JP3978998B2 - Rolling bearing - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rolling bearing suitable for a spindle bearing of a machine tool device represented by a lathe, drilling machine, boring machine, milling machine, grinding machine, honing machine, super finishing machine, lapping machine, etc. The present invention relates to a rolling bearing capable of improving bearing life in high-speed cutting or high-speed grinding.
[0002]
[Prior art]
The main shaft of a machine tool device generally rotates in a state of being supported by a rolling bearing of any one of an angular ball bearing, a cylindrical roller bearing, and a combination of these rolling bearings. The spindle of the machine tool device is required to increase the rotation speed in order to improve machining accuracy and productivity. However, the more the rolling bearing that supports the spindle is used under high speed rotation, the more heat generation and preload occur. The increase significantly increases the risk of seizures and bearing damage.
[0003]
In order to prevent such a situation and to prevent the entire machine tool from undergoing thermal deformation and reducing the machining accuracy, it is necessary to select an appropriate lubrication method and suppress the heat generation of the bearing supporting the spindle as much as possible. Don't be.
For this reason, conventionally, lubrication of a rolling bearing that supports a high-speed rotating machine tool spindle has a cooling effect, such as an oil-air lubrication method, a nozzle jet lubrication method, or an under-lace lubrication method (from the lower side to the raceway surface). The method of lubrication has been adopted.
[0004]
Here, oil lubrication is generally used as a lubrication method of the rolling bearing that supports the main shaft that rotates at a high speed.
[0005]
[Problems to be solved by the invention]
In any of the above conventional lubrication systems, it is essential to introduce a lubrication device that supplies lubricating oil into the bearing. Thus, incidental not only be necessary to secure the area occupied by the facilities of the lubricating device has become a disadvantageous from the viewpoint of reducing the operating costs.
For this reason, it is strongly desired to increase the spindle speed of machine tool equipment by using rolling bearings that employ grease lubrication, which can be expected to reduce machine tool equipment and reduce operating costs. However, grease lubrication generates heat due to shearing of grease. Therefore, the conventional lubrication method is unsuitable for speeding up the rotation.
[0006]
The present invention has been made by paying attention to the above points, and provides a rolling bearing in which grease can be increased even if grease lubrication is employed and grease that generates little heat even under high-speed rotation is enclosed. Is an issue. Specifically, the present invention provides a rolling bearing that can be used with grease lubrication and a dmn value of 1.3 million or more.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a rolling bearing for a spindle of a machine tool device that is used with a dmn of 1.3 million or more and employs grease lubrication. The grease enclosed in the rolling bearing is a base oil. 10% by weight or more and 100% by weight or less of the carbonic acid ester, and the kinematic viscosity of the base oil exceeds 50 × 10 ⁻⁶ (m ² / s) at 40 ° C. and 200 × 10 ⁻⁶ (m ² / s) or less, and the grease filling amount is 10 volume% or more and 50 volume% or less of the bearing space volume.
[0008]
According to the present inventors' investigation and research, the lubricating grease using carbonate as the base oil has less heat generation under high-speed shear, extends the life of the bearing, and further improves the machining accuracy of the machine tool. This is due to the fact that it has been found to bring about (see FIG. 3).
Further, the reason why 10% by weight or more and 100% by weight or less of the base oil is carbonated is as follows.
[0009]
The more the amount of carbonate ester distributed in the base oil, the more heat generation is reduced. And if the amount of carbonate is less than 10% by weight relative to the total amount of base oil, a sufficient heat generation reduction effect cannot be expected (see FIG. 4). For this reason, the lower limit is set to 10% by weight.
In particular, when the amount of carbonate ester relative to the total amount of base oil is 30% by weight or more, the effect of reducing heat generation due to the increase in carbonate ester is reduced, and the bearing outer ring temperature can be suppressed to 50 ° C. or less. Therefore, it is preferable to set the amount of carbonate to 30% by weight to 100% by weight with respect to the total amount of base oil (see FIG. 4).
