U.S. patent application number 16/394259 was filed with the patent office on 2019-08-15 for slide member and method for producing same.
This patent application is currently assigned to NTN CORPORATION. The applicant listed for this patent is NTN CORPORATION. Invention is credited to Takahiro GOTOU, Yoshinori ITO, Fuminori SATOJI.
Application Number | 20190249716 16/394259 |
Document ID | / |
Family ID | 58865582 |
Filed Date | 2019-08-15 |
View All Diagrams
United States Patent
Application |
20190249716 |
Kind Code |
A1 |
ITO; Yoshinori ; et
al. |
August 15, 2019 |
SLIDE MEMBER AND METHOD FOR PRODUCING SAME
Abstract
Raw material powder containing metal powder as a main component
is molded to form a metal powder molded body (3'), and the metal
powder molded body (3') is sintered to form a metal substrate (3).
Further, a lubricating member (4) is made of an aggregate of
graphite particles (13), and at least a part of a bearing surface
(11) is formed of the lubricating member (4). The lubricating
member (4) is fitted into the metal powder molded body (3'). After
that, the metal powder molded body (3') is sintered, and at this
time, the lubricating member (4) is fixed onto the metal substrate
(3) with a contraction force (F) generated in the metal powder
molded body (3').
Inventors: |
ITO; Yoshinori; (Aichi,
JP) ; GOTOU; Takahiro; (Aichi, JP) ; SATOJI;
Fuminori; (Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NTN CORPORATION |
Osaka |
|
JP |
|
|
Assignee: |
NTN CORPORATION
Osaka
JP
|
Family ID: |
58865582 |
Appl. No.: |
16/394259 |
Filed: |
April 25, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15511722 |
Mar 16, 2017 |
10323689 |
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PCT/JP2015/076545 |
Sep 17, 2015 |
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16394259 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16C 33/16 20130101;
B22F 3/162 20130101; F16C 33/26 20130101; C22C 32/0084 20130101;
F16C 2204/10 20130101; F16C 33/1095 20130101; B22F 1/02 20130101;
B22F 2998/10 20130101; F16C 2220/20 20130101; B22F 7/062 20130101;
F16C 33/10 20130101; F16C 33/14 20130101; B22F 5/106 20130101; B22F
2998/10 20130101; B22F 1/0059 20130101; B22F 3/10 20130101; B22F
7/062 20130101; B22F 2003/023 20130101; B22F 2003/166 20130101 |
International
Class: |
F16C 33/10 20060101
F16C033/10; B22F 3/16 20060101 B22F003/16; B22F 5/10 20060101
B22F005/10; F16C 33/14 20060101 F16C033/14; F16C 33/16 20060101
F16C033/16; B22F 1/02 20060101 B22F001/02; F16C 33/26 20060101
F16C033/26 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2014 |
JP |
2014-191487 |
Sep 24, 2014 |
JP |
2014-193833 |
Dec 26, 2014 |
JP |
2014-265215 |
Aug 18, 2015 |
JP |
2015-161126 |
Aug 26, 2015 |
JP |
2015-166754 |
Claims
1-10. (canceled)
11. A method of manufacturing a sliding member having a sliding
surface that slides with a mating member, the method comprising:
firing powder containing solid lubricant powder and a binder, to
thereby form a lubricating member; molding raw material powder
containing metal powder as a main component to form a metal powder
molded body, and bringing the lubricating member into contact with
the metal powder molded body so that a part of the lubricating
member appears on a surface to be the sliding surface; and heating
the lubricating member and the metal powder molded body at a
sintering temperature under a state in which the lubricating member
is brought into contact with the metal powder molded body, to
thereby form a metal substrate by sintering of the metal powder
molded body, and fix the lubricating member onto the metal
substrate with a contraction force generated in the metal powder
molded body during the sintering.
12. A method of manufacturing a sliding member having a sliding
surface that slides with a mating member, the method comprising:
molding first powder containing, as a main component, coated powder
formed by coating solid lubricant powder with a metal and second
powder containing metal powder as a main component so that the
first powder appears on a surface to be the sliding surface under a
state in which filling regions of the first powder and the second
powder are divided, to thereby form a molded body; heating the
molded body at a sintering temperature, to thereby form a
lubricating member by sintering of the first powder, and form a
metal substrate by sintering of the second powder; and diffusing,
during the sintering, the metal of the coated powder contained in
the first powder into the metal powder of the second powder, to
thereby fix the lubricating member onto the metal substrate.
13. The method of manufacturing a sliding member according to claim
11, wherein the coated powder comprises plated powder formed by
subjecting the solid lubricant powder to metal plating.
14. The method of manufacturing a sliding member according to claim
11, further comprising subjecting the sliding surface to sizing
after fixing the lubricating member onto the metal substrate.
15. The method of manufacturing a sliding member according to claim
12, further comprising subjecting the sliding surface to sizing
after fixing the lubricating member onto the metal substrate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sliding member and a
method of manufacturing the sliding member.
BACKGROUND ART
[0002] A sintered bearing, which is a kind of sliding member, is
obtained by impregnating lubricating oil into a porous metal body
produced by a powder metallurgical process. The lubricating oil
retained in inner pores of the bearing seeps out from the inside of
the bearing to a bearing surface serving as a sliding surface due
to the action of a pump and heat generation in association with the
rotation of a shaft, to thereby form a lubricating oil film on the
bearing surface (for example, Patent Literature 1).
CITATION LIST
[0003] Patent Literature 1: JP 2010-175002 A
[0004] Patent Literature 2: JP 2013-14645 A
[0005] Patent Literature 3: JP 06-32812 U
[0006] Patent Literature 4: JP 2000-266056 A
SUMMARY OF INVENTION
Technical Problem
[0007] In recent years, there has been a demand for a sintered
bearing that can be used even under a severe condition, such as
high contact pressure or high temperature. However, an existing
sintered bearing is liable to be brought into contact with a metal
due to the breakage of the lubricating oil film under high contact
pressure, and the lubricating oil is liable to be degraded early
under high temperature. Therefore, there is a problem in that it is
difficult to obtain stable lubricity. Therefore, in Patent
Literature 1, there is proposed that the composition and
characteristics of the lubricating oil to be impregnated into the
sintered bearing are improved to increase the strength of the
lubricating oil film, to thereby enable the sintered bearing to be
used even under high contact pressure. However, as long as the
lubricating oil mainly contributes to a lubricating function, there
is a limit to the use of the sintered bearing under the severe
condition. Further, there is also a problem in that the sintered
bearing impregnated with the lubricating oil as in Patent
Literature 1 cannot be used in an environment that avoids the
mixing of the lubricating oil.
[0008] Meanwhile, in the sintered bearing as disclosed in Patent
Literature 1, in order to compensate for the lubricity of the
bearing surface, a solid lubricant, such as graphite, is generally
blended with metal powder. However, when the blending amount of the
solid lubricant powder is increased excessively in order to enhance
the lubricity, there is a problem, for example, in that the binding
between metal particles is inhibited to decrease the strength of a
material. Therefore, there is a limit to an increase in amount of
the solid lubricant powder.
[0009] In view of the foregoing, a first object of the present
invention is to provide a sliding member, which has low cost and is
capable of maintaining stable lubricating performance even when
being used in a special environment, such as a severe environment,
and a method of manufacturing the sliding member.
[0010] Further, in Patent Literature 2, there is disclosed a
sliding member in which a lubricating member is embedded in a
sliding surface of a cylindrical substrate. In Patent Literature 2,
as an example of the lubricating member, there is given a fired
body containing artificial graphite as a main component. A through
hole in a radial direction is formed in the cylindrical substrate
of the sliding member, and the lubricating member is fitted into
the through hole to be bonded and fixed thereto.
[0011] However, with such sliding member, it is necessary to fix
the lubricating member onto the substrate with high accuracy, and
hence it takes time and labor to perform the fixing operation.
Further, it is necessary to process the through hole of the
substrate and an outer peripheral surface of the lubricating member
to be fitted into the through hole with high accuracy. Therefore,
the processing cost increases. In particular, when a carbon-based
fired body is used as the lubricating member, the carbon-based
fired body is not easily deformed plastically, and hence shaping,
such as cutting processing, is required in order to increase the
dimensional accuracy, with the result that the processing cost
further increases.
[0012] Further, in Patent Literature 3, there is disclosed an
internal gear pump for supplying gasoline as illustrated in FIG.
31. The gear pump includes an inner rotor 161, a main body 162
including a fixing shaft 162a inserted into an inner periphery of
the inner rotor 161, and an outer rotor 163 that is engaged with
the inner rotor 161 and is arranged so as to be eccentric with
respect to the inner rotor 161. When the outer rotor 163 is rotated
with a drive unit, the inner rotor 161 is rotated, and the outer
rotor 163, the inner rotor 161, and the main body 162 cooperate
with each other to exhibit pumping action.
[0013] The inner rotor 161 arranged in the gear pump is rotated
while sliding with the fixing shaft 162a inserted into the inner
periphery of the inner rotor 161, and hence the inner rotor 161 is
required to have lubricity. However, the inner rotor 161 is brought
into contact with gasoline, and hence lubricating oil that
contaminates gasoline cannot be used. Therefore, the inner rotor
161 may be used in a state in which a carbon ring 164 is
press-fitted into the inner periphery of a substrate of the inner
rotor 161.
[0014] Even in the inner rotor 161, it takes time and labor to
perform the operation of press-fitting the carbon ring 164 into the
inner periphery of the substrate, and it is necessary to process
the substrate and the carbon ring 164 with high accuracy.
Therefore, manufacturing cost increases.
[0015] In view of the foregoing, a second object of the present
invention is to increase the productivity of the sliding member
using a carbon-based fired body and to reduce the manufacturing
cost.
[0016] Further, a lubricating member having a sliding surface
mainly made of graphite is used as, for example, a rotor and a vane
for a vacuum pump, a bearing to be used in a high-temperature
environment exceeding 200.degree. C., or a bearing fora
construction machine. Such lubricating member is manufactured by
subjecting raw material powder mainly containing graphite particles
to compression molding to form a compact and sintering the compact.
However, the graphite particles themselves are hardly deformed
plastically. Therefore, when a large part of the raw material
powder is made of the graphite particles, the raw material powder
cannot be solidified by compression molding, and a compact cannot
be formed. Therefore, in general, when a compact containing
graphite as a main component is formed, raw material powder
containing a mixture of graphite particles and a binding agent,
such as tar pitch or coal tar, is used (see, for example, Patent
Literature 4).
[0017] However, in order to form a compact by the above-mentioned
method, it is necessary that the raw material powder contain about
50 wt % of the binding agent (see paragraph [0010] of Patent
Literature 4). Therefore, the binding agent is decomposed during
sintering to generate a large amount of decomposed gas, causing
problems of contamination of a sintering furnace and exhaust gas.
In order to alleviate the problems, it is necessary to perform
sintering slowly over a long time period, resulting in a
substantial decrease in productivity.
[0018] In view of the foregoing, a third object of the present
invention is to increase the productivity of the lubricating member
having the sliding surface mainly made of graphite.
Solution to Problem
[0019] According to a first invention of the present application,
there is provided a sliding member having a sliding surface that
slides with a mating member, comprising: a metal substrate, which
is formed by sintering raw material powder containing metal powder
as a main component; and a lubricating member, which is made of an
aggregate of solid lubricant particles, wherein at least a part of
the sliding surface is formed of the lubricating member, and
wherein the lubricating member is fixed onto the metal substrate by
a sintering operation of sintering the raw material powder.
[0020] In the above-mentioned configuration, the lubricating member
formed in at least a part of the sliding surface serves as a supply
source of a solid lubricant. The solid lubricant supplied from the
lubricating member permeates to the entire sliding surface due to
the relative sliding with respect to the mating member, and hence a
lubricating effect can be obtained on the entire sliding surface.
Further, in the sliding member, the mating member does not always
slide with the entire sliding surface, and a limited partial region
of the sliding surface may slide with the mating member. In this
case, the mating member can be allowed to slide always with the
lubricating member by designing the position and shape of the
lubricating member so that the lubricating member is positioned in
a sliding region with respect to the mating member or adjusting the
setting posture of the sliding member so that the lubricating
member is positioned in the sliding region. Further, when the area
of the lubricating member that appears on the sliding surface is
increased, the lubricating effect can be enhanced. Also in this
case, the binding force between the metal particles does not
decrease unlike the related-art product, and hence a decrease in
strength of the sliding member can be avoided.
