JP2016070367A - Heat resistant sintered oil impregnated bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a high temperature heat resistance characteristic, in particular, of sintered oil bearing.SOLUTION: A sintered bearing of this invention is immersed with straight chain type perfluoropolyether lubricant having no repeated structure of CFO of chemical formula. No evaporation of lubricant occurs also under a high temperature environment exceeding at least 180°C, a decomposition of fluorine lubricant under an action of Lewis acid catalyst is prohibited, corrosion of sliding surface of the sliding member under occurrence of hydrogen fluoride can be restricted and occurrence of abnormal wearing at the sliding surface can be restricted. In addition, usage of material with a kinematic viscosity 10 mm/s to 500 mm/s can be sufficiently immersed into the sintered bearing, resulting in that no occurrence of lack of amount of oil is attained and a sufficient performance can be realized as the oil bearing.SELECTED DRAWING: Figure 2

Description

  The present invention uses a perfluoropolyether (PFPE) lubricating oil that is difficult to decompose even at ultra-high temperatures by impregnating the sintered bearing material of a motor, thereby significantly increasing the high-temperature heat resistance of the bearing, and Lewis acid. The present invention relates to a sintered oil-impregnated bearing in which corrosion wear due to catalytic activity is remarkably reduced and durability is improved.

  In recent years, there has been a demand for small motors used in high-temperature environments such as around the engine of automobiles and ships, in EGR (Exhaust Gas Recirculation) and ETC (Electronic Throttle Control) systems, etc. It has increased. As the lubricant used by impregnating the sintered bearing of such a motor, even a conventional hydrocarbon lubricant can be used up to an environmental temperature of about 120 ° C. When a general-purpose lubricant based on hydrogen is used, there is a risk that the lubricant will deficit due to evaporation (oil shortage) or the lubricant will solidify due to oxidation / polymerization, resulting in a decrease in motor durability.

Therefore, in such a small motor, a fluorine-based lubricating oil such as perfluoropolyether (PFPE), which is relatively excellent in heat resistance compared to the general-purpose lubricant, is often used as a lubricant. (See Patent Document 1 and Patent Document 2).
In this case, in particular, “fomblin M series (trade name)” (manufactured by Solvay Specialty Polymers / hereinafter simply referred to as “fomblin”) having a linear structure is known as perfluoropolyether. This “fomblin M series” has a high viscosity index and is difficult to evaporate if it has a certain degree of viscosity. Therefore, the “fomblin M series” is often used in motors arranged in a relatively high temperature environment.

However, even the fluorine-based lubricating oils such as the above-mentioned “fomblin M series” have a limit of about 180 ° C. in heat resistance, and contact with the Lewis acid catalyst in an ultra-high temperature environment exceeding 180 ° C. Then, it has the property of causing rapid decomposition by the action and evaporating while generating hydrogen fluoride.
Therefore, when a fluorine-based lubricating oil is used as a lubricant for a sliding member made of a material containing a substance having a Lewis acid catalytic ability such as iron or other metals or graphite as a main component, a high temperature as described above. Under the environment, due to the high heat generated on the sliding surface of the inner periphery of the sintered bearing, the fluorine-based lubricating oil is rapidly decomposed by the action of a substance having a Lewis acid catalytic activity, and hydrogen fluoride is generated. The moving surface may rapidly corrode and the sliding surface may be abnormally worn.

For this reason, in sintered bearings in which fluorine-based lubricating oil is used as a lubricant, it has been attempted to limit the material to a material having a relatively low Lewis acid catalytic ability such as bronze. Sintered bearings made only of relatively low materials have low wear resistance and may cause abnormal wear depending on the conditions of use, especially when motors are used around the engine of automobiles and ships. It has been confirmed that tapping wear due to vibration is severe and is not sufficient in terms of durability. In addition, when the motor operating environment temperature exceeds 120 ° C, the viscosity of the lubricating oil is remarkably lowered, making it difficult to obtain sufficient lubricity. Therefore, a solid lubricant such as graphite can be included in the bearing material. It is desirable to assist lubrication.
Therefore, for example, a sintered bearing for a motor used around an engine of a car or a ship includes a material having Lewis acid catalytic ability such as iron or graphite in order to be able to sufficiently withstand an impact caused by vibration. Inevitable.

