Low-pressure forming high-frequency low-loss SMC magnetic powder core and preparation method and application thereof

Abstract

The application discloses a low-pressure forming high-frequency low-loss SMC magnetic powder core and a preparation method and application thereof, wherein amorphous iron-based alloy fine powder is added into iron-silicon-chromium coarse powder, different contents of nano calcium carbonate are added into the compounded magnetic powder, and then high-content epoxy resin is melted and mixed in a mixing mill to obtain a high-fluidity mixing material.After crushing, a low-pressure forming high-frequency low-loss SMC granular material is obtained, which is formed by hot pressing under low pressure, and the obtained annular magnetic powder core is annealed in a vacuum oven, so that the low-pressure high-frequency low-loss SMC magnetic powder core is obtained.Through the method, the SMC magnetic powder core with a forming pressure less than 50 MPa and a magnetic loss less than 2100 kW / m 3 under the conditions of 20 mT and 2 MHz can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of soft magnetic composite materials, and relates to low-pressure molded high-frequency low-loss SMC magnetic powder cores, their preparation methods, and applications. Background Technology

[0002] Soft magnetic composite materials (SMCs) possess high saturation magnetization and low power loss characteristics, and have been widely used in the fabrication of key magnetic components in the electronics, communications, and new energy industries, such as chip inductors, switching regulators, DC / DC converters, and active filters. The increasing frequency and miniaturization of power devices are placing higher performance demands on soft magnetic composite materials.

[0003] Most common SMCs fail to meet application requirements due to significant eddy current losses at high frequencies (MHz). Meanwhile, soft magnetic materials used for electromagnetic energy conversion / storage need to meet requirements for low magnetic loss at high frequencies, high saturation magnetic induction, and high permeability. In high-frequency applications, organic / inorganic materials are typically coated onto metal powder to achieve good electrical insulation of the magnetic powder core. Organic / inorganic coatings can significantly increase the resistivity and decrease the conductivity of the magnetic powder core; therefore, selecting a high-resistivity and uniformly dense insulating layer is crucial for achieving high-frequency applications. Furthermore, researchers are attempting to increase compaction density, enhance DC bias characteristics and magnetic properties, and reduce product costs by adding small-diameter particles to SMCs. Iron-based amorphous alloys, due to their high resistivity, exhibit extremely low eddy current losses at high frequencies and are attracting increasing attention from researchers. To achieve higher density and reduce the decrease in permeability and increase in magnetic loss caused by porosity, high-pressure (>500MPa) molding is often used in the manufacture of SMCs. However, the high-pressure molding process easily damages the insulating coating on the surface of the magnetic powder and generates internal stress, which deteriorates the magnetic stability of the magnetic medium and increases core loss. Heat treatment is used to mitigate the adverse effects of SMC compaction, eliminate internal stress and work hardening caused by high-pressure compaction, eliminate lattice distortion, promote grain growth, and facilitate domain wall movement and magnetization. Depending on the temperature limitations imposed by the organic / inorganic coating encapsulating the particles, SMC is annealed at sufficiently high temperatures to eliminate residual stress and defects; typically, the high-pressure forming heat treatment temperature is 400–800°C. If the annealing temperature is too low, the magnetic powder core cannot effectively mitigate the adverse effects of high-pressure compaction; conversely, if the annealing temperature is too high, the synthesized organic / inorganic coating may decompose and damage, or affect the phase structure of the magnetic powder core.

[0004] Based on the above problems, this invention proposes a new method for preparing SMC magnetic powder cores. Epoxy resin is used to cover magnetic powder particles as an insulating layer to reduce eddy current loss. Amorphous magnetic powder is used to adjust high-frequency loss performance. Inorganic nano-calcium carbonate powder and low-pressure molding are used to assist in low-temperature annealing to reduce internal stress and further reduce magnetic loss. This results in a high-frequency (2MHz) low-loss SMC magnetic powder core while ensuring a permeability of over 18.5. Summary of the Invention

[0005] One objective of this invention is to address the shortcomings of existing technologies by providing a method for preparing a low-pressure molded high-frequency, low-loss SMC magnetic powder core. The magnetic powder core is prepared by adding amorphous fine powder to iron-silicon-chromium magnetic powder, achieving a coarse-fine mixture, followed by the addition of calcium carbonate, and then ultrasonically mixing the mixture in anhydrous ethanol. Both the amorphous fine powder and calcium carbonate effectively improve resistivity and reduce coercivity. The dried magnetic powder is then melt-blended with a high-content epoxy resin in a Banbury mixer. The epoxy resin binder provides high fluidity to the magnetic powder, increases electrical insulation, and reduces coercivity (Hc). An annealing process reduces the internal stress generated during magnetic powder pressing, thereby lowering Hc. This process yields a low-pressure molded high-frequency, low-loss SMC magnetic powder core.

