Note: Descriptions are shown in the official language in which they were submitted.
CA 02255861 1998-11-17
IRON BASE POWDER MIXTURE FOR POWDER METALLURGY EXCELLENT
IN FLUIDITY AND MOLDABILITY, METHOD OF PRODUCTION THEREOF,
AND METHOD OF PRODUCTION OF MOLDED ARTICLE BY USING THE
IRON BASE POWDER MIXTURE
Technical Field
The present invention relates to an iron-based
powder composition for powder metallurgy comprising an iron-
based powder such as iron powders and alloy steel powders;
an alloying powder such as graphite powder, and copper
powder; and a lubricant. More particularly the present
invention relates to an iron-based powder composition for
powder metallurgy which causes less particle segregation of
the additive and less generation of dust, and has excellent
flowability and compactibility over a broad temperature
range from room temperature to about 200°C. The present
invention relates also to a process for production of the
iron-based powder composition and a process for production
of a compact from the composition.
Background Art
Iron-based powder compositions for powder metallurgy
have been produced generally by mixing an iron powder as the
base material, and an alloying powder such as copper
powders, graphite powders, and iron phosphide powders, and,
if necessary, a machinability-improving powder, and a
CA 02255861 1998-11-17
lubricant such as zinc stearate, aluminum stearate, and lead
stearate. The lubricant has been selected in consideration
of its mixability with the iron powder and its removability
in the sintering process.
In recent years, in powder metallurgy, sintered
members are demanded to have higher strength. To meet the
demand, a "warm compaction technique" has been developed in
which powdery material filled in a metal die is. compacted
with heating at a certain temperature to obtain a compact
having a higher density and a higher strength (See, for
example, Japanese Patent Application Laid-Open Gazette
(Kokai) No. Hei.2-156002, Japanese Patent Publication
(Kokoku) No. Hei.7-103404, U.S. Patent 5,256,185, and U.S.
Patent 5,368,630). The lubricant added to the iron powder
in the warm compaction technique should have lubricity in
the compaction process in addition to the above required
properties. This lubricity is important to improve the
compactibility by reducing frictional resistance between the
iron powder particles and between the metal die and the
formed compact by melting a part or the entire of the
lubricant and dispersing it uniformly throughout the iron
powder particle interspace. However, a conventional powder
mixture is liable to cause particle segregation of an
alloying powder or other additive disadvantageously. A
powder mixture generally contains powder particles having
various particle sizes, various particle shapes, and
different particle densities, so that segregation tends to
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occur during transportation after the mixing, on charging
into or discharging from a hopper, or during compacting.
For example, a mixture of iron-based powder and
graphite powder is known to undergo particle segregation
during truck transportation by vibration in a transporting
vessel to separate graphite particles on the powder surface.
A powder composition charged into a hopper undergoes
segregation during movement within the hopper, causing
variation of graphite powder content in the discharged
powder composition from the initial stage to the end stage
of the discharge. The final sintered articles produced from
the segregated nonuniform powder composition are liable to
vary in chemical composition, dimension, and strength, which
can make the products inferior. The graphite powder or an
additive, which is usually fine powdery, increases the
specific surface area of the powder composition to lower the
flowability of the composition. The lower flowability of
the composition decreases the speed of filling the powder
composition into a die cavity, lowering the compact
production rate.
For preventing the segregation of the powder
composition, addition of a binder is disclosed in Japanese
Patent Application Laid-Open Gazette Nos. Sho.56-136901 and
Sho.58-28321. However, a larger amount of addition of a
binder to prevent the segregation in the powder composition
poses another problem of fall of the flowability of the
entire powder composition disadvantageously.
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The inventors of the present invention disclosed use
of a co-melted mixture of a metal soap or a wax and an oil
as a binder in Japanese Patent Application Laid-Open Gazette
Nos. Hei.l-165701 and Hei.2-47201. The disclosed binder
reduces remarkably the segregation of the powder composition
and the scattering of dust, and improves the flowability.
However, this technique poses another problem of variation
of the flowability of the powder composition with lapse of
time owing to the above method of segregation prevention,.
namely the increase of the amount of the binder.
The inventors of the present invention disclosed use
of a co-melted mixture of a high-melting oil and a metal
soap as a binder in Japanese Patent Application Laid-Open
Gazette No. Hei.2-57602. This technique reduces
deterioration with time of the properties of the co-melted
mixture and deterioration with time of flowability of the
powder composition. This technique, however, poses still
another problem such that the apparent density of the powder
composition changes because a high-melting saturated fatty
acid in a solid state and a metal soap are mixed with the
iron-based powder. To solve this problem, the inventors of
the present invention disclosed, in Japanese Patent
Application Laid-Open Gazette No. Hei.3-162502, a method in
which the surface of the iron-based powder particles is
coated with a fatty acid, an alloying powder or a like
additive is allowed to adhere thereto through a co-melted
mixture of a fatty acid and a metal soap, and then a metal
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soap is added onto the outer surface thereof.
The above techniques disclosed in Japanese Patent
Application Laid-Open Gazette Nos. Hei.2-57602 and Hei.3-
162502 solve the problems of segregation in the powder
composition and generation of dust to a considerable extent.
With this technique, however, the flowability of the powder
composition is insufficient: especially the flowability in
"warm compaction" in which the powder composition heated to
about.150°C is filled in a hot die and is compacted.
Further, the improvements of compactibility of the powder
composition in warm compaction disclosed in Japanese Patent
Application Laid-Open Gazette Nos. Hei.2-156002, and Hei.7-
103404, U.S. Patent 5,256,185, and U.S. Patent 5,368,630
mentioned above are not sufficient in the flowability of the
powder composition in warm compaction owing to liquid bridge
formation by a low-melting lubricant component between
particles. The insufficient flowability not only reduces
the productivity of the compacts but also causes variation
of the density of the compacts and variation of the
properties of the final sintered products. Furthermore, the
warm compaction technique disclosed in above Japanese Patent
Application Laid-Open Gazette No. Hei.2-156002, etc. enables
production of iron-based compact having high density and
high strength, but requires stronger ejection force for
removal of the compact from the die and is liable to cause
scratches on the compact surface or to shorten the life of
the die.
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The present invention intends to provide an iron-
based powder composition for powder metallurgy excellent in
flowability and compactibility in comparison with
conventional ones at room temperature and in warm
compaction, and intends also to provide a process for
producing the powder composition, and a process for
producing a compact having a higher density and a higher
strength.
Disclosure of the Invention
Flowability of metal powder is extremely impaired
generally by addition of a lubricant or a like organic
material. The inventors of the present invention made
investigation on this problem, and found that frictional
resistance and adhesive force between the metal powder and
the organic material impairs the flowability. Therefore,
the inventors made comprehensive study on reduction of the
frictional force and the adhesive force, and found that the
frictional resistance can be reduced by surface treatment
(coating) of the metal powder particles with a certain
organic material which is stable up to the warm compaction
temperature (about 200°C), and that the adhesion by
electrostatic force can be decreased by bringing the surface
potential of the metal powder particles to the surface
potential of the organic material (except the above surface
treating material) to retard contact electrification between
different kind of particles on mixing.
Further, the inventors of the present invention made
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investigation on solid lubricants for improvement of
compactibility of a powder composition, and found that the
force for removing a compact from a die after compaction
(hereinafter referred to as ejection force) can be reduced
to improve compact productivity by use of an organic or
inorganic compound having a layer crystal structure in a
temperature range from room temperature to warm compaction
temperature, or by use of a thermoplastic resin or elastomer
capable of undergoing plastic deformation at a temperature
higher than 100°C in warm compaction. They also found that
the coating of the metal powder surface with the above
surface treating material for flowability improvement
reduces secondarily the ejection force to improve the
COmpaCt1b111ty. The present invention has been accomplished
on the basis of the above findings:
The present invention provides an iron-based powder
composition for powder metallurgy having higher flowability
and higher compactibility, comprising an iron-based powder,
a lubricant, and an alloying powder, at least one of the
iron-based powder, the lubricant, and the alloying powder
being coated with at least one surface treatment agent
selected from the group of surface treatment agents below:
Surface treatment agents
Surface treatment agents: organoalkoxysilanes,
organosilazanes, titanate coupling agents, fluorine-
containing silicon silane coupling agents.
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The present invention provides also an iron-based
powder composition for powder metallurgy having higher
flowability and higher compactibility, comprising an iron-
based powder, a lubricant fixed by melting to the iron-based
powder, an alloying powder fixed to the iron-based powder by
the lubricant, and a free lubricant powder, at least one of
the iron-based powder, the lubricant, and the alloying
powder being coated with at least one surface treatment
agent selected from the group shown above.
The surface treatment agent selected from the above
group may be replaced by a mineral oil or silicone fluid in
the present invention. The mineral oil is preferably an
alkylbenzene.
The iron-based powder as the base in the present
invention includes pure iron powder such as atomized iron
powder, and reduced.iron powder; partially diffusion-alloyed
steel powder; and completely alloyed steel powder. The
partially diffusion-alloyed steel powder is preferably a
steel powder alloyed partially with one or more of Cu, Ni,
and Mo. The completely alloyed steel powder is preferably a
steel powder alloyed with Mn, Cu, Ni, Cr, Mo, V, Co, and W.
The alloying powder includes graphite powders,
copper powders, and cuprous oxide powders as well as MnS
powders, Mo powders, Ni powders, B powders, BN powders, and
boric acid powders. The alloying powder may be used singly
or in combination of two or more thereof. Graphite powders,
copper powders, and cuprous oxide powders are especially
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CA 02255861 1998-11-17
s.
preferred since they increase the strength of the sintered
article as the final product. The alloying powder is
incorporated into the composition at a content ranging from
0.1 to 10 wt~ relative to the iron-based powder (100 wt~),
since the final sintered article has excellent strength at a
content of 0.1 wt~ or more of the graphite powder; a powder
of a metal such as Cu, Mo, and Ni; or a boron powder, but
impairs dimensional accuracy of the final sintered product
at a content of higher than 10 wt~.
