Manufacturing method for compacted magnetic core

Abstract

To provide a method for manufacturing a dust core capable of reducing iron loss.SOLUTION: A method for manufacturing a dust core includes: an insulating coating layer-forming step of covering a surface of a soft magnetic powder with an insulating coating layer containing a silicone resin; a molded body-producing step of producing a compacted molded body by pressing the soft magnetic powder covered with the insulating coating layer; and a heat treatment step of annealing the compacted molded body. The heat treatment step includes: a heating step of raising the temperature to a predetermined temperature; and a constant-temperature step of maintaining the predetermined temperature. In the heating step, the hydrogen concentration is controlled to 5.0% or more and 15.0% or less in a temperature range of 400°C or more and 640°C or less.SELECTED DRAWING: Figure 3

Description

[Technical Field] 【0001】 The present invention relates to a method for producing a compacted magnetic core composed of soft magnetic powder coated with an insulating film layer containing a silicone resin. [Background technology] 【0002】 Coil components such as reactors are used in a variety of applications, including office automation equipment, solar power generation systems, automobiles, and uninterruptible power supplies. For example, a reactor is an electromagnetic component that converts electrical energy into magnetic energy for storage and release. A reactor mainly consists of a core and a coil. The coil is wound around the core. When power is supplied to the coil, it generates a magnetic flux. The core is ring-shaped. The core becomes a magnetic path through which the magnetic flux generated by the coil flows. 【0003】 Compacted magnetic cores are sometimes used as the core of reactors. The method for manufacturing compacted magnetic cores involves first pressurizing soft magnetic powder, which has an insulating coating layer made of an insulating material such as silicone resin, to create a compacted body. Pressurization introduces strain into the soft magnetic powder. Therefore, the compacted body is subjected to a heat treatment called annealing to remove the strain. 【0004】 Compacted magnetic cores require magnetic properties that minimize energy loss during changes in magnetic flux density, in order to improve energy exchange efficiency and reduce heat generation. Specifically, the magnetic property related to energy loss is iron loss (Pcv). Iron loss (Pcv) is expressed as the sum of hysteresis loss (Phv) and eddy current loss (Pev). [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2000-030925 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 In recent years, there has been a growing demand for smaller and higher-performance coil components. Therefore, there is a need to improve the magnetic properties of the powdered magnetic cores that make up these coil components, and the demand for powdered magnetic cores with low iron loss is increasing. 【0007】 This invention was made to solve the above problems, and its purpose is to provide a method for manufacturing a compacted magnetic core that can reduce iron loss. [Means for solving the problem] 【0008】 As a result of diligent research, the inventors have found that in the heat treatment to remove strain from soft magnetic powder, the amount of methane gas generated increases sharply in the temperature range of 400°C to 640°C. This methane gas is presumed to be produced when the silicone resin reacts with hydrogen during heat treatment. Further research has revealed that by controlling the hydrogen concentration in this temperature range of 400°C to 640°C, iron loss can be reduced. 【0009】 The present invention is based on the above findings, and the method for manufacturing a powder magnetic core of the present invention includes an insulating coating layer forming step of coating the surface of soft magnetic powder with an insulating coating layer containing a silicone resin, a molded body manufacturing step of pressurizing the soft magnetic powder coated with the insulating coating layer to produce a powder compacted molded body, and a heat treatment step of annealing the powder compacted molded body, wherein the heat treatment step includes a heating step of raising the temperature to a predetermined temperature and a constant temperature step of maintaining the temperature at the predetermined temperature, and in the heating step 、4 In the temperature range of 00°C to 640°C, hydrogen concentration of It is characterized by controlling the level to between 5.0% and 15.0%. [Effects of the Invention] 【0010】 According to the present invention, a method for manufacturing a compacted magnetic core that can reduce iron loss can be obtained. [Brief explanation of the drawing] 【0011】 [Figure 1]It is a graph showing the relationship between the temperature inside the furnace and the generation amount of methane gas. [Figure 2] It is a graph showing the relationship between the hydrogen concentration and the iron loss Pcv. [Figure 3] It is a graph showing the relationship between the hydrogen concentration and the eddy current loss Pev. [Figure 4] It is a graph showing the relationship between the hydrogen concentration and the hysteresis loss Phv. [Figure 5] It is a graph comparing the carbon amount and the specific resistance value between Example 1 and Comparative Example 1. [Figure 6] It is a graph comparing the specific resistance values between Example 3 and Comparative Example 2. 