U.S. patent application number 10/609556 was filed with the patent office on 2004-01-01 for sliding member having excellent seizure resistance and method for producing the same.
This patent application is currently assigned to DOWA MINING CO., LTD.. Invention is credited to Kasamatsu, Toshiki, Ogawa, Osamu, Yamauchi, Motoyoshi.
Application Number | 20040000492 10/609556 |
Document ID | / |
Family ID | 17862300 |
Filed Date | 2004-01-01 |
United States Patent
Application |
20040000492 |
Kind Code |
A1 |
Ogawa, Osamu ; et
al. |
January 1, 2004 |
Sliding member having excellent seizure resistance and method for
producing the same
Abstract
A sliding member having excellent seizure resistance comprising
a metallic member provided with a sulfide-based solid lubricating
layer on the sliding surface thereof is provided, characterized in
that the interface of the metallic member in contact with said
solid lubricating layer is provided with a surface roughness Rmax
of 1 .mu.m or higher. The sliding member above is obtained by
preparing an aqueous solution dissolved therein one or two types or
more of thiocyanates or thiosulfates of alkali metals or alkaline
earth metals, and by performing electrolytic treatment in which a
steel member the surface roughness thereof is controlled is used as
the anode. In this manner, an iron sulfide based layer is formed on
the surface of the steel member by using the Fe component derived
from the steel and the S component from the solution as the
reacting agents.
Inventors: |
Ogawa, Osamu; (Hamakita-shi,
JP) ; Yamauchi, Motoyoshi; (Hamamatsu-shi, JP)
; Kasamatsu, Toshiki; (Hamamatsu-shi, JP) |
Correspondence
Address: |
McDermott, Will & Emery
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
DOWA MINING CO., LTD.
Tokyo
JP
|
Family ID: |
17862300 |
Appl. No.: |
10/609556 |
Filed: |
July 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10609556 |
Jul 1, 2003 |
|
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|
09684665 |
Oct 10, 2000 |
|
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|
6589412 |
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Current U.S.
Class: |
205/320 |
Current CPC
Class: |
C25D 5/36 20130101; C25D
11/34 20130101; F16C 33/10 20130101; C25D 7/10 20130101; C25D 5/48
20130101; C25D 9/06 20130101; F16C 2204/60 20130101; F16C 33/12
20130101 |
Class at
Publication: |
205/320 |
International
Class: |
C25D 009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 1999 |
JP |
11-298635 |
Claims
What is claimed is:
1. A sliding member having excellent seizure resistance comprising
a metallic member provided with a sulfide-based solid lubricating
layer on the sliding surface thereof, characterized in that the
interface of the metallic member in contact with said solid
lubricating layer is provided with a surface roughness Rmax of 1
.mu.m or higher.
2. A sliding member having excellent seizure resistance comprising
a steel member provided with an iron sulfide-based, a molybdenum
sulfide-based, or a tungsten sulfide-based solid lubricating layer
on the sliding surface thereof, characterized in that the interface
of the steel member in contact with said solid lubricating layer is
provided with a surface roughness Rmax of 1 .mu.m or higher.
3. A method for producing a sliding member having excellent seizure
resistance, comprising, in providing a sulfide-based solid
lubricating layer on the sliding surface of a metallic member,
forming the sulfide-based solid lubricating layer on the surface of
the metallic member whose surface roughness Rmax is controlled to
be 1 .mu.m or higher.
4. A method for producing a sliding member having excellent seizure
resistance, comprising preparing an aqueous solution by dissolving
one or two or more types of a thiocyanate or a thiosulfate of an
alkali metal or an alkaline earth metal to obtain an electrolytic
solution; dipping a steel member into the thus prepared
electrolytic solution; and performing electrolytic treatment by
using said steel member as the anode to form an iron sulfide based
coating layer on the surface of said steel member by using the Fe
component derived from the steel member and the S component of the
solution.
5. A method for producing a sliding member having excellent seizure
resistance as claimed in claim 4, wherein, the surface of the steel
member on which the iron sulfide based coating layer is formed is
controlled to yield a surface roughness Rmax of 1 .mu.m or
higher.
6. A method for producing a sliding member having excellent seizure
resistance as claimed in claim 5, wherein, the surface roughness is
controlled by performing mechanical grinding, chemical etching, or
by electrochemical etching treatment.
7. A method for producing a sliding member having excellent seizure
resistance, comprising preparing an aqueous solution by dissolving
one or two or more types of a thiocyanate or a thiosulfate of an
alkali metal or an alkaline earth metal to obtain an electrolytic
solution; dipping a steel member into the thus prepared
electrolytic solution; performing electrolytic treatment by using
said steel member as the anode to form an iron sulfide based
coating layer on the surface of said steel member by using the Fe
component derived from the steel member and the S component of the
solution; generating multiple cracks on said coating layer;
performing electrolysis in an aqueous alkaline solution by using
the steel member having generated thereon the cracks as the anode;
and performing electrolytic treatment in an aqueous solution
dissolved therein one or two or more types of a thiocyanate or a
thiosulfate of an alkali metal or an alkaline earth metal by using
the steel member subjected to the electrolysis, thereby forming an
iron sulfide based coating layer on the surface of said steel
member while simultaneously forming irregularities having an Rmax
of 1 .mu.m or higher on the interfacial surface of the steel member
in contact with the coating layer.
