U.S. patent application number 12/801122 was filed with the patent office on 2010-12-09 for method for producing powder mixture for powder metallurgy, and method for producing sintered body.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Takayasu Fujiura, Yoshihiro Ito.
Application Number | 20100310406 12/801122 |
Document ID | / |
Family ID | 43300879 |
Filed Date | 2010-12-09 |
United States Patent
Application |
20100310406 |
Kind Code |
A1 |
Fujiura; Takayasu ; et
al. |
December 9, 2010 |
Method for producing powder mixture for powder metallurgy, and
method for producing sintered body
Abstract
The present invention provides a method for producing a powder
mixture for powder metallurgy, which allows production of a green
compact having both high density and high lubricity (low demolding
force). The method, according to the present invention, for
producing a powder mixture for powder metallurgy including an
iron-base powder, a mechanical characteristic-improving powder and
a lubricant, the method includes the steps of: mixing the iron-base
powder and/or the mechanical characteristic-improving powder with
an amide-based lubricant solution; removing a solvent in the
solution; and coating the surface of the iron-base powder and/or
the mechanical characteristic-improving powder with an amide-based
lubricant.
Inventors: |
Fujiura; Takayasu;
(Kobe-shi, JP) ; Ito; Yoshihiro; (Kobe-shi,
JP) |
Correspondence
Address: |
Juan Carlos A. Marquez;c/o Stites & Harbison PLLC
1199 North Fairfax Street, Suite 900
Alexandria
VA
22314-1437
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
|
Family ID: |
43300879 |
Appl. No.: |
12/801122 |
Filed: |
May 24, 2010 |
Current U.S.
Class: |
419/32 ;
427/216 |
Current CPC
Class: |
B22F 2999/00 20130101;
B22F 2999/00 20130101; B22F 1/0059 20130101; B22F 2003/023
20130101; B22F 1/0059 20130101; B22F 1/0062 20130101; B22F 1/007
20130101; B22F 1/0003 20130101; C22C 33/02 20130101 |
Class at
Publication: |
419/32 ;
427/216 |
International
Class: |
B22F 1/02 20060101
B22F001/02; B22F 3/12 20060101 B22F003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2009 |
JP |
2009-138263 |
Claims
1. A method for producing a powder mixture for powder metallurgy
including an iron-base powder, a mechanical
characteristic-improving powder and a lubricant, the method
comprising the steps of: mixing the iron-base powder and/or the
mechanical characteristic-improving powder with an amide-based
lubricant solution; removing a solvent in the solution; and coating
the surface of the iron-base powder and/or the mechanical
characteristic-improving powder with an amide-based lubricant.
2. The method for producing the powder mixture for powder
metallurgy according to claim 1, wherein 0.01 to 2.0 parts by mass
of the amide-based lubricant is added to 100 parts by mass of total
amount of the iron-base powder and the mechanical
characteristic-improving powder.
3. The method for producing a powder mixture for powder metallurgy
according to claim 1, wherein the amide-based lubricant is composed
of an aliphatic amide and/or an aliphatic bisamide.
4. The method for producing a powder mixture for powder metallurgy
according to claim 3, wherein the aliphatic amide is N-oleyl
palmitic amide.
5. The method for producing a powder mixture for powder metallurgy
according to claim 3, wherein the aliphatic bisamide is
ethylene-bis-oleic amide.
6. The method for producing a powder mixture for powder metallurgy
according to claim 1, wherein the mechanical
characteristic-improving powder is composed of at least one element
selected from the group consisting of copper, nickel, chromium,
molybdenum, graphite and manganese sulfide.
7. A method for producing a sintered body, comprising the steps of:
mixing the iron-base powder and/or the mechanical
characteristic-improving powder with an amide-based lubricant
solution; removing a solvent in the solution; coating the surface
of the iron-base powder and/or the mechanical
characteristic-improving powder with an amide-based lubricant;
compression-molding the powder mixture for powder metallurgy
obtained by the producing method; and sintering.
8. The method for producing a sintered body according to claim 7,
wherein said compression molding is performed at ordinary
temperature.
9. The method for producing a sintered body according to claim 7,
wherein 0.01 to 2.0 parts by mass of the amide-based lubricant is
added to 100 parts by mass of total amount of the iron-base powder
and the mechanical characteristic-improving powder.
10. The method for producing a sintered body according to claim 7,
wherein the amide-based lubricant is composed of an aliphatic amide
and/or an aliphatic bisamide.
11. The method for producing a sintered body according to claim 10,
wherein the aliphatic amide is N-oleyl palmitic amide.
12. The method for producing a sintered body according to claim 10,
wherein the aliphatic bisamide is ethylene-bis-oleic amide.
13. The method for producing a sintered body according to claim 7,
wherein the mechanical characteristic-improving powder is composed
of at least one element selected from the group consisting of
copper, nickel, chromium, molybdenum, graphite and manganese
sulfide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for producing a
powder mixture for powder metallurgy and a method for producing a
sintered body using a powder mixture for powder metallurgy obtained
by the method.