【Mode for Carrying Out the Invention】 【0012】 (Embodiment) The configuration of the compacted powder core of the present embodiment will be described. Note that the present invention is not limited to the embodiments described below. 【0013】 Coil parts such as reactors include a core containing a magnetic material. As the core, a compacted powder core is used. The compacted powder core is produced by filling a powder for compacted powder core, in which the periphery of soft magnetic powder is coated with an insulating material, into a mold, pressure molding it to produce a compacted powder molded body, and subjecting this compacted powder molded body to a heat treatment called annealing. 【0014】 The soft magnetic powder has iron as the main component. As the soft magnetic powder, pure iron powder, permalloy (Fe-Ni alloy) having iron as the main component, Si-containing iron alloy (Fe-Si alloy), sendust alloy (Fe-Si-Al alloy), or a mixed powder of two or more of these powders can be used. Further, amorphous alloy or nanocrystalline alloy powder may be used as the soft magnetic powder. However, as the soft magnetic powder, it is preferable to contain pure iron, that is, to be pure iron or a mixed powder in which pure iron is mixed with other alloy powders. 【0015】 The Fe-Si-Al alloy powder contains, for example, about 7 wt% to 11 wt% of Si and about 4 wt% to 8 wt% of Al with respect to Fe. The Fe-Si-Al alloy powder may contain, for example, about 1 wt% to 3 wt% of Ni with respect to Fe. Further, the Fe-Si-Al alloy powder may contain Co, Cr, or Mn. 【0016】 The Si-containing iron alloy may contain Co, Al, Cr, or Mn. When using permalloy (Fe-Ni alloy), the ratio of Ni to Fe is preferably 50:50 or 25:75, but other ratios may also be used. For example, Fe-80Ni, Fe-36Ni, Fe-78Ni, Fe-47Ni may be used. In addition to Fe and Ni, it may contain Si, Cr, Mo, Cu, Nb, Ta, etc. Examples of Fe-Si alloy powder include Fe-3.5% Si alloy powder and Fe-6.5% Si alloy powder, but the ratio of Si to Fe may be other than 3.5% and 6.5%. The pure iron powder contains 99% or more of Fe. 【0017】 The soft magnetic powder may be produced by a pulverization method or an atomization method. The atomization method may be any of a water atomization method, a gas atomization method, and a water-gas atomization method. 【0018】 The circularity of the soft magnetic powder is preferably 0.85 or more in the powder having an average particle diameter (median diameter D50). When the circularity of the soft magnetic powder is 0.85 or more, the gaps between the soft magnetic powders are reduced, and the density and magnetic permeability can be improved. It is particularly preferable that the circularity of the soft magnetic powder for which the effect of improving the density and magnetic permeability is remarkable is 0.90 or more. Further, the average particle diameter (median diameter D50) of the soft magnetic powder is preferably 1 or more and 100 μm or less. 【0019】 An insulating film layer is formed on the surface of the soft magnetic powder. The insulating film layer is made of an insulating material. Silicone resin is an example of an insulating material. The insulating film layer may be made of silicone resin alone, or it may contain other insulating materials in addition to silicone resin. 【0020】 Examples of silicone resins include silicone resins and silicone oligomers. Silicone resins are resins that have a siloxane bond (Si-O-Si) as their main backbone. By using silicone resins, an insulating film layer with excellent flexibility can be formed. Examples of 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 silicone resins. 【0021】 As silicone oligomers, methyl and methylphenyl types having alkoxysilyl groups and no reactive functional groups, epoxy, epoxymethyl, mercaptomethyl, mercaptomethyl, acrylicmethyl, methacrylatemethyl, and vinylphenyl types having alkoxysilyl groups and reactive functional groups, or alicyclic epoxy types having reactive functional groups instead of alkoxysilyl groups can be used. 【0022】 The amount of silicone resin added is preferably 0.3 wt% to 2.0 wt% relative to the soft magnetic powder. If the amount added is less than 0.3 wt%, it will not function as an insulating film layer, and the magnetic properties will deteriorate due to increased eddy current losses. If the amount added is more than 2.0 wt%, it will lead to a decrease in the density of the compacted magnetic core. 【0023】 Furthermore, a silane coupling agent may be added as an insulating material constituting the insulating coating layer. The amount of silane coupling agent added is preferably 0.05 wt% or more and 3.0 wt% or less relative to the soft magnetic powder. By adding the silane coupling agent within this range, the fluidity of the soft magnetic powder can be improved, as well as the density, magnetic properties, and strength properties of the molded compacted magnetic core can be improved. 