary resin coating solution is formulated with bisphenol-modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, silane coupling agent, and anhydrous ethanol. This invention addresses the coating uniformity issue in cold-pressed integrally molded inductors through atomized drying granulation. It helps resolve internal cracks in cold-pressed integrally molded inductors. Using epoxy resin and low-viscosity modified silicone resin (<300 Pa*s) to coat the inductor powder improves coating uniformity and enhances the flowability of the granulated powder. This effectively prevents internal cracks in the inductor during molding.

[0024] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 A schematic diagram illustrating the causes of crack formation;

[0027] Figure 2 A schematic diagram comparing the coating effects of stirred granulated powder and atomized granulated powder;

[0028] Figure 3 This is a schematic diagram of the explosion-proof closed-loop centrifugal spray granulation system according to Embodiment 1 of the present invention;

[0029] Figure 4 This is a comparative diagram of the 7.0*7.0*3.0mm model of Embodiment 1 of the present invention and a comparative diagram of the internal cross-section of the embodiment;

[0030] Figure 5This is a comparative example of the 13*13*6.5mm model of Embodiment 1 of the present invention and a schematic diagram comparing the internal cross-sections of the embodiment. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Example 1:

[0034] Due to the high temperatures and limited space in the automotive environment, higher demands are placed on the durability and size of automotive inductors. Currently, the existing powder formulation process using mixing, coating, and extrusion granulation has the following shortcomings, considering the unique characteristics of the automotive environment:

[0035] The mixing and coating method for powder preparation involves immersing the raw powder in a resin-organic solvent mixture and stirring to create a slurry. After the organic solvent dries, the resin forms a coating layer on the powder surface. However, this method often results in unsatisfactory effects and uneven coating. Figure 2 The granulated powder is shown in the figure. Furthermore, the insulating layer coating on the surface of the ferromagnetic powder particles is not uniform; the lower the resistivity of the powder, the higher the inductor eddy current loss.

[0036] Furthermore, the viscosity of epoxy resin used for cold-pressed integrated inductor powder coating is in the thousands or even tens of thousands of Pa*s, which is not conducive to the uniform coating of ferromagnetic powder. In addition, epoxy resin has poor high-temperature resistance and cannot meet the 150℃+ temperature resistance requirements of automotive applications.

[0037] To address the aforementioned deficiencies in the prior art, this embodiment provides a method for preparing an automotive-grade cold-pressed integrally molded inductor. By performing a passivation step, a high-temperature resistant and stable passivation layer is formed on the surface of the alloy powder particles, which can improve the resistance of the powder and reduce powder loss.

[0038] Furthermore, atomized drying granulation is used to address the coating uniformity in cold-pressed integrally molded inductors. This helps resolve internal cracks in cold-pressed integrally molded inductors. A secondary coating of the inductor powder with epoxy resin and low-viscosity modified silicone resin (<300 Pa*s) improves coating uniformity and enhances the flowability of the granulated powder. This effectively prevents internal cracks in the inductor during compression molding.

[0039] Specifically, the following steps are included:

[0040] Step 1: One-time coating: Mix and stir the metal alloy powder and the modified phosphating solution, and after phosphating and drying, passivation powder is obtained.

[0041] Preferably, the modified phosphating solution with high temperature resistance is prepared by mixing phosphoric acid, zirconium dihydrogen phosphate, zirconium nitrate and anhydrous ethanol.

[0042] Phosphoric acid provides hydrogen ions, and nitrate provides nitrate ions. Because nitric acid has stronger oxidizing properties, it makes it easier for an oxide layer to form on the surface of iron-based powder. The deposited zirconium salt helps to improve the high-temperature stability of the oxide layer and increase its electrical resistance.

[0043] More preferably, the mass percentages of zirconium nitrate and phosphoric acid are 0.1%–0.5% and 0.5%–1.0%, respectively.

[0044] More preferably, the zirconium dihydrogen phosphate content is 0.1% to 0.5%, and ethanol as a solvent accounts for 8% to 12% of the powder mass fraction.

[0045] Preferably, during the phosphating process, the phosphating temperature is 25℃~60℃, the time is 1 hour, and the drying temperature is 80℃~120℃.

[0046] In one specific embodiment, iron-based, nickel-based, or cobalt-based alloy powders are selected as the base material, with a particle size controlled within the range of 1-100 micrometers. These alloy powders possess good mechanical properties and conductivity, making them suitable for inductor manufacturing. The prepared metal alloy powders are mixed with the modified phosphating solution at a weight ratio of 1:1 to 1:5. Stirring is performed using a mechanical stirrer or ultrasonic stirrer to ensure sufficient contact between the alloy powders and the phosphating solution, forming a homogeneous mixture. The temperature of the mixture is controlled between 25-60°C. This temperature range is beneficial for the phosphating reaction while avoiding excessively high temperatures that could lead to an overly rapid reaction and affect the formation of the passivation film. The mixture is maintained at the above temperature for 1 hour. This time is sufficient for the passivation film to form uniformly on the surface of the alloy powder, while avoiding an excessively long reaction time that could result in an excessively thick or uneven passivation film. After the passivation reaction is complete, the mixture is dried. The drying temperature is controlled between 80-120°C to ensure that moisture and solvents in the passivation film are effectively removed, while avoiding excessively high temperatures that could damage the passivation film. Finally, the passivation powder was tested for its performance through corrosion resistance and high temperature resistance tests.