[0010]
Further, the reason why the kinematic viscosity of the base oil is set to 10 × 10 ⁻⁶ to 200 × 10 ⁻⁶ (m ² / s) at 40 ° C. is as follows.
When the base oil kinematic viscosity at 40 ° C. is greater than 200 × 10 ⁻⁶ (m ² / s), heat generation increases rapidly due to increased viscosity during high-speed rotation, resulting in a rapid increase in the seizure life of the bearing. Shorter. For this reason, the upper limit value was set to 200 × 10 ⁻⁶ (m ² / s) (see FIG. 5).
[0011]
On the other hand, if the base oil kinematic viscosity at 40 ° C. is smaller than 10 × 10 ⁻⁶ (m ² / s), the thickness of the lubricating oil film formed during the rotation of the bearing is less than the minimum necessary level, and sufficient load carrying capacity is achieved. Cannot be maintained, and the baking life is shortened (see FIG. 5). For this reason, the lower limit was set to 10 × 10 ⁻⁶ (m ² / s).
And the long-term durability performance of a bearing can be ensured by setting the kinematic viscosity of the base oil to 10 × 10 ⁻⁶ to 200 × 10 ⁻⁶ (m ² / s) at 40 ° C.
[0012]
In particular, if the base oil kinematic viscosity at 40 ° C. of grease is 10 × 10 ⁻⁶ (m ² / s) or more and 130 × 10 ⁻⁶ (m ² / s) or less, the bearing outer ring temperature can be suppressed to 50 ° C. or less. The bearing life is the best. That is, it is more preferable that the base oil kinematic viscosity at 40 ° C. is 10 × 10 ⁻⁶ (m ² / s) or more and 130 × 10 ⁻⁶ (m ² / s) or less.
Here, the amount of grease to be enclosed is 10 volume% or more and 50 volume% or less with respect to the bearing space volume, which is effective for preventing temperature rise under high-speed rotation (see FIG. 6).
[0013]
The bearing space volume is a volume of a space formed between the inner ring and the outer ring.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, an angular ball bearing suitable for supporting a spindle of a machine tool rotating at high speed will be described as an example.
FIG. 1 is a sectional view of an essential part of the ball bearing. That is, the ball bearing 1 of the present embodiment is configured such that a plurality of balls 4 (rolling elements) are interposed between an inner ring 2 and an outer ring 3 arranged coaxially, and the inner diameter surface side of the inner ring 2 is the main shaft 6. It is fixed so as to be integrated. In FIG. 1, reference numeral 5 denotes a cage.
[0015]
Then, grease is sealed in the space between the inner and outer rings 3.
The grease contains 10 to 100% by weight of carbonate with respect to the total amount of base oil, and the kinematic viscosity of the base oil is 10 × 10 ⁻⁶ to 200 × 10 ⁻⁶ (m ² / s) at 40 ° C. Is set.
Here, the thickener of the grease is not particularly limited. For example, lithium soap, lithium complex soap, barium soap, barium complex soap, aluminum soap, aluminum complex soap, sodium soap, urea compound, calcium sulfonate, and mixed soap sodium-calcium soap, lithium-calcium soap, sodium -Aluminum soap can be used. Antioxidants added to the grease include amine compounds such as phenyl-α-naphthylamine, phenols such as di-t-butyl-P-cresol, thioamines such as phenothiazine, dialkyldithiophosphates, dialkyldithiocarbamine Examples thereof include acid salts.
[0016]
When the rolling bearing 1 having the above-described configuration is used, grease lubrication is required, so that it is not necessary to introduce a bearing lubrication device, and the machine tool incorporating the rolling bearing 1 can be reduced in size and the operation of the machine tool. Cost reduction can be expected.
In spite of grease lubrication, even if the main shaft 6 is rotated at a high speed with a dmn value of 1.3 million or more, the heat generation of the bearing 1 can be suppressed to 55 ° C. or less. This prevents the thermal deformation of the steel sheet and prevents the processing accuracy from being lowered.
[0017]
【Example】
For the rolling bearing according to the present invention, the bearing 1 was subjected to high-speed rotation heat generation evaluation.
