Background of the Invention
1. Technical Field
[0001] The present invention relates to a circuit breaker in which a switching mechanism
for switching a movable contact is accommodated in an insulating case.
2. Background Art
[0002] Hitherto, the Japanese Patent Publication (unexamined)
No.120888/1999 discloses a circuit breaker provided with a handle capable of connecting or disconnecting
a movable contact, and a switching mechanism accommodated in an insulating case for
separating the movable contact by activating a trip section when excess current has
been applied. A major part of the switching mechanism consists of an iron material
made of a nitrided cold rolled steel plate, sliding portion of which is coated with
Fe3O4 film or plated, and the surface is supplied or coated with a lubricant or grease
containing mineral oil or aliphatic synthetic hydrocarbon oil as base oil.
[0003] Under the background of growing demand for more compact products, it is a recent
trend that switching mechanism and insulating case of a circuit breaker is small-sized.
A further demand for a circuit breaker of higher performance has made it necessary
to incorporate, for instance, electronic parts for achieving new functions in the
insulating case, and therefore the switching mechanism of the same size as the conventional
switching mechanism has to be accommodated in the insulating case smaller than the
size of the conventional insulating case. Further, since the insulating case has become
smaller, temperature inside the insulating case as well as temperature of switching
mechanism itself will be higher than in the conventional circuit breaker of the same
rating, due to which a lubricant or grease containing mineral oil or aliphatic synthetic
hydrocarbon oil as base oil tends to be easily oxidized and deteriorated. Furthermore,
for making the switching mechanism smaller, each component has to be smaller and clearance
between components has to be narrower, and, as a result, film of a lubricant or grease
becomes thinner and therefore tends to be easily oxidized and deteriorated. Moreover,
as a result of such oxidation and deterioration, the lubricant or grease become sticky.
[0004] The Japanese Patent Publication (unexamined)
No.190518/1995 discloses a refrigerating cycle provided with a compressor. It is disclosed in this
literature that incompatible polyphenylether and additives such as molybdenum disulfide,
tungsten disulfide, fluorographite or polytetrafluoroethylene are added to a coolant
for the compressor. However, not only because a compressor belongs to a different
technical field from that of a circuit breaker, but also because a lubricant for a
compressor has different characteristics from those required in a lubricant for a
mechanism of a circuit breaker, especially in the aspect of oxidation resistance under
use in a high temperature, it will be impossible to make the present invention in
view of the mentioned compressor.
[0005] The present invention was made to solve the above-discussed problems, and has an
object of obtaining a circuit breaker capable of providing a stable operation for
a long time in which a lubricant of superior heat resistance and oxidation resistance
is used for a switching mechanism.
[0006] The invention also provides a circuit breaker in which only a lubricating oil of
superior heat resistance and oxidation resistance is used for lubrication of a switching
mechanism, resulting in a higher assembling efficiency.
Disclosure of Invention
[0007] A circuit breaker according to the present invention includes: an insulating case;
a switching mechanism that is accommodated in the mentioned insulating case and connects
and disconnects a movable contact to and from a fixed contact; and a trip mechanism
provided with an engaging section for engaging with the mentioned switching mechanism,
and disengaging the mentioned engaging section upon detecting any excess current on
any electric pathway in the circuit so that the mentioned movable contact is separated
from the mentioned fixed contact; in which a part of the mentioned switching mechanism
consists of a material containing iron or iron compound, and sliding portion of the
mentioned material containing iron or iron compound is provided with a phenylether
lubricant oil to which an antioxidant and molybdenum disulfide are added, and consequently,
the switching mechanism assures a superior heat resistance and oxidation resistance
in lubrication of the switching mechanism, and stable operation for a long time.
[0008] Further, the sliding portion consisting of a material containing iron or iron compound
is provided with Fe3O4 film or plated film, and therefore progress of oxidation and
deterioration of phenylether lubricant due to metal catalytic action of iron is restrained.
[0009] Further, a phenylether lubricant consists of phenylether oil, and consequently the
lubricant can be easily applied to the sliding portion of the mechanism that tends
to become small-sized.
[0010] Further, molybdenum disulfide is added to the phenylether oil, and consequently oil
film thickness can be better retained, resulting in a further improvement of oxidation
resistance as well as in a superior lubrication quality such as load resistance, persistence,
etc.
