Rolling bearings

Abstract

This invention provides a rolling bearing that can prevent bearing damage and lubrication degradation, thereby improving durability. [Solution] The rolling bearing 20 comprises a raceway consisting of an inner ring 1 and an outer ring 3, a plurality of rolling elements 5 that are held to roll freely between the inner ring 1 and the outer ring 3, and a sealing member 9 fixed to either the inner ring 1 or the outer ring 3 and attached to the other so as to slide against it. The sealing member 9 has a conductive resin portion 10 made of conductive fluororesin, and the conductive fluororesin contains fluororesin and a conductive component. The conductive component is exposed in the region of the sealing member that slides against the raceway.

Description

Technical Field

[0001] The present invention relates to rolling bearings, for example, rolling bearings of motors with inverters such as those for air conditioners and electric vehicles (EV: Electric Vehicle), and rolling bearings in which static electricity accumulates, such as pulley bearings.

Background Art

[0002] In motors, electrical components, pulley bearings, etc., when current flows through the bearings, bearing damage and lubrication deterioration occur, which limits the life of the bearings. To solve such problems, for example, in Patent Document 1, an appropriate amount of a conductive substance such as crystalline carbon black, metal powder, or metal fiber is blended in a sealing ring (sealing member), or the surface of the sealing ring is coated or impregnated with a conductive substance to make the sealing ring a conductor, and a rolling bearing has been devised.

[0003] In addition, as methods for insulating bearings, there are a method of making the balls of the bearing made of ceramic and a method of forming an insulating layer between the bearing and the housing or the shaft. Further, as a method of energizing in a region other than the balls between the inner ring and the outer ring, there are a method of enclosing a conductive agent such as a conductive lubricant or conductive grease in the bearing, and a method of energizing the housing and the shaft by passing a current-carrying brush, current-carrying ring, or current-carrying member between the housing and the shaft.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, rubber seals and resin seals are generally manufactured by compression molding or injection molding using a mold. However, in the rolling bearing described in Patent Document 1, when a sealing member is molded using a material containing a conductive substance, a skin layer is formed on its surface, making it impossible to obtain sufficient conductivity between the outer ring and the inner ring by the sealing member.

[0006] Furthermore, in the field of bearings, it is expected that the problems of bearing damage due to electrical conduction and lubrication deterioration will increase further with the future advancement of 5G (fifth-generation mobile communication) and EVs. Therefore, even when using various conventional rolling bearings, it is difficult to sufficiently achieve bearing isolation or electrical conduction in areas other than the balls, making it difficult to prevent bearing damage and lubrication deterioration.

[0007] This invention has been made in view of the above problems, and aims to provide a rolling bearing that can prevent bearing damage and lubrication deterioration, thereby improving durability. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the following configuration [1] relating to a rolling bearing.

[0009] [1] A raceway comprising an inner ring and an outer ring, a plurality of rolling elements held to roll freely between the inner ring and the outer ring, and a sealing member fixed to either the inner ring or the outer ring and attached to the other so as to slide against it, The sealing member has a conductive resin portion made of conductive fluororesin, The conductive fluororesin comprises a fluororesin and a conductive component. A rolling bearing characterized in that the conductive component is exposed in the region of the sealing member that slides against the raceway ring.

[0010] Furthermore, preferred embodiments of the present invention relating to rolling bearings are described in the following [2] to [7].

[0011] [2] The rolling bearing according to [1], characterized in that the conductive component is exposed in the region of the sealing member that is fixed to and in contact with the raceway ring.

[0012] [3] The rolling bearing according to [1] or [2], characterized in that the sealing member is composed solely of the conductive resin portion.

[0013] [4] The rolling bearing according to any one of [1] to [3], characterized in that the conductive component is at least one selected from carbon black, carbon nanotubes, carbon fibers, graphene, metal powders and metal fibers.

[0014] [5] The rolling bearing according to any one of [1] to [4], characterized in that the conductive fluororesin is a polytetrafluoroethylene resin in which conductive carbon is dispersed.

[0015] [6] When the surface of the sealing member on which the conductive component is exposed is referred to as the exposed surface, A rolling bearing according to any one of [1] to [5], characterized in that the concentration of the conductive component on the exposed surface of the conductive resin part and the concentration of the conductive component inside the conductive resin part are approximately equal.

