WO2018164139A1

WO2018164139A1 - Rolling bearing and method for producing same

Info

Publication number: WO2018164139A1
Application number: PCT/JP2018/008623
Authority: WO
Inventors: 雅樹中西; 三上　英信
Original assignee: Ntn株式会社
Priority date: 2017-03-07
Filing date: 2018-03-06
Publication date: 2018-09-13

Abstract

Provided is a rolling bearing which has excellent durability. This rolling bearing (1) is provided with an inner ring (2), an outer ring (3), a plurality of rolling bodies (4) and a hard film (8). The hard film (8) is formed on the surface of at least one component selected from the group consisting of the inner ring (2), the outer ring (3) and the rolling bodies (4). The inner ring (2), the outer ring (3) and the plurality of rolling bodies (4) are formed from an iron-based material. The hard film (8) comprises a base layer (8a), a mixed layer (8b) and a surface layer (8c). The base layer (8a) is mainly composed of Cr, and is formed directly on the above-mentioned surface. The mixed layer (8b) is mainly composed of WC and DLC, and is formed on the base layer (8a). The surface layer (8c) is mainly composed of DLC, and is formed on the mixed layer (8b). The mixed layer (8b) is configured such that the WC content in the mixed layer (8b) decreases and the DLC content in the mixed layer increases continuously or in stages from the base layer (8a) side toward the surface layer (8c) side.

Description

Rolling bearing and manufacturing method thereof

The present invention relates to a rolling bearing and a manufacturing method thereof, and more specifically to a rolling bearing in which a hard film containing diamond-like carbon is formed on the inner ring, outer ring, and rolling element surface, and a manufacturing method thereof.

The hard carbon film is a hard film generally called diamond-like carbon (hereinafter referred to as DLC. A film or layer mainly composed of DLC is also referred to as a DLC film or a DLC layer). In addition to the above, there are various names for hard carbon, such as hard amorphous carbon, amorphous carbon, hard amorphous carbon, i-carbon, diamond-like carbon, and these terms are clearly distinguished. Not.

The essence of DLC in which such terms are used is structurally a mixture of diamond and graphite. DLC has an intermediate structure between diamond and graphite. DLC is as hard as diamond and is excellent in wear resistance, solid lubricity, thermal conductivity, chemical stability, corrosion resistance, and the like. For this reason, for example, DLC is being used as a protective film for molds / tools, wear-resistant mechanical parts, abrasives, sliding members, magnetic / optical parts, and the like. As a method for forming such a DLC film, physical vapor deposition (hereinafter referred to as PVD) such as sputtering or ion plating, chemical vapor deposition (hereinafter referred to as CVD), unbalanced magnetron sputtering ( Hereinafter, a method such as UBMS) is employed.

Conventionally, attempts have been made to form a DLC film on the raceway surface of the bearing ring of the rolling bearing and the rolling surface of the rolling element. A DLC film generates extremely large internal stress during film formation. In addition, the DLC film has high hardness and Young's modulus, but has extremely low deformability. For this reason, the DLC film has weaknesses such as weak adhesion to the substrate and easy peeling. In the case where a DLC film is formed on the raceway surface of the bearing ring of the rolling bearing or the rolling surface of the rolling element, it is necessary to improve the adhesion.

For example, an intermediate layer is provided between the base material and the DLC film to improve the adhesion of the DLC film. On the raceway groove of the race ring formed of a steel material or the rolling surface of the rolling element, chromium ( Hereinafter, at least one of Cr (hereinafter referred to as Cr), tungsten (hereinafter referred to as W), titanium (hereinafter referred to as Ti), silicon (hereinafter referred to as Si), nickel (hereinafter referred to as Ni), and iron An underlayer having an element-containing composition, a constituent element of the underlayer and carbon, an intermediate layer having a carbon content rate opposite to the underlayer and larger than that of the underlayer, and argon and carbon There has been proposed a rolling device in which a DLC layer having a content rate of 0.02 mass% or more and 5 mass% or less is formed in this order (see Japanese Patent Application Laid-Open No. 2003-314560).

Further, assuming that the adhesion of the DLC film was improved by the anchor effect, irregularities with a height of 10 to 100 nm and an average width of 300 nm or less were formed on the raceway surface of the raceway by ion impact treatment, and the DLC was formed on this raceway surface. A rolling bearing in which a film is formed has been proposed (see JP 2001-304275 A).

JP 2003-314560 A JP 2001-304275 A

However, it is not easy to ensure the peeling resistance of the coating under the high contact surface pressure generated in the rolling bearing. In particular, it is more difficult to ensure the peeling resistance of the film under lubrication and operating conditions where a strong shearing force can be generated on the film due to sliding friction. Sliding surfaces for which application of DLC is considered are often in a state of poor lubrication or accompanied by slipping, and often have stricter conditions than operating conditions in a general rolling bearing.

In bearings, wear on the outer peripheral surface and end face as well as the rolling surface and sliding resistance in the seal groove may cause problems. For this reason, the DLC process other than the rolling surface in the bearing is also effective in improving the durability and functionality of the bearing.