【0024】 As silane coupling agents, aminosilane-based, epoxysilane-based, and isocyanurate-based silane coupling agents can be used, with tetraethoxysilane, diphenyldimethylsilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate being particularly preferred. The silane coupling agent may be used individually or in combination of two or more types. 【0025】 A compacted powder body is produced by pressure molding a soft magnetic powder on which an insulating coating layer has been formed as described above. Then, a compacted magnetic core is produced by subjecting this compacted powder body to a heat treatment called annealing. 【0026】 Next, the method for manufacturing a compacted magnetic core will be described in detail. The method for manufacturing a compacted magnetic core includes (1) an insulating film layer formation step, (2) a lubricant addition step, (3) a molded body manufacturing step, and (4) a heat treatment step. 【0027】 (1) Insulating coating layer formation process The insulating film layer formation process involves forming an insulating film layer made of an insulating material around the soft magnetic powder. An insulating material such as silicone resin is added to the soft magnetic powder and mixed, and then the mixture is heated and dried to form an insulating film layer on the surface of the soft magnetic powder. The heating and drying conditions are not limited to these, but are generally between 25°C and 350°C for about 2 hours. 【0028】 Furthermore, when a silane coupling agent is added as an insulating material, the insulating coating layer may be a mixed layer of the silane coupling agent and silicone resin, or it may be a layer of silane coupling agent and a layer of silicone resin laminated together. For example, if the insulating coating layer is laminated in the order of a silane coupling agent layer followed by a silicone resin layer, first, the silane coupling agent is added to and mixed with the soft magnetic powder, and then heated and dried. After that, the silicone resin is added to and mixed with the soft magnetic powder on which the silane coupling agent layer has formed, and then heated and dried, so that a layer of silicone resin is formed on the surface of the silane coupling agent layer. 【0029】 Furthermore, water may be added during the insulating film layer formation process. Examples of water include water and ethanol. The timing of adding water is either after mixing the insulating material with the soft magnetic powder, or in the initial stage of drying the insulating material. The water is added by spraying it as a mist or spray, or by dropping it as fine water droplets. Adding water improves the hydrolysis and condensation reactions necessary for silane coupling agents, etc., and improves the strength of the core. 【0030】 (2) Lubricant addition process After the insulating film layer formation process, the process moves to the lubricant addition process. The lubricant addition process involves adding a lubricant to the soft magnetic powder on which the insulating film layer has been formed. By mixing in the lubricant, the sliding action of the soft magnetic powder particles can be improved, thereby increasing the density of the compacted molded body. Furthermore, it is possible to reduce the punching pressure of the upper punch during pressure molding and prevent the occurrence of vertical lines on the wall surface of the compacted magnetic core due to contact between the mold and the soft magnetic powder. 【0031】 Lubricants are not limited to these, but examples include stearic acid, calcium stearate, lithium stearate, aluminum stearate, zinc stearate, ethylenebis-stearamide, ethylenebis-stearoamide, and ethylenebis-stearate amide. 【0032】 The amount of lubricant added is preferably about 0.2 wt% to 0.8 wt% relative to the soft magnetic powder. This range allows for improved sliding between the soft magnetic powder particles. The lubricant may also be added in two stages, before and after the insulating film layer formation process. 【0033】 (3) Molded product manufacturing process After the lubricant addition process, the molded body manufacturing process is carried out. The molded body manufacturing process is a process in which a compacted powder molded body is produced by pressure molding soft magnetic powder on which an insulating coating layer has been formed. First, the soft magnetic powder on which the insulating coating layer has been formed is filled into a mold, and then 5 ton / cm 2 ~20 tons / cm² 2 The powder is then pressed. In this way, a compacted molded body is produced. 【0034】 The molding pressure is 10 ton / cm². 2 The following is preferable. If the molding pressure is too high, the insulating coating layer may be destroyed. If the insulating coating layer is destroyed, the reduction reaction of the silicone resin will be accelerated in the heat treatment process described later, which may worsen the insulating performance of the insulating coating layer. Therefore, the molding pressure should be set to 10 ton / cm². 2 By following the steps below, an insulating coating layer with good insulating properties can be formed. 