[0016] [7] The rolling bearing according to any one of [1] to [6], characterized in that the surface on which the conductive component is exposed is a surface that has been machined, cut, polished, or treated with a solvent. [Effects of the Invention]

[0017] According to the present invention, it is possible to prevent bearing damage and lubrication deterioration, thereby providing a rolling bearing with improved durability. [Brief explanation of the drawing]

[0018] [Figure 1]FIG. 1 is a schematic cross-sectional view showing a rolling bearing according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] As a result of intensive studies by the inventor of the present application, it has been found that when a sealing member is formed using a material containing a conductive substance, the skin layer formed on its surface reduces the conductivity between the sealing member and the outer ring or the inner ring. Therefore, the inventor of the present application has found that by exposing the conductive substance on the surface at the portion where the sealing member slidably contacts the outer ring or the inner ring, the outer ring and the inner ring can be energized through the sealing member disposed between the outer ring and the inner ring, and damage to the bearing and deterioration of lubrication can be prevented. The present invention has been made based on the above findings.

[0020] [Rolling Bearing] Hereinafter, the rolling bearing according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be appropriately changed without departing from the gist of the present invention.

[0021] FIG. 1 is a schematic cross-sectional view showing a rolling bearing according to an embodiment of the present invention. As shown in FIG. 1, the rolling bearing 20 includes a raceway ring including an inner ring 1 having an inner ring raceway surface 1a and an outer ring 3 having an outer ring raceway surface 3a, and a plurality of rolling elements 5 that are held so as to be freely rotatable between the inner ring 1 and the outer ring 3. Further, a retainer 7 that holds the plurality of rolling elements 5 at substantially equal intervals in the circumferential direction is disposed between the inner ring 1 and the outer ring 3. Furthermore, sealing members 9 for sealing the internal space of the rolling bearing 20 are attached to both axial end portions between the inner ring 1 and the outer ring 3.

[0022] The seal member 9 is annular and includes a fixed end portion 9a that is fitted and fixed in a groove provided on the inner peripheral surface of the outer ring 3, a lip portion 9c that slidably contacts the outer peripheral surface of the inner ring 1, and a connecting portion 9b that connects the fixed end portion 9a and the lip portion 9c. Further, the seal member 9 is composed of a conductive resin portion 10. The conductive resin portion 10 is made of a conductive fluororesin containing a fluororesin and a conductive component, and connects the inner ring 1 and the outer ring 3. In this embodiment, the seal member 9 is composed only of the conductive resin portion 10, but the conductive resin portion 10 may be joined to a core metal 11 indicated by a broken line in the seal member 9. And in this embodiment, in the region of the lip portion 9c of the seal member 9 that slidably contacts the inner ring 1, the conductive component is exposed.

[0023] In the rolling bearing 20 configured as described above, the rolling elements 5 roll between the inner ring raceway surface 1a and the outer ring raceway surface 3a, so that the inner ring 1 rotates relative to the outer ring 3. At this time, the seal member 9 prevents foreign matter from entering from the outside of the rolling bearing 20 and the leakage of grease from the inside.

[0024] Also, in this embodiment, the seal member 9 is composed of a conductive resin portion 10 having conductivity, and in the region of the lip portion 9c that slidably contacts the inner ring 1, the conductive component is exposed. The lip portion side exposed surface 9e where the conductive component is exposed is a surface formed by performing cutting, cutting, polishing or solvent treatment. Specifically, the skin layer on the surface of the seal material formed by compression with a mold or injection molding is removed by the above cutting, cutting, polishing or solvent treatment to expose the conductive component. If this processing is not performed and the skin layer remains on the surface, the seal member will be insulated by the skin layer, and it will be difficult to achieve electrical connection between the inner ring 1 and the outer ring 3 by the seal member 9.

[0025] In contrast, in this embodiment, at least the skin layer in the region of the sealing member 9 that slides against the inner ring 1 is removed, and the conductive component is exposed. As a result, current can be passed between the inner ring 1 and the outer ring 3 without being insulated by the skin layer. Consequently, bearing damage and lubrication deterioration can be prevented, and the durability of the rolling bearing 20 can be improved.

