US20070172380A1 - Metal powder, green compact and production method thereof - Google Patents

Metal powder, green compact and production method thereof Download PDF

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Publication number
US20070172380A1
US20070172380A1 US11/656,907 US65690707A US2007172380A1 US 20070172380 A1 US20070172380 A1 US 20070172380A1 US 65690707 A US65690707 A US 65690707A US 2007172380 A1 US2007172380 A1 US 2007172380A1
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Prior art keywords
powder
metal powder
green compact
compacting
metal
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US11/656,907
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English (en)
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Hirohiko Tatsumoto
Masayuki Nashiki
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Denso Corp
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Denso Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0206—Manufacturing of magnetic cores by mechanical means
    • H01F41/0246—Manufacturing of magnetic circuits by moulding or by pressing powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/102—Metallic powder coated with organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/16—Metallic particles coated with a non-metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

  • the present invention relates to a metal powder as a raw material for obtaining a green compact by compacting, a green compact using the same and a production method thereof.
  • a green compact obtained by compacting a metal powder (hereinafter, sometimes simply referred to as a “powder”) is used, for example, as a material for a sprocket of gear parts or for a rotor or vane of pump parts, and attempts are being made to increase the density of such a green compact to as high as possible for enhancing a performance such as mechanical strength.
  • the approach from a material aspect includes a method of irregularly shaping the powder to enhance the compaction property of the powder.
  • the enhancement in compaction property of a powder is limited and the density of a green compact may not be sufficiently increased.
  • a method of enhancing the filling property of powder by using a mixture of powders differing in the particle size is known.
  • the gap formed between powders filled may not be sufficiently reduced.
  • a method using a spherical powder is also known, but in this case, the compaction property of powder may decrease. Therefore, in any of these methods, the density of a green compact may not be satisfactorily increased.
  • the approach from a compacting aspect includes a compacting method of applying a high pressure.
  • the quality of a green compact may deteriorate after compacting.
  • a compacting method using a lubricant is also known, but this has a problem that the lubricant remains inside the green compact after compacting and the density of a green compact may not be satisfactorily increased.
  • the green compact includes a powder magnetic core obtained by compacting a metal powder of which surface is coated with an insulating film.
  • a powder magnetic core is applied to a material placing importance on magnetic characteristics and is used, for example, as a material of power source parts such as noise filters and reactors.
  • application of the powder magnetic core to a motor core, a solenoid core or the like has been recently proposed by making use of the degree of freedom of its shape.
  • the great characteristic feature of the powder magnetic core includes a magnetic flux density and an iron loss.
  • a powder magnetic core When a powder magnetic core is applied to a motor core or the like, a higher output is obtained as the magnetic flux density is higher, and a higher-efficiency motor is obtained as the iron loss is lower.
  • the iron loss it is important to decrease the eddy loss in an AC magnetic field and furthermore decrease the hysteresis loss generated due to deformation (distortion) of the powder at compacting.
  • a powder for powder magnetic cores which can satisfy both high magnetic flux density and low iron loss of the powder magnetic core, a powder magnetic core using the powder, and a production method thereof have been recently disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) Nos. 2000-169901, 2001-155914, 2003-303711, 2003-332116, 2004-14614, 2004-221549, 2005-113258 and 2005-213639.
  • Kanai Japanese Unexamined Patent Publication
  • the present invention has been made by taking into consideration these conventional problems and an object of the present invention is to provide a metal powder having high filling property and capable of realizing a high-density green compact, a green compact using the same, and a production method thereof.
  • a first invention is a metal powder which is a raw material for obtaining a green compact by compacting.
  • the metal powder is a metal powder characterized by having a plurality of accessible surfaces allowing for surface contact of adjacent metal powders with each other when filled.
  • the metal powder of the present invention has a plurality of accessible surfaces allowing for surface contact of adjacent metal powders with each other when filled. That is, when the metal powder is filled, the metal powder can unfailingly make surface contact with the adjacent metal powder at a plurality of accessible surfaces, whereby the gap formed between these metal powders when filled can be reduced and the filling property of the metal powder can be enhanced.
  • a green compact obtained by densely filling this metal powder having high filling property and compacting it in the state of the gap between metal powders being reduced comes to have a high density with the presence of fewer voids after compacting.
  • the metal powder has high filling property
  • a high pressure for filling the gap between metal powders need not be applied at compacting, so that a high-density green compact can be obtained by performing the compacting at a pressure lower than ever.
