Grease composition and grease-filled bearing

Abstract

To provide a grease composition capable of effectively suppressing early separation due to hydrogen embrittlement, and a grease-sealed bearing in which the grease composition is sealed.SOLUTION: A grease composition 7 comprises a base oil, a thickener and an additive, wherein the additive contains sodium molybdate as an essential component, and contains either a sorbitan-based ester or a metal sulfonate, the metal sulfonate is Ca sulfonate or Zn sulfonate, and a content thereof is less than 3 pts.mass with respect to 100 pts.mass of a total amount of the base oil and the thickener.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a grease composition and a grease-filled bearing filled with the grease composition, particularly to a grease composition used in rolling bearings for automotive electrical equipment and accessories and servomotors. [Background technology]

[0002] Rolling bearings are used in the rotating parts of various components, such as electrical components and accessories in automobiles, and motors in industrial machinery. For example, automotive electrical components and accessories include alternators, pulleys, electromagnetic clutches for car air conditioners, fan coupling devices, and electric fan motors. Automotive idler pulleys are used as belt tensioners for the drive belt that transmits engine rotation to the automobile's accessories. The rolling bearings used in these components are filled with grease to provide lubrication.

[0003] In rolling bearings, severe operating conditions can lead to the early occurrence of peculiar spalling accompanied by white structural changes on the rolling surface. This peculiar spalling differs from the spalling that occurs from within the rolling surface due to ordinary metal fatigue. It is a fracture phenomenon that occurs relatively shallow on the rolling surface surface and is thought to be caused by hydrogen embrittlement. For example, grease decomposition generates hydrogen, which then penetrates into the steel of the rolling bearing, causing early spalling due to hydrogen embrittlement. Because hydrogen significantly reduces the fatigue strength of steel, even under conditions considered to be elastohydrodynamic lubrication, where contact elements are separated by an oil film, cracks can initiate and propagate near the interior of the rolling surface where alternating shear stress is greatest, leading to early spalling.

[0004] Various methods have been investigated to prevent this unique peeling phenomenon accompanied by early white structural changes, such as adding molybdate and organic acid salts to grease as additives (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-112902 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the operating conditions for rolling bearings have become increasingly severe, with high loads, high speeds, and sudden acceleration and deceleration being added to these conditions. Under these more severe conditions, the surface pressure between the rolling elements and the raceways increases, and slippage due to sudden acceleration and deceleration increases, making the oil film at the contact points more susceptible to breakdown (poor lubrication). To effectively prevent early flaking even under such conditions, further improvements in lubricants and other materials are required.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide a grease composition that can effectively suppress early flaking due to hydrogen embrittlement, and a grease-filled bearing in which this grease composition is filled. [Means for solving the problem]

[0008] The grease composition of the present invention is a grease composition containing a base oil, a thickener, and an additive, wherein the additive contains sodium molybdate as an essential component and contains a sorbitan ester or a metal sulfonate, the metal sulfonate being Ca sulfonate or Zn sulfonate, and the content of the additive is less than 3 parts by mass per 100 parts by mass of the total amount of the base oil and the thickener.

[0009] The additive is characterized in that it contains a sorbitan ester, the content of the sorbitan ester is equal to or less than the content of sodium molybdate, and the sorbitan ester is sorbitan trioleate.

[0010] The thickener is a diurea compound, and the base oil contains a poly-α-olefin oil (PAO oil).

[0011] The grease-packed bearing of the present invention is a grease-packed bearing having an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a grease composition packed around the plurality of rolling elements, wherein the grease composition is the grease composition described above. The grease-packed bearing is also characterized in that it is used under conditions of rapid acceleration and deceleration, and the grease composition lubricates the contact surfaces between iron-based metal members of the bearing. [Effects of the Invention]

[0012] The grease of the present invention contains additives that contain sodium molybdate as an essential component and also contain a sorbitan ester or a metal sulfonate, where the metal sulfonate is Ca sulfonate or Zn sulfonate, and the content is less than 3 parts by mass per 100 parts by mass of the combined amount of base oil and thickener, thereby effectively suppressing early flaking due to hydrogen embrittlement.

[0013] The sorbitan ester combined with sodium molybdate is sorbitan trioleate, which provides an excellent effect of suppressing peeling. Furthermore, the content of the sorbitan ester is equal to or less than the content of sodium molybdate, which provides an excellent effect of suppressing peeling.

