JP2015070028A - Dust core, method of producing green compact for core, press die and mold apparatus for manufacturing dust core, and lubricating liquid of press die for manufacturing dust core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core suitable for high frequency applications, in which insulation of soft magnetic powder particles in the surface layer is not destroyed when being extruded from a mold cavity.SOLUTION: The mold cavity of a mold is filled with soft magnetic powder, which is then compressed so that the density ratio of the soft magnetic powder becomes 91% or more thus molding a green compact, which is then extruded from the mold cavity. In such a method of manufacturing a dust core, a lubricant film containing a mold lubricant and insulating ceramics particles is formed on the inner surface, which slides on the green compact in the mold cavity before being filled with the soft magnetic powder. The extrusion sliding surface of the green compact has a surface layer of such a structure that the insulating ceramics particles are interposed between the particles of soft magnetic powder, and this green compact is used for composing the dust core.

Description

  The present invention relates to a powder magnetic core used for soft magnetic parts, a method for producing a powder compact for a magnetic core, a mold and mold apparatus for producing a powder magnetic core, and a lubricating liquid for a mold for producing a powder magnetic core, and in particular, high frequency. The present invention relates to a dust core suitable for use in a region, a method for manufacturing a powder for a magnetic core, a pressing core and a mold apparatus for manufacturing a dust core, and a lubricating liquid for a pressing core for manufacturing a dust core.

  Compared to laminated magnetic cores made from silicon steel plates, etc., the powder magnetic core made of soft magnetic powder bound with a binder such as resin has the advantage of better material yield and reduced material costs. have. In addition, there is an advantage that the degree of freedom in shape is high, and the magnetic characteristics can be improved by optimal design of the magnetic core shape. In such a powder magnetic core, an insulating material such as an organic binder or an inorganic powder and a soft magnetic powder are mixed, or an electric insulating film is coated on the surface of the soft magnetic powder to electrically insulate the metal powder. By improving the eddy current loss of the magnetic core can be greatly reduced.

  Because of these advantages, dust cores are used in transformers, reactors, thyristor valves, noise filters, choke coils, etc., and are also used in general consumer electronics motor cores, industrial equipment motor rotors and yokes, It is also used in solenoid cores (fixed iron cores) for solenoid valves incorporated in electronically controlled fuel injection devices for diesel engines and gasoline engines, and is being applied to various soft magnetic parts.

  The molding method of the powder magnetic core includes an injection molding method (such as Patent Document 1) in which a soft magnetic powder is injected together with a plastic raw material into a mold that defines a product shape, and a soft magnetic powder and a mold cavity. It is roughly classified into compression molding methods (Patent Documents 2, 3, etc.) in which raw material powder containing a binder is filled and compression molding is performed with upper and lower punches. The product shape of the powder magnetic core is imparted in the molding process, and the molding method employed depending on the application of the product is properly used.

  Under the recent demands for reducing the size and weight of various household and industrial devices, demands for improving magnetic properties such as magnetic flux density have been increasing. In the dust core, since the space factor of the soft magnetic powder is proportional to the magnetic flux density, it is necessary to increase the density in order to obtain a dust core having a high magnetic flux density. For this reason, a compression molding method that can reduce the amount of binder and increase the amount of soft magnetic powder and can be molded at a high density is widely used compared to an injection molding method that requires a large amount of binder.

  In the production of a powder magnetic core by the compression molding method, a raw material powder containing a binder resin and a soft magnetic powder or a raw material powder made of a soft magnetic powder having an insulating film on the surface is filled in a die hole of a mold device, Compress with upper and lower punches. A specific example of a process for forming a cylindrical magnetic core green compact by such a compression molding method is shown in FIG. The mold apparatus shown in FIG. 1 defines a pressing die 1 having a mold hole 1a that defines an outer peripheral side surface of a green compact with an inner diameter surface, a lower punch 2 that defines a lower surface of the green compact, and an upper surface of the green compact. The upper punch 3 is provided. Using such a mold apparatus, as shown in FIG. 1 (a), a cavity is formed by the mold hole 1a of the stamp 1 and the lower punch 2, and the raw material powder M is prepared by using a powder supply means such as a feeder 4. Fill the cavity. Next, as shown in FIG. 1B, the upper punch 3 is lowered and the lower punch 2 is raised relative to the pressing die 1 (in this case, the pressing die 1 is lowered) to enter the cavity. The filled raw material powder M is compression molded by the upper punch 3 and the lower punch 2 to obtain a green compact C. Thereafter, as shown in FIG. 1 (c), the upper punch 3 is moved upward to return to the standby position, and the lower punch 2 is raised relative to the pressing die 1 (in this case, the pressing die 1). Is further lowered), and the green compact C is extracted from the mold hole 1a of the pressing mold 1.

JP 2003-209010 A JP 2004-342937 A JP 05-217777 A

Iron loss W of the dust core is the sum of eddy current loss W _e and hysteresis loss W _h, eddy current loss W _e and hysteresis loss W _h are each represented by the following equation number 1 and the following Expression 2 From the above, the iron loss W is expressed by the following equation (3). In the equation, f is a frequency, B _m is an exciting magnetic flux density, ρ is a specific resistance value, t is a material thickness, and k ₁ and k ₂ are coefficients.

(Equation 1)
W _e = (k ₁ B _m ² t ² / ρ) f ²

(Equation 2)
W _h = k ₂ B _m ^1.6 f

(Equation 3)
W = W _e + W _h = (k ₁ B _m ² t ² / ρ) f ² + k ₂ B _m ^1.6 f

As is clear from the number 1 to 3 of formula, the eddy current loss W _e, since it increases in proportion to the square of the frequency f, to apply the powder core in the reactor or the like used in a high frequency region, suppression of eddy current loss W _e is essential. To suppress the eddy current loss W _e, it is necessary to confine the eddy currents to the small area. Therefore, in the dust core, by individual soft magnetic powder particles is configured to be insulated, achieving suppression of eddy current loss W _e. Accordingly, when the soft magnetic powder particles communicate with each other, a large eddy current is generated through the communicating portion, so it is important to ensure insulation of the individual soft magnetic powder particles.

  In recent years, further improvement in magnetic properties has been demanded, and in order to improve the magnetic flux density, compression molding of the green compact is performed at a higher pressure to increase the space factor of the soft magnetic powder. However, when the raw material powder is compression-molded at a high pressure, as shown in FIG. 2A, the pressure (spring back) at which the green compact expands to the side also increases and expands to the shape shown by the dotted line. try to. When the green compact acting by the spring back is extracted from the mold hole in this way, the side surface of the green compact is strongly pressed against the inner surface of the mold hole when the green compact slides through the mold hole. For this reason, as shown in FIG. 2 (b), the side surface of the green compact that has been extracted from the mold cavity is subjected to plastic flow in the surface layer portion, and the insulating coating formed on the surface of the soft magnetic powder particles is destroyed. In addition, the soft magnetic powder particles become conductive, and the eddy current increases.

