Insulating bearing

Abstract

In this insulating bearing, a mill scale surface is formed on at least a part of a contact surface of a bearing ring on which a resin layer is formed, the contact surface being in contact with the resin layer. Alternatively, instead of the mill scale surface, the surface roughness in the circumferential direction is roughened to Ra 3.2 μm or more or Sa 3.2 μm or more. As a result, the relative sliding between an outer ring and inner ring and an insulating film in the insulating bearing coated with the insulating film and the damage between the two surfaces due to the relative sliding can be prevented, and the deterioration of bearing accuracy and the occurrence of electrolytic corrosion can be suppressed for a longer period of time.

Description

Insulated bearings

[0001] The present invention relates to an insulating bearing that is mounted on the rotating shaft of a motor, generator, or the like, and is particularly suitable for mounting in a location where a current may flow.

[0002] Conventionally, in devices with rotating bodies, metal bearings have been attached to the rotating shafts to reduce frictional resistance caused by the rotation of the rotating body. For example, bearings are attached to the rotating shafts of motors that use electromagnetic force to rotate a rotating body (a so-called rotor) and generators that generate electricity by rotating a rotating body (a so-called turbine) using hydraulic power or the like.

[0003] These motors, generators, etc. have a problem in that current leaks into the bearings, and corrosion caused by the current flow (hereinafter referred to as "galvanic corrosion") easily progresses. Therefore, various techniques for preventing galvanic corrosion of bearings have been investigated.

[0004] For example, Patent Document 1 discloses an electrolytic corrosion-resistant rolling bearing having an insulating coating containing axially oriented fibers on the surface of the outer ring or inner ring, and Patent Document 2 discloses a rolling bearing including a conductive shield and an insulating coating.

[0005] International Publication No. 2021-220613 U.S. Patent No. 9,581,203

[0006] However, in insulated bearings configured in which the outer ring or inner ring is covered with an insulating coating, as in Patent Documents 1 and 2, the insulating coating is not subjected to a mechanical restraint force in the circumferential direction of the outer ring or inner ring, and is held to the outer ring or inner ring by friction alone.As a result, relative slippage may occur between the outer ring or inner ring and the insulating coating when rotating under high load, particularly high radial load.When significant relative slippage occurs, sliding occurs at specific locations between the outer ring or inner ring and the insulating coating, causing uneven wear and other problems that degrade bearing accuracy, and there is also concern that this may worsen gear tooth contact and acoustic and vibration performance in components to which the insulated bearing is applied.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide an insulated bearing that is coated with an insulating coating and that prevents relative sliding between the outer ring or inner ring and the insulating coating, and the resulting damage between the two surfaces, thereby making it possible to suppress deterioration of bearing accuracy and the occurrence of electrolytic corrosion for an extended period of time.

[0008] As a result of extensive research into solving the above problems, the inventors discovered that relative sliding between the outer ring or inner ring and the resin layer can be prevented by roughening the portions of the outer ring or inner ring that come into contact with the resin layer that serves as the insulating coating, or by specifying the roundness and concentricity of the outer ring or inner ring, thereby completing the present invention.

[0009] That is, the insulating bearing according to the present invention has the following configuration [1].

[0010] [1] An insulated bearing comprising a pair of raceways having a pair of raceways, a plurality of rolling elements held so as to be rollable between the pair of raceways, and a cage which holds the rolling elements so as to be rollable, and in which a resin layer is coated on a contact surface of the raceway with a mating member, wherein a black surface is formed on at least a part of the contact surface of the raceway coated with the resin layer which contacts the resin layer.

[0011] Further, preferred embodiments of the present invention relating to an insulated bearing relate to the following [2] to [3]. [2] The insulated bearing according to [1], wherein at least a part of the circumferential portion of the contact surface of the bearing ring on which the resin layer is formed that comes into contact with the resin layer has a circularity of 30 μm or more. [3] The insulated bearing according to [1] or [2], wherein at least two or more circumferential portions of the contact surface of the bearing ring on which the resin layer is formed that comes into contact with the resin layer have a coaxiality of 20 μm or more.

[0012] Furthermore, the insulating bearing according to the present invention has the following configuration [4].

