Powder magnetic core

Abstract

To provide a powder magnetic core that can achieve both high strength and low iron loss.SOLUTION: A powder magnetic core according to the present invention includes a plurality of soft magnetic particles with an insulating coating formed on the surface thereof and an intergranular layer of low-melting-point glass with a Na content of 3 at% or less between the soft magnetic particles. The soft magnetic powder is preferably pure iron powder or iron-based soft magnetic alloy powder. The insulating coating is preferably made of silicone resin or SiO2 derived from silicone resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a powder magnetic core that can achieve both high strength and low iron loss. [Background technology]

[0002] Powder magnetic cores used in reactors and motors are required to have low iron loss, and alloy materials such as sendust are used as powder magnetic core materials with low iron loss. These alloy materials are hard and difficult to plastically deform, so even if the powder of the alloy material is pressed to be molded, sufficient strength cannot be obtained. To compensate for the lack of strength, a method has been proposed in which low-melting-point glass is added to the powder of the alloy material and then compressed.

[0003] For example, Patent Document 1 below describes a technology in which a first coating layer of aluminum nitride is formed on the surface of a soft magnetic particle, and a second coating layer made of low-melting point glass having a softening point lower than the annealing temperature of the soft magnetic particle is formed. In addition, the following Patent Document 2 discloses a method for manufacturing a soft magnetic powder having an insulating coating and a magnetic annealing temperature of 100°C. End A technique is described in which glass frit having a low softening point is mixed with polyvinyl alcohol as a granulation binder in a specific ratio. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-058732 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-073447 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, soft magnetic particles for powder magnetic cores need to be coated with an insulating coating to suppress eddy current loss. A known method for forming an insulating coating is to form aluminum nitride on the surface of soft magnetic particles, as described in Patent Document 1. The insulating layer coated with aluminum nitride later suppresses the diffusion of components between the low-melting-point glass and the soft magnetic particles, thereby providing high resistivity and strength. However, to form the insulating layer, a long heat treatment of 500 hours at high temperatures of 1000-1200°C is required. Another known insulation method involves coating soft magnetic particles with silicone resin. However, because silicone resin insulating coatings have low heat resistance, the annealing temperature must be set low, and the low-melting-point glass used must also have a low softening point. However, when a powder magnetic core is formed using a low-melting-point glass with a softening point below 600°C, there is a problem in that the eddy current loss in the obtained powder magnetic core increases (worsens) in the high frequency range of 10 kHz to 100 kHz.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a powder magnetic core that can achieve both high strength and low iron loss. The present inventors have conducted extensive research into the cause of increased eddy current loss in the high frequency range when a powder magnetic core is formed using low-melting glass, and have found that the Na contained in the low-melting glass is related to eddy current loss in the high frequency range. Based on this finding, the present invention was completed. [Means for solving the problem]

[0007] (1) The powder magnetic core of the present invention is characterized by having a plurality of soft magnetic particles with an insulating coating formed on the surface thereof, and an intergranular layer of low-melting glass having an Na content of 3 at % or less between the soft magnetic particles. (2) In the dust core according to the present invention described in (1), the soft magnetic particles are preferably made of pure iron powder or iron-based soft magnetic powder. (3) In the dust core according to the present invention as set forth in (1) or (2), the insulating coating is preferably made of silicone resin or SiO2 derived from silicone resin. (4) In the dust core according to the present invention as set forth in (1) or (2), the low-melting glass preferably accounts for 1% by mass or more and 6% by mass or less of the amount of the soft magnetic particles. [Effects of the Invention]

[0008] According to the powder magnetic core of the present invention, it is possible to obtain a powder magnetic core that has high strength and low eddy current loss in the high frequency range. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of a powder magnetic core according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below. The dust core according to the present invention is obtained by mixing an insulating coated iron-based soft magnetic powder with a small amount of low-melting glass to prepare a mixed powder, molding this mixed powder into a desired shape, and annealing it at 600 to 700°C in an inert gas atmosphere.

[0011] The soft magnetic powder can be a mixture of one or more of the following: pure iron powder, FeSi alloy powder, FeNi alloy powder, FeSiAl alloy powder (Sendust powder), and iron-based amorphous metal powder. Most soft magnetic powders, except for pure iron powder, are hard and difficult to deform, so it is difficult to obtain a compact with the required strength even if the soft magnetic powder is compacted as is, or if insulating powder covered with an insulating film is compacted as is. For example, the sendust powder may be sendust powder having a composition of Fe-9.5%Si-5.5%Al by mass. For example, the iron-based amorphous metal powder may be Fe-Cr-Si-BC amorphous alloy powder. For example, the Fe-Si-Al alloy powder may contain 7-11% by mass of Si and 3-11% by mass of Al. For example, the Fe-Si alloy powder may contain 4.5% by mass or more and 7% by mass or less of Si. In addition, FeSi alloy powder, FeNi alloy powder, FeSiAl alloy powder (Sendust powder), and iron-based amorphous metal powder are known to have various compositions, and therefore, the compositions are not limited to those described above, and any known compositions may be used.

