JP2008169939A - Rolling bearing for vacuum pump and vacuum pump using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new rolling bearing for a vacuum pump and a vacuum pump using it which can deliver excellent durability for the long term. <P>SOLUTION: A surface hardening layer 20 is formed on the track surface of the inner rings 61, 71 and on either one or both of the track surfaces of the outer rings 62, 72 of the rolling bearings 6, 7 for the vacuum pump. The surface hardening layer 20 reduces frictional resistance with rolling bodies 63, 73. Because of this, the durability at the contact part between the track surface and the rolling body is increased. Thus, by applying the anti-friction bearing as a touch-down bearing for the vacuum pump or the like, excellent durability can be delivered for the long term without any generation of sudden friction even when an abrupt large sliding frictional force is generated between the track surface and the rolling bodies 63, 73. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention particularly relates to a rolling bearing suitable for a vacuum pump such as a turbo molecular pump or a dry vacuum pump, and a rolling bearing for a vacuum pump that can be applied as a touch-down bearing of the turbo molecular pump or a bearing of a dry vacuum pump. The present invention relates to a vacuum pump using this.

  Touchdown bearings that have been widely used in vacuum pumps such as turbomolecular pumps are rolling bearings that are used together with magnetic bearings. Normally, the rotating wheel (inner ring or outer ring) rotates on the rotor shaft or housing of the pump. When the magnetic bearing becomes uncontrollable due to some trouble without contact with the member, the surface facing the rotating member of the rotating wheel comes into contact with the rotating member (touched down), and functions as a bearing. The magnetic bearing and the rotating member are protected.

  Conventionally, it has been demanded to improve the durability of touchdown bearings. For this reason, in the case of touchdown bearings used in a vacuum as described above, for example, in Patent Documents 1 to 3 below, As shown, a film made of a solid lubricant (a coating film made of molybdenum disulfide or a plating film made of a soft metal such as gold, silver, or lead) is formed on the surfaces of the rolling elements and the inner and outer rings. Yes.

Further, in the touch-down bearing of Patent Document 4 below, the rolling elements are made of ceramics, and a chromium nitride (CrN ₂ or CrN) coating or zirconium nitride is formed on the raceway surface of the inner and outer rings and the surface facing the rotating member. By covering the (ZrN) film, durability in a corrosive atmosphere such as fluorine gas is enhanced.
As shown in Patent Document 5 below, most of the touchdown bearings currently used are formed of high carbon chrome bearing steel such as SUJ2 or martensitic stainless steel such as SUS440C. ing.
Japanese Utility Model Publication No. 64-48427 Japanese Utility Model Publication No. 5-71444 Japanese Utility Model Publication No. 5-209621 JP 2002-168252 A Japanese Utility Model Publication No. 3-88024 etc.

By the way, the touchdown bearing as described above is in a state where it is stationary or lightly idle so that unnecessary wear does not occur during normal operation, that is, when the magnetic bearing is functioning normally. When the magnetic bearing becomes uncontrollable and the rotating member of the vacuum pump comes into contact, a large sliding frictional force is suddenly generated between the members.
Therefore, as described above, the surface of each member constituting the touch-down bearing is coated with a film made of a solid lubricant or the like for reducing rapid sliding friction. Due to the large wear on the touchdown, a sufficiently satisfactory durability is not obtained.

Touchdown bearings that have become unusable due to wear will be replaced with new ones as appropriate. To replace them, disassemble the vacuum pump or the magnetic bearing device incorporated in it. After replacing the touchdown bearing with a new one, it is necessary to reassemble the magnetic bearing device etc. while adjusting the clearance between the inner ring of the bearing and the rotating shaft with high accuracy. There is a problem that it takes time and effort.
Therefore, the present invention has been devised to solve such problems, and the purpose thereof is a novel rolling bearing for a vacuum pump that can exhibit excellent durability over a long period of time and a vacuum using the same. A pump is provided.

The invention of claim 1 for solving the above-mentioned problem is
A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. A rolling bearing for a vacuum pump, characterized in that a hardened surface layer is formed on one or both of the raceway surfaces of the inner ring and the outer ring to reduce frictional resistance with the rolling elements. It is a bearing.
Thus, in the rolling bearing for vacuum pump of the present invention, the surface hardened layer that reduces the frictional resistance with the rolling element is formed on one or both of the raceway surface of the inner ring and the raceway surface of the outer ring. Durability at the contact area is improved.

