U.S. patent application number 11/222862 was filed with the patent office on 2006-05-04 for mixed powder for powder metallurgy and green compact using the same.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho(Kobe Steel, Ltd.). Invention is credited to Kazuhisa Fujisawa, Takayasu Fujiura, Hironori Suzuki.
Application Number | 20060090594 11/222862 |
Document ID | / |
Family ID | 35453310 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060090594 |
Kind Code |
A1 |
Fujisawa; Kazuhisa ; et
al. |
May 4, 2006 |
Mixed powder for powder metallurgy and green compact using the
same
Abstract
A mixed powder for powder metallurgy to be used as a feedstock
of a green compact includes an iron powder and/or an iron alloy
powder, a component for improving mechanical properties, and a
thermosetting resin powder. In the mixed powder, the thermosetting
resin powder is composed of at least one resin selected from the
group consisting of an epoxy-polyester-based resin, an epoxy-based
resin, and an acrylic-based resin. In addition, the average
particle diameter of the thermosetting resin powder is 100 .mu.m or
less, and the content of the thermosetting resin powder relative to
the total amount of the iron powder and/or the iron alloy powder is
0.05 to 1.0 mass percent.
Inventors: |
Fujisawa; Kazuhisa;
(Kobe-shi, JP) ; Fujiura; Takayasu; (Kobe-shi,
JP) ; Suzuki; Hironori; (Takasago-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Kobe Seiko
Sho(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
35453310 |
Appl. No.: |
11/222862 |
Filed: |
September 12, 2005 |
Current U.S.
Class: |
75/252 |
Current CPC
Class: |
B22F 1/0059 20130101;
Y10T 428/12014 20150115 |
Class at
Publication: |
075/252 |
International
Class: |
C22C 1/05 20060101
C22C001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2004 |
JP |
2004-314381 |
Claims
1. A mixed powder for powder metallurgy to be used as a feedstock
of a green compact, the mixed powder comprising: an iron powder
and/or an iron alloy powder; a component for improving mechanical
properties; and a thermosetting resin powder, wherein the
thermosetting resin powder comprises at least one resin selected
from the group consisting of an epoxy-polyester-based resin, an
epoxy-based resin, and an acrylic-based resin, the average particle
diameter of the thermosetting resin powder is 100 .mu.m or less,
and the content of the thermosetting resin powder relative to the
total amount of the iron powder and/or the iron alloy powder is
0.05 to 1.0 mass percent.
2. The mixed powder for powder metallurgy according to claim 1,
further comprising a lubricant.
3. The mixed powder for powder metallurgy according to claim 2,
wherein the lubricant is at least one compound selected from the
group consisting of ethylenebisstearamide, stearamide, zinc
stearate, and lithium stearate.
4. The mixed powder for powder metallurgy according to claim 1,
wherein the component for improving mechanical properties is at
least one substance selected from the group consisting of copper,
nickel, chromium, molybdenum, graphite, and manganese sulfide.
5. A green compact comprising the mixed powder for powder
metallurgy according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a mixed powder for powder
metallurgy to be used as a feedstock of a green compact having an
adequate density and strength even before the sintering process and
having an excellent machinability, and a green compact using the
mixed powder as a feedstock.
[0003] 2. Description of the Related Art
[0004] A powder metallurgy is a technology used for producing
machine parts and oil-impregnated bearings from a metal powder.
Since highly accurate products can be efficiently mass-produced,
the powder metallurgy is indispensable particularly in the
automobile industry and the like. In this powder metallurgy, in
general, a mixed powder including a metal powder is molded by
compression and the resultant green compact is then dewaxed.
Subsequently, for example, in an iron-based powder metallurgy, the
compact is sintered at a temperature of about 1,000.degree. C. to
about 1,300.degree. C. In this sintering process, the mixed metal
powder forms an alloy, thereby increasing the strength of the
compact. A cutting operation is then performed on the resultant
sintered compact.
[0005] However, such a sintered compact has an excessively high
strength from the viewpoint of a cutting operation. Furthermore,
the lifetime of a cutting tool used is shortened because of the
high strength of the sintered compact. On the other hand, a green
compact cannot be subjected to a cutting operation prior to
sintering because the green compact is brittle. Accordingly, a
technology is desired by which the strength of a green compact
prior to the sintering process is increased, so that the green
compact can subsequently be subjected to a cutting operation and
finally sintered.