  Therefore, it is a sliding member such as a sintered bearing comprising a metal and using a fluorine-based lubricating oil as a lubricant, and includes a nitride formed by subjecting the metal to nitriding treatment. In a sliding member in which a fluorinated lubricant is used as an agent, the technology has already been described in which the fluorinated lubricant is prevented from being decomposed by the action of a metal having a Lewis acid catalytic activity contained in the material of the sliding member. Patent applications have been filed by the present inventors.

  On the other hand, the side chain structure such as “Fomblin Y”, “Fomblin W”, or “Crytox” (registered trademark of DUPONT) is still more expensive than general lubricating oil, but it is a fluorine-based oil. Among them, since they are relatively inexpensive and excellent in corrosion resistance, those having a higher viscosity are often used because only heat resistance is required. However, it is completely unsuitable for use in motor bearings that can withstand a wide range of applications from -40 ° C to 180 ° C, such as automobiles. The side chain structure has a low viscosity index, so the viscosity increases significantly as the temperature decreases. As a result, the rotational torque increases greatly, and conversely, when a material with a viscosity adjusted to a low temperature is used, it is not suitable for oil-impregnated bearings corresponding to various environmental temperature changes in that it tends to evaporate due to temperature rise. I know that there is.

Under such circumstances, as a lubricant for oil-impregnated bearings recently,
(A) General formula
RfO (CF ₂ CF ₂ O) m (CF ₂ O) nRf
(Wherein Rf is a perfluoro lower alkyl group having 1 to 5 carbon atoms, m + n = 3 to 200, m: n = 10 to 90:90 to 10, and a CF ₂ CF ₂ O group and a CF ₂ O group) A perfluoropolyether oil represented by the following groups, which are randomly bonded in the main chain:
(B) General formula
RFO [CF (CF ₃ ) CF ₂ O] p (CF ₂ CF ₂ O) q (CF ₂ O) rRf
(Where Rf is a perfluoro lower alkyl group having 1 to 5 carbon atoms, p + q + r = 3 to 200, q and r can be 0, (q + r) / p = 0 to 2 and CF (CF ₃ ) CF ₂ O group, CF ₂ CF ₂ O group and CF ₂ O group are randomly bonded in the main chain) and (C) general formula
F (CF ₂ CF ₂ CF ₂ O) sC ₂ F ₅
(Where s = 2 to 100) represented by a base oil comprising at least one perfluoropolyether oil,
General formula
RCONHR ₁ NR ₃ R ₄
Where R: RfO [CF (CF ₃ ) CF ₂ O] aCF (CF ₃ )-, RfO (CF ₂ CF ₂ CF ₂ O) aCF ₂ CF _2- , RfO [(CF ₂ CF ₂ O] a ( CF ₂ O) b] CF ₂ -or RfO [(CF ₂ CF ₂ O) a (CF ₂ O) b] CF (CF ₃ )-, where Rf is a perfluoro lower alkyl group having 1 to 5 carbon atoms. Yes, a and b are integers from 1 to 30
R ₁ is an alkylene group having 1 to 30 carbon atoms, and part or all of the hydrogen atoms of the alkylene group may be substituted with a halogen atom.
R ₃ , R ₄ : Invention of an oil-impregnated bearing lubricant composition obtained by adding and mixing an amide compound having a perfluoropolyether group represented by a hydrogen atom or an alkyl group having 1 to 3 carbon atoms is disclosed as a patent publication (Patent Document 3).