Therefore, by applying this rolling bearing as a touchdown bearing for vacuum pumps, even if a large sliding frictional force is suddenly generated between the raceway surface and the rolling element, it will not be abruptly worn, resulting in excellent durability for a long time. It can be exhibited over a wide range.
In addition, on the raceway surface with this hardened surface layer, wear and damage are less likely to occur during assembly and rotation of the bearing, reducing the incidence of defective products, and greatly reducing torque and heat generated at the start of rotation. It becomes possible to make it.

  Here, as the hardened surface layer in the present invention, as shown in claim 4 below, a predetermined depth (for example, a depth from the surface) from the outermost surface is obtained by nitriding such as known carbonitriding or nitronitriding. May be a surface hardened layer having a nitride layer having a thickness of 3 to 100 μm), and may be a shot peening layer formed by shot peening treatment as shown in the following claims 5 and 6 or the following claim 7. A surface-hardened layer having a predetermined depth may be formed by coating a known diamond-like carbon layer (hereinafter abbreviated as “DLC layer” where appropriate) shown in FIG. In particular, in consideration of further improving the wear resistance, the surface hardened layer for reducing the coefficient of friction is preferably formed of a shot peening layer, a DLC layer, or a ceramic layer (the vacuums of claims 2 and 3 below). The same applies to rolling bearings for pumps).

  Further, the thickness of the surface hardened layer is not particularly limited, but when applied as a touchdown bearing for a vacuum pump or the like, if the thickness is about several μm, rapid sliding friction during the touchdown Since there is a possibility of being worn or peeled off by force, it is desirable to secure at least 20 μm or more.

The invention of claim 2
A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. A vacuum pump characterized in that a hardened surface layer that reduces frictional resistance with one or both of the raceway surfaces of the inner ring and the outer race is formed on the surface of the rolling element. This is a rolling bearing.

  As a result, the frictional resistance between the raceway surface, the rolling element and the contact portion is greatly reduced and the durability is improved as in the first aspect of the invention, so that the rolling bearing is used as a touchdown bearing for a vacuum pump or the like. Therefore, even if a large sliding frictional force is suddenly generated between the raceway surface and the rolling elements, excellent durability can be exhibited over a long period of time without significant wear.

The invention of claim 3
A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. A rolling bearing for use in which a hardened surface layer that reduces frictional resistance with the other rotating member is formed on one or both of the inner peripheral surface of the inner ring and the outer peripheral surface of the outer ring that are in contact with the other rotating member. It is a rolling bearing for vacuum pumps characterized by these.

  As a result, the frictional resistance of one or both of the inner peripheral surface of the inner ring and the outer peripheral surface of the outer ring that comes into contact with another rotating member such as a rotating shaft is greatly reduced and durability is improved. By using it as a touchdown bearing for vacuum pumps, etc., it will exhibit excellent durability over a long period of time without significant wear even if a large sliding frictional force suddenly occurs at the contact part with other rotating members. Can do.

The invention of claim 4
The rolling bearing for a vacuum pump according to any one of claims 1 to 3, wherein the hardened surface layer has a nitride layer on the outermost surface, and the nitride layer includes a compound layer having a surface hardness of Hv900 or more. A rolling bearing for a vacuum pump comprising a diffusion hardened layer and having a surface roughness Ra of 0.2 μm or less.
As a result, the hardness and smoothness of the hardened surface layer formed on the surface of each member is improved, so that the frictional resistance between the members is reduced and the surface wear is greatly reduced.

Here, since the nitride layer in the present invention is composed of a compound layer having a surface hardness of Hv 900 or more and a diffusion hardened layer, it exhibits an advantage that it has strong adhesion between the coating and the base material and is difficult to peel off. The compound layer is _{(Fe, Cr) 2,3or4 N,} CrN, Cr 2 N, Mo 2 N, are composed of dense nitride such as VN, has excellent surface properties. Further, the thickness of the compound layer is not particularly limited. However, if the thickness is too small, the characteristics cannot be sufficiently exhibited. For example, in the case of a rolling element, the thickness of the compound layer is preferably at least 3 μm and 2% or less of the diameter of the rolling element because the physical properties of the steel are impaired and impact resistance is reduced.

