Evaluation method for electrolytic corrosion suppression performance

Abstract

This provides an evaluation method that allows for verification of the effect of suppressing electrolytic corrosion in a short amount of time. [Solution] The method for evaluating the galvanic corrosion suppression effect is a method for evaluating the galvanic corrosion suppression effect in a test bearing 12 having an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, wherein the raceway surfaces of the inner ring and the outer ring and the rolling elements are lubricated with a lubricant, and the rolling bearing 12 is rotated while a predetermined current flows through the rolling bearing, and a lubricant with a relative permittivity of 2.5 or less is used as the lubricant.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the performance of electrolytic corrosion suppression, and more particularly to a method for evaluating the performance of electrolytic corrosion suppression in bearings used in automobiles, industrial machinery, wind turbines, and the like. [Background technology]

[0002] Rolling bearings are used in fan motors and servo motors used in industrial machinery, as well as in drive motors used in electric vehicles and hybrid vehicles. These rolling bearings are equipped with mechanisms that either contain a lubricant or allow a lubricant to penetrate the contact area to provide lubrication.

[0003] In recent years, most motors used in industrial machinery and drive motors are controlled by inverters to improve efficiency. Inverter control adjusts the voltage and frequency input to the motor according to the motor's set rotational speed. As the inverter's switching frequency increases, the frequency of motor shaft voltage generation also increases. As a result, a potential difference can occur between the outer and inner rings and the rolling elements in the rolling bearings incorporated into inverter-driven motors. If this potential difference becomes large and exceeds the dielectric breakdown voltage of the oil film formed between the raceway rings and rolling elements in the bearing, a discharge can occur between the raceway rings and rolling elements, causing damage called electrolytic corrosion inside the bearing. In addition, increasing the power supply voltage allows for a smaller current even at the same output, reducing copper losses in cables and inverter elements. However, this increases the potential difference between the shaft potential and the ground potential, making dielectric breakdown of the oil film more likely.

[0004] As bearing damage due to electrolytic corrosion progresses, striped, uneven surfaces called ridge marks form on the racing surfaces of the outer and inner rings. These ridge marks can cause noise and vibration in the bearings. Therefore, efforts are underway to develop bearings that are designed to suppress the formation of ridge marks on the racing surfaces.

[0005] For example, Patent Document 1 describes a bearing test method capable of testing the anti-corrosion property of a bearing under conditions where ridge marks are likely to occur. Specifically, in the test process, the current density, which is the current value per unit contact area between the raceway surface and a plurality of rolling elements, is set to 500 mA / mm 2 or more, and a test method is described in which the temperature of the lubricating oil, the relative rotational speed between the outer member and the inner member, and the radial load applied to the bearing are set so that the oil film coefficient is 2 or more.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, under the test conditions of Patent Document 1, in the test of a general bearing, an operating time of 250 hours or more is required, and it is difficult to evaluate in a short period in the verification of the anti-corrosion effect.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide an evaluation method capable of verifying the anti-corrosion effect in a short time.

Means for Solving the Problems

[0009] The evaluation method of the anti-corrosion effect of the present invention is a method for evaluating the anti-corrosion effect in a rolling bearing having an inner ring and an outer ring and a plurality of rolling elements interposed between the inner ring and the outer ring, and the method includes lubricating between the raceway surfaces of the inner ring and the outer ring and the rolling elements with a lubricant, and rotating the rolling bearing in a state where a predetermined current flows through the rolling bearing. The method is characterized in that a lubricating oil having a relative permittivity of 2.5 or less is used as the lubricating oil of the lubricant.

[0010] The above lubricating oil is characterized by being a synthetic hydrocarbon oil.

[0011] The above test is characterized by being performed under conditions where the oil film parameter Λ is greater than 3. Furthermore, it is preferable that the ratio of the relative permittivity of the lubricating oil to the oil film parameter Λ in the test (relative permittivity / oil film parameter) is 0.5 or less.

[0012] In the above test, the maximum surface pressure of the rolling bearing was 0.3 GPa to 2.0 GPa, and the rotational speed was 500 min⁻¹. -1 ~3000 min -1 It is characterized by being such.

