JP6461520B2 - Rolling bearings for machine tools - Google Patents

Description

  The present invention relates to a rolling bearing that is used in a machine tool and supports a rotating shaft such as a main shaft (spindle) that rotates at high speed.

  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, and is one of the causes of increasing the initial cost and running cost of the machine tool. On the other hand, grease lubrication is a preferable lubrication method because it requires less maintenance. For example, angular ball bearings and cylindrical roller bearings are used as rolling bearings that support rotating shafts that rotate at a high speed of 2000 to 8000 rpm or higher.

  As shown in FIG. 2, the angular ball bearing 11 can apply an axial load from one direction in addition to the 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 for rolling bearings for machine tools, including angular ball bearings and cylindrical roller bearings, does not require maintenance such as lubrication and uses lubricating grease adjusted to a consistency that does not pollute the surrounding environment. It is preferable.

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

    (I) When a rolling bearing is operated at high speed, the grease in the rolling bearing or grease flows out of the bearing due to centrifugal force, or the base oil in the grease separates and flows out, and the rolling surface has a large 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 a high speed, excess grease that is pushed out from the frictional part due to the motion of the rolling elements and the cage may recirculate to some extent inside the bearing and contribute to lubrication again depending on the rotation conditions. However, in a rolling bearing for spindle support that rotates at a high speed, the wind pressure generated inside the bearing hinders this recirculation, so that lubrication is liable to occur. For this reason, in a bearing rotating at high speed, only a small amount of grease contributes to lubrication, and the properties of the grease are particularly important. Moreover, it is necessary to maintain the lubrication performance 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 having 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 the 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) The low vibration grease may increase the vibration of the bearing depending on the type of thickener. 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 it cannot satisfy the required physical properties such as long life, low torque and low vibration when used in a high-speed rolling bearing of a machine tool. As countermeasures against these problems, grease compositions containing a predetermined urea compound have been proposed (see Patent Documents 1 to 3). For example, Patent Document 3 discloses that a base oil having a kinematic viscosity at 40 ° C. of 15 mm ² / s to 40 mm ² / s and a diurea compound having a content of 9% by mass to 14% by mass of the entire grease composition. And a thickener having a blending degree of 220 to 320.

  Further, in a machine tool, when water-soluble coolant used during processing enters the bearing, it causes rust, abnormal noise and damage to the bearing are accelerated, and the bearing needs to be replaced in a short time. In addition, the operating conditions become more severe with downsizing and speeding up, and there is a high possibility that peeling occurs on the rolling surface at an early stage. This exfoliation is a peculiar exfoliation accompanied by a change in white structure. Unlike exfoliation from the inside of the rolling contact surface caused by normal metal fatigue, it is a fracture phenomenon that occurs from a relatively shallow surface of the rolling contact surface. It is thought to be hydrogen embrittlement caused by hydrogen generated by coolant decomposition.

  As a method for suppressing such specific peeling that occurs at an early stage, for example, a method of adding a passivating agent to the grease composition (see Patent Document 4) or a method of adding bismuth dithiocarbamate (Patent Document 5). Have been proposed).

  In addition, as a grease composition with excellent heat resistance, mechanical stability, water resistance, rust resistance, load resistance, flame resistance, etc., a base oil composed of mineral oil or synthetic oil, tribasic calcium phosphate and diethanolamines The thing which mix | blended the grease structure stabilizers, such as these is proposed (refer patent document 6).

Japanese Patent Laid-Open No. 2000-169872 JP 2003-83341 A JP 2006-29473 A JP-A-3-210394 JP-A-2005-42102 JP 2008-156624 A

  However, in recent years, rolling bearings have been used in harsh conditions, and for machine tool spindles used at high speed rotations where the dmN value, which is the product of the pitch circle diameter dm (mm) and the rotational speed N (rpm), is 1.7 million or more. Rolling bearings are also increasing. As the rotational speed increases, it is difficult to satisfy all the required performances in a bearing in which an existing grease composition such as Patent Documents 1 to 3 is enclosed. Even in the grease composition of Patent Document 3, it is difficult to reduce the amount of grease charged, it is possible to sufficiently cope with high-speed rotation of the bearing, and it is not easy to make the machine tool compact and reduce the operating cost. Absent.