The aforementioned organoalkoxysilane as the surface
treatment agent is a substance having a structure of R4_mSi-
( OCnH2n+i ) ~ ( where R is an organic group, n and m aide
respectively an integer, and m=1-3). The organic group R
may have a substituent or be not substituted. In the
present invention, the organic group R preferably has no
substituent. The substituent is preferably selected from
the groups of acryl, epoxy, and amino.
The organosilazane includes those represented by any
of the general formulas : RnSi ( NHz ) 4_n, ( R3Si ) zNH,
R3SiNH( RZSiNH )nSiR3, ( R~S11NH )n, arid R3SiNH( RzSiNH )nSiR3.
The lubricant in the present invention is a fatty
acid amide and/or a metal soap. This lubricant prevents
surely segregation of the iron-based powder composition and
dust generation, and improves flowability and
compactibility. The fatty acid amide is contained
preferably at a content of from 0.01 to 1.0 wt~,.and the
metal soap is preferably contained at a content from 0.01 to
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1.0 wt~ based on the weight of the powder composition. The
fatty acid amide includes ethylenebis(stearamide), and bis-
fatty acid amides. The metal soap includes calcium
stearate, and lithium stearate.
The lubricant also includes inorganic compounds
having a layer crystal structure, organic compounds having a
layer crystal structure, thermoplastic resins, and
thermoplastic elastomers. The lubricant may be employed
singly or in combination of two or more thereof. The
inorganic compound having a layer crystal structure is
preferably one or more of graphite, carbon fluoride, and
MoSa. The organic compound having a layer crystal structure
is selected from melamine-cyanuric acid adduct (MCA) and a-
alkyl-N-alkylaspartic acid. The thermoplastic resin is
preferably one or more selected from polystyrene, nylon, and
fluoroplastics in a powder state having a particle size of
not more than 30 um. The thermoplastic elastomer is
preferably in a powder state having a particle size of not
more than 30 um. The thermoplastic elastomer is more
preferably one or more materials selected from styrene block
copolymer (SBC), thermoplastic elastomer olefin (TEO),
thermoplastic elastomer polyamide (TPAE), and thermoplastic
elastomer silicone. The fatty acid includes linoleic acid,
oleic acid, lauric acid, and stearic acid.
The "free lubricant powder" in the present invention
exists in a simple mixed state without adhering to the iron-
based powder or the alloying powder, and is contained in the
. ;,
CA 02255861 1998-11-17
iron-based powder composition in an amount preferably from
25~ to 80~ by weight based on the total weight of the
lubricants added.
The above iron-based powder composition of the
present invention is produced by the process described
below. This process is also included in the present
invention.
In a typical process for producing the iron-based
powder composition for powder metallurgy having higher
flowability and higher compactibility of the present
invention by fixing an alloying powder by a molten lubricant
onto an iron-based powder, the process comprises a first
mixing step of mixing, with the iron-based powder and the
alloying powder, two or more lubricants selected from the
lubricants shown below to obtain a mixture; a melting step
of stirring the mixture obtained in the first mixing step
with heating up to a temperature higher than the melting
point of one of the lubricants to melt the lubricant having
a melting point lower than that temperature; a surface
treating-fixing step of cooling with stirring the mixture
after the melting step, adding a surface treatment agent in
a temperature range from 100 to 140°C, and fixing the
alloying powder onto the surface of the iron-based powder by
the molten lubricant; and a second mixing step of mixing at
least one lubricant selected from the group of lubricants
shown below with the mixture after the surface treating-
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t,
fixing step.
Group
Lubricants: fatty acid amides, metal soaps, thermoplastic
resins, thermoplastic elastomers, inorganic materials having
layer crystal structure, and organic materials having a
layer crystal structure.
In the first mixing step in the present invention,
preferably one or more lubricants are selected from the
aforementioned group of the lubricants, and one of the
lubricants is preferably a fatty acid amide. Alteratively
in the first mixing step, one or more lubricants may be
selected from the metal soaps and the above lubricants, and
the aforementioned one of the lubricants may be a metal
soap. Only one lubricant may be used in the present
invention.
In another typical process for producing the iron-
based powder composition having excellent flowability and
compactibility of the present invention for powder
metallurgy by fixing an alloying powder by a molten
lubricant onto an iron-based powder, the process comprises a
surface-treating step of coating the iron-based powder and
the alloying powder with a surface treatment agent; a first
mixing step of mixing, with the iron-based powder and the
alloying powder after the surface-treating step, two or more
lubricants selected from the lubricants shown above to
obtain a mixture; a melting step of stirring the mixture
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after the first mixing step with heating up to a temperature
higher than the melting point of one of the lubricants; a
fixing step of cooling with stirring the mixture after the
melting step, and fixing the alloying powder onto the
surface of the iron-based powder by the molten lubricant;
and a secondary mixing step of mixing at least one lubricant
selected from the lubricants shown above with the mixture
after the fixing step.
In this embodiment also, in the first mixing step,
preferably the lubricants are selected from the
aforementioned group of the lubricants, and the
aforementioned one of the lubricants is preferably a fatty
acid amide. Alteratively, in the first mixing step, the one
or more lubricants are selected from the metal soaps and the
above lubricants, and one of the lubricants is a metal soap.
Otherwise, in the first mixing step, two or more lubricants
are selected from fatty acids, fatty acid amides, and metal
soaps, and the same lubricants are used in the second mixing
step. Use of only one lubricant is acceptable also in this
embodiment.
In the above production processes, one or more
surface treatment agents are employed which are selected
from organoalkoxysilanes, organosilazanes, titanate coupling
agents, and fluorine-containing silicon silane coupling
agents. The above surface treatment agent may be replaced
by a mineral oil or silicone fluid. The weight ratio of the
lubricant added in the second mixing step is preferably in
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the range of from 25~ to 80~ by weight based on the total
weight of the lubricants added in the first and second
mixing steps.
The process for producing a compact of the present
invention is characterized in that any of the aforementioned
iron-based mixture is compressed in a die and then the
formed compact is ejected therefrom wherein the temperature
of the iron-based powder composition in the die is
controlled to be higher than the lowest of the melting
points of the lubricants contained in the composition but is
lower than the highest thereof.
The main constitutional requirements of the present
invention are described above. The effects of the surface
treatment agent and the lubricants on the flowability and
the compactibility are described below in detail, which are
the most important points of the present invention.
Generally, flowability of a metal powder is
extremely impaired by addition of an organic material like a
lubricant as described above. This is caused by high
frictional resistance and strong adhesion force between the
metal powder and the organic material. This problem may be
solved by treating (coating) the surface of the metal powder
with a specific organic material to reduce the frictional
force and to retard electrostatic adhesion between the
different kinds of particles by bringing the surface
potential of the metal powder to that of the organic
material (excluding the surface treatment agent of the
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present invention). In other words, the flowability of the
powder composition can be improved by synergistic effects of
lowered frictional resistance and the lowered contact
electrification. Thereby, the flowability can be achieved
stably to enable warm compaction in a temperature range from
room temperature to about 200°C.
The organic material used therefor in the present
invention includes organoalkoxysilanes, organosilazanes,
silicone fluids, titanate coupling agents, and fluorine-.
containing silicon silane coupling agents. Such an organic
material, namely a surface treatment agent, has a
lubricating function owing to its bulky molecular structure
and is effective in a broad temperature range of from room
temperature to about 200°C because of its stability at high
temperatures in comparison with fatty acids, mineral oils,
and the like. In particular, the organoalkoxysilane,
organosilazane, titanate coupling agent or fluorine-
containing silicon silane coupling agent undergoes
condensation reaction by a functional group thereof with a
hydroxy group existing on the surface of a metal powder to
form chemical bonding of the organic material onto the
surface of the metal powder particle. Thereby, the surface
of the metal powder particles is modified, and the effect of
modification is remarkable at high temperatures without
separation or flowing-away of the organic material.
The organoalkoxysilane has an organic group or
groups which may be unsubstituted or substituted by a group
CA 02255861 1998-11-17
of acryl, epoxy, or amino, but unsubstituted one is
preferred. The organoalkoxysilane may be a mixture of
different ones. However, an epoxy-containing one and an
amino-containing one should not be mixed since they react
together to cause deterioration. The number of alkoxy group
( CnHzn+~O- ) in the organoalkoxysilane is preferably less .
The organoalkoxysilane having an unsubstituted
organic group includes methyltrimethoxysilane,
phenyltrimethoxysilane, and diphenyldimethoxysilane. The
one having an acryl-substituted organic group includes y-
methacryloxypropyl-trimethoxysilane. The one having an
epoxy-substituted organic group includes 'y-glycidoxypropyl-
trimethoxysilane. The one having an amino group includes N-
~i(aminoethyl)-y-aminopropyl-trimethoxysilane. Of the above
organoalkoxysilanes, the fluorine-containing silicon silane
coupling agents are useful in which a part of the hydrogen
atoms in the organic group are replaced by fluorine. The
titanate coupling agent includes isopropyltriisostearoyl
titanate.
The organosilazane is preferably an alkylsilazane.
A polyorganosilazane having a higher molecular weight may be
used.
In place of the above surface treatment agents,
silicone fluid, or a mineral oil is useful in the present
invention. The silicone fluid is bulky, and reduces
frictional resistance between particles by adhesion onto the
surface of the metal powder particles to improve flowability
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. x~
of the powder. This lubrication effect is given over a
broad temperature range owing to its thermal stability. The
silicone fluid useful as the surface treatment agent
includes dimethyl silicone fluid, methylphenyl silicone
fluid, methylhydrogen silicone fluid,
methylpolycyclosiloxanes, alkyl-modified silicone fluid,
amino-modified silicone fluid, silicone-polyether
copolymers, higher aliphatic acid-modified silicone fluid,
epoxy-modified silicone fluid, and fluorine-modified
silicone fluid. The mineral oil is useful because it
improves flowability of a powder and is thermally stable to
give the lubricating effect over a broad temperature range.