Japanese Patent No. 3918520 Japanese Patent Laid-Open No. 5-240251 Japanese Patent No. 4779343

  Recently, the environmental temperature range of motors has diversified, and there is a tendency for the demand in ultra-high temperature atmospheres exceeding 120 ° C to increase. It has increased. In such a case, obtaining a sintered oil-impregnated bearing for a motor that can withstand these high-temperature environments can be said to be a difficult task. In general, PFPE is expensive, and if the viscosity is low, the amount of evaporation tends to increase and the amount of oil tends to be insufficient. On the other hand, in the case of a high viscosity, PFPE generally has a high specific gravity and fluid resistance. As mentioned above, there is a problem that becomes large and unsuitable for high-speed rotation. Especially, the side chain type is excellent in wear resistance, but it is sintered because the applicable temperature range is limited. It is not very suitable for oil-impregnated bearings. On the other hand, since the linear type as described in Patent Document 3 described above has little change in viscosity due to temperature change, it can be said that it is suitable as oil for sintered oil-impregnated bearings.

  In addition, PFPE generally has low wear resistance. Therefore, when iron-based or carbon-containing bearing materials are used for the purpose of complementing this point, linear fomblin or a lubricating oil containing the same has a Lewis acid catalytic ability. There is also a difficult problem that hydrofluoric acid is decomposed by the action of a substance having a susceptibility, which easily leads to corrosion of the bearing. Therefore, the applicant has already filed a separate patent application to solve these problems by nitriding the bearing material itself to prevent decomposition of the fluorine oil.

Furthermore, in addition to the above, the present applicant has made various studies to improve the heat resistance and wear resistance of the sintered oil-impregnated bearing. As a method for preventing PFPE oil decomposition in the sintered oil-impregnated bearing, As a result of studying the use of a type of lubricating oil impregnated in the bearing that is not easily decomposed even in a high-temperature atmosphere exceeding 180 ° C. in a sintered bearing, this has been completed.
Specifically, the present invention relates to a heat-resistant sintered oil-impregnated bearing impregnated with linear perfluoropolyether (PFPE) oil having no molecular structure peculiar to fomblin.

The use of PFPE oil for oil-impregnated bearings has already been described in Patent Document 3 (Japanese Patent No. 4793443). This uses a linear fomblin, and its purpose is to improve wear resistance and low friction characteristics. However, the molecular structure shows that there are many oxygen molecules and C and O are combined one by one. Therefore, in the part where CF ₂ O continues at random, the connecting part of OCO is not covered with fluorine atoms. Will be exposed. When the exposed part of the OCO is exposed to a metal fluoride attack at a high temperature exceeding 180 ° C, it is decomposed by its catalytic action, resulting in the production of COF groups, which react with moisture to generate hydrogen fluoride. I understood.

Hydrogen fluoride has a serious weakness in that it dissolves in water to form hydrofluoric acid, which causes corrosion of the metal. The corroded metal becomes a metal fluoride, and the metal fluoride has a strong Lewis acid catalysis, so that the reaction is explosively accelerated by a chain reaction. However, since metal fluoride has the function of a solid lubricant, seizure is unlikely to occur even when the wear has progressed remarkably. It can hardly be used for sintered oil-impregnated bearings that add carbon and expect high wear resistance in addition to high temperature heat resistance.

As can be understood from the above, among PFPE oils excellent in wear resistance and low friction properties, those having different molecular structures, that is, types that are not easily decomposed even in a high temperature atmosphere exceeding 180 ° C., that is, oxygen in the molecule In addition to wear resistance and low friction characteristics, impregnated sintered bearing material with linear perfluoropolyether lubricating oil with low content and no repeating structure composed of a set of CF ₂ and O In particular, a sintered oil-impregnated bearing for a motor that is excellent in heat resistance and can cope with a wide temperature range from an extremely low temperature of −40 ° C. to at least 180 ° C. or higher can be obtained.

Regarding the kinematic viscosity, it is most practical and preferable that the kinematic viscosity at 40 ° C. of the lubricating oil used in the sintered oil-impregnated bearing is in the range of 10 mm ² / s to 500 mm ² / s. Further, regarding the material of the sintered bearing used in the present invention, at least one of bronze, iron, and graphite is used from the viewpoint of improving wear resistance due to the characteristics of the lubricant described above, and zinc is optionally used. Any conventionally used oil-impregnated bearing material such as nickel or nickel can be used.

