Lubricant composition and rolling bearing

Abstract

To provide a lubricant composition capable of curbing abrasion, etc. in a steel bearing part under severe conditions and a rolling bearing using the lubricant composition.SOLUTION: A lubricant composition 7 which is used in a steel bearing part contains inorganic sodium salt, where natural potential of copper is 0.04 V or higher in an aqueous solution at 25°C in which the organic sodium salt is dissolved at a 1 mass% concentration, and the inorganic sodium salt includes at least one kind selected from sodium molybdate and sodium sulfite. The lubricant composition further includes sorbitan-based ester or zinc alkyldithiophosphate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lubricant composition used for gears and bearings such as a continuously variable transmission of an automobile and a speed increaser of a wind power generation device, and a rolling bearing using this lubricating composition.

Background Art

[0002] In a hydraulic motor, a hydraulic pump, and an axle planetary part, bearings lubricated with gear oil or hydraulic operating oil are generally used. Generally, operating oil is used for these oils.

[0003] In recent years, with the deterioration of operating conditions such as high speed and high load, and the reduction in viscosity of lubricating oil due to energy saving, oil film breakdown is likely to occur. In bearings composed of steel bearing members, they tend to be operated in a lubricated state where steel contacts steel. As a result, surface damage (such as early flaking) accompanied by wear on the raceway surface of the bearing may occur.

[0004] Conventionally, as a countermeasure against bearing wear, known extreme pressure agents and oiliness agents are used to countermeasure the wear of the raceway surface of the bearing. For example, Patent Document 1 describes a lubricant composition containing a predetermined amount of a phosphorus-based extreme pressure agent and being excellent in metal fatigue life, wear resistance, and electrical insulation even when the viscosity is reduced.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the case of the lubricant composition described in Patent Document 1, even if metal fatigue life and wear resistance are good under normal operating conditions, it may be insufficient as a countermeasure against corrosive wear under harsh conditions such as high speed and high load under high humidity. For example, in order to save energy when electrifying automobiles, bearings using low viscosity lubricating oil may employ a seal structure that reduces sealing torque. In this case, water can easily enter the internal space of the bearing, and contact between steel surfaces due to oil film breakdown can easily cause adhesion, corrosive wear, and premature delamination at the contact points (raceway surfaces, etc.).

[0007] The present invention has been made in view of the above problems, and aims to provide a lubricant composition that can suppress wear on steel bearing parts under harsh conditions, and a rolling bearing using this lubricant composition. [Means for solving the problem]

[0008] The lubricant composition of the present invention is used in steel bearings, and the lubricant composition comprises an inorganic sodium salt (Na x M y O z The present invention is characterized by containing the above inorganic sodium salt, and having a natural potential of 0.04V or higher in an aqueous solution at 25°C in which the above inorganic sodium salt is dissolved at a concentration of 1% by mass.

[0009] The above inorganic sodium salt is characterized by containing at least one selected from sodium molybdate (Na2MoO4) and sodium sulfite (Na2SO3).

[0010] The above lubricant composition is characterized by containing a sorbitan-based ester. Furthermore, the above lubricant composition is characterized by containing zinc alkyldithiophosphate.

[0011] The above lubricant composition is characterized by being a grease containing a thickener.

[0012] The rolling bearing of the present invention is characterized in that it comprises an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a lubricant composition sealed or supplied in the bearing space, wherein the lubricant composition is the lubricant composition of the present invention described above. [Effects of the Invention]

[0013] The lubricant composition of the present invention is used in steel bearings and contains an inorganic sodium salt. In an aqueous solution at 25°C in which the inorganic sodium salt is dissolved at a concentration of 1% by mass, the natural potential of steel is 0.04V or higher. Therefore, a corrosion-resistant film (corrosion-resistant film) can be formed on the steel surface. Due to the effect of this film, adhesion and corrosive wear in steel bearings can be suppressed even under harsh conditions, resulting in excellent wear resistance. As a result, surface damage accompanied by wear on the bearing raceway surface can be suppressed.

[0014] Since the inorganic sodium salt contains at least one selected from sodium molybdate and sodium sulfite, the thickness of the corrosion-resistant coating formed on the steel surface is increased, resulting in superior corrosion wear resistance and adhesion suppression effects.

[0015] The lubricant composition contains a sorbitan-based ester or zinc alkyldithiophosphate, and therefore exhibits superior corrosion wear resistance and adhesion inhibition effects.

