JP2004296606A - Magnetic core of low coercive force, manufacturing method therefor and iron powder for magnetic core - Google Patents
Magnetic core of low coercive force, manufacturing method therefor and iron powder for magnetic core Download PDFInfo
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- JP2004296606A JP2004296606A JP2003084591A JP2003084591A JP2004296606A JP 2004296606 A JP2004296606 A JP 2004296606A JP 2003084591 A JP2003084591 A JP 2003084591A JP 2003084591 A JP2003084591 A JP 2003084591A JP 2004296606 A JP2004296606 A JP 2004296606A
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 55
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 239000002245 particle Substances 0.000 claims abstract description 16
- 238000000034 method Methods 0.000 claims description 11
- 238000000465 moulding Methods 0.000 claims description 6
- 238000003825 pressing Methods 0.000 claims description 4
- 239000000843 powder Substances 0.000 abstract description 9
- 229910052742 iron Inorganic materials 0.000 abstract description 6
- 239000000428 dust Substances 0.000 description 30
- 239000000463 material Substances 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 230000004907 flux Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 238000005121 nitriding Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 1
- 239000006247 magnetic powder Substances 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、保磁力の低い磁心とその製造方法およびその磁心の素材となる鉄粉に関し、特に高周波電流の電源装置（いわゆるスイッチング電源装置）に備えられるトランスやチョークコイル等に用いられる磁心とその製造方法およびその磁心用鉄粉に関するものである。
【０００２】
【従来の技術】
鉄粉を所定の形状に加圧成形して使用する圧粉磁心は、比抵抗が高いという特性を有している。したがって鉄粉を用いた圧粉磁心をトランス等の磁心（あるいは鉄心ともいう）として使用すると、鉄損（すなわち磁心における渦電流損失とヒステリシス損失，残留損失の合計値）が低減される。つまり比抵抗が高いことによって、渦電流損失が低く抑えられ、その結果、鉄損が低減されるのである。
【０００３】
上記した通り圧粉磁心は、比抵抗が高いために鉄損を低減できるという特性を有するので、電流を流すことによる発熱を抑制するという効果がある。そのため、圧粉磁心はパソコン等の高周波電源装置に備えられるチョークコイル等に使用されている。
ところが近年、パソコンの小型化，軽量化のニーズが著しく高まり、電源装置の小型化の必要性が増大している。そこでパソコンの電源装置に備えられるトランスやチョークコイルの小型化を達成するために、より高い周波数の高周波電流を使用する試みがなされている。つまり高周波電流を使用することによって、所定の誘導起電力を得るための磁束が小さくてすむので、消費電力が同一であっても電源装置の小型化を達成できる。
【０００４】
また、鉄粉を用いた圧粉磁心は、飽和磁束密度が高く、電源装置をより小型化することができる。また、その素材が鉄粉であるから、一般の金属材料と同様に温度が上昇することによって電気抵抗も増大するので、昇温により渦電流損失が低下して、発熱が抑制される利点がある。しかしながら鉄粉を用いた圧粉磁心は、十分に保磁力を低くすることができないので、ヒステリシス損失が問題となり、圧粉磁心を用い、かつ高周波電流を使用して電源装置を小型化する技術には限界があり、パソコンの小型化，軽量化のニーズに十分に対応できない。
【０００５】
そこで鉄系の酸化物磁性材料であるフェライトを素材として製造した磁心を用いて、電源装置の小型化がなされている。しかしフェライトは、高温域では電気抵抗が減少するので、昇温により渦電流損失が一層増加して、さらに激しく昇温する、いわゆる熱暴走を起こす欠点があり、小型化の制約となっている。またフェライトを用いて磁心を製造する工程では、原料コストが高い上に、フェライトの粉末を所定の形状に加圧成形した後、さらに焼結を行なうので、製造コストは圧粉磁心に比べて高くなる。