According to the sintered oil-impregnated bearing according to the present invention, by impregnating the sintered bearing material with a linear perfluoropolyether lubricant having no CF ₂ O repeating structure, in addition to wear resistance and low friction characteristics, In particular, it is possible to obtain a sintered oil-impregnated bearing for a motor that is excellent in heat resistance in an ultra-high temperature environment of 180 ° C. or higher and can cope with a wide temperature range. Also the above linear impregnated sintered oil-impregnated bearing kinematic viscosity of the perfluoropolyether lubricating oil to 10mm ² / s~500mm ² / when s is in the range of lubricating oil sintered in the bearing It is easy to impregnate, consumes less lubricating oil, has the best heat resistance, and has the highest practicality by improving the durability of the sintered bearing.

Basic chemical structural formula of a linear perfluoropolyether (PFPE) lubricating oil that has a low oxygen content in the molecule and does not have a CF ₂ O repeating structure used in the examples of the present invention . The table | surface showing the various test results of the sintered oil-impregnated bearing which concerns on the Example of this invention in high temperature, and Comparative Examples 1-3. The graph which represented the bearing outer-diameter expansion | variation change amount of the sintered oil-impregnated bearing which concerns on the Example of this invention and Comparative Examples 1-3 under high temperature.

Hereinafter, embodiments of the heat-resistant sintered oil-impregnated bearing according to the present invention will be described.
The heat-resistant sintered oil-impregnated bearing according to the present invention uses a special lubricating oil among the thermally and chemically stable fluorine-based lubricating oils as a lubricant, and in particular, special high temperature / low temperature / low pressure / chemical solvent atmosphere. The present invention relates to a sintered oil-impregnated bearing for a motor that operates in a rough environment (particularly, a sintered metal bearing having high heat resistance). The sintered oil-impregnated bearing according to the present invention has wear resistance, and is particularly suitable for application to a sintered oil-impregnated bearing forming a small motor used in an ultrahigh temperature environment exceeding 180 ° C. In the following description, an embodiment of a sintered oil-impregnated bearing manufactured by powder metallurgy is described.

(Configuration of sintered oil-impregnated bearing)
First, the structure of the sintered oil-impregnated bearing for motors according to this embodiment will be described.
The sintered oil-impregnated bearing according to the present embodiment forms a compact by compressing a raw material powder such as metal powder or graphite containing components such as copper, iron, tin, zinc and nickel in a mold. A sintered compact is formed by sintering a compact in a predetermined condition, and this sintered compact is subjected to sizing (recompression), washing, etc., and then impregnated with a lubricant (fluorinated lubricant). It is formed. In particular, the sintered bearing according to the present embodiment is impregnated with a special lubricating oil in its composition. Note that the sintered oil-impregnated bearing of the present invention is preferably an inner diameter relief bearing. The inner diameter relief type bearing is formed at each end in the axial direction, and is formed between a bearing portion that rotatably supports the rotating shaft and both end bearing portions of the bearing, and the inner diameter is between the bearing portions at both ends. This refers to a sintered oil-impregnated bearing in which a middle relief portion formed larger than the inner diameter is integrally formed (see JP-A-2-8302).

As the raw material powder of the sintered bearing material, for example, an iron-based material containing iron as a main component or a bronze-based material containing bronze can be used as a material for a sintered bearing. . In particular, small motors used in the vicinity of engines of automobiles and ships have characteristics as materials with high wear resistance such as iron and solid lubricants such as graphite so that they can sufficiently withstand tapping and abrasion due to vibration. It is essential to use the materials they have alone or in combination. In this embodiment, the raw material powder is a mixture of iron, bronze, and graphite, which could not be used at high temperatures exceeding 180 ° C. in the past.
Here, in the case where graphite is included in the raw material powder, if the graphite content is excessive, the strength of the sintered bearing may be reduced. Therefore, in order to enhance the lubrication effect while maintaining sufficient strength, the content of the material graphite in the sintered bearing is in the range of 0.1 to 10% by weight, preferably in the range of 0.5 to 5% by weight. It is preferable to set within.