8. A method for producing a sliding member having excellent seizure
resistance as claimed in claim 7, wherein the Rmax of the interface
is adjusted by quantitatively controlling the applied current.
9. A method for producing a sliding member having excellent seizure
resistance as claimed in claim 4 or 7, wherein the electrolytic
solution for forming the iron sulfide based coating layer contains
SCN.sup.- or S.sub.2O.sub.3.sup.2- at a concentration of 0.01
mol/liter, and the electrolytic treatment is performed by applying
the current at a current density of from 1 to 15 A/dm.sup.2 under
atmospheric pressure and at a temperature not lower than the
solidification point but not higher than the boiling point of the
electrolytic solution.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a surface treatment for
improving the seizure resistance of a mechanical element or
component having a sliding surface (referred to hereinafter as a
"sliding member") such as gears, bearings, etc., and in further
detail, it relates to a sliding member having excellent seizure
resistance having a sulfide-based solid lubricant layer on the
sliding surface of a metallic member.
[0003] 2. Description of the Related Art
[0004] Mechanical components such as various types of gears,
bearings, pins or pivots, pistons or cylinders, etc., which move in
contact with the surface of the metallic counter member, suffer
problems of abnormal wear and seizure even in the presence of a
lubricant oil. As a means of reducing such problems, it is known to
form a solid lubricant layer based on sulfides such as an iron
sulfide, a molybdenum sulfide, or a tungsten sulfide, etc., on the
surface of the sliding member (particularly, a steel member).
[0005] As a means for forming a sulfide-based solid lubricant layer
on the surface of a metallic member, generally known method is
employing an electrochemical process. A representative method
comprises performing electrolysis in an alkaline electrolytic
solution by using the metallic member as the anode, thereby
depositing a sulfide on the surface of the metallic member used as
the anode. In addition to the anodic sulfurization treatment above,
there is also known a special method comprising performing a
treatment in a fused salt bath by using the metallic member as the
cathode.
[0006] For instance, if an iron-based article is subjected to
electrolytic treatment in a fused salt of potassium thiocyanate and
sodium thiocyanate, the Fe component originating from the
iron-based component and the S component from the bath react to
form a sulfurized layer (an FeS based component) on the surface of
the component. The sulfurization treatment technology is disclosed
in Japanese Patent Publication JP-B 1809/1969, Japanese Patent
Publication JP-B 12158/1988, and Japanese Patent JP-A 220689/1994.
The patent publications above teach using a fused salt bath
containing potassium thiocyanate and sodium thiocyanate mixed at a
ratio of about 3 to 1, and preferably performing the electrolysis
at a temperature of about 190.+-.5.degree. C. and at a current
density in a range of from 1.5 to 4.0 A/dm.sup.2.
[0007] A sliding member having a sulfide-based solid lubricating
layer on the sliding plane thereof generally exhibits an excellent
seizure resistance; however, to improve the life of machines, it is
pertinently required to further increase the seizure
resistance.
SUMMARY OF THE INVENTION
[0008] Accordingly, an object of the present invention is to
fulfill this requirement. The present invention provides a novel
and a simple production method capable of realizing a sliding
member which achieves the requirement above in a industrially
advantageous manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a graph which relates the degree of roughness
(Rmax) at the interface between the generated iron sulfide layer
and the steel component to the applied electrolytic current in case
of performing anodic sulfurization in an aqueous solution according
to the method of the present invention; and
[0010] FIG. 2 is a graph which relates the maximum seizure load for
the treated article to the applied electrolytic current for a case
of performing the treatment under the same conditions as those of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] In accordance with the present invention, there is provided
a sliding member having a sulfide-based solid lubricating layer on
the sliding member of a metallic member, characterized in that the
interface of the metallic member in contact with said solid
lubricating layer is provided with a surface roughness Rmax of 1
.mu.m or higher. In particular, the present invention provides a
sliding member provided with an iron sulfide-based, a molybdenum
sulfide-based, or a tungsten sulfide-based solid lubricating layer
on the sliding surface thereof, characterized in that the interface
of the steel member in contact with said solid lubricating layer is
provided with a surface roughness Rmax of 1 .mu.m or higher.