[0014] The grease-sealed bearing of the present invention has an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and the grease composition of the present invention is sealed around the rolling elements, thereby suppressing early flaking caused by hydrogen embrittlement and enabling longer use even under harsh operating conditions. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a deep groove ball bearing, which is an example of a grease-sealed bearing of the present invention. [Figure 2]1 is a cross-sectional view showing an alternator using a grease-sealed bearing according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have conducted extensive research into grease compositions used for lubrication in order to suppress and prevent early flaking on rolling surfaces due to hydrogen embrittlement. As a result, they have discovered that an unexpectedly excellent effect of suppressing flaking can be achieved by using additives containing sodium molybdate as an essential component and a specified amount of either a sorbitan ester or a metal sulfonate (Ca sulfonate or Zn sulfonate).

[0017] In rolling bearings, when iron-based metal components, such as rolling elements and raceways or rolling elements and cages, are in rolling contact and sliding contact with grease, under severe conditions such as rapid acceleration and deceleration, the oil film at the contact surfaces between the iron-based metal components may be almost completely removed, resulting in boundary lubrication conditions in which the metal surfaces are in direct contact with each other in some areas. Even when the oil film thins under such severe conditions (boundary lubrication conditions), direct contact between the grease and the newly formed iron-based metal surface can be prevented by forming an oxide film using sodium molybdate and a coating (adsorption film) using sorbitan esters or metal sulfonates on the friction and wear surfaces at the contact points or on newly formed iron-based metal surfaces exposed by wear. This suppresses the generation of hydrogen due to grease decomposition and the penetration of hydrogen into the steel, thereby suppressing and preventing the unique spalling caused by hydrogen embrittlement and extending the life of the rolling bearing. The present invention is based on this finding.

[0018] The grease composition of the present invention includes a base oil, a thickener, and an additive. The additive contains sodium molybdate as an essential component and either a sorbitan ester or a metal sulfonate. When the grease composition includes the metal sulfonate, the metal sulfonate is a calcium sulfonate or a zinc sulfonate, and is contained in an amount of less than 3 parts by mass per 100 parts by mass of the combined amount of the base oil and the thickener.

[0019] The sodium molybdate used in the present invention can be either anhydrous or hydrated. The content of sodium molybdate is preferably 0.1 to 5 parts by mass per 100 parts by mass of the total amount of base oil and thickener. Within this range, specific peeling due to hydrogen embrittlement is easily suppressed. The content is more preferably 0.1 to 2 parts by mass, and even more preferably 1 to 2 parts by mass. As described above, sodium molybdate reacts with nascent iron-based metal surfaces to form an oxide film containing iron oxide and a molybdenum compound. As a result, decomposition of the grease composition catalyzed by the nascent metal surface is suppressed, and hydrogen generation is suppressed.

[0020] Examples of Ca sulfonates used in the present invention include calcium salts of petroleum sulfonic acids and calcium salts of alkyl aromatic sulfonic acids such as dinonylnaphthalene sulfonic acid and alkylbenzene sulfonic acid. These can be used alone or in combination. Examples of Zn sulfonates used in the present invention include zinc salts of petroleum sulfonic acids such as zinc phenolsulfonate and zinc salts of alkyl aromatic sulfonic acids such as dinonylnaphthalene sulfonic acid and alkylbenzene sulfonic acid.

[0021] The Ca sulfonate is not limited to neutral Ca sulfonate, but may also be an overbased Ca sulfonate (hereinafter also referred to as "basic Ca sulfonate") obtained by uniformly dispersing fine particles such as calcium hydroxide in neutral Ca sulfonate. The total base number (TBN) of the Ca sulfonate is not particularly limited, but is preferably 10 to 500 mgKOH / g, more preferably 50 to 400 mgKOH / g, and even more preferably 100 to 400 mgKOH / g. By using an overbased Ca sulfonate as the Ca sulfonate, the contained calcium carbonate and other components act similarly to a thickener, suppressing consistency changes and contributing to shear stability. TBN is measured in accordance with JIS K 2501. TBN is defined as the number of milligrams (mg) of potassium hydroxide equivalent to the amount of hydrochloric acid or perchloric acid required to neutralize all basic components contained in 1 g of sample. TBN is measured, for example, by the perchloric acid method.

