U.S. patent application number 14/443454 was filed with the patent office on 2015-10-29 for sliding member.
This patent application is currently assigned to SUMITOMO ELECTRIC SINTERED ALLOY, LTD.. The applicant listed for this patent is SUMITOMO ELECTRIC FINE POLYMER, INC., SUMITOMO ELECTRIC SINTERED ALLOY, LTD.. Invention is credited to Kazuaki IKEDA, Toshiyuki KOSUGE, Yasunori NAGAOKA, Kentaro YOSHIDA.
Application Number | 20150307800 14/443454 |
Document ID | / |
Family ID | 50827624 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150307800 |
Kind Code |
A1 |
YOSHIDA; Kentaro ; et
al. |
October 29, 2015 |
SLIDING MEMBER
Abstract
There is provided a sliding member that has sufficient wear
resistance and good adhesion to a base formed of a sintered body.
The sliding member includes a surface layer formed of a crosslinked
fluoropolymer and a base that adheres closely to the surface layer.
The base is a sintered body having a full density ratio in the
range of 0.75 to 0.96 and is formed of a material having higher
thermal conductivity than a fluoropolymer. The surface layer has a
thickness in the range of 1 to 300 .mu.m.
Inventors: |
YOSHIDA; Kentaro;
(Itami-shi, JP) ; KOSUGE; Toshiyuki; (Itami-shi,
JP) ; IKEDA; Kazuaki; (Sennan-gun, JP) ;
NAGAOKA; Yasunori; (Sennan-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC SINTERED ALLOY, LTD.
SUMITOMO ELECTRIC FINE POLYMER, INC. |
Takahashi-shi, Okayama
Sennan-gun, Osaka |
|
JP
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC SINTERED ALLOY,
LTD.
Takahashi-shi, Okayama
JP
SUMITOMO ELECTRIC FINE POLYMER, INC.
Sennan-gun, Osaka
JP
|
Family ID: |
50827624 |
Appl. No.: |
14/443454 |
Filed: |
October 24, 2013 |
PCT Filed: |
October 24, 2013 |
PCT NO: |
PCT/JP2013/078817 |
371 Date: |
May 18, 2015 |
Current U.S.
Class: |
508/106 |
Current CPC
Class: |
F16C 2240/60 20130101;
F16C 2208/32 20130101; F16C 2220/20 20130101; F16C 2202/10
20130101; C10M 107/38 20130101; F16C 33/128 20130101; F16C 2202/20
20130101; F16C 33/201 20130101 |
International
Class: |
C10M 107/38 20060101
C10M107/38 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2012 |
JP |
2012-262568 |
Claims
1. A sliding member comprising: a surface layer formed of a
crosslinked fluoropolymer; and a base that adheres closely to the
surface layer, wherein the base is a sintered body having a full
density ratio in the range of 0.75 to 0.96, the base is formed of a
material having higher thermal conductivity than a fluoropolymer,
and the surface layer has a thickness in the range of 1 to 300
.mu.m.
2. The sliding member according to claim 1, wherein the base is an
iron-based sintered body.
3. The sliding member according to claim 1, wherein the surface
layer has a thickness in the range of 10 to 100 .mu.m.
4. The sliding member according to claim 1, wherein the
fluoropolymer is at least one selected from the group consisting of
polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene
copolymers, and tetrafluoroethylene-perfluoroalkyl vinyl ether
copolymers.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sliding member in which a
sliding portion of a base formed of a sintered body contains a
fluoropolymer. The sliding member has high wear resistance and can
be suitably used in unlubricated bearings, oil pump rotors, cam
rings, or the like.
BACKGROUND ART
[0002] Fluoropolymers are chemically very stable and have low
adhesion and low frictional (low friction coefficient) properties.
Because of these characteristics, fluoropolymers are widely used in
various industrial products, such as seals and packing, and
consumer products, such as cooking utensils.
