JP2022025702A - Evaluation method of grease, grease, and rolling bearing - Google Patents

Abstract

To provide an evaluation method of grease, the grease, and a rolling bearing, wherein the evaluation method can select the grease showing channeling property without actually performing an evaluation test to rotate a bearing, the grease has excellent channeling property, and the rolling bearing contains the grease.SOLUTION: The evaluation method for evaluating the channeling property of the grease enclosed in the rolling bearing and containing base oil and thickener, is a method for evaluating the channeling property based on an elongation rate L of the grease 19 calculated from a spinnability test [(grease stretched length)/(initial thickness of grease)], a separation speed u between two surfaces during grease movement, base oil viscosity ηoil, apparent viscosity η1 of grease at a shear rate 10 s-1 measured by rheometer, a maximum peripheral speed u1 of a rolling element during bearing operation, and a thickener content Cth with respect to the entire grease.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for evaluating grease, grease, and a rolling bearing filled with the grease.

Grease is widely used as a lubricant for rolling bearings and the like. Most of the grease enclosed in the rolling bearing adheres to the rolling element and cage as the bearing rotates, and gradually enters the stationary space (the space excluding the area through which the rolling element and cage pass) while being agitated. Move and stand still. The behavior of grease when the bearing rotates includes churning and channeling. Specifically, the state in which the grease moves due to stirring and the bearing torque fluctuates is called churning, and the state in which the grease movement is almost completed and the bearing torque is stable is called channeling. In the present specification, the time from the start of operation to reaching channeling is referred to as "channeling transition time".

From the viewpoint of reducing power loss, it is desirable that the channeling transition time (hereinafter, also simply referred to as the transition time) is shorter, and whether the grease is churning or channeling depending on the length of the transition time. Is distinguished. Generally, in order to determine the churnability and channeling property, the bearing is actually rotated and evaluated. On the other hand, in Patent Document 1, a viscous transition stress is used as an index showing a change in the flow characteristics of grease. Patent Document 1 describes that the channeling property is enhanced by increasing the viscous transition stress of grease.

Japanese Unexamined Patent Publication No. 2016-204623

However, the viscous transition stress of the grease used as an index in Patent Document 1 does not necessarily correlate with the channeling transition time. In particular, it has been difficult to apply the grease under relatively low speed rotation conditions such that the grease adhering to the cage does not scatter due to centrifugal force.

The present invention has been made in view of such circumstances, and is a grease evaluation method capable of selecting a grease exhibiting channeling property without actually performing an evaluation test for rotating a bearing, a grease having excellent channeling property, and a grease having excellent channeling property. And it is an object of the present invention to provide a rolling bearing filled with the grease.

The method for evaluating grease of the present invention evaluates the channeling property of grease contained in a base oil and a thickener, which is encapsulated in a rolling bearing including an inner ring and an outer ring and a plurality of rolling elements interposed between the inner ring and the outer ring. In the evaluation method, the grease is sandwiched between the fixed plate and the movable plate, the movable plate is moved so as to be separated from the fixed plate, and the grease is stretched and broken. The elongation rate L of the grease calculated from the test [(the length of the grease stretched) / (the initial thickness of the grease)], the separation speed u between the two surfaces during the movement, and the base oil. The viscosity η _oil , the apparent viscosity η ₁ of the grease at γ = 10s ^-1 measured by a leometer, the maximum peripheral speed u ₁ of the rolling element during bearing operation, and the inclusion of the thickener in the entire grease. It is characterized in that it is a method for evaluating _{channelability} based on the rate Cth.

The above evaluation method is characterized in that the channeling property is evaluated by the magnitude of the channeling evaluation index CD obtained from the following formula (1).

In the spinnability test, the grease is sandwiched between the fixed plate and the movable plate with an initial thickness of 1 mm and a diameter of 7.5 mm, and the movable plate is pulled down from that state at a speed of 0.005 m / s. It is characterized by being carried out.

The grease is characterized in that it is a grease sealed in a rolling bearing used in a rotation speed range of 2000 min ^-1 or less and having an oil film parameter Λ of 1 or more.

