U.S. patent application number 11/629376 was filed with the patent office on 2007-10-11 for structural body and electric-corrosion prevention method for the same.
Invention is credited to Kyoichi Kinoshita, Manabu Miyoshi, Manabu Sugiura, Motoharu Tanizawa.
Application Number | 20070237974 11/629376 |
Document ID | / |
Family ID | 35503088 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070237974 |
Kind Code |
A1 |
Miyoshi; Manabu ; et
al. |
October 11, 2007 |
Structural Body and Electric-Corrosion Prevention Method for the
Same
Abstract
A structural body of the present invention comprises a first
member (1) having a first outside end portion (10) in which a first
metal element is adapted to a major component; a second member (2)
having a second outside end portion (20) in which a second metal
element, being different from the first metal element, is adapted
to a major component, and which is disposed to contact with the
first outside end portion (10); and a coating member (3) comprising
a coated film, at least whose outside superficial portion is
composed of a fluoropolymer substance, and coating at least a part
of both first outside end portion (10) and second outside end
portion (20) so as to cover the contact portion (50) between them.
Moreover, an electric-corrosion prevention method of the present
invention, in the aforementioned structural body, inhibits the
development of electric corrosion, which might possibly occur so as
to stride over the contact portion (50) between the first outside
end portion (10) and the second outside end portion (20), by
hindering the electric conduction between the first outside end
portion (10) and the second outside end portion (20) by means of
the coating member (3). In accordance with the structural body and
electric-corrosion prevention method of the present invention, the
electric corrosion between members of different metals can be
prevented effectively.
Inventors: |
Miyoshi; Manabu; (Aichi-ken,
JP) ; Sugiura; Manabu; (Aichi-ken, JP) ;
Kinoshita; Kyoichi; (Aichi-ken, JP) ; Tanizawa;
Motoharu; (Aichi-ken, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
35503088 |
Appl. No.: |
11/629376 |
Filed: |
May 13, 2005 |
PCT Filed: |
May 13, 2005 |
PCT NO: |
PCT/JP05/09222 |
371 Date: |
December 11, 2006 |
Current U.S.
Class: |
428/545 ;
148/527 |
Current CPC
Class: |
F04B 39/12 20130101;
B05D 5/083 20130101; F04B 39/00 20130101; F04B 53/00 20130101; F04B
53/16 20130101; Y10T 428/12007 20150115; B05D 7/16 20130101 |
Class at
Publication: |
428/545 ;
148/527 |
International
Class: |
C23F 15/00 20060101
C23F015/00; F04B 39/00 20060101 F04B039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2004 |
JP |
2004-173090 |
Claims
1. A structural body, being characterized in that it comprises: a
first member having a first outside end portion in which a first
metal element is adapted to a major component; a second member
having a second outside end portion in which a second metal
element, being different from the first metal element, is adapted
to a major component, and which is disposed to contact with the
first outside end portion; and a coating member comprising a coated
film, at least whose outside superficial portion is composed of a
fluoropolymer substance, and coating at least a part of both first
outside end portion and second outside end portion so as to cover
the contact portion between them.
2. The structural body set forth in claim 1, wherein said coating
member includes a sealing layer, which is made by applying a
fluorine-based sealing agent and then curing it.
3. The structural body set forth in claim 2, wherein said sealing
agent is a liquid fluorocarbon rubber.
4. The structural body set forth in claim 2, wherein said sealing
layer is such that the thickness is 100 .mu.m or more.
5. The structural body set forth in claim 1, wherein said coating
member is such that the width, which goes over said contact
portion, is 10 mm or more.
6. The structural body set forth in claim 1, wherein said first
metal element or said second metal element is Mg.
7. The structural body set forth in claim 1, wherein said first
metal element is Mg, and said second metal element is Fe.
8. The structural body set forth in claim 7, wherein said first
member is a rear housing for a compressor, and said second member
is a gasket therefor.
