JP2016072553A - Powder-compact magnetic core and method for manufacturing powder-compact magnetic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently increase a mechanical strength without worsening a magnetic property in the case of manufacturing a powder-compact magnetic core with powder for a magnetic core which is arranged by coating soft magnetic metal powder with a swelling lamellar clay mineral.SOLUTION: A powder-compact magnetic core 5 is formed by the steps of: mixing powder for a magnetic core arranged by covering the surface of soft magnetic metal powder 2 with an insulating coat 3 of a swelling lamellar clay mineral, and a resin having a siloxane bond, thereby producing raw material powder for a magnetic core; compacting the raw material powder for a magnetic core into a green compact; and performing a heat treatment on the green compact. In the raw material powder for a magnetic core, the content of the resin is 0.1 to less than 7 wt%. After the heat treatment, the insulating coats 3 of adjacent grains of the soft magnetic metal powder 2 are bound to each other by silica 6.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a dust core and a method for manufacturing a dust core.

  The dust core is an electromagnetic component obtained by compression molding magnetic powder that has been treated with an insulating coating, and is used as a core of a choke coil, a reactor, a transformer, or the like. In recent years, from the viewpoint of resource saving and energy saving, miniaturization and high efficiency of dust cores have been demanded. To meet this requirement, dust cores have excellent magnetic properties, especially high magnetic flux density and low iron. Loss is sought.

  In order to improve the magnetic properties of the dust core, it is effective to reduce the thickness of the insulating coating. For example, Patent Document 1 below shows a magnetic core powder in which a soft magnetic metal powder such as iron powder is coated with an insulating coating made of a swellable layered clay mineral. In this way, by forming the insulating coating with a swellable layered clay mineral, excellent heat resistance and insulating performance can be obtained even if the thickness of the insulating coating is reduced to several tens of nanometers. A lossy magnetic core is obtained.

JP 2014-116573 A Japanese Patent No. 2011-233827 JP 2014-120699 A JP 2014-120723 A

  The dust core must have sufficient mechanical strength to prevent not only excellent magnetic properties but also damage due to vibration applied during use, and damage during handling and coiling during the manufacturing process. However, an insulating coating made of a swellable lamellar clay mineral has a drawback in that a powder magnetic core using a magnetic core powder having such an insulating coating has poor mechanical strength because the binding force between the insulating coatings is low.

  As a method for improving the mechanical strength of the powder magnetic core, for example, in Patent Document 2 described above, iron powder is oxidized by heat-treating the compression-molded powder compact in an oxidizing atmosphere (for example, in steam). Is disclosed. However, since the iron powder is oxidized, distortion (particularly expansion) occurs due to the reaction, so that the insulating coating is deteriorated along with the deformation of the iron powder, and the iron loss may be increased. In addition, the drawback that the binding force between the insulating coatings made of the swellable layered clay mineral is still not solved, and the mechanical strength of the dust core cannot be sufficiently increased.

  On the other hand, in Patent Documents 3 and 4 described above, in order to increase the strength of the powder magnetic core, a raw material powder using a resin such as an acrylic resin (Patent Document 3) or a methylphenyl silicone resin (Patent Document 4) as a binder. Is disclosed. When using such a binder, it is necessary to set the addition amount appropriately. That is, if the added amount of the binder is too small, the insulating coatings formed on the soft magnetic metal powder cannot be sufficiently bound together, and sufficient mechanical strength of the dust core cannot be secured, and the added amount is too small. If the amount is too large, the ratio of the soft magnetic metal powder (iron powder or the like) contained in the dust core may be reduced, and the magnetic flux density or permeability of the dust core may be reduced. Therefore, if the amount of the binder to be added is not appropriate, either the mechanical strength or magnetic properties of the dust core will be impaired.

  In view of the above circumstances, the technical problem to be solved by the present invention is to reduce the magnetic properties when a powder magnetic core is produced using a magnetic core powder coated with a swellable layered clay mineral. Without increasing the mechanical strength sufficiently.

  As a result of intensive research, the inventors of the present application have focused on a resin having a siloxane bond as a binder to sufficiently increase the mechanical strength of the dust core, and an insulating coating made of a swellable layered clay mineral has been formed. It has been found that by adding an appropriate amount of this resin to the soft magnetic metal powder, it is possible to improve the mechanical strength while maintaining the magnetic properties of the dust core high, and the present invention has been completed. .