[0003] 2. Description of the Related Art
[0004] In general, a powder mixture for powder metallurgy is
produced by mixing an iron-base powder, as main raw materials, such
as pure iron powder or iron-base alloy powder, a mechanical
characteristic-improving powder, as a component for improving
mechanical characteristics (e.g., strength property, processing
characteristic, etc.) of a sintered body as final product, such as
alloying powder or graphite powder, and a powdery lubricant (refer
to, for example, Japanese Patent Application Laid-Open No.
2006-124777).
[0005] When the powder mixture for powder metallurgy is filled into
a mold and compression-molded to form a green compact, the
lubricant is added for reducing the frictional resistance between
the green compact and the mold wall surface so that the green
compact can be extracted from the mold with a low demolding force.
The lubricant is considered to have also a definite action on the
lubricity between powder particles during the rearrangement and
densification of the iron-base powder or the mechanical
characteristic-improving powder, which accompany the compression
molding.
[0006] A sintered body which is obtained by sintering the green
compact obtained by compression-molding the powder mixture for
powder metallurgy is, in general, frequently required to have
high-level mechanical characteristics including strength. The
mechanical characteristics of the sintered body are considered to
be greatly influenced by the density (degree of compaction index)
of the green compact before sintering, although they are also
dependent on the composition of the iron-base powder or the
mechanical characteristic-improving powder as the main component.
Namely, during the compression molding, the iron-base powder or
mechanical characteristic-improving powder is rearranged and
plastic-deformed. And as the green compact is more densified, or as
voids within the green compact are reduced sufficiently, it is
considered that the strength of the sintered body obtained with
using this green compact is improved
[0007] The improvement in density of the green compact can be
attained by optimizing (densifying) the shape, particle size and
particle size distribution of iron-base powder. However, it is
difficult to produce such an iron-base powder at industrially low
cost. Further, the green compact can be densified by increasing the
molding pressure during the compression molding. However, this
method has a limitation in respect of the capability of molding
equipment or the productivity of green compact.
[0008] These methods are not employed, but the addition amount of
the lubricant may be reduced to improve more easily the density of
the green compact. The reason is that the powdery lubricant used in
the field of powder metallurgy is generally composed of an organic
compound, and therefore the added lubricant is finally removed from
the green compact due to thermal decomposition at a dewaxing step
prior to sintering, however at the compression-molded stage, most
of the lubricant remains between particles of the iron-base powder
or the mechanical characteristic-improving powder within the green
compact. Therefore, the lubricant consequently occupies a certain
volume within the green compact, constituting a factor of
disturbing the densification of the green compact.
[0009] However, when the addition amount of the lubricant is
reduced, the frictional resistance between the green compact and
the mold wall surface increases, and the demolding force in the
extraction of the green compact from the mold is consequently
increases, causing mold damage such as mold galling. Further, the
lubricity between powder particles during the rearrangement of the
iron-base powder or the like which accompanies compression molding
is also deteriorated, limiting the improvement in density of the
green compact.
[0010] As described above, it is difficult to ensure both lubricity
(low demolding force) and high density in the green compact.
[0011] Further, a sintered body having good appearance and
characteristics is difficult to be obtained from the powder mixture
for powder metallurgy containing powdery lubricant. The reason is
that, at the production of the powder mixture for powder
metallurgy, the powdery lubricant exists in a dispersed state
within the powder mixture, however, in the course of handling to
compression molding operation, the lubricant approaches or contacts
with each other, and agglomerates due to an intermolecular force or
other effects, and the particle size may become larger than that of
the lubricant added in early stage. When the agglomerated lubricant
emerges on the surface of the green compact, it becomes the blot on
the surface of the sintered body. And when it remains within the
green compact, it becomes the surface roughness or internal defect
of the sintered body.
[0012] Further, this powder mixture for powder metallurgy involves
segregation of the mechanical characteristic-improving powder such
as alloying powder or graphite powder.
SUMMARY OF THE INVENTION
[0013] In view of the circumstances as described above, the present
invention is accomplished and has an object to provide a method for
producing a powder mixture for powder metallurgy, which can inhibit
segregation of the mechanical characteristic-improving powder while
giving high lubricity to powder particles in the powder mixture for
powder metallurgy, and thus can allow production of a green compact
having high density and yet high lubricity (low demolding force)
and further production of a sintered body with lesser surface blot,
surface roughness or internal defect.
[0014] Namely, as the method for solving the above object, the
present invention provides a method for producing a powder mixture
for powder metallurgy including an iron-base powder, a mechanical
characteristic-improving powder and a lubricant, the method
includes the steps of: mixing the iron-base powder and/or the
mechanical characteristic-improving powder with an amide-based
lubricant solution; removing a solvent in the solution; and coating
the surface of the iron-base powder and/or the mechanical
characteristic-improving powder with an amide-based lubricant.