As the bearing, an angular ball bearing 140BNC10TP4 was used, and 1.0 g of grease sealed in the bearing was used. The grease filling amount corresponds to 15% by volume of the bearing space volume.
[0018]
The grease used above uses lithium soap as a thickener, and the amount of the thickener is unified to be 15% by weight with respect to the total amount of grease. Further, as the base oil, oil having a kinematic viscosity at 40 ° C. of about 30 × 10 ⁻⁶ (m ² / s) was used. Then, four types of rolling bearings 20 each using 100% by weight of carbonate, ester, synthetic hydrocarbon, and mineral oil were prepared and tested as the base oil of the grease to be enclosed.
[0019]
That is, for each type of rolling bearing 1, two test bearings 1 were prepared and evaluated using a testing machine as shown in FIG.
The test machine has a spindle structure in which the main shaft 6 is supported by two test bearings 20 arranged in the rear combination, and the main shaft 6 is rotationally driven via a motor and a transmission (not shown). In addition, a through hole for supplying a lubricant in the radial direction is provided at an intermediate position between the two test bearings 20 in the substantially central portion of the test machine main body 24 in the axial direction. An air nozzle 21 is inserted. The oil air nozzle 21 has a structure replaceable with a grease nipple. Further, an exhaust path 23 is provided for exhausting air in the setting space of the bearing 20.
[0020]
Further, a thermocouple 25 is installed to measure the temperature rise of the bearing outer ring 20a. The preload (axial clearance) of the bearing 20 was adjusted to a constant value (60 kg) with a spacer or the like so that the temperature rise due to the difference in preload was not affected.
Then, after the rotation of the main shaft 6 reached a predetermined number of rotations, it was left for about 2 hours to saturate the heat generation temperature, and then the temperature of the bearing outer ring 20a was measured. The above test was repeated with various changes in the predetermined rotational speed.
[0021]
FIG. 3 shows the result. FIG. 3 summarizes the dependence of the heat generation characteristics of each prototype grease on the dmn value.
As can be seen from FIG. 3, when grease using a carbonate ester base oil is used as a lubricant, the bearing 20 generates less heat even when used under high speed rotation than when other greases are used as a lubricant. I know that there is. This is because the base oil using carbonate ester has a low viscosity and has good adhesion to the raceway surface of the bearing 20 and the rolling surface and sliding surface, which are metal surfaces such as rolling elements and cages. This is because it is superior in wettability compared to the base oil of No. 1, and has an effect of improving wear resistance and impact resistance by quickly forming a thin film on the raceway surface. Further, since the heat generation is low, the oil film forming ability at low torque is also excellent. Moreover, it is excellent also in heat resistance.
[0022]
From the viewpoint of the life of the grease, the less heat generated during rotation of the bearing 20, the more convenient it is. Specifically, a long life can be expected when the bearing outer ring temperature is 55 ° C. or lower. Then, as shown in FIG. 3, by using grease made of carbonate ester base oil as a lubricant, the bearing outer ring temperature is less than 55 ° C. even when the main shaft 6 is rotated at a high speed rotation with a dmn value of 1.3 million or more. It can be seen that it can be suppressed.
[0023]
Here, the same test was carried out by replacing barium complex soap and calcium sulfonate as the grease thickener, but the same tendency was observed, that is, without affecting the thickener. The superiority of the base oil using carbonate ester was confirmed.
Then, mixing of the mineral oil and the carbonate of kinematic viscosity of ^{30 × 10 -6 (m 2 /} s), also a kinematic viscosity at ^{40 ℃ 30 × 10 -6 (m} 2 / s) at 40 ° C. Using grease with oil as the base oil, a test was performed using the same testing machine as described above to determine the bearing outer ring temperature.
[0024]
Here, lithium soap was adopted as the thickener, and the amount thereof was 15% by weight with respect to the total amount of grease. The amount of grease filled is 15% by volume of the bearing 20 space volume.
The rotation test was performed with a dmn value of 1.3 million and a preload of 60 kg.
