JP2012243912A - Production method of green compact, and green compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of green compact capable of producing a green compact at low loss.SOLUTION: The method of producing a green compact by using coated soft magnetic powder, where a plurality of soft magnetic particles coated with an insulation coating are provided on the outer periphery of a soft magnetic particle, comprises: a raw material preparation step; a heat treatment step; and a surface treatment step. In the raw material preparation step, a raw material compact is prepared by pressure molding the coated soft magnetic powder. In the heat treatment step, the raw material compact is heat treated. In the surface treatment step, the surface of the raw material compact is partially subjected to acid treatment. Since the surface of the raw material compact is partially subjected to acid treatment, the conductive part where the constituent materials of multiple soft magnetic particles are conducting on the surface of the raw material compact can be removed, and thereby the loss of green compact can be reduced.

Description

  The present invention relates to a method for producing a green compact formed by pressure-molding a coated soft magnetic powder, and a green compact produced by the production method. In particular, the present invention relates to a method for producing a low-loss compact.

  A hybrid vehicle or the like includes a booster circuit in a power supply system to a motor. A reactor is used as one component of this booster circuit. The reactor has a configuration in which a coil is wound around a core. When the core is used in an alternating magnetic field, an energy loss called iron loss occurs in the core. The iron loss is generally represented by the sum of hysteresis loss and eddy current loss, and particularly increases significantly when used at high frequencies.

  In order to reduce iron loss in the core of the reactor, a core made of a green compact may be used. The compacted body is formed by pressurizing coated soft magnetic powder composed of coated soft magnetic particles in which an insulating film is formed on the surface of soft magnetic particles, and the magnetic particles are insulated from each other by the insulating film. The effect of reducing current loss is high.

  However, the green compact has a cavity formed by a relatively movable columnar first punch and a cylindrical die filled with coated soft magnetic powder, and the cavity is formed by the first punch and the columnar second punch. Since the coated soft magnetic powder is pressure molded, the insulating coating of the coated soft magnetic particles is damaged by the pressure during the pressure molding and the sliding contact with the mold when the molded product is removed. There is a fear. When the insulating coating is damaged, the soft magnetic particles may be exposed and spread, and as a result, the soft magnetic particles in the green compact are electrically connected to each other to form a substantially film-like conductive portion. The eddy current loss may increase.

  Therefore, in order to reduce the eddy current loss, for example, in Patent Document 1, the surface of a material molded body formed by press-molding a coated soft magnetic powder (soft magnetic powder) is surface-treated with concentrated hydrochloric acid. It is described. Specifically, the material molded body is immersed in concentrated hydrochloric acid, and the conductive portion on the entire surface of the material molded body is removed to form a powder molded body.

JP 2006-229203 A

  By subjecting the entire surface of the material molded body to surface treatment as described above, a certain reduction in loss can be achieved. However, if the entire surface of the molded body of the material is surface treated, the conductive portion can be removed, but on the other hand, the insulating coating of the coated soft magnetic particles that do not damage the insulating coating may also be damaged. There is also. As a result, the loss reduction effect may be reduced.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a method for producing a green compact that can efficiently produce a low-loss green compact. It is in.

  Another object of the present invention is to provide a green compact produced by the production method of the present invention.

  In order to achieve the above-mentioned object, the present inventors diligently studied about a method for producing a green compact. Specifically, the cause of the reduced loss reduction effect was investigated by manufacturing a compacted body with various surface treatment areas selected. As a result, the following knowledge was obtained.

  When the surface treatment is performed on the entire surface of the material molded body, the conductive portion generated at the portion (sliding contact surface) that is in sliding contact with the die is removed. On the other hand, in the first place, the conductive portion is unlikely to be formed at a position (pressure contact surface) in contact with the punches of the material molded body, and when the surface treatment is performed there, the insulating coating may be destroyed. Therefore, the soft magnetic particles are exposed at the pressure contact surface, and as a result, the effect of reducing iron loss may be reduced. Accordingly, the surface treatment is preferably performed on a part of the material molded body, and further on a part of the sliding contact surface, particularly on a region extending over the entire length in the magnetic flux direction on the sliding contact surface.

  From the above results, in order to efficiently produce a low-loss compacted body, the following method of applying a surface treatment to a specific region of the material compact can be mentioned.