[0022] The content of Ca sulfonate or Zn sulfonate is less than 3 parts by mass per 100 parts by mass of the total amount of base oil and thickener. While there is no particular lower limit, it is preferably 0.1 parts by mass or more relative to the total amount of base oil and thickener. Within this range, peculiar peeling due to hydrogen embrittlement can be sufficiently suppressed. It is more preferably 0.1 parts by mass or more but less than 2 parts by mass, and even more preferably 0.1 parts by mass or more but less than 1.5 parts by mass.

[0023] Examples of the sorbitan esters used in the present invention include sorbitan fatty acid esters such as sorbitan laurate, sorbitan monooleate, sorbitan trioleate, sorbitan tribeherate, sorbitan stearate, sorbitan tristearate, and sorbitan caprylate.

[0024] It is believed that the interaction between the sorbitan ester and the particle surfaces of sodium molybdate dispersed in the grease composition causes the sorbitan ester to form an adsorption film on the particle surfaces, stabilizing the particles. Specifically, the sorbitan ester has a tetrahydrofuran structure (a five-membered cyclic ether structure) with moderate coordination ability, which provides excellent dispersibility for sodium molybdate. As a result, it is believed that smaller sodium molybdate particles can remain stable in the grease composition for a long period of time without agglomeration, allowing for more effective formation of oxide films and other properties. Furthermore, the adsorption film of the sorbitan ester is also formed on the surface of the bearing rolling surface, which may contribute to improved spalling suppression.

[0025] From the viewpoint of dispersibility of sodium molybdate, the sorbitan ester is preferably sorbitan monooleate or sorbitan trioleate, and more preferably sorbitan trioleate. When the sorbitan ester is sorbitan trioleate, compared with sorbitan monooleate, it has more alkyl chains on the side chains of the tetrahydrofuran structure that can serve as coordination sites, resulting in greater steric hindrance. As a result, it is believed that the dispersibility of sodium molybdate microparticles in the grease composition is superior, oxide film formation is promoted, and the peeling occurrence suppression effect is superior.

[0026] The content of the sorbitan ester relative to 100 parts by mass of the total amount of the base oil and thickener is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 4 parts by mass, and even more preferably 0.5 to 2.5 parts by mass. If the content is less than 0.05 parts by mass, the dispersing effect of sodium molybdate and the improving effect of preventing peeling may be poor. If the content exceeds 5 parts by mass, the improving effect of dispersing sodium molybdate and the improving effect of preventing peeling may plateau.

[0027] The content of the sorbitan ester in the grease composition of the present invention is preferably equal to or less than the content of sodium molybdate. If the content of the sorbitan ester exceeds the content of sodium molybdate, the effect of suppressing peeling may be inferior.

[0028] In the present invention, a wet grinding method may be used to produce a grease composition containing dispersed sodium molybdate. For example, sodium molybdate, which has no affinity for the liquid phase, may be ground in a certain amount of base oil to form a liquid phase in the presence of a sorbitan ester, and then this mixture may be added to the base oil or base grease. This method makes it easier for sodium molybdate to be encapsulated in the sorbitan ester, improving dispersibility and reducing the likelihood of aggregation or precipitation.

[0029] The base oil used in the grease composition of the present invention can be any oil typically used in rolling bearings, without any particular limitations. Examples include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as PAO oil and alkylbenzene oil, ester oil, ether oil, silicone oil, and fluorine oil. These base oils may be used alone or in combination of two or more. Among these, it is preferable that the base oil contains at least a synthetic hydrocarbon oil.

[0030] The synthetic hydrocarbon oil is preferably PAO oil. PAO oil is a mixture of α-olefins or isomerized α-olefin oligomers or polymers. Specific examples of α-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 1-docosene, and 1-tetradocosene, and mixtures thereof are usually used.

[0031] More preferred embodiments of the base oil include when the base oil consists solely of PAO oil, when the base oil is a mixed oil of PAO oil and ether oil, and when the base oil is a mixed oil of PAO oil and ester oil.

[0032] Examples of ether oils include polyphenyl ether oil, alkyl diphenyl ether oil, alkyl triphenyl ether oil, and alkyl tetraphenyl ether oil. Among these, alkyl diphenyl ether oil is preferred because of its excellent durability at high temperatures. Examples of alkyl diphenyl ether oils include monoalkyl diphenyl ether oil, dialkyl diphenyl ether oil, and polyalkyl diphenyl ether.