[0006] A document by Tianjun Liu et al. (Funtai oyobi Funmatsu
yakin (Journal of the Japan Society of Powder and Powder
Metallurgy) Vol. 50, No. 11, pp. 832-836 (2003)) discloses an
example of such a technology. According to this technology, a
polymer lubricant is added to a mixed powder, which constitutes a
feedstock, and a green compact made of the resultant mixed powder
is heated at a temperature lower than the sintering temperature.
Consequently, the strength of the compact can be increased only by
this heat treatment and thus a cutting operation can be performed
prior to the sintering process. However, since a polymer lubricant
is used as a lubricant, its lubricity during compression molding
may be insufficient. In addition, although the temperature is as
relatively low as 190.degree. C., it takes about an hour to
complete the heat treatment before the cutting operation can be
performed. Therefore, this heat treatment decreases the
productivity.
[0007] In the powder metallurgy, when a mixed powder is discharged
from a storage hopper or when a die is filled with the mixed
powder, the fluidity of the mixed powder is one of its important
characteristics. Specifically, a low fluidity of a mixed powder
causes the following problems. For example, a bulging can occur at
the upper part of a discharging hole of a hopper, resulting in a
discharge failure. Also, the mixed powder can become clogged in a
hose connecting from the hopper to a shoe box. Furthermore, even if
a mixed powder having a low fluidity is compulsorily discharged
from the hose, the powder may not satisfactorily fill a die, in
particular, a die having thin walls. Consequently, a satisfactory
compact may not be formed. For these reasons, a raw powder for
powder metallurgy having excellent fluidity has been strongly
desired.
[0008] Although the object is different from that of the present
invention, the following technology for producing a bonded magnet
is known: A thermosetting resin is added to a magnetic powder or
the like, and a heat treatment is then performed. Thus, a compact
is cured without sintering while the magnetic properties of the
compact are ensured. The resultant compact is used without further
treatment. Accordingly, this manufacturing technology of a bonded
magnet may be applied to the powder metallurgy. However, known
manufacturing technologies of bonded magnets cannot be applied to
the powder metallurgy as they are.
[0009] For example, Japanese Unexamined Patent Application
Publication Nos. 4-284602 (paragraph No. 0007, and Examples),
6-112022 (paragraph Nos. 0015 and 0016, and Examples), 6-188137
(paragraph Nos. 0015 and 0020, and Examples), and 8-31677
(paragraph Nos. 0031 and 0033, and Examples) disclose methods for
producing a bonded magnet in which a mixture of an alloy powder and
a thermosetting resin (binder) is used as a feedstock. However, the
type and the particle diameter of the thermosetting resin are not
studied in detail because these technologies relate to a bonded
magnet and their objects are different from the object of the
present invention. In addition, the content of thermosetting resin
is relatively large from the viewpoint of application to the powder
metallurgy. For example, according to Japanese Unexamined Patent
Application Publication No. 4-284602, the content of a
thermosetting resin binder is 0.5 to 4 mass percent base on an
alloy. According to Japanese Unexamined Patent Application
Publication No. 6-112022, 0.5 to 5 parts by weight (in particular,
1 to 3 parts by weight) of a thermosetting resin is added to 100
parts by weight of a magnetic powder. However, in Examples in these
patent documents, the amount of a thermosetting resin relative to
the total amount of an alloy powder is 2 mass percent or more.
According to investigations made by the inventors of the present
invention, when a thermosetting resin is excessively added to a
mixed powder for powder metallurgy, the fluidity of the powder and
the density of the green compact are decreased.