The present invention has been made to cope with such problems. For example, the DLC film formed on the inner and outer ring raceways of a rolling bearing is improved in peel resistance and exhibits the original characteristics of the DLC film. Thus, an object of the present invention is to provide a rolling bearing having excellent durability.

The rolling bearing according to the present disclosure includes an inner ring, an outer ring, a plurality of rolling elements, and a hard film. The inner ring has an inner ring raceway surface on the outer periphery. The outer ring has an outer ring raceway surface on the inner periphery. The plurality of rolling elements roll between the inner ring raceway surface and the outer ring raceway surface. The hard film is formed on at least one surface selected from the group consisting of an inner ring, an outer ring, and a rolling element. The inner ring, the outer ring, and the plurality of rolling elements are made of an iron-based material. The hard film includes an underlayer, a mixed layer, and a surface layer. The underlayer is a layer mainly composed of chromium and formed directly on the surface. The mixed layer is a layer mainly composed of tungsten carbide (WC) and diamond-like carbon (DLC) formed on the base layer. The surface layer is a layer mainly composed of diamond-like carbon (DLC) formed on the mixed layer. In the mixed layer, the content of tungsten carbide (WC) in the mixed layer decreases continuously or stepwise from the base layer side to the surface layer side, and the diamond-like carbon (DLC) content in the mixed layer This is a layer with a higher rate.

The rolling bearing manufacturing method includes a step of preparing an inner ring, an outer ring, and a rolling element, and a step of forming a hard film. In the step of forming the hard film, the hard film is formed on at least one surface selected from the group consisting of an inner ring, an outer ring, and a rolling element. In the step of forming the hard film, an unbalanced magnetron sputtering apparatus using argon gas as the sputtering gas is used. In the step of forming the hard film, a graphite target and a hydrocarbon gas are used in combination as a carbon supply source, and the ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 of argon gas into the apparatus is 1 or more and 10 or less. To do. In the step of forming the hard film, the surface layer is formed by depositing carbon atoms generated from the carbon supply source on the mixed layer.

According to the above, the durability is improved by improving the peel resistance of the hard film including the layer mainly composed of DLC formed on the inner / outer ring raceway surfaces of the rolling bearing and exhibiting the original characteristics of DLC. Rolling bearings can be realized.

It is a cross-sectional schematic diagram of the rolling bearing which concerns on embodiment of this invention. It is a cross-sectional schematic diagram of the rolling bearing which concerns on embodiment of this invention. It is a cross-sectional schematic diagram of the rolling bearing which concerns on embodiment of this invention. It is a cross-sectional schematic diagram of the rolling element of the rolling bearing shown in FIG. It is a partial cross section schematic diagram of the hard film | membrane of the rolling bearing shown in FIG. It is a flowchart for demonstrating the manufacturing method of the rolling bearing which concerns on embodiment of this invention. It is a schematic diagram for demonstrating the film-forming principle of UBMS method. It is a schematic diagram which shows the structure of an example of a UBMS apparatus. It is a schematic diagram which shows the structure of a reciprocating sliding test air.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment)
A hard film such as a DLC film has residual stress in the film. The residual stress varies greatly depending on the film structure of the hard film, the film formation conditions, and the shape of the substrate on which the hard film is formed. As a result of repeated experiments, the present inventors have unexpectedly discovered that the influence of the substrate shape on the residual stress is large. For example, in a hard film formed on a flat surface, there is no peeling immediately after film formation, and the critical peeling load in the scratch test is large. However, when a hard film having the same structure is formed on curved surfaces such as the inner ring raceway surface and the outer ring raceway surface of the rolling bearing, it peels off immediately after film formation or does not peel immediately after film formation, but peels off during use. There was a case. As a result of intensive studies, the present inventors have determined that a hard film formed on the inner ring raceway surface, outer ring raceway surface, and rolling surface of the rolling element, which are curved surfaces, is a base layer (a layer mainly composed of Cr). It has been found that peeling resistance can be greatly improved by limiting to a predetermined structure comprising a mixed layer (layer having a WC / DLC gradient composition) and a surface layer (layer mainly composed of DLC). The hard film having such a configuration can suppress peeling even under actual use conditions of the bearing. Furthermore, when the indentation hardness of the surface layer was 10 to 20 GPa, the peel resistance could be further improved. The present invention has been made based on such findings.

<Configuration of rolling bearing>
1 to 3 are schematic cross-sectional views of rolling bearings according to an embodiment of the present invention (hereinafter also referred to as this embodiment). 4 is a schematic cross-sectional view of a rolling element of the rolling bearing shown in FIG. FIG. 5 is a schematic partial sectional view of a hard film of the rolling bearing shown in FIG.

The rolling bearing according to this embodiment will be described with reference to FIGS. FIG. 1 shows a cross-sectional view of a deep groove ball bearing which is an example of a rolling bearing in which a hard film described later is formed on the inner ring raceway surface. FIG. 2 shows a cross-sectional view of a deep groove ball bearing in which a hard film described later is formed on the outer ring raceway surface. FIG. 3 shows a cross-sectional view of a deep groove ball bearing in which a hard film is formed on the rolling surface of the rolling element.