[0015] According to this structure, the lubricant can be easily
spread over the whole surface of the iron-base powder or the
mechanical characteristic-improving powder since the lubricant is
added to these powders in a solution state.
[0016] The expression "coating the surface of powder with the
amide-based lubricant" herein includes the form of covering a part
of the surface of powder with the amide-based lubricant in addition
to the form of covering the whole surface of powder with the
amide-based lubricant.
[0017] In the method for producing a powder mixture for powder
metallurgy of the present invention, it is preferable that 0.01 to
2.0 parts by mass of the amide-based lubricant is added to 100
parts by mass of total amount of the iron-base powder and the
mechanical characteristic-improving powder.
[0018] The amide-based lubricant is preferably composed of an
aliphatic amide and/or an aliphatic bisamide. Concretely, it is
preferable that the aliphatic amide is N-oleyl palmitic amide, and
the aliphatic bisamide is ethylene-bis-oleic amide.
[0019] The mechanical characteristic-improving powder is preferably
composed of at least one element selected from the group consisting
of copper, nickel, chromium, molybdenum, graphite and manganese
sulfide.
[0020] The prevent invention includes a method for producing a
sintered body, including the step of: compression-molding the
powder mixture for powder metallurgy obtained by the above
producing methods; and sintering.
[0021] In this case, the compression molding is preferably
performed at ordinary temperature.
[0022] According to the present invention, a powder mixture for
powder metallurgy which allows production of a green compact with
high density and low demolding force can be obtained.
PREFERRED EMBODIMENTS OF THE PRESENT INVENTION
[0023] The method for producing a powder mixture for powder
metallurgy according to the present invention, is a method for
producing the powder mixture including an iron-base powder, a
mechanical characteristic-improving powder and a lubricant, and the
method includes the steps of mixing the iron-base powder and/or the
mechanical characteristic-improving powder with an amide-based
lubricant solution, removing a solvent in the solution, and coating
the surface of the iron-base powder and/or the mechanical
characteristic-improving powder with an amide-based lubricant.
[0024] In the method for producing a powder mixture for powder
metallurgy of the present invention, since a solution in which the
lubricant is dissolved is used to dispose the lubricant onto the
powder surface, the lubricant can be easily spread over the whole
surface of the powder. Therefore, the coating of the powder surface
with the lubricant can be easily preformed, and a uniform coating
state can be easily ensured. The addition amount of the lubricant
can be easily adjusted for uniformly disposing the lubricant over
the whole powder surface. Thus, the present invention has the
following advantages.
[0025] (Production of Densified Green Compact and Inhibition of
Segregation of Mechanical Characteristic-Improving Powder)
[0026] Namely, in a powder mixture for powder metallurgy obtained
by the above-mentioned method, since the surface of the iron-base
powder or the mechanical characteristic-improving powder is coated
with the lubricant, the lubricity between powder particles is
improved. Therefore, the iron-base powder or the mechanical
characteristic-improving powder is easily rearranged in compression
molding.
[0027] Even if the mechanical characteristic-improving powder is
smaller in specific gravity than the iron-base powder, for example,
and easy to be liberated and segregated in the powder mixture, it
is estimated that the lubricant existing on the particle surface
serves as a binder to allow the mechanical characteristic-improving
powder adhere to the iron-base powder surface, and therefore the
mechanical characteristic-improving powder can be inhibited from
being segregated within the powder mixture.
[0028] Further, the lubricant never hinders the densification of
green compact since it exists, within the powder mixture for powder
metallurgy, not as a powder but in the form of a film between the
particles of the iron-base powder or the mechanical
characteristic-improving powder. The green compact is rather
densified since the lubricant film is easily deformed and moved by
a stress in the compression molding, and pushed out of between the
powder particles.
[0029] As described above, the powder mixture for powder metallurgy
obtained by the method of the present invention allows production
of a green compact with high density, since the iron-base powder or
the mechanical characteristic-improving powder is easily rearranged
in the compression molding, and the residual quantity of the
lubricant in the green compact can be also kept low. Further,
prevention of segregation of the mechanical
characteristic-improving powder can be expected.
[0030] (Production of Green Compact Excellent in Lubricity)
[0031] According to the method of the present invention, since the
lubricant is adhered to the surface of the iron-base powder or the
mechanical characteristic-improving powder, the lubricant exists
also on the surface (the interface with the mold) of a resulting
green compact to reduce the frictional resistance with the
mold.
[0032] Further, since the lubricant pushed out of between the
powder particles by the stress in the compression molding is leaked
to the surface of the green compact to thinly cover the surface,
the frictional resistance with the mold is further more
reduced.
[0033] Therefore, the powder mixture for powder metallurgy obtained
by the method of the present invention allows production of a green
compact excellent in lubricity and reduced in demolding force.