An alkylbenzene is preferred as the mineral oil, but is not
limited thereto in the present invention.
The surface treatment agent is added to the iron-
based powder composition in an amount ranging from 0.001 to
1.0 wt~ based on treated powder (100 wt~). With the
addition of less than 0.001 wt~, the flowability will become
lower, whereas with the addition of more than 1.0 wt~, the
flowability will become lower.
Next, the lubricant is explained below. The
lubricant is incorporated into the powder composition for
the following reasons. Firstly, the lubricant serves as a
binder for fixing the alloying powder. to the iron-based
powder to prevent segregation of the alloying powder and
generation of dust. Secondly, the lubricant promotes
rearrangement and plastic deformation of the powder in the
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compaction process to increase the green density of the
compact owing to lubrication action mainly in a solid state.
Thirdly, the lubricant reduces frictional resistance between
the die wall and the formed compact at the ejection of the
compact from the die to decrease the ejection force.
For achieving such effects, the powder composition
in the present invention is prepared by mixing the alloying
powder and the lubricant into the iron-based powder, heating
the composition at a temperatufe higher than the melting.
point of at least one of the lubricants, and cooling it.
When only one kind of lubricant is used, the lubricant is
melted. When two or more kinds of lubricants are used, one
lubricant having a melting point of lower than the heating
temperature is melted. The melted lubricant forms liquid
bridges between the iron-based powder and the alloying
powder or the unmelted lubricant near the iron-based powder
particles to allow the alloying powder and/or the unmelted
lubricant to adhere to the surface of the iron-based powder.
By solidification of the melted lubricant, the alloying
powder is fixed to the iron-based powder. For example, with
two lubricants having respectively a melting point of 100°C
and 146°C, the composition may be heated to 160°C to melt
the two lubricants, or may be heated to 130°C to melt one
lubricant with the other lubricant kept unmelted.
If the heating temperature for melting the lubricant
exceed 250°C, oxidation of the iron-based powder proceed to
lower its compactibility. Therefore, at least one lubricant
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has preferably a melting point lower than 250°C to conduct
heating at a temperature lower than 250°C.
In compaction of the iron-based powder composition,
the lubricant as a binder promotes arrangement and plastic
deformation of the powder. Therefore, the lubricant is
desirably dispersed uniformly on the surface of the iron-
based powder. On the other hand, ejection force on removal
of the compact from the die is reduced by the lubricant
existing in a solid state on the surface of the compact,.the
lubricant liberated from the iron-based powder surface, and
the lubricant sticking onto the iron-based powder surface in
an unmelted state during the preparation of the composition.
The latter is more important.
For achieving both of the above effects
simultaneously, the amount of the free lubricant existing in
the interspace of the iron-based powder particles is
adjusted to be in the range from 25~ to 80~ by weight based
on the total amount of the lubricant. With the free
lubricant of less than 25~ by weight, the ejection force for
removing the compact is not decreased, and scratches can be
formed on the surface of the compact, whereas with the free
lubricant of more than 80~ by weight, the fixation of the
alloying powder onto the iron-based powder is weak, causing
segregation of the alloying powder to result in variation of
the quality of the final sintered product. Incidentally,
for increasing the free lubricant in the powder composition,
the lubricant is supplementally added in the second mixing
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step.
The lubricant is preferably a fatty acid amides
and/or a metal soaps, and additionally at least one material
selected from inorganic compounds having a layer crystal
structure, organic compounds having a layer crystal
structure, thermoplastic resins, and thermoplastic
elastomers is added preferably thereto. More preferably, a
fatty acid is added into a fatty acid amides and/or a metal
soaps.
The use of a material having a layer crystal
structure reduces the ejection force required after the
compaction, improving the compactibility. This is
considered to be due to the fact that the material can
readily be cleaved along the crystal plane by shearing force
in the compaction to reduce the frictional resistance
between the particles in the compact and facilitate slippage
between the compact and the die. The inorganic material
having a layer crystal structure includes graphite, MoSz, and
carbon fluorides. A smaller particle size is effective for
reduction of the ejection force.
The organic compound having a layer crystal
structure includes melamine-cyanuric acid adduct (MCA), and
R-alkyl-N-alkylaspartic acid.
Further addition of a thermoplastic resin or a
thermoplastic elastomer to the iron-based powder and the
alloying powder reduces the ejection force in compaction,
especially in warm compaction. The thermoplastic resin has
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CA 02255861 1998-11-17
lower yield stress at higher temperature, and is deformed
readily by lower pressure. In warm compaction of a metal
powder containing particulate thermoplastic resin by
heating, the thermoplastic resin particles undergoes plastic
deformation readily among the metal particles or between the
metal particles and the die wall to reduce the frictional
resistance between the metal faces.
The thermoplastic elastomer is a material having a
mixed phase texture having a thermoplastic resin (rigid
phase) and a rubber-structured polymer (flexible phase).
With elevation of the temperature, the yield stress of the
rigid phase of the thermoplastic resin decreases to cause
deformation readily at a lower stress. Therefore, the
particulate thermoplastic elastomer contained in the metal
particles gives the same effects as the aforementioned
thermoplastic resin in warm compaction. The suitable
particulate thermoplastic resin includes polystyrene, nylon,
polyethylene, and fluoroplastics. The thermoplastic
elastomer,has preferably a rigid phase of resins including
styrenic resins, olefinic resins, amide resins, and silicone
resins. Of these, styrene-acrylic copolymers, styrene-
butadiene copolymers are preferred. The above thermoplastic
resin or the thermoplastic elastomer has a particle size of
not larger than 30 um, preferably in the range of from 5 to
20 um. With the particle size of larger than 30 um, the
resin or elastomer does not dispersed sufficiently among the
metal particles, not giving the desired lubrication effects.
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Alternatively, the lubricant may be a fatty acid
amide and/or a metal soap, and if desired further, a fatty
acid may be incorporated. However, the fatty acid, which
has generally a low melting point, forms liquid bridges by
melting between the iron-based powder particles when exposed
to a temperature higher than 150°C, tending to lower the
flowability of the powder composition. Therefore, it should
be used at a temperature not higher than about 150°C.
The last description on the lubricant is shown .
below. The lubricant is incorporated into the iron-based
powder composition in a total amount ranging from 0.1 to 2.0
wt~ based on the iron-based powder (100 wt~). At the
lubricant content of less than 0.1 wt~, the compactibility
of the powder composition will be lower, whereas at the
lubricant content of more than 2.0 wt~, the green density of
the compact produced from the powder composition will be
lower to give lower strength of the compact. In the present
invention, one or more lubricants selected from metal soaps
and fatty acid amides are preferably incorporated as a part
or the entire of the lubricant. The metal soap includes
zinc stearate, lithium stearate, lithium hydroxystearate,
calcium stearate, and calcium laurate. The metal soap is
preferably incorporated at a content ranging from 0.01 to
1.0 wt~ based on the iron-based powder composition (100
wt~). At the metal soap content of higher than 0.01 wt~,
the flowability of the composition is improved, whereas at
the content of higher,than 1.0 wt~, the strength of the
22
CA 02255861 1998-11-17
compact produced from the composition is lower. The
aforementioned fatty acid amide is selected from fatty acid
monoamides and fatty acid bisamides. The fatty acid amide
is preferably incorporated into the iron-based powder
composition at a content ranging from 0.01 to 1.0 wt~ based
on the iron-based powder composition (100 wt~). At the
fatty acid amide content of higher than 0.01 wt~, the
compactibility of the powder composition is improved,
whereas at the content thereof higher than 1.0 wt~, the .
density of the compact is lower.
In the present invention, the surface treatment
agent employed for the purpose of improving flowability also
serves to decrease the ejection force of the compact in the
compaction of the powder composition as a secondary effect.
The mechanism thereof is described below.
In production of a compact from a powdery matter by
warm compaction, since the density of the compact is high,
the metal powder particles on the compact sixrface tend to
adhere to a die wall by compaction pressure, thereby a large
ejection force being required for removal of the compact
from the die, and the compact surface being scratched. By
preliminarily coating the metal powder surface with a
surface treatment agent of the present invention, a coating
film is formed between the die wall and the metal powder on
the compact surface. Thereby the ejection force is reduced,
and the scratching of the compact and other problems are
solved.
23
CA 02255861 1998-11-17
The present invention also provides a process for
producing a high-density compact from an iron-based powder
composition by utilizing the above secondary effects.
The process for producing a compact uses the
aforementioned iron-based powder composition of the present
invention. In the process, the composition is filled in a
die, and is compacted with heating to a prescribed
temperature to obtain a high-density compact.
The heating temperature thereof is selected in
consideration of melting points of two or more lubricants
added in the first mixing step. Specifically, the
temperature is set between the lowest melting point and the
highest melting point of the lubricants. When heated to a
temperature higher than the lowest melting point of the
mixed lubricants, the melted lubricant penetrates uniformly
into the interspace of the powder by capillarity, thereby
arrangement and plastic deformation of the powder is
effectively promoted in press compaction to increase the
density of the compact. In this step, the melted lubricant
serves as a binder for fixing an alloying powder to the
surface of the iron-based powder. The lubricant of the
higher melting point in an unmelted state is dispersed over
the surface of the iron-based powder or exists free state in
the powder composition during preparation of the powder
composition.
The lubricant existing in a free state or in a
unmelted solid state in the powder composition disperses in
24
t~
CA 02255861 1998-11-17
the gap between the die and the compact to reduce the
ejection force for removal of the high-density compact
formed by compaction from the die.
