U.S. patent application number 11/656907 was filed with the patent office on 2007-07-26 for metal powder, green compact and production method thereof.
This patent application is currently assigned to DENSO Corporation. Invention is credited to Masayuki Nashiki, Hirohiko Tatsumoto.
Application Number | 20070172380 11/656907 |
Document ID | / |
Family ID | 38285753 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070172380 |
Kind Code |
A1 |
Tatsumoto; Hirohiko ; et
al. |
July 26, 2007 |
Metal powder, green compact and production method thereof
Abstract
A metal powder becoming a raw material for obtaining a green
compact by compacting, the metal powder having a plurality of
accessible surfaces allowing for surface contact of adjacent metal
powders with each other when filled, and a method for producing a
green compact by compacting the metal powder, the method comprising
the steps of: a charging step of charging the metal powder into a
predetermined die, a compacting step of filling the metal powder in
the die, and a compacting step of compacting the metal powder to
obtain the green compact.
Inventors: |
Tatsumoto; Hirohiko;
(Kariya-city, JP) ; Nashiki; Masayuki;
(Komaki-city, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
DENSO Corporation
Kariya-city
JP
|
Family ID: |
38285753 |
Appl. No.: |
11/656907 |
Filed: |
January 23, 2007 |
Current U.S.
Class: |
419/66 ;
75/255 |
Current CPC
Class: |
B22F 2998/00 20130101;
B22F 2998/00 20130101; B22F 1/0003 20130101; B22F 2998/10 20130101;
B22F 2998/10 20130101; B22F 1/02 20130101; H01F 41/0246 20130101;
B22F 3/02 20130101; B22F 2202/01 20130101; B22F 3/02 20130101; B22F
3/004 20130101; B22F 1/02 20130101; B22F 1/0007 20130101; B22F 3/10
20130101 |
Class at
Publication: |
419/66 ;
75/255 |
International
Class: |
B22F 3/093 20060101
B22F003/093 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2006 |
JP |
2006-017362 |
Jan 26, 2006 |
JP |
2006-017363 |
Sep 8, 2006 |
JP |
2006-243959 |
Claims
1. A metal powder as a raw material for obtaining a green compact
by compacting, said metal powder having a plurality of accessible
surfaces allowing for surface contact of adjacent metal powders
with each other when filled.
2. The metal powder as claimed in claim 1, wherein the total area
of said accessible surfaces is 70% or more of the entire surface
area of said metal powder.
3. The metal powder as claimed in claim 1, wherein said metal
powder has any one shape of an approximate cube, an approximate
rectangular parallelepiped, an approximate triangular pyramid and
an approximate quadrangular pyramid and said accessible surface of
said metal powder has any one shape of an approximate square, an
approximate rectangle and an approximate triangle.
4. The metal powder as claimed in claim 3, wherein one side of said
metal powder has a length of 10 to 500 .mu.m.
5. The metal powder as claimed in claim 1, wherein assuming that
the tap density of said metal powder is A and the density of said
metal powder is B, the tapped filling rate represented by
(A/B).times.100(%) is 60% or more.
6. The metal powder as claimed in claim 1, wherein said metal
powder has fine irregularities on the surface and the depth in the
concave part of said irregularities is 10% or less of the outermost
diameter of said metal powder.
7. The metal powder as claimed in claim 6, wherein the depth of
said concave part is from 1 to 50 .mu.m.
8. The metal powder as claimed in claim 1, wherein said metal
powder is any one metal of Fe type, Fe--Al type, Fe--Si type,
Fe--Al--Si type, Fe--Co type and Fe--Ni type.
9. The metal powder as claimed in claim 1, wherein said metal
powder is a powder for powder magnetic cores, with the surface
being coated with an insulating film.
10. The metal powder as claimed in claim 9, wherein said metal
powder has an outermost diameter of 500 .mu.m or less.
11. The metal powder as claimed in claim 9, wherein the thickness
of said insulating film is from 10 to 1,000 nm.
12. The metal powder as claimed in claim 9, wherein said insulating
film is a ceramic film, a resin film or a mixed film of ceramic and
resin.