[0016] Because the rolling bearing of the present invention uses the above-mentioned lubricant composition, adhesion and corrosion wear of the steel bearing portion can be suppressed even under harsh conditions such as high speed and high load in high humidity. For this reason, it can be suitably used as a bearing in continuously variable transmissions of automobiles, speed increasers of wind power generation equipment, and the like. [Brief explanation of the drawing]

[0017] [Figure 1] This is a longitudinal cross-sectional view of the rolling bearing of the present invention. [Figure 2] This is a cross-sectional view of the speed increaser. [Figure 3] This is a schematic diagram illustrating a method for measuring natural potential. [Figure 4]It is a diagram showing the results of natural potential measurement. [Figure 5] It is a schematic diagram showing a method for measuring wear depth.

Embodiments for Carrying Out the Invention

[0018] The inventors of the present invention have intensively studied a lubricant composition for lubrication in order to suppress wear and the like in a steel bearing under severe conditions such as high speed and high load under high humidity. As a result, it has been found that when the lubricant composition contains an inorganic sodium salt (25 °C, 1% by mass aqueous solution) in which the natural potential of steel is 0.04 V or more, an unexpectedly excellent wear suppression effect can be obtained. The present invention is based on such findings.

[0019] The lubricant composition of the present invention is used for a steel bearing. This lubricant composition contains an inorganic sodium salt. In the present invention, this inorganic sodium salt is characterized in that the natural potential of steel in an aqueous solution at 25 °C in which it is dissolved at a concentration of 1% by mass is 0.04 V or more.

[0020] Here, the natural potential is the potential inherent to a metal maintained in the environment in which the metal exists. Specifically, it refers to the potential difference when a reference electrode, a counter electrode, and a sample electrode are immersed in a sample solution of a predetermined concentration, left standing for a certain period of time under predetermined temperature conditions, and the oxidation-reduction state on the surface of the sample electrode reaches equilibrium. As the sample electrode, a test piece having a free shape such as a plate shape or an annular shape can be used, and in the present invention, it is preferable to use an annular test piece.

[0021] As described above, the lubricant composition of the present invention contains an inorganic sodium salt (1% by mass aqueous solution at 25°C) that causes the natural potential of steel to be 0.04V or higher, so that a corrosion-resistant film (corrosion-resistant film) is formed on the steel surface. Generally, when the type of sample electrode and the concentration of the sample solution are the same, it is thought that the higher the natural potential, the thicker the oxide film formed on the surface of the sample electrode. And since this corrosion-resistant film is an oxide film, it is thought that a thicker oxide film is formed than when the natural potential of steel is less than 0.04V. Due to the effect of this film, the newly formed surface is less likely to be exposed in the case of slight wear, and it has excellent corrosion wear resistance and adhesion suppression effect. As a result, it has excellent wear resistance even in severe lubrication conditions where steels would normally be in contact with each other.

[0022] From the viewpoint of forming a thicker corrosion-resistant film and improving wear resistance, the inorganic sodium salt contained in the lubricant composition preferably has a natural potential of 0.06V or higher, more preferably 0.08V or higher, and even more preferably 0.10V or higher in an aqueous solution at 25°C in which it is dissolved at a concentration of 1% by mass. Furthermore, it is preferable that the inorganic sodium salt is water-soluble. When the inorganic sodium salt is water-soluble, it dissolves in the water that enters the bearing space, making it easier to form a corrosion-resistant film.

[0023] The inorganic sodium salt that can be used in the present invention preferably contains at least one selected from sodium molybdate and sodium sulfite, and more preferably contains sodium molybdate.

[0024] The sodium molybdate used in this invention can be used in either anhydrous or hydrated form. The amount of sodium molybdate is preferably 0.1 to 5% by mass, more preferably 0.1 to 2% by mass, and even more preferably 1 to 2% by mass, based on the total amount of the lubricant composition. If the amount of sodium molybdate is less than 0.1% by mass, it is difficult to obtain sufficient wear resistance.

[0025] Sodium molybdate is thought to react with the friction and wear surfaces of the bearing or with newly exposed ferrous metal surfaces due to wear, forming a film containing molybdenum compounds along with iron oxide. The bearing's racing surface is covered with a film of iron oxide and molybdenum compounds, increasing the thickness of the corrosion-resistant coating formed on the steel surface, resulting in superior corrosion wear resistance and adhesion inhibition.