[0012] Further according to the present invention, there is
proposed a method for producing a sliding member having excellent
seizure resistance, comprising, in providing a sulfide-based solid
lubricating layer on the sliding surface of a metallic member,
forming the sulfide-based solid lubricating layer on the surface of
the metallic member whose surface roughness Rmax is controlled to
be 1 .mu.m or higher. In particular, the present invention provides
a method for producing a sliding member having excellent seizure
resistance, comprising preparing an aqueous solution by dissolving
one or two or more types of a thiocyanate or a thiosulfate of an
alkali metal or an alkaline earth metal to obtain an electrolytic
solution; dipping a steel member into the thus prepared
electrolytic solution; and performing electrolytic treatment by
using said steel member as the anode to form an iron sulfide based
coating layer on the surface of said steel member by using the Fe
component derived from the steel member and the S component of the
solution. In the anodic sulfurization method using the aqueous
solution as above, a sliding member having particularly superior
seizure resistance can be achieved by controlling the surface
morphology of the steel member on which the iron sulfide based
coating layer is formed in such a manner to yield a surface
roughness Rmax of 1 .mu.m or higher, and more preferably, 2 .mu.m
or higher.
[0013] The present inventors found that, in a sliding member having
a sulfide-based solid lubricating layer on the sliding surface of a
metallic member, there is a clear correlation between the surface
roughness Rmax of the interface of the metallic member in contact
with the solid lubricating member before sliding and the seizure
resistance, and that the seizure resistance is improved with
increasing surface roughness Rmax of the interface. In practice,
the surface roughness of the interface corresponds to the surface
roughness of the surface of the metallic member from which the
solid lubricant layer is removed. Accordingly, the surface
roughness of the interface can be observed by measuring the surface
roughness of the metallic member from which the solid lubricant
layer is removed; still, it is also possible to obtain the surface
roughness by measuring the height of the irregularities on the
interface by performing microscopic observation on the cross
section of the member having the solid lubricant layer thereon.
[0014] As is shown in the examples hereinafter, it was found that a
distinguished improvement in seizure resistance can be obtained in
case the surface roughness Rmax of the interface between the solid
lubricant layer and the metallic member before subjecting to
sliding is 1 .mu.m or higher. The term "Rmax" as referred herein is
the maximum height (Rmax) as defined in JIS B 0601, and the surface
roughness referred in this specification is expressed by the Rmax
defined therein.
[0015] In general, the sliding surface of a mechanical component is
finished as smooth as possible. If irregularities are present on
the sliding surface, shortage of lubricant oil generates on the
protruded portions, and this leads to the acceleration of wear at
those protruded portions. Similarly, the surface of the sliding
members having solid lubricating layers has been finished as smooth
as possible to form a solid lubricating layer on the surface.
Accordingly, so long as it does not concern with special
exceptions, it was customary to provide an interface as smooth as
possible and having a Rmax of 1 .mu.m or lower between the metallic
member mother material and the solid lubricant layer.
[0016] However, according to the experience of the present
inventors, it has been found that the seizure resistance can be
greatly improved in case the mother material of the metallic member
and the sulfide-based solid lubricating layer are brought into
contact with each other by incorporating an interface having
irregularities, more specifically, with an interface having such
irregularities with a Rmax of 2 .mu.m or higher. The reason for
this is not completely clarified; however, it is presumed that,
even in case the sulfide-based solid lubricating layer is gradually
consumed to finally expose the protruded portion of the mother
material, there occurs a phenomenon as such that the sulfide-based
solid lubricating layer that is reserved in the surrounding concave
portions is supplied to the protruded portion as to reduce the wear
of the protruded portion. On the contrary, if the irregularities
provided to the interface are small in number, the layer of the
sulfide-based solid lubricating layer would be uniformly consumed
as to lose a concave portion which functions as a reservoir. At the
same time, furthermore, in this case, the area of the exposed
metallic portion of the mother portion changes from spots to a
planar area as to increase the contact area between the metals.
Presumably, these reasons synergistically increase the change in
causing seizure.
[0017] The sliding member to which the present invention is applied
is represented by various types mechanical components having a
sliding plane (inclusive of matching planes), such as various types
of gears, shafts, hubs, as well as mechanical components such as
pistons, cylinders, etc. As the representative sulfide-based solid
lubricating layer to be formed on the surface of these metallic
members, there can be mentioned those based on iron sulfide,
molybdenum sulfide, or tungsten sulfide. Although the sulfide-based
solid lubricating layers above are all applicable to the sliding
member according to the present invention, the explanation below is
made by taking an iron sulfide-based solid lubricating layer as an
example.
[0018] The technology of improving the wear resistance of an iron
or an iron-based alloy (which are collectively referred to
hereinafter as "steel"; the term "steel" hereinafter includes iron
and iron based alloys) member by forming an iron sulfide-based
solid lubricating layer on the surface thereof is prevailing in the
art. As a technique of forming a layer, anodic sulfurization in
fused salt bath as proposed in the patent publications referred
above is well known. However, in carrying out the sulfurization
method above, it is necessary to use an eutectic mixed salt of
potassium thiocyanate and sodium thiocyanate in order to lower the
melting point of the fused salt. This not only makes it difficult
to apply the low-cost single salts or other treatment agents, but
also requires a practical bath maintained at a temperature in the
vicinity of 190.degree. C. However, such a requirement not only
leads to dangerous operations, but also causes problems of lowering
the mechanical strength or surface hardness of the mechanical
components, because such mechanical components that are subjected
to the process are mainly quenched articles that suffer the
problems above when treated at a bath temperature in the vicinity
of 190.degree. C.