【0035】 (4) Heat treatment process After the molded body manufacturing process, the product undergoes a heat treatment process. The heat treatment process involves annealing the compacted molded body produced in the molded body manufacturing process to remove strain within the soft magnetic powder. The heat treatment process includes (4-1) a heating step and (4-2) a constant temperature step. 【0036】 (4-1) Heating process The heating process is the step in the constant-temperature process to raise the temperature to a predetermined level. In the heating process, first, the compacted body is placed in annealing equipment such as a furnace. Then, the temperature inside the annealing equipment is raised to the predetermined level. 【0037】 In the heating process, the hydrogen concentration is controlled to be between 5.0% and 15.0% in the temperature range of 400°C to 640°C. For example, in a mixed gas of nitrogen and hydrogen, the hydrogen concentration in the temperature range of 400°C to 640°C is controlled to be between 5.0% and 15.0%. 【0038】 Furthermore, if the predetermined temperature in the constant-temperature process described later is lower than 640°C, it is sufficient to control the hydrogen concentration from 400°C or higher down to the predetermined temperature. For example, if the predetermined temperature in the constant-temperature process is 600°C, it is sufficient to control the hydrogen concentration in the temperature range of 400°C to 600°C. 【0039】 In the heating process, it is not necessary to control the hydrogen concentration to be between 5.0% and 15.0% in temperature ranges other than 400°C to 640°C. That is, the heating process in the temperature range up to 400°C and the temperature range above 640°C may be carried out in an atmosphere where the hydrogen concentration is less than 5.0% or greater than 15.0%, such as a nitrogen gas atmosphere or a low-oxygen atmosphere of about 0.01%. However, the heating process may be carried out while controlling the hydrogen concentration to be between 5.0% and 15.0% in all temperature ranges. 【0040】 In particular, it is preferable to control the hydrogen concentration to be between 5.0% and 15.0% in the temperature range from the beginning of the heating process up to 400°C. That is, it is preferable to control the hydrogen concentration in the temperature range from the beginning of the heating process up to 640°C. Before 400°C, when the insulating film layer begins to decompose, the lubricant reacts with hydrogen and decomposes, so it is thought that the insulating film layer can be decomposed without any lubricant residue. Therefore, controlling the hydrogen concentration to be between 5.0% and 15.0% in the temperature range from 400°C to 640°C becomes more effective in forming a good insulating film layer. In addition, productivity is improved because the heating can be continued without changing the gas flowing into the furnace once 400°C is reached. 【0041】 The inventors of this invention, through diligent research, have found that a large amount of methane gas is generated during the heating process when the temperature exceeds approximately 400°C. This is a hypothesis and not limited to this mechanism, but it is thought to be caused by the reaction between the silicone resin constituting the insulating coating layer and hydrogen. When the amount of methane gas generated increases, the amount of silicone resin constituting the insulating coating layer decreases, weakening the insulating performance of the insulating coating layer and leading to an increase in eddy current loss. Furthermore, it is presumed that the peak amount of methane gas generation occurs in the range of approximately 550°C to 600°C, and after exceeding the peak, the amount of methane gas generated decreases sharply, and above 640°C, the amount of methane gas generated decreases significantly. Therefore, by controlling the hydrogen concentration in the temperature range of 400 to 640°C, the amount of methane gas generated can be suppressed, and a good insulating coating layer can be formed on the surface of the soft magnetic powder. 【0042】 Furthermore, as described above, the peak in methane gas generation occurs in the range of 550°C to 600°C or below, after which it decreases sharply. Therefore, in order to suppress the amount of methane gas generated and to form a good insulating film layer on the surface of the soft magnetic powder, it is preferable to control the hydrogen concentration in the temperature range from 400°C or above to 600°C or below, which is above the temperature at which the peak in methane gas generation occurs. In addition, by controlling the hydrogen concentration in this heating process to be between 5.0% and 15.0% in the temperature range of 400°C to 640°C, preferably between 400°C and 600°C, hysteresis loss can also be reduced. By controlling the hydrogen concentration in this heating process, iron loss can be reduced. 