JP5965190B2 - Method for producing green compact and green compact - Google Patents

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 manufacturing method capable of manufacturing a green compact with a low loss magnetic core with high productivity.

  Magnetic parts including a magnetic core made of a soft magnetic material such as iron, an alloy thereof, and an oxide such as ferrite and a coil disposed on the magnetic core are used in various fields. Specifically, for example, there are motor parts, transformers, reactors, choke coils, and the like that are used for in-vehicle parts mounted on vehicles such as hybrid cars and electric cars, and power circuit parts for various electric devices.

  When the magnetic component is used in an alternating magnetic field, an energy loss called iron loss (generally the sum of hysteresis loss and eddy current loss) occurs in the magnetic core. Since eddy current loss is proportional to the square of the operating frequency, when the magnetic component is used at a high frequency of several kHz or more, iron loss becomes significant.

  When the operating frequency is high in this way, for example, composite magnetic particles (covered with an insulating coating on the outer periphery of soft magnetic metal particles (soft magnetic iron-based particles) such as iron and iron alloy described in Patent Document 1 are used. It is preferable to use a dust compact made of soft magnetic iron-based particles as a dust core. This is because the insulating coating of each particle can suppress contact between the particles and ensure insulation between the particles, so that eddy current loss can be effectively reduced and iron loss can be reduced as a result.

JP 2010-183056 A

  The above-mentioned powder compact as the powder magnetic core is generally a coating comprising a plurality of coated soft magnetic iron-based particles in a cavity formed by a relatively movable columnar first punch and a cylindrical die. The soft magnetic iron-based powder is filled, and the coated soft magnetic iron-based powder in the cavity is pressure-molded by a first punch and a columnar second punch. Thereafter, the die is moved relatively to the first punch side with respect to the molded body, and then the second punch is moved to the side opposite to the first punch side to take out the molded body.

  Continuously repeating the process of filling and press-molding the coated soft magnetic iron-based powder increases the die temperature due to friction between the die during pressurization and the coated soft-magnetic iron-based powder. The temperature of the coated soft magnetic iron-based powder also increases. Thereby, since the coated soft magnetic iron-based powder is easily plastically deformed, a high-density powder compact is obtained, and it is considered that a powder compact excellent in magnetic properties can be produced.

  However, since the coated soft magnetic iron-based powder is easily plastically deformed in this way, the conductive part where the particles on the surface side of the molded body are expanded and brought into conduction by sliding contact with the die during pressurization and demolding. The eddy current loss (iron loss) increases and the magnetic properties may deteriorate due to warping. In addition, when the conductive portion is formed, the air included in the molded body at the time of pressure molding is difficult to escape from the molded body after molding. If the die and the second punch are moved as described above without sufficiently removing the air in the molded body, the compacted molded body may be destroyed due to a sudden release of pressure. Therefore, it is necessary to take a deaeration time until the air in the molded body is sufficiently removed, and it is difficult to increase the molding speed and it is difficult to improve productivity.

  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 capable of producing a green compact with a low loss magnetic core with high productivity. There is.

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

  The present invention achieves the above object by suppressing excessive plastic deformation of soft magnetic iron-based particles.

  The manufacturing method of the compacting body of this invention is a method which comprises a filling process, a pressurization process, and an extraction process, and repeats each of these processes and manufactures a several compacting body. In the filling step, a coated soft magnetic iron-based powder comprising a plurality of coated soft magnetic iron-based particles having an insulating coating coated on the outer periphery of the soft magnetic iron-based particles, and a first columnar punch that is relatively movable Fill a cavity made with a cylindrical die. In the pressing step, the coated soft magnetic iron-based powder in the cavity is pressed with a first punch and a columnar second punch to form a molded body. In the removal step, the molded body is removed from the cavity. Then, the die is cooled at least during the process of repeating each process.

  The production method of the present invention can produce a green compact with a low productivity and a low loss magnetic core. By cooling the die at least partway through the process, it is possible to suppress an excessive temperature rise of the die due to friction between the coated soft magnetic iron-based powder and the die. The temperature rise of the powder can be suppressed. Therefore, it is possible to suppress excessive plastic deformation of the soft magnetic iron-based particles, and to suppress the formation of a conductive portion that is in sliding contact with the die during pressurization and demolding so that the particles on the surface side of the molded body expand and conduct. . As a result, an eddy current associated with conduction between particles is unlikely to occur, so that an eddy current loss can be effectively reduced and an iron loss can be reduced.

