Cage and rolling bearing equipped with said cage

Abstract

To provide a resin bearing cage suitable for use in an environment where high-speed rotation is anticipated, and a rolling bearing equipped with the bearing cage. The present invention relates to a bearing cage that contains a resin and at least two different types of carbon fiber, and a rolling bearing that includes the bearing cage.

Description

[Technical field]

[0001] The present invention relates to a cage for use in a rolling bearing, and to a rolling bearing including such a cage. [Background technology]

[0002] Retainers, which play a role in holding the rolling elements (balls) inside rolling bearings, can be roughly divided by shape into corrugated retainers made from press-formed steel plates, and crown-shaped or machined retainers made by press-forming or cutting steel plates, or by molding resin. Resin retainers are used for high-speed rotation and low-noise applications, and their range of application is expanding due to their advantages over metal materials in that they are lightweight, easy to mold into complex shapes, and highly productive. In recent years, there has been a demand for even faster rotation of motors and bearings in order to achieve both smaller size and weight as well as higher output in various drive motors used in automobiles, cleaners, etc. In response to this demand, there is also a demand for cages that make up the bearings to be able to handle higher rotation speeds, for example products that can handle the friction, wear, and deformation that tend to occur with high speed rotation. As its name suggests, a crown cage has an external shape with multiple horns protruding in the axial direction from an annular base, and these horns are said to be easily deformed by the centrifugal force generated by rotation. For example, a crown cage made of a resin composition containing carbon fiber has been proposed as a crown cage that is less likely to deform even when the bearing is rotating at high speeds and has improved ball retention capacity (Patent Document 1). A machined cage refers to a cage obtained by forming ball retaining portions, etc., by cutting molded resin, for example, and is formed by forming ball retaining holes that penetrate radially into a cylindrical resin molding. Since a machined cage having such a shape does not have horns like the crown-shaped cage, it is said to be less susceptible to deformation due to high-speed rotation. For example, in a proposal for a ball bearing that aims to reduce strength in high-temperature and high-humidity environments, the use of a machined cage made of a resin composition containing carbon fiber has been proposed (Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-3070 A [Patent Document 2] Patent No. 6776485 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a resin bearing cage suitable for use in environments where high-speed rotation is anticipated, and a rolling bearing including such a bearing cage. [Means for solving the problem]

[0005] One aspect of the invention relates to a bearing cage comprising a resin and a fibrous reinforcement, the fibrous reinforcement including at least two different types of carbon fibers. The present invention also relates to a rolling bearing provided with the above-mentioned bearing cage. The present invention further relates to a motor equipped with the rolling bearing, and a dental handpiece equipped with the rolling bearing. [Brief description of the drawings]

