Pressure Powder Core

Abstract

To provide a dust core in which iron loss is suppressed. [Solution] The powder magnetic core 1 includes a plurality of metal grains 2 and an oxide 3 containing Si. The metal grains 2 are covered with the oxide 3. The plurality of metal grains 2 are soft magnetic particles of two or more types from among first metal grains, second metal grains, and third metal grains. The first metal grains and second metal grains are each an alloy containing Fe and Si. The third metal grains are pure iron or an alloy containing Fe. The Si content of the first metal grains is S1% by mass, the Si content of the second metal grains is S2% by mass, and the Si content of the third metal grains is S3% by mass, where S1, S2, and S3 satisfy S1>S2>S3≧0. The proportion of the first metal grains among all the metal grains 2 is M1% by mass, the proportion of the second metal grains among all the metal grains 2 is M2% by mass, and the proportion of the third metal grains among all the metal grains 2 is M3% by mass, where (M1+M2) is greater than M3.

Description

[Technical Field]

[0001] The present disclosure relates to dust cores. [Background technology]

[0002] Powder magnetic cores are used in various electric or electronic devices such as inductors (e.g., reactors) and motors. For example, as shown in Patent Document 1 below, powder magnetic cores are produced by compressing and heating a large number of metal powders (soft magnetic powders) covered with an insulating coating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-85967 Summary of the Invention [Problem to be solved by the invention]

[0004] Iron loss (in other words, core loss) in powder magnetic cores used in electrical or electronic devices reduces the energy efficiency of the electrical or electronic devices. Therefore, it is desirable to suppress iron loss in powder magnetic cores. For example, it is desirable to suppress iron loss in powder magnetic cores used in the stators of motors driven in the high frequency band (e.g., 2 kHz). In other words, as the rotation speed of motors increases, further suppression of iron loss in powder magnetic cores used in motor cores is required. However, it is difficult to achieve low iron loss with powder magnetic cores made from conventional soft magnetic powders (e.g., pure iron).

[0005] An object of one aspect of the present invention is to provide a powder magnetic core with reduced core loss. [Means for solving the problem]

[0006] For example, as described in [1] to [8] below, one aspect of the present invention relates to a powder magnetic core.

[0007] [1] A method for manufacturing a silicon-containing composite material, comprising: a part or all of the plurality of metal particles are covered with the oxide, the plurality of metal grains are two or more types of soft magnetic grains selected from the group consisting of a plurality of first metal grains, a plurality of second metal grains, and a plurality of third metal grains; the first metal particles and the second metal particles are each an alloy containing iron and silicon, the third metal particles are pure iron or an alloy containing iron, The silicon content of the first metal particles is expressed as S1% by mass, The silicon content in the second metal particles is expressed as S2% by mass, The silicon content of the third metal particles is expressed as S3% by mass, S1, S2, and S3 satisfy S1>S2>S3≧0, The ratio of the first metal particles to all the metal particles is expressed as M1 mass%, The ratio of the second metal particles to all the metal particles is expressed as M2 mass%, The ratio of the third metal particles to all the metal particles is expressed as M3 mass%, (M1+M2) is greater than M3, Powder magnetic core.

[0008] [2] The plurality of metal particles include all of the first metal particles, the second metal particles, and the third metal particles. [1] The powder magnetic core according to [1].

[0009] [3] The plurality of metal particles are composed only of the first metal particles and the second metal particles. [1] The powder magnetic core according to [1].

[0010] [4] The plurality of metal particles are composed only of the second metal particles and the third metal particles. [1] The powder magnetic core according to [1].

[0011] [5] The plurality of metal particles are composed only of the first metal particles and the third metal particles. [1] The powder magnetic core according to [1].

[0012] [6] The third metal particles are an alloy containing iron and nickel. [1] - [5] The powder magnetic core according to any one of [1] to [5].

[0013] [7] The first metal particles are spherical in shape; The second metal particles are spherical in shape, The shape of the third metal particles is different from the shape of the first metal particles and the shape of the second metal particles. [1] - [6] The powder magnetic core according to any one of [1] to [6].

[0014] [8] The first metal particles and the second metal particles are each manufactured by a gas atomization method; The third metal particles are manufactured by a water atomization method. [1] - [7] The powder magnetic core according to any one of [1] to [7]. [Effects of the Invention]

[0015] According to one aspect of the present invention, there is provided a powder magnetic core with reduced core loss. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1(a) is a schematic perspective view of one specific example of a powder magnetic core, and FIG. 1(b) is a schematic view showing an arbitrary cross section (partial cross section) of the powder magnetic core shown in FIG. 1(a). DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings, like elements are designated by like reference numerals. The present invention is not limited to the following embodiments.

[0018] Fig. 1(a) is a schematic perspective view of one specific example of a powder magnetic core 1. The powder magnetic core 1 shown in Fig. 1(a) has a ring shape, but the shape of the powder magnetic core 1 is not limited thereto. The shape of the powder magnetic core 1 may be changed as appropriate depending on the application of the powder magnetic core 1. Fig. 1(b) shows an arbitrary cross section (partial cross section 1cs) of the powder magnetic core 1.

