JP2002168252A - Touchdown bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the life of a bearing by forming a hard-to-exfoliate film on the surface of each inner and outer ring of a touchdown bearing used in a corrosive atmosphere such as fluorine gas. SOLUTION: A bearing having a rolling body made of ceramic wherein a chrome-nitride film (CrN2 or CrN) or a zirconium-nitride film (ZrN) is formed on the surface opposing a raceway plane of each inner and outer ring, and a rotating member is employed as the touchdown bearing 13 for holding a rotating shaft 12a of a crossflow fan 12 of a argon-fluoride excimer-laser oscillating device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is installed together with a magnetic bearing,
The present invention relates to a touchdown bearing that functions as a bearing when control of a magnetic bearing is impossible.

[0002]

2. Description of the Related Art A touchdown bearing is a rolling bearing installed together with a magnetic bearing. When the magnetic bearing becomes uncontrollable due to some trouble, the surfaces of the inner and outer rings facing the rotating member come into contact with the rotating member. It functions as a bearing (by touchdown) to protect the magnetic bearing and the rotating member.

[0003] Conventionally, it has been required to increase the durability of the touch-down bearing. Therefore, in the case of a touch-down bearing used in a vacuum, molybdenum disulfide or the like is formed on the surfaces of the rolling elements and the inner and outer rings. Of solid lubricants, and plating films of soft metals such as gold, silver, lead, and the like. On the other hand, the semiconductor integrated exposure by a laser beam having a short wavelength with the ultra-high integration has been performed in the circuit, the shortest wavelength (193 nm) Development of argon fluoride excimer laser in a noble gas halide excimer laser Has also been done. In a rare gas halide excimer laser, a raw material gas (a gas containing a rare gas and a halogen gas) is put in a space sealed to several atmospheric pressures, and a high-voltage pulse is applied to the gas to be composed of rare gas atoms and halogen atoms. This is a gas laser that produces excimer and oscillates a laser, and has a mechanism for circulating the source gas introduced into the closed space.

As this gas circulation mechanism, for example, a cross flow fan is disposed in a closed space. This cross flow fan is arranged in an enclosed space, and both ends of its rotating shaft are supported by magnetic bearings outside the enclosed space,
A touchdown bearing is provided between the rotating shaft and a housing forming a closed space.

[0005]

In a touchdown bearing in which the rotating shaft of a cross flow fan is supported by an argon fluoride excimer laser, the above-mentioned coating film or plating film is formed on the surfaces of the rolling elements and the inner and outer rings. In such a case, there is a problem that these films are partially peeled off at the time of touchdown and scattered in a closed space, thereby contaminating the raw material gas. Further, there is also a problem that the touchdown bearing is corroded by fluorine gas in the sealed space and the life of the bearing is shortened.

The present invention has been made in view of such problems of the prior art. In a touchdown bearing used in a corrosive atmosphere such as fluorine gas, the touchdown bearing is formed on the surface of an inner or outer ring or the like. An object of the present invention is to make it difficult for the coating to peel off and to improve the bearing life.

[0007]

In order to solve the above-mentioned problems, the present invention provides a touch-down bearing which is installed together with a magnetic bearing and functions as a bearing when the magnetic bearing cannot be controlled. A touch-down bearing characterized in that a chromium nitride (CrN ₂ or CrN) film or a zirconium nitride (ZrN) film is formed on a raceway surface of an inner / outer ring and a surface facing a rotating member (a rotating shaft or a housing). To provide.

[0008]

Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram showing an argon fluoride excimer laser oscillation device provided with a touchdown bearing according to an embodiment of the present invention. This device comprises a closed chamber 10, a laser oscillation section 11, a cross flow fan 12
, A rotary shaft 12a of the cross flow fan 12, a touchdown bearing 13, a radial magnetic bearing 14, a sensor coil 15, and a drive motor 16 for driving the rotary shaft 12a.
, A thrust magnetic bearing 17 and a sealed shield thin wall 20.