[0010] According to Japanese Unexamined Patent Application
Publication No. 10-303009 (Claims), an epoxy resin powder having an
average particle diameter of 50 .mu.m or less, which is used as a
resin binder, is mixed with a magnetic powder to mold a bonded
magnet. The compounding ratio of the epoxy resin powder to the
magnetic powder is 0.1 to 0.5 mass percent. An inorganic additive
is added to the mixed powder in order to suppress the abrasion with
a die during molding. However, in this mixed powder, a component
that improves the strength or machinability of the compact is not
considered. In addition, the content of this inorganic additive is
very small (20 to 40 mass percent of the total amount of the resin
binder, 0.02 to 0.2 mass percent of the total amount of the
magnetic powder). Therefore, even if the inorganic additive has a
function of enhancing the strength of the compact or the like, the
function may not be fulfilled in such a small content.
SUMMARY OF THE INVENTION
[0011] In view of the above-described situation, it is an object of
the present invention to provide a mixed powder for powder
metallurgy to be used as a feedstock of a green compact. Because of
its excellent fluidity, the mixed powder provides a high
productivity. Furthermore, a green compact using the mixed powder
as a feedstock has an adequate density and strength, and is
excellent in terms of machinability. Therefore, a cutting operation
can be performed prior to the sintering process, and in addition,
the lifetime of a cutting tool used can be extended. Also, it is an
object of the present invention to provide a green compact using
this mixed powder as a feedstock for powder metallurgy, the green
compact having an excellent strength and the like even before
sintering.
[0012] To solve the above-described problems, the inventors of the
present invention have extensively studied, in particular, the
composition of a mixed powder for powder metallurgy and found the
following: When a component for improving mechanical properties and
a thermosetting resin powder are added to a base powder, and in
addition, an appropriate thermosetting resin powder is used, a
green compact having an adequate density and strength can be
produced. The present invention has been made on the basis of this
finding.
[0013] Specifically, a mixed powder for powder metallurgy of the
present invention is used as a feedstock of a green compact, and
the mixed powder includes an iron powder and/or an iron alloy
powder, a component for improving mechanical properties, and a
thermosetting resin powder. In the mixed powder, the thermosetting
resin powder is composed of at least one resin selected from the
group consisting of an epoxy-polyester-based resin, an epoxy-based
resin, and an acrylic-based resin. In addition, the average
particle diameter of the thermosetting resin powder is 100 .mu.m or
less, and the content of the thermosetting resin powder relative to
the total amount of the iron powder and/or the iron alloy powder is
0.05 to 1.0 mass percent.
[0014] The mixed powder for powder metallurgy preferably further
includes a lubricant. This is because the lubricant can decrease
the coefficient of friction between the green compact and a die. As
a result, the generation of die galling and damage of the die can
be suppressed. The lubricant is preferably at least one compound
selected from the group consisting of ethylenebisstearamide,
stearamide, zinc stearate, and lithium stearate. This is because
these compounds are excellent as an additional component of the
mixed powder for powder metallurgy.
[0015] The component for improving mechanical properties is
preferably at least one substance selected from the group
consisting of copper, nickel, chromium, molybdenum, graphite, and
manganese sulfide. This is because these substances are diffused
into the iron powder or the like during the sintering process.
Consequently, the hardness or the toughness of the compact can be
improved or the machinability of the compact can be improved.
[0016] Furthermore, a green compact of the present invention is
made of the above-described mixed powder for powder metallurgy.
[0017] The mixed powder for powder metallurgy of the present
invention has excellent fluidity and the like and provides an
excellent productivity. Furthermore, since a green compact using
this mixed powder as a feedstock has an adequate density and
strength even before sintering, the green compact can be subjected
to a cutting operation. In addition, since the green compact does
not have an excessively high strength, the lifetime of a cutting
tool used can be extended. Accordingly, the mixed powder for powder
metallurgy of the present invention and the green compact using the
mixed powder as a feedstock are excellent for industrial
application from the viewpoint that the productivity of powder
metallurgy can be improved.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A mixed powder for powder metallurgy of the present
invention includes an iron powder and/or an iron alloy powder, a
component for improving mechanical properties, and a thermosetting
resin powder. The thermosetting resin powder is composed of at
least one resin selected from the group consisting of an
epoxy-polyester-based resin, an epoxy-based resin, and an
acrylic-based resin; the average particle diameter of the
thermosetting resin powder is 100 .mu.m or less; and the content of
the thermosetting resin powder relative to the total amount of the
iron powder and/or the iron alloy powder is 0.05 to 1.0 mass
percent.