[0006] A method for preparing a low-pressure molded high-frequency, low-loss SMC magnetic powder core includes the following steps:

[0007] Step (1): Add amorphous iron-silicon-boron-chromium magnetic powder to iron-silicon-chromium magnetic powder, use anhydrous ethanol as the dispersion medium, and perform ultrasonic dispersion to make it evenly mixed; then add nano calcium carbonate, continue to ultrasonically disperse evenly, and dry to obtain a composite magnetic powder with calcium carbonate attached to the surface.

[0008] Preferably, the iron-silicon-chromium magnetic powder has a mesh size of 500.

[0009] As a preferred embodiment, the mass ratio of iron-silicon-chromium magnetic powder to amorphous iron-silicon-boron-chromium magnetic powder is 80:(20-25);

[0010] Preferably, the mass ratio of calcium carbonate to epoxy resin binder is (0.5-7):(99.5-93);

[0011] Preferably, the drying temperature is 60-65℃ and the drying time is 12-15h.

[0012] Step (2): The composite magnetic powder with calcium carbonate attached to the surface obtained in step (1) is melt-mixed with epoxy resin binder and crushed to obtain low-pressure molded high-frequency low-loss SMC granules.

[0013] Preferably, the mass ratio of the composite magnetic powder to the sum of the masses of the epoxy resin binder and calcium carbonate is 92:8.

[0014] Preferably, the mixing temperature is 100–125℃ and the mixing time is 3–12 min.

[0015] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed into a ring-shaped magnetic powder core, and then annealed to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0016] Preferably, the hot pressing pressure is 30 MPa, the hot pressing temperature is 160–180 °C, and the holding time is 3–10 min.

[0017] Preferably, the annealing temperature is 170–175°C and the annealing time is 2–4 hours.

[0018] Another object of the present invention is to provide a low-pressure molded high-frequency, low-loss SMC magnetic powder core prepared by the above method.

[0019] Another object of the present invention is to provide the application of the above-mentioned low-pressure molded high-frequency low-loss SMC magnetic powder core in the preparation of magnetic components.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention utilizes an epoxy resin binder to fully cover the magnetic powder particles, enabling SMC to be molded under relatively low pressure (50 MPa). The resulting magnetic powder core exhibits low porosity and high density. Simultaneously, the epoxy resin binder's excellent insulating properties, dispersed between the magnetic powder particles, reduce eddy current losses. Furthermore, the addition of amorphous iron-based alloy powder to the iron-silicon-chromium magnetic powder separates the particles, reducing mutual contact, increasing resistivity, and lowering eddy current losses. Additionally, the lower coercivity of the amorphous alloy powder further reduces hysteresis losses.

[0022] This invention adds nano-calcium carbonate with high insulation properties, which reduces eddy current loss on the one hand, and forms an organic / inorganic insulating layer by dispersing nano-calcium carbonate in epoxy resin, and then disperses it between magnetic powder particles to reduce internal stress and hysteresis loss on the other hand. The low-pressure molded magnetic powder core is then subjected to low-temperature annealing to further release the internal stress generated during the pressing of the magnetic ring and reduce coercivity and hysteresis loss.

[0023] The method of this invention can achieve a molding pressure of less than 50 MPa and a loss of less than 2100 kW / m under conditions of 20 mT and 2 MHz. 3 SMC magnetic powder core. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the specific components and processes involved in the solution should not be construed as limitations on the present invention.

[0025] In a first aspect, the present invention provides a method for preparing a low-pressure molded high-frequency, low-loss SMC magnetic powder core, comprising the following steps:

[0026] Step (1): Add amorphous iron-silicon-boron-chromium magnetic powder to 500-mesh iron-silicon-chromium magnetic powder, and use anhydrous ethanol as the dispersion medium to perform ultrasonic dispersion to make it uniformly mixed; then add nano-calcium carbonate, continue to ultrasonically disperse uniformly, and dry at 60°C for 12-15 hours to obtain a composite magnetic powder with calcium carbonate adhering to the surface; the mass ratio of the iron-silicon-chromium magnetic powder to the amorphous iron-silicon-boron-chromium magnetic powder is 80:20; the mass ratio of calcium carbonate to epoxy resin binder is (0.5-7):(93-99.5);

[0027] Step (2): The composite magnetic powder with calcium carbonate adhering to the surface obtained in step (1) is melt-mixed with epoxy resin binder at 100-125℃ for 3-12 minutes, and then crushed to obtain low-pressure molded high-frequency low-loss SMC granules; the mass ratio of the composite magnetic powder to the sum of the mass of epoxy resin binder and calcium carbonate is 92:8.