When the compaction is conducted at a temperature
lower than the melting points of all of the lubricants, no
lubricant is melted, thereby arrangement and plastic
deformation of the powder not being caused; the lubricant in
the powder particle interspace does not emerge on the
surface of the compact, causing a lower density of the
produced compact. On the other hand, when the compaction is
conducted at a temperature higher than the melting points of
all of the lubricants, no lubricant is in a solid state,
thereby the ejection force for removal of the compact from
the die being increased and the compact surface being
scratched; and during the rise of the density of the
compact, the melted lubricants in the interspace of the
powder particles is driven out to the surface of the formed
compact to form coarse voids to lower the mechanical
properties of the compact. Accordingly, adjustment of the
amount of the free lubricant or unmelted lubricant in a
solid state and the amount of the melted lubricant is
especially important in the present invention.
Incidentally, the inorganic compound having a layer
crystal structure, the organic compound having a layer
structure, and the thermoplastic elastomer as the lubricants
have no melting point. For such kinds of lubricants, a
thermal decomposition temperature or a sublimation-beginning
CA 02255861 1998-11-17
temperature is taken in place of the melting point in the
present invention.
Best Mode for Practicing the Invention
The best mode of the present invention is described
below specifically by reference to examples.
(Embodiment 1)
A solution of a surface treatment agent was prepared
by dissolving an organoalkoxysilane, an organosilazane, a
titanate coupling agent, or a fluorine-containing silicon
silane coupling agent in ethanol, or silicone fluid, or a
mineral oil in xylene. The solution was sprayed in a proper
amount on a pure iron powder for powder metallurgy having an
average particle size of 78 um, natural graphite for
alloying powder having an average particle size of 23 um or
less, or a copper powder having an average particle size of
25 um or less. Each of the obtained powders was blended by
high-speed mixer at a mixing blade speed of 1000 rpm for one
minute. Then the solvent was removed by a vacuum dryer.
The powder sprayed with the silane, the silazane, or the
coupling agent was further heated at about 100°C for one
hour. The above treatment is referred to as Surface
Treatment Step A1.
Table 1 shows the surface treatment agents used in
Surface Treatment Step A1, and the added amounts thereof.
In Table 1, the symbols for the surface treatment agents are
as shown in Table 16.
26
CA 02255861 1998-11-17
An iron powder for powder metallurgy having an
average particle diameter of 78 um, a natural graphite
powder having a average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less, each having been subjected or not subjected to Surface
Treatment Step A1 respectively were mixed. Thereto, were
added 0.2 wt$ of stearamide (mp: 100°C), and 0.2 wt$ of
ethylenebis(stearamide) (mp: 146-147°C) as the lubricant.
The mixture was heated to 110°C with stirring (First Mixing
Step and Melting Step). Then the resulting mixture was
cooled to 85°C or lower with stirring (Fixing Step).
To the resulting powder composition, were added 0.2
wt~ of stearamide (mp: 100°C), and 0.15 wt~ of zinc stearate
(mp; 116°C). The mixture was blended uniformly, and was
discharged from the mixer (Second Mixing Step). The
obtained powder compositions were referred to as Examples 1-
11.
For comparison, a powder composition was prepared by
treating an iron powder for powder metallurgy having an
average particle diameter of 78 um, a natural graphite
powder having a average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less, each not having been subjected to Surface Treatment
Step A1 respectively in the same manner as above
(Comparative Example 1).
Subsequently, 100 g of each of the powder
compositions prepared above was allowed to pass through a
27
CA 02255861 1998-11-17
vertical discharging orifice of 5 mm diameter, and the time
of complete discharge (flow rate) was measured as the index
of the powder flowability. Table 1 shows the results.
Obviously from comparison of Comparatiave Example 1
with Examples 1-11, the flowability of the powder
composition having been subjected to the surface treatment
step of the present invention was greatly improved in
comparison with that of Comparative Example 1.
(Embodiment 2) _
A pure iron powder for powder metallurgy having an
average particle diameter of 78 um, a natural graphite
powder having a average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less were mixed. To the mixture, was sprayed the solution
of an organoalkoxysilane, an organosilazane, a titanate
coupling agent, a fluorine-containing silicon silane
coupling agent, silicone fluid, or a mineral oil in a proper
amount as the surface treatment agent (hereinafter referred
to as Surface Treating Step B1).
Each of the powder compositions having been coated
with the different surface treatment agent was blended
respectively by a high-speed mixer at a stirring blade rate
of 1000 rpm for one minute (First Mixing Step). Thereto,
0.1 wt~ of oleic acid (mp: 14°C), and 0.3 wt~ of zinc
stearate (mp: 116°C) was added as the lubricant, and the
mixture was heated to 110°C with stirring (Melting Step).
Then the mixture was cooled to 85°C or lower (Fixing Step).
28
CA 02255861 1998-11-17
ø,
Table 2 shows the surface treatment agents used in
Surface Treating Step B1, and the added amounts thereof. In
Table 2, the surface treatment agents are represented by the
symbols shown in Table 16.
To each of the resulting powder compositions, was
added 0.4 wt$ of zinc stearate (mp; 116°C). The mixture was
blended uniformly, and was discharged from the mixer (Second
Mixing Step). The obtained powder compositions were
referred to as Examples 12-17.
For comparison, a powder composition was prepared by
treating an iron powder for powder metallurgy having an
average particle diameter of 78 um, a natural graphite
powder having an average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less in the same manner as above except that Surface
Treatment Step B1 was not conducted (Comparative Example 2).
Subsequently, 100 g of each of the powder
compositions prepared above w~.s tested for flowability in
the same manner as in Embodiment 1. Table 2 shows the
experimental results.
Obviously from comparison of Comparative Example 2
with Examples 12-17, the flowability of the powder
composition having been subjected to the surface treatment
step of the present invention was greatly improved in
comparison with that of Comparative Example.
(Embodiment 3)
A pure iron powder for powder metallurgy having an
29
CA 02255861 1998-11-17
~, s
average particle diameter of 78 um, a natural graphite
powder having a average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less were mixed. Thereto, 0.2 wt~ of stearamide (mp:
100°C), and 0.2 wt~ of ethylenebis(stearamide) (mp: 146-
147°C) were added as the lubricant. The mixture was heated
to 110°C with stirring (First Mixing/Melting Step). To the
resulting mixture, was sprayed the solution of an
organoalkoxysilane, an organosilazane, a titanate coupling
agent, a fluorine-containing silicon silane coupling agent,
silicone fluid, or a mineral oil in a proper amount as the
surface treatment agent. Each of the powder compositions
having been coated with the different surface treatment
agent was blended respectively by a high-speed mixer at a
stirring blade rotation rate of 1000 rpm for one minute.
Then the mixture was cooled to 85°C or lower (Surface-
Treating/Fixing Step C1).
Table 3 shows the surface treatment agents used in
Surface Treating/Fixing Step C1, and the added amounts
thereof. In Table 3, the surface treatment agents are
represented by the symbols shown in Table 16.
To the resulting powder mixture, were added 0.2 wt$
of stearamide (mp: 100°C), and 0.15 wt~ of zinc stearate
(mp: 116°C) as the lubricant, and the mixture was blended
uniformly, and was discharged from the mixer (Second Mixing
Step). The obtained powder compositions were referred to as
Examples 18-22.
,a
t
:,t
CA 02255861 1998-11-17
For comparison, a powder composition was prepared by
treating an iron powder for powder metallurgy having an
average particle diameter of 78 um, a natural graphite
powder having an average particle diameter of 23 um or less,
and a copper powder having an average diameter of 25 um or
less in the same manner as above except that Surface-
Treating/Fixing Step Cl was not conducted (Comparative
Example 3).
Each of the powder compositions prepared above was
tested for flowability in the same manner as in Embodiment
1. Table 3 shows the experimental results.
Obviously from comparison of Comparative Example 3
with Examples 18-22, the flowability of the powder
composition having been subjected to the surface treatment
step of the present invention was greatly improved in
comparison with that of Comparative Example 3.
(Embodiment 4)
A solution of a surface treatment agent was prepared
by dissolving an organoalkoxysilane, an organosilazane, a
titanate coupling agent, or a fluorine-containing silicon
silane coupling agent in ethanol, or silicone fluid,. or a
mineral oil in xylene. The solution was sprayed in a proper
amount on an alloy steel powder (completely alloyed steel
powder having component composition of Fe-2wt~Cr-0.7wt$Mn-
0.3wt~Mo for powder metallurgy having an average particle
size of about 80 um, or natural graphite having an average
particle diameter of 23 um or less.
31
CA 02255861 1998-11-17
,;
Each of the obtained powders was mixed by a high-
speed mixer at a mixing blade rotation speed of 1000 rpm for
one minute. Then the solvent was removed by a vacuum dryer.
The powder sprayed with the silane, the silazane, or the
coupling agent was further heated at about 100°C for one
hour. The above treatment is referred to as Surface .
Treatment Step A2.
Table 4 shows the surface treatment agents used in
Surface Treatment Step A2, and the added amounts thereof..
In Table 4, the surface treatment agents are represented by
the symbols shown in Table 16.
The alloyed steel powder for powder metallurgy
having an average particle diameter of about 80 um, and a
natural graphite powder having a average particle diameter
of 23 um or less, each having been subjected or not
subjected to Surface Treating Step A2 respectively were
mixed. Thereto, were added 0.1 wto of stearamide (mp:
100°C), 0.2 wt~ of ethylenebis(stearamide) (mp: 146-147°C),
and 0.1 wt~ of lithium stearate (mp: 230°C) as the
lubricant, and the mixture was stirred (First Mixing Step).
Then the mixture was heated to 160°C with stirring (Melting
Step). Then the resulting mixture was cooled to 85°C or
lower (Fixing Step).
To the resulting powder composition, was added 0.4
wt$ of lithium stearate (mp: 230°C) as the lubricant. The
mixture was blended uniformly, and was discharged from the
mixer (Second Mixing Step). The obtained powder
32
CA 02255861 1998-11-17
compositions were referred to as Examples 23-27.