13. The metal powder as claimed in claim 12, wherein said ceramic
film comprises at least one or more members selected from the group
consisting of alumina, silica, magnesia, zirconia, titania, boron
nitride and silicon nitride.
14. The metal powder as claimed in claim 12, wherein said resin
film comprises at least one or more member(s) 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.
15. A method for producing a green compact by compacting the metal
powder claimed in claim 1, said method comprising: a charging step
of charging said metal powder into a predetermined die, a filling
step of filling said metal powder in said die, and a compacting
step of compacting said metal powder to obtain said green
compact.
16. The method for producing a green compact as claimed in claim
15, wherein in said filling step, said metal powder is filled by
vibrating said die.
17. The method for producing a green compact as claimed in claim
16, wherein in said filling step, said die is vibrated by using an
ultrasonic generator.
18. The method for producing a green compact as claimed in claim
15, wherein said metal powder is a powder for powder magnetic
cores, with the surface being coated with an insulating film, and
assuming that the surface area of said metal powder before said
compacting step is S1 and the surface area after said compacting
step is S2, the value of (S1-S2)/S1 is 0.2 or less.
19. A green compact produced by the method claimed in claim 15.
20. The green compact as claimed in claim 19, wherein said green
compact has a relative density of 95% or more.
21. The green compact as claimed in claim 19, wherein said green
compact is a powder magnetic core obtained by compacting a powder
for powder magnetic cores, which is said metal powder with the
surface being coated with an insulating film and has a density of
7.4 Mg/m.sup.3 or more.
22. The green compact as claimed in claim 21, wherein said green
compact has a saturation magnetic flux density of 1.6 T or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] The method for increasing the density of a green compact has
been conventionally disclosed, for example, in Japanese Unexamined
Patent Publication (kokai) Nos. 6-2007, 10-140207, 10-219302,
11-100602, 2001-254102, 2002-317204, 2003-171741 and
2004-342937.
[0006] For example, the approach from a material aspect includes a
method of irregularly shaping the powder to enhance the compaction
property of the powder. However, the enhancement in compaction
property of a powder is limited and the density of a green compact
may not be sufficiently increased.
[0007] Also, a method of enhancing the filling property of powder
by using a mixture of powders differing in the particle size is
known. However, in this case, 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.
[0008] The approach from a compacting aspect includes a compacting
method of applying a high pressure. However, in this case, 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.
[0009] That is, in conventional methods, the density of a green
compact cannot be satisfactorily increased or a further increase in
the density can be hardly realized.
[0010] The green compact includes a powder magnetic core obtained
by compacting a metal powder of which surface is coated with an
insulating film. Such 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. In addition to these uses, 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.
[0011] The great characteristic feature of the powder magnetic core
includes a magnetic flux density and an iron loss. 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. In
order to increase the magnetic flux density, it is important to
increase the density of the powder magnetic core. On the other
hand, in order to decrease 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.
[0012] Conventionally, a technique of coating the powder surface
with an insulating film and thereby ensuring electrical insulation
(hereinafter simply referred to as "insulation") between powders is
employed for the purpose of decreasing the eddy loss. On the other
hand, in order to obtain a high magnetic flux density, compacting
at a high pressure and reduction in the thickness of the insulating
film are necessary. However, the high-pressure compacting may cause
rupture of the insulating film due to deformation of the powder or
friction, and the reduced thickness of the insulating film may
bring about extreme decrease in the insulation between powders. As
a result, the eddy loss or hysteresis loss is disadvantageously
increased.
[0013] Accordingly, 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. However, in these patent
publications, either a magnetic flux density or an iron loss is not
satisfied. That is, it is difficult in conventional methods to
satisfy both high magnetic flux density and low iron loss.
SUMMARY OF THE INVENTION
[0014] 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.
[0015] A first invention is a metal powder which is a raw material
for obtaining a green compact by compacting.
[0016] 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.
[0017] As described above, 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.
[0018] 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.
[0019] Also, as 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.
[0020] In this way, according to the present invention, a metal
powder having high filling property and capable of realizing a
high-density green compact can be provided.