  • a metal powder having high filling property and capable of realizing a high-density green compact can be provided.
  • a second invention is a method for producing a green compact by compacting the metal powder of the first invention, the method comprising:
  • the metal powder of the first invention that is, the metal powder with high filling property is used and therefore, a green compact obtained according to this production method by densely filling the metal powder in a predetermined die and compacting it has a high density.
  • the metal powder has high filling property
  • a high pressure for filling the gap between metal powders need not be applied in the compacting step, so that a high-density green compact can be obtained by performing the compacting at a pressure lower than ever.
  • a third invention is a green compact produced by the method for producing a green compact of the second invention.
  • the green compact of the present invention is produced by the method for producing a powder compact of the second invention and therefore, the green compact comes to have a high density.
  • FIG. 1 is an explanatory view showing the metal powder in Example 1,
  • FIG. 2 is cross-sectional enlarged view showing the surface of the metal powder in Example 1,
  • FIG. 3 is a cross-sectional enlarged view showing the surface of the metal powder in Example 1,
  • FIG. 4 is an explanatory view showing the filled state of the metal powder in Example 1,
  • FIG. 5 is an explanatory view showing the green compact in Example 1,
  • FIG. 6 is an explanatory view showing the metal powder having other shape in Example 1,
  • FIG. 7 is an explanatory view showing the metal powder having other shape in Example 1,
  • FIG. 8 is an explanatory view showing the metal powder having other shape in Example 1,
  • FIG. 9 is an explanatory view showing the gear part (sprocket) in Example 2.
  • FIG. 10 is an explanatory view showing the pump part (rotor) in Example 2.
  • FIG. 11 is an explanatory view showing the powder for powder magnetic cores in Example 3,
  • FIG. 12 is a cross-sectional enlarged view showing the surface of the powder for powder magnetic cores in Example 3,
  • FIG. 13 is a cross-sectional enlarged view showing the surface of the powder for powder magnetic cores in Example 3,
  • FIG. 14 is an explanatory view showing the filled state of the powder for powder magnetic cores in Example 3.
  • FIG. 15 is an explanatory view showing the powder magnetic core in Example 3.
  • the total area of the accessible surfaces is preferably 70% or more of the entire surface area of the metal powder.
  • the metal powder when filled can ensure a sufficiently large area for the surface contact with the adjacent metal powder, so that the gap between those metal powders can be unfailingly reduced and the filling property can be satisfactorily enhanced.
  • the metal powder preferably has any one shape of an approximate cube, an approximate rectangular parallelepiped, an approximate triangular pyramid and approximate an quadrangular pyramid and the accessible surface of the metal powder preferably has any one shape of an approximate square, an approximate rectangle and an approximate triangle.
  • the metal powder when filled can be increased in the area for the surface contact with the adjacent metal powder, so that the gap between metal powders can be greatly reduced and the filling property can be more enhanced.
  • each accessible surface in the case where the shape of the metal powder is an approximate cube, all surfaces have an approximately square shape; in the case of an approximate rectangular parallelepiped, the surfaces have an approximately square or approximately rectangular shape; in the case of an approximate triangular pyramid, all surfaces have an approximately triangular shape; and in the case of an approximate quadrangular pyramid, one surface has an approximately square or approximately rectangular shape and the remaining four surfaces have an approximately triangular shape.
  • one side of the metal powder preferably has a length of 10 to 500 ⁇ m.
  • the metal powder when filled can efficiently make surface contact with the adjacent metal powder, so that the effect of reducing the gap between those metal powders and enhancing the filling property can be effectively exerted.
  • the tapped filling rate represented by (A/B) ⁇ 100(%) is preferably 60% or more.
  • the metal powder comes to have high filling property, so that the green compact obtained by using the metal powder can be satisfactorily and unfailingly increased in the density.
  • the tap density of the metal powder is measured by the following method. While charging the metal powder in an arbitrary weight a into a measuring cylinder, an operation of freely dropping the measuring cylinder from a height of 10 mm and an operation of pulling it up are repeated, thereby applying vibration to the bottom of the measuring cylinder. After the completion of charging of the metal powder, vibration is further applied 20 times to the bottom of the measuring cylinder. The volume b of the metal powder filled is measured and the a/b value is defined as the tap density A. Also, in the measurement of tap density, Tap Denser (KYT-2000, manufactured by Seishin Enterprise Co., Ltd.) or the like may be used.