  In such a severe environment, the method of adding a passivating agent or bismuth dithiocarbamate as in Patent Documents 4 and 5 has become insufficient as a measure for preventing the above-described peeling phenomenon. Yes. In addition, the grease composition of Patent Document 6 has not been studied for its ability to prevent the above peeling phenomenon, and may have an adverse effect depending on the specific combination of essential components.

  The present invention has been made to cope with such a problem, and as a rolling bearing used in a machine tool, it is excellent in lubricity and high temperature durability, and sufficiently responds to high-speed rotation, while being used internally. The purpose of this invention is to provide rolling bearings for machine tools that can prevent rusting and peeling at the rolling surface due to hydrogen embrittlement, and reduce operating costs.

A rolling bearing for a machine tool according to the present invention is a rolling bearing that supports a rotating shaft of a machine tool. The rolling bearing includes an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, the inner ring, A seal member that covers openings in both axial ends of the outer ring; and a grease composition that is sealed around the rolling element. The grease composition includes a base oil, a thickener, and an alkanolamine. The base oil has a kinematic viscosity at 40 ° C. of 12 to 30 mm ² / s, and the thickener contains a polyisocyanate component, a monoamine component, and an inorganic acid alkali metal salt and alkaline earth metal salt. The monoamine component is at least one monoamine selected from aliphatic monoamines and aromatic monoamines, and Ruamin is characterized to include 0.1 to 10 parts by weight per 100 parts by weight of the total amount of the base oil and thickener.

  The alkanolamine is diethanolamine.

  In the thickener, the aliphatic monoamine is contained in an amount of 50 mol% or more based on the total monoamine.

  The base oil is at least one oil selected from poly-α-olefin oil (hereinafter referred to as PAO), ester oil, and alkyl diphenyl ether oil.

  The base oil is at least one oil selected from mineral oil, highly refined mineral oil, and water-soluble lubricating oil.

  The rolling bearing is an angular ball bearing or a cylindrical roller bearing.

  The rolling bearing for machine tool of the present invention encloses a rolling element with grease containing a base oil having a predetermined kinematic viscosity, a thickener made of a predetermined urea compound, and a predetermined amount of alkanolamine. Therefore, it is excellent in lubricity and durability at high temperature, and can sufficiently cope with high-speed rotation, and can prevent the occurrence of rust inside and peeling on the rolling surface due to hydrogen embrittlement. Since the bearing has a long service life, the replacement cycle can be extended and the operating cost of the machine tool can be reduced. For this reason, it can be suitably used as a rolling bearing incorporated in the spindle support part of a machine tool that slides and rotates at high speed such as a lathe, drilling machine, boring machine, milling machine, grinding machine, super finishing machine, and lapping machine. . Further, unlike the method of continuously supplying the lubricating oil as in the oil-air lubrication method, the bearing can be used with the grease sealed, so that the operating cost of the machine tool can be reduced and the space can be saved.

It is sectional drawing which shows the angular ball bearing which is an example of the rolling bearing for machine tools of this invention. It is sectional drawing which shows an angular contact ball bearing.

  As a result of intensive studies on grease used for lubrication in rolling bearings for machine tools, the inventors have formulated alkanolamine as an essential additive in grease using a predetermined base oil and thickener, It has been found that it is possible to effectively prevent peeling on the rolling surface due to hydrogen embrittlement and generation of rust inside the bearing while having high temperature durability.