[0019] As shown in FIG. 1(b), the powder core 1 includes a plurality of metal grains 2 and an oxide 3 containing silicon (Si). In the present disclosure, the oxide containing silicon is referred to as "Si oxide." The powder core 1 may be composed only of the plurality of metal grains 2 and the Si oxide 3. As long as iron loss is suppressed, the powder core 1 may further include other components in addition to the plurality of metal grains 2 and the Si oxide 3.

[0020] Si oxide 3 is present between the multiple metal grains 2. However, one or more microscopic voids may be formed between the multiple metal grains 2. In other words, one or more microscopic voids may be present inside the powder core 1. Some or all of the multiple metal grains 2 are covered with Si oxide 3. Part or all of the surface of any one metal grain 2 may be covered with Si oxide 3. Because Si oxide 3 is electrically insulating, the multiple metal grains 2 in the powder core 1 are insulated from each other by Si oxide 3. As a result, iron loss (especially eddy current loss) of the powder core 1 is suppressed. Furthermore, because Si oxide 3 bonds the multiple metal grains 2 to each other in the powder core 1, the powder core 1 is likely to be densified, the shape retention of the powder core 1 is improved, and the powder core 1 is likely to have a high bulk density and high mechanical strength. For example, the Si oxide 3 may be silicon dioxide (SiO2). For example, the Si oxide 3 may be an oxide containing a siloxane bond represented as Si-O-Si. The Si oxide 3 may contain elements other than silicon and oxygen. For example, the Si oxide 3 may contain an element (e.g., carbon) derived from silicone, which is a raw material (precursor) of the Si oxide 3. The proportion (relative mass) of the Si oxide 3 relative to 100 parts by mass of the metal grains 2 may be 0.05 parts by mass or more and 1.00 parts by mass or less. The higher the proportion of the Si oxide 3, the more likely it is that the shape retention (mechanical strength) of the powder magnetic core 1 will improve. The lower the proportion of the Si oxide 3, the more likely it is that the magnetic flux density and magnetic permeability of the powder magnetic core 1 will increase. When the proportion of the Si oxide 3 is within the above range, the powder magnetic core 1 will easily achieve both shape retention and soft magnetic properties (high magnetic flux density, high magnetic permeability, and low coercivity).

[0021] The plurality of metal grains 2 in the dust core 1 are two or more types of soft magnetic grains selected from the group consisting of a plurality of first metal grains g1, a plurality of second metal grains g2, and a plurality of third metal grains g3. For example, the plurality of metal grains 2 in the powder core 1 may include all of the first metal grains g1, the second metal grains g2, and the third metal grains g3. The plurality of metal grains 2 in the powder core 1 may consist only of the first metal grains g1, the second metal grains g2, and the third metal grains g3. The powder core 1 may further include other metal grains having a composition different from that of the first metal grains g1, the second metal grains g2, and the third metal grains g3. For example, the metal grains 2 in the powder core 1 may consist only of first metal grains g1 and second metal grains g2. For example, the metal grains 2 in the powder core 1 may consist only of second metal grains g2 and third metal grains g3. For example, the metal grains 2 in the powder core 1 may consist only of first metal grains g1 and third metal grains g3.

[0022] When the plurality of metal grains 2 in the powder magnetic core 1 includes a plurality of first metal grains g1, the composition of all of the first metal grains g1 in the powder magnetic core 1 may be substantially or completely uniform (identical). When the plurality of metal grains 2 in the powder magnetic core 1 include a plurality of second metal grains g2, the composition of all the second metal grains g2 in the powder magnetic core 1 may be substantially or completely uniform (identical). When the plurality of metal grains 2 in the powder magnetic core 1 include a plurality of third metal grains g3, the composition of all the third metal grains g3 in the powder magnetic core 1 may be substantially or completely uniform (identical).

[0023] The first metal particles g1, the second metal particles g2, and the third metal particles g3 have different compositions. The first metal particles g1 and the second metal particles g2 are each an alloy containing iron (Fe) and silicon (Si). The third metal particles g3 are pure iron or an alloy containing iron. The multiple third metal particles g3 may include both one or more metal particles made of pure iron and one or more metal particles made of an alloy containing iron. The silicon content in the first metal particles g1 is expressed as S1% by mass. The silicon content in the second metal particles g2 is expressed as S2% by mass. The silicon content in the third metal particles g3 is expressed as S3% by mass.

