Compression Powder Core and Method for Producing the Same

Abstract

To provide a dust core with low core loss and a manufacturing method for the same.SOLUTION: A dust core 10 includes a soft magnetic powder 30. The density of the soft magnetic powder 30 is higher in the center than on surfaces such as a top 12 and a bottom 14. By increasing the density inside the dust core 10 in this way, hysteresis loss can be suppressed and eddy current loss can be lowered by increasing the surface resistance. The dust core 10 can be manufactured, for example, by pressure molding a raw material powder including soft magnetic material powder and binder resin with a mold preheated to a predetermined temperature of 250°C or higher.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a compacted powder core formed by pressure-molding soft magnetic powder and a method for manufacturing the same.

Background Art

[0002] As this type of compacted powder core, for example, there is one disclosed in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a compacted powder core with low core loss and a method for manufacturing the same.

Means for Solving the Problems

[0005] The present invention provides, as a first compacted powder core, a compacted powder core containing soft magnetic powder, in which the density of the soft magnetic powder is higher at the central portion than at the surface.

[0006] Further, the present invention provides, as a second compacted powder core, the first compacted powder core, wherein the surface area density, which is the areal density of the soft magnetic powder in a first predetermined region near the center of at least one of the pressing surfaces of the upper surface and the lower surface, and the internal area density, which is the areal density of the soft magnetic powder in a second predetermined region corresponding to the first predetermined region in a plane passing through the vertical center of the compacted powder core and parallel to the pressing surface, satisfy (Internal area density / Surface area density)>1 and provides a compacted powder core that satisfies the above.

[0007] Further, the present invention provides, as a third compacted powder magnetic core, the first or second compacted powder magnetic core, having a surface resistance of 50 Ω or more compacted powder magnetic core.

[0008] Further, the present invention provides, as a fourth compacted powder magnetic core, the third compacted powder magnetic core, having a surface resistance of 1000 Ω or more compacted powder magnetic core.

[0009] Further, the present invention provides, as a fifth compacted powder magnetic core, any one of the first to fourth compacted powder magnetic cores, wherein the soft magnetic powder is made of an amorphous alloy or a nanocrystalline alloy compacted powder magnetic core.

[0010] Furthermore, the present invention provides, as a sixth compacted powder magnetic core, any one of the first to fifth compacted powder magnetic cores, having a density of 5.84 × 10 3 kg / m 3 or more compacted powder magnetic core.

[0011] Further, the present invention provides, as a method for manufacturing the first compacted powder magnetic core, pressing and molding raw material powder containing soft magnetic material powder and binder resin in a mold preheated to a predetermined temperature of 250 °C or higher By doing so, the binder resin on the core surface is cured early, and with the density of the soft magnetic powder on the core surface being sparse, further pressure is applied by the mold to increase the density of the soft magnetic powder inside the core. method for manufacturing a compacted powder magnetic core.

[0012] Further, the present invention provides, as a method for manufacturing the second compacted powder magnetic core, the method for manufacturing the first compacted powder magnetic core, wherein the compacted powder magnetic core is made of a powder of a nanocrystalline alloy include and the predetermined temperature is equal to or lower than the second crystallization start temperature of the material powder, method for manufacturing a compacted powder magnetic core.

[0013] Furthermore, the present invention provides, as a method for manufacturing the third compacted powder magnetic core, the method for manufacturing the first compacted powder magnetic core, wherein the compacted powder magnetic core is made of a powder of an amorphous alloy includeA method for manufacturing a compacted powder magnetic core is provided, wherein the predetermined temperature is equal to or lower than the crystallization start temperature of the material powder.

Advantages of the Invention

[0014] Core loss can be broadly classified into hysteresis loss and eddy current loss. To reduce the former, it is effective to increase the density of the soft magnetic powder. On the other hand, as a method for reducing the latter, for example, forming an oxide film on the soft magnetic powder is known. According to the present invention, it is possible to achieve both high density inside the core and high resistivity on the core surface, thereby obtaining a compacted powder magnetic core with low core loss.