[0021] Meanwhile, when the lubricating member is arranged only in a
partial region of the sliding surface as described above, there is
a problem regarding how to fix the lubricating member onto the
metal substrate serving as a base. In order to address the problem,
the present invention adopts the following new technical means: the
lubricating member is fixed onto the metal substrate by the
sintering operation at a time of sintering the metal substrate.
When the lubricating member is fixed onto the metal substrate by
the sintering operation required in the course of manufacturing of
the sliding member, it is not necessary to perform a fixing
operation in a step that is not related to the original step of
manufacturing a sintered metal, such as press-fitting and bonding.
Therefore, the sliding member can be subjected to near-net-shape
molding, and the cost of the sliding member can be reduced.
[0022] As an example of the structure in which the lubricating
member is fixed onto the metal substrate, it is conceivable that
the lubricating member and the metal substrate are brought into an
interference fit state with a contraction force generated in the
metal substrate along with the sintering operation.
[0023] In this case, the lubricating member may be formed by firing
powder containing solid lubricant powder and a binder.
[0024] The lubricating member may also be formed by sintering,
through the sintering operation, coated powder formed by coating
solid lubricant powder with a metal. In this case, as another
example of the structure in which the lubricating member is fixed
onto the metal substrate, it is conceivable that the lubricating
member and the metal substrate are bound to each other by diffusing
the metal of the coated powder to the metal powder forming the
metal substrate.
[0025] When the sliding surface is subjected to sizing, the sliding
surface with high accuracy can be obtained at low cost. The sizing
may be performed with respect to only one of the metal substrate
and the lubricating member, instead of both the metal substrate and
the lubricating member. Surfaces other than the sliding surface, as
well as the sliding surface, may be subjected to sizing as
necessary. Sizing itself is generally performed even in an existing
sliding member made of a sintered metal, and hence the cost is not
increased even when such treatment is performed.
[0026] The above-mentioned sliding member may be manufactured by:
firing powder containing solid lubricant powder and a binder, to
thereby form a lubricating member; molding raw material powder
containing metal powder as a main component to form a molded body,
and bringing the lubricating member into contact with the molded
body so that a part of the lubricating member appears on a surface
to be the sliding surface; and heating the lubricating member and
the molded body at a sintering temperature under a state in which
the lubricating member is brought into contact with the molded
body, to thereby form the metal substrate by sintering of the
molded body, and fix the lubricating member onto the metal
substrate with a contraction force generated in the molded body
during the sintering.
[0027] Further, the sliding member may also be manufactured by:
molding first powder containing, as a main component, coated powder
formed by coating solid lubricant powder with a metal and second
powder containing metal powder as a main component so that the
first powder appears on a surface to be the sliding surface under a
state in which filling regions of the first powder and the second
powder are divided, to thereby form a molded body; heating the
molded body at a sintering temperature, to thereby form a
lubricating member by sintering of the first powder, and form a
metal substrate by sintering of the second powder; and diffusing,
during the sintering operation, the metal of the coated powder
contained in the first powder into the metal powder of the second
powder, to thereby fix the lubricating member onto the metal
substrate.
[0028] When the sliding surface is subjected to sizing after the
lubricating member is fixed onto the metal substrate, the sliding
surface with high accuracy can be obtained at low cost.
[0029] According to a second invention of the present application,
there is provided a sliding member having a sliding surface that
slides with a mating member, the sliding member comprising: a
carbon-based fired body which contains carbon as a main component
and forms at least a part of the sliding surface; and a resin
substrate which is an injection-molded product of a resin including
the carbon-based fired body as an insert component and is
integrated with the carbon-based fired body. The sliding member may
be manufactured through a fired body forming step of subjecting raw
material powder containing carbon-based powder as a main component
to compression molding to form a compact and firing the compact to
form a carbon-based fired body that forms at least a part of the
sliding surface, and an insert molding step of performing injection
molding with a resin through use of the carbon-based fired body as
an insert component, to thereby form a resin substrate integrated
with the carbon-based fired body.
[0030] As described above, in the sliding member according to the
present invention, the carbon-based fired body and the resin
substrate are integrated with each other by performing injection
molding with a resin through use of the carbon-based fired body as
an insert component. With this, the step of fixing the carbon-based
fired body and the resin substrate onto each other is not required.
Therefore, the number of steps is reduced and the productivity is
increased. Further, it is not necessary to form a through hole for
mounting the carbon-based fired body onto the resin substrate, and
it is not necessary to form the carbon-based fired body with high
accuracy so that the carbon-based fired body is fitted into the
through hole. Therefore, the manufacturing cost is reduced.
[0031] In the above-mentioned sliding member, when an integrated
product of the carbon-based fired body and the resin substrate is
subjected to sizing, the dimensional accuracy (in particular, the
surface accuracy of the sliding surface) in the state of the
integrated product can be enhanced. In particular, when the sliding
member comprises a plurality of carbon-based fired bodies that are
formed separately, the sliding surface of each carbon-based fired
body in the integrated product can be arranged at a predetermined
position (for example, on the same cylindrical surface) by
subjecting the integrated product of the plurality of carbon-based
fired bodies and the resin substrate to sizing.
[0032] When oil is impregnated into inner pores of the carbon-based
fired body in the above-mentioned sliding member, the oil seeps out
to the sliding surface, to thereby further enhance the lubricity.
In this case, the oil may be impregnated into the inner pores of
the carbon-based fired body by, for example, immersing the
integrated product of the carbon-based fired body and the resin
substrate into the oil.
[0033] In the above-mentioned sliding member, it is preferred that,
for example, a resin containing a crystalline resin as a main
component be used as the resin forming the resin substrate.
[0034] The above-mentioned sliding member can be used as, for
example, a bearing or a gear wheel having a sliding surface on an
inner peripheral surface. Specifically, the sliding member can be
used as, for example, a gear wheel for a fuel pump having a sliding
surface that slides with an outer peripheral surface of a shaft on
an inner peripheral surface and having a tooth surface on an outer
peripheral surface.
[0035] According to a third invention of the present application,
there is provided a method of manufacturing a lubricating member in
which graphite particles occupy the largest area of the sliding
surface, the method comprising: a compacting step of subjecting raw
material powder that contains the graphite particles having binder
metal powder adhering thereto to compression molding, to thereby
provide a compact; and a sintering step of sintering the compact at
a temperature equal to or less than the melting point of the binder
metal powder, to thereby bind the binder metal powder to each
other.
[0036] Through the above-mentioned manufacturing method, the
lubricating member can be obtained in which the graphite particles
occupy the largest area of the sliding surface and in which the
binder metal adheres to each graphite particle and the binder metal
is bound to each other by sintering.
[0037] As described above, in the lubricating member of the present
invention, the binder metal is interposed between the graphite
particles contained in the raw material powder through use of the
raw material powder containing the graphite particles having the
binder metal adhering thereto. With this, the binder metal is
deformed plastically during compression molding, to thereby
solidify the raw material powder, with the result that the compact
can be formed. Further, when the binder metal adhering to each
graphite particle is bound to each other by sintering, the graphite
particles can be bound to each other through the binder metal.
Thus, a binding agent of the raw material powder can be omitted (or
reduced). Therefore, the generation of decomposed gas during
sintering is suppressed, and the sintering time can be shortened to
increase the productivity.
Advantageous Effects of Invention
[0038] According to the first invention of the present application,
the sliding member having high lubricating performance can be
provided at low cost. This sliding member enables high lubricating
performance to be obtained even in a special environment, for
example, a severe environment, such as high temperature, high
contact pressure, and high-speed rotation, or an environment in
which it is difficult to use lubricating oil.
[0039] According to the second invention of the present
application, the productivity of the sliding member using the
carbon-based fired body can be increased, and the manufacturing
cost can be reduced.
[0040] According to the third invention of the present application,
the productivity of the lubricating member having the sliding
surface mainly made of graphite can be increased.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1A is a front view of a sintered bearing according to a
first embodiment of a first invention of the present
application.
[0042] FIG. 1B is a sectional view taken along the line B-B of the
sintered bearing of FIG. 1A.
[0043] FIG. 2A is a front view of a fired body.
[0044] FIG. 2B is a side view of the fired body.
[0045] FIG. 3 is a sectional view for illustrating granulated
powder.
[0046] FIG. 4 is a sectional view of a fired lubricating
member.
[0047] FIG. 5 is a front view of a metal substrate.
[0048] FIG. 6 is a sectional view of plated powder.
[0049] FIG. 7 is a sectional view for illustrating a compression
molding step.
[0050] FIG. 8 is a sectional view for illustrating the compression
molding step.
[0051] FIG. 9 is a sectional view for illustrating the compression
molding step.
[0052] FIG. 10 is a sectional view for illustrating the compression
molding step.
[0053] FIG. 11 is a sectional view for illustrating the compression
molding step.
[0054] FIG. 12 is a sectional view for illustrating the compression
molding step.
[0055] FIG. 13 is a front view and main part enlarged view of a
sintered bearing according to a second embodiment of the first
invention of the present application.
[0056] FIG. 14A is a front view for illustrating a sintered bearing
according to another embodiment.
[0057] FIG. 14B is a front view for illustrating a sintered bearing
according to another embodiment.
[0058] FIG. 15A is a model view for illustrating metal powder
before sintering.
[0059] FIG. 15B is a model view for illustrating metal powder after
sintering.
[0060] FIG. 16 is an exploded perspective view of an internal gear
pump.
[0061] FIG. 17 is a sectional view for illustrating a fitted
portion between an outer rotor and an inner rotor.
[0062] FIG. 18A is a front view of a sliding member (bearing)
according to one embodiment of a second invention of the present
application.
[0063] FIG. 18B is a sectional view taken along the line B-B of the
sliding member of FIG. 18A.
[0064] FIG. 19 is an enlarged sectional view of a carbon-based
fired body.
[0065] FIG. 20 is a sectional view for illustrating an insert
molding step.
[0066] FIG. 21 is a plan view of the insert molding step of FIG. 20
when viewed from a C-direction.
[0067] FIG. 22A is a sectional view for illustrating a sizing
step.
[0068] FIG. 22B is a sectional view for illustrating the sizing
step.
[0069] FIG. 23 is an enlarged sectional view of a carbon-based
fired body of a sliding member according to another embodiment.
[0070] FIG. 24 is a front view for illustrating a sliding member
according to another embodiment.
[0071] FIG. 25 is a front view for illustrating a sliding member
according to another embodiment.
[0072] FIG. 26 is a front view for illustrating a sliding member
according to another embodiment.
[0073] FIG. 27 is a front view for illustrating a sliding member
according to another embodiment.
[0074] FIG. 28 is a front view of a sliding member according to
another embodiment (inner rotor for a fuel pump).
[0075] FIG. 29 is a sectional view taken along the line A-A of the
sliding member of FIG. 28.
[0076] FIG. 30 is a front view of a sliding member according to
another embodiment (planetary gear).
[0077] FIG. 31 is an exploded perspective view of an internal gear
pump.
[0078] FIG. 32A is a sectional view of a particle of graphite
powder having copper adhering thereto in which the entire surface
of a graphite particle is coated with copper.
[0079] FIG. 32B is a sectional view of a particle of graphite
powder having copper adhering thereto in which a part of the
surface of the graphite particle is coated with copper.
[0080] FIG. 33 is an enlarged sectional view of the vicinity of a
sliding surface of a sliding member according to an embodiment of a
third invention of the present application.
DESCRIPTION OF EMBODIMENTS
[0081] Now, a sintered bearing is exemplified as an example of a
sliding member according to a first invention of the present
application, and the details thereof are described with reference
to FIGS. 1 to FIGS. 15.
[0082] As illustrated in FIG. 1A and FIG. 1B, a sintered bearing 1
has a cylindrical shape, and a bearing surface 11 having a
cylindrical surface shape serving as a sliding surface is formed on
an inner periphery of the sintered bearing 1. When a shaft 2
(represented by the alternate long and two short dashed line)
serving as a mating member is inserted into, the inner periphery of
the sintered bearing 1, the shaft 2 is supported by the bearing
surface 11 in a rotatable manner. When the shaft 2 is used as a
rotation shaft, an outer peripheral surface 12 of the sintered
bearing 1 is fixed onto an inner peripheral surface of a housing
(not shown) by means of, for example, press-fitting or bonding. The
shaft 2 may also be set to a stationary side instead of being set
to a rotation side as described above, and the sintered bearing 1
may be set to the rotation side.