[0019] For example, commercially available normal iron powders
and/or iron alloy powders used for a material for metallurgy can be
used in the present invention.
[0020] The component for improving mechanical properties is added
in order to improve the mechanical properties such as the hardness
and the toughness of a compact or to improve the machinability of
the compact by diffusing into a base iron powder or the like during
the sintering process. Examples of the component for improving
mechanical properties include metal powders used for alloys such as
copper, nickel, chromium, and molybdenum powders; and inorganic
powders such as graphite and manganese sulfide powders. These
components may be used alone or in combinations of two or more
powders. The component for improving mechanical properties may be
mixed with an iron powder or the like when used. Alternatively, for
example, graphite may be uniformly adhered to an iron powder or the
like with a binder therebetween when used.
[0021] The content of metal powder used for alloys serving as a
component for improving mechanical properties is 0.1 to 4 mass
percent (hereinafter, unless otherwise stated, the "mass percent"
is simply represented by "%") relative to the total amount of a
base iron powder or the like. At a content of less than 0.1%, a
satisfactory improvement of mechanical properties may not be
achieved because of a small amount of diffusion in the base powder.
On the other hand, at a content exceeding 4%, the improvement of
mechanical properties is also decreased. In addition, at such an
excessively high content, a green compact having a satisfactory
density may not be produced because the compressibility is
impaired. The content of inorganic powder such as graphite is 0.1%
to 1% relative to the total amount of a base iron powder or the
like. At a content of less than 0.1%, the improvement may not be
satisfactory. At a content exceeding 1%, the mechanical properties
may be impaired.
[0022] The thermosetting resin powder of the present invention is
cured on the surface or inside of a green compact by a simple heat
treatment to increase the bonding strength between base iron
particles or the like. As a result, even prior to the sintering
process, a cutting operation can be performed. Examples of the
material of the thermosetting resin powder of the present invention
mainly include (1) epoxy-polyester-based resins, (2) epoxy-based
resins, (3) acrylic-based resins, and (4) mixtures including at
least two of these.
[0023] The thermosetting resin powder is not a liquid but must be a
powder because it must exhibit fluidity during the production
process of a green compact. Accordingly, powder coatings that do
not include a pigment and are colorless (i.e., clear powder
coatings) can be used for the thermosetting resin powder.
[0024] The "epoxy-polyester-based resin" refers to an
epoxy-group-containing resin crosslinked with a
carboxylic-acid-group-containing polyester resin serving as a
curing agent.
[0025] Examples of the epoxy-group-containing resin include
compounds having at least two epoxy groups per molecule. More
specifically, examples of the epoxy-group-containing resin include
reaction products of a novolak-type phenolic resin and
epichlorohydrin; reaction products of a bisphenol resin (A, B, F
types, and the like) and epichlorohydrin; reaction products of a
novolak-type phenolic resin, a bisphenol resin (A, B, F types, and
the like), and epichlorohydrin; reaction products of a novolak-type
phenolic resin and a bisphenol resin (A, B, F types, and the like);
reaction products of a cresol compound such as cresol novolak, and
epichlorohydrin; glycidyl ethers obtained by reacting an alcohol
compound such as ethylene glycol, propylene glycol, 1,4-butanediol,
polyethylene glycol, polypropylene glycol, neopentyl glycol, or
glycerol with epichlorohydrin; glycidyl esters obtained by reacting
a carboxylic acid such as succinic acid, adipic acid, phthalic
acid, terephthalic acid, hexahydrophthalic acid, or trimellitic
acid with epichlorohydrin; reaction products of a hydroxycarboxylic
acid such as p-hydroxybenzoic acid or .beta.-oxynaphthoic acid and
epichlorohydrin; triglycidyl isocyanurate and derivatives thereof.
These epoxy-group-containing resins may be used in combinations of
two or more resins.
[0026] The "carboxylic-acid-group-containing polyester resin"
includes at least two carboxylic acid groups or carboxylic
anhydride groups. Examples of the carboxylic-acid-group-containing
polyester resin include resins obtained by condensation
polymerization using an acid component mainly composed of a
polycarboxylic acid and an alcohol component mainly composed of a
polyhydric alcohol.