[0026] Even if the skin layer on the surface of the sealing member 9 is not removed, but rather a conductive substance is applied to or impregnated onto the surface of the sealing member, the conductive substance will still be exposed on the surface of the sealing member. However, applying or impregnating the surface of the sealing member with a conductive substance may alter the mechanical properties of the material constituting the sealing member. Therefore, in this embodiment, where the skin layer on the surface of the sealing member is removed and the conductive component is exposed, a sealing member with the desired properties in line with the design can be obtained.

[0027] Furthermore, since the fixed end 9a of the sealing member 9 is fitted into the groove of the outer ring in a strongly compressed state, the contact rate between the conductive component present in the conductive resin part 10 and the outer ring 3 is high. Therefore, even if the skin layer in the area in contact with the outer ring 3 on the fixed end 9a side is not removed and the conductive component is not exposed, current flows between the sealing member 9 and the outer ring 3. However, if an exposed surface 9d on the fixed end side where the conductive component is exposed is formed in the area of ​​the fixed end 9a in contact with the outer ring 3, the conductivity between the inner ring 1 and the outer ring 3 can be further improved.

[0028] Furthermore, if a rubber material is used for the sealing member, a core metal 11 is required because rubber is highly flexible. This increases the number of steps required to manufacture the sealing member 9 by joining the rubber material to the core metal 11, thus increasing the manufacturing cost of the sealing member 9. In addition, using a rubber material for the sealing member 9 may cause bleeding components to be generated, leading to contamination.

[0029] In contrast, the conductive resin portion 10 of the sealing member 9 in this embodiment is made of a conductive fluororesin containing a fluororesin and a conductive component. The fluororesin has good chemical resistance to the lubricating oil, grease base oil and additives inside the rolling bearing 20, and can suppress the coefficient of friction and amount of wear generated at the lip portion 9c when the bearing rotates. Furthermore, unlike rubber members, the conductive resin portion 10 made of conductive fluororesin has high shape retention, so it can function as a sealing member without using a core. The sealing member 9 may also be composed of a core 11 and a conductive resin portion 10 joined to the core 11. However, when a metal core 11 is used, although the core 11 itself has excellent conductivity, an adhesive or the like is required to join the core 11 and the conductive resin portion 10, and an improvement in conductivity cannot be expected, so it is more preferable that the sealing member 9 is composed only of the conductive resin portion 10.

[0030] The conductive resin portion 10 preferably contains at least one conductive component selected from carbon black, carbon nanotubes, carbon fibers, graphene, metal powder, and metal fibers. In particular, using carbon black as the conductive component allows for stable and high conductivity.

[0031] Examples of fluororesins include PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene-propene copolymer), ETFE (ethylene-tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), and ECTFE (ethylene-chlorotrifluoroethylene copolymer). In particular, it is preferable to use PTFE (polytetrafluoroethylene) because of its excellent mechanical properties and dimensional stability.

[0032] Therefore, the conductive fluororesin is particularly preferably a polytetrafluoroethylene resin in which conductive carbon black is dispersed.

[0033] Furthermore, the conductive resin portion 10 may also contain, in addition to the conductive component and fluororesin, processing aids, reinforcing agents, antioxidants, elasticity modifiers, and the like.

[0034] As described above, when a conductive resin part is molded by a general method, a skin layer is formed on the surface, so the concentration of conductive components in the skin layer is lower than the concentration of conductive components inside the conductive resin part (i.e., the core layer, not the skin layer). In this embodiment, the lip-side exposed surface 9e is a surface that has been machined, cut, polished, or solvent-treated, and the skin layer has been removed. Therefore, the concentration of conductive components on the lip-side exposed surface 9e of the conductive resin part is approximately equal to the concentration of conductive components in the core layer. Furthermore, if the above processing is also performed on the fixed end 9a of the sealing member 9 to expose the conductive components and form a fixed end-side exposed surface 9d, the concentration of conductive components on this fixed end-side exposed surface 9d is also approximately equal to the concentration of conductive components in the core layer.

