JP2002174247A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing for a gyro device without generating damage such as a band-shaped mark and loss of luster on the surface of a rolling element. SOLUTION: This rolling bearing 10 is used for the gyro device. At least the rolling element 13 of an outer race 11, an inner race 12 and the rolling element 13 is made of ceramics. The rolling bearing 10 has a nitride layer on the surface of at least the rolling element 13 of the outer race 11 and the inner race 12 having bearing steel as base materials and the rolling body 13 having martensitic stainless steel as a base material. The nitride layer has hardness of Hv 1200 to 1500.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing suitably used for supporting a gyro rotor in a gyro device.

[0002]

2. Description of the Related Art Conventionally, a gyro device is provided on a moving body such as an automobile, a ship, and an aircraft. Some gyro devices have a gyro rotor. The gyro rotor is rotated in a case. As a rolling bearing for supporting the gyro rotor, for example, a combination angular ball bearing or the like to which a preload is applied is used. A rolling bearing for a gyro device is required to have low torque, minimize fluctuations in torque, and have a long life, in addition to durability and low dust generation. To meet these demands, it is required to stably supply lubricating oil while keeping the amount of lubricating oil to a minimum.

In this type of rolling bearing, a small amount of lubricating oil applied to the raceway surfaces of the inner and outer rings and lubricating oil impregnated in the cage are maintained for a certain period until lubricating oil is supplied from an external lubricating oil supply source. Lubrication is provided only by oil.

For example, in a gyro device for a ship, the gyro rotor is rotated at a high speed (for example, 12000 rpm) so that the support shaft of the gyro device always faces north in order to know the direction required for navigation. If the dynamic balance of the gyro rotor is at least slightly out of order, vibration and noise may occur when the gyro rotor rotates at a high speed. Therefore, it is necessary to accurately adjust the dynamic balance of the gyro rotor. Such balance adjustment work is performed not only at the time of manufacturing the gyro device, but also after replacing the rolling bearing that supports the rotating shaft of the gyro rotor. That is, the rolling bearing wears out due to its mechanical life, and therefore needs to be replaced periodically. However, simply replacing the bearing causes vibration and noise, so that it is necessary to adjust the balance at this time. The balance adjustment work at the time of bearing replacement is performed, for example, by checking the balance of the gyro rotor by a balancer with the gyro rotor incorporated in the gyro device, removing the gyro rotor from the gyro device, and performing cutting processing on the gyro rotor. However, such a balance adjustment operation is extremely complicated.

[0005]

SUMMARY OF THE INVENTION In a rolling bearing,
Until lubricating oil is supplied from an external lubricating oil supply source, lubrication is performed with a very small amount of lubricating oil. During this time, a band-shaped mark (band-shaped wear) is formed on the surface of the ball (rolling element). Troubles may occur, or the gloss of the surface of the ball may be lost. The band-shaped mark is formed solely by slippage between the ball and the inner and outer raceway surfaces when lubrication is not sufficient.
It is difficult to prevent such damages only by removing external foreign substances or improving the cleaning operation. The damage referred to here is visually identifiable that a band-shaped mark is formed on the ball or that the ball has lost its luster, but the order of wear is extremely small and the surface roughness is not so high. The change is only noticeable. However, even with such a degree of wear, the wear progresses after a long operation, and the function of the rolling bearing cannot be maintained. In such a case, it is necessary to replace the rolling bearing. However, as described above, when the rolling bearing of the gyro device is replaced, the balance adjustment work is extremely complicated. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rolling bearing for a gyro device that does not cause damage such as a band-like mark or loss of gloss on the surface of a rolling element.

