JP2018003028A - Grease composition for rolling shaft bearing and rolling shaft bearing, and machine tool main shaft device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grease composition hardly leaking from a shaft bearing, excellent in thermal stability and capable of reducing running-in time, a rolling shaft bearing which is lubricated by the grease composition, and a rolling shaft bearing suitable for shaft bearing for a machine tool operated under high speed and high load so that especially dmn is 800,000 or more and a PV value of a rolling connection part of an inner ring and an outer ring becomes 100 MPa m/s or more.SOLUTION: By a grease composition having cone penetration of 212 to 320, oil release degree of 4% or less and leakage rate of 40% or less, a shaft bearing for machine tool is lubricated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grease composition for a rolling bearing, a rolling bearing lubricated with the rolling bearing grease, and a machine tool spindle device including the rolling bearing.

Rolling bearings used for machine tools are often used in a high-speed rotation region exceeding dmn 800,000 (dmn: product of ball pitch circle diameter (mm) and rotation speed (min ⁻¹ )). In particular, in a machining center, the main shaft bearing is often used in the high-speed rotation region as described above, and the inner diameter of the bearing is generally about 30 to 140 mm.

  Also, in machine tools, high preload is sometimes applied to increase the rigidity of the main shaft, and the PV value of the rolling contact portion of the inner ring or outer ring is often 100 MPa · m / s or more. The load-bearing performance under high-speed rotation conditions is also required.

Further, when the rotation speed is increased, the rolling surface of the bearing becomes high temperature, and the grease having poor heat resistance is thermally deteriorated and the life of the grease is remarkably shortened. For such a problem, a heat-resistant thickener or base oil is used, or an antioxidant is added. For example, in consideration of heat resistance, in Patent Document 1, a urea compound as a thickener is added to a base oil having a kinematic viscosity at 40 ° C. of 15 to 40 mm ² / sec as 9 to 14% by mass of the entire grease composition. A grease composition having a blending degree of 220 to 320 is disclosed. Patent Document 2 discloses a grease for high-speed bearings in which a urea grease containing a urea compound as a thickener and a non-urea grease containing a composite amide lithium soap having an amide bond in the molecule as a thickener are blended. Has been.

  In Patent Document 3, a mixed oil of a polyol ester oil and an alkyldiphenyl ether oil is used as a base oil, and a dialkyldithiocarbamate oxide and a hindered phenol compound are mixed and added as an antioxidant.

  By the way, the machine tool is delivered to the customer after the manufacturer manufactures the product and performs a trial run. For this reason, it is desirable for bearings for machine tools to quickly finish the initial break-in operation in a short time.

  Also, machine tool bearings often use an open type grease lubrication that does not use seals on both end surfaces in the axial direction of the bearing, and particularly when used with a vertical spindle, there is a high risk of grease flowing out of the bearing due to gravity. For this reason, the grease to be sealed is required to have an appropriate adhesion force and base oil holding capacity in order to reduce the amount of leakage.

  Furthermore, machine tool bearings are also required to have a small temperature fluctuation during operation. This is because the heat generated in the bearing is transmitted to the machine tool spindle, and the temperature of the spindle changes, causing the spindle to expand and contract, affecting the machining accuracy of the machine tool. In particular, in the case of the fixed position preload method, the spacer expands and contracts due to a change in the temperature of the bearing, so that the preload greatly fluctuates, and in the worst case, the preload becomes excessive and seizure occurs.

  Conventional grease compositions including the grease compositions described in Patent Documents 1 to 3 described above cannot sufficiently cope with such demands and problems.

  In addition, as in Patent Document 4, in a grease composition for high speed, a urea compound is mostly used as a thickener, but dmn is 1 million or more and the maximum contact surface pressure exceeds 1.5 GPa. If the load is too high, the grease composition using a urea compound as a thickener will not have sufficient lubricity.

JP 2006-29473 A JP 2009-275176 A JP-A-8-188788 Japanese Patent No. 3519417

  Therefore, the present invention can be sufficiently operated for dmn of 800,000 or more, preferably 1,000,000 or more, and is operated under a high speed and high load such that the PV value of the rolling contact portion of the inner ring or outer ring is 100 MPa · m / s or more. It aims at providing a rolling device.