[0035] Here, the concentration of the conductive component on the lip-side exposed surface 9e and the fixed-end-side exposed surface 9d refers to the concentration of the conductive component in the region from the surface of the area in the lip portion 9c that slides against the outer circumferential surface of the inner ring 1, and the region in the fixed-end portion 9a that contacts the outer ring 3, up to a depth of 30 μm, respectively. Furthermore, in this specification, the statement that the concentration of the conductive component on the lip-side exposed surface 9e and the fixed-end-side exposed surface 9d is approximately equal to the concentration of the conductive component in the core layer means that the difference between the concentration of the conductive component on each exposed surface and the concentration of the conductive component in the core layer is, for example, within ±5% of the concentration of the conductive component in the core layer.

[0036] In Figure 1, the sealing member 9 of the rolling bearing 20 is fixed to the outer ring 3 and configured to slide against the inner ring 1. However, the raceway to which the sealing member 9 is fixed may also be the inner ring 1. That is, the sealing member 9 can be fixed to either the inner ring 1 or the outer ring 3 and mounted to slide against the other raceway. In either case, the effects of the present invention can be obtained if a conductive component is exposed in the region of the lip portion 9c of the sealing member 9 that slides against the raceway (inner ring 1 or outer ring 3).

[0037] Next, a brief explanation of the manufacturing method for rolling bearings will be given. Note that the manufacturing method described below is merely an example, and can be modified as appropriate, as long as it is a method that can manufacture the rolling bearing according to the present invention.

[0038] [Manufacturing method for rolling bearings] The inner ring 1, outer ring 3, and rolling elements 5 are manufactured using a general method. Furthermore, a seal material is produced by mixing a fluororesin with a conductive component, heating and melting the mixture, extruding it into a predetermined mold, and compressing it. The molding method is not particularly limited, and molding methods such as injection molding or transfer molding can be used. In this molding process, a skin layer with a low concentration of the conductive component is formed on the surface of the seal material.

[0039] Next, the skin layer is removed by machining the area of ​​the lip portion of the obtained seal material that slides against the inner or outer ring, thereby producing a seal member 9 having an exposed lip portion side surface 9e where the conductive component is exposed. Since the thickness of the skin layer varies depending on the mold temperature, the resin material temperature, the injection speed, etc., the machining conditions should be adjusted so that areas with a low concentration of conductive component are removed. Furthermore, the area to be machined may be limited to the area of ​​the lip portion 9c that slides against the inner ring 1 or outer ring 3, or it may be the area of ​​the lip portion 9c and the fixed end portion 9a that slides against or contacts the inner ring 1 or outer ring 3. Moreover, the entire surface of the seal material may be machined.

[0040] Subsequently, the sealing member 9 is fixed to the outer ring 3, and the rolling elements 5, along with lubricants and spacers as needed, are placed between the inner ring 1 and the outer ring 3. By assembling these components, the rolling bearing 20 can be manufactured.

[0041] In the process of manufacturing the above-mentioned sealing member, the processing method is not particularly limited, as long as the conductive component is exposed in a predetermined area. In addition to cutting to remove the skin layer, polishing to remove the skin layer or solvent treatment to remove the skin layer by treatment with a solvent may also be performed. Alternatively, a set of sealing materials may be injection molded in a shape with lip portions 9c facing each other, and then a cutting process may be performed to cut out the area that will become the lip portion 9c.

[0042] By manufacturing the sealing member 9 as described above, conductive components are exposed on a predetermined surface, and conductivity can be obtained between the inner ring 1 and the outer ring 3. As a result, a rolling bearing with improved durability can be manufactured.

[0043] As mentioned above, even if a method is used in which a conductive substance is applied to or impregnated onto the surface of the sealing member, the conductive substance will be exposed on the surface of the sealing member, but the manufacturing process is complicated and requires time for drying, etc. On the other hand, by using a method to remove the skin layer, as in the manufacturing method of this embodiment, the rolling bearing according to this embodiment can be manufactured very easily and in a short time. [Examples]

[0044] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples, and can be implemented with modifications to the extent that is consistent with its spirit, and all such modifications are included within the technical scope of the present invention.

[0045] <Measurement of volume resistivity> Various materials were used to prepare sealing components, and test specimens for volume resistivity measurement were created. Subsequently, the volume resistivity of each test specimen was measured in accordance with the four-probe resistivity test method for conductive plastics described in JIS K 7194:1994. The test specimens were prepared in such a way that the skin layer would not affect the volume resistivity measurement.