[0027] Examples of the acid component include terephthalic acid,
isophthalic acid, phthalic acid, and anhydrides thereof; aromatic
dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid,
2,7-naphthalenedicarboxylic acid, and anhydrides thereof; saturated
aliphatic dicarboxylic acids such as succinic acid, adipic acid,
azelaic acid, sebacic acid, dodecanedicarboxylic acid,
1,4-cyclohexanedicarboxylic acid, and anhydrides thereof; lactones
such as .gamma.-butyrolactone and .epsilon.-caprolactone; aromatic
hydroxymonocarboxylic acids such as p-hydroxyethoxybenzoic acid;
and hydroxycarboxylic acids corresponding to these. These acid
components may be used in combinations of two or more
components.
[0028] Examples of the alcohol component include ethylene glycol,
diethylene glycol, triethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,2-butanediol, 1,3-butanediol 1,4-butanediol,
1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol,
1,4-hexanediol, 1,5-hexanediol, 2,5-hexanediol,
1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, alkylene oxide
adducts of bisphenol A, alkylene oxide adducts of bisphenol S,
neopentyl glycol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol,
1,2-octadecanediol, trimethylolpropane, glycerin, and
pentaerythritol. These alcohol components may be used in
combinations of two or more components.
[0029] The molar ratio of the total amount of epoxy group in the
epoxy-group-containing resin to the total amount of acid group in
the carboxylic-acid-group-containing polyester resin is
appropriately determined according to the minimum melt viscosity.
In general, the molar ratio is preferably 1/1 to 1/0.5, and more
preferably 1/0.8 to 1/0.6.
[0030] The "epoxy-based resin" refers to an epoxy-group-containing
resin crosslinked with an amine curing agent or an acid curing
agent. The same epoxy-group-containing resins as those described as
a component of the above epoxy-polyester-based resin can be used
for this epoxy-group-containing resin.
[0031] Examples of the amine curing agent include chain aliphatic
amines such as ethylenediamine, diethylenetriamine,
triethylenetetramine, tetraethylenepentamine, dipropylenediamine,
diethylaminopropylamine, and hexamethylenediamine; cyclic aliphatic
amines such as menthanediamine, isophoronediamine,
bis(4-amino-3-methylcyclohexyl)methane, diaminocyclohexylmethane,
bis(aminomethyl)cyclohexane, N-aminoethylpiperazine, and
3,9-bis(3-aminopropyl)2,4,8,10-tetraoxaspiro[5.5]undecane; and
aromatic amines such as m-xylenediamine, metaphenylenediamine,
diaminodiphenylmethane, diaminodiphenylsulfone, and
diaminodiethyldiphenylmethane.
[0032] Examples of the acid curing agent include aliphatic acid
anhydrides such as dodecenylsuccinic anhydride, polyadipic
anhydride, polyazelaic anhydride, polysebacic anhydride,
poly(ethyloctadecanedioic) anhydride, and
poly(phenylhexadecanedioic) anhydride; alicyclic acid anhydrides
such as methyltetrahydrophthalic anhydride, methylhexahydrophthalic
anhydride, methyl himic anhydride, hexahydrophthalic anhydride,
tetrahydrophthalic anhydride, a trialkyltetrahydrophthalic
anhydride, and methylcyclohexenedicarboxylic anhydride; aromatic
acid anhydrides such as phthalic anhydride, trimellitic anhydride,
pyromellitic anhydride, benzophenonetetracarboxylic anhydride,
ethylene glycol bistrimellitate, and glycerol tristrimellitate; and
halogen-containing acid anhydrides such as chlorendic anhydride and
tetrabromophthalic anhydride.
[0033] The "acrylic-based resin" refers to an acrylic resin having
a glycidyl group in the side chain, the acrylic resin being
crosslinked with a dibasic acid serving as a curing agent.