In order to solve the above problems, the present invention provides a grease composition for a rolling bearing, a rolling bearing, and a machine tool spindle device as described below.
(1) A grease composition for a rolling bearing comprising a base oil and a thickener, having a consistency of 212 to 320, an oil separation of 4% or less, and a leakage rate of 40% or less. .
(2) The grease composition for a rolling bearing according to the above (1), wherein the base oil has a kinematic viscosity at 40 ° C. of 18 to 60 mm ² / s.
(3) The grease composition for a rolling bearing as described in (1) or (2) above, wherein the thickener is lithium soap.
(4) The rolling bearing grease according to any one of (1) to (3) above, wherein a plurality of rolling elements are rotatably held by a cage between the inner ring and the outer ring. A rolling bearing characterized in that it is lubricated by a composition.
(5) The rolling bearing according to (4) above, wherein the amount of the grease composition enclosed is 10 to 30% of the static space volume inside the bearing.
(6) The above (4) or (4), characterized in that, for machine tool spindle applications, dmn is 800,000 or more, and the PV value of any one of the inner and outer rings is 100 MPa · m / s or more. 5) The rolling bearing described.
(7) A machine tool spindle device comprising the rolling bearing according to any one of (4) to (6) above.

  The grease composition for lubricating the rolling device according to the present invention has excellent lubrication performance, low leakage, dmn 800,000 or more, and PV value of the rolling contact portion of the inner ring and outer ring of 100 MPa · m / s or more. It is durable enough to withstand use below and even dmn 1 million or more. Furthermore, fluctuations in heat generation during operation can be suppressed to a low level, and the applied operation of the apparatus can be completed in a short time.

  Therefore, the rolling device of the present invention has advantages such as load resistance, low leakage, shortening of the break-in time, etc., and machine tools, particularly dmn 800,000 or more, and the PV value of the rolling contact portion is 100 MPa · m / s or more. It is useful as a machine tool and can sufficiently withstand use at a dmn of 1 million or more.

It is sectional drawing which shows the angular ball bearing which is an example of the rolling bearing of this invention. It is sectional drawing which shows the (A) single row cylindrical roller bearing and (B) double row cylindrical roller bearing which are the other examples of the rolling bearing of this invention. It is the schematic of the testing apparatus used for the seizure resistance evaluation test. It is the schematic of the test apparatus used for the calorific value measurement test. It is a graph which shows the relationship between the kind of thickener, and durable time. It is a graph which shows the relationship between oil separation degree and a temperature stability evaluation score. 6 is a graph showing a time-series change in outer ring temperature when test grease E is used. It is a graph which shows the time-sequential change of outer ring temperature when test grease A is used. 6 is a graph showing a time-series change in outer ring temperature when test grease F is used. It is a graph which shows the relationship between a consistency and a running-in evaluation score. 6 is a graph showing time-series changes in outer ring temperature when test grease G is used. It is a graph which shows the relationship between base oil kinematic viscosity and calorific value.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  In the present invention, the type of rolling device is not limited, but the grease composition described below is excellent in lubricity, has a high base oil holding capacity, has little leakage, and has a short running-in time. It is suitable as a bearing for machines, particularly dmn 800,000 or more, and a PV value of a rolling contact portion of an inner ring or an outer ring of 100 MPa · m / s or more, and can sufficiently cope with dmn of 1 million or more.

  Angular ball bearings and roller bearings are common as machine tool bearings, and these bearings can also be exemplified in the present invention. FIG. 1 is a cross-sectional view showing an example of an angular ball bearing, and a plurality of balls, which are rolling elements 3, are rotatably held by a cage 4 between an inner ring 1 and an outer ring 2.

  Further, the present invention can be applied to a single row cylindrical roller bearing as shown in FIG. 2A, a double row cylindrical roller bearing as shown in FIG. In any case, a plurality of cylindrical rollers as rolling elements 31 are held between the inner ring 1 and the outer ring 2 by the cage 4 so as to be freely rollable.

