JP2009275176A - Grease for high-speed bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide grease for a high-speed bearing sufficiently complying with high-speed revolution with a dmN value of ≥1,700,000 and allowing compactification and reduction in operation cost of a machine tool. <P>SOLUTION: The grease for a high-speed bearing is obtained by blending a non-urea grease, which uses a composite amide lithium soap having an amide bond in a molecule as a thickener, with a urea grease using an urea compound as a thickener. The urea compound is obtained by reacting a polyisocyanate component with a monoamine component, and the monoamine component contains 46 mol% or more of aliphatic monoamines for the whole of monoamines. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high-speed bearing grease used for a rolling bearing that supports a high-speed rotating shaft such as a machine tool main spindle (spindle).

  The main spindle of the machine tool is preferably one that rotates at a high speed in order to increase machining efficiency, and various lubrication techniques are applied to the bearings. As a lubrication method suitable for the spindle rotating at high speed, for example, methods such as oil mist lubrication, air-oil lubrication, and jet lubrication are known. However, such a lubrication method requires ancillary equipment such as compressed air and an oil supply device, which is one of the causes of increasing the initial cost and running cost of machine tools. It can be said that this is a preferable lubrication method with less maintenance. For example, examples of the high-speed rolling bearing that supports a rotating shaft that rotates at a high speed of 2000 to 8000 rpm or higher include an angular ball bearing and a cylindrical roller bearing that support a spindle of a machine tool.

  As shown in FIG. 2, the angular ball bearing 11 can apply an axial load from one direction in addition to a radial load, and a straight line connecting the contact points of the steel ball 14 with the inner ring 12 and the outer ring 13 is formed. It has an angle (contact angle) α with respect to the radial direction. Grease is enclosed in a bearing space formed by the inner ring 12, the outer ring 13, and the steel ball 14. Lubricant used in high-speed rolling bearings such as angular ball bearings and cylindrical roller bearings does not require maintenance such as lubrication, and it is possible to use lubricating grease adjusted to a consistency that does not pollute the surrounding environment. preferable.

The following summarizes the lubrication characteristics and problems required for grease for high-speed bearings such as spindle rolling bearings.
(A) In order to extend the lubrication life of a long-life rolling bearing as much as possible, lubricant (grease or its base oil) is supplied from the rolling bearing as described in (i) to (iii) below. It is necessary that it is difficult to leak, has excellent heat resistance of grease, and can form an oil film thickness necessary for lubrication.

  (i) When rolling bearings are operated at high speeds, the grease in the rolling bearings or grease flows out of the bearings due to centrifugal force, or the base oil in the grease separates and flows out, which makes a significant contribution to lubrication. It is difficult to stay in the vicinity and is prone to poor lubrication. In order to prevent such a situation, a seal member such as a shield plate is attached to the rolling bearing. However, depending on the structure of the bearing, it may not be possible to attach the seal member. In some cases, the lubricant cannot be completely sealed.

  In the case of a rolling bearing that is not operated at high speed, excess grease that is pushed out from the frictional part due to the movement of the rolling elements and the cage may be recirculated to some extent inside the bearing and contribute to lubrication again depending on the rotation conditions. However, in rolling bearings for supporting a rotating shaft such as a machine tool that rotates at high speed, the wind pressure generated inside the bearing hinders this recirculation, so that lubrication is liable to occur. For this reason, in rolling bearings rotating at high speed, only a small amount of grease contributes to lubrication, and the properties of the grease are particularly important. Further, the grease for high speed bearings needs to maintain the lubricating performance even with a small amount of grease.

  (ii) When the operating conditions are increased, the rolling surface of the bearing locally generates heat and becomes high temperature. At this time, the grease with poor heat resistance is thermally deteriorated, and the life of the grease is remarkably shortened. For such problems, attempts have been made to use heat-resistant thickeners and base oils, or to add antioxidants. However, these attempts have not led to a sufficient improvement in durability.