And the grease which changed the compounding ratio of the mixed oil used as the said base oil was used, and it calculated | required about the bearing outer ring temperature. The measured temperatures were obtained by allowing them to stand for about 2 hours in a high-speed rotation state with a dmn value of 1.3 million and saturating the temperatures.
[0025]
FIG. 4 shows the result.
As can be seen from FIG. 4, when the blending ratio of the carbonic acid ester with respect to the entire base oil is 10% by weight or more, the bearing outer ring temperature can be suppressed to 55 ° C. or less, and severe operating conditions are eased.
In particular, when a grease having a carbonate ester blending ratio of 30% by weight or more with respect to the entire base oil is used, the bearing outer ring temperature can be suppressed to 50 ° C. or less. Further, even if the ratio of the carbonate ester to the whole base oil is more than 30% by weight, the effect of reducing the bearing outer ring temperature is diminished, and the bearing outer ring temperature does not change greatly.
[0026]
On the other hand, it can be seen that the effect of reducing the temperature of the outer ring of the bearing cannot be obtained when grease having a carbonate ester blending ratio of less than 10% by weight with respect to the total amount of the base oil is used.
That is, it can be seen that the heat generation of the bearing 20 can be effectively suppressed by setting the blending ratio of the carbonic acid ester with respect to the whole base oil to 10 wt% or more, preferably 30 wt% or more.
[0027]
Next, when the carbonate is used as the base oil, the relationship between the kinematic viscosity of the base oil and the bearing seizure life and the relationship between the kinematic viscosity and the temperature of the outer ring bearing during rotation are tested under the same conditions using the above test machine. went.
That is, the test conditions used were grease containing 15% by weight of lithium soap as a thickener in the total amount of grease, and the amount of grease charged in the bearing 20 was set to 15% of the bearing space volume. The rotation test was performed with a dmn of 1.3 million and a preload of 60 kg.
[0028]
And when the test was done about the several bearing 20 which changed the base oil kinematic viscosity in 40 degreeC of the said grease to fill, the result shown in FIG. 5 was obtained. Each bearing 20 is allowed to stand for about 2 hours at the target rotational speed to achieve saturation of the heat generation temperature.
Here, the concentration of the carbonate ester base oil shown on the horizontal axis in FIG. 5 is such that the carbon chain length of about C _{4 to} C ₁₀ is added to the carbonate esters having alkyl chain lengths of 1 and 2 such as dimethyl carbonate and diethyl carbonate. The carbonate ester was mixed to make the viscosity of various base oils (at 40 ° C.) and used for the above test. This is an example of changing the base oil viscosity.
[0029]
As can be seen from FIG. 5, when the base oil kinematic viscosity at 40 ° C. is larger than 200 × 10 ⁻⁶ (m ² / s), the heat generation due to the increase in viscosity rapidly increases, and as a result, the seizure life of the bearing 20 rapidly increases. Becomes shorter.
On the other hand, if the base oil kinematic viscosity at 40 ° C. is less than 10 × 10 ⁻⁶ (m ² / s), the thickness of the lubricating oil film formed during the rotation of the bearing 20 is below the minimum necessary level, and sufficient load is achieved. The supporting ability cannot be maintained and the baking life is shortened.
[0030]
As described above, by setting the base oil kinematic viscosity at 40 ° C. of grease to 10 × 10 ⁻⁶ (m ² / s) or more and 200 × 10 ⁻⁶ (m ² / s) or less, the long-term bearing 20 It can be seen that durability performance can be achieved.
In particular, if the base oil kinematic viscosity at 40 ° C. of grease is 10 × 10 ⁻⁶ (m ² / s) or more and 130 × 10 ⁻⁶ (m ² / s) or less, the bearing outer ring temperature can be suppressed to 50 ° C. or less. is, the shaft 受寿 life is the most favorable. That is, the base oil kinematic viscosity at 40 ° C. is more preferably in the range of 10 × 10 ⁻⁶ (m ² / s) to 130 × 10 ⁻⁶ (m ² / s).