[0034] Examples of a monomer constituting the "acrylic resin having
a glycidyl group in the side chain" include glycidyl acrylate,
glycidyl methacrylate, .beta.-methylglycidyl acrylate, and
.beta.-methylglycidyl methacrylate. These monomers may be used in
combinations of two or more monomers. Alternatively, these monomers
may be copolymerized with another monomer to prepare the acrylic
resin. Examples of the other monomer include alkyl vinyl ethers
such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether,
isobutyl vinyl ether, and cyclohexyl vinyl ether; esters of an
alkyl carboxylic acid and vinyl alcohol such as vinyl acetate,
vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl
valerate, and vinyl cyclohexanecarboxylate; alkyl allyl ethers such
as ethyl allyl ether, propyl allyl ether, butyl allyl ether,
isobutyl allyl ether, and cyclohexyl allyl ether; alkyl allyl
esters such as ethyl allyl ester, propyl allyl ester, butyl allyl
ester, isbbutyl allyl ester, and cyclohexyl allyl ester; alkenes
such as ethylene, propylene, butylene, and isobutylene; acrylics;
esters of acrylic acid or methacrylic acid such as ethyl acrylate,
propyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl
acrylate, ethyl methacrylate, propyl methacrylate, butyl
methacrylate, isobutyl methacrylate, and 2-ethylhexyl methacrylate;
styrene and derivatives thereof such as styrene and
.alpha.-methylstyrene; acrylamides such as acrylamide and
methacrylamide; acrylonitriles such as acrylonitrile and
methacrylonitrile; halogen-containing vinyl monomers; and
silicon-containing vinyl monomers. These monomers may be used in
combinations of two or more monomers.
[0035] The above-described monomers are polymerized and are then
crosslinked with a dibasic acid to prepare the acrylic-based resin
used in the present invention. The same acid curing agents as those
used in the epoxy-based resin can be used as this dibasic acid.
[0036] In addition to the above resins, another resin may be added.
Examples of the other resin include polyurethane-based resins
prepared by curing a hydroxyl-group-containing polyester resin with
an isocyanate curing agent, polyester-based resins prepared by
curing a carboxyl-group-containing polyester resin with triglycidyl
isocyanate or the like, resins prepared by curing a
hydroxyl-group-containing polyester resin with an acrylic resin
having an isocyanate group in the side chain, and resins prepared
by curing a carboxyl-group-containing polyester resin with an
acrylic resin having a glycidyl group in the side chain.
[0037] The average particle diameter of thermosetting resin powder
is 100 .mu.m or less. When a thermosetting resin powder having an
average particle diameter of exceeding 100 .mu.m is used, it is
difficult to coat entire base iron particles or the like with the
resin melted by a heat treatment. In such a case, the strength of a
compact may not be satisfactorily improved. The average particle
diameter of thermosetting resin powder is more preferably 80 .mu.m
or less, particularly 60 .mu.m or less. Although the lower limit is
not particularly limited, the lower limit is generally about 30
.mu.m. With respect to the "average particle diameter" in the
present invention, when a commercially available resin powder is
used, the value described in a catalog or the like should be
referred to as the average particle diameter. When the average
particle diameter is not known, the particle size distribution is
measured by a normal particle size distribution analyzer.
Subsequently, the particle diameter at the cumulative value of 50%
(D.sub.50) from the smallest particle diameter is determined from
the result and defined as the average particle diameter.
[0038] The content of resin powder is 0.05% to 1.0% relative to the
total amount of an iron powder and/or an iron alloy powder. At a
resin powder content of less than 0.05%, the strength of a green
compact cannot be satisfactorily improved and cutting operation
prior to the sintering process cannot be performed. On the other
hand, at a resin powder content exceeding 1.0%, the fluidity of a
mixed powder is decreased, thus reducing the productivity. In such
a case, the density of a green compact is also decreased.
[0039] Some of the commercially available resin powders include a
pigment for the purpose of coloring. A commercially available resin
powder including a pigment may be used for the resin powder in the
present invention. However, since the pigment may have an adverse
effect on the strength of a green compact, a pigment-free resin
powder is preferably used.
[0040] A lubricant may be added to the mixed powder for powder
metallurgy of the present invention. The lubricant decreases the
coefficient of friction between the green compact and a die,
thereby suppressing the generation of die galling and damage of the
die. Preferable examples of the lubricant usable in the present
invention include ethylenebisstearamide, stearamide, zinc stearate,
lithium stearate, and mixtures of at least two of these. These
lubricants should be selected according to the intended purpose of
the compact when used.