[0003] Sliding members, such as unlubricated bearings, require low
friction coefficients and often require heat resistance and
chemical stability. Thus, it is anticipated that sliding members
will be formed of fluoropolymers in the near future. However,
sliding members require high wear resistance, whereas
fluoropolymers have a wear problem. Thus, it is difficult to use
fluoropolymers in sliding members unless the wear resistance of the
fluoropolymers is improved.
[0004] It is known that the wear resistance of fluoropolymers can
be improved by adding filler to the fluoropolymers. However, filler
may impair the excellent inherent characteristics of
fluoropolymers, such as low frictional properties. In this
situation, Patent Literature 1 describes a method for improving the
wear resistance of fluoropolymers by ionizing radiation and
discloses a sliding member formed of a fluoropolymer subjected to
ionizing radiation.
[0005] It has been thought that radiation impairs the mechanical
characteristics of fluoropolymers. However, radiation under
particular conditions can improve mechanical characteristics. For
example, Patent Literature 2 discloses that ionizing radiation,
such as electron beam radiation, at a dose in the range of
approximately 1 kGy to 10 MGy in the absence of oxygen at a
temperature of crystalline melting point or higher, preferably
approximately 340.degree. C., can suppress reduction in the
elongation at break or breaking strength of polytetrafluoroethylene
(PTFE) resulting from radiation, and, conversely, induce rubber
elasticity with low crystallinity, and improve yield strength.
[0006] Sliding members have a problem in that an increase in the
surface temperature of a sliding member due to heat generation
resulting from sliding makes the sliding member more susceptible to
wear. To address this problem, a method for manufacturing a sliding
member by adhering a fluoropolymer closely to a heat dissipator
made of a metallic material serving as a base is known (Patent
Literature 3). In this sliding member, the heat dissipator can
dissipate heat and prevent an increase in the temperature of the
fluoropolymer due to heat generation resulting from sliding. In
this case, however, in addition to high wear resistance of the
fluoropolymer, good adhesion between the fluoropolymer film and the
base is required.
CITATION LIST
Patent Literature
[0007] PTL 1: Japanese Patent No. 3566805 [0008] PTL 2: Japanese
Patent No. 3317452 [0009] PTL 3: Japanese Unexamined Patent
Application Publication No. 2011-208802
SUMMARY OF INVENTION
Technical Problem
[0010] In Patent Literature 3, the metallic material base is coated
with the fluoropolymer. Considering more efficient heat dispersion,
however, the base may be formed of a sintered body. Patent
Literature 3 did not describe a base formed of a sintered body.
Furthermore, unlike metallic materials, sintered bodies have a
rough surface. Thus, the adhesion of a fluoropolymer film to
sintered bodies will be different from the adhesion of a
fluoropolymer film to metallic materials even if the fluoropolymer
films are formed under the same conditions.
[0011] Accordingly, it is an object of the present invention to
provide a sliding member that has sufficient wear resistance and
good adhesion to a base formed of a sintered body.
Solution to Problem
[0012] As a result of extensive studies to solve the problems
described above, the present inventors found that sufficient wear
resistance and low wear as well as improved adhesion to a base
formed of a sintered body can be achieved by adjusting the full
density ratio of the sintered body of the base within a
predetermined range.
[0013] The gist of the present invention consists in the following
[1] to [4]:
[0014] [1] A sliding member that includes a surface layer formed of
a crosslinked fluoropolymer; and a base that adheres closely to the
surface layer, wherein the base is a sintered body having a full
density ratio in the range of 0.75 to 0.96, the base is formed of a
material having higher thermal conductivity than a fluoropolymer,
and the surface layer has a thickness in the range of 1 to 300
.mu.m.
[0015] [2] The sliding member according to [1], wherein the base is
an iron-based sintered body.
[0016] [3] The sliding member according to [1] or [2], wherein the
surface layer has a thickness in the range of 10 to 100 .mu.m.
[0017] [4] The sliding member according to any one of [1] to [3],
wherein the fluoropolymer is at least one selected from the group
consisting of polytetrafluoroethylene,
tetrafluoroethylene-hexafluoropropylene copolymers, and
tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers.
