U.S. patent application number 13/377396 was filed with the patent office on 2012-04-12 for iron-based mixed powder for powder metallurgy.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Takashi Kawano, Tomoshige Ono, Yukiko Ozaki.
Application Number | 20120085201 13/377396 |
Document ID | / |
Family ID | 43386686 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120085201 |
Kind Code |
A1 |
Kawano; Takashi ; et
al. |
April 12, 2012 |
IRON-BASED MIXED POWDER FOR POWDER METALLURGY
Abstract
In an iron-based powder, 0.01% to 5.0% by mass of oxide
particles having an average size of 0.5 .mu.m or more are
contained, whereby the flowability of an iron-based mixed powder is
increased and thereby the density of a green compact is increased,
and ejection force is greatly reduced after compaction, thereby
accomplishing an increase in product quality and a reduction in
production cost.
Inventors: |
Kawano; Takashi; (Chiba,
JP) ; Ono; Tomoshige; (Chiba, JP) ; Ozaki;
Yukiko; (Chiba, JP) |
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
43386686 |
Appl. No.: |
13/377396 |
Filed: |
June 25, 2010 |
PCT Filed: |
June 25, 2010 |
PCT NO: |
PCT/JP2010/061297 |
371 Date: |
December 20, 2011 |
Current U.S.
Class: |
75/252 |
Current CPC
Class: |
C22C 33/0207 20130101;
C22C 1/10 20130101; C22C 33/0228 20130101; B22F 2001/0066 20130101;
B22F 1/0059 20130101 |
Class at
Publication: |
75/252 |
International
Class: |
B22F 1/00 20060101
B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2009 |
JP |
2009-152593 |
Jun 23, 2010 |
JP |
2010-142355 |
Claims
1. An iron-based mixed powder for powder metallurgy, containing an
iron-based powder and 0.01% to 5.0% by mass of particles of an
oxide that have an average size of 0.5 .mu.m or more.
2. The iron-based mixed power for powder metallurgy according to
claim 1, wherein the oxide contains at least one selected from the
group consisting of iron, aluminum, and silicon.
3. The iron-based mixed powder for powder metallurgy according to
claim 1, further containing powder for an alloy.
4. The iron-based mixed powder for powder metallurgy according to
claim 2, further containing powder for an alloy.
5. The iron-based mixed powder for powder metallurgy according to
claim 1, further containing an organic binder.
6. The iron-based mixed powder for powder metallurgy according to
claim 1, further containing a free lubricant.
7. The iron-based mixed powder for powder metallurgy according to
claim 5, further containing a free lubricant.
8. The iron-based mixed powder for powder metallurgy according to
claim 2, further containing an organic binder.
9. The iron-based mixed powder for powder metallurgy according to
claim 3, further containing an organic binder.
10. The iron-based mixed powder for powder metallurgy according to
claim 4, further containing an organic binder.
11. The iron-based mixed powder for powder metallurgy according to
claim 2, further containing a free lubricant.
12. The iron-based mixed powder for powder metallurgy according to
claim 3, further containing a free lubricant.
13. The iron-based mixed powder for powder metallurgy according to
claim 4, further containing a free lubricant.
14. The iron-based mixed powder for powder metallurgy according to
claim 8, further containing a free lubricant.
15. The iron-based mixed powder for powder metallurgy according to
claim 9, further containing a free lubricant.
16. The iron-based mixed powder for powder metallurgy according to
claim 10, further containing a free lubricant.
Description
TECHNICAL FIELD
[0001] The present invention relates to an iron-based mixed powder
suitable for use in powder metallurgy. In particular, the present
invention is intended to increase green density and is also
intended to advantageously reduce the ejection force necessary to
withdraw a green compact from a die after compaction.
BACKGROUND ART
[0002] In a powder metallurgy process, source powders are mixed
together; the mixture is transferred, is filled into a die, and is
then pressed into a formed body (hereinafter referred to as a green
compact); and the green compact is withdrawn from the die and is
then subjected to a post-treatment such as sintering as
required.