  That is, in order to solve the above-described problems, the present invention provides a magnetic core obtained by mixing a magnetic core powder obtained by coating a surface of a soft magnetic metal powder with an insulating coating made of a swellable layered clay mineral and a resin having a siloxane bond. A powder magnetic core formed by producing a raw material powder, compressing the magnetic core raw powder to form a green compact, and subjecting the green compact to a heat treatment, wherein the powder in the magnetic core raw powder Provided is a powder magnetic core in which the ratio of the resin is 0.1 wt% or more and less than 7 wt%, and the insulating coatings of the adjacent soft magnetic metal powders are bonded by silica after the heat treatment.

  As described above, when a resin having a siloxane bond is used as a binder, the resin remains as silica after the heat treatment of the green compact, and this silica strengthens the insulating films of the adjacent soft magnetic metal powders. Bind. This makes it possible to improve the insulation and mechanical strength of the dust core. The amount of resin added to the magnetic core raw material powder is such that if the proportion of the total magnetic core raw material powder is 0.1 wt% or more and less than 7 wt%, the mechanical strength of the powder magnetic core is improved and the magnetic flux density or High magnetic characteristics can be maintained without significantly losing iron loss. When the ratio of the resin is 7 wt% or more, the ratio of the soft magnetic metal powder in the powder magnetic core is decreased, so that the magnetic flux density of the powder magnetic core is decreased and the iron loss is increased. In addition, when the ratio of the resin is less than 0.1 wt%, the amount of the resin is too small, so that the function as a binder cannot be sufficiently exhibited, and a dust core having high mechanical strength can be obtained. Disappear.

  In the above dust core, the swellable smectite group clay mineral is preferably used as the swellable layered clay mineral constituting the insulating coating from the viewpoint of securing high magnetic properties.

  Further, as the film thickness of the insulating coating in the powder magnetic core increases, it becomes difficult to obtain a high-density powder compact, and the magnetic permeability of the powder magnetic core decreases. On the other hand, as the film thickness of the insulating coating becomes thinner, the magnetic properties (magnetic permeability) of the dust core can be improved. For this reason, the film thickness of the insulating coating is preferably set to 150 nm or less.

  The powder magnetic core includes a coating step in which an insulating coating made of a swellable layered clay mineral is coated on the surface of a soft magnetic metal powder to obtain a magnetic core powder, and a resin having a siloxane bond is added to the magnetic core powder. A mixing step of obtaining a raw material powder for a magnetic core by mixing so as to have a ratio of 1 wt% or more and less than 7 wt%; a compression forming step for obtaining a green compact by compressing the raw material powder for a magnetic core; and the green compact Can be manufactured through a heating step of heating in an inert atmosphere.

  In this case, the resin having the siloxane bond can be changed to silica in the heating step, and the insulating coatings of the adjacent soft magnetic metal powders can be bound with silica. Thereby, after improving the mechanical strength of a powder magnetic core, it becomes possible to maintain a high magnetic characteristic without significantly reducing the magnetic flux density and iron loss.

  In the heating step, the heating temperature is preferably 600 ° C. or higher and lower than 850 ° C. When the heating temperature is less than 600 ° C., the effect of removing distortion of the green compact by heating (annealing) cannot be obtained sufficiently, the iron loss of the dust core becomes high, and the heating temperature is 850 ° C. or higher. In this case, the iron loss of the dust core is increased due to deterioration of the insulating coating film due to high temperature.

  In the compression molding process, if the molding pressure is too low, a sufficient density of the green compact cannot be obtained, and if the molding pressure is too high, the life of the molding die may be shortened or the insulating coating may be destroyed. There is. For this reason, it is preferable that the molding pressure in the compression molding step be 980 MPa or more and less than 2000 MPa.

  In the mixing step, an appropriate amount of a lubricant may be mixed to produce a magnetic core raw material powder. If an appropriate amount of lubricant is mixed, the friction between soft magnetic metal powders can be reduced during molding of the green compact. In addition to making it easy to obtain a high density green compact, the soft magnetic metal powder This is because damage and peeling of the insulating coating due to friction between each other can be prevented as much as possible. In this case, it is preferable that the ratio of the lubricant to the whole magnetic core raw material powder is 0.1 wt% or more and less than 1.0 wt%. When the ratio of the lubricant is less than 0.1 wt%, mechanical destruction of the insulating coating due to friction between soft magnetic metal powders in the compression molding process, friction between soft magnetic metal powders and molding with soft magnetic metal powders Loss increases due to friction with the mold surface, and it becomes difficult to form a green compact that maintains high insulation. On the other hand, when the ratio of the lubricant is 1.0 wt% or more, the amount of the lubricant present in the green compact increases, the amount of the soft magnetic metal powder itself decreases, and the magnetic flux density and permeability of the powder magnetic core decrease. This is not preferable because the magnetic susceptibility is lowered.