[0012] Silicone resin can be used for the insulating coating. Silicone resin is a resin with a siloxane bond (Si-O-Si) as its main skeleton. Methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, rubber-based, etc. can be used as the silicone resin. Among these, it is preferable to use silicone resin composed of methyl groups and phenyl groups. These silicone resins can be mixed with a solvent. The amount of silicone resin added can be 3% by mass or less, for example, about 2% by mass, based on the magnetic alloy powder.

[0013] The powder core is made by adding 1.0 to 6.0 mass % of low-melting glass with a Na content limited to 3 at % or less to soft magnetic powder and uniformly mixing them to form a mixed powder. The mixed powder is then placed in a mold and compacted under a molding pressure of 10 to 14 t / cm. 2 The powder core is obtained by molding the powder into a shape close to the desired shape at a pressure of about 1000 to 700°C for about 30 minutes. The obtained dust core has a plurality of soft magnetic particles formed by sintering soft magnetic powder having an insulating coating, and an intergranular layer formed by sintering low-melting glass provided so as to fill the spaces between the soft magnetic particles.

[0014] As the low-melting glass, glass that can be softened and deformed in the low temperature range of about 500 to 610°C can be used, and glass whose main components are B2O3, Al2O3, SiO2, etc. Among these components, glass whose main components are B2O3 and SiO2, glass whose main component is B2O3, glass whose main components are SiO2, Al2O3, and B2O3, and glass whose main components are SiO2 and B2O3 can be used.

[0015] If the low-melting glass used in this embodiment contains Na, the Na content must be 3 at% or less. If the amount of Na contained in the low-melting glass exceeds 3 at%, the eddy current loss of the powder magnetic core increases. The Na content is preferably 3 at% or less, but may be 0 at%. The amount of low-melting-point glass to be blended is preferably 1.0% by mass or more and 6.0% by mass or less relative to the soft magnetic powder. If the amount of low-melting-point glass to be blended is less than 1.0% by mass, the desired radial crushing strength for a powder magnetic core cannot be obtained. If the amount of low-melting-point glass to be blended exceeds 6.0% by mass, the proportion of soft magnetic particles in the powder magnetic core decreases, and the desired magnetic flux density for a powder magnetic core cannot be obtained.

[0016] A predetermined amount of low-melting glass is added to the insulating coating powder, and then the powder is inserted into a mold or other device, and a molding pressure of 10 to 14 t / cm is applied. 2 The material is pressed and molded to a shape close to the desired shape using a pressure of about 100%. After this, annealing in an inert gas atmosphere such as N2 gas atmosphere at 600 to 700°C for several tens of minutes to an hour (for example, about 30 minutes) can produce a powder magnetic core with the desired strength and low eddy current loss in the high frequency range. When soft magnetic powder is produced by a method of rapid cooling from a melt, such as atomization, the soft magnetic powder generally becomes a spherical powder. From the viewpoints of ease of putting the soft magnetic powder into a mold when producing a powder compact, compactability, etc., it is desirable to regulate the average particle size of the soft magnetic powder to a range of approximately 10 μm to 100 μm.

[0017] According to the manufacturing method described above, the low-melting glass is sufficiently wetted and spread between the soft magnetic particles by heating to the annealing temperature, and the strength of the final powder magnetic core is improved. Furthermore, since the low-melting glass used in this embodiment contains 3 at % or less of Na, the increase in eddy current loss due to the influence of Na can be suppressed in the powder magnetic core obtained after annealing, and therefore the eddy current loss in the high frequency range can be reduced in the obtained powder magnetic core.

[0018] 1 is an enlarged view of a main portion of a powder magnetic core 1 obtained by the manufacturing method described in this embodiment. An insulating coating 3 is formed so as to cover the outer periphery of soft magnetic particles 2 made of soft magnetic powder, forming insulating coated soft magnetic particles 4. A plurality of insulating coated soft magnetic particles 4 are aggregated and consolidated, forming intergranular layers 5 made of a sintered product of low-melting point glass so as to fill the spaces between adjacent insulating coated soft magnetic particles 4. The intergranular layer 5 is made of a fired product of low-melting glass with an Na content of 3 at % or less, and therefore, in combination with the presence of the insulating coating 3, insulates the soft magnetic particles 2 well. As a result, the obtained powder magnetic core 1 has high strength and small eddy current loss in the high frequency range. Therefore, it is possible to provide a powder magnetic core 1 that can exhibit a high saturation magnetic flux density and contributes to the miniaturization of magnetic devices. Furthermore, according to the powder magnetic core 1 of this embodiment, it is possible to provide a powder magnetic core with small eddy current loss in the high frequency range.