[0041] The content of the lubricant is 0.05% to 1.0% relative to
the total amount of a base iron powder or the like. At a content of
less than 0.05%, the lubricity may be insufficient. At a content
exceeding 1.0%, the curing of a resin powder may not be
satisfactorily performed and the fluidity of mixed powder may be
insufficient.
[0042] The above-described mixed powder for powder metallurgy of
the present invention is molded by a normal method to produce a
green compact. For example, a die is filled with the mixed powder
and a pressure of 5 to 7 t/cm.sup.2 (490 to 686 MPa) is applied.
Subsequently, a heat treatment is performed in order that the
thermosetting resin powder is cured to increase the strength of the
green compact. Although the conditions for the heat treatment
mainly depend on the type of thermosetting resin powder added, in
general, the heat treatment is simply performed at about
150.degree. C. to about 200.degree. C. for 10 to 30 minutes (more
preferably 15 to 20 minutes).
[0043] In general, a green compact cannot be subjected to a cutting
operation prior to sintering because the green compact is brittle.
However, for example, when the mixed powder for powder metallurgy
of the present invention is molded at a pressure of 5 t/cm.sup.2
(490.3 MPa), the resultant green compact has a strength of at least
30 MPa measured in accordance with Japan Powder Metallurgy
Association (JPMA) Standard M09-1992. Thus, the use of the mixed
powder for powder metallurgy of the present invention as a
feedstock can provide a green compact capable of being subjected to
a cutting operation. In other words, since the green compact of the
present invention has an adequate density and strength even prior
to the sintering process, the green compact can be subjected to a
cutting operation, and in addition, the lifetime of a cutting tool
used can be extended.
[0044] The present invention will now be described in more detail
by way of examples, but the scope of the present invention is not
limited to these examples.
EXAMPLES
Example 1
[0045] A pure iron powder (trade name: "Atomel 300M", from Kobe
Steel, Ltd.) was used as a base metal powder. A commercially
available copper powder (2.0.mass percent of the amount of the pure
iron powder) (hereinafter, the "mass percent" is simply referred to
as "%"), a graphite powder (0.8%), ethylenebisstearamide (0.75%),
and a clear powder coating (0.3%) composed of an
epoxy-polyester-based resin (Konac No. 2700 from BASF NOF Coatings
Co., Ltd., a resin produced by reacting an epoxy resin with a
dibasic acid polyester, average particle diameter: 40 .mu.m) were
added to the pure iron powder. The mixture was agitated at a high
speed with a mixer with blades. The apparent density of the
resultant mixed powder was measured in accordance with Japanese
Industrial Standard (JIS) Z2504. The flow rate was also measured in
accordance with JIS Z2502.
[0046] A green compact having a diameter of 11.3 mm and a height of
10 mm was produced at a pressure of 5 t/cm.sup.2 (490.3 MPa) in
accordance with Japan Society of Powder and Powder Metallurgy
(JSPM) Standard 1-64 (a metal powder compressibility testing
method) using the above mixed powder as a feedstock. The green
compact was heated at 170.degree. C. for 15 minutes. The density of
the green compact was then measured. Also, the strength of the
green compact was measured in accordance with JPMA M09-1992.
[0047] Furthermore, a green compact having a diameter of 25 mm and
a height of 15 mm was produced at a surface pressure of 490 MPa
using the above mixed powder as a feedstock to measure a ejection
force, which is an indicator of lubricity. Specifically, the
draw-out pressure was calculated by dividing a load required for
drawing out the green compact from the die during molding by the
area of contact between the die and the green compact. These
samples are referred to as No. 1 and the results are shown in Table
1.
Example 2
[0048] A mixed powder was produced as in Example 1 except that a
clear powder coating composed of an acrylic-based resin (Konac No.
4600 from BASF NOF Coatings Co., Ltd., a resin produced by
crosslinking an acrylic resin having a glycidyl group in the side
chain with a dibasic acid, average particle diameter: 40 .mu.m) was
used instead of the clear powder coating composed of the
epoxy-polyester-based resin used in Example 1. Furthermore, a green
compact was produced as in Example 1 except that the green compact
was heated at 180.degree. C. for 15 minutes. These samples are
referred to as No. 2. The apparent density of the mixed powder, the
density of the green compact, and the like were measured as in
Example 1. Table 1 shows the results.
