JP2000097243A - Bearing and bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing capable of remarkably improving rigidity and longevity and capable of high speed rotation of a machine tool, rotation in high precision and corresponding to heavy cutting, reducing lowering of rigidity even in the case where it is miniaturized and capable of high speed rotation, rotation in high precision and increasing longevity at rational manufacturing cost. SOLUTION: A rolling element 4 is formed of a ceramic material and at least one of an inner ring 2 and an outer ring 3 is formed of tungsten alloy in a bearing 1 constituted of the inner ring 2 and the outer ring 3 concentrically arranged and the rolling element 4 arranged between the inner ring 2 and the outer ring 3 free to roll. This ceramic material is made of at least one kind of silicon nitride, silicon carbide, aluminum, zirconium and aluminum nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing and a bearing unit, and more particularly, to a bearing and a bearing unit capable of enhancing supporting rigidity and sufficiently coping with miniaturization, high precision, high speed, and long life.

[0002]

2. Description of the Related Art Machine tools, home appliances, industrial machines, etc. are equipped with bearings corresponding to each required characteristic in order to rotatably support a rotating shaft and to fix its axial position. Improvements in bearing characteristics are underway. For example, gas turbines, such as aircraft engines, are being improved year by year at higher temperatures and higher speeds, and bearings are also required to respond to sophistication. In machine tools as well, bearings with higher rigidity are required in order to achieve higher speed rotation, improved rotation accuracy, heavy duty cutting, and the like.

On the other hand, rotating components of electronic equipment, which are rapidly spreading in recent years, such as cylinders of consumer digital video tape recorders, spindle motors of hard disk drives, and spindle bearings used in seek mechanisms, etc. In order to achieve lighter and thinner and smaller, high-speed rotation, improved accuracy, etc., various ideas have been devised for the structure.

Conventionally, a typical example of a generally used bearing is, for example, a rolling bearing (single-row angular contact ball bearing) as shown in FIG. The bearing 1 includes an inner ring 2 and an outer ring 3 arranged concentrically, a plurality of spherical rolling elements 4 rotatably disposed between the inner ring 2 and the outer ring 3, and the rolling elements And a retainer 5 for maintaining a constant interval so as not to contact with the rolling element 4.
Has a structure in which the inner ring 2 and the outer ring 3 relatively rotate by the rolling motion.

On the other hand, in order to realize higher rotational accuracy, a bearing unit in which a plurality of raceway grooves are provided directly on a shaft (rotary shaft) corresponding to an inner race, and rolling bearings are respectively arranged so as to face each raceway groove. Widely adopted. FIG. 2 is a cross-sectional view showing a typical example of this type of bearing unit. In this bearing unit 11, two rows of grooves (track grooves) 16 for rolling the rolling elements 14 are formed on the outer peripheral surface of the shaft 12, and the respective grooves 16, 16 are formed.
And a rolling element 14, an outer ring 15, and a retainer 20 for holding the rolling element 14 are incorporated therein. A seal 21 is mounted on the outer side surface of each bearing 13. In this structure, a coil spring 17 is incorporated between the outer rings 15, 15 of the two bearings 13, 13, and each of the bearings 1 is driven by the spring force.
A predetermined preload is applied to 3,3. The coil spring 17 is disposed so as to abut a spring seat 19 mounted on a seal groove 18.

The above-described conventional bearing 1 and bearing unit 11
In the above, the inner race 2, the outer races 3, 15, the rolling elements 4, 14, and the shaft 12 are formed of heat-treated bearing steel or tool steel, while the retainers 5, 20 and the seal 21 are formed of a resin material or an iron plate material. Is done.

[0007]

However, if a conventional bearing used for a machine tool is to be used for higher speed rotation, improved rotation accuracy, and heavy cutting, the life of the bearing is shortened due to insufficient rigidity of the bearing. In addition, when the spindle is driven, heat generation due to friction between the rolling element, the inner ring and the outer ring tends to cause a temperature change of the bearing, and it is difficult to improve the machining accuracy due to deterioration of rotation accuracy due to insufficient rigidity.