  (iii) Conventional grease with improved lubricity (oil film thickness) increases shear friction resistance and increases rotational torque and heat generation when base oil viscosity is increased. The base oil viscosity is kept low. For this reason, the oil film of the lubricating oil that has become low viscosity due to a temperature rise accompanying high speed may become thin and cause sliding wear.

  (B) Low torque (inhibition of temperature rise) Existing high-speed bearing grease keeps the base oil viscosity low as described above, but when the bearing rotates at high speed, the viscosity increases due to temperature rise. There is a problem that the oil film is remarkably lowered and an oil film having a thickness necessary for lubrication cannot be formed.

  (C) About low vibration property, the vibration of the bearing may be increased depending on the type of the thickener of grease. That is, with a grease containing a thickener that forms large and hard aggregates, the vibration of the rolling bearing to be lubricated becomes large.

  As described above, the conventional grease has a problem that when it is used for a high-speed rolling bearing, required properties such as long life, low torque, and low vibration cannot be satisfied. As a countermeasure, grease containing a urea compound has been proposed (see Patent Documents 1 to 3), but it is insufficient to obtain higher speed performance.

For example, Patent Document 3 discloses that a base oil having a kinematic viscosity at 40 ° C. of 15 mm ² / sec or more and 40 mm ² / sec or less and a content of 9 mass% or more and 14 mass% or less of the entire grease composition. A grease composition containing a diurea compound thickener and having a miscibility of 220 to 320 is disclosed. However, even in the above grease composition, it is difficult to reduce the amount of grease filled, it is not possible to sufficiently cope with high-speed rotation of the bearing, and it is difficult to make the machine tool compact and reduce the operating cost.

In recent years, rolling bearings have been used more and more severely, and the rolling for spindles used at high-speed rotation with a dmN value, which is the product of pitch circle diameter dm (mm) and rotation speed N (rpm), is 1.7 million or more. The number of bearings is increasing. As the rotational speed of the bearing increases, it is difficult to satisfy all the performance required for the bearing with existing grease.
Japanese Patent Laid-Open No. 2000-169872 JP 2003-83341 A JP 2006-29473 A

  The present invention has been made to cope with such a problem. Even if the amount of grease is small, for example, the dmN value which is the product of the pitch circle diameter dm (mm) and the rotation speed N (rpm) is The purpose is to provide grease for high-speed bearings that can sufficiently handle high-speed rotations of 1.7 million or more, and that can make machine tools compact and reduce operating costs.

  The grease for high-speed bearings of the present invention is for high-speed bearings comprising 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. Grease, wherein the urea compound is obtained by reacting a polyisocyanate component and a monoamine component, and the monoamine component is a monoamine component containing 46 mol% or more of an aliphatic monoamine based on the total monoamine. Features.

  The non-urea grease is characterized in that the blending ratio with respect to the whole grease is 10 wt% to 80 wt%.

  The composite amidolithium soap is characterized in that the blending ratio with respect to the whole non-urea grease is 3% by weight to 40% by weight.

The base oil used in the urea grease and the non-urea grease, kinematic viscosity, characterized in that a ^{15 mm 2 / sec~40 mm 2 /} sec.

  The base oil used for the urea grease and the non-urea grease is at least one selected from a synthetic hydrocarbon oil, an ester oil, and an alkyl diphenyl ether oil.

  The grease for high-speed bearings is characterized in that at least one selected from an organic molybdenum compound and an organic zinc compound is added as an additive.

  The grease for high-speed bearings of the present invention is formed by blending a urea grease containing a predetermined urea compound as a thickener with a non-urea grease containing a composite amide lithium soap having an amide bond in the molecule as a thickener. Even if a small amount of grease is charged, the oil supply capacity to the raceway surface is excellent under high-speed rotation while maintaining the load resistance of the rolling bearing filled with this grease.