1 to 3 includes an inner ring 2 having an inner ring raceway surface 2a on an outer periphery, an outer ring 3 having an outer ring raceway surface 3a on an inner periphery, and an inner ring raceway surface 2a and an outer ring raceway surface 3a. And a plurality of rolling elements 4 that roll. The rolling elements 4 are held at regular intervals by a cage 5. The seal member 6 seals both axial end openings between the inner ring and the outer ring. Grease 7 is sealed in the bearing space sealed by the seal member 6. As the grease 7 enclosed around the rolling element 4, a known grease for a rolling bearing can be used.

For example, in the rolling bearing 1 shown in FIG. 1, a hard film 8 is formed on the outer peripheral surface of the inner ring 2 including the inner ring raceway surface 2a. In the rolling bearing 1 shown in FIG. 2, a hard film 8 is formed on the inner peripheral surface of the outer ring 3 including the outer ring raceway surface 3a.

In the rolling bearing 1 shown in FIG. 3, a hard film 8 is formed on the rolling surface which is the surface of the rolling element 4 as shown in FIG. Since the rolling bearing 1 of FIG. 3 is a deep groove ball bearing, the rolling element 4 is a ball, and its rolling surface is the entire spherical surface. Cylindrical roller bearings or tapered roller bearings may be used as rolling bearings other than those shown in FIGS. At this time, when the hard film 8 is formed on the surface of the rolling element, the hard film 8 may be formed on at least the rolling surface of the rolling element such as the outer peripheral surface of the cylindrical roller. In the rolling bearing 1, the hard film 8 only needs to be formed on at least one surface of the inner ring 2, the outer ring 3, or the rolling element 4 according to the application.

As shown in FIGS. 1 to 3, the inner ring raceway surface 2a of the deep groove ball bearing is a circular curved surface having an arc-shaped cross section in the axial direction in order to guide the balls as the rolling elements 4. Similarly, the outer ring raceway surface 3a is also a circular curved surface having an arc-shaped cross section in the axial direction. The radius of curvature of the arc groove is generally about 0.51 dw to 0.54 dw, where dw is the diameter of the ball (steel ball diameter). Further, when cylindrical roller bearings or tapered roller bearings are used as rolling bearings other than those shown in FIGS. 1 to 3, the inner ring raceway surface and the outer ring raceway surface are at least circumferential in order to guide the rollers of these bearings. It becomes a curved surface in the direction. In addition, when a self-aligning roller bearing is used as a rolling bearing, since a cylindrical roller is used as a rolling element, the inner ring raceway surface and the outer ring raceway surface are curved in the axial direction in addition to the circumferential direction. In the rolling bearing 1 according to this embodiment, the inner ring raceway surface 2a and the outer ring raceway surface 3a may have any of the above shapes.

In the rolling bearing 1 according to the present embodiment, the inner ring 2, the outer ring 3, and the rolling element 4, which are bearing members for which the hard film 8 is to be formed, are made of an iron-based material. Here, the iron-based material is a material mainly composed of iron. As the iron-based material, any steel material generally used as a bearing member can be used, and examples thereof include high carbon chromium bearing steel, carbon steel, tool steel, martensitic stainless steel, and the like.

In these bearing members, the surface on which the hard film 8 is formed may have a Vickers hardness of Hv650 or higher. By setting it as Hv650 or more, the hardness difference with the hard film 8 (more specifically, the base layer 8a shown in FIG. 5) can be reduced, and the adhesion of the hard film 8 to the bearing member can be improved.

A nitride layer may be formed by nitriding treatment on the surface of the bearing member on which the hard film 8 is formed before the hard film 8 is formed. As the nitriding treatment, it is preferable to perform a plasma nitriding treatment that hardly forms an oxide layer that hinders adhesion on the surface of the bearing member as a base material. Further, the hardness of the nitrided layer surface after the nitriding treatment may be Vickers hardness of Hv1000 or more. In this case, the adhesion of the hard film 8 to the bearing member can be further improved.

The surface roughness Ra of the surface of the bearing member on which the hard film 8 is formed may be 0.05 μm or less. When the surface roughness Ra exceeds 0.05 μm, it is difficult to form the hard film 8 at the tip of the concavo-convex protrusion on the surface, and the film thickness of the hard film 8 may be locally reduced.

In the rolling bearing 1, the indentation hardness of the surface layer 8c may be 10 GPa or more and 20 GPa or less. In this case, the peel resistance of the hard film 8 can be improved. The indentation hardness may be 18 GPa or less, or 15 GPa or less. The indentation hardness may be 12 GPa or more, or 13 GPa or more.