In order to solve the above-mentioned problems, the rolling element is formed of a ceramic material, the inner ring which rotates integrally with the rotating shaft in addition to the rolling element is formed of a ceramic material, or the rolling element, the inner ring and the outer ring are formed. There have been many attempts to employ so-called ceramic bearings, which are all formed of ceramic materials.

However, when the rolling elements and the inner ring are formed of ceramics, or when the rolling elements and the inner and outer rings are all formed of ceramics, the current ceramic processing technology uses the inner diameter processing of the inner ring and the outer ring and the raceway grooves (races). ) Since the processing is very difficult, there is a problem that the production yield is remarkably reduced and the cost is extremely high. For this reason, while popular bearings use bearings with only inexpensive rolling elements made of ceramics, custom-designed machines use bearings with rolling elements and inner rings made of ceramics. It is currently used.

According to the knowledge of the present inventors, a bearing in which the rolling elements and the inner ring are formed of ceramics and a bearing in which all of the rolling elements and the inner and outer rings are formed of ceramics, all components are made of bearing steel or the like. Compared to conventional bearings made of tool steel, the stiffness is improved about 4 times and the service life is about 3 times.
Although it can be expected to be twice as long, there is a problem that the manufacturing cost is significantly increased due to the above-mentioned difficult workability.

On the other hand, a bearing in which only the rolling elements are formed of ceramics has about 20% improvement in rigidity as compared with a conventional steel bearing, but there is no significant difference in the service life, and the bearing is evaluated from the viewpoint of performance versus cost. There is no denying that it is overpriced, and it has not yet reached the stage where it is widely used.

On the other hand, when the conventional constituent material is used for the bearing unit, the rigidity becomes insufficient due to the downsizing of the bearing and the shortening of the bearing span. , May cause poor accuracy,
There has been a problem that damage occurs, the life is shortened, and in any case, the durability is reduced.

[0013] In recent years, in a situation where technical requirements for downsizing, high speed, and high rotational accuracy of rotating components of electronic equipment have been further increased, insufficient rigidity has been more remarkable in conventional steel bearing units. In addition, there has been a problem that the frequency of breakage during use increases, and the labor required for replacement and maintenance management increases significantly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can significantly improve rigidity and life, and can cope with high-speed rotation, high-precision rotation, and heavy cutting of a machine tool. The aim is to provide a bearing unit that can reduce the rigidity even when the size is reduced, and that can increase the speed, increase the precision of rotation, and extend the service life at a reasonable manufacturing cost. I do.

[0015]

In order to achieve the above object, a bearing according to the present invention is provided with an inner ring and an outer ring which are arranged concentrically, and is rotatably disposed between the inner ring and the outer ring. The rolling element is formed of a ceramic material, and at least one of the inner ring and the outer ring is formed of a tungsten alloy.

Further, the bearing unit according to the present invention comprises: a shaft; a plurality of outer rings arranged concentrically at intervals in the axial direction of the shaft; and a rotatable roller between the outer ring and the shaft. In the bearing unit including the rolling elements provided, the rolling elements are formed of a ceramic material, and at least one of the shaft and the outer ring is formed of a tungsten alloy.

Further, in the above bearing and bearing unit, the ceramic material for forming the rolling elements is made of at least one of silicon nitride, silicon carbide, alumina, zirconia and aluminum nitride. The ceramic material has a Young's modulus of 200 GPa.
It is preferable that it is above.

On the other hand, the tungsten alloy constituting at least one of the inner ring (shaft) and the outer ring has a Young's modulus of 2
Desirably, it is not less than 00 GPa. The tungsten alloy preferably has a Rockwell hardness of 60 or more. Furthermore, the coefficient of thermal expansion of the tungsten alloy is 2 × 1
0 ^{-6 to} 12 × 10 ^-6 / ° C. Further, it is desirable that the tungsten alloy is an ultrafine-grain cemented carbide having an average crystal grain size of 0.5 μm or less.