  • the metal powder preferably has fine irregularities on the surface and the depth in the concave part of the irregularities is preferably 10% or less of the outermost diameter of the metal powder.
  • the gap between metal powders is increased when filled and the filling property may decrease.
  • the depth of the concave part is preferably from 1 to 50 ⁇ m.
  • the metal powder is preferably any one metal of Fe type, Fe—Al type, Fe—Si type, Fe—Al—Si type, Fe—Co type and Fe—Ni type.
  • the green compact obtained by using the metal powder comes to have magnetic characteristics.
  • the green compact has a high density and therefore, the magnetic flux density as one of magnetic characteristics becomes high, so that when the green compact with excellent magnetic characteristics is applied as a powder magnetic core to a core, a solenoid or the like for motors, the performance can be enhanced.
  • the performance can be more enhanced by using a metal powder having formed on the surface thereof an insulating film.
  • the metal powder is preferably a powder for powder magnetic cores, with the surface being coated with an insulating film.
  • a high-density powder magnetic core can be obtained by compacting the powder for powder magnetic cores, which is the above-described metal powder.
  • the thus-obtained high-density powder magnetic core comes to have a high magnetic flux density.
  • the compacting can be performed at a pressure lower than ever, so that the metal powder can be reduced in the deformation (distortion) generated due to pressure imposed at the compacting and the hysteresis loss of the powder magnetic core after compacting can be decreased.
  • the deformation/rupture of the insulting film coated on the surface of the metal powder can also be reduced and the insulation between metal powders can be satisfactorily ensured.
  • the powder magnetic core after compacting can be decreased in the eddy loss and a powder magnetic core with low iron loss can be obtained.
  • the metal powder is a powder for powder magnetic cores
  • the preferred conditions are described below.
  • the metal powder preferably has an outermost diameter of 500 ⁇ m or less.
  • the thickness of the insulating film is preferably from 10 to 1,000 nm.
  • the insulating film is preferably a ceramic film, a resin film or a mixed film of ceramic and resin.
  • the ceramic film preferably comprises at least one or more member selected from the group consisting of alumina, silica, magnesia, zirconia, titania, boron nitride and silicon nitride.
  • the insulating film comes to have a high volume resistivity and therefore, the insulation between the metal powders can be enhanced.
  • the resin film preferably comprises at least one or more members selected from the group consisting of a silicone resin, a polyimide resin, a polyphenylene sulfide resin, a phenol resin, a polyether ketone-based resin, a silicone resin and a silane coupling agent.
  • the insulating film comes to have high electrical insulation and therefore, the insulation between the metal powders can be enhanced.
  • the metal powder is preferably filled by vibrating the die in the filling step.
  • the metal powder can be filled in a sufficiently dense state, whereby the density of the obtained green compact can be increased.
  • the die is preferably vibrated by using an ultrasonic generator.
  • the metal powder can be filled in a denser state, whereby the density of the obtained green compact can be more increased.
  • a powder for powder magnetic cores with the surface being coated with an insulating film, may also be used.
  • a high-density powder magnetic core can be obtained by compacting the powder for powder magnetic cores, which is the above-described magnetic metal.
  • the thus-obtained high-density powder magnetic core comes to have a high magnetic flux density.
  • the compacting can be performed at a pressure lower than ever, so that deformation (distortion) of the metal powder and deformation/rupture of the insulating film can be reduced.
  • the hysteresis loss and eddy loss of the powder magnetic core after compacting can be decreased and a powder magnetic core with low iron loss can be thereby obtained.
  • the value of (S 1 ⁇ S 2 )/S 1 is preferably 0.2 or less.
  • the green compact preferably has a relative density of 95% or more.
  • the green compact comes to a sufficiently high density with less voids.
  • the green compact may be a powder magnetic core obtained by compacting a powder for powder magnetic cores, which is the above-described metal powder with the surface being coated with an insulating film.
  • the green compact can satisfy both high magnetic flux density and low iron loss.
  • the green compact is a powder magnetic core
  • the preferred conditions are described below.
  • the green compact preferably has a density of 7.4 Mg/m 3 or more.
  • the green compact comes to have a sufficiently high density, whereby the magnetic flux density of the green compact becomes sufficiently high.