[0083] The sintered bearing 1 illustrated in FIG. 1A and FIG. 1B
comprises a metal substrate 3, which is made of a sintered metal,
and lubricating members 4, each of which is made of an aggregate of
a large number of graphite particles. The metal substrate 3
comprises retaining parts 3a configured to retain the lubricating
members 4 in a plurality of portions equally arranged in a
circumferential direction of the metal substrate 3. Each retaining
part 3a is a recessed part-opened to an inner peripheral surface 3b
of the metal substrate 3, and a cross-section (cross-section in a
direction orthogonal to the axial direction) of the retaining part
3a is formed into a shape matched with the sectional shape of the
lubricating member 4. The retaining part 3a in this embodiment has
a partially cylindrical surface shape obtained by cutting off a
partial circumferential region of a cylindrical surface and is
formed into the same shape over the entire length in the axial
direction of the metal substrate 3 so as to be opened to both axial
end surfaces of the metal substrate 3.
[0084] The lubricating member 4 is formed into a shape (partially
cylindrical shape) matched with the shape of the retaining part 3a
of the metal substrate 3. The peripheral surface of the lubricating
member 4 comprises an outer side surface 4a opposed to the
retaining part 3a of the metal substrate 3 and an inner side
surface 4b opposed to an outer peripheral surface of the shaft 2.
The outer side surface 4a is formed into a protruding cylindrical
surface shape that is brought into surface contact with the
retaining part 3a of the metal substrate 3, and the inner side
surface 4b is formed into a recessed cylindrical surface shape that
continues without any step from the inner peripheral surface 3b of
the metal substrate 3. The inner peripheral surface 3b of the metal
substrate 3 and the inner side surface 4b of the lubricating member
4 form the bearing surface 11 having a true circle shape in
cross-section as the sliding surface.
[0085] In the sintered bearing 1, the lubricating member 4 formed
in a part of the bearing surface 11 serves as a supply source of
graphite particles. The graphite particles supplied from the
lubricating member 4 permeate to the entire bearing surface 11 due
to the relative motion of the bearing surface 11 and the shaft 2,
and hence a lubricating effect can be obtained on the entire
bearing surface 11.
[0086] Further, in the sintered bearing 1, the shaft 2 does not
always slide with the entire bearing surface 11, and a limited
partial region of the bearing surface 11 slides with the shaft 2 in
most cases. For example, when the shaft 2 is in a horizontal
posture, the shaft 2 sinks due to the force of gravity to be
brought into sliding contact with the bearing surface 11 in a lower
side region of the bearing surface 11 in most cases. In this case,
the shaft 2 can be allowed to slide always with the lubricating
member 4 by designing the position and shape of the lubricating
member 4 so that the lubricating member 4 is positioned in a
sliding region with respect to the shaft 2 or by adjusting the
phase in the circumferential direction of the sintered bearing 1 so
that the lubricating member 4 is positioned in the sliding region.
Therefore, a high lubricating effect can be obtained, and the shaft
2 can be supported even in an oil-less state in which lubricating
oil is not present on the bearing surface 1. Thus, the sintered
bearing 1 can be provided, which can withstand the use under a
severe condition, such as high temperature, high contact pressure,
or high-speed rotation.
[0087] In the case where the graphite particles are dispersed onto
the bearing surface as in an existing sintered bearing, even when
the blending ratio of the graphite powder with respect to the raw
material powder is increased to increase the concentration of the
graphite particles on the bearing surface in order to enhance the
lubricity, the graphite particles that are blended excessively
inhibit the binding between metal particles, and hence the strength
of the sintered bearing is decreased. Thus, there is a limit to the
enhancement of the lubricity. In contrast, when at least a part of
the sliding surface is formed of the lubricating member 4 made of
an aggregate of solid lubricant particles (graphite particles,
etc.) as described above, the amount of the graphite particles to
be supplied to the bearing surface 11 can be increased to enhance
the lubricating effect merely by increasing the number of the
lubricating members 4 or enlarging the lubricating member 4. Also
in this case, the binding strength between the metal particles in
the metal substrate 3 is not decreased, and hence a decrease in
strength of the sintered bearing 1 can be avoided.
[0088] Meanwhile, when a part of the bearing surface 11 is formed
of the lubricating member 4 made of an aggregate of graphite
particles as described above, there is a problem regarding how to
fix the lubricating member 4 onto the metal substrate 3. When
press-fitting is adopted as fixing means, it is necessary to
process fitting surfaces of both the lubricating member 4 and the
metal substrate 3 with high accuracy by mechanical processing or
the like in order to obtain an appropriate press-fitting margin,
with the result that processing cost increases. Further, when
bonding is adopted as fixing means, a bonding step is newly
required, resulting in a decrease in productivity. In any case, the
largest advantage of the sintered bearing 1, that is, the reduction
in cost by near-net-shape molding is reduced.
[0089] In view of the above-mentioned problem, in the invention of
the present application, a new configuration is adopted in which
the lubricating member 4 is fixed onto the metal substrate 3 by the
sintering operation at a time of sintering the raw material powder
to form the metal substrate 3. This configuration relies on the new
concept that the fixing force is ensured by a physical change or a
chemical change of the metallic structure caused by the sintering
operation.
[0090] As a first procedure for fixing the lubricating member 4
onto the metal substrate 3 by the sintering operation as described
above, it is conceivable to utilize a contraction force F of the
metal substrate 3 generated along with the sintering operation.
Now, a manufacturing process of the sintered bearing 1 by this
procedure is described as a first embodiment.
[0091] The lubricating member 4 is formed by molding and firing raw
material powder containing graphite powder serving as solid
lubricant powder and a binder. In this case, when mixed powder
containing simple substance powder of the binder and the graphite
powder is used as the raw material powder, the flowability of the
graphite powder is low, and hence it is difficult to mold the mixed
powder into a predetermined shape when a large amount of the
graphite powder is contained in the mixed powder. Therefore, it is
preferred that granulated graphite powder 7 obtained by granulating
a plurality of graphite powders 6 in the presence of a binder 5 as
illustrated in FIG. 3 be used as the raw material powder.
[0092] As the graphite powder to be used in the granulated graphite
powder 7, any of natural graphite powder and artificial graphite
powder may be used. The natural graphite powder generally has a
feature of having a scale-like shape and being excellent in
lubricity. Meanwhile, the artificial graphite powder has a feature
of having a lump shape and being excellent in moldability. Thus,
when the lubricity is regarded as important, it is preferred that
the granulated graphite powder using the natural graphite powder be
used. When the moldability is regarded as important, it is
preferred that the artificial graphite powder be used. As the
binder, for example, a resin material, such as a phenol resin,
maybe used.
[0093] The granulated graphite powder 7 described above is
uniformly mixed with a molding aid, a lubricant, a modifier, or the
like as necessary. This mixture is supplied into a mold and
subjected to pressure molding, to thereby form a molded body 4'
(graphite powder molded body) conforming to the shape of the
lubricating member 4 as illustrated in FIG. 2A and FIG. 2B. After
that, the graphite powder molded body 4' is fired at a furnace
temperature of, for example, from 900.degree. C. to 1,000.degree.
C. to provide a porous fired body (lubricating member 4). The
firing is performed in an atmosphere free of oxygen, for example,
an atmosphere of inert gas, such as nitrogen gas, or a vacuum
atmosphere. This is because, when oxygen is present in the
atmosphere, the graphite powder volatilizes as CO or CO.sub.2
during firing to dissipate.
[0094] FIG. 4 is a schematic view of a microstructure of the fired
lubricating member 4. The resin binder contained in the granulated
graphite powder is formed into a carbonization product (amorphous
carbon) due to firing, to thereby form a binder component 14 having
a network structure. Graphite particles 13 serving as solid
lubricant particles derived from the graphite powder are retained
in the network of the binder component 14. The graphite particles
13 are retained in the network when the surface of the binder
component 14 intertwines with the surfaces of the graphite
particles 13. In FIG. 4, a large number of pores formed in the
microstructure are denoted by reference numeral 15. On the surface
of the lubricating member 4, the graphite particles 13 occupy an
area ratio of 60% or more, preferably 80% or more, and hence high
lubricity is obtained during sliding with the shaft 2.
[0095] Meanwhile, the metal substrate 3 is manufactured by a
general manufacturing process adopted in a sintered bearing, that
is, by subjecting raw material powder containing metal powder as a
main component to compression molding with a mold and heating and
sintering the molded body (metal powder molded body). As the metal
substrate 3, any kinds of sintered metals, such as a copper-based
metal containing copper as a main component, an iron-based metal
containing iron as a main component, and a copper-iron based metal
containing copper and iron as main components, may be used. Besides
those metals, a special sintered metal, such as an aluminum-bronze
based metal, may also be used.
[0096] For example, in a copper-iron based sintered bearing, a
mixture of iron powder, copper powder, and low-melting-point metal
powder is used as the raw material powder. The low-melting-point
metal is a component that is melted itself during sintering to
cause liquid phase sintering to proceed, and a metal having a
melting point lower than that of copper is used. Specifically, a
metal having a melting point of 700.degree. C. or less, for
example, tin (Sn), zinc (Zn), phosphorus (P), or the like may be
used. Of those, Sn having satisfactory compatibility with copper is
preferably used. The low-melting-point metal may be added to the
mixed powder not only by adding simple substance powder thereof to
the mixed powder but also by alloying the simple substance powder
with other metal powders.
[0097] Besides the above-mentioned metal powder, a sintering aid,
for example, calcium fluoride and a lubricant, for example, zinc
stearate may be added to the raw material powder as necessary, and
further, graphite powder may also be added to the raw material as
solid lubricant powder. Through addition of the graphite powder,
the graphite particles can be dispersed into a sintered structure
of the metal substrate 3 after sintering, and hence the lubricity
of a portion of the bearing surface 11 formed of the metal
substrate 3 can be further enhanced.
[0098] In a molding step, the raw material powder is filled into
the mold, followed by being compressed, to thereby form a molded
body 3' (metal powder molded body) having a shape conforming to
that of the metal substrate 3 as illustrated in FIG. 5. In the
metal powder molded body 3', recessed parts 3a' corresponding to
the retaining parts 3a of the metal substrate 3 are formed during
the molding.
[0099] Then, the fired body (lubricating member 4) manufactured by
the above-mentioned procedure is fitted into each recessed part 3a'
of the metal powder molded body 3' through gap fit. Then, an
assembly of the metal powder molded body 3' and the lubricating
member 4 is heated at a sintering temperature required for
sintering the metal powder molded body 3' (for example, from about
750.degree. C. to about 900.degree. C. when the metal powder molded
body 3' is made of a copper-iron based metal), to thereby sinter
the metal powder molded body 3'. During sintering, the fired
lubricating member 4 is also heated. However, the structure of the
lubricating member 4 does not change during heating, and the
structure and form of the lubricating member 4 are maintained
before and after firing.
[0100] In a stage of the metal powder molded body before sintering,
metal powders P1 and P2 are held in contact with each other
(interparticle distance in this case is represented by E) as
illustrated in FIG. 15A. Meanwhile, when the metal powder molded
body is sintered, a part of the structure of adjacent metal powders
P1' and P2' diffuses to a counterpart side as illustrated in FIG.
15B, and hence an interparticle distance e after sintering is
smaller than the interparticle distance E before sintering
(E>e). The interparticle distance is reduced along with
sintering as described above. Therefore, the contraction force F
(see FIG. 1A) in a direction in which both a radially inner surface
and a radially outer surface are reduced in diameter is generated
in the metal substrate 3 after sintering, and the fitting between
the metal substrate 3 and the lubricating member 4 is shifted from
the gap fit state to an interference fit state due to the
contraction force F. Thus, the lubricating member 4 can be reliably
fixed onto the metal substrate 3, and hence the lubricating member
4 during use can be prevented from dropping out. In particular, as
illustrated in FIG. 1A, when an opening width D0 of the retaining
part 3a in the metal substrate 3 is set to be smaller than a
maximum width D (diameter dimension) of the lubricating member 4,
the dropout of the lubricating member 4 to a radially inner side
can be more reliably regulated.