[0021] A second invention is a method for producing a green compact
by compacting the metal powder of the first invention, the method
comprising:
[0022] a charging step of charging the metal powder into a
predetermined die,
[0023] a filling step of filling the metal powder in the die,
and
[0024] a compacting step of compacting the metal powder to obtain
the green compact.
[0025] In the production method for a green compact of the present
invention, 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.
[0026] Also, as 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.
[0027] In this way, according to the production method of the
present invention, a high-density green compact can be
obtained.
[0028] A third invention is a green compact produced by the method
for producing a green compact of the second invention.
[0029] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is an explanatory view showing the metal powder in
Example 1,
[0031] FIG. 2 is cross-sectional enlarged view showing the surface
of the metal powder in Example 1,
[0032] FIG. 3 is a cross-sectional enlarged view showing the
surface of the metal powder in Example 1,
[0033] FIG. 4 is an explanatory view showing the filled state of
the metal powder in Example 1,
[0034] FIG. 5 is an explanatory view showing the green compact in
Example 1,
[0035] FIG. 6 is an explanatory view showing the metal powder
having other shape in Example 1,
[0036] FIG. 7 is an explanatory view showing the metal powder
having other shape in Example 1,
[0037] FIG. 8 is an explanatory view showing the metal powder
having other shape in Example 1,
[0038] FIG. 9 is an explanatory view showing the gear part
(sprocket) in Example 2,
[0039] FIG. 10 is an explanatory view showing the pump part (rotor)
in Example 2,
[0040] FIG. 11 is an explanatory view showing the powder for powder
magnetic cores in Example 3,
[0041] FIG. 12 is a cross-sectional enlarged view showing the
surface of the powder for powder magnetic cores in Example 3,
[0042] FIG. 13 is a cross-sectional enlarged view showing the
surface of the powder for powder magnetic cores in Example 3,
[0043] FIG. 14 is an explanatory view showing the filled state of
the powder for powder magnetic cores in Example 3, and
[0044] FIG. 15 is an explanatory view showing the powder magnetic
core in Example 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] In the first invention, the total area of the accessible
surfaces is preferably 70% or more of the entire surface area of
the metal powder.
[0046] In this case, 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.
[0047] 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.
[0048] In this case, 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.
[0049] As for the shape of 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.
[0050] Also, one side of the metal powder preferably has a length
of 10 to 500 .mu.m.
[0051] In this case, 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.
[0052] Assuming that the tap density of the metal powder is A and
the density of the metal powder is B, the tapped filling rate
represented by (A/B).times.100(%) is preferably 60% or more.
[0053] In this case, 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.
[0054] Incidentally, 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.
[0055] 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.
[0056] In this case, the mechanical connection of those metal
powders to each other during compacting can be enhanced, so that
the green compact obtained by using the metal powder can be
increased in the strength.
[0057] If the depth in the concave part of the irregularities
exceeds 10%, the gap between metal powders is increased when filled
and the filling property may decrease.
[0058] The depth of the concave part is preferably from 1 to 50
.mu.m.
[0059] In this case, the mechanical connection of the metal powders
to each other during compacting can be more strengthened.
[0060] 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.
[0061] In this case, the green compact obtained by using the metal
powder comes to have magnetic characteristics. Also, 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. Incidentally, in this
case, the performance can be more enhanced by using a metal powder
having formed on the surface thereof an insulating film.
[0062] That is, the metal powder is preferably a powder for powder
magnetic cores, with the surface being coated with an insulating
film.
[0063] In this case, 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.
[0064] Furthermore, in the present invention, 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. At the same
time, 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. By virtue of
the presence of this insulating film, 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.
[0065] In this way, a powder magnetic core satisfying both high
magnetic flux density and low iron loss can be obtained. In the
case where the metal powder is a powder for powder magnetic cores,
the preferred conditions are described below.
[0066] The metal powder preferably has an outermost diameter of 500
.mu.m or less.
[0067] In this case, the effect of enhancing the filling property
of the metal powder at the compacting can be satisfactorily and
unfailingly obtained.