[0033] Examples of ester oils include polyol ester oils, phosphate ester oils, polymer ester oils, aromatic ester oils, carbonate ester oils, diester oils, and polyglycol oils. Among these, polyol ester oils are preferred because of their high viscosity index and wide operating temperature range. Examples of polyol ester oils include trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, and pentaerythritol pelargonate.

[0034] The kinematic viscosity of the base oil (in the case of a mixed oil, the kinematic viscosity of the mixed oil) is 10 to 200 mm at 40°C. 2 / s is preferable, and 20 to 100 mm is more preferable. 2 / s, and more preferably 40 to 100 mm 2 / s.

[0035] The base oil is preferably contained in an amount of 60 to 95% by mass of the total amount of base oil and thickener (base grease). If the base oil content is less than 60% by mass, the service life may be shortened, and if it exceeds 95% by mass, the amount of thickener becomes relatively small, making it difficult to produce a grease. More preferably, the base oil is contained in an amount of 70 to 90% by mass of the total amount of base oil and thickener.

[0036] The thickener used in the grease composition of the present invention is not particularly limited, and any commonly used thickener in the field of greases can be used. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentone, silica gel, urea compounds, and urea-urethane compounds can be used. Examples of metal soaps include sodium soaps, calcium soaps, aluminum soaps, and lithium soaps. Examples of urea compounds and urea-urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds. Among these, it is preferable to use a diurea compound as the thickener.

[0037] Diurea compounds are obtained by reacting a diisocyanate component with a monoamine component. Examples of diisocyanate components include phenylene diisocyanate and diphenylmethane diisocyanate (MDI). Diurea compounds include aliphatic diurea compounds, alicyclic diurea compounds, and aromatic diurea compounds, which are classified according to the type of substituent on the monoamine component used. In the case of aliphatic diurea compounds, an aliphatic monoamine (e.g., octylamine) is used as the monoamine component. In the case of alicyclic diurea compounds, an alicyclic monoamine (e.g., cyclohexylamine) is used as the monoamine component. In the case of aromatic diurea compounds, an aromatic monoamine (e.g., p-toluidine) is used as the monoamine component. Base greases using diurea compounds as thickeners are produced by reacting a diisocyanate component with a monoamine component in a base oil.

[0038] The thickener is preferably contained in an amount of 5 to 30 mass % and more preferably 10 to 20 mass % based on the total amount of the base oil and thickener (base grease).

[0039] The grease composition of the present invention may further contain other additives within the scope of the present invention, such as antioxidants such as amine-based, phenol-based, and sulfur-based compounds, rust inhibitors such as sulfonates, and oiliness agents such as esters and alcohols.

[0040] The worked penetration (JIS K 2220) of the grease composition of the present invention is preferably in the range of 200 to 350. If the penetration is less than 200, oil separation may be small, resulting in poor lubrication. On the other hand, if the penetration exceeds 350, the grease composition becomes soft and tends to flow out of the bearing, which is undesirable. The worked penetration is more preferably in the range of 250 to 300.

[0041] A grease-filled bearing filled with the grease composition of the present invention will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view of a deep groove ball bearing. Rolling bearing 1 comprises an inner ring 2 having an inner ring rolling surface 2a on its outer peripheral surface and an outer ring 3 having an outer ring rolling surface 3a on its inner peripheral surface, which are concentrically arranged, with a plurality of rolling elements 4 disposed between inner ring rolling surface 2a and outer ring rolling surface 3a. These rolling elements 4 are held in place by a cage 5. Openings 8a, 8b at both axial ends of the inner and outer rings are sealed by sealing members 6, and the above-described grease composition 7 is filled in the bearing interior space at least around the rolling elements 4. The inner ring 2, outer ring 3, and rolling elements 4 are made of steel, and grease composition 7 is present at the rolling surfaces with the rolling elements 4 to provide lubrication.

[0042] In the rolling bearing 1, the steel materials constituting the bearing components, such as the inner ring 2, outer ring 3, and rolling elements 4, may be any material commonly used as a bearing material, such as high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; JIS G 4805), carburized steel (SCr420, SCM420, etc.; JIS G 4053), stainless steel (SUS440C, etc.; JIS G 4303), high-speed steel (M50, etc.), and cold-rolled steel. The sealing member 6 may be made of metal or a rubber molded body alone, or it may be a composite of a rubber molded body and a metal, plastic, or ceramic plate. A composite of a rubber molded body and a metal plate is preferred for its durability and ease of attachment.