Further, the induced current generated in the dust core flows more concentrated on the surface as the frequency becomes higher. For this reason, if a powder magnetic core in which the plastic flow is generated in the surface layer as described above and the insulating coating of the soft magnetic powder particles is broken is used for high frequency applications such as a reactor, the insulating coating is broken and the soft magnetic powder particles are There induced current flows concentrated in the surface layer portion which conducts and iron loss W are increased eddy current loss W _e becomes increasingly larger.

  In such a dust core having a surface layer portion in which the insulating coating is broken and the soft magnetic powder particles are electrically connected to each other, by removing the surface portion of the green compact as in Patent Document 3, the metal magnetic powder particles are separated from each other. The surface portion of the powder magnetic core is in a healthy state in which the soft magnetic powder particles are covered with the insulating coating. However, such surface removal treatment requires a special technique different from normal cutting, leading to an increase in manufacturing cost. For this reason, it is possible to obtain a green compact in a healthy state in which the soft magnetic powder is prevented from plastic flow in the surface layer portion of the magnetic core green compact that has been compression molded and extracted from the mold cavity. Technology is required.

The present invention is to solve the above problems, an insulating film of soft magnetic powder particle surfaces without breaking in the surface layer, showed a healthy insulated state, an eddy current loss W _e and iron loss even when used in high frequency applications An object is to provide a dust core in which an increase in W is suppressed.

  Also provided is a method for producing a magnetic core compact in which the formation of conduction due to plastic flow is suppressed in the surface layer portion of the core compact extruded from the mold hole even if compression molding is performed at high density using high pressure. This is the issue.

  Furthermore, when extruding the green compact from the mold hole in the production of the green compact for the magnetic core, the die and die apparatus for producing the dust core capable of suppressing conduction formation due to plastic flow in the surface layer portion of the green compact, and It is an object of the present invention to provide a lubricating liquid for a pressing mold for producing a dust core.

  In order to solve the above-described problem, according to one aspect of the present invention, the dust core is formed of a green compact in which a soft magnetic powder is compression-molded to a density ratio of 91% or more. The gist of the contact surface is that it has a surface layer portion in which insulating ceramic particles are interposed between the particles of the soft magnetic powder.

In the above powder magnetic core, the insulating ceramic particles are interposed between the soft magnetic powder particles, thereby supporting the soft magnetic powder particles to suppress deformation and plastic flow and prevent dielectric breakdown on the surface of the soft magnetic powder particles. To do. Moreover, the specific resistance of the surface layer portion on the side surface of the green compact increases due to the insulating properties of the insulating ceramic particles themselves. Therefore, when the induced on the surface of the powder magnetic core current is used as a dust core for high frequency flowing concentrated, and is excellent in reducing the eddy current loss W _e.

  When the surface state of the side surface of the powder magnetic core is observed, adjacent soft magnetic powder particles are preferably in a discontinuous state due to the interposition of the insulating ceramic particles. Moreover, in the surface observation of the side surface, the area ratio of the insulating ceramic particles is preferably 30% or more. The particle size of the insulating ceramic particles is preferably 50 to 1000 nm, and more preferably, an organic coating of Si and / or Al-containing compound is formed on the surface of the insulating ceramic particles.

  According to another aspect of the present invention, there is provided a method for producing a green compact for a magnetic core, wherein a soft magnetic powder is filled in a mold hole of a green mold, and the density ratio of the soft magnetic powder is 91%. A method for producing a green compact for compacting a green compact by compressing the soft magnetic powder as described above, and extruding the green compact from the mold cavity, before filling the soft magnetic powder Further, the gist of the invention is to form a lubricating coating containing a pressing lubricant and insulating ceramic particles on the inner surface of the mold hole that is in sliding contact with the green compact during extrusion.

  In the above manufacturing method, a solution of a pressing lubricant in which insulating ceramic particles are dispersed is applied to the inner surface of the mold hole, dried to provide a lubricating film, and the mold powder is filled with a raw material powder containing soft magnetic powder. . As a result, the raw material powder comes into contact with the surface of the mold cavity via the pressing lubricant and the insulating ceramic particles. When compression molding is performed in such a state, the compression proceeds with the insulating ceramic particles entering between the soft magnetic powder particles pressed against the inner surface of the mold cavity, and the compact after completion of molding contacts the mold cavity. At the contact surface, that is, the surface layer portion on the side surface of the green compact, insulating ceramic particles are interposed between the soft magnetic powder particles, and the insulating ceramic particles are dispersed in the soft magnetic powder. When extrusion is performed in this state, the insulating ceramic particles that are hard to be plastically deformed with an appropriate hardness suppress the plastic flow of the soft magnetic powder, and a green compact having a healthy side surface that is not dielectrically broken can be obtained.

  In the method for producing a magnetic core green compact of the present invention, it is preferable that the thickness of the lubricant film formed on the inner surface of the mold cavity is 0.1 to 20 μm. More preferably, the insulating ceramic particles have a particle size of 50 to 1000 nm, and the insulating ceramic particles have an organic coating of a Si-containing compound and / or an Al-containing compound formed on the surface of the titanium oxide particles. More preferably, it is a powder.

  Furthermore, according to one aspect of the present invention, a pressing core for manufacturing a powder magnetic core includes a mold hole for compressing a raw material powder to form a green compact, and a green compact during extrusion of the green compact to be formed. The gist of the invention is to have a lubricating coating containing a pressing lubricant and insulating ceramic particles provided on the inner surface of the mold hole in sliding contact.

According to another aspect of the present invention, a mold apparatus for producing a dust core includes the above-described mold for producing a dust core and an upper and lower punch for compressing the raw material powder in the mold hole. The gist.
Furthermore, according to one aspect of the present invention, the lubricating liquid of the pressing mold for producing a dust core includes a pressing lubricant, insulating ceramic particles, and a volatile solvent.

According to the present invention, in the dust core, the plastic flow of the soft magnetic powder accompanying the extraction after compression molding is suppressed on the side surface of the dust core formed by the inner surface of the mold hole of the mold, and the surface of the soft magnetic powder particles because of the insulating coating are broken can be prevented, the eddy current loss W _e is a dust core which is suppressed to a low level may be manufactured, good product even in high frequency applications is provided. In addition, the insulating ceramic particles are dispersed between the soft magnetic powder particles in the surface layer portion on the side surface of the dust core, and the specific resistance of the surface layer portion on the side surface of the dust core increases due to the insulating property of the insulating ceramic particles themselves. , even induced current on the surface of the dust core flow concentrates when used as dust core for high frequency, it is possible to suppress an increase in eddy current loss W _e, exhibits excellent performance in high frequency applications It is possible to provide a powder magnetic core.

