JPH11257353A - Touch-down bearing for magnetic bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize maximum life by forming a holder of copper metal including lead, and arranging a ball rolling surface on which a lead coated film is formed and a surface which is brought into contact with a rotating member at the time of touch-down when molybdenum disulfide coated film is formed, on surfaces of inner and outer wheels arranged opposing to the rotating member. SOLUTION: A holder 9 is formed on an annular member of copper metal including lead such as lead bronze by mechanically working a pocket hole to which a ball 10 is fitted. A lead coated film 16 is formed on a ball rolling surface 15 of an inner wheel 7 opposed to a rotary shaft 2, and a coated film 17 of molybdenum disulfide is formed on a surface of the other inner wheel 7 by means of sputtering. Lead of the lead coated film 16 on the ball rolling surface 15 is transferred to a ball 10 surface by rotating motion, and it is lubricated. When lead on the rolling surface 15 or the ball 10 surface is shortened by repeating of abrasion between the inner and outer wheels 7, 8 and the ball 10, lead contained in the holder 9 is filled. At the time of touch-down, a contact surface is lubricated by the coated film 17. It is thus possible to resist this device under several times of touch-down, and it is also possible to stabilize a performance, and improve a work efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a touch-down bearing for supporting a rotating member when a magnetic bearing device cannot be controlled.

[0002]

2. Description of the Related Art In a conventional magnetic bearing device, as shown in FIG. 1, touch-down bearings 3 and 4 are disposed at both ends of a rotating shaft 2 which is supported in a non-contact manner by a magnetic bearing 1, so that sudden disconnection or disconnection may occur. When the magnetic bearing 1 becomes uncontrollable due to a power failure or the like, the touchdown bearings 3 and 4 support the rotating shaft 2 to prevent the magnetic bearing 1 and the rotating shaft 2 from being damaged.

FIG. 2 shows the structure of the lower touch-down bearing 3 in the above-mentioned device. This bearing 3 is a front combination of two angular ball bearings 5 and 6, both of a radial load and an axial load. I am receiving it.
Each of the angular ball bearings 5, 6 is formed by incorporating a plurality of balls 10 held by a retainer 9 between an inner ring 7 and an outer ring 8. Is provided so that a preload is not applied to the bearing due to thermal expansion of the inner ring.

In the touch-down bearing 3 having the above structure, the inner ring 7 faces the rotating shaft 2 and the inner diameter surface thereof is the touch-down surface 1.
It becomes 2. On the other hand, in FIG. 1, in a structure in which the housing is rotated and the housing is supported by a magnetic bearing provided on a central shaft, the outer ring 8 of the touch-down bearing is provided.
Is opposed to the housing which is a rotating member, and touchdown is performed on the outer diameter surface thereof.

[0005]

The above-mentioned touch-down bearing has conventionally been considered as an emergency use, so that it is unavoidable that the touch-down bearing becomes unusable by one or two touch-downs. I was But,
To replace the unusable touchdown bearing, disassemble the magnetic bearing device, replace the bearing, and then adjust the touchdown clearance between the inner ring or outer ring and the rotating member to the bearing clearance of the magnetic bearing. Since it is necessary to perform an operation of assembling the bearing device while adjusting with high accuracy, there is a problem that the operation is extremely troublesome. For this reason, recently, there has been a demand for a structure capable of increasing the durability of the touch-down bearing and enduring a large number of touch-downs.

However, in the conventional touchdown bearing, the ball rolling surface and the sliding surface are formed of a combination of a ball and a cage material which does not cause seizure, or a solid lubricant for lubrication in a vacuum. Although a lubricating structure is used, no consideration is given to the combination of materials and lubricants for obtaining optimal durability, and no guideline has been established for improving the service life. It is.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a touchdown bearing capable of providing a condition of an optimal combination of a lubricant and a material of a cage and realizing a longest life.

[0008]

In order to solve the above-mentioned problems, the present invention comprises an inner ring, an outer ring, and a ball held by a retainer incorporated between the inner ring and the outer ring. Or, in the touch-down bearing of a magnetic bearing device in which one of the outer rings is arranged to face a rotating member supported by a magnetic bearing, the retainer is formed of a lead-containing copper-based metal,
A structure having a ball rolling surface on which a lead coating is formed and a surface which is in contact with the rotating member at the time of touchdown, on which a coating of molybdenum disulfide is formed, on a surface of an inner ring or an outer ring which is disposed to face the rotating member. It was done.

Here, the above-mentioned lead-containing copper-based metal is desirably three kinds of lead bronze.