  Moreover, since formation of a conduction | electrical_connection part can be suppressed, the air included in the molded object in the case of pressure molding becomes easy to escape | emit outside the molded object after a pressurization process. Therefore, it is possible to suppress the rapid release of pressure during demolding and to suppress the destruction of the green compact, and therefore it is possible to shorten the deaeration time of the air in the compact when demolding. As a result, the molding speed of the molded body can be increased, and the productivity of the molded body can be improved.

As one form of the production method of the present invention, when the volume of the molded body is Vmm ³ and the circumferential length of the molded body is Lmm, the ratio V / L of the volume V of the molded body to the circumferential length L is V / L. > 100 mm ² . Here, the circumferential length L refers to the circumferential length of a cross section orthogonal to the opposing direction of both punches in the molded body.

  According to the said structure, it is much more effective in the reduction of eddy current loss and the improvement of the productivity of a molded object. This is because, if a molded body that satisfies the above ratio V / L is manufactured without cooling the die as in the prior art, the green compact is easily broken. This is because the region in sliding contact with the die of the green compact becomes long, so that a conductive portion is easily formed and the air inside the compact is difficult to escape.

  One form of the production method of the present invention includes cooling the die at least during the pressing step.

  According to the above configuration, excessive plastic deformation of the soft magnetic iron-based particles can be effectively suppressed by cooling the die during the pressurizing step in which the temperature of the die is likely to rise in the process of repeating each step.

  As one form of the manufacturing method of this invention, it is mentioned that the temperature of die | dye is always maintained at 40 degrees C or less in the process of repeating each process.

  According to said structure, if the temperature of die | dye is always 40 degrees C or less, it can suppress that the temperature of a soft magnetic iron base particle rises to the temperature of the extent which a soft magnetic iron base particle deform | transforms excessively.

  As one form of the manufacturing method of this invention, it is mentioned to always cool a die | dye in the whole process which repeats each process.

  According to said structure, the temperature rise of a soft magnetic particle can be suppressed reliably by always cooling die | dye in the said whole process.

  One form of the production method of the present invention is that the iron-based particles are pure iron.

  According to said structure, even if iron base particle | grains are pure iron, the compacting body which can obtain a low-loss magnetic core can be manufactured with sufficient productivity. Pure iron is softer than ferrite, so it is easily deformed when it is pressure-molded, and the insulation film of the coated soft magnetic iron-based powder may be damaged along with the deformation, resulting in the formation of a conductive part on the surface. Although it is easy, according to the manufacturing method of the present invention, excessive plastic deformation of the soft magnetic iron-based particles can be suppressed, so that formation of the conductive portion can be suppressed.

  As one form of the manufacturing method of this invention, it is mentioned that the average particle diameter of an iron base particle is 100 micrometers or less.

  According to the above configuration, by setting the average particle size to 100 μm or less, the contact area with the die per soft magnetic iron-based particle is small, so that the insulating coating is hardly damaged and the conductive portion is formed. hard.

  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 magnetic core 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 manufacture the compacting body from which a low-loss magnetic core is obtained with sufficient productivity.

  The green compact of the present invention can be a low-loss magnetic core.

It is process explanatory drawing which shows an example of the procedure in the manufacturing apparatus of the compacting body used in embodiment, and the manufacturing method of a compacting body.

  Embodiments of the present invention will be described below.

<< Method for Producing Green Compact >>
The manufacturing method of the compacting body of this invention is a method which comprises a filling process, a pressurization process, and an extraction process, and manufactures several compacting body by repeating these each process. This manufacturing method is characterized in that the die is cooled at least during the process of repeatedly performing each process. Hereinafter, in describing in detail, an example of an apparatus for producing a green compact is first described, and then a raw material of the green compact and the above-described steps are described in this order.