[0024] S1, S2, and S3 satisfy the relationship S1>S2>S3≧0. The inequality S1>S2>S3≧0 means that the multiple metal grains 2 in the powder magnetic core 1 are two or more types of soft magnetic grains that differ in their silicon content. As described above, the two or more types of soft magnetic grains that differ in their silicon content refer to two or more types of soft magnetic grains selected from the group consisting of multiple first metal grains g1, multiple second metal grains g2, and multiple third metal grains g3. If all metal grains in a powder magnetic core have the same composition, the iron loss of the powder magnetic core tends to decrease as the silicon content (unit: mass %) in the metal grains increases. However, the hardness of the metal grains also tends to increase as the silicon content in the metal grains increases. As the hardness of the metal grains increases, the metal grains become less likely to deform and be compressed during the powder magnetic core manufacturing process (the molding process described below). As a result, the shape retention of the powder magnetic core deteriorates. In other words, the higher the silicon content in the metal grains, the more difficult it is for the powder magnetic core to maintain its shape and the more susceptible the powder magnetic core is to break. For these reasons, it is difficult for conventional powder magnetic cores containing multiple metal grains containing silicon to achieve both low iron loss and sufficient shape retention (mechanical strength). In contrast, the powder magnetic core 1 according to this embodiment includes two or more types of soft magnetic particles that differ in their silicon content. Of the two or more types of soft magnetic particles, those with the highest silicon content reduce the iron loss of the powder magnetic core 1. Meanwhile, of the two or more types of soft magnetic particles, those with the lowest silicon content have lower hardness than the other soft magnetic particles. In other words, the soft magnetic particles with the lowest silicon content are softer than the other soft magnetic particles, and therefore more easily deformed and compressed during the manufacturing process (compacting process) of the powder magnetic core 1. Therefore, the soft magnetic particles with the lowest silicon content improve the shape retention (mechanical strength) of the powder magnetic core 1. For these reasons, the powder magnetic core 1 according to this embodiment can achieve both low iron loss and sufficient shape retention (mechanical strength).

[0025] The first metal particles g1 are superior to the second metal particles g2 in that they can easily suppress the iron loss of the powder core 1. Because the iron loss of the powder core 1 can be easily suppressed, the silicon content (S1) of the first metal particles g1 may be 3.5% by mass or more and 7.5% by mass or less. Iron may be the main component of the first metal particles g1. That is, the iron content (unit: mass%) of all elements in the first metal particles g1 may be the largest. For example, the iron content of the first metal particles g1 may be 92.5% by mass or more and 96.5% by mass or less. As long as S1, S2, and S3 satisfy S1>S2>S3≧0, the composition of the multiple first metal particles g1 in the powder core 1 may be non-uniform.

[0026] The silicon content (S2) in the second metal particles g2 may be 0.5% by mass or more and less than 3.5% by mass, because this facilitates suppression of iron loss in the powder magnetic core 1 and an increase in the magnetic flux density of the powder magnetic core 1. Iron may be the main component of the second metal particles g2. That is, the iron content (unit: mass%) of all elements in the second metal particles g2 may be the largest. For example, the iron content in the second metal particles g2 may be more than 96.5% by mass and 99.5% by mass or less. As long as S1, S2, and S3 satisfy S1>S2>S3≧0, the composition of the multiple second metal particles g2 in the powder magnetic core 1 may be non-uniform.

[0027] As long as S1, S2, and S3 satisfy the relationship S1>S2>S3≧0, the silicon content (S3) in the third metal particles g3 is not limited. The third metal particles g3 may contain silicon, but the third metal particles g3 do not need to contain silicon. That is, the silicon content (S3) in the third metal particles g3 may be zero mass%. Iron may be the main component of the third metal particles g3. That is, the iron content (unit: mass%) of all elements in the third metal particles g3 may be the largest. As long as S1, S2, and S3 satisfy the relationship S1>S2>S3≧0, the composition of the multiple third metal particles g3 in the powder magnetic core 1 may be non-uniform.

[0028] The proportion of the first metal particles g1 in all the metal particles 2 is expressed as M1 mass %, the proportion of the second metal particles g2 in all the metal particles 2 is expressed as M2 mass %, and the proportion of the third metal particles g3 in all the metal particles 2 is expressed as M3 mass %. (M1+M2) is greater than M3. In other words, M1, M2, and M3 satisfy (M1+M2)>M3≧0. Furthermore, M1, M2, and M3 may satisfy M1+M2+M3=100. In other words, the total mass of the multiple first metal particles g1, the multiple second metal particles g2, and the multiple third metal particles g3 may be 100% by mass. As the silicon content in metal grains 2 decreases, the iron loss of the powder magnetic core tends to increase. Furthermore, among first metal grains g1, second metal grains g2, and third metal grains g3, the silicon content (S3) in third metal grains g3 is the smallest. Therefore, if (M1 + M2) is less than or equal to M3, the proportion (M3) of third metal grains g3, which has the lowest silicon content, becomes too high, resulting in a silicon deficiency in powder magnetic core 1 and making it difficult to suppress iron loss. On the other hand, if (M1 + M2) is greater than M3, the silicon deficiency in powder magnetic core 1 is sufficient, allowing powder magnetic core 1 to achieve both low iron loss and sufficient shape retention (mechanical strength).

[0029] The plurality of metal grains 2 in the powder core 1 preferably include all of the first metal grains g1, second metal grains g2, and third metal grains g3 because this makes it easier to achieve both low iron loss and sufficient shape retention (mechanical strength) in the powder core 1. For the same reason, when the plurality of metal grains 2 in the powder core 1 include all of the first metal grains g1, second metal grains g2, and third metal grains g3, the proportion of the first metal grains g1 (M1) may be 5% by mass or more and 90% by mass or less, the proportion of the second metal grains g2 (M2) may be 5% by mass or more and 90% by mass or less, and the proportion of the third metal grains g3 (M3) may be 5% by mass or more and less than 50% by mass.