[0019] Accordingly, the present inventors attempted to develop an
anodic sulfurization process using an aqueous solution in the place
of the problematic fused salts. To accomplish this attempt, the
present inventors extensively carried out tests and researches to
obtain sliding members having excellent resistance against seizure
by forming an iron sulfide-based solid lubricating layer on the
surface of the steel while employing anodic sulfurization in
aqueous solution. As a result, the present inventors realized the
process, which is explained in detail below.
[0020] Conventionally employed sulfurization using fused salts is
based on the knowledge that a favorable iron sulfide layer cannot
be obtained by an electrolysis in an aqueous solution of a
thiocyanate, and this knowledge led to the use of an eutectic salt
of potassium thiocyanate and sodium thiocyanate. However, on
attempting electrolysis in an aqueous solution of thiocyanates or
thiosulfates, the present inventors found that, opposing to the
common knowledge, and by properly selecting the conditions, it is
possible to form iron sulfide on the surface of steel similar to
the case of performing electrolysis in fused salt.
[0021] First, similar to the known processes, the surface of the
steel component to be electrolyzed is cleaned by degreasing,
pickling, rinsing, etc., and then, the surface roughness is
controlled to yield a pertinent roughness of, for example, a Rmax
of 1 .mu.m or higher, and preferably, 2 .mu.m or higher. The steel
component is preferably subjected to carburization and
quenched.
[0022] As the electrolytic solution, an aqueous solution containing
SCN.sup.- ions or S.sub.2O.sub.3.sup.2- ions at a concentration of
at least 0.01 mol/liter or higher is used. As an agent to supply
the SCN.sup.- ions, there can be used a thiocyanate of an alkali
metal or an alkaline earth metal, and as an agent to supply
SCN.sup.- ions, there can be used a thiosulfate of an alkali metal
or an alkaline earth metal. These salts may be used either singly
or as a mixture of two or more types selected therefrom. In order
to maintain the solution at a sufficiently high concentration,
these salts may be incorporated into water at a quantity exceeding
the solubility limit to keep the undissolved salts in the solution.
It is also preferred to incorporate FeSO.sub.4 and the like at a
proper amount to maintain the bath constant.
[0023] The electrolysis is preferably carried out under the
atmospheric pressure and at a temperature not lower than the
solidification point but at a temperature not higher than the
boiling point of the electrolytic solution, while applying the
current set at a density in a range of from 1 to 15 A/dm.sup.2.
[0024] In this manner, an iron sulfide layer having a composition
represented by a general formula of Fe.sub.1-xS (where x is in a
range of from 0 to 1 inclusive of 0) is formed on the surface of
the steel component. The iron sulfide layer not necessary have a
stoichiometric composition, but a thin coating (e.g., about 4 to 6
.mu.m in thickness) formed on the surface of the steel component
can improve the wear resistance and the seizure resistance of the
surface.
[0025] A representative electrolysis can be carried out under
conditions as follows.
1 Article: Carburized and heat treated case hardened steel Bath
composition: An aqueous solution containing 2 mol/liter of SCN Bath
temperature: 20.degree. C. Current density: 3.2 A/dm.sup.2 Duration
of electrolysis: 10 minutes Distance between the electrodes: 10
mm
[0026] In case of forming an iron sulfide layer on the surface of a
steel component by performing anodic electrolysis in an aqueous
solution under the conditions above, the degree of irregularities
formed at the interface between the steel component and the iron
sulfide layer greatly influences the seizure resistance of the
steel component. Accordingly, the irregularities of the interface
is preferably provided at a Rmax of 1 .mu.m or higher, and more
preferably, at a Rmax of 2 .mu.m or higher. Further preferably, it
is provided at a Rmax of 5 .mu.m or higher. However, an excessively
high degree of irregularities is not necessary, and is provided at
a Rmax of 40 .mu.m or lower, and preferably, 30 .mu.m or lower.
[0027] On performing the anodic electrolysis in an aqueous solution
as above to form such an interface having irregularities between
the sulfide based layer and the steel member, the surface roughness
of the steel component to be subjected to the electrolysis is
preferably controlled to yield a Rmax of 1 .mu.m or higher, and
more preferably, at a Rmax of 2 .mu.m or higher. To control the
surface roughness of the steel component, there can be applied a
mechanical method a chemical etching method, an electrochemical
method, etc., and there can be applied, as a special method, an
electrolytic etching method taking advantage of a particular
phenomenon which occurs by anodic electrolysis using the aqueous
solution according to the present invention.
[0028] In the case of applying a mechanical method, the surface of
the steel component is uniformly ground by employing a grinding
machine using an abrasive having a predetermined granularity to
control the surface roughness at a targeted Rmax value. In case of
using a chemical etching method, an etching solution may be sprayed
to the surface of the steel member to form pits, or an etching
process using a masking material may be employed to form an
irregular pattern. The latter masking treatment can be employed in
an electrochemical etching process.