  As described above, according to the present invention, when a powder magnetic core is produced using a magnetic core powder in which a soft magnetic metal powder is coated with a swellable layered clay mineral, the mechanical strength is reduced without deteriorating the magnetic properties. Can be increased sufficiently.

(A) is a figure which shows typically a part of powder production | generation process (coating process), (b) figure is a schematic sectional drawing of the powder for magnetic cores obtained through a powder production | generation process (coating process). FIGS. 4A and 4B are diagrams schematically showing the main part of the compression molding step, and FIG. 4C is a diagram schematically showing a part of the green compact obtained through the compression molding step. It is a figure which shows typically a part of powder magnetic core obtained through a heating process. It is a top view of the stator core which is an example of a powder magnetic core. It is a figure which shows the test result (Example) of a confirmation test. It is a figure which shows the test result (comparative example) of a confirmation test.

  The method for manufacturing a dust core according to the present invention mainly includes a powder generating step for generating a core raw material powder including the core powder 1 shown in FIG. 1 (b), and a magnetic core shown in FIG. 2 (c). The compression molding process for obtaining the green compact 4 by the raw material powder for heating, and the heating process which heat-processes the green compact 4 are included. Hereinafter, each process will be described in detail with reference to the drawings.

[Powder production process]
The powder generation step includes a coating step of coating the surface of the soft magnetic metal powder 2 with the insulating coating 3 made of a swellable layered clay mineral to obtain the magnetic core powder 1, and the magnetic core powder 1 by mixing a binder and the like. Mixing step of obtaining raw material powder.

  In the coating step, the insulating coating 3 is formed on the soft magnetic metal powder 2 by using, for example, a method of immersing the soft magnetic metal powder 2 in a solution for forming a coating or a rolling flow method. In the method of immersing the soft magnetic metal powder 2 in the solution, as shown in FIG. 1 (a), after the soft magnetic metal powder 2 is immersed in the container 10 filled with the solution 11 containing the compound to be the insulating coating 3. Then, the liquid component of the solution 11 is removed to obtain the magnetic core powder 1 composed of the soft magnetic metal powder 2 whose surface is coated with the insulating coating 3.

  In order to form the insulating coating 3 on the soft magnetic metal powder 2 by the rolling flow method, first, the soft magnetic metal powder 2 is put into the container of a rolling flow coating apparatus (not shown), An air flow is generated inside the container, and the soft magnetic metal powder 2 is stirred and fluidized in a state of being suspended inside the container. While maintaining this state, a solution obtained by cleaving the swellable lamellar clay mineral is sprayed in a mist form to adhere to the soft magnetic metal powder 2. At this time, the solvent component of the solution adhering to the soft magnetic metal powder 2 disappears due to the airflow. As a result, the insulating coating material (swellable layered clay mineral) is deposited and deposited on the surface of the soft magnetic metal powder 2 to form the insulating coating 3. In this case, the film thickness of the insulating coating 3 can be adjusted by adjusting the concentration (amount) of the insulating coating material supplied to the inside of the container, the operation time of the rolling fluid coating apparatus, and the like. Therefore, the insulating coating 3 having a thin and uniform film thickness with little variation can be obtained. In addition, in the rolling flow method, since the coating of the soft magnetic material powder 2 with the insulating lubricant and the drying thereof can proceed simultaneously, the insulating coating 3 can be rapidly formed.

  As the soft magnetic metal powder 2, pure iron powder, Fe—Al alloy powder, silicon steel powder, permalloy powder, sendust powder, permendur powder, and other iron-based alloy powders and amorphous powders can be appropriately selected. Of these, pure iron powder, silicon steel powder, and permendurous powder can obtain particularly high magnetic flux density and magnetic permeability, and therefore it is preferable to use one or more of these composite powders as a main component. In addition, a main component here means occupying 50% or more in the soft-magnetic metal powder 2 to comprise. Note that an amorphous alloy powder may be used as the soft magnetic metal powder 2. Since the amorphous alloy powder has higher hardness than pure iron powder, the amount of plastic deformation at the time of molding is small, and the insulating coating 3 is not easily damaged.

  For example, when a pure iron powder is employed for the soft magnetic metal powder 2, it is preferable to use an atomized pure iron powder having a purity of 97% or more manufactured by the atomizing method. In this atomized pure iron powder, the higher the purity of iron, the lower the loss and the higher the relative permeability. In addition, although the atomizing method here includes both the gas atomizing method and the water atomizing method, since the insulating coating 3 can be uniformly coated and eddy current loss between iron particles can be reduced, the gas atomized pure iron powder by the gas atomizing method can be used. Is preferably used.