The grease of the present invention is a grease encapsulated in a rolling bearing including an inner ring and an outer ring and a plurality of rolling elements interposed between the inner ring and the outer ring, and contains a base oil and a thickener. The elongation rate L of the grease calculated from the spinnability test in which the grease is sandwiched between the fixed plate and the movable plate and the movable plate is moved so as to be separated from the fixed plate to stretch and break the grease. The length of the grease stretched) / (initial thickness of the grease)] is 3 or more and less than 7, and the kinematic viscosity of the base oil at 40 ° C. is 20 mm ² / s or more and less than 40 mm ² / s. The content of the thickener _Cth with respect to the entire grease is 15% by mass or more and less than 30% by mass.

ただし、式中の記号は、η_１：レオメータで測定したγ＝１０ｓ^－１での上記グリースの見かけ粘度［Ｐａ・ｓ］、ｕ_１：軸受運転時の上記転動体の最大周速度［ｍ／ｓ］、η_ｏｉｌ：上記基油の粘度［Ｐａ・ｓ］、ｕ：上記曳糸性試験における上記固定板と上記可動板との２面間の離間速度［ｍ／ｓ］である。 Further, the channeling evaluation index CD obtained from the following equation ( ¹ ) is larger than 100 × 105.

However, the symbols in the formula are η ₁ : apparent viscosity of the grease at γ = 10s ^-1 measured with a leometer [Pa · s], u ₁ : maximum peripheral speed of the rolling elements during bearing operation [m / s], η _oil : Viscosity of the base oil [Pa · s], u: Separation speed [m / s] between the two surfaces of the fixed plate and the movable plate in the spinnability test.

The rolling bearing of the present invention is a rolling bearing comprising an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease enclosed around the rolling element, wherein the grease is used. It is a grease of the present invention.

The grease evaluation method of the present invention is an evaluation method for evaluating the channeling property of grease encapsulated in a rolling bearing and containing a base oil and a thickener, and the grease elongation rate L calculated from a spinnability test. The separation speed u between the two surfaces during movement, the viscosity η _oil of the base oil, the apparent viscosity η ₁ of the grease at γ = 10s ^-1 measured by the leometer, and the maximum rolling element during bearing operation. Since the channeling property is evaluated based on the peripheral speed u ₁ and the content rate _Cth of the thickener, that is, whether the grease is channeling property or churn property is actually determined. Grease that exhibits channeling properties can be selected without performing an evaluation test that rotates the bearing.

In the above evaluation method, the channeling property is evaluated by the magnitude of the channeling evaluation index CD obtained from a predetermined formula, so that the channeling property can be quantitatively evaluated. For example, the magnitude of the channeling evaluation index CD of a plurality of greases can be evaluated quantitatively. By comparing, it is possible to select a grease that shows better channeling properties.

Whereas the conventional index (viscous transfer stress) is difficult to apply to grease used under relatively low speed rotation conditions, the index (channeling evaluation index) by the evaluation method of the present invention is 2000 min ^-1 or less. It is particularly suitable for the evaluation of grease for rolling bearings used in the rotation speed range of 2000 min ^-1 or less because it shows a good correlation with the channeling transition time even under the rotational conditions of.

The grease of the present invention has a grease elongation rate L [(grease stretched length) / (grease initial thickness)] of 3 or more and less than 7, and the kinematic viscosity of the base oil at 40 ° C. is 20 mm ² / s. Since the thickness is 40 mm ² / s or more and the thickener content _Cth with respect to the entire grease is 15% by mass or more and less than 30% by mass, the channeling property is excellent.

Since the rolling bearing of the present invention is filled with the grease of the present invention, it can quickly shift to the channeling state during bearing operation and reduce the bearing torque.

It is a figure which shows the rolling bearing which filled with the grease which concerns on this invention. It is a figure which shows the outline of the threading tester. It is a figure which shows the elongation of grease in a spinning test. It is a figure which shows the outline of a bearing torque test. It is a correlation diagram of the channeling transition time and the channeling evaluation index CD.

As a result of diligent studies on the flow characteristics (charging property and channeling property) of grease in the bearing, the present inventors have determined that the flow characteristics are the viscosity of the base oil and the ease of grease elongation (spinning property). It was found that there is a correlation between the relative speed between the two surfaces at the time of spinnability measurement, the peripheral speed of the rolling element, the content of the thickener, and the apparent viscosity of the grease. Specifically, it was found that the channeling evaluation index CD calculated using each of the above parameters has a substantially linear relationship with the channeling transition time of grease. The present invention is based on such findings.

The grease used in the evaluation method of the present invention contains a base oil and a thickener. The base oil is not particularly limited, and general oils usually used in the field of grease can be used. For example, highly refined oils, mineral oils, ester oils, ether oils, synthetic hydrocarbon oils (PAO oils), silicone oils, fluorine oils, and mixed oils thereof can be used.