  • the green compact preferably has a saturation magnetic flux density of 1.6 T or more.
  • the green compact comes to have a sufficiently high magnetic flux density.
  • the green compact can be used, as a high-density sintered part, for gear parts (e.g., sprocket), pump parts (e.g., rotor, vane) and the like.
  • gear parts e.g., sprocket
  • pump parts e.g., rotor, vane
  • the green compact is a powder magnetic core
  • the green compact can be used for a motor core, a solenoid core, a reactor and the like.
  • the metal powder according to the example of the present invention is described below.
  • the metal powder 1 of this example is, as shown in FIG. 1 , a metal powder which is a raw material for obtaining a green compact by compacting.
  • the metal powder 1 has a plurality of accessible surfaces 11 allowing for surface contact of adjacent metal powders 1 with each other when filled.
  • the metal powder 1 of this example is pure iron (Fe) and, as shown in FIG. 1 , has an approximately cubic shape with a one-side length of 100 ⁇ m. The outermost diameter of the metal powder 1 is 170 ⁇ m. Also, the metal powder 1 has six accessible surfaces 11 allowing for surface contact of adjacent metal powders 1 with each other when filled. The accessible surface 11 has an approximately square shape. Although a cubic metal powder 1 which is most ideal is shown in FIG. 1 for the sake of simplifying the drawing, the metal powder is practically not such an exact cube but has a shape with the corners rounded in many cases.
  • fine irregularities are provided on the surface 10 of the metal powder 1 .
  • an irregularity shape having square corners, which is most ideal, is shown for the sake of simplifying the drawing, but as shown in FIG. 3 , the irregularity practically has a corner-rounded shape in many cases.
  • the depth D in the concave part 101 of those irregularities was about 5 ⁇ m.
  • the total area of six accessible surfaces 11 is 90% of the entire surface area (the entire area of the surface 10 ) of the metal powder 1 , that is, the metal powder 1 when filled can make surface contact with the adjacent metal powder 1 at many parts of the surface 10 (see, FIG. 4 ).
  • the production method of the metal powder 1 is briefly described below. As for the production method of the metal powder 1 of this example, a cast-molding method was used.
  • pure iron working out to a material constituting the metal powder 1 is melted to prepare a molten iron.
  • This molten iron is then cast into a casting mold having a concave part in an approximately cubic shape with a one-side length of 100 ⁇ m.
  • fine irregularities are provided on the inner surface of the casting mold and the depth in the concave part of the inner surface is 5 ⁇ m.
  • the molten iron is cooled and solidified in the casting mold.
  • a metal powder 1 is taken out from the casting mold.
  • the construction material of the casting mold which can be used, is a ceramic such as silicon nitride, alumina and magnesia, or a metal such as iron. From the standpoint of ease in taking out the metal powder 1 from the casting mold, a ceramic having a small thermal expansion coefficient is preferably used. Also, in view of thermal shock when casting the molten iron into the casting mold, silicon nitride, as a ceramic, is preferred.
  • an extrusion-molding method, a draw-molding method and the like may also be used.
  • an angular wire rod having a 100 ⁇ m-square cross-section is molded by extrusion or draw-molding and cut at a pitch of 100 ⁇ m, whereby the same metal powder as the metal powder 1 of this example can be obtained.
  • the production method of a green compact 2 of this example comprises a charging step of charging the metal powder 1 into a predetermined die, a filling step of filling the metal powder 1 in the die, and a compacting step of compacting the metal powder 1 to obtain a green compact 2 .
  • the metal powder 1 is charged into a die having a shape of the green compact 2 to be molded.
  • the die is vibrated by using an ultrasonic generator to densely fill the metal powder 1 .
  • the metal powders 1 are aligned as neatly as possible to bring the accessible surfaces 11 into surface contact with each other.
  • the filling is performed to give as small a gap as possible between the metal powders 1 .
  • the filling density of the metal powder 1 in the die after filling was 4.6 Mg/m 3 .
  • the metal powder 1 filled in a die is shown by extracting a part thereof. In the figure, the ideal filled state is shown, but in practice, there may be produced a portion where the accessible surfaces 11 are not contacted with each other.
  • a pressure of 800 MPa is applied to the metal powder 1 after filling so as to effect compacting.
  • the green compact 2 produced by the above-described production method is described below.
  • the green compact 2 of this example has a cylindrical shape (ring shape).