  The method for producing a green compact is a method for producing a green compact using a coated soft magnetic powder comprising a plurality of coated soft magnetic particles in which a soft magnetic particle is coated with an insulating coating. And a surface treatment process. In the material preparation step, a material molded body obtained by pressure-molding the coated soft magnetic powder is prepared. In the surface treatment step, the conduction portion where the constituent materials of the plurality of soft magnetic particles are conducted on the surface of the material molded body is removed. The said surface treatment process is given to a part of surface of the said raw material molded object. The surface treatment step here includes any surface treatment that can remove the conductive portion by chemical, mechanical, electrical, optical, thermal, or a combination of these treatments. Specifically, acid treatment is used as the chemical treatment method, electrolytic treatment is used as the electrochemical treatment method, and cutting, grinding, or water jet is used as the mechanical treatment method. Any of the processing methods is considered to be able to remove the conductive portion.

  The following present invention is mentioned as a more concrete method.

  The method for producing a powder compact according to the present invention is a method for producing a powder compact using a coated soft magnetic powder comprising a plurality of coated soft magnetic particles having an insulating coating coated on the outer periphery of the soft magnetic particles. It includes a material preparation process, a heat treatment process, and a surface treatment process. In the material preparation step, the coated soft magnetic powder is pressure-molded to prepare a material molded body. In the heat treatment step, the material molded body is heated and heat treated. In the surface treatment step, a part of the surface of the material molded body is acid-treated.

  According to the production method of the present invention, the conductive portion can be partially removed by acid-treating a part of the surface of the material molded body. As a result, since eddy current conduction can be cut off at the acid-treated portion, loss of the green compact can be reduced. In addition, the possibility of damaging the insulating coating of the coated soft magnetic particles whose insulating coating is not damaged is reduced, and the loss reduction effect is not reduced. As a result, it is possible to produce a compacted product having a low loss comparable to that obtained when the entire surface of the material molded product is surface-treated. In addition, it is possible to obtain a powder compact having a lower loss than the powder compact when the loss reduction effect is reduced, and it is possible to efficiently produce a powder compact having a low loss.

  As one form of the manufacturing method of this invention, the said surface treatment process is given to the surface of the raw material molded object used as at least one part of a parallel surface with a magnetic flux direction, when exciting the said compacting body as a magnetic core. Is mentioned.

  According to said structure, the part which surface-treats is the surface of the raw material molded object used as at least one part among the parallel surfaces with a magnetic flux direction, Therefore The eddy current which flows into the circumferential direction centering on a magnetic flux direction is used. Can be blocked at the location where the surface treatment is applied. Therefore, eddy current loss can be reduced, and a low-loss compacting body can be manufactured.

  As one form of the manufacturing method of this invention, the said surface treatment process is at least one part of a parallel surface with the magnetic flux direction, when the said powder compact body is excited as a magnetic core, and the said powder compact body in the said parallel surface. It is mentioned that it is given to the surface of the material molding which becomes the field over the whole magnetic flux direction.

  According to said structure, the area | region which surface-treats is a surface which becomes an area | region covering the magnetic flux direction full length of a compacting body in the parallel surface in the surface of a raw material molded body at least one part of the said parallel surface. By doing so, it is considered that the eddy current flowing in the circumferential direction around the magnetic flux direction can be divided over the entire length. Therefore, the eddy current loss can be further reduced, and a green compact with lower loss can be manufactured.

  As one form of the manufacturing method of this invention, the said surface treatment process includes making the surface treatment liquid of pH 1-4 contact the said raw material molded object for 1 minute-40 minutes.

  According to said structure, it is easy to remove the said conduction | electrical_connection part by using the surface treatment liquid of the said range, and making it contact for the said range, and removes the surface of raw material molded objects other than the said conduction | electrical_connection part. Never too much.

  The green compact of the present invention is a green compact manufactured by the manufacturing method of the present invention.

  According to the green compact of the present invention, a low-loss compact with low eddy current loss can be obtained. Therefore, for example, it can be suitably used for a reactor core, and in that case, even when the coil is excited by high-frequency alternating current, the iron loss characteristic can be improved.

  The manufacturing method of the compacting body of this invention can reduce an eddy current loss, and can manufacture a compacting body with a low loss efficiently.

  The green compact of the present invention can be a low-loss compact with low eddy current loss.