  In the sintered bearing according to the present embodiment, the perfluoropolyether (perfluoropolyether) is used for the lubricant to be impregnated so that the sintered bearing has high strength and wear resistance and can exhibit sufficient heat resistance even in an extremely high temperature environment. Among the PFPE), a lubricant capable of maintaining stability and durability without bearing seizure and abnormal wear over a long period of time without causing oil shortage due to evaporation even in an ultra-high temperature environment exceeding 180 ° C. It is used by impregnating the bearing material.

  Examples of the perfluoropolyether (PFPE) include the “fomblin Y series” already described as the side chain type fluorine oil, “Crytox (trade name)” manufactured by DuPont, and “Varielta” (manufactured by NOK Kluber). Product name) ". In addition, as the linear fluorine oil, the “fomblin M series” described above, the “fomblin Y series” which is a side chain type fluorine oil, “Crytox” which is a side chain type fluorine oil manufactured by DuPont, and NOK Clew There are various types such as “Varielta” which is a side chain type fluorinated oil manufactured by Bar Inc. Among them, “Fomblin M Series” is relatively excellent in thermal stability, evaporation characteristics and chemical stability. In addition, it is somewhat advantageous in that it has a high viscosity index, a good yield in the manufacturing process, and a stable supply, but according to our research results, in a high temperature environment exceeding 180 ° C. It has been found that the durability as a motor bearing is not sufficient in terms of long-term durability.

In our research process, general PFPE such as Fomblin has many oxygen atoms in its molecular structure, and there are many structures in which one C and one O are combined. In the part where CF ₂ O continues at random, the OCO connection part is not covered with fluorine atoms and the surface is exposed, and the exposed OCO connection part is subjected to the attack of metal fluoride under high temperature and the catalyst Decomposes by action, resulting in the production of COF groups, which react with moisture to generate hydrogen fluoride. Further, hydrogen fluoride has a serious weak point that it dissolves in moisture to produce hydrofluoric acid, which causes corrosion of the metal. Furthermore, the corroded metal becomes a metal fluoride, and the reaction is explosively accelerated by a chain reaction caused by an increase in the catalyst.

Therefore, in the present invention, among PFPE oils excellent in wear resistance and low friction coefficient characteristics, they have different molecular structures, that is, types that are difficult to be decomposed even at high temperatures exceeding 180 ° C., that is, linear chains other than fomblin. Clarified that the use of a type of lubricant is preferred. According to our research, specifically, high temperature is obtained by impregnating sintered bearing material with linear perfluoropolyether lubricant which has low oxygen content in the molecule and does not have CF ₂ O repeating structure. In addition to wear resistance and low friction properties, it has excellent heat resistance and can be used in a wide range of temperatures from -40 ° C to over 180 ° C. The oil-impregnated bearing has been developed.

Specifically, the sintered bearing is impregnated with a linear perfluoropolyether lubricating oil having no CF ₂ O repeating structure. An example of such a linear perfluoropolyether lubricating oil is “DEMNUM (trade name)” which is a linear fluorine oil manufactured by Daikin Industries, Ltd., for example. Since these hard-to-decompose oils have a molecular structure that does not easily decompose even in an ultra-high temperature environment exceeding 180 ° C, use materials with excellent heat resistance and wear resistance, including iron and carbon, as sintered bearing materials. Can do. However, it is not preferable to use fomblin as impregnating oil in this case because the fomblin decomposes first in a high temperature atmosphere during use of the motor and corrodes the sintered bearing surface.

Regarding the kinematic viscosity of the linear perfluoropolyether lubricating oil described above, the low viscosity PFPE having a kinematic viscosity at 40 ° C. of less than 10 mm ² / s causes the evaporation from the bearing because the molecular weight is small. It became clear that the use of fluorine oil to increase heat resistance and the use of fluorine oil disappeared, and it could not be used in a high temperature environment exceeding 120 ° C. In addition, when the sintered bearing is impregnated with lubricating oil, the sintered bearing is immersed in the oil and decompressed to 10 Torr or less to extract air in the holes, and then returned to normal pressure to return to the inside of the holes. In general, when the lubricating oil has a high kinematic viscosity at 40 ° C exceeding 500 mm ² / s, sintering is performed despite the above-described extraction of air by decompression. It is difficult to sufficiently impregnate the bearing, and the amount of oil becomes insufficient, so that the oil-impregnated bearing cannot exhibit sufficient performance.