For comparison, a powder composition was prepared by
treating the alloy steel powder (completely alloyed steel
powder having component composition of Fe-2.Owt~Cr-0.7wt~Mn-
0.3wt$Mo) for powder metallurgy having an average particle
diameter of about 80 um, and natural graphite having an
average particle diameter of 23 um or less, each not having
been subjected to Surface Treatment Step A2 respectively
(Comparative Example 4).
Subsequently, 100 g of each of the powder
compositions prepared above was heated to a prescribed
temperature ranging from 20 to 140°C and was allowed to pass
through an orifice of 5 mm diameter to measure the
flowability in the same manner as in Embodiment 1. Table 4
shows the experimental results.
Obviously from comparison of Comparative Example 4
with Examples 23-27, the flowability of the powder
composition having been subjected to the surface treatment
step of the present invention was greatly improved in
comparison with that of Comparative Example 1.
(Embodiment 5)
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5 wt~Mo) for
powder metallurgy having an average particle size of about
80 um, and natural graphite having an average particle
diameter of 23 um or less were mixed. To the mixture, a
solution of a surface treatment agent containing an
33
CA 02255861 1998-11-17
organoalkoxysilane, an organosilazane, a titanate coupling
agent, a fluorine-containing silicon silane coupling agent,
silicone fluid, or a mineral oil was sprayed in a proper
amount (Surface Treating Step B2).
Each of the powders coated with the surface
treatment agent was blended by a high-speed mixer at a
mixing blade rotation speed of 1000 rpm for one minute
(First Mixing Step). To the resulting mixture, were added
0.2 wt$ of stearamide (mp: 100°C), and 0.2 wt$ of
ethylenebis(stearamide) (mp: 146-147°C) as the lubricant.
Then the mixture was heated to 160°C with stirring (Melting
Step). The resulting mixture was cooled to 85°C or lower
(Fixing Step).
Table 5 shows the surface treatment agents used in
Surface Treatment Step B2, and the added amounts thereof.
In Table 5, the surface treatment agents are represented by
the symbols shown in Table 16.
To each of the powder mixtures obtained above, was
added 0.4 wt$ of lithium hydroxystearate (mp: 216°C) as the
lubricant, and the mixture was mixed uniformly by stirring,
and discharged from the mixer (Second Mixing Step). The
powder compositions are referred to as Examples 28-31.
For comparison, a powder composition was prepared by
treating the partially diffusion-alloyed steel powder
(having component composition of Fe-4.Owt$Ni-l.5wt$Cu-
0.5wt$Mo) for powder metallurgy having an average particle
diameter of about 80 um, and natural graphite having an
34
CA 02255861 1998-11-17
average particle diameter of 23 um or less in the same
manner as above except that Surface Treatment Step B2 was
not conducted (Comparative Example 5).
Each of the powder compositions prepared'above was
tested for flowability in the same manner as in Embodiment
1. Table 5 shows the experimental results.
Obviously from comparison of Comparative Example 5
with Examples 28-31, the flowability of the powder
composition having been subjected to the surface treatment
step of the present invention was greatly improved in
comparison with that of Comparative Example 5.
(Embodiment 6)
A partially diffusion-alloyed steel powder (having a
component composition of Fe-2.Owt~Cu) for powder metallurgy
having an average particle size of about 80 um, and natural
graphite having an average particle diameter of 23 dam or
less were mixed (First Mixing Step). Thereto, were added
0.2 wt~ of stearamide (mp: 100°C), and 0.2 wt~ of
ethylenebis(stearamide) (mp: 146-147°C) as the lubricant.
Then the mixture was heated to 160°C with stirring (Melting
Step). The resulting mixture was cooled to about 110°C. To
the powder mixture, a solution of a surface treatment agent
containing an organoalkoxysilane, an organosilazane, a
titanate coupling agent, a fluorine-containing silicon
silane coupling agent, silicone fluid, or a mineral oil was
sprayed in a proper amount. Each of the powder mixtures
coated with the surface treatment agent was blended by a
CA 02255861 1998-11-17
high-speed mixer at a mixing blade rotation speed of 1000
rpm for one minute, and was cooled to 85°C or lower
(Surface-Treating/Fixing Step C2).
Table 6 shows the surface treatment agents used in
Surface-Treating/Fixing Step C2, and the added amounts
thereof. In Table 6, the surface treatment agents are
represented by the symbols shown in Table 16.
To each of the powder mixtures obtained above, was
addedØ4 wt~ of lithium hydroxystearate (mp: 216°C) as the
lubricant , and the mixture was blended uniformly by
stirring, and was discharged from the mixer (Second Mixing
Step). The powder compositions are referred to as Examples
32-34.
Each of the powder compositions prepared above was
tested for flowability in the same manner as in Embodiment
1. Table 6 shows the experimental results.
Obviously from comparison of Comparative Example 5
with Examples 32-34, the flowability of the powder
composition having been subjected to the surface
treating/fixing step of the present invention was greatly
improved in comparison with that of Comparative Example 5.
(Embodiment 7)
A solution of a surface treatment agent was prepared
by dissolving an organoalkoxysilane, an organosilazane, a
titanate coupling agent or a fluorine-containing silicon
silane coupling agent in ethanol, or silicone fluid, or a
mineral oil in xylene. The solution was sprayed in a proper
36
CA 02255861 1998-11-17
amount on a partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt$Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, or natural graphite having an average particle
diameter of 23 um or less. Each of the obtained powders was
blended by a high-speed mixer at a mixing blade rotation
speed of 1000 rpm for one minute. Then the solvent was
removed by a vacuum dryer. The powder sprayed with the
silane, the silazane, or the coupling agent was heated at
about 100°C for one hour (Surface Treating Step A2).
Tables 7 and 8 show the surface treatment agents
used in Surface Treatment Step A2, and the added amounts
thereof. In Tables 7 and 8, the surface treatment agents
are represented by the symbols shown in Table 16.
The alloyed steel powder for powder metallurgy
having an average particle diameter of about 80 um, and a
natural graphite powder having a average particle diameter
of 23 um or less, each having been subjected or not
subjected to Surface Treating Step A2 respectively were
mixed. Thereto, were added 0.1 wt~ of stearamide (mp:
100°C), 0.2 wt~ of ethylenebis(stearamide) (mp: 146-147°C),
and 0.1 wt~ of one of a thermoplastic resin, a thermoplastic
elastomer, and a material having a layer crystal structure
as the lubricant, and the mixture was blended (First Mixing
Step). The mixture was heated to 160°C (Melting Step).
Then the resulting mixture was cooled to 85°C or lower
(Fixing Step) to obtain a powder mixture.
37
CA 02255861 1998-11-17
~ ,
Tables 7 and 8 show the lubricants used
(thermoplastic resiri, thermoplastic elastomer, or material
having layer crystal structure), and the added amounts
thereof. In Tables 7 and 8, the lubricants are represented
by the symbols shown in Table 17.
For comparison, a powder mixture was prepared by
mixing the partially diffusion-alloyed steel powder (haviizg
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 ~.~m, and the natural graphite having an average
particle diameter of 23 dam or less, and treating the mixture
as above without adding the lubricant.
To the resulting powder composition, was added at
least one lubricant of lithium stearate (mp: 230°C), lithium
hydroxystearate, (mp: 216°C), and calcium laurate (mp:
170°C) in a total amount of 0.2 wt~. The mixture was
blended uniformly by stirring, and was discharged from the
mixer (Second Mixing Step). The obtained powder
compositions were referred to as Examples 35-39, and
Comparative Example 6.
The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1.
Besides the flowability measurement, the powder
composition discharged from the mixer was compacted into a
tablet of 11 mm diameter in a die by heating to 150°C at a
compaction pressure of 7 ton/cm~, and the ejection force and
the density of the compact (green density in Tables) were
38
CA 02255861 1998-11-17
,,>
measured. Tables 7 and 8 show the experimental results.
Obviously from comparison of Comparative Example 6
with Examples 35-39, the flowability of the powder
composition was improved markedly by the surface treatment
of the present invention at the measured temperatures. The
powder composition containing a thermoplastic resin, a
thermoplastic elastomer, or a material having a layer
crystal structure and having been treated with a surface
treatment agent of the present invention was improved in .
compactibility, giving a compact with a higher green density
at a lower compact ejection force.
(Embodiment 8)
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt$Mo) for
powder metallurgy having an average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 um or less were mixed. To the mixture, a
solution of a surface treatment agent containing an
organoalkoxysilane, an organosilazane, a titanate coupling
agent, a fluorine-containing silicon silane coupling agent,
silicone fluid, or a mineral oil was sprayed in a proper
amount (Surface Treating Step B2).
Each of the powders coated with the surface
treatment agent was blended by a high-speed mixer at a
mixing blade rotation speed of 1000 rpm for one minute. To
the resulting mixture, were added 0.2 wt~ of stearamide (mp:
100°C), 0.2 wt~ of ethylenebis(stearamide) (mp: 146-147°C),
39
CA 02255861 1998-11-17
i~~
and 0.1 wt$ of one of a thermoplastic resin, a thermoplastic
elastomer, and a material having a layer crystal structure
as the lubricant, and the mixture was stirred (First Mixing
Step). Then the mixture was heated to 160°C with stirring
(Melting Step). The resulting mixture was cooled to 85°C or
lower (Fixing Step).
Table 9 shows the surface treatment agents used in
Surface Treatment Step B2, and the lubricants used in First
Mixing Step (thermoplastic resin, thermoplastic elastomer.,
and material having a layer crystal structure), and the
added amounts thereof. In Table 9, the surface treatment
agents are represented by the symbols shown in Table 16, and
the lubricants are represented by the symbols shown in Table
17.
To the resulting powder mixture, was added at least
one of lithium stearate (mp: 230°C), lithium
hydroxystearate, (mp: 216°C), and calcium laurate (mp:
170°C) in a total amount of 0.2 wt$ as the lubricant. The
mixture was blended uniformly, and was discharged from the
mixer (Second Mixing Step). The obtained powder
compositions were referred to as Examples 40-43.