[0010]

In the above-mentioned structure, the lead of the lead coating on the ball rolling surface is transferred to the ball surface by the rotational movement of the inner and outer races and the ball, thereby performing a lubricating action. Further, when lead on the rolling surface or the ball surface becomes insufficient due to repetition of friction between the inner and outer rings and the ball, lead contained in the cage is replenished to the rolling surface or the ball surface, thereby preventing depletion of the lubricant.

On the other hand, at the time of touchdown, the coating of molybdenum disulfide lubricates the contact surface between the inner ring or the outer ring and other members to prevent seizure and suppress wear.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of a touch-down bearing according to the present invention is the same as that of the conventional one shown in FIG. 2, in which a plurality of balls 10 are interposed between an inner ring 7 and an outer ring 8, and the balls 10 9 holds.

As shown in FIG. 3, the retainer 9 includes an annular member 13 made of a lead-containing copper-based metal such as lead bronze.
The pocket hole 14 into which the ball 10 fits is machined.

A lead coating 16 is formed on the ball rolling surface 15 of the inner ring 7 facing the rotating shaft 2. Molybdenum disulfide (sputtering) is formed on the surface of the inner ring 7 other than the ball rolling surface 15 by sputtering. A coating 17 of MoS ₂ ) is formed. In this case, molybdenum disulfide is sputtered on the surface of the inner ring 7 in a state where the ball rolling surface 15 is masked, since lead is not easily transferred onto the molybdenum disulfide coating 17. Lead is rubbed in, for example, by pressing a lead bar to form a lead coating 16.

The lead coating 16 thus formed on the ball rolling surface 15 acts as a lubricant for the ball 10 in the initial stage of rotation, and the lead transferred to the ball 10 is the lead contained in the cage 9. Serve to bring out

Further, lead-containing copper-based metals such as lead bronze and the like include:
Since the amount of released gas is smaller than other heat-resistant polymer materials under the conditions of vacuum and high temperature, the use in a high vacuum does not adversely affect the degree of vacuum.

The lead coating 16 and the molybdenum disulfide coating 17 as described above may be provided on the surface of the outer ring 8 on the fixed side, or may be provided only on the surface of the inner ring 7 in contact with the rotating shaft 2. A sufficient lubrication effect can be obtained.

On the other hand, the inner ring 7 and the outer ring 8 are formed of bearing steel such as SUJ2 or stainless steel such as SUS440C, and the ball 10 is formed of hardened steel or ceramics. In particular, since ceramic balls such as SiN hardly adhere to the iron material, there is no seizure and high wear resistance can be obtained. However, the material is not limited to such a material, and any other material can be selected as long as the combination has high abrasion resistance and hardly causes seizure.

The touch-down bearing shown in FIG. 2 has a structure in which the angular ball bearings 5 and 6 are combined in a front view. However, in the case of a structure that receives only a radial load (the upper touch-down in the magnetic bearing device shown in FIG. 1). As the bearing 4), a single-row deep groove ball bearing as shown in FIG. 4 can be used.
In this case, as shown in FIG. 5, the retainer 9 'is configured such that the annular members 18a and 18b divided into two in the width direction are attached to the rivet 1.
9 to be integrally fixed.

In the embodiment, the structure in which the rotating shaft 2 is touched down by the inner ring 7 is shown. However, the present invention can be applied to a device in which the inner ring 7 is fixed and the outer ring 8 is touched down by the rotating member. In this case, a lead coating 16 is formed on at least the ball rolling surface of the outer ring 8, and a molybdenum disulfide coating 17 is formed on the other surfaces of the outer ring 8.

-Experimental Examples- The present inventor conducted various experiments in order to find out the most suitable cage material, lubricant type, and the best combination thereof in order to bring out the improvement of the durability life. Next, an experimental example will be described.

(Experimental Example 1) The cage has an important role of guiding the ball rotatably and replenishing lead as a lubricant to the ball member rolling surface, and has stable torque characteristics,
A lead-containing structure suitable for replenishment is required.

Therefore, in Experimental Example 1, in order to know the material of the cage having the above-mentioned optimum characteristics, the cage was made of two types, three types, and four types of lead bronze having the components shown in Table 1. Each was formed, and a rotation test was performed using them to examine the torque characteristics of the bearing and the weight change of each part.

[0024]

[Table 1]

In the rotation test, the various cages described above were mounted on a ball bearing in which lead was previously rubbed into the ball rolling surface, and the ball bearing was mounted on a rotating shaft placed under high vacuum and high temperature. , And the change in friction torque of the bearing when the rotating shaft was rotated to a predetermined total load speed was measured.
Table 2 shows the conditions of the rotation test.

[0026]

[Table 2]

FIG. 6 to FIG. 8 show the test results of the torque characteristics. As shown in FIG. 6, when two kinds of lead bronze were used for the retainer, a sudden increase in torque occurred until the total load rotational speed was reached, and the life was extended. On the contrary,
As shown in FIGS. 7 and 8, when three or four types of lead bronze were used, a stable torque was obtained until the total load rotational speed was reached. In this case, the four types of lead bronze exhibited higher torque values than the three types.

