JP2002206095A - Grease composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grease composition which can sufficiently deal with a high speed rotation and can make a machine tool compact and reduce the operation cost. SOLUTION: This grease composition to be sealed in the main shaft- supporting rolling bearing of a machine tool is characterized by containing at least one compound selected from monosulfide compounds, disulfide compounds, sulfoxide compounds and thiolsulfinate compounds in an amount of 0.001 to 5 wt.% converted into sulfur on the basis of the total amount of the grease composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lathe, drilling machine, boring machine, milling machine, grinding machine, honing machine,
The present invention relates to a grease composition sealed in a rolling bearing incorporated in a main shaft support portion of a machine tool that slides and rotates at high speed, such as a super finishing machine and a lapping machine.

[0002]

2. Description of the Related Art A spindle of a machine tool as described above usually incorporates a rolling bearing for supporting a main shaft, and is generally used in combination with an angular ball bearing or a cylindrical roller bearing. The processing accuracy and productivity of a machine tool greatly depend on the rotation speed of the spindle, and to increase productivity, the rotation speed of the spindle must be increased. However, when rolling bearings are used under high-speed rotation, heat generation of the bearings becomes remarkable, and the contact surface pressure between the rolling elements and the inner and outer rings increases due to centrifugal force. As a result, the risk of bearing damage typified by wear and seizure increases. In addition, since heat generation is increased by high-speed rotation, there is a risk that a machine tool may be thermally deformed, which also has an effect on machining accuracy.

In order to prevent a fatal situation from occurring in such a bearing system and to prevent a reduction in machining accuracy due to thermal deformation of the entire machine tool, an appropriate lubrication method is selected under high-speed rotation. Heat generation in the supporting rolling bearing must be minimized. Conventionally, oil-air lubrication, nozzle jet lubrication, and under-race lubrication have been adopted for lubricating rolling bearings for supporting the main shaft of machine tools that rotate at high speed because of the cooling effect associated with lubricating oil supply. . However, in these lubrication systems,
Since the introduction of the lubricating oil supply device is indispensable, an installation area for the lubricating oil supply device must be ensured, which hinders downsizing of the entire machine tool. Further, in these lubrication methods, since the lubricating oil is continuously consumed and the operating cost of the lubricating oil supply device is also required, the operating cost of the machine tool as a whole increases. Various measures have been taken to reduce operating costs, but the situation has almost reached its limit.

[0004] As a lubrication system for bearings, a system in which grease is sealed is also common. However, since the bearing generates a large amount of heat due to shearing of the grease, the reliability of bearing durability is lower than that of the oil-air lubrication method and the like. This lubrication system is essentially unsuitable for the main shaft supporting rolling bearing of a machine tool accompanied by high-speed rotation. However, if grease lubrication can be realized, advantages such as downsizing of a machine tool and reduction of operating costs, which cannot be handled by each of the above lubrication methods for continuously supplying lubricating oil, can be enjoyed. In addition, grease lubrication does not consume a large amount of lubricating oil, unlike oil-air lubrication, etc., and thus has the advantage of contributing to environmental conservation.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a grease composition which can sufficiently cope with high-speed rotation and which can make a machine tool compact and reduce operating costs. The purpose is to provide.

[0006]

An object of the present invention is to provide a grease composition sealed in a rolling bearing for supporting a main shaft of a machine tool, comprising a monosulfide compound, a disulfide compound, a sulfoxide compound and a thiol sulfinate. The grease composition is characterized in that at least one selected from compounds is contained in a ratio of 0.001% by weight or more and 5% by weight or less in terms of sulfur with respect to the total amount of the grease composition.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[0008] In the grease composition of the present invention, the base oil and the thickener are not particularly limited. Examples of the base oil include mineral oil-based and synthetic oil-based lubricating oils. Mineral oil-based lubricating oils include mineral oil under reduced pressure distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing,
Purified materials obtained by appropriately combining white clay purification, hydrogenation purification, and the like can be used. Examples of the synthetic oil-based lubricating base oil include a hydrocarbon-based oil, an aromatic base oil, an ester-based oil, and an ether-based oil. As the hydrocarbon oil,
Examples thereof include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and poly-α-olefins such as 1-decene and ethylene cooligomer. Examples of the aromatic oil include alkylnaphthalene oils such as monoalkylnaphthalene, dialkylnaphthalene, and polyalkylnaphthalene. Examples of the ester-based oils include dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl talate, diester oils such as methyl acetyl sinolate, trioctyl trimellitate, Aromatic ester oils such as tridecyl trimellitate and tetraoctyl pyromellitate, and polyol esters such as trimethylolpropane caprylate, trimethylolpropane belargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol belargonate Oil, carbonated oil and the like. As the ether-based oil,
Polyethylene glycol, polypropylene glycol,
Polyglycol such as polyethylene glycol monoether and polypropylene glycol monoether, or phenyl ether oil such as monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, monoalkyl tetraphenyl ether, dialkyl tetraphenyl ether And the like. These base oils can be used alone or as a mixture.

