JP2022112866A - Rolling bearing and vacuum pump comprising the same - Google Patents

Abstract

To provide a rolling bearing that is rendered resistant to wear, and a vacuum pump comprising the same.SOLUTION: A rolling bearing 100 has an inner ring 11, an outer ring 13 and a plurality of balls 15 disposed between the inner ring 11 and the outer ring 13, with a lubricant added to the inside of the bearing. The inner ring 11 and the outer ring 13 are made up of bearing steel. The ball 15 is made up of martensitic stainless steel. The surface of the ball is provided with a passivated coat for wear resistance.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rolling bearing and a vacuum pump having the same.

For example, in semiconductor manufacturing and transport processes, the processing space must be in a vacuum state in which no active gas exists. Such a vacuum state is obtained by driving a vacuum pump. In the case of a dry vacuum pump, a pair of rotary rotors are rotatably supported inside a housing via rolling bearings such as ball bearings, and the rotary rotors are rotationally driven. As a result, the gas sucked into the wave groove space of the rotating rotor is discharged from the discharge port, and the airtight chamber connected to the vacuum pump is evacuated.

JP 2005-201326 A JP 2008-169939 A

However, when the rolling bearings of the above-mentioned vacuum pump, such as those described in Patent Documents 1 and 2, are extremely worn, the amount of axial movement of the shaft that supports the rotating rotor increases, and the rotating rotor rattles. becomes more likely to occur. As a result, the pair of rotating rotors come into contact with each other and the rotation resistance increases, so that the number of rotations of the rotating rotors decreases. As a result, there is a possibility that a space with a desired degree of vacuum cannot be formed. Moreover, if the space between the rotating rotors becomes too wide, it may become difficult to maintain the desired degree of vacuum.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a rolling bearing that is configured to be less prone to wear in order to hold a pair of rotating rotors at predetermined positions, thereby suppressing deterioration in the performance of a vacuum pump equipped with rolling bearings.

The present invention consists of the following configurations.
(1) A rolling bearing comprising an inner ring, an outer ring, and a plurality of balls arranged between the inner ring and the outer ring, wherein a lubricant is applied inside the bearing,
The material of the inner ring and the outer ring is bearing steel,
The ball is made of martensitic stainless steel,
A passivation coating is formed on the surface of the ball to provide wear resistance.
rolling bearing.
(2) a rotating rotor;
a housing that accommodates the rotating rotor;
a rolling bearing according to (1), which is provided inside the housing and rotatably supports the rotating rotor while maintaining airtightness with the outside of the housing;
A vacuum pump with

ADVANTAGE OF THE INVENTION According to this invention, a rolling bearing can be made into the structure which wear does not produce easily. Therefore, it is possible to suppress deterioration in the performance of a vacuum pump using this rolling bearing.

1 is a sectional view of a rolling bearing according to the present invention; FIG. FIG. 2 is a cross-sectional view schematically showing the configuration of a dry vacuum pump including the rolling bearing shown in FIG. 1; FIG. 4 is an explanatory diagram schematically showing functions of a vacuum pump; It is a graph which shows the result of having conducted the comparative test of the wear amount of a ball.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view of a rolling bearing according to the invention.
A rolling bearing 100 shown in FIG. 1 is an angular contact ball bearing including an inner ring 11 , an outer ring 13 , a plurality of balls 15 arranged between the inner ring 11 and the outer ring 13 , and a retainer 17 . A lubricant (not shown) is applied inside the rolling bearing 100 .

The material of the inner ring 11 and the outer ring 13 is bearing steel such as SUJ material (JIS G 4805:2019), which is high carbon chromium bearing steel.

The material of the ball 15 is martensitic stainless steel such as SUS440C, and a passivation film in which oxygen and hydroxyl groups are mainly bonded to chromium is formed on the surface of the ball 15 to form hard chromium carbide.

Although the material and shape of the retainer 17 are not particularly limited, for example, if the retainer is made by processing a steel plate, it can be manufactured at low cost.

The rolling bearing 100 configured as described above has a bearing sectional height H, that is, a ratio D/ It is preferable that H is 0.47 to 0.64. By setting the ratio D/H within this range, the load applied from the balls 15 to the inner ring 11 and the outer ring 13 can be kept relatively small, and the rolling bearing 100 can be designed with sufficient load resistance.

On the other hand, when the ratio D/H is less than 0.47, the diameter of the ball 15 becomes too small with respect to the inner ring 11 and the outer ring 13, and the ball 15 does not have a sufficient life. Moreover, when the ratio D/H exceeds 0.64, there is concern that the inner ring 11 and the outer ring 13 may be damaged.

