Evaluation method for rolling bearing grease

Abstract

To provide a rolling bearing excellent in channeling performance, and an electric motor incorporated with the rolling bearing.SOLUTION: A rolling bearing 1 has an inner ring 2 and an outer ring 3, a plurality of rolling elements 4 disposed between the inner ring 2 and the outer ring 3, and grease 7 sealed into a bearing internal space. The grease 7 includes a base oil having a kinematic viscosity at 40°C of 6.12 mm2 / s to 74.8 mm2 / s, and a thickener, and apparent viscosity gradient n in a formula (1) calculated from the apparent viscosity of the grease at an arbitrary shearing speed of at least two points or more measured by using a rheometer, is 0.84 or less. In the formula (1), η:apparent viscosity [Pa s], n:apparent viscosity gradient, γ:shearing speed [s-1], and a:constant inherent to each king of grease.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a grease-filled rolling bearing and an electric motor incorporating the rolling bearing. [Background technology]

[0002] In recent years, due to environmental issues such as global warming, automobiles and industrial machinery are required to be even more energy-efficient. In particular, industrial motors are said to account for about 40% of the world's total electricity consumption, and therefore require high efficiency.

[0003] Against this backdrop, motor efficiency regulations are being implemented in countries around the world. In Japan, a new premium efficiency standard has been applied to induction motors with a power output of 0.75kW or more but less than 7.5kW sold since January 2017. Furthermore, there is a movement toward next-generation efficiency regulations, and the development of even higher-efficiency motors is progressing. In order to achieve these standards, efficiency improvements are essential for each component of the motor, and rolling bearings, one of these components, are required to have even lower torque.

[0004] Grease is generally used as a lubricant for rolling bearings. Most of the grease sealed in a rolling bearing adheres to the rolling elements and cage as the bearing rotates, and gradually moves into a stationary space (the space excluding the area through which the rolling elements and cage pass) while being agitated, and then comes to rest. Here, the agitation state of the grease inside the bearing during grease lubrication can be classified into churning and channeling (see, for example, Non-Patent Document 1). Specifically, the state in which the grease moves due to agitation and the bearing torque fluctuates is called churning, and the state in which the grease movement is largely complete and the bearing torque stabilizes is called channeling. In this specification, the time from the start of operation to reaching channeling is called the "channeling transition time".

[0005] Furthermore, churning is a state where the grease inside the bearing flows with significant agitation and shearing, and the grease impedes the rotation of the cage and rolling elements, so bearing torque tends to increase. In contrast, channeling is a state where most of the grease inside the bearing does not flow, and grease flows only in limited areas such as the vicinity of the lubrication parts between the rolling elements and the race rings, so bearing torque tends to decrease. PRIOR ART DOCUMENTS NON-PATENT LITERATURE

[0006] NON-PATENT LITERATURE 1 Lugt, P.M., "Grease Lubrication in Rolling Bearings", John Wiley & Sons, 2013, p.149-155 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0007] From the viewpoint of energy conservation, it is desirable for rolling bearings to be operated in a channeling state. However, the relationship between channeling, the physical properties of grease, and the operating conditions of bearings is not well understood.

[0008] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a rolling bearing excellent in channeling properties, and an electric motor incorporating the rolling bearing. MEANS FOR SOLVING THE PROBLEM

[0009] The rolling bearing of the present invention is 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 grease sealed in the inner space of the bearing, wherein the grease has a kinematic viscosity at 40°C of 6.12 mm 2 / s to 74.8 mm 2comprises a base oil / s and a thickener, wherein an apparent viscosity gradient n in the following formula (1) calculated from the apparent viscosity of the grease at any shear rate of at least two or more points measured using a rheometer is 0.84 or less. [Mathematical formula] wherein in the formula, η: apparent viscosity [Pa·s], n: apparent viscosity gradient, γ: shear rate [s -1 , a: a unique constant for each grease type.

[0010] the apparent viscosity gradient n is a gradient between the apparent viscosity at a shear rate of 10 s -1 to 300 s -1 and the apparent viscosity at a shear rate of 1000 s -1 to 5000 s -1 , which is characterized in that

[0011] the apparent viscosity gradient n is 0.75 to 0.84.

[0012] the rolling bearing has a dm·n value of 6.5×10 4 or less, and is a bearing used for low-speed rotation.