[0011] Further, 1.0 to 5.0 wt% molybdenum disulfides are contained, and consequently improvement
can be achieved both in the aspect of oil film thickness that is superior in oxidation
resistance and in the aspect of dispersion stability of molybdenum.
[0012] Further, phenylether oil is provided to the engaging portion located between a latch
section and an urging section, and consequently superior oxidation resistance is achieved
and operation is stable for a long time.
[0013] Furthermore, the phenylether lubricant is phenylether grease containing a urea thickener,
and therefore the phenylether lubricant is superior in retaining a shape under a high
temperature. Consequently superior oxidation resistance is achieved and operation
is stable for a long time.
Brief Description of the Drawings
[0014]
Fig. 1 is a perspective view of a circuit breaker according to Embodiment 1 of the
present invention.
Fig. 2 is a sectional view of the circuit breaker taken along the lines II-II of Fig.
1.
Fig. 3 is a bar graph showing evaluation results of the lubricant according to the
Embodiment 1 of the invention.
Fig. 4 is a bar graph showing evaluation results of the grease according to the Embodiment
1 of the invention.
Fig. 5 is a bar graph showing lubrication characteristics of a lubricant and grease
under the state of withstand load according to Embodiment 2 of the invention.
Best Mode for Carrying out the Invention
[0015] Several embodiments of the present invention are hereinafter described in detail
with reference to the accompanying drawings.
Embodiment 1.
[0016] Fig. 1 is a perspective view of a circuit breaker according to Embodiment 1 of the
invention, and Fig. 2 is a sectional view of the circuit breaker taken along the lines
II-II of Fig. 1.
[0017] Referring to Figs. 1 and 2, reference numeral 1 is an insulating case made of an
insulating resin material and consisting of base 1a on which a fixed contact 2, a
switching mechanism A and so on are mounted, and a cover 1b provided with an opening
through which a handle 22 is protruded. Numeral 2 is the fixed contact fixed on the
base 1a, and numeral 3 is a movable contact operated by the switching mechanism. Numeral
4 is an insulating holder for holding the movable contact 2 made of an insulating
resin material, to which a force is transmitted from a connecting pin 15a of a toggle
link 15 inserted in the opening. Numeral 11 is a hasp engaged with a latch 12 at one
end and with a trip bar 19 at the other end. Numeral 12 is the latch urged counterclockwise
at all times by an urging spring (not shown) round a connecting pin 12a and engaged
with a lever 13. Numeral 15 is a toggle link consisting of a lower link connected
to the insulating holder 4 and an upper link connected to the lower link by a lever
13'and a connecting pin 15b. Numeral 16 is a main spring disposed between the connecting
pin 15b that connects the upper link and the lower link and a handle arm 23 fixing
handle 22. Numeral 17 is a bimetal that is disposed between a flexible stranded wire
25 connected to the movable contact 3 and an external terminal 26 and deforms due
to heat generation corresponding to the current applied to the electric pathway. Numeral
18 is an electromagnetic device that is disposed on an electric pathway between a
flexible stranded wire : 25 connected to the movable contact 3 and an external terminal
26 and is activated by a magnetic force corresponding to the current applied to the
electric pathway exceeding a predetermined value. 19 is a trip bar that is urged counterclockwise
at all times by an urging spring, and rotates clockwise by the bimetal 17 or the electromagnetic
device 18 when an excess current is applied to the electric pathway. Numeral 20 is
a switching contact provided at an end of the fixed contact 2 and the movable contact
3. The hasp 11, latch 12 and lever 13 are rotatably supported on an iron frame by
shaft pins 11a, 12a, 15a, 15b and 19a.
[0018] At the time of applying an excess current, the trip bar 19 is turned either by the
bimetal 17 or by the electromagnetic device 18 thereby disengaging the hasp 11 and
the latch 12, and the latch 12 disengages the lever 13. Then the urging force of the
main spring 16 releases the switching contact 20 to break the circuit. After the trip
operation in the circuit breaker, disengagement of hasp 11, latch 12 and lever 13
can be recovered by resetting operation, and the switching contact 20 is closed, whereby
the circuit breaker becomes ready for further possible circuit breaking.
