JP2006153240A - Touchdown bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide superior durability compared to the case of using balls made of conventional stainless steel or bearing steel, and to carry around at the time of non-touchdown as in the case of using balls made of ceramics, and difficulty in ground treatment. Provided is a touch-down bearing capable of overcoming the poor adhesion of a solid lubricant and the like.
SOLUTION: By making balls 3 made of high-speed tool steel, the hardness at a temperature (200 to 300 ° C.) expected at the time of touchdown as compared with stainless steel and bearing steel used for inner ring 1 and outer ring 2 is achieved. To prevent premature damage due to the heat generated by the balls 3, thereby improving the durability of the bearing.
[Selection] Figure 1

Description

  The present invention relates to a touch-down bearing for protecting a rotating body supported by a magnetic bearing in a turbo molecular pump when the rotation is stopped or abnormal.

  In the turbo molecular pump, a configuration in which a rotating body including an exhaust blade is supported by a magnetic bearing in a non-contact manner is often used. An example is shown in a sectional view in FIG. In this example, a fixed blade 11 is disposed on the inner periphery of the case 10, and a rotating shaft 13 having a rotating blade 12 fixed on the outer periphery is rotatably disposed in the case 10. The rotary shaft 13 is rotated by an electric motor 14, and in the rotated state, the rotary shaft 13 is integrally formed with the two radial magnetic bearings 15 and 16 disposed close to the outer peripheral surface of the rotary shaft 13 and the rotary shaft 13. A pair of axial magnetic bearings 17 disposed above and below the flange portion 13a are supported in a non-contact state in a magnetically levitated state. In the figure, 9 is an intake port and 8 is an exhaust port.

  In the case 10, one full ball type deep groove ball bearing 21 and a pair of angular ball bearings 22 in which the oblique contact directions are combined in opposite directions are arranged as touchdown bearings. These touch-down bearings 21 and 22 are rolling bearings for protecting the rotating shaft 13 from the radial magnetic bearings 15 and 16 and the axial magnetic bearing 17 from being damaged when the rotating shaft 13 is stopped or when the control is abnormal. The gap between the outer peripheral surface of the rotary shaft 13 and the inner peripheral surface of the inner ring of each touchdown bearing 21, 22 is slightly smaller than the gap between the rotary shaft 13 and the magnetic bearings 15, 16, and 17. Is intervening. Thereby, in the state where the rotating shaft 13 is rotatably supported by the magnetic bearings 15, 16 and 17 in a magnetically levitated state, the rotating shaft 13 maintains a non-contact state with respect to the touchdown bearings 21, 22. When the shaft 13 is stopped or when the control is abnormal due to the action of an external force or the like, the rotating shaft 13 contacts the inner rings of the touch-down bearings 21 and 22 and is rotatably supported before contacting the magnetic bearings 15, 16 and 17.

  Although the example in which the inner ring is a rotating ring has been described above, a structure in which a touch-down bearing is arranged inside the cylindrical rotating body using a cylindrical rotating body having rotating blades is known. It has been. In this structure, the outer ring of the touch-down bearing is arranged on the inner peripheral surface of the cylindrical rotating body through a predetermined gap, and the inner peripheral surface of the rotating body is the touch-down bearing when the rotating body is stopped or when the control is abnormal. The rotating body is rotated and supported in contact with the outer circumferential surface of the outer ring.

In the touchdown bearing in the vacuum pump as described above, the rolling element (ball) is made of stainless steel such as SUS440C, bearing steel such as SUJ2, or ceramics. Similarly, stainless steel such as SUS440C and bearing steel such as SUJ2 are often used as materials for the inner ring and the outer ring. In addition, since lubricating oil cannot be used due to its use environment, a coating made of various solid lubricants including molybdenum disulfide is formed on at least the contact surfaces of these members with other members (for example, patents). Reference 1).
JP 2002-221226 A

  By the way, in the touchdown bearing as described above, the rotating body comes into contact with the rotating wheel to start high-speed rotation at a stretch. Ball bearings often generate heat rapidly due to friction between the balls, and the balls are often damaged first. Therefore, when there is a problem in durability, ceramic balls are used.

  However, when ceramic balls are used, since ceramics are non-magnetic, the raceway ring (rotating ring) made of a ferromagnetic material is not touched by the magnetic field created by the magnetic bearing located close to the touch-down bearing. There is a problem in that the magnetic ball of the magnetic bearing is not in contact with the rotating body when it is down, but the ball made of ceramics is expensive and causes an increase in bearing cost. In addition, as described above, since this type of bearing cannot use lubricating oil, a solid lubricant film is formed on the surface of each component of the bearing. In the case of ceramic balls, a fixed lubricant film is used. Therefore, there is a problem that it is difficult to form a solid solid lubricant film.

  The present invention has been made in view of such circumstances, and has excellent durability as compared with the case of using conventional balls made of stainless steel or bearing steel, and various problems as in the case of using ceramic balls. The challenge is to provide a touch-down bearing that does not cause any problems.

  In order to solve the above-described problems, the touchdown bearing of the present invention is used in a turbo molecular pump having a rotating body supported by a magnetic bearing, and the inner ring or outer ring is applied to the rotating body only when the rotating body is stopped or abnormally rotated. In the touch-down bearing that supports the rotating body in contact with each other, the ball that is rotatably arranged between the inner ring and the outer ring is characterized by being made of high-speed tool steel.