  In rolling bearings, when the rolling elements and raceway rings, or rolling elements and cages make rolling contact / sliding while in contact with lubricating oil or grease, the contact surfaces between the iron based metallic members (main On the rolling surface), there is a case where the oil film is almost lost and the boundary lubrication condition is such that the surfaces of the metals are in direct contact with each other. As described above, rolling bearings for machine tools in recent years tend to cause an oil film breakage on the rolling surface due to severe use conditions such as high speed. Thus, even when the oil film becomes thin on the rolling surface, the alkanolamine adsorbs on the frictional wear surface or the new iron metal surface exposed by wear, and so on. Direct contact with coolant can be prevented. As a result, it is considered that the generation of hydrogen due to the decomposition of the grease and the coolant can be suppressed, the specific peeling due to the hydrogen embrittlement can be suppressed, and at the same time the generation of rust can be prevented, and the life of the rolling bearing can be extended. The present invention is based on these findings.

  A grease composition used for a rolling bearing for machine tools according to the present invention includes a base oil, a thickener, and an alkanolamine as an additive, and contains an alkali metal salt of an inorganic acid and an alkaline earth metal salt of an inorganic acid. Not included. Here, examples of the inorganic acid include phosphoric acid (orthophosphoric acid), hydrochloric acid, nitric acid, sulfuric acid, and boric acid. Examples of the alkali metal and alkaline earth metal include lithium, sodium, potassium, calcium, strontium, and barium. Is mentioned. Specific examples include tricalcium phosphate (calcium salt of orthophosphoric acid).

  Examples of the alkanolamine used in the grease composition include primary alkanolamines such as monoisopropanolamine, monoethanolamine, and mono-n-propanolamine, secondary alkanolamines such as N-alkylmonoethanolamine, and N-alkylmonopropanolamine. Examples include tertiary alkanolamines such as alkanolamines, triethanolamine, cyclohexyldiethanolamine, tri (n-propanol) amine, triisopropanolamine, N, N-dialkylethanolamine, and N-alkyl (or alkenyl) diethanolamine. Moreover, it is classified into monoalkanolamine, dialkanolamine, and trialkanolamine according to the number of alkanol groups. In the present invention, iron ions are sandwiched by chelating action of a plurality of hydroxyl groups (alkanol groups) and amino groups, and iron It is preferable to use dialkanolamine or trialkanolamine because it is easy to prevent exposure of the new metal surface.

  Among these, it is preferable to use N-alkyl (or alkenyl) diethanolamine of the following formula (1) because it is excellent in compatibility with the base oil, excellent in the ability to prevent rust and peeling phenomenon, and excellent in availability.

R ₁ in the formula represents a linear or branched alkyl group or alkenyl group having 1 to 20 carbon atoms. Moreover, 1-12 are preferable and, as for carbon atom number, 1-8 are more preferable. Specific examples of the compound include N-methyldiethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N-butyldiethanolamine, N-pentyldiethanolamine, N-hexyldiethanolamine, N-heptyldiethanolamine, N-octyldiethanolamine, N -Nonyldiethanolamine, N-decyldiethanolamine, N-undecyldiethanolamine, N-lauryldiethanolamine, N-tridecyldiethanolamine, N-myristyldiethanolamine, N-pentadecyldiethanolamine, N-palmityldiethanolamine, N-heptadecyldiethanolamine, N -Oleyl diethanolamine, N-stearyl diethanolamine, N-isostearyl Ethanolamine, N- nonadecyl diethanolamine, N- such eicosyl diethanolamine.

Alkanolamines may be used alone or in combination of two or more. The alkanolamine is preferably liquid or pasty at room temperature and operating temperature. Further, it may be dispersed in a solvent or the like. By using such an alkanolamine, even when the oil film on the rolling contact surface becomes thin under severe conditions in a machine tool, the alkanolamine easily enters the portion. The kinematic viscosity of the alkanolamine, preferably 10 to 100 mm ² / s at 40 ° C., and more preferably 40~70mm ² / s at 40 ° C..

  Examples of commercially available products of alkanolamine (tertiary diethanolamine) include ADEKA COLUMB FM-812 and ADEKA COLUMB FM-832 manufactured by ADEKA.

  The blending ratio of the alkanolamine in the grease composition is 0.1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener. Within this range, the occurrence of rust and unique peeling due to hydrogen embrittlement can be prevented without other adverse effects. If it exceeds 10 parts by weight, the consistency will be too high and there is a risk of leakage from within the bearing. Preferably it is 0.3-10 weight part, More preferably, it is 1.0-5.3 weight part.