Further, by forming a nitride layer on the surface, not only the wear of itself but also the damage of the mating member in contact with it can be suppressed, so that the fretting resistance can be improved. Further, when this nitrided layer is formed on the surface of the rolling element, ball scratches during assembly are extremely reduced, and an effect such as poor quality can be expected.
Further, if the surface roughness Ra exceeds 0.2 μm, the frictional resistance is increased and the effects as described above become poor. Therefore, the surface roughness Ra is preferably 0.2 μm.

The invention of claim 5
The rolling bearing for a vacuum pump according to any one of claims 1 to 3, wherein the surface hardened layer is a shot peening layer formed by shot peening treatment, and the shot peening layer has a surface hardness. Is a rolling bearing for a vacuum pump, wherein Hv is 900 or more and the maximum surface roughness Ra is 2.5 μm or less.

The invention of claim 6
6. A rolling bearing for a vacuum pump according to claim 5, wherein a film in which a solid lubricant is dispersed is formed on the surface of the shot peening layer.
According to the structures of the fifth and sixth aspects, since the surface has a surface structure in which minute irregularities are uniformly dispersed, the lubricant is held in the concave portions of the irregularities so that the lubricant film is uniformly formed. Will be.

This prevents direct contact between the members, and increases the compressive residual stress due to shot peening, thereby increasing the hardness of each member and improving the wear resistance, and reducing the frictional resistance. It is possible to reduce wear and heat generation at the contact portion.
Further, by holding the lubricant in the concave and convex portions, it is possible to reliably prevent the oil film from being cut, and thus good lubricity can be maintained over a long period of time.

In view of the effect of retaining the lubricant in the concave portion of the shot peening layer, the maximum surface roughness Ra should be at least “0.5 μm”, more preferably “1.0 μm” or more. Desirably, on the other hand, if the maximum surface roughness Ra is too large, the surface becomes non-uniform and the frictional resistance increases. Therefore, the maximum surface roughness Ra needs to be not more than “2.5 μm”. is there.
Further, by setting the surface hardness to Hv 900 or more, the wear resistance can be improved more reliably.

In addition, as a method for forming a film in which a solid lubricant is dispersed on the surface of a shot peening layer as in the present invention, for example, a spray powder used for shot peening treatment, molybdenum disulfide (MoS ₂ ), or disulfide If a mixture of solid lubricant particles such as tungsten (WS ₂ ), boron nitride (BN), and fluororesin (for example, PTFE) is used, the shot peening process can be performed as usual. It is possible to easily form a film in which the solid lubricant is uniformly dispersed on the surface of the peening layer.

The invention of claim 7
The rolling bearing for a vacuum pump according to any one of claims 1 to 3, wherein the hardened surface layer is composed of a diamond-like carbon layer (hereinafter referred to as "DLC layer" as appropriate). It is a rolling bearing.
As a result, the hardness of the surface hardened layer is increased, and the DLC layer has a sliding friction coefficient as small as “0.1” or less as compared with the conventional surface hardened layer. It can reduce more reliably.

  In addition, since the diamond-like carbon layer can be easily formed at a low processing temperature (for example, 200 ° C. or less), each member forming the diamond-like carbon layer is not easily affected by heat at the time of layer formation. Even when a high-alloy steel such as stainless steel or high-speed steel is subjected to quenching and tempering, it has an excellent advantage that the hardness after quenching and tempering can be maintained. This advantage makes it possible to maintain the bearing performance characteristics because the bearing shape and the bearing gap at the initial design are hardly changed.

The invention of claim 8
The rolling bearing for a vacuum pump according to any one of claims 1 to 3, wherein the hardened surface layer is made of a ceramic layer.
Thereby, since the hardness of the sliding contact surface in which this hardened surface layer is formed is high and the sliding friction coefficient is small, the sliding friction between the respective members can be greatly reduced.
Moreover, this ceramic layer has the advantage that hardness and a friction coefficient can be changed with the kind etc. of the alloy which forms this layer.

Here, the material for forming the ceramic layer is not particularly limited, but specific examples include TiN (hardness Hv 2000 to 2400, friction coefficient 0.40 to 0.45), TiCN ( Hardness Hv 3000-3500, friction coefficient 0.12-0.15), TiAlN (hardness Hv 2300-2800, friction coefficient 0.3-0.4), TiC (hardness Hv 3000-3500, friction coefficient 0 .40 to 0.45), CrN (hardness Hv 2000 to 2200, friction coefficient 0.25 to 0.35), TiC / TiN, TiC / TiCN / Al ₂ O ₃ , TiC / Al ₂ Examples thereof include a ceramic layer having a laminated structure such as O ₃ / TiN, TiC / TiCN / TiC / Al ₂ O ₃ .