[0009] As thickeners, Li, Na,
Metal soaps such as complex metal soaps selected from Ba, Ca, Al, etc., bentone, silica gel, urea compounds,
Non-soaps such as a urea / urethane compound and a urethane compound can be appropriately selected and used, but in consideration of the heat resistance of grease, a urea compound, a urea / urethane compound, a urethane compound, or a mixture thereof is preferable. In consideration of heat resistance and acoustic characteristics, diurea compounds are particularly preferred. For high-speed applications, barium composite soap is particularly desirable, and the amount of thickener required to form grease is relatively large compared to other types (about 30% by weight of the total amount of grease). It has good oil retention performance and has moderate oil release properties even under high-speed rotation. for that reason,
A large amount of grease can be retained inside the bearing without the grease adhering to the outer ring portion of the bearing being washed away by the oil separated during rotation. The amount of the thickener is not particularly limited as long as it can form grease with the base oil, and is generally 10 to 30% by weight of the total amount of the grease composition.

In the present invention, at least one of sulfur-based extreme-pressure additives consisting of a monosulfide compound, a disulfide compound, a sulfoxide compound and a thiolsulfinate compound is blended as an essential component with the grease. The form of the compound is preferably a monosulfide, disulfide, sulfoxide or thiol sulfinate into which an alkyl chain has been introduced.
It is preferably 0 g / mol or less, particularly preferably 1500 g / mol or less. The action of the sulfur-based extreme pressure additive is that tribochemical reaction occurs on the contact friction surface between the rolling elements and the raceway surface, producing iron sulfide, which is softer than the bearing steel and reduces the contact surface pressure to reduce the bearing pressure. However, if the molecular size of the sulfur-based extreme pressure agent additive is too large, that is, if the alkyl chain length is too long, steric hindrance due to the alkyl chain becomes significant, and the tribochemical reaction described above occurs. Are less likely to occur, and the production of iron sulfide is inhibited. Therefore, the sulfur-based extreme pressure additive used in the present invention preferably has a molecular weight within the above range.

The sulfur-based extreme pressure additive is contained in a ratio of 0.001% by weight or more and 5% by weight or less in terms of sulfur based on the total amount of the grease composition. If the amount of sulfur is less than 0.001% by weight, the amount of produced iron sulfide is too small to contribute to the improvement of the durability of the bearing. On the other hand, when the sulfur amount is 5
If the amount exceeds 10% by weight, not only the effect corresponding to the increased amount cannot be obtained, but also the base oil amount becomes relatively small, and as a result, the lubricating properties of the bearing deteriorate. The amount of sulfur is particularly preferably from 0.003% by weight to 1% by weight based on the total amount of the grease composition.

The grease composition of the present invention may contain, if necessary, an antioxidant, a rust preventive, an oil agent, and an extreme pressure agent other than the above sulfur extreme pressure additive. These may be any of known ones. For example, examples of the antioxidant include amine compounds such as phenyl-α-naphthylamine, phenols such as di-t-butyl-p-cresol, thioamines such as phenothiazine, dialkyldithiophosphates, and dialkyldithiocarbamates. it can. It is preferable that the content of these additives is individually 0.05% by weight or more of the total amount of the grease composition, and the total amount is in the range of 0.15 to 10% by weight of the total amount of the grease composition. In particular, when the total amount exceeds 10% by weight, not only the effect corresponding to the increase in the content cannot be expected, but also the content of the base oil and the sulfur-based extreme pressure additive becomes relatively small, and the grease composition contains In some cases, these additives may aggregate to cause undesirable phenomena such as an increase in torque.

The grease composition of the present invention has an effect of preventing bearing seizure under high-speed rotation by reducing surface pressure of iron sulfide derived from a sulfur-based extreme pressure additive on a friction contact surface. Therefore, even among machine tools that slide and rotate at high speed, higher performance is exhibited in a fixed position preload type spindle in which surface pressure increases with the number of rotations, rather than a constant pressure preload type spindle. Specifically, it is effective to use a fixed position preload spindle having a preload at stop of 98 N or more.

[0014]

The present invention will be further described below with reference to examples. However, the present invention is not limited at all by the examples.

(Verification of Sulfur Content) A test grease was prepared by mixing a barium composite soap with an ester oil having a kinematic viscosity at 40 ° C. of 20 mm ² / s, and further changing the amount of diethyl disulfide added. Then, the test grease is applied to an angular contact ball bearing for machine tools (inner diameter 65 mm,
2.3 g (15% of the bearing space volume) was sealed in an outer diameter of 100 mm, a width of 18 mm, and a ceramic ball to prepare a test bearing. Further, the same angular contact ball bearing for machine tools was filled with the same amount of grease to which no diethyl disulfide was added, to produce a comparative bearing.