[0030] When the multiple metal grains 2 in the powder magnetic core 1 consist only of first metal grains g1 and second metal grains g2, the proportion of the first metal grains g1 (M1) may be 5 mass% or more and 95 mass% or less, and the proportion of the second metal grains g2 (M2) may be 5 mass% or more and 95 mass% or less.

[0031] When the multiple metal grains 2 in the powder magnetic core 1 consist only of second metal grains g2 and third metal grains g3, the proportion of the second metal grains g2 (M2) may be greater than 50 mass% and less than 95 mass%, and the proportion of the third metal grains g3 (M3) may be greater than 5 mass% and less than 50 mass%.

[0032] When the multiple metal grains 2 in the powder magnetic core 1 consist only of first metal grains g1 and third metal grains g3, the proportion of the first metal grains g1 (M1) may be greater than 50 mass% and less than 95 mass%, and the proportion of the third metal grains g3 (M3) may be greater than 5 mass% and less than 50 mass%.

[0033] Each of the first metal particles g1, the second metal particles g2, and the third metal particles g3 may further include an element other than iron and silicon. For example, the element other than iron and silicon may be at least one element selected from the group consisting of a base metal element, a noble metal element, a transition metal element, a rare earth element, and a non-metal element. For example, each of the first metal particles g1, the second metal particles g2, and the third metal particles g3 may further include, as an element other than iron and silicon, at least one metal element selected from the group consisting of cobalt (Co), nickel (Ni), copper (Cu), titanium (Ti), manganese (Mn), zinc (Zn), aluminum (Al), tin (Sn), arsenic (As), antimony (Sb), chromium (Cr), beryllium (Be), barium (Ba), strontium (Sr), lead (Pb), bismuth (Bi), silver (Ag), niobium (Nb), hafnium (Hf), zirconium (Zr), tantalum (Ta), molybdenum (Mo), tungsten (W), and vanadium (V). For example, each of the first metal particles g1, the second metal particles g2, and the third metal particles g3 may further contain at least one non-metallic element selected from the group consisting of oxygen (O), carbon (C), nitrogen (N), sulfur (S), phosphorus (P), and boron (B) as an element other than iron and silicon.

[0034] For example, the third metal particles g3 may be an alloy containing iron and nickel. Alloys containing nickel tend to be softer than alloys containing silicon but not nickel. Therefore, the third metal particles g3, which are alloys containing iron and nickel, are easily deformed and compressed during the manufacturing process (compacting process) of the powder magnetic core 1. As a result, the shape retention (mechanical strength) of the powder magnetic core 1 is likely to be improved. Furthermore, the nickel in the third metal particles g3 is likely to reduce the iron loss (particularly hysteresis loss) and coercive force of the powder magnetic core 1. Because the above-mentioned effects attributable to the alloy containing iron and nickel are easily obtained, the nickel content in the third metal particles g3 may be 10% by mass or more and 80% by mass or less.

[0035] The shape of the first metal particles g1 (first powder described later) may be approximately or completely spherical. For example, the sphericity of the first metal particles g1 (first powder) may be 0.7 or more and 1.0 or less. For example, the cross-sectional area of ​​any one metal particle 2 may be represented as S, and the length of the periphery (outline) of the cross section of any one metal particle 2 may be represented as L. In the present invention, the sphericity of any one metal particle 2 is 4πS / L. 2 For example, S and L of any one metal grain 2 may be measured on a cross section of the powder core 1 using a scanning electron microscope (SEM). The shape of the second metal grains g2 (second powder, described later) may also be approximately or completely spherical. For example, the sphericity of the second metal grains g2 (second powder) may also be 0.7 or more and 1.0 or less. Because multiple spherical metal grains are easily compressed during the manufacturing process (molding step) of the powder core 1, the magnetic flux density and bulk density of the powder core 1 containing multiple spherical metal grains are likely to increase. The shape of the third metal particles g3 (third powder described below) may be different from the shape (spherical) of each of the first metal particles g1 and the second metal particles g2. For example, the shape of the third metal particles g3 (third powder) may be irregular, uneven, or irregular. When the shape of the third metal particles g3 (third powder) is different from a sphere, or when the shape of the third metal particles g3 (third powder) is uneven or irregular, the third metal particles g3 are more likely to fill between the other multiple metal particles 2 (multiple spherical metal particles 2), making the powder core 1 more dense and improving the shape retention (mechanical strength) of the powder core 1. In other words, the shape retention of a powder core 1 including not only multiple spherical metal particles 2 but also third metal particles g3 having a shape other than a sphere is superior to the shape retention of a powder core 1 including only spherical metal particles 2 as the multiple metal particles 2.