【0043】 In particular, for the temperature range of 400°C to 640°C, preferably 400°C to 600°C, it is preferable to control the hydrogen concentration to 5.0% to 10.0%. By controlling the heating process in this way, a higher loss reduction effect can be obtained. 【0044】 Furthermore, in the heating process, it is particularly preferable to control the hydrogen concentration to 5.0% to 15.0% or 5.0% to 10.0% in the temperature range of 600°C, which is above the temperature at which the amount of methane gas generated peaks. The amount of methane gas generated increases rapidly from around 425°C during the heating process. Therefore, by controlling the hydrogen concentration between 425°C and 600°C, a reduction in eddy current losses can be achieved more effectively. 【0045】 (4-2) Constant temperature process In the heating process, once the temperature reaches a predetermined level, the process moves to the constant temperature process. In the constant temperature process, the temperature is kept constant while the compacted powder molded body is heat-treated. 【0046】 The constant-temperature process is carried out in a non-oxidizing atmosphere such as a nitrogen gas atmosphere, a hydrogen gas atmosphere, a mixed gas atmosphere of nitrogen and hydrogen, or a low-oxygen atmosphere of about 0.01%. In the constant-temperature process, the temperature is kept constant at 600°C or higher and lower than the temperature at which the insulating coating layer formed around the soft magnetic powder is destroyed (for example, 900°C), and the compacted molded body is heat-treated. The heat treatment time is not limited to this, but is, for example, 1 hour or less. A compacted magnetic core is produced by going through this constant-temperature process. 【0047】 (effect) As described above, the method for manufacturing a compacted magnetic core of this embodiment includes an insulating coating layer formation step of covering the surface of soft magnetic powder with an insulating coating layer containing silicone resin, a molded body manufacturing step of pressurizing the soft magnetic powder covered with the insulating coating layer to produce a compacted molded body, and a heat treatment step of annealing the compacted molded body. The heat treatment step includes a heating step of raising the temperature to a predetermined temperature and a constant temperature step of maintaining the temperature at the predetermined temperature. In the heating step, the hydrogen concentration is controlled to be between 5.0% and 15.0% in a temperature range of at least 400°C to 640°C. 【0048】 This allows for the suppression of the reaction between silicone resin and hydrogen in the temperature range of 400°C to 640°C, where the reaction between silicone resin and hydrogen is activated. As a result, the amount of methane gas generated can be suppressed, an insulating film layer can be formed without deterioration of the insulating function, and eddy current losses can be reduced. Hysteresis losses are also reduced, and iron losses can be reduced. Furthermore, since the amount of methane gas generated can be suppressed, compacted magnetic cores can be manufactured in an environmentally friendly manner. 【0049】 In particular, during the heating process, the hydrogen concentration is controlled to be between 5.0% and 10.0% in the temperature range of at least 400°C to 600°C. This further suppresses the reaction between the silicone resin and hydrogen, resulting in a significant reduction in eddy current loss. 【0050】 The soft magnetic powder contains pure iron, which helps reduce hysteresis loss. 【0051】 (Examples) The present invention will be described in more detail based on the examples. However, the present invention is not limited to the following examples. Compacted magnetic cores of Examples 1-3 and Comparative Examples 1 and 2 were prepared. 【0052】 The compacted magnetic core in Example 1 used pure iron powder produced by water atomization of soft magnetic powder. The pure iron powder had an average particle size of 44 μm. An insulating coating layer was formed on this pure iron powder. 【0053】 As insulating materials, a silicone resin and a silane coupling agent were used. A methylphenyl-based silicone resin was used. The silicone resin was added at a concentration of 1.8 wt% relative to the pure iron powder. The silane coupling agent was added at a concentration of 0.5 wt% relative to the pure iron powder. After adding the silicone resin and silane coupling agent, they were mixed. Then, 0.5 wt% water was added relative to the pure iron powder and mixed. After adding and mixing the water, the mixture was heated and dried. The drying temperature was 180°C and the drying time was 2 hours. This resulted in pure iron powder with an insulating film layer formed on top. 【0054】 After heating and drying, the pure iron powder was passed through a 500 μm sieve to break up any aggregates. Then, a lubricant was added and mixed. Zinc stearate was used as the lubricant. The lubricant was added at a concentration of 0.45 wt% relative to the pure iron powder. 【0055】 After adding and mixing a lubricant, the pure iron powder with the lubricant attached was filled into a mold and pressure-molded to produce a toroidal powder compact with an outer diameter of 20.85 mm, an inner diameter of 12.4 mm, and a height of 5.0 mm. The pressure used for pressure molding was 10.0 ton / cm². 2 I went there. 