In the present invention, the ceramic material constituting the rolling element includes silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), and aluminum nitride. (AlN) or a composite material thereof is used. The type of the ceramic material is appropriately selected according to the operating temperature of the bearing or the bearing unit, the atmospheric conditions, and the lubrication method.

In general, silicon nitride (Si ₃ N ₄ ) is considered to be superior in terms of heat resistance, light weight, high rigidity, seizure resistance, low thermal expansion, corrosion resistance, insulation, non-magnetism and the like. Optimum as a bearing material.

However, bearing materials used in a particularly corrosive environment include silicon carbide (SiC) and alumina (Al
₂ O ₃ ) and zirconia (ZrO ₂ ) are preferred. When used under high temperature conditions, silicon carbide (Si
C) may be suitable in some cases. In order to further enhance the heat radiation from the bearing itself, aluminum nitride (AlN) having a high thermal conductivity is suitable. The types of ceramic materials are
The ceramic material is selected according to the operating conditions such as the actual rotational speed, load, lubrication conditions, etc., the temperature, and the atmosphere of the bearing, and a composite of one or more of the above-mentioned ceramic materials is used.

In order to increase the rigidity of the whole bearing, the Young's modulus of the ceramic material needs to be 200 GPa or more, more preferably 300 GPa or more. This is because the Young's modulus is 200 GPa
If it is less than the above, the Young's modulus of the conventional bearing material is almost the same, and no improvement in performance can be expected.

By forming the rolling element from a ceramic material in this manner, it is lightweight, rich in rigidity, and excellent in seizure resistance, heat resistance, and abrasion resistance as compared with a conventional rolling element formed from bearing steel. Therefore, even when used as a bearing for a main shaft of a machine tool, high-speed rotation becomes possible. In addition, when using a combination of different materials with ceramics for the rolling elements, the effect of preventing oil film breakage is greater than when all bearing materials are made of metal, and the seizure accident due to oil film breakage is more effectively prevented. it can.

Further, since the rolling elements are formed of a lightweight ceramic material having a density about half that of a conventional steel material, the moment and inertia force acting on the rolling elements are reduced even at high speed rotation. In addition, wear and damage due to the occurrence of skid (revolving slip) can be prevented, which is effective for improving the life of the bearing and preventing temperature rise.

On the other hand, in the present invention, the inner ring (shaft)
At least one of the outer ring and the outer ring is formed of a tungsten alloy. Specific examples of the tungsten alloy include a doped tungsten alloy to which a dopant such as potassium (K), aluminum (Al), and silicon (Si) is added, and a thoriated alloy to which thorium (Th) and / or thorium oxide is added. -Tungsten alloy and rhenium-tungsten alloy to which rhenium (Re) is added can be exemplified. These tungsten alloys are all excellent in hardness, mechanical strength and wear resistance, and are suitable as materials for forming the inner and outer rings and the shaft of the bearing and the bearing unit according to the present invention.

As the tungsten alloy constituting the inner and outer rings and the shaft, the following cemented carbide materials can be used. That is, a material consisting of only a cemented carbide crystal, or titanium (Ti), tantalum (T
a), a cemented carbide in which a carbide such as niobium (Nb) and a solid carbide of a cemented carbide are combined with cobalt (Co),
It has excellent strength and abrasion resistance, and is suitable as a constituent material of inner and outer rings of a bearing and a shaft of a bearing unit.

In particular, 0.5 μm as a tungsten alloy
When an ultrafine-grained cemented carbide having the following average crystal grain size is used, its Young's modulus is as large as 520 to 600 MPa, and its hardness (Hv) is extremely good as 1500 to 1950. The required strength and hardness can be secured.

Even if the material is other than the above, it may be a tungsten alloy having a Young's modulus of 200 GPa or more, preferably 300 GPa or more, or a tungsten alloy having a Rockwell hardness of 60 or more, preferably 70 or more, as compared with conventional materials. For example, it can be used as a constituent material of an inner or outer ring or a shaft such as the bearing of the present invention. If the tungsten alloy has a Young's modulus of less than 200 MPa or a Rockwell hardness of less than 60, the deformation of the rolling contact portions of the inner and outer rings of the bearing increases, and the bearing rigidity of the shaft of the bearing unit decreases.