A laser oscillation section 11 is provided in an upper portion of the closed chamber 10. A cross flow fan 12 is provided below the laser oscillation unit 11 in the closed chamber 10. The gas (gas containing argon gas and fluorine gas) in the closed chamber 10 is circulated and sent to the laser oscillation unit 11 by the cross flow fan 12. Both ends of the rotation shaft 12a of the cross flow fan 12 are
On the outer side of the shaft 0, it is supported by the radial magnetic bearing 14 and the thrust magnetic bearing 17 in a non-contact state. The touchdown bearing 3 is provided between the rotation shaft 12 a of the cross flow fan 12 and the housing of the closed chamber 10.

The radial magnetic bearing 14 includes a stator portion 14b having a coil 14a and a rotor portion 1 on the rotating shaft 12 side.
4c. Since the inductance of the sensor coil 15 changes based on the change in the radial gap between the radial magnetic bearing 14 and the rotating shaft 12a, the sensor coil 15
Is detected by the controller, and feedback control is performed to increase or decrease the amount of current flowing through the coil 14a of the stator portion 14b in accordance with the detected value.
The radial gap is kept constant.

The drive motor 16 includes a stator 16b having a coil 16a and a rotor 16c on the rotating shaft 12a side.
Consists of A portion of the rotating shaft 12 protruding from the sealed chamber 10 is surrounded by a sealed shield thin wall 20, and the radial magnetic bearing 14, the drive motor 16, and the thrust magnetic bearing 17 are
It is arranged outside this closed shield thin wall 20. This prevents the gas in the sealed chamber 10 from leaking to the outside.

The touch-down bearing 13 has a reference number 6814.
Of consists of a deep groove ball bearings, ball is made of ceramics, S
A chromium nitride (CrN ₂ or CrN) film or a zirconium nitride (ZrN) film having a thickness of 2 to 3 μm is formed on the entire surface of an inner ring and an outer ring made of US440C by an ion plating method. Touchdown bearing 1
A gap smaller than the gap between the radial magnetic bearing 14 and the rotating shaft 12a is provided between the inner ring 3 and the rotating shaft 12a. Inner ring of touchdown bearing 13 and rotating shaft 12a
A gap smaller than the gap between the radial magnetic bearing 14 and the rotating shaft 12a in the radial direction
Small gap than the gap between the thrust magnetic bearing 17 and the rotary shaft 12a is provided, respectively.

[0013] Thus, the rotary shaft 12a is in the normal, it is rotatably supported by the radial magnetic bearing 14 and the thrust magnetic bearing 17, the inner ring of the touchdown bearing 13 when these bearings becomes uncontrollable touchdown bearing Will function as For example, when the radial magnetic bearing 14 cannot be controlled, contact between the ceramic ball and the coating on the raceway surface and contact between the coating on the inner peripheral surface of the inner ring and the rotating shaft occur. Absent. Moreover, since it is difficult this film is corroded by fluorine gas,
The bearing life of the touch-down bearing 13 is longer than that of the conventional product.

[0014]

Embodiments of the present invention will be described below. The deep groove ball bearing model numbers 6814 was prepared by the following method.
The ball was made of zirconia. The inner ring and outer ring were obtained by the following procedure. First, after forming a SUS440C material into a predetermined shape, quenching and tempering were performed. Next, chromium nitride (CrN ₂ or CrN) is formed by ion plating.
A film was formed on the entire surface. Next, quenching and tempering in a vacuum furnace were performed to recover the hardness reduction due to the formation of the film, thereby obtaining HRCs 58 to 62.