[0101] The contraction of the metal powder molded body during
sintering can be reinforced through use of, for example, particles
having irregular shapes as particles forming the metal powder. In
this case, the particles having irregular shapes are spheroidized
along with sintering, and the interparticle distance is reduced.
Therefore, the contraction of the molded body 3' becomes even more
remarkable. As iron powder and copper powder, there are typically
given reduced powder, atomized powder, electrolytic powder, and the
like. However, when reduced iron powder having a porous sponge-like
shape is used as iron powder, and electrolytic copper powder having
a dendritic shape is used as copper powder, both the powders have
high irregularity, and hence the high contraction force F can be
obtained. Thus, when the contraction force F is intended to be
increased, it is preferred that the reduced iron powder or the
electrolytic copper powder be used as the iron powder or the copper
powder in the raw material powder. The magnitude of the contraction
force F generated during sintering can be adjusted by adding iron
powder of a kind other than the reduced iron powder to the reduced
iron powder or adding copper powder of a kind other than the
electrolytic copper powder to the electrolytic copper powder.
[0102] The sintered product having passed through the sintering
step is transferred to a sizing step, and the dimensions of each
part of the surface (inner peripheral surface, outer peripheral
surface, and both end surfaces) is corrected by re-compression in a
mold. In this case, when at least the inner peripheral surface
serving as the bearing surface 11 is subjected to sizing, the
bearing surface 11 having high circularity can be obtained, and
stable bearing performance can be obtained. The bearing surface 11
is finally finished by sizing as just described, and hence a step
may be present between the inner peripheral surface 3b of the metal
substrate 3 and the inner side surface 4b of the lubricating member
4 at the end of sintering. When a step that cannot be corrected by
sizing is present, sizing is performed after the entire inner
peripheral surface of the sintered product, that is, the entire
inner peripheral surface 3b of the metal substrate 3 and the entire
inner side surface 4b of the lubricating member 4 are subjected to
mechanical processing, such as cutting.
[0103] Through the sizing step, the sintered bearing 1 as
illustrated in FIG. 1A and FIG. 1B is completed. The sintered
bearing 1 is used as a dry bearing that is not basically
impregnated with lubricating oil, liquid grease, or the like. As
necessary, oil impregnation treatment of impregnating the
lubricating oil, liquid grease, or the like into the sintered
bearing 1 may be performed after sizing so that the lubricating oil
component is retained in pores of any one or both of the metal
substrate 3 and the lubricating member 4.
[0104] As a second procedure for fixing the lubricating member 4
onto the metal substrate 3 by the sintering operation, it is
conceivable to form the lubricating member 4 with a material that
can be sintered. Now, the configuration and manufacturing process
of the sintered bearing 1 by this procedure are described as a
second embodiment.
[0105] In the second embodiment, the lubricating member 4 is formed
by sintering the molded body obtained by molding the raw material
powder. In this case, the raw material powder contains, as a main
component, coated powder in which solid lubricant powder is coated
with a metal. As the coated powder, for example, plated powder 9 in
which solid lubricant powder 6 is plated with a metal 8
(non-electrolytic plating) as illustrated in FIG. 6 may be used (in
the following description, the metal 8 is referred to as "coating
metal"). It is preferred that graphite powder be used as the solid
lubricant powder 6, and copper (Cu) or nickel (Ni) be used as the
coating metal 8. As the plated powder 9, the graphite powder 6
having its entire surface coated with the coating metal 8 is most
preferred. However, it is not necessarily required that the entire
surface be coated, and a part of the surface of the graphite powder
6 may be exposed to outside of the simple substance plated powder
9. The ratio of the coating metal 8 in the plated powder 9 is about
10 wt % or more and about 80 wt % or less, preferably about 15 wt %
or more and about 60 wt % or less, more preferably about 20 wt % or
more and about 50 wt % or less. When the amount of the coating
metal 8 is too small, the ratio of the graphite powder 6 exposed to
the surface of the plated powder 9 increases, and the binding
strength between particles after sintering becomes insufficient.
Meanwhile, when the amount of the coating metal 8 is too large, the
amount of graphite exposed to the inner side surface 4b of the
lubricating member 4 serving as the bearing surface 11 decreases,
and the lubricity of the lubricating member 4 is degraded. The
specific gravity of copper and that of nickel are substantially the
same. Therefore, irrespective of whether copper or nickel is used
as the coating metal 8, there is no substantial difference in
preferred weight ratio.
[0106] As the graphite powder 6 to be used in the plated powder 9,
artificial graphite powder is preferably used. This is because,
when natural graphite powder having a scale-like shape is used, it
is difficult to sufficiently coat the graphite powder 6 with the
coating metal 8. When the coating of the graphite powder 6 with the
coating metal 8 is insufficient, the coating metals 8 of the plated
powder cannot be bound to each other in a later sintering step, and
hence the strength cannot be ensured.
[0107] In order to strongly bind the coating metals 8 of the plated
powder 9 to each other, a low-melting-point metal is incorporated
into the raw material powder. As a procedure for incorporating the
low-melting-point metal into the raw material powder, it is
conceivable to add simple substance powder of the low-melting-point
metal to the plated powder 9 or precipitating the coating metal 8
alloyed with the low-melting-point metal on the periphery of the
graphite powder 6 during plating. As the low-melting-point metal, a
metal having a melting point of 700.degree. C. or less, for
example, tin (Sn), zinc (Zn), phosphorus (P), or the like may be
used in the same manner as in the first embodiment, and of those,
Sn is preferably used.
[0108] In this case, the ratio of the low-melting-point metal with
respect to the coating metal 8 is set to a range of from 0.3 wt %
to 5 wt %, preferably from 0.5 wt % to 3 wt %. When the ratio of
the low-melting-point metal is too small, the liquid phase
sintering does not proceed, and hence the required strength cannot
be obtained. Meanwhile, when the ratio of the low-melting-point
metal is too large, the amount of graphite exposed to the inner
side surface 4b of the lubricating member 4 serving as the bearing
surface 11 decreases, and the inner side surface 4b is
unnecessarily hardened to degrade the lubricity of the lubricating
member 4. Therefore, the above-mentioned ratio is adopted.
[0109] A sintering aid and a lubricant are added as necessary to
the raw material powder forming the lubricating member 4 in
addition to the above-mentioned powders (plated powder and
low-melting-point metal powder as necessary).
[0110] In the second embodiment, raw material powder for forming
the metal substrate 3 is common to the raw material powder forming
the metal substrate 3 according to the first embodiment, and hence
overlapping description of the same part is omitted. Now, the
manufacturing process of the sintered bearing 1 is described with
use of first powder Ma as the raw material powder (containing the
plated powder 9) of the lubricating member 4 and second powder Mb
as the raw material powder of the metal substrate 3.
[0111] In a molding step of this embodiment, there is adopted a
so-called two-color molding (multicolor molding) procedure
involving supplying the first powder Ma and the second powder Mb
into the same mold and simultaneously molding the first powder Ma
and the second powder Mb. In the two-color molding, two cavities
are defined in the mold, and powder is filled into each cavity and
molded.
[0112] FIG. 7 is an example of a mold for two-color molding. The
mold comprises a die 21, a core pin 22 arranged on an inner
periphery of the die 21, a lower punch 23 arranged between an inner
peripheral surface of the die 21 and an outer peripheral surface of
the core pin 22, a partition member 25 (see FIG. 8), a guide 28
having a conical surface shape (see FIG. 8), and an upper punch 29
(see FIG. 12). The guide 28 is arranged so as to facilitate the
filling of the first powder Ma into the cavity, and the guide 28
may be omitted as long as such filling is performed smoothly.
[0113] As illustrated in FIG. 8, the partition member 25 comprises
an inside partition 26 and an outside partition 27 that are
arranged concentrically. The partitions 26 and 27 are formed so as
to be raised and lowered independently. The inside partition 26 is
formed into a shape conforming to that of each lubricating member 4
illustrated in FIGS. 1.
[0114] In the compression molding step, first, as illustrated in
FIG. 7, under a state in which the partition member 25 and the
guide 28 are retreated from the mold, the core pin 22 and the lower
punch 23 are raised, and upper end surfaces of the core pin 22 and
the lower punch 23 are arranged at the same level as that of an
upper end surface 21a of the die 21. The retreat direction of the
partition member 25 and the guide 28 from the mold may be an upper
direction or a side direction.
[0115] Then, as illustrated in FIG. 8, the partition member 25 and
the guide 28 are arranged on the mold, and a lower end surface of
the inside partition 26 is brought into contact with the upper end
surface of the lower punch 23, to thereby bring a lower end surface
of the outside partition 27 into contact with the upper end surface
21a of the die 21. Further, a lower end surface of the guide 28 is
brought into contact with the upper end surface of the core pin 22.
Under this state, a space between the inside partition 26 and the
guide 28 is filled with the first powder Ma, and a space between
the inside partition 26 and the outside partition 27 is filled with
the second powder Mb.
[0116] Then, as illustrated in FIG. 9, while the positions of the
lower punch 23 and the inside partition 26 are held, the die 21,
the core pin 22, and the outside partition 27 are raised in tandem
with each other. Thus, an inside cavity 24a between the inside
partition 26 and the core pin 22 is filled with the first powder
Ma, and an outside cavity 24b between the inside partition 26 and
the die 21 is filled with the second powder Mb.
[0117] Next, as illustrated in FIG. 10, the inside partition 26 is
raised. As a result, the inside partition 26 that defines the
inside cavity 24a and the outside cavity 24b is removed, and both
the cavities 24a and 24b are integrated. Even when the inside
partition 26 is removed as just described, the first powder Ma and
the second powder Mb are not completely mixed with each other, and
both the powders Ma and Mb are kept in a separated state (broken
line of FIG. 10 is a line for representing the boundary between the
powder Ma and the powder Mb for convenience).
[0118] Next, as illustrated in FIG. 11, the partition member 25 and
the guide 28 are removed, and further, surplus powder having flown
out of the cavities 24a and 24b is removed. Then, as illustrated in
FIG. 12, the upper punch 29 is lowered to compress the first powder
Ma and the second powder Mb in the cavities, to thereby produce a
molded body 1'.
[0119] After that, the molded body 1' is taken out from the mold
and sintered at a temperature (for example, from about 750.degree.
C. to about 900.degree. C.) that is higher than the melting point
of the low-melting-point metal and is lower than the melting point
of the coating metal 8 (copper or nickel) of the plated powder 9,
to thereby complete the sintered bearing 1 illustrated in FIG. 13.
In this case, the lubricating member 4 is formed by sintering the
first powder Ma, and the metal substrate 3 is formed by sintering
the second powder Mb.
[0120] During the sintering, the low-melting-point metal contained
in the first powder Ma on the inner side is melted, and the molten
low-melting-point metal wets the coating metal 8 (for example,
copper) of the plated powder 9 to form an alloy with the coating
metal 8. Due to this alloying, the surface of the coating metal 8
is melted at a temperature lower than the melting point thereof,
and the melt binds the coating metals 8 of the plated powder 9 to
each other, with the result that the first powder Ma is formed into
a sintered body.
[0121] The alloy melt of the coating metal 8 and the
low-melting-point metal permeates the molded body made of the
second powder Mb and diffuses to the metal powder contained in the
second powder Mb, to thereby bind the metal powders (for example,
iron powders, copper powders, or iron powder and copper powder) to
each other. When the second powder Mb contains the
low-melting-point metal, copper, and the like, the metal powders
contained in the second powder Mb are bound to each other due to
the same action. Further, even when the second powder Mb is made of
iron-based powder and does not contain the low-melting-point metal
or copper, the alloy melt generated in the first powder Ma diffuses
to the iron powder of the second powder Mb to bind the iron powders
to each other. Due to the above-mentioned action, the entire molded
body 1' is formed into a sintered body, and hence the sintered
bearing 1 having high strength is obtained. Further, the boundary
portion between the metal substrate 3 and the lubricating member 4
is formed into a sintered structure without an interface, and hence
the lubricating member 4 can be more reliably fixed onto the metal
substrate 3.
[0122] Meanwhile, the graphite powder 6 contained in the plated
powder 9 of the first powder Ma basically remains without moving to
the second powder Mb side, and hence the lubricating member 4 is
formed into a structure rich in graphite particles.
[0123] After that, in the same manner as in the first embodiment,
at least the bearing surface 11 is subjected to sizing, and
further, oil impregnation is performed as necessary. Thus, the
sintered bearing 1 as illustrated in FIG. 1B and FIG. 13 is
completed.
