CN117733138A - Method for producing powder for dust core, and powder for dust core - Google Patents
Method for producing powder for dust core, and powder for dust core Download PDFInfo
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- CN117733138A CN117733138A CN202311183809.8A CN202311183809A CN117733138A CN 117733138 A CN117733138 A CN 117733138A CN 202311183809 A CN202311183809 A CN 202311183809A CN 117733138 A CN117733138 A CN 117733138A
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- Powder Metallurgy (AREA)
- Soft Magnetic Materials (AREA)
Abstract
The invention provides a method for producing powder for dust core, wherein inorganic insulating powder is uniformly adhered around soft magnetic powder, and powder for dust core. The method for producing a powder for a dust core includes a mixing step in which a soft magnetic powder and an inorganic insulating powder are added to a mixing vessel, and the inorganic insulating powder is attached to the periphery of the soft magnetic powder. In the mixing step, the soft magnetic powder and the inorganic insulating powder are mixed so as to be dispersed and scattered in a plurality of directions other than one direction in the mixing vessel, whereby the inorganic insulating powder is attached to the periphery of the soft magnetic powder.
Description
Technical Field
The present invention relates to a method for producing a powder for a dust core, the powder being obtained by mixing an inorganic insulating powder with a soft magnetic powder, and the powder for a dust core.
Background
Coil components such as reactors are used in various applications such as office automation (office automation, OA) equipment, solar power generation systems, and automobiles. The coil component is provided with a coil in the core. As the core, a dust core is used.
The dust core is produced by the following operations: in tons (ton)/cm 2 About tens of tons/cm 2 Such high pressure presses the powder for the powder magnetic core to produce a pressed powder compact, and the pressed powder compact is subjected to a heat treatment called annealing. Annealing is performed to remove strain generated during press forming.
The powder for dust core contains a soft magnetic powder and an inorganic insulating powder. An inorganic insulating powder is attached around the soft magnetic powder. By attaching the inorganic insulating powder around the soft magnetic powder, the soft magnetic powder can be insulated from each other, and the heat treatment temperature at the time of annealing can be increased.
[ Prior Art literature ]
[ patent literature ]
[ patent document 1] Japanese patent laid-open No. 2021-145065
Disclosure of Invention
[ problem to be solved by the invention ]
On the other hand, the inorganic insulating powder may not be uniformly adhered around the soft magnetic powder. That is, the inorganic insulating powder may be coagulated and attached to one site in a concentrated manner, or conversely, the inorganic insulating powder may not be attached, and the surface of the soft magnetic powder may be exposed.
When the inorganic insulating powder is not uniformly adhered, the flowability of the soft magnetic powder deteriorates and cannot be filled into the corners of the mold, thereby affecting the dimensional accuracy and weight of the powder magnetic core. In addition, when the insulating film is formed using a silicone resin or the like, the adhesion of the insulating film becomes unstable, and the magnetic characteristics are affected. Further, when the soft magnetic powder to which the inorganic insulating powder is attached is subjected to heat treatment, the soft magnetic powder is solidified, and is required to be knocked and crushed by a hammer or the like, and productivity is also poor.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing a powder for dust core, in which an inorganic insulating powder is uniformly adhered around a soft magnetic powder, and a powder for dust core.
[ means of solving the problems ]
The method for producing a powder for a dust core of the present invention is characterized by comprising a mixing step in which a soft magnetic powder and an inorganic insulating powder are added to a mixing container and the inorganic insulating powder is attached to the periphery of the soft magnetic powder, and in which the soft magnetic powder and the inorganic insulating powder are mixed so as to be dispersed and scattered in a plurality of directions other than one direction in the mixing container.
The powder for a dust core of the present invention is characterized by comprising: soft magnetic powder; and an inorganic insulating powder attached to the periphery of the soft magnetic powder, wherein when an average value of oxygen amounts of the soft magnetic powder attached to the inorganic insulating powder collected from a plurality of positions on an upper surface of a mixing vessel is X and a standard deviation is sigma, a coefficient of variation CV value obtained by dividing the standard deviation sigma by the average value X is 0.023 or less.
[ Effect of the invention ]
The present invention provides a method for producing a powder for dust core, wherein an inorganic insulating powder is uniformly adhered around a soft magnetic powder, and a powder for dust core.
Drawings
Fig. 1 is a schematic view showing a place where powder for a dust core is collected from a mixer.
Fig. 2 is a graph of the coefficient of variation CV values of examples 1 to 4 and comparative example 1.
Fig. 3 (a) and 3 (b) are SEM images at magnification 5000, fig. 3 (a) is an SEM image of example 2, and fig. 3 (b) is an SEM image of comparative example 1.
Fig. 4 (a) and 4 (b) are SEM images at a magnification of 10000, fig. 4 (a) is an SEM image of example 2, and fig. 4 (b) is an SEM image of comparative example 1.
Fig. 5 is a graph of the densities of examples 1 to 4 and comparative example 1.
