JP3915877B2 - Grease composition and angular contact ball bearings for spindle support of machine tools - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is incorporated to support a spindle of a machine tool that slides and rotates at a high speed represented by, for example, a lathe, drilling machine, boring machine, milling machine, grinding machine, honing machine, super finishing machine, and lapping machine. angular contact ball bearings, as well as to a grease composition sealed in the angular ball bearings.
[0002]
[Prior art]
A spindle of a machine tool such as that described above usually incorporates a rolling bearing for supporting the spindle, and is generally used in combination with an angular ball bearing or a cylindrical roller bearing. Machining accuracy and productivity of machine tools largely depend on the rotation speed of the spindle, and in order to increase productivity, it is necessary to increase the rotation speed of the spindle. However, if the rolling bearing is used under high speed rotation, the heat generation of the bearing becomes noticeable, or 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 represented by wear and seizure increases. In addition, since heat generation increases due to high-speed rotation, there is a risk of thermal deformation of the machine tool, which also affects machining accuracy.
[0003]
In order to prevent a fatal situation from occurring in such a bearing system and to avoid a decrease in machining accuracy due to thermal deformation of the entire machine tool, an appropriate lubrication method is selected under high-speed rotation to rotate the spindle support. Heat generation in the bearing must be suppressed as much as possible. Conventionally, the lubrication of rolling bearings for supporting spindles of machine tools that rotate at high speeds has achieved the cooling effect associated with the supply of lubricating oil, so the oil-air lubrication method, nozzle jet lubrication method, and underlace lubrication method have been adopted. . However, in these lubrication methods, since it is indispensable to introduce a lubricating oil supply device, an installation area for that purpose must be ensured, and the overall machine tool is prevented from being made compact. Further, in these lubrication methods, the lubricating oil is continuously consumed, and the operating cost of the lubricating oil supply device is also required, so that the operating cost of the entire machine tool increases. Various measures have been taken to reduce operating costs, but the situation is almost reached.
[0004]
Grease is generally used as a lubrication system for bearings, but bearing heat generation due to grease shearing is large, and the reliability of bearing durability is low compared to the above oil-air lubrication methods. This is a lubrication system that is essentially unsuitable for rolling bearings for supporting the spindle of machine tools. However, if grease lubrication can be realized, it is possible to enjoy merits such as downsizing of the machine tool and reduction of operation costs that cannot be supported by the above-described respective lubrication methods that continuously supply the lubricating oil. Grease lubrication also has the advantage of contributing to environmental conservation because it does not consume a large amount of lubricating oil, unlike an oil-air lubrication system.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation, and a grease composition that can sufficiently cope with high-speed rotation and that enables downsizing of a machine tool and reduction of operation costs, and the grease composition are enclosed. It is an object of the present invention to provide an angular contact ball bearing for supporting a spindle of a machine tool.
[0006]
[Means for Solving the Problems]
The object of the present invention, there is provided a grease composition sealed in angular contact ball bearing for supporting the spindle of a machine tool, in Lee Ou terms, total sulfur content in the grease composition is 0.001% by weight or more 1 A grease composition containing a disulfide compound in an amount of not more than% by weight, and a machine tool that is incorporated to support a spindle of a machine tool and encloses the grease composition This is achieved by an angular contact ball bearing for supporting the main shaft.
[0007]
DETAILED DESCRIPTION OF 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 oils and synthetic oils. As the mineral oil-based lubricating oil, it is possible to use a refined oil obtained by appropriately combining mineral oil under reduced pressure distillation, oil removal, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay refining, hydrorefining, etc. . Examples of the synthetic oil-based lubricating base oil include hydrocarbon-based oils, aromatic base oils, ester-based oils, ether-based oils, and the like. Examples of the hydrocarbon oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, and poly-α-olefin such as 1-decene and ethylene co-oligomer. Examples of the aromatic oil include alkyl naphthalene oils such as monoalkylnaphthalene, dialkylnaphthalene, and polyalkylnaphthalene. Examples of the ester oil include dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl tartrate, and diester oil such as methyl acetyl cinolate, trioctyl trimellitate, Aromatic ester oils such as tridecyl trimellitate and tetraoctyl pyromellitate, polyol esters such as trimethylolpropane caprylate, trimethylolpropane verargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol verargonate Oil, carbonate ester oil and the like. Examples of the ether oil include polyglycols such as polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether, or monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, tetraphenyl ether, and monoalkyl. Examples thereof include phenyl ether oils such as tetraphenyl ether and dialkyl tetraphenyl ether. These base oils can be used alone or as a mixture.