  Moreover, the soft magnetic metal powder 2 can reduce eddy current loss, so that a particle size is small. On the other hand, when the particle size is increased, the interface between the powders is reduced, so that hysteresis loss can be reduced. In order to enjoy the benefits of both of these, the particle diameter of the soft magnetic metal powder 2 is preferably 30 μm or more and 100 μm or less. The particle size of the powder can be measured by a laser diffraction / scattering method.

  Examples of the swellable layered clay mineral which is the insulating coating 3 include kaolinite clay minerals such as halosite, kaolinite, enderite, dickite and nacrite, antigolite group clay minerals such as antigolite and chrysotile, montmorillonite and beidellite. , Nontronite, saponite, hectorite, saconite, stevensite, smectite clay minerals, vermiculite clay minerals such as vermiculite, mica such as muscovite and phlogopite, mica such as margarite, tetrasilic mica, and teniolite A group clay mineral can be used by 1 type or in combination of 2 or more types.

  Among these, a smectite clay mineral can be preferably used as the material of the insulating coating 3. A smectite group mineral is a phyllosilicate crystallized by laminating two or more silicate layers having a sandwich type three-layer structure with an octahedral layer sandwiched between tetrahedral layers such as Si-O and Al-O. It is a kind of. Of the smectite group clay minerals exemplified above, it is preferable to select and use at least one of saponite and hectorite from the viewpoint of producing a powder core 5 (see FIG. 3) having a low iron loss.

  As the film thickness of the insulating coating 3 increases, it becomes more difficult to obtain a high-density green compact 4, and the magnetic permeability of the powder magnetic core 5 decreases. On the other hand, the thinner the insulating coating 3 is, the higher the magnetic properties (magnetic permeability) of the dust core 5 can be. Therefore, the thickness of the insulating coating 3 is preferably 20 nm or more and less than 200 nm, and more preferably 20 nm or more and 150 nm or less.

  In the mixing step, a binder is mixed with the magnetic core powder 1 in order to improve the mechanical strength of the powder magnetic core 5. As the binder, a resin having a siloxane bond is used. As this resin, for example, silicone resin, silicone epoxy resin, silicone alkyd resin, silicone polyester resin, and silicone urethane resin are preferably used. For example, a silicone resin cures in a temperature range of 200 ° C. or higher because an intramolecular dehydration condensation reaction occurs and the molecular weight increases. Then, the methyl group and phenyl group in the molecule are eliminated at a temperature range of 300 ° C. or higher, and ceramic silica 6 (see FIG. 3) is obtained at 600 ° C. or higher. The silica 6 firmly binds the insulating coatings 3 in the adjacent soft magnetic metal powders 2 through a heating process described later. Since the more resin (silica) remaining after the heating step is, the higher the strength is, the higher the mechanical strength is, the more the siloxane bonds contained in the resin per unit weight are as much as possible. Better. Further, strong adhesion between the insulating coating 3 and the silicone resin is realized by intermolecular hydrogen bonding between the hydroxyl group contained in the swellable clay mineral and the hydroxyl group contained in the silicone resin in the insulating coating 3.

  About the compounding quantity of resin as a binder, it is preferable that the ratio of the resin to the whole raw material powder for magnetic cores shall be 0.1 wt% or more and less than 7 wt%. When the proportion of the resin is 7 wt% or more, the proportion of the soft magnetic metal powder 2 is low, the magnetic flux density of the dust core 5 is low, and the iron loss is high, which is not preferable. Further, when the resin ratio is less than 0.1 wt%, the amount of the resin is too small, so that a sufficient function as a binder is not exhibited, and the powder magnetic core 5 having high mechanical strength cannot be obtained. It is not preferable.

  In this mixing step, in order to bond the insulating coating 3 and the binder more firmly, a silane coupling agent may be further mixed to produce a magnetic core raw material powder. Since the inorganic substance in the silane coupling agent has a high insulating property, a function of assisting the insulating property of the swellable layered clay mineral can be expected. As the organic functional group of the silane coupling agent, for example, an amino group, an epoxy group, or an ethylene group that is highly compatible with the resin can be selected.