Fig. 6 is a graph showing hysteresis loss, eddy current loss, and core loss in examples 1 to 4 and comparative example 1.
FIG. 7 is a graph of initial magnetic conductivities μ0 and 10kA/m for example 1 to example 4 and comparative example 1, and a magnetic permeability μ10k.
Fig. 8 is a graph of resistivity values of examples 1 to 4 and comparative example 1.
Fig. 9 is a graph of wear values of examples 1A to 4A and comparative example 1A.
Detailed Description
(embodiment)
Hereinafter, the powder for dust core and the dust core according to the present embodiment will be described in detail. The present invention is not limited to the embodiments described below.
The dust core is a magnetic material used for a core of a coil component mounted in OA equipment, a solar power generation system, an automobile, or the like. The powder magnetic core is formed by compacting and annealing powder for the powder magnetic core. The powder for dust core contains soft magnetic powder and inorganic insulating powder. The powder for a dust core is obtained by mixing a soft magnetic powder with an inorganic insulating powder, and uniformly adhering the inorganic insulating powder around the soft magnetic powder.
An insulating film containing an insulating material is formed around the powder for a dust core. A powder for a powder magnetic core covered with the insulating coating film is press-molded to produce a powder compact, and the powder compact is annealed to produce a powder magnetic core.
The soft magnetic powder contains iron as a main component. As the soft magnetic powder, pure iron powder, permalloy (Fe-Ni alloy) containing iron as a main component, si-containing iron alloy (Fe-Si alloy), sendust (Fe-Si-Al alloy), or a mixed powder of two or more of these powders can be used. As the soft magnetic powder, amorphous alloy or nanocrystalline alloy powder may be used. The particle diameter (median diameter D50) of the soft magnetic powder is preferably 1 μm or more and 200 μm or less.
The Fe-Si-Al alloy powder contains, for example, about 7 to 11wt% of Si and about 4 to 8wt% of Al relative to Fe. The Fe-Si-Al alloy powder may contain, for example, about 1 to 3wt% of Ni relative to Fe. Further, co, cr or Mn may be contained in the Fe-Si-Al alloy powder.
The Si-containing ferroalloy may also contain Co, al, cr or Mn. In the case of using permalloy (fe—ni alloy), the ratio of Ni to Fe is preferably 50:50 or 25:75, but other ratios are possible. For example, fe-80Ni, fe-36Ni, fe-78Ni, fe-47Ni may be used. In addition to Fe and Ni, si, cr, mo, cu, nb, ta and the like may be included. Examples of the Fe-Si alloy powder include Fe-3.5% Si alloy powder and Fe-6.5% Si alloy powder, and the Si content relative to Fe may be other than 3.5% or 6.5%. The pure iron powder contains more than 99% of Fe.
An inorganic insulating powder is attached around the soft magnetic powder. By attaching an inorganic insulating powder around the soft magnetic powder, the soft magnetic powder can be insulated from each other. The inorganic insulating powder is uniformly adhered around the soft magnetic powder. The uniformity as referred to herein means a state in which the inorganic insulating powder is attached to the periphery of the soft magnetic powder in an equal amount without omission. In other words, the inorganic insulating powder is not coagulated and aggregated, or the inorganic insulating powder is not attached, and the surface of the soft magnetic powder is not exposed. Whether the adhesion was uniform or not was confirmed by observation under an electron microscope at 5000 times or 10000 times or whether the coefficient of variation CV value described later was 0.023 or less.
The inorganic insulating powder is uniformly adhered around the soft magnetic powder, so that the fluidity of the powder for a dust core is improved and the density is improved, thereby reducing hysteresis loss. In addition, the inorganic insulating powder ensures a distance between soft magnetic powders, and thus an adhesive effect by an insulating material such as a silicone resin or a silane coupling agent constituting an insulating film can be obtained more satisfactorily, and strength becomes extremely high.
If the inorganic insulating powder is agglomerated and unevenly adheres to the periphery of the soft magnetic powder, there is a possibility that the insulating material is not adhered to the agglomerated site or the amount of the adhering material becomes small. If the amount of the insulating material to be adhered is small, the adhesion between the soft magnetic powders at the above-mentioned portions becomes weak, and chipping or cracking of the core tends to occur.
On the other hand, as in the present embodiment, when the inorganic insulating powder is uniformly adhered to the periphery of the soft magnetic powder, it is possible to suppress the occurrence of a portion where the insulating material is not adhered or is less adhered around the soft magnetic powder (strictly, around the periphery of the inorganic insulating powder adhered to the periphery of the soft magnetic powder). Therefore, the adhesion between the soft magnetic powders is improved and the strength is improved. Thus, chipping or cracking of the core can be prevented.
As the inorganic insulating powder, aluminum oxide powder, magnesium oxide powder, silicon dioxide powder, titanium dioxide powder, zirconium oxide powder, or the like can be used. The particle size of the inorganic insulating powder is smaller than that of the soft magnetic powder. The particle diameter (median diameter D50) of the inorganic insulating powder is preferably 7nm or more and 200nm or less.
