Pressure Powder Core

Abstract

To provide a powder magnetic core that achieves both low hysteresis loss and improved strength.SOLUTION: A powder magnetic core includes FeSiAl alloy powder and an insulating layer made of an insulating resin that covers the surface of the FeSiAl alloy. The insulating layer contains carbon, and the proportion of carbon in the powder magnetic core is 0.01% or more. Furthermore, the upper limit of the carbon content is preferably 0.1%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a powder magnetic core. [Background technology]

[0002] A reactor is an electromagnetic component that converts electrical energy into magnetic energy, then stores and releases it. Reactors are used in a variety of fields, including drive systems for hybrid vehicles, electric vehicles, and fuel cell vehicles, as well as office equipment, solar power generation systems, automobiles, and uninterruptible power supplies.

[0003] A reactor has an annular core and a coil, with the coil attached to the annular core. This annular core is often a powder magnetic core. A powder magnetic core is made by filling a mold of a specific shape with soft magnetic powder, press-molding it to produce a powder compact, and then annealing this powder compact.

[0004] Due to demands for improved energy exchange efficiency and low heat generation, powder magnetic cores are required to have magnetic properties that minimize energy loss when magnetic flux density changes. One magnetic property related to energy loss is iron loss (Pcv), also known as core loss. Iron loss is expressed as the sum of hysteresis loss (Ph) and eddy current loss (Pe).

[0005] Research is being conducted into reducing hysteresis loss in order to reduce iron loss. For example, as disclosed in Patent Document 1, a method is known in which soft magnetic powder on which an insulating layer made of aluminum oxide is formed is press-molded and the powder compact is annealed at 500°C to 900°C to remove distortion within the powder compact and reduce hysteresis loss. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-088529 Summary of the Invention [Problem to be solved by the invention]

[0007] While it is important to reduce hysteresis loss, it is also important to improve the strength of the powder magnetic core. If the strength of the powder magnetic core is low, cracks may occur in the powder magnetic core during the manufacturing process, adversely affecting the magnetic properties, and when the powder magnetic core is installed in an electromagnetic component that is placed in a vibrating environment, such as an automobile, cracks may occur in the powder magnetic core due to the vibration, which may reduce the durability of the electromagnetic component.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a powder magnetic core that achieves both low hysteresis loss and improved strength. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a powder magnetic core comprising an FeSiAl alloy powder and an insulating layer that covers the surface of the FeSiAl alloy powder and that is made of an insulating resin that adheres to the surface of the FeSiAl alloy powder, wherein the insulating layer contains carbon, and the carbon content of the powder magnetic core is 0.01% or more. 0.1% or less It is characterized by the fact that [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a powder magnetic core that achieves both low hysteresis loss and improved strength. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph showing the relationship between carbon content and strength. [Figure 2] 1 is a graph showing the relationship between carbon content and hysteresis loss. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Embodiment) The powder magnetic core of the present embodiment will be described below. However, the present invention is not limited to the embodiment described below.

[0013] Powder cores are magnetic materials used in the cores of coil components such as reactors installed in office equipment, solar power generation systems, automobiles, etc. Powder cores are made by forming an insulating layer around soft magnetic powder and then compacting it under pressure to create a powder compact. This compact is then annealed to create a powder core.

[0014] The insulating layer contains carbon. Carbon remains in the insulating layer due to the thermal decomposition of the insulating resin, which will be described later. The carbon percentage (hereinafter also referred to as "carbon amount") is 0.01% or more. The carbon percentage here refers to the percentage of carbon in the powder magnetic core. That is, it is the percentage of carbon in all materials constituting the powder magnetic core. By setting the carbon amount to 0.01% or more, strength can be increased and hysteresis loss can be reduced. The upper limit of the carbon amount is preferably 0.1%. By setting the upper limit to 0.1%, hysteresis loss can be reduced compared to when the upper limit exceeds 0.1%, resulting in a more well-balanced powder magnetic core. In order to further reduce hysteresis loss while maintaining high strength, it is more preferable to set the upper limit of the carbon amount to 0.025%. Note that it is sufficient for the insulating layer to contain carbon, and it does not matter whether the carbon is left intentionally or unintentionally.

[0015] The carbon content can be adjusted by the annealing conditions for annealing the powder compact. For example, increasing the oxygen concentration during annealing tends to decrease the carbon content, while decreasing the oxygen concentration tends to increase the carbon content. The carbon content can also be adjusted by the annealing temperature and annealing time. Furthermore, the carbon content can also be adjusted by increasing or decreasing the amount of insulating resin added to form the insulating layer.