[0006]

An object of the present invention is to provide a rolling bearing used in a gyro apparatus, wherein at least the material of the outer ring, inner ring and rolling element is ceramics. Achieved. In such a rolling bearing, the oil film between the inner and outer races and the rolling element becomes thin during operation, and even if their surfaces may come into direct contact with each other, the material of the rolling element is ceramic. No surface damage occurs. No band mark is formed. The type of ceramic is not particularly limited. Conventionally, rolling bearings provided with rolling elements made of ceramics have not been used in gyro devices. Ceramics have significantly different elastic coefficients and linear expansion coefficients than steel. Therefore, in a rolling bearing with a ceramic rolling element, the durability when a large load is applied to the bearing is insufficient, and when a large temperature change occurs, a torque fluctuation caused by a preload change occurs. , Was generally considered. However, as a result of diligent studies based on a change in the ideas of the present inventors, a large load is not applied to the rolling bearing and the temperature change is small in the gyro device. In addition to being sufficiently applicable to the device, it has been found that the use of this rolling bearing can dramatically increase the bearing replacement span in the gyro device.

Another object of the present invention is to provide a rolling bearing for use in a gyro device, wherein at least a rolling element of an outer ring and an inner ring of bearing steel as a base material and a rolling element of martensitic stainless steel as a base material. The rolling bearing has a nitrided layer on the surface thereof, and the nitrided layer has a hardness of Hv1200 to 1500.
In the above-described rolling bearing, even when the oil film between the inner and outer races and the rolling element becomes thin during operation and their surfaces come into direct contact with each other, Hv (Vickers hardness) is obtained.
Is from 1200 to 1500, so that at least the rolling element surface is not damaged. For a gyro device, a rolling bearing is generally used in the form of a pair of combined bearings and in a state where it is preloaded in a fixed position. Bearing steels such as high carbon chromium bearing steel (SUJ2) have a smaller linear expansion coefficient than martensitic stainless steels such as SUS440C. The change in preload is smaller than when the inner and outer races and rolling elements are all made of martensitic stainless steel, and wear and seizure of the inner and outer raceway surfaces can be significantly prevented. As bearing steel, in addition to high carbon chromium bearing steel (SUJ2), carburized steel, heat-resistant steel, stainless steel,
Alloy tool steel, high speed tool steel, chrome steel, chromium molybdenum steel, etc. can be adopted.

As a method for forming a nitrided layer (a layer having an appropriate nitrogen concentration and hardness), a liquid nitriding treatment using a salt bath, a gas nitriding treatment, or an ion nitriding treatment may be mentioned. Of these, the ion nitriding treatment requires a relatively high treatment temperature, and it is difficult to obtain a sufficient hardness of the base even in consideration of the heat resistance of the base material, or it is possible to form a uniform nitrided layer on the surface of the spherical body. Since it may be difficult, it is preferable to use salt bath nitriding or gas nitriding. The preferred nitriding temperature is 480 ° C. or lower. In addition, in particular, when the processing temperature is high, a fragile compound layer (pseudo-ceramic layer composed of a single phase of ξ phase or ε phase) of about several microns may be formed on the outermost surface of the nitride layer. Therefore, the nitriding temperature is more preferably set to 460 ° C. or lower. Further, when the processing temperature is lower, the nitrided layer becomes denser and a rough porous layer is not generated.

In the present invention, the nitride layer has a ξ phase (Fe
₂ N), epsilon phase _{(Fe 2 ~ 3 N),} γ ' phase (Fe ₄ N), Cr
One or more nitrides of N, Cr ₂ N, etc. are precipitated in a large amount on the martensite ground, and have extremely high hardness and high toughness. Can be extremely suppressed. Further, since the base metal is made of martensitic stainless steel and bearing steel, it is possible to secure a sufficient hardness of the underlayer of about HRC 57 to 59 even under the above nitriding conditions. In addition, it is preferable that the rolling element on which the nitrided layer is formed is subsequently subjected to a finishing process to have a surface roughness of 0.1 μmRa or less. This can reduce the aggressiveness of the surface of the mating member with which the nitride layer surface contacts.