The coefficient of variation CV value of a powder (hereinafter, also referred to as "mixed powder") in which an inorganic insulating powder is attached to the periphery of the soft magnetic powder is 0.023 or less. The variation coefficient CV value was measured by collecting the mixed powder from a plurality of parts in the mixing vessel and measuring the oxygen amount of each collected part. The average value X and standard deviation sigma of the oxygen amount were calculated from the respective measurement results. Then, a coefficient of variation CV value obtained by dividing the standard deviation σ by the average value X is calculated.
The collection site is not limited to this, and collection is performed from five sites on the upper surface of the mixing vessel. As shown in fig. 1, for example, the five parts are the center part of the mixer (fig. 1 (1)), and the four part centers (fig. 1 (2) to (5)) at equal intervals along Zhou Xiangwei, and the positions of 12, 3, 6, and 9 points are the positions of a timepiece. In this way, by measuring the oxygen amount of the mixed powder at a plurality of dispersed sites other than one site, the accurate coefficient of variation CV value can be calculated.
In the case where the mixer is rectangular, five parts in total may be provided at the center and each vertex. In addition, the collection may be performed not only from the upper surface of the mixing vessel, but also from the bottom surface of the mixing vessel or from a central portion between the upper surface and the bottom surface, and may be performed from the upper surface, the bottom surface, and the central portion, respectively.
An insulating film is formed around the powder for a dust core. The insulating film contains an insulating material. As the insulating material, a silane compound, a silicone resin, a silicone oligomer can be used. Further, one kind of insulating material may be used as the insulating film, or two or more kinds may be used. When two or more kinds of insulating films are used, various insulating films may be laminated, or a single layer formed by mixing two or more kinds of insulating materials may be used. That is, for example, when a silane compound and a silicone resin are used, an insulating film layer containing a silane compound may be formed around the powder for a dust core, an insulating film layer containing a silicone resin may be formed around the insulating film layer, or a single-layer insulating film layer may be formed by mixing a silane compound and a silicone resin.
The silane compound contains 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 group or a methoxy group can be used, and tetraethoxy silane is particularly preferable. As the silane coupling agent, an aminosilane-based, epoxysilane-based, or isocyanurate-based silane coupling agent can be used, and 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, or tris- (3-trimethoxysilylpropyl) isocyanurate is particularly preferable.
The amount of the silane compound to be added is preferably 0.05wt% or more and 1.0wt% or less with respect to the soft magnetic powder. By setting the addition amount of the silane compound to the above range, the flowability of the soft magnetic powder can be improved, and the density, magnetic properties, and strength properties of the molded dust core can be improved.
The silicone resin is a resin having a siloxane bond (si—o—si) in the main skeleton. By using a silicone resin, a film having excellent flexibility can be formed. Examples of the silicone resin include methyl group, methylphenyl group, propylphenyl group, epoxy resin modified group, alkyd resin modified group, polyester resin modified group, and rubber group. Among them, in particular, when a methylphenyl silicone resin is used, an insulating film having a small heating loss and excellent heat resistance can be formed.
The addition amount of the silicone resin is preferably 0.6wt% or more and 2.5wt% or less with respect to the soft magnetic powder. If the amount is less than 0.6wt%, the insulating film cannot function, and eddy current loss increases, resulting in a decrease in magnetic properties. If the amount is more than 2.5wt%, the density of the powder magnetic core is lowered.
As silicone oligomer, use can be made of: a methyl-based or methylphenyl-based silicone oligomer having an alkoxysilane group and having no reactive functional group; or epoxy, epoxymethyl, mercapto, mercaptomethyl, methyl acrylate, methyl methacrylate, vinylphenyl silicone oligomers having alkoxysilane groups and reactive functional groups; or an alicyclic epoxy-based silicone oligomer having a reactive functional group other than an alkoxysilane group. In particular, a thick and hard insulating film can be formed by using a methyl-or methylphenyl-based silicone oligomer. In addition, in view of ease of forming the insulating film, a methyl group or a methylphenyl group having a relatively low viscosity may be used.
The addition amount of the silicone oligomer is preferably 0.1wt% or more and 2.0wt% or less with respect to the soft magnetic powder. If the amount is less than 0.1wt%, the film cannot function as an insulating film, and eddy current loss increases, thereby deteriorating magnetic properties. If the amount is more than 2.0wt%, the density of the powder magnetic core is lowered.
When an insulating film is formed around the powder for a dust core, pure water may be added in addition to the insulating material. By adding pure water, the reaction of the insulating material is promoted.
The powder for a powder magnetic core having an insulating film formed thereon is filled into a mold, and the powder is subjected to press molding at a predetermined pressure, thereby forming a powder compact. Then, the compact is annealed to form a powder magnetic core.
