Patent Application
20190276763
The present disclosure relates to a grease composition and a rolling bearing, and particularly to a grease composition realizing excellent acoustic characteristics not only under a high temperature and high speed environment but also under a high load environment, and a rolling bearing suitable for a small motor.
As a rolling bearing used for small motors such as a fan motor and a high speed motor used for automobiles, there is for example, so-called small diameter ball bearing having an outer diameter of 22 mm or less. Since such a small diameter ball bearing is required to have durability under a high temperature environment, a fluorine-based grease excellent in heat resistance and oxidation resistance, a hybrid grease of a fluorine-based grease and a urea-based grease excellent in heat resistance, and the like are conventionally used as lubricants.
For example, Patent Document 1 discloses a rolling bearing filled with a grease containing fluororesin particles as a thickener, a specific aspartic acid ester-based rust inhibitor and an oiliness agent in a fluorine-based base oil (perfluoropolyether oil), in order to realize high temperature durability and low temperature torque property.
In addition, a grease composition containing a perfluoropolyether base oil and a specific carboxylic acid metal salt as a thickener is proposed, which can improve wear resistance with respect to counterpart materials, leakage resistance, washability and the like while taking the cost into consideration (Patent Document 2).
Although the above fluorine-based grease, particularly a fluorine-based grease using perfluoropolyether as a base oil, is excellent in heat resistance, it is known that when the fluorine-based grease is used under a high load or an overload condition due to mis-assembly, the fluorine oil (perfluoropolyether) which is a base oil decomposes to generate hydrofluoric acid, whereby corrosion on a metal surface such as a raceway surface of the bearing is caused. The metal corrosion on the raceway surface may become a cause of deterioration of acoustic characteristic and occurrence of rotation failure.
Therefore, there is a demand for a grease capable of preventing rotation failure and noise increase in rolling bearings not only under a high temperature and high speed condition but also under a high load condition.
The present disclosure has been conceived in view of such a situation, and an object of the present disclosure is to provide a grease composition capable of preventing noise increase under high temperature and high speed condition as well as under a high load condition, and also a rolling bearing excellent in heat-resistant acoustic characteristic and load-bearing acoustic characteristic by applying the grease composition of the present disclosure.
The inventors of the present application have conducted intensive studies to achieve the above object and, as a result, found that by blending in base oil specific amounts of three types of thickeners, i.e., a fluorine-based thickener, a urea-based thickener and a soap-based thickener such as a calcium complex soap thickener, a grease composition excellent in heat resistance and load resistance and capable of preventing noise increase in a high temperature and high speed test and a high load test can be obtained.
That is, one aspect according to the present disclosure relates to a grease composition, containing a fluorine-based base oil and a non-fluorine-based base oil as base oils; and a fluorine-based thickener, a urea-based thickener and at least one soap-based thickener selected from the group consisting of a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener and a sodium soap thickener as thickeners.
As a preferred embodiment according to the present disclosure, it is preferable that the urea-based thickener contains at least one of an aliphatic-aromatic urea, an alicyclic-aliphatic urea and an aliphatic urea.
It is preferable that the urea-based thickener contains a diurea compound represented by the following General Formula (1):
R1—NHCONH—R2—NHCONH—R3 (1)
(in the formula, R1 and R3 each independently represent a monovalent aliphatic hydrocarbon group, a monovalent alicyclic hydrocarbon group or a monovalent aromatic hydrocarbon group, and at least one of R1 and R3 represents a monovalent aliphatic hydrocarbon group or a monovalent alicyclic hydrocarbon group, and
R2 represents a divalent aromatic hydrocarbon group).
It is preferable that the grease composition contains 70 mass % to 90 mass % of a total amount of the fluorine-based base oil and the non-fluorine-based base oil, 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium complex soap thickener, based on a total amount (100 mass %) of the grease composition. It is further preferable that the calcium complex soap thickener is a calcium complex soap of an aliphatic dicarboxylic acid and a monoamide monocarboxylic acid.
Alternatively, it is preferable that the grease composition contains 70 mass % to 90 mass % of a total amount of the fluorine-based base oil and the non-fluorine-based base oil, 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium soap thickener, based on a total amount of the grease composition.
Alternatively, it is preferable that the grease composition contains 70 mass % to 90 mass % of a total amount of the fluorine-based base oil and the non-fluorine-based base oil, 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the barium soap thickener, based on a total amount of the grease composition.
Alternatively, it is preferable that the grease composition contains 70 mass % to 90 mass % of a total amount of the fluorine-based base oil and the non-fluorine-based base oil, 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the magnesium soap thickener, based on a total amount of the grease composition.
Alternatively, it is preferable that the grease composition contains 70 mass % to 90 mass % of a total amount of the fluorine-based base oil and the non-fluorine-based base oil, 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the sodium soap thickener, based on a total amount of the grease composition.