9. An electric-corrosion prevention method for structural bodies,
being characterized in that, in a structural body comprising: a
first member having a first outside end portion in which a first
metal element is adapted to a major component; a second member
having a second outside end portion in which a second metal
element, being different from the first metal element, is adapted
to a major component, and which is disposed to contact with the
first outside end portion; and a coating member comprising a coated
film, at least whose outside superficial portion is composed of a
fluoropolymer substance, and coating at least a part of both first
outside end portion and second outside end portion so as to cover
the contact portion between them, the development of electric
corrosion, which might possibly occur so as to stride over the
contact portion between the first outside end portion and the
second outside end portion, is inhibited by hindering the electric
conduction between said first outside end portion and said second
outside end portion by means of said coating member.
Description
TECHNICAL FIELD
[0001] The present invention relates to a structural body, which
can effectively prevent the electric corrosion occurring between
different metals, and an electric-corrosion prevention method for
the same.
BACKGROUND ART
[0002] Usually, even if being any apparatus, it is constituted of a
combination of members, which are composed of metals. And, the
types of used metals, too, are diverse, depending on the
performance required for the respective parts. Therefore, such a
construction that members of different metals are disposed in
proximity to each other within an apparatus is not rare.
[0003] When disposing members of different metals in proximity to
each other, it has been known that electric decay (electric
corrosion) occurs between their both sides through water, and the
like, as a medium. This electric corrosion takes place by means of
the fact that various metals possess their intrinsic decay
potentials (reference potentials) so that potential differences
arise between them. That is, the electric corrosion develops by
means of the fact that a local cell is formed while adapting both
metals to electrodes and additionally adapting water or salt water,
and the like, to an electrolyte. Therefore, not only the electric
corrosion occurs between members of different metals by means of
the fact that water, and so forth, invades between the contact
surfaces of both of them, but also the electric corrosion develops
because, when water, and so forth, adheres onto the outer periphery
of members of different metals being in proximity to each other,
the water, and so on, plays a role of an electrolyte so that a
local cell is formed so as to stride over the contact portion
between both of them.
[0004] Namely, in order to effectively suppress or prevent the
electric corrosion, it is needed that no local cell is formed not
only by water (electrolyte), which invades between the contact
surfaces of members of different metals, but also by means of
water, which strides over the contact portions of the members of
different metals to adhere them.
[0005] And, depending on the service environments and service
conditions of apparatuses, it is inevitable that rainwater or
seawater, dew condensate, and the like, adhere onto members of
different metals. As a result, electric corrosion develops while
adapting the adhered water, and so forth, to an electrolyte so that
the functional degradation of the members, and so on, occurs and
accordingly it becomes impossible to secure the durability or
reliability of apparatuses, and the like. Hence, many
electric-corrosion prevention measures have been proposed ever
since conventionally.
[0006] Japanese Unexamined Patent Publication Gazette (KOKAI) No.
6-136,295, Japanese Unexamined Patent Publication Gazette (KOKAI)
No. 2003-64,492, and Japanese Unexamined Patent Publication Gazette
(KOKAI) No. 2003-253,481 disclose methods in which an insulative
material is interposed between members of different metals so as
not to contact the members of different metals with each other
directly, thereby suppressing electric corrosion. Moreover,
Japanese Unexamined Patent Publication (KOKAI) Gazette No.
6-287,778 discloses a method in which a conductive painting
material, which covers the boundary portion between members of
different metals, which are disposed to neighbor to each other, is
painted so that the members of different metals are short-circuited
to each other electrically, thereby suppressing electric
corrosion.
[0007] However, when an insulative member is interposed between
members of different metals as disclosed in Japanese Unexamined
Patent Publication Gazette(KOKAI) No. 6-136,295, and the like, in
the instance that they are fastened with a bolt, and so forth, or
by means of vibration, and so on, during service, there is a fear
that the insulative member might be damaged so that defects might
possibly be brought about. When defects generate, water, and the
like, intrude through defective sections, and thereby electric
corrosion develops. Further, in an apparatus such as compressors
for which airtightness is required, since there is a possibility
that pressure leakage takes place through defective sections, it is
not desired to use any intervening substance.