It is a graph which shows the loss of each sample in a test example. It is a microscope picture which shows the surface state of the molded object in the manufacture process of this invention, Comprising: (A) shows the surface state of the heat processing molded object before surface treatment, (B) is compacting after a surface treatment process. Indicates the surface condition of the body.

  Hereinafter, the manufacturing method of the compacting body which concerns on embodiment of this invention is demonstrated.

<< Method for Producing Green Compact >>
The manufacturing method of the compacting body of this invention is a method of manufacturing a compacting body using a covering soft magnetic powder, and comprises a raw material preparation process, a heat treatment process, and a surface treatment process. Each of the above steps will be described in order.

[Material preparation process]
In the raw material preparation process, a coated soft magnetic powder constituting the green compact is prepared, and the powder is pressure-molded to produce a raw material compact, or a previously molded material compact is purchased in advance. Prepare. In the former case, a raw material preparation step and a raw material forming step of forming a raw material molded body from the raw material are provided. As the raw material preparation step, a coated soft magnetic powder constituting the green compact is prepared. The coated soft magnetic powder includes a plurality of coated soft magnetic particles in which an insulating coating is coated on the outer periphery of the soft magnetic particles.

[Coated soft magnetic powder]
(Soft magnetic particles)
<composition>
The soft magnetic particles preferably contain 50% by mass or more of iron, and examples thereof include pure iron (Fe). In addition, iron alloys such as Fe-Si alloys, Fe-Al alloys, Fe-N alloys, Fe-Ni alloys, Fe-C alloys, Fe-B alloys, Fe-Co alloys, Fe An alloy composed of at least one selected from a -P alloy, an Fe-Ni-Co alloy, and an Fe-Al-Si alloy can be used. In particular, from the viewpoint of magnetic permeability and magnetic flux density, pure iron in which 99% by mass or more is Fe is preferable.

<Particle size>
The average particle diameter of the soft magnetic particles may be any size that contributes to low loss as a green compact. That is, although it can select suitably, without specifically limiting, For example, if it is 1 micrometer or more and 150 micrometers or less, it is preferable. By setting the average particle size of soft magnetic particles to 1 μm or more, the increase in coercive force and hysteresis loss of compacts made using soft magnetic powder is suppressed without reducing the fluidity of soft magnetic powder. it can. Conversely, by setting the average particle size of the soft magnetic particles to 150 μm or less, eddy current loss that occurs in a high frequency region of 1 kHz or more can be effectively reduced. The average particle size of the soft magnetic particles is more preferably 40 μm or more and 100 μm or less. If the lower limit of the average particle diameter is 40 μm or more, an effect of reducing eddy current loss can be obtained, and handling of the coated soft magnetic powder becomes easy, and a molded body having a higher density can be obtained. The average particle diameter means a particle diameter of particles in which the sum of masses from particles having a small particle diameter reaches 50% of the total mass in the particle diameter histogram, that is, 50% particle diameter.

<shape>
The shape of the soft magnetic particles is preferably such that the aspect ratio is 1.2 to 1.8. The aspect ratio is the ratio between the maximum diameter and the minimum diameter of the particles. Soft magnetic particles having an aspect ratio in the above range can increase the demagnetizing factor when formed into a compact, compared to those having a small aspect ratio (close to 1.0), and have excellent magnetic properties. It can be set as a molded body. In addition, the strength of the green compact can be improved.

<Production method>
The soft magnetic particles are preferably produced by an atomizing method such as a water atomizing method or a gas atomizing method. Since the soft magnetic particles produced by the water atomization method have many irregularities on the particle surface, it is easy to obtain a high-strength molded product by meshing the irregularities. On the other hand, the soft magnetic particles produced by the gas atomization method are preferable because the particle shape is substantially spherical, and there are few irregularities that break through the insulating coating. A natural oxide film may be formed on the surface of the soft magnetic particles.

(Insulation coating)
The insulating coating is coated on the outer periphery of the soft magnetic particles in order to insulate adjacent soft magnetic particles. By covering the soft magnetic particles with an insulating film, the contact between the soft magnetic particles can be suppressed, and the relative magnetic permeability of the compact can be suppressed low. In addition, the presence of the insulating coating can suppress the eddy current from flowing between the soft magnetic particles, thereby reducing the eddy current loss of the green compact.