【０００６】
つまり電源装置のさらなる小型化を低コストで達成するためには、フェライトに比べて安価な鉄粉を所定の形状に加圧成形した磁心（すなわち圧粉磁心）を用いることが有効である。ところが圧粉磁心の小型化は上記したように限界に達しており、さらなる小型化を達成するためには圧粉磁心の保磁力を低下させ、ヒステリシス損失を低減する必要がある。
【０００７】
そこで圧粉磁心の保磁力を低下させるために、種々の技術が提案されている。たとえば特開平４−２９３７０２号公報には、保磁力の小さい軟磁性粉末の製造法が開示されている。この技術は鉄粉を窒素と反応（すなわち窒化処理）させて、鉄粉の保磁力を低下させるものである。しかしながら、この技術では鉄粉に窒化処理を施すので、鉄粉の製造コストが上昇し、圧粉磁心の製造コストも上昇する。
【０００８】
【特許文献１】
特開平４−２９３７０２号公報
【０００９】
【発明が解決しようとする課題】
本発明は上記のような問題を解消し、保磁力の低い安価な磁心とその製造方法およびその磁心用鉄粉を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明者らは、保磁力の低い安価な圧粉磁心を得る技術について鋭意検討を行なった。その結果、圧粉磁心の素材となる鉄粉の粒径を規定し、かつ加圧成形した後の密度を規定することによって、従来から知られている鉄粉を用いて保磁力の低い安価な圧粉磁心を製造できることを見出した。
【００１１】
本発明は、鉄粉を所定の形状に加圧成形した磁心であって、磁心を形成する鉄粉の全量に対して９０体積％以上が７５μｍ以下の粒径を有し、かつ磁心の密度が６ｇ／ｃｍ３ 以下である磁心である。
また本発明は、鉄粉を型枠内に充填して加圧し、所定の形状の磁心を製造する磁心の製造方法おいて、全量に対して９０体積％以上が７５μｍ以下の粒径を有する鉄粉を型枠内に充填して加圧し、磁心の密度を６ｇ／ｃｍ３ 以下とする磁心の製造方法である。
【００１２】
また本発明は、磁心の加圧成形に用いる磁心用鉄粉であって、全量に対して９０体積％以上が７５μｍ以下の粒径を有する磁心用鉄粉である。
【００１３】
【発明の実施の形態】
本発明では圧粉磁心の素材である鉄粉は、全量に対して９０体積％以上が７５μｍ以下の粒径を有する鉄粉を用いる。このように粒径の小さい粒子が多量に含まれる鉄粉を、所定の形状の型枠内に充填して加圧し、圧粉磁心を製造する。その際、得られる圧粉磁心の密度は６ｇ／ｃｍ３ 以下とする。このようにして圧粉磁心を形成する鉄粉を小粒化し、かつ圧粉磁心の密度を低減することによって、保磁力の低い圧粉磁心（保磁力 １２０Ａ／ｍ以下）が得られる。しかも素材として鉄粉を使用し、その鉄粉を加圧成形するのみ（すなわち焼結を行なわない）で製造できるので、安価な圧粉磁心が得られる。
【００１４】
圧粉磁心の素材となる鉄粉は、大径の粒子が多量に含まれると、低い保磁力が得られない。したがって鉄粉は、全量に対して９０体積％以上が７５μｍ以下の粒径を有するものを使用する必要がある。なお、 全量に対して９０体積％以上が５０μｍ以下の粒径を有する鉄粉を使用するのが一層好ましい。
また圧粉磁心の密度が６ｇ／ｃｍ３ を超えると、成形歪みが大きくなるので保磁力を低下させることが困難となる。したがって圧粉磁心の密度は６ｇ／ｃｍ３ 以下とする必要がある。ただし密度が５ｇ／ｃｍ３ 未満では、飽和磁束密度が低下するとともに、圧粉磁心が脆くなり容易に破損する。したがって圧粉磁心の密度は、５〜６ｇ／ｃｍ３ の範囲内が好ましい。
【００１５】
なお本発明で使用する鉄粉の製造方法は、特定の技術に限定せず、従来から知られている方法で製造した鉄粉が使用できる。また本発明は、表面に絶縁被覆を有する鉄粉も支障なく適用できる。つまり、本発明では鉄粉を加圧成形した後、焼結を行なわないので、絶縁被膜が焼失することなく残存する。したがって鉄粉と絶縁被膜の特性の劣化は生じない。
【００１６】
【実施例】
表１に示す３種類の粒径を有する還元鉄粉を用いて、円筒形状（外径２０．２ｍｍ，内径１２．６ｍｍ，高さ９．５ｍｍ ）の圧粉磁心を製造した。圧粉磁心の密度は、それぞれ表１に示す値になるように、加圧成形の圧力を調整した。
こうして得られた各圧粉磁心の保磁力（Ａ／ｍ）を測定した。その結果を表１に併せて示す。
【００１７】
なお表１の発明例１，２は、還元鉄粉の粒径が本発明の範囲を満足する例であり、比較例は、還元鉄粉の粒径が本発明の範囲を外れる例である。
【００１８】
【表１】
表１から明らかなように、発明例１，２では、圧粉磁心の密度が５〜６ｇ／ｃｍ３ の範囲内で保磁力が １２０Ａ／ｍ以下（すなわち６０〜１１０ Ａ／ｍ）であった。特に発明例２は、圧粉磁心の密度が ６．５ｇ／ｃｍ３ であっても保磁力は １２０Ａ／ｍ以下（すなわち １００Ａ／ｍ）を達成した。
一方、比較例では、保磁力は １４０〜２００ Ａ／ｍであり、 １２０Ａ／ｍ以下は達成されなかった。
【００２０】
【発明の効果】
本発明によれば、保磁力が低くかつ安価な圧粉磁心を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic core having a low coercive force, a method for manufacturing the same, and iron powder used as a material of the magnetic core. The present invention relates to a manufacturing method and iron powder for a magnetic core.