  In this mixing step, a solid lubricant is added in order to prevent friction between the soft magnetic metal powders 2 and friction between the soft magnetic metal powder 2 and the molding die that may occur in the compression forming step described later. The The solid lubricant may be appropriately selected from metal soaps such as Al stearate and Zn stearate, amide waxes such as stearamide and bis stearamide, and inorganic solid lubricants such as graphite and molybdenum disulfide.

  It is desirable that the ratio of the solid lubricant to the whole magnetic core raw material powder is 0.1 wt% or more and less than 1.0 wt%. When the ratio of the solid lubricant is less than 0.1 wt%, mechanical destruction of the insulating coating 3 due to friction between the soft magnetic metal powders 2, friction between the soft magnetic metal powders 2 during compression molding, and soft magnetism Loss due to friction between the metal powder 2 and the molding die increases, and molding with high insulation becomes difficult. On the other hand, when the ratio of the solid lubricant is 1.0 wt% or more, the ratio of the solid lubricant present in the green compact 4 is increased, and the ratio of the soft magnetic metal powder 2 itself is decreased. This is not preferable because the magnetic permeability and magnetic flux density of the dust core 5 are reduced.

  As described above, in the powder production step, the core raw material powder in which the magnetic core powder 1, the binder, and the solid lubricant are mixed at a suitable ratio is obtained through the coating step and the mixing step.

[Compression molding process]
Next, in the compression molding step schematically shown in FIGS. 2 (a) and 2 (b), as schematically shown in FIG. 2 (c), a molding die having a die 12 and a punch 13 arranged coaxially is used. A compact 4 is compression molded. In this compression molding process, as shown in FIGS. 2 (a) and 2 (b), after filling the core raw material powder into the cavity of the molding die, the punch 13 is moved relatively close to the die 12 to press the pressure. The powder 4 is compression molded. The molding pressure in the compression molding step is preferably 800 MPa or more and less than 2200 MPa, more preferably 980 MPa or more and less than 2000 MPa, and most preferably 980 MPa or more and 1800 MPa or less. If the molding pressure is less than 800 MPa, it is difficult to obtain a green compact 4 having a sufficient density. Conversely, if the molding pressure is 2200 MPa or more, the mold life may be reduced, or the insulating coating 3 may be mechanically broken due to friction between the soft magnetic metal powders 2. May occur and the electrical insulation may be reduced. In order to reduce friction between the molding die and the soft magnetic metal powder 2 that may occur in the compression molding step, a hard coating such as DLC or TiAlN may be coated on the molding die as a lubricant. Through the compression molding process described above, a high-density green compact 4 in which the soft magnetic metal powders 2 are firmly adhered to each other is obtained as schematically shown in FIG. In FIG. 2C, illustration of the binder and the lubricant is omitted.

[Heating process]
The green compact 4 obtained through the compression molding process is transferred to a heating process (annealing process). In this heating step, the green compact 4 is heated in an inert gas (eg, nitrogen gas, argon gas) atmosphere. The heating temperature in this heating step is preferably 600 ° C. or higher and lower than 850 ° C. If the temperature is lower than 600 ° C., the distortion removal effect of the green compact 4 due to annealing cannot be sufficiently obtained, and the dust core 5 may have a high iron loss. On the other hand, at a temperature of 850 ° C. or higher, the insulating coating 3 is deteriorated due to a high temperature, and the dust core 5 may have a high iron loss. In addition, the soft magnetic metal powders 2 may be fused with each other at a high temperature.

  The powder magnetic core 5 shown in FIG. 3 is produced by performing the heat treatment of the powder compact 4 at the above heating temperature. The powder magnetic core 5 has high strength as a result of the silica 6 firmly binding the insulating coatings 3 in the adjacent soft magnetic metal powders 2 with excellent magnetic properties (high magnetic flux density, low iron loss). )become. Specifically, by producing by the method as described above, the magnetic flux density in an environment of a DC magnetic field of 10000 A / m is 1.30 T or more, and the iron loss under the conditions of an AC magnetic field, a frequency of 1000 Hz, and a magnetic flux density of 1 T. Is less than 120 W / kg, and a dust core 5 having a crushing strength of 60 MPa or more is obtained.

  The dust core 5 can be preferably used as a magnetic core of a motor for a transport machine such as an automobile or a railway vehicle that is constantly exposed to vibration at a high rotational speed and high acceleration. In addition, the dust core 5 can be preferably used as a magnetic core for power circuit components such as a choke coil, a power inductor or a reactor. As a specific example, the dust core 5 obtained by the manufacturing method according to the present invention can be used as a stator core 20 as shown in FIG. The stator core 20 shown in the figure is used by being assembled to, for example, a base member constituting the stationary side of various motors, and has a cylindrical portion 21 having a mounting surface for the base member, and a radial shape radially outward from the cylindrical portion 21. And a coil (not shown) is wound around the outer periphery of the protrusion 22. Since the powder magnetic core 5 has a high degree of freedom in shape, not only the stator core 20 as shown in FIG. 4 but also a core having a more complicated shape can be easily mass-produced.