The kinematic viscosity of the base oil at 40 ° C. is not particularly limited, but is preferably 20 mm ² / s to 180 mm ² / s. By setting the kinematic viscosity within such a range, the channeling property can be evaluated accurately.

Further, the thickener is not particularly limited, and general ones usually used in the field of grease can be used. For example, soap-based thickeners such as metal soaps and composite metal soaps, and non-soap-based thickeners such as Benton, silica gel, urea compounds, and urea-urethane compounds can be used. Examples of the metal soap include sodium soap, calcium soap, aluminum soap, lithium soap and the like, and examples of the urea compound and the urea / urethane compound include a diurea compound, a triurea compound, a tetraurea compound, another polyurea compound and a diurethane compound.

The content rate _Cth of the thickener is not particularly limited, but is preferably 5 to 30% by mass with respect to the entire grease. By setting it within such a range, the channeling property can be evaluated accurately.

In addition, the grease may contain other known additives, if necessary. Examples of this additive include amine-based and phenol-based antioxidants, chlorine-based, sulfur-based, phosphorus-based compounds, extreme pressure agents such as organic molybdenum, petroleum sulfonates, dinonylnaphthalene sulfonates, and rust preventives such as sorbitan esters. Can be mentioned.

An example of a rolling bearing filled with grease according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a deep groove ball bearing. In the rolling bearing 1, an inner ring 2 having an inner ring raceway surface 2a on the outer peripheral surface and an outer ring 3 having an outer ring raceway surface 3a on the inner peripheral surface are arranged concentrically, and a plurality of rolling bearings 1 are arranged between the inner ring raceway surface 2a and the outer ring raceway surface 3a. Individual balls 4 are arranged. The ball 4 is held by the cage 5. Further, the openings 8a and 8b at both ends in the axial direction of the inner and outer rings are sealed by the sealing member 6, and the grease 7 is sealed at least around the ball 4. The inner ring 2, the outer ring 3 and the ball 4 are made of an iron-based metal material, and grease 7 is interposed in the raceway surface with the ball 4 to be lubricated.

The flow characteristics of grease are greatly involved in the bearing torque of rolling bearings. For example, in the case of channeling, the grease is squeezed out during rotation, the amount of grease adhering to the surface of the rolling element or the raceway surface is reduced, and the torque tends to be low. On the other hand, in the case of churning, the grease that has been scraped off by rotation returns to the raceway surface again, so that the amount of grease adhering to the rolling element surface or the raceway surface always increases, and the torque tends to be high. Therefore, a grease having high channeling property, that is, a grease having a short channeling transition time is desired.

In the evaluation method of the present invention, the elongation rate L of grease calculated from the spinnability test, the separation speed u between the two surfaces at the time of movement thereof, the viscosity η _oil of the base oil, and γ = 10s measured by a leometer. This is a method for evaluating the channeling property of grease based on the apparent viscosity η ₁ of the grease in ^-1 , the maximum peripheral speed u ₁ of the rolling element during bearing operation, and the content rate _Cth of the thickener. .. In the spinnability test, grease is filled between parallel flat plates (between two surfaces) adjusted to a predetermined area and a predetermined interval, and the distance between the flat plates is widened to break the grease. In the present invention, the ratio of the interval between the flat plates at the time of breaking to the initial interval, that is, the elongation rate is used as a numerical value for evaluating the spinnability.

The spinnability test will be described with reference to FIG. FIG. 2 shows a schematic view of the spinnability tester. The spinnability tester 11 includes a columnar fixing plate 12 fixed to the top wall, a columnar movable plate 13, and a driving device 14 for moving the movable plate 13 up and down with respect to the fixing plate 12. .. The lower surface of the fixed plate 12 and the upper surface of the movable plate 13 are parallel to each other. The drive device 14 includes a stage 15 on which the movable plate 13 is placed, a linear guide 16 that regulates the movement of the stage 15, a motor 17, and a ball screw 18 that is rotated by driving the motor 17. The stage 15 is screwed into the thread groove of the ball screw 18, and is relatively moved while sliding on the shaft due to the rotation of the ball screw 18.

The procedure of the spinnability test will be described below.

(1) First, a predetermined amount of grease 19 to be measured is filled on the upper surface of the movable plate 13. The filling amount of the grease 19 is, for example, 1 cm ³ to 5 cm ³ .