[0019] (Manufacturing method) The method for manufacturing the powder magnetic core 1 includes (1) a resin coating step for forming an insulating film, (2) a low-melting-point glass adding step, (3) a press molding step, and (4) an annealing step. In the resin coating process, silicone resin is dissolved in an organic solvent, and this organic solvent is sprayed onto the magnetic alloy powder to the required thickness. The organic solvent is then evaporated by a drying process such as vacuum drying to form an insulating coating. By vacuum drying, an insulating coated soft magnetic powder can be obtained whose surface is covered with an insulating coating layer (resin coating layer) of the required thickness.

[0020] In the low-melting glass adding step, about 1.0 to 6.0 mass % of low-melting glass is mixed with the insulating coated soft magnetic powder, and if necessary, a lubricant is further added and mixed, and if necessary, the mixed powder is dried. After drying, the powder is poured into the cavity of the mold and compressed at 10 to 14 ton / cm 2 The material is then press-molded into the desired shape at a pressure of about 1000°C (press molding process), and then subjected to an annealing process in which it is heated to a high temperature of about 600 to 700°C for about 30 minutes in an inert gas atmosphere such as a nitrogen gas atmosphere. Through the above manufacturing steps, a powder magnetic core can be obtained in which the insulating coated soft magnetic powder is bound with the low melting point glass and compacted.

[0021] This dust core has a structure in which intergranular layers 5 made of sintered low-melting-point glass are present between a plurality of insulating-coated soft magnetic particles 4 obtained by pressure-sintering a plurality of insulating-coated soft magnetic powders. The insulating coating 3 formed around the insulating-coated soft magnetic particles 4 is an insulating coating made of silicone resin or SiO2 derived from silicone resin. The intergranular layers 5 are obtained by sintering low-melting-point glass in which the Na content is suppressed to 3 at% or less.

[0022] In the powder magnetic core 1 having the structure shown in FIG. 1 , the outer periphery of the soft magnetic particles 2 made of soft magnetic powder is covered with an insulating coating 3, and the insulating-coated soft magnetic particles 4 having the insulating coating 3 are consolidated via intergranular layers 5. This makes it possible to provide a powder magnetic core that is high in strength and has low eddy current loss in the high-frequency range, resulting in low iron loss. [Example]

[0023] The present invention will be described in more detail below by showing examples, but the present invention is not limited to the following examples. As the soft magnetic powder, a mixed powder obtained by mixing pure iron powder (average particle size D50=50 μm) and sendust powder (average particle size D50=50 μm) in a 1:1 ratio was used. Xylene was mixed with a silicone resin solvent and sprayed onto the mixed powder to form an insulating coating at a loading of 2 mass%, yielding an insulating-coated soft magnetic powder. For comparison, a mixed powder without an insulating coating was also prepared.

[0024] Low-melting point glass was added to the insulating coated soft magnetic powder in the amount shown in Table 1 below, and the mixture was uniformly mixed to obtain a mixed powder, which was then used to produce a powder core as described below.Low-melting point glass was also added to the mixed powder not forming an insulating coating as shown in Table 1, and the mixture was uniformly mixed and used to produce a powder core as described below. Using the above-mentioned mixed powder, a mold was used to produce 14t / cm 2 The mixture was compacted under a compacting pressure of 1000 MPa to obtain a ring-shaped compact having an inner diameter of 25 mm, an outer diameter of 35 mm, and a height of 5 mm. This ring-shaped compact was heated to 640° C. for 0.5 hours in an inert gas atmosphere, and then subjected to an annealing step in which it was slowly cooled to obtain a powder magnetic core.

[0025] The obtained ring-shaped powder magnetic core was subjected to measurement of radial crushing strength and magnetic flux density by the following methods. Iron loss (0.1T, 50kHz) was separated into hysteresis loss (0.1T, 50kHz) and eddy current loss (0.1T, 50kHz) using the following formula and understood. Pc=Ph+Pe Pc=af+bf 2 Pc / f=a+bf where Pc is iron loss, Ph is hysteresis loss, Pe is eddy current loss, f is frequency, and a and b are proportionality constants. The eddy current loss (0.1T, 50kHz) of each sample is shown as a relative ratio, with the eddy current loss of the comparative sample No. 1 in Table 1 set to 1.00. If the eddy current loss is up to 1.4 times that of the comparative sample No. 1, it is judged as pass (◯), and if it exceeds this, it is judged as fail (×). The magnetic flux density is shown as a relative ratio, with the magnetic flux density of the comparative sample No. 1 in Table 1 set to 1.00. If the magnetic flux density is within a range of 50% reduction compared to the comparative sample No. 1, it is judged as pass (◯), and if the reduction in magnetic flux density exceeds 50%, it is judged as fail (×).