[0036] The first metal particles g1 (first powder described below) may be produced by gas atomization. The second metal particles g2 (second powder described below) may also be produced by gas atomization. Gas atomization is a method of forming multiple tiny droplets from molten metal by spraying a high-pressure inert gas as a cooling medium onto the molten metal. The multiple tiny droplets become multiple metal particles upon cooling. Metal particles produced by gas atomization tend to be spherical. Furthermore, the impurity content (e.g., oxygen) in metal particles produced by gas atomization tends to be lower than the impurity content in metal particles produced by water atomization. As the impurity content (e.g., oxygen) in the metal particles 2 contained in the powder core 1 decreases, the iron loss of the powder core 1 also tends to decrease. The third metal particles g3 (the third powder described below) may be produced by water atomization. Water atomization is a method of forming multiple tiny droplets from molten metal by spraying high-pressure water as a cooling medium onto the molten metal. The multiple tiny droplets become multiple metal particles upon cooling. The shape of the metal particles produced by water atomization tends to be different from a sphere (distorted shape) and tends to be uneven or irregular. Water atomization implies gas-water atomization, which uses a mixture of water and an inert gas as a cooling medium. Except for the cooling medium, gas-water atomization is the same as water atomization.

[0037] The first metal particles g1, the second metal particles g2, and the third metal particles g3 may each be crystalline. For example, the first metal particles g1, the second metal particles g2, and the third metal particles g3 may each include nanocrystals. The first metal particles g1, the second metal particles g2, and the third metal particles g3 may each be amorphous. For example, the first metal particles g1, the second metal particles g2, and the third metal particles g3 may each include metallic glass. When the first metal particles g1, the second metal particles g2, and the third metal particles g3 each include an amorphous metal, the iron loss of the powder magnetic core 1 is likely to be suppressed. The first metal particles g1, the second metal particles g2, and the third metal particles g3 may each be a mixture of a crystalline metal and an amorphous metal.

[0038] The applications of the powder magnetic core 1 are not limited, and the powder magnetic core 1 may be used in various electric or electronic devices. For example, the powder magnetic core 1 may be used in reactors, stators of motors (e.g., axial gap motors), motor yokes, inductors, power supply modules, transformers, thyristor valves, noise filters (e.g., EMI filters), choke coils, solenoid cores, and the like.

[0039] For example, the composition and structure of the powder core 1 may be analyzed and identified by one or more analytical methods or devices selected from the group consisting of X-ray fluorescence (XRF), inductively coupled plasma (ICP) emission spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), electron probe microanalyzer (EPMA), electron diffraction (ED), mass spectrometry (MS), scanning electron microscope (SEM), transmission electron microscope (TEM), and scanning transmission electron microscope (STEM). For example, the internal composition and structure of the powder core 1 may be analyzed and identified in any cross section of the powder core 1.

[0040] (Method of manufacturing powder magnetic core) The raw materials of the powder magnetic core 1 include at least metal powder and silicone.

[0041] The metal powder is two or more types of soft magnetic powder selected from the group consisting of a first powder, a second powder, and a third powder. The first powder corresponds to the plurality of first metal particles g1 described above. The composition, shape, and particle size of the first powder may be substantially or completely the same as the composition, shape, and particle size of the first metal particles g1. The second powder corresponds to the plurality of second metal particles g2 described above. The composition, shape, and particle size of the second powder may be substantially or completely the same as the composition, shape, and particle size of the second metal particles g2. The third powder corresponds to the plurality of third metal particles g3 described above. The composition, shape, and particle size of the third powder may be substantially or completely the same as the composition, shape, and particle size of the third metal particles g3.

[0042] The silicon content (unit: mass %) in the first powder is the same as S1 (i.e., the silicon content in the first metal particles g1) described above. The silicon content in the second powder is the same as S2 (i.e., the silicon content in the second metal particles g2) described above. The silicon content in the third powder is the same as S3 (i.e., the silicon content in the third metal particles g3) described above.

[0043] The proportion (unit: mass %) of the first powder in the entire metal powder is the same as M1 described above (i.e., the proportion of first metal particles g1 in all metal particles 2). The proportion (unit: mass %) of the second powder in the entire metal powder is the same as M2 described above (i.e., the proportion of second metal particles g2 in all metal particles 2). The proportion (unit: mass %) of the third powder in the entire metal powder is the same as M3 described above (i.e., the proportion of third metal particles g3 in all metal particles 2).

[0044] For example, the particle size (e.g., median diameter D50) of the first powder (or first metal particles g1) may be 5 μm or more and 200 μm or less. For example, the particle size (e.g., median diameter D50) of the second powder (or second metal particles g2) may be 5 μm or more and 200 μm or less. For example, the particle size (e.g., median diameter D50) of the third powder (or third metal particles g3) may be 5 μm or more and 200 μm or less. The particle size (e.g., median diameter D50) of each of the first powder, second powder, and third powder may be determined based on the particle size distribution of each metal particle based on the number of each metal particle. For example, the particle size distribution of each metal powder may be measured using a laser diffraction particle size distribution analyzer. Before starting production of the powder magnetic core 1, the particle size distribution of each of the first powder, second powder, and third powder may be measured in advance.