It is preferable that the non-fluorine-based base oil is one or more selected from the group consisting of a hydrocarbon-based synthetic oil, an ether-based synthetic oil, an ester-based synthetic oil, and a silicone-based synthetic oil.
The present disclosure also relates to a rolling bearing in which the grease composition is filled.
According to the present disclosure, it is possible to provide a rolling bearing having a good acoustic performance under a high temperature and a high load and excellent in heat resistance and load resistance by applying the grease composition having the above constitution to a rolling bearing.
As described above, the fluorine-based grease has a problem that fluorine oils (base oils) decompose during use under a high load and corrosion of the metal surface occurs due to generation of hydrofluoric acid, and among the fluorine oils, this problem particularly easily occurs in a grease using perfluoropolyether having a straight chain structure as a base oil.
In order to solve this problem, the inventors of the present application have investigated a preferred constitution of a grease composition having heat resistance and load resistance, and it is found that blending a hybrid grease of a fluorine-based grease and a urea-based grease which has good heat resistance, with a soap-based grease containing a soap-based thickener such as a calcium complex soap thickener, as a thickener, can lead to solution against corrosion on the raceway surface in a high load condition.
Then, the inventors of the present application first compared and examined the influence of the changes in the blending amounts of the urea-based grease and the calcium complex soap grease on the heat resistance and load resistance of a mixed grease by changing their blending amounts while maintaining constant the blending amount of the fluorine-based grease to eliminate the influence of the fluorine-based grease in the mixed grease of the three types of greases (the fluorine-based grease, the urea-based grease, and the calcium complex soap grease as an example of the soap-based grease). In the present disclosure, a bearing using the mixed grease was rotated under a high temperature and high speed condition or a high load condition, then the acoustic performance was measured using an Anderon meter, and the obtained Anderon value was used as an indicator of heat resistance and load resistance. Therefore, as described later, in the present disclosure, a load resistance test (load resistance evaluation) means an acoustic evaluation test after rotating the bearing under a high load condition, and a heat resistance test (heat resistance evaluation) means an acoustic evaluation test after rotating the bearing under a high temperature environment.
Surprisingly, when the content of the calcium complex soap thickener was larger than a specific amount, it was confirmed that, in the load resistance test, the noise increase evaluated by the Anderon value can be prevented, and the acoustic evaluation becomes better as the content increases.
On the other hand, in the heat resistance test, the noise increase was prevented until the content of the calcium complex soap thickener reached a specific amount, but the noise increase occurred once the specific amount was exceeded.
Based on these findings, the similar evaluation was performed also for different blending amount of the fluorine-based grease, and the blending amount for obtaining good acoustic characteristic was confirmed in both the load resistance test and the heat resistance test.
Further, the similar evaluation was performed by using a calcium soap grease, a barium soap grease, a magnesium soap grease and a sodium soap grease as soap-based greases, and in these soap-based greases, a blending amount capable of obtaining good acoustic characteristics was also confirmed in both the load resistance test and the heat resistance test.
As one example,
In detail,
As shown in
On the other hand, in the heat resistance test (high temperature and high speed test: ⋄ (diamond)), although the prevention of noise increase is achieved until the content of the calcium complex soap thickener reaches a specific amount (about 3 mass % in the case of
As shown in the results of
Based on the results shown in
A grease composition to be filled in a rolling bearing according to the present disclosure (hereinafter simply referred to as “grease composition”) is characterized by combining specific thickeners as described below in detail.
First, preferred embodiments of a rolling bearing according to the present disclosure will be described in detail with reference to the accompanying drawings. The invention according to the present disclosure is not limited by the following embodiments.
The rolling bearing 10 has a basic structure similar to that of the conventional rolling bearing and includes an annular inner ring 11, an annular outer ring 12, a plurality of rolling elements 13, a cage 14, and annular sealing members 15 (15a, 15b). The inner ring 11 is a cylindrical structure to be disposed coaxially with a central axis of a shaft.
The outer ring 12 is a cylindrical structure disposed coaxially with the inner ring 11 on an outer circumferential side of the inner ring 11.
Each of the plurality of rolling elements 13 is a sphere (ball) disposed on a raceway in a bearing space (annular space) 16 formed between the inner ring 11 and the outer ring 12. That is, the rolling bearing 10 in the present embodiment is a ball bearing.
In the bearing space 16, a grease composition G is filled as a lubricant. The annular sealing members 15 (15a, 15b) are formed of, for example, a steel plate extending from an inner circumferential surface of the outer ring 12 toward the inner ring 11 side, and seal the bearing space 16 from the outside. The amount of the grease composition G filled in the bearing space 16 is, for example, 5% to 50% of the volume of the bearing space 16. An amount of about 25% to 35% is preferred in order to achieve both the torque performance and the life performance.