[0029] The electrolytic etching method comprises forming an iron
sulfide layer in the aqueous solution above by means of anodic
electrolysis, while controlling the behavior of Fe which elutes out
from the steel component used as the anode to control the degree of
irregularities formed in the interface between the steel member and
the sulfide based layer. In employing this method, the present
inventors have found that, by properly roughening the surface of
the steel component on which the iron sulfide layer is formed, a
favorable correlation can be obtained between the number of sites
from which Fe is eluted out from the steel component and the
quantity of applied current. More specifically, in case of forming
a layer of iron sulfide on the steel component by performing
anodization in the aqueous solution, it was found that a higher
value for Rmax can be obtained with increasing quantity of applied
current. The correlation between the applied current and the value
of Rmax is believed to be influenced by the surface state of the
steel component that is present on initiating the application of
current. Accordingly, it is preferred to control the surface state
at a properly roughened state, and, in practice, it is convenient
to employ a process comprising first forming a layer of iron
sulfide, followed by forming cracks on the layer and generating
pits at the crack portions using an alkaline solution.
[0030] Thus, in accordance with the present invention, an aqueous
solution containing dissolved therein one type or two types or more
of thiocyanates or thiosulfates of alkali metals or alkaline earth
metals is prepared to use it as the electrolytic solution, and a
steel member is immersed in the electrolytic solution to carry out
the electrolysis using the steel member as the anode. In this
manner, an iron sulfide based layer is formed on the surface of the
steel member by using the Fe component from the steel and the S
component from the solution as the reacting agents, followed by
forming multiple cracks in the resulting layer. The steel component
having the layer on which cracks are generated thereon is then
electrolytically etched in an alkaline aqueous solution by using it
as the anode, and the steel component is further subjected to
electrolytic treatment in an aqueous solution containing dissolved
therein one type or two types or more of thiocyanates or
thiosulfates of alkali metals or alkaline earth metals by using it
as the anode. In this manner, an iron sulfide based layer is formed
on the surface of the steel component while forming an interface
having irregularities at a Rmax value or 1 .mu.m or higher between
the steel member and the layer. Thus, the present invention
provides a method of producing a sliding member having excellent
seizure resistance in this manner. The degree of Rmax of the
interface can be controlled by adjusting the applied current.
[0031] The present invention is described in further detail below
by referring to non-limiting examples below.
EXAMPLE 1
[0032] A SCM415 case hardening steel was machined to obtain
necessary number of Fabily test pins (pins to be subjected to
seizure test) each having an outer diameter of 6.5 mm and a length
of 4 mm. Each of the pins was subjected to carburization treatment
at 930.degree. C. for a duration of 5 hours, and was then subjected
to oil quenching from 830.degree. C. and tempering at 180.degree.
C. The carburized and tempered pins thus obtained were used as the
test specimens to be subjected to the treatments below.
[0033] One end of a pin was fixed to a chuck of a rotary polishing
machine, and while inserting the body of the pins between Emery
papers, the pin was moved along the axial direction while rotating
and reversely rotating it around the axis. In this manner, a
cross-hatched rough surface was uniformly formed on the outer
peripheral plane of the pin body. In forming the roughened
peripheral plane of the pin body, it was devised as such that the
ground peripheral plane should have an area greater than that of
the peripheral plane of the pin body to be brought into contact in
sliding it against the V block when set on a Fabilly test machine.
The surface roughness was controlled by changing the types of Emery
paper, such that a surface having Rmax value of 2.5 .mu.m, 8.2
.mu.m, or 10.1 .mu.m, can be obtained on the pins.
[0034] After degreasing, pickling, and rinsing, the pins were
subjected to electrolytic sulfurization using them as the anodes.
More specifically, a mixture of 7.5 parts by weight of NaSCN and
22.5 parts by weight of KSCN was dissolved into 100 parts by weight
of water to obtain an aqueous solution, and 10 parts by weight of
FeSO.sub.4 was added therein as a bath controller to prepare an
aqueous solution. A 500-ml portion of the aqueous solution thus
obtained was placed in a 1-liter glass container, and the bath
temperature thereof was maintained at the room temperature.
[0035] One of the pins was vertically immersed to use it as the
anode at the central portion of the container having therein the
aqueous solution, and two SUS304 cathode plates were each immersed
at the same distance of 10 mm from the pin in such a manner that
the pin may be inserted between the cathode plates. Then, the three
pins differing in surface roughness prepared above were each
subjected to electrolytic treatment by using the pin as the
positive electrode and the cathode plate as the negative electrode
under the same conditions by applying current at a density of 3.2
A/dm.sup.2 for a duration of 10 minutes. As a result, iron sulfide
layers each having a thickness of 4 to 6 .mu.m were formed on the
surface of the pins.
[0036] One end of each of the thus obtained pins was set in a chuck
of a Fabily test machine manufactured by H.E.F Co., Ltd. (Hydro
Mechanic Wear Laboratory), and while clamping the body of the pins
with two blocks each having a V-shaped contact plane, the pins were
each rotated around the axis at a rate of 300 rpm while applying a
load along the pin direction. Thus, the load at initiating seizure
(denoted as "maximum seizure resistance load") was measured. As a
result, the following maximum seizure loads were obtained in
accordance with the surface roughness of the pins.