[0045] Before the metal powder is mixed with the silicone, the metal powder may be annealed. As a result of annealing the metal powder, the strain (internal stress) within each metal particle constituting the metal powder is relieved, the metal particles become soft, and the brittleness of each metal particle is reduced. Therefore, the annealed metal powder is easily deformed and compressed in the molding process described below, and the shape retention (mechanical strength) of the powder core 1 is likely to be improved. For example, the temperature of the metal powder during annealing may be 750°C or higher and 900°C or lower. For example, the annealing time may be several hours. The annealing may be performed in a non-oxidizing atmosphere (e.g., vacuum). If the metal powder agglomerates due to annealing, the agglomerated metal powder may be passed through a sieve to return it to a powder state.

[0046] Silicone is an organosilicon compound such as silanes. Silicone may be a synthetic polymer (silicone resin or organopolysiloxane) containing a siloxane bond (represented as Si-O-Si) as the main backbone of its molecular structure. Silicone may also be a monomer of the synthetic polymer. Silicone is a precursor of the Si oxide 3 in the powder core 1. In other words, the Si oxide 3 in the powder core 1 is derived from silicone. For example, the silicone may be at least one selected from the group consisting of silyl alcohol, alkyl silane, epoxy silane, mercapto silane, amino silane, ureido silane, acid anhydride silane, methacryl silane, and vinyl silane.

[0047] The proportion of silicone (relative mass) per 100 parts by mass of metal powder may be 0.05 parts by mass or more and 1.00 parts by mass or less. The higher the proportion of silicone, the more likely it is that the shape retention (mechanical strength) of the powder core 1 will improve. The lower the proportion of silicone, the more likely it is that the magnetic flux density and magnetic permeability of the powder core 1 will increase. When the proportion of silicone is within the above range, the powder core 1 will easily achieve both shape retention and soft magnetic properties (high magnetic flux density, high magnetic permeability, low coercivity, etc.).

[0048] A metal powder is mixed with a solvent containing silicone to prepare a slurry. The silicone in the slurry coats the surface of each metal particle that constitutes the metal powder. By removing the solvent from the slurry, a compound powder consisting of multiple metal particles coated with silicone is obtained. For example, the solvent may be water or an organic solvent. By removing the solvent, oxidation (rust) of each metal particle in the compound powder is suppressed.

[0049] The silicone covering the surface of each metal particle is hardened by heating the compound powder at the silicone hardening temperature. For example, the silicone hardening temperature may be 150°C or higher and 200°C or lower. For example, the time required for the silicone to harden may be several hours. For example, the hardening of the silicone may involve the synthesis of polymers by polymerization (dehydration condensation) of monomers and the bonding between multiple polymers. If the compound powder aggregates as the silicone hardens, the agglomerated compound powder may be passed through a sieve to return it to a powder state.

[0050] After the silicone in the compound powder has hardened, a molding process is carried out. In the molding process, a compact having a desired shape and dimensions is formed from the compound powder by compressing the compound powder using a mold. For example, the pressure (molding pressure) exerted by the mold on the compound powder is 10 t / cm. 2 More than 20t / cm 2 It may be the following:

[0051] The compact is annealed to form the powder magnetic core 1. For example, the temperature of the compact during annealing may be 650°C or higher and 750°C or lower. For example, the time required for annealing the compact may be several tens of minutes. The annealing of the compact may be carried out in an inert gas.

[0052] Annealing the compact eliminates distortion (internal stress) in the compact. As a result, the shape retention (mechanical strength) of the powder magnetic core 1 is improved. Furthermore, annealing the compact forms Si oxide 3 from the cured silicone in the compact, and the multiple metal grains 2 in the compact are firmly bonded to each other by Si oxide 3. As a result, the shape retention (mechanical strength) of the powder magnetic core 1 is improved. If hydrocarbon groups derived from silicone remain in the compact, the hydrocarbon groups may be thermally decomposed during annealing of the compact. In other words, elements other than silicon and oxygen among the multiple elements derived from silicone may be removed from the compact by annealing. If a conventional thermosetting resin (organic binder other than silicone), such as an epoxy resin or bismaleimide, were used instead of silicone as the raw material for powder core 1, the thermosetting resin (organic binder) would be burned away during annealing of the compact. As a result, it would be difficult to achieve sufficient shape retention (mechanical strength) for powder core 1. In other words, it would be difficult to manufacture powder core 1 using an organic binder other than silicone.

[0053] The above-described steps before the molding step may be performed separately for the first powder, the second powder, and the third powder, i.e., three types of compound powders made from the first powder, the second powder, and the third powder, respectively, may be mixed in the molding step. Before mixing with silicone, two or more types of soft magnetic powders selected from the group consisting of the first powder, the second powder, and the third powder may be annealed all at once, that is, a mixture of two or more types of soft magnetic powders selected from the group consisting of the first powder, the second powder, and the third powder may be annealed.

