JP2000186722A - Rolling ball bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an acoustic life and reduce a rotation torque. SOLUTION: Contact surface stress is reduced, seizure is prevented for a long term, and the surface is prevented from roughing by setting a radius of curvature on an inner wheel raceway surface to more than 50.5% and less than 52% of a ball diameter. An area of the contact surface is reduced to reduce a differential slide, and low torque and long life is realized by setting a radius of curvature on an outer wheel raceway surface to more than 53% and less than 55% of the ball diameter. Since a rolling element is made of ceramics, inertia is reduced to reduce slide and abrasion, whereby friction is reduced and low torque is realized. Durability in a high temperature area is improved by using ester oil as a base oil of a pre-charged grease. Since a retainer is made of synthetic resin, torque can be reduced due to a light weight, and generation of heat and abrasion powder is prevented thereby enhancing a long life.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling ball bearing, and more particularly to a high-speed fine rotation or a rapid acceleration / deceleration rotation in both forward and reverse directions or one direction such as an AC or DC servomotor or a drive system using the same. It is suitable for the one used under the conditions of rubbing.

[0002]

2. Description of the Related Art In a machine tool controlled by NC, an AC or DC servomotor is widely used for moving a workpiece or a tool post. These motors repeat high-speed fine rotation and rapid acceleration / deceleration rotation in both forward and reverse directions in order to accurately and quickly move an object to a target position. In a drive system using these motors, a bearing used is used. In addition, it is required that the rotation be stable over a long period under the same use conditions.

At present, as rolling ball bearings used in such applications, high carbon chromium steel (SUJ2) is used for the inner and outer rings and rolling elements, and a cold-rolled steel plate (SPC) is used for the cage.
C), the radius of curvature of the raceway surfaces of the inner ring and the outer ring is generally 50.5 to 52% of the ball diameter (= rolling element diameter).

[0004]

However, in the above-mentioned conventional rolling ball bearing, local wear (hereinafter, also referred to as fretting) due to high-speed fine rotation in both forward and reverse directions, rolling element slip during rapid acceleration / deceleration rotation, and oil film. Problems such as surface roughness, minute peeling, and seizure of the inner and outer raceway surfaces resulting from the cutting shorten the bearing life. In particular, regarding rolling element slip,
This also causes an increase in bearing torque, and limits the reaching response characteristic to a target rotational speed required for rapid acceleration / deceleration rotation.

[0005] Therefore, in particular, when slippage caused by the inertial force of the rolling element during forward / reverse fine movement rotation causes fretting, the rolling element may be mounted as described in, for example, Japanese Utility Model Registration No. 2510408. It is considered that ceramics can be used. However, sufficient effects cannot be obtained with respect to surface roughness, minute peeling, seizure, etc. due to internal friction of the bearing due to rapid acceleration / deceleration rotation, and improvement including the internal design of the bearing is required.

The present invention has been developed in order to solve the above-mentioned problems. As in the case of an AC or DC servomotor or a drive system using the same, the present invention is capable of high-speed fine rotation in both forward and reverse directions or one direction, or rapid acceleration. It is an object of the present invention to provide a long-life rolling ball bearing having a small rotating torque even under a condition where deceleration rotation is repeated.

[0007]

In order to achieve the object, a rolling ball bearing according to the present invention is a sealed ball bearing in which lubricating grease is sealed. A ceramic rolling element is held between the outer ring and the radius of curvature of the raceway surface of the inner ring is 50.5% of the ball diameter.
Not more than 52%, the radius of curvature of the raceway surface of the outer ring is not less than 53% and less than 55% of the ball diameter, and the base oil of the lubricating grease to be enclosed contains ester oil as an essential component. Things.

[0008]

Embodiments of the present invention will be described below. If ceramic rolling elements are used,
Since a combination of different materials is used for the inner and outer races made of the bearing steel and the specific gravity is smaller than that of the steel rolling elements, friction and wear inside the bearings are reduced. Here, silicon nitride (Si ₃ N ₄ ), zirconia (ZrO ₂ ), alumina (Al ₂ O ₃ ), silicon carbide (SiC), and the like can be used as ceramics as the rolling elements. Considering specific gravity and the like, silicon nitride is particularly desirable. These ceramic rolling elements are primarily molded by die molding or granulation molding, and the elementary balls obtained by secondary molding by normal pressure sintering, pressure sintering, HIP sintering, etc. are finished by wrapping etc. It is a completed ball. Among these, granulation molding and normal pressure sintering can provide the cheapest elementary sphere, but if higher performance is required, it is preferable to perform HIP sintering or pressure sintering.