[0124] Substantially the entire surface of the plated powder 9 is
coated with the coating metal 8. Therefore, immediately after the
sintering step, most of the inner side surface 4b of the
lubricating member 4 is coated with metal particles derived from
the coating metal 8. When the metal particles of the inner side
surface 4b of the lubricating member 4 are peeled or dropped out
due to sliding with a sizing die (for example, a core rod) in a
later sizing step of the bearing surface 11, a large amount of the
graphite particles can be exposed to the inner side surface 4b, and
the distribution amount (area ratio) of the graphite particles on
the inner side surface 4b can be increased to the same degree as
that of the first embodiment. In order to effectively perform
peeling or dropout of the metal particles, when the bearing surface
11 is subjected to sizing, it is preferred to perform an operation
involving squeezing the inner peripheral surface of the sintered
product with the sizing die, for example, an operation involving
press-fitting the sintered product into the die to press the inner
peripheral surface of the sintered product onto the sizing die, and
under this state, sliding the sizing die in the axial
direction.
[0125] Even in the case where the amount of the graphite particles
exposed to the inner side surface 4b of the lubricating member 4 is
insufficient in an initial state, when the shaft 2 (see FIG. 1B) is
rotated later, the metal particles with which the inner side
surface 4b is coated are peeled and dropped out due to the sliding
with the shaft 2, and a necessary and sufficient amount of graphite
particles appears on the inner side surface 4b.
[0126] In the sintered bearing 1 according to the second
embodiment, when the inside partition 26 is removed, the first
powder Ma and the second powder Mb cannot be prevented from being
mixed with each other in the vicinity of the boundary therebetween.
Therefore, a clear interface is not present between the metal
substrate 3 and the lubricating member 4, and a transition layer X
having a concentration gradient of each element is formed
therebetween from the metal substrate 3 side to the lubricating
member 4 side as illustrated in an enlarged view of FIG. 13.
[0127] As a third embodiment, the sintered bearing 1 may also be
manufactured by a combination of the first embodiment and the
second embodiment. The manufacturing procedure of the sintered
bearing 1 in the third embodiment is as follows. Specifically, raw
material powder containing the plated powder 9 as a main component
is molded and sintered to form the lubricating member 4 by the same
procedure as that of the second embodiment. Next, the lubricating
member 4 is fitted into the recessed parts 3a' of the metal powder
molded body 3' (see FIG. 5) described in the first embodiment, and
under this state, an assembly formed of the metal powder molded
body 3' and the lubricating member 4 is heated at a sintering
temperature to sinter the metal powder molded body 3'. During this
sintering, the lubricating member 4 is fixed onto the metal
substrate 3 with the contraction force F generated in the metal
powder molded body 3'. After that, at least the bearing surface 11
is subjected to sizing. Thus, the sintered bearing as illustrated
in FIG. 1A and FIG. 1B can be obtained.
[0128] In the above-mentioned description, the bearing is
exemplified as an example of the sliding member, but the sliding
member of the present invention can be widely used as a member
configured to support a mating member that performs relative
motion. The relative motion as used herein is not limited to
rotation motion and also includes linear motion. Further, as the
form of the mating member, any form, such as a flat shape, may be
adopted in addition to the shaft shape. Further, the sliding member
also has any form and is not limited to the cylindrical shape as in
the sintered bearing 1. A form such as a flat shape called a
sliding pad may also be adopted.
[0129] Further, in the above-mentioned description, there is
illustrated the case where the plurality of lubricating members 4
are arranged in the circumferential direction of the metal
substrate 3, but the configuration of the lubricating member 4 is
not limited thereto. For example, the lubricating member 4 that
continues in the circumferential direction may be arranged so as to
cover a substantially half periphery of the bearing surface 11 as
illustrated in FIG. 14A or may also be arranged so as to cover
substantially the entire periphery of the bearing surface 11 as
illustrated in FIG. 14B.
[0130] Further, the lubricating members 4 may also be arranged in a
spiral manner with an axial center being the center, instead of
being arranged along the axial direction as illustrated in FIG. 1A
and FIG. 1B. With this, each part of the shaft 2 in the axial
direction is allowed to pass by the lubricating member 4 at least
once during one rotation, and hence satisfactory lubricity is
obtained. Further, the lubricating members 4 may also be arranged
in a limited partial region in the axial direction, instead of
being arranged over the entire length of the metal substrate 3 in
the axial direction as illustrated in FIG. 1A and FIG. 1B. In any
case, the effect of the invention of the present application can be
attained as long as at least a part of the bearing surface 11 is
formed of the lubricating member 4.
[0131] Besides the foregoing, a part of a mounting surface (for
example, the outer peripheral surface 12 of the metal substrate 3)
of the sliding member with respect to another member may also be
formed of the lubricating member 4 by extending the lubricating
member 4 in a radial direction.
[0132] Further, in the above-mentioned description, there is
illustrated the case where graphite is used as the solid lubricant
forming the lubricating member 4. However, a solid lubricant other
than graphite, for example, molybdenum disulfide may also be widely
used.
[0133] There is no particular limitation on the application of the
sliding member described above, but the sliding member is
particularly suitable for use under a severe condition, such as
high temperature, high contact pressure, or high-speed rotation.
For example, the sliding member can be used in a bearing for a fuel
pump in an automobile engine, a bearing for an exhaust gas
recirculation (EGR) valve of an EGR device to be installed for the
purpose of reducing nitrogen oxide (NOx) in exhaust gas, and the
like. In those applications, corrosion resistance of the bearing
with respect to gasoline and exhaust gas is also required, and
hence it is preferred that an aluminum-bronze based substrate
excellent in corrosion resistance be used as the metal substrate 3.
Besides the foregoing, the sliding member can also be used as, for
example, a bearing to be used in a joint portion of an arm in a
construction machine (bulldozer, hydraulic shovel, etc.)
[0134] Further, the sliding member described above can also be used
as a driven element (gear, pulley, etc.) to be supported in a
rotatable manner by a fixing shaft in a torque transmission
mechanism. Depending on the application to the driven element, it
is not preferred, in some cases, that lubricating oil be interposed
in a sliding part between the driven element and the fixing shaft,
and the sliding member of the present invention is suitable for
such application. For example, a gear pump for fueling is arranged
in a weighing machine to be installed in a gas station or the like,
and a driven gear may be arranged in a fueling path of the gear
pump for fueling. In this case, in order to avoid the mixing of
lubricating oil into fuel, kerosene, or the like, it is not
preferred that lubricating oil be impregnated into the driven gear.
Thus, it is preferred that the sliding member of the present
invention, which enables high lubricity to be obtained even without
using lubricating oil, be used as the driven gear to be used for
such application.
[0135] FIG. 16 is an exploded perspective view of an internal gear
pump to be used as the above-mentioned gear pump for fueling. As
illustrated in FIG. 16, the gear pump comprises a main body 51
serving as a stationary side, an external tooth-type inner rotor 52
(driven gear), and an internal tooth-type outer rotor 53. The outer
rotor 53 comprises a drive shaft 53a that is driven by a rotation
drive source, such as a motor. The main body 51 comprises a fixing
shaft 51a eccentric with respect to the drive shaft 53a, and a
shaft hole 52a of the inner rotor 52 is fitted in a rotatable
manner onto an outer periphery of the fixing shaft 51a. As
illustrated in FIG. 17, the inner rotor 52 is arranged so as to be
eccentric toward a radially inner side of the outer rotor 53 in a
state in which external teeth of the inner rotor 52 are engaged
with internal teeth of the outer rotor 53. The number of the teeth
of the outer rotor 53 is set to be larger by one or two or more
than the number of the teeth of the inner rotor 52.
[0136] When the outer rotor 53 is rotationally driven in such
configuration, the inner rotor 52 also receives a rotation force
due to the engagement of the tooth parts and is rotated in the same
direction following the outer rotor 53. With this, the volume of a
space between the tooth parts is enlarged and reduced, and hence
gasoline or the like can be sucked in and discharged.
[0137] In the gear pump for fueling, the inner rotor 52 serving as
the driven gear comprises the metal substrate 3 and the lubricating
member 4 fixed onto the inner peripheral surface of the metal
substrate 3 in the same manner as in the sintered bearing 1
described above. The metal substrate 3 is obtained by sintering raw
material powder containing metal powder as a main component and
forms a gear shape including a plurality of tooth parts on an outer
periphery and a hole on an inner periphery. The lubricating member
4 is made of an aggregate of graphite particles and is fixed onto
the inner peripheral surface of the metal substrate 3 by the
sintering operation of sintering the raw material powder of the
metal substrate 3. The inner peripheral surface of the lubricating
member 4 forms a sliding surface (shaft hole 52a) that slides with
the outer peripheral surface of the fixing shaft 51a. Each
configuration of the metal substrate 3 and the lubricating member 4
and a fixing procedure thereof are common to those of the first to
third embodiments of the sintered bearing 1. The metal substrate 3
is also required to have corrosion resistance to gasoline, and
hence it is preferred that an aluminum-bronze based substrate
excellent in corrosion resistance be used as the metal substrate
3.
[0138] When the inner peripheral surface of the lubricating member
4 is subjected to finishing processing, such as sizing and cutting,
as necessary after the lubricating member 4 is fixed onto the metal
substrate 3, the inner rotor 52 illustrated in FIG. 16 is
completed. Lubricating oil is not impregnated into the metal
substrate 3 or the lubricating member 4.
[0139] The inner rotor 52 having such configuration does not
contain lubricating oil, and hence the mixing of lubricating oil
into fuel and kerosene supplied by a weighing machine can be
avoided. Meanwhile, the sliding surface has high lubricity, and
hence the torque loss in the inner rotor 52 can be minimized.
[0140] Next, a bearing is given as an example of a sliding member
according to a second invention of the present application, and the
details thereof are described with reference to FIGS. 18 to FIG.
27.
[0141] As illustrated in FIG. 18A and FIG. 18B, a bearing 101 has a
cylindrical shape, and a shaft 102 (represented by the chain line)
is inserted as a mating member into an inner periphery of the
bearing 101. A bearing surface 111 serving as a sliding surface
that slides with the shaft 102 is formed on an inner peripheral
surface of the bearing 101. In this embodiment, an outer peripheral
surface 112 of the bearing 101 is fixed onto an inner peripheral
surface of a housing (not shown) by means of, for example,
press-fitting or bonding, and the shaft 102 inserted into the inner
periphery of the bearing 101 is supported in a rotatable manner.
The shaft 102 may also be set to a stationary side instead of being
set to a rotation side as just described, and the bearing 101 may
be set to the rotation side.
[0142] The bearing 101 comprises carbon-based fired bodies 103
containing carbon as a main component (component having the largest
weight ratio) and a resin substrate 104 configured to retain the
carbon-based fired bodies 103. In this embodiment, a plurality of
(five in the illustrated example) carbon-based fired bodies 103 are
arranged at equal intervals in the circumferential direction, and
the plurality of carbon-based fired bodies 103 are collectively
retained by the resin substrate 104. Each carbon-based fired body
103 is exposed to the inner peripheral surface of the bearing 101
to forma part of the bearing surface 111. In the illustrated
example, each carbon-based fired body 103 comprises an inner side
surface 103a exposed to the inner peripheral surface of the bearing
101 and an outer side surface 103b that is held in close contact
with the resin substrate 104. The inner side surface 103a of each
carbon-based fired body 103 is formed into a recessed cylindrical
surface shape that continues without any step from an inner
peripheral surface 104a of the resin substrate 104. In this
embodiment, the inner side surface 103a of each carbon-based fired
body 103 and the inner peripheral surface 104a of the resin
substrate 104 form the bearing surface 111 having a true circle
shape in cross-section. The outer side surface 103b of each
carbon-based fired body 103 is formed into a protruding cylindrical
surface shape and is held in close contact with the entire region
of a retaining surface 104b having a recessed cylindrical surface
shape of the resin substrate 104.
[0143] In the bearing 101, the carbon-based fired body 103 forming
a part of the bearing surface 111 serves as a supply source of
graphite particles. The graphite particles supplied from the
carbon-based fired body 103 permeate to the entire bearing surface
111 due to the relative motion between the bearing surface 111 and
the shaft 102, and hence the lubricating effect of the graphite
particles can be obtained on the entire bearing surface 111.