[0026] The lubricant composition preferably contains a sorbitan ester. Examples of sorbitan esters include, but are not limited to, sorbitan fatty acid esters such as sorbitan laurate, sorbitan monooleate, sorbitan trioleate, sorbitan tribeherate, sorbitan stearate, sorbitan tristearate, and sorbitan caprylate. From the viewpoint of dispersibility of inorganic sodium salts, the sorbitan ester is more preferably sorbitan monooleate or sorbitan trioleate.

[0027] It is believed that the sorbitan ester interacts with the particle surface of the inorganic sodium salt dispersed in the lubricant composition, forming an adsorbent film on the particle surface and stabilizing the particles. Specifically, the sorbitan ester possesses a tetrahydrofuran structure (a cyclic ether structure with a 5-membered ring) with appropriate coordination ability, resulting in excellent dispersibility of inorganic sodium salts. As a result, it is believed that finer inorganic sodium salt particles can remain stable in the lubricant composition for a long period of time without aggregation, and a corrosion-resistant film can be formed more effectively. Furthermore, the adsorbent film of the sorbitan ester can also be formed on the surface of the bearing racing surface, potentially contributing to improved wear resistance.

[0028] The blending ratio of sorbitan-based ester in the lubricant composition of the present invention is preferably 0.05 to 5% by mass. Below 0.05% by mass, the dispersion effect of the inorganic sodium salt and the wear resistance improvement effect may be inferior. Above 5% by mass, the dispersion effect of the inorganic sodium salt and the wear resistance improvement effect may plateau.

[0029] In the present invention, a wet grinding method may be employed in the production of a lubricant composition in which inorganic sodium salts are dispersed. For example, an inorganic sodium salt that has no affinity for the liquid phase is ground in a certain amount of base oil which forms the liquid phase, in the presence of a sorbitan ester, and then this mixture is diluted with base oil to a predetermined concentration, and other additives are added as needed. As a result, inorganic sodium salts such as molybdate are more easily encapsulated by the sorbitan ester, improving dispersibility and making aggregation and precipitation less likely to occur.

[0030] The lubricant composition preferably contains zinc alkyldithiophosphate. The film formation by zinc alkyldithiophosphate protects the corrosion-resistant coating, further improving corrosion wear resistance and adhesion suppression. The above-mentioned coating is a reaction film with the oxide film or molybdenum compound described above.

[0031] The alkyldithiophosphate zinc is more preferably alkyldithiophosphate zinc having a primary alkyl group with 1 to 30 carbon atoms (hereinafter referred to as pri-ZnDTP). In the present invention, pri-ZnDTP is represented by the following formula (1).

[0032] [ka]

[0033] In formula (1), R1 and R2 are each primary alkyl groups having 1 to 30 carbon atoms. A primary alkyl group is defined as a carbon atom in substituents R1 and R2 that is directly bonded to the oxygen atom in zinc dialkyldithiophosphate, and is a primary carbon atom. Examples of R1 and R2 include methyl, ethyl, propyl, butyl, isobutyl, pentyl, isopentyl, hexyl, isohexyl, 2-ethylhexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, and tetracosyl groups. R1 and R2 may be the same or different. In formula (1), substituents R1 and R2 preferably have 6 to 24 carbon atoms, and more preferably 8 to 16 carbon atoms.

[0034] In this invention, by using zinc alkyldithiophosphate, wear on the rolling surface can be effectively prevented through a synergistic effect with inorganic sodium salts, particularly sodium molybdate. This effect is especially excellent when using pri-ZnDTP. Note that one type of pri-ZnDTP represented by the above formula (1) may be used, or two or more types may be used in combination.

[0035] The amount of zinc alkyldithiophosphate is preferably 0.1 to 5% by mass of the total lubricant composition. More preferably, it is 0.1 to 2% by mass, and even more preferably 1 to 2% by mass. If the amount of zinc alkyldithiophosphate is less than 0.1% by mass, it is difficult to obtain improvements in corrosion wear resistance and adhesion inhibition effect.

[0036] The base oil used in the lubricant composition of the present invention is not particularly limited as long as it is commonly used in rolling bearings. Examples include mineral oils such as paraffinic mineral oil and naphthenic mineral oil, synthetic hydrocarbon oils such as poly-α-olefin oil (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.

[0037] PAO oil is more preferred as a synthetic hydrocarbon oil. PAO oil is a mixture of α-olefins or oligomers or polymers of isomerized α-olefins. 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 of these are usually used. 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.