A specific structure of the hard film 8 in the rolling bearing 1 according to the present embodiment will be described with reference to FIG. FIG. 5 shows the structure of the hard film 8 in the rolling bearing 1 shown in FIG. As shown in FIG. 5, the hard film 8 has a three-layer structure including a base layer 8a, a mixed layer 8b, and a surface layer 8c. The foundation layer 8a is a layer formed directly on the inner ring raceway surface 2a of the inner ring 2 and mainly composed of Cr. The mixed layer 8b is formed on the underlayer 8a and is a layer mainly composed of WC and DLC. The surface layer 8c is formed on the mixed layer 8b and is a layer mainly composed of DLC. Here, in the mixed layer 8b, the WC content in the mixed layer 8b decreases continuously or stepwise from the base layer 8a side to the surface layer 8c side, and the DLC content in the mixed layer 8b. The rate is high.

Since the foundation layer 8a is a layer mainly composed of Cr, the compatibility between the inner ring 2 which is a bearing member made of an iron-based material as a base material and the foundation layer 8a is good. Therefore, compared with the case where W, Ti, Si, etc. are used as the foundation layer 8a, the adhesion of the foundation layer 8a to the bearing member as the base material is high. In particular, when high carbon chromium bearing steel used as a material for the bearing race is used as a material for the bearing member, the base layer 8a mainly composed of Cr is excellent in adhesion to the bearing member.

WC used for the mixed layer 8b has intermediate hardness and elastic modulus between Cr and DLC. For this reason, concentration of residual stress after the hard film 8 is formed hardly occurs. Thus, when it is going to form the hard film 8 containing DLC excellent in peeling resistance in the inner ring raceway surface, outer ring raceway surface of the rolling bearing which is a curved surface, and the rolling surface of the rolling element, the intermediate in the hard film 8 Material selection in the mixed layer 8b as a layer is also an important factor.

The mixed layer 8b has a gradient composition in which the WC content decreases toward the surface layer 8c and the DLC content increases. Therefore, the mixed layer 8b has excellent adhesion on both the interface with the base layer 8a and the interface with the surface layer 8c. In particular, the mixed layer 8b has a structure in which WC and DLC are physically combined, and the DLC content is increased on the surface layer 8c side in the mixed layer 8b. Therefore, the surface layer 8c and the mixed layer 8b Excellent adhesion.

The surface layer 8c is a film mainly composed of DLC. The surface layer 8c has an inclined layer portion 8d whose hardness increases continuously or stepwise from the mixed layer 8b side to the opposite side (upper surface side of the surface layer 8c) on the side adjacent to the mixed layer 8b. preferable. This is because when the bias voltage at the time of film formation is different between the mixed layer 8b and the surface layer 8c, the bias voltage is changed continuously or stepwise in order to avoid a sudden change in the bias voltage (for example, a set value of the bias voltage). This is the part obtained by raising the The inclined layer portion 8d changes the bias voltage in this way, and as a result, the hardness changes in the thickness direction of the surface layer 8c as described above. The reason why the hardness increases continuously or stepwise is that the constituent ratio of the graphite structure (sp2) and the diamond structure (sp3) in the DLC structure is biased toward the latter as the bias voltage increases. Thereby, a sudden change in hardness in the interface region between the mixed layer 8b and the surface layer 8c is reduced, and the adhesion between the mixed layer 8b and the surface layer 8c is further improved.

The film thickness of the hard film 8 (the total film thickness of the base layer 8a, the mixed layer 8b, and the surface layer 8c) may be 0.5 μm or more and 3.0 μm or less. If the film thickness is less than 0.5 μm, the hard film 8 may have insufficient wear resistance and mechanical strength. If the film thickness exceeds 3.0 μm, the hard film 8 may be easily peeled off. Furthermore, the ratio of the thickness of the surface layer 8c to the thickness of the hard film 8 is preferably 0.8 or less. If this ratio exceeds 0.8, the gradient structure for physically bonding WC and DLC in the mixed layer 8b becomes a discontinuous structure, so that the adhesion of the hard film 8 may deteriorate.

In the rolling bearing 1 according to the present embodiment, the hard film 8 has a three-layer structure including the base layer 8a, the mixed layer 8b, and the surface layer 8c having the above-described composition, thereby realizing excellent peeling resistance.

<Effects of rolling bearing>
A rolling bearing 1 according to this embodiment includes an inner ring 2, an outer ring 3, a plurality of rolling elements 4, and a hard film 8. The inner ring 2 has an inner ring raceway surface 2a on the outer periphery. The outer ring 3 has an outer ring raceway surface 3a on the inner periphery. The plurality of rolling elements 4 roll between the inner ring raceway surface 2a and the outer ring raceway surface 3a. The hard film 8 is formed on at least one surface selected from the group consisting of the inner ring 2, the outer ring 3, and the rolling elements 4. The inner ring 2, the outer ring 3, and the plurality of rolling elements 4 are made of an iron-based material. The hard film 8 includes a base layer 8a, a mixed layer 8b, and a surface layer 8c. The underlayer 8a is a layer mainly composed of chromium (Cr), which is directly formed on the surface. The mixed layer 8b is a layer mainly composed of tungsten carbide (WC) and diamond-like carbon (DLC) formed on the base layer 8a. The surface layer 8c is a layer mainly composed of diamond-like carbon (DLC) formed on the mixed layer 8b. In the mixed layer 8b, the content of tungsten carbide (WC) in the mixed layer 8b decreases continuously or stepwise from the base layer 8a side to the surface layer 8c side, so that the diamond-like carbon ( DLC) is a layer with a high content.