[0002]
[Prior art]
A powder magnetic core formed by pressing iron powder into a predetermined shape has a characteristic of high specific resistance. Therefore, when a powder magnetic core using iron powder is used as a magnetic core of a transformer or the like (or also referred to as an iron core), iron loss (that is, the total value of eddy current loss, hysteresis loss, and residual loss in the magnetic core) is reduced. That is, the eddy current loss is suppressed low by the high specific resistance, and as a result, the iron loss is reduced.
[0003]
As described above, the dust core has a characteristic that iron loss can be reduced due to its high specific resistance, and thus has an effect of suppressing heat generation caused by flowing an electric current. Therefore, the dust core is used for a choke coil and the like provided in a high-frequency power supply device such as a personal computer.
However, in recent years, the need for miniaturization and weight reduction of personal computers has increased remarkably, and the necessity for miniaturization of power supply devices has increased. Attempts have been made to use higher-frequency high-frequency currents in order to reduce the size of transformers and choke coils provided in power supply devices for personal computers. In other words, by using the high-frequency current, the magnetic flux for obtaining the predetermined induced electromotive force can be small, and thus the power supply device can be downsized even if the power consumption is the same.
[0004]
In addition, a dust core using iron powder has a high saturation magnetic flux density, and can further reduce the size of the power supply device. In addition, since the material is iron powder, the electric resistance increases as the temperature rises in the same manner as a general metal material. Therefore, there is an advantage that the eddy current loss is reduced by the temperature rise and heat generation is suppressed. . However, dust cores using iron powder cannot reduce the coercive force sufficiently, so hysteresis loss becomes a problem. Are limited and cannot adequately meet the needs for smaller and lighter personal computers.
[0005]
Therefore, a power supply device has been downsized using a magnetic core manufactured using ferrite, which is an iron-based oxide magnetic material. However, ferrite has a drawback in that the electric resistance decreases in a high temperature range, so that the eddy current loss further increases due to the temperature rise, and the temperature rises more severely, that is, a so-called thermal runaway occurs, which restricts miniaturization. Also, in the process of manufacturing a magnetic core using ferrite, the raw material cost is high, and the ferrite powder is pressed into a predetermined shape and then sintered, so the manufacturing cost is higher than the dust core. Become.
[0006]
That is, in order to achieve further miniaturization of the power supply device at low cost, it is effective to use a magnetic core (that is, a dust core) obtained by pressing iron powder, which is less expensive than ferrite, into a predetermined shape. However, miniaturization of the dust core has reached the limit as described above, and in order to achieve further miniaturization, it is necessary to reduce the coercive force of the dust core and reduce the hysteresis loss.
[0007]
Therefore, various techniques have been proposed to reduce the coercive force of the dust core. For example, Japanese Patent Application Laid-Open No. 4-293702 discloses a method for producing a soft magnetic powder having a small coercive force. In this technique, iron powder is reacted with nitrogen (that is, nitriding treatment) to reduce the coercive force of the iron powder. However, in this technique, since the iron powder is subjected to the nitriding treatment, the manufacturing cost of the iron powder increases, and the manufacturing cost of the dust core also increases.
[0008]
[Patent Document 1]
JP-A-4-293702
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems and to provide an inexpensive magnetic core having a low coercive force, a method for manufacturing the same, and iron powder for the magnetic core.
[0010]
[Means for Solving the Problems]
The present inventors have intensively studied a technique for obtaining an inexpensive dust core having a low coercive force. As a result, by defining the particle size of the iron powder used as the material of the dust core, and by defining the density after the pressure molding, a coercive force having a low coercive force using a conventionally known iron powder is used. It has been found that a dust core can be manufactured.
[0011]
The present invention relates to a magnetic core obtained by pressing iron powder into a predetermined shape, wherein 90% by volume or more of the total amount of the iron powder forming the magnetic core has a particle size of 75 μm or less, and the density of the magnetic core is The magnetic core is 6 g / cm 3 or less.
Further, the present invention provides a method of manufacturing a magnetic core in which iron powder is filled in a mold and pressed to form a magnetic core having a predetermined shape. This is a method for manufacturing a magnetic core in which powder is filled in a mold and pressed to reduce the density of the magnetic core to 6 g / cm 3 or less.