[Mold for molding]
As a molding die to be used, typically, a cylindrical die provided with a through hole, and a pair of columnar first punch and second punch that can be inserted from each opening of the through hole of the die, respectively. With. The pair of first punch and second punch are arranged to face each other in the through hole. In this mold, a bottomed cylindrical cavity (molding space) is formed by one surface of one punch (pressure contact surface facing the other punch) and the inner peripheral surface of the die. A raw material powder, which will be described later, is filled in the molding space, and pressed and compressed with both punches to produce a compacted body. Each opposing surface of both punches forms each end face of the green compact, and the inner peripheral surface of the die forms the side surface of the green compact.

  More specifically, as shown in FIG. 1, a molding die provided with a cylindrical die 10 provided with a through hole 10 h and a pair of prismatic upper punch 20 and lower punch 30 inserted into and removed from the through hole 10 h. Mold 1 can be used. The shape of the through-hole 10h and the cross-sectional shape of the punches 20 and 30 are rectangular here, but are not particularly limited. For example, an elliptical shape including a circle, a polygon other than a rectangle, or a straight line and an arc Any of different shapes such as a combined fan shape may be used.

  In this molding die 1, the lower punch 30 is fixed to a main body device (not shown), and the die 10 and the upper punch 20 can be moved in the vertical direction by a moving mechanism (not shown). Of course, the die 10 may be fixed and the punches 20 and 30 may be movable, or the die 10 and the punches 20 and 30 may be movable.

  Examples of the constituent material of the molding die 1 include an appropriate high-strength material (such as high-speed steel) that has been conventionally used for forming a compact of a metal material.

(Cooling mechanism)
The molding die 1 of this embodiment includes a cooling mechanism that cools the die 10. This cooling mechanism is for cooling (maintaining) the die 10 to a desired temperature, and may be an external cooling type that cools from the outside of the die 10 or an internal cooling type that cools from the inside of the die 10. In the former case, for example, a cooling jacket in which a coolant is circulated is attached to the outer periphery of the die 10 to cool through the cooling jacket, or the coolant is directly applied to the surface of the die 10 (specifically, the upper surface 10u or the lower surface). Can be mentioned. In the latter case, a coolant can be circulated inside the die 10. Here, an internal cooling type is adopted. That is, the die 10 includes a cooling mechanism. Specifically, the cooling mechanism 15 includes a circulation groove 15 t that allows the refrigerant to flow inside the die 10, an inflow path 15 i, and an outflow path 15 o.

  Here, the die 10 including the cooling mechanism 15 is composed of a plurality of cylindrical members. Specifically, the inner die member 11 having an inner peripheral surface constituting the molding space 40 with the lower punch 30 and the outer die member 12 surrounding the outer periphery of the inner die member 11 are provided. The die 10 is integrally formed by shrink-fitting the outer die member 12 and the inner die member 11.

  And the circulation groove 15t which comprises the cooling mechanism 15 is a groove | channel which distribute | circulates a refrigerant | coolant in order to cool die | dye 10 (inner side die member 11) to desired temperature. The circulation groove 15t is provided on the inner peripheral surface of the outer die member 12, and is here formed in a spiral shape. The cross-sectional contour shape of the circulation groove 15t can be selected as appropriate. For example, the cross-sectional contour shape may be a circle, a rectangle, a trapezoid, or the like. The size of the circulation groove 15t and the number of rounds of the inner peripheral surface of the outer die member 12 of the circulation groove 15t can be selected as appropriate.

  The inflow passage 15i constituting the cooling mechanism 15 is a flow path for supplying the refrigerant from a refrigerant circulation device (not shown) for circulating the refrigerant to the circulation groove 15t (on the inner die member 11 side). The inflow passage 15i is provided in the outer die member 12, and is connected to one end of the circulation groove 15t. The outflow path 15o is a flow path for returning the refrigerant that has flowed through the circulation groove 15t from the circulation groove 15t (on the inner die member 11 side) to the refrigerant circulation device. The outflow path 15o is provided in the outer die member 12, and is connected to the other end of the circulation groove 15t.

  Thus, in the die 10, the cooling mechanism 15 is configured by the circulation groove 15 t, the inflow path 15 i, and the outflow path 15 o. The die 10 can be cooled by circulating the coolant through the cooling mechanism 15.

  In addition, a temperature sensor (not shown) for measuring the temperature of the die 10, a refrigerant flow meter and thermometer, and control means (not shown) for controlling the flow rate and temperature of the refrigerant based on measurement data obtained by the temperature sensor of the die 10. Preferably). This makes it easy to control the temperature of the die 10 to a desired temperature.

