JP4713329B2 - Rolling bearing - Google Patents

Description

  The present invention relates to a rolling bearing used in a vacuum environment.

Among bearings used in a vacuum environment, especially bearings that do not allow oil content, bearings that are made by sintering a solid lubricant such as tungsten disulfide as spacers in the bearing have superior characteristics. It is known by showing (refer patent document 1). Such a bearing exhibits good bearing characteristics when the spacer and the rolling element are in sliding contact with each other and the lubricant is supplied to the rolling part.
However, since the sintered body of solid lubricant has low mechanical strength and lacks flexibility, it uses a bearing such as a touch-down bearing where centrifugal force and impact force are applied to the sintered body at a high rotational speed. Not applicable under conditions.

On the other hand, a bearing having a form in which a tungsten disulfide film using an inorganic binder is applied to a cage and a lubricant is supplied from the cage in the same manner as described above (see Patent Document 2) is known as an inorganic material with poor flexibility. Since the binder is used, the film itself is not very flexible, and when it comes into sliding contact with the rolling elements, it falls off in large units, and the hard inorganic binder becomes a foreign substance and damages the bearing. Therefore, the life of the bearing is not sufficient.
Further, a bearing in which a cage is provided with a solid lubricant film using a relatively soft thermosetting resin as a binder is known (see Patent Document 3), but the wear resistance of the film itself is often emphasized. Therefore, the blending ratio of the solid lubricant is at most 40% by volume, which is not sufficient to maintain the bearing life.
Japanese Patent No. 3550689 Japanese Patent Laid-Open No. 10-205541 JP 2002-130300 A

  The present invention has been made to cope with such problems, and is intended to provide a bearing that is used in a vacuum environment that does not allow oil, and that can be used at a high rotational speed and has a long life. .

Rolling bearing of the present invention, the inner and outer rings, the plurality of rolling elements interposed between the inner ring and the outer ring, Ri Na and a cage holding sliding contact with the rolling elements of said plurality of not allow oil environment A rolling bearing used below, which contains tungsten disulfide powder on at least one surface of the cage surface, and the binder component is a thermosetting polyamide-imide resin, a thermosetting polyimide resin, or fluorine. A coating film which is a resin is formed, and the blending ratio of the tungsten disulfide powder in the coating film is 80 volume% to 95 volume%, and the coating film supplies the tungsten disulfide powder from the coating film to the rolling part. It is the film which carries out.
The rolling bearing is a bearing used in a vacuum environment. Further, the rolling bearing is a touch-down bearing used for a turbo molecular pump.

The rolling bearing according to the present invention is a bearing in which at least one surface of the cage surface is coated with a resin in which tungsten disulfide powder is blended in an amount of 70% by volume to 98% by volume. Tungsten enters the rolling part and functions as a lubricant, and even when the bearing is used at a high rotational speed, it is not damaged.
Further, since it contains a large amount of tungsten disulfide as a lubricant, the bearing has a longer life compared to the conventional bearing in the same application, and at the same time, the amount of gas generated is reduced because the amount of binder is small.
In addition, since high strength materials such as metal can be arbitrarily used as the cage as the base material of the coating, the cage can be damaged even when the bearing is used at high speeds by adopting these high strength materials. And can exhibit excellent bearing characteristics.

In the case of a cage used for severe operating conditions that rotate at high speed in a vacuum such as a touchdown bearing, if there is too much organic binder, the supply of lubricant from the cage cannot catch up, and seizure occurs in the bearing at the beginning of operation. On the other hand, if there is no or too little organic binder, the lubricant will fall off when assembling the bearing, and even during operation, it will drop off in large units and continuous supply of lubricant will not be possible, and the bearing will seize at the beginning of operation.
The present invention has been made paying attention to these points. In a rolling bearing used in a vacuum environment, tungsten disulfide powder is 70% by volume to 98% by volume on at least one surface of the cage surface. It has been found that excellent bearing characteristics can be obtained during high-speed rotation by supplying a smooth lubricant by coating a resin blended in%.

An example of a rolling bearing according to the present invention is shown in FIG. FIG. 1 is a cross-sectional view of a deep groove ball bearing.
As shown in FIG. 1, in a rolling bearing 1, an inner ring 2 having an inner ring rolling surface 2a on an outer peripheral surface and an outer ring 3 having an outer ring rolling surface 3a on an inner peripheral surface are arranged concentrically, and an inner ring rolling surface 2a. A plurality of rolling elements 4 are arranged between the outer ring rolling surface 3a. The plurality of rolling elements 4 are constituted by a retainer 5 that is slidably held and a seal member 6 that is fixed to the outer ring 3 or the like. Of these, a film containing 70% by volume to 98% by volume of tungsten disulfide is formed on at least one surface of the cage 5 surface. The binder component of the coating is preferably a resin, and the coating is stably formed on the surface of the cage 5 by the binder.
In the present invention, at least one or more surfaces of the cage surface is a surface at which the lubricant can enter the rolling part such as the surface of the rolling element from the coating formed on the surface. Sliding surface, etc.