[0047] Step 2: Secondary coating: The passivation powder and coating solution are stirred in a solvent to form a slurry, which is then spray-granulated. The solid content of the slurry is 72wt% to 78wt%.

[0048] Preferably, the coating liquid comprises bisphenol-modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, and a silane coupling agent. The bisphenol-modified epoxy resin achieves modification by increasing oxygen-containing functional groups and improving the chain length of the silicone, thereby reducing resin viscosity and avoiding agglomeration effects. The epoxy equivalent of the epoxy resin in the bisphenol-modified epoxy resin is 188 eq / 100g to 195 g / eq / 100g, and the epoxy value of the epoxy-modified silicone resin is 0.05 eq / 100g to 0.13 eq / 100g.

[0049] More preferably, the mass percentages of the modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, and silane coupling agent are 0.1%–0.5%, 1%–2%, 1%–2%, and 0.1%–0.2%, respectively.

[0050] The coupling agent activates the powder surface and facilitates better bonding with the resin. Epoxy resin provides the main adhesive strength during cold pressing, preventing cracking. Silicone resin, after curing, offers better bonding strength, and modified silicone exhibits better temperature resistance. The combined effect of these two components enhances the crack resistance of the cold-pressed inductor, particularly against internal cracks.

[0051] Preferably, an explosion-proof closed-loop centrifugal spray granulation system is used for the spray granulation process. The explosion-proof closed-loop centrifugal spray granulation system operates in a closed environment, using inert gas N2 as the drying medium and circulation carrier. The drying tower is under positive pressure and maintains predetermined inlet air temperature, outlet air temperature and rotation speed.

[0052] More preferably, such as Figure 3 As shown, the explosion-proof closed-loop centrifugal spray granulation system includes a mixing chamber, a conveying pipeline, a spray granulation drying tower, and a granulated powder collection device. The slurry is stirred in the mixing chamber, and the stirred slurry enters the spray granulation drying tower through the conveying pipeline (which contains a pipeline pump). The spray granulation drying tower includes a rotary atomizer at the top and an upper chamber and a lower chamber separated by a partition plate. The upper chamber, located in the upper half of the spray granulation drying tower, is cylindrical, and the lower chamber, located in the lower half, is inverted conical. The bottom of the conical chamber is connected to the bottom of the upper chamber by the partition plate, and the granulated powder collection device is installed at the top of the conical chamber to collect the granulated powder. A partition layer filled with cooling water surrounds the upper and lower chambers. A hot air outlet is provided on the partition plate to blow hot air into the upper chamber.

[0053] In this embodiment, the slurry refers to a mixture of powder, resin, and solvent. The role of hot air here is to rapidly evaporate and carry away the solvent, leaving the resin on the surface of the powder to form uniformly sized granulated powder. Cooling water is supplied to the walls of the spray tower, which rapidly cools the granulated powder after it splashes onto the pipe wall, preventing the granulated powder from thermally solidifying. The slurry is centrifugally rotated and blown apart by high-speed hot air, forming droplets. The solvent in the droplets evaporates rapidly and splashes onto the pipe wall, where it cools and reaches the discharge port under gravity.

[0054] Preferably, the conditions for spray granulation are: inlet air temperature 120℃~150℃, outlet air temperature 80℃~95℃, rotation speed 4000rpm~7000rpm, and drying tower pressure 0.1MPa~0.2MPa.

[0055] In one specific embodiment, the coating solution is prepared by selecting a bisphenol-modified epoxy resin with an epoxy equivalent of 188-195 g / eq / 100 g. This resin provides good adhesion and mechanical strength. An epoxy-modified silicone resin with an epoxy value of 0.05-0.13 eq / 100 g is selected. This resin helps improve the high-temperature resistance of the final product. 1%-2% of methylphenyl silicone resin is added to further enhance the high-temperature resistance and surface properties of the particles. 0.1%-0.2% of a silane coupling agent is added to improve the bond strength between the resin and the metal alloy powder.

[0056] The passivated metal alloy powder is mixed with the above-mentioned resin in a solvent. The mixture is stirred using a high-speed mixer or a three-roll mill until a homogeneous slurry is formed. The solid content of the slurry is adjusted to 72-78 wt%. Controlling the solid content is crucial for subsequent spray granulation and compression molding, as it affects the particle flowability and molding density. An appropriate solvent, such as acetone, toluene, or dimethylformamide, is selected to ensure that the resin is fully dissolved and uniformly coats the powder.