In particular, ceramic layers such as TiN, TiAlN, and TiCN, ceramic layers having a laminated structure including these, and ceramic layers such as CrN have high hardness, low friction coefficient, and high adhesion. Wear and damage can be effectively prevented.
Among these, ceramic layers such as TiN and TiC / TiN are excellent in terms of wear resistance and peel resistance. Similarly, a ceramic layer having a laminated structure such as TiC / TiCN / Al ₂ O ₃ , TiC / Al ₂ O ₃ / TiN, TiC / TiCN / TiC / Al ₂ O ₃ has a point of wear resistance and adhesion prevention. Is excellent. Furthermore, a ceramic layer such as CrN is excellent in terms of corrosion resistance, oxidation resistance, and seizure resistance.

The invention of claim 9
The rolling bearing for a vacuum pump according to any one of claims 1 to 8, wherein bearing steel or martensitic stainless steel is used as a base material of the inner and outer rings or rolling elements on which the surface hardened layer is formed. It is a rolling bearing for vacuum pumps characterized by these.
As a result, materials that have been conventionally used as bearing base materials can be used as they are, so performance and reliability equivalent to or better than conventional bearings, such as strength and workability, can be expected, and material costs can be kept low. Can do.

  That is, for example, when a nitrided layer is employed as the surface hardened layer as described in claim 4, the nitriding treatment is generally performed in the range of 400 to 600 ° C., preferably 400 to 480 ° C. Later, the deep part may be softened by tempering and the hardness may be significantly reduced. Usually, after the nitriding treatment, a compound layer is formed on the surface, and at a deeper depth, a diffusion hardened layer is formed by nitrogen diffusion. And since nitriding has this diffusion hardened layer, the adhesiveness of a film and a base material is strong, and it is hard to peel. However, when a large shearing force is received at the maximum shearing stress position deeper than that of the nitrided layer when the bearing is operated, the hardened surface layer may be damaged with plastic deformation if the portion does not have sufficient strength. There is. This is the same even when a shot peening layer, a DLC layer, or a ceramic layer is employed as the surface hardened layer as in the fifth to eighth aspects.

  Accordingly, the material used for the rolling elements as well as the inner and outer rings must be a material having sufficient hardness to withstand the shear stress even after the surface hardened layer is formed. Specifically, it is desirable to use bearing steel or martensitic stainless steel as a base material for the inner and outer rings or rolling elements on which a hardened surface layer is formed as in the present invention.

  Here, the "bearing steel or martensitic stainless steel" used as the base material of the inner and outer rings or rolling elements constituting the rolling bearing of the present invention includes carburized steel, heat resistant steel, Stainless steel, alloy tool steel, high speed steel, chrome steel, chrome molybdenum steel, etc. For example, SUJ2 described in JIS G 4805 as well as SUS440C, 0.7C-13Cr stainless steel, or M50 conventionally used for bearings Common steel can be used. However, in the case of a high carbon martensitic stainless steel such as conventional SUS440C, since it contains many coarse eutectic carbides, it is inferior to SUJ2 in terms of quietness and wear resistance. Therefore, SUJ2 should be used if possible. preferable. In particular, when the lubrication conditions are poor, such as a dry vacuum pump that uses fluorinated oil as a lubricant, it is preferable to positively use SUJ2.

  Further, when a nitride layer as shown in claim 4 is adopted as the surface hardened layer, an alloy element such as Cr, Mo, V, Nb, W, Ti, Al, Si, etc. is preferably used at a ratio of 2 to 25%, for example. When a nitride layer is formed on the surface using the steel contained in the above, fine nitrides containing these elements are precipitated in the nitride layer, thereby improving fretting durability, seizure resistance, and wear resistance.