[0019] A switching mechanism A for operating the movable contact 3 is comprised of the iron
frame, the handle arm 23, the handle 22, the lever 13 and the toggle link mechanism
(consisting of toggle links 15 and main spring 16). A linkage section B to be engaged
with the switching mechanism A through the latch 12 consists of the hasp 11 and the
latch 12. The trip mechanism C for releasing the latching engagement of the linkage
section B consists of the bimetal 17, the electromagnetic device 18 and the trip bar
19.
[0020] The mentioned frame, hasp 11, latch 12, lever 13, toggle links 15, etc. are usually
formed by pressing a cold rolled steel plate of low carbon steel (SPCC-SD), and a
nitriding treatment (nitrocarburizing by gas) is applied to them for surface curing,
improvement of strength and rust prevention.
[0021] Further, the following phenylether lubricant is applied to bearing portions of shaft
pins 11a 12a, 15a, 15b and 19a and sliding portions of hasp 11, latch 12, toggle links
15, for reducing friction due to sliding contact between the parts and smoothly operating
the respective components.
[Lubricant]
[0022] The lubricant employed in Embodiment 1 contains 93 to 98.9 wt% of alkyldiphenylether
oil as base oil, 1 to 5 wt% of molybdenum disulfide and 0.1 to 2wt% of antioxidant
both as additives.
[0023] In the experiments performed by the inventors, it was found that when 1 to 5 wt%
molybdenum disulfide is added as an inorganic chemical compound to alkyldiphenylether
oil, oxidation resistance of the lubricant is remarkably improved, which was beyond
expectation. On the other hand, when molybdenum disulfide was less than 1 wt%, oxidation
resistance was not significantly improved, while the quality of lubricant (homogeneity)
was lowered when more than 5 wt%.
[0024] Further, in the experiments performed by the inventors, when graphite was added to
alkyldiphenylether oil as an inorganic chemical compound, oxidation resistance was
inferior to the case of adding molybdenum disulfide, though oil film thickness was
similarly increased.
[Base oil]
[0025] The Alkyldiphenylether oil is mainly composed of either dialkyldiphenylether or monoalkyldiphenylether,
and has a viscosity of 80 to 150mm2/s (40° C).
[Additives]
[0026] Molybdenum disulfide (average particle diameter is 0.5µm) is involved in maintenance
of oil film retention. Molybdenum disulfide is preferable since it can also serve
as a solid lubricant.
[0027] Further, the antioxidant is composed of either aromatic amine or phenol. For example,
if composed of amine, the antioxidant is phenyl-α-naphthylamine or phenothiazine.
If composed of phenol, the antioxidant is 2.6-di-tert-buthylparacresol or 2.6-di-tert-buthylphenol,
6-tert-buthyl-0-cresol, etc.
[0028] As described above, the phenylether lubricating oil, that has never been so far employed
as a lubricant for a circuit breaker, is applied to the bearing portions of the shaft
pins 11a, 12a, 15a, 15b and 19a and to the sliding portions of the hasp 11, latch
12, lever 13 and toggle links 15. Therefore, the lubricating oil can be easily applied
in a short time and assembling efficiency of the circuit breaker is improved. After
all, it becomes possible to provide a circuit breaker in which lubricating oil has
superior heat resistance and oxidation resistance, and of which operation is stable
for a long period.
Embodiment 2.
[0029] Embodiment 2 of the invention is hereinafter described.
[0030] In this Embodiment 2, the following phenylether grease is applied to the bearing
portions of shaft pins 11a, 12a, 15a, 15b and 19a and to the sliding portions of hasp
11, latch 12, lever 13 and toggle links 15 of the circuit breaker. Note that the grease
means a semisolid lubricant composed of a liquid lubricant (base oil) and a thickener.
[Lubricant]
[0031] The lubricant employed in this Embodiment 2 contains 77.0 to 97.8 wt% alkyldiphenylether
oil as base oil, 2 to 20 wt% a urea soap as a thickener and 0.2 to 3 wt% antioxidant
as an additive. More preferable composition range is 88.0 to 94.0 wt% alkyldiphenylether
oil as base oil, 5 to 10 wt% urea soap as a thickener and 1.0 to 2.0 wt% antioxidant
as an additive.