In the rolling bearing 1, the underlying layer 8 a mainly composed of Cr formed directly on the surface has good compatibility with the iron-based material, and is more closely adhered to the iron-based material than the layer mainly composed of W or Si. Excellent in properties. Since the WC used for the mixed layer 8b has intermediate hardness and elastic modulus between Cr and DLC, it is possible to suppress the concentration of residual stress in the mixed layer 8b after the hard film 8 is formed. Further, the mixed layer 8b mainly composed of WC and DLC has a gradient composition as described above, so that the mixed layer 8b has a structure in which WC and DLC are physically coupled.

Due to the above structure, even if the hard film 8 is formed on any of the surfaces of the inner ring 2, the outer ring 3, and the rolling element 4, the peel resistance is excellent. For this reason, the hard film 8 formed on any of the inner ring raceway surface 2a, the outer ring raceway surface 3a, and the rolling surface of the rolling element 4 can exhibit the original characteristics of DLC without peeling off. As a result, the rolling bearing 1 has excellent seizure resistance, wear resistance, and corrosion resistance, and has a long life with little damage to the raceway surface even under severe lubrication.

From a different point of view, in the rolling bearing 1 according to this embodiment, by forming the hard film 8 having the above-described structure and properties, even when the hard film 8 receives a load such as rolling contact when the bearing is used. The wear and peeling of the hard film 8 can be suppressed. For this reason, the rolling bearing 1 having a long service life with little damage to the raceway surface and the like can be obtained even in a severely lubricated state. Further, in the rolling bearing 1 in which the grease 7 is sealed, if the new metal surface is exposed due to damage to the race rings such as the inner ring 2 and the outer ring 3, the grease is promoted to be deteriorated by the catalytic action. However, in the rolling bearing 1 according to the present embodiment, since the hard film 8 is formed, damage to the inner ring raceway surface 2a, the outer ring raceway surface 3a and the rolling surfaces of the rolling elements 4 due to metal contact can be suppressed. Deterioration can also be suppressed.

<Rolling bearing manufacturing method>
FIG. 6 is a flowchart for explaining a method of manufacturing the rolling bearing shown in FIGS. FIG. 7 is a schematic diagram for explaining the film forming principle of the UBMS method. FIG. 8 is a schematic diagram illustrating a configuration of an example of the UBMS apparatus.

As shown in FIG. 6, in the method of manufacturing a rolling bearing, first, a preparation step (S10) is performed. In this step (S10), parts to be a bearing member constituting the rolling bearing 1 are prepared. Examples of the parts include the inner ring 2, the outer ring 3, the rolling element 4, and the seal member 6.

Next, a film forming step (S20) is performed. In this step (S20), a hard film is formed on the surface of the component prepared in the above step (S10). Details of the film forming step (S20) will be described later. Thereafter, a post-processing step (S30) is performed in which finishing processing, assembly processing, or the like of the part on which the hard film is formed is performed. In this way, the rolling bearing 1 shown in FIGS. 1 to 3 can be obtained.

Hereinafter, the formation method of the hard film in the step (S20) will be described. The hard film 8 is obtained by forming the base layer 8a, the mixed layer 8b, and the surface layer 8c in this order on the film formation surface of the component to be the bearing member.

The underlayer 8a and the mixed layer 8b are preferably formed using a UBMS apparatus using Ar gas as a sputtering gas. The film forming principle of the UBMS method using the UBMS apparatus will be described with reference to the schematic diagram shown in FIG. In FIG. 7, the base material 12 is an inner ring 2, an outer ring 3, or a rolling element 4 that is a component to be a bearing member to be formed, but is schematically illustrated as a flat plate shape. The substrate 12 is connected to a bias power source 11. As shown in FIG. 7, the target 15 is disposed so as to face the substrate 12. The planar shape of the target 15 which is a supply source of the film forming raw material is, for example, a round shape. An inner magnet 14 a and an outer magnet 14 b having different magnetic characteristics in the central portion and the peripheral portion of the round target 15 are disposed below the round target 15. For example, the outer magnet 14b forms a relatively strong magnetic field, and the inner magnet 14a forms a relatively weak magnetic field.

In the UBMS method, an inner magnet is formed such that a portion 16a of the magnetic force lines 16 generated by the inner magnet 14a and the outer magnet 14b reaches the vicinity of the substrate 12 while forming a high-density plasma 19 from Ar gas near the target 15. A magnetic field is formed by 14a and the outer magnet 14b. A part of the high-density plasma 19 (Ar plasma) generated at the time of sputtering diffuses to the vicinity of the substrate 12 along a part 16a of the lines of magnetic force. In such a UBMS method, the Ar plasma 17 and electrons reach the base material 12 more than the amount of ionized particles 18 derived from the target 15 along the part 16a of the magnetic field lines reaching the vicinity of the base material 12 than during normal sputtering. Let Such an effect is called an ion assist effect. In the UBMS method, a dense film 13 can be formed on the surface of the substrate 12 by an ion assist effect.