  Further, as described above, the nitriding treatment for forming the nitrided layer is usually performed at a relatively high processing temperature of about 400 to 600 ° C. Therefore, when the base material does not have sufficient durability, The strength of the base that supports the nitride layer is insufficient, and the nitride layer is easily damaged. Accordingly, the hardness at the maximum shear stress position is secured at least Hv653. Specifically, the heat resistance is improved by adding the alloy element, or a diffusion hardened layer of a nitride layer is provided deeper. Further, carburization and carbonitriding may be performed before nitriding to ensure heat resistance. Further, martensitic stainless steel or high speed steel is more preferable because it has sufficient heat resistance and can maintain sufficient hardness even after nitriding treatment. Further, when the nitriding temperature is high, the heat resistance of the base material may be insufficient and sufficient base hardness may not be obtained. Therefore, the nitriding temperature is preferably 500 ° C. or less, more preferably 460 or less. To do.

  In addition, since the surface roughness Ra after nitriding is as large as about 0.5 to 2.5 μm, if it remains as it is, the surface is highly attackable and the surface nitride or oxide particles peel off at the same time. It is possible to have an adverse effect such as dropping off. Therefore, the nitride layer surface needs to be finished after nitriding. Specifically, when the surface roughness Ra exceeds 0.2 μm, the frictional resistance becomes high and the effects as described above become poor. Therefore, the surface roughness Ra is desirably 0.2 μm.

The invention of claim 10 provides
The rolling bearing for a vacuum pump according to claim 1 or 3, wherein the rolling element is made of a ceramic material.
Thereby, the hardness of the rolling element itself is high and the sliding friction coefficient is small, so that the sliding friction with the raceway surface can be greatly reduced.

On the other hand, the invention of claim 11
A vacuum pump comprising a magnetic bearing that supports a rotating member by magnetism, and a touchdown bearing that functions as a spare bearing for the rotating member when the magnetic bearing becomes uncontrollable, A vacuum pump using the rolling bearing for a vacuum pump according to any one of Items 1 to 10.

As a result, even if the touchdown repeatedly occurs, the touchdown bearing is not worn and the durability is greatly improved.
Further, since the frequency of disassembling the pump and replacing the bearing is greatly reduced, the reliability of the pump is improved and the operating cost is reduced.

  According to the present invention, the surface hardened layer that reduces the frictional resistance composed of a nitride layer, a shot peening layer, a ceramic layer, a diamond-like carbon layer, etc. is formed on the surface of each member constituting the rolling bearing for the vacuum pump. The wear at the contact portion between the surface, the rolling element and the rotating member is greatly reduced, and the durability as a bearing can be exhibited over a long period of time. Accordingly, the life of the vacuum pump can be extended by using the rolling bearing as a touchdown bearing for a vacuum pump.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an embodiment of a magnetic levitation turbomolecular pump using a rolling bearing according to the present invention as a touchdown bearing among vacuum pumps according to the present invention.
In the figure, reference numeral 1 denotes a rotor blade, and a rotor shaft 2 that rotates integrally with the rotor blade 1 is rotatable in a non-contact state by a pair of axial magnetic bearings 3 and two sets of radial magnetic bearings 4 and 5. It is supported by.

Further, an all-ball type deep groove ball bearing (rolling bearing) 6 that receives a radial load and a combined angular ball bearing (rolling bearing) 7 that receives an axial load are provided as touchdown bearings.
The rotor shaft 2 is a rotating shaft extending in the vertical direction, and a flange 21 is formed integrally with the lower portion of the rotor shaft 2. The axial magnetic bearing 3 is arranged so that the flange 21 is sandwiched between a pair of electromagnets 3a and 3b.

  Reference numeral 8A denotes an upper casing, and 8B denotes a lower casing. Reference numeral 81 denotes a member that forms part of the upper casing 8 </ b> A, and serves as a housing for the radial magnetic bearings 4 and 5 and the deep groove ball bearing 6. Reference numeral 82 denotes an intake port, 83 denotes an exhaust port, 84 denotes a power supply terminal, and 85 denotes a protective net. Reference numeral 9 denotes an electric motor that rotates the rotor shaft 2 at a high speed.

Then, the deep groove ball bearing 6 that functions as one touch-down bearing is above the rotor shaft 2, and the angular ball bearing 7 that functions as the other touch-down bearing is above the flange 21 below the rotor shaft 2. is set up.
FIG. 2 shows an enlarged view of the installation position of the deep groove ball bearing 6, and FIG. 3 shows an enlarged view of the installation position of the angular ball bearing 7.