<composition>
The insulating coating is not particularly limited as long as it has excellent insulating properties that can ensure insulation between soft magnetic particles. For example, examples of the material for the insulating film include phosphate, titanate, silicone resin, and two layers of phosphate and silicone resin.

  In particular, since the insulating coating made of phosphate is excellent in deformability, even when soft magnetic particles are deformed when a soft magnetic material is pressed to produce a compact, a deformation follows the deformation. Can do. Further, the phosphate coating has high adhesion to iron-based soft magnetic particles and is difficult to fall off from the surface of the soft magnetic particles. As the phosphate, a metal phosphate compound such as iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate, or aluminum phosphate can be used.

  In the case of an insulating coating made of a silicone resin, it is excellent in heat resistance, so that it is difficult to be decomposed in a heat treatment step to be described later, and the insulation between soft magnetic particles can be maintained well until the compacting body is completed.

  When the insulating coating has a two-layer structure of the phosphate and the silicone resin, it is preferable to coat the phosphate on the soft magnetic particle side and the silicone resin directly on the phosphate. Since the silicone resin is coated directly on the phosphate, it is possible to have the characteristics of both the phosphate and the silicone resin described above.

<Film thickness>
The average thickness of the insulating coating may be a thickness that can insulate adjacent soft magnetic particles. For example, it is preferably 10 nm or more and 1 μm or less. By setting the thickness of the insulating coating to 10 nm or more, it is possible to effectively suppress contact between soft magnetic particles and energy loss due to eddy current. On the other hand, by setting the thickness of the insulating coating to 1 μm or less, the ratio of the insulating coating to the coated soft magnetic particles does not become too large, and the magnetic flux density of the coated soft magnetic particles can be prevented from significantly decreasing.

  The thickness of the insulating coating can be examined as follows. First, the film composition obtained by composition analysis (TEM-EDX: transmission electron microscopic energy dispersive X-ray spectroscopy), and the amount of inductively coupled plasma mass (ICP-MS) obtained by inductively coupled plasma Considering this, a considerable thickness is derived. Then, the film is directly observed with a TEM photograph, and the average thickness determined by confirming that the order of the equivalent thickness derived earlier is an appropriate value is used.

<Coating method>
The method of covering the soft magnetic particles with the insulating coating may be selected as appropriate. For example, the film may be formed by hydrolysis / polycondensation reaction. Soft magnetic particles and a material constituting the insulating coating are blended, and the blend is mixed in a heated state. By doing so, the soft magnetic particles can be sufficiently dispersed in the coating material, and the insulating coating can be coated on the outside of the individual soft magnetic particles.

  The heating temperature and mixing time may be appropriately selected. By selecting the heating temperature and mixing time, the soft magnetic particles can be more sufficiently dispersed, and it becomes easy to coat the individual particles with the insulating coating.

[Raw material forming process]
In the raw material forming step, a coated soft magnetic powder composed of a plurality of coated soft magnetic particles prepared in the raw material preparing step is pressure-molded to produce a raw material compact.

  In the raw material forming step, typically, the coated soft magnetic powder is injected into a molding die composed of a punch and die having a predetermined shape, and is pressed and hardened. When the punch and die are used, the coated soft magnetic powder is pressure-molded so that the compact is not baked on the mold by pressurization and the insulating coating of the coated soft magnetic powder is not destroyed. As the means, an external lubrication molding method in which a lubricant is applied to a portion (inner wall) in contact with the coated soft magnetic powder of at least one of the punch and the die and the coated soft magnetic powder is pressed, or the coated soft magnetic powder is previously applied to the coated soft magnetic powder. An internal lubrication molding method may be used in which a mixture is prepared by mixing a lubricant, and the mixture is pressurized with a mold. In the former case, since the lubricant is applied to the inner wall, it is possible to reduce friction with the coated soft magnetic powder and to form a high-density material molded body. In the latter case, the lubricant adhering to the surface of the coated soft magnetic powder reduces friction between particles in the coated soft magnetic powder, so that the insulating coating of the coated soft magnetic particles can be prevented from being broken.

  When pressurizing, the molding die may be heated and then press-molded. In that case, for example, the mold temperature is set to 50 to 200 ° C. By heating the mold, a high-density material molded body can be obtained.

  Although the pressure to pressurize can be selected suitably, for example, if the compacting body used as the core for reactors is manufactured, it is preferred to set it as about 490-1470 MPa, especially about 588-1079 MPa.