[0038] The kinematic viscosity of the base oil (or the kinematic viscosity of the mixed oil in the case of a mixed oil) is 10 to 150 mm at 40°C. 2 / s is preferred. More preferably 10-100 mm 2 The interval is / s, and more preferably 20-80 mm 2 The interval is / s, and most preferably 20-40 mm 2 It is / s.

[0039] The lubricant composition of the present invention may further contain other additives, as long as they do not impair the objectives of the present invention. Examples include antioxidants such as amine-based, phenol-based, and sulfur-based compounds; rust inhibitors such as sulfonates; and oily agents such as esters and alcohols.

[0040] Examples of the lubricant composition of the present invention include (1) a lubricating oil composition comprising a base oil and an inorganic sodium salt, and (2) a grease composition comprising a base oil, a thickener, and an inorganic sodium salt.

[0041] When the lubricant composition of the present invention is a lubricating oil composition, the base oil is the same as described above, except for the inorganic sodium salt and other additives. When the lubricant composition of the present invention is a grease composition, the base oil is preferably present in an amount of 60% to 95% by mass relative to the total amount of the base oil and thickener. If the base oil content is less than 60% by mass, the lifespan may be reduced, and if it exceeds 95% by mass, the amount of thickener will be relatively small, which may make it difficult to form a grease.

[0042] The thickener used when the lubricant composition of the present invention is used as a grease composition is not particularly limited, and general thickeners commonly used in the field of grease 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 soap, calcium soap, aluminum soap, and lithium soap, while examples of urea compounds and urea-urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds.

[0043] Urea compounds are obtained by reacting a polyisocyanate component with a monoamine component. Examples of polyisocyanate components include phenylenediisocyanate, tolylenediisocyanate, diphenyldiisocyanate, diphenylmethanediisocyanate, octadecanediisocyanate, decanediisocyanate, and hexanediisocyanate. The monoamine component can be an aliphatic monoamine, a alicyclic monoamine, or an aromatic monoamine. Examples of aliphatic monoamines include hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, and oleylamine. Examples of alicyclic monoamines include cyclohexylamine. Examples of aromatic monoamines include aniline and p-toluidine.

[0044] When using the lubricant composition of the present invention as a grease composition, the mixed consistency (JIS K 2220) is preferably in the range of 200 to 350. If the consistency is less than 200, oil separation is poor and lubrication may be inadequate. On the other hand, if the consistency exceeds 350, the grease composition becomes soft and easily leaks out of the bearing, which is undesirable. A mixed consistency in the range of 250 to 300 is more preferable.

[0045] A rolling bearing containing the lubricant composition of the present invention will be described with reference to Figure 1. Figure 1 is a cross-sectional view of a deep groove ball bearing. The rolling bearing 1 has an inner ring 2 having an inner ring racing surface 2a on its outer circumference and an outer ring 3 having an outer ring racing surface 3a on its inner circumference, arranged concentrically, with a plurality of rolling elements 4 arranged between the inner ring racing surface 2a and the outer ring racing surface 3a. These rolling elements 4 are held by a cage 5. In addition, the axial openings 8a and 8b at both ends of the inner and outer rings are sealed by a sealing member 6, and the above-mentioned lubricant composition 7 is sealed in the bearing space, at least around the rolling elements 4. The inner ring 2, outer ring 3 and rolling elements 4 are made of steel, and the lubricant composition 7 is interposed on the racing surfaces with the rolling elements 4 to provide lubrication.

[0046] In the rolling bearing 1, the steel materials constituting the bearing members such as the inner ring 2, outer ring 3, and rolling elements 4 can be any material commonly used as a bearing material. Examples include high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; JIS G4805), carburized steel (SCr420, SCM420, etc.; JIS G4053), stainless steel (SUS440C, etc.; JIS G4303), 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 plate, plastic plate, or ceramic plate. A composite of a rubber molded body and a metal plate is preferred due to its durability and ease of adhesion.

[0047] Figure 1 illustrates a ball bearing (with a sealing member) as an example of a bearing, but the form of the rolling 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, self-aligning roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust tapered roller bearing, thrust needle roller bearing, thrust self-aligning roller bearing, etc.