[0057] An explosion-proof, closed-loop centrifugal spray granulation system is used. This system operates in a sealed environment, using an inert gas (such as nitrogen N2) as the drying medium and circulation carrier. Positive pressure is maintained inside the drying tower to prevent external air ingress, ensuring safety and product quality during the granulation process. The inlet air temperature is set between 120°C and 150°C to provide sufficient heat for rapid solvent evaporation. The outlet air temperature is controlled between 80°C and 95°C to ensure the granules are fully dried before leaving the granulation system. The centrifugal spray system speed is set between 4000 rpm and 7000 rpm to ensure the slurry is uniformly dispersed into fine droplets. The pressure in the drying tower is controlled between 0.1 MPa and 0.2 MPa to ensure adequate hot air flow and solvent evaporation during the granulation process.

[0058] The particle size distribution, morphology and surface properties of the granulated powder were then evaluated using methods such as sieving analysis, flowability test and microscopic observation.

[0059] Step 3: The granulated powder is cold-pressed into shape to obtain a one-piece molded inductor.

[0060] Preferably, the pressing pressure during cold pressing is 500MPa to 800MPa. Hot pressing requires holding pressure for 180 seconds, which is inefficient. Therefore, this embodiment uses the more efficient cold pressing, but cold pressing results in poor density and slightly lower electromagnetic properties. To overcome these shortcomings, the coating method in steps 1 and 2 is used to enhance the electromagnetic properties, enabling them to meet the requirements of the automotive environment.

[0061] To further illustrate the superiority of the method in this embodiment, Comparative Example 1 and Comparative Example 2 were constructed, and the method in this embodiment was used to conduct experiments in Example 1 and Example 2. The experimental parameters are shown in Table 1.

[0062] Table 1. Comparison of Experimental Parameters

[0063] project model Covering method Internal cross-section Temperature rise current / A Insulation withstand voltage / V Comparative Example 1 0730-220M Mixing, extrusion, and granulation cracking 2.1 80 Comparative Example 2 1264-3R3M Mixing, extrusion, and granulation cracking 21.4 81 Example 1 0730-220M Spray granulation No cracks 2.5 114 Example 2 1264-3R3M Spray granulation No cracks 25.3 112

[0064] like Figure 4 and Figure 5 As shown, Figure 4 and Figure 5The left side shows the experimental results of the comparative examples, and the right side shows the experimental results of the specific examples. It can be seen that the inductors were molded using inductors with a higher coil height (0730-220M) and a thicker coil (1264-3R3M). The granulated powder was obtained through both stirring-extrusion granulation and spray granulation methods to form the cold-pressed inductors. The passivation and coating adhesive ratios used in the powder formulation were the same. It can be seen that the integrally molded inductor obtained by spray granulation has no internal cracks, higher insulation withstand voltage, and lower loss.

[0065] Example 2:

[0066] Embodiment 2 of the present invention provides an automotive cold-pressed integral molded inductor, which is manufactured using the preparation method of the automotive cold-pressed integral molded inductor described in Embodiment 1.

[0067] The steps and methods involved in the above embodiment two correspond to those in embodiment one. For specific implementation details, please refer to the relevant description section of embodiment one.

[0068] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for fabricating a vehicle-mounted cold-pressed integrally molded inductor, characterized in that, Includes the following steps: Metal alloy powder and modified phosphating solution are mixed and stirred, and after phosphating and drying, passivation powder is obtained; the modified phosphating solution is prepared by mixing phosphoric acid, zirconium dihydrogen phosphate, zirconium nitrate and anhydrous ethanol; during the phosphating process, the phosphating temperature is 25℃~60℃, the time is 1h, and the drying temperature is 80℃~120℃. Passivation powder and coating liquid are stirred in a solvent to form a slurry, which is then spray-granulated. The coating liquid includes bisphenol-modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, and silane coupling agent. An explosion-proof closed-loop centrifugal spray granulation system is used for the spray granulation process. This system operates in a sealed environment, using inert gas N2 as the drying medium and circulation carrier. The drying tower is under positive pressure, and predetermined inlet air temperature, outlet air temperature, and rotation speed are maintained. The spray granulation conditions are: inlet air temperature 120℃~150℃, outlet air temperature 80℃~95℃, rotation speed 4000rpm~7000rpm, and drying tower pressure 0.1MPa~0.2MPa. The granulated powder is cold-pressed to form an integral inductor; during the cold-pressing process, the pressing pressure is 500MPa to 800MPa.

2. An automotive-grade cold-pressed integral molded inductor, manufactured using the preparation method of the automotive-grade cold-pressed integral molded inductor as described in claim 1.

Images