[0013] The above lubricant contains additives in addition to the above lubricating oil, and as a comparison to the above lubricant, a comparative lubricant containing the above lubricating oil but with different amounts or absences of the above additive is prepared, and tests are conducted using the above lubricant and the comparative lubricant to evaluate the effect of the above additive on the anti-electrolytic corrosion effect. [Effects of the Invention]

[0014] The present invention provides a method for evaluating the galvanic corrosion suppression effect, which involves lubricating the raceway surfaces of the inner and outer rings with a lubricant and the rolling elements, and then rotating the rolling bearing while a predetermined current flows through it. Since the lubricant used has a relative permittivity of 2.5 or less, conditions are created that are prone to galvanic corrosion, as shown in the examples described later, allowing for verification of the galvanic corrosion suppression effect in a short time.

[0015] Since the above lubricating oil is a synthetic hydrocarbon oil, it can eliminate the influence of components that affect the electrolytic corrosion suppression effect, compared to mineral oils that may contain sulfur-based impurities, for example, and can properly evaluate the electrolytic corrosion suppression effect.

[0016] Since the above test is performed under conditions where the oil film parameter Λ is greater than 3, a fluid lubrication state is achieved, making it easier for sparks to occur between the inner and outer rings and the rolling elements via the oil film, and consequently creating conditions under which electrolytic corrosion is more likely to occur.

[0017] In the above test, the maximum surface pressure in the rolling bearing was 0.3 GPa to 2.0 GPa, and the rotational speed was 500 min⁻¹. -1 ~2000 min -1 Therefore, the oil film thickness tends to increase, and as a result, the dielectric breakdown voltage tends to increase.

[0018] The above lubricant contains additives in addition to lubricating oil. As a comparison to the above lubricant, comparative lubricants containing lubricating oil but with different amounts or absence of additives are prepared. Tests are conducted using the lubricant and the comparative lubricant separately to evaluate the effect of the additives on the galvanic corrosion suppression effect. For example, the effect of the additives on the galvanic corrosion suppression effect can be properly evaluated compared to using a lubricant (ester oil) with a relative permittivity exceeding 2.5. [Brief explanation of the drawing]

[0019] [Figure 1] This is a cross-sectional view of an example of a rolling bearing used in the evaluation method of the present invention. [Figure 2] This is a schematic diagram of the configuration for the electrolytic corrosion test performed using the evaluation method of the present invention. [Figure 3] This is a schematic diagram of a device for measuring relative permittivity. [Figure 4] These are observational photographs of the inner track surface for Test Examples 1 to 4. [Figure 5] This is a diagram illustrating the Anderon trial. [Modes for carrying out the invention]

[0020] The inventors investigated a method for evaluating the effectiveness of galvanic corrosion suppression in a short period of time. In their investigation, they considered that the higher the dielectric breakdown voltage, the more likely ridge marks are to develop, and based on the knowledge of the relationship between dielectric breakdown voltage and polarity, they focused on the relative permittivity of the lubricating oil in the lubricant. As a result, they found that evaluation could be performed in a short time by using a lubricating oil with a relative permittivity of 2.5 or less. This invention is based on these findings.

[0021] First, an example of a rolling bearing that is the subject of the evaluation method 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 raceway surface 2a on its outer circumference and an outer ring 3 having an outer ring raceway surface 3a on its inner circumference, arranged concentrically, and a plurality of balls 4 as rolling elements are arranged between the inner ring raceway surface 2a and the outer ring raceway surface 3a. These balls 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 lubricant 7 is sealed in the bearing space at least around the balls 4. The inner ring 2, outer ring 3 and balls 4 are made of steel, and lubrication is provided by the lubricant 7 interposed between them and the balls 4.

[0022] Lubricant 7 includes at least lubricating oil, and specific embodiments include (A) a lubricating oil composition comprising lubricating oil (base oil) and additives as essential components, and (B) a grease composition comprising lubricating oil (base oil), a thickener, and additives as essential components. The thickener is not particularly limited and can be any common thickener used in the field of rolling bearings. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentonite, 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.