Next, a method of manufacturing the powder for a powder magnetic core will be described. The method for producing the powder for a dust core includes a mixing step. The method for producing the powder magnetic core includes a powder heat treatment step, an insulating film formation step, a lubricant addition step, a press molding step, and an annealing step.
The mixing step is a step of adding and mixing the soft magnetic powder and the inorganic insulating powder into a mixing vessel. In the mixing step, the soft magnetic powder and the inorganic insulating powder are mixed so as to be scattered in all directions. That is, the soft magnetic powder and the inorganic insulating powder are dispersed and moved back and forth in a plurality of directions in addition to a predetermined direction in the mixing container. For example, a hemispherical elastic member (e.g., a rubber ball) having flexibility may be provided on the bottom surface of the mixing container, and the soft magnetic powder or the inorganic insulating powder may be scattered in all directions by expanding and contracting the elastic member while swinging the mixing container and rotating the elastic member. Further, the soft magnetic powder or the inorganic insulating powder may be scattered in all directions by irregularly eccentrically rotating the mixing vessel. By passing through the mixing process, the inorganic insulating powder is uniformly attached around the soft magnetic powder.
The mixing time is preferably 2 minutes to 20 minutes, more preferably 5 minutes to 20 minutes. When the range is set, the inorganic insulating powder adheres uniformly around the soft magnetic powder, and the coefficient of variation CV value is 0.023 or less. In general, it is considered that the inorganic insulating powder adheres more uniformly when mixed for a long period of time, but when mixed for a long period of time, aggregation sites of the inorganic insulating powder further occur around the uniformly adhered inorganic insulating powder, and there is a possibility that the inorganic insulating powder adheres unevenly.
In the present invention, the effect is more obtained when the particle size of the soft magnetic powder is 1 μm or more and 200 μm or less, and the particle size of the inorganic insulating powder is 7nm or more and 200nm or less. In particular, the small powder having a particle diameter of 1 μm or more and 5 μm or less is a soft magnetic powder, and the inorganic insulating powder has a particle diameter of 7nm or more and 200nm or less, which shows more remarkable effects.
For example, when soft magnetic powder exceeding 5 μm and not more than 200 μm is mixed with inorganic insulating powder of 7nm or more and not more than 200nm, if dispersion in a plurality of directions is impossible as in the conventional V-type mixer, the particle size difference is large and only the inorganic insulating powder is agglomerated. On the other hand, as in the present embodiment, the inorganic insulating powder can be prevented from agglomerating by dispersing in all directions, that is, in a plurality of directions instead of in one direction.
When a soft magnetic powder having a particle size of 1 μm or more and 5 μm or less is mixed with an inorganic insulating powder having a particle size of 7nm or more and 200nm or less, the nano-sized inorganic insulating powder is subjected to primary and secondary agglomeration by van der Waals force (van der Waals force) to form a primary agglomeration of the soft magnetic powder and a secondary agglomeration of the inorganic insulating powder, respectively. However, as in the present embodiment, the primary coagulation and the secondary coagulation can be suppressed by dispersing the particles in all directions, that is, in a plurality of directions instead of in one direction.
After the mixing process, a powder heat treatment process is performed. The powder heat treatment step is a step of heat treating a powder for a dust core. That is, the process is a process of heat-treating a soft magnetic powder having an inorganic insulating powder attached around the powder. In the powder heat treatment step, the powder is heated in a non-oxidizing atmosphere for 1 to 6 hours. The non-oxidizing atmosphere includes a low oxygen atmosphere such as 0.01% of the atmosphere, an inert gas atmosphere, or a reducing gas atmosphere. The inert gas may be a rare gas such as Ar or N 2 . Further, as the reducing gas, H may be mentioned 2 . The heat treatment temperature is 400 ℃ to 1200 ℃.
The insulating film forming step is a step of forming an insulating film around the powder for a dust core. In the insulating coating step, an insulating material is added to the powder for a dust core and mixed. After the insulating material is mixed, the mixture is heated and dried, whereby an insulating film is formed around the powder for a dust core. The heating and drying conditions are not limited to these, and the drying is performed at a temperature of 25 ℃ or higher and 350 ℃ or lower for about 2 hours.
The lubricant adding step is a step of adding a lubricant to the powder for a dust core on which the insulating film is formed. Examples of the lubricant include, but are not limited to, stearic acid and metal salts thereof, ethylene bis-stearamide (ethylene bisstearamide), ethylene bis-stearamide (ethylene bisstearoamide), and ethylene bis-stearamide (ethylene bisstearateamide). The amount of the lubricant to be added is preferably about 0.2wt% to about 0.8wt% based on the powder for the dust core. By setting the range as described above, the sliding between powders for the dust core can be further improved.
The press molding step is a step of producing a pressed powder compact by press molding a powder for a pressed powder magnetic core to which a lubricant is added. First, a powder for a dust core is filled into a mold, and then, the powder is fed at a rate of 5ton/cm 2 ～20ton/cm 2 Pressurization is performed. Thus, a compact was produced.