As described above, by forming the inner and outer rings with a tungsten alloy having a Young's modulus and a Rockwell hardness greater than that of the conventional material, the amount of deformation of the inner and outer rings with respect to a stress load can be reduced, and the bearing rigidity of the entire bearing is improved. be able to. In other words, it means that it is possible to reduce the size, increase the speed, increase the rotation accuracy, and extend the life of the bearing without reducing the rigidity of the bearing. These improvements are mainly achieved by the high Young's modulus, hardness and wear resistance of the tungsten alloy.

By forming the shaft and outer ring of the bearing unit using the above-mentioned tungsten alloy,
The amount of deformation due to stress load on the raceway surfaces of the ceramic ball, the shaft, and the outer race, which are the rolling elements, is also reduced, and the rigidity of the shaft with respect to the bearing can be improved. Further, when the above-mentioned tungsten alloy is used for the raceway surface of the rolling element, the wear resistance is excellent, so that the life of the bearing unit can be extended.

The thermal expansion coefficient of the tungsten alloy forming the inner and outer rings of the bearing is desirably in the range of 2 × 10 ^{-6 to} 12 × 10 ^-6 / ° C. from the viewpoint described below. That is, conventionally, the inner ring of the bearing and the rotating shaft have been integrally fixed by giving an appropriate interference. However, the ceramic material used for bearings has a smaller coefficient of thermal expansion than conventional steel, so when the main spindle (rotating shaft) rotates on the inner ring, the inner ring etc. is broken due to the difference in thermal expansion between the rotating shaft and the inner ring. Had to be done. Therefore, it is necessary to adjust the thermal expansion coefficient of the rotating shaft to a value close to the thermal expansion coefficient of the ceramic material (8 × 10 ^{−6 to} 12 × 10 ⁻⁶ / ° C.) depending on the operating temperature conditions. Correspondingly, the above-mentioned destruction is effectively prevented by adjusting the coefficient of thermal expansion of the tungsten alloy constituting the inner ring and the outer ring of the bearing to a range of 2 × 10 ^{−6 to} 12 × 10 ⁻⁶ / ° C. be able to.

On the other hand, the thermal expansion coefficient of the tungsten alloy forming the shaft and the outer ring of the bearing unit is also
From the following viewpoints, it is desirable to set the range of 2 × 10 ^{−6 to} 12 × 10 ⁻⁶ / ° C. That is, conventionally, as shown in FIG. 2, the bearing unit includes a shaft 12 in which a plurality of raceway grooves 16 are simultaneously formed on the outer periphery of the shaft 12 using a diamond forming grindstone, a rolling element 14 such as a ball, and an outer ring 15. And a bearing unit that assembles the lubricant, the seal, and the preload adjustment when mounted on the housing.

The mounting method of the bearing unit, which is set to a predetermined preload in advance as described above, to the housing is generally performed by the following method.
While one outer ring having a larger outer diameter is press-fitted into the housing with an appropriate interference, the other outer ring having a smaller outer diameter is
To prevent interference with the housing, heat the housing, insert it into the housing with a clearance fit, and assemble it into an intermediate fit at room temperature, then glue and fix the housing and the outer ring, or secure them with a clearance fit. Was.

On the other hand, the latter method of mounting the bearing, which has not been preloaded adjusted, to the housing is generally such that one outer ring is press-fitted into the housing with an appropriate interference, and the other outer ring is fixed to the housing by a clearance fit. Later, the outer ring was bonded and fixed while adjusting the preload.

However, similarly to the above, since the ceramic material used for the bearing has a smaller coefficient of thermal expansion than the conventional steel, the bearing component is destroyed due to the difference in thermal expansion between the shaft and the bearing component. There was a problem. Therefore, depending on the operating temperature conditions, the thermal expansion coefficient of the shaft is set to the thermal expansion coefficient of the ceramic material (8 × 10 ⁻⁶ to 1).
It is necessary to adjust to a value close to 2 × 10 ⁻⁶ / ° C.). Correspondingly, the coefficient of thermal expansion of the tungsten alloy constituting the shaft and outer ring of the bearing unit is set to 2 × 10 ^−6.
The above-mentioned destruction can be effectively prevented by adjusting the range to 12 × 10 ⁻⁶ / ° C.