[0046] <Measurement of electrical resistance of rolling bearings> A sealing component was fabricated using the various sealing components described above, and this component was assembled between the inner and outer rings to manufacture a 608-size rolling bearing. Ceramic rolling elements were used as the rolling elements, and no lubrication oil was used. Subsequently, the impedance between the inner and outer rings was measured while the rolling bearing was rotated at a speed of 2000 rpm. The measurement conditions were a frequency of 10 kHz and an applied voltage of 0.2 V.

[0047] The components of each sealing material are shown in Table 1 below, and the measurement results of the volume resistivity of the sealing materials and the electrical resistance of the rolling bearings are shown in Table 2 below. In Comparative Examples 1, 2, and 3, FEF (Fast Extrusion Furnace) and Ketjenblack were used as carbon black, one of the conductive components. In the column for whether or not machining was performed in Table 2 below, "Yes" means that the skin layer on the surface of the molded sealing material was removed by machining. "No" means that the molded sealing material was used as a sealing material as is.

[0048] [Table 1]

[0049] [Table 2]

[0050] Invention Example 1 uses a conductive fluororesin containing a fluororesin and a conductive component, while Comparative Examples 1 to 3 use a rubber material with a conductive component blended into it. When comparing the resistivity of the sealing member materials, the volume resistivity of material M1 in Invention Example 1 and material M2 in Comparative Example 1 were equal, and they had similar conductivity. However, Invention Example 1, in which the sealing material was molded using material M1 and a predetermined area of ​​the lip portion was ground, showed a significantly lower electrical resistance (impedance) between the inner and outer rings when used as a rolling bearing compared to Comparative Example 1, which was not ground.

[0051] Comparative Examples 2 and 3 are examples in which the content of the conductive material was changed compared to Comparative Example 1, and Comparative Example 4 is an example in which the test was conducted without using a sealing member. In all of Comparative Examples 2 to 4, the electrical resistance value (impedance) between the inner ring and the outer ring was significantly reduced compared to Invention Example 1. These results indicate that by using a conductive material and fluororesin as the material for the sealing member, and by processing the area of ​​the sealing member that slides against the raceway ring to expose the conductive component, a sealing member with excellent conductivity can be obtained, thereby improving the durability of the rolling bearing. [Explanation of Symbols]

[0052] 1 Inner ring 1a Inner ring raceway surface 3 Outer ring 3a Outer ring raceway surface 5 Rolling element 7 Cage 9. Sealing member 20 bearings 9a Fixed end 9b Connecting part 9c Lip part 9d Fixed end side exposed surface 9e Exposed surface on the lip side 10 Conductive resin part 11 Mandrel

Claims

1. It comprises a raceway consisting of an inner ring and an outer ring, a plurality of rolling elements held to roll freely between the inner ring and the outer ring, and a sealing member fixed to either the inner ring or the outer ring and attached to the other so as to slide against it. The sealing member has a conductive resin portion made of conductive fluororesin, The conductive fluororesin comprises a fluororesin and a conductive component. A rolling bearing characterized in that the conductive component is exposed in the region of the sealing member that slides against the raceway ring.

2. The rolling bearing according to claim 1, characterized in that the conductive component is exposed in the region of the sealing member that is fixed to and in contact with the raceway ring.

3. The rolling bearing according to claim 1 or 2, characterized in that the sealing member is composed solely of the conductive resin portion.

4. The rolling bearing according to claim 1 or 2, characterized in that the conductive component is at least one selected from carbon black, carbon nanotubes, carbon fibers, graphene, metal powder, and metal fibers.

5. The rolling bearing according to claim 1 or 2, characterized in that the conductive fluororesin is a polytetrafluoroethylene resin in which conductive carbon is dispersed.

6. When the surface of the sealing member on which the conductive component is exposed is referred to as the exposed surface, The rolling bearing according to claim 1 or 2, characterized in that the concentration of the conductive component on the exposed surface of the conductive resin portion and the concentration of the conductive component inside the conductive resin portion are substantially equal.

7. The rolling bearing according to claim 1 or 2, characterized in that the surface on which the conductive component is exposed is a surface that has been subjected to cutting, slicing, polishing, or solvent treatment.

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