  In addition, according to the present invention, by forming a lubricating coating containing insulating ceramic particles on the inner surface of the mold hole, plastic flow on the side surface of the green compact extracted from the mold hole can be effectively suppressed, and the surface layer Because it is possible to obtain a green compact that maintains good insulation without destroying the insulating coating on the surface of the soft magnetic powder particles, it is possible to obtain a high-quality green compact by a simple method. A method for producing a green compact is provided. In addition, the green compact for a magnetic core obtained by the production method of the present invention has a surface structure in which insulating ceramic particles are dispersed between soft magnetic powder particles, and has a surface layer portion with improved insulation on the side surface. A compact for a magnetic core that exhibits excellent characteristics in use can be obtained, and a method for producing a compact for a magnetic core with high applicability is provided.

It is a schematic diagram explaining the shaping | molding process by a compression molding method. It is a schematic diagram explaining the state of the green compact for magnetic cores when the raw material powder containing soft magnetic powder is compression molded at high pressure. It is a SEM image (upper left) and component map at the time of observing the side of the green compact of the sample number 1 created in the Example with an EPMA apparatus. It is a SEM image (upper left) and component map at the time of observing the side surface of the compact of the sample number 9 created in the Example with an EPMA apparatus.

  As shown in FIG. 1 and FIG. 2, in the green compact molding by the compression molding method, the side surface of the green compact formed by the inner surface of the mold hole is the inner surface of the mold hole when the green compact is extruded from the mold hole. It becomes an extruded sliding contact surface that makes sliding contact with. The higher the density of the green compact, the greater the springback that presses the green compact against the inner surface of the mold cavity, so when pressing the green compact out of the mold cavity, The frictional resistance acting between them increases, and plastic flow occurs in the surface layer portion on the side surface of the green compact. This is recognized as a preferable phenomenon that smoothes the side of the green compact and beautifies the appearance in general applications, but as a dust core, it is a phenomenon that causes dielectric breakdown of the surface layer and an increase in iron loss. Therefore, it is necessary to prevent plastic flow due to frictional resistance. In order to reduce the frictional resistance of the sliding contact surface, usually a push-type lubricant is used. However, in forming a high-density green compact, the frictional resistance becomes very large. However, it is difficult to suppress plastic flow in the surface layer portion.

  In the present invention, a lubricating coating containing a pressing lubricant and insulating ceramic particles is formed on the inner surface of the mold cavity, and compression molding of soft magnetic powder is performed using the mold cavity having this lubricating coating. Such a green compact that is compactly molded in the mold cavity is soft on the side of the green compact, even though the inner surface of the mold cavity and the side of the green compact are in sliding contact with each other when extruded from the mold cavity. The plastic flow of the magnetic powder particles is suppressed. The reason for this can be considered as follows. When the soft magnetic powder is compression-molded, the ceramic particles contained in the lubricating coating are pressed between the soft magnetic powder particles that are pressed against the inner surface of the mold cavity and sandwiched between the soft magnetic powder particles on the surface of the green compact that is formed. It is. For this reason, the side surface of the green compact molded in the mold cavity has a surface layer portion having a structure in which ceramic particles are interposed between soft magnetic powder particles. When such a green compact is extruded from the mold cavity, the extrusion lubricant contained in the lubricating coating reduces the static frictional force and dynamic frictional force to some extent to facilitate extrusion, and ceramic particles interposed between the soft magnetic powder particles The soft magnetic powder particles are supported to suppress deformation and plastic flow. In the meantime, if the stress applied to the soft magnetic powder particles by the frictional resistance exceeds a certain level, the ceramic particles themselves are broken and the stress applied to the soft magnetic powder particles is reduced. The ceramic particles are gradually broken according to the frictional resistance during extrusion, but the broken ceramic particles are interposed between the soft magnetic powder particles. Is prevented. That is, first, it is effective that the ceramic particles have an appropriate hardness to support the soft magnetic powder particles by entering between the soft magnetic powder particles in the surface layer portion on the side of the green compact. Thus, the plastic flow of the soft magnetic powder particles is suppressed against the frictional resistance, and the contact and bonding between the soft magnetic powder particles are prevented. Secondly, the ceramic particles exhibiting moderate brittleness or cleavage are effective in relieving stress due to frictional resistance during extrusion, thereby suppressing deformation and plastic flow of the soft magnetic powder particles. Is done. Thirdly, it is effective for the ceramic particles to be insulative to ensure the insulation between the soft magnetic powder particles in the surface layer portion on the side of the green compact, rather to strengthen it.

In the green compact that is compression-molded using the mold hole with the lubricating coating as described above, the insulating ceramic particles are interposed between the soft magnetic powder particles in the surface layer portion of the side surface (that is, the extruded sliding contact surface). It has the structure to do. Therefore, when the surface of such a green compact is observed by, for example, electron probe microanalysis (EPMA), the insulating ceramic particles are dispersed in the gaps between the soft magnetic powder particles in the SEM image or component map. You can check the status. When soft magnetic powder with an insulating coating formed on the particle surface is used as a raw material powder, the insulation coating on the surface of the soft magnetic powder is prevented from being destroyed, and the soft magnetic powder is well coated on the insulating coating. A green compact is formed. Even when a mixture of soft magnetic powder and resin binder is compression-molded, it is difficult to suppress the plastic flow of soft magnetic powder particles due to frictional resistance during extrusion when using a normal pressing lubricant. Insulating ceramic particles are similarly pushed between the soft magnetic powder particles on the side of the green compact to be molded by using a mold hole in which a lubricating coating containing conductive ceramic particles is formed. A surface layer portion in which the insulating ceramic particles are dispersed is formed. When a dust core having such a healthy surface is used under a high frequency, the insulation of the dust core surface is secured as described above, so that the induced current flows concentrated on the surface of the dust core. It is, can be effectively suppressed eddy current loss W _e.

  When the amount of the insulating ceramic particles contained in the lubricating coating formed on the inner surface of the mold hole increases, the excess insulating ceramic particles that cannot be pushed in between the soft magnetic powder particles on the side of the formed green compact will be compressed. A thin layer of insulating ceramic particles located on the side surface of the body and covering the surface layer portion of the green compact is formed. In the present invention, the entire side surface of the green compact may be coated with the thin-layered insulating ceramic particles as described above, and the surplus insulating ceramic particles covering the side of the green compact may be used as a dust core. There is no obstacle. As long as the blending balance between the insulating ceramic particles and the pressing lubricant in the lubricating coating and the thickness of the coating are good, the ceramic particles suitably enter between the soft magnetic powder particles to suppress plastic flow. As long as the dimensional accuracy is not adversely affected, excess insulating ceramic particles are allowed.

In addition, the presence of insulating ceramic particles dispersed in the gaps between the soft magnetic powder particles improves the insulation between the soft magnetic powder particles, and the insulating ceramic particles introduced from the lubricating coating can reach the inside of the green compact. Therefore, the specific resistance value of the surface layer portion of the side surface of the dust core is higher than that of the inside. The height of the specific resistance of the surface layer portion, an induced current under a high frequency environment in a state that flows to concentrate on the surface of the powder magnetic core, particularly effectively suppressing the eddy current loss W _e.