The base oil of the above grease composition has a kinematic viscosity at 40 ° C. (in the case of a mixed oil, the kinematic viscosity of the mixed oil) is 12 to 30 mm ² / s. More preferably, it is 15-30 mm < ² > / s. If the kinematic viscosity is less than 12 mm ² / s, the viscosity is too low and sufficient load resistance may not be obtained. Moreover, when kinematic viscosity exceeds 30 mm < ² > / s, supply of the oil to a rolling surface is insufficient with high speed rotation, and there exists a possibility of reaching a bearing life at an early stage.

  As the base oil of the grease composition, for example, at least one oil selected from PAO, ester oil, and alkyl diphenyl ether oil can be employed. When these mixed oils are used, it is preferable to use PAO as an essential component, and it is preferable that PAO is equal to or more than the ester oil or alkyldiphenyl ether oil in the weight ratio.

  PAO is usually a mixture of oligomers or polymers of α-olefins or isomerized α-olefins. Specific examples of the α-olefin include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1 -Nonadecene, 1-eicosene, 1-docosene, 1-tetradocosene, etc. can be mentioned, Usually, these mixtures are used.

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

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

  Further, as the base oil of the grease composition, for example, at least one oil selected from mineral oil, highly refined mineral oil, and water-soluble lubricating oil can be employed. Examples of the mineral oil include spindle oil, refrigerator oil, turbine oil, machine oil, dynamo oil and the like. Highly refined mineral oil can be obtained by, for example, catalytic hydrothermal decomposition of slag wax obtained from the residue of vacuum distillation and synthesizing. Moreover, the GTL oil etc. which are synthesize | combined by the Fischer-Tropsch method are mentioned. The highly refined mineral oil preferably has a sulfur content of less than 0.1% by weight, more preferably less than 0.01% by weight. Examples of the water-soluble lubricating oil include water-glycol hydraulic oil.

  The thickener of the grease composition is a urea compound obtained by reacting a polyisocyanate component and a monoamine component. Urea compounds are excellent in heat resistance and durability, and also have excellent intervention and adhesion to rolling surfaces. Examples of the polyisocyanate component include phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, and hexane diisocyanate. Examples of the monoamine component include aliphatic monoamines, alicyclic monoamines, and aromatic monoamines. Aliphatic monoamines include hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, stearylamine, oleylamine and the like. Examples of the alicyclic monoamine include cyclohexylamine. Aromatic monoamines include aniline, p-toluidine and the like.

  In the present invention, among the monoamines, at least one monoamine selected from aliphatic monoamines and aromatic monoamines is used. In particular, the aliphatic monoamine is preferably contained in an amount of 50 mol% or more based on the total monoamine. As a result, the thickener has high shear stability and is not easily destroyed even at high speeds, and the base oil in the grease can be supplied to the rolling surface by the capillary action of the thickener.

  A base grease can be obtained by blending a base compound with a urea compound as a thickener. This base grease is produced by reacting the polyisocyanate component and the monoamine component in a base oil. The blending ratio of the thickener in the base grease is 3 to 20% by weight, preferably 5 to 15% by weight. If the content of the thickener is less than 3% by weight, the base oil holding ability is not sufficient, and a large amount of oil may be separated at one time at the initial stage of rotation, resulting in leakage of grease, which may shorten the bearing durability life. On the other hand, if it exceeds 20% by weight, the amount of the base oil is relatively reduced, the oil supply performance is insufficient, and there is a possibility that the bearing endurance life is similarly shortened due to insufficient lubrication at an early stage.

  As a method for preparing the above grease composition, first, alkanolamine is blended in the base oil, and a thickener is prepared using this base oil. Any method of adding liquid may be used. Since the alkanolamine contains an amino group, when a urea compound is used as a thickener, it is possible to add the alkanolamine after preparing the base grease by reacting the polyisocyanate component and the monoamine component in the base oil. This is the preferred method.