  The monoamine component that constitutes the urea compound contains 46 mol% or more of aliphatic monoamine with respect to the total monoamine, so that the thickener is not easily destroyed against shearing force under high speed, and the thickener Due to the capillary action of the fibers, the oil in the grease can be stably supplied to the rolling surface.

As an example of the high-speed bearing in which the grease for high-speed bearings of the present invention is enclosed, an angular ball bearing shown in FIG. 1 can be exemplified. FIG. 1 is a longitudinal sectional view showing an angular ball bearing in which grease for high-speed bearings according to the present invention is enclosed.
As shown in FIG. 1, the angular ball bearing 1 has a bearing space in which a rolling element 4 is held by a cage 5 between an inner ring 2 and an outer ring 3. The bearing is sealed with a seal member 6 fixed in the groove. The grease 8 for high-speed bearings of the present invention is enclosed at least around the rolling element 4 in a bearing space formed by the inner ring 2, the outer ring 3 and the rolling element 4. In the angular ball bearing 1, a circumferential groove-like grease pocket 7 is formed on the inner diameter surface of the outer ring 3 to physically prevent leakage of grease. A straight line connecting the contact points of the rolling elements 4 with the inner ring 2 and the outer ring 3 has a contact angle β with respect to the radial direction, and can carry a radial load and an axial load in one direction. Moreover, the rolling element 4 can also be made from ceramics, such as silicon nitride and silicon carbide.

  When the grease for high-speed bearings of the present invention is enclosed in the bearing, it is preferable to enclose an amount of 1 volume% or more and less than 10 volume% of the volume of the bearing gap. If it is less than 1% by volume, the amount of grease necessary for lubrication is insufficient and depleted, resulting in poor durability. If it is 10% by volume or more, the durability is not improved by heat generation due to the torque increase by stirring, and the cost is increased, which is not preferable in the environment.

  In addition to the angular ball bearing shown in FIG. 1, the high-speed bearing capable of enclosing the high-speed bearing grease of the present invention includes a deep groove ball bearing, a cylindrical roller bearing, a tapered roller bearing, a self-aligning roller bearing, a needle roller bearing, and a thrust cylinder. Examples thereof include a roller bearing, a thrust tapered roller bearing, a thrust needle roller bearing, and a thrust self-aligning roller bearing.

In the present invention, the base oil that can be used for the urea grease and the non-urea grease is preferably a lubricating oil having a kinematic viscosity at 40 ° C. (hereinafter simply referred to as kinematic viscosity) of 15 to 40 mm ² / sec. In particular, a lubricating oil having a kinematic viscosity of 18 to 30 mm ² / sec is more preferable. When the kinematic viscosity is less than 15 mm ² / sec, the viscosity is too low to obtain sufficient load resistance. Also, if the kinematic viscosity exceeds 40 mm ² / sec, oil supply to the raceway surface becomes insufficient with high-speed rotation, and the bearing life will be reached early.

  Examples of the base oil of the urea grease and the non-urea grease include synthetic hydrocarbon oil, ester oil, alkyl diphenyl ether oil, mineral oil, GTL oil, and the like. These base oils can be used alone or in combination of two or more. Among these, it is preferable to use a synthetic hydrocarbon oil, an ester oil, or an alkyl diphenyl ether oil.

Further, it is preferable that the kinematic viscosities of synthetic hydrocarbon oil, ester oil, and alkyl diphenyl ether oil are 10 to 40 mm ² / sec. Even if it is a mixed oil as it is this range, the range of kinematic viscosity can be 10-40 mm < ² > / sec mentioned above. When the mixed oil is used, it is preferable that the synthetic hydrocarbon oil is an essential component, and the synthetic hydrocarbon oil is preferably equal to or more in weight than the ester oil or the alkyl diphenyl ether oil.

  Examples of the synthetic hydrocarbon oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, poly-α-olefin such as 1-decene and ethylene co-oligomer, and the like.