[0015] According to the present invention, by pressure-molding a raw material powder containing a soft magnetic material powder and a binder resin in a mold preheated to a predetermined temperature of 250°C or higher, the binder resin on the core surface can be cured early, and the density of the soft magnetic powder on the core surface can be made sparse. In that state, by further applying pressure with the mold to increase the density of the soft magnetic powder inside the core, it is possible to manufacture the above-described compacted powder magnetic core with low core loss.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] As shown in FIG. 1, the compacted magnetic core 10 according to the embodiment of the present invention contains soft magnetic powder 30 and has an upper surface 12 and a lower surface 14 pressed by a mold (described later). That is, in the present embodiment, both the upper surface 12 and the lower surface 14 are pressing surfaces. As shown in FIGS. 1 and 2, the upper surface 12, which is a pressing surface, is rough, and the soft magnetic powder 30 is sparsely present, with gaps being prominent. In contrast, as shown in FIG. 1, the soft magnetic powder 30 is densely arranged at the central portion between the upper surface 12 and the lower surface 14.

[0018] In particular, the compacted magnetic core 10 of the present embodiment has a rough surface only and a high density inside. Here, "only the surface" means that, as shown in FIG. 2, it has a thickness of one or more powder layers in the cross section. However, if the cross section has a rough state (low density) over a thickness exceeding five powder layers, the entire compacted magnetic core 10 cannot be made to have a high density. Therefore, the low-density layer needs to be five powder layers or less in the cross section.

[0019] More specifically, in the compacted magnetic core 10 of FIG. 1, the surface area density of the soft magnetic powder 30 and the internal area density of the soft magnetic powder 30 are (Internal area density / Surface area density) > 1 is satisfied. Here, the surface area density is the area density of the soft magnetic powder 30 within the first predetermined region 20, and the internal area density is the area density of the soft magnetic powder 30 within the second predetermined region 24. Also, the first predetermined region 20 is a region near the center of the upper surface 12, which is a pressing surface, and the second predetermined region 24 at the central portion between the upper surface 12 and the lower surface 14 is a region corresponding to the first predetermined region 20 within a plane passing through the vertical center of the compacted magnetic core 10 and parallel to the upper surface 12, which is a pressing surface.

[0020] In the present embodiment, the surface area density and the internal area density are obtained as follows. The surface area density is obtained, for example, by buff-polishing the upper surface 12 (press surface) of the compacted powder core 10 to remove dirt, observing the first predetermined region 20, specifying the area occupied by the soft magnetic powder 30 within the first predetermined region 20, and calculating from the ratio of the specified area to the area of the first predetermined region 20. The internal area density is obtained, for example, by cutting the compacted powder core 10 so that the second predetermined region 24 is included in the cut surface, observing the second predetermined region 24, specifying the area occupied by the soft magnetic powder 30 within the second predetermined region 24, and calculating from the ratio of the specified area to the area of the second predetermined region 24.

[0021] In this way, when the soft magnetic powder 30 is densely present inside the compacted powder core 10, good magnetic properties can be obtained and the hysteresis loss can be suppressed low. Specifically, the density of the compacted powder core 10 of the present embodiment is 5.84× 10 3 kg / m 3 The above is the case. In this way, the compacted powder core 10 has a high density and a high magnetic permeability.

[0022] On the other hand, when the surface of the compacted powder core 10 is roughened, the surface resistance can be made relatively high compared to the case where the surface is formed with the same density as the inside, and the eddy current loss can be suppressed. Specifically, the surface resistance of the compacted powder core 10 of the present embodiment is such that the surface resistance is 50 Ω or more. From the viewpoint of effectively suppressing the effect of the eddy current layer, it is desirable that the surface resistance of the compacted powder core 10 be 1000 Ω or more.

[0023] The soft magnetic powder 30 constituting the compacted powder core 10 of the present embodiment is made of an amorphous alloy or a nanocrystalline alloy. In the case of the soft magnetic powder 30 made of a nanocrystalline alloy, it contains crystal grains having an average particle size of 50 nm or less, preferably 40 nm or less, made of αFe or αFe-Si. However, the present invention is not limited to this. The soft magnetic powder 30 may contain magnetic powders other than amorphous alloys or nanocrystalline alloys. The compacted powder core 10 may contain ceramic powders or the like in addition to the soft magnetic powder 30.

