JP2008223806A - Touchdown bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a touchdown bearing capable of improving durability thereof by inhibiting rolling of balls. <P>SOLUTION: This touchdown bearing for a magnetic bearing device has one of an inner ring 8 and an outer ring 7 arranged to face a rotary member 30 supported by a magnetic bearing, and has the balls 9 retained by a retainer 10 built between the inner ring 8 and the outer ring 7. The retainer 10 includes a weight adding part 10a projecting axially downward more than end surfaces 8b, 7b of the inner ring 8 or the outer ring 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a touchdown bearing. More specifically, the present invention relates to a touch-down bearing for supporting and protecting a rotating body supported by a magnetic bearing in a vacuum pump or a turbo molecular pump when it cannot be controlled.

  Magnetic bearings do not wear due to non-contact support by magnetic levitation, and therefore no lubrication oil is required, so they are used for rotating machines in special environments such as vacuum environments and ultra-low temperature environments that were difficult with conventional bearings. Has been.

  FIG. 2 is a cross-sectional explanatory diagram of an example in which a magnetic bearing is applied to a turbo molecular pump. A plurality of fixed blades 21 are arranged at predetermined intervals along the axial direction on the inner peripheral surface of the cylindrical casing 20, and a rotary shaft 23 having a rotary blade 22 fixed to the outer periphery is provided in the casing 20. It is rotatably arranged. The rotating shaft 23 is rotated by an electric motor 24, and in a normal rotating state, two radial magnetic bearings 25 and 26 arranged close to the outer peripheral surface of the rotating shaft 23 and the vicinity of the lower end of the rotating shaft 23 Are supported in a non-contact manner by a set of axial magnetic bearings 27 disposed above and below a flange portion 23a formed integrally with the rotary shaft 23.

  Further, in the casing 20, a single deep groove ball bearing 28 as a radial receiver and a pair of angular ball bearings 29 in a front combination as an axial receiver are arranged as a touch-down bearing. These touchdown bearings 28 and 29 are damaged by contact between the rotary shaft 23 and the magnetic bearings 25, 26, 27 when the magnetic bearings 25, 26, 27 become uncontrollable due to disconnection or power failure. This is to prevent this from happening. A gap slightly smaller than the gap between the rotary shaft 23 and the magnetic bearings 25, 26, 27 between the inner peripheral surface of the rotary shaft 23 and the inner ring inner peripheral surfaces of the touchdown bearings 28, 29. Is provided. Thereby, when the rotary shaft 23 is rotationally supported while being magnetically levitated by the magnetic bearings 25, 26, 27, the rotary shaft 23 remains in a non-contact state with respect to the touchdown bearings 28, 29, When the magnetic bearings 25, 26, 27 cannot be controlled, the rotary shaft 23 comes into contact with the inner rings of the touchdown bearings 28, 29 and is rotatably supported before contacting the magnetic bearings 25, 26, 27.

  Such a touch-down bearing has been conventionally considered as an emergency or emergency member, and has been inevitably stopped even if it becomes unusable due to about one or two touch-downs. Since work such as adjusting the clearance with the rotating shaft takes time, various attempts have been proposed to improve durability so as to withstand many touchdowns (see, for example, Patent Documents 1 and 2).

  In Patent Document 1, a ball rolling surface in which a lead coating is formed on the surface of an inner ring or an outer ring arranged to face the rotating member, and a surface that contacts the rotating member at the time of touchdown in which a molybdenum disulfide coating is formed. A touch-down bearing provided with is described. Patent Document 2 discloses a touch-down bearing in which a zinc-calcium phosphate film is formed on a contact surface with other members in an inner ring, an outer ring, a ball, and a cage, and a molybdenum disulfide film is further formed thereon. Is described.

JP-A-11-257353 JP 2006-183867 A

The proposals described in Patent Documents 1 and 2 all form a film made of a solid lubricant on the surface of a member constituting a touchdown bearing, and suppress wear of the member at the time of touchdown. This is to improve the durability of the touchdown bearing.
As a result of intensive studies to further improve the durability of the touchdown bearing, the present inventors have found that the life of the bearing can be extended by suppressing the rolling of the ball itself, and the present invention is completed. It came to.

  The objective of this invention is providing the touchdown bearing which can improve the durability by suppressing rolling of a ball | bowl.