[0013] [4] An insulated bearing comprising a pair of raceways having a pair of raceways, a plurality of rolling elements held so as to be rollable between the pair of raceways, and a cage which holds the rolling elements so as to be rollable, and in which a resin layer is coated on a contact surface of the raceway with a mating member, wherein at least a part of the contact surface of the raceway on which the resin layer is formed, which contacts the resin layer, has a circumferential surface roughness of Ra 3.2 μm or more, or Sa 3.2 μm or more.

[0014] By roughening the portions of the outer ring or inner ring that come into contact with the resin layer, and specifying the circularity and concentricity of the outer ring or inner ring, the insulated bearing of the present invention can prevent relative sliding between the outer ring or inner ring and the resin layer, and resulting damage between the two surfaces, and can suppress deterioration of bearing accuracy and the occurrence of electrolytic corrosion over the long term.

[0015] FIG. 1 is an axial cross-sectional view showing an example of an insulated bearing of the present invention. FIG. 2 is a partially cutaway perspective view of an insulated bearing having a black surface formed on the outer ring. FIGS. 3(a) and (b) are views showing a first embodiment, with FIG. 3(a) being an axial cross-sectional view thereof and FIG. 3(b) being a cross-sectional view taken along line III-III in FIG. 3(a). FIGS. 4(a) and (b) are views showing a second embodiment, with FIG. 4(a) being an axial cross-sectional view thereof and FIG. 4(b) being a cross-sectional view taken along line IV-IV in FIG. 4(a). FIGS. 5(a) and (b) are views showing a third embodiment, with FIG. 5(a) being an axial cross-sectional view thereof and FIG. 5(b) being a cross-sectional view taken along line V-V in FIG. 5(a). FIGS. 6(a) and (b) are views showing a fourth embodiment, with FIG. 6(a) being an axial cross-sectional view thereof and FIG. 6(b) being a cross-sectional view taken along line VI-VI in FIG. 7 is a partially cutaway perspective view showing a fifth embodiment. Fig. 8 is a cross-sectional view of the boundary between the outer peripheral surface of the outer ring and the main chamfer in embodiment 5. Fig. 9 is a partially cutaway perspective view showing embodiment 6. Fig. 10 is a cross-sectional view of the boundary between the outer peripheral surface of the outer ring and a groove in embodiment 6. Fig. 11 is a partially cutaway perspective view showing an example of an insulated bearing in which the portion that comes into contact with the resin layer is roughened. Figs. 12(a) to 12(c) are cross-sectional views showing ways of forming the resin layer. Figs. 13(a) and 13(b) are cross-sectional views showing other examples of ways of forming the resin layer.

[0016] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the embodiments described below.

[0017] 1 is an axial cross-sectional view showing an example of an insulated bearing of the present invention. As shown in the figure, the insulated bearing 10 has an outer ring 1 which is one of the raceways and an inner ring 2 which is the other of the raceways arranged concentrically, balls 3 which are multiple rolling elements held in a rollable manner between a raceway groove (raceway surface) 1x of the outer ring 1 and a raceway groove (raceway surface) 2x of the inner ring 2, and a cage 4 which holds the balls 3 in a rollable manner. The balls 3 are held at equal intervals in the circumferential direction by the cage 4.

[0018] A resin layer 5 is continuously formed to cover the outer peripheral surface 1a of the outer ring 1, both axial side surfaces 1b continuing from the outer peripheral surface 1a, and inner peripheral surfaces 1c extending inward from the inner diameter ends of both axial side surfaces 1b. An annular groove 1c1 is formed along the circumference in the inner peripheral surface 1c of the outer ring 1, and an end of the resin layer 5 fits into the annular groove 1c1.

[0019] In addition, a resin layer 5 is formed on the inner peripheral surface 2a of the inner ring 2, on both axial side surfaces 2b continuing from the inner peripheral surface 2a, and on the outer peripheral surface 2c extending inward from the outer diameter side ends of both axial side surfaces 2b, and the ends of the resin layer 5 are fitted into annular grooves 2c1 formed on the outer peripheral surface 2c.

[0020] There are no restrictions on the resin that constitutes the resin layer 5, but it is preferable that the resin has heat resistance and durability (mechanical strength) as well as insulation properties. For example, polyphenylene sulfide, polyphthalamide, polyphenylene ether, polyether ether ketone, fluororesin, polyamide, etc. can be suitably used.