[Raw material powder]
Next, the raw material powder used in the production method of the present invention will be described. In the production method of the present invention, the raw material powder is composed of a coated soft magnetic iron-based powder comprising a plurality of coated soft magnetic iron-based particles in which an insulating coating is coated on the outer periphery of the soft magnetic iron-based particles.

(Soft magnetic iron-based particles)
<composition>
The soft magnetic iron-based 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 iron-based 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 100 micrometers or less, it is preferable. By setting the average particle diameter of the soft magnetic iron-based particles to 1 μm or more, the coercive force of the green compact produced using the soft magnetic iron-based powder and the fluidity of the soft magnetic iron-based powder are reduced. An increase in hysteresis loss can be suppressed. Conversely, by setting the average particle size of the soft magnetic iron-based particles to 100 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 iron-based particles is more preferably 40 μm or more and 75 μm or less. If this average particle diameter is 40 μm or more, an effect of reducing eddy current loss can be easily obtained, and handling of the coated soft magnetic iron-based 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 iron-based 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 iron-based particles having an aspect ratio in the above range can have a larger demagnetizing factor when formed into a green compact than those having a small aspect ratio (close to 1.0) and have excellent magnetic properties. It can be set as a compacting body. In addition, the strength of the green compact can be improved.

<Production method>
The soft magnetic iron-based particles are preferably produced by an atomizing method such as a water atomizing method or a gas atomizing method. Since the soft magnetic iron-based 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, soft magnetic iron-based particles produced by the gas atomization method are preferable because the particle shape is almost 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 iron-based particles.

(Insulation coating)
The insulating coating is coated on the outer periphery of the soft magnetic iron-based particles in order to insulate adjacent soft magnetic iron-based particles. By covering the soft magnetic iron-based particles with an insulating coating, the contact between the soft magnetic iron-based 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 iron-based 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 secure insulation between soft magnetic iron-based 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 has excellent deformability, even when soft magnetic iron-based particles are deformed when a soft magnetic material is pressed to produce a compacted body, the deformation follows the deformation. it can. Further, the phosphate coating has high adhesion to iron-based soft magnetic iron-based particles and is difficult to fall off from the surface of the soft magnetic iron-based particles. As the phosphate, metal phosphate compounds such as iron phosphate, manganese phosphate, zinc phosphate, calcium phosphate, and 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 described later, and the insulation between soft magnetic iron-based 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 iron-based particle side and the silicone resin directly on the phosphate. Since the silicone resin is coated directly on the phosphate, the above-described characteristics of both the phosphate and the silicone resin can be provided.

<Film thickness>
The average thickness of the insulating coating may be a thickness that can insulate adjacent soft magnetic iron-based 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 iron-based 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 iron-based particles does not become too large, and the magnetic flux density of the coated soft magnetic iron-based particles can be prevented from being significantly reduced.

  The thickness of the insulating coating can be examined as follows. First, a film composition obtained by composition analysis (TEM-EDX: transmission electron microscopic energy dispersive X-ray spectroscopy), and an inductively coupled plasma mass analysis (ICP-MS: inductively coupled plasma quantity) 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 iron-based particles with the insulating coating may be appropriately selected. For example, it may be coated by hydrolysis / polycondensation reaction. Soft magnetic iron-based particles and raw materials constituting the insulating coating are blended, and the blend is mixed in a heated state. By doing so, the soft magnetic iron-based particles can be sufficiently dispersed in the coating material, and the insulating coating can be coated on the outside of the individual soft magnetic iron-based particles.

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

[Molding procedure]
Next, the molding procedure of the manufacturing method of the present invention will be described using the molding die 1 described above. Specifically, after preparing the raw material powder P of the green compact, a filling step for filling the molding die 1 with the raw material powder P, and pressurizing the raw material powder P to form the compact 50 The process and the extraction process for taking out the molded body 50 from the molding die 1 are repeated.

(Preparation process)
The above-mentioned coated soft magnetic iron-based powder is prepared as the raw material powder P of the green compact.