An example of the touchdown rolling bearing according to the present invention is shown in FIG. FIG. 2 is a view showing an example of a cross-section of a touchdown rolling bearing used in a turbo molecular pump. As shown in FIG. 2, the touch-down rolling bearings 14a and 14b are used together with magnetic bearings 12a, 12b, 12c, and 12d as bearings of the turbo molecular pump 7 for forming a high vacuum (> 1 × 10 ⁻¹ Pa). used. The turbo molecular pump 7 is attached to a system that forms a high vacuum with an intake port 8, and the rotation of a rotor 10 driven by a motor 13 sucks the gas in the system from the intake port 8 and discharges it to the exhaust port 9. This keeps the inside of the system at a high vacuum.

Normally, the magnetic bearings 12a, 12b, 12c, and 12d are operated in a state where the rotor 10 and the stator 11 do not come into contact with each other due to the magnetic force of the magnetic bearings 12a, 12b, 12c, and 12d. There is a risk that the load capacity of 12d is lost instantaneously, the rotor 10 and the stator 11 come into contact with each other, and the turbo molecular pump 7 is damaged. The touchdown rolling bearings 14a and 14b are configured so that the rotor 10 and the stator 11 are brought into contact with and supported from the rotor 10 and the stator 11 from the maximum rotation state when the predetermined clearance between the rotor 10 and the stator 11 is reduced. 11 is prevented.
Since the touchdown rolling bearings 14a and 14b are coated with a resin in which 70% to 98% by volume of tungsten disulfide powder is blended on at least one surface of the cage surface, high speed is achieved under high vacuum. Can respond to rotation.

  The tungsten disulfide powder used in the present invention is not particularly limited by the particle diameter, shape, purity, production method and the like, and any commercially available one can be adopted. When it is necessary to form a homogeneous thin film, those having an average particle size of 50 μm or less are preferred.

  In the present invention, the blending amount of the tungsten disulfide powder in the coating is required to be 70% by volume to 98% by volume. If it is less than 70% by volume, solid disulfide tungsten disulfide cannot be stably supplied from the cage to the sliding interface. Moreover, when it exceeds 98 volume%, there exists a possibility that a film may fall from a cage.

In the present invention, other solid lubricants and reinforcing materials can be used in combination with the tungsten disulfide powder as long as the properties of the coating are not impaired.
For example, a part of tungsten disulfide powder as a solid lubricant can be replaced with molybdenum disulfide powder to form a coating. The blending ratio of molybdenum disulfide powder in the mixture of tungsten disulfide powder and molybdenum disulfide powder is preferably 30% by volume or less. If it exceeds 30% by volume, the prescribed lubrication characteristics cannot be obtained.

  The resin used as the binder is not particularly limited, and any of a thermoplastic resin and a thermosetting resin can be used. Among these resins, thermosetting polyamide-imide (hereinafter referred to as PAI) resin and thermosetting polyimide resin are preferable because outgas is small even in a high vacuum environment and a film is easily formed. Or the dispersion of a fluororesin is also preferable.

The method of forming a film on the surface of the cage is not particularly limited, and a mixture of tungsten disulfide and a resin is laminated on the surface of the cage by a method such as dipping, coating, spraying, etc. A film can be formed by fixing the components to the cage body (dipping method or the like).
The thickness of the coating is preferably 10 μm to 1000 μm. If it is less than 10 μm, the lubricant is consumed at the familiar stage in the initial stage of operation, so that sufficient bearing characteristics cannot be exhibited.If it exceeds 1000 μm, uniform and high-quality film formation is difficult, so cracks and pins are not formed on the film. Defects such as holes are likely to occur, and there is a high possibility of dropping in large units during operation.
In addition, when a resin-rich layer is used as an adhesive layer in order to improve the adhesion between the cage and the coating, the lubricant is prevented from falling off and the life can be extended.

  As a material of the cage, a metal material such as a copper alloy, stainless steel (SUS), an aluminum alloy, or a titanium alloy, or a heat resistant resin material such as a polyimide resin or a polyetheretherketone resin can be employed. When the rolling bearing of the present invention is used as a touch-down bearing, it is exposed to severe conditions such as impact load and sudden acceleration. Therefore, it is preferable to employ a copper alloy having a good balance between flexibility and strength.