The applications of the bearing and the bearing unit according to the present invention are not limited to general-purpose ball bearings, but include cylindrical roller bearings,
It can be applied to all radial rolling bearings such as needle roller bearings and tapered roller bearings.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be specifically described based on the following examples and comparative examples.
The basic structure of the bearing or bearing unit according to each embodiment and comparative example is the same as the conventional structure of the bearing and bearing unit shown in FIGS. 1 and 2, respectively. Wherein the ceramic material is used as the material for the rolling elements, and the tungsten alloy is used as a material for forming at least one of the inner ring, the shaft, and the outer ring.

Example 1 and Comparative Example 1 To a silicon nitride raw material powder, predetermined amounts of yttria (Y ₂ O ₃ ) and alumina (Al ₂ O ₃ ) as sintering aids were added, and pulverized using a ball mill. Mixing was performed to prepare a raw material slurry. The obtained raw material slurry was granulated with a spray drier to prepare granulated powder for molding. After forming the granulated powder into a spherical shape by a mold press, the temperature was 400
Degreased at a temperature of 1600 ° C. in a nitrogen gas atmosphere.
Sintering was performed at a temperature of 1950 ° C. to obtain a spherical sintered body. A rolling element was produced by polishing this sintered body.

On the other hand, a doped tungsten alloy and an ultrafine cemented carbide (Tungaloy AE60: average crystal grain
5 μm, Young's modulus 549 GPa) were processed into a ring shape to prepare inner rings having predetermined dimensions. Further, a bearing steel (SUJ-2), which is a conventional material, was processed into a ring shape to prepare an outer ring having a predetermined size.

The bearing according to the first embodiment as shown in FIG. 1 was assembled by combining the rolling elements and the inner and outer rings prepared as described above. On the other hand, a bearing according to Comparative Example 1 having the same dimensions as in Example 1 was prepared, in which the rolling elements and the inner and outer races were all made of conventional bearing steel (SUJ-2).

In order to evaluate the characteristics of the bearings according to the above Examples and Comparative Examples, each bearing was incorporated into a spindle of a machine tool, and heavy cutting was performed for a long time. As a result, in the bearing according to the first embodiment using the rolling element made of Si ₃ N ₄ and the inner ring made of the dope / W alloy and the cemented carbide, the bearing according to the comparative example 1 in which all the bearing components are formed of bearing steel. As compared with, the deflection of the bearing portion under a predetermined stress was small, and the support rigidity could be increased. Therefore, even when heavy cutting of difficult-to-cut materials or the like is performed at high speed, high-precision cutting can be performed without lowering the spindle accuracy.

Further, when the bearing according to Comparative Example 1 was incorporated into a spindle spindle of a machine tool and a continuous machining operation was performed for 7 hours, the temperature rise of the outer ring of the bearing mounted on the spindle spindle became 10 ° C. or more. In contrast, Example 1
The temperature rise of the outer ring of the bearing converges at about 6 ° C., the temperature stability is improved, and high-precision cutting can be performed. This is because, in the bearing of Example 1, the thermal expansion coefficient of the ceramic rolling element and the inner ring made of the doped W alloy and the super-hard alloy is the same as the thermal expansion coefficient of the main shaft equipped with the bearing of Comparative Example 1 and the outer ring of the bearing. This is because it has been reduced to 1/3 or less.

Example 2 and Comparative Example 2 While using the rolling element made of Si ₃ N ₄ and the outer ring made of bearing steel (SUJ-2) prepared in Example 1, the doped tungsten alloy used in Example 1 Shafts having predetermined dimensions were prepared using fine-grain cemented carbide. By assembling these rolling elements, outer rings, and shafts, a second embodiment in which a bearing and a shaft as shown in FIG.
Was manufactured. On the other hand, the rolling elements, outer ring, and shaft are all formed from bearing steel (SUJ-2),
A bearing unit according to Comparative Example 2 having the same dimensions as Example 2 was prepared. Then, the rigidity of the shaft of each bearing unit was comparatively evaluated.