[0032] In the experiments performed by the inventors, it was found that phenylether grease,
especially the one that contains any urea soap shows a superior oxidation resistance.
Assumingly, this is because the urea soap has a sufficient shape retentiveness under
a high temperature, due to which the film is difficult to lose the shape or to be
thinned as compared with a general-purpose type lithium soap that is inferior in heat
resistance. In other words, it is assumed that when the coated film is thicker, substantial
volume of the film becomes greater, and therefore it takes a long time for oxidation
and consequently the oxidation resistance of the film is improved. It is further assumed
that since the thicker the oxidized film is the easier it becomes for molecules composing
the base oil to move, and the thicker coated film attains an improved resistance to
oxidation and deterioration as compared with a thinner film in which molecules tend
to remain immobile.
[Grease]
[0033] The grease employed in this embodiment is a grease containing alkyldiphenylether
as base oil and urea soap as a thickener. The alkyldiphenylether oil contained in
the grease is mainly composed of either dialkyldiphenylether or monoalkyldiphenylether.
[Additives]
[0034] Further, the antioxidant is composed of either aromatic amine or phenol. For example,
if composed of amine, the antioxidant is phenyl-α-naphthylamine or phenothiazine.
If composed of phenol, the antioxidant is 2.6-di-tert-buthylparacresol or 2.6-di-tert-buthylphenol,
6-tert-buthyl-0-cresol, etc.
[0035] As described above, the phenylether grease, that has never been so far employed as
a lubricant for a circuit breaker, is applied to the bearing portions of the shaft
pins 11a 12a, 15a, 15b and 19a and to the sliding portions of the hasp 11, latch 12,
lever 13 and toggle links 15 (including engaging portions between the latch 12 and
lever 13, where a particularly heavy load is imposed). Therefore, it becomes possible
to provide a circuit breaker superior in lubrication performance under a heavy load
and superior in oxidation resistance, and of which operation is stable for a long
period. Further, since the grease provides a superior performance under a heavy load,
it is preferable to use as a lubricant for a portion between the insulating holder
holding the movable contact and the base of the circuit breaker. In this case, the
grease can be used as a common lubricant for the mechanism and for the portion between
the insulating holder and the base, thereby the application efficiency being improved,
and there is no change in lubricating characteristic unlike a case where lubricants
of different compositions are used. It is also preferable to apply a lubricating oil
(for example, the one described in Embodiment 1) to the sliding portions of the bearing
portions of the shaft pins 11a, 12a, 15a and 19a, in which case work efficiency is
improved.
Examples:
[0036] The embodiments of the invention are now described in further details in the form
of following examples.
Example 1.
[0037] For the purpose of simulating a sticking state of deteriorated lubricating oil and
grease applied between mechanical parts, various lubricants as shown in Table 1 (lubricating
oils) and Table 2 (greases) given below were put between iron substrates on which
oxidized film was formed. Shearing force after retention at a high temperature was
evaluated.
[Test substrate]
[0038]
Substrate 1: 10mm long, 10mm wide and 2mm thick
Substrate 2: 30mm long, 30mm wide and 2mm thick
Cold rolled steel plate (SPCC-SD)
Nitriding: Retained for 1.5 hours in a mixed gas atmosphere of ammonia, carbon dioxide
and nitrogen under a temperature of 580° C, thus a nitrided layer of 10 to 15µm was
formed.
[0039] After nitriding, the substrates were steam-treated as follows:
Being retained for 0.5 hour in steam of 550° C, a film of Fe3O4 of 2 µm in thickness
was formed on the surface of nitrided layer.
[Lubricants]
Lubricating oil
(Alpha-olefin lubricating oil: Comparative example)
[0040] Lubricating oil of the following composition was used as a comparative example of
conventional lubricating oil.