(Filling process)
First, as shown in FIG. 1A, the upper punch 20 is moved to a predetermined standby position above the through hole 10 h in the die 10. The die 10 is moved upward, and a predetermined molding space 40 is formed by the upper surface 30 u of the lower punch 30 and the inner peripheral surface (through hole 10 h) of the die 10.

  Next, as shown in FIG. 1 (B), the raw material powder P of the green compact formed in the preparation step is filled into the molding space 40 by a powder feeder not shown.

(Pressure process)
Subsequently, as shown in FIG. 1C, the upper punch 20 is moved downward and inserted into the through hole 10 h of the die 10, and the raw material powder P is pressurized and compressed by both punches 20 and 30. At that time, after the upper punch 20 comes into contact with the raw material powder P, the die 10 is moved downward similarly to the upper punch 20. By moving the die 10 together with the upper punch 20, among the raw material powder P in the molding space 40, the amount of powder that contacts the upper punch 20 and the powder existing in the vicinity of the upper punch 20 moves to the lower punch 30 side is reduced. It is possible to prevent damage to the insulating film due to excessive movement. Moreover, the pressure applied to the raw material powder P of both the punches 20 and 30 can be made uniform.

  Although the pressure to pressurize can be selected suitably, for example, if a compacting body used as a core for a reactor is manufactured, it is preferable to set it as about 490-1470 MPa, especially about 588-1079 MPa. By setting it as 490 Mpa or more, the raw material powder P can fully be compressed, the relative density of a compacting body can be raised, and by setting it as 1470 Mpa or less, it is by contact of the covering soft magnetic iron base particles which comprise the raw material powder P Damage to the insulating coating can be suppressed.

(Removal process)
After performing the predetermined pressurization, the die 10 is moved relative to the molded body 50 as shown in FIG. Here, only the die 10 is moved downward without moving the molded body 50. At this time, of the outer peripheral surface of the molded body 50, the contact area with the die 10 is in sliding contact with the through hole 10 h of the die 10 by the reaction force from the die 10.

  The die 10 is moved until the upper surface 10 u of the die 10 and the upper surface 30 u of the lower punch 30 are flush with each other, or until the upper surface 30 u of the lower punch 30 is positioned above the upper surface 10 u of the die 10. When the molded body 50 is completely exposed from the die 10, the upper punch 20 is moved upward as shown in FIG. Here, the die 10 is moved in a state where the molded body 50 is sandwiched between the lower surface 20d of the upper punch 20 and the upper surface 30u of the lower punch 30, and the upper punch 20 is moved in a subsequent process. At the same time, the upper punch 20 may be moved upward, or the upper punch 20 may be moved before the die 10.

  Since the molded body 50 can be taken out by moving the upper punch 20, the molded body 50 can be taken out by, for example, a manipulator.

  These steps are repeated. That is, when the molded body 50 is taken out from the molding die 1, in forming the next molded body, as described above, formation of a molding space → filling of raw material powder into the molding space → pressing of raw material powder → molded body Repeat the removal.

(cooling)
In the manufacturing method of the present invention, the die 10 is cooled at least halfway through the process of repeatedly performing the above steps.

  Specifically, the cooling time of the die 10 is filled before the filling process, at the filling process, before the pressurizing process after the filling process, at the pressurizing process, before the unloading process after the pressurizing process, at the unloading process, and after the unloading process. One before the process is mentioned. The die 10 is cooled in at least one of these periods. Especially, it is preferable that the cooling time of the die | dye 10 is at least at the time of a pressurization process. Then, excessive plastic deformation of the soft magnetic iron-based particles can be effectively suppressed. This is because the temperature of the die 10 is likely to increase during the pressing step, and the temperature of the soft magnetic iron-based particles is likely to increase. And it is preferable to always cool in the whole process which repeats each process. By doing so, excessive plastic deformation of the soft magnetic iron-based particles can be reliably suppressed. Here, the die 10 is always cooled in the whole process of repeating each process.

  It is preferable that the temperature of the die 10 is always maintained at 40 ° C. or lower by cooling the die 10. When the die is not cooled, in the process of repeating each step as described above, the temperature of the die is 50 ° C. or higher, sometimes 60 ° C. or higher, and even 70 ° C. to 80 ° C. in some cases. In this case, the soft magnetic iron-based particles are excessively plastically deformed. The lower limit of the temperature of the die 10 is preferably about 10 ° C. By setting the temperature of the die 10 to 10 ° C. or higher, it is possible to cause plastic deformation to an extent that contributes to higher density while suppressing excessive plastic deformation of the soft magnetic iron-based particles. In addition, the die 10 can be prevented from being overcooled, and the inner dimension of the molding space 40 can be prevented from becoming too smaller than the specified dimension.