[0003] In the powder metallurgy process, in order to achieve an
increase in product quality and a reduction in production cost, it
is necessary to ensure all of high powder flowability in a
transferring step, high compressibility in a pressing step, and low
ejection force in a step of withdrawing the green compact from the
die.
[0004] As for techniques for improving the flowability of
iron-based mixed powders, Patent Literature 1 discloses that the
flowability of an iron-based mixed powder can be improved by adding
a fullerene, which serves as a carbon supply component,
thereto.
[0005] Furthermore, Patent Literature 2 discloses a technique for
improving the flowability of a powder composition for metallurgy by
adding a particulate inorganic oxide with an average particle size
of less than 500 nm thereto.
[0006] However, the use of these techniques is insufficient to
achieve high compressibility and low ejection force while
flowability is maintained.
[0007] In order to increase the density of a green compact or in
order to reduce the ejection force thereof, it is effective to use
a lubricant that has ductility and that is soft at a temperature at
which an iron-based mixed powder is pressed. This is because the
lubricant seeps out of the iron-based mixed powder during pressing
to adhere to a surface of a die and therefore reduces the friction
between the die and the green compact.
[0008] However, the lubricant has ductility and therefore is likely
to adhere to particles of an iron powder and powder for an alloy.
Hence, there is a problem in that the flowability and filling
ability of an iron-based mixed powder are impaired.
[0009] The blending of the above carbon material, fine particles,
and lubricant reduces the theoretical density (the density
determined assuming that the voidage is zero) of the iron-based
mixed powder to cause a reduction in green density; hence, it is
not preferable to blend large amounts of these materials.
[0010] It has been extremely difficult to balance the flowability
of a conventional iron-based mixed powder, high green density, and
low ejection force.
[0011] As for techniques relating to additives for iron-based mixed
powders, Patent Literature 3 discloses a technique in which a
powder of iron oxide (such as mill scale) is added to a powder of
finish-reduced iron to control a dimensional change of a sintered
body.
[0012] As for techniques relating to iron oxide powders, Patent
Literature 4 discloses a method for synthesizing micaceous iron
oxide (MIO) known as a pigment for rust-proof paints for steel
materials. According to the method disclosed in Patent Literature
4, primary particles of .alpha.-iron oxide that have a size of 1
.mu.m to 100 .mu.m and an aspect ratio of 5 to 30 are obtained.
Related Art Document
Patent Literature
[0013] PTL 1: Japanese Unexamined Patent Application Publication
No. 2007-31744
[0014] PTL 2: PCT Japanese Translation Patent Publication No.
2002-515542
[0015] PTL 3: Japanese Unexamined Patent Application Publication
No. 8-325667
[0016] PTL 4: Japanese Unexamined Patent Application Publication
No. 3-131526
SUMMARY OF INVENTION
Problems to be Solved by the Invention
[0017] The present invention has been developed in view of the
aforementioned circumstances and has an object to suggest an
iron-based mixed powder for powder metallurgy. The iron-based mixed
powder can accomplish both an increase in product quality and a
reduction in production cost in such a way that the density of a
green compact is increased by increasing the flowability of the
iron-based mixed powder and ejection force is greatly reduced after
compaction.
Solution to Problem
[0018] The inventors have investigated various additives for use in
iron-based powders for the purpose of achieving the above
object.
[0019] As a result, the inventors have found that the addition of
an appropriate amount of oxide particles with an average size of
0.5 .mu.m or more to an iron-based powder provides significantly
improved flowability and also provides improved green density and
ejection force.
[0020] The present invention is based on the above finding.
[0021] The present invention is as summarized below.
1. An iron-based mixed powder for powder metallurgy contains an
iron-based powder and 0.01% to 5.0% by mass of particles of an
oxide that have an average size of 0.5 .mu.m or more. 2. In the
iron-based mixed powder for powder metallurgy specified in Item 1,
the oxide contains at least one selected from the group consisting
of iron, aluminum, and silicon.
[0022] Needless to say, the oxide refers to an oxide forming the
oxide particles.