  Examples of ester oils include dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl tartrate, and methyl acetyl cinnolate, trioctyl trimellitate, trioctyl trimellate Aromatic ester oils such as decyl trimellitate and tetraoctyl pyromellitate, polyol ester oils such as trimethylolpropane caprylate, trimethylolpropane verargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol verargonate And carbonate ester oil.

  Examples of the alkyl diphenyl ether oil include monoalkyl diphenyl ether, dialkyl diphenyl ether, and polyalkyl diphenyl ether.

  As the mineral oil, use can be made of a lubricant obtained from crude oil subjected to vacuum distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay purification, hydrorefining, and the like. .

  The urea grease in the present invention is a grease obtained by blending a urea compound as a thickener in the above base oil. The urea compound (urea thickener) that can be used in the present invention is obtained by reacting a polyisocyanate component and a monoamine component.

  Examples of the polyisocyanate component include phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. Of these, aromatic diisocyanates are preferred. Moreover, the polyisocyanate obtained by reaction with excess diisocyanate by molar ratio with respect to diamine and this diamine can be used. Examples of the diamine include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane.

  The monoamine component is a monoamine component containing an aliphatic monoamine in an amount of 46 mol% or more, preferably 80 mol% or more based on the total monoamine. By containing 46 mol% or more, the thickener has strong shear stability and is not easily destroyed even at high speeds, and the base oil in the grease can be supplied to the rolling section by the capillary action of the thickener. Examples of monoamines other than aliphatic monoamines constituting the monoamine component include alicyclic monoamines and aromatic monoamines.

  Examples of the aliphatic monoamine include hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, and oleylamine. Among these, octylamine is preferable. Examples of the alicyclic monoamine include cyclohexylamine. Examples of the aromatic monoamine include aniline and p-toluidine, and among these, aniline is preferably used.

  In the present invention, the urea-based thickener is preferably blended in an amount of 3 to 20% by weight based on the entire urea grease. In particular, the blending amount is preferably 5 to 16% by weight. If the blending amount is less than 3% by weight, the base oil retention capacity is not sufficient, and especially at the beginning of rotation, a large amount of oil is separated at one time and grease leakage occurs, resulting in a shortened bearing durability life. On the other hand, if the blending amount exceeds 20% by weight, the amount of the base oil is relatively small, the oil supply ability is insufficient, the lubrication is insufficient early, and the bearing durability life is similarly shortened.

  The non-urea grease in the present invention is a metal composite soap-based grease which does not contain a urea-based compound and is obtained by blending a complex amide lithium soap as a thickener with the above base oil.

  The composite amidolithium soap used in the present invention is synthesized from an aliphatic dicarboxylic acid, an aliphatic monoamine, lithium hydroxide or the like, and particularly has an amide bond in the molecule. As a commercial product of non-urea grease using composite amidolithium soap as a thickener, Kyodo Yushi Co., Ltd .: Palmax RBG can be mentioned.

  In the present invention, the composite amidolithium soap is preferably blended in an amount of 3 to 40% by weight based on the whole non-urea grease. If the blending amount is less than 3% by weight, the grease is soft and easily leaks from the bearing due to shearing. On the other hand, if the blending amount exceeds 40% by weight, the oil content in the grease is small and there is a risk that the oil supply performance will deteriorate.

  In the grease for high-speed bearings of the present invention, the non-urea grease is preferably blended at a ratio of 10 to 80% by weight with respect to the total amount of grease. In particular, the blending amount is preferably 20 to 50% by weight. As non-urea grease, if the blending amount is less than 10% by weight, the oil supply to the rolling section is poor. If the blending amount exceeds 80% by weight, the fiber of the thickener tends to be broken at high speed, and the base oil cannot be supplied to the rolling section due to the capillary action of the thickener.