  Specifically, the refrigerant is circulated inside the die 10 by the refrigerant mechanism 15 described above. Here, the coolant flows from the lower punch 30 side of the die 10 toward the upper punch 20 side of the die 10. That is, the refrigerant flows from a refrigerant circulation device (not shown) from one end (lower punch 30 side) to the other end (upper punch 20 side) of the circulation groove 15 through the inflow path 15i of the outer die member 12. Meanwhile, the die 10 is cooled. Then, the refrigerant is returned to the refrigerant circulation device through the outflow path 15o. In this manner, the die 10 is cooled by circulating the refrigerant. Examples of the type of refrigerant used include liquid refrigerants such as water.

  The shape of the molded body 50 manufactured through the above steps is a shape in which the inner peripheral shape of the die 10 and the shapes of the lower surface 20d of the upper punch 20 and the upper surface 30u of the lower punch 30 are transferred. That is, here, the molded body 50 is a prismatic body (cuboid). In this molded body 50, the opposing surfaces pressed by the upper punch 20 and the lower punch 30 do not slidably contact the mold at the time of pressurization or demolding. It is difficult to form a part. Further, since the die 10 is cooled and molded, excessive plastic deformation of the soft magnetic particles can be suppressed, so that a conductive portion is hardly formed on the sliding contact surface with the inner peripheral surface of the die 10 in the molded body.

The size of the green compact to be molded is set such that the volume of the green compact is Vmm ³ , the opposing direction of both punches in the compact, that is, the circumferential length of the cross section perpendicular to the pressing direction is L mm, The ratio V / L between the volume V and the circumferential length L is preferably V / L> 100 mm ² . The production method of the present invention is particularly effective when producing a green compact that satisfies the above ratio V / L> 100 mm ² . This is because when a green compact that satisfies the range of the above ratio V / L is manufactured without cooling the die as in the prior art, the green compact is particularly easily broken. This is because when the volume of the green compact is increased and the circumference is shortened, the height is relatively high, and the area in sliding contact with the die is increased during pressurization and demolding. This is because it is easy to form and it is difficult for air inside the molded body to escape. In particular, the ratio V / L between the volume V and the circumferential length L is more effective when it is 120 mm ² or more. Here, when the cross section orthogonal to the pressurizing direction in the green compact is not uniform, for example, the die has an inclined surface that inclines so that the inner space of the die widens in the direction of extracting the green compact from the die. In the case of a green compact produced using a die, the circumference of the green compact is obtained by subtracting the surface area of the surface formed by the upper punch and the lower punch from the total surface area of the green compact. The value divided by the height is the circumference.

  (1) In the preparation step, a lubricant (raw material lubricant) is mixed with the coated soft magnetic iron-based powder to produce a mixed material. (2) When forming the molding space 40 in the filling step In addition, it is preferable to perform at least one of applying a lubricant (mold lubricant) to a portion (particularly the inner wall of the die 10) that comes into contact with the coated soft magnetic iron-based powder of the punch or die. If it does so, it can suppress that the molded object 50 seizes on the metal mold | die 1 for a shaping | molding by a pressurization process, and the insulation film of a covering soft magnetic iron base powder is destroyed. In addition, in the former case, since the raw material lubricant suppresses the contact between the particles in the coated soft magnetic iron-based powder and easily secures insulation between the particles, eddy current loss can be reduced. In the latter case, since the mold lubricant is applied to the inner wall, friction with the coated soft magnetic powder can be reduced and a high-density molded body 50 can be molded.