2 Surface roughness Maximum seizure Rmax (.mu.m) of pin resistance
load (Kgf) 2.5 880 8.2 1020 10.1 1030
[0037] As a comparative example, a pin was prepared in the same
manner as above except for not applying grinding in a rotary
polishing machine. A maximum seizure resistance load of 780 Kgf was
obtained for this specimen. The surface roughness of the specimen
in this comparative example (i.e., an as-carburized and quenched
pin without applying grinding) was found to be about 0.6 .mu.m.
EXAMPLE 2
[0038] The same as-carburized and quenched pins as those used in
Example 1 were used as the specimens. More specifically, unlike the
case in Example 1, precision machined, as-carburized and quenched
pins having a surface roughness Rmax of 1 .mu.m or lower and not
subjected to surface grinding using a polishing machine was
degreased, pickled, and rinsed, followed by electrolytic treatment
below by using them as anodes. The electrolysis described below
were all performed under an ordinary temperature of 25.degree.
C.
[0039] First, an aqueous solution containing. 1 mol/liter of sodium
thiosulfate was placed inside the same container as that used in
Example 1, and one of the pins was vertically immersed into the
aqueous solution at the central portion. Then, two SUS304 cathode
plates were each immersed at the same distance of 10 mm from the
pin in such a manner that the pin may be inserted between the
cathode plates. Then, the pin was subjected to electrolytic
treatment by using the pin as the positive electrode and the
cathode plates as the negative electrodes by applying current at a
density of 3.2 A/dm.sup.2 for 40 C (Coulombs). As a result, iron
sulfide layer was formed on the surface of the pin (the treatment
is referred to hereinafter as "a precoating treatment").
[0040] Then, after taking out the pin from the electrolytic
solution and exposing it to air for 30 seconds, it was immersed in
another electrolytic solution (an aqueous solution of sodium
hydroxide at a pH value of 9). During the exposure to air, uniform
cracks were found to form on the layer generated by the precoating
treatment. The pin having formed thereon the layer in which the
cracks were generated was subjected to electrolysis in an aqueous
sodium hydroxide solution of pH 9 by applying a current at a
density of 0.8 A/dm.sup.2 for 40 C (Coulomb) between the pin used
as the anode and the cathode plates similar to above. By performing
the electrolysis above, it was found that exposed metallic surface
portions generate while eluting out a part of the coating, and that
irregularities form on the surface of the pin (metallic plane and
the layer plane). This treatment is referred to hereinafter as an
"alkali coating treatment".
[0041] After the alkali coating treatment above, the pin was rinsed
and allowed to stand under air for a duration of 30 seconds,
followed by a subsequent electrolytic sulfurizatin treatment. More
specifically, electrolytic sulfurization treatment is performed in
the same electrolytic solution and under the same current density
as those used in the precoating treatment above while using the pin
subjected to alkali coating treatment as the anode. During this
treatment, there occurs a phenomenon as such that the surface
roughness of the interface between the pin and the iron sulfide
layer changes depending on the applied current. More specifically,
a plurality of pins subjected to a treatment performed under the
same conditions as above were prepared except for the final
electrolytic sulfurization above (that is, pins were prepared by
the same alkali coating treatment), and the same pins were covered
with iron sulfide layers while differing the applied current during
the electrolytic sulfurization. The electrolysis was performed
under the conditions of using a 1-mol/liter sodium thiocyanate bath
while applying current at a density of 3.2 A/dm.sup.2. Each of the
pins thus obtained was stripped off of the iron sulfide layer to
measure the roughness of the interface between the layer and the
pin (i.e., the surface roughness of the pin surface). FIG. 1 shows
the plots obtained for the thus observed surface roughness Rmax of
the pin at the interface in relation with the current applied at
the electrolytic sulfurization treatment.
[0042] Referring to FIG. 1, there can be read a clear correlation
between the quantity of applied current and the surface roughness
Rmax of the mother material under the layer. It can be understood
therefrom that the Rmax increases with increasing quantity of
applied current. The reason for this is believed that, if
irregularities are properly provided to the surface of the pins or
to the coating planes by applying alkali coating treatment, there
is a behavior as such that the sites from which Fe elute out from
the mother material segregate upon electrolytic sulfurization, and
thereby deep sites, at which layers of iron oxide deposit, tend to
form more easily.
[0043] In FIG. 2 are plotted the maximum seizure resistant load in
relation with the quantity of applied current for a plurality of
pins subjected to the treatment following the same conditions as
above up to the electrolytic sulfurization treatment except for the
electrolytic sulfurization performed under differing amount of
applied current, and to the Fabilly test performed in a manner
similar to that described in Example 1. From the results shown in
FIG. 2, it can be understood that a clear correlation is found
between the applied current and the maximum seizure resistant load,
and that the resistance load increases with increasing applied
current. This fact in combination with the results of FIG. 1 shows
that the maximum seizure resistance load is improved with
increasing roughness (i.e., the surface roughness of the mother
material Rmax) of the interface between the mother material and the
layer.