3. The iron-based mixed powder for powder metallurgy specified in
Item 1 or 2 further contains powder for an alloy. 4. The iron-based
mixed powder for powder metallurgy specified in any one of Items 1
to 3 further contains an organic binder. 5. The iron-based mixed
powder for powder metallurgy specified in any one of Items 1 to 4
further contains a free lubricant.
Advantageous Effects of Invention
[0023] According to the present invention, not only increased
flowability but also high green density and low ejection force can
be achieved by adding an appropriate amount of oxide particles
having an average size of 0.5 .mu.m or more to an iron-based
powder. This results in an increase in production efficiency and a
reduction in production cost.
BRIEF DESCRIPTION OF DRAWING
[0024] FIG. 1 is a schematic view illustrating the aspect ratio of
powder.
DESCRIPTION OF EMBODIMENTS
[0025] The present invention will now be described in detail.
[0026] In the present invention, oxide particles are used as a
component for imprbving the flowability of an iron-based powder.
The reason is as described below.
[0027] Common iron-based mixed powders contain about 1% by mass of
organic lubricants for the purpose of increasing the flowability of
powder or decreasing the ejection force of green compacts. The
organic lubricants have a specific gravity of about 1.0 and are
significantly lower in specific gravity than iron powders, which
have a specific gravity of 7.8. In general, in the case of mixing
powders that are significantly different in specific gravity from
each other, segregation occurs during mixing to cause a reduction
in flowability or differences in properties between lots.
[0028] Thus, in the case of mixing different types of powders, it
is important that the difference in specific gravity therebetween
is as small as possible.
[0029] When the oxide particles used herein are made of, for
example, iron oxide (hematite), the oxide particles have a specific
gravity of 5.3 and are higher in specific gravity than the organic
lubricants. Therefore, the oxide particles are less affected by the
flow of air in a powder bed during fluidization as compared to the
organic lubricants. In an iron-based mixed powder according to the
present invention, presumably, an organic lubricant is entirely or
partially replaced with the oxide particles and therefore the
segregation of various additives is prevented. This probably
results in the improvement of the flowability of the iron-based
mixed powder.
[0030] In the present invention, when the oxide particles have a
large size, the oxide particles do not cover the surface of the
iron-based powder unlike a flowability-improving powder, disclosed
in Patent Literature 2, containing primary particles with a size on
the order of nanometers but are probably filled in voids in the
iron-based powder in a preferred manner. Thus, in a forming step
presumably, the effective contact area between a green compact and
a die is increased and therefore the springback stress is
distributed. This probably results in a reduction in ejection
force.
[0031] In order to exhibit the above effect, the oxide particles
need to have an average size of 0.5 .mu.m or more. When the average
size of the oxide particles is less than 0.5 .mu.m, the effect of
reducing ejection force cannot be sufficiently obtained. However,
when the average size of the oxide particles is more than 100
.mu.m, the oxide particles cannot be uniformly mixed with
iron-based mixed powders (an average size of about 100 .mu.m)
usually used in powder metallurgy and therefore cannot exhibit the
above effect. Thus, the average size of the oxide particles is
preferably 100 .mu.m or less. The average size of the oxide
particles is more preferably 40 .mu.m or less and further more
preferably 20 .mu.m or less. The average size of the oxide
particles is preferably determined by a method described in Example
1.
[0032] The oxide particles may contain about 20% by mass or less
(the percentage with respect to the oxide particles) of an impurity
other than the oxide. Those having lower impurity content (for
example, 10% by mass or less or 2% by mass or less) are preferably
used if the commercial availability thereof is not difficult. The
impurity is not particularly limited and any impurity (for example,
a metal or another inorganic compound) contained in oxide particles
produced by a known commercial process is not particularly
problematic.
[0033] In the present invention, particles containing an oxide
containing at least one selected from the group consisting of iron,
aluminum, and silicon are particularly advantageous and are
appropriate to the oxide particles. Examples of the oxide include
Fe.sub.2O.sub.3, Al.sub.2O.sub.3, and SiO.sub.2 and are not
particularly limited in component or crystal structure. The content
of an oxide of at least one selected from the group consisting of
iron, aluminum, and silicon in the oxide particles is preferably
about 80% by mass or more (the percentage with respect to the
oxide) and more preferably 98% or more in total.