  A grease composition is enclosed for lubrication. The grease composition used in the present invention contains a base oil and lithium soap as a thickener, and has a blending degree of 212 to 320. The oil separation degree specified in JIS K 2220 is 4.0% by mass or less at 100 ° C. for 24 hours. In the following description, the degree of oil separation defined by JIS K 2220 and held at 100 ° C. for 24 hours is simply referred to as “degree of oil separation”. Moreover, it is preferable that the leakage rate is adjusted to 40% or less.

  The initial break-in operation of the grease-lubricated bearing is performed in order to scrape the grease accumulated on the raceway surface by rotating the bearing to the surroundings by a rolling element and to arrange it at an appropriate location by a force such as centrifugal force. In this running-in operation, heat generation can be suppressed more quickly and lower as the fluidity of the grease is higher. Therefore, the time required for the running-in operation is reduced as the consistency is increased. On the other hand, the thickener has a function of retaining the base oil. The higher the proportion of the thickener in the grease, the higher the retention capacity of the base oil, the less leakage, and the longer the lubrication life. The greater the amount of thickener that holds the base oil, the harder the grease and the lower the consistency.

  In the present invention, the grease composition has a consistency of 212 to 320, preferably 240 to 320, more preferably 250 to 295, so that it is possible to satisfy both the good running-in and the high base oil retention capability at the same time. I found it.

  In addition, the degree of oil separation is an index representing the supply ability of the base oil to the lubricating surface. If the degree of oil separation is too low, base oil sufficient for sufficient lubrication cannot be supplied to the raceway surface. In particular, during operation under high-speed and high-load conditions, an oil film is difficult to form, and metal contact occurs below the rolling contact surface with sliding at high speed rotation, increasing the risk of seizure. On the other hand, if the degree of oil separation is too high, the supply of the base oil to the lubrication surface becomes excessive, the oil film thickness on the lubrication surface is not constant, and the variation in the amount of generated heat increases. In addition, the base oil is rapidly separated from the grease, resulting in a decrease in the lubrication life.

  In the present invention, the oil separation degree of the grease composition is 4% or less, preferably 0.1 to 4%, more preferably 0.2 to 1.2%, still more preferably 0.2 to 1 in mass%. It was found that the oil film forming ability necessary for lubrication, the temperature stability during operation, and the high base oil retention ability can be satisfied at the same time by setting to 0.0%.

  Also, in machine tool spindle bearings, the amount of grease enclosed is generally 10 to 30% of the static space inside the bearing, and grease is added to rolling bearings used in general industrial machines such as motor rolling bearings. As little as 50-60% of the amount. This is a specification unique to machine tool spindle bearings that require low heat generation characteristics and reduced running-in time. By satisfying the above physical properties, the PV value of the rolling contact portion is 100 MPa · m / s or more. Under the oil separation conditions used in the above, a remarkable effect appears in the lubrication performance and heat generation characteristics. Further, even under conditions specific to machine tools in which the grease filling amount is as small as 10 to 30%, the lubrication life required by satisfying the oil separation degree within the above range can be satisfied.

  In addition, the leakage rate of the grease composition is preferably as low as possible, and is preferably 40% or less.

In order to achieve the above physical properties, the base oil kinematic viscosity is preferably 18 to 60 mm ² / s at a value at 40 ° C. In machine tool bearings, lubricating oil with relatively low viscosity or grease with low base oil viscosity is often used for heat generation and torque reduction. If the viscosity is too low at this time, it is difficult to form an oil film, and there is an increased risk of seizure due to metal contact occurring under the rolling contact surface with slipping at high speed rotation. Conversely, if the viscosity is too high, the formation of the oil film is good, but the temperature rise of the bearing increases due to the oil stirring resistance and viscosity resistance, and the oil film formation deteriorates. Further, many machine tools cool only the housing side, and a temperature difference occurs between the outer ring and the inner ring of the bearing. And since the temperature difference between the inner and outer rings becomes large, there is a difference in the amount of extension of the spacer between the inner and outer rings, and the preload becomes excessive, which may lead to seizure. Therefore, by setting the base oil kinematic viscosity within this range, it is possible to realize an operating condition in which the oil film thickness necessary for lubrication is maintained and the amount of generated heat is not excessive. More preferably, base oil kinematic viscosity in 40 degreeC shall be 18-40 mm < ² > / s.