[0009]
Further, as the thickener, metal soaps such as composite metal soaps selected from Li, Na, Ba, Ca, Al, etc., non-soaps such as benton, silica gel, urea compounds, urea / urethane compounds, urethane compounds, etc. However, in view of the heat resistance of the grease, a urea compound, a urea / urethane compound, a urethane compound, or a mixture thereof is preferable. In view of heat resistance performance and acoustic characteristics, a diurea compound is particularly preferable. For high-speed rotation 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). Good oil retention performance and moderate oil release characteristics even under high speed rotation. Therefore, a large amount of grease can be retained inside the bearing without washing away the grease adhering to the outer ring portion of the bearing with the oil released during rotation. The amount of the thickener is not particularly limited as long as it can form a grease with the base oil, and is generally 10 to 30% by weight of the total amount of the grease composition.
[0010]
In the present invention, the above grease blending disulfide compound as an essential component. As the form of the compound, those having an alkyl chain introduced are preferable, and those having a molecular weight of 2000 g / mol or less, particularly 1500 g / mol or less are particularly preferable. The action of the disulfide compound is to produce iron sulfide by a tribochemical reaction at the contact friction surface between the rolling element and the raceway surface, and this iron sulfide is softer than the bearing steel, reducing contact surface pressure and suppressing bearing seizure. However, if the molecular size of the disulfide compound is too large, that is, if the alkyl chain length is too long, the steric hindrance due to the alkyl chain becomes remarkable, and the tribochemical reaction described above becomes difficult to occur, and iron sulfide is generated. Is inhibited. Therefore, the disulfide compound used in the present invention is preferably in the above range as the molecular weight.
[0011]
Further, the above disulfide compound, the total sulfur content in the grease compositions (sulfur conversion; hereinafter referred to as "sulfur content") is contained in an amount of 1 wt% or less than 0.001 wt%. If the sulfur content is less than 0.001% by weight, the amount of iron sulfide produced is too small and does not contribute to improving the durability of the bearing. On the other hand, when the sulfur content exceeds 1 % by weight, not only an effect commensurate with the increase is not obtained, but also the amount of the base oil is relatively reduced, resulting in a deterioration in the lubrication characteristics of the bearing. In particular, the sulfur content is preferably 0.003% by weight or more and 1% by weight or less based on the total amount of the grease composition.
[0012]
If necessary, an antioxidant, a rust inhibitor, an oily agent, and an extreme pressure agent other than the above-described disulfide compound may be added to the grease composition of the present invention. Any of these may be known ones. Examples of antioxidants include amine compounds such as phenyl-α-naphthylamine, phenols such as di-t-butyl-p-cresol, thioamines such as phenothiazine, dialkyldithiophosphates, dialkyldithiocarbamates, etc. it can. The content of these additives is preferably individually 0.05% by weight or more of the total amount of the grease composition, and the total amount is preferably 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 an effect commensurate with the increase in content cannot be expected, but the content of the base oil or disulfide compound is relatively reduced, and these additives are added in the grease composition. May agglomerate and cause an undesirable phenomenon such as an increase in torque.
[0013]
The grease composition of the present invention has an effect of preventing seizure of the bearing under high speed rotation by lowering the surface pressure of the iron sulfide derived from the disulfide compound on the friction contact surface. Therefore, among machine tools that slide and rotate at high speed, a 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, use in a fixed position preload spindle having a preload at a stop of 98 N or more is effective.
[0014]
【Example】
Hereinafter, the present invention will be further described with reference to examples. However, the present invention is not limited to the examples.
[0015]
(Verification of sulfur content)
Barium composite soap was blended with ester oil having a kinematic viscosity at 40 ° C. of 20 mm ² / s, and a test grease was prepared by changing the addition amount of diethyl disulfide. Then, 2.3 g (occupying 15% of the bearing space volume) of the test grease was enclosed in an angular ball bearing for machine tools (inner diameter 65 mm, outer diameter 100 mm, width 18 mm, ceramic ball) to prepare a test bearing. In addition, a comparative bearing was manufactured by enclosing the same amount of grease without adding diethyl disulfide in the same angular contact ball bearing for machine tools.