[0034] In order to carry out the present invention at low cost, a
particulate oxide satisfying the above is preferably readily
available at low cost. In view of availability, an oxide of iron or
an iron-based oxide containing an oxide of iron as a major
component is particularly preferred. Commercially available
examples of the iron-based oxide include those containing about 70%
to 95% by mass (the percentage with respect to the oxide) of an
oxide of iron and about 5% to 30% by mass of an oxide of Al and/or
an oxide of Si in total.
[0035] When the form of powder is viewed form the viewpoint of
aspect ratio, particles with high aspect ratio can be artificially
synthesized. For example, Patent Literature 4 discloses a method
for synthesizing a-iron oxide with an aspect ratio of 5 to 30.
However, this method requires heating and pressurizing for a long
time in the course of synthesis, is irreversibly high in production
cost, and also is not readily available. Thus, the aspect ratio is
preferably less than 5.
[0036] In the present invention, the aspect ratio refers to the
ratio of the thickness to the longitudinal size of powder as shown
in FIG. 1. The aspect ratio of the oxide particles is preferably
determined by a method described in Example 1.
[0037] In the present invention, when the content of the oxide
particles in the iron-based mixed powder is less than 0.01% by
mass, the effect of adding the oxide particles is not obtained.
However, when the content thereof is more than 5.0% by mass, an
extreme increase in ejection force is caused, which is not
preferred. Thus, the content of the oxide particles is 0.01% to
5.0% by mass.
[0038] The lower limit is preferably 0.05% by mass. The upper limit
is preferably 1.0% by mass.
[0039] In the present invention, the following powders are examples
of the iron-based powder, which is a major component of the
iron-based mixed powder: pure iron powders such as atomized iron
powders and reduced iron powders, diffusion alloyed steel powders,
prealloyed steel powders, and hybrid steel powders produced by
diffusion alloy components in prealloyed steel powders. The
iron-based powder preferably has an average particle size of 1
.mu.m or more and more preferably about 10 .mu.m to 200 .mu.m. The
term "major component" as used herein means that the content of the
iron-based powder in the iron-based mixed powder is 50% by mass or
more.
[0040] Examples of powder for an alloy include graphite powders;
powders of metals such as Cu, Mo, and Ni; and metal compound
powders. Other known powders for alloys also can be used. The
strength of a sintered body can be increased by mixing the
iron-based powder with at least one of these powders for
alloys.
[0041] The sum of the contents of these powders for alloys in the
iron-based mixed powder is preferably about 0.1% to 10% by mass.
This is because when the content of these powders for alloys is
0.1% by mass or more or more than 10% by mass, the strength of an
obtained sintered body is advantageously increased or the
dimensional accuracy of the sintered body is reduced,
respectively.
[0042] The powder for an alloy is preferably in such a state
(hereinafter referred to as an iron powder with alloy component
adhered thereon) that the powder for an alloy is attached to the
iron-based powder with an organic binder therebetween. This
prevents the segregation of the powder for an alloy and allows
components in powder to be uniformly distributed therein.
[0043] Herein, an aliphatic amide, a metallic soap, or the like is
particularly advantageous and appropriate to the organic binder.
Other known organic binders such as polyolefins, polyesters,
(meth)acrylic polymers, and vinyl acetate polymers can be used.
These organic binders may be used alone or in combination. In the
case of using two or more the organic binders, at least a part of
the organic binders may be used in the form of a composite melt.
When the content of the organic binder is less than 0.01% by mass,
the powder for an alloy cannot be uniformly or sufficiently
attached to iron powders. However, when the content thereof is more
than 1.0% by mass, the iron powders adhere to each other to
aggregate and therefore flowability may possibly be reduced. Thus,
the content of the organic binder preferably ranges from 0.01% to
1.0% by mass. The content (mass percent) of the organic binder
refers to the percentage of the organic binder in the iron-based
mixed powder for powder metallurgy.