  In the conventional manufacturing method, the plastic flow of soft magnetic powder particles due to the frictional resistance during extrusion from the mold cavity occurs most strongly on the outermost surface of the green compact side, and the influence of the frictional resistance is generally the depth from the outermost surface. Covers an area up to about 20 μm. However, when a mold cavity having a lubricating coating containing insulating ceramic particles formed on the inner surface according to the present invention is used, the insulating ceramic particles support the soft magnetic powder particles on the surface of the green compact side surface. The flow is suppressed, and accordingly, the influence of the frictional resistance is also suppressed to the inside. Therefore, if the depth of the surface layer portion where the insulating ceramic particles are dispersed on the side surface of the dust core is about 1 to 100 μm from the surface, the effect of suppressing the plastic flow of the soft magnetic powder particles is good, and at most A depth of up to about 1 mm is sufficient. Further, if compression molding is performed using a mold hole in which the above-described lubricating coating is formed on the inner surface, a surface layer portion in which such insulating ceramic particles are dispersed is formed on the side surface of the green compact. In addition, the depth of the surface region where the induced current is concentrated in the dust core in a high frequency environment depends on the frequency, but at least at a frequency of about 1 kHz to 50 kHz, the insulating layer is insulated at the depth of the surface layer as described above. The specific resistance value is increased by the ceramic particles, which can be sufficiently handled.

  Since the plastic flow of the soft magnetic powder particles in the green compact occurs on the side surface of the green compact, the above-mentioned lubricating coating may be formed at least on the inner surface of the mold cavity. A surface layer portion in which the insulating ceramic particles are dispersed may be formed between the magnetic powder particles. Therefore, it is not necessary to form a lubricating film having the above composition on the upper and lower punches that form the upper and lower surfaces of the green compact. However, the green compact may be compression-molded by forming a lubricating coating containing insulating ceramic particles on the upper and lower punches. In this case, the surface layer portion where the insulating ceramic particles are dispersed is also formed on the upper and lower surfaces of the green compact. Thus, the soft magnetic powder particles are prevented from being crushed and contacting each other on the uppermost and lowermost surfaces.

  In the surface layer part of the side surface of the green compact, the insulating ceramic particles surround and restrain the periphery of the soft magnetic powder particles, and when adjacent soft magnetic powder particles become discontinuous, adjacent soft magnetic powder particles Conduction between the powder particles is completely prevented. That is, the higher the discontinuity, the more the specific resistance in this region is improved, which is preferable as a dust core.

  The powder compact preferable as the powder magnetic core has an area ratio of the insulating ceramic particles of about 8% or more, preferably 20% or more, more preferably 30% or more in the surface observation of the side surface based on the component map by EPMA. good. When the area ratio of the insulating ceramic particles in the side surface observation is less than 8%, the effect of preventing the plastic deformation of the soft magnetic powder particles by the insulating ceramic particles becomes insufficient, and the plastic flow of the soft magnetic powder occurs, and the adjacent ceramic particles are adjacent to each other. There is a risk of conduction of the soft magnetic powder. In addition, as the area ratio of the insulating ceramic particles on the surface of the green compact increases, the space factor of the soft magnetic powder on the surface decreases. Inside the deep green compact, the space factor of the soft magnetic powder can be increased to a desired space factor according to the degree of compression. Accordingly, there is no particular upper limit on the area ratio of the insulating ceramic particles on the outermost surface of the green compact side surface, and as described above, the green compact side surface may be completely covered with the insulating ceramic particles. When the side of the green compact is covered with a thin layer of insulating ceramic particles, the surface ratio of the insulating ceramic particles interposed between the soft magnetic powder particles can be determined by removing the thin layer and observing the surface of the surface layer portion. Is generally in the range of about 65% or less.

  As described above, since the insulating ceramic particles are introduced from the lubricating coating formed on the inner surface of the mold cavity, the surface layer portion on the side of the green compact formed by the inner surface of the mold cavity (that is, the surface and the vicinity of the surface) Only exists. Such a structure cannot be obtained by compression molding of raw material powder in which insulating ceramic particles are blended with soft magnetic powder. When the insulating ceramic particles are added to the soft magnetic powder and compression molded, the flowability of the raw material powder is reduced, the filling property of the raw material powder into the cavity of the mold apparatus is lowered, and the compressibility of the raw material powder itself is reduced. It will become low and it will become difficult to shape | mold a powder magnetic core in high density. Even if it is forcibly molded to a high density, the space factor of the soft magnetic powder in the powder magnetic core decreases due to the presence of the insulating ceramic particles dispersed throughout the powder compact, and the magnetic flux density decreases. Therefore, the structure of the present invention in which the insulating ceramic particles are dispersed only in the surface layer portion on the side surface of the green compact by forming a lubricating film on the inner surface of the mold cavity does not disperse the insulating ceramic particles in the green compact. Therefore, it is very advantageous in high-density compression molding.

The raw material of the green compact for a magnetic core according to the present invention will be described. In the following description, the particle diameter of the powder means the average particle diameter by laser diffraction method for the powder in μm unit, and the average particle diameter by TEM observation for the powder in nm unit.
As the soft magnetic powder, any of soft powder and hard powder may be used. Pure iron, Fe-Si alloy, Fe-Al alloy, permalloy, sendust, permendur, soft ferrite, amorphous magnetic alloy, nano An iron-based metal powder containing an iron alloy such as a crystal magnetic alloy can be used, and pure iron powder is superior in terms of high magnetic flux density and formability. In order to obtain a high-density powder magnetic core suitable for high frequency use, a soft magnetic powder having a particle size of about 1 to 300 μm is preferable. The present invention is particularly effective in the use of a soft soft magnetic powder that is easily plastically deformed during compression molding. Iron powder and an iron-based low alloy powder in which the amount of addition of alloy elements such as Si and Al is 3% or less. It is most effective against this. However, it is also effective when using hard soft magnetic powder that hardly undergoes plastic deformation in extrusion after molding, and when the soft magnetic powder particles are crushed in compression molding, insulating ceramic particles between the crushed pieces of soft magnetic powder particles. Has the effect of forming an insulation between the crushed pieces. In addition, even in the case of soft magnetic powder that is difficult to plastically deform but is not hard enough to be crushed, the insulating ceramic particles are dispersed between the soft magnetic powder particles on the side of the green compact, thereby improving the specific resistance on the side of the green compact. Effect can be obtained.

  In order to ensure insulation of the individual soft magnetic powder particles, the surface of the soft magnetic powder particles is preferably covered with an insulating film. In this case, an inorganic insulating film such as a phosphoric acid-based chemical film, a silicone resin film, and the like are preferable. Such an insulating coating on the particle surface may be formed by chemical conversion treatment or contact coating according to a conventional method. For example, the descriptions in Japanese Patent Nos. 4044591 and 49279983 can be referred to. Moreover, you may use it, selecting suitably from commercially available powder products, for example, Somaloy110i (5P) by Höganäs AB company, MH20D by Kobe Steel, etc. are mentioned.