[Heat treatment process]
In the heat treatment step, the material molded body is heated and heat-treated in order to remove the distortion and transition introduced into the soft magnetic particles in the material molding step.

  The higher the heat treatment temperature, the more strain can be removed. Therefore, the heat treatment temperature is preferably 300 ° C. or higher, particularly 400 ° C. or higher. From the viewpoint of removing strain and the like of the soft magnetic particles, the upper limit of the heat treatment is about 800 ° C. With such a heat treatment temperature, not only strain can be removed, but also lattice defects such as transition introduced into the soft magnetic particles during pressurization can be removed. Thereby, the hysteresis loss of a compacting body can be reduced effectively.

  What is necessary is just to select the time which heat-processes suitably according to the said heat processing temperature and the volume of a raw material molded object so that the distortion | strain, transition, etc. which were introduce | transduced into the soft-magnetic particle in the raw material formation process may fully be removed. For example, in the above temperature range, it is preferably 10 minutes to 1 hour.

  The atmosphere at the time of performing the heat treatment may be in the air, but it is particularly preferable to apply in an inert gas atmosphere. Thereby, it can suppress that a coated soft magnetic particle is oxidized with oxygen in air | atmosphere.

  This heat treatment may be performed on the material molded body after the surface treatment process described later, but is preferably performed on the material molded body before the surface treatment process.

[Surface treatment process]
In the surface treatment step, a part of the surface of the material molded body is acid-treated. By this acid treatment, the conduction portion where the constituent materials of the plurality of soft magnetic particles are conducted on the surface of the material molded body is removed.

  The surface of the material molded body to be acid-treated is preferably at least a part of a plane (parallel plane) that is parallel to the magnetic flux direction when the produced powder compact is excited as a magnetic core, for example, a reactor core. When the compacted compact and the coil are combined and the coil is excited, a magnetic flux along the axial direction of the coil is formed in the compact. Therefore, for example, when the green compact is a cube, if the surfaces orthogonal to the magnetic flux direction (orthogonal surfaces) are both end surfaces of the cube, the other four side surfaces become the parallel surfaces and are subjected to surface treatment. The region may be at least a part of the surface of the material molded body that serves as the side surface. In addition, when the green compact is a cylinder, if the surfaces perpendicular to the magnetic flux direction are both end faces, the parallel surface to the magnetic flux direction is the side surface of the cylinder. It may be at least part of the surface of the molded body. In this way, the surface treatment was applied to the eddy current flowing in the circumferential direction around the magnetic flux direction by subjecting a part of the surface of the material molded body to be parallel to the magnetic flux direction. It is thought that it can be cut off at the location. Therefore, eddy current loss can be reduced, and a low-loss compacting body can be manufactured.

  The region to be acid-treated in the parallel surface is at least a part of the parallel surface, and in the parallel surface, is a surface of the material molded body that is a region extending over the entire length in the magnetic flux direction of the green compact. preferable. For example, when the green compact is a rectangular parallelepiped, its both end faces are perpendicular to the magnetic flux direction, and the other faces are parallel faces, the surface treatment area is from one end face side to the other in the parallel face. It is set as the surface of the raw material molded object used as the area | region over an end surface side. In addition, when the green compact is a cylinder, both bottom surfaces thereof are orthogonal to the magnetic flux direction, and the other surfaces (side surfaces) are parallel surfaces, the region to be surface-treated is one end surface in the parallel surface. It is set as the surface of the raw material molded object used as the area | region ranging from the other end surface side from the side. By doing so, it is considered that the eddy current flowing in the circumferential direction around the magnetic flux direction can be divided over the entire length. Therefore, the eddy current loss can be further reduced, and a powder compact with a lower loss can be manufactured.

  When a surface treatment is performed on a region extending from one end face side to the other end face side in the parallel plane, the area of the parallel plane is longitudinal t in a direction parallel to the magnetic flux direction in the parallel plane and the magnetic flux direction as an axis. When the total length in the circumferential direction of the compacted green body is 1, the total area of the parallel surface is t × 1, and the width of the region actually surface-treated on the parallel surface (direction perpendicular to the magnetic flux direction) Is the processing width w, this region is represented as t × w. This treatment width w preferably satisfies d <w ≦ l, where d is the average particle diameter of the coated soft magnetic powder. By setting the processing width w within the above range, an effect of reducing eddy current loss can be effectively obtained. More preferably, the ratio w / l of the processing width w to the total length l is 30% or less, further 20% or less, 10% or less, and particularly 5% or less.