(2) Next, the movable plate 13 is raised to a position where the grease 19 comes into contact with the lower surface of the fixing plate 12. At this time, the position of the movable plate 13 is adjusted so that the grease 19 has a predetermined initial thickness A (see FIG. 3A). In the initial state of FIG. 3A, the distance between the fixed plate 12 and the movable plate 13 is the initial thickness A of the grease 19. The initial thickness A is set to, for example, 0.5 mm to 2 mm, specifically 1 mm. The diameter φ of the grease 19 in the initial state is set to, for example, 5 mm to 10 mm, specifically 7.5 mm. As shown in FIG. 3A, the movable plate 13 is used so that the grease 19 spreads over the entire fixed plate 12 and the movable plate 13 by using the fixed plate 12 and the movable plate 13 having the same diameter size as the diameter φ of the grease 19. You may adjust the position of. The diameter size and shape of the fixed plate 12 and the movable plate 13 are not limited to FIG. 3A. For example, the fixed plate 12 or the movable plate 13 may have a shape other than a columnar shape, and a circular grease filling region may be provided on one of the facing surfaces.

(3) Next, as shown by the black arrow in FIG. 2, the movable plate 13 is lowered at a predetermined speed. The descending speed of the movable plate 13 is set to, for example, 0.0001 m / s to 0.1 m / s, specifically 0.005 m / s. As shown in FIG. 2, a part of the grease 19 is reduced in diameter by lowering the movable plate 13. The presence or absence of breakage of the grease 19 can be confirmed visually, by a high-speed camera, or by measuring the load applied to the fixed end side generated when the grease is stretched. In this case, the descending speed of the movable plate 13 corresponds to the separation speed u between the two surfaces.

(4) As the movable plate descends, the grease finally breaks. FIG. 3B shows a state in which the grease 19 is broken. The distance between the fixed plate 12 and the movable plate 13 at the time of breaking is the breaking length B of the grease 19. Using the breaking length B and the initial thickness A, the elongation ratio L of the grease is calculated by the following formula.
Elongation rate L = [(grease stretched length) / (initial thickness of grease)] = [(BA) / A]
The value of the elongation rate L is not particularly limited, but is preferably 3 or more and less than 7. By setting it within such a range, the channeling property can be evaluated accurately.

The configuration of the spinnability tester shown in FIG. 2 is not limited to this. For example, the movable plate 13 may be integrally formed with the stage 15. Further, instead of the configuration in which the movable plate 13 is pulled down vertically, a configuration in which the movable plate is pulled up vertically may be used.

The apparent viscosity η ₁ of the grease is obtained by rheological measurement using a rheometer. The rheology measurement conditions are constant temperature and rotation in a constant direction, and the temperature is 25 ° C. The shear rate is 10 (unit: 1 / s), and the viscosity at the steady state at the shear rate is the apparent viscosity.

The maximum peripheral speed u ₁ of the rolling element is calculated by the following formula.
Maximum peripheral speed of rolling element u ₁ = rolling element rotation number (Hz) x rolling element diameter x π

The elongation rate L of grease calculated from the spinnability test, the separation speed u between the two surfaces during movement, the viscosity η _oil of the base oil, the apparent viscosity η ₁ of the grease, and the rolling elements during bearing operation. The channeling evaluation index CD can be calculated from the following equation (1) using the maximum peripheral speed u ₁ and the thickener content _Cth .

The calculated channeling evaluation index CD shows a substantially linear relationship with the channeling transition time, as shown in Examples described later. Specifically, the larger the channeling evaluation index CD, the shorter the channeling transition time. Therefore, in the evaluation method of the present invention, the channeling property can be evaluated by the magnitude of the calculated channeling evaluation index CD. For example, when the channeling evaluation index CD is compared with a predetermined threshold value and the channeling evaluation index CD is smaller than the predetermined threshold value, it is determined that the grease is churn, and the channeling evaluation index CD is predetermined. When it is larger than the threshold value of, it can be determined that the grease has channeling property. A predetermined threshold value can be set in advance by an experiment or the like performed in advance. For example, the threshold can be set to 100 × ¹⁰⁵ .

Further, by comparing the magnitude of the channeling evaluation index CD among a plurality of greases, the grease having the highest channeling property can be selected.