[0031]
Next, the relationship between the amount of grease to be filled, the temperature of the outer ring of the rotating bearing and the remaining amount of grease after rotating for a fixed time (after 20 hours) was determined using the above tester.
The grease (lubricant) used is carbonated ester as the base oil, the kinematic viscosity at 40 ° C. of the base oil is 30 × 10 ⁻⁶ (m ² / s), and lithium soap (grease) as the thickener. 15% by weight based on the total amount) was used. The rotation test was performed with a dmn of 1.3 million and a preload of 60 kg.
[0032]
The result is shown in FIG.
Here, the remaining amount of grease was determined by measuring the mass of the bearing 20 by stopping the rotation 20 hours after the target rotational speed was reached, disassembling the testing machine. Further, the initial grease filling amount and the remaining grease amount were evaluated by the ratio of the bearing space volume.
[0033]
As can be seen from FIG. 6, it can be seen that when the initial grease filling amount is less than 10% by volume of the bearing space volume , lubrication is insufficient and the temperature rises abnormally.
On the other hand, as the initial sealed amount increases, the amount of residual grease in the bearing 20 increases slightly, which is advantageous for durability. However, if the amount exceeds 50% by volume, abnormal temperature rise due to the stirring resistance of the lubricant occurs. . Thus, more than 10 vol% between the axes 受空 volume 50% by volume or less is desirable as the tolyl lease amount be encapsulated.
[0034]
The above test results are summarized as shown in FIG. That is, it can be seen that the rolling bearing 20 according to the present invention is a good bearing 20 that can suppress heat generation even when it is used at high speed rotation, even though grease lubrication is employed.
[0035]
【The invention's effect】
As described above, when the present invention is adopted, it is possible to provide a grease lubricated rolling bearing capable of suppressing heat generation even when used in a rotational state where the rotational speed is a dmn value of 1.3 million or more.
Moreover, since it is a grease lubrication system, the apparatus incorporating the rolling bearing can be made compact and the operating cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a rolling bearing according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a testing machine used in Examples.
FIG. 3 is a diagram showing a relationship between a dmn value and a bearing outer ring temperature in an example.
FIG. 4 is a graph showing the relationship between the concentration of carbonate in the base oil and the bearing outer ring temperature.
FIG. 5 is a graph showing the relationship between base oil kinematic viscosity, bearing outer ring temperature and bearing seizure life.
FIG. 6 is a diagram showing a relationship between an initial grease filling amount, a bearing outer ring temperature, and a residual grease amount.
FIG. 7 is a table summarizing all test results of Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ball bearing 2 Inner ring 3 Outer ring 4 Ball 6 Main shaft 20 Test bearing 20a Outer ring 25 Thermocouple

Claims (5)

In rolling bearings for spindles of machine tool devices that are used at dmn of 1.3 million or more and grease lubrication is adopted,
In the grease sealed in the rolling bearing, 10% by weight or more and 100% by weight or less of the base oil is carbonate ester, and the kinematic viscosity of the base oil is 50 × 10 ⁻⁶ (m ² / s at 40 ° C. ) or less of the past and ^{200 × 10 -6 (m 2 /} s), rolling bearing grease amount is equal to or less than 50 vol% 10 vol% or more of the bearing space volume.   The rolling bearing according to claim 1, wherein the rolling bearing is an angular ball bearing. Ri 100% by weight or less carbonate der 30% by weight or more of the base oil, with a kinematic viscosity of the base oil is ^{40 ℃ 50 × 10 -6 (m} 2 / S) and 130 × 10 ⁻⁶ (m ² / S) or less, The rolling bearing according to claim 1 or 2.   The rolling bearing according to any one of claims 1 to 3, wherein a grease filling amount is 15 volume% or more of a bearing space volume. The kinematic viscosity of the base oil exceeds 50 × 10 ⁻⁶ (m ² / s) at 40 ° C. and is not more than 130 × 10 ⁻⁶ (m ² / s). The rolling bearing described in any one of the items.

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