Advantageous Effects of Invention
[0018] The present invention can provide a sliding member that has
sufficient wear resistance and improved adhesion to a base formed
of a sintered body.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a schematic perspective view of a thrust wear test
(ring-on-disk wear evaluation) in examples and comparative
examples.
DESCRIPTION OF EMBODIMENTS
[0020] Embodiments of the present invention will be described
below. The present invention is not limited to these embodiments
and examples. These embodiments and examples may be modified,
provided that the gist of the present invention is not
compromised.
[0021] A sliding member according to the present invention includes
a surface layer formed of a crosslinked fluoropolymer and a base
that adheres closely to the surface layer.
[0022] The fluoropolymer refers to a resin containing fluorine. The
fluoropolymer that forms the surface layer is preferably
polytetrafluoroethylene (PTFE), a
tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or a
tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) in
terms of mechanical strength and chemical resistance. Among these,
PTFE is more preferred because of its particularly high mechanical
strength, chemical resistance, and heat resistance. The
fluoropolymer may contain another component, provided that the gist
of the present invention is not compromised. For example, PTFE may
contain a minute amount of polymerization unit based on a
copolymerizable monomer, such as perfluoro(alkyl vinyl ether),
hexafluoropropylene, (perfluoroalkyl)ethylene, or
chlorotrifluoroethylene. The fluoropolymer may be a mixture of two
or more fluoropolymers.
[0023] The surface layer formed of the fluoropolymer must adhere to
the base. When the surface layer peels off, and the base is
exposed, the sliding member cannot perform its function.
[0024] Thus, in order to improve adhesion to the base, the
fluoropolymer and the base are simultaneously exposed to ionizing
radiation. No cross-linking or insufficient cross-linking results
in low wear resistance and low mechanical strength of the
fluoropolymer, and the sliding member cannot be used. The dose of
ionizing radiation generally ranges from approximately 1 to 1500
kGy.
[0025] The surface layer formed of the fluoropolymer preferably has
a thickness of 1 .mu.m or more, more preferably 10 .mu.m or more. A
surface layer having an excessively small thickness is unfavorable
because protrusions of the base appear on the surface layer. The
upper limit of the thickness of the surface layer is preferably 300
.mu.m, more preferably 100 .mu.m. When the surface layer has an
excessively large thickness, heat generated on the surface of the
member by sliding is not easily conducted to the base, and it is
difficult to prevent an increase in the surface temperature of the
member. This tends to result in insufficient wear resistance. When
the surface layer has a thickness in the preferred range, heat
generated on the sliding surface by sliding can be effectively
conducted to the base and is readily dissipated. This can suppress
an increase in the surface temperature of the sliding member and
improve wear resistance.
[0026] Wear resistance is often evaluated by a thrust wear test
(ring-on-disk wear evaluation) by rotating a cylinder on a sample
under pressure to measure wear. In particular, wear resistance and
the coefficient of kinetic friction (.mu.) are often evaluated as a
multiplier (critical PV) of a pressure (P) and a rotation speed (V)
at which rapid wear occurs in this test method. A sliding member
according to the present invention has a very high critical PV,
good lubricity, high wear resistance, and a low coefficient of
kinetic friction.
[0027] The base is formed of a sintered body that has higher
thermal conductivity than the fluoropolymer. This sintered body is
formed by heating an aggregate of a raw powder at a temperature
lower than the melting point of the raw powder. More specifically,
the sintered body is formed by charging a metal mold having a
product shape with a raw powder, compressing the raw powder at a
predetermined pressure, and sintering the resulting compact.
[0028] The raw powder may be a metal powder or a nonmetal powder.
The metal powder may be an iron powder or a nonferrous metal
powder. The iron powder may be a pure iron powder, an iron alloy
powder, such as a carbon steel powder, or a partially sintered iron
powder. The nonferrous metal powder may be a powder of a metal such
as copper, nickel, manganese, chromium, or aluminum or an alloy not
containing iron. The nonmetal powder may be a powder of nonmetal,
such as a graphite powder or a ceramic powder.