Hereinafter, a method for manufacturing a rolling element will be described. First, using a wire drawn in a cold process, a raw ball is manufactured by cold working or cutting with a header and flashing, etc., and the raw ball is quenched, tempered, and cured by using sub-zero processing in some cases. Let it. Thereafter, grinding is performed to a target size, that is, a size obtained by adding a set allowance to the finished product size, and a semi-processed ball is manufactured. The set allowance specifically means a necessary allowance for performing finishing processing to a target accuracy, but also includes an amount of expansion and contraction due to nitriding.

In the case where the elementary sphere before the nitriding treatment is in a quenched state, the sphericity or the difference between the diameters is very large, and generally a setting margin of about several tens μm to about 100 μm is required. is there. Therefore, if a nitrided layer is formed on the as-quenched elementary sphere, the nitrided layer will be unevenly etched, and the thickness of the nitrided layer will be uneven, and at the same time, the balance of the internal stress caused by the nitriding treatment will be lost. In some cases, it takes a long time for finishing to obtain the required accuracy, or the target accuracy cannot be achieved. Further, the durability of the rolling elements may be affected in some cases. These problems are particularly remarkable in the as-quenched elemental ball, but if the accuracy of the semi-finished ball is insufficient, the required accuracy cannot be satisfied or the finishing process requires a long time. In some cases, the sphericity of the semi-finished sphere needs to be 3.0 μm or less, preferably 1.0 μm or less.

If the semi-finished ball is not tempered after quenching, the internal residual stress accumulated during quenching may have an adverse effect on the quality of the finished product. It is good to perform tempering. Furthermore, in order to prevent the occurrence of surface scratches during handling or from the aspect of strength, heat treatment is performed on the production of semi-finished balls, followed by mechanical hardening such as barrel or ball peening.
The hardness may be further increased.

As a result, in the obtained rolling element, a very hard and tough nitride layer having an Hv of 1200 to 1500 is formed on the surface thereof to have a very uniform film thickness, and further, the nitride layer is supported. Since the base is configured to satisfy HRC 57 or more, durability can be maintained even when the bearing operates under a high load condition.

If the thickness of the nitrided layer is too large, not only does the processing cost increase, but also the expansion and contraction and deformation after nitriding become remarkable, the finishing cost increases, and the physical properties of the steel also increase. 3% or more and 2% Da (2% of diameter)
The following is preferred. Further, for the above-mentioned reason, the uniformity of the thickness of the nitride layer is preferably within 5 μm.

Although the rolling elements of ball bearings have been described above, the same applies to the rolling elements (rollers and the like) of other rolling bearings.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. An angular contact ball bearing 10 according to a first embodiment of the present invention shown in FIG. 1 includes an inner ring 11, an outer ring 12, and an inner and outer ring 1.
A plurality of balls 13 arranged between the first and second balls 12 and a holder 14 for holding the balls 13 at equal intervals in the circumferential direction are provided. This embodiment is a gyro rotor supporting rolling bearing in a gyro device.

In the present embodiment, the inner and outer rings 11, 12
Is formed of martensitic stainless steel (SUS440C). The balls 13 are formed of ceramics.

In the above-described angular ball bearing 10, even if the oil film between the inner and outer rings 11, 12 and the ball 13 becomes thin during operation, the surfaces thereof may come into direct contact with each other. Since the material of 13 is ceramics, no surface damage occurs and no band mark is formed on the surface of ball 13.

An angular contact ball bearing 20 according to a second embodiment of the present invention shown in FIG. 2 includes an inner ring 21, an outer ring 22, and inner and outer rings 21 and 22.
A plurality of balls 23 arranged between the two and a holder 24 for holding the balls 23 at equal intervals in the circumferential direction are provided. In the present embodiment,
It is a gyro rotor supporting rolling bearing in a gyro device.