  It is preferable that the penetration degree (JIS K 2220) of the grease composition is in the range of 200 to 350. When the consistency is less than 200, oil separation is small and there is a risk of poor lubrication. On the other hand, if the consistency exceeds 350, the grease is soft and easily flows out of the bearing, which is not preferable.

  In the grease composition used for the rolling bearing for machine tools of the present invention, the alkanolamine is not present in the form of a reaction product like a salt with an acid, but is present as it is. Therefore, as other additives, an additive which forms a salt with an alkanolamine such as a fatty acid is not included. The grease composition may contain a known additive as necessary within the range not impairing the object of the present invention. Examples of 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 thereof include solid lubricants, metal sulfonates, rust inhibitors such as polyhydric alcohol esters, oil agents such as esters and alcohols, and other antiwear agents. These can be added alone or in combination of two or more. Further, in the present invention, even when an organic molybdenum compound such as molybdenum dithiophosphate and molybdenum dithiocarbamate is not blended, peeling at the rolling surface due to hydrogen embrittlement can be prevented.

  The rolling bearing for machine tool of the present invention is not particularly limited in terms of structure, and for example, an angular ball bearing 1 shown in FIG. 1 can be exemplified. FIG. 1 is a longitudinal sectional view showing a grease-filled angular ball bearing. As shown in FIG. 1, this angular bearing 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 in a locking groove provided on an inner peripheral surface of the outer ring 3. It is an angular ball bearing sealed with a fixed seal member 6. The grease composition is sealed at least around the rolling element 4 and a circumferential groove-like grease pocket 7 is formed on the inner diameter surface of the outer ring 3 to physically prevent the grease composition from leaking. 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. In the present invention, the predetermined grease composition described above is enclosed in a bearing space formed by the inner ring 2, the outer ring 3, and the rolling elements 4.

  In the rolling bearing for machine tool of the present invention, it is preferable to enclose grease 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. When it is 10% by volume or more, durability is not improved by heat generation due to an increase in torque due to agitation, and the cost is increased, which is not preferable from an environmental viewpoint.

  As the rolling bearing for machine tool of the present invention, in addition to the angular ball bearing shown in FIG. 1, deep groove ball bearing, cylindrical roller bearing, tapered roller bearing, self-aligning roller bearing, needle roller bearing, thrust cylindrical roller bearing, thrust Tapered roller bearings, thrust needle roller bearings, thrust spherical roller bearings, and the like can also be used. Among them, it is preferable to use an angular ball bearing or a cylindrical roller bearing because it has both rotational accuracy at high speed and load bearing performance.

  The present invention will be specifically described with reference to examples and comparative examples, but is not limited to these examples.

Example 1 to Example 3, Comparative Example 1 to Comparative Example 2
In half of the base oil shown in Table 1, 4,4′-diphenylmethane diisocyanate (Millionate MT manufactured by Nippon Polyurethane Industry, hereinafter referred to as “MDI”) is dissolved in the ratio shown in the table, and the remaining half of the base oil is dissolved. A monoamine that was twice the equivalent of MDI was dissolved. Each blending ratio and type are as shown in the table. A solution in which monoamine was dissolved was added while stirring the solution in which MDI was dissolved, and then the reaction was continued with stirring at 100 to 120 ° C. for 30 minutes to produce a diurea compound in the base oil to obtain a base grease. Each additive was added to this at a blending ratio shown in Table 1 and further sufficiently stirred. Thereafter, it was homogenized with three rolls to obtain a test grease. The kinematic viscosity of the base oil (mixed oil) is 22 mm ² / s (40 ° C.).

  The obtained grease was sealed in a rolling bearing and subjected to the following rapid acceleration / deceleration test, high temperature durability test, and rust test. Test methods and test conditions are shown below.