A01: 99.5 wt% alpha-olefin base oil, and 0.5 wt% phenol antioxidant
(Phenylether lubricating oils)
[0041]
B01*: 99.5 wt% alkyldiphenylether base oil, and 0.5 wt% phenol antioxidant
B02: 98.5 wt% alkyldiphenylether base oil, 1.0 wt% molybdenum disulfide, and 0.5 wt%
phenol antioxidant
B03: 97.0 wt% alkyldiphenylether base oil, 2.5 wt% molybdenum disulfide, and 0.5 wt%
phenol antioxidant
B04: 94.5 wt% alkyldiphenylether base oil, 5 wt% molybdenum disulfide, and 0.5 wt%
phenol antioxidant
B05: 97.0 wt% alkyldiphenylether base oil, 2.5 wt% graphite, and 0.5 wt% phenol antioxidant
* B01 and B05 are comparative examples.
Table 1
No. |
Base oil |
Additive |
Antioxidant |
A01 |
99.5 wt% alpha-olefin base oil |
- |
0.5 wt% phenol antioxidant |
B01 |
99.5 wt% alkyldiphenylether base oil |
- |
0.5 wt% phenol antioxidant |
B02 |
98.5 wt% alkyldiphenylether base oil |
1.0 wt% molybdenum disulfide |
0.5 wt% phenol antioxidant |
B03 |
97.0 wt% alkyldiphenylether base oil |
2.5 wt% molybdenum disulfide |
0.5 wt% phenol antioxidant |
B04 |
94.5 wt% alkyldiphenylether base oil |
5.0 wt% molybdenum disulfide |
0.5 wt% phenol antioxidant |
B05 |
97.0 wt% alkyldiphenylether base oil |
2.5 wt% Graphite |
0.5 wt% phenol antioxidant |
Grease
(Alpha-olefin grease)
[0042] Grease of the following composition was used as a comparative example of conventional
grease.
C01: 84.5 wt% alpha-olefin base oil, 7.0 wt% lithium soap, 8.0 wt% molybdenum disulfide,
and 0.5 wt% phenol antioxidant
(Phenylether greases)
[0043]
D01: 88.0 wt% alkyldiphenylether base oil, 10.0 wt% lithium soap, and 2.0 wt% antioxidant
D02: 88.0 wt% alkyldiphenylether base oil, 10.0 wt% urea soap, and 2.0 wt% antioxidant
Table 2
No. |
Base oil |
Thickener |
Additives |
Antioxidant |
C01 |
84.5 wt% alpha-olefin base oil |
7.0 wt% lithium soap |
8.0 wt% molybdenum disulfide |
0.5 wt% antioxidant |
D01 |
88.0 wt% alkyldiphenylether base oil |
10.0 wt% lithium soap |
- |
2.0 wt% antioxidant |
D02 |
88.0 wt% alkyldiphenylether base oil |
10.0 wt% urea soap |
- |
2.0 wt% antioxidant |
[140° C thermal deterioration test (shear test)]
(Test conditions)
[0044] Various lubricating oils were applied between the test substrates 1 and 2, and those
substrates were retained in a constant-temperature tank containing atmospheric air
of 140 C. Coating amount was 17mg in case of lubricating oil, and 7mg in case of grease.
After passing predetermined times (1, 3, 5, 7, 10, 20, 30, 50, 70, 100, 200, 300,
500, 700, 1000, 2000 and 3000 hours), the substrates were taken out and each shear
force was measured. Shear force is to be understood as sticking force caused by oxidation
and deterioration of the lubricant applied between the substrates.
(Evaluation standards)
[0045] Shear forces were measured with a precision universal tester AG-1000B (manufactured
by Shimadzu Corporation). Shear force is the maximum force required for sliding the
substrate 2 in the direction of the surface of the substrate 1 when the substrate
1 is fixed.
[0046] If the shear force of a lubricant was not more than a predetermined value (not more
than 2N for the circuit breaker corresponding to Embodiment 1) when a mechanism of
the circuit breaker provided with such a lubricant was smoothly operated, the lubricant
was considered as "acceptable" and "being within the life ". The life referred to
in this experiment means a range of time period during which a lubricant can maintain
the desired lubrication characteristics in the aspects of heat resistance and oxidation
resistance.
[Test results]
[0047] The results of thermal deterioration test (life test) of the aforementioned lubricating
oils are shown in Fig. 3. Fig. 3 shows relative proportions of the results of thermal
deterioration tests of respective test samples when the life of the comparative example
A01 is defined as 1. The results of thermal deterioration test (life test) of the
greases are shown in Fig. 4. Fig. 4 shows the relative proportions of the results
of thermal deterioration tests of respective test samples when the life of the comparative
example B01 is defined as 1.
