JPH06272715A - Rolling member - Google Patents

Abstract

PURPOSE:To form a lubricating film on a rolling member that has a long life and has been enhanced in reliability without dispersion in the load-resisting performance. CONSTITUTION:When a lubricating film by means of molybdenum disulfide MoS2 is formed on a rolling member such as a screw spindle of a ball screw, ball nut and ball, inner or outer race and ball of a rolling bearing, a high frequency voltage is applied both to the electrode 21 of the base table 22 on which a rolling member W has been placed and to the electrode 23 arranged thereabove so as to be opposite to the electrode 21 through a high-frequency power supply 24; thereby ion bombardment is carried out, for example, for 60 minutes or more for cleaning the rolling member W. Then, the polarities of the electrodes 21 and 23 are reversed, and prespattering is carried out while inserting a shutter between the electrode 23 and the rolling member W, for cleaning a target T, and further after the shutter has been removed, regular spattering is carried out while keeping the rolling member W at a temperature below 50 deg.C, so that a film in which the molecular weight ratio S/Mo of MoS2 is 1.7 or more and is less than 2.0 and whose thickness is approximately 1mum is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to rolling bearings used in space equipment, semiconductor manufacturing equipment and the like in the atmosphere, vacuum and special environments, and rolling members such as ball screws.

[0002]

2. Description of the Related Art As a conventional rolling bearing as a rolling member, for example, Japanese Patent Application Laid-Open No. 2-24 previously proposed by the present applicant.
There is one disclosed in Japanese Patent No. 5514. This conventional example is an outer ring, an inner ring, a plurality of rolling elements interposed between the outer ring and the inner ring, and a rolling bearing consisting of a cage that divides and holds the rolling elements equally in the circumferential direction, A lubricating film made of molybdenum disulfide (MoS ₂ ) is formed on at least the rolling elements of the outer ring, the inner ring and the rolling elements by sputtering means, and the cage is made of linear polyphenylene sulfide as a matrix and at least the fluororesin of 10 to 6 is used.
By including 0 wt%, lubricity is imparted to both the rolling elements and the cage that are slippery, sufficient lubricating performance is obtained, and low torque and long life can be achieved. .

[0003]

However, in the above-mentioned conventional rolling bearing, in the lubricating coating formed by simply using the molybdenum disulfide sputtering method,
Film forming conditions of spatter, sliding life, surface morphology, composition ratio,
Although the relationship with orientation, etc. has been described, the relationship between rolling life and surface shape, composition ratio, and orientation has not been studied at the present time. There is an unsolved problem that load bearing performance varies due to the absence of the above, and there is a problem in life and reliability.

That is, as described in Proceedings of Tribology Conference of Japan Society of Lubrication (Fukuoka) (1991), page 563, and Aerospace Laboratory Report TR-903, the wear life of MoS ₂ sputtered film which is a solid lubricating film. Is described to be affected by a cleaning method, an ion pumping treatment, etc., but those treatment methods and the surface morphology and orientation of the coating are not mentioned.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and provides a rolling member which has no variation in load-carrying performance, has a long life, and can improve reliability. It is intended to be provided.

[0006]

In order to achieve the above object, the rolling member according to the present invention has a lubricating coating formed by coating molybdenum disulfide on the rolling surface with which the mating member makes rolling contact. In the rolling member, the lubricating coating is
1. The molecular weight ratio S / Mo of sulfur and molybdenum is 1.7 or more.
It is characterized by being formed of a molybdenum disulfide film having a composition selected to be less than 0.

[0007]