  Hereafter, the method and result of the test performed in order to confirm the effect of this invention are demonstrated. 5 and 6 show the production conditions and test results of the test pieces according to the examples and comparative examples used in the test.

[Example 1]
First, conditions for producing each test piece will be described. Example 1 was produced under the following conditions. That is, an insulating coating was formed on the soft magnetic metal powder using a rolling fluidized coating apparatus (MP-01 manufactured by Paulec Co., Ltd.). Specifically, the surface of water atomized pure iron powder (particle diameter 30-300 μm) produced by the water atomization method was covered with completely cleaved saponite to form an insulating film having a thickness of 50 nm. Next, stearamide as a solid lubricant is mixed with pure iron powder after coating so that the ratio is 0.3 wt% and methyl silicone resin as a binder is 1 wt%. And sufficiently mixed to obtain a magnetic core raw material powder. Further, the raw material powder for magnetic core was filled in a molding die and compression molded at a molding pressure of 1470 MPa to produce a ring-shaped green compact having an outer diameter of 20 mm, an inner diameter of 12 mm, and an axial width of 7 mm. The green compact was subjected to a heat treatment in nitrogen at a heating temperature of 750 ° C. for 60 minutes to produce a ring-shaped test piece (dust core) according to Example 1.
[Example 2]
The test piece of Example 2 was produced under the same conditions as Example 1 except that the ratio of the silicone resin as the binder was 4 wt%.
[Example 3]
The test piece of Example 3 was produced under the same conditions as Example 1 except that the binder was a silicone epoxy resin.
[Example 4]
The test piece of Example 4 was produced under the same conditions as in Example 1 except that the heating temperature was 600 ° C.
[Example 5]
The test piece of Example 5 was produced under the same conditions as in Example 1 except that the heating temperature was 800 ° C.
[Example 6]
The test piece of Example 6 was produced under the same conditions as in Example 1 except that the thickness of the insulating coating was 20 nm.
[Example 7]
The test piece of Example 7 was produced under the same conditions as Example 1 except that the film thickness of the insulating coating was 100 nm.
[Example 8]
The test piece of Example 8 was produced under the same conditions as Example 1 except that the ratio of stearamide as a solid lubricant was 0.1 wt%.
[Example 9]
The test piece of Example 9 was produced under the same conditions as Example 1 except that the ratio of stearamide as a solid lubricant was 0.8 wt%.
[Example 10]
The test piece of Example 10 was produced under the same conditions as in Example 1 except that the molding pressure was 980 MPa.
[Example 11]
The test piece of Example 11 was produced under the same conditions as in Example 1 except that the molding pressure was 1800 MPa.
[Example 12]
The test piece of Example 12 was produced under the same conditions as in Example 1 except that gas atomized pure iron powder was produced by the gas atomization method.
[Example 13]
The test piece of Example 13 was produced under the same conditions as Example 1 except that a gas atomized silicon steel powder containing 3.0 mass% silicon was produced by the gas atomization method.
[Example 14]
The test piece of Example 14 was produced under the same conditions as Example 1 except that a gas atomized silicon steel powder containing 6.5 mass% silicon was produced by the gas atomization method.

Next, the test piece which concerns on Comparative Examples 1-12 is demonstrated.
[Comparative Example 1]
The test piece of Comparative Example 1 was produced under the same conditions as in Example 1 except that the ratio of the silicone resin as the binder was 7 wt%.
[Comparative Example 2]
For the test piece of Comparative Example 2, a ring-shaped test piece was prepared in the same manner as in Example 1 except that an epoxy resin was used as the binder.
[Comparative Example 3]
The test piece of Comparative Example 3 was produced under the same conditions as in Example 1 except that the heating atmosphere was air.
[Comparative Example 4]
The test piece of Comparative Example 4 was produced under the same conditions as in Example 1 except that the insulating coating was silicon oxide (SiO ₂ ).
[Comparative Example 5]
The test piece of Comparative Example 5 was produced under the same conditions as in Example 1 except that the heating temperature was 850 ° C.
[Comparative Example 6]
The test piece of Comparative Example 6 was produced under the same conditions as in Example 1 except that the heating temperature was 550 ° C.
[Comparative Example 7]
The test piece of Comparative Example 7 was produced under the same conditions as in Example 1 except that the film thickness of the insulating coating was 200 nm.
[Comparative Example 8]
The test piece of Comparative Example 8 was produced under the same conditions as in Example 1 except that the ratio of stearamide as a solid lubricant was 0.05 wt%.
[Comparative Example 9]
The test piece of Comparative Example 9 was produced under the same conditions as in Example 1 except that the ratio of stearamide as a solid lubricant was 1.0 wt%.
[Comparative Example 10]
The test piece of Comparative Example 10 was produced under the same conditions as in Example 1 except that no binder was added.
[Comparative Example 11]
The test piece of Comparative Example 11 was produced under the same conditions as in Example 1 except that the molding pressure was 784 MPa.
[Comparative Example 12]
The test piece of Comparative Example 12 was produced under the same conditions as in Example 1 except that the molding pressure was 2200 MPa.