  First, as shown in FIG. 2, the deep groove ball bearing 6 has an inner ring (rotating wheel) 61 having a raceway surface on the outer circumferential surface and a raceway surface 62a facing the raceway surface 61a of the inner ring 61 on the inner circumferential surface. The outer ring 62 is composed of a plurality of rolling elements 63 arranged so as to be able to roll between the raceway surfaces 61a and 62a. A predetermined gap in the radial direction is provided between the inner ring 61 and the rotor shaft 2. 6A is provided. The gap 6A is smaller than the radial gap with respect to the rotor shaft 2 of the radial magnetic bearings 4 and 5.

  On the other hand, as shown in FIG. 3, the angular ball bearing 7 also has an inner ring (rotating wheel) 71 having a raceway surface on the outer peripheral surface and a raceway surface 72a facing the raceway surface 71a of the inner ring 71 on the inner peripheral surface. The outer ring 72 has a plurality of rolling elements 73 that are arranged to freely roll between the raceway surfaces 71a and 72a. A radius between the inner ring (rotating ring) 71 and the rotor shaft 2 is included. A predetermined gap 7A is provided in the direction. The clearance 7A is also smaller than the radial clearance with respect to the rotor shaft 2 of the radial magnetic bearings 4 and 5. The outer ring 72 of the angular ball bearing 7 is attached to the housing 31 of the axial magnetic bearing 3.

  Accordingly, the rotor shaft 2 is normally rotatably supported by the radial magnetic bearings 4 and 5 and the axial magnetic bearing 3. Further, when these magnetic bearings become uncontrollable, the rotor shaft 2 touches down the inner grooves 61 and 71 of the deep groove ball bearing 6 and the angular ball bearing 7, and these bearings 6 and 7 function as touchdown bearings. To come.

<First Embodiment>
In the first embodiment, the raceway surfaces 61a, 62a, 71a, 72a on the inner peripheral sides of the inner and outer rings 61, 62, 71, 72 of the deep groove ball bearing 6 and the angular ball bearing 7 that function as the touch-down bearings, and The rolling elements 63 and 73, and the inner peripheral surface 61b of the inner ring 61 that contacts the rotor shaft (rotating member) 2 at the time of touchdown, are made of a nitride layer on the base material 10 as shown in FIG. The surface hardened layer 20 is formed by coating.

  As described above, this nitride layer is composed of a compound layer having a surface hardness of Hv 900 or higher and a diffusion hardened layer, and has a surface roughness of 0.2 μmRa or less. Therefore, if a rolling bearing having such a nitride layer is used as a touchdown bearing such as the deep groove ball bearing 6 or the angular ball bearing 7 described above, the hardness of the contact portion is high and the sliding friction coefficient is small. The sliding friction during touchdown can be greatly reduced.

<Second Embodiment>
In the second embodiment, as shown in FIG. 4, a hardened surface layer 20 made of a shot peening layer formed by shot peening is formed on the base material 10.
This shot peening layer has a maximum roughness of the surface of 2.5 μm or less, and the surface has a surface structure in which minute irregularities are uniformly dispersed. Therefore, the lubricant is held in the concave portions of the irregularities. Thus, a lubricating film is formed.

Thereby, by controlling the surface roughness optimally, direct metal contact between the members can be prevented, and wear can be prevented by increasing the compressive residual stress due to shot peening.
Furthermore, since friction on the contact surfaces of these members can be reduced, heat generation can be reduced. In addition, holding the lubricant in the concave portion also has an effect of eliminating the breakage of the lubricating film on the contact surface of each member, and the lubrication state can be well maintained over a long period of time.

Here, as this shot peening process, it is effective to use, for example, a WPC (Wonder Process Craft) process (shot peening process (registered trademark) provided by Fuji Seisakusho and Fuji Machine Sales Co., Ltd.). It is.
For example, a powder having a particle size of 40 to 200 μm and a hardness equal to or higher than the hardness of the base material 10 (for example, the same material as that of the base material 10 or SiO ₂ ) is used as an injection granule. By spraying the surface of the base material at a speed of 100 m / sec or more for about several seconds to several tens of seconds, rapid heating / cooling in the temperature range above the A3 transformation point of the surface of the base material 10 is instantaneously repeated. The process which has the heat processing effect of this and a training effect will be performed. As a result, martensite, recrystallization, and refinement of the retained austenite in the metal surface layer are performed, and a dense, high hardness and tough structure can be obtained. In addition, the internal residual compressive stress on the surface can be increased.

