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

Abstract

The invention discloses a vehicle-mounted cold-pressed integrally-formed inductor and a preparation method thereof, and relates to the technical field of vehicle-mounted inductors. The method comprises the steps that metal alloy powder and a modified phosphating solution are mixed and stirred, and passivated powder is obtained after phosphating and drying; stirring the passivation powder and the coating liquid in a solvent to form slurry, and performing spray granulation on the slurry; and carrying out cold pressing molding on the granulation powder to obtain the integrally molded inductor. From the perspective of uniform coating of the granulation powder, a spray drying granulation mode is adopted to replace a traditional stirring coating-extruding granulation mode, the technological process is shortened, the uniformly coated powder can be obtained, the particle size distribution of the granulation powder is controllable, and the fluidity is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle-mounted inductors, and in particular to a vehicle-mounted cold-pressed integrated inductor and a preparation method thereof. Background Art

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

[0003] One-piece molded inductors are made by embedding metal alloy powder into coils and pressing them. The powder used in one-piece molded inductors in the industry is generally made by iron-based raw powder passivation-resin coating-granulation drying-mixing release agent and other processes to obtain granulated powder for molding. One of the problems that plagues one-piece molded inductors is that it is impossible to eliminate the internal cracks of the one-piece inductor, such as Figure 1 As shown. Through a large number of experiments, it is found that the internal cracks of the one-piece inductor often occur in the inductor baking and curing stage. The internal cracks are caused by the inconsistency between the thermal expansion coefficient of the copper wire and the thermal expansion coefficient of the magnetic powder core. It takes a certain amount of time for the resin to completely cure to produce a cross-linking reaction. Therefore, the bonding force between the granulated powders at this time is not enough to resist the thermal expansion force of the copper wire. The density of the middle column of the one-piece molded inductor is low relative to the edge magnets. It is relatively weak here and cracks are easy to occur here. On the one hand, cracks will affect the magnetic properties of the inductor and cause its reliability to deteriorate. Therefore, solving the internal cracks of the one-piece molded inductor is a key link. By changing the molding process and using prefabricated Tcore or E-core, the density of the magnetic powder core at the middle column position is increased, reducing the risk of cracks. However, the production efficiency of this process is low and hot pressing is required, which greatly increases the production cost.

[0004] In summary, how to achieve a low-cost solution to the internal crack problem of the one-piece molded inductor has become an urgent problem to be solved in the existing technology. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a vehicle-mounted cold-pressed one-piece molded inductor and a preparation method thereof. From the perspective of uniform coating of granulated powder, a spray drying granulation method is adopted to replace the traditional stirring coating-extrusion granulation method, which not only shortens the process flow but also obtains uniformly coated powder, and the particle size distribution of the granulated powder is controllable, and the fluidity is greatly improved.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A first aspect of the present invention provides a method for preparing a vehicle-mounted cold-pressed integrated inductor, comprising the following steps:

[0008] The metal alloy powder and the modified phosphating solution are mixed and stirred, and after phosphating and drying, a passivation powder is obtained;

[0009] The passivation powder and the coating liquid are stirred in a solvent to form a slurry, and the slurry is sprayed and granulated;

[0010] The granulated powder is cold pressed and molded to obtain an integrally 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 of the zirconium nitrate and the mass percentage of the phosphoric acid are 0.1% to 0.5% and 0.5% to 1.0% respectively.

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

[0014] Furthermore, the coating liquid includes bisphenol modified epoxy resin, epoxy modified silicone resin, methyl phenyl 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% to 0.5%, 1% to 2%, 1% to 2% and 0.1% to 0.2% respectively.

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

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

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

[0019] A second aspect of the present invention provides a vehicle-mounted cold-pressed one-piece molded inductor, which is manufactured using the method for preparing the vehicle-mounted cold-pressed one-piece molded inductor described in the first aspect.

[0020] One or more of the above technical solutions have the following beneficial effects:

[0021] The invention discloses a vehicle-mounted cold-pressed integrated inductor and a preparation method thereof. The soft magnetic alloy raw powder is Zr-containing 4+The phosphating liquid performs phosphating treatment on the surface of the metal magnetic powder, and increases the resistance between the particles and reduces the eddy current loss by generating an inorganic phosphate layer. In order to overcome the problem that the passivation layer formed by single phosphoric acid has poor high temperature resistance, the present invention designs a modified phosphoric acid liquid with high temperature resistance for passivating the alloy raw powder. The modified phosphoric acid liquid contains zirconium dihydrogen phosphate, zirconium nitrate or a mixture thereof. The weakly acidic solution contains nitrates, which can enhance its oxidation ability and is beneficial to the passivation of the powder surface. Zr 4+ The salt layer can improve the high temperature stability of the passivation layer.