[0048] Now test results of respective samples are described.
Lubricating oils
(Alpha-olefin lubricating oil)
[0049] A01: The oil composed of 99.5wt% alpha-olefin base oil and 0.5 wt% phenol antioxidant
was inferior in lubricity and oxidation resistance.
(Phenylether lubricating oils)
[0050]
B01: The oil composed of 99.5 wt% alkyldiphenylether base oil and 0.5 wt% phenol antioxidant
was inferior in lubricity but relatively superior in oxidation resistance.
B02: The oil composed of 98.5 wt% alkyldiphenylether base oil, 1.0 wt% molybdenum
disulfide and 0.5 wt% phenol antioxidant was superior in lubricity as well as in oxidation
resistance.
B03: The oil composed of 97.0 wt% alkyldiphenylether base oil, 2.5 wt% molybdenum
disulfide and 0.5 wt% phenol antioxidant was superior in lubricity as well as in oxidation
resistance.
B04: The oil composed of 94.5 wt% alkyldiphenylether base oil, 5 wt% molybdenum disulfide
and 0.5 wt% phenol antioxidant was superior in lubricity as well as in oxidation resistance.
B05: The oil composed of 97.0 wt% alkyldiphenylether base oil, 2.5 wt% graphite and
0.5 wt% phenol antioxidant was superior in lubricity and relatively superior in oxidation
resistance.
[0051] These results can be summarized as follows. B01 to B05 containing alkyldiphenylether
as base oil showed a superior oxidation resistance as compared with A01 (comparative
example) containing alpha-olefin base oil to which only an antioxidant was added.
B01 containing alkyldiphenylether as base oil to which only an antioxidant was added
showed a life approximately five times longer than A01, and B02 to B04 to which molybdenum
disulfide was added showed a life nearly twenty times longer than A01 and nearly four
times longer than B01, and besides proved to have a remarkably superior oxidation
resistance. On the other hand, life of B05 to which graphite was added instead of
molybdenum disulfide was equivalent to that of B01, in other words, no significant
effect of extending the life was observed at all. In conclusion, alkyldiphenylether
to which an antioxidant, in particular a predetermined amount of molybdenum disulfide,
was added showed a remarkably superior oxidation resistance when using, at a high
temperature, an iron material having a surface on which Fe3O4 film of 2 µm in thickness
was formed after nitriding thereof.
[0052] The foregoing results lead to the following assumptions.
[0053] The alkyldiphenylether with an addition of an antioxidant is unsusceptible to any
chemical reaction or catalytic action by an iron material having a nitrided surface
on which a Fe3O4 film of 2µm in thickness is formed, and is therefore compatible with
such an iron material under the use at a high temperature.
[0054] Also, it is assumed that the addition of molybdenum disulfide that is lipophilic
with alkyldiphenylether and has a large specific surface area makes the oil film thicker
and the substantial volume as much larger, and therefore it takes a longer time for
oxidation thereof and, as a result, the oxidation resistance is further improved.
In addition, it is assumed that molybdenum disulfide is unsusceptible to any chemical
reaction or catalytic action by an iron material having a nitrided surface on which
a Fe3O4 film of 2 µm in thickness is formed, and is therefore compatible with such
an iron material under the use at a high temperature. Further, it is assumed that
when the oil film is thicker it is easier for molecules composing the oil to move,
and therefore it becomes easier for the antioxidant to move toward the surface portion
being subject to oxidation as compared with a thinner film (for example, an oil film
without an additive) in which molecules tend to remain immobile, and consequently
the oxidation resistance is improved. However, when molybdenum disulfide is less than
1 wt%, the mentioned effect of improving oxidation resistance is lowered, which is
assumingly because the oil film is not thick enough. On the contrary, whenmolybdenumdisulfide
is more than 5 wt%, quality of lubricating oil (homogeneity) is lowered, which is
assumed to be a result of lowered dispersion stability of molybdenum disulfide.