[0034] (Production of Sintered Body Excellent in Appearance)
[0035] According to the production method of the present invention,
since the lubricant exists in a state in which it is adhered onto
the surface of the iron-base powder or the mechanical
characteristic-improving powder, the lubricant is inhibited from
aggregating in the course of handling before compression molding
and being exposing to the outer surface of the green compact or
staying within the green compact.
[0036] Therefore, the powder mixture for powder metallurgy obtained
by the production method of the present invention allows the
production of a sintered body with lesser surface blot, surface
roughness or internal defect.
[0037] The method for producing a powder mixture for powder
metallurgy of the present invention will be then described in
detail.
[0038] [Production Method of Powder Mixture for Powder
Metallurgy]
[0039] (Iron-Base Powder)
[0040] Examples of the iron-base powder used in the present
invention include pure iron powder and iron-base alloy powder.
[0041] The pure iron includes an iron powder containing 97% by mass
or more of iron powder, with the balance being inevitable
impurities (e.g., oxygen, silicon, carbon, manganese, etc.), which
can be substantially regarded as a pure iron component.
[0042] The iron-base alloy powder contains, as a component other
than iron, alloy components such as copper, nickel, chromium,
molybdenum, sulfur, or manganese for improving characteristics of
sintered body. The iron-base alloy powder is roughly classified to
a partially alloyed powder (produced by diffusion-joining the alloy
element to base iron powder) and a prealloyed powder (produced by
adding the alloy element in dissolution step).
[0043] In the present invention, these iron-base powders may be
used singly or in combination of two or more kinds thereof.
[0044] The iron-base powder can be produced, for example, by making
molten iron (or molten iron alloy) into fine particles by
atomization and then performing reduction and pulverization. An
iron-base powder obtained by such a production method has a
particle size (median diameter) of about 20 to 25 .mu.m, which
corresponds to 50% accumulated particle size distribution in
particle size distribution evaluated by sieving method. In the
present invention, an iron-base powder with a particle size (median
diameter) of about 50 to 150 .mu.m (micro track method) is
preferably used.
[0045] (Mechanical Characteristic-Improving Powder)
[0046] As the mechanical characteristic-improving powder used in
the present invention, any powder, for example, metal powder,
inorganic powder or the like, can be used without limitation, as
long as it can improve mechanical characteristics such as hardness
and toughness of sintered body or can enhance machinability thereof
by diffusing into the iron-base powder in sintering to be
subsequently performed.
[0047] Examples of the metal powder include copper, nickel,
chromium, molybdenum, tin, vanadium, manganese, and ferro
phosphorus. Particularly in case where pure iron powder is used as
the iron-base powder, it is preferred to add such a metal powder.
The metal powder may be composed of a ferroalloy alloyed with iron,
or an alloy powder composed of two kinds or more of elements other
than iron.
[0048] Examples of the inorganic powder include sulfide such as
manganese sulfide or manganese disulfide; nitride such as boron
nitride; an oxide such as boric acid, magnesium oxide, potassium
oxide, or silicon oxide; graphite such as natural graphite or
artificial graphite; phosphorus, sulfur, and the like.
[0049] The above-mentioned mechanical characteristic-improving
powders may be used singly or in combination of two or more kinds
thereof.
[0050] In the present invention, a mechanical
characteristic-improving powder having a particle size (median
diameter) of about 2 to 150 .mu.m (micro-track method) is
preferably used.
[0051] The total mixing amount of the mechanical
characteristic-improving powders is preferably set to 0.1 parts by
mass or more but not exceeding 10 parts by mass relative to 100
parts by mass of the iron-base powder, although it can be
optionally determined according to various characteristics required
in a final product (sintered body) without particular limitation.
In case of the above-mentioned range, the mechanical
characteristic-improving component can sufficiently diffuse into
the iron-base powder, and therefore the mechanical
characteristic-improving effect can be developed. Further,
deterioration of compaction property can be prevented to ensure a
green compact having a sufficient density. Particularly for the
mixing amount of the inorganic powder such as graphite, it is
preferable to set to 0.1 parts by mass or more but not exceeding 10
parts by mass relative to 100 parts by mass of the iron-base
powder. In case of the above-mentioned range, the addition effect
can be sufficiently developed while preventing the deterioration of
the mechanical characteristics of sintered body due to the adverse
effect of the mixing of the inorganic powder.
[0052] When pure iron powder is used as the iron-base powder, for
example, the preferable mixing amount of each mechanical
characteristic-improving powder relative to 100 parts by mass of
the pure iron powder is such that copper: 0.1 to 5 parts by mass,
nickel: 0.1 to 10 parts by mass, chromium: 0.1 to 8 parts by mass,
molybdenum: 0.1 to 5 parts by mass, graphite: 0.1 to 2 parts by
mass, or manganese sulfide: 0.1 to 5 parts by mass.
[0053] (Lubricant)
[0054] In the present invention, the powder mixture for powder
metallurgy is prepared by use of an amide-based lubricant as the
lubricant, whereby a green compact with high density and excellent
lubricity and a sintered body with excellent appearance can be
obtained.