【0056】 Finally, the compacted body was subjected to heat treatment. First, the compacted body was placed in a furnace (heating furnace: tubular furnace KTF1100℃ series (manufactured by JTEKT Thermo Systems Co., Ltd.)) and heated to 640℃. In Example 1, the heating was carried out in a mixed gas atmosphere of 5% hydrogen and 95% nitrogen. In Example 1, the heating was carried out in this mixed gas atmosphere from the start until it reached 640℃. The flow rate of the mixed gas was 3 L / min. 【0057】 After reaching 640°C during the heating process, the compacted body was annealed for 50 minutes while maintaining the furnace temperature at 640°C. This constant-temperature process was carried out in a mixed gas atmosphere of 5% hydrogen and 95% nitrogen, similar to the heating process. In this way, the compacted magnetic core of Example 1 was manufactured. 【0058】 Examples 2 and 3 differ only in the hydrogen concentration of the atmosphere during the heating process when heat-treating the compacted molded body; otherwise, the materials, manufacturing method, and conditions are the same as in Example 1. In Example 2, the heat treatment of the compacted molded body (both the heating process and the constant temperature process) was carried out in a mixed gas atmosphere with a hydrogen concentration of 10% and a nitrogen concentration of 90%. In Example 3, the heat treatment of the compacted molded body (both the heating process and the constant temperature process) was carried out in a mixed gas atmosphere with a hydrogen concentration of 15% and a nitrogen concentration of 85%. 【0059】 Comparative Examples 1 and 2 differ only in the hydrogen concentration of the atmosphere during the heating step when heat-treating the compacted molded body; otherwise, they use the same materials, manufacturing method, and conditions as Example 1. Comparative Example 1 was carried out in a nitrogen gas atmosphere with a hydrogen concentration of 0%, i.e., a nitrogen concentration of 100%, during both the heating step and the constant temperature step. Comparative Example 2 was carried out in a mixed gas atmosphere with a hydrogen concentration of 50% and a nitrogen concentration of 50% during both the heating step and the constant temperature step. 【0060】 The amount of methane gas (CH4) generated from the compacted magnetic cores prepared as described above in Examples 1-3 and Comparative Examples 1 and 2 was measured. The amount of methane gas generated was measured using a gas analyzer (gas chromatograph Agilent 490 microGC (GL Sciences Co., Ltd.)). The measurement conditions were an analysis range of 10 ppm to 100% and an analysis rate of 2 min / cycle. 【0061】 The results are shown in Figure 1. In the graph shown in Figure 1, the horizontal axis is time (min), and the vertical axis shows the furnace temperature (heat treatment temperature) on the right and the amount of methane gas generated on the left. In Figure 1, the thick solid line shows the furnace temperature during heat treatment, the dashed line shows the amount of methane gas generated in Example 1 with a hydrogen concentration of 5%, the dashed line shows the amount of methane gas generated in Example 2 with a hydrogen concentration of 10%, the long dashed line shows the amount of methane gas generated in Example 3 with a hydrogen concentration of 15%, the short dashed line shows the amount of methane gas generated in Comparative Example 1 with a hydrogen concentration of 0%, and the thin solid line shows the amount of methane gas generated in Comparative Example 2 with a hydrogen concentration of 50%. 【0062】 As shown in Figure 1, it was confirmed that when the temperature exceeded 400°C during the heating process, the amount of methane gas generated exceeded 100 ppm. This is presumed to be due to the start of a reaction between the silicone resin formed as the insulating coating layer and hydrogen. In particular, it was confirmed that the amount of methane gas generated increased sharply when the temperature exceeded 425°C. 【0063】 On the other hand, the peak in methane gas generation occurs in the range of 550°C to 600°C, and after exceeding the peak, the amount of methane gas generated decreases sharply. Therefore, it was confirmed that the reaction between the silicone resin and hydrogen can be suppressed in the temperature range of 400°C to 600°C during the heating process, and a good insulating film layer can be formed. 【0064】 Furthermore, methane gas is also generated in the dotted-line frame (100 min to 250 min) in the graph of Figure 1. However, the generation of methane gas in this range is thought to be due to the reaction between the carbon component in the lubricant and hydrogen. Therefore, the generation of methane gas in this range does not affect the formation of the insulating material layer. In addition, methane gas is also generated in Comparative Example 1, where the hydrogen concentration is 0%, but this is thought to be due to the addition of water. 