In the present invention, the molecular weight ratio S / Mo of molybdenum disulfide constituting the lubricating coating is selected to be 1.7 or more and less than 2.0, whereby a hilllike and dense lubricating coating is formed. Therefore, the load bearing performance is improved, the coating life is extended and stabilized, and the reliability can be improved. When the molecular weight ratio S / Mo of molybdenum disulfide is set to less than 1.7, the surface shape does not become a hill-like dense film,
It is a wavy short fiber, that is, a worm-like and rough lubricating film, which reduces load bearing performance and shortens the service life. On the other hand, sulfur S is blown out by the current sputtering method, so the molecular weight of molybdenum disulfide is reduced. The ratio S / Mo is exactly 2.
It is difficult to set it to 0, and as the molecular weight ratio S / Mo approaches 2.0 as much as possible, a hill-shaped and dense lubricating coating can be formed.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 respectively show a ball screw 1 and a rolling bearing 10 to which the present invention is applied. The ball screw 1 is made of a stainless steel (SUS630) screw shaft 2 having a thread groove 2a and a stainless steel (SUS440C). A lubricating film made of molybdenum disulfide (hereinafter referred to as MoS ₂ ) having a molecular weight ratio S / Mo of 1.7 or more and less than 2.0 is coated on the entire circumference of the ball 4 housed in the ball nut 3 by a sputtering process. Has been done,
The rolling bearings 10 are at least made of stainless steel (SU
The molecular weight ratio S / Mo is 1. on the inner circumference side raceway surface of the outer ring 11, the outer circumference side raceway surface of the inner ring 12, and the entire circumference of the ball 13 interposed between the outer ring 11 and the inner ring 12 manufactured in S440C).
A lubricating coating made of MoS ₂ of 7 or more and less than 2.0 is coated by the sputtering process,
Are held by the cage 14 at predetermined intervals.

The MoS ₂ sputtering process was performed using a high frequency magnetron sputtering apparatus 20 as shown in FIG. This high-frequency magnetron sputtering apparatus 20 includes a base 22 provided with an electrode 21.
A member W to be sputtered is placed on the upper surface of which an electrode 23 having, for example, MoS ₂ as a target T is placed in opposition thereto, and, for example, 13.56 MHz is placed between both electrodes 21 and 23.
The high frequency power source 24 is connected to the base 22 and the anode electrode 21, and cooling passages 25 and 26 through which a cooling medium flows are individually provided. In FIG. 3, 27 is an exhaust system including a vacuum rotary pump 28 and a turbo molecular pump 29, 30 is an argon cylinder, and 31 is a vacuum gauge.

Then, with the member W to be sputtered set in the high frequency magnetron sputtering apparatus, first, in a low pressure argon atmosphere with a pressure of 0.8 Pa, the electrode 21 is used as a cathode and the electrode 23 is used as an anode.
A high-frequency power of 800 W is supplied between them to perform low-pressure glow discharge, ion bombarding (reverse sputtering) for 180 minutes to clean the member W to be sputtered, and then reversing the polarities of the electrodes 21 and 23. In addition, the distance between the target T and the member W to be sputtered is set to 70 mm, the high frequency power density is set to 3.30 w / cm ^{2 in} a low pressure argon atmosphere of 0.67 Pa, and the distance between the target T and the member W to be sputtered is set. After the target T is cleaned by pre-sputtering for 30 minutes by inserting a shutter into the substrate, the shutter is removed and main sputtering is performed for 10 minutes.
And the molecular weight ratio S / Mo of the film thickness 0.3 to 1.0 μm is 1.7.
A MoS ₂ coating having a thickness of not less than 2.0 was formed. During this main sputtering, the temperature of the member W to be sputtered was controlled to 50 ° C. or lower.

Then, in order to test the durability life of the MoS ₂ coating formed by the above-mentioned sputtering treatment with the ball-on-disk tester in vacuum shown in FIG. 4, the material is stainless steel (SUS440C), the diameter is 52 mm, and the thickness is 52 mm. Three 10 mm discs were prepared, and two of these were subjected to the above-mentioned sputtering treatment so that the molecular weight ratio S / Mo was 1.
Test pieces (hereinafter referred to as Example 1 and Example 2) on which a MoS ₂ coating film having a thickness of 1 μm was formed at 9 and 1.7 were formed, and the molecular weight ratio S / Mo was 1.6 and during the main sputtering. The temperature of the disk as the member W to be sputtered is 150
A test piece (hereinafter referred to as a comparative example) on which a MoS ₂ coating was formed was formed by controlling the temperature to around 0 ° C., and a life test was performed on this in a ball-on-disk tester 40 in vacuum.