[0049] A mixed powder and a green compact made of the mixed powder
were produced as in Example 1 except that a clear powder coating
composed of an epoxy-based resin (Konac No. 3700 from BASF NOF
Coatings Co., Ltd., a resin produced by curing an uncured epoxy
resin with an amine curing agent, average particle diameter: 40
.mu.m) was used as a thermosetting resin powder, and the green
compact was heated at 160.degree. C. for 15 minutes. These samples
are referred to as No. 3. The apparent density of the mixed powder
and the like were measured by the same methods. Table 1 shows the
results.
Example 3
[0050] Mixed powders and green compacts made of the mixed powders
were produced as in Example 1 except that the content of the clear
powder coating composed of the epoxy-polyester-based resin (Konac
No. 2700 from BASF NOF Coatings Co., Ltd., average particle
diameter: 40 .mu.m) was 1.0% (No. 4) or 0.1% (No. 5). The apparent
density of the mixed powders and the like were measured as in
Example 1. Table 1 shows the results.
Comparative Example 1
[0051] Mixed powders and green compacts made of the mixed powders
were produced as in Example 1 except that the clear powder coating
composed of the epoxy-polyester-based resin (Konac No. 2700 from
BASF NOF Coatings Co., Ltd., average particle diameter: 40 .mu.m)
was not contained (No. 6), or the content of the clear powder
coating composed of the epoxy-polyester-based resin (Konac No. 2700
from BASF NOF Coatings Co., Ltd., average particle diameter: 40
.mu.m) was 0.03% (No. 7) or 1.2% (No. 8).
[0052] Furthermore, mixed powders and green compacts made of the
mixed powders were produced as in Example 1 except that the average
particle diameter of the clear powder coating composed of the
epoxy-polyester-based resin was 150 .mu.m (No. 9) or 250 .mu.m (No.
10) instead of 40 .mu.m.
[0053] The apparent density of these mixed powders and the like
were measured as in Example 1. Table 1 shows the results.
TABLE-US-00001 TABLE 1 Density Strength Apparent of green of green
Ejection density Flow rate compact compact force (g/cm.sup.3)
(sec/50 g) (g/cm.sup.3) (MPa) (MPa) No. 1 3.14 27.8 6.87 52 12.0
No. 2 3.15 29.1 6.87 50 11.8 No. 3 3.16 28.3 6.86 48 12.1 No. 4
3.08 32.5 6.80 105 12.3 No. 5 3.16 28.2 6.92 35 11.7 No. 6 3.17
27.8 6.94 25 11.5 No. 7 3.16 28.1 6.93 26 11.8 No. 8 3.01 35.3 6.75
108 12.2 No. 9 3.13 29.7 6.85 29 11.9 No. 10 3.14 30.1 6.82 27
12.2
[0054] The results showed that the green compacts composed of a
mixed powder for powder metallurgy that did not contain a resin
powder or a mixed powder for powder metallurgy in which the content
of a resin powder was less than the amount specified in the present
invention had an insufficient strength and could not be subjected
to a cutting operation (Nos. 6 and 7). The green compacts composed
of a mixed powder in which the average particle diameter of the
resin powder exceeded the range in the present invention also
showed the same results (Nos. 9 and 10). In addition, when the
content of the resin powder exceeded the range specified in the
present invention, the green compact had a satisfactory strength,
but had a low density. This green compact was also not suited for a
cutting operation, and in addition, the mixed powder itself had a
low fluidity (No. 8).
[0055] In contrast, the mixed powders for powder metallurgy
containing a resin powder within the content range specified in the
present invention had excellent fluidity, and green compacts made
of these mixed powders had an adequate density and strength and
thus were suited for a cutting operation. These examples
demonstrates that, according to the present invention, since the
green compact has an adequate density and strength even prior to
the sintering process, the green compact can be subjected to a
cutting operation, and in addition, the lifetime of a cutting tool
used can be extended.
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