[0055] Examples of the amide-based lubricant used in the present
invention include aliphatic amide and aliphatic bisamide.
[0056] Examples of the aliphatic amide include lauric amide,
palmitic amide, stearic amide, behenic amide, hydroxy stearic
amide, oleic amide, erucamide, ricinoleic amide, N-lauryl lauric
amide, N-palmityl palmitic amide, N-stearyl stearic amide, N-oleyl
oleic amide, N-stearyl oleic amide, N-oleyl stearic amide,
N-stearyl erucamide, N-oleyl palmitic amide, N-stearyl-hydroxy
stearic amide, N-oleyl-hydroxy stearic amide, methylol stearic
amide, and methylol behenic amide.
[0057] Examples of the aliphatic bisamide include
methylene-bis-stearic amide, methylene-bis-lauric amide,
methylene-bis-hydroxy stearic amide, ethylene-bis-caprylic amide,
ethylene-bis-capric amide, ethylene-bis-lauric amide,
ethylene-bis-stearic amide, ethylene-bis-isostearic amide,
ethylene-bis-hydroxy stearic amide, ethylene-bis-behenic amide,
hexamethylene-bis-stearic amide, hexamethylene-bis-behenic amide,
hexamethylene-bis-hydroxy stearic amide, butylene-bis-hydroxy
stearic amide, N,N'-distearyl adipic amide, N,N'-distearyl sebacic
amide, methylene-bis-oleic amide, ethylene-bis-oleic amide,
ethylene-bis-erucamide, hexamethylene-bis-oleic amide, N,N'-dioleyl
adipic amide, N,N'-dioleyl sebacic amide, m-xylylene stearic amide,
and N,N'-distearyl isophthalic amide.
[0058] These amide-based lubricants may be used singly or in
combination of two or more kinds thereof. It is particularly
preferred to use N-oleyl palmitic amide (melting point: about
62.degree. C.) as the aliphatic amide, and ethylene-bis-oleic amide
(melting point: about 120.degree. C.) as the aliphatic bisamide. In
the present invention, since the amide-based lubricant is added to
the iron-base powder and the like not in a melt state but in a
solution state, such an amide-based lubricant having a high melting
point can be used.
[0059] The amide-based lubricant is preferably contained in the
powder mixture for powder metallurgy within the range of 0.01 to
2.0 parts by mass relative to 100 parts by mass of the total of the
iron-base powder and the mechanical characteristic-improving
powder. When the content of the amide-based lubricant is within the
above-mentioned range, the effects by the addition of lubricant
(application of lubricity to powder particles and densification of
green compact) can be sufficiently exhibited without the risk of
inhibiting the densification of green compact by the addition of
lubricant. The content of the amide-based lubricant is set more
preferably to 0.05 to 1.2 parts by mass, further more preferably to
0.1 to 1.0 part by mass.
[0060] (Lubricant Solution)
[0061] The present invention is characterized by using a solution
in which the amide-based lubricant is dissolved to coat the surface
of the iron-base powder and the mechanical characteristic-improving
powder with the lubricant.
[0062] In the present invention, the solvent used to prepare the
amide-based lubricant solution is not particularly limited as long
as the amide-based lubricant can dissolve into the solvent, and the
solvent can be easily removed by heating or decompression after
mixed with the iron-base powder and the like. Examples of such a
solvent includes aromatic hydrocarbon such as benzene or toluene;
and alcohol such as methanol, ethanol, isopropanol, n-butanol,
isobutanol, sec-butanol, t-butanol, pentanol, ethylene glycol,
propylene glycol, or 1,4-butane diol. These solvents may be used
singly or in combination of two or more kinds thereof.
[0063] A known method can be used to prepare the amide-based
lubricant solution. For example, the amide-based lubricant solution
can be prepared by adding the solvent to the amide-based lubricant
followed by stirring. When the amide-based lubricant is hardly
soluble to the solvent, the preparation can be performed while
properly heating the solvent. When toluene, for example, is used as
the solvent, the toluene is heated to about 60.degree. C.
[0064] The addition amount of the amide-based lubricant to the
solvent is not particularly limited, but it is preferable that the
content of the amide-based lubricant in the powder mixture for
powder metallurgy is within the above-mentioned range, the
amide-based lubricant solution can be uniformly spread over the
whole surface of the iron-base powder or the mechanical
characteristic-improving powder, and then rapidly removing the
solvent. For example, the addition amount relative to 100 parts by
mass of the solvent is set to preferably 1 part by mass or more,
more preferably 2 parts by mass or more and to preferably 40 parts
by mass or less, more preferably 25 parts by mass or less.
[0065] (Coating with Amide-Based Lubricant)
[0066] The coating of the surface of the iron-base powder or the
mechanical characteristic-improving powder with the amide-based
lubricant by use of the amide-based lubricant solution can be
performed by a known method.