The annealing step is a step of annealing the compact produced by the press molding step to remove strain in the soft magnetic powder. In the annealing step, the heat treatment of the compact is performed at 600 ℃ or higher and at a temperature lower than the temperature at which the insulating film formed around the soft magnetic powder is broken (for example, 900 ℃) in a non-oxidizing atmosphere such as nitrogen gas, hydrogen gas, a mixed gas of nitrogen and hydrogen, or a low oxygen atmosphere of about 0.01%. The powder magnetic core is produced by the annealing step.
Example (example)
The present invention will be described in more detail based on examples. Further, the present invention is not limited to the following examples. Powder for dust cores of examples 1 to 4 and comparative example 1 and dust cores were produced.
First, the powder for dust core of example 1 was prepared. Pure iron powder having an average particle diameter of 43 μm was used as the soft magnetic powder, and Al having an average particle diameter of 13nm was used as the inorganic insulating powder 2 O 3 Powder (alumina powder). 1.0wt% of Al is used with respect to the pure iron powder 2 O 3 And (3) powder.
Pure iron powder and Al 2 O 3 The powder was added to a swing mixer (Qiandao field machine (Chiyoda Machinery) Co., ltd., OM30 SA) andmixing is performed. The swing mixer is used for mixing pure iron powder and Al 2 O 3 The powder is mixed while being scattered all around in the mixing vessel. The mixing time was 5 minutes. Thus, powder for dust core of example 1 was produced.
The powder for dust cores of examples 2 to 4 was different from example 1 only in mixing time, and other materials, production processes, and production conditions were the same as in example 1. The mixing time was 10 minutes in example 2, 15 minutes in example 3, and 20 minutes in example 4.
In comparative example 1, as in example 1, pure iron powder having an average particle diameter of 43 μm was used as the soft magnetic powder, and Al having an average particle diameter of 13nm was used as the inorganic insulating powder 2 O 3 And (3) powder. 1.0wt% Al is used with respect to pure iron powder 2 O 3 And (3) powder. Then, pure iron powder and Al are added 2 O 3 The powder was added to a V-type mixer (German and shou Co., ltd., V-60) and mixed. Since the V-type mixer is used, pure iron powder and Al 2 O 3 The powder moves only in a certain direction in the mixer and is mixed. In other words, in comparative example 1, pure iron powder and Al 2 O 3 The powder does not fly all around. The mixing time was 5 minutes. Thus, powder for dust core of comparative example 1 was produced.
The powder for dust cores of examples 1 to 4 and comparative example 1 thus produced was collected from the mixer, and the oxygen amount was measured. In each of examples 1 to 4 and comparative example 1, powder for dust cores was collected from five positions on the upper surface of the mixer. As shown in fig. 1, four parts (fig. 1 (2) to (5)) equally spaced along Zhou Xiangwei are collected from the center part of the circular mixer (fig. 1 (1)). The amount collected was 50g at each site. Further, since the V-type mixer was used in comparative example 1, the sample was temporarily transferred to a circular container, and collected from the positions (1) to (5) shown in fig. 1.
The oxygen amount was measured using an oxygen-nitrogen analyzer (manufactured by LECO corporation, TC 500). For the measurement, the collected pressure0.1g of the powder for powder magnetic core was charged into a carbon crucible and heated at 2000℃to produce CO or CO by infrared absorption 2 The gas calculates the oxygen content. Oxygen amounts were measured for the powder for dust cores collected at five positions, and the average value X and standard deviation σ thereof were calculated. Further, a coefficient of variation CV value obtained by dividing the standard deviation σ by the average value X is calculated. In examples 1 to 4 and comparative example 1, the oxygen amounts at five locations were measured, and the average value X, standard deviation σ, and coefficient of variation CV were calculated.
The calculated results are shown in table 1. Fig. 2 is a graph showing the coefficient of variation CV values of examples 1 to 4 and comparative example 1.
TABLE 1
As shown in table 1 and fig. 2, pure iron powder and Al were mixed 2 O 3 The coefficient of variation CV value of examples 1 to 4, in which the powder was scattered in all directions, was 0.023 or less, which was about 0.005 smaller than CV0.0278 of comparative example 1.
Further, in example 2 and comparative example 1 among the collected powder for dust core, in order to obtain a powder for dust core containing Al 2 O 3 The adhesion of the powder to the pure iron powder was confirmed, and observed by a field emission scanning electron microscope (JSM-7001F manufactured by japan electronics corporation). A predetermined amount of powder was attached to a carbon tape in a dispersed state, and a secondary electron image was observed and photographed at 10kV under a vacuum environment.
The imaging results are shown in fig. 3 (a) and 3 (b) and fig. 4 (a) and 4 (b). Fig. 3 (a) and 3 (b) are SEM images at magnification 5000, fig. 3 (a) is an SEM image of example 2, and fig. 3 (b) is an SEM image of comparative example 1. Fig. 4 (a) and 4 (b) are SEM images at a magnification of 10000, fig. 4 (a) is an SEM image of example 2, and fig. 4 (b) is an SEM image of comparative example 1. In each SEM image, white portions represent Al 2 O 3 And (3) powder.