[0021] The thickness of the resin layer 5 is preferably 50 μm or more, more preferably 100 μm or more, in order to ensure insulation. On the other hand, the upper limit of the thickness of the resin layer 5 is preferably 2 mm or less, more preferably 1 mm or less. If the resin layer 5 is made thicker than 2 mm, further improvement in insulation cannot be expected, and it only leads to an increase in costs.

[0022] Furthermore, injection molding, in which the outer ring 1 or inner ring 2 on which resin layer 5 is to be formed is used as an insert component, is simple and preferable for forming resin layer 5. Other methods that can also be used include spraying (including thermal spraying), electrostatic coating (powder / liquid), and fluidized bed immersion.

[0023] (Formation of black surface) In the present invention, to prevent relative sliding between the outer ring 1 or the inner ring 2 and the resin layer 5, a black surface 8 is formed on the portion of the outer ring 1 or the inner ring 2 that contacts the resin layer 5; specifically, for the outer ring 1, on all or part of the outer peripheral surface 1a, both axial side surfaces 1b, and inner peripheral surface 1c, including the annular groove 1c1, and for the inner ring 2, on all or part of the inner peripheral surface 2c, including the inner peripheral surface 2a, both axial side surfaces 2b, and the annular groove 2c1. Note that while Figure 2 is a partially cutaway perspective view showing an example in which a black surface is formed on the outer ring 1, the black surface 8 is formed on the outer peripheral surface 1a and annular groove 1c1 of the outer ring 1, and the resin layer 5 is formed on top of the black surface 8 by injection molding.

[0024] The black surface 8 is an oxide film formed on the steel material by heat treatment, giving the steel material the appearance of being covered with a black skin. In other words, the black surface 8 is an unprocessed surface that is not cut or ground after heat treatment. This black surface has pinholes and irregularities on the surface, making it rough. Therefore, the formation of a black surface on the portions of the outer ring 1 and inner ring 2 that come into contact with the resin layer 5 prevents relative sliding between them.

[0025] (Specifications for Circularity or Coaxiality) The black surface 8 is formed by heat treating the outer ring 1 or the inner ring 2, which increases the geometric tolerances of the circularity and coaxiality of the outer ring 1 or the inner ring 2. This allows a circumferential restraining force to act on the resin layer 5, preventing relative slippage. Specifically, the circularity is preferably 30 μm or more, and the coaxiality is preferably 20 μm or more. However, the greater the circularity and coaxiality, the greater the effect on bearing rotation, so it is preferable that the circularity be 500 μm or less, and the coaxiality be 200 μm or less.

[0026] 3(a) to 10 describe embodiments of insulated bearings in which the circularity or coaxiality of the outer ring 1 or inner ring 2 is defined by changing the shape of the outer ring 1 or inner ring 2, but all of the figures exaggerate the circularity and coaxiality of the outer ring 1, inner ring 2, and resin layer 5 to make them easier to see. Note that FIGS. 3(a) to 6(b) show embodiments relating to circularity, and FIGS. 7 to 10 show embodiments relating to coaxiality.

[0027] Embodiment 2 Fig. 3 shows an embodiment in which a resin layer 5 is formed on the outer peripheral surface 1a of an outer ring 1 with high circularity, with Fig. 3(a) being an axial cross-sectional view and Fig. 3(b) being a cross-sectional view taken along line III-III in Fig. 3(a). As shown in Fig. 3(b), the outer peripheral surface 1a of the outer ring 1 (the surface that contacts the resin layer 5) shares a center C1 with the center C of the bearing, and the outer diameter in the left-right direction is larger than the outer diameter in the up-down direction. This difference in diameter is the circularity, and if it is 30 µm or more, relative slippage can be effectively prevented. Accordingly, the thickness of the resin layer 5 is thinner in the left-right direction than in the up-down direction so that the outer diameter is a perfect circle.

[0028] Embodiment 3 Figure 4 shows an embodiment in which the circularity of the annular groove 1c1 of the outer ring 1 is increased, with Figure 4(a) being its axial cross-sectional view and Figure 4(b) being a cross-sectional view taken along line IV-IV in Figure 4(a). As shown in Figure 4(b), the center C1 of the annular groove 1c1 (the surface that contacts the resin layer 5) of the outer ring 1 coincides with the center C of the bearing, and the groove depth of the annular groove 1c1 is greater in the left-right direction than in the up-down direction. Accordingly, the thickness of the resin layer 5 within the annular groove 1c1 is greater in the left-right direction than in the up-down direction so that the inner diameter is a perfect circle.