  For the ring-shaped test pieces of Examples 1 to 14 and Comparative Examples 1 to 12 obtained under the above conditions, (1) magnetic flux density, (2) iron loss, and (3) crushing strength were measured. The measurement conditions and evaluation method will be described below.

(1) Magnetic flux density Magnetic flux density [T] of each test piece in a magnetic field of 10000 A / m was measured using a DC BH measuring device (SK-110 type manufactured by Metron Engineering Co., Ltd.). The higher the magnetic flux density, the better. The following evaluation points were given according to the measured value of magnetic flux density.
3 points: 1.50T or more 2 points: 1.30T or more and less than 1.50T 1 point: less than 1.30T

(2) Iron loss The iron loss [W / kg] of each test piece at a frequency of 1000 Hz was measured using an AC BH measuring device (BH analyzer SY-8218, manufactured by Iwatatsu Measurement Co., Ltd.). The smaller the iron loss, the better. The following evaluation points were given according to the measured values of iron loss. In this evaluation, a higher evaluation score indicates a lower iron loss, and a lower evaluation score indicates a higher iron loss.
4 points: less than 80 W / kg 3 points: 80 W / kg or more and less than 100 W / kg 2 points: 100 W / kg or more and less than 120 W / kg 1 point: 120 W / kg or more

(3) Crushing strength The crushing strength of each test piece was measured using a precision universal testing machine Autograph (manufactured by Shimadzu Corporation). In this test, stress was applied by compressing the ring surface of the ring-shaped test piece, and the value obtained by dividing the load at the time of fracture by the fracture cross-sectional area was defined as the crushing strength [MPa]. The compression speed was 1 mm / min. The higher the crushing strength, the better. The following evaluation points were assigned according to the calculated value of the crushing strength.
4 points: 80 MPa to 3 points: 60 MPa to less than 80 MPa 2 points: 40 MPa to less than 60 MPa 1 point: less than 40 MPa

  Based on the measurement result obtained by said test, comprehensive evaluation of the test piece concerning Examples 1-14 and Comparative Examples 1-12 was performed. In this evaluation, for any of the three items of magnetic flux density, iron loss, and crushing strength, a test piece to which at least one evaluation point “1” is assigned is regarded as an overall evaluation “x” (impossible), and an evaluation point “1” is assigned The test piece which was not evaluated was made into comprehensive evaluation "(circle)" (good).

The matters clarified by this test will be described below.
[binder]
Regarding the binder used for the raw material powder for the magnetic core, when an epoxy resin having no siloxane bond is used as in Comparative Example 2 or when no binder is used as in Comparative Example 10, the mechanical strength of the test piece is low. Declined. From this matter and the test results of Examples 1 to 14, it was confirmed that a resin having a siloxane bond (silicone resin, silicone epoxy resin) was optimal as the binder. In addition, regarding the blending ratio of the binder, when the ratio of the binder in the entire magnetic core raw material powder is 1 wt% or more as in Examples 1 to 14, the test piece does not deteriorate in magnetic properties and has a mechanical strength. However, when the binder ratio was 7 wt% as in Comparative Example 1, the magnetic flux density of the test piece was lowered. Considering this, the ratio of the binder to the whole magnetic core raw material powder is preferably 0.1 wt% or more and less than 7 wt%, and more preferably 1 wt% or more and 6 wt% or less.