  Specific examples of the lubricant include those containing metal elements, typically metal soaps such as lithium stearate and zinc stearate, and those not containing metal elements, typically stearic acid and lauric acid. Solid lubricants such as fatty acid amides such as amides, stearic acid amides, and palmitic acid amides, and higher fatty acid amides such as ethylenebisstearic acid amides may be mentioned. In addition, a dispersion obtained by dispersing a solid lubricant in a liquid medium such as water, a liquid lubricant, an inorganic lubricant having a hexagonal crystal structure, such as boron nitride, molybdenum sulfide, tungsten sulfide, and graphite Examples include inorganic substances to be selected. You may use combining this inorganic substance and the metal soap mentioned above. When both the raw material lubricant and the mold lubricant are used, the material of the raw material lubricant and the material of the mold lubricant may be the same or different.

  When the raw material lubricant is used, the larger the amount of the raw material lubricant, the more the insulation film of the coated soft magnetic iron-based particles can be prevented from being broken. As a result, the obtained green compact also has a lot of healthy insulating coatings. When a magnetic core is produced from the green compact, this magnetic core is excellent in insulation. However, if the amount of the raw material lubricant is too large, the magnetic flux density of the green compact is reduced. Therefore, the amount of the raw material lubricant is preferably 0.3% by mass or more and 1.0% by mass or less.

<Process after molding>
After the molded body 50 is molded, it is preferable to heat-treat the molded body 50 in order to remove the strain introduced into the soft magnetic iron-based particles in the pressing step.

  Since the higher the heat treatment temperature is, the more strain can be removed, the heat treatment temperature is preferably 300 ° C. or higher, particularly 400 ° C. or higher, and the upper limit is preferably 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 suitably the time which performs heat processing according to the said heat processing temperature and the volume of a molded object so that the distortion introduce | transduced into the soft-magnetic iron base particle | grains by the pressurization 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. As a result, adhesion of soot and the like to the material molded body due to combustion of the lubricant can be suppressed.

<Effect>
According to the manufacturing method described above, the following effects are obtained.

  (1) In the process of repeatedly performing each step for producing a green compact, the temperature can be suppressed from rising to the extent that the raw material powder is excessively plastically deformed by cooling the die. As a result, excessive pressure deformation of the raw material powder can be suppressed when the raw material powder is pressure-molded, and the particles on the surface side of the molded body can be prevented from spreading and forming a conductive portion by sliding contact with the die. Eddy current loss (iron loss) can be suppressed. Therefore, it is possible to manufacture a green compact that can provide a low-loss magnetic core.

  (2) Since it can suppress that a conduction | electrical_connection part is formed in the molded object surface, the air included in the molded object in the case of pressure molding becomes easy to escape | emit outside the molded object after a pressurization process. Therefore, it is possible to suppress the sudden release of pressure during demolding and to suppress the destruction of the molded body. Therefore, the time for degassing the air in the molded body can be shortened when demolding, so that the molding speed of the molded body can be increased and the productivity of the molded body can be improved.

《Test example》
As a test example, using the molding die 1 shown in FIG. 1, a plurality of samples 1 and 2 of a green compact were produced, and the test described below for the magnetic properties of each sample was performed. Sample 1 is manufactured by constantly cooling the die 10 in the whole process of repeating each process, and sample 2 is different in that the die 10 is manufactured without cooling the die 10 in the whole process.

  First, as a constituent material of a green compact, a lubricant made of zinc stearate is added to a coated soft magnetic iron-based powder in which an insulating coating made of iron phosphate is coated on the surface of soft magnetic iron-based particles made of iron powder. A mixed material containing 6 mass% was prepared. The iron powder was produced by a water atomization method and had a purity of 99.8% or more. The soft magnetic iron-based 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 iron-based particles, and the average thickness was 20 nm.

Next, in accordance with the molding procedure described above, the prepared mixed material is filled into the molding space 40, and a pressure of 730 MPa is applied to the length 30 mm × width 30 mm × height 20 mm (volume V: 18000 mm ³ , circumference L: A rectangular parallelepiped shaped body of 120 mm, V / L: 150 mm ² ) is produced, and the shaped body is taken out. This was repeated continuously to obtain 1000 compacts.

  At this time, the molding speed per piece was calculated from the time taken to produce all molded bodies in each sample. In addition, the temperature of the die 10 in the whole process of each sample was measured. These results are shown in Table 1.

[Evaluation]
In Samples 1 and 2, a plurality of compacted compacts appropriately selected from the compacted compacts produced respectively were heat-treated in a nitrogen atmosphere at 400 ° C. for 30 minutes, and the heat-treated compacted compacts were combined in an annular shape. A test magnetic core was prepared. Each test core was provided with a coil composed of a winding to produce a measurement member for measuring magnetic properties, and the following magnetic properties were measured.