  • the density of the green compact 2 was 7.8 Mg/m 3 , and the relative density was 99.4%.
  • the green compact 2 can be molded into various shapes according to usage by changing the shape of the die.
  • the metal powder 1 of this example has a plurality of accessible surfaces 11 .
  • the metal powder 1 when filled can unfailingly make surface contact with the adjacent metal powder 1 at a plurality of accessible surfaces 11 , whereby the gap formed between metal powders 1 filled can be reduced and the filling property of the metal powder 1 can be enhanced.
  • the green compact 2 obtained by densely filling this metal powder 1 having high filling property and compacting it in the state of the gap between metal powders 1 being reduced comes to have a high density with the presence of less voids after compacting.
  • the metal powder 1 has a high filling property
  • a high pressure for filling the gap between metal powders 1 need not be applied at compacting, so that a high-density green compact 2 can be obtained by performing the compacting at a pressure lower than ever.
  • the total area of the accessible surfaces 11 is 90% of the entire surface area of the metal powder 1 . Therefore, the metal powder 1 when filled can ensure a sufficiently large area for the surface contact with the adjacent metal powder 1 , whereby the gap between the metal powders 1 can be unfailingly reduced and the filling property can be satisfactorily enhanced.
  • the metal powder 1 has an approximately cubic shape with a one-side length of 100 ⁇ m and has approximately square accessible surfaces 11 . Therefore, the metal powder 1 when filled can efficiently make surface contact with the adjacent metal powder 1 and at the same time, can be increased in the area for the surface contact, whereby the gap between metal powders 1 can be greatly reduced and the filling property can be more enhanced.
  • the tapped filling rate of the metal powder 1 is 90% as measured by the method described above and therefore, the metal powder 1 comes to have high filling property, whereby the green compact 2 obtained by using the metal powder 1 can be satisfactorily and unfailingly increased in the density.
  • the metal powder 1 has fine irregularities on the surface 10 and the depth D in the concave part 101 of the irregularities is 10% or less of the outermost diameter of the metal powder 1 and is 5 ⁇ m. Therefore, the mechanical connection of those metal powders 1 to each other during compacting can be enhanced, whereby the green compact 2 obtained by using the metal powder 1 can be increased in the strength.
  • the metal powder 1 is filled by vibrating the die with use of an ultrasonic generator and therefore, the metal powder 1 can be filled in a denser state, whereby the density of the obtained green compact 2 can be more increased.
  • a metal powder having high filling property and capable of realizing a high-density green compact, a green compact using the same, and a production method thereof can be provided.
  • pure iron (Fe) is used as the metal powder 1 , but other than this, a metal of Fe—Al type, Fe—Si type, Fe—Al—Si type, Fe—Co type, Fe—Ni type or other various species may be used.
  • an approximate cube is employed as the shape of the metal powder 1 , but other various shapes may be employed.
  • a shape such as approximate rectangular parallelepiped ( FIG. 6 ), approximate triangular pyramid ( FIG. 7 ) or approximate quadrangular pyramid ( FIG. 8 ) may be employed.
  • the accessible surface 11 has an approximately square or approximately rectangular shape; in the case of an approximate triangular pyramid, all surfaces have an approximately triangular shape; and in the case of an approximate quadrangular pyramid, one surface has an approximately square or approximately rectangular shape and the remaining four surfaces have an approximately triangular shape.
  • the total area of the accessible surfaces 11 is preferably 70% or more of the entire surface area of the metal powder 1 .
  • the tapped filling rate is preferably 60% or more, more preferably 70% or more.
  • This example demonstrates an application example of the green compact 2 obtained by using the metal powder 1 of Example 1.
  • the green compact 2 can be used, as a high-density sintered part, for a sprocket ( FIG. 9 ) of gear parts, a rotor ( FIG. 10 ) of pump parts, a vane and the like.
  • the green compact 2 can be molded into various shapes according to usage and can be applied to various materials.
  • This example demonstrates a case where a powder for powder magnetic cores, with the surface being coated with an insulating film, is used as the metal powder.
  • the powder 3 for powder magnetic cores of this example is a metal powder which becomes a raw material for obtaining, as shown in FIG. 11 , a powder magnetic core by compacting.
  • the powder 3 for powder magnetic cores has a plurality of accessible surfaces 11 allowing for surface contact with the adjacent powder 3 for powder magnetic cores, and the surface 10 thereof is coated with an insulating film 12 .