  In addition, when insulation of each soft magnetic powder particle is ensured by blending a binder such as a resin into the soft magnetic powder, an insulating coating may not be formed on the particle surface of the soft magnetic powder. In this case, as the green compact for the magnetic core, a green compact in which individual soft magnetic powder particles are bound by a binder such as a resin is obtained. However, as the amount of the binder increases, the proportion of the soft magnetic powder decreases accordingly. As a result, the space factor of the soft magnetic powder in the powder compact decreases, and the magnetic flux density of the powder magnetic core decreases. For this reason, the amount of the binder should be adjusted to 2% by mass or less of the green compact.

Next, the raw material for the lubricating coating formed on the inner surface of the mold cavity according to the present invention will be described.
The particles introduced into the lubricating coating are dispersed between the soft magnetic powder particles to prevent plastic flow of the soft magnetic powder and to electrically insulate the soft magnetic powder. And that it does not show conductivity (insulation). For this reason, insulating ceramic particles are suitable. As the insulating ceramic particles, oxide-based, nitride-based, carbide-based ceramic particles can be used. As the oxide-based ceramic particles, aluminum oxide (Al ₂ O ₃ ), titanium dioxide (TiO ₂ ). , Silicon dioxide (SiO ₂ ), magnesium oxide (MgO), zirconium dioxide (ZrO ₂ ), steatite (MgO · SiO ₂ ), zircon (ZrSiO ₄ ), ferrite (M ²⁺ O · Fe ₂ O ₃ ), mullite ( 3Al ₂ O ₃ .2SiO ₂ ), forsterite (2MgO.SiO ₂ ), yttria (Y ₂ O ₃ ) and the like. Examples of the nitride ceramic particles include powders of aluminum nitride (AlN), titanium nitride (TiN), silicon nitride (Si ₃ N ₄ ), and the like. Examples of the carbide-based ceramic particles include powders such as titanium carbide (TiC) and tungsten carbide (WC). In addition, oxynitride ceramic particles such as sialon (Si-Al-ON-based compounds), carbonitride ceramic particles such as titanium carbonitride (TiCN), cordierite particles, machinable ceramics (SiO ₂ · Al ₂ O ₃ , AlN · BN) particles and the like can also be used. Such ceramics have a yield stress value of about 2000 to 10000 MPa, and are larger than low alloy steels of about 200 to 2000 MPa, so that the soft magnetic powder particles are supported against the stress due to frictional resistance, and the plastic flow is reduced. Can be suppressed. Furthermore, it has an appropriate hardness (Vickers hardness) of about 200 to 1800, and the fracture strain is zero. Therefore, for excessive stress, it breaks itself by brittle fracture and causes stress on the soft magnetic powder particles. ease. As will be described later, fine particles are suitable for the insulating ceramic particles. However, since fine powder increases the risk of dust explosion, in this regard, it is in a sufficiently oxidized state and dust. It is preferable to use an oxide-based insulating ceramic that is less likely to explode. Alternatively, a plurality of different types of ceramic particles as described above may be selected and mixed to be used as insulating ceramic particles.

  If the insulating ceramic particles are coarse, a large amount of insulating ceramic particles are required to ensure insulation of the soft magnetic powder, and the mass of the individual insulating ceramic particles increases. It becomes easy to drop off from the formed film. In addition, when the compacted compact is pushed out from the mold cavity while the coarse insulating ceramic particles are present between the inner surface of the mold hole and the filled soft magnetic powder, the coarse insulating ceramic particles are The inner surface of the mold cavity is worn away to cause wear, and the stress relaxation due to self-breaking is hardly effective, so the deformation of the soft magnetic powder particles cannot be sufficiently suppressed. Further, when the surface of the soft magnetic powder is coated with an insulating coating, there is a possibility that the insulating coating is broken. Furthermore, there is a possibility that the wear powder of the stamping die and soft magnetic powder generated by abrasion adheres to the surface of the green compact and joins adjacent soft magnetic powder particles, which may cause dielectric breakdown between the soft magnetic powder particles. is there. For this reason, it is preferable to use the insulating ceramic particles having a maximum particle size of 1000 nm or less. On the other hand, since the excessively fine insulating ceramic particles are difficult to manufacture and handle, it is preferable to use a powder having a maximum particle size of 50 nm or more.

  The green compact of the soft magnetic powder having the surface layer on which the insulating ceramic particles are dispersed on the side surface can be manufactured as follows. First, in the method of manufacturing a green compact for a magnetic core according to the present invention, a lubricating liquid containing insulating ceramic particles and a pressing lubricant is applied to a surface that defines a cavity of a mold apparatus, particularly an inner surface of a mold hole. After forming the solid lubricating film, the raw material powder containing the soft magnetic powder is filled into the cavity of the mold apparatus. At this time, the raw material powder filled in the cavity comes into contact with the mold hole through a pressing lubricant in which the insulating ceramic particles are dispersed.

  Next, when the raw material powder is compression-molded using the upper punch, the pressing lubricant and the insulating ceramic particles infiltrate between the soft magnetic powder particles as the soft magnetic powder is compressed, and the insulating ceramics are interposed between the soft magnetic powder particles. Particles intervene. When the compression of the raw material powder further proceeds, the distance between the soft magnetic powder particles decreases, and most of the push lubricant that has entered between the soft magnetic powder particles is extruded together with some of the insulating ceramic particles, and the green compact is compressed. The remaining insulating ceramic particles remain between the soft magnetic powder particles together with a small amount of the pressing lubricant. On the side surface of the green compact after completion of the compression molding, that is, the surface of the green compact in contact with the mold cavity, the insulating ceramic particles are dispersed between the soft magnetic powder particles.

  In this way, when the compressed compact is extruded with the insulating ceramic particles dispersed between the soft magnetic powder particles on the side surface of the green compact in contact with the mold cavity inner surface, the soft powder in contact with the mold cavity inner surface is extruded. The magnetic powder tries to plastically deform due to frictional resistance, but the plastic deformation of the soft magnetic powder is prevented by the appropriate hardness of the insulating ceramic particles that are difficult to plastically deform between the soft magnetic powder particles. During the extraction of the powder, it is possible to prevent plastic flow of the soft magnetic powder in contact with the inner surface of the mold cavity.