[0029] Embodiment 4 Figure 5 shows an embodiment in which a resin layer 5 is formed on the inner circumferential surface 2a of an inner ring 2 with high circularity, with Figure 5(a) being an axial cross-sectional view and Figure 5(b) being a cross-sectional view taken along line VV in Figure 5(a). As shown in Figure 5(b), the inner circumferential surface 2a of the inner ring 2 (the surface that comes into contact with the resin layer 5) has a center C2 that coincides with the center C of the bearing, and the inner diameter in the vertical direction is smaller than the inner diameter in the horizontal direction. Accordingly, the thickness of the resin layer 5 is greater in the horizontal direction than in the vertical direction, so that the inner diameter is a perfect circle.

[0030] Embodiment 5 Figure 6 shows an embodiment in which the circularity of the annular groove 2c1 of the inner ring 2 is increased, with Figure 6(a) being an axial cross-sectional view and Figure 6(b) being a cross-sectional view taken along line VI-VI in Figure 6(a). As shown in Figure 6(b), the center C2 of the annular groove 2c1 (the contact surface with the resin layer 5) of the inner ring 2 coincides with the center C of the bearing, and the groove depth of the annular groove 2c1 is deeper in the vertical direction than in the horizontal direction. Accordingly, the thickness of the resin layer 5 is thinner in the horizontal direction than in the vertical direction so that the outer diameter is a perfect circle.

[0031] 7 and 8 both show an embodiment in which the outer peripheral surface 1a of the outer ring 1 and the main chamfer 1d of the outer ring 1, which have different concentricities, form the contact surface with the resin layer 5, with FIG. 7 being a partially cutaway perspective view and FIG. 8 being a cross-sectional view at the boundary between the outer peripheral surface 1a of the outer ring 1 and the main chamfer 1d. The main chamfer 1d is formed from the outer peripheral surface 1a of the outer ring 1 to the axial side surface 1b. As shown in FIG. 8, the thickness of the outer peripheral surface 1a of the outer ring 1 gradually increases from left to right, and the center C1 of the outer peripheral surface 1a of the outer ring 1 is offset to the right relative to the center C of the bearing. Along these lines, the thickness of the resin layer 5 decreases from left to right so that the outer diameter is a perfect circle.

[0032] As shown in FIG. 8, if the distance between the center C1 of the outer peripheral surface 1a of the outer ring 1 and the center C of the bearing is concentric and is 20 μm or more, relative slippage can be effectively prevented.

[0033] 9 and 10 both show an embodiment in which the outer peripheral surface 1a of the outer ring 1 and the annular groove 1c1 of the outer ring 1, which have different degrees of concentricity, form the contact surfaces with the resin layer 5, with Fig. 9 being a partially cutaway perspective view and Fig. 10 being a cross-sectional view at the boundary between the outer peripheral surface 1a of the outer ring 1 and the annular groove 1c1. As shown in Fig. 10, the depth of the annular groove 1c1 of the outer ring 1 increases from left to right, and the center C1 of the annular groove 1c of the outer ring 1 is offset to the right relative to the center C of the bearing. Accordingly, the thickness of the resin layer 5 increases from left to right so that the inner diameter is a perfect circle.

[0034] In addition, in Embodiments 6 and 7, two or more circumferential portions of the outer peripheral surface 1a, inner peripheral surface 1c, and main chamfer 1d may be formed with different coaxialities. By making the offset directions different, relative slippage can be more effectively prevented. That is, in Embodiments 2 to 7, the thickness of the resin layer formed on the raceway rings (outer ring or inner ring) with different circularity and coaxiality is adjusted circumferentially so that the circumferential surface (outer peripheral surface or inner peripheral surface) of the resin layer in contact with the raceway ring and the circumferential surface (inner peripheral surface or outer peripheral surface) on the radially opposite side are perfectly circular.