In addition, the rolling bearing 100 is likely to wear if the rotation speed is 0.4 times or more the allowable rotation speed, and in that case, it is important to improve the above-described load resistance.

Examples of lubricants that can be used include fluorine-based lubricants such as PFPE oil (perfluoropolyether), CTFE oil (low polymer of chlorotrifluoroethylene), and PTFE (polytetrafluoroethylene) grease. Fluorine-based lubricants have properties such as resistance to temperature, oxidation stability, and difficulty in evaporating. Evaporation of the lubricant can be effectively suppressed. Therefore, high lubricity can be maintained inside the rolling bearing 100 .

However, the decomposition of the fluorine-based lubricant may corrode bearing parts made of steel. Therefore, in this configuration, by making the ball 15 of martensitic stainless steel, the passivation film on the surface of the ball 15 suppresses corrosion due to fluorine. Further, since hard chromium carbide is formed on the surface of the ball 15, the wear resistance is improved and the service life can be extended. Although it is conceivable that both the inner ring 11 and the outer ring 13 are made of martensitic stainless steel, in that case, there is a disadvantage that the material cost and the processing cost increase.

As in this configuration, the inner ring 11 and the outer ring 13 are made of bearing steel, and the balls 15 are made of martensitic stainless steel. Material costs and processing costs can be reduced compared to the case of forming. In addition, since the surfaces of the inner ring 11 and the outer ring 13 can suppress wear due to the rolling of the worn balls 15, a practically sufficient long life can be achieved. Therefore, by forming only the balls 15, which are bearing members with a relatively high contact frequency per unit area, of martensitic stainless steel, the rolling bearing 100 as a whole can be reduced in cost and extended in service life. can be made into a well-balanced configuration.

Further, since the ball 15, which is a bearing member with a relatively high contact frequency per unit area, is selectively made of martensitic stainless steel, even if a fluorine-based lubricant is used, the ball 15 will be corroded by fluorine. become difficult. As a result, adverse effects on the rolling bearing 100 due to corrosion are greatly reduced.

By setting the ratio D/H in the range of 0.47 to 0.64, the load applied from the ball 15 to the inner ring 11 and the outer ring 13 can be reduced, and the wear resistance is improved to extend the life. The effect and the corrosion suppression effect can be synergistically improved.

In addition, in the case of an angular contact ball bearing, since loads in the radial direction and loads in the axial direction are applied, it is particularly important to suppress wear. Since corrosion due to corrosion is suppressed, deterioration of bearing performance can be minimized.

Next, an example in which the rolling bearing 100 configured as described above is applied as a support member for a rotating rotor of a vacuum pump will be described.
FIG. 2 is a schematic cross-sectional view of a vacuum pump 200 including rolling bearing 100 shown in FIG. FIG. 3 is an explanatory diagram schematically showing the functions of the vacuum pump.
As shown in FIG. 2, the vacuum pump 200 is a dry vacuum pump, and includes a housing 21, a rotating rotor 23, and a pair of bearings (see FIG. 1) and a bearing 25 consisting of a deep groove ball bearing.

The housing 21 is formed by a main housing 21A and a discharge side housing 21B.
The rotating rotor 23 consists of a male rotor 23A and a female rotor 23B arranged in the inner space between the main housing 21A and the discharge-side housing 21B. The male rotor 23A and the female rotor 23B are rotatably supported by the housing 21 with a pair of rolling bearings 100 at one end (right side in FIG. 2) and a bearing 25 at the other end (left side in FIG. 2). be.

Further, the vacuum pump 200 is configured to seal the lubricating oil of the rolling bearing 100 and the bearing 25 by the shaft sealing mechanisms 27A and 27B.

Further, the shaft 29A of the male rotor 23A is directly connected to the shaft 33 of the electric motor 31, and the female rotor 23B is rotated by the timing gears 35, 35 while keeping a minute distance from the male rotor 23A. The gas sucked from the suction port 37 passes through the suction port 39, is sucked into the tooth gap space formed by the rotor chamber wall of the main housing 21A and the male rotor 23A and the female rotor 23B, and is discharged through the compression process. It is designed to be discharged from a discharge port 43 via a port 41 . The timing gears 35 , 35 are covered with a gear cover 45 , and the electric motor 31 is covered with an electric motor cover 47 .

As shown in FIG. 2, rolling bearing 100 and bearing 25 rotatably support shaft 29A of male rotor 23A and shaft 29B of female rotor 23B, respectively. As a result, as shown in FIG. 3, intake and exhaust are performed by the rotation of the rotating rotor.