[0015] Incidentally, coating by ion plating
Is formed using the apparatus shown in FIG. 2 as follows.
Was. First, open the upper lid 1 of this device, and
Work (inner and outer rings) W to form a film
I do. After closing the upper lid 1, the inside of the chamber 2 is evacuated to
Vacuum (10^-Ten-10^-13Torr). Next, the evaporation material
Put chromium (Cr) into crucible 4
The deposition material (chromium) 3 is heated and melted by the beam gun 5.
To evaporate. At the same time, the reaction gas is
Nitrogen as a carrier gas with argon gas as a carrier gas
To increase the pressure in the chamber 2 to 10 ^-3-10^-FourTorr
Adjust to Further, the temperature of the work W is maintained at 400 ° C.
You.

Next, chromium vapor is glow-discharged by the plasma electron gun 6 to convert chromium into plasma. At the same time, the number negative high voltage (several hundreds to the work W 10
00V). As a result, chromium ions (Cr ²⁺ ) in the plasma move toward the negatively charged work W. The reaction between the chromium ions and the nitrogen gas in the chamber 2 occurs, and the surface of the work W has chromium nitride. Film (C
(rN ₂ or CrN) is formed.

In addition, as a comparative example, the same deep groove ball bearing having the same inner groove and outer ring with a titanium nitride film having a thickness of 2.5 μm and other points formed in the same manner as above was prepared. . This titanium nitride film was formed using the apparatus of FIG. 2 using titanium instead of chromium as the deposition material 3. The deep groove ball bearing thus obtained is attached to the argon fluoride excimer laser oscillation device of FIG. 1 as a touch-down bearing 13, and the touch is performed while supplying a gas containing argon gas and fluorine gas into the closed chamber 10. A life test of the down bearing 13 was performed. As the life test, the radial load was set to 78 N per one of the two touch-down bearings 13 installed, and the radial magnetic bearing 14 and the thrust magnetic bearing 17 were operated at a rotational speed of 5000 rpm for 30 minutes. After rotating 12a, the supply of power to the radial magnetic bearing 14 and the thrust magnetic bearing 17 was stopped for 5 minutes, and the vibration generated in the touch-down bearing 13 was measured. The touch-down bearing 13 was not lubricated.

For vibration measurement, a piezoelectric vibration sensor S
Was installed so as to contact the outer peripheral surface of the outer ring of the touchdown bearing 13. The drive motor 6 is stopped at the point where the vibration detection value from the sensor S sharply rises to stop the rotation of the rotating shaft 12a. At this time, the touch-down bearing 13 had damage on the coating on the inner peripheral surface of the inner ring, which is the touch-down surface (the damage caused unstable contact with the outer peripheral surface of the rotating shaft, and the vibration value suddenly increased. ), But there was little damage to the coating on the raceway surface.

This life test was conducted by preparing a large number of samples in which the thickness of the film formed on the inner ring and the outer ring was changed. The thickness of the coating performs film formation simultaneously to the inner ring and the test piece with the outer ring was measured by examining a cross section taken out of the test piece. In one sample, the inner ring and the outer ring having the same thickness of the film were combined.

FIG. 3 is a graph showing the results of the life test. The life ratio is a value where the life when the titanium nitride film having a thickness of 2.5 μm is “1”. The cost ratio is a ratio of the cost required for forming the film, and is a value in which the film forming cost in the case of forming a 0.5 μm-thick chromium nitride film is “1”. The horizontal axis of the graph in FIG. 3 indicates the thickness of the chromium nitride film.

As can be seen from this graph, by providing the inner ring and the outer ring with the chromium nitride film having a thickness of 0.5 μm or more, the life is longer than when the inner ring and the outer ring are provided with the titanium nitride film having a thickness of 2.5 μm. become longer. This is presumably because the titanium nitride film has a larger surface roughness than the chromium nitride film and has a higher wear coefficient under non-lubricated conditions, even if the film is formed by the same ion plating method. Up to 5 μm, the life becomes longer in proportion to the thickness of the chromium nitride film, but if it exceeds 5 μm, the life improvement effect is saturated. On the other hand, the cost increases in proportion to the thickness of the chromium nitride film and does not saturate.