[0013] the rolling bearing is a bearing that supports a spindle of a machine tool.

[0014] An electric motor of the present invention comprises a stator, a rotor, and a rolling bearing that rotatably supports a rotating shaft, wherein the rolling bearing is the rolling bearing of the present invention. [Advantageous Effects of Invention]

[0015] The rolling bearing of the present invention is a bearing filled with grease, and the grease has a kinematic viscosity at 40°C of 6.12 mm 2 / s to 74.8 mm 2The grease contains a base oil and thickener of / s, and the apparent viscosity gradient n in formula (1) calculated from the apparent viscosity of the grease measured using a rheometer is 0.84 or less. Therefore, it quickly transitions to a channeled state during bearing operation and exhibits excellent channeling properties. This makes it possible to reduce bearing torque.

[0016] The above rolling bearing is filled with grease having a predetermined viscosity characteristic, so the dm·n value is 6.5 × 10 4 Even when used at the following low rotational speeds, the grease adhering to the vicinity of the retainer can be scattered, allowing for a quick transition to the channeling state.

[0017] The bearings supporting the spindle of a machine tool are susceptible to heat generation due to grease agitation during churning, which can lead to a deterioration in machining accuracy and a shortened lifespan of the bearings themselves. In contrast, using the above-mentioned rolling bearings, which have excellent channeling properties, as the spindle bearings of a machine tool can suppress the deterioration of machining accuracy and shorten the lifespan of the bearings.

[0018] Since the electric motor of the present invention incorporates the rolling bearing of the present invention as a rolling bearing that rotatably supports the rotating shaft, it contributes to increasing the efficiency of the electric motor. [Brief explanation of the drawing]

[0019] [Figure 1] This figure shows an example of a rolling bearing of the present invention. [Figure 2] This is a schematic diagram showing an example of a rotary rheometer. [Figure 3] This is a diagram showing the apparent viscosity gradient of the grease. [Figure 4] This is a schematic diagram showing an example of a capillary rheometer. [Figure 5] This figure shows the relationship between channeling transition time and apparent viscosity gradient. [Modes for carrying out the invention]

[0020] The inventors of this invention have conducted extensive research on the stirring state (churning and channeling) of grease within bearings and have found a correlation between the stirring state and the apparent viscosity gradient of the grease. This invention is based on these findings.

[0021] An example of a rolling bearing 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, with a plurality of balls 4 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 grease 7 is sealed around at least the balls 4. The inner ring 2, outer ring 3 and balls 4 are made of an iron-based metal material, and the grease 7 is interposed on the raceway surface with the balls 4 to lubricate them.

[0022] The grease sealed in the rolling bearing of the present invention has a kinematic viscosity of 6.12 mm at 40°C. 2 / s~74.8mm 2 It contains a base oil of / s and a thickener, and is characterized in that the apparent viscosity gradient n of the grease, as described later, is 0.84 or less.

[0023] Generally, bearing torque is greatly influenced by the agitation state of the grease. For example, in the case of channeling, the grease is agitated during rotation, reducing the amount of grease adhering to the rolling element surface and raceway surface, which tends to result in low torque. On the other hand, in the case of churning, the grease agitated by rotation returns to the raceway surface, resulting in a consistently high amount of grease adhering to the rolling element surface and raceway surface, which tends to result in high torque. Therefore, grease with high channeling properties, that is, grease with a short channeling transition time, is desired.

[0024] The rolling bearing of the present invention can improve channeling performance and reduce bearing torque due to stirring resistance by using grease with the specified physical properties as described above. In particular, as shown in the examples, it exhibits excellent channeling performance even under low-speed rotation conditions where grease adhering to the cage and other components does not scatter due to centrifugal force.

[0025] In the grease used in the present invention, the base oil, thickener, and additives added as needed can be any known combination within a range where the kinematic viscosity of the base oil and the apparent viscosity gradient n of the grease satisfy the above numerical range.

[0026] The base oil can be a common type typically used in the grease field. For example, highly refined oils, mineral oils, ester oils, ether oils, synthetic hydrocarbon oils (PAO oils), silicone oils, fluorinated oils, and mixtures thereof can be used. The kinematic viscosity of the base oil at 40°C is 6.12 mm². 2 / s~50.0mm 2 It is preferable that it be / s.