[0055] On the other hand, when graphite was added as an inorganic chemical compound, the
thickness of oil film was increased in the same manner as molybdenum disulfide, however
oxidation resistance was inferior. It is assumed that this is because the oil was
affected by any chemical reaction or catalytic action caused by an iron material having
nitrided surface on which a Fe3O4 film of 20m in thickness is formed, or because impurities
contained in graphite contain iron or any iron compound performing any metal catalytic
action, unlike impurities contained in molybdenum disulfide, a major part of which
is silicon oxide that is nonmetallic.
Grease
(Alpha-olefin grease)
[0056] C01: The grease composed of 84.5 wt% alpha-olefin base oil, 7.0 wt% lithium soap,
8.0 wt% molybdenum disulfide and 0.5 wt% phenol antioxidant was superior in lubricity
but inferior in oxidation resistance.
(Phenylether greases)
[0057]
D01: The grease composed of 88.0 wt% alkyldiphenylether base oil, 10.0 wt% lithium
soap and 2.0 wt% antioxidant was superior in lubricity and relatively superior in
oxidation resistance.
D02: The grease composed of 88.0 wt% alkyldiphenylether base oil, 10.0 wt% urea soap
and 2.0 wt% antioxidant was superior in both lubricity and oxidation resistance.
[0058] These results can be summarized as follows. D01 and D02 have a life three to five
times longer than that of C01, and D02 containing urea soap as a thickener has a life
approximately 1.7 times longer than that of D01 containing lithium soap as a thickener.
[0059] The foregoing results lead to the following assumptions.
[0060] The grease containing alkyldiphenylether as base oil with an addition of any antioxidant
is unsusceptible to any chemical reaction or catalytic action by an iron material
having a nitrided surface on which a Fe3O4 film of 2
µm in thickness is formed, and is therefore compatible with such an iron material under
the use at a high temperature.
[0061] Also it is assumed that urea soap has an excellent shape retentiveness at a high
temperature, due to which the film is less prone to lose the shape or to be thinned
as compared with general purpose type lithium soap that is inferior in heat resistance,
and therefore the substantial volume of the film becomes larger and it takes a longer
time for oxidation thereof, and as a result the oxidation resistance is improved.
In addition, it is assumed that since the thicker the oxidized film is the easier
it becomes for molecules composing the base oil to move, the thicker film attains
an improved resistance to oxidation and deterioration as compared with a thinner film
in which molecules tend to remain immobile.
[0062] In conclusion, it is preferable to use alkyldiphenylether as base oil and urea soap
as a thickener.
Example 2.
[0063] Lubricity characteristics of a lubricating oil and a grease shown in the Table 3
were compared under the following conditions.
Table 3
No. |
Base oil |
Thickener |
Additive |
Antioxidant |
B03 |
97.0 wt% alkyldiphenylether base oil |
- |
2.5 wt% molybdenum disulfide |
0.5 wt% phenol antioxidant |
D02 |
38.0 wt% alkyldiphenylether base oil |
10.0 wt% urea soap |
- |
2.0 wt% antioxidant |
(Test conditions)
[0064] A steel ball was rotated at 750rpm while being pressed onto three fixed steel balls
of 19.05mm in diameter on which respective lubricants were applied, with a pressure
increasing in an increment of 0.049Mpa, and acceptable load limits were measured by
using a Soda Four Ball Tester for obtaining an oil pressure load that does not cause
any seizure among the balls.
(Test results)
[0065] Test results of acceptable load limits are shown in Fig. 5.
Lubricating oil
[0066] B03: Acceptable load limit of the oil composed of 97.0 wt% alkyldiphenylether base
oil, 2.5 wt% molybdenum disulfide and 0.5 wt% phenol antioxidant was 0.2MPa.
Grease
[0067] D02: Acceptable load limit of the grease composed of 88.0 wt% alkyldiphenylether
base oil, 10.0 wt% urea soap and 2.0 wt% antioxidant was 0.34Mpa.
[0068] In view of the foregoing results, it is understood that when comparing the load resistance
of lubricating oil and grease, both of which have a superior oxidation resistance,
the grease has a superior load resistance. Therefore, it is preferable to use grease
when mechanism of a circuit breaker requires a high load resistance.
Industrial applicability
[0069] The circuit breaker according to the invention accommodates a switching mechanism
for switching a movable contact in an insulating case thereof, and is preferable for
stable operation even under a high temperature or high humidity.