[0008] Moreover, in the method disclosed in Japanese Unexamined
Patent Publication Gazette (KOKAI) No. 6-287,778, although it might
be possible to short-circuit members of different metals to each
other, it is difficult to say that it is a secure means for
preventing electric corrosion because there is no such thought as
preventing water, and the like, from permeating a painting material
and then preventing it from intruding into the boundary portion
between members of different metals.
DISCLOSURE OF THE INVENTION
[0009] The present invention is one which has been done in view of
the aforementioned problematic points, and it is an object to
provide a structural body and an electric-corrosion prevention
method for the same, which can prevent the electric corrosion
between members of different metals more effectively than having
been done conventionally.
[0010] A structural body of the present invention, which solves the
aforementioned problems, is characterized in that a first member
having a first outside end portion in which a first metal element
is adapted to a major component; a second member having a second
outside end portion in which a second metal element, being
different from the first metal element, is adapted to a major
component, and which is disposed to contact with the first outside
end portion; and a coating member comprising a coated film, at
least whose outside superficial portion is composed of a
fluoropolymer substance, and coating at least a part of both first
outside end portion and second outside end portion so as to cover
the contact portion between them.
[0011] Moreover, an electric-corrosion prevention method of the
present invention for structural bodies is characterized in that,
in a structural body comprising: a first member having a first
outside end portion in which a first metal element is adapted to a
major component; a second member having a second outside end
portion in which a second metal element, being different from the
first metal element, is adapted to a major component, and which is
disposed to contact with the first outside end portion; and a
coating member comprising a coated film, at least whose outside
superficial portion is composed of a fluoropolymer substance, and
coating at least a part of both first outside end portion and
second outside end portion so as to cover the contact portion
between them, the development of electric corrosion, which might
possibly occur so as to stride over the contact portion between the
first outside end portion and the second outside end portion, is
inhibited by hindering the electric conduction between said first
outside end portion and said second outside end portion by means of
said coating member.
[0012] In accordance with the structural body of the present
invention and the electric-corrosion prevention method for the
same, by means of the coating member with the aforementioned
construction, the intrusion or adhesion of water, and the like,
which connects between the first outside end portion and the second
outside end portion electrically, can be prevented, and accordingly
it is possible to prevent electric corrosion, which occurs so as to
stride over the contact portion.
[0013] Further, since the aforementioned coating member can simply
coat at least a part of both first outside end portion and second
outside end portion so as to cover the contact portion between
them, it is not necessary to interpose an intervening substance,
such as insulative substances, between the first outside end
portion and the second outside end portion.
[0014] Moreover, since the aforementioned coating member comprises
a coated film, even if the structural member has a complicated
configuration, it is possible to coat the coating member by means
of ordinary paint application methods.
[0015] Here, the nominal terms, such as "first" and "second," are
nothing but nominal terms for the sake of convenience for
distinguishing members, and the like. For example, it does not
matter whether either one of the first metal element and second
metal element is an electrically base metal (metal with a lower
reference potential) or a noble metal (metal with a higher
reference potential). If distinguishing them daringly for the sake
of convenience, it is advisable to adapt the first metal element to
a base metal (Mg, for instance), and to adapt the second metal
element to a noble metal (Fe, for instance).
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] With reference to the following detailed description and the
accompanying drawings, the present invention can be understood more
profoundly. Hereinafter, the brief description of the drawings will
be done.
[0017] FIG. 1 is a diagram for schematically illustrating a test
piece, which comprises members of different metals of an example
and comparative examples, and is a side view in which the test
piece is viewed from the outside surface. Moreover, FIG. 2 is a
diagram for schematically illustrating the test piece, which
comprises members of different metals of an example and comparative
examples, and is a partially-enlarged cross-sectional view which
cuts FIG. 1 axially.
[0018] FIG. 3 is a photograph, which was taken from the axial side
while adapting a surface, which was equivalent to the contact
portion of an Mg-alloy member in Example No. 1, to the front face,
and is a photograph for substituting a drawing for showing the
state of decay. Moreover, FIG. 4 is a photograph, which was taken
from the axial side while adapting a surface, which was equivalent
to the contact portion of an Mg-alloy member in Comparative Example
No. 2, to the front face, and is a photograph for substituting a
drawing for showing the state of decay.