On the inner circumferential surface of the outer ring 12, a raceway 12a being a concave portion having an arc-shaped cross section is formed in a circumferential direction of the outer ring 12. In addition, on an outer peripheral surface of the inner ring 11, a raceway 11a being a concave portion having an arc-shaped section is formed in a circumferential direction of the inner ring 11. The plurality of rolling elements 13 are guided in the circumferential direction by the raceway 11a and the raceway 12a.
The cage 14 is disposed in the track and is configured to retain the plurality of rolling elements 13. The cage 14 is an annular member installed coaxially with the central axis of the shaft, and includes a plurality of concave portions (ball pockets) for retaining the rolling elements 13 around the central axis. The shape (such as crown shape or ribbon type) and the material (such as steel plate or resin) of the cage 14 can be selected appropriately and are not limited to specific shapes and materials. In the rolling bearing 10 having the above configuration, the grease composition G acts to reduce the friction between the rolling elements 13 and the cage 14 and the friction between the rolling elements 13 and the inner ring 11 or the outer ring 12. As can be seen from the configuration shown in
Next, the grease composition to be filled in the rolling bearing of the present disclosure will be described.
In the grease composition to be filled in the rolling bearing according to the present embodiment, a fluorine-based base oil and a non-fluorine-based base oil are used as base oils.
Examples of the fluorine-based base oil include those containing perfluoropolyether (PFPE) as a main component. PFPE is a compound represented by the general formula: RfO(CF2O)p(C2F4O)q(C3F6O)rRf (Rf: perfluoro lower alkyl group; p, q, and r: integer).
Perfluoropolyether is broadly classified into a linear perfluoropolyether and a side-chain perfluoropolyether, and the linear perfluoropolyether has a smaller temperature dependency of kinetic viscosity than the side-chain perfluoropolyether. This means that the linear perfluoropolyether has a lower viscosity than the side-chain perfluoropolyether in a low temperature environment and has a higher viscosity than the side-chain perfluoropolyether in a high temperature environment. In particular, when it is assumed to be used in a high temperature environment, from the viewpoint of preventing the leakage of the grease from the applied portion and resulting lack of the grease, it is desirable that the viscosity in a high temperature environment be high, that is, it is preferable to use a linear perfluoropolyether.
The non-fluorine-based base oil is not particularly limited, and hydrocarbon-based synthetic oils, ether-based synthetic oils such as alkyl ether oils and alkyl diphenyl ether oils, ester-based synthetic oils, and silicone-based synthetic oils, which are generally used as a grease base oil, can be used alone or in combination as the non-fluorine-based base oil.
Examples of the hydrocarbon-based synthetic oils include polyalphaolefins (PAO) such as normal paraffin, isoparaffin, polybutene, polyisobutylene, a 1-decene oligomer, a 1-decenethylene oligomer or the like.
Examples of the ester-based synthetic oils include: diester oils such as dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl phthalate, and methyl acetylcinolate; aromatic ester oils such as trioctyl trimellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate and tetra-2-ethylhexyl pyromellitate; polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate and pentaerythritol pelargonate; and carbonate ester oils.
Examples of the alkyl diphenyl ether oils include monoalkyl diphenyl, dialkyl diphenyl, polyalkyl diphenyl, or the like.
Among the above, the aromatic ester oils are preferred, and can be used alone or in combination.
The blending proportion of the fluorine-based base oil and the non-fluorine-based base oil is not particularly limited, and for example, the ratio (fluorine-based base oil: non-fluorine-based base oil) based on the total amount (100 mass %) of the base oils can be (95 mass % to 5 mass %: 5 mass % to 95 mass %), or more preferably, (95 mass % to 40 mass %: 5 mass % to 60 mass %),
In addition, the total amount of the fluorine-based base oil and the non-fluorine-based base oil in the total amount of the grease composition according to the present disclosure can be 70 mass % to 90 mass %, preferably 75 mass % to 95 mass % and more preferably 75 mass % to 85 mass %.
A fluorine-based thickener, a urea-based thickener and at least one soap-based thickener selected from the group consisting of a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener and a sodium soap thickener are added as thickeners to the grease composition according to an embodiment of the present invention.
Among these, it is preferable to contain 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium complex soap thickener, based on the total amount of the grease composition.
Alternatively, it is preferable to contain 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium soap thickener, based on the total amount of the grease composition.
Alternatively, it is preferable to contain 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the barium soap thickener, based on the total amount of the grease composition.
Alternatively, it is preferable to contain 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the magnesium soap thickener, based on the total amount of the grease composition.
Alternatively, it is preferable to contain 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the sodium soap thickener, based on the total amount of the grease composition.