[0016]
Then, under conditions of an ambient temperature of 20 ° C., a preload of 98 N, and a dmn of 1.6 million, the time until the bearing was 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, bearing durability life and bearing outer ring temperature. The bearing endurance life and the bearing outer ring temperature are shown as a ratio to the measured value of the comparative bearing.
[0017]
As is clear from FIG. 1, when the sulfur content in the grease exceeds 0.001% by weight, the bearing life ratio becomes 1.5 times or more, and good durability performance can be imparted to the bearing. it can. In particular, the sulfur content is highest in the range of 0.003% to 1% by weight, and the life is about twice as long. Further, when the sulfur content exceeds 5% by weight, the bearing life ratio is drastically decreased. On the other hand, the bearing outer ring temperature decreases with the addition of diethyl disulfide, but a large decrease is observed when the sulfur content is 0.001% by weight, and becomes more prominent at 0.003% by weight.
[0018]
From these results, by adding 0.001 wt% or more and 1 wt% of sulfur in the grease composition, the bearing is provided with a significant extension of the durability life under high-speed rotation and suppression of heat generation. You can see that In particular, the spindle bearing can be used in an optimum state by setting the sulfur amount to 0.003% by weight or more and 1% by weight or less.
[0019]
(Verification of molecular weight of disulfide compound )
A disulfide compound in which barium composite soap is blended with an ester oil having a kinematic viscosity at 40 ° C. of 20 mm ² / s and the molecular weight is changed by an introduced alkyl group so that the content is 0.005% by weight in terms of sulfur. Test greases were prepared by addition. Then, 2.3 g (occupying 15% of the bearing space volume) of the test grease was enclosed in an angular ball bearing for machine tools (inner diameter 65 mm, outer diameter 100 mm, width 18 mm, ceramic ball) to prepare a test bearing. Further, a comparative bearing was manufactured by enclosing the same amount of grease without adding a disulfide compound in the same angular contact ball bearing for machine tools.
[0020]
Then, the time (bearing durability life) until the bearing was seized was measured under the conditions of an atmospheric temperature of 20 ° C., a preload of 98 N, and a dmn of 1.6 million. FIG. 2 shows the relationship between the molecular weight of the disulfide compound and the bearing durability life as a ratio to the measured value of the comparative bearing.
[0021]
As is apparent from FIG. 2 , when the molecular weight of the disulfide compound exceeds 1500 g / mol, the bearing life ratio starts to gradually decrease, and when the molecular weight exceeds 2000 g / mol, it rapidly decreases. From this, it can be seen that any disulfide compound having a molecular weight of 2000 g / mol or less can be suitably used.
[0022]
【The invention's effect】
As described above, in accordance with the present invention, the disulfide compounds, by entrapping the grease composition in a proportion of less than 1 wt% 0.001 wt% or more sulfur terms, bearing life under high-speed rotation It can be used for the spindle support of machine tools that slide and rotate at high speeds, such as lathes, drilling machines, boring machines, milling machines, grinding machines, honing machines, super finishing machines, and lapping machines. It is suitable for an angular ball bearing to be incorporated. In addition, unlike the method of continuously supplying the lubricating oil such as the oil-air lubrication method, the grease composition can be enclosed and used, so that the operating cost can be reduced and the space can be saved.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the sulfur content of grease, bearing durability life and bearing outer ring temperature, obtained in an example.
FIG. 2 is a graph showing the relationship between the molecular weight of a disulfide compound and the bearing durability life obtained in an example.

Claims (3)

A grease composition sealed in angular contact ball bearing for supporting the spindle of the machine tool, Lee at Ou terms, the amount of disulfide total sulfur content in the grease composition is 1 wt% or less than 0.001 wt% compound grease composition characterized by containing a. It incorporated to support the spindle of a machine tool, and a machine tool spindle supporting angular contact ball bearing, characterized in that encapsulates the grease composition according to claim 1, wherein Rukoto. Rolling machine tool spindle supporting the angular ball bearing of claim 1, wherein the moving object and wherein the ceramic der Rukoto.

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