The present invention will be specifically described with reference to examples and comparative examples, but is not limited to these examples.
The bearing life test of the rolling bearing for a test of the Example and comparative example which were produced using the raw material of a film shown below, the film formation method, and the bearing life test method was done.
<Raw material>
Tungsten disulfide powder: manufactured by Nippon Lubricant Co., Ltd., WS2-B special, average particle size 0.6 μm
Molybdenum disulfide powder: manufactured by Daizo, A powder, average particle size 0.6μm
Polytetrafluoroethylene (hereinafter referred to as PTFE) powder: manufactured by Daikin Industries, Ltd., M15, average particle size 15 μm
Thermosetting PAI resin: made by Hitachi Chemical Co., Ltd., HPC-4250-30
Water glass (sodium silicate): Wako Pure Chemical Industries, reagent <film formation method>
The film was formed by the dipping method shown below.
A paint was obtained by weighing the resin and the solid lubricant powder so that the blending ratio was a predetermined ratio and adjusting the solid content of the paint to be 20 wt% to 30 wt%. The operation of immersing the cage in the obtained coating material and pre-heat-treating at 100 ° C. for 30 minutes was repeated three times, followed by baking at 200 ° C. (300 ° C. in the case of water glass) for 3 hours. The film thickness after firing was set to 50 μm to 100 μm.
<Bearing life test>
A bearing life test in which a thrust load was applied to the test bearing in vacuum, the inner ring was rotated, and the torque was measured was performed under the following conditions. The bearing life was defined as the time required for the torque to become significantly higher than when it was stable. For Example 1 and Comparative Example 5, high-speed rotation conditions were applied in addition to low-speed rotation conditions.
Test bearing: Angular type equivalent to 608 made of SUS440C Cage: Machined cage made of CAC301 Coating: Forming a film thickness of 50 μm to 100 μm on the entire surface of the cage Vacuum degree: 1 to 10 × 10 ⁻⁵ Pa
Temperature: Normal temperature Low-speed rotation condition: Load: 490 N (maximum contact surface pressure 2.2 GPa), rotation speed: 500 rpm
High-speed rotation conditions: Load: 49 N (maximum contact surface pressure 1.1 GPa), rotation speed: 10000 rpm

Examples 1 to 3 and Comparative Examples 1 to 5
Test bearings having the configuration shown in Table 1 were prepared and a bearing life test was performed. For Example 1 and Comparative Example 5, high-speed rotation conditions were applied in addition to low-speed rotation conditions. The results are also shown in Table 1.

表１に示すように、実施例の保持器は比較例１〜比較例４に比べて優れた軸受寿命を示した。比較例５の市販品を切削加工して得た保持器は、低速回転条件では実施例と同等の軸受寿命を示したが、高速回転条件では、実施例１の 100 時間に比べてわずか 5分間の短寿命であり、試験後の保持器は破損していた。

As shown in Table 1, the cage of the example showed a bearing life superior to that of Comparative Examples 1 to 4. The cage obtained by cutting the commercial product of Comparative Example 5 showed a bearing life equivalent to that of the example under low speed rotation conditions, but only 5 minutes under the high speed rotation condition compared to 100 hours of Example 1. The cage after the test was broken.

  The rolling bearing of the present invention can extend the life of the bearing by stably supplying the lubricant from the tungsten disulfide coating applied to the cage to the rolling part, and a high-strength metal can be used as the cage material. Therefore, the cage is not damaged even under high-speed rotation conditions, and can be suitably used as a rolling bearing used under high vacuum and high-speed rotation conditions.

It is sectional drawing of a deep groove ball bearing. It is a figure which shows an example of the touchdown rolling bearing used for a turbo molecular pump.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing 2 Inner ring 2a Inner ring rolling surface 3 Outer ring 4 Rolling body 3a Outer ring rolling surface 5 Cage 6 Seal member 7 Turbo molecular pump 8 Intake port 9 Exhaust port 10 Rotor 11 Stator 12a Magnetic bearing 12b Magnetic bearing 12c Magnetic bearing 12d Magnetic bearing 13 Motor 14a Touchdown bearing 14b Touchdown bearing

Claims (4)

An inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, Ri Na and a cage holding against said plurality of rolling elements and sliding, rolling bearings are used in an environment that does not allow oil Because
Forming a film containing tungsten disulfide powder on at least one surface of the cage surface, the binder component being a thermosetting polyamideimide resin, a thermosetting polyimide resin, or a fluorine resin, A rolling bearing characterized in that a compounding ratio of tungsten disulfide powder in the coating is 80 vol% to 95 vol%, and the coating is a coating for supplying the tungsten disulfide powder from the coating to a rolling part. .   The rolling bearing according to claim 1, wherein the rolling bearing is a bearing used in a vacuum environment.   The rolling bearing according to claim 1, wherein the rolling bearing is a touch-down bearing.   The rolling bearing according to claim 3, wherein the rolling bearing is a touch-down bearing used for a turbo molecular pump.

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