It is preferable that the total amount of the fluorine-based thickener, the urea-based thickener and at least one soap-based thickener selected from the group consisting of a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener and a sodium soap thickener (the total amount of the thickeners) is 10 mass % to 30 mass %, particularly 10 mass % to 20 mass %, based on the total amount of the grease composition.
As the fluorine-based thickener, fluororesin particles are preferred, and for example, particles of polytetrafluoroethylene (PTFE) are preferably used. PTFE is a polymer of tetrafluoroethylene and is represented by the general formula: [C2F4]n (n: degree of polymerization).
Other examples of the fluorine-based thickener that can be adopted include a perfluoroethylene propylene copolymer (FEP), an ethylene tetrafluoroethylene copolymer (ETFE), and a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA).
The size of the PTFE particles is not particularly limited, and for example, polytetrafluoroethylene having an average particle size of 0.5 μm to 100 μm can be used. The shape of the PTFE particles is not particularly limited, and may be spherical, polyhedral, needle-like, or other shapes.
The fluorine-based thickener is preferably used in an amount of 9 mass % to 18 mass % based on the total amount of the grease composition.
Since the urea compound is excellent in both heat resistance and water resistance, and is particularly excellent in stability at a high temperature, it is suitably used as a thickener for the parts subjected to a high temperature environment.
A urea compound such as a diurea compound, a triurea compound, and a polyurea compound can be used as the urea-based thickener. Particularly, from the viewpoint of heat resistance and acoustic characteristic (quietness), it is preferable to use a diurea compound. The type of the urea compound preferably includes at least one of an aliphatic-aromatic urea, an alicyclic-aliphatic urea and an aliphatic urea.
Urea compounds conventionally known can be used as the above mentioned urea-based thickeners.
Among these urea compounds, the diurea compound represented by the following General Formula (1) is a urea-based thickener suitable for an embodiment according to the present invention.
R1—NHCONH—R2—NHCONH—R3 (1)
In addition, R2 represents a divalent aromatic hydrocarbon group.
Examples of the monovalent aliphatic hydrocarbon group include a linear or branched, saturated or unsaturated alkyl group having 6 to 26 carbon atoms.
Examples of the monovalent alicyclic hydrocarbon group include a cycloalkyl group having 5 to 12 carbon atoms.
In addition, examples of the aromatic hydrocarbon group include a monovalent or divalent aromatic hydrocarbon group having 6 to 20 carbon atoms.
The urea compound used as the urea-based thickener can be synthesized using an amine compound and an isocyanate compound.
Examples of the amine compound to be used here include: aliphatic amines represented by hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, oleylamine or the like; cycloaliphatic amines represented by cyclohexylamine or the like; and aromatic amines represented by aniline, p-toluidine, ethoxyphenylamine or the like.
Examples of the isocyanate compound include: aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, and diphenylmethane diisocyanate; and aliphatic diisocyanates such as octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate.
Among these, it is preferable to use an aliphatic-aromatic diurea compound obtained by using an aliphatic amine and an aromatic amine as an amine raw material and an aromatic diisocyanate to carry out the synthesis.
When an aromatic diurea compound obtained from an aromatic monoamine and an aromatic diisocyanate is used as a urea-based thickener, there is a possibility of causing a1 noise, so its use should be carefully considered.
The urea-based thickener is preferably used in an amount of 0.5 mass % to 7 mass % based on the total amount of the grease composition.
A soap-based thickener is used in an embodiment according to the present invention, in addition to the above fluorine-based thickener and urea-based thickener.
In an embodiment according to the present invention, a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener, and a sodium soap thickener can be used as the soap-based thickener.
It is preferable to use a calcium complex soap having improved heat resistance in an embodiment according to the present invention. For example, a calcium complex soap of a higher fatty acid and a lower fatty acid, a calcium complex soap containing a calcium salt of a dibasic acid and a fatty acid, or the like can be used.
Among these, it is preferable to use a calcium complex soap of an aliphatic dicarboxylic acid and a monoamide monocarboxylic acid, as the calcium complex soap thickener to be used in the grease composition according to an embodiment of the present invention.
A saturated or unsaturated dicarboxylic acid having 2 to 20 carbon atoms is used as the aliphatic dicarboxylic acid.