  In addition, there is no restriction | limiting in the kind of base oil, Lubricating oil of said kinematic viscosity can be selected suitably. Synthetic hydrocarbon oils such as mineral oil, hydrocarbon oils, aromatic oils, ester oils, ether oils, etc. can be used, but in order to suppress seizure under high speed and high load, heat resistant lubricating oil Is preferably used.

  Moreover, it is preferable to use lithium soap as a thickener. As the lithium soap, general soaps containing lithium as a metal species, such as lithium soap and lithium complex soap, can be used. Other metal soap-based thickeners, such as barium-based soap, have a high oil separation and are liable to leak grease compositions. In addition, the urea compound cannot achieve the desired low leakage and the effect of shortening the break-in time.

  In particular, it is preferable to contain at least one of 12 hydroxy lithium stearate and lithium stearate and lithium caprate as a thickener. Lubricating with a grease composition containing such a specific thickener is sufficiently applicable to various rolling devices used for high speed and high load applications exceeding DmN 1 million.

  In high-speed and high-load bearings, the device is usually cooled to prevent an abnormal temperature rise, but extremely large frictional heat is generated locally. Therefore, as one component of the thickener, at least one of 12 hydroxy lithium stearate and lithium stearate which are low heat generation and low noise, preferably a mixture of both, is used. However, since 12 hydroxy lithium stearate and lithium stearate have high thickening properties, the amount of thickening agent is usually as small as about 10% by mass of the total amount of grease, and grease leakage is likely to occur under high speed and high load.

  Therefore, lithium caprate is used in combination to suppress thickening as compared with the case of using 12 hydroxy lithium stearate or lithium stearate alone. Along with this, the amount of thickener can be increased, and the scattering of the grease composition is suppressed, making it difficult to leak. Specifically, the amount of thickener can be increased to 13 to 21% by mass of the total amount of grease. Also, when this specific thickener is used, the consistency is NLGI No. It is preferable to set it as 2-3.

  Under high speed and high load, the shear deterioration of the grease composition progresses at an accelerated rate due to the effect of shearing, which leads to softening and leakage of the grease composition. By using such grease properties, the grease composition on the friction surface Excessive supply can be suppressed, and an increase in surface pressure due to heat generation and promotion of grease deterioration can be prevented, and a long life can be realized. Furthermore, even when the base oil is exhausted, a thickener is present in the lubrication part, so that a very speedy supply of grease can be expected.

  In order to effectively express such an action, the ratio of lithium caprate / (lithium stearate + 12 hydroxylithium stearate) is preferably 0.25 to 0.50 in terms of mass ratio, and 0.25. It is more preferable to set it to -0.40.

  When the torque of the bearing is emphasized, the amount or ratio of lithium stearate is reduced, or lithium caprate and 12 hydroxystearate are added to obtain lithium stearate / (lithium caprate + 12 hydroxylithium stearate / 6) The ratio is preferably 0 to 2.0 in terms of mass ratio.

  In consideration of use at high speed and high load, it is preferable to add an antioxidant or an extreme pressure agent to the grease composition, and an appropriate amount can be added within a range not impairing the effects of the present invention. In addition, an appropriate amount of various additives can be added depending on the purpose.

  The amount of grease filled is preferably 10 to 30% of the static space volume inside the bearing formed by the inner ring 1, the outer ring 2, the rolling elements 3 and the cage 4.

  By using the above grease composition, it is suitable for lubrication of bearings for machine tools and has a high load with a dmn of 800,000 or more and a PV value of a rolling contact portion of either the inner ring or the outer ring of 100 MPa · m / s or more. It is possible to improve seizure resistance during operation, reduce heat fluctuation during operation, reduce the amount of grease leakage, and further shorten the running-in time. Furthermore, it is possible to sufficiently cope with cases where dmn is 1 million or more.

  The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

<Test 1>
(Preparation of base oil)
As shown in Table 1, test greases A to I were prepared by using oils containing mineral oils having different kinematic viscosities at 40 ° C., ethers, esters, poly-α-olefins, etc. Was prepared while adjusting the kneading. Further, the test greases D to G include at least one of 12 hydroxy lithium stearate and lithium stearate as a thickener and lithium caprate, and lithium caprate / (lithium stearate + 12 hydroxy lithium stearate. The rate ratio is 0.25 to 0.50 in mass ratio. The same additive was added to any test grease. Moreover, about each test grease, the blending degree and the oil separation degree when it left still at 100 degreeC for 24 hours were measured. The measurement results are also shown in Table 1.