[0019] FIG. 5 is a schematic diagram for explaining the development
of electric corrosion in members of different metals.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] Hereinafter, the best mode for carrying out a structural
body of the present invention and an electric-corrosion prevention
method for the same will be explained, using FIG. 5.
[0021] A first member has a first outside end portion in which a
first metal element is adapted to a major component, and a second
member has a second outside end portion in which a second metal
element, being different from the first metal element, is adapted
to a major component. The first outside end portion and second
outside end portion are such that, as far as they are composed of
different metals, their configurations and material qualities do
not matter. It is because, as far as they are different metals,
electric corrosion might possibly occur between both of them more
or less. In particular, when the first metal element (or second
metal element) is Mg, that is, when the first outside end portion
is magnesium or a magnesium alloy, since electric corrosion is more
likely to develop, the present invention is effective in this case.
In this instance, there is not any limitation on the second metal
element especially; although it can be any one of Al, Zn, Fe, Cu,
and the like, among them, it is Fe, which has been used often in
ordinary apparatuses, and by which a local cell is likely to be
formed.
[0022] That is, it is sufficient that the first member and second
member can be equipped with such outside end portions as described
above. Namely, it is not necessary that the entirety is composed of
a metallic material; for example, they can be composite members
whose sections other than the outside end portions are made from
resins, and the like. Moreover, both members are such that the
forms or functions, and so forth, do not matter.
[0023] Although the second outside end portion is disposed to
contact with the first outside end portion, either one of the
contacting states, such as point contact, linear contact or planar
contact, is allowable. Further, even when the first member does not
contact with the second member directly, they can even be in states
being united with a fastening tool, such as bolts, electrically.
Moreover, as illustrated in FIG. 5, the end surfaces (11, 21) of
both of them cannot be present on an identical plane, but can even
protrude.
[0024] Note that the "outside end portion" referred to in the
present invention is not one whose specific area is identified. It
is because, depending on the forms of the members or the service
environments, and the like, the range where electric corrosion
might possibly occur differs. If referring to it daringly, it turns
out to be regions that include at least the contact portion at
which both of them contact.
[0025] As for the structural body of the present invention,
compressors, engine blocks, hydraulic pumps, and the like, can be
named. In particular, in a compressor, which comprises a front
housing, a cylinder, and a rear housing, and in which a gasket is
interposed between the cylinder and the rear housing, in the case
of using a rear housing, in which Mg is adapted to a major
component, and a gasket, in which Fe is adapted to a major
component, if water droplets of rainwater, dew condensate, and so
forth, adhere onto the outer peripheral surface so that electric
corrosion develops, there is a possibility that pressure leakage
occurs by means of the fact that the rear housing (Mg) is decayed,
and accordingly this influences the compressor's performance
greatly.
[0026] Here, a partially-enlarged cross-sectional diagram in the
instance that a first outside end portion 10 of a first member 1
and a second outside end portion 20 of a second member 2 are
disposed to contact with each other is shown in FIG. 5. In FIG. 5,
for explanation, a metal constituting the first member 1 is adapted
to magnesium, and a metal constituting the second member 2 is
adapted to iron. Depending on environments in which this structural
body is employed, on the outer peripheral sides (11, 21) of the
first member 1 and second member 2, water droplets 4 of rainwater,
dew condensate, and the like, might adhere in such a state that
they stride over the contact portion 50 of both of them. Thus, a
local cell is formed, local cell in which the first member 1 and
second member 2, the members of different metals, are adapted to
electrodes and the water droplets 4 are adapted to an electrolyte.
And, from the end surface 11 of the first outside end portion 10,
Mg whose decay potential is very low turns into Mn.sup.2+ to start
eluting out into the water droplets 4. Namely, the electric
corrosion of the first member 1, which is composed of magnesium,
comes to develop. Of course, when the water droplets 4 intrude
between the contact surfaces of the contact portion 50, too,
similar electric corrosion develops.