[0027] The thickener can be one of the common types used in the field of grease. 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. The amount of thickener added is not particularly limited, but it is preferable that it be included in an amount of 5% to 30% by mass relative to the total amount of grease.

[0028] Examples of additives include amine-based and phenol-based antioxidants, chlorine-based, sulfur-based, and phosphorus-based compounds, extreme pressure agents such as organic molybdenum, and rust inhibitors such as petroleum sulfonates, dinonyl naphthalene sulfonates, and sorbitan esters.

[0029] Here, the apparent viscosity gradient n can be calculated using the following method.

[0030] First, the apparent viscosity of the grease at at least two arbitrary shear rates is measured by rheological measurement using a rheometer. Preferably, a rotary rheometer having a cone-plate type cell is used as the rheometer. An overview of such a rheometer is shown in Figure 2. As shown in Figure 2, the rotary rheometer 11 consists of a cone-plate type cell 12 and a horizontal disc plate 13. The cell 12 and the plate 13 are arranged to be in contact at one point (with a slight gap), and the sample grease 14 is placed between them. In this rheometer, the shear rate applied to the grease 14 is the same at any position, regardless of the distance from the center of the cell. Conditions for rheological measurement include (1) dependence on rotational speed at constant temperature and constant rotation direction, (2) dependence on vibration frequency at constant temperature and constant shear strain, and (3) dependence of dynamic viscoelasticity on shear stress at a constant frequency, but in this invention, measurements are mainly performed under condition (1).

[0031] The specific rheological measurement conditions involve using a rotary rheometer (Thermo Fisher Scientific HAAKE RheoWin MARS1) with a cone-plate type cell having a diameter of 20 mm and a tip angle of 178°, at a constant temperature and direction of rotation, such as at 20°C. In this case, the apparent viscosity is defined as the viscosity at which steady states are reached at at least two arbitrary shear rates. There are no particular restrictions on the apparent viscosity measured by the rheometer, but 10s -1 ~300s -1 The apparent viscosity at the shear rate and 1000 s -1 ~10000s -1 Preferably, it contains apparent viscosity at the shear rate, 10s -1 ~100s -1 The apparent viscosity at the shear rate and 1000 s -1 ~5000s -1 It is more preferable to include the apparent viscosity at the shear rate.

[0032] Figure 3 shows an example with a shear rate of 100 s. -1 and shear rate 3000s -1 The results of measuring the apparent viscosity at 100 s are shown. Figure 3 is a log-log graph with the logarithmic scale of shear rate γ on the horizontal axis and the logarithmic scale of the apparent viscosity η of the grease on the vertical axis, plotting the measurement results. The straight line connecting each plot is represented by equation (1) below, and the apparent viscosity gradient n can be calculated from this equation (1). In Figure 3, the apparent viscosity gradient n is given by the shear rate 100 s -1 ~3000s -1 This is calculated as a viscosity gradient relative to [the given value].

number

[0033] In the above, the apparent viscosity gradient n is calculated from the measurement results of two apparent viscosity points, but the apparent viscosity gradient n may also be calculated based on the measurement results of three or more apparent viscosity points. For example, the shear rate between the two shear rates mentioned above (in the case of Figure 3, for example, a shear rate of 1000 s) -1 The apparent viscosity may be measured at ) and the apparent viscosity gradient n may be calculated using three points including that point. Alternatively, the apparent viscosity at shear rates lower or higher than the range of the two points may be used. When using measurement results from three or more points, the apparent viscosity gradient n is calculated from the regression line obtained by the least squares method.

[0034] Furthermore, the apparent viscosity of grease can be measured not only using a rotary rheometer, but also, for example, using a capillary rheometer. An overview of viscosity measurement using a capillary rheometer is shown in Figure 4. As shown in Figure 4, the capillary rheometer 21 has a cylinder 23 with a capillary 24 at the bottom, a piston 22 that can move up and down inside the cylinder 23, and a load cell 26 provided at one end of the piston 22. With grease 25 filled inside the cylinder 23, the piston 22 is lowered at a constant speed, and the load p when the grease 25 is pushed out is detected by the load cell 26. Using the dimensions of each part of the capillary rheometer 21, the apparent viscosity η at at least two arbitrary shear rates (unit: 1 / s) can be determined according to equations (2) to (4) below. Then, the apparent viscosity gradient n is calculated from the obtained equation (1) above.