As shown in fig. 3 (a) and 4 (a), it can be seen that,in example 2, the white portion was not condensed at one site, al 2 O 3 The powder is uniformly dispersed around the pure iron powder. On the other hand, in comparative example 1, as shown by the black circles in FIG. 3 (b) and FIG. 4 (b), it is seen that white blocks, al are scattered 2 O 3 The powder is agglomerated. Thus, in the process of mixing pure iron powder with Al 2 O 3 When the powders were mixed so as to be scattered all around, the coefficient of variation CV value became 0.023 or less, and it was confirmed that Al was contained 2 O 3 The powder is uniformly adhered.
As shown in table 1 and fig. 2, the variation coefficient CV value of example 4, in which the mixing time was 20 minutes, increased toward the peak of the lower limit of the variation coefficient CV value in the vicinity of example 2 and example 3. From this, it was confirmed that the mixing time was not long, but may be 5 minutes to 20 minutes.
Then, powder for dust cores of examples 1 to 4 and comparative example 1 were used to produce dust cores, respectively. The method for producing each of the powder magnetic cores of examples 1 to 4 and comparative example 1 is the same as described below.
In the process of mixing pure iron powder with Al 2 O 3 After the powder is mixed, the powder for dust core is subjected to powder heat treatment. The powder heat treatment is performed at 1000 ℃ in a non-oxidizing atmosphere in which a mixed gas of hydrogen and nitrogen is injected. The heat treatment time was 2 hours.
After the powder heat treatment, a silicone resin and a silane coupling agent are added to form an insulating film around the powder for a dust core. 1.8wt% of silicone resin was added to the pure iron powder, 0.5wt% of silane coupling agent was added to the pure iron powder, and the mixture was mixed for 1 minute. Then, 0.5wt% pure water was added to the pure iron powder, and the mixture was further mixed for 1 minute. Then, the insulating film was formed by exposing the film to a drier maintained at 180℃for 2 hours and then drying the film by heating.
After the insulating film was formed, the powder for a powder magnetic core at room temperature was passed through a sieve having a pore size of 850 μm for the purpose of pulverizing the powder. Then, the lubricant was added and mixed for 1 minute. Zinc stearate is used as a lubricant. 0.5wt% of lubricant is added relative to the pure iron powder.
After the lubricant was mixed, the powder for a powder magnetic core to which the lubricant was added was filled into a mold, and press-molded, thereby producing an annular powder compact having an outer diameter of 20.97mm, an inner diameter of 12.48mm, and a height of 4.8 mm. The pressure of the press forming was 9.5ton/cm 2 Is carried out.
After the press molding, the densities of the compact powders of examples 1 to 4 and comparative example 1 were measured. Density (kg/m) 3 ) Is apparent density. The outer diameter, inner diameter and height of the powder magnetic core were measured, and based on these values, pi× (outer diameter 2 -inner diameter 2 ) The volume (m) of the compact was calculated from the X height 3 ). Then, the weight of the powder magnetic core is measured, and the density is calculated by dividing the measured weight by the calculated volume.
The calculated results are shown in table 2. Fig. 5 shows graphs of densities of examples 1 to 4 and comparative example 1.
TABLE 2
| Density (kg/m) 3 ) | |
| Comparative example 1 | 6.77 |
| Example 1 | 6.80 |
| Example 2 | 6.79 |
| Examples3 | 6.77 |
| Example 4 | 6.79 |
As shown in table 2 and fig. 5, the densities of examples 1 to 4 were equal to or higher than those of comparative example 1. Specifically, only example 3 had the same density as that of comparative example 1, but it was confirmed that example 1, example 2 and example 4 had an increased density as compared with comparative example 1.
Further, the respective compact bodies of examples 1 to 4 and comparative example 1 were annealed to remove strain generated by press molding. Annealing was performed at 620 ℃ in a non-oxidizing atmosphere in which a mixed gas of hydrogen and nitrogen was injected. The heat treatment time was 2 hours. Thus, powder magnetic cores of examples 1 to 4 and comparative example 1 were produced.
The dust cores of examples 1 to 4 and comparative examples were measured for core loss, magnetic permeability, specific resistance value, and abrasion value (Rattler value).
In measuring the core loss, a copper wire having a diameter of 0.5mm was wound around the powder magnetic core for 30 turns as a primary winding, and 30 turns as a secondary winding. Then, using a BH analyzer (rock-through measurement Co., ltd.: SY-8219) as a magnetic measuring device, iron loss Pcv (kW/m) was measured at a frequency of 20kHz and a maximum magnetic flux density Bm of 200mT 3 ) Is measured. From the measurement result of the core loss Pcv, hysteresis loss Phv (kW/m) 3 ) Eddy current loss Pev (kW/m) 3 ). Hysteresis loss Phv (kW/m) 3 ) And eddy current loss Pev (kW/m) 3 ) This is done by: the hysteresis loss coefficient (Kh) and the eddy current loss coefficient (Ke) are calculated by the least square method using the following equations (1) to (3) for the frequency curve of the core loss Pcv.