[0043] 1 shows a ball bearing as an example of the bearing, but the grease-sealed bearing of the present invention is not limited to this. For example, it can also be used as a cylindrical roller bearing, tapered roller bearing, spherical roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, or thrust spherical roller bearing.

[0044] The configuration in which the grease-filled bearing of the present invention is applied to automotive electrical equipment and accessories is described with reference to FIG. 2. FIG. 2 is a cross-sectional view of an alternator structure. The alternator includes a pair of frames 11a, 11b that form a housing, which is a stationary member, and a rotor shaft 13, on which a rotor 12 is mounted, that is rotatably supported by a pair of rolling bearings 1, 1, each filled with the above-described grease composition. A rotor coil 14 is attached to the rotor 12, and a stator 15, arranged around the outer periphery of the rotor 12, is fitted with a three-winding stator coil 16, with a phase difference of 120°. The rotor shaft 13 is driven to rotate by a pulley 17 attached to its end, which is transmitted by a belt (not shown). The pulley 17 is attached to the rotor shaft 13 in a cantilevered manner, and vibrations occur as the rotor shaft 13 rotates at high speed, so the rolling bearing 1, which supports the pulley 17, is subjected to particularly severe loads.

[0045] The grease-sealed bearing of the present invention has a wide range of industrial applications and can be used in a variety of equipment, for example, as a bearing for motors such as motors for industrial machinery, such as ventilator motors, blower motors for fuel cells, cleaner motors, fan motors, servo motors, and stepping motors, motors for electrical equipment, such as automobile starter motors, electric power steering motors, tilt motors for steering adjustment, wiper motors, and power window motors, and motors for driving electric vehicles.

[0046] The grease-sealed bearing of the present invention can suppress early flaking caused by hydrogen embrittlement even under severe operating conditions, enabling it to be used for a longer period of time. For this reason, the grease-sealed bearing of the present invention can be suitably used as a rolling bearing used under belt-driven conditions and under rapid acceleration and deceleration conditions, such as in electrical accessories and servomotors. [Example]

[0047] The present invention will be specifically explained by way of examples and comparative examples, but is not limited to these examples in any way.

[0048] Grease compositions were prepared according to the compositions shown in Table 1. In Table 1, the contents of the base oil and thickener indicate the content (parts by mass) relative to 100 parts by mass of the base grease (base oil + thickener), and the content of the additive indicates the content (parts by mass) relative to 100 parts by mass of the total amount of the base grease. All of the grease compositions of Examples 1 to 9 contained sodium molybdate as an additive. Furthermore, the grease compositions of Examples 1 to 4, 8, and 9 contained a sorbitan ester as an additive, and the grease compositions of Examples 5 to 7 contained a Ca sulfonate (basic Ca sulfonate, neutral Ca sulfonate) or Zn sulfonate as a metal sulfonate.

[0049] Each grease composition was filled into a rolling bearing (inner ring, outer ring, and steel balls made of SUJ2 bearing steel) with an inner ring rotating and supporting a rotating shaft, simulating an alternator, an example of an electrical auxiliary device, and subjected to a rapid acceleration / deceleration test. The load on the pulley attached to the end of the rotating shaft was set to 2334 N, and the rotational speed was set to 0 rpm to 18,000 rpm. Furthermore, the test was performed with a current of 0.5 A flowing through the test bearing (6203). The time (flake occurrence life time, h) until abnormal flaking occurred in the bearing and the vibration of the vibration detector exceeded the set value and the bearing stopped was measured. Table 1 lists the average life for n=6.

[0050] [Table 1]

[0051] Comparative Example 8 was a case where no additive was added, while Comparative Examples 1, 3, and 7 were cases where only sodium molybdate was added as an additive. Comparative Examples 9 and 10 were cases where sodium molybdate and zinc dithiocarbamate (ZnDTC) were added as additives. In contrast, Examples 1 to 4, 8, and 9, which contained sodium molybdate and a sorbitan ester as additives, exhibited a peel life that was 1.4 times longer than the above comparative examples. In particular, Example 4 exhibited a peel life that was twice as long as Comparative Example 3, which differed only in that it did not contain sorbitan trioleate. Furthermore, Example 4, which contained sorbitan trioleate, exhibited a peel life that was approximately 1.2 times longer than Example 8, which contained sorbitan monooleate. In a composition using an aromatic diurea compound as a thickener, Example 4, which contained twice the amount of sodium molybdate as the sorbitan ester, exhibited a peel life that was approximately 1.1 times longer than Example 9, which contained the same amount of sodium molybdate as the sorbitan ester.