[0024] Referring to FIG. 3 in addition to FIG. 1, the compacted magnetic core 10 of the present embodiment is manufactured by pressure-molding raw material powder 40 containing soft magnetic powder (i.e., material powder of soft magnetic material) serving as a raw material of soft magnetic powder 30 and binder resin in mold 50. Mold 50 includes upper punch 52, lower punch 54, and die 56. Raw material powder 40 is placed in the space formed by lower punch 54 and die 56, and compacted magnetic core 10 is manufactured by pressing it toward lower punch 54 with upper punch 52.

[0025] In particular, in the method for manufacturing compacted magnetic core 10 of the present embodiment, mold 50 is pre-heated to a predetermined temperature of 250°C or higher. Thereby, on the surface in contact with mold 50 (i.e., the pressing surface), the binder resin cures early, so a rough state (a state where the density of soft magnetic powder 30 is low) occurs. In that state, when pressure is applied, internal densification can be achieved.

[0026] The material powder of the soft magnetic material may be, for example, a mixture of amorphous alloy powder and other magnetic powders such as Fe powder, Fe-Si powder, Fe-Si-Cr powder, Fe-Si-Al, and Fe-Ni. The material powder of the soft magnetic material may be not only of a single particle size but also a mixture of multiple particle sizes. In order to increase the resistance of compacted magnetic core 10, an oxide film may be formed on the material powder of the soft magnetic material. Also, although the shape of the material powder of the soft magnetic material in the present embodiment is spherical, the strength of compacted magnetic core 10 may be increased by mixing filamentous ones.

[0027] When soft magnetic powder 30 is made of a nanocrystalline alloy, that is, when compacted magnetic core 10 contains powder made of a nanocrystalline alloy, it is desirable that the aforementioned predetermined temperature, that is, the heating temperature of mold 50, be equal to or lower than the second crystallization start temperature (Tx2) of the material powder of the soft magnetic material. This is because when the second crystallization start temperature (Tx2) is exceeded, a compound phase precipitates and the characteristics deteriorate.

[0028] When the soft magnetic powder 30 is made of an amorphous alloy, that is, when the compacted powder core contains a powder made of an amorphous alloy, it is desirable that the aforementioned predetermined temperature be equal to or lower than the crystallization start temperature (Tx) of the soft magnetic material powder. This is because if the temperature exceeds the crystallization start temperature (Tx), the crystals will coarsen and the characteristics will deteriorate.

[0029] In addition to the soft magnetic material powder described above, the raw material powder 40 may further contain ceramic powder or the like.

[0030] When manufacturing the compacted powder core 10 of the present embodiment, preliminary molding may be performed in the same manner as the general method for manufacturing the compacted powder core 10.

[0031] Furthermore, in order to protect the surface of the compacted powder core 10, the molded compacted powder core 10 may be impregnated with resin to fill the gaps between the soft magnetic powders 30 on the surface of the compacted powder core 10 with resin.

[0032] Note that the mold 50 may be heated partially. However, considering that the surface of the compacted powder core 10 corresponding to the heated portion becomes rough and contributes to suppressing eddy current loss, it is desirable to heat the entire mold 50.

[0033] Hereinafter, the soft magnetic powder 30 before molding, that is, the soft magnetic material powder, will be described in more detail.

[0034] From the viewpoint of easily improving the density at the center of the compacted powder core 10, the soft magnetic material powder is preferably an amorphous alloy powder that softens before and after crystallization. In particular, among amorphous alloy powders, metal glass powders having a supercooled liquid region before crystallization are preferred. Also, the amorphous alloy powder may be used as a raw material and nanocrystallized by heating during molding to further improve the magnetic properties. At that time, considering its soft magnetic properties and formability, the crystallinity of the amorphous alloy powder is preferably less than 10%, and more preferably less than 2%.

[0035] The average particle size of the soft magnetic material powder is preferably 1 μm or more and 100 μm or less. In particular, when the average particle size of the material powder is 40 μm or less, the stacking characteristics of the compacted powder core 10 can be improved. Further, when the average particle size of the material powder is 15 μm or less, the high-frequency characteristics of the compacted powder core 10 can be improved.

[0036] Considering formability, the crystallization temperature of the amorphous alloy powder as the material powder is preferably 550 °C or less. In particular, in the case of metal glass powder, the glass transition temperature of the material powder is preferably 520 °C or less. Further, when the soft magnetic powder 30 is made of a nanocrystalline alloy, the crystallization temperature of the amorphous alloy powder as the material powder is preferably 500 °C or less.