[0029] The full density ratio of the base, that is, the ratio of
the density of the sintered body that forms the base to the density
of the metal that composes the base is preferably 0.75 or more,
more preferably 0.80 or more. A full density ratio of less than
0.75 may result in insufficient strength of the sliding member. The
upper limit of the full density ratio is preferably 0.96, more
preferably 0.89. A full density ratio of more than 0.96 tends to
result in low surface porosity and insufficient adhesion to the
surface layer formed of the fluoropolymer.
[0030] The base has a larger volume than the surface layer formed
of the fluoropolymer. The base has high heat resistance so as to
withstand heat generated by sliding. When the sintered body that
forms the base has lower thermal conductivity than the
fluoropolymer of the surface layer, it is difficult to dissipate
heat generated on the surface of the member by sliding and to
prevent an increase in the surface temperature of the member. When
the base has a small volume and accordingly small heat capacity, it
is difficult to dissipate heat generated in the same manner and to
prevent an increase in the surface temperature of the member.
[0031] The base preferably has a thermal conductivity of 0.001
cal/.degree. C.cms or more, more preferably 0.01 cal/.degree. C.cms
or more, still more preferably 0.1 cal/.degree. C.cms or more.
[0032] The base is formed of a material having a higher thermal
conductivity than a fluoropolymer. A fluoropolymer not containing
filler has a thermal conductivity of approximately 0.0005
cal/.degree. C.cms (0.0005 cal/.degree. C.cms for PTFE). Thus, when
the base has a thermal conductivity of less than 0.001 cal/.degree.
C.cms, this may result in insufficient heat transfer from the
surface layer formed of a fluoropolymer to the base. The base
preferably has as high a thermal conductivity as possible.
[0033] As described above, the base has a larger volume than the
surface layer formed of the fluoropolymer and preferably has as
large a volume as possible in terms of heat dissipation. More
specifically, when X denotes the thermal conductivity of the base
expressed in cal/.degree. C.cms, and Y denotes (the volume of the
base)/(the volume of the surface layer formed of the
fluoropolymer), XY is preferably 0.005 or more, more preferably
0.05 or more, still more preferably 0.5 or more.
[0034] Examples of the material for the base and the thermal
conductivity of the material are as follows: iron: 0.18
cal/.degree. C.cms, aluminum: 0.53 cal/.degree. C.cms, and ceramic
(brick): 0.07 cal/.degree. C.cms.
[0035] A process for manufacturing a sliding member according to
the present invention will be described below.
[0036] First, a base having a predetermined shape is formed. The
shape may be tabular, convex, or concave, or may be cylindrical or
tubular and have a sliding portion on the outer surface thereof, or
may be tubular and have a sliding portion on the inner surface
thereof.
[0037] A fluoropolymer is then applied to a surface of the base,
that is, a portion that will become a sliding portion to form a
fluoropolymer layer. The fluoropolymer may be applied by a method
of applying a fluoropolymer film; a powder coating method, for
example, an electrostatic coating method using a fluoropolymer
powder or a method of spraying a fluoropolymer powder; or a method
of applying a fluoropolymer dispersion (a liquid containing a
fluoropolymer powder uniformly dispersed in a dispersion medium)
and removing the dispersion medium by drying.
[0038] Among these, a method of applying a fluoropolymer dispersion
is preferred because this method can easily form a fluoropolymer
layer having a uniform thickness. In the case of fluoropolymers
that are soluble in a solvent, a fluoropolymer solution may be
applied, and the solvent may be removed by drying. However, this
method cannot be applied to fluoropolymers that are insoluble in a
solvent, such as PTFE.
[0039] In a method of applying a fluoropolymer dispersion, the
dispersion medium may be a mixed solvent of water and an
emulsifier, water and an alcohol, water and acetone, or water, an
alcohol, and acetone. After a fluoropolymer dispersion is applied,
the dispersion medium is removed by air drying or hot-air drying.