The touchdown bearing according to the present invention is a magnetic bearing in which one of an inner ring and an outer ring is arranged opposite to a rotating member supported by a magnetic bearing, and a ball held by a cage is incorporated between the inner ring and the outer ring. A device touchdown bearing,
The retainer has a weight adding portion that protrudes downward in the axial direction from an end face of the inner ring or the outer ring.

  In the touchdown bearing according to the present invention, the cage for holding the ball is provided with a weight addition portion that protrudes downward in the axial direction from the end face of the inner ring or the outer ring. For this reason, when a rotational force is applied to the ball at the time of touchdown, the cage whose weight is increased by the weight addition portion becomes a resistance, and the rotation of the ball can be converged quickly. As a result, the rolling distance of the ball can be reduced and consumption of the solid lubricant coated on the rolling surface of the ball can be suppressed. Thereby, the possible number of touchdowns can be extended.

  It is preferable that at least an axially upper portion of the inner circumferential surface of the pocket of the cage is processed into a spherical shape along the shape of the ball. According to this configuration, since the contact area between the inner circumferential surface of the pocket of the cage and the ball is large during touchdown, the rotation of the ball can be converged more quickly. As a result, the relative rotation between the inner ring and the outer ring can be converged more quickly.

  According to the touchdown bearing of the present invention, the durability of the touchdown bearing can be improved by suppressing the rolling of the ball.

Hereinafter, embodiments of a touchdown bearing according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional explanatory view of a touchdown bearing T according to an embodiment of the present invention. This touch-down bearing T is composed of two angular ball bearings 1 and 2 in front combination, and is used as an axial receiver in the lower portion of the rotating shaft of the turbo molecular pump shown in FIG. 2, for example.

  The upper angular ball bearing 1 is disposed between the outer ring 3, the inner ring 4 disposed concentrically with the outer ring 3 on the inner diameter side of the outer ring 3, and the outer ring 3 and the inner ring 4. The ball 5 is a plurality of rolling elements, and a cage 6 that holds the balls 5 at a predetermined interval in the circumferential direction. Similarly to the upper angular ball bearing 1, the lower angular ball bearing 2 also includes an outer ring 7, an inner ring 8, a ball 9 and a cage 10.

Between the inner peripheral surfaces 4a and 8a of the inner rings 4 and 8 and the outer peripheral surface 30a of the rotating shaft 30 as a rotating member, there are an inner peripheral surface of a magnetic bearing (not shown) and an outer peripheral surface 30a of the rotating shaft 30. The gap C is adjusted to be smaller than the gap between them. As a result, when the rotary shaft 30 is rotatably supported in a state of being magnetically levitated by the magnetic bearing, the rotary shaft 30 remains in a non-contact state with respect to the touchdown bearing T, but when the magnetic bearing cannot be controlled, Before the rotary shaft 30 comes into contact with the magnetic bearing, the rotary shaft 30 comes into contact with the inner rings 4 and 8 of the touchdown bearing T and is rotatably supported. The outer rings 3, 7, the inner rings 4, 8 and the cage 10 are made of SUS440C. The cage 6 is made of SUS304, and the balls 5 and 9 are made of silicon nitride.
Further, wear of the balls 5 and 9 and the like is suppressed on the ball rolling surfaces of the outer rings 3 and 7 and the inner rings 4 and 8 and pocket inner peripheral surfaces of the cages 6 and 10 that are in contact with the balls 5 and 9. Therefore, a film made of a solid lubricant such as molybdenum, molybdenum disulfide, or tungsten disulfide is formed.

During the touchdown, the balls 5 and 9 disposed between the inner rings 4 and 8 and the outer rings 3 and 7 roll with the rotation of the inner rings 4 and 8. In order to suppress this rolling, the weight of the cage 10 that holds the ball 9 is increased to brake the rotation of the ball 9. Specifically, the cage 10 of the angular ball bearing 2 disposed on the lower side is protruded downward in the axial direction (of the rotary shaft 30) from the end surface 7b of the outer ring 7 or the end surface 8b of the inner ring 8, and the weight The additional unit 10a is used. By providing the weight adding portion 10a, the weight of the cage 10 can be increased, and a large resistance is given to the ball 9 that rolls in the circumferential direction in the space between the outer ring 7 and the inner ring 8 together with the cage 10. be able to. Thereby, rotation of the ball | bowl 9 can be suppressed and the rolling distance of the said ball | bowl 9 can be made small. As a result, consumption of the solid lubricant coated on the rolling surface of the ball 9 can be suppressed, and the number of possible touchdowns can be extended.
The length L projecting downward from the weight adding portion 10a is not particularly limited in the present invention, and can be appropriately selected in consideration of an allowable space around the touch-down bearing.