[0016] The soft magnetic powder is made of FeSiAl alloy powder. The FeSiAl alloy powder is a powder containing iron, silicon, and aluminum. The FeSiAl alloy powder contains, for example, about 7 wt% to 11 wt% of Si and about 4 wt% to 8 wt% of Al relative to Fe. The FeSiAl alloy powder may also contain, for example, about 1 wt% to 3 wt% of Ni relative to Fe. Furthermore, the FeSiAl alloy powder may also contain Co, Cr, or Mn.

[0017] FeSiAl alloy powder is produced by the pulverization method or the gas atomization method. The pulverization method mechanically crushes the FeSiAl alloy powder clumps. If the FeSiAl alloy powder clumps are large, they are crushed using a jaw crusher, hammer mill, stamp mill, etc., while if the FeSiAl alloy powder clumps are small, they are pulverized using a ball mill, vibration mill, etc. The gas atomization method pulverizes the FeSiAl alloy powder melted at high temperature by spraying gas onto it, and then cools and solidifies it.

[0019] An insulating layer is formed on the surface of the FeSiAl alloy powder. Forming an insulating layer on the surface of the FeSiAl alloy powder provides insulation between the FeSiAl alloy powder particles and reduces eddy current loss. The insulating layer is made of an insulating resin, and this insulating resin is attached to the surface of the FeSiAl alloy powder. As long as the insulating layer is attached to the surface of the FeSiAl alloy powder, the manner in which the insulating resin is attached does not matter. That is, the insulating resin may be attached so as to completely cover the periphery of the FeSiAl alloy powder, or it may be attached so as to partially cover the periphery of the FeSiAl alloy powder, leaving part of the surface of the FeSiAl alloy powder exposed. Furthermore, the insulating resin may be attached to the surface of each particle of the FeSiAl alloy powder, or to the surface of the aggregates of the FeSiAl alloy powder, or it may be attached in a mixture of these manners.

[0020] The insulating resin may be a silane compound, a silicone resin, a silicone oligomer, or a mixture thereof. That is, the silane compound, the silicone resin, or the silicone oligomer may be used alone, or, for example, a mixture of a silane compound and a silicone oligomer, or a mixture of a silane compound and a silicone resin, may be used. In the annealing process described below, the powder compact is heat-treated at a high temperature to decompose the carbon of the organic components contained in the insulating resin, but some of the carbon remains undecomposed, or some of the carbon remains as SiC after reacting with the silicone, remaining in the insulating layer as carbon.

[0021] The insulating layer may be a single layer or multiple layers. For example, the insulating layer may be composed of multiple layers divided into different types, or may be composed of a single layer of insulating resin made of one type or a mixture of two or more types.

[0022] The silane compound includes a silane compound having no functional group and a silane coupling agent. As the silane compound having no functional group, for example, an alkoxysilane such as an ethoxy-based or methoxy-based silane can be used, with tetraethoxysilane being particularly preferred. As the silane coupling agent, an aminosilane-based, epoxysilane-based, or isocyanurate-based silane coupling agent can be used, with 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate being particularly preferred.

[0023] The amount of the silane compound added is preferably 0.05 wt% to 1.0 wt% of the FeSiAl alloy powder, which improves the flowability of the FeSiAl alloy powder and also improves the density, magnetic properties, and strength properties of the compacted powder core.

[0024] Silicone resin is a resin with a siloxane bond (Si-O-Si) as its main skeleton. By using silicone resin, an insulating layer with excellent flexibility can be formed. Silicone resins that can be used include methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, and rubber-based. Among these, when using methylphenyl-based silicone resin in particular, it is possible to form an insulating layer with little loss on heating and excellent heat resistance.

[0025] The amount of silicone resin added is 0.4 wt% or more and 3.0 wt% or less of the FeSiAl alloy powder, and more preferably 0.6 wt% or more and 2.0 wt% or less. If the amount of silicone resin added is too small, the contraction action that attracts the FeSiAl alloy powder particles when the powder compact is annealed is weak, making it impossible to ensure high density and increase magnetic permeability. On the other hand, if the amount added is too large, the insulating layer formed on the surface of the FeSiAl alloy powder becomes too thick, making it impossible to ensure high density and increase magnetic permeability.