Here, when a rolling bearing filled with grease is used for grease lubrication, a break-in operation is first performed. The break-in operation is generally completed by moving the encapsulated grease from the inside of the bearing to a predetermined position (stationary space). That is, the break-in operation is completed when the grease is in the channeling state. According to the present invention, the time required for running-in can be estimated based on the channeling evaluation index CD by utilizing the good linear relationship between the channeling evaluation index CD and the channeling transition time.

Generally, the shorter the break-in time, the better. For example, in order to complete the break-in operation in one hour, a motor bearing of a general-purpose motor having a rotation speed of 1800 min ^-1 requires about 100,000 rotations. By dividing such a total rotation speed by the rotation speed in the bearing torque test, the reference time T for the break-in operation can be obtained. By comparing this reference time T with the channeling transition time (estimated value) estimated from the correlation between the channeling evaluation index CD and the channeling transition time (measured value), the grease can be used at an appropriate time. It is possible to determine whether or not the break-in operation is completed.

For example, in a bearing torque test conducted under the condition of a rotation speed of 900 min ^-1 , the total rotation speed of the bearing reaches 100,000 rotations in 111 min (reference time T).

FIG. 4 shows an outline of the bearing torque test. As shown in FIG. 4, the bearing torque tester 21 has a structure in which the load of the weight 22 is applied in the axial direction of the test bearing 24 via the pneumatic static pressure table 23. The test bearing 24 is fitted in a housing 25 connected to the load cell 27. When the inner ring of the test bearing 24 is rotated by the spindle 26, the tangential force acting on the housing 25 is measured by the load cell 27, and the bearing torque is calculated from the outer diameter dimension of the housing.

In FIG. 1, a ball bearing is exemplified as a rolling bearing in which grease is filled, which is the subject of the evaluation method of the present invention. In addition to the ball bearing, a cylindrical roller bearing, a conical roller bearing, a self-aligning roller bearing, and a needle shape It can also be applied to roller bearings, thrust cylindrical roller bearings, thrust conical roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like.

Since the evaluation method of the present invention can appropriately evaluate the channeling property even with grease used under relatively low speed rotation conditions, a rotation speed range of 2000 min ^-1 or less, more preferably 1500 min ^-1 or less. Especially suitable for the evaluation of grease for rolling bearings used in. For example, it is suitable for evaluating grease such as a motor bearing of a general-purpose motor having a rotation speed of 1800 min ^-1 and an axle bearing having a rotation speed of 1500 min ^-1 .

Further, the grease to be evaluated in the present invention is preferably the grease enclosed in the rolling bearing used when the oil film parameter Λ is 1 or more. The oil film parameter Λ is an index of the lubrication state, and is expressed by the ratio of the oil film thickness formed between the two rolling surfaces to the square root of the sum of squares of the root mean square roughness of the two surfaces. For example, in the case of rolling bearings, it is preferable that the value of the oil film parameter Λ in the region between the outer ring and each of the plurality of rolling elements and the region between the inner ring and each of the plurality of rolling elements is 1 or more. .. As a result, the formation of an oil film on the rolling surface is ensured, and it is possible to prevent the bearing life from being shortened.

The grease of the present invention is a grease sealed in a rolling bearing as shown in FIG. 1, and contains a base oil and a thickener. As the base oil and the thickener, those listed above can be appropriately used. In addition, other known additives may be contained, if necessary.

The grease of the present invention has an elongation ratio L calculated from the above-mentioned spinnability test of 3 or more and less than 7, and the kinematic viscosity of the base oil at 40 ° C. is 20 mm ² / s or more and less than 40 mm ² / s. The thickener content _Cth is 15% by mass or more and less than 30% by mass. As shown in Examples described later, a grease satisfying these conditions has a short channeling transition time and is excellent in channeling property. When the elongation ratio L is less than 3, the grease stirred in the raceway surface of the bearing breaks immediately, so that the grease exists in a state of having an irregular fracture surface, and the torque fluctuation tends to be large. Further, when the elongation rate L is 7 or more, the fluidity is also increased at the same time, so that there is a possibility that grease leakage is likely to occur or the semi-solid state cannot be maintained in the first place.

The preferred form of the grease of the present invention is that the elongation rate L is 4 or more and less than 7, the kinematic viscosity of the base oil at 40 ° C. is 30 mm ² / s or more and less than 40 mm ² / s, and the content of the thickener is increased. _Cth is 15% by mass or more and less than 25% by mass. Further, it is more preferable that the elongation rate L is 5 or more and less than 7.