Here, the in-vacuum ball-on-disk testing machine 40 has a vacuum degree of 10 ^-4 to 10 ^-5 P as shown in FIG.
A rotary work table 44 having a rotary shaft 42 rotatably supported by a bearing 43 is rotatably disposed in a vacuum chamber 41 controlled by a, and a test piece W is placed on the rotary work table 44. On the upper surface side of the test piece W, a 5/16 inch ball 45 made of the same material as that of the test piece is weighted 4
Vertical load adjusted by 6 and balance weight 47 9.8N
The rotary shaft 42 is connected to the motor 49 via the magnetic fluid seal unit 48 and is rotationally driven so that the sliding speed with respect to the ball 45 is 1.5 m / s. The load cell 50 detects the torque according to the friction coefficient between the test piece W and the test piece W, that is, the contact resistance.

The above-mentioned ball-on-disk tester in vacuum was set in each of Examples 1 and 2 and Comparative Example, and tests were conducted to measure the total number of revolutions until the friction coefficient exceeded 0.2 as the coating life. The measurement results are shown in Table 1 below.

[0014]

[Table 1] As is clear from Table 1, the coating life of Examples 1 and 2 is significantly longer than that of Comparative Example, and in particular, Example 1 has a MoS ₂ molecular weight ratio S / Mo close to 2.0. The coating life is 5.0 × 10 ^5, and the molecular weight ratio S / Mo is 1.7, which is longer than 2.5 × 10 ⁵ in Example 2, and the molecular weight ratio S / Mo is 2.0. It was proved that the shorter the life, the longer the life.

Further, in order to investigate the relationship between the ion bombardment time in the above-mentioned sputtering process and the durability life of the MoS ₂ coating, the ion bombardment time was 20 minutes,
About the example and the comparative example which were 60 minutes and 180 minutes,
As a result of performing a durability life test by a ball-on-disk tester in vacuum, as shown in FIG. 5, the durability life of the MoS ₂ coating of the example subjected to ion bombardment for 60 minutes or more is 1.8 to 2.6 × 10. There is little variation at ⁵ rev, whereas the comparative example has the longest length of 6.3 × 10 ⁴
It is about rev, and when compared with the average value, the durability coating of the example coating is 6 times or more that of the comparative coating. Further, when the ion bombardment is about 20 minutes, the variation of the life is large, and the life is shorter than that of the example coating which is ion bombarded for 60 minutes or more. Therefore, the ion bombardment time is preferably 60 minutes or more.

Further, the surface morphology of Examples 1 and 2 and Comparative Example was observed with a scanning electron microscope at an accelerating voltage of 15 kV and 20000 times.
As shown in FIG. 6, the hill-like and dense surface morphology of Example 2 is shown, and the comparative example is shown in FIG.
m) -like and rough.

Further, regarding Example 1, Example 2 and Comparative Example, the crystal structure of the film was measured by using an X-ray diffractometer for a thin film, the incident angle of X-ray was 2 °, and CuKα-ray was used as the X-ray source. As a result of using it and diffracting it with a tube voltage of 40 kV and a tube current of 300 mA, the X-ray diffraction pattern of Example 1 shows that hexagonal MoS ₂ (002), (100),
Diffraction peaks were observed at (110), especially (00
2) It was found that the planes were strongly oriented, and X in the comparative example
In the line diffraction pattern, as shown in FIG. 9, it was found that the diffraction peak of the (002) plane was small, and in order to judge the orientation by X-ray diffraction, the X of the (002) plane and the (100) plane were determined. The line intensity ratio (area ratio) (002) / (100) obtained for each of Example 1, Example 2 and Comparative Example is shown in Table 1 described above.

Therefore, as is clear from Table 1, Mo
By setting the molecular weight ratio S / Mo of S ₂ to be 1.7 or more and less than 2.0, it is possible to form a dense coating with a hilllike surface morphology and to significantly improve the coating life. It was found that the slip plane is perpendicular to the loading direction by preferentially orienting the (002) plane with the X-ray intensity ratio (002) / (100) in X-ray diffraction of 1.0 or more. Is increased, the load-bearing performance is increased, and the coating life is extended and stabilized.

Further, by maintaining the temperature of the member W to be sputtered at the time of main sputtering in the sputtering apparatus at 50 ° C. or less, it is possible to form a film having a hill-like surface morphology and a dense member W. When the temperature exceeds 50 ° C., the surface morphology begins to be affected, and when the temperature is 100 ° C. or higher as in the case of normal sputtering without cooling, it becomes worm-like and rough. here,
The temperature of the member W to be sputtered is preferably as low as possible (for example, room temperature), but the cooling device becomes large and a large amount of cooling medium is required.