[0027] The coating member of the present invention is one which
inhibits the development of electric corrosion, which might
possibly occur so as to stride over the contact portion between the
first outside end portion and the second outside end portion, by
hindering the electric conduction between the first outside end
portion and the second outside end portion. That is, by means of
the coating member, the continuation of the electrolyte, such as
water, which connects between the first outside end portion and the
second end portion, is canceled.
[0028] For that purpose, it is necessary that the coating member
can comprise a coated film, at least whose outside superficial
portion is composed of a fluoropolymer substance. Note that the
"outside superficial portion" designates the superficial portion of
the coating member onto which water, and the like, can adhere. That
is, the outside superficial portion, when the coated film is a
strip shape, for instance, includes not only the surfaces, which
comprise the width-wise direction and length-wise direction of the
strip, but also the thickness-wise-direction side surfaces.
Further, the coating member is such that it is necessary that it
can coat at least a part of both first outside end portion and
second outside end portion so as to cover the contact portion
between them.
[0029] Since the coated film, at least whose outside superficial
portion is composed of a fluoropolymer substance, is such that at
least the outside superficial portion is a coated film whose
moisture permeability and water immersibility is low and which is
of high density, it is possible to inhibit the intrusion or
adhesion of water, and the like, by means of the coated film; as a
result, the continuation of an electrolyte, which connects between
both members electrically, is prevented. That is, it can prevent
electric corrosion satisfactorily. Note that, in a coated film
including a silicon-based polymer substance, such as silicone
rubbers or silicone resins, since water permeates into the coated
film, depending on the content of silicon, so that the continuation
of an electrolyte, which connects between both members
electrically, is formed within the contact portion or the coated
film, it cannot suppress electric corrosion effectively.
[0030] Further, for the coating member, the adhesiveness to members
of different metals is required as well. When it is a coating
member which is of high adhesiveness, it can prevent the intrusion
of water, and the like, through the interface between members of
different metals and the coating member. Accordingly, if the
adhesiveness is poor only by the coating member, which is composed
of a fluoropolymer substance, it is advisable to adapt it to a
multi-layered structural member in which an undercoating layer,
which can enhance the adhesiveness between both of them and prevent
coming-off, is formed. Note that, although the higher the
adhesiveness becomes the rougher the surface roughness of members
of different metals is made, the rougher the surface roughness is
the more likely it is that they are corroded electrically.
[0031] And, the coating member can preferably include a sealing
layer, which is made by applying and then curing a fluorine-based
sealing agent. This sealing layer can be either a single-layered
construction or a multi-layered construction. A sealing layer,
which is composed of a fluorine-based sealing agent is a coated
film whose moisture permeability and water immersibility is low and
which is of high density; and, even when being a single layer, it
is good in terms of the adhesiveness to members of different
metals, and accordingly it does not come off by means of vibration.
Moreover, the heat resistance is satisfactory, too. Accordingly,
the coating member, which includes the aforementioned sealing
layer, is suitable for members of different metals, which are
employed in apparatuses, such as compressors, which are employed
under high-temperature conditions or in which vibrations generate
during the apparatuses' service. Moreover, as for a fluorine-based
sealing agent being adequate for a sealing layer of the coating
member, although it is possible to name a fluorocarbon silicone
rubber, and the like, it can preferably be a liquid fluorocarbon
rubber especially.
[0032] The coating member is such that, although it depends on the
type of fluoropolymeror the construction (single layer/multi layer)
of the coating member, its sealing layer's thickness can be 100
.mu.m or more when using a fluorine-based sealing agent. When the
thickness of a sealing layer is 100 .mu.m or more, it is sufficient
to prevent the intrusion of water, and the like, and the effect of
suppressing electric corrosion can be obtained satisfactorily.