When forming the foundation layer 8 a, a Cr target is used as the target 15. When the mixed layer 8 b is formed, a WC target and a graphite target are used in combination as the target 15. The mixed layer 8b is formed in a continuous or stepwise manner while increasing the power applied to the graphite target serving as the carbon supply source and decreasing the power applied to the WC target. Thereby, in the mixed layer 8b, the WC content rate decreases continuously or stepwise from the base layer 8a side to the surface layer 8c side, and the DLC content rate increases continuously or stepwise. The part which became the layer of can be formed.

The surface layer 8c may also be formed using a UBMS apparatus using Ar gas as the sputtering gas. More specifically, the following conditions can be used as conditions for forming the surface layer 8c. That is, using a UBMS apparatus, a graphite target and a hydrocarbon gas are used in combination as a carbon supply source. The ratio of the introduction amount of the hydrocarbon-based gas to the introduction amount 100 of the Ar gas into the UBMS apparatus is set to 1 or more and 10 or less. The degree of vacuum in the UBMS device is set to 0.2 Pa or more and 0.8 Pa or less. It is preferable to form the surface layer 8c which is a DLC film by depositing particulate carbon generated by sputtering from the carbon supply source on the mixed layer 8b using such conditions. The conditions described above will be described below.

The hardness and elastic modulus of the DLC film can be adjusted by using a graphite target and a hydrocarbon-based gas in combination as a carbon supply source. Gases such as methane, acetylene, and benzene can be used as the hydrocarbon gas. Although it does not specifically limit as hydrocarbon type gas, It is preferable to use methane gas from the point of cost and handleability.

The ratio of the introduction amount of the hydrocarbon-based gas is 1 to 10 (volume part) with respect to 100 introduction amount (volume part) of Ar gas into the UBMS apparatus (specifically, in the film forming chamber of the UBMS apparatus). As a result, the adhesion to the mixed layer 8b can be improved without deteriorating the wear resistance of the surface layer 8c.

The degree of vacuum in the film forming chamber is preferably 0.2 Pa or more and 0.8 Pa or less as described above. More preferably, the degree of vacuum is 0.25 Pa or more and 0.8 Pa or less. When the degree of vacuum is less than 0.2 Pa, since the amount of Ar gas in the film formation chamber is small, Ar plasma is not generated and the surface layer 8c may not be formed. Further, when the degree of vacuum in the film forming chamber is higher than 0.8 Pa, reverse sputtering phenomenon tends to occur, and the wear resistance of the surface layer 8c may be deteriorated.

<Operational effects of the rolling bearing manufacturing method>
As shown in FIG. 6, the method for manufacturing the rolling bearing 1 includes a step of preparing an inner ring, an outer ring, and a rolling element (S10), and a step of forming a hard film (film formation step (S20)). In the step of forming the hard film (S20), the hard film 8 is formed on at least one surface selected from the group consisting of the inner ring 2, the outer ring 3, and the rolling element 4. In the step of forming the hard film (S20), an unbalanced magnetron sputtering (UBMS) apparatus using argon gas as the sputtering gas is used. In the step of forming the hard film (S20), a graphite target and a hydrocarbon gas are used in combination as a carbon supply source, and the ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 of argon gas into the apparatus is 1 or more. 10 or less. In the step of forming the hard film (S20), the surface layer 8c is formed by depositing carbon atoms generated from the carbon supply source on the mixed layer 8b. If it does in this way, the rolling bearing 1 excellent in durability which concerns on this embodiment can be obtained.

In the rolling bearing manufacturing method, the surface layer 8c formed by the step (S20) has an inclined layer portion 8d whose hardness increases continuously or stepwise from the mixed layer 8b side on the side adjacent to the mixed layer 8b. You may have. In this case, in the step of forming the hard film (S20), the bias voltage applied to at least one selected from the group consisting of the inner ring 2, the outer ring 3, and the rolling element 4 including the surface is increased continuously or stepwise. However, the inclined layer portion 8d is formed. In this way, the inclined layer portion 8d can be easily formed.

In the rolling bearing manufacturing method, in the step of forming the hard film (S20), the base layer 8a and the mixed layer 8b are formed using the UBMS apparatus using argon gas as the sputtering gas as described above. Also good. In the step (S20) of forming the hard film, the mixed layer is continuously or stepwise increased while increasing the sputtering power applied to the graphite target serving as the carbon supply source and lowering the power applied to the tungsten carbide target. 8b may be formed. In this way, the composition of WC and DLC in the mixed layer 8b can be changed in the thickness direction.

The method for manufacturing a rolling bearing includes a step of forming a nitride layer by performing nitriding treatment on the surface on which the hard film 8 is formed before the step of forming the hard film (S20). Also good. The nitriding treatment may be a plasma nitriding treatment.

In the rolling bearing manufacturing method, the surface roughness Ra of the surface on which the hard film 8 is formed in the step of forming the hard film (S20) may be 0.05 μm or less. In this case, the hard film 8 in which the film thickness variation is suppressed can be formed.