As a result, in the bearing unit according to the second embodiment, in which a shaft made of a dope-W alloy and a superfine-grain cemented carbide is used and the bearing and the shaft are integrated, the rolling element,
The shaft and outer ring are all made of conventional bearing steel (SUj-
Compared with the bearing unit according to Comparative Example 2 formed in 2), the deflection of the shaft under a predetermined stress was small, and the support rigidity could be increased.

Therefore, even in the case where the size of the bearing unit is reduced, breakage during the assembling process can be effectively prevented. That is, after assembling the bearing unit into the applicable device, assembling is performed to improve the mounting accuracy. Specifically, for example, a shaft of a bearing unit mounted on a spindle motor is directly supported and driven by itself to perform high-precision machining of the component.However, as the size of the bearing unit progresses, the diameter of the shaft decreases. As the process proceeds, the bearing strength of the bearing decreases, and the bearing rigidity required during assembling may be insufficient. Such insufficient rigidity has deteriorated the processing accuracy in assembling processing, and has been a major factor causing damage to the bearing. However, in the composite part incorporating the bearing unit according to the second embodiment, even at the time of high-speed rotation of the machine tool, no breakage occurred, and high-precision machining was enabled.

The rigidity of the bearing unit of the second embodiment is high, so that high-precision machining can be performed without being affected by a load or cutting resistance during self-driving. Furthermore, as a result of reducing the diameter of the shaft, even if the rotating members become unbalanced or the like under high-speed rotation conditions, the rotation accuracy does not change, and a longer life and a smaller size can be achieved.

Example 3 While using the rolling element made of Si ₃ N ₄ and the outer ring made of bearing steel (SUJ-2) prepared in Example 1, the thermal expansion coefficient was 4
A cemented carbide as a tungsten alloy of × 10 ^-6 / ° C is machined to a predetermined size to prepare a shaft, and these rolling elements, outer ring, and shaft are assembled to form a bearing, a shaft and a shaft as shown in FIG. A bearing unit according to Example 3 in which was integrated.

Then, the bearing unit according to the third embodiment and the bearing unit according to the comparative example 2 in which all the constituent materials are formed of conventional bearing steel (SUJ-2) are incorporated into a spindle motor, respectively, and the rotation of the spindle is performed. Number 900
A reliability test was carried out with no-load continuous high-speed operation at 0 rpm.

As a result, in the bearing unit according to the third embodiment, even if the dm · N value (bearing inner diameter (mm) × rotation speed (rpm)) is 2.7 million units, abnormalities such as breakage, deformation, and peeling occur. And excellent durability was confirmed. On the other hand, in the bearing unit according to Comparative Example 2, when the dm · N value was 2.5 million, surface separation of the rolling elements, separation of the raceway surface of the shaft corresponding to the inner ring, and the like occurred, and the bearing portion was damaged.

The bearing unit according to the above embodiment is mounted on a consumer digital video tape recorder (VTR) to prepare a cylinder unit as a composite part.
The assembling process was carried out in order to improve the precision of the lead and the reference surface, which are the tape guide portions. This assembling process is performed by directly supporting the shaft of the bearing unit mounted on the cylinder unit on the fixed support part so that it is coaxial with the main shaft of the machine tool, and directly driving a part of the cylinder with burrs etc. did.

In this assembling process, the bearing unit mounted on the cylinder unit can be used even when a driving load propagated by vignetting caused by the main shaft of the machine tool rotating at high speed or a cutting resistance transmitted from the cutting tool acts.
Efficient machining was possible without damaging the bearing unit, and the cylinder could be made more precise.
As a result, even when the bearing unit is downsized, breakage that is likely to occur during assembling processing can be eliminated, and a highly rigid and highly reliable bearing unit can be realized.