Further, it is preferable that the grease of the present invention has a channeling evaluation index CD calculated by the above-mentioned formula ( ¹ ) larger than 100 × 105.

The rolling bearing of the present invention is the above-mentioned bearing filled with the grease of the present invention, and is not limited to the ball bearing of FIG. 1, a cylindrical roller bearing, a conical roller bearing, a self-aligning roller bearing, a needle roller bearing, and a thrust. It can also be applied to cylindrical roller bearings, thrust conical roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like.

Further, since the rolling bearing of the present invention quickly shifts to the channeling state even in the low rotation speed range, 2000 min such as a motor bearing of a general-purpose motor having a rotation speed of 1800 min ^-1 and an axle bearing having a rotation speed of 1500 min ^-1 . It is suitable as a rolling bearing used in the rotation speed range of ^-1 or less.

Two types of greases of Examples and 14 types of greases of Comparative Examples having different types of base oil, kinematic viscosity of base oil, and types of thickener were prepared. For each grease, the viscosity η _oil of the base oil, the elongation rate L of the grease, the apparent viscosity η ₁ of the grease, the channeling transition time (actual measurement value), and the channeling evaluation index CD were obtained as shown below.

The viscosity η _oil of the base oil was calculated by Walther's formula.

The grease elongation rate L was calculated from the spinnability test shown in FIGS. 2 and 3. The thickness of the grease (initial thickness A) before the start of the test was 1 mm, and the diameter φ was 7.5 mm. Further, as the fixing plate and the movable plate, a cylindrical flat plate having a diameter of 7.5 mm was used. Under the condition of 25 ° C., the movable plate was pulled down at a speed of 0.005 m / s, and the breaking length B when the grease broke was measured. The elongation rate L was calculated from the initial thickness A and the breaking length B. The separation speed u between the two surfaces was 0.005 m / s.

The apparent viscosity η ₁ of the grease was measured using a rheometer (HAAKE RheoWin MARS1 manufactured by Thermo Fisher Scientific) of a cone plate type (diameter 20 mm, tip angle 178 °) cell. For each grease, the shear stress that became a steady flow at a temperature of 25 ° C. and a shear rate of 10s ^-1 was obtained, and the apparent viscosity η ₁ of the grease was calculated. The maximum peripheral speed u ₁ of the rolling element was calculated by the above formula and was 0.77 m / s.

The channeling transition time (actual measurement value) was calculated by carrying out the bearing torque test shown in FIG. A test bearing was obtained by enclosing each grease in a deep groove ball bearing 6204 (bearing dimensions: inner diameter 20 mm, outer diameter 47 mm, width 14 mm) so that the encapsulation amount was 50% of the rest space ratio. The test bearing was rotated on the inner ring under the conditions of an axial load of 20 N, a rotation speed of 900 min ^-1 , and a room temperature of 25 ° C. The tangential force acting on the housing during rotation was measured with a load cell, and the bearing torque was calculated from the outer diameter of the housing. Bearing torque was calculated over time (every minute) from the start of the test. The time when the fluctuation of the bearing torque changed to 5% or less in the last 3 hours or the time when the bearing torque changed to 3 Nmm or less was defined as the channeling transition time. In Examples 1 and 2 and Comparative Examples 1 to 11, the bearing torque test was carried out twice, respectively.

Substituting the elongation rate L, the velocity u between the two surfaces, the viscosity η _oil of the base oil, the apparent viscosity η ₁ of the grease, the maximum peripheral velocity u ₁ , and the content rate C _th of the thickener into the following equation (1). , Channeling evaluation index CD was calculated.

Table 1 shows each parameter for Examples 1 and 2 and Comparative Examples 1 to 14, and FIG. 5 shows a correlation diagram between the channeling transition time (measured value) and the channeling evaluation index CD.

As shown in FIG. 5, the larger the channeling evaluation index CD, the shorter the channeling transition time. It can be seen that the relationship between the channeling evaluation index CD and the channeling transition time is generally linear in the log-log graph.

Here, for example, when the motor bearing of a general-purpose motor having a rotation speed of 1800 min ^-1 is to be run-in within 1 hour, about 100,000 rotations are required. The reference time T until the ring transition is 111 min. From the experimental results in Table 1, the greases of Examples 1 and 2 have been channeled by 111 min. Therefore, when used as a motor bearing of a general-purpose motor having a rotation speed of 1800 min ^-1 , it is within 1 hour. The break-in can be completed.