  In the present invention, a known grease additive may be contained in the mixed grease of urea grease and non-urea grease, if necessary. Examples of the additives include antioxidants such as organic zinc compounds, amines, and phenolic compounds, metal deactivators such as benzotriazole, viscosity index improvers such as polymethacrylate and polystyrene, molybdenum disulfide, and graphite. Examples include solid lubricants, metal sulfonates, rust preventive agents such as polyhydric alcohol esters, friction reducing agents such as organic molybdenum compounds, oily agents such as esters and alcohols, and antiwear agents such as phosphorus compounds. These can be added alone or in combination of two or more.

  Of these additives, the organic zinc compound and the organic molybdenum compound are excellent in extreme pressure properties, and are effective in preventing seizure even in a state where the supply of oil to the rolling surface is insufficient.

  The content of these additives is preferably individually 0.05% by weight or more of the total amount of grease, and the total amount is preferably in the range of 0.15 to 10% by weight of the total amount of grease. In particular, when the total amount exceeds 10% by weight, not only an effect commensurate with the increase in content can be expected, but also the content of other components becomes relatively small, and these additives aggregate in the grease, Undesirable phenomena such as an increase in torque may be caused.

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

<Preparation of urea grease>
Urea grease U1-U7
In half of the base oil shown in Table 1, 4,4′-diphenylmethane diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd .: Millionate MT, hereinafter referred to as MDI) is dissolved in the proportion shown in Table 1, and the remaining half of the base oil is dissolved. A monoamine having a double equivalent of MDI was dissolved in the solution. The respective blending ratios and types are shown in Table 1. After adding a solution in which monoamine was dissolved while stirring a solution in which MDI was dissolved, stirring was continued for 30 minutes at 100 ° C. to 120 ° C. to produce a diurea compound in the base oil to obtain a urea grease sample. .

<Preparation of non-urea grease>
Non-urea grease NU1 to NU4
A mixture containing a complex amidolithium soap in the base oil shown in Table 1 (a mixture of a lithium salt of an N-alkyl-substituted monoamidic acid (see formula (1) below), a lithium salt of a dibasic acid, and an N-alkyl-substituted diamide ) Was added as a thickener to obtain a non-urea grease sample. The respective blending ratios and types are shown in Table 1.

Examples 1 to 12
The above urea grease and non-urea grease were mixed at the ratio shown in Table 2 to obtain a grease sample. In Example 11, 2% by weight of zinc dithiophosphate and molybdenum dithiocarbamate were added to 100% by weight of the mixed grease of urea grease and non-urea grease, respectively. The obtained grease samples were subjected to a centrifugal oil separation test and a deep groove ball bearing (6204) shown below, and a normal temperature high speed grease test was performed to measure centrifugal oil separation and grease life time. About Example 1, Example 4, Example 6, Example 9, Example 11, and Example 12, the normal temperature high speed grease test by the angular ball bearing shown below was also implemented. These measurement results are also shown in Table 2.

<Centrifuge oil separation test>
Using a centrifuge, a 50 g grease sample was placed in a centrifuge tube, and the oil separation by centrifugation was calculated using the following formula when acceleration of 23000 G was applied for 7 hours at 40 ° C. If the centrifugal oil separation is 20% or more, the oil supply capacity will be sufficient.
(Centrifugal oil separation,%) = (1−thickener concentration before test / thickener concentration after test) × 100

<Normal Temperature High Speed Grease Test-Deep Groove Ball Bearing (6204)>
A grease bearing sample was sealed in a deep groove ball bearing (6204) aiming at the rolling surface (0.14 g (about 3% by volume of the total bearing space)), and a non-contact seal was made to produce a test bearing. The test bearing was loaded with an axial load of 670 N and a radial load of 67 N, and rotated at a rotational speed of 15000 rpm in a normal temperature environment. The time until seizure was measured as the grease life time. In this test, if the grease life time is 1000 hours or more, the durability is excellent. The dmN value, which is the product of the pitch circle diameter (mm) and the rotational speed (rpm) of the bearing in this durability test, is 520,000.