[Molding pressure]
Regarding the molding pressure in the compression molding process, when the molding pressure was 784 MPa as in Comparative Example 11, a sufficient density of the green compact could not be secured, and the test piece had a reduced magnetic flux density. When the molding pressure was 2200 MPa as in Comparative Example 12, the test piece had a high iron loss due to the breakdown of the insulating coating due to the high pressure. From this, it is preferable that the molding pressure in the compression molding step is a pressure exceeding Example 784 MPa, for example, 800 MPa or more, and more preferably 980 MPa or more as in Examples 1-14. Further, the molding pressure is preferably less than 2200 MPa, more preferably less than 2000 MPa, and most preferably 1800 MPa or less (see Example 11).

[Heating temperature]
Regarding the temperature condition of the heating step, when the heating temperature is 550 ° C. as in Comparative Example 6, the effect of removing the green compact by annealing cannot be sufficiently obtained, and the test piece has high iron loss. Oops. Further, when the heating temperature was 850 ° C. as in Comparative Example 5, the test piece had a high iron loss due to the deterioration of the insulating film due to the high temperature. From these matters and the test results of Examples 1 to 14, it is preferable that the heating temperature in the heating step be 600 ° C. or higher and lower than 850 ° C. In addition, when the green compact was heat-treated in the atmosphere as in Comparative Example 3, the test piece had a high iron loss, so the heat treatment was not as in Examples 1-14. It is desirable to carry out in an active gas (nitrogen gas) atmosphere.

[Insulation coating]
Regarding the insulating coating, when silicon oxide (SiO ₂ ) was used as in Comparative Example 4, the test piece had high iron loss. Therefore, it is desirable to use a swellable layered clay mineral (saponite) as in Examples 1 to 14 as the insulating coating. Moreover, regarding the film thickness of this insulating film, when the film thickness was 200 nm as in Comparative Example 7, the magnetic flux density of the test piece was lowered. From this matter and the test results of Examples 1 to 14, the thickness of the insulating coating is preferably 20 nm or more and less than 200 nm, and more preferably 20 nm or more and 150 nm or less.

[lubricant]
Regarding the blending ratio of the lubricant, when the ratio of the lubricant is 0.05 wt% as in Comparative Example 8, the effect of the lubricant is not sufficiently exhibited during compression molding, and the test piece has a high iron loss. It is had. In addition, when the ratio of the lubricant is 1.0 wt% as in Comparative Example 9, the ratio increases to cause a decrease in the ratio of the soft magnetic metal powder, and the magnetic flux density of the test piece decreases. Oops. From these matters and the test results of Examples 1 to 14, it is preferable that the ratio of the lubricant to the whole core raw material powder is 0.1 wt% or more and less than 1.0 wt%.

DESCRIPTION OF SYMBOLS 1 Magnetic core powder 2 Soft magnetic metal powder 3 Insulation film 4 Powder compact 5 Powder magnetic core 6 Silica 20 Stator core

Claims (8)

  A magnetic core powder obtained by coating a surface of a soft magnetic metal powder with an insulating coating made of a swellable layered clay mineral and a resin having a siloxane bond to produce a magnetic core powder, and compressing the magnetic core powder Then, the powder magnetic core is formed by forming the green compact and heat-treating the green compact, and the ratio of the resin in the raw material powder for the magnetic core is 0.1 wt% or more and less than 7 wt%. A dust core in which the insulating coatings of the adjacent soft magnetic metal powders are bound by silica after the heat treatment.   The dust core according to claim 1, wherein the swellable layered clay mineral is a swellable smectite group clay mineral.   The dust core according to claim 1 or 2, wherein the insulating coating has a thickness of 150 nm or less. A coating step of coating the surface of the soft magnetic metal powder with an insulating coating made of a swellable layered clay mineral to obtain a powder for a magnetic core;
A mixing step of mixing a resin having a siloxane bond with the magnetic core powder in a proportion of 0.1 wt% or more and less than 7 wt% to obtain a magnetic core raw material powder;
A compression molding step of obtaining a green compact by compression molding the magnetic core raw material powder;
And a heating step of heating the green compact in an inert atmosphere.   The method for producing a powder magnetic core according to claim 4, wherein the resin having the siloxane bond is changed to silica in the heating step, and the insulating coatings of the adjacent soft magnetic metal powders are bound to each other with silica.   The method for manufacturing a dust core according to claim 4 or 5, wherein a heating temperature in the heating step is 600 ° C or higher and lower than 850 ° C.   The method for producing a dust core according to any one of claims 4 to 6, wherein a molding pressure in the compression molding step is 980 MPa or more and less than 2000 MPa. In the mixing step, a magnetic core raw material powder is obtained by mixing the magnetic core powder and the resin with a lubricant in a proportion of 0.1 wt% or more and less than 1.0 wt%. 2. A method for producing a dust core according to item 1.

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