[0006] [Figure 1] FIG. 2 is a schematic diagram illustrating an example of the structure of a bearing cage (crown cage) according to the present invention. [Diagram 2] FIG. 1 is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. [Diagram 3] 1 is a schematic diagram illustrating an example of a structure of a motor according to the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating an example of the structure of a bearing cage (machined cage) according to the present invention. [Diagram 5] FIG. 1 is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. [Figure 6]FIG. 2 is a schematic diagram illustrating an example of a dental handpiece of the present invention, in which (A) is an external view of the dental handpiece and (B) is an enlarged cross-sectional view of the periphery of a head portion of the dental handpiece. [Figure 7] FIG. 1 shows the results of frictional heat generation [°C] for Examples 1 to 5, 9, and 10, and the results of frictional heat generation [°C] for Examples 11 to 13, versus the proportion [%] of carbon fiber 1A (PAN type) in a friction and wear test (load 9.8 N). [Figure 8] FIG. 1 shows the results of frictional heat generation [°C] for Examples 1 to 5, 9, and 10, and the results of frictional heat generation [°C] for Examples 11 to 13, versus the proportion [%] of carbon fiber 1A (PAN type) in a friction and wear test (load 49 N). [Figure 9] FIG. 1 is a graph showing the results of frictional heat generation [° C.] in Examples 6 to 8 versus the proportion [%] of carbon fiber 1A (PAN-based) in a friction and wear test. [Figure 10] FIG. 1 is a graph showing the results of the wear scar width [mm] of Examples 1 to 5 versus the ratio [%] of carbon fiber 1A (PAN-based) in a friction and wear test. [Figure 11] FIG. 1 is a diagram showing the results of the tensile strength [MPa] of Examples 1 to 5 (●) and the results of Examples 6 to 8 (◯) versus the proportion [%] of carbon fiber 1A (PAN-based) in a tensile test. [Figure 12] FIG. 1 is a graph showing the results of durability life [hrs] of Examples 1 to 5 versus the ratio [%] of carbon fiber 1A (PAN-based) in a durability life test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] As cited in the aforementioned Patent Document 1, there have been proposals to date that address issues with the annular cage that arise as the bearing rotates, such as deformation due to centrifugal force, by studying materials and cage shapes to suppress this. However, in recent years, when bearings are used in higher speed rotation environments, the heat generated by the high speed rotation and the increasing centrifugal force make the cages in the bearings more susceptible to friction, wear, and deformation. In addition, the heat generated by the high speed rotation can affect the performance of the lubricant. Depending on the change in the performance of the lubricant, the life of the bearings may be shortened. Although the machined cage described above is said to be less susceptible to deformation caused by high-speed rotation than a crown cage, the effects of centrifugal force cannot be avoided depending on the rotational speed, and because it is a sliding component, it faces issues such as friction and wear, just like a crown cage. As described above, whether a crown cage or a machined cage is used, durability at high speeds is required for rolling bearings equipped with such cages.

[0008] While the inventors of the present invention were studying the problem of providing a cage suitable for high-speed rotation, they noticed that when heat is generated by the high-speed rotation of a bearing, deformation itself is unavoidable, no matter how difficult the material is to deform in response to heat. Furthermore, as described above, it is considered that heat generation also affects the lubricant. Therefore, they studied the cage from the viewpoint of suppressing heat generation itself, and found for the first time that frictional heat generation is specifically suppressed by adopting an embodiment in which two different types of carbon fibers are present in the bearing cage, and further, by adopting an embodiment in which two types of carbon fibers with different thicknesses and lengths are present, and that the durable life of the bearing is improved by adopting this embodiment in the cage of a rolling bearing. In general, it is known that reinforcing materials such as carbon fibers can impart specific properties to matrix resins depending on the type and amount of the reinforcing materials. Therefore, it is expected that the addition of pitch-based carbon fibers, which are considered to have high heat transfer performance, will further suppress heat generation in the bearing cage. However, as shown in the results of the examples described below, although the presence of pitch-based carbon fibers certainly suppressed the frictional heat generation temperature, when the ratio of pitch-based carbon fibers was increased and only pitch-based carbon fibers were used, a higher frictional heat generation temperature was observed. This result shows that the effect of suppressing heat generation cannot be obtained by simply adding carbon fibers that are thought to be able to impart properties, and that heat generation can only be suppressed by the presence of two different types of carbon fibers, and the present inventors have discovered this fact, and have completed the present invention. The details are explained below.

[0009] [Bearing cage] The bearing cage according to the present invention includes a resin and a fibrous reinforcing material. Each component constituting the bearing cage will be described in detail below.

[0010] <Fiber reinforcement> The fibrous reinforcing material used in the present invention contains at least two different kinds of carbon fibers, and the carbon fibers may be, based on their raw materials, PAN-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers. In the present invention, the at least two different types of carbon fibers can be PAN-based carbon fibers made from polyacrylonitrile, and pitch-based carbon fibers made from a by-product (pitch) of coal, petroleum, or coal tar. The pitch-based carbon fibers are classified into isotropic pitch-based carbon fibers that are optically isotropic (do not exhibit polarization) and anisotropic pitch-based carbon fibers that are optically anisotropic, depending on the process of modifying the raw pitch and heat treatment. In the present invention, isotropic pitch-based carbon fibers can be used.

[0011] The content ratio of the pitch-based carbon fiber and the PAN-based carbon fiber in the bearing cage of the present invention can be, in mass ratio, pitch-based carbon fiber:PAN-based carbon fiber=1:5 to 5:1, or, for example, 1:4 to 4:1, or 1:3 to 3:1.