<Normal Temperature High Speed Grease Test-Angular Contact Ball Bearing>
Angular contact ball bearing (outer diameter 150 mm x inner diameter 100 mm, inner and outer rings SUJ2, rolling element 13/32 inch silicon nitride ball) with grease sample aiming at rolling surface 3.0 g (about 10% by volume of total bearing space) A test bearing was made by sealing and non-contact sealing. The test bearing is cooled by outer cylinder cooling under a constant pressure of 1.8 GPa, and the bearing outer ring is rotated at a rotational speed of 14500 rpm while keeping the bearing outer ring at 50 ° C or less. The time until seizure is measured as the grease life time. did. The dmN value, which is the product of the bearing pitch circle diameter (mm) and the rotational speed (rpm), in this durability test is 1.85 million.

Comparative Example 1 to Comparative Example 10
Urea grease or non-urea grease shown in Table 2 was used as a grease sample. The same items as in Example 1 were measured for this grease sample. For Comparative Example 1 and Comparative Example 7, a normal temperature high speed grease test using the angular ball bearing described above was also performed. These measurement results are also shown in Table 2.

As shown in Table 2, the grease used in the present invention is (1) a grease containing a urea grease and a non-urea grease, and the thickener of urea urea reacts with the polyisocyanate component and the monoamine component. The monoamine component is a monoamine component containing 46 mol% or more of aliphatic monoamine based on the total amount of monoamine, and (2) blending ratio of non-urea grease with complex amide lithium soap as a thickener to the total grease. 10 to 80% by weight, and (3) the base oil preferably has a kinematic viscosity of 10 to 40 mm ² / sec.

  The grease for high-speed bearings of the present invention is a grease containing a predetermined urea grease and a non-urea grease grease containing a composite amide lithium soap as a thickener, so that it can improve the bearing durability life under high-speed rotation. Can do. For this reason, high-speed bearings enclosed in rolling bearings built into spindle support parts of machine tools that slide and rotate at high speed such as lathes, drilling machines, boring machines, milling machines, grinding machines, super finishing machines, lapping machines, etc. It can be suitably used as a grease. In addition, unlike a method of continuously supplying lubricating oil such as the oil-air lubrication method, grease can be enclosed and used, so that the operating cost can be reduced and the space can be saved.

It is a longitudinal cross-sectional view which shows the angular ball bearing with which the grease for high-speed bearings of this invention was enclosed. It is sectional drawing which shows an angular contact ball bearing.

Explanation of symbols

1,11 Angular contact ball bearings 2,12 Inner ring 3,13 Outer ring 4,14 Rolling elements (steel balls)
5 Cage 6 Sealing member 7 Grease pocket 8 Grease

Claims (6)

A grease for high-speed bearings comprising 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,
The urea compound is obtained by reacting a polyisocyanate component and a monoamine component, and the monoamine component is a monoamine component containing 46 mol% or more of an aliphatic monoamine based on the total monoamine. For grease.   The high-speed bearing grease according to claim 1, wherein the non-urea grease has a blending ratio of 10 to 80% by weight with respect to the whole grease.   The grease for high-speed bearings according to claim 1 or 2, wherein the composite amidolithium soap has a blending ratio of 3 to 40 wt% with respect to the whole non-urea grease. 4. The grease for high-speed bearings according to claim 1, wherein the base oil used for the urea grease and the non-urea grease has a kinematic viscosity of 15 to 40 mm ² / sec.   The base oil used for the urea grease and the non-urea grease is at least one oil selected from a synthetic hydrocarbon oil, an ester oil, and an alkyl diphenyl ether oil. The grease for high-speed bearings according to one item.   6. The high speed bearing grease according to claim 1, wherein at least one selected from an organic molybdenum compound and an organic zinc compound is added as an additive to the high speed bearing grease.

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