EP1229566B1

EP1229566B1 - Circuit breaker

Info

Publication number: EP1229566B1
Application number: EP00953482A
Authority: EP
Inventors: Hitoshi c/o Mitsubishi Electric Corporation ITO; Koji c/o Mitsubishi Electric Corporation HIKAKE; Hiroyuki c/o Mitsubishi Electric Corporation KAKISAKO; Susumu c/o Mitsubishi Electric Corporation TAKAHASHI
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2000-08-18
Filing date: 2000-08-18
Publication date: 2007-07-11
Anticipated expiration: 2020-08-18
Also published as: TW464895B; CN1379911A; WO2002017343A1; JP4445197B2; CN1233010C; DE60035521T2; EP1229566A1; EP1229566A4; DE60035521D1

Abstract

A circuit breaker which is excellent in heat resistance and oxidation resistance in lubricating an open/close mechanism and provides an extended, stable operation, and which comprises an open/close mechanism (A) housed in an insulating case (1) and for opening/closing a movable contact (3) from/to a fixed contact (2), an engaging unit (B) engaging with the open/close mechanism (A), and a tripping mechanism (C) for freeing the engagement of the engaging unit (B) when an over-current is detected in a cable way and separating the movable contact (3) from the fixed contact (2), wherein a part of the open/close mechanism (A) is formed of a material containing iron or iron compound, and its sliding portion is provided with a lubricating oil formed by adding 1 to 5wt.% of molybdenum disulfide to an oxidation inhibitor-added phenyl ether oil.

Description

Background of the Invention

1. Technical Field

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

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.
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.
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.
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.
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

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.
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.
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.
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.
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.
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.
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

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

Several embodiments of the present invention are hereinafter described in detail with reference to the accompanying drawings.

Embodiment 1.

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.
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.
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.
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.
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.
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]

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.
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%.
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]

The Alkyldiphenylether oil is mainly composed of either dialkyldiphenylether or monoalkyldiphenylether, and has a viscosity of 80 to 150mm2/s (40° C).

[Additives]

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.
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.
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.

Embodiment 2 of the invention is hereinafter described.
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]

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.
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]

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]

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.
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:

The embodiments of the invention are now described in further details in the form of following examples.

Example 1.

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]

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.

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)

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)

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

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)

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)

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)

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)

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.
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]

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.
Now test results of respective samples are described.

Lubricating oils

(Alpha-olefin lubricating oil)

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)

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.

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.
The foregoing results lead to the following assumptions.
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.
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.
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)

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)

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.

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.
The foregoing results lead to the following assumptions.
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.
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.
In conclusion, it is preferable to use alkyldiphenylether as base oil and urea soap as a thickener.

Example 2.

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)

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)

Test results of acceptable load limits are shown in Fig. 5.

Lubricating oil

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

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.
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

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.

Claims

A circuit breaker comprising: an insulating case (1); a switching mechanism (A) that is accommodated in said insulating case (1) and connects and disconnects a movable contact (3) to and from a fixed contact (2); and a trip mechanism (C) provided with an engaging section (B) for engaging with said switching mechanism (A), and disengaging said engaging section (B) upon detecting any excess current on any electric pathway in the circuit so that said movable contact (3) is separated from said fixed contact (2); in which a part of said switching mechanism (A) consists of a material containing iron or iron compound;
characterized in that
sliding portion of said material containing iron or iron compound is provided with a phenylether lubricating oil to which an antioxidant and molybdenum disulfide are added.
The circuit breaker according to claim 1, characterized in that the sliding portion consisting of a material containing iron or iron compound is provided with Fe₃O₄ film or plated film.
The circuit breaker according to claim 1 or 2, characterized in that 1.0 to 5.0 wt % molybdenum disulfides are contained.
The circuit breaker according to claim 1 or 2, characterized in that the engaging portion located between a latch section (12) and an urging section is provided with phenylether lubricating oil.