[0026] Examples of silicone oligomers that can be used include methyl-based and methylphenyl-based oligomers that have an alkoxysilyl group but no reactive functional group, epoxy-based, epoxymethyl-based, mercapto-based, mercaptomethyl-based, acrylic methyl-based, methacrylic methyl-based, and vinylphenyl-based oligomers that have an alkoxysilyl group and a reactive functional group, and alicyclic epoxy-based oligomers that have a reactive functional group instead of an alkoxysilyl group. In particular, the use of methyl-based or methylphenyl-based silicone oligomers allows for the formation of a thick, hard insulating layer. Furthermore, in consideration of the ease of forming an insulating layer, methyl-based and methylphenyl-based oligomers with relatively low viscosity may also be used.

[0027] The amount of silicone oligomer added is preferably 0.1 wt% to 2.0 wt% of the FeSiAl alloy powder. If the amount added is less than 0.1 wt%, it will not function as an insulating layer, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.0 wt%, it will result in a decrease in the density of the powder magnetic core.

[0028] After adding and mixing the insulating resin to the FeSiAl alloy powder, the mixture is heated and dried. The heating and drying conditions are not limited to the above, but the mixture is dried at a temperature of 25°C to 350°C for about 2 hours. By heating and drying, an insulating layer is formed on the surface of the FeSiAl alloy powder.

[0029] The insulating layer is formed by adding a lubricant to the formed FeSiAl alloy powder and then compacting it. Examples of lubricants include stearic acid and its metal salts, as well as ethylene bisstearamide, ethylene bisstearamide, and ethylene bisstearamide. Adding a lubricant reduces the pressure required to release the powder from the die and prevents the FeSiAl alloy powder from sticking to the die, improving the quality of the green compact. After adding the lubricant, the FeSiAl alloy powder is filled into a die of the desired shape and compacted by compaction to produce a green compact. The compacting pressure is 10 to 20 ton / cm. 2 is.

[0030] Finally, the compacted powder is annealed. This annealing removes strain within the FeSiAl alloy powder. This annealing is performed in an inert atmosphere or in the air. The inert atmosphere is an atmosphere filled with a low amount of reactive gas and an inert or neutral gas. The reactive gas is oxygen, water vapor, or carbon dioxide. The inert gas is argon or helium. The neutral gas is nitrogen or ammonia. Annealing is preferably performed at 700°C or higher and 850°C or lower for approximately two hours. If the temperature is lower than 700°C, the strain removal effect is limited, and the deterioration of the insulating resin is also limited, which may weaken the bonds between the FeSiAl alloy powder. On the other hand, if the temperature exceeds 850°C, the insulating layer may be destroyed due to the temperature exceeding the heat resistance temperature of the insulating resin, resulting in a risk of deterioration of eddy current loss. Note that a reducing atmosphere filled with hydrogen gas or the like is undesirable because carbon is prone to react and decompose.

[0031] (Example) The present invention will now be described in more detail with reference to examples, although the present invention is not limited to the following examples.

[0032] The powder magnetic cores of Examples 1 to 4 and Comparative Examples 1 to 5 were produced as follows: Examples 1 to 4 and Comparative Examples 1 to 5 differ in the carbon content.

[0033] First, FeSiAl alloy powder was prepared as soft magnetic powder. This FeSiAl alloy powder was produced by gas atomization. 0.5 wt% of a silane coupling agent and 1.5 wt% of a silicone resin were added and mixed with this FeSiAl alloy powder as insulating resins, and then dried in air for 2 hours.

[0034] To eliminate aggregation, the FeSiAl alloy powder was passed through a 500-mesh sieve, and 0.5 wt% of ethylene bisstearamide (Acrawax®) was added as a lubricant. The FeSiAl alloy powder with the added lubricant was filled into a mold and subjected to a pressure of 15 ton / cm. 2 The powder compact was then pressure-molded at 700°C for 2 hours in an atmosphere with an oxygen concentration shown in Table 1 below. In this manner, powder magnetic cores of Examples 1 to 4 and Comparative Examples 1 to 5 were produced.

[0035] The carbon content (%), strength (MPa), hysteresis loss (kw / m 3 ) was measured.

[0036] The carbon content was measured using a carbon / sulfur analyzer (EMIA-Expert) manufactured by Horiba, Ltd. Specifically, 0.5 g of powder core fragments were placed in a crucible and heated with high frequency, which gasified the carbon contained in the powder core and extracted carbon monoxide or carbon dioxide. This extracted carbon monoxide or carbon dioxide was then measured using infrared absorption spectroscopy and converted into the carbon content.

[0037] The strength was measured by measuring radial crushing strength at a measurement condition of 0.5 mm / min using an automatic load testing machine (MAX-5KN-H) manufactured by Japan Measurement Systems Co., Ltd.