The lubricating liquid used when forming the lubricating coating on the inner surface of the mold cavity will be described.
The lubricating liquid is a liquid in which insulating ceramic particles and a pressing lubricant are mixed in a volatile solvent, and a lubricating film containing insulating ceramic particles and the pressing lubricant is formed by distilling off the volatile solvent. Can do. The pressing lubricant is used to provide lubrication between the inner surface of the mold hole and the soft magnetic powder when the green compact that has been compressed is extruded from the mold hole.
In the present invention, the lubricating coating is provided by applying a lubricating liquid to the inner surface of the mold hole in accordance with the so-called “push-type lubrication method”. As the pressing lubricant, waxes, higher fatty acids, and higher fatty acid metal salts that have been conventionally used for pressing lubrication can be used. That is, it is a semi-solid or solid lubricant capable of forming a film. Specifically, as the wax, for example, higher fatty acid amide wax such as ethylene bis stearamide, ethylene bis stearamide and aliphatic What added carboxylic acid monoamide etc. can be used. Examples of higher fatty acids include saturated or unsaturated fatty acids having about 12 to 28 carbon atoms such as stearic acid, 12-hydroxystearic acid, ricinoleic acid, behenic acid, montanic acid, lauric acid, and palmitic acid. it can. As the higher fatty acid metal salt, the higher fatty acid having a metal salt such as lithium, magnesium, calcium, barium, zinc, aluminum, sodium, strontium, or the like can be used. Liquid lubricants such as mineral oil have very effective lubricity in reducing dynamic friction, but tend to be insufficient in reducing static friction. A solid or solid lubricant is effective, and exhibits lubricity that effectively reduces friction with respect to both static friction and dynamic friction generated when the green compact is extruded.

  In the lubricating coating formed on the inner surface of the mold hole, the ratio of the insulating ceramic particles is 1 to 70% by mass, preferably 10 to 65% by mass, more preferably the total amount of the pressing lubricant and the insulating ceramic particles. It is preferable to have a composition of 40 to 60% by mass. When the ratio of the insulating ceramic particles is less than 1% by mass, it becomes difficult to effectively interpose the insulating ceramic particles between the soft magnetic powder particles. On the other hand, when the ratio of the insulating ceramic particles exceeds 70% by mass, the amount of the pressing lubricant is relatively small, and the lubrication between the inner surface of the mold hole and the soft magnetic powder is insufficient, and mold galling is likely to occur. This causes plastic flow of the soft magnetic powder. Therefore, the lubricating liquid used when forming the lubricating coating on the inner surface of the mold hole is prepared so that the ratio of the insulating ceramic particles is 1 to 70% by mass with respect to the total amount of the pressing lubricant and the insulating ceramic particles. To do. In the preparation of the lubricating liquid, it is possible to prepare it well by dissolving a pressing lubricant in a solvent to prepare a pressing lubricant solution, and adding and mixing insulating ceramic particles thereto and uniformly dispersing it.

  The lubricating coating formed on the inner surface of the mold cavity after applying the lubricating liquid to the mold apparatus is preferably present as a solid coating, that is, a dry coating. When the coating containing the solvent as it is applied, that is, a wet coating, when the raw material powder is filled into the cavity of the mold apparatus, the mold lubricant in the solution state is placed in the gap between the filled raw material powder. The amount of the pressing lubricant that is absorbed by the capillary force and lubricates between the inner surface of the mold cavity and the raw material powder is reduced. Therefore, it is desirable that the solvent used for the preparation of the lubricating liquid be easy to dry after being applied to the inner surface of the mold cavity.

  Therefore, a volatile solvent is used as a solvent for preparing the lubricating liquid. Examples of volatile solvents that can be used include organic solvents such as various alcohols such as ethyl alcohol, methyl alcohol, and isopropyl alcohol, and ethers such as dimethyl ether, ethyl methyl ether, and diethyl ether. By applying a lubricating liquid in which insulating ceramic particles are dispersed in a solution in which a pressing lubricant is dissolved in such a volatile solvent, to the inner surface of the mold hole of the mold apparatus, the solvent is distilled off by drying, A solid lubricating film in which insulating ceramic particles are dispersed in the pressing lubricant is formed.

  The lubricating coating formed on the inner surface of the mold hole of the mold apparatus preferably has a thickness of about 0.1 to 20 μm. If the thickness is less than 0.1 μm, the amount of the pressing lubricant is insufficient, and the friction between the formed green compact and the inner surface of the mold hole cannot be sufficiently reduced, and plastic flow of the soft magnetic powder is likely to occur. . At the same time, the amount of insulating ceramic particles is insufficient, and plastic flow of the soft magnetic powder is likely to occur. On the other hand, when the thickness of the coating film of the solid lubricant is excessive, the size of the green compact to be molded is reduced correspondingly, and the dimensional accuracy is deteriorated. In addition, it is necessary to increase the clearance between the mold hole and the punch.

  When insulating ceramic particles whose surface has been modified with a coupling agent are used as insulating ceramic particles, organic (lipophilic) properties are imparted to the surface. The particles can be uniformly dispersed in the solvent, which is effective in forming a uniform lubricating film in which the insulating ceramic particles are uniformly dispersed on the inner surface of the mold cavity. As the coupling agent, a silane coupling agent, an aluminate coupling agent, a titanate coupling agent, or the like can be used, and these coupling agents may be used in combination. When the silane coupling agent is used, the surface treatment layer is formed of a compound containing Si on the surface of the insulating ceramic particles. When an aluminate coupling agent is used, a surface treatment layer is formed of a compound containing Al on the surface of the insulating ceramic particles. Further, when a titanate coupling agent or the like is used, a surface treatment layer is formed of a compound containing Ti on the surface of the insulating ceramic particles. These organic surface treatment layers are also insulating films. When the soft magnetic powder used as the powder compact material has a silicone resin-based insulating coating on the particle surface, the use of insulating ceramic particles whose surface is modified with a silane coupling agent has a high affinity with each other, Insulating ceramic particles can easily enter between soft magnetic powder particles during compression molding, and the surface of soft magnetic powder particles can be easily covered with insulating ceramic particles. Direct contact between the inner surface of the mold cavity and the soft magnetic powder particles is also reduced. Therefore, the effectiveness of the present invention is remarkably enhanced when the insulating ceramic particles subjected to suitable surface modification are used according to the surface properties of the soft magnetic powder particles.

  As a general method for forming a coating film of a solid lubricant in a mold hole of a mold apparatus, there is a so-called electrostatic coating method other than the coating method as described above. In the electrostatic coating method, the lubricant powder is charged and sprayed, and the lubricant is adsorbed on the inner surface of the mold cavity by utilizing the Coulomb force generated by the charge of the charged lubricant. When forming a lubricating coating containing a pressing lubricant and insulating ceramic particles by an electrostatic coating method, a mixed powder of the pressing lubricant powder and insulating ceramic particles is electrostatically applied, but the lubricant charged on the inner surface of the mold hole Since the portion to which is attached is charged, it is difficult for the lubricant to be laminated on the already adsorbed lubricant, and it is difficult to attach a desired amount of insulating ceramic particles. Further, when a lubricant powder having a large particle size is used to thicken the adhered lubricant layer, the lubricant powder has a large mass, so that it is difficult to be adsorbed by Coulomb force and easily falls off. Furthermore, in the case of electrostatic coating, adhesion to the mold hole surface is likely to be non-uniform, and it is difficult to form a lubricating coating with a constant thickness.