Next, the outer ring of the angular contact ball bearing by a sputtering process for forming the MoS ₂ coating described above, the inner ring and the molecular weight ratio S / Mo in the rolling element is in MoS ₂ is less than 1.7 to 2.0 0. Applying a PTFE self-lubricating cage as a cage by forming a lubricating film of 5 μm,
An inner diameter of 8 mm, an outer diameter of 22 mm, a width of 7 mm, and a contact angle of 30 ° were assembled, and this angular contact ball bearing was subjected to a bearing performance evaluation test in vacuum using the vacuum bearing test device shown in FIG. , Especially the torque fluctuation of the bearing and the behavior of the lubricant accompanying it were investigated, the wear life of the MoS ₂ coating in vacuum was determined, and the influence of the rotational speed, operating pattern, and axial load on the wear life of the MoS ₂ coating was examined. did.

Here, the in-vacuum bearing testing device 50 shown in FIG.
Is a rotary shaft 52 extending horizontally in a vacuum chamber 51 having a vacuum degree of 3 × 10 ⁻⁵ Pa or less and a temperature of room temperature.
Is supported by a bearing device 53 and is rotatably disposed. Two sets of test bearings 54a and 54b are mounted on the rotary shaft 52, and a 100N axial force is applied to the test bearings 54a and 54b by a spring 55. A tip of a rotating arm 57 fixed to a cylindrical body 56 fitted to the outer rings of the test bearings 54a, 54b is brought into contact with a minute load converter 58 by applying a load, and the minute load converter 58 causes the rotary shaft to rotate. 42 is sealed with the magnetic fluid seal unit 59 to extend to the outside of the vacuum chamber 51, and the pulley 60 attached to the end thereof is connected to the pulley 63 fixed to the rotary shaft of the drive motor 62 via the belt 61. 500 rp
The torque generated in the outer rings of the test bearings 54a and 54b when driven to rotate at m is detected.

As the operation pattern of the test bearing, forward and reverse rotations were carried out after 800 rotations were stopped for 30 seconds after normal rotation, and thereafter were stopped for 30 seconds after 800 rotations were reversed, which was repeated as one cycle. As a result, an axial load of 100N,
The transition of the dynamic torque at the time of normal and reverse rotation at a rotation speed of 500 rpm is as shown in FIG. 11, and the total rotation speed is 6.8 × 10re.
Up to v, it shows a stable value as low as torque or 1 × 10 ⁻³ Nm, and 1 to 15 up to 1.2 × 10 ⁶ rev.
It shows a large fluctuation of about × 10 ^-3 NM, and then the torque shows a stable value of about 1 to 2 × 10 ^-3 Nm.

Next, a PTFE meter self-lubricating cage is incorporated into the angular contact ball bearing coated with the molybdenum disulfide coating, and the behavior of PTFE is observed. In FIG. 11, the cause of torque fluctuation is due to lubrication by the MoS ₂ coating due to the PTF of the cage.
Considering that the lubrication by E will be performed, the test is temporarily stopped at the arrows indicated by ,, and in FIG.
When wavelength-dispersive EPMA analysis was performed on the surface of the ball, changes in the characteristic X-ray intensities of Mo, S, and F were shown along with the total number of revolutions, and the results shown in FIG. 12 were obtained. According to FIG. 12, the main character of lubrication when the torque is low and stable is M
It is oS ₂ , and when the MoS ₂ coating disappears due to wear, P
TFE transition film lubrication begins. In addition, the peaks of Mo and S seen at are due to MoS ₂ contained in the cage material. At the initial stage of the PTFE transition film lubrication, the lubrication is insufficient and a large torque fluctuation occurs, but when the lubricant is sufficiently supplied from the balls to the raceway surface, the torque shows a low and stable value. Here, when the total number of revolutions before lubrication by the PTFE transition film starts is L _C , the total number of revolutions L _C is Mo.
This shows the wear life of the S ₂ coating, and in the case of FIG. 11, it can be seen that the total number of revolutions L _C is 6.8 × 10 ⁵ rev.