In particular, when used in a small motor, the specific gravity of fluorine oil is originally large, so if the viscosity is too high, loss will increase and energy efficiency will deteriorate. Furthermore, for example, in a low temperature atmosphere of minus 40 ° C., it was found that the oil becomes too hard and the impregnated oil does not easily come out from the inside of the sintered bearing to the sliding surface, which may cause trouble due to lack of lubricating oil. Therefore, it was clarified that the range of 10 mm ² / s to 500 mm ² / s is appropriate for the kinematic viscosity of the linear perfluoropolyether lubricating oil impregnated in the sintered bearing.

(Operation / effect of sliding member)
Next, the operation and effect of the sintered bearing according to this embodiment will be described.
As described above, in a sintered oil-impregnated bearing used in a high temperature environment exceeding 120 ° C., when a lubricant based on a general-purpose hydrocarbon is used as a lubricant, a lubricant shortage due to evaporation (oil amount) Insufficient) or solidification of the lubricant due to oxidation / polymerization may occur, and seizure or abnormal wear may occur on the inner peripheral sliding surface of the bearing.
In contrast, fluorine-based lubricants such as perfluoropolyethers are superior in thermal stability, evaporation characteristics, chemical stability, etc. compared to the above-mentioned general-purpose lubricants. Evaporation and solidification (oxidation / polymerization) are unlikely to occur even when exposed to, and seizure and abnormal wear on the sliding surface of the sintered oil-impregnated bearing can be suppressed. And a fluorine-type lubricant coat | covers a bearing inner peripheral surface by couple | bonding firmly with the metal surface through the functional group couple | bonded with a metal, and improves the lubricity in a bearing sliding surface.

However, as for the lubricating oil impregnated in the sintered bearing, even the fluorine-based PFPE as described in Patent Documents 1 to 3 described above, the action of a strong Lewis acid catalyst in an ultrahigh temperature environment exceeding 180 ° C. It has the property of rapidly evaporating and evaporating while generating hydrogen fluoride. Therefore, when fluorine-based lubricating oil is used as a lubricant for sintered bearings made of materials containing Lewis acid-catalyzing substances such as iron and other metals and graphite, it occurs on the inner peripheral sliding surface. Due to the high heat, the fluorine-based lubricating oil reacts with a substance having Lewis acid catalytic ability and evaporates while generating hydrogen fluoride. As a result, the sliding surface of the sintered oil-impregnated bearing rapidly corrodes, Abnormal wear of the sliding surface may occur.

On the other hand, in the sintered bearing according to the present embodiment, at least 200 is obtained by impregnating the sintered bearing member with a lubricating oil that can sufficiently withstand an ultra-high temperature exceeding 180 ° C. among PFPE. It is possible to exhibit high performance that can sufficiently withstand even in a high temperature environment of about ° C. In other words, the sintered bearing is impregnated with a linear perfluoropolyether lubricating oil that is difficult to decompose even at high temperatures exceeding 180 ° C, that is, with a low oxygen content in the molecule and no CF ₂ O repeating structure. This can be realized. Moreover, since the lubricating oil to be impregnated has hard-to-decompose characteristics at ultra-high temperatures, it is necessary to maintain high wear resistance and lubricity by mixing materials such as iron or graphite in the components of sintered bearing materials. Can do.

As described above, in the sintered bearing according to the present embodiment, the sintered bearing is impregnated with a linear perfluoropolyether lubricating oil that has a low oxygen content in the molecule and does not have a CF ₂ O repeating structure. As a result, decomposition under Lewis acid catalysis can be suppressed even in an ultra-high temperature environment exceeding 180 ° C., and there is no problem even if iron-based or graphite is used as a main component of the sintered material. Therefore, it is possible to suppress the occurrence of abnormal wear of the bearing inner peripheral sliding surface.
In addition, in the sintered bearing according to the present embodiment, as a result of suppressing the action of the Lewis acid catalyst, a material having high wear resistance such as iron so that it can sufficiently withstand tapping wear due to vibration (on the other hand, high Lewis A material having acid catalytic ability) and a substance having characteristics as a solid lubricant such as graphite (on the other hand, a substance having high Lewis acid catalytic ability) can be included in the material, and the wear resistance of the sintered bearing Can be improved.