<Rapid acceleration / deceleration test>
The above grease was sealed in a rolling bearing for inner ring rotation supporting the rotating shaft (bearing steel SUJ2, model number: 6203 LLU (with seal) for inner ring, outer ring, and steel ball), and a rapid acceleration / deceleration test was performed. The rapid acceleration / deceleration test conditions were set in a room temperature (25 ° C.) atmosphere with a load applied to the pulley attached to the tip of the rotary shaft of 1960 N, a rotational speed of 0 rpm to 20000 rpm, and 0.5 A in the test bearing. The test was conducted in a state where the current of Then, abnormal peeling occurred in the bearing, and the time when the vibration of the vibration detector exceeded the set value and stopped (peeling life time, h) was measured. The results are shown in Table 1.

<High temperature durability test>
The above grease is enclosed in a rolling bearing (inner diameter 20 mm × outer diameter 47 mm × thickness 14 mm, model number: 6204ZZ (with seal)), under an axial load of 67 N and a radial load of 67 N, at a bearing temperature of 150 ° C. and a rotational speed of 10,000 rpm. It was rotated and the time until seizure (high temperature endurance life time, h) was measured. The results are shown in Table 1. In addition, the said result is an average value (time, h) of the test frequency | count of 3 times.

<Rust test>
In accordance with the rust test method specified in ASTM D 1743, the test conditions were conducted under conditions more severe with respect to rust generation. After 2.0 g of the obtained grease was sealed in a tapered roller bearing 30204 that had been degreased and dried in advance with an organic solvent, an axial load was applied to 98 N, and running-in was performed for 1 minute at 1800 rpm. Next, after immersing in 1% by weight saline solution, the bearing was placed in a sealed high-humidity container that reached a saturated water vapor pressure at 40 ° C. and left at 40 ° C. for 48 hours, and then the rusting state was examined. As for the rusting situation, the outer race was divided into 32 equal parts in the circumferential direction, the number of rusted sections was counted, and the probability of rusting was measured. The results are shown in Table 1. The number of tests is 4 times (the total number of sections is 128).

  As shown in Table 1, the generation of rust could be prevented by blending alkanolamine (diethanolamine). In particular, by adding a predetermined amount of alkanolamine, it was possible to prevent the occurrence of rust while maintaining anti-peeling properties and high temperature durability.

  The rolling bearings for machine tools of the present invention are excellent in lubricity and high temperature durability, and can sufficiently prevent high-speed rotation, while preventing rust generation and peeling on the rolling surface due to hydrogen embrittlement. , Lathes, drilling machines, boring machines, milling machines, grinding machines, honing machines, super finishing machines, lapping machines, etc., can be suitably used as rolling bearings incorporated in spindle support parts of machine tools that slide and rotate at high speed.

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

Claims (5)

A rolling bearing that supports a rotating shaft of a machine tool,
The rolling bearing includes an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, a seal member that covers both axial end openings of the inner ring and the outer ring, and grease sealed around the rolling element. Having a composition,
The grease composition includes a base oil, a thickener, and an alkanolamine , and does not include an alkali metal salt , an alkaline earth metal salt , and a dithiocarbamic acid metal salt of an inorganic acid,
The base oil has a kinematic viscosity at 40 ° C. of 12 to 30 mm ² / s,
The thickener is a urea compound obtained by reacting a polyisocyanate component and a monoamine component, and the monoamine component is at least one monoamine selected from an aliphatic monoamine and an aromatic monoamine,
The rolling bearing for machine tools, wherein the alkanolamine is diethanolamine and is contained in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener.   The rolling bearing for machine tools according to claim 1, wherein the thickener contains 50 mol% or more of the aliphatic monoamine based on the total monoamine. The rolling bearing for machine tools according to claim 1 or 2 , wherein the base oil is at least one oil selected from poly-α-olefin oil, ester oil and alkyl diphenyl ether oil. The rolling bearing for machine tools according to claim 1 or 2 , wherein the base oil is at least one oil selected from mineral oil, highly refined mineral oil, and water-soluble lubricating oil. The rolling bearing for a machine tool according to any one of claims 1 to 4 , wherein the rolling bearing is an angular ball bearing or a cylindrical roller bearing.

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