Pcv＝Kh×f+Ke×f 2 ‥(1)
Phv＝Kh×f‥(2)
Pev＝Ke×f 2 ‥(3)
Pcv: iron loss of
Kh: hysteresis loss coefficient
Ke: coefficient of eddy current loss
f: frequency of
Phv: hysteresis loss
Pev: eddy current loss
The measurement results are shown in table 3. Fig. 6 shows graphs of hysteresis loss, eddy current loss, and core loss in examples 1 to 4 and comparative example 1. In the bar chart of fig. 6, hysteresis loss is darkened.
TABLE 3
| Pcv(kW/m 3 ) | Phv(kW/m 3 ) | Pev(kW/m 3 ) | |
| Comparative example 1 | 1504 | 1219 | 285 |
| Example 1 | 1210 | 1025 | 185 |
| Example 2 | 1232 | 1049 | 183 |
| Example 3 | 1241 | 1058 | 183 |
| Example 4 | 1267 | 1075 | 192 |
As shown in Table 3 and FIG. 6, al 2 O 3 The eddy current loss of examples 1 to 4, in which the powder was uniformly adhered, was reduced by 100 (kW/m) as compared with comparative example 1 3 ) Left and right. In addition, the hysteresis loss was also reduced by 150 to 200 (kW/m) in examples 1 to 4 as compared with comparative example 1 3 ) Left and right. Thus, in examples 1 to 4, eddy current loss and hysteresis loss were each drastically reduced by 100 (kW/m 3 ) As a result, the iron loss was greatly reduced by 200 (kW/m 3 ) The above. Namely, by making Al 2 O 3 The effect of uniform adhesion of the powder is remarkably exhibited.
Regarding the magnetic permeability, two copper wires with a diameter of 0.5mm were wound side by side on the dust core for 30 turns. Then, using an inductance/capacitance/resistance (Inductance Capacitance Resistance, LCR) table (manufactured by Hewlett packard, 4284A), initial magnetic permeability μ0 of 0A/m and magnetic permeability μ10k of 10kA/m were measured from the inductance of the magnetic field at 20kHz and 1.0V.
The measurement results are shown in table 4. Fig. 7 is a graph showing initial magnetic conductivities μ0 and 10kA/m of example 1 to example 4 and comparative example 1, respectively, and magnetic conductivities μ10k. In addition, in the bar chart of fig. 7, the initial magnetic permeability μ0 is darkened.
TABLE 4
As shown in Table 4 and FIG. 7, al 2 O 3 In examples 1 to 4, in which the powder was uniformly adhered, the initial magnetic permeability μ0 and the magnetic permeability μ10k of 10kA/m were both improved as compared with comparative example 1. In particular, in examples 1 to 4, the distance between pure iron powders was calculated by Al 2 O 3 Since the powder was uniformly ensured and a minute gap was formed, the magnetic permeability μ10k of 10kA/m at the time of the superposition was 32.5 or more, which was significantly improved as compared with comparative example 1.
The specific resistance value was obtained by measuring four sites on the circular surface of the annular core at equal intervals on the circumference by using a resistivity meter (Lorsta) -GX MCP-T700, manufactured by Analytech, inc.), and calculating the average value of the measurement results of the four sites.
The calculated results are shown in table 5. Fig. 8 is a graph showing resistivity values of examples 1 to 4 and comparative example 1.
TABLE 5
| Resistivity (omega) | |
| Comparative example 1 | 8.7×10 5 |
| Example 1 | 2.8×10 6 |
| Example 2 | 4.3×10 6 |
| Example 3 | 4.5×10 6 |
| Example 4 | 4.1×10 6 |
As shown in table 5 and fig. 8, the resistivity values of examples 1 to 4 were significantly higher than those of comparative example 1. As described above, it is presumed that eddy current loss in examples 1 to 4 was reduced by 100 (kW/m) as compared with comparative example 1 3 ) Left and right, al 2 O 3 The powder adheres uniformly, and as a result, the resistivity value increases and eddy current loss decreases.
Next, the powder compacts of examples 1A to 4A and comparative example 1A were produced. Materials, production steps and production conditions used as examples 1A to 4A and comparative example 1A were the same as examples 1 to 4 and comparative example 1, respectively, up to the step of adding the lubricant. For example, the process up to the lubricant addition in example 1A was performed under the same materials, the same process, and the same conditions as in example 1.
After mixing the lubricant, each of the samples of examples 1A to 4A and comparative example 1A was filled into a die, and press-molded, to prepare a cylindrical compact having an outer diameter of 11.3mm and a height of 10 mm. The pressure of the press forming was 9.0ton/cm 2 Is carried out. Thus, the powder compacts of examples 1A to 4A and comparative example 1A were produced.