According to the vacuum pump 200 of this configuration, since the wear resistance of the rolling bearing 100 is improved, deterioration of the pump performance is suppressed, and a vacuum space with a desired air pressure can be always stably formed. In addition, by using a fluororesin-based lubricant for the rolling bearing 100, evaporation of the lubricant is suppressed, and stable rotational operation is obtained.

Although the vacuum pump 200 described above is configured to include a pair of rotating rotors, the present invention is not limited to this. For example, the rolling bearing 100 of the present invention can be suitably applied to pump devices having other configurations such as impeller pumps having a single blade.

In order to confirm the action and effect of the present invention, a comparison test of the amount of wear of the ball of the present invention example and the comparative example was carried out under the following conditions. The results are shown in FIG.
Bearing: Thrust ball bearing with inner diameter Φ25mm, outer diameter Φ52mm, width 18mm Axial load: 6860N (700kgf)
Rotation speed: 3000min ^-1
Test temperature: 130°C
Lubrication method: fluorine oil (oil bath)
Test time: 255hrs
Outer ring and inner ring material: High carbon chromium bearing steel SUJ2
Ball material of the example of the present invention: martensitic stainless steel SUS440C
Comparative ball material: High carbon chromium bearing steel SUJ2

As shown in FIG. 4, when the wear amount of the ball of the comparative example is 100%, the wear amount of the ball of the example of the present invention is 17%, and the ball of the example of the present invention wears more than the ball of the comparative example. quantity has decreased significantly.

As described above, the present invention is not limited to the above-described embodiments, and those skilled in the art can make modifications and applications by combining each configuration of the embodiments with each other, based on the description of the specification and well-known techniques. It is also contemplated by the present invention that it falls within the scope of protection sought.

As described above, this specification discloses the following matters.
(1) A rolling bearing comprising an inner ring, an outer ring, and a plurality of balls arranged between the inner ring and the outer ring, wherein a lubricant is applied inside the bearing,
The material of the inner ring and the outer ring is bearing steel,
The ball is made of martensitic stainless steel,
A passivation coating is formed on the surface of the ball to provide wear resistance.
rolling bearing.
According to this rolling bearing, material costs and processing costs can be reduced by forming the inner ring and the outer ring from bearing steel and forming the balls from martensitic stainless steel. In addition, since the balls that contact with a particularly high frequency of contact are made of martensitic stainless steel, even if fluorine-based lubricants are used, corrosion due to fluorine can be prevented from adversely affecting rolling bearings. It is possible to achieve a well-balanced configuration while maintaining the performance of the bearing.

(2) The rolling bearing according to (1), wherein at least one of the inner ring and the outer ring is made of high-carbon chromium bearing steel SUJ.
According to this rolling bearing, material costs and processing costs can be reduced.

(3) The rolling bearing according to (1) or (2), wherein the lubricant is fluorine-based grease or fluorine-based lubricating oil.
According to this rolling bearing, evaporation of the lubricant is suppressed, and high lubricity can be obtained even under vacuum.

(4) The rolling bearing according to any one of (1) to (3), which is an angular contact ball bearing or a deep groove ball bearing.
According to this rolling bearing, good rotation can be obtained while supporting a radial load and an axial load.

(5) a rotating rotor;
a housing that accommodates the rotating rotor;
a rolling bearing according to any one of (1) to (4), which is provided inside the housing and rotatably supports the rotating rotor while maintaining airtightness with the outside of the housing;
A vacuum pump with
According to this vacuum pump, stable operation can be performed for a long period of time, and a desired degree of vacuum can be easily obtained.

11 inner ring 13 outer ring 15 ball (rolling element)
21 housing 21A main housing 21B discharge side housing 23 rotating rotor 23A male rotor 23B female rotor 100 rolling bearing 200 vacuum pump

Claims (5)

A rolling bearing comprising an inner ring, an outer ring, and a plurality of balls arranged between the inner ring and the outer ring, wherein a lubricant is applied inside the bearing,
The material of the inner ring and the outer ring is bearing steel,
The ball is made of martensitic stainless steel,
A passivation film is formed on the surface of the ball to provide wear resistance.
rolling bearing. At least one of the inner ring and the outer ring is made of high carbon chromium bearing steel SUJ,
A rolling bearing according to claim 1 . The lubricant is fluorine-based grease or fluorine-based lubricating oil,
A rolling bearing according to claim 1 or 2. Angular ball bearings or deep groove ball bearings,
A rolling bearing according to any one of claims 1 to 3. a rotating rotor;
a housing that accommodates the rotating rotor;
A rolling bearing according to any one of claims 1 to 4, which is provided inside the housing and supports the rotating rotor rotatably while maintaining airtightness with the outside of the housing;
A vacuum pump with

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