[0023] In the rolling bearing 1, the steel materials constituting the bearing members such as the inner ring 2, outer ring 3, and balls 4 can be any material commonly used as a bearing material. Examples include high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; ISO 683-17), carburized steel (SCr420, SCM420, etc.; ISO 683-5), stainless steel (SUS440C, etc.; ISO 16143-2), 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.

[0024] The rolling bearings targeted by the evaluation method of the present invention may be any bearings in which ridge marks may occur due to galvanic corrosion, and may include deep groove ball bearings, as well as, for example, angular contact ball bearings, cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like.

[0025] The rolling bearings described above can be used in environments and applications where electrolytic corrosion is likely to occur. For example, they are suitable for bearings that rotatably support the rotating shafts of motors and refrigerant compressors, as well as for inverter bearings. They can also be used as motor bearings in electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0026] The evaluation method of the present invention will be described below.

[0027] The present invention provides an evaluation method for a rolling bearing having an inner ring, an outer ring, and a plurality of rolling elements interposed between the inner and outer rings, as described above, for evaluating the effect of suppressing electrolytic corrosion. The outline of the test apparatus used in this method will be explained with reference to Figure 2. Note that the connection configuration of the test bearing and circuit is simplified in Figure 2. The rolling bearing described above can be used as the test bearing as appropriate.

[0028] As shown in Figure 2, the test apparatus 11 includes a test bearing 12, a shaft 13 fitted into the shaft hole of the test bearing 12, an outer member 14 on which the test bearing 12 is fitted to the inner circumference, a housing (not shown) that houses these members on the inside, and a power supply device 15. In the test apparatus 11, an electrical circuit is formed with the test bearing 12 as a component, and it is configured to allow current to flow inside the bearing.

[0029] The shaft 13 is connected to a rotating mechanism (not shown) and is configured to rotate relative to the outer member 14. The rotational drive of the rotating mechanism causes the inner ring of the test bearing 12 to rotate relative to the outer ring, and the rolling elements to roll. The shaft 13 is conductive and, for example, is rotatably supported on both sides of the housing. In the configuration of Figure 2, a slip ring 13a is electrically connected to the shaft 13. The slip ring 13a is mounted so as not to rotate relative to the housing and is electrically connected to one electrode connected to the power supply 15.

[0030] The outer member 14 is conductive, and the outer ring of the test bearing 12 is fitted onto it. The outer member 4 is electrically connected to the other electrode connected to the power supply unit 15. The outer member 14 is fixed inside the housing via an insulator, and electrical contact with the housing is blocked.

[0031] The power supply unit 15 has a constant current control function. Specifically, it adjusts the voltage so that the current flowing through the test bearing 12 is constant, based on the current value flowing through the test bearing 12. The current value set by the constant current control is not particularly limited, but from the viewpoint of causing electrolytic corrosion in a short time, it is preferable to set it to, for example, 1.0A to 10A and 2.0A to 8.0A.

[0032] For example, the current density between the inner or outer ring raceway and the rolling element is 0.50 A / mm². 2 It is controlled to be above 1.0 A / mm 2It is preferable that the current is controlled to be as described above. The current density is calculated by dividing the current flowing through the test bearing by the sum of the contact areas between the raceway surface of the inner or outer ring and each rolling element. This contact area is established by Hertz contact theory. Note that, for example, in a fluid lubrication state, the raceway rings and rolling elements do not actually come into contact, but Hertz contact theory does not take lubricating oil into consideration.

[0033] The evaluation method of the present invention involves, for example, using the test apparatus 11 shown in Figure 2, lubricating the space between the inner and outer ring raceways and the rolling elements with a lubricant, and performing a test in which the rolling bearing is rotated while a predetermined current flows through the rolling bearing.