Further, the axial load is 100 N and the rotation speed is 1
FIG. 13 shows changes in the total number of revolutions L _C , which represents the wear life of the MoS ₂ coating when it is rotated in the normal and reverse directions at 0 to 1000 rpm and is rotated one way. It can be seen from FIG. 13 that the wear life of the MoS ₂ coating is hardly affected by the rotation speed and the operation pattern. Further, the change in the total rotational speed L _C , which represents the wear life of the MoS ₂ coating when the axial load was changed to 60 to 500 N, in the forward / reverse rotation of the rotational speed of 100 rpm, was changed as shown in FIG. It is decreasing monotonically with the increase. Here, since the total number of revolutions L _C does not represent the life of the bearing, the PTF is not used thereafter.
Due to the E-transition film lubrication, it will rotate until the end of its life. In addition, in a durability test in vacuum at a maximum contact surface pressure of 880 MPa (corresponding to an axial load of 60 N here) and a rotation speed of 2000 rpm, it has been confirmed by a test that the durability life is 1 × 10 ⁸ rev or more.

The outer and inner rings, rolling elements, and cage materials are not limited to those in the above embodiment, but ceramics (for example, nitrogen-based Si ₃ N ₄ , zirconia, alumina, carbide-based materials,
The object of the present application can be achieved even with stainless steel such as SiC or SUS630.

[0026]

As described above, according to the present invention,
In a rolling member having a lubricating coating formed by coating molybdenum disulfide on a rolling surface with which a mating member makes rolling contact, the lubricating coating is formed by using a molecular weight ratio S of sulfur and molybdenum.
Since the molybdenum disulfide coating has a composition selected from / Mo of 1.7 or more and less than 2.0, the surface morphology of the coating has a dense hill-like structure, and the coating wear life is significantly improved. By forming this molybdenum disulfide coating on the rolling surfaces of rolling bearings and ball screws, it is possible to improve the service life and reliability of the rolling bearings and ball screws.

[Brief description of drawings]

FIG. 1 is a front view showing an example of a ball screw to which the present invention is applied.

FIG. 2 is a sectional view showing an example of an angular ball bearing to which the present invention is applied.

FIG. 3 is a schematic diagram showing an example of a sputtering apparatus applicable to the present invention.

FIG. 4 is a schematic configuration diagram showing a ball-on-disk tester in vacuum.

FIG. 5 is a graph showing the relationship between the ion bombardment time and the durable life of the example coating and the comparative example coating.

FIG. 6 is an electron micrograph showing the surface morphology of a MoS ₂ thin film according to an example of the present invention.

FIG. 7 is an electron micrograph showing the surface morphology of a MoS ₂ thin film in a comparative example.

FIG. 8 is a graph showing an X-ray diffraction pattern of Example 1.

FIG. 9 is a graph showing an X-ray diffraction pattern of a comparative example.

FIG. 10 is a schematic configuration diagram showing an example of a bearing testing device in vacuum.

11 is a characteristic diagram showing the relationship between the dynamic torque and the total number of rotations, which represents the test results using the test apparatus of FIG.

FIG. 12 is a diagram showing the EPMA analysis result at each point in FIG. 11.

FIG. 13 is a characteristic diagram showing the relationship between the total rotation speed and the rotation speed.

FIG. 14 is a characteristic diagram showing the relationship between the total load and the axial load.

[Explanation of symbols]

 1 Ball Screw 2 Screw Shaft 3 Ball Nut 4 Ball 10 Rolling Bearing 11 Outer Ring 12 Inner Ring 13 Ball 14 Cage 20 Sputtering Equipment 21,23 Electrode 24 High Frequency Power Supply 27 Exhaust System 30 Argon Cylinder 31 Vacuum Gauge 40 Vacuum Ball-on-Disk Tester 50 Vacuum bearing test equipment

Claims (1)

[Claims] 1. A rolling member having a lubricating coating formed by coating molybdenum disulfide on the rolling surface with which the mating member is in rolling contact, wherein the lubricating coating has a molecular weight ratio S / Mo of sulfur to molybdenum of 1 A rolling member formed of a molybdenum disulfide coating having a composition selected from 0.7 to less than 2.0.