[0144] Further, in the bearing 101, the shaft 102 does not always
slide with the entire bearing surface 111, and a limited partial
region of the bearing surface 111 slides with the shaft 102 in most
cases. For example, when the shaft 102 is in a horizontal posture,
the shaft 102 sinks due to the force of gravity to slide with the
bearing surface 111 in a lower side region of the bearing surface
111 in most cases. In this case, the shaft 102 can be allowed to
slide always with the carbon-based fired body 103 by designing the
position and shape of the carbon-based fired body 103 in the
bearing 101 or by adjusting the phase in the circumferential
direction of the bearing 101 so that the carbon-based fired body
103 is positioned in a sliding region with respect to the shaft
102. With this, a high lubricating effect can be obtained, and
hence the shaft 102 can be supported, for example, even in an
oil-less state in which lubricating oil is not interposed between
the bearing surface 111 and the shaft 102. Needless to say, the
bearing 101 may also be used in a state in which lubricating oil is
interposed between the bearing surface 111 and the shaft 102, and
in this case, the lubricating effect is further enhanced. In this
embodiment, lubricating oil is interposed between the bearing
surface 111 and the shaft 102, and oil is impregnated into inner
pores of the carbon-based fired body 103. In this case, oil seeps
out from the surface (inner side surface 103a) of the carbon-based
fired body 103 due to an increase in temperature in association
with the rotation of the shaft 102, and the oil is supplied to the
sliding region between the bearing surface 111 and the shaft 102,
with the result that the loss of an oil film in the sliding region
is reliably avoided to maintain an excellent sliding property.
[0145] The bearing 101 is manufactured through a fired body forming
step, an insert molding step, a sizing step, and an oil
impregnation step. Now, each step is described in detail.
Fired Body Forming Step
[0146] The carbon-based fired body 103 is formed through use of raw
material powder containing carbon-based powder and resin binder
powder. As the carbon-based powder, for example, graphite powder
may be used, and specifically, any of natural graphite powder and
artificial graphite powder may be used. The natural graphite powder
has a feature of being excellent in lubricity because of a
scale-like shape. Meanwhile, the artificial graphite powder has a
feature of being excellent in moldability because of a lump shape.
The carbon-based powder is not limited to graphite powder that is
crystalline powder, and amorphous powder, such as pitch powder or
coke powder, may also be used. As the resin binder powder, for
example, phenol resin powder may be used.
[0147] A molding aid, a lubricant, a modifier, or the like is added
as necessary to the above-mentioned graphite powder and resin
binder powder and uniformly mixed therewith. This mixture is
supplied into a mold and subjected to compression molding, to
thereby form a compact conforming to the shape of the carbon-based
fired body 103. After that, the compact is fired at a furnace
temperature of, for example, from 900.degree. C. to 1,000.degree.
C., to thereby provide the porous carbon-based fired body 103. The
firing is performed in an atmosphere free of oxygen, for example,
an atmosphere of inert gas, such as nitrogen gas, or a vacuum
atmosphere. This is because, when oxygen is present in the
atmosphere, the graphite powder volatilizes as CO or CO.sub.2 to
dissipate.
[0148] As the raw material powder of the carbon-based fired body
103, granulated graphite powder obtained by granulating graphite
powder in the presence of a resin binder may also be used instead
of the above-mentioned mixed powder of graphite powder and resin
binder powder. The granulated graphite powder has a large specific
gravity and high flowability as compared to simple substance resin
binder or graphite powder. Therefore, the granulated graphite
powder is easily supplied into the mold and can be molded into a
predetermined shape with high accuracy.
[0149] FIG. 19 is a schematic view of a microstructure of the
carbon-based fired body 103. The resin binder contained in the
granulated graphite powder is formed into a carbonization product
(amorphous carbon) due to firing, to thereby form a binder
component 114 having a network structure. Graphite particles 113
serving as solid lubricant particles derived from the graphite
powder are retained in the network of the binder component 114. The
graphite particles 113 are retained in the network when the surface
of the binder component 114 intertwines with the surfaces of the
graphite particles 113. In FIG. 19, a large number of pores formed
in the microstructure are denoted by reference numeral 115. On the
surface (in particular, the inner side surface 103a) of the
carbon-based fired body 103, the graphite particles 113 occupy an
area ratio of 60% or more, preferably 80% or more, and hence high
lubricity is obtained during sliding with the shaft 102.
Insert Molding Step
[0150] An integrated product of the plurality of carbon-based fired
bodies 103 and the resin substrate 104 configured to retain the
plurality of carbon-based fired bodies 103 is formed by performing
injection molding with a resin through use of the carbon-based
fired bodies 103 as an insert component. Arnold 120 to be used here
comprises a stationary die 121 and a movable die 122 as illustrated
in FIG. 20. The stationary die 121 comprises a columnar part 121a,
and an outer peripheral surface of the columnar part 121a forms the
inner peripheral surface 104a of the resin substrate 104. In the
stationary die 121, gates 121b are formed on a molding surface 121c
forming an end surface of the resin substrate 104. In this
embodiment, a plurality of (three in the illustrated example) gates
121b are arranged at equal intervals in the circumferential
direction on the molding surface 121c of the stationary die 121
(see FIG. 21). The kind of the gate is not limited to a point-like
gate as in the illustrated example, and for example, an annular
film gate may be used.
[0151] In the insert molding step, first, the plurality of
carbon-based fired bodies 103 are arranged in predetermined
portions of an outer periphery of the columnar part 121a of the
stationary die 121. Under this state, the movable die 122 and the
stationary die 121 are clamped on each other to form a cavity 123,
and the plurality of carbon-based fired bodies 103 are arranged in
the cavity 123. In this case, each carbon-based fired body 103 is
sandwiched between the stationary die 121 and the movable die 122
from both sides in the axial direction. With this, each
carbon-based fired body 103 is fixed onto a predetermined portion
in the cavity 123 so that the positional displacement of a molten
resin during injection is prevented.
[0152] Then, the molten resin is injected into the cavity 123 from
a runner 121d through the gate 121b, with the result that the
cavity 123 is filled with the molten resin. As a synthetic resin
serving as a main component (component having the largest weight
ratio) of the molten resin, there are given, for example, polyamide
(PA), polycarbonate (PC), polybutylene terephthalate (PBT),
polyacetal (POM), a liquid crystal polymer (LCP), a wholly aromatic
polyester, polyphenylene sulfide (PPS), polyether ether ketone
(PEEK), polyamide imide (PAI), polyether imide (PEI), polyimide
(PI), fluorine resins (fluorinated polyolefin-based resins), such
as a polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer
(PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP),
and an ethylene-tetrafluoroethylene copolymer (ETFE), and
olefin-based resins, such as polyethylene. Each of those synthetic
resins may be used alone, or a polymer alloy of a mixture of two or
more kinds thereof may be used.
[0153] It is preferred that a crystalline resin be used as a main
component of the resin forming the resin substrate 104. The
crystalline resin is excellent in mechanical strength and has a
large molding contraction ratio as compared to an amorphous resin.
When the crystalline resin excellent in mechanical strength is
used, the rigidity of the resin substrate 104 is enhanced. Further,
when the crystalline resin having a large molding contraction ratio
is used, the retaining surface 104b of the resin substrate 104 is
reduced in diameter due to the molding contraction during
solidification after the molten resin is injected into the cavity,
and the resin substrate 104 reliably grabs the carbon-based fired
body 103 (described later in detail). Examples of the crystalline
resin include LCP, PEEK, PBT, PPS, PA, and POM. For example, at
least one or more kinds of crystalline resins selected from a group
of crystalline resins consisting of LCP, PEEK, and PPS are
excellent in chemical resistance, heat resistance, and the like. In
addition, of the crystalline resins, PPS is a particularly
preferred material by virtue of its excellence in chemical
resistance and cost. In this embodiment, the resin substrate 104
contains PPS as a main component, and is formed of a resin
composition containing various fillers. As the PPS, cross-linked
PPS, semi-cross-linked PPS, linear PPS, or the like may be used,
and for example, linear PPS excellent in toughness is preferably
used.
[0154] The filler is added in order to improve the friction wear
characteristics and reduce a linear expansion coefficient. Specific
examples of the filler include: fibers, such as a glass fiber, a
carbon fiber, an aramid fiber, an alumina fiber, a polyester fiber,
a boron fiber, a silicon carbide fiber, a boron nitride fiber, a
silicon nitride fiber, and a metal fiber, and a product produced by
weaving any of the fibers into a cloth form; minerals, such as
calcium carbonate, talc, silica, clay, andmica; inorganic whiskers,
such as an aluminum borate whisker and a potassium titanate
whisker; and various heat resistant resins, such as a polyimide
resin and polybenzimidazole. Other additives, such as an antistatic
agent (for example, carbon nanofiber, carbon black, or graphite), a
release agent, a flame retardant, a weatherability improver, an
antioxidant, and a pigment, may also be appropriately added.
[0155] In this embodiment, a carbon fiber serving as a fibrous
reinforcing material and PTFE serving as a solid lubricant are
added as the fillers. The blending of the carbon fiber leads to
improvement in mechanical strength, such as bending modulus, and
the blending of PTFE leads to improvement in sliding
characteristics with respect to the shaft 102 or the columnar part
121a of the mold 120. The carbon fiber is roughly classified into a
pitch-based carbon fiber and a PAN-based carbon fiber, and any of
the carbon fibers may be used. The carbon fiber to be used has, for
example, an average fiber diameter of 20 .mu.m or less and an
average fiber length of from 0.02 mm to 0.2 mm. The blending ratio
of the carbon fiber is, for example, 10 mass % or more and 40 mass
% or less, preferably 20 mass % or more and 30 mass % or less with
respect to the entirety of the resin substrate 104. The blending
ratio of PTFE is, for example, 1 mass % or more and 40 mass % or
less, preferably 2 mass % or more 30 mass % or less with respect to
the entirety of the resin substrate 104.
[0156] After that, the resin filled into the cavity 123 is cooled
to be solidified, to thereby form the resin substrate 104. In this
case, due to the molding contraction of the resin, the retaining
surface 104b of the resin substrate 104 is reduced in diameter to
press the outer side surface 103b of the carbon-based fired body
103 (see the arrow F of FIG. 18A). With this, the retaining surface
104b of the resin substrate 104 and the outer side surface 103b of
the carbon-based fired body 103 are brought into close contact with
each other with an interference margin, and hence the resin
substrate 104 and the carbon-based fired body 103 are strongly
fixed onto each other. In this case, when the opening width D0
(that is, the circumferential width of the inner side surface 103a
of the carbon-based fired body 103) in the circumferential
direction of the retaining surface 104b of the resin substrate 104
is set to be smaller than the maximum width D in the
circumferential direction (diameter of the carbon-based fired body
103) of the retaining surface 104b, the dropout of the carbon-based
fired body 103 onto the radially inner side can be more reliably
regulated. When the resin substrate 104 is subjected to molding
contraction, the inner peripheral surface 104a of the resin
substrate 104 is reduced in diameter as described above. When the
carbon-based fired body 103 moves to the radially inner side along
with the reduction in diameter of the resin substrate 104, the
inner side surface 103a of the carbon-based fired body 103 and the
inner peripheral surface 104a of the resin substrate 104 are
maintained in a continuous state.
Sizing Step
[0157] Next, an integrated product 101' of the carbon-based fired
body 103 and the resin substrate 104 is subjected to sizing by die
molding. Specifically, first, as illustrated in FIG. 22A, a core
pin 131 is inserted into an inner periphery of the integrated
product 101'. In this case, an inner peripheral surface 111' (the
inner side surface 103a of the carbon-based fired body 103 and the
inner peripheral surface 104a of the resin substrate 104) of the
integrated product 101' and an outer peripheral surface of the core
pin 131 are fitted with each other through a slight radial gap.
Then, under a state in which an axial width of the integrated
product 101' is defined by an upper punch 132 and a lower punch
133, the integrated product 101', the core pin 131, and the upper
and lower punches 132 and 133 are integrally lowered to press-fit
the integrated product 101' into an inner periphery of a die 134 as
illustrated in FIG. 22B. With this, an outer peripheral surface
112' of the integrated product 101' is molded with an inner
peripheral surface of the die 134, and the integrated product 101'
is simultaneously compressed from an outer periphery, with the
result that the inner peripheral surface 111' of the integrated
product 101' is pressed against the outer peripheral surface of the
core pin 131. With this, the inner peripheral surface 104a of the
resin substrate 104 is deformed plastically in conformity with the
outer peripheral surface of the core pin 131, and the radial
position of each carbon-based fired body 103 is corrected.