The use of the synthetic resin crown retainer reduces the friction between the rolling element and the retainer pocket as compared with the conventional steel (SPCC) retainer, and furthermore, the retainer Since itself is lightweight, the rotational torque is reduced. In addition, heat generation inside the bearing during rapid acceleration / deceleration rotation, which is one of the causes of poor lubrication and seizure, can also be suppressed. Further, in the cage made of synthetic resin, the generation of iron-based abrasion powder, which has been one of the causes of grease deterioration in the steel cage, is suppressed, which is effective for extending the life of the bearing. As the material of the synthetic resin cage, a material obtained by reinforcing a synthetic resin such as nylon, polyamide, polyacetal, phenol, polypropylene, or polyphenylene sulfide with glass fiber or the like is preferable. In particular, nylon resin (6-6 nylon) is preferable. A material obtained by adding a glass fiber as a reinforcing material to a base material is preferable in terms of strength and friction performance.

[0010] By making the radius of curvature of the outer raceway surface larger than before, the contact area between the rolling element and the outer raceway surface can be reduced, and the differential slip on the contact surface can be reduced. As a result, the internal friction and wear of the bearing are reduced, and lower torque and longer life of the bearing can be realized. However, a decrease in the contact area between the rolling element and the outer raceway surface leads to an increase in the contact surface pressure therebetween, which may cause problems such as seizure and surface roughness. In consideration of this, the optimum value of the radius of curvature is 50.5% or more of the ball diameter in the inner ring.
It is desirable that the diameter be less than 2%, 53% to less than 55% of the ball diameter for the outer ring, particularly 50.5% to 51.5% of the ball diameter for the inner ring, and 53% to 54% of the ball diameter for the outer ring.

A grease composition containing a base oil and a thickener enclosed in a bearing contains an ester as an essential component as a base oil and has a viscosity at 40 ° C. of 11 to 150 mm ² /.
s, preferably 20 to 50 mm ² / s. Ester oils used as base oils include Gestel oil obtained from the reaction of dibasic acids and branched alcohols, aromatic ester oil obtained from the reaction of aromatic tribasic acids and branched alcohols, polyhydric alcohols and monobasic oils Hindered ester oils obtained from the reaction with acids are preferably used.
In consideration of heat resistance as in this case, it is selected from aromatic ester oils and hindered ester oils and used alone or in combination.

[0012] Among them, the gesture oils include dioctyl adipate (DOA), diisobutyl adipate (DIBA), dibutyl adipate (DBA), dioctyl azelate (DOZ), and dibutyl sebacate (D
BS), dioctyl sebacate (DOS), methyl acetyl ricinoleate (MAR-N) and the like. This grease has a low viscosity and easily forms an oil film, and also has a low resistance to bearing rotation.

As the aromatic ester oil, trioctyl trimellitate (TOTM), tridecyl trimellitate, tetraoctyl pyromellitate and the like can be mentioned. Examples of the hindered ester oil include those obtained by appropriately reacting a polyhydric alcohol and a monobasic acid. The monobasic acid reacted with the polyhydric alcohol may be used alone or in combination. Further, it may be used as a complex ester which is an oligoester of a polyhydric alcohol and a mixed fatty acid of a dibasic acid / monobasic acid.

The monobasic acids mainly include C ₄ -C ₁₈
Is used. Specifically, for example, butyric acid,
Valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, mystyric acid, palmitic acid, tallow fatty acid, threic acid,
Caproleic acid, undecylenic acid, lindelic acid, tuzunic acid, fiseteric acid, myristoleic acid, palmitoleic acid, peterothenic acid, oleic acid, elaidic acid, ascrepic acid, vaccenic acid, sorbic acid, linoleic acid,
Linolenic acid, sabinic acid, ricinoleic acid and the like.

These ester oils are desirably at least 50 wt.% Or more of the total amount of the base oil. If the ester oil is less than this, sufficient high-temperature durability cannot be obtained. Further, other than the above, synthetic hydrocarbon oil and ether oil can be blended as base oil components. Examples of the synthetic hydrocarbon oil include poly-α-olefin oil, cooligomer synthetic oil of α-olefin and ethylene, and the like.

As ether oils, diphenyl,
C for triphenyl and tetraphenyl ₁₂~ C₂₀No
There are phenyl ether oils from which alkyl chains have been derived. Special
In consideration of high temperature and high speed durability, (di) alkyl poly
Phenyl ether oils are preferred. The mixing ratio of these is 5
0 wt.% Or less.