  The kind of surface treatment liquid should just be a treatment liquid of the grade which can remove the conduction | electrical_connection part of a raw material molded object surface. For example, an acidic treatment solution having a pH of about 1 to 4 is preferable, and specific examples include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and concentrated hydrochloric acid is particularly preferable.

  The temperature of the surface treatment liquid can be appropriately selected. For example, use of a treatment liquid at 20 ° C. to 50 ° C. can be mentioned. If it is said temperature range, surface treatment can be accelerated | stimulated.

  Further, the time for bringing the material molded body into contact with the surface treatment liquid may be appropriately selected according to the type and temperature of the surface treatment liquid, the region to be removed, and the like. In particular, when the pH of the surface treatment liquid is in the above range, it may be 1 min to 40 min. That is, the surface treatment liquid that satisfies the above pH range makes it easy to remove the conductive part by contacting the material molded body for the time in the above range, and the surface of the material molded body other than the conductive part is excessively removed. There is nothing.

  The method for bringing the material molded body into contact with the surface treatment liquid is not particularly limited as long as it is a method capable of performing surface treatment on a desired portion. For example, the batch type which immerses a raw material molded object in the liquid tank containing surface treatment liquid is mentioned. In this batch method, the material molded body side may be put into the liquid tank, and the material molded body may be brought into contact with the surface treatment liquid, or the material molded body may be fixed and the liquid tank side moved to use the surface treatment liquid as the material. You may make it contact a molded object. It is preferable to mask the area that is not in contact with the surface treatment liquid so as not to contact the surface treatment liquid. What is necessary is just to use what is excellent in acid resistance for this masking, for example, the tape made from a commercially available PTFE etc. can be used.

[Other processes]
(Washing process)
After the surface treatment step, it is preferable to wash the surface of the green compact in order to wash away the surface treatment liquid adhering to the surface of the green compact in the surface treatment step.

  The cleaning liquid used in this cleaning process only needs to be able to clean the surface treatment liquid. For example, use of water or the like can be mentioned. The temperature of the cleaning liquid and the cleaning time may be appropriately selected so that the surface treatment liquid can be sufficiently removed from the surface of the green compact.

<Effect>
According to embodiment mentioned above, there exist the following effects.

  (1) A low-loss compacting body with little eddy current loss can be produced.

  (2) The compacting body manufactured by the above manufacturing method can be suitably used for the core for the reactor. In that case, for example, a coil having a pair of coil elements and arranged side by side so that the axes of the coil elements are parallel, a pair of columnar inner core parts (middle core parts) in which the coil elements are respectively disposed, and In a reactor including a magnetic core having an outer core portion (side core portion) that is not disposed with a coil element and is connected to the inner core portion to form a closed magnetic path, the reactor can be suitably used for the inner core portion. When the inner core portion is configured by combining a plurality of divided core pieces, at least one, preferably all of the divided core pieces can be formed by the green compact of the present invention. At this time, in the inner core portion or the divided core piece, the region to be subjected to the surface treatment is at least a part of a surface parallel to the magnetic flux direction when the coil is excited. When the reactor is assembled with the split core pieces, the surface of the split core pieces that has been subjected to the surface treatment is opposed to the inner peripheral surface of the coil. Thereby, when the coil is excited, eddy current loss can be reduced by dividing the eddy current generated in the circumferential direction of the inner core portion in the surface-treated region. For example, if the region to be subjected to the surface treatment is a region extending from one end surface side to the other end surface side of the inner core portion or each divided piece in the parallel plane, the region is the inner side when the reactor is assembled. Covers the entire length of the core in the magnetic flux direction. Therefore, since the eddy current can be divided over the entire length of the inner core in the magnetic flux direction, the eddy current loss can be further reduced. The outer core portion is typically U-shaped or trapezoidal in the end surface. Also in this outer core part, you may use the compacting body obtained by the manufacturing method of this invention.

  (3) Since the portion to be surface-treated by dipping in the surface treatment liquid is a part of the surface of the material molded body, the surface treatment liquid can be reduced compared to the case where the entire surface of the material molded body is treated. The deterioration of the surface treatment liquid can be reduced and the surface treatment liquid can be used for a long time. Therefore, the waste liquid of the used surface treatment liquid can be reduced, and the surface treatment liquid need not be frequently replaced. Accordingly, the manufacturing cost can be reduced.