[0044] In order to improve the flowability and formability of the
iron-based mixed powder for powder metallurgy, a free lubricant
(powder) may be added thereto. The content of the free lubricant in
the iron-based mixed powder for powder metallurgy is preferably
1.0% by mass or less. On the other hand, the content of the free
lubricant is preferably 0.01% by mass or more (the percentage with
respect to the iron-based mixed powder). The free lubricant is
preferably a metallic soap (for example, zinc stearate, manganese
stearate, lithium stearate, or the like), a bis amide (for example,
ethylene bis-stearamide or the like), an aliphatic amide (for
example, monostearamide, erucamide, or the like) including an
monoamide, an aliphatic acid (for example, oleic acid, stearic
acid, or the like), a thermoplastic resin (for example, an
polyamide, polyethylene, polyacetal, or the like), which has the
effect of reducing the ejection force of a green compact. A known
free lubricant other than the above free lubricant can be used.
[0045] In the present invention, the content of the organic
lubricant is less than ever and the organic lubricant is replaced
with the oxide particles, whereby flowability and green density can
be improved while excellent ejection force is maintained. That is,
the reduction in content of the organic lubricant usually degrades
ejection force; however, in the present invention, this adverse
effect can be avoided by the addition of the oxide. The use of the
oxide instead of the organic lubricant improves green density.
Furthermore, the presence of the oxide particles improves fluidity.
In order to obtain the above advantages, the content of the organic
lubricant in the iron-based mixed powder is preferably 0.8% by mass
or less, more preferably 0.7% by mass or less, and further more
preferably 0.6% by mass or less. The lower limit of the content of
the organic lubricant is preferably 0.02% by mass, which is the sum
of the lower limit of the content of the organic binder and that of
the free lubricant.
[0046] The organic lubricant contains at least one of the organic
binder, an organic free lubricant, and an organic non-free
lubricant (an organic lubricant attached to an iron powder with a
binder therebetween). The organic non-free lubricant is frequently
substituted by that of the organic binder in view or the function
thereof. Therefore, the sum of the content of the organic binder
and that of the organic free lubricant corresponds to the content
of the organic lubricant.
[0047] The content of iron in the iron-based mixed powder is
preferably 50% by mass or more.
[0048] A method for producing the iron-based mixed powder according
to the present invention is described below.
[0049] The iron-based powder is mixed with the oxide particles
according to the present invention and additives such as a binder
and a lubricant and is further mixed with powder for an alloy as
required. The additives, such as the binder and the lubricant, need
not be necessarily added to the iron-based powder at once. After
primary mixing is performed using a portion of additives, secondary
mixing may be performed using the rest thereof.
[0050] A mixing method is not particularly limited. Any
conventionally known mixer can be used. The following mixer can be
used: for example, an impeller-type mixer (for example, a Henschel
mixer or the like) or a rotary mixer (for example, a V-type mixer,
a double-cone mixer, or the like), which is conventional known.
When heating is necessary, the following mixer is particularly
advantageous and appropriate: a high-speed mixer, a disk
pelletizer, a plough share mixer, a conical mixer, or the like,
which is suitable for heating.
[0051] In the present invention, an additive for property
improvement may be used in addition to the above additives
according to purpose. For example, the addition of a powder of MnS
or the like for machinability improvement is exemplified for the
purpose of improving the machinability of a sintered body.
EXAMPLES
Example 1
[0052] Prepared iron-based powders were two types: Pure Iron Powder
A (an atomized iron powder with an average particle size of 80
.mu.m) and iron powder with alloy component adhered thereon B
prepared by attaching powders for alloys to this pure iron powder
with organic binders therebetween. The powders, for alloys, used
for B were 2.0% by mass of a Cu powder (an average particle size of
25 .mu.m) and 0.8% by mass of a graphite powder (an average
particle size of 5.0 .mu.m). The organic binders used were 0.05% by
mass of monostearamide and 0.05% by mass of ethylene
bis-stearamide. The percentage of each of these additives is a
proportion to iron-based mixed powder.