[0067] For example, the coating can be performed by mixing the
amide-based lubricant solution to the iron-base powder, removing
the solvent (by heating or decompression), adding the mechanical
characteristic-improving powder thereto, and mixing, or by mixing
the amide-based lubricant solution to the mechanical
characteristic-improving powder, removing the solvent, and adding
the iron-base powder thereto, and mixing. According to this, only
one of the iron-base powder and the mechanical
characteristic-improving powder can be covered with the amide-based
lubricant.
[0068] The coating can be performed also by mixing the iron-base
powder to the amide-based lubricant solution, and further adding
the mechanical characteristic-improving powder thereto, and mixing,
or by mixing the amide-based lubricant solution to a mixture of the
iron-base powder and the mechanical characteristic-improving
powder, and then removing the solvent. According to this, both the
iron-base powder and the mechanical characteristic-improving powder
can be coated with the amide-based lubricant.
[0069] In the present invention, since it is preferred to improve
the lubricity between powder particles to promote the rearrangement
of the powder particles in the compression molding, the method for
coating both the iron-base powder and the mechanical
characteristic-improving powder with the amide-based lubricant is
preferably adopted.
[0070] The addition amount of the amide-based lubricant solution to
the iron-base powder or the mechanical characteristic-improving
powder is set, relative to 100 parts by mass of the iron-base
powder or the mechanical characteristic-improving powder, to
preferably 1 part by mass or more, more preferably 5 parts by mass
or more, and to preferably 20 parts by mass or less, more
preferably 10 parts by mass or less, although it depends on the
density of the amide-based lubricant in the solution. According to
this, the amide-lubricant solution can be spread over the whole
surface of the iron-base powder or the mechanical
characteristic-improving powder while keeping the content of the
amide-based lubricant in the powder mixture for powder metallurgy
within the above-mentioned range, and the solvent can be rapidly
removed thereafter.
[0071] The mixing of the iron-base powder or the mechanical
characteristic-improving powder with the amide-based lubricant
solution can be performed by use of a generally-used mixer such as
a mixer with blade, a V-shape mixer, or a double conical mixer (W
cone). A high-speed mixer of a type capable of mixing and stirring
contents by a rotary blade and further performing heating or
decompression is preferably used.
[0072] [Method for Producing Sintered Body]
[0073] The present invention includes also a method for producing a
sintered body by compression-molding the powder mixture for powder
metallurgy obtained by the above-mentioned method followed by
sintering.
[0074] (Compression Molding)
[0075] In the present invention, a known method can be adopted to
perform the compression molding of the powder mixture for powder
metallurgy without particular limitation. Concrete molding
conditions such as molding temperature and molding pressure are
varied depending on the kinds or addition amounts of the components
constituting the powder mixture or the shape of green compact. The
powder mixture for powder metallurgy obtained by the method of the
present invention is used for the compression molding, and a green
compact having a density of about 6.85 g/cm.sup.3 or more can be
consequently produced. The molding temperature in the compression
molding in the present invention is preferably room
temperature.
[0076] In the present invention, the powder mixture for powder
metallurgy obtained by the above-mentioned method is used for
compression molding, and the demolding pressure of the green
compact can be consequently reduced. When the compression is
performed at a molding pressure of 490.3 MPa (5 t/cm.sup.2), the
concrete demolding pressure can be made to 10.0 MPa or less, more
preferably to 9.5 MPa or less, further preferably to 9.0 MPa or
less. When the compression is performed at a molding pressure of
686.5 MPa (7 t/cm.sup.2), the demolding pressure can be made to
15.0 MPa or less, more preferably to 14.0 MPa or less.
[0077] (Dewaxing)
[0078] In the present invention, it is preferred to include, prior
to sintering of the green compact obtained by the compression
molding, a dewaxing step of removing the amide-based lubricant
remaining within the green compact. Such a dewaxing step can be
performed, for example, by heating the green compact to thermally
decompose the amide-based lubricant within the green compact. The
heating condition in the dewaxing step can be appropriately
adjusted according to the kind of the amide-based lubricant used,
and in general, simple heating at about 150 to 200.degree. C. for
10 to 30 minutes (more suitably 15 to 20 minutes) is
sufficient.
[0079] (Sintering)
[0080] The method obtaining a sintered body with using the
above-mentioned green compact is not particularly limited, and the
general sintering method can be adopted. Concrete sintering
conditions are varied depending on the kinds or addition amounts of
the components constituting the green compact, the kind of final
products, or the like. The sintering is preferably performed, for
example, in an atmosphere of N.sub.2, N.sub.2-H.sub.2, hydrocarbon
or the like, at a temperature of about 1000 to 1300.degree. C. for
5 to 60 minutes.
EXAMPLES
[0081] The present invention will be further described in detail
based on Examples. The present invention is never limited to the
following examples, and all variations and modifications made
within the range not departing from the gist of the present
invention are included in the technical scope of the present
invention. "Part" and "%" referred to in Examples mean "part by
mass" and "% by mass" respectively unless a notice is given
thereto.