[0037] The amorphous alloy powder as the material powder preferably contains a P element with a low crystallization temperature and glass transition temperature and is easily softened, and the effect is enhanced by making the P element more than the Si element in atomic percentage units.

[0038] The composition system is preferably FeBP. On the other hand, an Nb element for increasing the amorphous forming ability, a Cr element for increasing the corrosion resistance, and a Cu element for promoting nanocrystallization may be added in the range of 3 atomic% or less, respectively. Further, Si and C may be added to the above composition system in the range of 5 atomic% or less as metalloid elements to adjust the amorphousness, crystallization temperature, and magnetic properties.

[0039] The metal glass powder preferably satisfies the following formula. Formula: (Fe1-αTMα)100-w-x-y-zPwBxLySiz However, inevitable impurities are included, TM is one or more selected from Co and Ni, L is one or more of Ca, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, Y, Cu, C, S, N, O and rare earth elements, and it has a composition represented by 0≦α≦0.98, 2≦w≦18 atomic %, 2≦x≦16 atomic %, 0<y≦10 atomic %, 0≦z≦8 atomic %, the crystallization start temperature (Tx) is 550 °C or lower, the glass transition temperature (Tg) is 520 °C or lower, and the supercooled liquid region represented by ΔTx = Tx - Tg is 20 °C or higher.

[0040] In the above metal glass powder, P element and B element are essential elements responsible for amorphous phase formation. In particular, the supercooled liquid region appears in the range of 2≦w≦18 atomic % and 2≦x≦18 atomic %, and the amorphous forming ability becomes high. When 3≦w≦16 atomic % and 3≦x≦16 atomic %, the amorphous forming ability becomes even higher and amorphous powdering is possible even with a general-purpose atomizing device.

[0041] In the above metal glass powder, Si element is an essential element responsible for amorphous phase formation. When the Si content exceeds 8 at%, the amorphousness decreases, so it is preferably 8 at% or less. Also, when Si is added, the crystallization temperature increases, so the Si content is preferably 4 at% or less.

[0042] In the above metal glass powder, L element is an essential element for improving the amorphous forming ability, corrosion resistance, nanocrystallization, and thermal stability. When the L element exceeds 10 at%, the decrease in saturation magnetic flux density is significant, so it is preferably 10 at% or less, and more preferably 4 at% or less.

[0043] When the soft magnetic powder 30 is made of a nanocrystalline alloy, the material powder of the soft magnetic material preferably satisfies the following formula. Formula: Fe100-a-b-c-d-eBaSibPcCdCue However, inevitable impurities are included, 4≦a≦13 at%, 0≦b≦8 at%, 1≦c≦12 at%, 0≦d≦5 at%, 0.4≦e≦1.4 at%, and 0.05≦e / c≦0.8.

[0044] In the above formula, 3 at% or less of Fe may be substituted with one or more elements among Ca, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Co, Ni, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, Y, S, N, O, and rare earth elements.

[0045] In the material powder for the nanocrystalline alloy described above, the B element is an essential element responsible for the formation of the amorphous phase. If the proportion of B is less than 4 at%, the formation of the amorphous phase becomes difficult. If the proportion of B is more than 13 at%, ΔT decreases, a homogeneous nanocrystalline structure cannot be obtained, and the alloy composition will have deteriorated soft magnetic properties. Therefore, it is desirable that the proportion of B is 4 at% or more and 13 at% or less. In particular, when the alloy composition needs to have a low melting point for mass production, it is preferable that the proportion of B is 11 at% or less.

[0046] In the material powder for the nanocrystalline alloy described above, the P element is an essential element responsible for the formation of the amorphous phase and the formation of fine nanocrystals. If the proportion of P is less than 1 at%, the melting point rises and the formation of the amorphous phase becomes difficult. For the formation of nanocrystals, 3 at% or more is preferable, and further 5 at% or more is more preferable. If the proportion of P is more than 12 at%, ΔT decreases and the formation of nanocrystals becomes difficult. For increasing Bs, 9 at% or less is preferable.