  The cage 10 is made of SUS440C like the outer ring 7 and the inner ring 8, and has a long rolling life. The cage 10 including the vicinity of the inner peripheral surface of the pocket 11 is subjected to a heat treatment such as quenching and tempering, and its HRC hardness is in a range of 58 to 62. As a result, the cage 10 can be hardened, and when the ball 9 is given a greater resistance, the ball 9 and the cage 10 can rotate without excessive wear. Can be quickly converged.

In the present embodiment, at least the axially upper portion 11 a of the inner peripheral surface of the pocket 11 of the cage 10 that accommodates the ball 9 is processed into a spherical shape that follows the shape of the ball 9. Yes. Thereby, since the contact area with the axial direction upper part 11a of the pocket internal peripheral surface of the holder | retainer 10 is large at the time of touchdown, rotation of the said ball | bowl 9 can be converged earlier. As a result, the relative rotation between the inner ring and the outer ring can be converged more quickly.
Further, in the present embodiment, the weight of the retainer 10 is large due to the weight addition portion 10a protruding vertically downward from the angular ball bearing, and the retainer 10 has a rotating shaft 30 that is not connected to the touchdown bearing T. At the time of contact, the ball 9 is urged vertically downward. For this reason, it is possible to suppress the inner ring 8 not in contact with the rotary shaft 30 from being rotated by the rotation of the rotary shaft 30 due to the magnetism of the rotary shaft 30.

In addition, although the above description is performed about the touchdown bearing which consists of an angular ball bearing, this invention is not limited to an angular ball bearing, For example, it applies also to the deep groove ball bearing used as a radial receiver. be able to.
In the present embodiment, the outer rings 3, 7, the inner rings 4, 8 and the cage 10 are made of SUS440C. However, the outer rings 3, 7, the inner rings 4, 8 and the cage 10 are made of high carbon such as SUS630 or SUJ2. You may form from any one of chromium bearing steel, skin burned steel, and high-speed tool steel. Moreover, in this Embodiment, the holder | retainer 6 was produced with SUS304, However, You may form from resin. In the present embodiment, the balls 5 and 9 are made of silicon nitride. However, the balls 5 and 9 may be made of any one of high carbon chromium bearing steels such as SUS440C, SUS630, SUJ2, skin brushed steel, and high speed tool steel. Good.

  Further, in the present embodiment, the rotary shaft 30 is touched down to the inner peripheral surfaces of the inner rings 4 and 8, but the inner rings 4 and 8 are fixed and the rotating member is touched down to the outer peripheral surfaces of the outer rings 3 and 7. The touchdown bearing of the present invention can also be applied to the device.

It is a section explanatory view of one embodiment of the touchdown bearing of the present invention. It is a section explanatory view of a turbo molecular pump provided with a magnetic bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Angular contact ball bearing 2 Angular contact ball bearing 3 Outer ring 4 Inner ring 5 Ball (rolling element)
6 Cage 7 Outer ring 8 Inner ring 9 Ball (rolling element)
DESCRIPTION OF SYMBOLS 10 Cage 10a Weight addition part 11 Pocket 11a Upper part 23 of pocket inner peripheral surface Rotating shaft 25 Radial magnetic bearing 26 Radial magnetic bearing 27 Axial magnetic bearing 28 Touchdown bearing (deep groove ball bearing)
29 Touchdown bearings (angular ball bearings)
30 Rotating shaft (Rotating member)

Claims (2)

A touch-down bearing for a magnetic bearing device in which one of an inner ring and an outer ring is arranged to face a rotating member supported by a magnetic bearing, and a ball held by a cage is incorporated between the inner ring and the outer ring. ,
The touch-down bearing according to claim 1, wherein the cage includes a weight addition portion that protrudes downward in the axial direction from an end surface of the inner ring or the outer ring.   The touch-down bearing according to claim 1, wherein at least an axially upper portion of a pocket inner peripheral surface of the cage is processed into a spherical shape along the shape of the ball.

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