(1) -1: Seizure resistance evaluation test Test grease was sealed in an angular ball bearing 50BNR10ST having an inner diameter of 50 mm to produce a test shaft bearing. Then, seizure resistance was evaluated using the test apparatus shown in FIG. In the illustrated test apparatus, a test spindle and a pair of upper and lower support bearings (angular ball bearings 50BNR10HTYN) are mounted, and a test spindle to which a predetermined preload is applied by a preload spring from the support shaft side is coupled to the support spindle. And the inner ring of the test bearing is rotated at a predetermined rotational speed. The test conditions were an ambient temperature of 25 ° C., a rotational speed of 18000 min ⁻¹ (dmn 1.15 million), a preload load of 2200 N, and the grease filling amount was 15% of the static space volume inside the bearing, and the following four items were evaluated under these conditions. The results are also shown in Table 1.
(A) From the time until bearing seizure occurs to seizure resistance under high load (b) From the amount of temperature fluctuation of the evaluated bearing during steady rotation after the initial running-in operation, temperature stability (c ) From the ratio (leakage rate) of the grease spilled before and after the evaluation test to low leakage (d) from the time required for the amount of heat generated to be constant after finishing the initial running-in operation (see Fig. 4) Use the test equipment shown)
The leakage rate is a value at the time when 200 hours have elapsed when the mass of the grease in the bearing is measured before and after the test in this test and the ratio of the leaked grease is approximated by a logarithmic function.

(1) -2: Calorific value measurement test A test bearing was manufactured by enclosing a test grease in an angular ball bearing 50BNR10HT. And the emitted-heat amount of the test bearing was measured using the test apparatus shown in FIG. In the illustrated test apparatus, a pair of test bearings are mounted, a test spindle to which a predetermined preload is applied by a preload spring, and a support spindle are connected via a coupling, and an inner ring is rotated by a drive spindle. In addition, a dynamic torque meter was installed between the test spindle and the support spindle, and the dynamic torque value input to drive the test spindle was measured as the heat generation amount of the bearing. The test conditions were: ambient temperature 25 ° C., rotation speed 28000 min ⁻¹ (dmn 1.8 million), preload load 650 N, the amount of grease filled was 15% of the static space volume inside the bearing, and the heat generation amount was constant after the initial break-in operation. The time required to become was measured.

  From the above evaluation test, the following can be understood.

(A) Seizure resistance performance FIG. 5 shows the durability time until the bearing is seized for each type of thickener of the test grease. Test grease A using barium complex soap as a thickener and test greases B and C using urea were baked in 15 hours and 50 hours, respectively. On the other hand, the test greases D to I using lithium soap or lithium complex soap as a thickener were durable without being baked for 200 hours or more in all tests. From this, it can be seen that the use of lithium soap or lithium complex soap (lithium-based soap) as the thickener is superior in seizure resistance under load than other thickeners.

  Further, among the test greases D to I using lithium soap or lithium complex soap as a thickener, the test grease G having an oil separation degree of 0.1% was seized in about 200 hours, but the oil separation degree was 0.2% or more. The test grease was not seized even after 250 hours had elapsed, and was able to continue operation. From this, in order to obtain sufficient seizure resistance, the oil separation degree is set to 0.1% or more, preferably 0.2% or more. A remarkable difference was observed at an oil separation degree of around 0.2%.

(B-1) Temperature stability FIG. 6 shows the degree of variation in the temperature of the bearing outer ring at the time of steady operation after the running-in operation has been sufficiently completed. The scores are shown in Table 1. ◎ is represented by 3 points, ◯ is 2 points, Δ is 1 point, and x is 0 point, and the higher the score, the smaller the temperature fluctuation during steady operation. The grade of each grease is determined based on the following criteria.
A: In both (1) -1 and (1) -2, the fluctuation range of the bearing outer ring temperature during steady operation is less than 1 ° C. ○: Steady in either (1) -1 or (1) -2 The fluctuation range of the bearing outer ring temperature during operation is 1 ° C. or more and less than 2 ° C. Δ: In any one of (1) -1 and (1) -2, the fluctuation range of the bearing outer ring temperature during steady operation is 2 ° C. or more and 3 ° C. Less than x: In any one of (1) -1 and (1) -2, the fluctuation range of the bearing outer ring temperature during steady operation is 3 ° C. or more.