Further, from the plot of FIG. 5, a regression line as shown in the following equation (2) can be drawn, for example.
Channeling transition time t = a × Channeling evaluation index CD ^b ... (2)
Here, a and b in the above equation (2) are constants, and in this example, a = 2.231 × 10 ⁹ and b = −1.024.

In this case, the channeling evaluation index CD is calculated for the grease different from the grease used in the examples and the comparative examples, and the calculated CD is substituted into the above equation (2) to obtain the channeling transition time t (estimated). Value) can be estimated. Therefore, by comparing the estimated value with the threshold value of the reference time T until the channeling transition, it is possible to determine whether or not each grease is suitable for the specifications.

According to the evaluation method of the present invention, it is considered that the channeling property can be quantitatively evaluated even under relatively low rotation conditions. Therefore, it is possible to select grease or the like having a short channeling transition time without actually performing an evaluation test for rotating the bearing.

The grease evaluation method of the present invention can be widely used for selecting grease because it is possible to select grease showing channelability without actually performing an evaluation test for rotating the bearing.

1 Rolling bearing 2 Inner ring 3 Outer ring 4 Ball (rolling element)
5 Cage 6 Seal member 7 Grease 8 Opening 11 Spindle tester 12 Fixed plate 13 Movable plate 14 Drive device 15 Stage 16 Linear guide 17 Motor 18 Ball screw 19 Grease 21 Bearing torque tester 22 Weight 23 Pneumatic static pressure table 24 Test bearing 25 Housing 26 Spindle 27 Load cell

Claims (7)

It is an evaluation method for evaluating the channeling property of grease containing a base oil and a thickener, which is enclosed in a rolling bearing including an inner ring and an outer ring and a plurality of rolling elements interposed between the inner ring and the outer ring.
The evaluation method is the grease calculated from a spinnability test in which the grease is sandwiched between a fixed plate and a movable plate, the movable plate is moved so as to be separated from the fixed plate, and the grease is stretched and broken. Elongation rate L [(length at which the grease was stretched) / (initial thickness of the grease)], the separation speed u between the two surfaces during movement, the viscosity η _oil of the base oil, and a leometer. Based on the apparent viscosity η ₁ of the grease at the measured shear rate 10s ^-1 , the maximum peripheral speed u ₁ of the rolling element during bearing operation, and the content rate _Cth of the thickener with respect to the entire grease. , A method for evaluating grease, which is a method for evaluating channelability. The grease evaluation method according to claim 1, wherein the evaluation method evaluates the channeling property according to the magnitude of the channeling evaluation index CD obtained from the following formula (1).

In the spinnability test, the grease is sandwiched between the fixed plate and the movable plate with an initial thickness of 1 mm and a diameter of 7.5 mm, and the movable plate is pulled down from that state at a speed of 0.005 m / s. The grease evaluation method according to claim 1 or 2, wherein the grease is evaluated. Any of claims 1 to 3, wherein the grease is a grease sealed in a rolling bearing used in a rotation speed range of 2000 min ^-1 or less and having an oil film parameter Λ of 1 or more. The grease evaluation method according to item 1. A grease encapsulated 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 containing a base oil and a thickener.
The grease is calculated from a spinnability test in which the grease is sandwiched between a fixed plate and a movable plate, and the movable plate is moved so as to be separated from the fixed plate to stretch and break the grease. The elongation rate L [(the length of the grease stretched) / (the initial thickness of the grease)] is 3 or more and less than 7, and the kinematic viscosity of the base oil at 40 ° C. is 20 mm ² / s or more and 40 mm ² / s. A grease having a content of less than 15% by mass and having a content ratio _Cth of the thickener with respect to the entire grease of 15% by mass or more and less than 30% by mass. The grease according to claim ⁵ , wherein the channeling evaluation index CD obtained from the following formula (1) is larger than 100 × 105.

However, the symbols in the formula are η ₁ : apparent viscosity [Pa · s] of the grease at a shear rate of 10s ^-1 measured by a leometer, u ₁ : maximum peripheral speed [m / s] of the rolling element during bearing operation. s], η _oil : Viscosity of the base oil [Pa · s], u: Separation speed [m / s] between the two surfaces of the fixed plate and the movable plate in the spinnability test. A rolling bearing comprising an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease enclosed around the rolling element.
A rolling bearing according to claim 5, wherein the grease is the grease according to claim 6.

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