The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted into a tablet, and
the ejection force and the density of the compacted powder
were measured in the same manner as in Embodiment 7. Table
CA 02255861 1998-11-17
9 shows the experimental results.
Obviously from comparison of Comparative Example 6
with Examples 40-43 in Table 9, the flowability of the
powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition containing a
thermoplastic resin, a thermoplastic elastomer, or a
material having a layer crystal structure and having been
treated with a surface treatment agent of the present
invention was improved in compactibility, giving a compact
with a higher green density at a lower compact ejection
force.
(Embodiment 9)
A partially diffusion-alloyed. steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 dam or less were mixed. Thereto, were added
0.2 wt~ of stearamide (mp: 100°C), 0.2 wt$ of
ethylenebis(stearamide) (mp: 146-147°C), and 0.1 wt~ of one
of a thermoplastic resin, a thermoplastic elastomer, and a
material having a layer crystal structure as the lubricant,
and the mixture was blended. Then the mixture was heated to
160°C with stirring (First Mixing Step, Melting Step). The
resulting mixture was cooled to about 110°C.
To the powder mixture, a solution of a surface
treatment agent containing an organoalkoxysilane, an
41
CA 02255861 1998-11-17
organosilazane, a titanate coupling agent, a fluorine-
containing silicon silane coupling agent, silicone fluid, or
a mineral oil was sprayed in a proper amount. Each of the
powder mixtures was blended by a high-speed mixer at a
mixing blade rotation speed of 1000 rpm for one minute, and
was cooled to 85°C or lower (Surface-Treating/Fixing Step
C2).
Tables 10 and 11 show the surface treatment agents
used in Surface-Treating/Fixing Step C2, and the lubricants
used in First Mixing Step (thermoplastic resin,
thermoplastic elastomer, and material having a layer crystal
structure), and the added amounts thereof. In Tables 10 and
11, the surface treatment agents are represented by the
symbols shown in Table 16, and the lubricants are
represented by the symbol shown in Table 17.
To each of the powder mixtures obtained above, was
added 0.4 wt~ of lithium hydroxystearate (mp: 216°C) as the
lubricant, and the mixture was blended uniformly by
stirring, and was discharged from the mixer (Second Mixing
Step). The powder compositions are referred to as Examples
44-48. The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted with dies into
tablets of 11 mm diameter by heating respectively to
temperatures of 130°C, 150°C, 170°C, 19.0°C and
210°C at a
compaction pressure of 7 ton/cm2. The ejection force and the
42
CA 02255861 1998-11-17
density of the compacted powder were measured in the same
manner as above. Table 10 and 11 show the experimental
results.
Obviously from comparison of Comparative Example 6
with Examples 44-48 in Table 10 and 11, the flowability of
the powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition containing a
thermoplastic resin, a thermoplastic elastomer, or a
material having a layer crystal structure and having been
treated with a surface treatment agent of the present
invention gave compacts with a higher green density at a
lower compact ejection force over a broad compaction
temperature range from 130°C to 210°C as shown by Example
44. The compact produced at the compaction temperature of
70°C or 90°C had a slightly low green density, whereas the
compacts produced at the compaction temperature of 220°C or
240°C were inferior in compactibility and required greater
ejection force, in comparison with the compact produced at
the compaction temperature of 130-210°C.
(Embodiment 10)
A solution of a surface treatment agent was prepared
by dissolving an organoalkoxysilane, an organosilazane, a
titanate coupling agent, or a fluorine-containing silicon
silane coupling agent in ethanol, or silicone fluid, or a
mineral oil in xylene. The solution was sprayed in a proper
amount on a partially diffusion-alloyed steel powder (having
43
CA 02255861 1998-11-17
t:'
component composition of Fe-4.Owt$Ni-l.5wt$Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, or natural graphite having an average particle
diameter of 23 um or less. Each of the obtained powders was
mixed by a high-speed mixer at a mixing blade rotation speed
of 1000 rpm for one minute. Then the solvent was removed by
a vacuum dryer. The mixture containing the powder sprayed
with the silane, the silazane, or the coupling agent was
heated at about 100°C for one hour (Surface Treating Step
A2).
Table 12 shows the surface treatment agents used in
Surface Treating Step A2, and the added amounts thereof. In
Table 12, the surface treatment agents are represented by
the symbols shown in Table 16.
The partially alloyed steel powder for powder
metallurgy having an average particle diameter of about 80
~.~m, and a natural graphite powder having a average particle
diameter of 23 dam or less, each having been subjected or not
subjected to Surface Treating Step A2 respectively were
mixed. Thereto, were added 0.1 wt~ of stearamide (mp:
100°C), 0.2 wt~ of ethylenebis(stearamide) (mp: 146-147°C),
and O.l wt~ of one of a thermoplastic resin, a thermoplastic
elastomer, and a material having a layer crystal structure
as the lubricant, and the mixture was blended (First Mixing
Step). The mixture was heated to 160°C with stirring
(Melting Step). Then the resulting mixture was cooled with
stirring to 85°C or lower (Fixing Step).
44
CA 02255861 1998-11-17
Table 12 shows the lubricants used (thermoplastic
resin, thermoplastic elastomer, or material having layer
crystal structure), and the.added amounts thereof. In Table
12, the lubricants are represented by the symbols shown in
Table 17.
To the resulting powder mixture, was added at least
one of lithium stearate (mp: 230°C), lithium hydroxystearate
(mp: 216°C), and calcium laurate (mp: 170°C) in a total
amount of 0.2 wtg as the lubricant. The mixture was blended
uniformly, and was discharged from the mixer (Second Mixing
Step). The obtained powder compositions were referred to as
Examples 49-52. The flowability of the obtained powder
composition was measured in the same manner as in Embodiment
1. Besides the flowability measurement, the powder
composition discharged from the mixer was compacted into a
tablet of 11 mm diameter in a die by heating to 150°C at a
compaction pressure of 7 ton/cmz, and the ejection force and
the green density of the compact were measured. Tables 12
shows the experimental results.
Obviously from comparison of Comparative Example 6
with Examples 49-52 in Table 12, the flowability of the
powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition containing a
thermoplastic resin, a thermoplastic elastomer, or a
material having a layer crystal structure and having been
treated with a surface treatment agent of the present
CA 02255861 1998-11-17
invention had a higher green density and was ejected at a
lower compact ejection force.
(Embodiment 11)
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 um or less were mixed. To the mixture, a
solution of a surface treatment agent containing an
organoalkoxysilane, an organosilazane, a titanate coupling
agent, a fluorine-containing silicon silane coupling agent,
silicone fluid, or a mineral oil was sprayed in a proper
amount (Surface Treating Step B2).
Each of the powder mixtures was blended by a high-
speed mixer at a mixing blade rotation speed of 1000 rpm for
one minute. To the resulting mixture, were added 0.1 wt~ of
calcium stearate (mp: 148-155°C), and 0.3 wt~ of lithium
stearate (mp: 230°C) as the lubricant, and the mixture was
blended (First Mixing Step). Then the mixture was heated to
160°C with stirring (Melting Step). The resulting mixture
was cooled to 85°C or lower (Fixing Step).
Table 13 shows the surface treatment agents used in
Surface Treatment Step B2, and the added amounts thereof.
In Table 13, the surface treatment agents are represented by
the symbols shown in Table 16.
To the resulting powder mixture, were added 0.1 wt~
of lithium stearate (mp: 230°C), and additionally, at least
46
CA 02255861 1998-11-17
one of a thermoplastic resin, a thermoplastic elastomer, and
a material having a layer crystal structure in a total
amount of 0.2 wt~ as the lubricant. The mixture was blended
uniformly, and was discharged from the mixer (Second Mixing
Step). The obtained powder compositions were referred to as
Examples 53-56. Table 13 shows the lubricants added and the
amount thereof. In Table 13, the lubricants are represented
by the symbols shown in Table 17.
The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted into a tablet under
the same conditions in Embodiment 10. Table 13 shows the
compact ejection forces, the green densities, and the
flowabilities of the powder compositions.
Obviously from comparison of Comparative Example 6
with Examples 53-56 in Table 13, the flowability of the
powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition containing a -
thermoplastic resin, a thermoplastic elastomer, or a
material having a layer crystal structure and having been
treated with a surface treatment agent of the present
invention was improved in compactibility, giving a compact
with a higher compact density at a lower compact ejection
force.
(Embodiment 12)
47
CA 02255861 1998-11-17
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an.average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 um or less were mixed, and thereto, were
added 0.2 wt~ of stearamide (mp: 100°C), and 0.2 wto of
ethylenebis(stearamide) (mp: 146-147°C) as the lubricant,
and the mixture was blended (First Mixing Step). Then the
mixture was heated to 160°C with stirring (Melting Step).
The resulting mixture was cooled to about 110°C. To the
powder mixture, a solution of a surface treatment agent
containing an organoalkoxysilane, an organosilazane, a
titanate coupling agent, a fluorine-containing silicon
silane coupling agent, silicone fluid, or a mineral oil was
sprayed in a proper amount. Each of the powder mixtures
coated with the surface treatment agent was blended by a
high-speed mixer at a mixing blade rotation speed of 1000
rpm for one minute, and was cooled to 85°C or lower
(Surface-Treating/Fixing Step C2).
Table 14 shows the surface treatment agents used in
Surface-Treating/Fixing Step C2, and the added amounts
thereof. In Table 14, the surface treatment agents are
represented by the symbols shown in Table 16.
To the resulting powder mixture, were added 0.1 wt~
of lithium stearate (mp: 230°C), and additionally at least
one of a thermoplastic resin, a thermoplastic elastomer, and
a material having a layer crystal structure in a total
48
CA 02255861 1998-11-17
amount of 0.2 wt~ as the lubricant. The mixture was blended
uniformly, and was discharged from the mixer (Second Mixing
Step). The obtained powder.compositions were referred to as
Examples 57-59. Table 14 shows the lubricants added and the
amount thereof. In Table 14, the lubricants are represented
by the symbols shown in Table 17.