[0053] Pure Iron Powder A and iron powder with alloy component
adhered thereon B were mixed with oxide particles with an aspect
ratio of less than 5 and free lubricants at various ratios, whereby
iron-based mixed powders for powder metallurgy were obtained. The
oxide particles used were JC (TM) (Fe.sub.2O.sub.3 produced by JFE
Chemical Corporation), MIOX (TM) (an
Fe.sub.2O.sub.3--SiO.sub.2--Al.sub.2O.sub.3 mixture, containing 90%
by mass of Fe.sub.2O.sub.3, 5% by mass of SiO.sub.2, and 3% by mass
of Al.sub.2O.sub.3, the remainder being impurities (each is an
approximate value), produced by Karntner Montanindustrie
Gesellschaft mbH), and A31 (TM) (Al.sub.2O.sub.3 produced by Nippon
Light Metal Company, Ltd.). The free lubricants used were zinc
stearate, ethylene bis-stearamide, and erucamide in addition to
0.1% by mass of lithium stearate. The iron powders and the oxide
particles were measured for average particle size by a laser
diffraction/scattering method (according to JIS R 1629) and the
particle size at 50% in the particle size distribution (the
cumulative volume fraction) was used. The oxide particles were
observed with a scanning electron microscope. The average of the
aspect ratios of randomly selected 50 particles was used as the
aspect ratio.
[0054] The blending ratio of these mixed powders is shown in Table
1. The blending ratio is a proportion to each iron-based mixed
powder for powder metallurgy. For Pure Iron Powder A, the content
(mass percent) of an organic lubricant is equal to the content of a
free lubricant shown in Table 2. For iron powder with alloy
component adhered thereon B, the content thereof is equal to the
sum of the content (0.1% by mass) of an organic binder and the
content of a free lubricant shown in Table 2.
[0055] Each obtained iron-based mixed powder was filled into a die
and was then pressed at room temperature with a pressure of 980
MPa, whereby a cylindrical green compact with a diameter of 11 mm
and a height of 11 mm was obtained. In this operation, the
flowability of the iron-based mixed powder, the ejection force
needed to withdraw the green compact from the die, and the density
of the green compact were measured. The measurement results are
shown in Table 1. The flowability of the iron-based mixed powder
was evaluated in accordance with JIS Z 2502.
[0056] Herein, the flowability is good when the fluidity is not
more than 30 seconds per 50 grams, the compressibility is good when
the green density is 7.35 Mg/m.sup.3 or more, and the drawability
is good when the ejection force is 25 MPa or less.
TABLE-US-00001 TABLE 1 Oxide particles Average Free lubricant
Properties Type of particle Content Content Green Ejection
iron-based size Aspect (mass (mass Fluidity density force No.
powder Type (.mu.m) ratio percent) Type percent) (sec/50 g)
(Mg/m.sup.3) (MPa) Remarks 1 B Iron oxide 1.0 1 0.05 Zinc stearate
0.4 23.9 7.38 17 Example 1 2 A Iron oxide 1.0 1 1.0 Zinc stearate
0.4 23.9 7.36 17 Example 2 3 B
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 0.8 2 0.2
Ethylene 0.1 21.0 7.42 18 Example 3 mixture bis-stearamide 4 B
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 4.0 2 0.2
Ethylene 0.1 21.1 7.42 18 Example 4 mixture bis-stearamide 5 B
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 18 3 0.2
Erucamide 0.1 21.8 7.43 21 Example 5 mixture 6 B
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 38 4 0.2
Ethylene 0.1 21.3 7.42 22 Example 6 mixture bis-stearamide 7 A
Aluminum oxide 5.0 1 0.1 Erucamide 0.4 23.1 7.38 19 Example 7 8 B
Aluminum oxide 0.2 1 0.2 Erucamide 0.4 Not flow 7.33 16 Comparative
Example 1 9 A Iron oxide 0.08 1 0.2 Erucamide 0.8 Not flow 7.29 45
Comparative Example 2 10 B Iron oxide 180 2 0.2 Erucamide 0.8 Not
flow 7.29 45 Comparative Example 3 11 B
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 38 4 0.005
Erucamide 0.3 Not flow 7.31 25 Comparative mixture Example 4 12 B
Iron oxide 20 1 6.0 Zinc stearate 0.2 30.7 7.31 35 Comparative
Example 5 *A: Pure iron powder, B: Iron powder with alloy component
adhered thereon
[0057] As is clear from Table 1, an iron-based mixed powder
excellent in flowability, compressibility, and ejection force can
be obtained by the addition of an appropriate amount of oxide
particles according to the present invention.