Examples of the saturated dicarboxylic acid include an oxalic acid, a malonic acid, a succinic acid, a methylsuccinic acid, a glutaric acid, an adipic acid, a pimelic acid, a suberic acid, an azelaic acid, a sebacic acid, a nonamethylenedicarboxylic acid, a decamethylene dicarboxylic acid, an undecane dicarboxylic acid, a dodecane dicarboxylic acid, a tridecane dicarboxylic acid, a tetradecane dicarboxylic acid, a pentadecane dicarboxylic acid, a hexadecane dicarboxylic acid, a heptadecane dicarboxylic acid, and an octadecane dicarboxylic acid. Preferably used are an adipic acid, a pimelic acid, a suberic acid, an azelaic acid, a sebacic acid, a nonamethylenedicarboxylic acid, a decamethylene dicarboxylic acid, an undecane dicarboxylic acid, a dodecane dicarboxylic acid, a tridecane dicarboxylic acid, a tetradecane dicarboxylic acid, a pentadecane dicarboxylic acid, a hexadecane dicarboxylic acid, a heptadecane dicarboxylic acid, and an octadecane dicarboxylic acid.
In addition, as the unsaturated dicarboxylic acid, for example, a maleic acid, a fumaric acid, alkenyl succinic acids such as a 2-methylene succinic acid, a 2-ethylene succinic acid, and a 2-methylene glutaric acid are used.
These saturated or unsaturated dicarboxylic acids may be used alone or in combination of two or more.
Examples of the monoamide monocarboxylic acid include those in which one carboxyl group in the aliphatic dicarboxylic acid is amidated.
At this time, examples of the amine for amidating the carboxyl group include: aliphatic primary amines such as butylamine, amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristylamine, palmitylamine, stearylamine, and behenylamine; aliphatic secondary amines such as dipropylamine, diisopropylamine, dibutylamine, diamylamine, dilaurylamine, monomethyllaurylamine, distearylamine, monomethylstearylamine, dimyristylamine, and dipalmitylamine; aliphatic unsaturated amines such as allylamine, diallylamine, oleylamine, and dioleylamine; alicyclic amines such as cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine; and aromatic amines such as aniline, methylaniline, ethylaniline, benzylamine, dibenzylamine, diphenylamine, and α-naphthylamine.
Among these, hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristylamine, palmitylamine, stearylamine, behenylamine, dibutylamine, diamylamine, monomethyllaurylamine, monomethylstearylamine, and oleylamine are preferably used.
A commercially available product can suitably be used as the calcium complex soap thickener.
In addition, a calcium complex soap, obtained by adding an aliphatic dicarboxylic acid and a monoamide monocarboxylic acid to a non-fluorine-based base oil, performing heating and stirring under a temperature at which stirring is possible, the reaction proceeds efficiently, and the base oil does not deteriorate (for example, about 80° C. to 180° C.), and adding calcium hydroxide thereto, may also be used.
The calcium complex soap thickener is preferably used in an amount of 0.3 mass % to 3 mass % based on the total amount of the grease composition.
A metal salt of an aliphatic monocarboxylic acid, that is, a calcium salt, a barium salt, a magnesium salt or a sodium salt of an aliphatic monocarboxylic acid, can be used as the calcium soap thickener, the barium soap thickener, the magnesium soap thickener and the sodium soap thickener.
The aliphatic carboxylic acid may be any of linear, branched, saturated and unsaturated, and generally fatty acids having about 2 to 30 carbon atoms, for example, 12 to 24 carbon atoms can be used. Specific example thereof include: saturated fatty acids such as a butyric acid, a caproic acid, a caprylic acid, a pelargonic acid, a capric acid, a lauric acid, a myristic acid, a palmitic acid, a stearic acid, and a behenic acid; and unsaturated fatty acids such as an oleic acid, a linoleic acid, a lysic acid, and a ricinoleic acid (ricinoleic acid).
Among these, a calcium salt, a barium salt, a magnesium salt, a sodium salt of the stearic acid, the lauric acid and the ricinoleic acid can be used as representative examples of the calcium soap thickener, the barium soap thickener, the magnesium soap thickener and the sodium soap thickener.
Commercially available products of the calcium soap thickener, the barium soap thickener, the magnesium soap thickener and the sodium soap thickener can be suitably used.
The calcium soap thickener is preferably used in an amount of 0.3 mass % to 3 mass % based on the total amount of the grease composition.
In addition, with regard to the barium soap thickener, the magnesium soap thickener and the sodium soap thickener, the barium soap thickener is preferably used in an amount of 0.6 mass % to 3.6 mass % based on the total amount of the grease composition; the magnesium soap thickener is preferably used in an amount of 0.6 mass % to 3.6 mass % based on the total amount of the grease composition; and the sodium soap thickener is preferably used in an amount of 0.6 mass % to 3.6 mass % based on the total amount of the grease composition.
In addition to the above essential components, the grease composition may contain additives usually used in the grease composition, if necessary, within a range not hindering the effects of the present invention.
Examples of the additives include an antioxidant, an extreme pressure agent, a metal deactivator, a friction inhibitor (anti-wear agent), a rust inhibitor, an oiliness improver, a viscosity index improver, and a viscosifier.