[0047] In the material powder for the nanocrystalline alloy described above, the Si element is an element responsible for the formation of the amorphous phase. During nanocrystallization, ΔT increases and it contributes to the stabilization of the nanocrystals. If the proportion of Si is more than 8 at%, the formation of the amorphous phase decreases and a more homogeneous nanocrystalline structure cannot be obtained. As a result, the soft magnetic properties deteriorate. Also, when the Fe content exceeds 80 at%, if the Si content is high, the ability to form the amorphous phase decreases, so the Si content is preferably 3 at% or less.

[0048] In the above-described material powder for nanocrystalline alloys, the C element is an element responsible for amorphous formation, and by combining it with B, P, and Si elements, the amorphous formation ability and magnetic properties can be improved. However, if the proportion of C exceeds 5 at%, the amorphous formation ability decreases, so it is preferably 5 at% or less. Also, in order to suppress the coarsening of nanocrystalline grains, the C content is preferably 3 at% or less.

[0049] In the above-described material powder for nanocrystalline alloys, the Cu element is an essential element responsible for creating crystal nuclei and nanocrystallization. In particular, by combining it with the P element, the refinement of crystal grains becomes possible. Note that if the proportion of Cu is less than 0.4 at%, nanocrystallization becomes difficult, and if the proportion of Cu is more than 1.4 at%, the crystal nuclei become inhomogeneous. Therefore, when forming an Fe-based nanocrystalline alloy, a homogeneous nanocrystalline structure cannot be obtained, and the soft magnetic properties deteriorate. Since it becomes difficult to form an amorphous phase, the proportion of Cu is preferably 0.4 at% or more and 1.4 at% or less. For the formation of the amorphous phase, less than 1.0 at% is more preferable.

[0050] In the above-described material powder for nanocrystalline alloys, in order to improve the amorphous formation ability, corrosion resistance, nanocrystallization, and thermal stability, 3 at% or less of Fe may be substituted with one or more elements among Ca, V, Ti, Zr, Hf, Nb, Ta, Mo, W, Cr, Co, Ni, Al, Mn, Ag, Zn, Sn, As, Sb, Bi, Y, S, N, O, and rare earth elements.

[0051] Hereinafter, embodiments of the present invention will be described more specifically with reference to examples.

[0052] (Examples 1 to 9 and Comparative Examples 1 to 7) Under the conditions described in Table 1 below, Fe 80.9 Si3B6P 8.5 Cr1Cu 0.6 (nanocrystalline alloy), Fe 84.3 B6P9Cu 0.7 (nanocrystalline alloy), Fe 80.4 Si3B6P9Cr1Cu 0.6 (nanocrystalline alloy), Fe 77.1 B14.4 P 5.5 Cr1Nb2 (metallic glass (amorphous alloy)), Fe 80.9 Si3B6P 8.5 Cr1Cu 0.6 (nanocrystalline alloy), the ring-shaped compacted powder cores 10 of Examples 1 to 9 and Comparative Examples 1 to 7 were fabricated. That is, in Examples 1 to 3 and Comparative Examples 1 and 2, Fe 80.9 Si3B6P 8.5 Cr1Cu 0.6 (nanocrystalline alloy) is a ring core having the powder as the soft magnetic powder 30. In Examples 4 and 5 and Comparative Example 3, Fe 84.3 B6P9Cu 0.7 (nanocrystalline alloy) is a ring core having the powder as the soft magnetic powder 30. In Examples 6 and 7 and Comparative Example 4, Fe 80.4 Si3B6P9Cr1Cu 0.6 (nanocrystalline alloy) is a ring core having the powder as the soft magnetic powder 30. In Examples 8 and 9 and Comparative Examples 5 and 6, Fe 77 B5P 15 Nb 1.5 Cr 1.5 (metallic glass (amorphous alloy)) is a ring core having the powder as the soft magnetic powder 30. In Comparative Example 7, Fe 80.9 Si3B6P 8.5 Cr1Cu 0.6 (nanocrystalline alloy) is a ring core having the powder as the soft magnetic powder 30. In the table, Tx1 is the first crystallization start temperature in the soft magnetic powder for nanocrystallization. In this regard, for Fe 77 B5P 15 Nb 1.5 Cr 1.5 (metallic glass (amorphous alloy)), the crystallization start temperature Tx is denoted as Tx1 for convenience of expression. Also, in the table, Comparative Example 7 was heated from a mold temperature of 25°C to 500°C during molding. In any of Examples 1 to 9 and Comparative Examples 1 to 7, the hot pressing time was about 5 minutes, and at most less than 10 minutes. The core loss was measured using a B-H analyzer under a magnetic flux density of 100 mT and a frequency of 50 kHz. The surface resistance was measured by bringing the tester needle into contact at a distance of about 1 cm.