  For this reason, the method of preparing the lubricating liquid and forming the lubricating film by coating and drying as described above is excellent, and it is possible to supply the insulating ceramic particles together with the required amount of the pressing lubricant by coating. The lubricating film can be easily and uniformly formed by drying. Therefore, in the method for molding a green compact for a magnetic core according to the present invention, a solid lubricant is formed on the inner surface of a mold cavity by using a lubricating liquid in which insulating ceramic particles are dispersed in a solution obtained by dissolving a pressing lubricant in a volatile solvent. A coating is provided.

  As described above, in the method for manufacturing a green compact for a magnetic core according to the present invention, the green compact formed by the pressing lubricant and the insulating ceramic particles contained in the lubricating coating formed on the inner surface of the mold hole of the mold apparatus. Since the frictional resistance when extruding the body from the mold cavity is reduced and deformation and plastic flow of the soft magnetic powder particles are suppressed, it is not necessary to add a molding lubricant to the raw material powder itself. This point is advantageous in increasing the space factor of the soft magnetic powder in the green compact after molding, and lowers the fluidity of the raw material powder caused by adding a molding lubricant to the raw material powder, It is possible to avoid a decrease in the filling factor and a decrease in the space factor of the soft magnetic powder due to the volume occupied by the molding lubricant itself.

  In addition, since said insulating ceramic particle has a low magnetic permeability, it does not exclude that the insulating ceramic particle is contained in the raw material powder in the present invention. In other words, the insulating ceramic particles are dispersed in the pores of the powder compact, so that when used as a powder magnetic core, the magnetic gap is dispersed to form a powder core having a constant permeability. In this case, however, excessive insulating ceramic particles do not impair the fluidity and formability of the raw material powder and make high density compression difficult, and the insulating film is insulated from the compressed soft magnetic powder particles. It is desirable to adjust the amount of insulating ceramic particles added to the raw material powder so as not to lose room for receiving the ceramic particles. From this point, when adding insulating ceramic particles to the raw material powder, the amount of the insulating ceramic particles added is limited to 1.5% by volume or less with respect to the raw material powder, and the soft magnet is formed. It is preferable that a sufficient amount of insulating ceramic particles be allowed to enter from the lubricating coating on the inner surface of the mold cavity between the powder particles.

  The magnetic core green compact formed as described above may be further heat-treated according to the purpose. For example, when the green compact for a magnetic core contains a thermosetting resin as a binder, a heat treatment for heating to the curing temperature of the thermosetting resin can be performed. Alternatively, when the magnetic core green compact contains a thermoplastic resin as a binder, a heat treatment can be performed by heating to the softening temperature of the thermoplastic resin. Regardless of the presence or absence of a binder, in order to improve the hysteresis loss when used as a dust core, annealing heat treatment may be performed to release the compressive strain accumulated in the soft magnetic powder of the core compact. However, it is possible to perform such heat treatment. Such heat treatment may be performed according to a conventional method. When the heat treatment as described above is performed, the mold lubricant is decomposed and disappears in the temperature rising process of the heat treatment.

  It is also possible to directly use the compressed powder for magnetic core as a dust core without heat treatment. In this case, since the molding lubricant does not disappear, it remains attached to the side surface of the dust core.

  By manufacturing the green compact for the magnetic core as described above, the insulating ceramic particles are dispersed on the surface by being pushed between the soft magnetic powder particles. Plastic flow of the soft magnetic powder due to frictional resistance is suppressed, and conduction between the soft magnetic powder particles can be prevented. Accordingly, steps such as pickling and cutting performed to remove the surface layer portion in which the soft magnetic powder particles are plastically flowed and conducted in the green compact obtained by the conventional manufacturing method are unnecessary in the present invention. In addition, since the insulating ceramic particles are filled between the soft magnetic powder particles in the surface layer portion on the side surface of the manufactured magnetic core green compact, the specific resistance on the side surface when used as a dust core. Is particularly suitable for suppressing an increase in iron loss when used in a high-frequency region in which an induced current is concentrated on the surface.

(Preparation of lubricating liquid)
As insulating ceramic particles, titanium oxide powder (particle size: 100 nm), alumina powder (particle size: 200 nm), silica powder (particle size: 100 nm), aluminum nitride powder (particle size: 100 nm), titanium nitride powder (particle size) : 800 nm) and titanium carbide powder (particle size: 1000 nm). Further, ethylene bis stearamide, stearic acid, zinc stearate, and lithium stearate were prepared as the press lubricant.
Lubricating liquids of sample numbers 1 to 20 were prepared by blending with ethyl alcohol so that the ratio of the insulating ceramic particles to the total amount of the pressing lubricant and the insulating ceramic particles was the ratio described in Table 1. At this time, the amount of ethyl alcohol to be used was adjusted so that the total amount of the pressing lubricant and the insulating ceramic particles was 10% by mass with respect to ethyl alcohol.

(Green compact molding)
A lower punch is fitted to a pressing mold having a cylindrical mold hole with an inner diameter of 20 mm to form a molding cavity, and one of the lubricating liquids of sample numbers 1 to 20 prepared above is applied to the inner diameter surface of the mold hole. Then (coating amount: 0.1 cc) was dried to form a lubricating film having a thickness of about 20 μm on the inner surface of the mold cavity.
As a raw material powder, an iron-based soft magnetic powder (Somaloy 110i (5P) manufactured by Höganäs AB) whose surface is insulated and coated, a main particle fraction in the particle size distribution: 45 to 75 μm), and a mold hole in which a lubricating film is formed as described above 60 g was added to the raw material, and the raw material powder was compression-molded with a molding pressure of 1200 MPa using an upper punch and extruded to obtain a cylindrical compact. The length of the green compact was measured and the density ratio of the green compact was calculated. The results are shown in Table 1.

(Surface observation of green compact side)
The side surface of the obtained green compact was observed using an EPMA apparatus, and the area ratio (%) of the insulating ceramic particles in the component map on the side surface was examined. The area ratio was measured by analyzing a photographed image with a magnification of 100 times using an image analysis software (Quick grain standard) (threshold: RGB: 160). Furthermore, in order to evaluate the state of the soft magnetic powder particles on the side surface of the green compact, the presence or absence of bonding of the soft magnetic powder particles was examined in the SEM image of the side surface. The presence or absence of bonding is determined by the presence or absence of sliding traces in the SEM image, and in the component map by EPMA, the presence or absence of Fe element flow, that is, whether or not Fe element is detected between soft magnetic powder particles. Judged. That is, when a sliding mark is confirmed, a clear soft magnetic powder joining occurs. Even if no clear sliding trace is confirmed, if Fe element is detected between the particles of the soft magnetic powder, the soft magnetic powder is considered to be joined due to plastic flow. Table 1 shows the results of the determination on whether or not the soft magnetic powder was joined.
FIG. 3 shows an SEM image and component map of the side surface of the green compact of sample number 1, and FIG. 4 shows an SEM image and component map of the green compact of sample number 9.