[0048] In the rolling bearing of the present invention, since the above-mentioned lubricant composition is supplied and sealed within the bearing's internal space (bearing portion), adhesion and corrosion wear in the steel bearing portion can be suppressed even under harsh conditions such as high humidity, high speed, and high load, resulting in excellent wear resistance. For this reason, it can be suitably used as a bearing in continuously variable transmissions of automobiles, speed increasers of wind power generation equipment, and the like.

[0049] Figure 2 shows an example of a speed increaser for a wind power generation device to which the rolling bearings of the present invention are applied. Figure 2 is a cross-sectional view of the speed increaser. The speed increaser body 21 is provided between the input shaft 22 and the output shaft 23 with a planetary gear mechanism 26 which serves as a primary speed increaser and a secondary speed increaser 27. The planetary gear mechanism 26 has planetary gears 29 mounted on a carrier 28 which is integrated with the input shaft 22, and the planetary gears 29 mesh with an internally toothed ring gear 30 and a sun gear 31, with the shaft integrated with the sun gear 31 serving as the intermediate output shaft 32. The secondary speed increaser 27 consists of a gear train that transmits the rotation of the intermediate output shaft 32 to the output shaft 23 via a plurality of gears 33 to 36. The planetary gears 29, the rolling bearings 37 made of bearing steel that support the planetary gears 29, the ring gear 30, and the gears 33 of the secondary speed increaser 27 are immersed in lubricating oil 25 in a lubricating oil storage tank 24a inside the housing 24. This lubricating oil 25 is the lubricant composition described above. The lubricating oil storage tank 24a is circulated by a circulation lubrication means (not shown) consisting of a pump and piping. Note that the circulation lubrication means is not necessarily required, and an oil bath lubrication system may be used instead.

[0050] In this wind power generation system, the gearbox is installed outdoors and is exposed to fluctuations in humidity and wind and rain, which can cause moisture to mix into the lubricating oil. The lubricant composition of the present invention can suppress adhesion and corrosion wear in the steel bearing section even under such lubrication conditions, thereby extending the lifespan of the gearbox. As a result, the frequency of maintenance of the wind power generation system can be reduced. [Examples]

[0051] To evaluate the corrosion-resistant film-forming ability and wear resistance of inorganic sodium salts, the spontaneous potential of various inorganic sodium salts was measured, and wear depth tests were performed on lubricant compositions containing them.

[0052] <Natural potential> As an example of spontaneous potential measurement, the measurement results for three test solutions—sodium molybdate aqueous solution (0.5% by mass, 1% by mass) and sodium tungstate aqueous solution (1% by mass)—are described below. For each sample solution, spontaneous potential measurements were performed using the apparatus shown in Figure 3 under the following measurement conditions. Before measurement, the sample solutions were subjected to nitrogen bubbling for 40 hours to remove dissolved oxygen. During measurement, bubbling was stopped, and the potential difference was measured for approximately 40 hours. The potential difference 30 hours after the start of measurement was adopted as the spontaneous potential value.

[0053] Measurement conditions Device: Potentiostat manufactured by Hokuto Denko Reference electrode: Saturated calomel electrode (SCE) Counter electrode: Platinum electrode Sample electrode: SUJ2 test piece (annular shape) Measurement temperature: 25℃

[0054] Figure 4 shows the results of the spontaneous potential measurement. It can be seen that the potential difference for all three sample solutions increased significantly at the beginning of the measurement, and remained almost constant after 10 hours from the start of the measurement. At a solution concentration of 1% by mass, the spontaneous potential of sodium molybdate was 0.05–0.06 V, while that of sodium tungstate was 0.02–0.03 V, indicating that sodium molybdate showed a relatively higher spontaneous potential. This result suggests that sodium molybdate forms a thicker oxide film than sodium tungstate. The spontaneous potential of 0.5% by mass sodium molybdate was 0.07–0.09 V.

[0055] <Abrasion resistance (abrasion depth)> The wear depth test was performed using the test apparatus shown in Figure 5 under the following test conditions. An annular steel plate and three steel balls were immersed in a bath of various lubricant compositions, and the steel balls were rotated along the annulus for a predetermined time while a load was applied to the steel plate in the direction of the steel plate. The wear depth was measured by measuring the depth of the slight indentation formed on the rolling surface of the steel plate after the steel balls had been rotated for the predetermined time. The area enclosed by the dotted line in Figure 5 is the measurement area.