[0022] The invention forms a high-temperature resistant stable passivation layer on the surface of alloy powder particles through the passivation step, thereby increasing the resistance of the powder and reducing the loss of the powder.

[0023] The secondary resin coating method of the present invention is different from the traditional stirring method, and uses explosion-proof spray drying granulation equipment for resin coating. The secondary resin coating liquid is prepared with bisphenol-type modified epoxy resin, epoxy-modified silicone resin, methylphenyl silicone resin, silane coupling agent, and anhydrous ethanol. The present invention solves the coating uniformity of the one-piece inductor cold pressing through atomization drying granulation. It is helpful to solve the internal cracks of the cold-pressed one-piece inductor. The inductor powder is coated with epoxy resin and low-viscosity modified silicone resin (<300pa*s), which can improve the uniformity of the coating and improve the fluidity of the granulated powder. The internal cracks of the inductor can be effectively solved during compression molding.

[0024] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 Schematic diagram of the causes of cracks;

[0027] Figure 2 This is a schematic diagram comparing the coating effects of stirred granulation powder and atomized granulation powder;

[0028] Figure 3 This is a schematic structural diagram of an explosion-proof closed-cycle centrifugal spray granulation system according to an embodiment of the present invention;

[0029] Figure 4 It is a schematic diagram of the internal cross-section comparison between the 7.0*7.0*3.0 mm model comparative example and the embodiment of the present invention;

[0030] Figure 5It is a schematic diagram comparing the internal cross-sections of a 13*13*6.5 mm model comparison example and an embodiment of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or their combinations;

[0033] Embodiment 1:

[0034] Since the temperature of the vehicle environment is high during operation and the available space is limited, higher requirements are placed on the durability and volume of vehicle-mounted inductors. At present, in view of the particularity of the vehicle environment, the mixing coating-extrusion granulation process powder preparation in the industry has the following shortcomings:

[0035] The method of mixing and coating powder making is to soak the original powder in resin-organic solvent, mix the slurry by stirring, and after the organic solvent dries, the resin forms a resin coating layer on the surface of the powder. The effect is often not ideal and the coating is uneven. Figure 2 The ferromagnetic powder is stirred and granulated as shown in the figure. In addition, the insulating layer coating uniformity of the ferromagnetic powder particle surface is poor, and the lower the resistivity of the powder, the higher the inductor eddy current loss.

[0036] In addition, the viscosity of epoxy resin used for cold-pressed integrated inductor powder coating is several thousand 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 is difficult to meet the 150℃+ temperature resistance requirements for vehicles.

[0037] In view of the above-mentioned defects of the prior art, the present embodiment provides a method for preparing a vehicle-mounted cold-pressed one-piece molded inductor, which performs a passivation step to form a high-temperature resistant stable passivation layer on the surface of the alloy powder particles, thereby increasing the resistance of the powder and reducing the loss of the powder.

[0038] The uniformity of coating for cold-pressed one-piece inductors is also solved by atomization drying and granulation. This is conducive to solving the internal cracks of cold-pressed one-piece inductors. The use of epoxy resin and low-viscosity modified silicone resin (<300pa*s) for secondary coating of inductor powder can improve the uniformity of coating and the fluidity of granulated powder. It can effectively solve the internal cracks of inductors during compression molding.

[0039] The specific steps include:

[0040] Step 1: Primary coating: The metal alloy powder and the modified phosphating solution are mixed and stirred, and after phosphating and drying, the 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 is used to provide hydrogen ions and nitrates are used to provide nitrate ions. Since nitric acid has stronger oxidizing properties, it is easier for an oxide layer to form on the surface of the iron-based powder. The deposited zirconium salt helps to improve the high-temperature stability of the oxide layer and increase resistance.

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

[0044] More preferably, the content of zirconium dihydrogen phosphate 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°C to 60°C, the time is 1 hour, and the drying temperature is 80°C to 120°C.