EXAMPLE 3
[0044] The precision machined, as-carburized and quenched pins same
as those employed in Example 1 (i.e., the pins having a surface
roughness Rmax of 1 .mu.m or lower up to a process of carburization
quenching) were subjected to degreasing, pickling, rinsing, and
drying. Then, a polyethylene film perforated with numerous holes
each 4 mm in diameter was wound around the body of the pins in such
a manner that numerous exposing holes might be formed at an
interval of about 0.1 mm on the body, such that the surface of the
mother material may be exposed there through. The pins were then
subjected to the electrolytic sulfurization treatment below.
[0045] One of the pins was vertically immersed as an anode at the
central portion of the same container as that used in Example 1
having provided therein a 20 wt. % aqueous solution of sodium
thiosulfate, and two SUS304 cathode plates were each immersed at
the same distance of 10 mm from the pin in such a manner that the
pin may be inserted between the cathode plates. Then, the pins were
each subjected to electrolytic treatment by using the pin as the
positive electrode and the cathode plates as the negative
electrodes under the same conditions while applying current at a
density of 3.2 A/dm.sup.2 and for 60 C. After the treatment, the
pins were rinsed, and subsequent to the removal of the film, they
were immersed again in the electrolytic solution to apply current
at a density of 1.6 A/dm.sup.2 for 18 C by using the pin as the
positive electrode. Accordingly, an iron sulfide layer having
irregularities was formed by the first electrolytic sulfurization
in such a manner that the masking portion have irregularities which
avoid the formation of a layer, and a layer of iron sulfide formed
on the portions free of films by the subsequent electrolytic
sulfurization treatment.
[0046] The pins having thereon the iron sulfide layer thus obtained
were subjected to Fabilly test in the same manner as in Example 1,
and a maximum seizure resistance load of 1,080 Kgf was obtained. On
measuring the surface roughness Rmax of the mother material of the
pin on another pin from which the iron sulfide layer was stripped
off, it was found to yield a value of 13.2 .mu.m.
EXAMPLE 4
[0047] The same procedure as that performed in Example 3 was
followed, except for applying current at a density of 16 A/dm.sup.2
and for 18 C after removing the film. The thus obtained pin having
the iron sulfide thereon was subjected to Fabilly test in the same
manner as in Example 1 to obtain a maximum seizure resistance of
1,060 Kgf. Similarly, on measuring the surface roughness Rmax of
the mother material of the pin on another pin from which the iron
sulfide layer was stripped off, it was found to yield a value of
10.7 .mu.m.
EXAMPLE 5
[0048] Two as-carburized and quenched pins same as those described
in Example 1 (having a surface roughness Rmax of 1 .mu.m or lower
at the carburized and quenched state) were degreased, pickled,
rinsed, and dried, which were then subjected to electrolytic
treatment using the pins as the anode and to the treatment of
forming a layer of molybdenum disulfide.
[0049] One of the pins thus obtained was vertically immersed as an
anode at the central portion of the same container as that used in
Example 1 having provided therein a 10 wt. % aqueous solution of
sodium thiocyanate, and two SUS304 cathode plates were each
immersed at the same distance of 10 mm from the pin in such a
manner that the pin may be inserted between the cathode plates.
Then, the pins were each subjected to electrolytic treatment by
using the pin as the positive electrode and the cathode plates as
the negative electrodes while applying current at a density of 3.2
A/dm.sup.2 and for 40 C (Coulomb). Thus was obtained an iron
sulfide based layer by the treatment.
[0050] Then, after taking out the pin from the electrolytic
solution and exposing it to air for 30 seconds, it was immersed in
another electrolytic solution (an aqueous solution of sodium
hydroxide at a pH value of 9). During the exposure to air, uniform
cracks were found to form on the layer generated by the precoating
treatment. The pin having formed thereon the layer in which the
cracks were generated was subjected to electrolysis in an aqueous
sodium hydroxide solution of pH 9 by applying a current at a
density of 0.8 A/dm.sup.2 for 40 C (Coulomb) between the pin used
as the anode and the cathode plates similar to above. Similar to
the case of Example 2, electrolytic corrosion occurs to the crack
portions to elute out the metal. Thus, it was found that exposed
metallic surface portions generate, and at the same time, a part of
the layer elute out as to generate irregularities on the surface of
the pin (metallic plane and the layer plane).
[0051] After the alkali coating treatment above, the pin was rinsed
and allowed to stand under air for a duration of 30 seconds,
followed by a subsequent electrolytic sulfurizatin treatment. More
specifically, electrolytic sulfurization treatment. was performed
in a 20% aqueous solution of sodium thiosulfate as the electrolytic
solution while applying current at a density of 3.2 A/dm.sup.2 by
using the pins as anodes. The two pins were treated under the same
conditions up to this step, but in the electrolytic sulfurization,
they were treated under different applied current conditions. More
specifically, one pin was treated with applied current of 10C,
while the other was applied under a current of 30 C. On removing
the iron sulfide layer formed on each pins, the Rmax of the layer
interface for one pin was found to be 10.2 .mu.m and that for the
other was found to be 14.8 .mu.m.