The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted into a tablet under
the same conditions in Embodiment 11. The compact ejection
force, and the green density of the compact were measured.
Table 14 shows the results.
Obviously from comparison of Comparative Example 6
with Examples 57-59 in Table 14, the flowability of the
powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition having been surface-
treated according to the present invention was improved in
compactibility, giving a compact with a higher green density
at a lower compact ejection force.
(Embodiment 13)
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt$Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 um or less were mixed, and thereto, were
49
CA 02255861 1998-11-17
a
added 0.2 wt~ of stearamide (mp: 100°C), and 0.2 wt~ of
ethylenebis(stearamide) (mp: 146-147°C) as the lubricant,
and the mixture was blended.(First Mixing Step). Then the
mixture was heated to 160°C with stirring (Melting Step).
The resulting mixture was cooled to about 110°C. To the
powder mixture, a solution of a surface treatment agent
containing an organoalkoxysilane, an organosilazane, a
titanate coupling agent, a fluorine-containing silicon
silane coupling agent, silicone fluid, or a mineral oil was
sprayed in a proper amount. Each of the powder mixtures
coated with the surface treatment agent was blended by a
high-speed mixer at a mixing blade rotation speed of 1000
rpm for one minute, and was cooled to 85°C or lower
(Surface-Treating/Fixing Step C2).
Table 15 shows the surface treatment agents used in
Surface-Treating/Fixing Step C2, and the added amounts
thereof. In Table 15, the surface treatment agents are
represented by the symbols shown in Table 16.
To the resulting powder mixture, were added 0.1 wt~
of lithium stearate (mp: 230°C), and additionally at-least
one of a thermoplastic resin, a thermoplastic elastomer, and
a material having a layer crystal structure in a total
amount of 0.2 wt~ as the lubricant. The mixture was blended
uniformly, and was discharged from the mixer (Second Mixing
Step). The obtained powder compositions were referred to as
Examples 60-63. Table 15 shows the lubricants added and the
amount thereof. In Table 15, the lubricants are represented
CA 02255861 1998-11-17
by the symbols shown in Table 17.
The flowability of the obtained powder composition
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted into a tablet under
the same conditions in Embodiment 12. The compact ejection
force, and the green density of the compact were measured.
Table 15 shows the results.
Obviously from comparison of Comparative Example 6
with Examples 60-63 in Table 15, the flowability of the
powder composition was improved markedly by the surface
treatment of the present invention at the measured
temperatures. The powder composition having been subjected
to the surface treatment of the present invention gave a
compact with a higher green density at a lower compact
ejection force.
(Embodiment 14)
An alloyed steel powder was surface-treated in the
same manner as in Embodiment 4 according to Surface Treating
Step A2 except that the iron-based powder shown in Tables
18-21 was used. Tables 18-21 shows the surface treatment
agent used in Surface Treating Step A2, and the, amount
thereof. In Tables 18-21, the surface treatment agents are
represented by the symbols shown in Table 16.
The alloyed steel powder having been treated through
Surface Treating Step A2 was mixed with natural graphite.
Thereto were added 0.15 wt~ of calcium stearate (mp: 148-
51
CA 02255861 1998-11-17
155°C), and 0.2 wt~ of one of a thermoplastic resin, a
thermoplastic elastomer, and a material having a layer
crystal structure of average particle diameter of about 10-
20 um as the lubricant, and blended (First Mixing Step).
The mixture was heated to 160°C with stirring (Melting
Step), and was cooled to 85°C or lower (Fixing Step).
Table 18-21 shows the employed lubricants
(thermoplastic resins, thermoplastic elastomers, and
materials having a layer crystal structure), and the amount
thereof. In Tables 18-21, the lubricants are represented by
the symbols shown in Table 17.
To the resulting powder mixture, were added at least
one of lithium stearate (mp: 230°C) and lithium
hydroxystearate (mp: 216°C) in a total amount of 0.4 wt~ as
the lubricant, and the mixture was blended uniformly, and
discharged from the mixer (Second Mixing Step). The
obtained powder compositions were referred to as Examples
64-67.
For comparison, powder compositions were prepared in
the same manner as in Examples 64-67 except that the Surface
Treating Step A2 was omitted (Comparative Examples 7, 9, 11,
and 13). Further, powder compositions were prepared in the
same manner as in Examples 64-67 except that the alloyed
steel powder not treated through Surface Treating Step A2
and natural graphite were mixed without addition of a
lubricant (Comparative Examples 8, 10, 12, and 14).
The flowability of the obtained powder composition
52
CA 02255861 1998-11-17
4~
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted with dies into
tablets of 11 mm diameter by heating respectively to
temperatures of 150°C, 180°C, and 210°C at a compaction
pressure of 7 ton/cm2. The ejection force and the green
density were measured in the same manner as above. Table
18-21 show the experimental results.
From comparison of Comparative Examples 7, 9, 11,
and 13 respectively with Examples 64, 65, 66, and 67, it is
clear that the flowability of the powder composition was
improved markedly by the surface treatment of the present
invention at the measured temperatures. From comparison of
Comparative Examples 8, 10, 12, and 14 with Examples 64, 65,
66, and 67, it is clear that the powder compositions of the
present invention had improved flowability and excellent
compactibility in the temperature range from 150°C to 210°C
owing to the effect of the surface treatment of the iron-
based powder and the effect of the lubricant. The
composition of Example 64, when compacted at a compaction
temperature of 110°C or 130°C, gave a lower green density,
and when compacted at a compaction temperature of 240°C or
260°C, required greater ejection force with lower
compactibility. However, the composition of Example 64 was
slightly better than that of Comparative Example 7 in the
green density and the ejection force at the compaction
temperatures of 110°C and 130°C, and slightly better in the
53
CA 02255861 1998-11-17
t
green density, and considerably better in the election force
than that of Comparative Example 8 at the compaction
temperature of 240°C, and 26.0°C.
(Embodiment 15)
An alloy steel powder of an average particle
diameter of about 80 um shown in Tables 22-25, and natural
graphite having an average particle diameter of 23 um were
mixed together. To the mixture, a solution of a surface
treatment agent containing an organoalkoxysilane, an
organosilazane, a titanate coupling agent, a fluorine-
containing silicon silane coupling agent, silicone fluid, or
a mineral oil was sprayed in a proper amount (Surface
Treating Step B3).
Tables 22-25 show the surface treatment agents used
in Surface Treating Step B3, and the added amounts thereof.
In Tables 22-25, the surface treatment agents are
represented by the symbols shown in Table 16.
Each of the powder mixtures coated with the surface
treatment agent was blended by a high-speed mixer at a
mixing blade rotation speed of 1000 rpm for one minute.
Thereto, were added 0.15 wt~ of calcium stearate (mp: 148-
155°C), and 0.2 wtg of particles of an average diameter of
about 10 um of one of a thermoplastic resin, a thermoplastic
elastomer, and a material having a layer crystal structure
as the lubricant. The mixture was stirred (First Mixing
Step). The mixture was heated to 160°C with stirring
(Melting Step), and was then cooled to 85°C or lower with
54
CA 02255861 1998-11-17
stirring (Fixing Step).
Tables 22-25 shows the employed lubricants
(thermoplastic resins, thermoplastic elastomers, and
materials having a layer crystal structure), and the amounts
thereof. In Tables 22-25, the lubricants are represented by
the symbols shown in Table 17.
To the resulting powder mixture, were added at least
one of lithium stearate (mp: 230°C), lithium hydroxystearate
(mp: 216°C), and calcium laurate (mp: 170°C) in a total
amount of 0.4 wt~. The mixture was blended uniformly, and
discharged from the mixer (Second Mixing Step). The
obtained powder compositions are referred to as Examples 68-
71.
For comparison, powder compositions were prepared in
the same manner as in Examples 68-71 except that the Surface
Treating Step A2 was omitted (Comparative Examples 15, 17,
19, and 21). Separately for comparison, powder compositions
were prepared in the same manner as in Examples 68-71 except
that the alloyed steel powder not treated through Surface
Treating Step A2 and natural graphite having an average
particle diameter of about 23 um were mixed'together without
addition of a lubricant (Comparative Examples 16, 18, 20,
and 22).
The flowability of the obtained powder compositions
was measured in the same manner as in Embodiment 1. Besides
the flowability measurement, the powder composition
discharged from the mixer was compacted with a die into a
CA 02255861 1998-11-17
\.
tablet of 11 mm diameter by heating to 180°C at a compaction
pressure of 7 ton/cm2. The ejection force and the green
density of the compact were measured in the same manner as
above. Tables 22-25 show the experimental results.
From comparison of Comparative Examples 15, 17, 19,
and 21 respectively with Examples 68, 69, 70, and 71, it is
clear that the flowability of the powder composition was
improved markedly by the surface treatment of the present
invention at the measured temperatures. From comparison of
Comparative Examples 16, 18, 20, and 22 respectively with
Examples 68, 69, 70, and 71, it is clear that the powder
compositions of the present invention had improved
flowability and excellent compactibility owing to the effect
of the surface treatment of the iron-based powder and the
effect of the lubricant.
(Embodiment 16)
An alloy steel powder of an average particle
diameter of about 80 um shown in Tables 26-29, and natural
graphite having an average particle diameter of 23 um were
mixed together. To the mixture, were added 0.20 wt~ of
calcium stearate (mp: 148-155°C), and particles of an
average diameter of about 10 um of at least one of a
thermoplastic resin, a thermoplastic elastomer, and a
material having a layer crystal structure in a total amount
of 0.2 wt~ as the lubricant, and the mixture was stirred
(First Mixing Step). Then the mixture was heated to 160°C
with stirring (Melting Step), and was then cooled to 110°C
56
>,~
CA 02255861 1998-11-17
with stirring. Thereon, a solution of a surface treatment
agent containing an organoalkoxysilane, an organosilazane, a
titanate coupling agent, a fluorine-containing silicon
silane coupling agent, silicone fluid, or a mineral oil was
sprayed in a proper amount, and the mixture was stirred by a
high-speed mixer at a mixing blade rotation speed of 1000
rpm for one minute (Surface Treating Step C3).