  • the powder 3 for powder magnetic cores of this example is pure iron (Fe) and, as shown in FIG. 11 , has an approximately cubic shape with a one-side length of 100 ⁇ m.
  • the outermost diameter of the powder 3 for powder magnetic cores is 170 ⁇ m.
  • the powder 3 for powder magnetic cores has six accessible surfaces 11 allowing adjacent powders 3 for powder magnetic cores to make surface contact with each other when filled.
  • the accessible surface 11 has an approximately square shape.
  • fine irregularities are provided on the surface 10 of the powder 3 for powder magnetic cores.
  • an irregularity shape having square corners which is most ideal, is shown for the sake of simplifying the drawing, but as shown in FIG. 13 , the irregularity practically has a corner-rounded shape in many cases.
  • the depth d in the concave part 101 of those irregularities was about 5 ⁇ m.
  • the surface 10 of the powder 3 for powder magnetic cores is entirely coated with an insulating film 12 comprising a silicone resin and having an average thickness of 50 nm.
  • the total area of six accessible surfaces 11 is 90% of the entire surface area (the entire area of the surface 10 ) of the powder 3 for powder magnetic cores, that is, the powder 3 for powder magnetic cores when filled can make surface contact with the adjacent powder 3 for powder magnetic cores at many parts of the surface 10 (see, FIG. 14 ).
  • the tap density of the powder 3 for powder magnetic cores is A and the density of the powder 3 for powder magnetic cores is B
  • the tap density A of the powder 3 for powder magnetic cores was measured by the same method as in Example 1.
  • pure iron working out to a material constituting the powder 3 for powder magnetic cores is melted to prepare a molten iron.
  • This molten iron is then cast into a casting mold having a concave part in an approximately cubic shape with a one-side length of 100 ⁇ m.
  • fine irregularities are provided on the inner surface of the casting mold and the depth in the concave part of the inner surface is 10 ⁇ m.
  • the molten iron is cooled and solidified in the casting mold.
  • a powder 3 for powder magnetic cores is taken out from the casting mold, whereby a powder 3 for powder magnetic cores having an approximately cubic shape with a one-side length of 100 ⁇ m is obtained.
  • an insulating film 12 comprising a silicone resin and having an average thickness of 50 nm is formed, for example, by a method of spray-coating a silicone resin solution or a method of dipping the powder 3 for powder magnetic cores in a silicone resin solution and pulling it up.
  • the construction material of the casting mold which can be used, is a ceramic such as silicon nitride, alumina and magnesia, or a metal such as iron. From the standpoint of ease in taking out the powder 3 for powder magnetic cores from the casting mold, a ceramic having a small thermal expansion coefficient is preferably used. Also, in view of thermal shock when casting the molten iron into the casting mold, silicon nitride, as a ceramic, is preferred.
  • an extrusion-molding method, a draw-molding method and the like may also be used.
  • an angular wire rod having a 100 ⁇ m-square cross-section is molded by extrusion or draw molding and cut at a pitch of 100 ⁇ m, whereby the same powder as the powder 3 for powder magnetic cores of this example can be obtained.
  • the method for coating an insulating film 12 in the case where the insulating film 12 is a resin film, for example, a method of mixing the powder 3 for powder magnetic cores with a resin powder and attaching the resin powder to the surface 10 of the powder 3 for power magnetic cores, or a method of spraying a resin in a solution state on the powder 3 for powder magnetic cores can be used.
  • the insulating film 12 is a ceramic film
  • a method of coating the surface 10 of the powder 3 for powder magnetic cores with the film through a chemical reaction of alkoxide, sol-gel or the like, a method of spraying a ceramic fine powder on the powder 3 for powder magnetic cores, a PVD method or a CVD method can be used.
  • the insulating film 12 is a mixed film of ceramic and resin
  • a method of dispersing a ceramic powder in a resin in a solution state and spraying the resulting mixed solution on the powder 3 for powder magnetic cores can be used.
  • the production method of a powder magnetic core 4 of this example comprises a charging step of charging the powder 3 for powder magnetic cores into a predetermined die, a filling step of filling the powder 3 for powder magnetic cores in the die, and a compacting step of compacting the powder 3 for powder magnetic cores to obtain a powder magnetic core 4 .
  • the powder 3 for powder magnetic cores is charged into a die having a shape of the powder magnetic core 4 to be molded.