【0065】 Next, hysteresis loss, eddy current loss, and iron loss were measured for the compacted magnetic cores in Examples 1-3 and Comparative Examples 1 and 2. 【0066】 Iron loss was measured by winding a φ0.45 mm copper wire 30 turns as the primary winding and another 30 turns as the secondary winding around a compacted magnetic core. Then, using a magnetic measuring instrument, a BH analyzer (Iwatsu Instruments Co., Ltd.: SY-8219), the hysteresis loss Phv, eddy current loss Pev, and iron loss Pcv (kW / m) were measured under measurement conditions of a frequency of 20 kHz and a maximum magnetic flux density Bm200 mT. 3 Measurements were taken of the following: 【0067】 This measurement was performed by calculating the hysteresis loss coefficient and eddy current loss coefficient using the least squares method with the following equations (1) to (3) on the frequency curve of iron loss. 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 【0068】 The measurement results are shown in Table 1. Also, Table 1 shows the total amount of methane gas generated up to 470 (min) when the amount of methane gas generated became stable (when the change in the gas generation amount was stable at about 5 ppm) from the time when the heat treatment temperature reached 400 °C or higher. Also, a graph showing the results of the hydrogen concentration and the iron loss Pcv is shown in Figure 2. A graph showing the results of the hydrogen concentration and the eddy current loss Pev is shown in Figure 3. A graph showing the results of the hydrogen concentration and the hysteresis loss Phv is shown in Figure 4. In addition, the total amount of methane gas is also shown in Figures 2 and 3. 【0069】 【Table 1】 【0070】 As shown in Table 1 and Figure 2, in Examples 1 to 3 with a hydrogen concentration of 5% or more and 15% or less, the iron loss is reduced compared to Comparative Examples 1 and 2. In particular, in Examples 1 and 2 with a hydrogen concentration of 5% or more and 10% or less, the iron loss is lower than 1240 (kW / m 3 ), and it was confirmed that it is significantly reduced compared to Example 3 and Comparative Examples 1 and 2. 【0071】 As a factor, as shown in Table 1 and Figure 3, the eddy current losses of Examples 1 to 3 are lower than 600 (kW / m 3 ), and are at good values. Also, for Examples 1 and 2, they are 100 (kW / m 3 ) or more lower than the eddy current loss of Comparative Example 1 with a hydrogen concentration of 0%. On the other hand, the eddy current loss of Comparative Example 2 with a hydrogen concentration of 50% rapidly increases to 1300 (kW / m 3 ). 【0072】 Based on these results and Figure 1, it appears that by maintaining a hydrogen concentration of 5% to 15% in the temperature range of 400°C to 640°C during the heating process, the reaction between the silicone resin and hydrogen can be suppressed, allowing for the formation of a high-quality insulating film layer and thus reducing eddy current losses. 【0073】 Furthermore, the hysteresis loss in Examples 1-3 was reduced compared to Comparative Examples 1 and 2. This confirms that hysteresis loss can be reduced by setting the hydrogen concentration in the range of 5% to 15%. 【0074】 Next, the carbon content and resistivity of the compacted magnetic cores of Example 1 and Comparative Example 1 were measured. The compacted magnetic cores of Example 1 and Comparative Example 1 differed only in shape from those of the above-mentioned Examples, and were otherwise manufactured using the same method and under the same conditions as Example 1 and Comparative Example 1. Specifically, the compacted magnetic core of Example 1 was heat-treated with a hydrogen concentration of 5%, and the compacted magnetic core of Comparative Example 1 was heat-treated with a hydrogen concentration of 0% (100% nitrogen gas). For Example 1 and Comparative Example 1, U-shaped compacted magnetic cores with a length of 73.4 mm, a width of 27.8 mm, and a height of 23.4 mm were manufactured. 【0075】 The carbon content was determined by crushing the compacted magnetic core, which was produced through a heating process and a constant-temperature process, and measuring the amount of carbon remaining. A carbon-sulfur analyzer (EMIA-Pro (manufactured by Horiba, Ltd.)) was used to measure the carbon content. 【0076】 Resistivity was measured using a resistivity meter (Loresta-GX MCP-T700, manufactured by Nitto Seikou Analytech Co., Ltd.). The measurement method used was the four-terminal method. 【0077】 The measurement results are shown in Table 2 below. Figure 5 shows a graph comparing the carbon content and resistivity of Example 1 and Comparative Example 1. In Figure 5, resistivity is shown as a bar graph, and carbon content is shown as a line graph. 【0078】 [Table 2] 【0079】 As shown in Table 2 and Figure 5, Example 1 has a lower residual carbon concentration compared to Comparative Example 1. Furthermore, the resistivity of Example 1 is significantly higher than that of Comparative Example 1, confirming that it has excellent insulating performance. 