[0046] In a specific embodiment, iron-based, nickel-based or cobalt-based alloy powder is selected as the base material, and the particle size is controlled within the range of 1-100 microns. These alloy powders have good mechanical properties and electrical conductivity and are suitable for the manufacture of inductors. The prepared metal alloy powder is mixed with the modified phosphating solution in a weight ratio of 1:1 to 1:5. A mechanical stirrer or an ultrasonic stirrer is used for stirring to ensure that the alloy powder is in full contact with the phosphating solution to form a uniform mixed solution. The temperature of the mixed solution is controlled between 25-60°C. This temperature range is conducive to the phosphating reaction, while avoiding too high a temperature causing too fast a reaction and affecting the formation of a passivation film. Keep the mixed solution reacting at the above temperature for 1 hour. This time length is sufficient to allow the passivation film to be uniformly formed on the surface of the alloy powder, while avoiding too long a reaction causing the passivation film to be too thick or uneven. After the passivation reaction is completed, the mixture is dried. The drying temperature is controlled at 80-120°C to ensure that the moisture and solvent in the passivation film are effectively removed, while avoiding too high a temperature causing the passivation film to be destroyed. Finally, the performance of the passivation powder was tested through corrosion resistance test and high temperature resistance test.

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

[0048] Preferably, the coating liquid includes bisphenol modified epoxy resin, epoxy modified silicone resin, methyl phenyl silicone resin and silane coupling agent. Among them, the bisphenol modified epoxy resin is modified by increasing oxygen-containing functional groups and improving the chain length of silicone, which can reduce the viscosity of the resin and avoid agglomeration effect. The epoxy equivalent of the epoxy resin in the bisphenol modified epoxy resin is 188eq / 100g to 195g / eq / 100g, and the epoxy value in the epoxy modified silicone resin is 0.05eq / 100g to 0.13eq / 100g.

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

[0050] Among them, the coupling agent plays a role in activating the powder surface and can also better transition and connect with the resin. Epoxy resin provides the main strength of the magnet bonding during the cold pressing process to avoid cracking during pressing. The silicone resin has better bonding strength after curing, and the modified silicone has better temperature resistance. The combined effect of the two can increase the crack resistance effect of the cold pressed inductor, especially the internal cracks, which have a very good crack resistance effect.

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

[0052] More preferably, Figure 3 As shown, the explosion-proof closed-cycle centrifugal spray granulation system includes a stirring chamber, a conveying pipeline, a spray granulation drying tower and a granulation powder collecting device. The slurry is stirred by the stirring chamber, and the stirred slurry enters the spray granulation drying tower through the conveying pipeline (a pipeline pump is provided in the pipeline). 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 is located in the upper half of the spray granulation drying tower and is cylindrical. The lower chamber is located in the lower half of the spray granulation drying tower and is in an inverted cone shape. The bottom of the cone is connected to the bottom of the upper chamber through a partition plate. A granulation powder collecting device is provided at the top of the cone for collecting the obtained granulation powder. A partition is provided around the upper chamber and the lower chamber, and cooling water is provided in the partition. A hot air outlet is provided on the partition plate for blowing hot air to the upper chamber.

[0053] In this embodiment, the slurry refers to a mixture of powder, resin, and solvent. The role of the hot air here is to volatilize the solvent quickly and take away the solvent, and the resin remains on the surface of the powder to form granulated powder with uniform particle size. The cooling water is filled in the spray tower wall. When the granulated powder splashes onto the tube wall, it is quickly cooled down to avoid thermal solidification of the granulated powder. The slurry is centrifugally rotated and blown away by high-speed hot air to form droplets. The droplet solvent evaporates quickly and splashes onto the tube wall to cool and reach the discharge port under the action of gravity.

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

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

[0056] Mix the passivated metal alloy powder with the above resin in a solvent. Use a high-speed stirrer or a three-roller mill to stir until a uniform slurry is formed. Adjust the solid content of the slurry to 72-78wt%. The control of solid content is crucial for subsequent spray granulation and compression molding, which affects the fluidity and molding density of the particles. Choose an appropriate solvent, such as acetone, toluene or dimethylformamide, to ensure that the resin can fully dissolve and evenly wrap the powder.

[0057] Use an explosion-proof closed-loop centrifugal spray granulation system. The system can work in a closed environment, using inert gas (such as nitrogen N2) as the drying medium and circulating carrier. Maintain a positive pressure in the drying tower to prevent outside air from entering, ensuring the safety of the granulation process and product quality. Set the inlet air temperature between 120℃ and 150℃ to provide enough heat to evaporate the solvent quickly. Control the outlet air temperature between 80℃ and 95℃ to ensure that the particles are fully dried when they leave the granulation system. Set the speed of the centrifugal spray system between 4000rpm and 7000rpm to ensure that the slurry is evenly dispersed into fine droplets. The pressure of the drying tower is controlled at 0.1MPa to 0.2MPa to ensure the flow of hot air and evaporation of the solvent during the granulation process.