The above rolling bearing manufacturing method may further include a step of enclosing grease around the rolling element 4. In this case, the rolling bearing 1 in which the grease 7 is enclosed can be obtained.

(Example)
In order to confirm the effect of the hard film formed on the rolling bearing according to the present embodiment, a hard film was formed on a predetermined substrate, and the physical properties of the hard film were evaluated. The peel resistance was evaluated by a friction and wear test using a reciprocating sliding tester. This will be specifically described below.

<Sample>
Sample No. Seven types of test pieces 1 to 7 were prepared. The material of the test piece used for the evaluation of the hard film and the conditions for forming the hard film are as follows.
(1) Base material: JIS standard SUJ2, quenching and tempering product, surface hardness 780Hv
(2) Base material: A flat plate (surface roughness 0.02 μmRa) made of the above-mentioned base material and mirror-polished, and the shape of the base material: the planar shape is circular, diameter 33 mm × thickness 6 mm
(3) UBMS device: manufactured by Kobe Steel; UBMS202
FIG. 8 is a schematic diagram of a UBMS apparatus. The UBMS apparatus shown in FIG. 8 is a UBMS apparatus having an arc ion plating (hereinafter referred to as AIP) function. As shown in FIG. 8, the UBMS apparatus instantaneously vaporizes and ionizes the AIP evaporation source material 22a using the vacuum arc discharge to the base material 21 arranged on the disk 20, and based on this. It has an AIP function of depositing on the material 21 to form a film. Further, the UBMS apparatus forms a non-equilibrium magnetic field between the target 22b, which is a sputter evaporation source material, and the base material 21, and increases the plasma density near the base material 21 by the magnetic field to increase the ion assist effect. (See FIG. 7), it has a UBMS function capable of controlling the characteristics of the film deposited on the substrate. With this apparatus, a composite film in which an AIP film and a plurality of UBMS films (including a composition gradient portion) are arbitrarily combined can be formed on the substrate 21. Sample No. In Nos. 1 to 7, a base layer, a mixed layer, and a surface layer are formed as a UBMS film on the surface of a flat plate as a base material.
(4) Sputtering gas: Ar gas (5) Conditions for forming the underlayer and the mixed layer:
Underlayer: The inside of the deposition chamber is evacuated to about 5 × 10 ⁻³ Pa, the test piece is baked with a heater, and the surface of the test piece is etched with Ar plasma. Then, the sputtering power applied to the Cr target and WC target is adjusted by the UBMS method, the composition ratio of Cr and WC is tilted, and a Cr / WC graded layer with a lot of Cr on the substrate side and a lot of WC on the surface side is formed. did.

Mixed layer: Adjust the sputtering power applied to the WC target and the graphite target by the UBMS method, tilt the composition ratio of WC and DLC, and tilt the WC / DLC with a lot of WC on the base layer side and a lot of DLC on the surface side A layer was formed. The formation conditions of the mixed layer are basically the same as the formation conditions of the underlayer except for the sputtering power described above. Sample No. Regarding 1 to 7, the above-described underlayer and mixed layer were formed under the same conditions.
(6) Surface layer formation conditions:
Sample No. For each of 1 to 7, a surface layer was formed under the conditions shown in Table 1.
(7) Manufacturing method of each sample:
The substrate shown in Table 1 described later was ultrasonically cleaned with acetone and then dried. After drying, the substrate was attached to a UBMS apparatus, and an underlayer and a mixed layer were formed under the above-described formation conditions. A DLC film, which is a surface layer, was formed on the film formation conditions shown in Table 1 to obtain a test piece having a hard film. Note that “degree of vacuum” in each table is the degree of vacuum in the film forming chamber in the above apparatus.

<Test method>
Reciprocating sliding test:
The obtained sample No. With respect to 1 to 7, a peel resistance test by sliding was performed using a reciprocating sliding tester shown in FIG. The reciprocating sliding test machine shown in FIG. 9 includes a pedestal 32 that holds a sample on which a base material 21 and a hard film 8 are formed, a load cell 27 and an acceleration sensor 28 installed on the pedestal 32, and a hard film 8 of the sample. A silicon nitride sphere 25 as a sphere to be brought into contact with, a holder 26 for holding the silicon nitride sphere 25, an arm 31 connected to the holder 26, and a vibrator 29 for vibrating the arm 31 in the lateral direction. The holder 26 can apply a load from the direction indicated by the arrow 30.

The test was performed without lubrication. In the test, the load was increased, and the load when the friction coefficient increased due to the peeling of the hard film 8 was defined as the limit load. Specific test conditions are shown below.

(Test conditions)
Lubrication: No lubrication Ball: 3/8 inch, silicon nitride ball Load: 30-80N
Load increase speed: 10 N / min
Vibration frequency: 60Hz
Amplitude: 2mm
Indentation hardness measurement:
For the hard film 8 of each sample, the indentation hardness was measured using a nanoindenter (G200) manufactured by Agilent Technologies. In addition, the measured value has shown the average value of the depth (location where hardness is stabilized) which is not influenced by surface roughness, and measured 10 places for each sample.