[0028] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed at 30MPa and 160-180℃ for 3-10 minutes to form a ring-shaped magnetic powder core, and then annealed at 170-175℃ for 2-4 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0029] Secondly, the present invention provides a low-pressure molded high-frequency low-loss SMC magnetic powder core prepared by the above method.

[0030] Thirdly, the present invention provides the application of the above-mentioned low-pressure molded high-frequency low-loss SMC magnetic powder core in the preparation of magnetic components.

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Example 1

[0033] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 0.08g (0.5%) of nano calcium carbonate and continue ultrasonic dispersion for 20min. Place in a 60℃ oven and dry for 12h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0034] Step (2): Weigh 15.92g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 100℃ for 12min, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0035] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed into a ring-shaped magnetic powder core with an outer diameter of 12.8 mm, an inner diameter of 7.5 mm, and a height of 3.8 mm on a hot press molding machine at a temperature of 180°C and a holding pressure of 30 MPa for 3 min.

[0036] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 170°C for 4 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0037] The permeability of the low-pressure molded high-frequency low-loss SMC magnetic powder core was measured using an Agilent E4980ALCR precision tester, and the core loss of the magnetic powder core was measured using an Iwasaki SY-8218 AC magnetic automatic tester.

[0038] Example 2

[0039] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 0.16g (1%) of nano calcium carbonate and continue ultrasonic dispersion for 20min. Place in a 60℃ oven and dry for 12h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0040] Step (2): Weigh 15.84g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 100℃ for 12min, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0041] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed at 180°C and 30MPa for 3 minutes to form an annular magnetic powder core with an outer diameter of 12.8mm, an inner diameter of 7.5mm, and a height of 3.8mm.

[0042] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 175°C for 2 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0043] The permeability and loss of the magnetic powder core obtained in step (4) were measured according to the method in Example 1.

[0044] Example 3

[0045] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 0.48g (3%) of nano calcium carbonate and continue ultrasonic dispersion for 20min. Place in a 60℃ oven and dry for 12h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0046] Step (2): Weigh 15.52g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 125℃ for 3 minutes, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0047] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed at 160°C and 30MPa for 10 minutes on a hot press molding machine to form a ring-shaped magnetic powder core with an outer diameter of 12.8mm, an inner diameter of 7.5mm, and a height of 3.8mm.

[0048] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 175°C for 4 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0049] The permeability and loss of the magnetic powder core obtained in step (4) were measured according to the method in Example 1.

[0050] Example 4

[0051] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 0.8g (5%) of nano calcium carbonate and continue ultrasonic dispersion for 20min. Place in a 60℃ oven and dry for 15h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0052] Step (2): Weigh 15.2g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 125℃ for 3 minutes, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0053] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed at 160°C and 30MPa for 10 minutes on a hot press molding machine to form a ring-shaped magnetic powder core with an outer diameter of 12.8mm, an inner diameter of 7.5mm, and a height of 3.8mm.

[0054] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 175°C for 4 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0055] The permeability and loss of the magnetic powder core obtained in step (4) were measured according to the method in Example 1.

[0056] Example 5

[0057] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 1.12g (7%) of nano calcium carbonate and continue ultrasonically dispersing for 20min. Place in a 60℃ oven and dry for 15h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0058] Step (2): Weigh 14.88g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 125℃ for 3 minutes, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0059] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed at 160°C and 30MPa for 10 minutes to form a ring-shaped magnetic powder core with an outer diameter of 12.8mm, an inner diameter of 7.5mm, and a height of 3.8mm.

[0060] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 175°C for 4 hours to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core.

[0061] The permeability and loss of the magnetic powder core obtained in step (4) were measured according to the method in Example 1.

[0062] Comparative Example 1

[0063] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min to mix evenly. Then add 0.48g (3%) of nano calcium carbonate and continue ultrasonic dispersion for 20min. Place in a 60℃ oven and dry for 12h to obtain a composite magnetic powder with calcium carbonate adhering to the surface.