Removal of the dispersion medium by drying results in a film formed
of the fluoropolymer powder.
[0040] After the fluoropolymer coating film is formed by the
application or the like, the fluoropolymer coating film is fired at
a temperature equal to or higher than the melting point of the
fluoropolymer, and the fluoropolymer powder is fused and forms a
fluoropolymer layer. The firing is preferably performed at a
temperature in the range of 350.degree. C. to 400.degree. C. The
dispersion medium may be removed in the firing step without the
drying step.
[0041] A surface of the fluoropolymer layer thus formed is then
irradiated with ionizing radiation to cross-link the fluoropolymer.
When the combination of the fluoropolymer and the base material is
appropriate, the cross-linking also improves the adhesion between
the fluoropolymer layer and the base.
[0042] For cross-linking, a surface of the fluoropolymer film is
irradiated with ionizing radiation in an oxygen-free atmosphere,
more specifically, in an atmosphere having an oxygen concentration
of 1000 ppm or less, preferably 10 ppm or less, at a temperature in
the range of the crystalline melting point of the fluoropolymer to
approximately 400.degree. C., preferably at a temperature 0.degree.
C. to 30.degree. C. higher than the crystalline melting point of
the fluoropolymer. The radiation dose generally ranges from 1 to
1500 kGy, preferably 100 to 1000 kGy.
[0043] The firing and ionizing radiation may be simultaneously
performed. An excessively low temperature atmosphere inhibits the
cross-linking reaction of the fluoropolymer. An excessively high
temperature atmosphere, particularly having a temperature of more
than 400.degree. C., promotes thermal decomposition of the
fluoropolymer and impairs material properties. A radiation dose of
less than 1 kGy results in an insufficient cross-linking reaction
and no characteristic improvement. A radiation dose of more than
1500 kGy tends to result in an increased decomposition rate of the
fluoropolymer.
[0044] Examples of ionizing radiation for use in the cross-linking
of fluoropolymers include charged particle beams, such as electron
beams and high-energy ion beams, high-energy electromagnetic waves,
such as gamma rays and X-rays, and neutron beams. Electron beams
are preferred because electron beam generators are relatively
inexpensive and can produce high-power electron beams, and the
degree of cross-linking can be easily controlled with electron
beams.
[0045] The adhesion of a surface layer of a sliding member
manufactured by the method described above can be measured by a
cross-cut test. The cross-cut test is a test method described in
JIS-K-5400 (1998). More specifically, 100 squares are scratched on
a surface layer, and a tape is repeatedly attached to and peeled
from the surface layer. The number of squares that remain on the
surface layer is counted. 99/100 or more means that 99 or more
squares of the 100 squares remain on the surface layer.
[0046] Poor adhesion between the surface layer and the base tends
to result in insufficient contact (adhesion) between the surface
layer and the base. In particular, sliding is likely to cause
problems, such as the formation of voids. In particular, the
formation of voids due to insufficient contact makes it difficult
to conduct heat generated on the surface layer to the base and to
prevent an increase in the surface temperature of the member. This
tends to result in insufficient wear resistance. Thus, the surface
layer preferably does not peel off from the base during 100 or more
repetitions in the cross-cut test.
[0047] A sliding member according to the present invention has a
low friction coefficient similar to the friction coefficient of
known sliding members formed of a fluoropolymer and higher wear
resistance than the known sliding members. Thus, a sliding member
according to the present invention can be suitably used in
applications that require high wear resistance, such as
unlubricated bearings for use in industrial machinery and consumer
products.
EXAMPLES
[0048] The present invention will be further described below with
examples. First, the evaluation method will be described below.
<Evaluation Method>
[Measurement of Wear Resistance]
[0049] The wear resistance of a fluoropolymer coating was evaluated
by a thrust wear test (ring-on-disk wear evaluation, Suzuki wear
evaluation). More specifically, as illustrated in FIG. 1, the wear
of a test sample is measured by rotating a metal cylinder (mating
shaft) on the test sample under a predetermined load (contact
pressure: P) and at a predetermined speed (rotation speed: V).