[0054] The present invention is not necessarily limited to the above-described embodiments. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the present invention. [Example]

[0055] The present invention will be described in detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0056] Example 1 The first powder, second powder, and third powder were the only metal powders (soft magnetic powders) used in producing the powder core of Example 1. As described above, the first powder corresponds to the multiple first metal particles in the powder core, the second powder corresponds to the multiple second metal particles in the powder core, and the third powder corresponds to the multiple third metal particles in the powder core. The first powder was an alloy made of Fe and Si. The main component of the first powder was Fe. The content of Si (S1) in the first powder was 6.5 mass%. The median diameter D50 of the first powder was 80 μm. The first powder was produced by gas atomization. The shape of the first powder was spherical. The proportion (M1) of the first powder in the entire metal powder is shown in Table 1 below. The second powder was an alloy consisting of Fe and Si. The main component of the second powder was Fe. The content of Si (S2) in the second powder was 3.0 mass%. The median diameter D50 of the second powder was 77 μm. The second powder was produced by gas atomization. The shape of the second powder was spherical. The proportion (M2) of the second powder in the entire metal powder is shown in Table 1 below. The third powder was an alloy consisting of Fe and Ni. The main component of the third powder was Fe. The content of Si in the third powder (S3) was zero mass%. In other words, the third powder did not contain Si. The content of Ni in the third powder was 50 mass%. The median diameter D50 of the third powder was 85 μm. The third powder was produced by water atomization. The shape of the third powder was different from a sphere. The proportion of the third powder in the entire metal powder (M3) is shown in Table 1 below.

[0057] Annealing was previously carried out separately for each of the first, second, and third powders. For annealing the first powder, the first powder was heated in a vacuum at 900°C for 3 hours. For annealing the second powder, the second powder was heated in vacuum at 850°C for 3 hours. For annealing the third powder, the third powder was heated in vacuum at 900°C for 3 hours.

[0058] After annealing, the first powder, the second powder, and the third powder were each individually mixed with a solvent containing silicone to prepare three types of slurries. Silyl alcohol was used as the silicone, and ethyl alcohol was used as the solvent. The ratio of silicone to 100 parts by mass of each powder was 0.1 parts by mass.

[0059] Each slurry was transferred onto an aluminum vat, and the slurries on the vat were heated at 70°C to remove the solvent from the slurry, and the surfaces of the metal particles constituting each of the first, second, and third powders were coated with silicone.

[0060] After the surfaces of the metal particles constituting the first, second, and third powders were coated with silicone, the powders were heated at 180°C for 2 hours to harden the silicone coating on the surfaces of the metal particles. The powders, which had aggregated as the silicone hardened, were passed through a sieve to return them to a powder state. The sieve had openings of 180 μm.

[0061] After all the steps described above, a compacting step was carried out. In the compacting step, a mixture of the first powder, the second powder, and the third powder was compressed in a mold to form a ring-shaped (cylindrical) compact. The compacting pressure was 15 t / cm. 2 The inner diameter of the molded body was 20 mm, the outer diameter of the molded body was 30 mm, and the length of the molded body was 5 mm.

[0062] The compact was annealed to complete the powder magnetic core. The temperature of the compact during annealing was 650°C. The annealing time for the compact was 30 minutes. The annealing of the compact was carried out in an inert gas.

[0063] <Iron loss measurement> A measurement sample consisting of a powder magnetic core, a primary coil, and a secondary coil was obtained by winding a copper wire around the powder magnetic core. The primary coil had 200 turns, and the secondary coil had 20 turns. The measurement sample was used to measure the iron loss of the powder magnetic core. The iron loss was measured using a BH analyzer (SY-8218) manufactured by Iwasaki Electric Co., Ltd. TM ) was used. The maximum magnetic flux density of the powder magnetic core in measuring the iron loss was 1 T (tesla). The AC frequency in measuring the iron loss was 2 kHz. The iron loss IL is approximately or completely equal to the sum of the hysteresis loss HL and the eddy current loss ECL. The iron loss IL (unit: W / kg), hysteresis loss HL, and eddy current loss ECL in Example 1 are shown in Table 1 below. The iron loss IL is preferably 160 W / kg or less.

[0064] <Measurement of various magnetic properties> The magnetic flux density, relative permeability, and coercive force of the powder magnetic core were measured using the above measurement samples. A BH curve tracer manufactured by Riken Denshi Co., Ltd. was used to measure the various magnetic properties. The direct current used in measuring the various magnetic properties was 10,000 A / m. The maximum magnetic flux density Bm (unit: T), relative permeability (no unit), and coercive force (unit: A / m) of Example 1 are shown in Table 1 below.

[0065] <Measurement of bulk density> The mass of the powder core itself was measured. The volume of the powder core itself was calculated from the dimensions of the powder core. The bulk density of the powder core was calculated by dividing the mass of the powder core by the volume of the powder core. The bulk density (unit: g / cm) of Example 1 was 3 ) are shown in Table 1 below.

[0066] (Examples 2 to 9 and Comparative Examples 1 to 4) M1, M2, and M3 for each of Examples 2 to 9 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0067] In Example 2, the second powders used were Powder A and Powder B. In Example 2, the third powder was not used. Powder A was the same as the second powder in Example 1. The proportion of Powder A in the entire metal powder in Example 2 was 40 mass %. Powder B was an alloy consisting of Fe and Si. The main component of Powder B was Fe. The content of Si (S2) in Powder B was 3.0 mass%. The median diameter D50 of Powder B was 90 μm. Powder B was produced by a water atomization method. The shape of Powder B was not spherical. The proportion of Powder B in the entire metal powder was 20 mass%. In the case of Example 2, the sum of the proportion of powder A (40 mass%) and the proportion of powder B (20 mass%) corresponds to the proportion M2 of the second powder (60 mass%).