[0034] Incidentally, electrolytic corrosion in rolling bearings occurs when the potential difference between the outer and inner rings and the rolling elements becomes large, exceeding the dielectric breakdown voltage of the oil film formed between the raceway rings and rolling elements within the bearing, causing a discharge between the raceway rings and rolling elements. As a result, ridge marks are formed on the raceway surface. Considering this mechanism of ridge mark formation, it is thought that the higher the dielectric breakdown voltage of the oil film, the larger the current that flows during discharge, and as a result, ridge marks are more likely to develop. On the other hand, there are reports that the dielectric breakdown voltage of organic materials tends to be higher for nonpolar materials than for polar materials.

[0035] Taking these factors into consideration, the evaluation method of the present invention focuses on relative permittivity as an indicator of polarity, and uses a lubricating oil with a relative permittivity of 2.5 or less as the lubricant. Relative permittivity is a parameter that indicates the degree of polarization inside a dielectric, and is defined as the ratio of the dielectric constant of the substance to the dielectric constant in a vacuum. The relative permittivity of the above lubricating oil may be 2.3 or less, or 2.2 or less. The lower limit of the relative permittivity is, for example, 2.0.

[0036] As the lubricating oil with a relative permittivity of 2.5 or less used in the evaluation method of the present invention, for example, synthetic hydrocarbon oils, paraffinic mineral oils, naphthenic mineral oils, and other mineral oils can be used. These oils may be used individually or in combination of two or more types. When two or more types are used in combination, the relative permittivity of the mixed oil must be 2.5 or less, and oils other than those mentioned above may also be used.

[0037] As synthetic hydrocarbon oils, aliphatic synthetic hydrocarbon oils such as normal paraffin oil, polybutene oil, polyisobutylene oil, and poly-α-olefin (PAO) oil, and aromatic synthetic hydrocarbon oils such as alkylbenzene oil and alkylnaphthalene oil can be used. In particular, 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.

[0038] On the other hand, lubricating oils with a relative permittivity exceeding 2.5 include ester oils and ether oils. 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. Such polar oils have a relatively low dielectric breakdown voltage, and polar groups are thought to easily adsorb onto the raceway surface to form a protective film. Therefore, as shown in the examples described later, ridge marks are less likely to form compared to non-polar oils.

[0039] The relative permittivity of the lubricating oil is measured, for example, as the relative permittivity at a frequency of 200 kHz. The relative permittivity of the lubricating oil can be measured by a well-known method such as the capacitance method. For example, in the capacitance method, an impedance measuring instrument is used as the measuring device. Specifically, a capacitor is formed by sandwiching the lubricating oil between two electrodes, an alternating current of voltage or current is applied to the lubricating oil, and the amplitude and phase difference of the alternating current of the responding current or voltage are measured to obtain the impedance Z. Then, based on the following formula (1) and the following formula (2), the relative permittivity ε r can be obtained. The relative permittivity can also be measured by the method of the examples described later. [Number]

[0040] C: Capacitance [F] S: Area of the electrode [m 2 d: Distance between electrodes [m] ε r : Relative permittivity of the lubricating oil ε0: Permittivity of vacuum (8.85 × 10 -12 [F / m]) |Z|: Absolute value of impedance [Ω] ω: Angular frequency (= 2πf), f is the measured frequency [Hz]

[0041] The kinematic viscosity of the above lubricating oil at 40 °C is not particularly limited, but for example, it is 10 mm 2 / s to 80 mm 2 / s, and it is preferably 10 mm 2 / s to 50 mm 2 / s, and it may be 20 mm 2 / s to 40 mm 2 / s. Also, the kinematic viscosity of the above base oil at 100 °C is, for example, 5.0 mm 2 / s to 12 mm 2 / s.

[0042] The above tests are preferably performed under conditions that form an oil film sufficiently thicker than the surface roughness of the rolling elements and raceways. For example, under boundary lubrication conditions (oil film parameter Λ < 1) and mixed lubrication conditions (1 < oil film parameter Λ < 3), current conduction occurs due to contact between the rolling elements and raceways, so electrolytic corrosion due to discharge is unlikely to occur. On the other hand, under fluid lubrication conditions (3 < oil film parameter Λ), an oil film is interposed between the rolling elements and raceways. Therefore, the potential difference between the two becomes large and exceeds the dielectric breakdown voltage of the oil film, causing discharge and making damage due to electrolytic corrosion (occurrence of ridge marks) more likely. From this viewpoint, it is preferable to perform the tests under conditions where the oil film parameter Λ is greater than 3. The oil film parameter is a parameter that gives the degree of interprotrusion interference in the elastohydrodynamic lubrication (EHL) region, and as shown in equation (3) below, the oil film thickness h min It is calculated by the ratio of the standard deviations of the surface roughness σ1 and σ2.