[0056] Test conditions Test piece: Steel ball / Steel flat plate Steel material: SUJ2 P max :3.0GPa Rotation (sliding) speed: 300 mm / s Time: 20 hours Oil temperature: 100℃

[0057] Table 1 shows the composition, spontaneous potential, and wear depth results for lubricant compositions containing various inorganic sodium salts. The spontaneous potentials listed in Table 1 are those of steel in an aqueous solution at 25°C in which the inorganic sodium salt contained in each composition is dissolved at a concentration of 1% by mass. Regarding the preparation of the lubricant compositions, the content of base oil, additives, and inorganic sodium salts are indicated as the content (mass %) relative to the lubricant composition (base oil + additives + inorganic sodium salt), respectively. In Examples 1 to 8, the lubricant compositions contain inorganic sodium salts in which the spontaneous potential of steel in an aqueous solution at 25°C in which the inorganic sodium salt is dissolved at a concentration of 1% by mass is 0.04V or higher.

[0058] [Table 1]

[0059] Table 1 shows that while Examples 1-8 had a wear depth of 3 μm or less, Comparative Examples 1-8 had a wear depth of 8 μm or more, indicating that the lubricant composition containing an inorganic sodium salt exhibiting a natural potential of 0.04 V or higher has excellent wear resistance. Since a higher natural potential indicates that the steel surface is less susceptible to oxidation (corrosion), it can be considered that Examples 1-8 have formed a thicker oxide film than Comparative Examples 1-8, thus protecting them from wear, especially corrosive wear.

[0060] The wear depth was smaller in Example 2 than in Example 8, and it was found that sodium molybdate, which has a higher spontaneous potential than sodium sulfite, is superior in improving wear resistance. Furthermore, the wear depth was smaller in Examples 3 and 2 than in Example 4, and it was found that the combined use of sorbitan esters and sodium molybdate is superior in improving wear resistance. In addition, since the wear depth decreased in the order of Example 3 > Example 2 > Example 6, it was found that, for the same amount of compounding, the wear resistance improvement effect was greatest in the order of sorbitan monooleate < sorbitan trioleate < zinc dithiophosphate.

[0061] Furthermore, since Example 7 showed a smaller wear depth than Examples 2 and 6, it was found that the combined use of sorbitan ester, zinc dithiophosphate, and sodium molybdate is particularly effective in improving wear resistance. This is thought to be due to the synergistic effect of the sorbitan ester's adsorption film formation effect on the surface of sodium molybdate particles and the zinc dithiophosphate reaction film's effect of protecting (strengthening) the corrosion-resistant coating of sodium molybdate. Also, since Example 5 showed a smaller wear depth than Example 2, it was found that PAO oil is more effective than ester oil in improving wear resistance. Although Example 1, which contained a relatively small amount of sodium molybdate, showed a higher spontaneous potential than Example 2, the wear depth was comparable. [Industrial applicability]

[0062] The lubricant composition of the present invention can suppress wear on steel bearing parts under harsh conditions such as high speed and high load in high humidity, and exhibits excellent wear resistance. For this reason, it can be widely used in bearings used in continuously variable transmissions of automobiles, speed increasers of wind power generators, and the like. [Explanation of Symbols]

[0063] 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Rolling elements 5 Cage 6. Sealing member 7. Lubricant Compositions 8a, 8b Axial openings at both ends 21 Speed ​​increaser unit 22 Input axes 23 Output shaft 24 Housing 25 Lubricating oil 26 Planetary gear mechanism 27 Secondary speed increaser 28 Carriers 29 Planetary gears 30 Ring Gear 31 Sun Gear 32 Intermediate output shaft 33-36 Gears 37 Rolling bearings

Claims

1. A lubricant composition used in steel bearing parts, The aforementioned lubricant composition comprises an inorganic sodium salt and a sorbitan ester. A lubricant composition characterized in that the spontaneous potential of the steel in an aqueous solution at 25°C in which the inorganic sodium salt is dissolved at a concentration of 1% by mass is 0.04 V or higher.

2. The lubricant composition according to claim 1, characterized in that the inorganic sodium salt comprises at least one selected from sodium molybdate and sodium sulfite.

3. The lubricant composition according to claim 1 or 2, characterized in that it comprises zinc alkyldithiophosphate.

4. The lubricant composition according to any one of claims 1 to 3, characterized in that the lubricant composition is a grease containing a thickener.

5. A rolling bearing comprising an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a lubricant composition sealed or supplied to the bearing space, A rolling bearing characterized in that the lubricant composition is the lubricant composition according to any one of claims 1 to 4.

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