Tables 26-29 show the employed lubricants
(thermoplastic resins, thermoplastic elastomers, and
materials having a layer crystal structure), and the added
amounts thereof. In Tables 26-29, the lubricants are
represented by the symbols shown in Table 17.
The mixture was cooled to 85°C ~r lower (Fixing
Step). To the resulting powder mixture, were added at least
one of lithium stearate (mp: 230°C), lithium
hydroxystearate, and calcium laurate (mp: 170°C) as a filler
in a total amount of 0.3 wt~ based on the weight of alloy
steel powder, and the mixture was blended uniformly, and
discharged from the mixer (Second Mixing Step). The
obtained powder compositions are referred to as Examples 72-
75.
Tables 26-29 show the surface treatment agents
employed in Surface Treatment Step C3, and the added amounts
thereof. In Tables 26-29, the surface treatment agents are
represented by the symbols shown in Table 16.
For comparison, powder compositions were prepared in
the same manner as in Examples 72-75 except that the Surface
57
CA 02255861 1998-11-17
Treating Step C3 was omitted (Comparative Examples 23, 25,
27, and 29). Separately for comparison, powder compositions
were prepared in the same manner as in Examples 72-75 except
that the alloyed steel powder not treated through Surface
Treating Step C3 and natural graphite of an average diameter
of about 23 um were mixed together without addition of a
lubricant to obtain a powder composition (Comparative
Examples 24, 26, 28, and 30).
The flowability of the obtained powder composition
was determined in such a manner that 100 g of the powder
composition was heated to a temperature ranging from 20°C to
170°C, and measuring the time for the composition to pass
entirely through an orifice of 5 mm. Besides the
flowability measurement, the powder composition discharged
from the mixer was compacted with a die into a tablet of 11
mm diameter by heating to 180°C at a compaction pressure of
7 ton/cmz. The ejection force and the green density of the
compact were measured in the same manner as above. Tables
26-29 show the experimental results.
From comparison of Comparative Examples 23, 25, 27,
and 29 respectively with Examples 72, 73, 74, and 75, it is
clear that the flowability of the powder composition was
improved markedly by the surface treatment of the present
invention at the measured temperatures,. From comparison of
Comparative Examples 24, 26, 28, and 30 respectively with
Examples 72, 73, 74, and 75, it is clear that the powder
compositions of the present invention had improved
58
CA 02255861 1998-11-17
flowability and excellent compactibility owing to the effect
of the surface treatment of the iron-based powder and the
effect of the lubricant.
(Embodiment 17)
A partially diffusion-alloyed steel powder (having
component composition of Fe-4.Owt~Ni-l.5wt~Cu-0.5wt~Mo) for
powder metallurgy having an average particle diameter of
about 80 um, and natural graphite having an average particle
diameter of 23 um were mixed. Thereto, were added 0.15 wt~
of stearic acid (mp: 70.1°C), 0.15 wt~ of lithium stearate
(mp: 230°C), and 0.15 wt~ of a melamine-cyanuric acid adduct
as the lubricant. The mixture was heated to 160°C with
stirring (First Mixing Step, and Melting Step).
The resulting mixture was cooled to I10°C with
stirring. To the powder mixture, a solution of a surface
treatment agent containing an organoalkoxysilane was sprayed
in a proper amount. The powder mixture was blended by a
high-speed mixer at a mixing blade rotation speed of 1000
rpm for one minute (Surface Treating Step C3). Tables 30
and 31 show the surface treatment agents used in Surface
Treating Step C3, and the added amounts thereof. In Tables
30 and 31, the surface treatment agents are represented by
the symbols shown in Table 16.
The resulting powder mixture was cooled to 85°C or
lower (Fixing Step). To each of the powder mixtures
obtained above, was added at least one of lithium stearate
(mp: 230°C) and calcium laurate (mp: 170°C) in a total
59
CA 02255861 1998-11-17
amount of 0.3 wt~ as the lubricant, and the mixture was
blended uniformly, and was discharged from the mixer (Second
Mixing Step). The powder compositions are referred to as
Examples 76 and 77.
For comparison, powder compositions were prepared in
the same manner as in Examples 76-77 except that the Surface
Treating Step C3 was omitted (Comparative Examples 31 and
33). Separately for comparison, powder compositions were
prepared in the same manner as in Examples 76-77 except that
the alloyed steel powder not treated through Surface
Treating Step C3 and natural graphite were mixed without
addition of a lubricant (Comparative Examples 32 and 34).
The flowability of the obtained powder composition
was determined in such a manner that 100 g of the powder
composition is heated to a temperature ranging from 20°C to
150°C, and the time is measured for the composition to pass
entirely through an orifice of 5 mm diameter. Besides the
flowability measurement, the powder composition discharged
from the mixer was compacted with a die into a tablet of 11
mm diameter by heating to 150°C at a compaction pressure of
7 ton/cm~. The ejection force and the green density of the
compact were measured in the same manner as above. Tables
30-31 show the experimental results.
From comparison of Comparative Examples 31 and 33
with Examples 76 and 77, it is clear that the flowability of
the powder composition was improved markedly by the surface
treatment of the present invention at the measured
CA 02255861 1998-11-17
temperatures. From comparison of Comparative Examples 32,
and 34 with Example 76, and 77, it is clear that the powder
composition prepared with iron powder surface-treated
without addition of a lubricant has lower flowability, and
lower green strength, and requires stronger ejection force,
and that the composition of the present invention has
improved flowability and excellent compactibility owing to
the effect of the surface treatment of the iron-based powder
and the effect of the lubricant.
61
CA 02255861 1998-11-17
Industrial Applicability
The present invention provides an iron-based powder
composition for powder metallurgy having higher flowability
and higher compactibility not only in ordinary temperature
compaction but also in warm compaction, and provides also a
process for producing the powder composition. Present
invention provides further a process for compaction to
produce a compact of a high density before sintering.
Therefore, the present invention meets the demand for high-
strength of sintered members, and is highly useful for
industrial development.
62
CA 02255861 1998-11-17
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64
.y
CA 02255861 1998-11-17
Table 4
CarpletelySurface GraphiteSurface MeasurementFiow
* * * * * teiperaturerate
alloYed reatrnent reatment ~
s~~r agent ~ ~eo graphite (s~t00g)
~ ~tqsteel l
r
a )
20 11.7
50 11.7
Exanple 10D0 a x 5 -
23 02) 80 11.8
. 100 11.
9
120 12.0
140 12.1
20 11.6
50 11.5
80 11.6
Exampl 1000 c ~ 5 d ~
a 24 02) 5 )
. . 100 11.8
120 11.9
140 12.
0
20 11.8
50 11.8
Fxanple 1000 h x.02) 5 -
25 80 11.9
100 12.0
120 12.1
140 12.2
20 11.1
50 11.
3
Fxar~ple1000 m Q7.01) 5 f (0
26 5) 80 11.2
. 100 11.8
120 12.
9
140 12.1
~ 11.5
50 11.6
80 11.8
Exanple 1000 - 5 g (0
27 5)
. 100 11.9
120 12.0
140 12.7
20 12.
5
50 12.5
-
Carparative1~ - 5 - 80 12.8
Exar~p 100 12.
I a 9
4
120 13.1
140 13.
5
* ~ urface rea ~letely alloyed steel er
anent agents are represented y~the syrti~ol shaNn in Table 16.
.v
CA 02255861 1998-11-17
Table 5
Partially Gr~iteSurface treatmentMeasurementFlow
~k (~ ~k~k temp r rate
alloyed ent ture (sec/100g)
teel ~wt% to steel (~C~
powder powder )
~
20 11.2
50 11.
3
80 11.
Exam I 1000 6 c (0 3
a 28 03)
. 100 11.5
120 11.6
140 11.
7
20 11.0
50 11.0
g0 11.
Example 1000 6 f (0 2
29 03)
. 100 11.3
120 11.
5
140 11.
5
20 11.
5
50 11.7
80 11.7
Examp 1000 6 h (0
I a 30 04)
. 100 11.8
120 11.
9
140 12.
0
20 11.8
50 11.8
80 12.
Examp 1000 6 j (0 0
I a 31 01 )
. 100 12.2
120 12.1
140 12.
5
20 12.
7
50 12.
8
Comparat 80 12.
i ve 1000 6 - 8
Example
100 13.0
120 13.
2
140 14.
5
(Note)
x~ Cu
-Ni -Mo
type
partially
diffusion-alloyed
steel
poder
~ Surface
treatment
agents
are represented
by the
symbol
shown
in Table
16.
66
. 1
CA 02255861 1998-11-17
Table 6
Partially GraphiteSurface treatmentMeasurementFlow rate
~ (g) ~ ~x temperature(sec/t00g)
alloyed agent ~ (C)
steel ( wt~ to graphite
powder (g) )
20 11. 5
50 11.5
80 11.6
Examp I 1000 6 I (0
a 32 03)
. 100 11.l
120 11.8
140 12.0
20 11.4
50 11. 5
80 11.5
Example 1000 6 g (0
33 04)
. 100 11.7
120 11.8
140 12. 3
20 11.8
50 11, 9
80 12. 0
Examp I 1000 6 j (0
a 34 01 )
. 100 12.1
120 12. 5
140 13. 1
(Note) x~ Cu type partially diffusion-alloyed steel poder
~ ~k Surface treatment agents are represented by the symbol shown in Table 16.
67
CA 02255861 1998-11-17
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