  • the die is vibrated by using an ultrasonic generator to densely fill the powder 3 for powder magnetic cores.
  • the powders 3 for powder magnetic cores are aligned to bring the accessible surfaces 11 into surface contact with each other.
  • the filling is performed to give as small a gap as possible between the powders 3 for powder magnetic cores.
  • the filling density of the powder 3 for powder magnetic cores in the die after filling was 5.5 Mg/m 3 .
  • the powder 3 for powder magnetic cores filled in a die is shown by extracting a part thereof. In the figure, the ideal filled state is shown, but in practice, there may be produced a portion where the accessible surfaces 11 are not contacted with each other.
  • a pressure of 800 MPa is applied to the powder 3 for powder magnetic cores after filling so as to effect compacting.
  • the surface area of the powder 3 for powder magnetic cores was measured before and after compacting.
  • the surface area S 1 before compacting was 755 m 2 /m 3
  • the surface area S 2 after compacting was 650 m 2 /m 3
  • the rate of change in the surface area between before and after compacting represented by (S 1 ⁇ S 2 )/S 1 , was 0.14.
  • the powder magnetic core 4 produced by the above-described production method is described below.
  • the powder magnetic core 4 of this example has a cylindrical shape (ring shape) and is used as a stator core for motors.
  • the density of the powder magnetic core 4 was 7.70 Mg/m 3 and the relative density was 98.7%.
  • the saturation magnetic flux density measured by a BH analyzer was 1.82 T and the iron loss in an AC magnetic field at 400 Hz was 40 W/kg.
  • the powder magnetic core 4 can be molded into various shapes, according to usage, by changing the shape of the die.
  • the powder 3 for powder magnetic cores of this example has a plurality of accessible surfaces 11 allowing for surface contact with the adjacent powder 3 for powder magnetic cores when filled. That is, the powder 3 for powder magnetic cores when filled can unfailingly make surface contact with the adjacent powder 3 for powder magnetic cores at a plurality of accessible surfaces 11 , whereby the gap formed between powders 3 for powder magnetic cores filled can be reduced and the filling property of the powder 3 for powder magnetic cores can be enhanced.
  • the powder magnetic core 4 obtained by densely filling this powder 3 for powder magnetic cores having high filling property and compacting it in the state of the gap between powders 3 for powder magnetic cores being reduced comes to have a high density with the presence of less voids after compacting, and the powder magnetic core 4 having such a high density comes to have a high magnetic flux density.
  • the powder 3 for powder magnetic cores has high filling property and therefore, a high pressure for filling the gap between powders 3 for powder magnetic cores need not be applied at compacting.
  • a powder magnetic core 4 with high density and high magnetic flux density can be obtained by performing the compacting at a pressure lower than ever.
  • the powder 3 for powder magnetic cores can be reduced in the deformation (distortion) generated due to a pressure imposed during compacting, and the hysteresis loss of the powder magnetic core 4 after compacting can be decreased.
  • the deformation/rupture of the insulating film 12 coated on the surface 10 of the powder 3 for powder magnetic cores can also be decreased, and the insulation between powders 3 for powder magnetic cores can be satisfactorily ensured.
  • the powder magnetic core 4 after compacting can be decreased in the eddy loss and a powder magnetic core 4 with low iron loss can be obtained.
  • the total area of accessible surfaces 11 is 90% of the entire surface area of the powder 3 for powder magnetic cores. Therefore, the powder 3 for powder magnetic cores when filled can ensure a sufficiently large area for the surface contact with the adjacent powder 3 for powder magnetic cores, whereby the gap between the powders 3 for powder magnetic cores can be unfailingly reduced and the filling property can be satisfactorily enhanced.
  • the powder 3 for powder magnetic cores has an approximately cubic shape with a one-side length of 100 ⁇ m and has approximately square accessible surfaces 11 . Therefore, the powder 3 for powder magnetic cores when filled can efficiently make surface contact with the adjacent powder 3 for powder magnetic cores and at the same time, can be increased in the area for the surface contact, whereby the gap between powders 3 for powder magnetic cores can be greatly reduced and the filling property can be more enhanced.
  • the tapped filling rate of the powder 3 for powder magnetic cores is 90% as measured by the method described above and therefore, the powder 3 for powder magnetic cores comes to have high filling property, whereby the powder magnetic core 4 obtained by using the powder 3 for powder magnetic cores can be satisfactorily and unfailingly increased in the magnetic flux density and reduced in the iron loss.