[0052] Examples 5 to 7, which contained sodium molybdate and a metal sulfonate, either Ca sulfonate or Zn sulfonate, as additives, exhibited a peeling life that was 2.4 times or more longer than Comparative Example 8. Furthermore, Examples 5 to 7 exhibited a peeling life that was 1.7 times or more longer than Comparative Examples 2 and 4, which contained Ba sulfonate. In particular, Example 5, which contained basic Ca sulfonate, exhibited a peeling life that was approximately 1.2 times longer than Example 4. Furthermore, Example 5 exhibited a peeling life that was 1.2 times or more longer than Example 7, which contained neutral Ca sulfonate, and Example 6, which contained Zn sulfonate, demonstrating that among metal sulfonates, basic Ca sulfonate has a particularly high effect of suppressing peeling.

[0053] Examples 5 to 7, which contain sodium molybdate and a metal sulfonate, either Ca sulfonate or Zn sulfonate, as additives and in which the content of the metal sulfonate is 1 part by mass per 100 parts by mass of the total amount of base oil and thickener, have a peeling life that is more than twice as long as Comparative Examples 5 and 6, in which the content of Ca sulfonate or Zn sulfonate is 3 parts by mass.

[0054] Example 4, which used an aromatic diurea compound as the thickener, had a peeling life that was approximately 1.2 times longer than Example 1, which used a semi-aromatic (having both an aliphatic structure and an aromatic structure) diurea compound as the thickener.Comparative Examples 9 and 10, which contained ZnDTC as an additive together with sodium molybdate, had a peeling life that was 0.6 times or less longer than Examples 4 to 8, which had the same base grease composition and sodium molybdate content.

[0055] From the above, it was found that the combined use of sodium molybdate and a sorbitan ester (particularly sorbitan trioleate) or a metal sulfonate (in a specified amount) has an excellent effect in suppressing peeling. Furthermore, when a grease composition contains a metal sulfonate, such as calcium sulfonate or zinc sulfonate, even when combined with sodium molybdate, the effect of suppressing peeling is significantly reduced when the content of the metal sulfonate is 3 parts by mass or more per 100 parts by mass of the total amount of base oil and thickener. [Industrial Applicability]

[0056] The grease composition of the present invention effectively suppresses the specific early flaking accompanied by white structural changes that occurs on the rolling surfaces, thereby extending the bearing life of rolling bearings, and is particularly suitable for rolling bearings of automotive electrical components and accessories such as alternators, electromagnetic clutches for car air conditioners, intermediate pulleys, and electric fan motors, as well as bearings for motors such as servomotors. [Explanation of symbols]

[0057] 1. Rolling bearings 2. Inner circle 3 outer ring 4 rolling elements 5 Cage 6 Sealing material 7 Grease composition 8a, 8b opening 11a, 11b frames 12 rotors 13 Rotor shaft 14 rotor coil 15 Stator 16 stator coil 17 Pulley

Claims

1. A grease composition comprising a base oil, a thickener, and an additive, the additive contains sodium molybdate as an essential component and a sorbitan ester, A grease composition characterized in that the sorbitan ester is sorbitan trioleate.

2. 2. The grease composition according to claim 1, wherein the content of the sorbitan ester is equal to or less than the content of the sodium molybdate.

3. 3. The grease composition according to claim 1, wherein the thickener is a diurea compound.

4. 4. The grease composition according to claim 1, wherein the base oil contains a poly-α-olefin oil.

5. A grease-filled bearing having an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a grease composition filled around the plurality of rolling elements, A grease-sealed bearing, wherein the grease composition is the grease composition according to any one of claims 1 to 4.

6. 6. A grease-sealed bearing according to claim 5, wherein the grease-sealed bearing is used under conditions of rapid acceleration and deceleration, and the grease composition lubricates the contact surfaces between the iron-based metal members of the bearing.

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