[0068] The thickness of the insulating film is preferably from 10
to 1,000 nm.
[0069] In this case, the insulation between metal powders at the
compacting can be satisfactorily ensured.
[0070] The insulating film is preferably a ceramic film, a resin
film or a mixed film of ceramic and resin.
[0071] In this case, the insulation between metal powders at the
compacting can be satisfactorily ensured.
[0072] 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.
[0073] In this case, the insulating film comes to have a high
volume resistivity and therefore, the insulation between the metal
powders can be enhanced.
[0074] 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.
[0075] In this case, the insulating film comes to have high
electrical insulation and therefore, the insulation between the
metal powders can be enhanced.
[0076] In the second invention, the metal powder is preferably
filled by vibrating the die in the filling step.
[0077] In this case, the metal powder can be filled in a
sufficiently dense state, whereby the density of the obtained green
compact can be increased.
[0078] Also, in the filling step, the die is preferably vibrated by
using an ultrasonic generator.
[0079] In this case, the metal powder can be filled in a denser
state, whereby the density of the obtained green compact can be
more increased.
[0080] As for the metal powder, a powder for powder magnetic cores,
with the surface being coated with an insulating film, may also be
used.
[0081] In this case, 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.
[0082] Furthermore, in the production method of the present
invention, 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. At the
same time, 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.
[0083] In this way, a powder magnetic core satisfying both high
magnetic flux density and low iron loss can be obtained.
[0084] In the metal powder which is a powder for powder magnetic
cores, with the surface being coated with an insulating film,
assuming that the surface area before the compacting step is S1 and
the surface area after the compacting step is S2, the value of
(S1-S2)/S1 is preferably 0.2 or less.
[0085] In this case, deformation (distortion) of the metal powder
and deformation/rupture of the insulating film can be reduced,
whereby the iron loss of the obtained powder magnetic core can be
more decreased.
[0086] In the third invention, the green compact preferably has a
relative density of 95% or more.
[0087] In this case, the green compact comes to a sufficiently high
density with less voids.
[0088] 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.
[0089] In this case, the green compact can satisfy both high
magnetic flux density and low iron loss.
[0090] In the case where the green compact is a powder magnetic
core, the preferred conditions are described below.
[0091] The green compact preferably has a density of 7.4 Mg/m.sup.3
or more.
[0092] In this case, 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.
[0093] In this case, the green compact comes to have a sufficiently
high magnetic flux density.
[0094] 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.
[0095] Also, in the case where 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.
EXAMPLES
[0096] The present invention will be further described with
reference to the examples thereof.
Example 1
[0097] The metal powder according to the example of the present
invention is described below.
[0098] 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.
[0099] This is described in detail below.
[0100] 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 .mu.m. The outermost diameter of the metal powder 1
is 170 .mu.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.
[0101] As shown in FIG. 2, fine irregularities are provided on the
surface 10 of the metal powder 1. In the figure, 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.
[0102] Also, when the surface 10 of the metal powder 1 was examined
by using a three-dimensional shape measuring microscope (VK-8500,
manufactured by Keyence Corp.), the depth D in the concave part 101
of those irregularities was about 5 .mu.m.
[0103] In the metal powder 1 of this example, 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).
[0104] Assuming that the tap density of the metal powder 1 is A and
the density of the metal powder 1 is B, the tapped filling rate
represented by (A/B).times.100(%) was 90% (A=7.06 Mg/m.sup.3,
B=7.85 Mg/m.sup.3).
[0105] The tap density of the metal powder 1 of this example was
measured by using Tap Denser (KYT-2000, manufactured by Seishin
Enterprise Co., Ltd.). To speak specifically, while charging the
metal powder 1 in a weight of 300 g (=a) into a 100 ml-volume
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 1, vibration is further applied 20 times to the bottom of
the measuring cylinder, and the volume b of the metal powder 1
filled is measured. In this example, the volume was 42.5 ml (=b).
Then, the tap density A (=a/b) was determined.
[0106] 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.
[0107] First, 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 .mu.m.
Incidentally, 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 .mu.m. Subsequently, the molten iron is cooled and
solidified in the casting mold. Finally, a metal powder 1 is taken
out from the casting mold.