number

[0043] In the above test, the oil film parameter Λ may be 4 or greater, or 5 or greater. As the oil film parameter Λ increases, the oil film becomes thicker, making it more difficult for the raceway rings and rolling elements to conduct electricity, and increasing the damage during discharge, thus making ridge marks more likely to progress. On the other hand, if the oil film parameter Λ becomes too large, the bearing torque will increase, which may increase, for example, the power consumption of the motor. The oil film parameter Λ may be, for example, 10 or less, 8 or less, or 6 or less.

[0044] In the above test, the mean square roughness of the raceway surface is preferably 0.01 μm or less. Furthermore, the mean square roughness of the rolling element surface is preferably about 0.001 μm.

[0045] The oil film thickness can be calculated using a theoretical formula. When using a theoretical formula, for example, Cittenden's formula, represented by equation (4) below (Reference: Chittenden, RJ, Dowson, D., Dunn, JF, Taylor, CM, Proc. Roy. Soc. London, A397 (1985) 271), can be used to calculate the thickness using lubricant data and test conditions. As shown in equation (4) below, the oil film thickness depends on the velocity parameter, material parameter, and load parameter in the test.

number

[0046] In the above equation (4), R x R is the equivalent radius of curvature in the direction of flow. y R is the equivalent radius of curvature in the direction perpendicular to the flow. x is 1 / R x =(1 / R x1 )+(1 / R x2 ) is calculated by R y is 1 / R y =(1 / R y1 )+(1 / R y2 It is calculated by R. x1 R is the radius of curvature in the flow direction of one of the cylindrical bodies. x2 R is the radius of curvature in the flow direction of the other cylindrical body. y1 R is the radius of curvature in the direction perpendicular to the flow of one of the cylindrical bodies. y2 is the radius of curvature in the direction perpendicular to the flow of the other cylindrical body. Also, in equation (4) above, U is the velocity parameter, and (η0 × u) / (E' × R x It is calculated by η0 being the viscosity at normal pressure. η0 is calculated by ρ × ν, where ρ is the density of the lubricating oil and ν is the kinematic viscosity of the lubricating oil. u is the average value of the peripheral speed of one cylinder and the peripheral speed of the other cylinder. E' is the equivalent Young's modulus. E' is given by 2 / E' = {(1-ν1 2 ) / E1}+{(1-ν2 2It is calculated by {E1 / E2}, where E1 is the Young's modulus of one cylinder and E2 is the Young's modulus of the other cylinder. ν1 is the Poisson's ratio of one cylinder and ν2 is the Poisson's ratio of the other cylinder.

[0047] In equation (4) above, G is a material parameter and is calculated by α × E′. α is the viscosity-pressure coefficient. α is calculated by the Wu-Klaus-Duda equation. More specifically, α is (0.1657 + 0.2332 × log 10 ν) × m × 10 -8 It is calculated by the following: ν is the kinematic viscosity of the lubricating oil. m is a constant determined by the lubricating oil and is calculated by the Walther-ASTM formula. More specifically, m is log 10 { 10 (ν+0.7) = -m × log 10 It is calculated by T + K. T is the temperature, and K is a constant determined by the lubricating oil. By substituting the two temperatures and the kinematic viscosity at those temperatures into the Walther-ASTM equation and solving the simultaneous equations, the values ​​of m and K can be calculated. W is the load parameter, and w / (E' × R x 2 It is calculated by ), where w is the load.