Furthermore, it is a material powder for conventional general sintered bearings. If a material mainly composed of bronze is used as a material having higher corrosion resistance than iron, the corrosion itself remains only on the surface, but as described above, the temperature is high. If the product is used in a harsh environment such as a high load, the wear of the sliding surface will proceed due to insufficient strength and slidability, and it will be corroded again when it becomes a new surface. However, the sintered bearing of the present invention has a low oxygen content in the molecule and does not have a CF ₂ O repeating structure. The impregnation of the polyether lubricant into the sintered bearing can suppress the decomposition by the Lewis acid catalyst, and therefore, various types of motors can be used regardless of the type of metal, not only copper. It is possible to use a fee. In particular, when at least one of iron and graphite is used in combination, the strength as a bearing is increased, or the wear resistance can be improved by improving the slidability.
As described above, according to the sintered bearing according to the present embodiment, decomposition due to the action of the Lewis acid catalyst can be suppressed even when the motor is used in an ultra-high temperature atmosphere exceeding 180 ° C., and remarkable heat resistance is maintained. And the durability of the bearing can be improved.

Next, examples of the present invention will be described.
(Bearing configuration)
As an example of the present invention, a mixed powder of iron, bronze, and graphite is used as a raw material powder for a sintered bearing material, and this raw material powder is compression-molded in a mold to form a powder body. And sizing. Each sintered bearing is formed by the powder metallurgy method described in the above embodiment. As shown in FIG. 1, the molded sintered bearing is a linear perfluoropolyether (PFPE) lubricating oil having a low oxygen content in the molecule and not having a CF ₂ O repeating structure by a normal filling method. A lubricating oil (demnum) represented by the chemical formula (structural formula) shown was impregnated.

The above-mentioned linear perfluoropolyether (PFPE) lubricating oil having a low oxygen content in the molecule and not having a CF ₂ O repeating structure has a low vapor pressure, so that it is long in a high temperature environment of 120 ° C. or higher. Even after use over a period of time, the evaporation loss of the lubricating oil is very small. It is nonflammable and stable to oxygen, and has little viscosity change due to temperature. From our experimental results, it is good in a wide range from a very low temperature of about -60 ° C to an ultrahigh temperature of at least 200 ° C. It can exhibit lubricating properties and has a very small surface tension, so it can be impregnated by impregnating and sucking even a very narrow gap like a compacted sintered bearing. I found it to be the best.

(Test method)
As summarized in the table of FIG. 2, in the examples of the present invention, iron: 35 to 45% (weight%, the same applies hereinafter), tin: 2 to 7%, graphite: 1 to 3%, and the balance copper. This was impregnated with demnum S-65 as a lubricant. On the other hand, in Comparative Example 1, the sintered bearing material was 8 to 11% tin and the balance was copper, and this was impregnated with fomblin. In Comparative Example 2, iron: 35-45%, tin: 2-7%, graphite: 1-3%, balance: copper, and impregnated with fomblin as a lubricant. Furthermore, in Comparative Example 3, the sintered bearing material was tin: 8 to 11% and the balance: copper, and this was impregnated with demnum S-65 as a lubricant.