[0082] Evaluation methods used in Examples will be described
first.
[0083] (Green Compact Density)
[0084] The green compact density was calculated based on
mass/volume by measuring the mass of a powder mixture for powder
metallurgy, and measuring, after compression molding thereof, the
diameter and length of a green compact (cylinder) by a micrometer
to determine the volume.
[0085] (Demolding Pressure)
[0086] An Instron tester was used to measure the demolding pressure
in extraction of a green compact from a mold after molding.
Example 1
Preparation of Amide-Based Lubricant Solution
[0087] An amide-based lubricant solution was prepared by adding, to
20 parts of toluene as the solvent, 4 parts of N-oleyl palmitic
amide (by NIPPON FINE CHEMICAL) as the amide-based lubricant, and
mixing them with heated to about 60.degree. C.
[0088] <Preparation of Powder Mixture for Powder
Metallurgy>
[0089] The obtained amide-based lubricant solution was added and
mixed to 100 parts of pure powder (by KOBE STEEL, 300 M, particle
size 50-150 .mu.m) as the iron-base powder, and then 2.0 parts of
copper powder (MAKIN METAL POWDERS, AHF-100, particle size 30-50
.mu.m), and 0.8 parts of graphite powder (by NIPPON GRAPHITE
INDUSTRIES, JCPBK, particle size 3-5 .mu.m), as the mechanical
characteristic-improving powders, were added and mixed thereto, and
the toluene was distilled under reduced pressure, and a powder
mixture for powder metallurgy was consequently obtained (the
addition amount of the amide-based lubricant based on 100 parts in
total of the iron-base powder and the mechanical
characteristic-improving powder: 0.3 part).
[0090] <Compression Molding>
[0091] To a metal mold (cylindrical mold, 11.28.phi.), 7.0 g of the
powder mixture for powder metallurgy was put, and compression
molding was performed thereto, at room temperature (25.degree. C.),
at surface pressures of 490.3 MPa (5 t/cm.sup.2) or 686.5 MPa (7
t/cm.sup.2), and thereby green compact 1-1 and green compact 1-2
were obtained respectively.
[0092] <Characteristics of Green Compact>
[0093] The density and demolding pressure in the extraction from
the mold were measured for each of the resulting green compacts 1-1
and 1-2. The results are shown in Table 1.
Examples 2 and 3
Preparation of Amide-Based Lubricant Solution, Preparation of
Powder Mixture for Powder Metallurgy, and Compression Molding
[0094] Green compacts 2-1 and 2-2 (Example 2) and green compacts
3-1 and 3-2 (Example 3) were produced in the same manner as in
Example 1, except that the amide-based lubricant solution was added
so that the addition amount of the amide-based lubricant is 0.4
part (Example 2) or 0.5 part (Example 3) based on 100 parts in
total of the iron-base powder and mechanical
characteristic-improving powder.
[0095] <Characteristics of Green Compact>
[0096] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 2-1
and 2-2 and green compacts 3-1 and 3-2. The results are shown in
Table 1.
Example 4
Preparation of Amide-Based Lubricant Solution, Preparation of
Powder Mixture for Powder Metallurgy, and Compression Molding
[0097] Green compacts 4-1 and 4-2 were produced in the same manner
as in Example 1, except that ethylene-bis-oleic amide (by DIC) was
used as the amide-based lubricant in stead of N-oleyl palmitic
amide used in Example 1.
[0098] <Characteristics of Green Compact>
[0099] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 4-1
and 4-2. The results are shown in Table 1.
Examples 5 and 6
Preparation of Amide-Based Lubricant Solution, Preparation of
Powder Mixture for Powder Metallurgy, and Compression Molding
[0100] Green compacts 5-1 and 5-2 (Example 5) and green compacts
6-1 and 6-2 (Example 6) were produced in the same manner as in
Example 4, except that the amide-based lubricant solution was added
so that the addition amount of the amide-based lubricant was 0.4
part (Example 5) or 0.5 part (Example 6) based on 100 parts in
total of the iron-base powder and the mechanical
characteristic-improving powder.
[0101] <Characteristics of Green Compact>
[0102] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 5-1
and 5-2 and green compacts 6-1 and 6-2. The results are shown in
Table 1.
Example 7
Preparation of Powder Mixture for Powder Metallurgy
[0103] As the amide-based lubricant, N-oleyl palmitic amid powder
was added and mixed to 100 parts of pure iron powder as the
iron-base powder, and 2.0 parts of copper powder and 0.8 parts of
graphite powder, as the mechanical characteristic-improving powder,
were added and mixed thereto, and thereby a powder mixture for
powder metallurgy was obtained (the addition amount of the
amide-based lubricant based on 100 parts in total of the iron-base
powder and the mechanical characteristic-improving powder: 0.3
part).