[Magnetic property test]
For each measurement member, the eddy current loss We (W) and hysteresis loss Wh (W) of the sample at an 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 results are shown in Table 1.

〔result〕
In Sample 1, the temperature of the die 10 was constantly maintained at 40 ° C. or lower throughout the entire process. In Sample 2, the temperature of the die 10 was in the range of 50 ° C to 60 ° C throughout the entire process. Sample 1 had a higher molding speed than sample 2 and had a small eddy current loss (iron loss).

  Sample 1 was able to suppress the temperature rise of the raw material powder by cooling the die 10 and maintaining the temperature of the die 10 at 40 ° C. or lower in the process of repeating each process. This is probably because excessive plastic deformation of the powder could be suppressed. As a result, the formation of the conduction part due to the sliding of the particles on the surface of the molded body in contact with the die 10 can be suppressed, so that the eddy current accompanying the conduction between the particles can be suppressed, and the eddy current loss (iron loss). Is considered to have been reduced. In addition, since the formation of the conductive portion could be suppressed, it was possible to prevent the air contained in the molded body from being difficult to escape to the outside after the pressurizing process. The air degassing time was shortened. Therefore, it is considered that the molding speed could be increased. On the other hand, in Sample 2, the temperature of the die 10 was as high as 50 ° C. or higher, and the soft magnetic iron-based particles were excessively plastically deformed, so that the eddy current loss could not be reduced and the molding speed could not be increased.

  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. For example, the die can be cooled by wiping the coolant directly on the die itself from the outside of the die. In this case, the timing of wiping the refrigerant includes, for example, before the filling step or at the pressurizing step. The refrigerant to be used is preferably liquid nitrogen which has high volatility and hardly reacts with the raw material powder. Further, at least one of the upper punch and the lower punch may be cooled by a cooling mechanism similar to that of the die. Then, the raw material powder can be cooled through the punch so that the raw material powder is not excessively plastically deformed.

  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.

DESCRIPTION OF SYMBOLS 1 Mold for die 10 Die 10h Through-hole 10u Upper surface 11 Inner die member 12 Outer die member 15 Cooling mechanism 15t Circulation groove 15i Inflow passage 15o Outflow passage 20 Upper punch 20d Lower surface 30 Lower punch 30u Upper surface 40 Molding space (cavity) 50 Molding Body P Raw material powder

Claims (6)

A coated soft magnetic iron-based powder comprising a plurality of coated soft magnetic iron-based particles whose outer periphery is coated with an insulating coating on the outer periphery of a soft magnetic iron-based particle. A filling process for filling a cavity made of
A pressing step of pressing the coated soft magnetic iron-based powder in the cavity with the first punch and the columnar second punch to form a molded body;
A step of removing the molded body from the cavity,
A method for producing a green compact by repeatedly performing each of these steps to produce a plurality of green compacts,
In the process of repeating the respective steps such that said temperature of the die is kept below 40 ° C. at all times 10 ° C. or more, the production of the at least the middle of the process of repeating the steps, cool the die pressure powder compact Method. When the volume of the molded body is Vmm ³ and the circumferential length of the cross section perpendicular to the opposing direction of the two punches in the molded body is Lmm,
The volume V and the ratio V / L of the circumferential length L is, V / L> 120 mm ² der Ru請 Motomeko 1 manufacturing method of the green compact according to.
However, when the cross section orthogonal to the opposing direction of the two punches in the molded body is not uniform, the peripheral length L is formed by the first punch and the second punch from the total surface area of the molded body. Subtract the surface area of the surface to be obtained and divide by the height of the compact. Method for producing at least said you cool the die during pressing step 請 Motomeko 1 or claim 2 green compact according to. Wherein the entire process of repeating the steps, the production method of the green compact according to any one of the die at all times cool 請 Motomeko 1 to claim 3. The iron-based particles, method for producing a green compact according to any one of pure iron Der Ru請 Motomeko 1 to claim 4. Method for producing a green compact according to any one of the average particle diameter of Ru der less 100μm 請 Motomeko 1 to claim 5 of the iron-based particles.

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