[0035] γ = 32Q / πD 3 ...(2) τ = pD / 4L···(3) η = τ / γ···(4) However, the symbols in equations (2) to (4) above represent: Q: Volumetric flow rate [mm 3 [s], D: capillary inner diameter [mm], p: detected load [Pa], L: capillary length [mm], γ: shear rate [s] -1 Q is the cross-sectional area of ​​the piston [mm²]. 2 This value is obtained by multiplying [ ] by the piston speed [mm / s].

[0036] In the rolling bearing of the present invention, the apparent viscosity gradient n of the grease calculated as described above is 0.84 or less, preferably 0.60 to 0.84, and more preferably 0.75 to 0.84.

[0037] In Figure 1, a deep groove ball bearing is shown as an example of a rolling bearing according to the present invention, but it can also be applied to 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.

[0038] The rolling bearing of the present invention is applicable, for example, to motor bearings incorporated into electric motors, bearings supporting the spindles of machine tools, axle bearings, and the like. Furthermore, because the rolling bearing of the present invention exhibits excellent channeling even at low rotational speeds, it is particularly suitable for low-speed rotation applications. For example, a dm·n value of 20 × 10⁻¹⁰ 4 This applies to bearings used in the following applications, where the dm·n value is 20 × 10. 4 The following conditions for use refer to the main rotational speed (steady-state rotational speed) of the bearing under its operating conditions, where the dm·n value is 20 × 10⁻¹⁰. 4 The following applies: The dm·n value is 10 × 10 4 The following is also acceptable: 6.5 × 10 4 The following is also acceptable: 3.0 × 10 4 The following is also acceptable. In this case, the lower limit of the dm·n value is not particularly limited, but for example, 1.0 × 10 4 That is the case.

[0039] Furthermore, the rolling bearing of the present invention can be used, for example, for 2000 min -1 This applies to bearings used in the following rotational speed range: 1500 min⁻¹. -1 The following is also acceptable. Specifically, a rotational speed of 1800 min⁻¹ -1 Motor bearings for general-purpose motors, and rotational speed 1500 min⁻¹ -1 This applies to axle bearings, etc.

[0040] The electric motor of the present invention comprises a stator, a rotor, and rolling bearings that rotatably support the rotating shaft. More specifically, the electric motor has a casing, a stator fixed to the casing, a rotor positioned opposite the stator, a rotating shaft that rotates integrally with the rotor, and rolling bearings that rotatably support the rotating shaft relative to the casing. Generally, two rolling bearings are provided spaced apart from the rotating shaft. The rolling bearings incorporated into this electric motor correspond to the rolling bearings of the present invention. One embodiment of the electric motor of the present invention is a sinusoidal three-phase AC motor.

[0041] In recent years, the international standard IEC60034-30 has been published, which defines the efficiency classes of motors driven at a constant speed. Efficiency classes are classifications of efficiency standards, with IE1 (standard efficiency), IE2 (high efficiency), and IE3 (premium efficiency) defined. Due to the trend towards energy conservation, motors that conform to IE2 and IE3 standards are in demand.

[0042] The rolling bearing of the present invention offers excellent channeling and low torque, resulting in superior motor efficiency and making it suitable for electric motors that meet the IE3 standard. The IE3 standard, for example, requires an efficiency of 80.7% for a three-phase AC motor with 2 poles and a rated output of 0.75 kW.

[0043] This invention can also be used as a method for evaluating grease to assess its channeling properties. Specifically, the above evaluation method is an evaluation method for evaluating the channeling properties of a grease containing a base oil and a thickener, which is sealed in a rolling bearing comprising an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and is characterized in that the apparent viscosity of the grease is measured at at least two arbitrary shear rates using a rheometer, and the channeling properties of the grease are evaluated based on the apparent viscosity gradient n in the following formula (1) calculated from the measurement results and the kinematic viscosity of the base oil at 40°C.

number

[0044] Here, "evaluating channeling properties" means determining the quality of the channeling properties of the grease. High channeling properties refer to the grease having a short channeling transition time (e.g., within 120 minutes) and being able to maintain a stable channeled state.