  (4) Since the region to be surface-treated is a part of the surface of the material molded body, the area to be washed in the washing step after the surface treatment is small, and the washing work time can be shortened. Therefore, the manufacturing operation can be simplified.

《Test example》
As test examples, the following samples 1 to 4 were prepared, and the test described below was performed for the magnetic properties of each sample.

[Sample 1]
Sample 1 is manufactured through the following steps in the order of step a → step b → step c → step d → step e.
(Step a) Raw material preparation step of preparing coated soft magnetic powder.
(Step b) A material molding step of producing a material molded body by press-molding the coated soft magnetic powder.
(Process c) A heat treatment step of heating the material molded body to produce a heat treated molded body.
(Step d) A surface treatment step of acid-treating the surface of the heat-treated molded body.
(Step e) A cleaning step of cleaning the surface of the green compact.

(Process a)
As a constituent material of the green compact, the coated soft magnetic powder in which the surface of soft magnetic particles made of iron powder was coated with an insulating coating made of iron phosphate contained 0.6% by mass of a lubricant made of zinc stearate. A mixed material was prepared. The iron powder was produced by a water atomization method and had a purity of 99.8% or more. The soft magnetic particles had an average particle size of 50 μm and an aspect ratio of 1.2. This average particle size was determined from the particle size of particles in which the sum of masses from particles with small particle sizes reached 50% of the total mass, that is, 50% particle size, in the particle size histogram. The insulating coating substantially covered the entire surface of the soft magnetic particles, and the average thickness was 20 nm. In addition, a lubricant composed of at least one of a metal soap and an inorganic lubricant having a hexagonal crystal structure can be suitably used as the lubricant.

(Process b)
The mixed material prepared in step a was poured into a mold having a predetermined shape, and pressure-molded by applying a pressure of 588 MPa without heating the mold to produce a material molded body. Here, a plurality of rectangular parallelepiped material molded bodies were produced. The material molded body produced here may include a prismatic body having a trapezoidal surface or a U-shaped body having a U-shaped surface.

(Process c)
The material molded body produced in step b was heat-treated at 400 ° C. for 30 minutes in a nitrogen atmosphere to obtain a plurality of heat-treated molded bodies.

(Process d)
In step d, at least a part of the heat-treated molded body is acid-treated when a plurality of rectangular parallelepiped heat-treated molded bodies obtained in step c are combined in a ring shape to produce a test piece for evaluating iron loss. Here, of the surface of the heat-treated molded body, acid treatment was performed on a part of the surface of the heat-treated molded body on which the coil is arranged in the magnetic property measurement test described later. At that time, the following acid treatment was performed on a region extending over the entire length in the magnetic flux direction of a surface (parallel surface) parallel to the direction of the magnetic flux generated in the sample. The acid treatment was performed while immersing the region in a liquid tank containing concentrated hydrochloric acid having a pH of 1 and a temperature of 26 ° C. for 20 minutes while stirring the concentrated hydrochloric acid. As a result, the ratio w / l of the treatment width w of the surface treatment to the total length l in the circumferential direction of the heat-treated molded body with the magnetic flux direction as an axis was 10%. Moreover, you may acid-treat also to the heat processing molded object (outer core part) in which a coil is not arrange | positioned. The heat-treated molded body that has undergone this surface treatment is a green compact.

(Process e)
The green compact obtained through step d was washed with water. The green compact after the washing is designated as sample 1.

[Sample 2]
The sample 2 is different from the sample 1 in the region where the heat treatment molded body is subjected to the surface treatment in the step d (surface treatment step). In Sample 2, the entire heat-treated molded body was immersed in the concentrated hydrochloric acid, and the entire surface was subjected to surface treatment to produce a green compact. Thereafter, like the sample 1, the green compact is washed to obtain a sample 2.

[Sample 3]
The sample 3 differs from the sample 1 in the order in which the steps are performed as follows. Further, in the step d, the region of the surface treatment applied to the heat-treated molded body is different. That is, the sample 3 is manufactured through the respective steps in the order of the above step a → step b → step d → step e → step c. And in the surface treatment process of the process d, the whole raw material molded object which passed the process b is immersed in the said concentrated hydrochloric acid, and the whole surface of the raw material molded object is surface-treated. Thereafter, the surface that has been subjected to the surface treatment in step e is washed, and subsequently, heat treatment is performed in step c.