[0068] In Example 3, the second powders used were Powder A and Powder C. In Example 3, the third powder was not used. As described above, Powder A was the same as the second powder in Example 1. The proportion of Powder A in the entire metal powder in Example 3 was 40 mass %. Powder C was an alloy consisting of Fe and Si. The main component of Powder C was Fe. The content of Si (S2) in Powder B was 3.0 mass%. The median diameter D50 of Powder C was 54 μm. Powder C was produced by a gas-water atomization method. The shape of Powder C was not spherical. The proportion of Powder C in the entire metal powder was 20 mass%. In the case of Example 3, the sum of the proportion of powder A (40 mass%) and the proportion of powder C (20 mass%) corresponds to the proportion M2 of the second powder (60 mass%).

[0069] The third powder was the only metal powder (soft magnetic powder) used in producing the dust core of Comparative Example 1. The third powder of Comparative Example 1 was pure iron. The median diameter D50 of the third powder of Comparative Example 1 was 56 μm. Silicone was not used in the production of the powder magnetic core of Comparative Example 1. That is, in the molding step of Comparative Example 1, a compact was formed solely from the third powder, which had not been processed at all.

[0070] The second powder was the only metal powder (soft magnetic powder) used in producing the powder magnetic core of Comparative Example 2. The second powder of Comparative Example 2 was the same as the second powder of Example 1. In the case of Comparative Example 2, the ratio of silicone to 100 parts by mass of the second powder was 0.3 parts by mass.

[0071] The first powder was the only metal powder (soft magnetic powder) used in the production of the dust core of Comparative Example 3. The first powder of Comparative Example 3 was the same as the first powder of Example 1.

[0072] The third powder was the only metal powder (soft magnetic powder) used in the production of the dust core of Comparative Example 4. The third powder of Comparative Example 4 was the same as the third powder of Example 1.

[0073] Except for the above-mentioned points, attempts were made to manufacture the powder magnetic cores of each of Examples 2 to 9 and Comparative Examples 1 to 4 using the same method as Example 1. The powder magnetic cores of Examples 2 to 9 and Comparative Examples 1, 2, and 4 were completed. However, in the manufacture of the powder magnetic core of Comparative Example 3, the shape retention (mechanical strength) of the compact and the powder magnetic core was not obtained. In other words, the powder magnetic core of Comparative Example 3 could not be manufactured.

[0074] Measurements were carried out using the powder magnetic cores of Examples 2 to 9 and Comparative Examples 1, 2, and 4 in the same manner as in Example 1. The results of the measurements for Examples 2 to 9 and Comparative Examples 1, 2, and 4 are shown in Table 1 below.

[0075] [Table 1] [Industrial Applicability]

[0076] For example, a powder magnetic core according to one aspect of the present invention may be used in the stator of an axial gap motor. [Explanation of symbols]

[0077] 1...sintered powder core, 1cs...partial cross section of the powder core, 2...metal grains, 3...silicon-containing oxide, g1...first metal grains, g2...second metal grains, g3...third metal grains.

Claims

1. A plurality of metal particles and an oxide containing silicon, a part or all of the plurality of metal particles are covered with the oxide, the plurality of metal particles are two or more types of soft magnetic particles selected from the group consisting of a plurality of first metal particles, a plurality of second metal particles, and a plurality of third metal particles; the first metal particles and the second metal particles are each an alloy containing iron and silicon, the third metal particles are pure iron or an alloy containing iron, The silicon content in the first metal particles is expressed as S1% by mass, The silicon content in the second metal particles is expressed as S2% by mass, The silicon content in the third metal particles is expressed as S3% by mass, S1, S2, and S3 satisfy S1>S2>S3≧0, The ratio of the first metal particles to all the metal particles is expressed as M% by mass, The ratio of the second metal particles to all the metal particles is expressed as M2 mass%, The ratio of the third metal particles to all the metal particles is represented as M3 mass%, (M1+M2) is greater than M3, Powder magnetic core.

2. The plurality of metal particles include all of the first metal particles, the second metal particles, and the third metal particles. The powder magnetic core according to claim 1 .

3. The plurality of metal particles are composed only of the first metal particles and the second metal particles. The powder magnetic core according to claim 1 .

4. the plurality of metal particles are composed only of the second metal particles and the third metal particles, The powder magnetic core according to claim 1 .

5. the plurality of metal particles are composed only of the first metal particles and the third metal particles, The powder magnetic core according to claim 1 .

6. the third metal particles are an alloy containing iron and nickel; The powder magnetic core according to claim 1 .

7. The first metal particles are spherical in shape, The second metal particles are spherical in shape, The shape of the third metal particles is different from the shape of the first metal particles and the shape of the second metal particles. The powder magnetic core according to any one of claims 1 to 6.

8. the first metal particles and the second metal particles are each manufactured by a gas atomization method; The third metal particles are manufactured by a water atomization method. The powder magnetic core according to any one of claims 1 to 6.

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