In addition, a SiO ₂ powder having a hardness of Hv 800 or more and a particle size of _{20 to 200} μm is used as an injection granule, and this is injected onto the surface of the base material at an injection speed of 50 m / sec or more to control the temperature near the surface. By raising the oil temperature above the A3 transformation point and forming an oil sump consisting of innumerable concave portions having a minute cross-sectional arc shape on the surface, it is possible to prevent wear due to running out of lubricating oil.

Further, when a cemented carbide powder such as TiC or TiN is used as the spray powder, a cemented carbide material such as cobalt deposited on the surface is pushed into the interior and refined, and the interior of the surface of the base material 10 is reduced. The residual stress is also increased, the surface is smoothed, and the friction coefficient can be further reduced.
Further, when performing such shot peening treatment, metal particles forming the parent phase of the base material 10, molybdenum disulfide (MoS ₂ ), tungsten disulfide (WS ₂ ), boron nitride (BN), fluororesin If a jet particle formed by mixing a solid lubricant particle (for example, PTFE) is used, a film in which the solid lubricant is dispersed in the shot peening layer is formed. It is possible to further improve the effect.

  In addition, this shot peening process can remove burrs and turning marks in the turning process and pressing process, scales and welds in the heat treatment process, etc., and is therefore effective in improving cleanliness. The contact state inside the bearing such as a moving body is improved. Therefore, this shot peening process is preferably performed at least on the entire surface of the base material 10.

  Therefore, if a rolling bearing provided with such a shot peening layer is used as a touchdown bearing such as a deep groove ball bearing 6 or an angular ball bearing 7, the contact portion has high hardness as in the first embodiment. Moreover, since the sliding friction coefficient becomes small, the sliding friction at the time of touchdown can be greatly reduced.

<Third Embodiment>
In the third embodiment, as shown in FIG. 4, a hardened surface layer 20 made of a DLC layer or a ceramic layer is formed on the base material 10 by a PVD method or the like.
As described above, even when the DLC layer or the ceramic layer is formed on the surface of the base material 10 of each member, the surface has a high hardness and the sliding friction coefficient is small as in the second and third embodiments. Therefore, sliding friction at the time of touchdown can be reduced.
Here, the method for forming the DLC layer is not particularly limited, and a conventionally known method using a PVD method or the like can be applied as it is.

  For example, first, the surface of the base material 10 is subjected to shot blasting using steel beads having a particle diameter of 20 to 30 μm, and after adjusting the surface roughness Ra, the surface is degreased. Then, the surface of the member is bombarded by sputtering using argon plasma. Then, sputtering is performed on the surface of the base material using tungsten, chromium, or the like as a target to form a metal layer. Next, while continuing sputtering of these two kinds of metals, carbon sputtering using carbon as a target is started. By such sputtering, a composite layer made of metal carbide in which the two kinds of metals and carbon are bonded is formed on the metal layer. Further, when the sputtering efficiency of carbon is gradually increased while the sputtering efficiency of the two kinds of metals is gradually decreased, and the sputtering of the two kinds of metals is completed, the composite layer is formed only as the sputtering of carbon. A carbon layer is formed on the substrate.

  Thereby, a DLC layer in which the composition of the layer is gradually and gradually changed from the layer composed of two kinds of metals (metal layer) toward the layer composed of carbon (carbon layer) can be formed. it can. The DLC layer having such a structure has a thickness of about 1.0 to 4.0 μm and has excellent adhesion between the layers, and a carbon layer and a base material excellent in lubricity. It has the feature that the adhesiveness with the steel is very excellent.

In each of the above embodiments, the raceway surfaces 61a, 62a, 71a, 72a on the inner peripheral sides of the inner and outer rings 61, 62, 71, 72 of the deep groove ball bearing 6 and the angular ball bearing 7 that function as touchdown bearings, and Although the example which formed the surface hardening layer 20 in all the inner peripheral surfaces 61b of the inner ring | wheel 61 which contacts the rotor shaft | shaft (rotating member) 2 at the time of touchdown was demonstrated by the rolling elements 63 and 73, track surface 61a, 62a, 71a. 72a, or only on the surfaces of the rolling elements 63 and 73, or only on the inner peripheral surface 61b of the inner ring 61 that contacts the rotor shaft (rotating member) 2 at the time of touchdown. In particular, since a large frictional force is momentarily generated on the inner peripheral surface 61b of the inner ring 61 at the time of touchdown, it is desirable to form the hardened surface layer 20 in this part as thick as possible (for example, 20 μm or more). ).
Further, if the entire rolling elements 63 and 73 are formed of a ceramic material, the processing for the rolling elements 63 and 73 becomes unnecessary, and even if the surface is worn, excellent durability is exhibited over a long period of time. Can do.