[0048] In the tests performed using the evaluation method of the present invention, radial and axial loads may be applied to the test bearing 12. For example, in Figure 2, the shaft 13 has a stepped portion that contacts the width surface of the inner ring of the test bearing 12, allowing an axial load to be applied to the test bearing 12. These loads are applied to the oil film thickness h min Since this depends on the surface pressure between the raceway and the rolling element, the oil film thickness h minIt is preferable to adjust the value to be greater than, for example, 3. Specifically, the radial load is 30N to 200N and the axial load is 30N to 200N, and in the embodiment below, the axial load is greater than the radial load. Furthermore, the maximum surface pressure in the rolling bearing in the above test is, for example, 0.3 GPa to 3.0 GPa, and preferably 0.3 GPa to 2.0 GPa.

[0049] In the tests conducted using the evaluation method of the present invention, the rotational speed of the test bearing 12 is not particularly limited, but in order to make the oil film parameter Λ in the test greater than 3, for example, 500 min -1 ~5000min -1 And, 500 min -1 ~3000 min -1 It is preferable.

[0050] Furthermore, the ratio of the relative permittivity of the lubricating oil to the oil film parameter Λ in the test (relative permittivity / oil film parameter) is preferably 0.5 or less, and may also be 0.4 or less.

[0051] According to the evaluation method of the present invention, ridge marks associated with electrolytic corrosion can be easily generated on the raceway surface in the above test. Therefore, evaluation can be performed in a short time. Specifically, in the above test, ridge marks are generated in 30 hours or less, preferably in 10 hours or less. In other words, the electrolytic corrosion suppression effect can be evaluated in 30 hours or less, preferably in 10 hours or less, using this test. Therefore, the electrolytic corrosion suppression effect can be evaluated more quickly than conventional tests that require a long time, improving the workability of screening and other tasks. The presence or absence of ridge marks can be confirmed by observing the surface of the raceway (visual inspection or optical observation, etc.).

[0052] One aspect of the above evaluation method is to evaluate the effect of additives on the anti-electrolytic corrosion effect. Specifically, a lubricant containing the additive in addition to the above lubricating oil is prepared, and a comparative lubricant containing the above lubricating oil but with different amounts or absences of the additive is prepared as a comparison to the above lubricant. Then, tests are conducted using the lubricant and the comparative lubricant, and the effect of additives on the anti-electrolytic corrosion effect can be evaluated from the test results obtained. Furthermore, by using different types of additives, it is also possible to evaluate the superiority or inferiority of different additives in terms of anti-electrolytic corrosion effect.

[0053] In the evaluation method of the present invention, the additive to be evaluated is not particularly limited, but examples include phosphorus-based additives containing phosphorus (P) in their molecular structure, and sulfur-based additives (such as sulfide compounds) containing sulfur (S) in their molecular structure.

[0054] For example, phosphorus-based additives include phosphate esters, acidic phosphate esters, phosphite esters, acidic phosphite esters, thiophosphates, thiophosphites, zinc alkyldithiophosphate (ZnDTP), and molybdenum alkyldithiophosphate (MoDTP). These can be used individually or in combination.

[0055] The phosphorus-based additives listed above are generally used as extreme pressure additives and are known to adsorb to the surface of raceway surfaces. From the examples below, it has been found that phosphorus-based additives also contribute to the suppression of electrolytic corrosion. Therefore, the evaluation method of the present invention can be suitably used for screening phosphorus-based additives. For example, by using a lubricating oil with a relative permittivity of 2.5 or less as a base oil, and varying the type and amount of phosphorus-based additives to create multiple test lubricants, the optimal type and amount of phosphorus-based additive can be obtained in a short time by performing the above test using these multiple test lubricants. Sulfur-based additives can be investigated in a similar manner.

[0056] The content of the above-mentioned additive is, for example, 0.1% to 10% by mass, preferably 0.1% to 5.0% by mass, relative to the total amount of the lubricant. If the above-mentioned additive is a phosphorus-based additive, the phosphorus content is preferably 0.2% by mass or more and less than 2.0% by mass, relative to the total amount of the lubricant. The above-mentioned phosphorus content is preferably derived solely from the phosphorus-based additive contained in the lubricant.

[0057] The evaluation method of the present invention is not limited to the configuration described above and can be modified as appropriate. [Examples]

[0058] The present invention will be specifically described by the following test examples, but the invention is not limited in any way by these examples.