[0038] Furthermore, when measuring the hysteresis loss, 15 turns of φ0.5 mm copper wire were wound as a primary winding and 15 turns as a secondary winding around the powder magnetic cores of Examples 1 to 4 and Comparative Examples 1 to 5. Then, using a BH analyzer (Iwatsu Measurement Corporation: SY-8219), which is a magnetic measuring device, the hysteresis loss Ph and eddy current loss Pe were calculated under measurement conditions of a frequency of 100 kHz and a maximum magnetic flux density Bm of 100 mT, and the relationship between the carbon content and hysteresis loss Ph was summarized.

[0039] The hysteresis loss Ph and eddy current loss Pe were calculated by using the least squares method to calculate the hysteresis loss coefficient (Kh) and eddy current loss coefficient (Ke) from the frequency curve of the iron loss Pcv using the following equations (1) to (3). Pcv = Kh×f + Ke×f 2 (1) Ph = Kh × f (2) Pe = Ke × f 2 (3) Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: frequency Ph: Hysteresis loss Pe: Eddy current loss

[0040] The measurement results of the carbon content, hysteresis loss, and strength of Examples 1 to 4 and Comparative Examples 1 to 5 are shown in Table 1. A graph showing the relationship between the carbon content and strength is shown in Figure 1, and a graph showing the relationship between the carbon content and hysteresis loss is shown in Figure 2. [Table 1]

[0041] As shown in Table 1 and Figure 1, Examples 1 to 4, which have a carbon content of 0.01% or more, have strengths higher than 40 (MPa), which are improved compared to all of Comparative Examples 1 to 5. Furthermore, the hysteresis loss of Examples 1 to 4 was 300 (kw / m) even in Example 1, which had the highest value. 3 ), which is not a significant increase. Therefore, it was confirmed that a carbon content of 0.01% or more can achieve both improved strength and low hysteresis loss.

[0042] Although this is only a guess and the mechanism is not limited to this, it is speculated that by increasing the amount of carbon remaining in the insulating layer, the insulating resin adheres to the surface of the FeSiAl alloy powder as a mass, thereby strengthening the bond between the FeSiAl alloy powder particles.

[0043] In addition, in Example 2, the strength was 53 (MPa), which was a higher strength, and the hysteresis loss was 300 (kw / m 3 ) lower than 285 (kw / m 3 ), which means that the hysteresis loss is further reduced compared to Example 1. Therefore, it was confirmed that in order to further reduce the hysteresis loss while improving the strength, it is preferable to set the carbon content to 0.1% or less.

[0044] Furthermore, in Examples 3 and 4, the strength was 40 (MPa) or more and the hysteresis loss was 250 (kw / m 3 ), resulting in a reduction in hysteresis loss compared to Examples 1 and 2. Therefore, it was confirmed that the range of carbon content that can further reduce hysteresis loss and improve strength is 0.01% or more and 0.025% or less.

[0045] Although Example 2 has a slightly higher hysteresis loss than Examples 3 and 4, it has an improved strength of 53 (MPa). When priority is given to strength over magnetic properties, it is preferable to use the powder magnetic core of Example 2, which has a carbon content of 0.1%.

[0046] Next, powder magnetic cores of Examples 5 and 6 were produced. The only difference between the powder magnetic cores of Examples 5 and 6 was the temperature at which the powder compact was annealed, and the other manufacturing methods and conditions were the same as those of Example 1. In Example 5, the powder compact was annealed at 750°C, and in Example 6, the powder compact was annealed at 780°C.

[0047] Then, the carbon content (%), strength (MPa), and hysteresis loss (kw / m) were measured using the same method and conditions as in the above examples. 3 The results are shown in Table 2. [Table 2]

[0048] As shown in Table 2, in both Example 5, which was annealed at 750°C, and Example 6, which was annealed at 780°C, the carbon content was 0.01% or more. In addition, in both Example 5 and Example 6, the strength was improved, exceeding 45 (MPa). In addition, looking at the hysteresis loss, both Example 5 and Example 6 had a value of 300 (kW / m 3 ), and low hysteresis loss was achieved. Therefore, it was confirmed that the effects of the present invention can be achieved even when the annealing temperature is 700°C or higher.

[0049] (Other embodiments) Although the present specification describes an embodiment of the present invention, this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-described embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. The embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

Claims

1. FeSiAl alloy powder; an insulating layer made of an insulating resin adhered to the surface of the FeSiAl alloy powder and covering the surface of the FeSiAl alloy powder; Equipped with the insulating layer contains carbon; the proportion of carbon in the powder magnetic core is 0.01% or more and 0.1% or less; A powder magnetic core characterized by:

2. The carbon content is 0.025% or less. The powder magnetic core according to claim 1 ,

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