It is a longitudinal cross-sectional view which shows one Embodiment of the magnetic levitation type turbo molecular pump which shows an example of the vacuum pump which concerns on this invention. It is an expanded sectional view which shows the deep groove ball bearing which is one of the rolling bearings of this invention. It is an expanded sectional view which shows the angular ball bearing which is one of the rolling bearings of this invention. It is an expanded section which shows the surface structure of each member which comprises the rolling bearing of this invention.

Explanation of symbols

100: Magnetically levitated turbo molecular pump (vacuum pump)
DESCRIPTION OF SYMBOLS 1 ... Rotor blade 2 ... Rotor shaft 3 ... Magnetic bearing (Axial magnetic bearing)
4, 5 ... Magnetic bearing (radial magnetic bearing)
6 ... Deep groove ball bearing (rolling bearing for vacuum pump)
7. Angular contact ball bearings (rolling bearings for vacuum pumps)
10 ... Base material 20 ... Hardened surface layer (nitride layer, shot peening layer, DLC layer, ceramic layer)
61, 71 ... inner ring 62, 72 ... outer ring 63, 73 ... rolling element

Claims (11)

A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. Rolling bearing for
A rolling bearing for a vacuum pump, wherein a hardened surface layer for reducing frictional resistance with the rolling elements is formed on one or both of the raceway surfaces of the inner ring and the outer race. A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. Rolling bearing for
A rolling bearing for a vacuum pump, wherein a surface hardened layer is formed on the surface of the rolling element to reduce frictional resistance with one or both of the raceway surface of the inner ring and the raceway surface of the outer ring. A vacuum pump having an inner ring having a raceway surface on the outer peripheral surface, an outer ring having a raceway surface facing the raceway surface of the inner ring on the inner peripheral surface, and a plurality of rolling elements arranged to be freely rollable between the raceway surfaces. Rolling bearing for
For a vacuum pump, wherein a hardened surface layer is formed on one or both of the inner peripheral surface of the inner ring and the outer peripheral surface of the outer ring that comes into contact with another rotating member to reduce frictional resistance with the other rotating member. Rolling bearing. In the rolling bearing for vacuum pumps of any one of Claims 1-3,
The surface hardened layer has a nitride layer on the outermost surface,
The nitrided layer is composed of a compound layer having a surface hardness of Hv 900 or more and a diffusion hardened layer, and has a surface roughness Ra of 0.2 μm or less. In the rolling bearing for vacuum pumps of any one of Claims 1-3,
The surface hardened layer is composed of a shot peening layer formed by a shot peening process,
The shot peening layer has a surface hardness of Hv900 or more and a maximum surface roughness Ra of 2.5 μm or less. In the rolling bearing for vacuum pumps of Claim 5,
A rolling bearing for a vacuum pump, wherein a film in which a solid lubricant is dispersed is formed on the surface of the shot peening layer. In the rolling bearing for vacuum pumps of any one of Claims 1-3,
A rolling bearing for a vacuum pump, wherein the hardened surface layer is made of a diamond-like carbon layer. In the rolling bearing for vacuum pumps of any one of Claims 1-3,
A rolling bearing for a vacuum pump, wherein the surface hardened layer is made of a ceramic layer. In the rolling bearing for vacuum pumps of any one of Claims 1-8,
A rolling bearing for a vacuum pump, wherein bearing steel or martensitic stainless steel is used as a base material of the inner and outer rings or rolling elements on which the surface hardened layer is formed. In the rolling bearing for vacuum pumps of Claim 1 or 3,
A rolling bearing for a vacuum pump, wherein the rolling element is made of a ceramic material. A vacuum pump comprising a magnetic bearing that supports a rotating member by magnetism, and a touchdown bearing that functions as a spare bearing for the rotating member when the magnetic bearing becomes uncontrollable,
The vacuum pump using the rolling bearing for vacuum pumps of any one of Claims 1-10 as said touchdown bearing.

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