[0050] The mating shaft was an S45C cylinder having an outer
diameter/inner diameter=11.5/7.4. Wear was measured under dry
(greaseless) lubrication conditions. The rotation speed (V) was
constant at 1800 rpm. The critical PV (PV at which rapid wear
occurs) was determined by changing the contact pressure (P). The
critical PV is listed in Table, wherein a circle denotes 100
MPam/min or more (good), a triangle denotes 1 to 100 MPam/min
(fair), and a cross denotes less than 1 MPam/min (poor). With
respect to lubricity, the coefficient of kinetic friction (.mu.) is
listed in Table, wherein a circle denotes less than 0.5 (good), and
a cross denotes 0.5 or more (poor).
[Measurement of Adhesion]
[0051] The peel resistance of a fluoropolymer coating was measured
by a cross-cut test. More specifically, 100 squares were scratched
on a fluoropolymer coating sample, and a tape was repeatedly
attached to and peeled from the sample. The number of squares that
remained on the sample was counted. The results after 10
repetitions are listed in Table, wherein a cross means that all the
100 squares peeled off from the sample (poor), a triangle means
that 1 to 99 of 100 squares peeled off from the sample (fair), and
a circle means that all the 100 squares remained on the sample
(good).
[Measurement of Strength]
[0052] A tensile test was performed according to JIS Z 2241. The
results are listed in Table, wherein a circle denotes a tensile
strength of 300 MPa or more (good), and a dash (-) means
unmeasurable. Members having a tensile strength of 300 MPa or more
can be used as structural members of automobiles or the like.
Examples 1 to 3, Comparative Examples 1 to 6
[0053] A fluoropolymer dispersion (manufactured by Daikin
Industries, Ltd.: D10-FE, resin type: PTFE) was applied to an iron
sintered material (2.0% Cu-0.8% C-Fe) having a density listed in
Table and a thickness of 20 mm, was dried, and was fired in a
nitrogen atmosphere at 380.degree. C. for 10 minutes. Thus, the
iron sintered material was coated with a fluoropolymer film having
a thickness of 15 .mu.m. The iron sintered material coated with the
fluoropolymer film was then heated to 330.degree. C. in a nitrogen
atmosphere (oxygen concentration: 5 ppm) and was irradiated at 300
kGy using an irradiation apparatus manufactured by Nissin Electric
Co., Ltd. (Sagatron: accelerating voltage 1.13 MeV). A test sample
was prepared in this manner.
[0054] The test sample was subjected to the tests described above.
Table shows the results.
[0055] Steel used in Comparative Example 2 was SNCM630 steel. In
the same manner as described above, a fluoropolymer film was
formed, and electron beam irradiation was performed.
TABLE-US-00001 TABLE Comparative example Example Comparative
example 1 1 2 3 2 3 4 5 6 Base Material Iron based Iron- Iron-
Iron- Steel Iron- Iron- Iron- Iron- sintered based based based
sheet based based based based body sintered sintered sintered
sintered sintered sintered sintered body body body body body body
body Density 5.6 6.4 6.8 7.2 7.8 6.4 6.8 7.2 6.8 (g/cm.sup.2) Full
density 0.72 0.82 0.87 0.9 1 0.82 0.87 0.9 0.87 ratio Coating Yes
Yes Yes Yes Yes Yes Yes Yes No Presence Electron Yes Yes Yes Yes
Yes No No No No beam radiation Physical Adhesion to .largecircle.
.largecircle. .largecircle. .largecircle. .DELTA. .DELTA. .DELTA.
.DELTA. -- properties base (cross- cut test) Wear .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X X X X
resistance (Critical PV) Lubricity .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. X (kinetic friction coefficient .mu.)
Tensile -- .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
strength
[0056] These embodiments of the present invention are only
examples. The scope of the present invention should not be limited
to these embodiments. The scope of the present invention is defined
by the appended claims and embraces all changes that fall within
the scope of the claims and the equivalents thereof.
* * * * *