【0080】 This suggests that hydrogen contributes to the decomposition of the lubricant. The lubricant begins to decompose in the temperature range (100°C to 250°C) before 400°C, when the decomposition of the insulating film layer begins. At this time, the presence of hydrogen accelerates the decomposition of the lubricant, and in Example 1, it appears that the decomposition of the insulating film layer occurred without any lubricant residue. 【0081】 On the other hand, in Comparative Example 1, the lubricant was not completely decomposed and lubricant residue remained before the decomposition of the insulating film layer began. It is presumed that the insulating performance deteriorated due to the influence of the lubricant residue. As a result, it is presumed that although the amount of methane gas generated in Comparative Example 1 was less than that in Example 1, the eddy current loss worsened to more than twice that of Example 1. Therefore, it is considered that controlling the hydrogen concentration in the heating process, even in the temperature range up to 400°C from the beginning, will further enhance the effect of controlling the hydrogen concentration to between 5% and 15% in the temperature range between 400°C and 640°C. 【0082】 Furthermore, the resistivity values ​​of the powder-compacted magnetic cores of Example 3 and Comparative Example 2 were measured. The powder-compacted magnetic cores of Example 3 and Comparative Example 2 differed only in shape from those of the above examples; otherwise, they were manufactured using the same method and under the same conditions as Example 3 and Comparative Example 2. Specifically, the powder-compacted magnetic core of Example 3 was heat-treated with a hydrogen concentration of 15%, and the powder-compacted magnetic core of Comparative Example 2 was heat-treated with a hydrogen concentration of 50%. For Example 3 and Comparative Example 2, U-shaped powder-compacted magnetic cores of the above dimensions were manufactured. The measurement of resistivity values ​​was the same as described above. 【0083】 The measurement results are shown in Table 3 below. Figure 6 shows a graph comparing the resistivity values ​​of Example 3 and Comparative Example 2. 【0084】 [Table 3] 【0085】 As shown in Table 3 and Figure 6, the resistivity of Example 3 is significantly larger than that of Comparative Example 2. As shown in Table 1, the amount of methane gas generated in Example 3 and Comparative Example 2 is about the same. This is because the amount of methane gas generated is maximum at a hydrogen concentration of 15%, reaching a saturation state, and therefore, even when the hydrogen concentration exceeds 15%, there is no significant change in the amount of methane gas generated. 【0086】 However, since Comparative Example 2 had a high hydrogen concentration, the reaction between the silicone resin in the insulating film layer and hydrogen proceeded quickly, leading to the deterioration of the insulating film layer and a significant decrease in resistivity. As a result, although the amount of methane gas generated was the same in Example 3 and Comparative Example 2, the eddy current loss in Example 3 was less than half that of Comparative Example 2, indicating a significant effect of reducing eddy current loss. Based on the above, it appears that in the temperature range of 400°C to 640°C where the insulating film layer decomposes, a good insulating film layer cannot be formed if the hydrogen concentration is too high. By controlling the concentration to 5% to 15%, an insulating film layer with excellent insulating performance can be formed, eddy current loss can be reduced, and as a result, iron loss can also be reduced. 【0087】 (Other embodiments) While embodiments of the present invention have been described herein, these embodiments are presented as examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. Embodiments and their variations are included in the scope and essence of the invention, as well as in the claims and their equivalents.

Claims

[Claim 1] An insulating coating layer formation step in which the surface of soft magnetic powder is coated with an insulating coating layer containing silicone resin, A molded body manufacturing step involves pressurizing the soft magnetic powder coated with the insulating film layer to produce a compacted powder molded body, A heat treatment step for annealing the powder compacted body, Includes, The aforementioned heat treatment step is A heating step to raise the temperature to a predetermined temperature, A constant temperature step in which the temperature is maintained at the predetermined temperature, Includes, In the aforementioned heating step, the hydrogen concentration is controlled to be between 5.0% and 15.0% in the temperature range of 400°C to 640°C. A method for manufacturing compacted magnetic cores characterized by the following. [Claim 2] In the aforementioned heating step, the hydrogen concentration is controlled to be between 5.0% and 10.0% in the temperature range of 400°C to 600°C. A method for manufacturing a compacted magnetic core according to claim 1, characterized by the above. [Claim 3] The aforementioned soft magnetic powder contains pure iron. A method for manufacturing a compacted magnetic core according to claim 1 or 2, characterized by the above.

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