[0035] Eighth Embodiment While the above describes the case where a black surface 8 is formed, the portion in contact with the resin layer 5 can also be roughened instead of forming the black surface 8. FIG. 11 is a partially cutaway perspective view showing one example, in which the outer peripheral surface 1a of the outer ring 1, the inner peripheral surface 1c including the annular groove 1c1, and the main chamfer 1d are roughened. The resin layer 5 is then formed on these roughened surfaces (1a, 1c, 1d). The anchor effect of the roughened surfaces exerts a restraining force on the outer ring 1 in the circumferential direction.

[0036] Regarding the degree of roughness, if the surface roughness in the circumferential direction of any of the surfaces (1a, 1c, 1d) is Ra 3.2 μm or more or Sa 3.2 μm or more, relative slippage can be effectively prevented. The roughening method is not limited, and general methods such as machining, shot blasting, and chemical treatment can be used. Therefore, if both Ra and Sa are too large, the load required for roughening will be large, so Ra and Sa are preferably 25.0 μm or less.

[0037] The present invention is not limited to the above-described embodiment, and various modifications and improvements are possible. The embodiments and modifications described in this specification can be combined and applied within the scope of feasibility.

[0038] For example, there are no restrictions on the shape of the contact surface of the outer ring 1 with the resin layer 5 or the contact surface of the inner ring 2 with the resin layer 5; for example, the outer ring 1 can have any of the cross-sectional shapes shown in FIGS. 12(a) to 13(b).

[0039] As shown in Figures 12(a) to 12(c), resin layer 5 is bent in a generally L-shaped cross section from the portion covering the axial side surface 1b so as to cover the inner circumferential surface 1c of outer ring 1, and the end of resin layer 5 is fitted into annular groove 1c1 in Figures 12(a) and 12(c). The cross-sectional shape of annular groove 1c1 is droplet-shaped with an arc in Figure 12(a), and hook-shaped in Figure 12(c). Also, as shown in Figure 12(b), annular groove 1c1 may be omitted.

[0040] The main chamfer 1d may be linear as shown in FIG. 12(a), or may be arcuate as shown in FIGS. 12(b) and 12(c).

[0041] Alternatively, as shown in Figure 13(a), the outer ring 1 may not have an annular groove 1c1, and the resin layer 5 may be formed up to the inner diameter end of the axial side surface 1b. Alternatively, as shown in Figure 13(b), the resin layer 5 may be formed up to the inner diameter end of the axial side surface 1b, without the end of the resin layer 5 reaching the annular groove 1c1. In this case, a seal member can be attached to the annular groove 1c1.

[0042] This application is based on a Japanese patent application (Patent Application No. 2023-103604) filed on June 23, 2023, the contents of which are incorporated herein by reference.

[0043] DESCRIPTION OF SYMBOLS 1 Outer ring 1a Outer peripheral surface of outer ring 1b Axial side surface of outer ring 1c1 Annular groove of outer ring 1d Main chamfer 1x Raceway groove (raceway surface) 2 Inner ring 2a Inner peripheral surface of inner ring 2b Axial side surface of inner ring 2c1 Annular groove of inner ring 2x Raceway groove (raceway surface) 3 Ball (rolling element) 4 Cage 5 Resin layer 8 Black surface 10 Insulated bearing

Claims

1. An insulated bearing comprising a pair of raceways having a pair of raceways, a plurality of rolling elements held for free rollability between the pair of raceways, and a cage for holding the rolling elements for free rollability, wherein the contact surfaces of the raceways that come into contact with a mating member are covered with a resin layer, wherein at least a portion of the contact surface of the raceway on which the resin layer is formed that comes into contact with the resin layer is formed with a black surface.

2. The insulated bearing according to claim 1, wherein at least a portion of the circumferential portion of the contact surface of said raceway on which said resin layer is formed that comes into contact with said resin layer has a circularity of 30 μm or more.

3. An insulated bearing as claimed in claim 1 or 2, wherein at least two or more circumferential surfaces of the contact surface of the raceway on which the resin layer is formed that comes into contact with the resin layer have a concentricity of 20 µm or more.

4. An insulated bearing comprising a pair of raceways having a pair of raceways, a plurality of rolling elements held for free rollability between the pair of raceways, and a cage for holding the rolling elements for free rollability, and in which the contact surfaces of the raceways with a mating member are coated with a resin layer, wherein at least a portion of the contact surface of the raceway on which the resin layer is formed that comes into contact with the resin layer has a circumferential surface roughness of Ra 3.2 μm or more, or Sa 3.2 μm or more.