[0058] In contrast, comparative examples are poor in at least one
of flowability, green density, and ejection force.
Example 2
[0059] A prepared iron-based powder was the same as iron powder
with alloy component adhered thereon B described in Example 1. The
iron-based powder was mixed with oxide particles (an aspect ratio
of less than 5) and free lubricants as shown in Table 2, whereby
iron-based mixed powders for powder metallurgy were obtained. The
oxide particles used were similar to the commercial products
described in Example 1. The percentage of each additive shown in
Table 2 is a proportion to corresponding iron-based mixed powder.
The flowability of each iron-based mixed powder, the ejection force
needed to withdraw a green compact (obtained from the iron-based
mixed powder) from the die, and the density of the green compact
were measured in the same manner as that described in Example 1.
The measurement results are summarized in Table 2.
TABLE-US-00002 TABLE 2 Content of Oxide powder Content of Free
lubricant organic Average Properties binder Content lubricant
particle Content Green Ejection mass mass mass size Aspect mass
Fluidity density force No. percent Type percent percent Type
(.mu.m) ratio percent sec/50 g Mg/m.sup.3 MPa Remarks 13 0.1
Ethylene bis- 0.1 0.20
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 4 2 0.05 24.6
7.41 20 Example stearamide mixture 14 0.1 Ethylene bis- 0.3 0.40
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 4 2 0.2 23.8
7.43 19 Example stearamide mixture 15 0.1 Ethylene bis- 0.4 0.50
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 4 2 0.2 24.2
7.42 19 Example stearamide mixture 16 0.1 Ethylene bis- 0.7 0.80
Fe.sub.2O.sub.3.cndot.SiO.sub.2.cndot.Al.sub.2O.sub.3 4 2 0.2 29.0
7.35 15 Example stearamide mixture 17 0.1 Ethylene bis- 0.1 0.20
Not used -- -- -- 28.2 7.34 35 Compar- stearamide ative Example 18
0.1 Ethylene bis- 0.4 0.50 Not used -- -- -- Not flow 7.33 22
Compar- stearamide ative Example 19 0.1 Ethylene bis- 0.5 0.60 Not
used -- -- -- Not flow 7.30 20 Compar- stearamide ative Example 20
0.1 Ethylene bis- 0.7 0.80 Not used -- -- -- Not flow 7.27 18
Compar- stearamide ative Example 21 0.1 Ethylene bis- 0.2 0.30 Iron
oxide 1 1 0.2 24.2 7.41 16 Example stearamide 22 0.1 Ethylene bis-
0.4 0.50 Aluminum 5 1 0.2 24.6 7.42 15 Example stearamide oxide
[0060] Table 2 shows that iron-based mixed powders (Nos. 14 and 15)
which contain iron oxide particles (particles of an
Fe.sub.2O.sub.3--SiO.sub.2--Al.sub.2O.sub.3 mixture) and which have
a reduced organic lubricant content of 0.4% to 0.5% by mass have
substantially equal ejection force and also have significantly
improved green density and flowability as compared to, for example,
an iron-based mixed powder (No. 20) containing 0.8% by mass of an
organic lubricant. As is clear from No. 13, good flowability, green
density, and ejection force can be obtained even though an organic
lubricant is further reduced.
[0061] In the case of changing an organic binder, a free lubricant,
powder for an alloy, and/or oxide particles (in particular, oxide
particles containing iron, aluminum, and/or silicon) or in the case
of adding powder for machinability improvement, substantially the
same results as those described in Example 1 or 2 were
obtained.
INDUSTRIAL APPLICABILITY
[0062] Not only flowability but also green density and ejection
force can be improved by adding an appropriate amount of oxide
particles according to the present invention to an iron-based
powder. Therefore, production efficiency can be increased and
production costs can be reduced.
REFERENCE SIGNS LIST
[0063] 1 longitudinal size
[0064] 2 thickness
* * * * *