[0108] In this way, a metal powder 1 having an approximately cubic
shape with a one-side length of 100 .mu.m is obtained.
[0109] In the production method of the metal powder 1 of this
example, 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.
[0110] As for the production method of the metal powder 1, in
addition to the cast-molding method of this example, an
extrusion-molding method, a draw-molding method and the like may
also be used. For example, an angular wire rod having a 100
.mu.m-square cross-section is molded by extrusion or draw-molding
and cut at a pitch of 100 .mu.m, whereby the same metal powder as
the metal powder 1 of this example can be obtained.
[0111] The production method of a green compact 2 (see FIG. 5)
using the above-described metal powder 1 is described below.
[0112] 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.
[0113] This is described in detail below.
[0114] In the charging step, the metal powder 1 is charged into a
die having a shape of the green compact 2 to be molded.
[0115] Subsequently, in the filling step, the die is vibrated by
using an ultrasonic generator to densely fill the metal powder 1.
At this time, as shown in FIG. 4, 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.sup.3. Incidentally, in FIG. 4, 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.
[0116] Subsequently, in the compacting step, a pressure of 800 MPa
is applied to the metal powder 1 after filling so as to effect
compacting.
[0117] In this way, a green compact 2 of FIG. 5 is obtained.
[0118] The green compact 2 produced by the above-described
production method is described below.
[0119] As shown in FIG. 5, 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 .sup.3, and the relative density was 99.4%.
[0120] The green compact 2 can be molded into various shapes
according to usage by changing the shape of the die.
[0121] The operational effect of the metal powder 1 of this example
is described below.
[0122] The metal powder 1 of this example has a plurality of
accessible surfaces 11. By virtue of this constitution, 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.
[0123] 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.
[0124] Also, as 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.
[0125] In this example, 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.
[0126] The metal powder 1 has an approximately cubic shape with a
one-side length of 100 .mu.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.
[0127] 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.
[0128] 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 .mu.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.
[0129] In the production method of this example, in the filling
step, 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.
[0130] In this way, according to this example, 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.
[0131] In this example, 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.
[0132] Also, an approximate cube is employed as the shape of the
metal powder 1, but other various shapes may be employed. For
example, a shape such as approximate rectangular parallelepiped
(FIG. 6), approximate triangular pyramid (FIG. 7) or approximate
quadrangular pyramid (FIG. 8) may be employed.
[0133] In the case of an approximate rectangular parallelepiped,
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.
[0134] Even when these shapes are employed, 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.
Example 2
[0135] This example demonstrates an application example of the
green compact 2 obtained by using the metal powder 1 of Example
1.
[0136] 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.
[0137] Also, the green compact 2 can be molded into various shapes
according to usage and can be applied to various materials.
Example 3
[0138] 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.
[0139] 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.
[0140] This is described in detail below.
[0141] 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 .mu.m. The outermost diameter
of the powder 3 for powder magnetic cores is 170 .mu.m. Also, 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. Although a cubic powder 3 for
powder magnetic cores, which is most ideal, is shown in FIG. 11 for
the sake of simplifying the drawing, the powder for powder magnetic
cores is practically not such an exact cube but often has a shape
with the corners rounded.
[0142] As shown in FIG. 12, fine irregularities are provided on the
surface 10 of the powder 3 for powder magnetic cores. In the
figure, 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.
[0143] Also, when the surface 10 of the powder 3 for powder
magnetic cores was examined by the same method as in Example 1, the
depth d in the concave part 101 of those irregularities was about 5
.mu.m.
[0144] As shown in FIGS. 11 to 13, 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.
[0145] In the case of the powder 3 for powder magnetic cores of
this Example, 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).
[0146] Assuming that 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 tapped filling rate represented by
(A/B).times.100(%) was 90% (A=7.02 Mg/m.sup.3, B=7.80 Mg/m.sup.3).
Incidentally, the tap density A of the powder 3 for powder magnetic
cores was measured by the same method as in Example 1.