(B-2) Oil separation degree Fig. 7 shows test grease E (oil separation degree 0.2%), Fig. 8 shows test grease A (oil separation degree 1.0%), and Fig. 9 shows test grease F (oil separation degree). 1.2%) shows the transition of the bearing outer ring temperature after the initial break-in operation in the (1) -1 seizure resistance evaluation test. 7-9, the fluctuation range of the outer ring temperature of the test bearings in which the test greases E and A having an oil separation degree of 0.2% and an oil separation degree of 1% are sealed is about 0.5 ° C. The fluctuation range of the outer ring temperature of the test bearing in which the test grease F having an oil level of 1.2% is sealed is slightly increased to about 2.5 ° C. However, this grease F (a) has a durability time exceeding 250 hours in the durability test. The oil separation degree affects the temperature stability of the rotating bearing, and if the oil separation degree exceeds 1.0%, a large temperature fluctuation of 2 ° C. or more occurs. Accordingly, the grease sealed in the machine tool spindle bearing is required to have a degree of oil separation of 4% or less, preferably 1.2% or less, more preferably 1.0% or less.

(C) Leakage rate During the vertical operation, the ratio of grease that flows out before and after operation after 200 hours of operation at the maximum rotation speed is defined as “leakage rate”. Table 1 shows the leakage rate when 200 hours have elapsed. When the leakage rate is 40% or more, ×, when it is 35% or more and less than 40%, and when it is less than 35%, it is indicated by ◎.

  Further, test grease E and test grease E ′ having the same components as test grease E but having a reduced proportion of the thickener were prepared, and the seizure resistance evaluation test of (1) -1 was performed. Table 2 shows the leakage rate at 200 hours and the leakage rate at 3000 hours obtained by logarithmic function approximation, respectively. The thickening agent amount of grease E is 11.3% and the grease E ′ is 8.3%. In the grease of the present invention, a large difference occurs in the leakage rate when the thickening agent amount is about 10%.

  In the test grease E ′, when the leakage rate at 200 hours is about 40%, the leakage rate at 3000 hours is about 50%, and the supply capacity of the base oil is lowered, and the lubrication becomes severe. In general, machine tools are processed under various conditions such as heavy cutting at low speed to light cutting at high speed. Therefore, if the continuous speed operation time at the maximum speed exceeds 3000 hours, it will be practically used. In this vertical operating condition, it is required that the leakage rate when operating at the maximum rotation speed for 200 hours is less than 40%.

(D) Running-in FIG. 10 shows the results of the running-in evaluation test, and FIG. 11 shows the temperature transition graph of the bearing outer ring after the start of the seizure resistance evaluation test of the test grease G. The graph of FIG. 10 shows the amount of increase in temperature when the number of revolutions is increased in the running-in operation in the seizure resistance evaluation test of (1) -1 and the calorific value measurement test of (1) -2, and the running-in after the start of the test. The running-in is determined from the time required for the bearing temperature to settle to a certain degree after the operation is finished, and is indicated by a score. The score is shown in Table 1. ◎ is 3 points, ◯ is 2 points, Δ is 1 point, and X is 0 point, and the higher the score, the better the wear-in of the bearing. The grade of each grease is determined based on the following criteria.
A: A temperature peak does not occur after increasing the number of revolutions in the running-in operation, and the temperature becomes steady within approximately one hour.
○: The temperature peak after increasing the number of revolutions in the running-in operation is about +3 to + 5 ° C. during steady operation, or the temperature becomes steady within approximately 2 hours.
Δ: It takes 2 to 5 hours for the temperature graph to swell after increasing the number of revolutions in the running-in operation or until the temperature becomes steady.
X: It takes 5 hours or more for the temperature graph to swell greatly after increasing the number of revolutions in the running-in operation or until the temperature becomes steady.