  Here, in this invention, the structure (Claim 2) whose touchdown bearing of Claim 1 is a ball bearing of a total ball type can be employ | adopted suitably.

  The present invention intends to solve the problem by using a high-speed tool steel, which is a metal material having high high-temperature hardness, as the material of the ball that is a neck for durability of the bearing.

  That is, high-speed tool steel such as SKH4 is expected to reach the ball in the touchdown bearing at the time of touchdown, compared to bearing steel such as SUJ2 and stainless steel such as SUS440C. Hardness at a temperature of 200 to 300 ° C. is about 5 to 15 HRC. Therefore, it is possible to prevent early damage due to heat generation due to friction with the raceway due to rapid acceleration at the time of touchdown, and in addition, heat generation due to friction between balls in the case of the total ball type. Examples of the high-speed tool steel used for the balls include SKH4 and heat-resistant M50 (AISI standard).

  Since the high-speed tool steel is a magnetic material, the magnetic flux generated by the magnetic field of the magnetic bearings arranged close to each other reaches the fixed wheel through the rotating wheel and the ball, so that the rotating wheel does not rotate during non-touchdown. In addition, the ground treatment for the solid lubricant film is easy, and further, an increase in cost can be suppressed.

  According to the present invention, since the ball material is a high-speed tool steel, the hardness of the ball during heat generation during touchdown is higher than when using conventional stainless steel or bearing steel. It is possible to improve the durability of the bearing without causing early damage of the ball which is a neck of the durability of the bearing, and this effect is caused by the heat generated by friction between the balls as in the invention according to claim 2. By applying the present invention to the resulting all-ball type touchdown bearing, it becomes even larger.

  Also, compared to conventional touch-down bearings that use ceramic balls, the rotation of the rotating wheel is prevented, the adhesion of the solid lubricant film is improved due to the ease of surface treatment, and the cost is reduced. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a front view of an embodiment in which the present invention is applied to a touch-down bearing comprising a full ball type deep groove ball bearing in FIG. 3, and FIG. 2 is an enlarged axis parallel sectional view thereof.

  In this example, the inner ring 1 and the outer ring 2 are each SUS440C that is martensitic stainless steel, and a plurality of balls 3 made of SKH4 that is high-speed tool steel are disposed therebetween.

  On the surfaces of the inner ring 1 and the outer ring 2, fine irregularities by shot blasting or the like are formed as a base treatment, and a molybdenum disulfide film that is a solid lubricant is formed thereon, whereby the molybdenum disulfide film is formed on the inner ring 1 and the outer ring 2 are in close contact with the surface.

On the other hand, the surface of the ball 3 is formed with a zinc calcium phosphate-based film represented by the chemical formula (Zn ₂ Ca) (PO ₄ ) ₂ .2H ₂ O by chemical conversion treatment. A molybdenum disulfide film is formed. The zinc calcium phosphate coating bites into and firmly adheres to the surface of the ball 3 made of SKH4 which is a base material during chemical conversion treatment, and fine irregularities due to crystal grains are formed on the coating surface. The adhesion of the molybdenum disulfide film formed to the zinc calcium phosphate film becomes strong, and the molybdenum disulfide film adheres firmly to the balls 3.

  According to the embodiment of the present invention described above, the SKH 4 that is the material of the ball 3 is in a high temperature (200 to 300 ° C.) state that is expected due to heat generated by friction between the inner ring 1, the outer ring 2, and the ball 3 at the time of touchdown. Hardness is about 5 to 15 higher in HRC than in the case of using SUJ2, SUS440C, etc. Therefore, premature damage due to heat generation during touchdown is less likely to occur, and the ball 3 of molybdenum disulfide film formed on the surface Combined with the high adhesion to the bearing, the durability of the bearing is greatly improved.

  In addition, the cost can be reduced compared with the case where ceramic balls are used, and the inner ring 1 can be rotated at the time of non-touchdown by the magnetic field of the magnetic bearing close to the turbo molecular pump when it is incorporated. Absent.

  In the above embodiment, an example in which the present invention is applied to a full-groove type deep groove ball bearing has been described. However, the present invention can be equally applied to ball bearings other than the full-ball type provided with a cage. The high-speed tool steel used for the balls 3 is not necessarily limited to SKH4, but it is preferable to use SKH4 or a similar high-speed tool steel from the viewpoints of availability, cost, workability, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of an embodiment in which the present invention is applied to a touch-down bearing composed of a full ball type deep groove ball bearing for a turbo molecular pump. FIG. 2 is an enlarged axis parallel cross-sectional view of FIG. 1. It is sectional drawing which shows the structural example of the turbo-molecular pump provided with the touchdown bearing.

Explanation of symbols

1 Inner ring 2 Outer ring 3 Ball

Claims (2)

In a touchdown bearing that is used for a turbo molecular pump having a rotating body supported by a magnetic bearing and supports the rotating body by contacting the rotating body with the inner ring or the outer ring only when the rotating body is stopped or rotating abnormally,
A touch-down bearing, wherein a ball that is freely rollable between the inner ring and the outer ring is made of high-speed tool steel.   The touchdown bearing according to claim 1 is a ball bearing of a total ball type.

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