[0104] Namely, the powder mixture for powder metallurgy was
produced in the same manner as in Example 1 except that the
amide-based lubricant powder (powder of N-oleyl palmitic amide) was
used instead of the amide-based lubricant solution of Example
1.
[0105] <Compression Molding>
[0106] Green compacts 7-1 and 7-2 were produced by performing the
same compression molding as in Example 1 with use of the obtained
powder mixture for powder metallurgy.
[0107] Characteristics of Green Compact>
[0108] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 7-1
and 7-2. The results are shown in Table 2.
Examples 8 and 9
Preparation of Powder Mixture for Powder Metallurgy and Compression
Molding
[0109] Green compacts 8-1 and 8-2 (Example 8) and Green compacts
9-1 and 9-2 (Example 9) were produced in same manner as in Example
7, except that the amide-based lubricant powder was added so that
the addition amount of the amide-based lubricant was 0.4 part
(Example 8) or 0.5 part (Example 9) based on 100 parts in total of
the iron-base powder and the mechanical characteristic-improving
powder.
[0110] <Characteristics of Green Compact>
[0111] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 8-1
and 8-2 and green compacts 9-1 and 9-2. The results are shown in
Table 2.
Example 10
Preparation of Powder Mixture for Powder Metallurgy and Compression
Molding
[0112] Green compacts 10-1 and 10-2 (Example 10) were produced in
the same manner as in Example 7, except that powder of
ethylene-bis-oleic amide was used as the amide-based lubricant
instead of the powder of N-oleyl palmitic amide used in Example
7.
[0113] Namely, the green compacts were produced in the same manner
as Example 4, except that the amide-based lubricant powder (the
powder of ethylene-bis-oleic amide) was used instead of the
amide-based lubricant solution of Example 4.
[0114] <Characteristics of Green Compact>
[0115] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 10-1
and 10-2. The results are shown in Table 2.
Examples 11 and 12
Preparation of Powder Mixture for Powder Metallurgy and Compression
Molding
[0116] Green compacts 11-1 and 11-2 (Example 11) and green compacts
12-1 and 12-2 (Example 12) were produced in the same manner as in
Example 10, except that the amide-based lubricant solution was
added so that the addition amount of the amide-based lubricant was
0.4 part (Example 11) or 0.5 part (Example 12) based on 100 parts
in total of the iron-base powder and the mechanical
characteristic-improving powder.
[0117] <Characteristics of Green Compact>
[0118] The density and demolding pressure in the extraction from
the mold were measured for each of the obtained green compacts 11-1
and 11-2 and green compacts 12-1 and 12-2. The results are shown in
Table 2.
TABLE-US-00001 TABLE 1 Characteristics of Green Compact Surface
Pressure 5 t/cm.sup.2 Surface Pressure 7 t/cm.sup.2 Content of
Green Compact Demolding Green Compact Demolding Amide-based
Lubricant Lubricant Density Pressure Density Pressure Example
(Toluene Solution) (Part) (g/cm.sup.3) (Mpa) (g/cm.sup.3) (Mpa) 1
N-oleyl Palmitic 0.3 6.90 9.63 7.22 14.27 2 Amide (PNT) 0.4 6.92
9.50 7.21 13.82 3 0.5 6.90 8.52 7.19 11.37 4 Ethylene-bis-oleic 0.3
6.94 8.96 7.26 13.31 5 Amide (OBA-N) 0.4 6.94 9.35 7.25 12.44 6 0.5
6.93 8.20 7.20 10.59
TABLE-US-00002 TABLE 2 Characteristics of Green Compact Surface
Pressure 5 t/cm.sup.2 Surface Pressure 7 t/cm.sup.2 Content of
Green Compact Demolding Green Compact Demolding Amide-based
Lubricant Lubricant Density Pressure Density Pressure Example
(Powder) (Part) (g/cm.sup.3) (Mpa) (g/cm.sup.3) (Mpa) 7 N-oleyl
Palmitic 0.3 6.86 12.03 7.19 17.41 8 Amide (PNT) 0.4 6.86 11.52
7.18 15.40 9 0.5 6.87 9.48 7.11 10.10 10 Ethylene-bis-oleic 0.3
6.91 11.79 7.22 17.27 11 Amide (OBA-N) 0.4 6.91 11.33 7.21 15.87 12
0.5 6.94 9.59 7.21 11.89
[0119] It was found from the comparisons of Examples 1 to 6 with
Examples 7 to 12 that by preparing the powder mixture for powder
metallurgy with use of the solution of amide-based lubricant, the
green compact density (strength) is enhanced, and the demolding
pressure is reduced, compared with the case of using the powder of
amide-based lubricant. Further, the results of Examples 1 to 6 show
that the larger the addition amount of the amide-based lubricant
is, the lower the demolding pressure is.
INDUSTRIAL AVAILABILITY
[0120] The present invention is useful for production of a sintered
body with high strength and good appearance.
* * * * *