[0045] Generally, churning and channeling properties are evaluated by actually rotating the bearing, but this evaluation takes several tens of minutes to several days. In contrast, the above evaluation method evaluates channeling properties based on the apparent viscosity gradient n of the grease and the kinematic viscosity of the base oil at 40°C, for example, by evaluating the length of the channeling transition time. Therefore, it is possible to determine the superiority or inferiority of channeling properties without actually performing an evaluation test by rotating the bearing.

[0046] Furthermore, while viscous migration stress (see Japanese Patent Publication No. 2016-204623) has been conventionally known as an index for evaluating channeling performance, viscous migration stress does not necessarily correlate with channeling performance, and in particular, it has been difficult to apply under relatively low rotational conditions where the grease adhering to the retainer does not scatter due to centrifugal force. In contrast, the index (apparent viscosity gradient n) obtained by the above evaluation method is suitable for 2000 min -1 Because it shows a good correlation with channeling transition time even under the following rotational conditions, it can be used to evaluate greases for rolling bearings used in all rotational speed ranges.

[0047] The apparent viscosity gradient n, as shown in the examples described later, correlates with the channeling transition time. Specifically, in the region where the apparent viscosity gradient n is above a certain threshold, the channeling transition time tends to increase as the apparent viscosity gradient n increases. Therefore, the evaluation method of the present invention can evaluate channeling properties based on the magnitude of the calculated apparent viscosity gradient n. For example, by comparing the apparent viscosity gradient n with a predetermined threshold, if the apparent viscosity gradient n is below the predetermined threshold, it can be determined that the grease has high channeling properties, and if the apparent viscosity gradient n is greater than the predetermined threshold, it can be determined that the grease has low channeling properties or is churning. The predetermined threshold can be set in advance by experiments conducted beforehand. For example, the threshold can be set to 0.84.

[0048] In this case, the kinematic viscosity of the base oil at 40°C is 6.12 mm². 2 / s~74.8mm 2In the case of / s, greases with an apparent viscosity gradient n of 0.84 or less can be evaluated as having higher channeling properties compared to greases with an apparent viscosity gradient n greater than 0.84.

[0049] Furthermore, by comparing the magnitude of the apparent viscosity gradient n among multiple greases, it is possible to select the grease with the highest channeling properties. [Examples]

[0050] The apparent viscosity gradient n was calculated for eight types of grease (Examples 1-3 and Comparative Examples 1-5). First, the apparent viscosity of each grease was measured using a rheometer (Thermo Fisher Scientific HAAKE RheoWin MARS1) with a cone-plate type cell having a diameter of 20 mm and a tip angle of 178°. Shear rate: 100 s -1 and shear rate 3000s -1 The apparent viscosity of each grease was measured when it reached a steady state. Using the above equation (1) derived from the obtained measurement results, the apparent viscosity gradient n and the intrinsic constant a for each type of grease were calculated. The apparent viscosity gradient n for each grease is shown in Table 1.

[0051] Furthermore, of the eight types of grease, the base oils of the greases in Examples 1-3 and Comparative Examples 1-3 are within the range specified for General Purpose Grease Type 1 in JIS K2220:2013 (kinematic viscosity at 40°C: 6.12 mm²). 2 / s~74.8mm 2 It is within / s). On the other hand, the base oils of Comparative Examples 4 and 5 have a kinematic viscosity of 100 mm at 40°C. 2 It is / s.

[0052] Furthermore, to evaluate the channeling properties of each grease, bearing torque tests were conducted to measure the bearing torque over time. The testing machine is designed to apply a load in the axial direction of the bearing. The test bearing rotates at the inner ring, and a load cell is connected to the housing of the outer ring to measure the bearing torque. A deep groove ball bearing 6204 (bearing dimensions: inner diameter 20 mm, outer diameter 47 mm, width 14 mm) was filled with each grease so that the amount of grease filled was 50% of the static space to obtain a test bearing. The test bearing was subjected to an axial load of 20 N and a rotational speed of 900 min⁻¹. -1 The inner ring was rotated under the following conditions. The dm·n value under these conditions is approximately 3.0 × 10⁻⁶. 4 That is the case.

[0053] In the test, the tangential force acting on the housing during bearing rotation was measured using a load cell, and the bearing torque was calculated from the outer diameter of the housing. The bearing torque was calculated over time (every minute) from the start of the test. The channeling transition time was defined as the time when the fluctuation in bearing torque fell to 5% or less in the most recent 3 hours, or when the bearing torque fell to 3 Nmm or less. The channeling transition times for each grease are listed in Table 1.