Specifically, when the plurality of carbon-based fired bodies 103
are pressed against the common core pin 131, each carbon-based
fired body 103 is arranged at a predetermined radial position, and
the inner side surface 103a of each carbon-based fired body 103 is
arranged on the same cylindrical surface.
[0158] As described above, when the integrated product 101' of the
carbon-based fired body 103 and the resin substrate 104 is
subjected to sizing, the surface accuracy (cylindricity and
circularity, coaxiality with respect to the outer peripheral
surface 112', etc.) of the inner peripheral surface 111' (bearing
surface 111) can be enhanced without performing high-accuracy
processing with respect to each of the carbon-based fired body 103
and the resin substrate 104. In this embodiment, the carbon-based
fired body 103 is mainly formed of carbon (the graphite particles
113 and the binder component 114 made of a carbonization product of
a resin binder), and hence plastic deformation hardly occurs. Thus,
each carbon based fired body 103 itself is hardly subjected to
sizing, and the surface of the inner side surface 103a pressed
against the core pin 131 is slightly adjusted.
Oil Impregnation Step
[0159] After that, oil is impregnated into the inner pores of the
carbon-based fired body 103 of the integrated product 101' (bearing
101) having passed through the sizing step. Specifically, oil is
impregnated into the inner pores of the carbon-based fired body 103
by immersing the integrated product 101' into lubricating oil in a
reduced-pressure environment and then returning the integrated
product 101' to an atmospheric pressure. Thus, the bearing 101 is
completed.
[0160] The present invention is not limited to the above-mentioned
embodiment. Now, description is made of other embodiments of the
present invention. Redundant description of parts having the same
functions as those in the above-mentioned embodiment is
omitted.
[0161] In the above-mentioned embodiment, there is described the
case where the resin serves as a binder for retaining graphite
particles of the carbon-based fired body 103. However, the present
invention is not limited thereto, and the carbon-based fired body
103 may also be formed of a metal binder. Specifically, for
example, raw material powder is used, which contains, as a main
component, coated powder in which a part or a whole of the surface
of carbon-based powder is coated with a metal. As the coated
powder, for example, plated powder in which graphite particles are
plated with a metal (non-electrolytic plating) may be used. It is
preferred that, for example, copper or nickel be used as the metal
with which the graphite particles are coated (hereinafter referred
to as "coating metal"). In this embodiment, graphite powder coated
with copper in which the surfaces of graphite particles are coated
with copper is used as the plated powder.
[0162] The ratio of the coating metal in the plated powder is set
to about 10 mass % or more and about 80 mass % or less, preferably
about 15 mass % or more and about 60 mass % or less, more
preferably about 20 mass % or more and about 50 mass % or less.
When the amount of the coating metal is too small, the ratio of the
graphite powder exposed to the surface of the plated powder
increases, and the binding strength between particles after firing
becomes insufficient. Meanwhile, when the amount of the coating
metal is too large, the amount of graphite exposed to the inner
side surface 103a of the carbon-based fired body 103 forming the
bearing surface 111 decreases, and the lubricity of the
carbon-based fired body 103 is degraded. The specific gravity of
copper and that of nickel are substantially the same. Therefore,
irrespective of whether copper or nickel is used as the coating
metal, there is no substantial difference in preferred weight
ratio.
[0163] As the graphite powder to be used in the plated powder,
artificial graphite powder is preferably used. This is because,
when natural graphite powder having a scale-like shape is used, it
is difficult to sufficiently coat the graphite powder with the
coating metal. When the coating of the graphite powder with the
coating metal is insufficient, the coating metals of the plated
powder cannot be bound to each other in a later firing step, and
hence the strength cannot be ensured. Particles that are not
granulated are preferably used as the graphite particles in order
to increase the ratio of graphite in each particle.
[0164] When the graphite particles having a small specific gravity
are coated with a metal as described above, the apparent density
increases to enhance the flowability of the graphite particles.
Therefore, the filling property with respect to the mold is
enhanced, and the raw material powder can be uniformly filled into
the mold. Further, when the raw material powder is subjected to
compression molding, the graphite particles are not deformed
plastically. However, when the metals with which each graphite
particle is coated are engaged with each other while being deformed
plastically, the raw material powder can be molded into a
predetermined shape without using a resin binder.
[0165] In order to strongly bind the coating metals of the plated
powder to each other, a low-melting-point metal is incorporated
into the raw material powder. As a procedure for incorporating the
low-melting-point metal into the raw material powder, it is
conceivable to add simple substance powder of the low-melting-point
metal to the plated powder or to precipitate the coating metal
alloyed with the low-melting-point metal on the periphery of the
graphite particles during plating. The low-melting-point metal is a
component that is melted itself during sintering to cause liquid
phase sintering to proceed. As the low-melting-point metal, a metal
having a melting point lower than the sintering temperature is
used. Specifically, a metal having a melting point of 700.degree.
C. or less, for example, tin (Sn), zinc (Zn), phosphorus (P), or
the like is used. When a general sintered metal, such as a
copper-based metal, an iron-based metal, or a copper-iron based
metal, is used, Sn having satisfactory compatibility with copper is
preferably used.
[0166] In this case, the ratio of the low-melting-point metal with
respect to the coating metal is set to a range of from 0.3 mass %
to 5 mass %, preferably from 0.5 mass % to 3 mass %. When the ratio
of the low-melting-point metal is too small, the liquid phase
sintering does not proceed, and hence the required strength cannot
be obtained. Meanwhile, when the ratio of the low-melting-point
metal is too large, the amount of graphite exposed to the inner
side surface 103a of the carbon-based fired body 103 forming the
bearing surface decreases, and the inner side surface 103a is
unnecessarily hardened to degrade the lubricity of the carbon-based
fired body 103. Therefore, the above-mentioned ratio is
adopted.
[0167] A sintering aid and a lubricant are added as necessary to
the raw material powder forming the carbon-based fired body 103 in
addition to the above-mentioned powders (plated powder and
low-melting-point metal powder as necessary).
[0168] The raw material powder having the above-mentioned
composition is subjected to compression molding to form a compact,
and the compact is heated at a sintering temperature that is lower
than the melting point of the coating metal and higher than the
melting point of the low-melting-point metal, to thereby provide a
sintered body (carbon-based fired body 103). Specifically, the
low-melting-point metal (for example, tin) in the raw material
powder is melted, and a part of the molten low-melting-point metal
diffuses into the coating metal, to thereby form an alloy layer on
the surface of the coating metal. The alloy layers are subjected to
diffusion joining in a solid phase state, with the result that the
plated powders are bound to each other. Further, of the molten
low-melting-point metals, those which have not diffused into the
coating metal are solidified between the plated powders to serve as
paste or the like, to thereby contribute to the enhancement of the
binding force between the plated powders.
[0169] When the raw material powder of the compact contains a resin
binder, the resin binder is decomposed to generate decomposed gas
during firing, and a dimensional change caused by the dissipation
of the resin binder due to firing increases. In order to suppress
the generation of the decomposed gas and the dimensional change, it
is necessary to heat the compact over a long time period to cause
firing to proceed slowly. In contrast, in this embodiment, the
compact does not contain the resin binder as described above, and
hence sintering can be performed within a relatively short time
period, and the productivity can be increased.
[0170] The carbon-based fired body 103 thus formed has a structure
in which the graphite particles 113 are retained in a network in
which copper 116 serving as the coating metal is bound to each
other by sintering as illustrated in FIG. 23. In FIG. 23, the
illustration of the low-melting-point metal is omitted.
[0171] In the later insert molding step, an integrated product in
which the carbon-based fired body 103 is retained by the resin
substrate 104 is formed, and the integrated product is subjected to
a sizing step. As illustrated in FIG. 23, in the carbon-based fired
body 103 of this embodiment, the copper 116 that is easily deformed
plastically is interposed between the graphite particles 113, and
hence the carbon-based fired body 103 can be subjected to sizing by
die molding. Thus, in the sizing step, the inner side surface 103a
of the carbon-based fired body 103 as well as the inner peripheral
surface 104a of the resin substrate 104 is subjected to sizing, and
hence the surface accuracy of the bearing surface 111 can be even
further enhanced.
[0172] In the above-mentioned embodiment, there is described the
case where the carbon-based fired body 103 is exposed to only the
inner peripheral surface (bearing surface 111) of the bearing 101,
but the present invention is not limited thereto. For example, in
an embodiment illustrated in FIG. 24, the carbon-based fired body
103 is exposed to the outer peripheral surface 112 as well as the
inner peripheral surface of the bearing 101. In this case, each
carbon-based fired body 103 can be compressed from both sides in
the radial direction in the sizing step, and hence sizing is easily
performed. In this embodiment, it is preferred that the
carbon-based fired body 103 using the metal binder illustrated in
FIG. 23 be used.
[0173] Further, in the above-mentioned embodiment, there is
described the case where the plurality of carbon-based fired bodies
103 are arranged at equal intervals in the circumferential
direction, but the present invention is not limited thereto. For
example, as illustrated in FIG. 25, the carbon-based fired body 103
having a semi-cylindrical shape that continues in the
circumferential direction may be arranged so as to cover a
substantially half periphery of the bearing surface 111.
Alternatively, as illustrated in FIG. 26, the carbon-based fired
body 103 having a cylindrical shape may cover the entire periphery
of the bearing surface 111.
[0174] Further, in the above-mentioned embodiment, there is
described the case where the inner side surface 103a of the
carbon-based fired body 103 and the inner peripheral surface 104a
of the resin substrate 104 are arranged on the same cylindrical
surface and form the bearing surface 111, but the present invention
is not limited thereto. For example, as illustrated in FIG. 27, the
inner side surface 103a of the carbon-based fired body 103 may be
arranged on the radially inner side from the inner peripheral
surface 104a of the resin substrate 104 to form the bearing surface
111 only of the inner side surface 103a of the carbon-based fired
body 103. In this case, the inner side surfaces 103a of the
plurality of carbon-based fired bodies 103 are arranged on the same
cylindrical surface.
[0175] Further, the carbon-based fired bodies 103 may be arranged
only in a partial region of the axial direction instead of being
arranged over the entire axial length of the bearing 101 as
illustrated in FIG. 18B, and the carbon-based fired bodies 103 may
be arranged, for example, in a plurality of portions isolated in
the axial direction.
[0176] Further, the present invention is not limited to the bearing
configured to support the relative rotation of the shaft, and can
also be applied to a bearing configured to support the axial motion
of the shaft. Further, the present invention is not limited to the
cylindrical sliding member, and can also be applied to a sliding
member having another shape (for example, a semi-cylindrical shape
or a rectangular box shape).
[0177] The sliding member according to the present invention can be
used as a gear wheel having a sliding surface on an inner
peripheral surface.
[0178] The sliding member according to the present invention can be
used as, for example, a gearwheel fora fuel pump, in particular, an
inner rotor 141 to be incorporated into a positive-displacement
rotary gear pump as illustrated in FIG. 31. As illustrated in FIG.
28 and FIG. 29, the inner rotor 141 comprises the carbon-based
fired body 103 containing carbon as a main component and the resin
substrate 104 configured to retain the carbon-based fired body 103.
In this embodiment, the carbon-based fired body 103 is formed into
a cylindrical shape, and the entire surface of the outer peripheral
surface 103b of the carbon-based fired body 103 is retained by the
resin substrate 104. The inner peripheral surface 103a of the
carbon-based fired body 103 is exposed to an inner peripheral
surface of the inner rotor 141 and serves as the bearing surface
111 that slides with an outer peripheral surface of the fixing
shaft 162a (see FIG. 31). A tooth surface 141a that is engaged with
the outer rotor 163 (see FIG. 31) is formed on the outer peripheral
surface of the resin substrate 104. The inner rotor 141 is
manufactured through the fired body forming step and the insert
molding step. Further, an integrated product of the carbon-based
fired body 103 and the resin substrate 104 obtained in the insert
molding step is subjected to a sizing step as necessary. Each step
is the same as that of the above-mentioned embodiments, and hence
overlapping description of the same part is omitted.