[0147] The production method of the powder 3 for powder magnetic
cores is briefly described below. As for the production method of
this example, a cast-molding method was used similarly to Example
1.
[0148] First, 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 .mu.m. Incidentally, 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 .mu.m. Subsequently, the molten iron is
cooled and solidified in the casting mold. Finally, 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 .mu.m is obtained.
[0149] Throughout the surface 10 of the obtained powder 3 for
powder magnetic cores, 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.
[0150] In this way, a powder 3 for powder magnetic cores of FIG. 11
is obtained.
[0151] In the production method of this example, 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.
[0152] As for the production method of the powder 3 for powder
magnetic cores, in addition to the cast-molding method of this
Example, an extrusion-molding method, a draw-molding method and the
like may also be used. For example, an angular wire rod having a
100 .mu.m-square cross-section is molded by extrusion or draw
molding and cut at a pitch of 100 .mu.m, whereby the same powder as
the powder 3 for powder magnetic cores of this example can be
obtained.
[0153] As for 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.
[0154] In the case where the insulating film 12 is a ceramic film,
for example, 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.
[0155] In the case where the insulating film 12 is a mixed film of
ceramic and resin, for example, 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.
[0156] The production method of a powder magnetic core 4 (see, FIG.
15) using the above-described powder 3 for powder magnetic cores is
described below.
[0157] 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.
[0158] This is described in detail below.
[0159] In the charging step, the powder 3 for powder magnetic cores
is charged into a die having a shape of the powder magnetic core 4
to be molded.
[0160] Subsequently, in the filling step, the die is vibrated by
using an ultrasonic generator to densely fill the powder 3 for
powder magnetic cores. At this time, as shown in FIG. 14, 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.sup.3. Incidentally, in FIG. 14, 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.
[0161] Subsequently, in the compacting step, a pressure of 800 MPa
is applied to the powder 3 for powder magnetic cores after filling
so as to effect compacting.
[0162] In this way, a powder magnetic core 4 of FIG. 15 is
obtained.
[0163] In order to evaluate the deformation (distortion) of the
powder 3 for powder magnetic cores, which is generated due to a
pressure imposed during compacting in the production method of this
example, the surface area of the powder 3 for powder magnetic cores
was measured before and after compacting. The surface area S1
before compacting was 755 m.sup.2/m.sup.3, the surface area S2
after compacting was 650 m.sup.2/m.sup.3, and the rate of change in
the surface area between before and after compacting, represented
by (S1-S2)/S1, was 0.14.
[0164] The powder magnetic core 4 produced by the above-described
production method is described below.
[0165] As shown in FIG. 15, 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.sup.3 and the relative density was 98.7%. Also, 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.
[0166] The powder magnetic core 4 can be molded into various
shapes, according to usage, by changing the shape of the die.
[0167] The operational effect of the powder 3 for powder magnetic
cores of this example is described below.
[0168] 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.
[0169] 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.
[0170] Also, 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. In other words, 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.
[0171] Furthermore, since the compacting can be performed 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. At the
same time, 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. By virtue of the
presence of this insulating film 12, 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.
[0172] In this example, 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.
[0173] The powder 3 for powder magnetic cores has an approximately
cubic shape with a one-side length of 100 .mu.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.
[0174] 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.
[0175] 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 .mu.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.
[0176] 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.
[0177] In the production method of the powder magnetic core 4 of
this example, in the filling step, 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.
[0178] In the powder 3 for powder magnetic cores, assuming that the
surface area before the compacting step is S1 and the surface area
after the compacting step is S2, the value of (S1-S2)/S1 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.
[0179] Also, 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.
[0180] Furthermore, the powder magnetic core 4 has a density of
7.70 Mg/m.sup.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.
[0181] In this way, according to this example, 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, can be provided. 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.
[0182] In this example, 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.
[0183] Furthermore, as regards the insulating film 12, for example,
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.
[0184] As for the resin film, 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.
[0185] As for 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.
[0186] Also, 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. For example, 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.
[0187] In the case of an approximate rectangular parallelepiped,
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.
[0188] Even when these shapes are employed, 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.
[0189] 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.
* * * * *