[Sample 4]
The sample 4 is different from the sample 1 in that the surface treatment is not performed on the surface of the heat-treated molded body. That is, the sample 4 is manufactured through the respective steps in the order of the above step a → step b → step c. The heat-treated molded body after step c is designated as sample 4.

[Evaluation 1]
In Samples 1 and 2 produced through the above steps, a test magnetic core was produced by combining a plurality of cuboid compacts in an annular shape. Each test magnetic core was provided with a coil composed of a winding to produce a measurement member for measuring magnetic characteristics, and the following magnetic characteristic values were measured. On the other hand, in Samples 3 and 4, a plurality of rectangular parallelepiped heat-treated molded bodies were prepared in the same manner as Samples 1 and 2, and the following magnetic property values were measured.

[Magnetic property test]
For each measurement member, the hysteresis loss Wh (W) and eddy current loss We (W) of the sample at the excitation magnetic flux density Bm: 1 kG (= 0.1 T) and measurement frequency: 5 kHz are obtained using an AC-BH curve tracer. The iron loss W (W) was calculated.

  The characteristic values obtained from the above tests are summarized in Table 1 and FIG.

〔result〕
Samples 1 and 2 subjected to surface treatment after heat treatment had less eddy current loss and less iron loss and loss than sample 3 subjected to surface treatment before heat treatment. And the loss of the sample 1 which surface-treated a part of surface of the heat processing molded object was able to reduce the loss especially eddy current loss compared with the sample 2 which surface-treated the said whole surface.

  From the above test results, it is considered that the sample 1 subjected to the surface treatment after the heat treatment has a different magnetic property from the sample 3 subjected to the heat treatment after the surface treatment, and thus the powder compact itself can be different. The surface treatment performed after heat treatment reduces eddy current loss and iron loss when applied to a part of the surface of the heat-treated molded body, particularly a part parallel to the magnetic flux direction when excited as a reactor core. It turns out to be effective.

[Evaluation 2]
[Surface observation]
In the process of preparing Sample 1, the surface of the heat-treated molded body before the surface treatment process and the surface of the green compact after the surface treatment process were observed with a microscope. The photograph is shown in FIG.

〔result〕
In FIG. 2A, it is difficult to confirm grain boundaries on the surface of the heat-treated molded body before the surface treatment, whereas in FIG. 2B, grain boundaries are formed on the surface of the compacted molded body after the surface treatment. I can confirm. This is because the insulating coating on the surface of the preform is damaged by rubbing with the mold in the molding process, and the soft magnetic particles are spread to form conductive parts on the surface. It is thought that this is because On the other hand, it is considered that the conductive portion was removed by performing the surface treatment.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.

  The manufacturing method of this invention compacting body can be utilized suitably for preparation of various magnetic cores. Further, the green compact of the present invention can be suitably used as a core material for a transformer or a choke coil in addition to a booster circuit such as a hybrid vehicle or a reactor used in power generation / transforming equipment.

Claims (5)

A method for producing a green compact using a coated soft magnetic powder comprising a plurality of coated soft magnetic particles having an outer periphery of a soft magnetic particle coated with an insulating coating,
A material preparation step of preparing a material molded body obtained by pressure-molding the coated soft magnetic powder;
A heat treatment step of heating and heat-treating the material molded body;
And a surface treatment step of acid-treating a part of the surface of the material molded body.   The said surface treatment process is given to the surface of the raw material molded object used as at least one part of a parallel surface with a magnetic flux direction, when exciting the said compacting body as a magnetic core. A method for producing a green compact.   The said surface treatment process is given to the surface of the raw material molded object used as the area | region covering the magnetic flux direction full length of the said compacted compact in the said parallel surface, The compacted compact of Claim 2 characterized by the above-mentioned. Production method.   The said surface treatment process makes the surface treatment liquid of pH 1-4 contact the said raw material molded object for 1 minute-40 minutes, The manufacturing method of the compacting body of any one of Claims 1-3 characterized by the above-mentioned. .   The compacting body manufactured by the manufacturing method of the compacting body of any one of Claims 1-4.