[0053]

Table 1

[0054] Referring to Examples 1 to 3 and Comparative Examples 1 and 2, when the surface temperature of the mold during molding is less than 250°C, (internal area density / surface area density) is 1 or less, and the core loss is large. On the other hand, when the surface temperature of the mold during molding is 250°C or higher, (internal area density / surface area density) is greater than 1, and the core loss can be suppressed.

[0055] Similarly, referring to Examples 4 and 5 and Comparative Example 3, when the surface temperature of the mold during molding is less than 250°C, (internal area density / surface area density) is 1 or less, and the core loss is large. On the other hand, when the surface temperature of the mold during molding is 250°C or higher, (internal area density / surface area density) is greater than 1, and the core loss can be suppressed.

[0056] Also, referring to Examples 6 and 7 and Comparative Example 4, in all cases, the surface temperature of the mold during molding is 250°C or higher, (internal area density / surface area density) is greater than 1, and the core loss can be relatively suppressed. However, only in Comparative Example 4, the surface resistance is as low as 10 Ω, so the core loss is slightly increased due to the eddy current loss. Based on this, it is desirable that the surface resistance is 50 Ω or more, and more preferably 1000 Ω or more.

[0057] Referring to Examples 8 and 9 and Comparative Examples 5 and 6, when the surface temperature of the mold during molding is less than 250°C, (internal area density / surface area density) is 1 or less, and the core loss is large. On the other hand, when the surface temperature of the mold during molding is 250°C or higher, (internal area density / surface area density) is greater than 1, and the core loss can be suppressed.

[0058] Referring to Comparative Example 12, when pressure is applied while gradually increasing the surface temperature of the mold during molding from 25°C to 500°C, (internal area density / surface area density) is 1, the surface resistance cannot be increased, and the core loss is large.

[0059] As described above, the present invention has been specifically described with reference to embodiments. However, the present invention is not limited thereto, and various modifications and changes are possible.

Explanation of Reference Numerals

[0060] 10 Compression powder magnetic core 12 Upper surface 14 Lower surface 20 First predetermined region 24 Second predetermined region 30 Soft magnetic powder 40 Raw material powder 50 Mold 52 Upper punch 54 Lower punch 56 Die

Claims

1. A compacted powder core containing soft magnetic powder, wherein the density of the soft magnetic powder is higher at the central part than at the surface, the surface area density which is the area density of the soft magnetic powder within a first predetermined region near the center of at least one of the pressing surfaces of the upper and lower surfaces, and the internal area density which is the area density of the soft magnetic powder within a second predetermined region corresponding to the first predetermined region in a plane passing through the vertical center of the compacted powder core and parallel to the pressing surface satisfy (Internal area density / Surface area density) > 1 A compacted powder core satisfying the above.

2. The compacted powder core according to Claim 1, wherein the surface resistance is 50 Ω or more A compacted powder core.

3. The compacted powder core according to Claim 2, wherein the surface resistance is 1000 Ω or more A compacted powder core.

4. The compacted powder core according to any one of Claims 1 to 3, wherein the soft magnetic powder is made of an amorphous alloy or a nanocrystalline alloy A compacted powder core.

5. The compacted powder core according to any one of Claims 1 to 4, with a density of 5.84×10 ３ kg / m ３ or more A compacted powder core.

6. A method for manufacturing a compacted powder core, wherein raw material powder containing soft magnetic material powder and a binder resin is pressure-molded in a mold preheated to a predetermined temperature of 250 °C or higher to cure the binder resin on the core surface early, and then the mold is further pressed to increase the density of the soft magnetic powder inside the core while making the density of the soft magnetic powder on the core surface sparse.

7. The method for manufacturing a compacted powder core according to Claim 6, wherein the compacted powder core contains powder made of a nanocrystalline alloy, and the predetermined temperature is equal to or lower than the second crystallization start temperature of the material powder.

8. The method for manufacturing a compacted powder core according to Claim 6, wherein the compacted powder core contains powder made of an amorphous alloy, and the predetermined temperature is equal to or lower than the crystallization start temperature of the material powder.

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