Then, the abrasion value was measured. The abrasion value was measured using an abrasion device (manufactured by IntesUKO Co., ltd.). The abrasion value was measured by the abrasion value measurement method (JPMA P11 1992) based on the metal compact of the japanese powder metallurgy industry (Japan Powder Metallurgy Association, JPMA) standard. That is, the core was put into a cylindrical basket having a pore diameter 1180 μm and on which a stainless steel wire net was laid, and the basket was rotated at a rotation speed of 87rpm for 1000 turns, and then the weight of the compact was measured, and the weight was subtracted from the weight measured before rotation to obtain a mass reduction rate, whereby the abrasion value was calculated.
The calculated results are shown in table 6. Fig. 9 shows graphs of wear values of examples 1A to 4A and comparative example 1A.
TABLE 6
| Abrasion value (%) | |
| Comparative example 1A | 3.34 |
| Example 1A | 0.79 |
| Example 2A | 0.78 |
| Example 3A | 0.79 |
| Example 4A | 0.74 |
As shown in table 6 and fig. 9, the abrasion values of examples 1A to 4A were about 1/5 of those of comparative example 1A, and it was confirmed that the strength was extremely improved. Therefore, by making Al 2 O 3 The powder is uniformly adhered to pure iron powder, can be used for manufacturing powder magnetic core with improved strength, and can be used for vehicle-mounted vehicle with high vibration resistance requirementCoil parts such as reactors.
As described above, in each measurement item, examples 1 to 4 had at least equal or higher results than comparative example 1. In particular, the abrasion value was about 1/5 of that of comparative example 1A, which significantly decreased and the strength was improved. It is considered that by making pure iron powder and Al 2 O 3 The powder is dispersed and scattered in all directions to lead Al to 2 O 3 The powder is uniformly adhered around the pure iron powder, the fluidity of the powder is improved, the powder spreads over all corners of the mold, and the strength is improved.
(other embodiments)
In the present specification, embodiments of the present invention have been described, but the embodiments are presented as examples, and are not intended to limit the scope of the invention. The above-described embodiments can be implemented in other various forms, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. The embodiments and modifications thereof are included in the scope and gist of the invention, and are similarly included in the invention described in the claims and their equivalents.
Claims (9)
1. A method for producing a powder for a dust core, characterized by comprising a mixing step,
in the mixing step, soft magnetic powder and inorganic insulating powder are added into a mixing container, the inorganic insulating powder is attached to the periphery of the soft magnetic powder,
in the mixing step, the soft magnetic powder and the inorganic insulating powder are mixed so as to be dispersed and scattered in a plurality of directions other than one direction in the mixing container.
2. The method for producing a powder for dust cores according to claim 1, wherein,
the mixing vessel comprises a hemispherical elastic member having flexibility at the bottom surface,
in the mixing step, the mixing vessel is oscillated and the elastic member is rotated, and the soft magnetic powder and the inorganic insulating powder are dispersed and scattered in a plurality of directions other than one direction in the mixing vessel by the expansion and contraction of the elastic member.
3. The method for producing a powder for dust cores according to claim 1 or 2, characterized in that,
in the mixing step, the mixing vessel is irregularly eccentrically rotated.
4. The method for producing a powder for dust cores according to claim 1 or 2, characterized in that,
in the mixing step, the mixing time is 5 minutes to 20 minutes.
5. The method for producing a powder for dust cores according to claim 3, wherein,
in the mixing step, the mixing time is 5 minutes to 20 minutes.
6. The method for producing a powder for dust cores according to claim 1, wherein,
after the mixing step, regarding the soft magnetic powder to which the inorganic insulating powder is attached, when an average value of oxygen amounts of the soft magnetic powder to which the inorganic insulating powder is attached, which are collected from a plurality of positions on an upper surface of a mixing container, is X and a standard deviation is σ, a coefficient of variation CV value obtained by dividing the standard deviation σ by the average value X is 0.023 or less.
7. The method for producing a powder for dust cores according to claim 1 or 2, characterized in that,
the particle diameter of the soft magnetic powder is 1 μm or more and 200 μm or less,
the particle diameter of the inorganic insulating powder is 7nm to 200 nm.
8. The method for producing a powder for dust cores according to claim 3, wherein,
the particle diameter of the soft magnetic powder is 1 μm or more and 200 μm or less,
the particle diameter of the inorganic insulating powder is 7nm to 200 nm.
9. A powder for a dust core, characterized by comprising:
soft magnetic powder; and
an inorganic insulating powder attached to the periphery of the soft magnetic powder,
regarding the soft magnetic powder to which the inorganic insulating powder is attached, when the average value of the oxygen amounts of the soft magnetic powder to which the inorganic insulating powder is attached, which are collected from a plurality of positions on the upper surface of the mixing vessel, is X and the standard deviation is σ, the coefficient of variation CV value obtained by dividing the standard deviation σ by the average value X is 0.023 or less.
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