[0033] The coating member is such that, as far as a portion, among
the contact portion between the first outside end portion and the
second outside end portion, portion onto which water, and the like,
can adhere, is coated at least, there is not any limitation on its
configuration and dimensions particularly. However, regarding the
width of the coating member, although it depends on the
configurations of members of different metals or the sizes of
adhering water droplets, the width going over the contact portion
can preferably be 10 mm or more. When the width of the coating
member is 10 mm or more, even when water, and so forth, adheres, it
is possible to get rid of the continuation of an electrolyte, such
as water, which connects between the first outside end portion and
the second outside end portion electrically, and accordingly it is
possible to shut off or suppress the formation of local cell in
which members of different metals are adapted to electrodes.
[0034] Note that, since the coating member is a coated film, it is
possible to coat the coating member even when a objective section,
among the members of different metals, on which the coating member
is formed, is a portion which has a complicated configuration (for
example, has a step at the contact portion as illustrated in FIG.
5). As for the forming method of a coated film, it can be obtained
by applying a paint onto the objective section, drying it and then
curing it by means of an ordinary paint application method, such as
applying methods, flow-coating methods, spray-coating methods,
spin-coating methods and roll-coating methods. In this instance,
the drying condition, and the like, are such that, depending on the
types of paints, it is advisable to select optimum conditions
appropriately.
[0035] Note that the structural body of the present invention is
not one which is limited to the above-described embodiment modes;
but it is advisable to add another construction, such as forming a
protective layer for protecting the coating member, for
instance.
[0036] Moreover, the present invention can be grasped not only as
the aforementioned structural body but also as an
electric-corrosion prevention method for the same.
[0037] Hereinafter, an example of the structural body of the
present invention and an electric-corrosion prevention method for
the same will be explained, using FIG. 1 and FIG. 2. Note that FIG.
1 and FIG. 2 are diagrams for schematically illustrating a test
piece, which comprises members of different metals; FIG. 1 is a
side view in which the test piece is viewed from the outside
surface; and FIG. 2 is a partially-enlarged cross-sectional view in
which the test piece of FIG. 1 is cut axially.
EXAMPLE NO. 1
[0038] A test piece, which possessed members of different metals,
was prepared. This test piece comprises an Mg-alloy member 1, and
an Fe-alloy member 2. The Mg-alloy member 1 is 16 mm.times.16
mm.times.35 mm, is an AZ91 (JIS) Mg-alloy block, and is such that a
screwed hole 16 extends in the longitudinal direction at its
central portion. The Mg-alloy member 1 is such that a surface
treatment (electrodeposition coating) was performed to the entire
surface, and its surface roughness was Ra=0.11 [.mu.m]. Moreover,
the Fe-alloy member 2 is 16 mm.times.16 mm.times.16 mm, is a
cold-rolled steel-plate SPCC (JIS) Fe-alloy block, and is such that
a screwed hole 26, whose diameter is the same as that of the
screwed hole 16, extends at its central portion.
[0039] And, a bolt 6 was screwed into the screwed holes 16, 26 of
the aforementioned Mg-alloy member 1 and Fe-alloy member 2, thereby
fastening them coaxially so as to contact with each other. As a
result, a test piece was obtained, test piece which comprised
rectangular-column-shaped members of different metals in which an
outside end portion 10 of the Mg-alloy member 1 and an outside end
portion 20 of the Fe-alloy member 2 contacted with each other so
that end surfaces 11, 21 of the outside end portions 10, 20 were
positioned on an identical plane.
[0040] And, onto the outer peripheral surface of the test piece, a
coating member 3 was formed so as to cover a contact portion 50
between the outside end portion 10 of the Mg-alloy member 1 and the
outside end portion 20 of the Fe-alloy member 2. Specifically, the
coating member 3 covered the contact portion 50 by means of
covering a part of the end surface 11 of the outside end portion 10
and a part of the end surface 21 of the outside end portion 20 in
such a state that included a contact end portion 51, which existed
linearly on the outer-peripheral-surface side of the test piece,
among the contact portion 50 between the outside end portions 10
and 20.