On the other hand, Table 3 shows the weight change of each part after the test in the various test bearings described above.

[0029]

[Table 3]

As shown in this table, when three types of lead bronze are used for the retainer, the weight change of each part and the retainer is the smallest, efficient lubrication is achieved with a slight wear of the retainer, and It can be seen that the lubrication state was maintained for a long time. Also,
The ball rolling surface after the test showed a smooth surface, confirming the low wear torque.

On the other hand, in the case of the four types of lead bronze, the wear loss of the cage was large, and the weight increase of the steel ball due to the transfer of the material was large. In addition, it was observed that a large amount of lead remained on the surface of the ball rolling surface after the test, and it was considered that the residual lead caused a higher friction torque 7 than the three types of lead bronze. Can be

On the other hand, in the case of the two types of lead bronze, although the test time was shorter than that of the other test products, the friction loss of the cage was large, and the ball rolling surface after the test showed a rough state. .
This is because the two types of lead bronze do not have enough lead content to compensate for the shortage of lead on the ball rolling surface, and when the lubrication effect of lead previously rubbed into the ball rolling surface disappears, lubricant depletion occurs. ,
As a result, it is inferred that the wear of the cage rapidly progressed, and the life of the cage was reached due to the bite of the wear powder.

From the above, lead bronze types 3 and 4 include:
Although there is enough lead content to replenish the lack of lubricant on the ball rolling surface, the three types of lead bronze are superior in terms of strength and torque characteristics for holding the ball. It has been shown that three types of lead bronze are most suitable as the material for the above.

(Experimental Example 2) On the other hand, it is known that a fixed lubricant film having a low evaporation pressure exhibits good lubricity on a sliding surface in a vacuum. Therefore, in Experimental Example 2, various solid lubricants (molybdenum disulfide (MoS ₂ ), silver (A
g) and lead (Pb)) were examined to show the best lubrication performance.

The test was conducted by forming a film of the above-mentioned various lubricants on the rolling surface of the rolling bearing, and applying a 1 kgf thrust load in a vacuum to the rolling bearing at a rotation speed of 2500 rpm. Then, the change in friction torque of the bearing was measured. FIG. 9 shows the test results divided into the initial, middle, and late stages of the rotation test.

As shown in FIG. 9, in the case of silver or lead, the torque gradually increases, whereas in the case of molybdenum disulfide, the torque change falls within an extremely small range.
It was shown that molybdenum disulfide exerts excellent lubrication performance on sliding surfaces in vacuum.

(Experimental Example 3) According to the experimental examples 1 and 2, the results were obtained that three kinds of lead bronze were most suitable as the material of the cage and molybdenum disulfide was most suitable as the lubricant of the sliding surface. In Experimental Example 3, the optimum conditions for improving the life were determined for the combination of these materials with the materials of the inner and outer rings and the balls.

FIG. 10 shows the structure of the test apparatus used in this experiment. This test apparatus rotatably supports a main shaft 25 inside a housing 21 having a vacuum port (exhaust port) 22 via a test bearing 23 and a dummy bearing 24, and rotates the main shaft 25 inside the housing 21. An induction motor 26 to be driven is incorporated. Also, the housing 21
A load adjusting screw 27 and a disk spring 28 are attached to the end of the test bearing 23 so that the axial preload and load applied to the test bearing 23 can be adjusted by operating the screw 27.

As the test bearing 23, a single-row ball bearing was used, so that only a load in the axial direction was received. Further, an infrared radiation thermometer was attached to the inner ring of the test bearing, and a measurement window 29 for reading the temperature of the radiation thermometer was provided on the front surface of the housing 21.

In the test, first, the preload of the test bearing 23 was adjusted by the load adjusting screw 27, the inside of the housing 21 was evacuated, and then the main shaft 25 was rotated at rated speed. Next, 300 kgf is applied to the test bearing 23 by operating the load adjusting screw 27.
The axial load was applied, and at the same time, the main shaft 25 was decelerated at a constant acceleration. At that time, the output value Kw of the induction motor 26 and the temperature change of the inner ring of the test bearing 23 were measured until the test bearing 23 was completely stopped. . In this case, the acceleration for decelerating the main shaft 25 was a constant acceleration of -70 rpm / min.

Table 4 shows the test bearing combination conditions used in this experiment.

[0042]

[Table 4]

In the above table, both the inner and outer rings are SU
A hardened product of J2 was used. In addition, the sample No. 5
In order to see the effect of replenishing the lubricant by the cage made of lead bronze, a total ball type ball bearing in which only the balls are incorporated between the inner and outer rings without using the cage is used.