[0058] The prepared granulated powder was then subjected to sieving analysis, flowability test and microscopic observation to evaluate the particle size distribution, morphology and surface characteristics of the granulated powder.

[0059] Step 3: Cold-press the granulated powder to obtain an integrated inductor.

[0060] Preferably, during the cold pressing process, the pressing pressure is 500MPa to 800MPa. Since hot pressing requires holding pressure for 180s, the efficiency is too low. Therefore, this embodiment uses more efficient cold pressing, but the cold pressing has poor compactness and slightly lower electromagnetic properties. In order to overcome the above shortcomings, the coating method of step 1 and step 2 is used to enhance the electromagnetic properties so that it can meet the requirements of the vehicle environment.

[0061] In order to further illustrate the superiority of the method of this embodiment, comparative examples 1 and 2 were constructed, and the method of this embodiment was used to carry out experiments of examples 1 and 2. The experimental parameters are shown in Table 1.

[0062] Table 1. Comparison of experimental parameters

[0063] project model Coating method Internal Section Temperature rise current / A Insulation withstand voltage / v Comparative Example 1 0730-220M Mixing extrusion granulation Cracking 2.1 80 Comparative Example 2 1264-3R3M Mixing extrusion 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 is the experimental result of the comparative example, and the right side is the experimental result of the embodiment. It can be seen that the inductor models with higher wire package height 0730-220M and thicker thickness 1264-3R3M are selected for molded inductors, and the granulated powder is obtained by stirring-extrusion granulation and spray granulation to form cold pressed inductors, wherein the ratio of passivation and coating glue used in powder preparation is the same. It can be seen that the one-piece molded inductor obtained by spray granulation has no cracks inside, and has high insulation withstand voltage and low loss.

[0065] Embodiment 2:

[0066] A second embodiment of the present invention provides a vehicle-mounted cold-pressed one-piece formed inductor, which is manufactured using the method for manufacturing the vehicle-mounted cold-pressed one-piece formed inductor described in the first embodiment.

[0067] The steps involved in the above embodiment 2 correspond to those in the method embodiment 1. For the specific implementation method, please refer to the relevant description part of the embodiment 1.

[0068] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it 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 on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for preparing a vehicle-mounted cold-pressed integrated inductor, characterized in that: The following steps are involved: The metal alloy powder and the modified phosphating solution are mixed and stirred, and after phosphating and drying, a passivation powder is obtained; The passivation powder and the coating liquid are stirred in a solvent to form a slurry, and the slurry is sprayed and granulated; The granulated powder is cold pressed and molded to obtain an integrally molded inductor.

2. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 1, characterized in that: The modified phosphating solution is prepared by mixing phosphoric acid, zirconium dihydrogen phosphate, zirconium nitrate and anhydrous ethanol.

3. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 2, characterized in that: The mass percentages of the zirconium nitrate and the phosphoric acid are 0.1% to 0.5% and 0.5% to 1.0% respectively.

4. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 1, characterized in that: During the phosphating process, the phosphating temperature is 25°C ~ 60°C, the time is 1 hour, and the drying temperature is 80°C ~ 120°C.

5. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 1, characterized in that: The coating liquid comprises bisphenol modified epoxy resin, epoxy modified organic silicon resin, methyl phenyl silicone resin and silane coupling agent.

6. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 5, characterized in that: The mass percentages of the modified epoxy resin, epoxy-modified organic silicon resin, methylphenyl silicon resin and silane coupling agent are 0.1%-0.5%, 1%-2%, 1%-2% and 0.1%-0.2% respectively.

7. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 1, characterized in that: The spray granulation process is carried out using an explosion-proof closed-cycle centrifugal spray granulation system, which works in a closed environment, uses inert gas N2 as a drying medium and a circulating carrier, has a positive pressure in the drying tower, and maintains a predetermined inlet air temperature, outlet air temperature and rotation speed.

8. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 7, characterized in that: The conditions for spray granulation are: inlet air temperature 120°C to 150°C, outlet air temperature 80°C to 95°C, rotation speed 4000rpm to 7000rpm, and drying tower pressure 0.1MPa to 0.2MPa.

9. The method for preparing the vehicle-mounted cold-pressed integrated inductor according to claim 1, characterized in that: During the cold pressing process, the pressing pressure is 500MPa to 800MPa.

10. An on-vehicle cold-pressed one-piece molded inductor, manufactured by the method for preparing an on-vehicle cold-pressed one-piece molded inductor according to any one of claims 1 to 9.

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