In the bearings and bearing units according to the first to third embodiments described above, the rigidity of the rolling elements, the inner ring (shaft), and the outer ring is about 3 as compared with the bearing and the bearing unit in which all of the rolling elements are formed of bearing steel. And the life can be stretched about twice. on the other hand,
Comparing the manufacturing costs, the bearing and bearing unit of each embodiment are intermediate between the conventional one in which only the rolling elements are formed of a ceramic material and the conventional one in which the rolling elements and the inner ring (shaft) are formed of a ceramic material. It can be manufactured at the manufacturing cost, and has excellent cost performance.

[0053]

As described above, according to the bearing and the bearing unit of the present invention, the rolling element is formed of a ceramic material, and at least one of the inner ring (shaft) and the outer ring is formed of a tungsten alloy. Bearings that have excellent overall rigidity and wear resistance, exhibit excellent durability and reliability even when formed in a small size, and can sufficiently respond to the miniaturization, high precision, high speed, and long life of rotating equipment. And a bearing unit can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structural example of a bearing.

FIG. 2 is a sectional view showing a structural example of a bearing unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bearing 2 Inner ring 3 Outer ring 4 Rolling member 5 Cage 11 Bearing unit 12 Shaft 13 Bearing 14 Rolling member 15 Outer ring 16 Groove (track groove) 17 Coil spring (preload spring) 18 Seal groove 19 Spring seat 20 Cage 21 Seal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Ouchi 8 Shinsugitacho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Yutaka Abe 2--4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Address F-term in Toshiba Keihin Works (reference) 3J101 AA03 AA32 AA43 AA54 AA62 AA72 BA10 BA70 EA02 EA42 EA43 EA44 FA31 FA53 GA31

Claims (14)

[Claims] An inner ring and an outer ring arranged concentrically;
In a bearing comprising a rolling element rotatably disposed between the inner ring and the outer ring, the rolling element is formed of a ceramic material, and at least one of the inner ring and the outer ring is formed of a tungsten alloy. Features bearings. 2. The bearing according to claim 1, wherein the ceramic material comprises at least one of silicon nitride, silicon carbide, alumina, zirconia, and aluminum nitride. 3. The ceramic material has a Young's modulus of 200G.
The bearing according to claim 1, wherein the pressure is Pa or more. 4. The bearing according to claim 1, wherein a Young's modulus of a tungsten alloy forming at least one of the inner ring and the outer ring is 200 GPa or more. 5. The bearing according to claim 1, wherein the Rockwell hardness of the tungsten alloy is 60 or more. 6. The tungsten alloy has a coefficient of thermal expansion of 2 × 1.
2. The bearing according to claim 1, wherein the temperature is in the range of 0 ^{-6 to} 12 × 10 ^-6 / ° C. 7. The bearing according to claim 1, wherein the tungsten alloy is an ultrafine cemented carbide having an average crystal grain size of 0.5 μm or less. 8. A shaft, a plurality of outer rings arranged concentrically at intervals in an axial direction of the shaft, and a rolling element rotatably arranged between the outer ring and the shaft. A bearing unit according to claim 1, wherein the rolling element is formed of a ceramic material, and at least one of the shaft and the outer ring is formed of a tungsten alloy. 9. The bearing unit according to claim 8, wherein the ceramic material comprises at least one of silicon nitride, silicon carbide, alumina, zirconia, and aluminum nitride. 10. The ceramic material has a Young's modulus of 200.
9. The bearing unit according to claim 8, wherein the bearing unit has a GPa or more. 11. A tungsten alloy constituting at least one of a shaft and an outer ring has a Young's modulus of 200 GPa.
9. The bearing unit according to claim 8, wherein: 12. The bearing unit according to claim 8, wherein the Rockwell hardness of the tungsten alloy is 60 or more. 13. The tungsten alloy having a coefficient of thermal expansion of 2 ×
The bearing unit according to claim 8, characterized in that the ^{10 -6 ~12 × 10 -6 / ℃} . 14. The bearing unit according to claim 8, wherein the tungsten alloy is an ultrafine cemented carbide having an average crystal grain size of 0.5 μm or less.