[0179] Further, the sliding member according to the present
invention can be used as a planetary gear 151 (see FIG. 30) forming
a planetary gear reducer. The planetary gear 151 is arranged in a
plurality of portions in the circumferential direction between a
sun gear and an internal gear (not shown), which are coaxially
arranged, in the radial direction, and each planetary gear 151 is
engaged with both the sun gear and the internal gear.
[0180] As illustrated in FIG. 30, the planetary gear 151 comprises
the carbon-based fired body 103 containing carbon as a main
component and the resin substrate 104 configured to retain the
carbon-based fired body 103. In the illustrated example, the
carbon-based fired body 103 is formed into a cylindrical shape, and
the entire surface of the outer peripheral surface 103b of the
carbon-based fired body 103 is retained by the resin substrate 104.
The inner peripheral surface 103a of the carbon-based fired body
103 is exposed to an inner peripheral surface of the planetary gear
151 and serves as the bearing surface 111 that slides with an outer
peripheral surface of the shaft 102. A tooth surface 151a that is
engaged with the sun gear and the internal gear is formed on the
outer peripheral surface of the resin substrate 104. The planetary
gear 151 is manufactured through the fired body forming step and
the insert molding step. Further, an integrated product of the
carbon-based fired body 103 and the resin substrate 104 obtained in
the insert molding step is subjected to one or both of a sizing
step and an oil impregnation step as necessary. Each step is the
same as that of the above-mentioned embodiments, and hence
overlapping description of the same part is omitted.
[0181] Next, a sliding member according to an embodiment of a third
invention of the present application is described with reference to
FIGS. 32 and FIG. 33.
[0182] The sliding member is manufactured through: a compacting
step of subjecting raw material powder to compression molding, to
thereby provide a compact; a sintering step of sintering the
compact to provide a sintered body; and a sizing step of subjecting
the sintered body to sizing by recompression. Now, each step is
described in detail.
(1) Compacting Step
[0183] First, various powders containing graphite particles, a
binder metal, and a low-melting-point metal are mixed to prepare
raw material powder.
[0184] As the graphite particles, artificial graphite or natural
graphite may be used. It is preferred that the graphite particles
have a granular shape (excluding scale-shaped graphite and earthy
graphite). In this embodiment, the granular artificial graphite is
used. Further, both the graphite particles that are not granulated
and the graphite particles that are granulated may be used. In
order to granulate the graphite particles, a binder for binding
each graphite particle is required to decrease the ratio of
graphite in each particle. Therefore, it is preferred that the
graphite particles that are not granulated be used.
[0185] The binder metal adheres to the surface of each graphite
particle. As the binder metal, a metal having a melting point
higher than a sintering temperature described later is used. A
material that has hardness lower than that of the graphite
particles and is easily deformed plastically is used as the binder
metal. Specifically, as the binder metal, for example, copper or
nickel may be used, and copper is used in this embodiment.
[0186] As the low-melting-point metal, a metal having a melting
point lower than the sintering temperature described later is used.
As the low-melting-point metal, for example, tin or zinc may be
used, and tin is used in this embodiment.
[0187] The raw material powder is prepared by, for example, mixing
graphite powder having copper adhering thereto in which copper
adheres as a binder metal to the surface of each graphite particle
and tin powder serving as a low-melting-point metal. In this
embodiment, graphite powder plated with copper in which the surface
of each graphite particle is plated with copper is used as the
graphite powder having copper adhering thereto. Further, as the
graphite powder having copper adhering thereto, for example,
graphite powder in which the entire surface of a graphite particle
(Gr) is coated with copper (Cu) as illustrated in FIG. 32A may be
used. Alternatively, as the graphite powder having copper adhering
thereto, graphite powder in which copper (Cu) is dispersed in an
island manner onto the surface of the graphite particle (Gr) to
adhere thereto as illustrated in FIG. 32B may be used. The graphite
powder having copper adhering thereto illustrated in FIG. 32A and
the graphite powder having copper adhering thereto illustrated in
FIG. 32B may each be used alone, or maybe mixed with each other. In
this embodiment, the graphite powder having copper adhering thereto
illustrated in FIG. 32B is used alone.
[0188] The above-mentioned raw material powder is filled into a
mold. In general, the fineness of the graphite particles is very
high. Therefore, the flowability of the graphite particles is
unsatisfactory, and the filling property thereof with respect to
the mold is unsatisfactory. In this embodiment, when copper is
caused to adhere to the graphite particles, the apparent density
increases to enhance the flowability of the graphite particles.
Therefore, the filling property with respect to the mold is
enhanced, and the raw material powder can be uniformly filled into
the mold.
[0189] When the raw material powder filled into the mold as
described above is subjected to compression molding, a compact is
formed. In this case, the graphite particles are not deformed
plastically. However, when copper adhering to each graphite
particle is engaged with each other while being deformed
plastically, the raw material powder can be molded into a
predetermined shape. With this, a compact containing the graphite
particles as a main component can be formed without using a binding
agent, such as tar pitch or coal tar.
(2) Sintering Step
[0190] Next, the compact obtained in the above-mentioned compacting
step is heated in a sintering furnace, with the result that copper
adhering to each graphite powder is bound to each other by
sintering, to thereby form a sintered body. Specifically, when the
compact is heated, tin powder contained in the compact is melted,
and a part thereof diffuses into the surface layer of copper
adhering to each graphite particle, to thereby form a copper-tin
alloy layer on the surface of copper. The copper-tin alloy layers
are subjected to diffusion joining in a solid phase state, with the
result that the graphite powders plated with copper are bound to
each other to form a sintered body. The sintering temperature in
this case is lower than the melting point of copper and higher than
the melting point of tin.
[0191] When the compact contains a binding agent, such as tar pitch
or coal tar, as in the related-art lubricating member, decomposed
gas of the binding agent is generated during sintering, and the
binding agent almost dissipates due to sintering. Therefore, a
dimensional change caused by sintering (difference in dimension
between the compact and the sintered body) increases. In this case,
when sintering is performed rapidly within a short time period,
there is a risk in that cracks and the like may occur in the
sintered body due to a rapid dimensional change, and hence it is
necessary to heat the compact over a long time period to cause
sintering to proceed slowly. In contrast, in this embodiment, the
compact does not contain the binding agent, such as tar pitch or
coal tar, as described above, and hence the decomposed gas of the
binding agent is not generated during sintering, and the
dimensional change caused by sintering can be suppressed. Thus, the
concern about the cracks and the like of the sintered body is
small, and the sintering time can be relatively shortened.
(3) Sizing Step
[0192] When the compact is sintered as described above, contraction
occurs. Therefore, it is desired that the sintered body be
subjected to sizing after sintering. For example, the related-art
lubricating member obtained by firing a compact containing graphite
particles and a binding agent is brought into a state in which the
graphite particles are bound to each other with a binding agent
carbonized by firing. When the lubricating member is subjected to
sizing, the graphite particles themselves are hardly deformed
plastically as described above, and hence there is a high risk in
that the lubricating member may be broken. Therefore, the sizing of
the related-art lubricating member needs to be performed by
mechanical processing, with the result that there are problems of
an increase in cost and a decrease in productivity.
[0193] The sintered body of this embodiment contains the binder
metal between the graphite particles. Therefore, when the sintered
body is subjected to sizing, the sizing can be performed while the
binder metal is deformed plastically. Specifically, when the
sintered body is compressed with a sizing die (die, core, upper
punch, and lower punch), the sintered body is subjected to sizing
to desired dimensions. With this, shaping by mechanical processing
as in the related-art lubricating member is not required. Thus, the
cost is reduced, and the productivity is increased. With the
foregoing, the lubricating member is completed.
[0194] In the sizing step, the sintered body and the die and core
of the sizing die slide with each other in a pressure contact
state. With this, copper of the graphite powder plated with copper
that is exposed to the surface of the sintered body can be peeled
from the graphite particles to increase the ratio of the graphite
particles exposed to the surface of the sintered body. Thus, when a
portion of the sintered body serving as the sliding surface is
caused to slide with the sizing die in a pressure contact state,
the ratio of the graphite particles exposed to the sliding surface
can be increased to enhance the sliding property. Needless to say,
when it is not necessary to peel copper of the graphite powder
plated with copper of the sliding surface by sizing as described
above, the portion of the sintered body serving as the sliding
surface may be brought into abutment against a surface (for
example, end surfaces of the upper and lower punches) that do not
slide with the sizing die.
[0195] As illustrated in an enlarged state in FIG. 33, a
lubricating member 201 formed as described above contains graphite
particles (Gr), copper (Cu) serving as a binder metal, and tin (Sn)
serving as a low-melting-point metal. In FIG. 33, the graphite
particles (Gr) are represented by scattered points, copper (Cu) is
represented by hatching, and tin (Sn) is not shown.
[0196] Copper adhering to each graphite particle is bound to each
other by sintering. Copper is not melted at the sintering
temperature and is bound to copper adhering to the other graphite
particles in a solid phase state. Specifically, a part or a whole
of tin melted by sintering diffuses into copper, to thereby form a
copper-tin alloy layer on a surface layer, and the copper-tin alloy
(bronze) regions are subjected to diffusion joining. Further, of
tin melted by sintering, those which have not diffused into copper
are solidified between copper adhering to each graphite particle to
serve as paste or the like, to thereby contribute to the
enhancement of the binding force between copper.
[0197] On the surface of the lubricating member 201, in particular,
the sliding surface 201a that slides with another component, the
graphite particles occupy the largest area, and the area ratio of
the graphite particles on the sliding surface is, for example, 50%
or more, preferably 80% or more, more preferably 90% or more. In
this embodiment, the lubricating member 201 contains the graphite
particles in the largest volume ratio and contains the graphite
particles in a volume ratio of, for example, 50% or more.
[0198] As described above, the graphite particles are exposed to
the sliding surface in a large amount, with the result that the
sliding property between the lubricating member 201 and the mating
member is enhanced due to the self-lubricity of the graphite.
Therefore, the lubricating member 201 is preferably used as a
lubricating member that slides with a mating member in a
non-lubricating environment (that is, without interposing a
lubricant, such as oil). Specifically, the lubricating member 201
can be used as, for example, a rotor and a vane for a vacuum pump,
a bearing to be used in a high-temperature environment exceeding
200.degree. C., or a bearing for a construction machine. The
lubricating member 201 is not limited to an application to be used
in a non-lubricating environment, and can also be used in an
application to be used in a lubricating environment in which the
lubricating member 201 slides with a mating member through
intermediation of a lubricant, such as oil.
[0199] The present invention is not limited to the above-mentioned
embodiments. For example, in the above-mentioned embodiments, the
raw material powder is formed of graphite powder having copper
adhering thereto and tin powder. However, the present invention is
not limited thereto, and for example, powder further having a
low-melting-point metal adhering to the surface of a binder metal
adhering to graphite powder may be used. For example, powder may be
used, which is obtained by subjecting graphite powder plated with
copper further to tin plating, to thereby cause tin to adhere to
the surface of copper.
[0200] Further, in the above-mentioned embodiments, there is
described the case where the lubricating member is made of graphite
particles, a binder metal, and a low-melting-point metal, but the
lubricating member may further contain another metal, such as
iron.
[0201] Further, in the above-mentioned embodiments, there is
described the case where the sintered component contains a
low-melting-point metal, but the low-melting-point metal may be
omitted when the low-melting-point metal is not particularly
required. In this case, copper adhering to each graphite particle
does not form an alloy layer, and pure copper is subjected to
diffusion joining by sintering.
[0202] Further, in the above-mentioned embodiments, there is
described the case where the sintered body is subjected to sizing
treatment, but the sizing treatment may be omitted when the sizing
treatment is not particularly required.
[0203] The configurations of the embodiments of the first
invention, the second invention, and the third invention of the
present application described above maybe combined appropriately.
For example, the lubricating member according to the embodiment of
the third invention of the present application may be used as the
sliding member (bearing, etc.) according to the embodiment of the
first invention or the second invention of the present
application.
REFERENCE SIGNS LIST
[0204] 1 sintered bearing (sliding member) [0205] 2 shaft (mating
member) [0206] 3 metal substrate [0207] 4 lubricating member [0208]
5 resin binder [0209] 6 graphite powder (solid lubricant powder)
[0210] 7 coating metal (metal) [0211] 8 plated powder (coated
powder) [0212] 9 bearing surface (sliding surface) [0213] 11
graphite particle (solid lubricant particle) [0214] 13 inner rotor
(sliding member) [0215] F contraction force
* * * * *