FIG. 10 shows that the running-in of the bearing greatly depends on the consistency of the grease to be enclosed. Further, as shown in FIG. 11, in the test grease G having a consistency of 212, the outer ring temperature has a larger peak than after the start of the test, and it takes 10 hours or more for the temperature to settle to a steady state. In rolling bearings for machine tool main spindles, it is desirable to finish the initial break-in operation in a short time. However, in order to satisfy the minimum rating of 1, a consistency of 240, more desirably a consistency of 260 is required. I can say that. Also, if the consistency exceeds 320, the retention of grease decreases and the fluidity becomes too high, so that the grease once discharged from the rolling contact surface or the raceway groove returns to the raceway groove again. Occurs, the position of the grease is not fixed, and the break-in is not completed.

(E) Base oil kinematic viscosity Each of the above test greases has a kinematic viscosity at 40 ° C. of the base oil in the range of 18 to 33 mm ² / s. We investigated the relationship with the thickness. FIG. 12 shows the calorific value and the oil film thickness when the parameters other than the base oil kinematic viscosity are all the same from the calculation and the base oil kinematic viscosity of the grease to be filled is changed.

As shown in the drawing, when the kinematic viscosity at 40 ° C. of the base oil is less than 18 mm ² / s, metal contact occurs under the contact surface, and the heat generation amount increases rapidly. Conversely, in the region where the kinematic viscosity at 40 ° C. of the base oil exceeds 60 mm ² / s, the amount of heat generation increases due to the oil stirring resistance and viscosity resistance, while the rate of increase in the oil film thickness decreases. In bearings for machine tools, lubrication in a boundary lubrication region where the amount of generated heat is small is desirable. As shown in the figure, it is necessary if the kinematic viscosity at 40 ° C. of the base oil is 60 mm ² / s or less. An oil film thickness is obtained, and the calorific value is suppressed to 100 W or less. Moreover, in order to suppress the emitted-heat amount to 100 W or less, the kinematic viscosity in 40 degreeC should just be 20 mm < ² > / s or more. Therefore, it can be said that the kinematic viscosity at 40 ° C. of the base oil is preferably 18 to 60 mm ² / s. More preferably, it is 20-40 mm < ² > / s. By using such a base oil kinematic viscosity, an operating condition that keeps the oil film thickness necessary for lubrication and keeps the heat generation amount low is satisfied.

From the above results, like the test grease E, lithium soap is blended as a thickener in a base oil having a kinematic viscosity at 40 ° C. of ²⁰ to 60 mm ² / s, and the consistency is further adjusted to 240 to 320. As a result, the degree of oil separation satisfies 0.2 to 1.2%, the leakage rate becomes 40% or less, and the durability, temperature stability, and break-in under high load become excellent. It turns out that it is especially preferable.

  Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

  The rolling device of the present invention is suitable for use under a high speed and high load like a rolling bearing used for supporting a main shaft of a machine tool. More specifically, the rolling device has a dmn of 800,000 or more and an inner ring. It is useful for applications in which the PV value of the rolling contact portion of the outer ring is 100 MPa · m / s or more, and even if it is dmn 1 million or more, it can be used sufficiently.

1 Inner ring 2 Outer ring 3, 31 Rolling element 4 Cage

Claims (7)

  A grease composition for a rolling bearing, comprising a base oil and a thickener, having a consistency of 212 to 320, an oil separation of 4% or less, and a leakage rate of 40% or less. The rolling bearing grease composition according to claim 1, wherein the base oil has a kinematic viscosity at 40 ° C. of 18 to 60 mm ² / s.   The grease composition for a rolling bearing according to claim 1 or 2, wherein the thickener is lithium-based soap.   A plurality of rolling elements are rotatably held by a cage between the inner ring and the outer ring, and are lubricated by the rolling bearing grease composition according to any one of claims 1 to 3. A rolling bearing characterized by that.   The rolling bearing according to claim 4, wherein an amount of the grease composition enclosed is 10 to 30% of a static space volume inside the bearing.   The rolling bearing according to claim 4 or 5, wherein the rolling bearing is used for a machine tool spindle with a dmn of 800,000 or more and a PV value of a rolling contact portion of either the inner ring or the outer ring of 100 MPa · m / s or more. .   A machine tool spindle device comprising the rolling bearing according to any one of claims 4 to 6.

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