[0026] "Ring crushing strength" The radial crushing strength of the powder magnetic core was measured by measuring the breaking load with a universal testing machine using a ring-shaped test piece of φ35 (outer diameter) × φ25 (inner diameter) × 5H (height). The radial crushing strength was calculated from the dimensions of the compact (ring dimensions) according to the following relational expression. K = (F × (De)) / (L × e 2 ) K = radial crushing strength (MPa), F = maximum load at break (N), D = outer diameter of sample (mm), e = wall thickness of sample (mm), L = length / thickness of sample (mm). The above results are summarized in Table 1 below. The radial crushing strength is shown as a relative value to the radial crushing strength shown by Comparative Example No. 1 in Table 1. If the radial crushing strength is increased compared to Comparative Example No. 1, it is judged as passing (◯) and breaking, and if it is decreased, it is judged as failing (×).

[0027] [Table 1]

[0028] As shown in Table 1, the example samples (dust cores) Nos. 3 to 9 are dust cores obtained by mixing low-melting glass with a softening point of 515 to 603° C. with insulating coated soft magnetic powder and compacting the mixture. Comparative example sample No. 1 is a sample in which a powder magnetic core was produced using only insulating coated soft magnetic powder without using low-melting point glass, and comparative example No. 12 is a powder magnetic core obtained by directly consolidating soft magnetic powder that was not formed with an insulating coating, without using low-melting point glass. Compared to Comparative Sample No. 12, Comparative Sample No. 1 has significantly improved eddy current loss and superior radial crushing strength. For this reason, Table 1 shows the eddy current loss and radial crushing strength of each sample relative to Comparative Sample No. 1.

[0029] The example samples Nos. 3 to 9 exhibited values ​​for eddy current loss that were generally similar to that of the comparative sample No. 1, although there was some variation. The example samples Nos. 3 to 9 exhibited radial crushing strengths (0.95 to 1.30) that were equal to or superior to that of the comparative sample No. 1. The example samples Nos. 3 to 9 exhibited magnetic flux densities equivalent to that of the comparative sample No. 1, or magnetic flux densities (0.56 to 0.98) sufficient for use as magnetic cores.

[0030] Comparative Example Sample No. 2 is a sample to which 0.5 mass% of low-melting point glass was added, but the radial crushing strength was lower than that of Comparative Example Sample No. 1. Example Sample No. 3, to which 1.0 mass% of low-melting point glass was added, showed improved radial crushing strength, and it is believed that the amount of low-melting point glass added should be 1.0 mass% or more.

[0031] Comparative sample No. 7 is a sample to which 7 mass% of low-melting point glass was added, but its magnetic flux density was reduced by more than 50% compared to comparative sample No. 1. From the viewpoint of magnetic flux density, it can be determined that the upper limit of the amount of low-melting point glass to be added is 6 mass%. The comparative sample No. 10 is a sample in which the amount of Na contained in the low-melting-point glass is 4.9 at%. This sample uses soft magnetic powder with an insulating coating, but it exhibits high eddy current loss and a decrease in radial crushing strength. The example sample No. 9 is a sample in which the amount of Na contained in the low-melting-point glass is 3.0 at% but exhibits low eddy current loss. For this reason, it was found that the amount of Na contained in the low-melting-point glass needs to be kept below 3.0 at%.

[0032] Comparative example sample No. 11 is a sample in which the amount of Na contained in the low-melting point glass is 4.9 at%. This sample uses soft magnetic powder without an insulating coating, but the eddy current loss is significantly increased and the radial crushing strength is also significantly reduced. From the above comparison, it was found that in order to suppress eddy current loss, have excellent radial crushing strength, and obtain the magnetic flux density required for a magnetic core, it is desirable to manufacture a powder core using an insulating coated soft magnetic powder and adding 1 to 6 mass% of low-melting glass with an Na content of 3 at% or less. [Explanation of symbols]

[0033] 1... powder core, 2... soft magnetic particles, 3... insulating coating, 5... intergranular layer.

Claims

1. A powder magnetic core comprising: a plurality of soft magnetic particles each having an insulating coating formed on its surface; and an intergranular layer of low-melting glass having an Na content of 3 at % or less between the soft magnetic particles.

2. 2. The dust core according to claim 1, wherein the soft magnetic particles are made of pure iron powder or iron-based soft magnetic powder.

3. The insulating coating is made of silicone resin or SiO derived from silicone resin. ２ 3. The powder magnetic core according to claim 1, comprising:

4. 3. The powder magnetic core according to claim 1, wherein the low-melting glass is present in an amount of 1% by mass or more and 6% by mass or less with respect to the amount of the soft magnetic particles.

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