  • the powder 3 for powder magnetic cores has fine irregularities on the surface 10 and the depth d in the concave part 101 of the irregularities is 10% or less of the outermost diameter of the powder 3 for powder magnetic cores and is 5 ⁇ m. Therefore, the mechanical connection of those powders 3 for powder magnetic cores to each other during compacting can be enhanced, whereby the powder magnetic core 4 obtained by using the powder 3 for powder magnetic cores can be increased in the strength.
  • the insulating film 12 is a resin film comprising a silicone resin and having a thickness of 50 nm and therefore, the insulating film 12 comes to have high electrical insulation, whereby the insulation between powders 3 for powder magnetic cores can be enhanced.
  • the powder 3 for powder magnetic cores is filled by vibrating the die with use of an ultrasonic generator and therefore, the powder 3 for powder magnetic cores can be filled in a denser state, whereby the obtained powder magnetic core 4 can be more increased in density and in magnetic flux density.
  • the value of (S 1 ⁇ S 2 )/S 1 is 0.14. Therefore, deformation (distortion) of the powder 3 for powder magnetic cores and deformation/rupture of the insulating film 12 can be satisfactorily reduced, whereby the powder magnetic core 4 can be more decreased in the iron loss.
  • the powder magnetic core 4 produced by the production method of the powder magnetic core 4 of this Example has a relative density of 98.7%. Therefore, the powder magnetic core 4 comes to have a high density with less voids.
  • the powder magnetic core 4 has a density of 7.70 Mg/m 3 and a saturation magnetic flux density of 1.82 T. Therefore, the powder magnetic core 4 comes to have a satisfactorily high density and at the same time, a high magnetic flux density.
  • a powder 3 for powder magnetic cores capable of giving a powder magnetic core having high filling property and satisfying both high magnetic flux density and low iron loss.
  • the powder magnetic core 4 obtained by using this powder 3 for powder magnetic cores comes to satisfy both high magnetic flux density and low iron loss.
  • pure iron (Fe) of this example is used as the material constituting the powder 3 for powder magnetic cores, but other than this, a metal of Fe—Al type, Fe—Si type, Fe—Al—Si type, Fe—Co type, Fe—Ni type or the like may be used.
  • a ceramic film or a mixed film of ceramic and resin may be used other than the resin film of this Example comprising a silicone resin.
  • a film comprising one resin species or a plurality of resin species, such as the silicone resin of this Example, a polyimide resin, a polyphenylene sulfide resin, a phenol resin, a polyether ketone-based resin, a silicone resin and a silane coupling agent, may be used.
  • a resin species or a plurality of resin species such as the silicone resin of this Example, a polyimide resin, a polyphenylene sulfide resin, a phenol resin, a polyether ketone-based resin, a silicone resin and a silane coupling agent.
  • the ceramic film a film comprising one ceramic species or a plurality of ceramic species such as alumina, silica, magnesia, zirconia, titania, boron nitride and silicon nitride may be used.
  • an approximate cube is employed as the shape of the powder 3 for powder magnetic cores of this Example, but other various shapes may be used.
  • a shape such as approximate rectangular parallelepiped (see, FIG. 6 ), approximate triangular pyramid (see, FIG. 7 ) or approximate quadrangular pyramid (see, FIG. 8 ) may be employed.
  • the accessible surfaces 11 have an approximately square or approximately rectangular shape; in the case of an approximate triangular pyramid, all surfaces have an approximately triangular shape; and in the case of an approximate quadrangular pyramid, one surface has an approximately square or approximately rectangular shape and the remaining four surfaces have an approximately triangular shape.
  • the total area of the accessible surfaces 11 is preferably 70% or more of the entire surface area of the powder 3 for powder magnetic cores.
  • the tapped filling rate is preferably 60% or more, more preferably 70% or more.
  • the powder magnetic core 4 of this example is molded into the shape of a stator core for motors but may be molded into various shapes according to usage by changing the shape of the die for compacting the powder 3 for powder magnetic cores. Other than the usage described above, the powder magnetic core 4 can be applied to a rotor core for motors, a noise filter, a reactor and the like.
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US11833583B2 (en) 2019-07-10 2023-12-05 Lawrence Livermore National Security, Llc Tailored particles for powder-based additive manufacturing

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