<Result>
Table 1 shows the sample conditions and test results.

In addition, since the base layer and the mixed layer in Table 1 are mixed with two components, they are indicated as “first component / second component”. The methane gas introduction ratio is the ratio of the methane gas introduction amount to the argon gas introduction amount 100.

As can be seen from Table 1, when the indentation hardness of the surface layer of the hard film 8 is changed, in the region where the indentation hardness is 15 GPa or less, the limit load in the reciprocating sliding test is large when the hardness is low. Tend.

Although the embodiments of the present invention have been described above, the above-described embodiments can be variously modified. Further, the scope of the present invention is not limited to the above-described embodiments and examples. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Sliding surfaces and rolling surfaces for which application of DLC is considered are often in a severely lubricated state such as poor lubrication or high sliding speed. In the rolling bearing according to the present embodiment, for example, DLC is formed on the inner and outer ring raceway surfaces and the rolling surfaces of the rolling elements. Therefore, even when operated in a severely lubricated state, the rolling bearing has excellent peeling resistance, and The characteristics can be demonstrated. For this reason, the rolling bearing is excellent in seizure resistance, wear resistance, and corrosion resistance. Therefore, the rolling bearing can be applied to various uses including use in severe lubrication.

1 Rolling bearing, 2 Inner ring, 2a Inner ring raceway surface, 3 Outer ring, 3a Outer ring raceway surface, 4 Rolling element, 5 Cage, 6 Seal member, 7 Grease, 8 Hard film, 8a Underlayer, 8b Mixed layer, 8c Surface layer 8d inclined layer portion, 11 bias power source, 12, 21 base material, 13 film, 14a inner magnet, 14b outer magnet, 15, 22b target, 16 magnetic field lines, 16a part, 17 Ar plasma, 18 particles, 19 high density plasma 20 disc, 22a evaporation source material, 25 silicon nitride sphere, 26 holder, 27 load cell, 28 acceleration sensor, 29 shaker, 30 arrow, 31 arm, 32 pedestal.

Claims

An inner ring having an inner ring raceway surface on the outer periphery;
An outer ring having an outer ring raceway surface on the inner periphery;
A plurality of rolling elements rolling between the inner ring raceway surface and the outer ring raceway surface;
A hard film formed on at least one surface selected from the group consisting of the inner ring, the outer ring, and the rolling element,
The inner ring, the outer ring, and the plurality of rolling elements are made of an iron-based material,
The hard film is
An underlayer mainly composed of chrome directly formed on the surface;
A mixed layer mainly composed of tungsten carbide and diamond-like carbon formed on the underlayer;
A surface layer mainly composed of diamond-like carbon formed on the mixed layer,
In the mixed layer, the content of the tungsten carbide in the mixed layer decreases continuously or stepwise from the base layer side to the surface layer side, and the diamond-like carbon in the mixed layer decreases. Rolling bearing that is a layer with a high content.
The rolling bearing according to claim 1, wherein the indentation hardness of the surface layer is 10 GPa or more and 20 GPa or less.
The rolling bearing according to claim 1 or 2, wherein the surface layer has an inclined layer portion whose hardness increases continuously or stepwise from the mixed layer side on a side adjacent to the mixed layer.
The rolling bearing according to any one of claims 1 to 3, wherein the iron-based material is one selected from the group consisting of high-carbon chromium bearing steel, carbon steel, tool steel, and martensitic stainless steel. .
It is a manufacturing method of the rolling bearing according to claim 1,
Preparing the inner ring, the outer ring, and the rolling element;
Forming a hard film on at least one surface selected from the group consisting of the inner ring, the outer ring, and the rolling elements,
In the step of forming the hard film, an unbalanced magnetron sputtering apparatus using argon gas as a sputtering gas is used, and a graphite target and a hydrocarbon-based gas are used in combination as a carbon supply source. The ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 in the apparatus is set to 1 to 10, and carbon atoms generated from the carbon supply source are deposited on the mixed layer to form the surface layer. A method for manufacturing a rolling bearing.
The method for manufacturing a rolling bearing according to claim 5, wherein the hydrocarbon-based gas is methane gas.
The surface layer has an inclined layer portion whose hardness increases continuously or stepwise from the mixed layer side on the side adjacent to the mixed layer,
In the step of forming the hard film, the inclination is applied while continuously or stepwise increasing a bias voltage applied to at least one selected from the group consisting of the inner ring, the outer ring, and the rolling element including the surface. The manufacturing method of the rolling bearing of Claim 5 or 6 with which a layer part is formed into a film.
In the step of forming the hard film, the underlayer and the mixed layer are formed using the unbalanced magnetron sputtering apparatus using argon gas as a sputtering gas.
In the step of forming the hard film, the mixed layer is formed continuously or stepwise while increasing the sputtering power applied to the graphite target serving as the carbon supply source and lowering the power applied to the tungsten carbide target. The method for manufacturing a rolling bearing according to any one of claims 5 to 7, wherein a film is formed.