[0054] [Table 1]

[0055] Figure 5 shows the relationship between channeling transition time and the apparent viscosity gradient n of the grease. Compared to the greases in Examples 1-3, which had large apparent viscosity gradients n, the time to transition to the channeling state was longer. Furthermore, from the intersection of the approximate line a obtained from the results of Examples 1-3 and the approximate line b obtained from the results of Comparative Examples 1-3, it was found that if the apparent viscosity gradient n is 0.84 or less, the channeling transition time can be kept short. Also, in Comparative Examples 4-5, which had high kinematic viscosity of the base oil, the channeling transition time increased as the apparent viscosity gradient n increased, similar to the greases with low kinematic viscosity. Furthermore, the greases in Comparative Examples 4-5 had longer channeling transition times compared to the greases with low kinematic viscosity.

[0056] Next, we examined the relationship between the dm·n value and the channeling transition time. Except for changing the dm·n value, the procedure was carried out in the same manner as the bearing torque test described above, and the channeling transition time was determined for each test example. A channeling transition time of 100 min or less was evaluated as "○", and a time exceeding 100 min was evaluated as "×". The results are shown in Table 2. Note that the dm·n value in Table 2 is 3.0 × 10⁻⁶. 4 The results correspond to the test results in Table 1 above.

[0057] [Table 2]

[0058] As shown in Table 2, the dm·n value is 20 × 10 4 In all of these test examples, the channeling transition time was 100 minutes. It is thought that at high rotational speeds, the grease inside the bearing is easily scattered and moves to stationary spaces such as the sealing surface, leading to an earlier transition to channeling. On the other hand, as the dm·n value decreased, the number of test cases where the channeling transition time exceeded 100 mins increased. It is thought that the channeling transition time increased because grease adhering to the cage and other parts is less likely to scatter at low rotational speeds. Among these, Examples 1 to 3 maintained a short channeling transition time even at low rotational speeds, demonstrating excellent channeling performance.

[0059] Based on the above, the rolling bearing of the present invention has a base oil with a kinematic viscosity of 6.12 mm at 40°C. 2 / s~74.8mm 2 Since the rotation speed is / s and the apparent viscosity gradient n of the grease is 0.84 or less, it exhibits excellent channeling performance even at low rotational speeds. [Industrial applicability]

[0060] The rolling bearing of the present invention has excellent channeling properties and can therefore be widely used as a low-torque bearing. It is particularly suitable for bearings that operate at low rotational speeds. [Explanation of Symbols]

[0061] 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Balls (rolling elements) 5 Cage 6. Sealing member 7. Grease 8 openings 11. Rotary Rheometer 12 cone plate type cells 13 Horizontal disc plate 14 Grease 21 Capillary Rheometer 22 pistons 23 liters 24 capillaries 25 Grease 26 load cells

Claims

1. An evaluation method for evaluating the channeling properties of a grease containing a base oil and a thickener, which is sealed in the internal space of 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 aforementioned rolling bearing has a dm·n value of 6.5 × 10 ４ This bearing is used for the following low-speed rotations: The evaluation method is based on the kinematic viscosity of the base oil of the grease at 40°C being 6.12 mm². ２ / s ~ 74.8mm ２ In the case of / s, the measurement is taken using a rheometer at 20°C and 100s. －１ The apparent viscosity of the grease at the shear rate, and at 20°C and 3000 s －１ A method for evaluating grease for rolling bearings, characterized by evaluating channeling properties based on the value of the apparent viscosity gradient n in the following formula (1), which is calculated from the apparent viscosity of the grease at a shear rate. [Math 1] However, the symbols in the formula represent: η: apparent viscosity [Pa·s], n: apparent viscosity gradient, γ: shear rate [s] －１ ], a: a constant specific to each type of grease.

2. The method for evaluating rolling bearing grease according to claim 1, characterized in that grease with an apparent viscosity gradient n of 0.84 or less is evaluated as having higher channeling properties than grease with an apparent viscosity gradient n greater than 0.

84.

3. The method for evaluating the grease of a rolling bearing according to claim 1 or 2, characterized in that the rolling bearing is a bearing that supports the spindle of a machine tool or a bearing that rotatably supports the rotating shaft of an electric motor.

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