As the thickener used in the grease composition, a urea-based or lithium soap-based thickener is used.
When the initial sound is mainly a problem, use a lithium soap type. Also, the thickener during the grease composition,
The content is 5 wt.% To less than 20 wt.% In the lithium soap type, and 5 wt.% To less than 30 wt.% In the urea type.
If the thickener is less than 5 wt.%, The consistency increases,
Since the grease is softened, grease may leak from the bearing. On the other hand, if the content is more than the upper limit, the consistency becomes too small, so that the grease becomes hard and causes an increase in rotational torque.

Next, three types of greases were prepared by combining base oils and thickeners shown in Table 1 below, and Examples 1 and 2 and Comparative Examples 1 to 4 shown in Table 2 were prepared. Comparative Example 1 is a conventional average rolling ball bearing, and Comparative Example 2 uses a synthetic resin cage instead of the cage. In Comparative Example 3, a ceramic rolling element was used instead of the rolling element in Comparative Example 2, and in Comparative Example 4, the radius of curvature of the outer raceway surface was 53% as in Examples 1 and 2. The base oil of grease C is a mineral oil type.

[0019]

[Table 1]

[0020]

[Table 2]

Next, these prototype bearings are assembled in an actual AC servomotor, and as shown in FIG.
Rotate rapidly to 10,000 rpm in 1 second, then 1
After maintaining the state for 0 second, the rotation is rapidly reduced to the stop state in 0.1 second, and the cycle of maintaining the stop state for 10 seconds is defined as one cycle. After repeating this cycle for 100,000 cycles, the rotational torque at that time is obtained. Was measured, the bearing was removed, and the time-dependent change of the bearing rotation sound was measured at room temperature with an Anderometer. FIG. 2 shows the ratio of each of the examples and the comparative example based on the comparative example 1. As is clear from the figure,
Although the anderon value and the torque are smaller in the order of Comparative Example 2 to Comparative Example 3 and Comparative Example 4, Examples 1 and 2 have further smaller Anderon value and torque.

Next, in addition to Example 1, bearings of Examples 3 to 6 and Comparative Examples 5 to 8 as shown in Table 3 below were prepared. Comparative Examples 5 and 6 are different from the present invention in the radius of curvature of the inner raceway surface, and Comparative Examples 7 and 8 are different in the radius of curvature of the outer raceway surface. The material and grease are the same as in the present invention. Each of these Examples and Comparative Examples was subjected to the same repetitive test as described above, and the Anderon value and the torque were measured in the same manner. FIG. 3 shows the ratio of the Anderon value and the torque based on Comparative Example 1 to the radius of curvature of the inner raceway surface (groove in the figure) and FIG. 2 shows the ratio of anderon value and torque based on Example 1. As is clear from these figures, as in the present invention, the radius of curvature of the inner raceway surface is 50.5% or more and less than 52% of the ball diameter, and the radius of curvature of the outer raceway surface is 53% or more and less than 55% of the ball diameter. , It can be seen that both the anderon value and the torque are reduced.

[0023]

[Table 3]

[0024]

As is clear from the above description, according to the rolling ball bearing of the present invention, a ceramic rolling element is held between an inner ring and an outer ring via a synthetic resin cage, The radius of curvature of the raceway is 50.5% or more and less than 52% of the ball diameter, and the radius of curvature of the raceway of the outer race is 53% or more of the ball diameter.
Less than 5%, and the base oil of the lubricating grease to be enclosed is made of ester oil as an essential component. Therefore, even when high-speed fine rotation or rapid acceleration / deceleration rotation is repeated, deterioration of bearing sound is reduced and torque is reduced. Can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a rapid acceleration / deceleration rotation test performed as an embodiment of a rolling ball bearing of the present invention.

FIG. 2 is an explanatory diagram of an anderon value and a torque of a rolling ball bearing according to an embodiment of the present invention and a comparative example.

FIG. 3 is an explanatory diagram of a radius of curvature of an inner raceway surface, an Anderon value, and torque.

FIG. 4 is an explanatory diagram of a radius of curvature of an outer raceway surface, an Anderon value, and a torque.

Continuation of front page (72) Inventor Tsuyoshi Koshi 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 BA02 BA10 BA25 BA50 BA53 BA54 BA55 EA31 EA36 EA37 EA38 EA41 EA43 EA44 EA63 EA76 FA33 FA51 GA24

Claims (1)

[Claims] In a sealed rolling ball bearing filled with lubricating grease, a ceramic rolling element is held between an inner ring and an outer ring via a synthetic resin cage, and the radius of curvature of the raceway surface of the inner ring is reduced. 50.5% or more and less than 52% of the ball diameter,
A rolling ball bearing wherein the radius of curvature of the raceway surface of the outer ring is 53% or more and less than 55% of the ball diameter, and the base oil of the lubricating grease to be sealed contains ester oil as an essential component.