[0064] Step (2): Weigh 15.52g of epoxy resin binder, melt and mix the composite magnetic powder with calcium carbonate attached to the surface obtained in (1) with epoxy resin binder, mix in an internal mixer at 125℃ for 3 minutes, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0065] Step (3): The high-frequency, low-loss SMC granules obtained in step (2) are hot-pressed at 160°C and 30MPa for 10 minutes on a hot press molding machine to form an annular magnetic powder core with an outer diameter of 12.8mm, an inner diameter of 7.5mm, and a height of 3.8mm.

[0066] The permeability and loss of the annular magnetic powder core obtained in step (3) were measured according to the method in Example 1.

[0067] Comparative Example 2

[0068] Step (1): Weigh 147.2g of 500-mesh iron-silicon-chromium magnetic powder and 36.8g of amorphous iron-silicon-boron-chromium magnetic powder and place them in a beaker. Pour in 300ml of anhydrous ethanol and ultrasonically disperse for 20min. After mixing evenly, place in an oven and dry at 60℃ for 12h. After drying, the compound magnetic powder is obtained.

[0069] Step (2): Weigh 16g of epoxy resin binder, melt and mix the compound magnetic powder obtained in step (1) with epoxy resin binder, mix in an internal mixer at 100℃ for 12 minutes, and crush to obtain low-pressure molded high-frequency low-loss SMC granules.

[0070] Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed into a ring-shaped magnetic powder core with an outer diameter of 12.8 mm, an inner diameter of 7.5 mm, and a height of 3.8 mm on a hot press molding machine at 180°C and 30 MPa for 3 min.

[0071] Step (4): Place the annular magnetic powder core from step (3) into a vacuum oven and keep it at 175°C for 2 hours to obtain a high-frequency, low-loss SMC magnetic powder core.

[0072] The permeability and loss of the magnetic powder core obtained in step (4) were measured according to the method in Example 1.

[0073] The results obtained from the above embodiments and comparative examples are shown in Table 1.

[0074] Table 1. Magnetic permeability and magnetic loss of Examples 1-5 and Comparative Examples 1-2

[0075]

[0076]

[0077] Test conditions: Permeability was tested at 100kHz, and magnetic loss was tested at 20mT and 2MHz.

[0078] The data in the table above shows that the addition of amorphous iron-based alloys reduces the overall loss of the magnetic powder core. Adding different amounts of calcium carbonate increases density and overall magnetic properties, improving permeability (18.7–22.1) while simultaneously reducing magnetic loss. At the same mass ratio (calcium carbonate:epoxy resin), the magnetic loss of the magnetic powder core significantly decreases after annealing, reaching a minimum of 1750 kW / m at 20 mT and 2 MHz. 3 nearby.

Claims

1. A method for preparing a low-pressure molded high-frequency, low-loss SMC magnetic powder core, characterized in that, The preparation method includes the following steps: Step (1): Add amorphous iron-silicon-boron-chromium magnetic powder to iron-silicon-chromium magnetic powder, use anhydrous ethanol as the dispersion medium, and perform ultrasonic dispersion to make it uniformly mixed; then add nano-calcium carbonate, continue to ultrasonically disperse uniformly, and dry to obtain a composite magnetic powder with calcium carbonate attached to the surface; the mass ratio of the iron-silicon-chromium magnetic powder to the amorphous iron-silicon-boron-chromium magnetic powder is 80:(20~25). Step (2): The composite magnetic powder with calcium carbonate adhering to the surface obtained in step (1) is melt-blended with epoxy resin binder, and crushed to obtain low-pressure molded high-frequency low-loss SMC granules; wherein, the mass ratio of calcium carbonate to epoxy resin binder is (0.5~7):(99.5~93). Step (3): The high-frequency low-loss SMC granules obtained in step (2) are hot-pressed into a ring-shaped magnetic powder core, and then annealed to obtain the low-pressure molded high-frequency low-loss SMC magnetic powder core; wherein, the hot pressing pressure is 30MPa, the hot pressing temperature is 160~180℃, and the holding time is 3~10min; the annealing temperature is 170~175℃, and the annealing time is 2~4h.

2. The preparation method according to claim 1, characterized in that, The iron-silicon-chromium magnetic powder has a mesh size of 500.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the composite magnetic powder to the sum of the masses of epoxy resin binder and calcium carbonate is 92:

8.

4. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 60-65℃ and the drying time is 12-15h.

5. The preparation method according to claim 1, characterized in that, In step (2), the mixing temperature is 100-125℃ and the mixing time is 3-12 min.

6. A low-pressure molded high-frequency, low-loss SMC magnetic powder core, characterized in that, It is prepared by the method described in any one of claims 1-5.

7. The application of the low-pressure molded high-frequency low-loss SMC magnetic powder core as described in claim 6 in the preparation of magnetic components.

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