In the case of containing the other additives, the total amount of the additives is generally 0.1 mass % to 10 mass % based on the total amount of the grease composition.
Examples of the antioxidant include: hindered phenol-based antioxidants such as octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,2-thio-diethylene bis[3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], and N,N′-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide); phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-t-butylphenol); amine-based antioxidants such as triphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, and alkylated phenothiazine.
Examples of the extreme pressure agent include: phosphorus compounds such as phosphate ester, phosphite ester, and phosphate ester amine salt; sulfur compounds such as sulfides and disulfides; chlorinated compounds such as chlorinated paraffin and chlorinated diphenyl; and metal salts of a sulfur compound such as zinc dialkyldithiophosphate and molybdenum dialkyldithiocarbamate.
Examples of the metal deactivator include benzotriazole and sodium nitrite.
Examples of the anti-wear agent include tricresyl phosphate and polymer esters.
Examples of the polymer esters include esters of aliphatic monovalent carboxylic acids and divalent carboxylic acids with polyhydric alcohols. Specific examples of the polymer esters include, but are not limited to, PRIOLUBE (registered trademark) series manufactured by Croda Japan KK.
The grease composition according to an embodiment of the present invention can be obtained by mixing the above various base oils and various thickeners at a predetermined proportion and optionally adding other additives.
The grease composition may also be produced by blending three types of greases, i.e., a fluorine-based grease containing a fluorine-based base oil and a fluorine-based thickener, a urea-based grease containing a non-fluorine-based base oil and a urea-based thickener, and a soap-based grease (a calcium complex soap grease, a calcium soap grease, a barium soap grease, a magnesium soap grease, or a sodium soap grease) containing a non-fluorine-based base oil and a soap-based thickener (a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener, or a sodium soap thickener), with other additives if desired. Alternatively, the grease composition may also be produced by blending one or two of the above base greases with the remaining base oil and thickener and, if desired, other additives.
Usually, the content of the thickener based on the base grease is about 10 mass % to 30 mass %. For example, in the three types of base greases, the content of each thickener based on the respective base grease is as follows: fluorine-based thickener: 15 mass % to 30 mass %; urea-based thickener: 10 mass % to 20 mass %; and soap-based thickener (calcium complex soap thickener, calcium soap thickener, barium soap thickener, magnesium soap thickener, or sodium soap thickener): 10 mass % to 20 mass %.
The rolling bearing of the present embodiment is particularly preferably used as a rolling bearing of small motors (e.g., brushless motors and fan motors) of automobiles, household electric appliances, information equipment and the like.
The invention according to the present disclosure is not limited to the embodiments and specific examples described in this specification and various changes and modifications can be made within the scope of the technical idea described in the claims.
For example, although the rolling bearing is cited as a ball bearing in the above embodiment, the present invention is not limited to this but can be applied to other rolling bearings, for example, roller bearings.
Hereinafter, the embodiments of the invention according to the present disclosure will be described in more detail by examples. However, the present invention is not limited thereto.
Grease compositions to be used in Examples 1 to 66 and Comparative Examples 1 to 51 were prepared with the blending amounts shown in the following tables.
The details and the abbreviations of each component used for the preparation of the grease are as follows.
(a1) fluorine-based base oil: linear perfluoropolyether (PFPE)
(a2) non-fluorine-based base oil: synthetic oil 1, mixed oil of polyalphaolefin oil and ester oil
(a3) non-fluorine-based base oil: synthetic oil 2, polyalphaolefin oil
(b1) fluorine-based thickener: PTFE (polytetrafluoroethylene, particle size 10 μm to 25 μm
(b2-1) urea-based thickener: urea compound containing aliphatic-aromatic urea
(b2-2) urea-based thickener: urea compound containing alicyclic-aliphatic urea
(b2-3) urea-based thickener: urea compound containing aliphatic urea
(b3-1) Ca complex soap thickener: calcium complex soap of aliphatic dicarboxylic acid and monoamide monocarboxylic acid
(b3-2) Ca soap thickener: 12OHCa soap (calcium 12-hydroxystearate)
(b3-3) Ba soap thickener: 12OHBa soap (barium 12-hydroxystearate)
(b3-4) Mg soap thickener: 12OHMg soap (magnesium 12-hydroxystearate)
(b3-5) Na soap thickener: 12OHNa soap (sodium 12-hydroxystearate)
(b3-6) Li soap thickener: 12OHLi soap (lithium 12-hydroxystearate)
Generally, the urea-based thickeners (b2-1 to b2-3) are added in an amount of 10 mass % to 20 mass % based on the total amount of the base grease containing the urea-based thickener and the non-fluorine-based base oil: synthetic oil 1 (a2). The Ca complex soap thickener (b3-1), the Ca soap thickener (b3-2), the Ba soap thickener (b3-3), the Mg soap thickener (b3-4), the Na soap thickener (b3-5), or the Li soap thickener (b3-6) is added in an amount of 10 mass % to 20 mass % based on the total amount of the base grease containing the complex soap thickener, the Ca soap thickener, the Ba soap thickener, the Mg soap thickener, the Na soap thickener, or the Li soap thickener and the non-fluorine-based base oil: synthetic oil 2 (a3).