[0041] The coating member 3 comprises a coated film of liquid
fluorocarbon rubber ("SIFEL600" series produced by SIN-ETSU KAGAGU
KOGYO Co., Ltd.). The liquid fluorocarbon rubber was applied onto
the outer peripheral surface of the test piece so that the width
(with the contact end portion 51 being adapted to the center)
became 10 mm, and was made into a coated film, which was composed
of a fluoropolymer substance being obtained by drying and curing it
at 150.degree. C. for 1 hour. Moreover, the filmthickness of the
coating member 3 was 100-200 .mu.m.
[0042] And, a member, which was obtained by the aforementioned
procedure, was labeled Sample "A."
COMPARATIVE EXAMPLE NO. 1
[0043] By applying a commercially available silicone-based sealing
agent onto the test piece of Example No. 1 as the coating member 3
and then drying and curing it at room temperature for 5 days, a
coated film, which was similar to that of Example No. 1, was
formed. An obtained member was labeled Sample "B."
COMPARATIVE EXAMPLE NO. 2
[0044] By applying a fluorine-containing silicone-resin-based paint
onto the test piece of Example No. 1 as the coating member 3 and
then drying and curing it at room temperature for 24 hours, a
coated film, which was similar to that of Example No. 1, was
formed. An obtained member was labeled Sample "C."
[0045] [Evaluation]
[0046] In order to evaluate the electric-corrosion prevention
effects, a salt-water spraying test was carried out. The salt-water
spraying test was carried out for 250 hours under such fixed
conditions that a salt-water concentration: 5%, a spraying amount:
1-2 mL/hr., a spraying pressure: 0.098.+-.0.002 MPa, a testing
temperature: 35.degree. C., and an air saturator: 47.degree. C.
[0047] After the test, the fastening between the Mg-alloy member 1
and the Fe-alloy member 2 was excluded, and then the appearance of
the Mg-alloy member 1 was observed visually from the axial side
while adapting the contact portion 50 to the front face. The
results are set forth in Table 1. Note that FIG. 3 and FIG. 4,
regarding Sample "A" and Sample "C," are photographs, which were
taken from the axial side while adapting a surface, which was
equivalent to the contact portion 50 of the Mg-alloy member 1 to
the front face, and are photographs for substituting drawings for
showing the states of decay. TABLE-US-00001 TABLE 1 State after
Salt-water Spraying Test Sample (Visual Observation) Sample "A"
(Ex. No. 1) Satisfactory Sample "B" (Comp. Ex. No. 1) Decay Existed
Sample "C" (Comp. Ex. No. 2) Large Decay Existed Locally
[0048] Samples "A"-"B," as illustrated in FIG. 1 and FIG. 2, are
such that the coating member 3, which possesses a width with a
certain extent, is coated sufficiently all over the entire
periphery of the contact portion 51. Therefore, even when water
droplets adhere onto the surface of the test piece, no electric
conduction should be formed between the end surface 11 and the end
surface 21 so that no electric corrosion should occur, either.
[0049] However, only Sample "A" was such that the appearance after
the test was satisfactory, and decay occurred in Sample "B" and
Sample "C." The coating member 3 of Sample "A" comprised a coated
film, which was composed of a fluoropolymer substance, and could
prevent the intrusion of salt water through the interfaces between
the test pieces (1, 2) and the coating member 3, too, and through
the surface of the coating member 3, too, effectively; as a result,
it was possible to prevent the electric corrosion of the Mg-alloy
member 1. On the contrary, with the coating member 3, which used
the silicone-based sealing agent like Sample "B," it was not
possible to prevent the intrusion of salt water. Further, in Sample
"C," the fluorine-containing silicone-resin paint was employed;
although a fluoropolymer substance was present in a part of the
coating member 3, large decay was formed locally because salt water
intruded partially through sections in which a silicone resin was
present.
[0050] Note that, since the aforementioned members of different
metals use the combination of alloys of the same species as those
for a compressor having a rear housing, in which Mg is adapted to a
major component, and a gasket, in which Fe is adapted to a major
component, for instance, it is needless to say that similar results
are obtainable even when the evaluation is carried out, using the
coating members set forth in the example and comparative examples
for the aforementioned compressor.
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