In the present embodiment, the inner and outer rings 21 and 22
Is formed of high carbon chromium bearing steel (SUJ2). The ball 23 is formed of martensitic stainless steel (SUS440C), and the surface of the ball 13 has a nitride layer 23a of Hv1200 to 1500.
Are formed. The longitudinal elastic modulus of the nitrided layer 13a is 2
It is about 40 GPa. On the other hand, the longitudinal modulus of SUJ2 is about 208 GPa. The linear expansion coefficient of SUS440C is about 12.5 × 10 ⁻⁶ . On the other hand, the linear expansion coefficient of SUJ2 is about 10.1 × 10 ⁻⁶ .

In the angular ball bearing 20 as described above, even if the oil film between the inner and outer races 21 and 22 and the ball 23 becomes thin during operation, and their surfaces may come into direct contact with each other, Hv (Vickers hardness) 1200-150
Since it is 0, at least the surface of the ball 23 is not damaged. Further, since the longitudinal elastic modulus of the nitrided layer 23a is larger than that of SUJ2, the contact ellipse is extremely small and no slip occurs. Therefore, no band mark is formed on the ball 23. Furthermore, SUJ2 is SUS440
Since the coefficient of linear expansion is smaller than C, even if the bearing temperature increases and a temperature difference occurs between the inner and outer rings, the preload change in the present bearing 20 is smaller than when the inner and outer rings 21, 22 and the ball 23 are all made of SUS440C. It is small, and the seizure of wear on the raceways of the inner and outer rings 21 and 22 can be significantly prevented.

[0022]

Embodiment 1 An angular contact ball bearing (inner diameter 10 mm, ceramic ball diameter 4.762 mm, number of balls 9) having an arrangement as shown in FIG. And rotated. Rotation speed 12000 min ^-1 . Preload 25N. Uses 32cSt lubricating oil at 40 ° C. A total of 4 mg of lubricating oil is applied to each raceway surface of the inner and outer rings. About 20 mg of lubricating oil was impregnated in the cage. Continuous rotation for 40 hours.

As shown in FIG. 3A, the ball 13 after rotation
No band-like mark was formed on the surface of the sample, and gloss was not lost. For comparison, when the conventional angular ball bearing was rotated under the above conditions, a band mark was formed on the surface of the rotated ball 53 as shown in FIG. 3B.

Embodiment 2 An angular contact ball bearing (inner diameter 10 mm, diameter of a ball having a nitrided layer 4.762 mm, number of balls 9) having an arrangement as shown in FIG. Rotated under conditions. Rotation speed 12000 min ^-1 . Preload 25N. Uses 32cSt lubricating oil at 40 ° C. A total of 4 mg of lubricating oil is applied to each raceway surface of the inner and outer rings. About 20 mg of lubricating oil was impregnated in the cage. Continuous rotation for 40 hours. Also in this example, no band mark was formed on the surface of the ball after rotation, and gloss was not lost.

The present invention is not limited to the above-described embodiments and examples, but can be appropriately modified and improved. For example, the rolling bearing of the present invention may be combined into a combined bearing. For example, the present invention can be applied to a rotating unit other than the gyro rotor in the gyro device. In addition, the present invention can be used for devices other than the gyro device, and can be applied to, for example, a semiconductor manufacturing device or the like that requires low dust generation.

[0026]

As described above, according to the present invention,
A rolling bearing for a gyro device can be provided which does not cause damage such as band marks or loss of gloss on the surface of a rolling element.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of the present invention and a comparative example.

[Explanation of symbols]

 10, 20 Angular contact ball bearing (rolling bearing) 11, 21 Inner ring 12, 22 Outer ring 13, 23 Ball (rolling element) 14, 24 Cage 23a Nitride layer

Claims (2)

[Claims] 1. A rolling bearing for use in a gyro device, wherein at least the material of the outer ring, the inner ring, and the rolling element is ceramics. 2. A rolling bearing used in a gyro device, wherein a nitride layer is formed on at least a surface of a rolling element among an outer ring and an inner ring formed of bearing steel as a base material and a rolling element formed of martensitic stainless steel as a base material. And the nitrided layer is Hv
A rolling bearing having a hardness of 1200 to 1500.