[0059] Lubricants with the compositions shown in Table 1 were prepared. These lubricants are lubricating oil compositions consisting of lubricating oil and additives. Three types of lubricating oils, shown in the lower column of Table 1, were used. The relative permittivity of each lubricating oil was measured using a commercially available capacitance transducer (30°C, 100kHz). In Table 1, the values ​​in the "Additives" column represent the mass percentage of phosphorus (P) relative to the total amount of lubricant.

[0060] For measuring the relative permittivity of the lubricating oil, a capacitance transducer MC-130 and electrode cell manufactured by YEI Corporation were used. Figure 3 shows a schematic diagram of the measurement apparatus 16. The capacitance transducer 17 used corresponds to a capacitor component fluctuation of 1 pF at an output of 1 V. The capacitance value of the electrode cell 18 used is 5.17 pF. For the measurement method, a metal container was prepared with the electrode cell 18 and a thermocouple for measuring the temperature of the sample fixed in it, and the output voltage V0 of the capacitance transducer 17 in air was obtained. Next, the metal container was heated with a ring heater 19 to adjust the temperature of the sample 20 to an arbitrary value. The voltage value V1 output by the capacitance transducer 17 was converted to the relative permittivity using the following formula (5).

number

[0061] A rolling bearing (inner ring, outer ring, and steel balls made of bearing steel SUJ2) supporting the rotating shaft, simulating an industrial motor, was sealed with various lubricants and tested under the following conditions: combined load of 59N, rotational speed of 1600 min⁻¹. -1 The operating conditions were set, and the test was conducted with a constant current of 5.0A flowing through the test bearing (6206). Table 1 shows the applied voltage adjusted to ensure a constant current flow.

[0062] <Test Conditions> Bearing: 6206T2X2CMLLU Rolling element: Steel ball (standard bearing) Power supply current: 5.0A Test machine rotation speed: 1600 min⁻¹ -1 Radial load: 38.2N Axial load: 101N Maximum surface pressure: 0.74GPa Oil film parameter Λ(35℃): 6.56 Exam duration: 7 hours Number of test samples: 1 of each

[0063] The oil film parameter Λ under the above test conditions was calculated using equation (3) above. The oil film thickness in equation (3) was calculated using Cittenden's formula, with the base oil data and test conditions. The surface roughness (mean square roughness) of the rolling elements and the inner ring (mean square roughness) were measured using a stylus-type surface roughness measuring instrument for the rolling elements and inner ring before the test. Under these test conditions, the oil film parameter Λ is 3 or greater. Generally, when the oil film parameter Λ is 3 or greater, fluid lubrication occurs between the two surfaces, resulting in non-contact. Therefore, under the above test conditions, it can be said that the steel balls do not come into contact with the inner and outer rings and wear. In Test Examples 1 and 2, the ratio of the relative permittivity of each lubricating oil to the oil film parameter Λ in the test (relative permittivity / oil film parameter) was 0.33 and 0.35, respectively.

[0064] Then, the surface of the inner ring raceway was optically observed 7 hours after the test. Observation photographs of Test Examples 1 to 4 are shown in Figure 4. As shown in Figure 4, in Test Example 1 (PAO oil only), ridge marks (striped irregularities) were clearly formed on the inner ring raceway surface. In Test Example 2 (mineral oil only), faint ridge marks were also observed. On the other hand, in Test Example 3 (ester oil only), no ridge marks were observed.

[0065] In contrast, no ridge marks were observed in Test Example 4, where a phosphorus-based additive was added to mineral oil. This result indicates that galvanic corrosion was prevented by the addition of the phosphorus-based additive. In other words, the evaluation method of the present invention allows for the proper evaluation of the galvanic corrosion suppression effect in a short time (7 hours in this test), and in this case, the addition of a phosphorus-based additive (trioctyl phosphate, phosphorus content 0.5% by mass) can be evaluated as having a positive effect on the galvanic corrosion suppression effect. Similarly, no ridge marks were observed in Test Example 5, where a phosphorus-based additive was added to PAO oil (not shown).