[Test 1] Heat resistance test In the heat resistance test, the specimens of the respective sintered oil-impregnated bearings (Examples, Comparative Examples 1, 2, and 3) were left in a high temperature environment of 200 ° C. for 2,000 hours. The change was measured by comparing the subsequent outer diameter with the outer diameter before the test to determine the coefficient of expansion.
[Test 2] High-temperature wear resistance test In the high-temperature wear resistance test, test pieces of each sintered oil-impregnated bearing (Example, Comparative Examples 1, 2, and 3) Specimen dimensions: Inner diameter φ6 x Outer diameter φ12 x Length 4 mm
Shaft specifications: Material S45C, dimension φ6 x length 80mm, clearance 20μm
Shaft speed: 3,000rpm
Bearing side pressure load: 49N
Bearing inner surface pressure: 2.2MPa
A shaft rotation test was conducted in a high temperature environment of 200 ° C. with a lateral pressure applied to the bearing test piece.
The degree of wear resistance was determined by using the roundness of the inner diameter of the bearing after 24 hours from the start of the test as an indicator of the depth of wear.

(Test results)
As shown in the table of FIG. 2, according to the results of various tests performed on each bearing test piece, in Comparative Example 1, Test 1 (heat resistance) is ○ (good), but Test 2 (wear resistance) The result was Δ (insufficient). Although significant corrosion does not occur when left at high temperatures, it has been found in the wear resistance test that wear proceeds due to insufficient material strength.
In Comparative Example 2, Test 1 (heat resistance) and Test 2 (wear resistance) were x (defect). Since the impregnated oil decomposes only by leaving it at high temperature, the bearing material is corroded, and the original model cannot be retained. The same reason is considered to be the reason why the wear resistance at high temperatures is greatly inferior.

In Comparative Example 3, Test 1 (heat resistance) was ○ (good), but Test 2 (wear resistance) was Δ (insufficient). In this case, as in Comparative Example 1, the corrosion does not proceed when left at a high temperature. However, in the wear resistance, the wear proceeds due to insufficient strength of the material, but the wear amount is smaller than that of Comparative Example 1 due to the resistance to decomposition.
On the other hand, in the examples of the present invention, both test 1 (heat resistance) and test 2 (wear resistance) were ○ (good), and it was confirmed that both heat resistance and wear resistance at 200 ° C. were good.
In the examples of the present invention, the kinematic viscosity of the linear perfluoropolyether lubricating oil impregnated in the sintered bearing was in the range of 10 mm ² / s to 500 mm ² / s.

  Moreover, the result of having observed the heat resistance test in the Example of this invention mentioned above and the test 1 (heat resistance) of Comparative Examples 1-3 for every elapsed time, and having measured the bearing outer-diameter expansion coefficient is shown in FIG. (In FIG. 3, the present embodiment and comparative example 3 are represented by substantially the same locus). The sintered oil-impregnated bearing according to the example of the present invention has sufficient high-temperature heat resistance, and Comparative Examples 1 and 3 also have heat resistance substantially similar to this, but the sintered oil-impregnated bearing of Comparative Example 2 The expansion of the outer diameter becomes severe from around 500 hours.

As described above, it can be seen that in the sintered oil-impregnated bearing according to this example, the decomposition of the fluorine-based lubricating oil is greatly suppressed as compared with the sintered oil-impregnated bearings according to Comparative Examples 1 and 2. It can also be seen that the wear resistance is greatly improved because the strength and lubricity are improved as compared with the sintered oil-impregnated bearing according to Comparative Example 3. In particular, in the sintered oil-impregnated bearing according to the present embodiment, since the impregnated lubricating oil does not have a CF ₂ O repeating structure, there is no OCO connecting portion, and therefore no CO bond is exposed on the bearing surface. Therefore, it can be seen that even when the motor is used in an ultra-high temperature atmosphere exceeding 180 ° C., the decomposition due to the action of the Lewis acid catalyst is suppressed.

Claims (4)

A sintered oil-impregnated bearing impregnated with a linear perfluoropolyether lubricating oil that has a chemical formula and does not have a CF ₂ O repeating structure. The sintered oil-impregnated bearing according to claim 1, wherein the kinematic viscosity at 40 ° C of the lubricating oil is in the range of 10 mm ² / s to 500 mm ² / s.   The sintered oil-impregnated bearing according to claim 1 or 2, wherein the sintered bearing material contains iron and / or graphite. The sintered oil-impregnated bearing according to any one of claims 1 to 3, wherein graphite is contained in the sintered bearing material in a range of 0.1 to 10% by weight.

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