The other additives were added such that the total amount of the above antioxidant and extreme pressure agent was 3 mass % based on the grease composition (total mass) of Examples and Comparative Example.
With respect to the characteristics of the obtained grease composition, a heat resistance test and a load resistance test were performed using the following procedures, and the acoustic characteristics were evaluated.
The test grease composition was filled in a steel shielded ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm) at 25% to 35% of the bearing volume. The ball bearing was set in a housing and a preload of 39 N was applied to the outer ring from the axial direction. Then a shaft was inserted into the inner diameter of the bearing and the shaft was connected to a rotation shaft of a test motor, so that the inner ring of the ball bearing was arranged to be rotated.
Next, the housing was heated to 180° C., the ball bearing was rotated at a test temperature of 180° C. and a rotation speed of 21,000 rpm for 200 hours, and then subjected to an acoustic evaluation test according to the following procedures. Each test grease of examples and comparative example was tested three times to obtain the average value.
The test grease composition was filled in a steel shielded ball bearing (inner diameter 8 mm, outer diameter 22 mm, width 7 mm) at 25% to 35% of the bearing volume. The ball bearing was set in a housing and a preload of 500 N was applied to the outer ring from the axial direction. Then a shaft was inserted into the inner diameter of the bearing and the shaft was connected to a rotation shaft of a test motor, so that the inner ring of the ball bearing was arranged to be rotated.
Next, the ball bearing was rotated at room temperature at a rotation speed of 3,000 rpm for 100 hours, and then subjected to an acoustic evaluation test according to the following procedures. Each test grease of examples and comparative example was tested three times to obtain the average value.
The acoustic performance of the ball bearing using the test grease composition was evaluated by measuring the Anderon value of M band (300 Hz to 1800 Hz) using an Anderon meter.
In detail, after each ball bearing was rotated for a predetermined time following the above procedures, under the preload, temperature condition and rotation speed as described above, the speed-type pickup was brought into contact with the outer circumference of the outer ring of the ball bearing in the radial direction, the mechanical vibration transmitted to the outer ring was detected to calculate the Anderon value, and the acoustic performance in each test was evaluated based on the following criteria (maximum measurable value of Anderon value: 50). The sound in the frequency of the M band which corresponds to 300 Hz to 1800 Hz is considered an unpleasant sound for human.
In the test conditions of Examples, significant wear is observed when the Anderon value is 15 or more, so that less than 15 is evaluated as suitable.
The results are shown in Tables 1 to 9 and in
As described above,
As shown in
Similarly,
Examples 40 to 44) in which the content of the sodium soap thickener based on the total amount of the grease composition is in the range of 0 mass % to 5.4 mass % (blending amount of the sodium soap grease based on the total amount of the grease composition: 0 mass % to 36 mass %). In the graph shown in
As shown in
On the other hand,
As shown in
For the acoustic characteristic after the load resistance test, the Anderon value remains higher than 15, regardless of the content of the lithium soap thickener. In addition, for the acoustic characteristics after the heat resistance test, when the content of the lithium soap thickener is less than 0.6 mass %, the Anderon value is less than 15, but when the content of the lithium soap thickener is larger than 0.6 mass %, the Anderon value is higher than 15. Accordingly, it is confirmed that when the fluorine-based thickener and the urea-based thickener are used in combination with the lithium soap thickener, good acoustic characteristic cannot be obtained in neither the load resistance test nor the heat resistance test.
As a result of the tests, in a grease composition containing the fluorine-based thickener, the urea-based thickener and the calcium complex soap thickener in a specific proportion, that is, a grease composition containing 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium complex soap thickener based on the total amount of the grease composition as shown in Table 1, the average Anderon value is less than 15 and the acoustic performance is good in both the heat resistance test (180° C., 21,000 rpm, preload: 39 N, 200 hours rotation) and the load resistance test (room temperature, 3,000 rpm, preload: 500 N, 100 hours rotation).