  According to the results of sample numbers 2 to 12 in Table 1, by forming a lubricating film with titanium oxide particles and a push-type lubricant on the inner surface of the mold cavity, titanium oxide is interposed between the soft magnetic powder particles, It can be seen that the plastic flow of the soft magnetic powder can be suppressed when the powder is extruded. Also, from the results of sample numbers 13 to 17, alumina powder, silica powder, aluminum nitride powder, titanium nitride powder and titanium carbide powder can be used as insulating ceramic particles in the same manner, and plastic flow is interposed between soft magnetic powder particles. It can be seen that this can be suppressed.

  According to FIG. 3, on the side of the green compact of the sample 1 that does not use the insulating ceramic particles, streaks along the axial direction appear in the SEM image, and galling occurs with the inner surface of the mold cavity. I understand. Further, since Fe is detected over the entire surface of the component map, it can be seen that the gaps between the soft magnetic powder particles are filled. That is, the soft magnetic powder particles on the side of the green compact are crushed, and plastic flow is clearly generated. On the other hand, according to FIG. 4, streaks do not appear in the SEM image on the side of the green compact of the sample 9 using the insulating ceramic particles, and no galling with the inner surface of the mold hole occurs, and good lubrication is obtained. It has been. In the component map, Fe derived from the soft magnetic powder is detected in the particle shape, and Ti derived from the insulating ceramic particles is detected in a portion where Fe is not detected. That is, the insulating ceramic particles are filled in the gaps between the soft magnetic powder particles, the plastic flow of the soft magnetic powder particles is suppressed, and the insulation between the particles is maintained.

  For confirmation, each of the green compacts of sample numbers 1, 2 and 12 was used as a core, and the coil was wound with the same number of turns, under the same conditions of frequency: 50 kHz and magnetic flux density: 0.1 T. When the eddy current loss was measured and compared, the eddy current loss in the green compacts of sample numbers 2 and 12 was clearly smaller than that of the green compact of sample number 1.

  The dust core of the present invention can be applied to a transformer, a reactor, a thyristor valve, a noise filter, a choke coil, and the like. Also, a motor iron core, a motor rotor and yoke for general household appliances and industrial equipment, and a diesel engine It can also be applied to a solenoid core (fixed iron core) for a solenoid valve incorporated in an electronically controlled fuel injection device of a gasoline engine. In particular, it is highly effective in application to a reactor or the like used in a high frequency region.

  DESCRIPTION OF SYMBOLS 1 ... Stamping die, 1a ... Mold hole, 2 ... Lower punch, 3 ... Upper punch, 4 ... Feeder, M ... Raw material powder, C ... Green compact

Claims (16)

  A surface layer having a structure in which soft magnetic powder is formed of a green compact that is compression-molded to a density ratio of 91% or more, and an extruded sliding contact surface of the green compact has insulating ceramic particles interposed between the soft magnetic powder particles. Powder magnetic core having a part.   The powder magnetic core according to claim 1, wherein the powder compact further includes insulating ceramic particles that cover the extruded sliding contact surface.   3. The dust core according to claim 1, wherein an area ratio of the insulating ceramic particles is 30% or more in a component map obtained by electronic probe microanalysis of the extruded sliding contact surface.   The dust core according to any one of claims 1 to 3, wherein the insulating ceramic particles have a particle size of 50 to 1000 nm.   The insulating ceramic particles are particles composed of at least one ceramic selected from the group consisting of oxide ceramics, nitride ceramics, carbide ceramics, carbonitride ceramics, and oxynitride ceramics. Selected from the group consisting of aluminum oxide, titanium dioxide, silicon dioxide, magnesium oxide, zirconium dioxide, steatite, zircon, ferrite, mullite, forsterite and yttria, and the nitride ceramics are aluminum nitride, titanium nitride and silicon nitride The dust core according to any one of claims 1 to 4, wherein the carbide ceramics is selected from the group consisting of titanium carbide and tungsten carbide.   The pressure according to any one of claims 1 to 5, wherein the insulating ceramic particles have a coating film formed of a compound containing at least one element selected from Si, Al, and Ti formed on a surface thereof. Powder magnetic core. The mold hole of the green compact mold is filled with soft magnetic powder, the soft magnetic powder is compressed so that the density ratio of the soft magnetic powder is 91% or more, and the green compact is molded, A method for producing a green compact for extruding a green compact from the mold cavity,
Manufacture of a green compact for a magnetic core in which a lubricating coating containing a pressing lubricant and insulating ceramic particles is formed on the inner surface of the mold hole in sliding contact with the green compact during extrusion before filling with the soft magnetic powder. Method. The impression lubricant is at least one semi-solid or solid lubricant selected from the group consisting of wax, higher fatty acids and higher fatty acid metal salts,
The said lubricating coating is formed by apply | coating the lubricating liquid which mix | blended the said lubricant and the said insulating ceramic particle | grain in the volatile solvent to the inner surface of the said mold hole, and removing a volatile solvent. Of manufacturing green compact for magnetic cores.   The magnetic core dust according to claim 7 or 8, wherein the lubricating coating contains the insulating ceramic particles in a ratio of 20 to 60% by mass with respect to a total amount of the insulating ceramic particles and the pressing lubricant. Body manufacturing method.   The method for producing a green compact for a magnetic core according to any one of claims 7 to 9, wherein the thickness of the lubricating coating is 0.1 to 20 µm.   The method of manufacturing a green compact for a magnetic core according to any one of claims 7 to 10, wherein the insulating ceramic particles have a particle size of 50 to 1000 nm.   The insulating ceramic particles are particles composed of at least one ceramic selected from the group consisting of oxide ceramics, nitride ceramics, carbide ceramics, carbonitride ceramics, and oxynitride ceramics. The manufacturing method of the compact for magnetic cores of any one of Claims 1.   The surface of the insulating ceramic particles is modified by at least one coupling agent selected from the group consisting of a silane coupling agent, an aluminate coupling agent, and a titanate coupling agent. The manufacturing method of the compact for magnetic cores of any one of Claims 1. A mold hole for compressing the raw material powder to form a green compact;
A pressing mold for producing a dust core, comprising: a pressing lubricant and a lubricating coating containing insulating ceramic particles provided on an inner surface of the mold hole that is in sliding contact with the green compact during extrusion of the green compact to be molded.   A mold apparatus for producing a dust core, comprising: the mold for producing a dust core according to claim 14; and an upper and lower punch for compressing the raw material powder in the mold hole.   A lubricating liquid for a pressing mold for producing a dust core, which includes a pressing lubricant, insulating ceramic particles, and a volatile solvent.