11 to 15 show sample Nos. In Table 4 respectively. 1 to No. 5 shows the test results.

The following summarizes these test results.

(1) As shown in FIGS. 11 and 13 (Sample No. 1 and Sample No. 3), when molybdenum disulfide (MoS ₂ ) was used as the lubricant on the ball rolling surface, immediately after touch down In many cases, the torque suddenly increased. This indicates that the coating of molybdenum disulfide is not suitable for lubrication of the ball rolling surface, and that replenishment of lubricant from a lead bronze cage cannot be expected.

(2) As shown in FIGS. 12 and 14 (Sample Nos. 2 and 4), when lead (Pb) is used as the lubricant on the ball rolling surface, good touch-down characteristics are obtained. was gotten. Further, according to the test results, when SUJ2 was used as the ball material (sample No. 2),
The torque fluctuation during the touchdown was large, and when ceramics (Si ₃ N ₄ ) was used as the ball material (sample No. 4), more stable torque characteristics were exhibited.

(3) As shown in FIG.
o. 5) In the case of the total ball type, the torque immediately after the touchdown is low, but after a short time, the torque rapidly increases. It is considered that the lack of a lubricant replenishing function from the cage resulted in insufficient lubrication of the ball rolling surface, which caused an increase in torque.

From the above test results, it is understood that lead is suitable for the lubricant on the ball rolling surface, and stable torque characteristics can be obtained by replenishing lead from the cage. However, according to the results of Experimental Example 2, molybdenum disulfide shows better lubrication performance than lead on the sliding surface between metals, and the lubrication of the touch-down surface on the inner ring and the guide surface of the cage is It is believed that a molybdenum coating is more suitable.

From the results of Experimental Examples 1, 2, and 3, the following combinations can be cited as conditions for realizing the optimum durability life.

For lubrication, a coating of lead is applied to the ball rolling surface, and a coating of molybdenum disulfide is applied to the surface of the raceway which comes into contact with other members.

The retainer is made of three types of lead bronze.

The material of the ball is ceramics (SiN
system).

Under the above conditions, even if the retainer is made of four kinds of lead bronze, the lubricant can be stably replenished for a long time.

Further, even if the material of the ball is SUJ2, although the torque is slightly increased, it can be sufficiently used.

[0056]

As described above, the present invention provides a condition for providing an optimal durability life for a touch-down bearing, which has not been established in the past, and realizes a durability that can withstand a large number of touch-downs. This has the effect of stabilizing the performance of the magnetic bearing device and improving the work efficiency.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a magnetic bearing device.

FIG. 2 is a sectional view showing a touch-down bearing.

FIG. 3 is a perspective view showing a part of the retainer according to the first embodiment;

FIG. 4 is a sectional view showing another touchdown bearing.

FIG. 5 is a perspective view showing a part of the retainer of the above.

FIG. 6 is a graph showing torque characteristics of a cage made of two kinds of lead bronze.

FIG. 7 is a graph showing torque characteristics of a cage made of three kinds of lead bronze.

FIG. 8 is a graph showing torque characteristics of a cage made of four kinds of lead bronze.

FIG. 9 is a graph showing torque characteristics of various fixed lubricants.

FIG. 10 is a structural diagram of a test apparatus of Experimental Example 3;

11 shows the results of Sample No. 3 in Experimental Example 3. FIG. 1 is a graph showing a touch-down characteristic.

FIG. 2 is a graph showing a touchdown characteristic.

FIG. Graph showing the touchdown characteristics of No. 3

FIG. 14 shows sample Nos. 4 is a graph showing a touch-down characteristic.

FIG. 5 is a graph showing a touchdown characteristic.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic bearing 2 Rotating shaft 3, 4 Touchdown bearing 5, 6 Angular contact ball bearing 7 Inner ring 8 Outer ring 9, 9 'Cage 10 Ball 12 Touchdown surface 15 Ball rolling surface 16 Lead coating 17 Molybdenum disulfide coating

Claims (2)

[Claims] 1. An inner ring, an outer ring, and a ball held by a retainer incorporated between the inner ring and the outer ring. One of the inner ring and the outer ring is opposed to a rotating member supported by a magnetic bearing. In the touch-down bearing of the magnetic bearing device, the retainer is formed of a lead-containing copper-based metal, and a ball coating is formed on the surface of an inner ring or an outer ring that is disposed to face the rotating member, with a lead coating formed thereon. A touch-down bearing for a magnetic bearing device, comprising: a surface; and a surface in contact with a rotating member at the time of touch-down, in which a molybdenum disulfide coating is formed. 2. The touch-down bearing for a magnetic bearing device according to claim 1, wherein the lead-containing copper-based metal is made of three kinds of lead bronze.