An atmosphere temperature of 20 ° C., a preload of 98 N,
Under the condition of dmn 1.6 million, the time until the bearing seized (bearing durability life) and the temperature of the bearing outer ring were measured.
FIG. 1 shows the relationship between the content of diethyl disulfide in terms of sulfur, the bearing durability life, and the temperature of the bearing outer ring.
Note that the bearing durability life and the bearing outer ring temperature are shown as ratios to measured values of comparative bearings.

As is apparent from FIG. 1, when the sulfur content in the grease exceeds 0.001% by weight, the durability life ratio becomes 1.5 times or more, and good durability performance is imparted to the bearing. can do. In particular, the sulfur content is highest in the range of 0.003% by weight to 1% by weight, and the life is about twice as long. When the sulfur content exceeds 5% by weight, the bearing life ratio sharply decreases. On the other hand, the temperature of the outer ring of the bearing is lowered by the addition of diethyl disulfide. However, when the sulfur content becomes 0.001% by weight, a large decrease is observed, and it becomes more remarkable at 0.003% by weight.

From these results, it can be seen that by adding 0.001% by weight or more and 5% by weight of sulfur to the grease composition, it is possible to greatly increase the durability life under high-speed rotation and suppress heat generation in the bearing. It can be seen that it can be provided. In particular, when the sulfur content is 0.003% by weight or more and 1% by weight or less, the spindle bearing can be used in an optimal state.

(Verification of molecular weight of sulfur-based extreme pressure additive) 4
To an ester oil having a kinematic viscosity at 0 ° C. of 20 mm ² / s,
A test grease was prepared by mixing barium composite soap and further adding a disulfide-based sulfur-based extreme pressure additive whose molecular weight was changed by an introduced alkyl group so that the content became 0.005% by weight in terms of sulfur. . Then, the test grease is applied to an angular contact ball bearing for machine tools (inner diameter 65 mm,
2.3 g (15% of the bearing space volume) was sealed in an outer diameter of 100 mm, a width of 18 mm, and a ceramic ball to prepare a test bearing. Further, the same angular contact ball bearing for machine tools was filled with the same amount of grease to which no sulfur-based extreme pressure additive was added, to prepare a comparative bearing.

Then, an ambient temperature of 20 ° C., a preload of 98 N,
Under the condition of dmn 1.6 million, the time until the bearing seized (bearing durability life) was measured. FIG. 2 shows the relationship between the molecular weight of the sulfur-based extreme pressure additive and the durability life of the bearing in terms of the ratio to the measured value of the comparative bearing.

As apparent from FIG. 2, when the molecular weight of the sulfur-based extreme pressure additive exceeds 1500 g / mol, the bearing life ratio starts to decrease gradually, and the molecular weight becomes 2000 g / mol.
If it exceeds, it will drop sharply. From this, the molecular weight of 2000
It can be seen that a sulfur-based extreme pressure agent of g / mol or less can be suitably used.

[0022]

As described above, according to the present invention, a sulfur-based extreme-pressure additive selected from a monosulfide compound, a disulfide compound, a sulfoxide compound and a thiolsulfinate compound is added in an amount of 0.001% by weight or more in terms of sulfur. By enclosing the grease composition containing 5% by weight or less, it is possible to improve the bearing life under high-speed rotation and to suppress heat generation, and to use a lathe, drilling machine, boring machine, milling machine, grinding machine, It is suitable for a rolling bearing incorporated in a main shaft support portion of a machine tool that slides and rotates at high speed, such as a honing machine, a super finishing machine, and a lapping machine. Moreover, unlike the method of continuously supplying lubricating oil, such as the oil-air lubrication method, the grease composition can be enclosed and used.
Operation costs can be reduced and space can be saved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the sulfur content of grease, the bearing durability life, and the bearing outer ring temperature, obtained in an example.

FIG. 2 is a graph showing the relationship between the molecular weight of a sulfur-based extreme-pressure additive and the durability life of a bearing obtained in an example.

Continued on the front page. (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C10N 50:10 C10N 50:10 (72) Inventor Sumio Sugita 1-5-50 Kumeinuma Shinmei 1-chome, Nippon Seiko Stock Company In-house F-term (reference) 4H104 BG05C BG11C LA03 PA01 QA18

Claims (1)

[Claims] 1. A grease composition sealed in a rolling bearing for supporting a main shaft of a machine tool, wherein at least one selected from a monosulfide compound, a disulfide compound, a sulfoxide compound and a thiol sulfinate compound is used. 0.0% of sulfur
A grease composition characterized in that the grease composition is contained in a proportion of from 01% by weight to 5% by weight.