Here, the radial gap between the touchdown bearing and the rotating shaft needs to be smaller than that of the radial magnetic bearing as described above. However, a radial gap that is relatively larger than that of a general rolling bearing can be provided. the thickness of the coating provided on the inner and outer races of the touchdown bearing is acceptable to 10 [mu] m. Therefore, the chromium nitride film is 0.5μ
It can be provided with a thickness in the range of m to 10 μm, but is preferably in the range of 1.0 to 5 μm.
If the thickness is less than 1.0 μm, the life-improving effect cannot be stably obtained,
If it exceeds 5 μm, the cost will increase despite the effect of improving the life being saturated.

It should be noted that a similar effect of improving the life can be obtained even when a zirconium nitride film is provided instead of the chromium nitride film. In the case of providing a zirconium nitride film, FIG.
In this case, zirconium may be used instead of chromium as the deposition material 3 to form a film. As can be seen from the above description, the rolling elements (balls) of the touch-down bearing arranged in the closed chamber (space in which the raw material gas (gas containing fluorine gas) is introduced) of the argon fluoride excimer laser oscillation device are made of zirconia. By providing a titanium nitride film or a zirconium nitride film on the inner ring and the outer ring, the life of the touch-down bearing is improved. Further, it is possible to prevent the film from peeling off at the time of touchdown and scattering into the closed space, thereby preventing the raw material gas from being contaminated.

In this embodiment, SUS440C is used as the material for the inner and outer rings, but high carbon chromium bearing steel (such as SUJ2) may be used. In this case, quenching and tempering for recovering the hardness are performed in a vacuum furnace. Further, in this embodiment, since holding the temperature of the workpiece W to 400 ° C. during the film formation, a strong film having adhesion can be obtained, it is carried out back hardened baked to restore hardness. If this temperature is set to 160 ° C., the adhesion of the obtained film is lower than that at 400 ° C., but quenching and tempering for recovering the hardness become unnecessary.
It is preferable in terms of cost. Thickness range of the film also in this case is preferably 1.0μm or more 5μm or less.

In this embodiment, the touchdown bearing for the rotating shaft of the crossflow fan of the argon fluoride excimer laser oscillation device (that is, the touchdown bearing used in an atmosphere containing fluorine gas) has been described. The present invention can also be applied to a touchdown bearing (for example, for a rotary shaft of a turbo-molecular pump) used in a usage environment where a lubricant cannot be used under vacuum.

[0026]

As described above, according to the present invention,
In a touchdown bearing used in a corrosive atmosphere such as fluorine gas, a film formed on the surface of the inner and outer rings and the like is less likely to peel off, and the life of the bearing is improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an argon fluoride excimer laser oscillation device provided with a touchdown bearing according to an embodiment of the present invention.

FIG. 2 is a view showing an apparatus for forming a film by an ion plating method used in Examples.

FIG. 3 is a graph showing a result of a life test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Top cover 2 Chamber 3 Evaporation material (chrome) 4 Crucible 5 Electron beam gun 6 Plasma electron gun 10 Enclosed chamber 11 Laser oscillation part 12 Cross flow fan 12a Cross-flow fan rotating shaft (rotating member) 13 Touch-down bearing 14 Radial magnetic bearing 15 Sensor coil 16 Drive motor 17 Thrust magnetic bearing 20 Sealed shield thin wall S Vibration sensor W Work

Continuation of the front page (72) Inventor Kazutoshi Sakaguchi 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA54 AA62 BA10 DA05 EA41 EA42 EA78 FA08 FA31 GA60 3J102 AA01 AA09 BA03 BA19 CA08 CA14 FA06 FA12 GA18 5F071 AA06 EE04 FF09 JJ03

Claims (1)

[Claims] 1. A touch-down bearing which is installed together with a magnetic bearing and functions as a bearing when control of the magnetic bearing is impossible. The rolling element is made of ceramic, and a chromium nitride is provided on a raceway surface of the inner and outer rings and a surface facing the rotating member. (CrN ₂ or C
(Nr) coating or zirconium nitride (ZrN) coating.