[0012]
The present invention is also an iron powder for a magnetic core used for pressure molding of a magnetic core, wherein 90% by volume or more of the total amount has a particle size of 75 μm or less.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the iron powder used as the material of the dust core uses iron powder having a particle diameter of 90% by volume or more to 75 μm or less based on the total amount. The iron powder containing a large amount of particles having a small particle diameter is filled in a mold having a predetermined shape and pressed to manufacture a dust core. At this time, the density of the obtained dust core is 6 g / cm 3 or less. By reducing the size of the iron powder forming the dust core and reducing the density of the dust core in this way, a dust core having a low coercive force (a coercive force of 120 A / m or less) can be obtained. Moreover, since iron powder is used as a raw material and the iron powder can be manufactured only by pressure molding (ie, without sintering), an inexpensive dust core can be obtained.
[0014]
When the iron powder used as the material of the dust core contains a large amount of large-diameter particles, a low coercive force cannot be obtained. Therefore, it is necessary to use iron powder having a particle diameter of 90% by volume or more with respect to the total amount of 75 μm or less. It is more preferable to use iron powder having a particle diameter of 90% by volume or more to 50 μm or less based on the total amount.
If the density of the dust core exceeds 6 g / cm 3 , the molding distortion becomes large and it becomes difficult to lower the coercive force. Therefore, the density of the dust core needs to be 6 g / cm 3 or less. However, when the density is less than 5 g / cm 3 , the saturation magnetic flux density decreases, and the dust core becomes brittle and easily broken. Therefore, the density of the dust core is preferably in the range of 5 to 6 g / cm 3 .
[0015]
The method for producing iron powder used in the present invention is not limited to a specific technique, and iron powder produced by a conventionally known method can be used. The present invention can also be applied to iron powder having an insulating coating on the surface without any trouble. That is, in the present invention, since the sintering is not performed after the iron powder is pressed and formed, the insulating coating remains without being burned out. Therefore, the characteristics of the iron powder and the insulating film do not deteriorate.
[0016]
【Example】
A dust core having a cylindrical shape (outer diameter: 20.2 mm, inner diameter: 12.6 mm, height: 9.5 mm) was manufactured using the reduced iron powder having three types of particle diameters shown in Table 1. The pressure of the pressure molding was adjusted so that the density of the dust core became a value shown in Table 1, respectively.
The coercive force (A / m) of each powder magnetic core thus obtained was measured. The results are shown in Table 1.
[0017]
Examples 1 and 2 of Table 1 are examples in which the particle size of the reduced iron powder satisfies the range of the present invention, and Comparative Examples are examples in which the particle size of the reduced iron powder is out of the range of the present invention.
[0018]
[Table 1]
As is clear from Table 1, in Invention Examples 1 and 2, the coercive force was 120 A / m or less (that is, 60 to 110 A / m) when the density of the dust core was in the range of 5 to 6 g / cm 3 . . In particular, Invention Example 2 achieved a coercive force of 120 A / m or less (ie, 100 A / m) even when the density of the dust core was 6.5 g / cm 3 .
On the other hand, in the comparative example, the coercive force was 140 to 200 A / m, and 120 A / m or less was not achieved.
[0020]
【The invention's effect】
According to the present invention, an inexpensive dust core having a low coercive force can be obtained.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003084591A JP2004296606A (en) | 2003-03-26 | 2003-03-26 | Magnetic core of low coercive force, manufacturing method therefor and iron powder for magnetic core |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2003084591A JP2004296606A (en) | 2003-03-26 | 2003-03-26 | Magnetic core of low coercive force, manufacturing method therefor and iron powder for magnetic core |
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|---|---|
| JP2004296606A true JP2004296606A (en) | 2004-10-21 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008141011A (en) * | 2006-12-01 | 2008-06-19 | Hitachi Powdered Metals Co Ltd | Amorphous dust core |
| WO2019026612A1 (en) * | 2017-08-02 | 2019-02-07 | 株式会社デンソー | Powder for magnetic powder core and magnetic powder core |
-
2003
- 2003-03-26 JP JP2003084591A patent/JP2004296606A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008141011A (en) * | 2006-12-01 | 2008-06-19 | Hitachi Powdered Metals Co Ltd | Amorphous dust core |
| WO2019026612A1 (en) * | 2017-08-02 | 2019-02-07 | 株式会社デンソー | Powder for magnetic powder core and magnetic powder core |
| JP2019026912A (en) * | 2017-08-02 | 2019-02-21 | 株式会社デンソー | Powder for powder magnetic core and powder magnetic core |
| US11532414B2 (en) | 2017-08-02 | 2022-12-20 | Denso Corporation | Powder for dust core and dust core |
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