Similarly, the results show that, in a grease composition containing 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass %% of the urea-based thickener, and 0.3 mass % to 3 mass % of the calcium soap thickener, based on the total amount of the grease composition, as shown in Table 2; a grease composition containing 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the barium soap thickener, based on the total amount of the grease composition, as shown in Table 3; a grease composition containing 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the magnesium soap thickener, based on the total amount of the grease composition as shown in Table 4; and a grease composition containing 9 mass % to 18 mass % of the fluorine-based thickener, 0.5 mass % to 7 mass % of the urea-based thickener, and 0.6 mass % to 3.6 mass % of the sodium soap thickener, based on the total amount of the grease composition, as shown in Table 5, the average Anderon value is less than 15 and the acoustic performance is good in any of the above heat resistance test and load resistance test.
On the other hand, as shown in Table 6, when only one type of thickener is contained (Comparative Example 1 to Comparative Example 10), the acoustic performance relating to the load resistance deteriorates when only fluorine-based thickener is contained (Comparative Example 1), and the acoustic performance relating to the heat resistance deteriorates when only urea-based thickener (Comparative Example 2 to Comparative Example 4) or only soap-based thickener (Comparative Example 5 to Comparative Example 10) is contained.
In addition, when only a fluorine-based thickener and a urea-based thickener are contained without a soap-based thickener (Comparative Example 11 to Comparative Example 13), the heat resistance is good but the acoustic performance relating to the load resistance deteriorates.
Further, when a fluorine-based thickener and a calcium complex soap thickener are contained without a urea-based thickener (Comparative Example 14 to Comparative Example 16), a fluorine-based thickener and a calcium soap thickener are contained without a urea-based thickener (Comparative Example 19 to Comparative Example 21), a fluorine-based thickener and a barium soap thickener are contained without a urea-based thickener (Comparative Example 24 and Comparative Example 25), a fluorine-based thickener and a magnesium soap thickener are contained without a urea-based thickener (Comparative Example 31 and Comparative Example 32), or a fluorine-based thickener and a sodium soap thickener are contained without a urea-based thickener (Comparative Example 38 and Comparative Example 39), the load resistance is good but the acoustic performance relating to the heat resistance deteriorates (see Table 7 and Table 8).
Furthermore, in the case where three types of thickeners, i.e., a fluorine-based thickener, a urea-based thickener and a soap-based thickener are contained, and when the blending amount of the calcium complex soap thickener is out of (larger than) the range specified by the embodiment of the present invention (Comparative Example 17 and Comparative Example 18), the blending amount of the calcium soap thickener is too large (Comparative Example 22 and Comparative Example 23), the blending amount of the barium soap thickener is too large (Comparative Example 29 and Comparative Example 30), the blending amount of the magnesium soap thickener is too large (Comparative Example 36 and Comparative Example 37), or the blending amount of the sodium soap thickener is too large (Comparative Example 43 and Comparative Example 44), the load resistance is good, but the acoustic performance relating to the heat resistance deteriorates. On the other hand, also in the case where three types of thickeners are contained, and when the blending amount of the barium soap thickener is out of (smaller than) the specified range specified by the present invention (Comparative Example 26 to Comparative Example 28), the blending amount of the magnesium soap thickener is too small (Comparative Example 33 to Comparative Example 35), or the blending amount of the sodium soap thickener is too small (Comparative Example 40 to Comparative Example 42), the heat resistance is good, but the acoustic performance relating to the load resistance deteriorates (see Table 7 and Table 8).
When a lithium soap thickener is used in combination as a soap-based thickener (Comparative Example 45 to Comparative Example Comparative Example 51), the acoustic performance relating to the load resistance deteriorates. When the blending amount of the lithium soap thickener is larger than 1.3 mass %, the acoustic performance relating to the heat resistance also deteriorates (see Table 9 and
As described above, it is confirmed that, the grease composition of the present invention, to which a fluorine-based thickener, a urea-based thickener, and a soap-based thickener selected from the group consisting of a calcium complex soap thickener, a calcium soap thickener, a barium soap thickener, a magnesium soap thickener and a sodium soap thickener are added, can prevent noise increase and have good heat resistance (high temperature high speed characteristic) and load resistance (high load characteristic) even in use under a high temperature environment (for example, 180° C. or higher) and under a high load condition (for example, 500 N).
In Examples, the acoustic characteristic is evaluated using a standard small diameter ball bearing having an outer diameter of 22 mm. However, the rolling bearing to which the present disclosure is directed is not limited to this size, and the size of the rolling bearing according to the embodiment of the present disclosure can be suitably selected, and also the type of the rolling bearing can be suitably selected.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-233443 | Nov 2016 | JP | national |
| 2017-220393 | Nov 2017 | JP | national |
This is a continuation of International Application No. PCT/JP2017/043140 filed on Nov. 30, 2017, and claims priority from Japanese Patent Application JP2016-233443 filed on Nov. 30, 2016, and Japanese Patent Application JP2017-220393 filed on Nov. 15, 2017, the disclosures of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2017/043140 | Nov 2017 | US |
| Child | 16425508 | US |