[0066] On the other hand, when ester oil is used, for example (Test Example 3), ridge marks do not occur in the first place, making it difficult to properly evaluate the additives.

[0067] Next, an Anderon test was performed. The inner ring after the above-mentioned electrolytic corrosion test, a new outer ring, a crown-type cage, and ceramic rolling elements were prepared. They were ultrasonically cleaned using petroleum benzine and assembled so that the outer ring markings, inner ring markings, and the openings of the retaining claws of the crown-type cage were on the same plane (see Figure 5). 10 μL of PAO6 was dropped onto the raceway surface and the inner ring 22 was rotated gently. The Anderon measuring machine was mounted so that the opening of the crown-type cage 25 was facing forward. An axial load of 100 N was applied to the outer ring 23 of the rolling bearing 21, and the Anderon value was measured while rotating at a rotation speed of 1800 rpm. The frosted portion of the inner ring 22 is shown with cross-hatching. Sampling was performed by acquiring one data point for every 10 seconds of rotation, and the average value of five samples was calculated for each band.

[0068] Since the Anderon H band (frequency 1800Hz to 10000Hz) is particularly useful for evaluating electrolytic corrosion, the calculated Anderon values ​​were categorized as follows: less than 100 was designated as "A", 100 to less than 200 as "B", and 200 or more as "C".

[0069] As shown in Table 1, the Anderon value correlated with the degree of ridge marking. Specifically, the Anderon value was highest in Test Example 1, where ridge marks were prominent, and lower in Test Examples 3 to 5, where no ridge marks occurred. [Industrial applicability]

[0070] Since the evaluation method of the present invention allows for verification of the galvanic corrosion suppression effect in a short time, it can be suitably used in studying countermeasures against galvanic corrosion in rolling bearings used in automobiles, industrial machinery, wind turbines, and the like. [Explanation of Symbols]

[0071] 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Balls (rolling elements) 5 Cage 6. Sealing member 7 Lubricant 8a opening 8b opening 11 Test equipment 12 Test bearings 13 shafts 14 Outer member 15 Power supply 16 Measuring device 17 Capacitive Converters 18 electrode cells 19 Ring Heater 20 samples 21 Rolling bearings 22 Inner Ring 23 Outer ring 24 Rolling elements 25 Crown retainer

Claims

1. A method for evaluating the effect of suppressing electrolytic corrosion in a rolling bearing having an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, The above method involves lubricating the raceway surfaces of the inner and outer rings with a lubricant and the rolling elements, and rotating the rolling bearing while a predetermined current flows through it. A method for evaluating the effect of suppressing electrolytic corrosion, characterized in that a lubricating oil with a relative permittivity of 2.5 or less is used as the lubricating oil for the aforementioned lubricant.

2. The method for evaluating the electrolytic corrosion suppression effect according to claim 1, characterized in that the lubricating oil is a synthetic hydrocarbon oil.

3. A method for evaluating the galvanic corrosion suppression effect according to claim 1 or 2, characterized in that the rolling bearing is rotated under the condition that the oil film parameter Λ is greater than 3.

4. The method for evaluating the galvanic corrosion suppression effect according to claim 3, characterized in that the ratio of the relative permittivity of the lubricating oil to the oil film parameter Λ (relative permittivity / oil film parameter) is 0.5 or less.

5. The maximum surface pressure in the aforementioned rolling bearing is 0.3 GPa to 2.0 GPa, and the rotational speed is 500 min. －１ ~3000 min －１ A method for evaluating the electrolytic corrosion suppression effect according to claim 1 or 2, characterized in that it is the same as the present invention.

6. The method for evaluating the effect of suppressing electrolytic corrosion according to claim 1 or 2, characterized in that the lubricant contains a phosphorus-based additive in addition to the lubricating oil, and a comparative lubricant containing the lubricating oil and having different amounts or absences of the phosphorus-based additive is prepared as a comparison target for the lubricant, and the rolling bearing is rotated using the lubricant and the comparative lubricant, respectively, to evaluate the effect of the phosphorus-based additive on the effect of suppressing electrolytic corrosion.

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