[0052] Then, a paint obtained by mixing molybdenum disulfide with
epoxy resin at a ratio by weight of 1:2 was sprayed to the two pins
differed in surface roughness at a spray pressure of 2 kg/cm.sup.2
to coat the pin surfaces with a film 5 .mu.m in thickness. The pins
thus coated with films were both calcined at 180.degree. C. for a
duration of 30 minutes as to obtain pins having thereon a solid
lubricating layer of molybdenum disulfide. The pins were subjected
to Fabilly test in the same manner as in Example 1, and the pin
having a surface roughness Rmax of 10.2 .mu.m was found to yield a
maximum seizure resistance load of 1,550 Kgf, while the other pin
having the Rmax of 14.8 .mu.m was found to yield 1,650 Kgf.
EXAMPLE 6
[0053] The same procedure as that of Example 1 was performed,
except for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 30 parts by weight of KSCN in 100 parts by
weight of water and adding therein 10 parts by weight of FeSO.sub.4
as the bath controller. However, the surface the pin was ground to
yield a roughness Rmax of 10.4 .mu.m by using the same rotary
polishing machine as that used in Example 1. As a result, an iron
sulfide layer having a thickness of from 4 to 6 .mu.m was formed on
the surface of the pin, and the pin yielded a maximum seizure
resistance load of 1,035 Kgf.
EXAMPLE 7
[0054] The same procedure as that of Example 1 was repeated, except
for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 30 parts by weight of NaSCN in 100 parts by
weight of water and adding therein 10 parts by weight of FeSO.sub.4
as the bath controller. The surface of the pin was ground to a
roughness Rmax of 5.2 .mu.m by using the same rotary polishing
machine as that used in Example 1. As a result, an iron sulfide
layer having a thickness of from 4 to 6 .mu.m was formed on the
surface of the pin, and the pin yielded a maximum seizure
resistance load of 974 Kgf.
EXAMPLE 8
[0055] The same procedure as that of Example 1 was repeated, except
for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 50 parts by weight of NaSCN in 100 parts by
weight of water and adding therein 10 parts by weight of FeSO.sub.4
as the bath controller. The surface of the pin was ground to a
roughness Rmax of 8.3 .mu.m by using the same rotary polishing
machine as that used in Example 1. As a result, an iron sulfide
layer having a thickness of from 4 to 6 .mu.m was formed on the
surface of the pin, and the pin yielded a maximum seizure
resistance load of 962 Kgf.
EXAMPLE 9
[0056] The same procedure as that of Example 1 was repeated, except
for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 30 parts by weight of Ca(SCN).sub.2 in 100
parts by weight of water and adding therein 10 parts by weight of
FeSO.sub.4 as the bath controller. The surface of the pin was
ground to a roughness Rmax of 2.6 .mu.m by using the same rotary
polishing machine as that used in Example 1. As a result, an iron
sulfide layer having a thickness of from 4 to 6 .mu.m was formed on
the surface of the pin, and the pin yielded a maximum seizure
resistance load of 818 Kgf.
EXAMPLE 10
[0057] The same procedure as that of Example 1 was repeated, except
for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 30 parts by weight of Ba(SCN).sub.2 in 100
parts by weight of water and adding therein 10 parts by weight of
FeSO.sub.4 as the bath controller. The surface of the pin was
ground to a roughness Rmax of 4.2 .mu.m by using the same rotary
polishing machine as that used in Example 1. As a result, an iron
sulfide layer having a thickness of from 4 to 6 .mu.m was formed on
the surface of the pin, and the pin yielded a maximum seizure
resistance load of 915 Kgf.
EXAMPLE 11
[0058] The same procedure as that of Example 1 was repeated, except
for using, as the electrolytic solution, an aqueous solution
obtained by dissolving 30 parts by weight of Na.sub.2S.sub.2O.sub.3
in 100 parts by weight of water and adding therein 10 parts by
weight of FeSO.sub.4 as the bath controller. The surface of the pin
was ground to a roughness Rmax of 3.4 .mu.m by using the same
rotary polishing machine as that used in Example 1. As a result, an
iron sulfide layer having a thickness of from 4 to 6 .mu.m was
formed on the surface of the pin, and the pin yielded a maximum
seizure resistance load of 846 Kgf.
[0059] As described above, the present invention provides sliding
components having a sulfide based solid lubricating layer improved
in seizure resistance. In accordance with the present invention,
electrolytic sulfurization treatment in an aqueous solution is
performed without employing fused salt electrolysis. Thus, sliding
components having excellent seizure resistance can be produced at a
low cost and with improved operability. Accordingly, the present
invention can greatly contribute to the improvement of machine
life.
[0060] While the invention has been described in detail by making
reference to specific examples, it should be understood that
various changes and modifications can be made without departing
from the scope and the spirit of the present invention.
* * * * *