[0012] In the bearing cage (product) of the present invention, the average fiber diameter and average fiber length of the pitch-based carbon fibers and PAN-based carbon fibers can be selected as appropriate, but in one embodiment, the pitch-based carbon fibers can have a larger (thicker) average fiber diameter than the PAN-based carbon fibers, and in another embodiment, the pitch-based carbon fibers can have a shorter average fiber length than the PAN-based carbon fibers. Furthermore, in the bearing retainer (product) of the present invention, the quartile range of the fiber length (75% fiber length - 25% fiber length) of the PAN-based carbon fiber can be 90 μm or more, for example, 90 μm or more and 200 μm or less, and the quartile range of the fiber length (75% fiber length - 25% fiber length) of the pitch-based carbon fiber can be 40 μm or less, for example, 10 μm or more and 40 μm or less. The average fiber length of the PAN-based carbon fibers can be, for example, 90 μm to 180 μm, or, for example, 100 μm to 180 μm, or, for example, 110 μm to 170 μm, and the average fiber diameter of the PAN-based carbon fibers can be, for example, 5 μm to 10 μm, or, for example, 7 μm to 8 μm. The average fiber length of the pitch-based carbon fibers can be, for example, 35 μm to 55 μm, or 40 μm to 50 μm, and the average fiber diameter of the pitch-based carbon fibers can be, for example, 12 μm to 18 μm, or 14 μm to 16 μm.

[0013] In the present invention, the "average fiber diameter" and "average fiber length" of pitch-based carbon fiber and PAN-based carbon fiber, as well as the "interquartile range" calculated from the "75% fiber length" and "25% fiber length" are values ​​obtained by two-dimensional image analysis of the residue (fibrous reinforcement: carbon fiber) after removing the resin component of the bearing cage by heat treatment (it has been confirmed that the heat treatment of the resin component does not cause any degeneration of the pitch-based carbon fiber and PAN-based carbon fiber). In detail, the residue is image-analyzed, and the fiber diameter is classified into intervals at 1 μm intervals to create a frequency distribution, and the fiber length is classified into intervals at 10 μm intervals to create a frequency distribution (see below). At this time, it is considered that the fiber diameter of the carbon fiber does not change due to the melt mixing operation with the resin, and in fact, in the examples described later, it has been confirmed that the frequency distribution of the fiber diameter when the pitch-based carbon fiber and the PAN-based carbon fiber are mixed is a frequency distribution of only the pitch-based carbon fiber and a frequency distribution of only the PAN-based carbon fiber superimposed according to the blending ratio (the frequency belonging to each class (fiber diameter) increases or decreases according to the blending ratio). In the examples described later, the average values ​​of the fiber diameter and fiber length are calculated for each carbon fiber classification. In addition, a frequency distribution of the fiber length is created for each carbon fiber classification, and quartiles are obtained from this to determine the quartile range (75% fiber length (3rd quartile) - 25% fiber length (1st quartile)).

[0014] In the bearing cage of the present invention, the fibrous reinforcing material such as carbon fiber (pitch-based carbon fiber or PAN-based carbon fiber) can be contained in a total amount of 10 to 35 parts by mass when the mass of the bearing cage is 100 parts by mass.

[0015] <Resin> As the resin constituting the bearing cage of the present invention, a polyamide resin having excellent heat resistance can be selected. Among these, semi-aromatic polyamides, which have improved heat resistance etc. by partially introducing aromatic components, and polyamide 46 (PA46), which has improved heat resistance by increasing the concentration of amide groups, can be used. The semi-aromatic polyamide refers to one that has an aromatic component in the dicarboxylic acid component or diamine component that constitutes the polyamide. Examples include polynonamethylene terephthalamide (also called polyamide 9T or PA9T) whose main components are nonanediamine and terephthalic acid, polyhexamethylene terephthalamide (polyamide 6T or PA6T) whose main components are hexamethylenediamine and terephthalic acid, and polydecamethylene terephthalamide (polyamide 10T or PA10T) whose main components are decanediamine and terephthalic acid.

[0016] The resin may contain a thermoplastic elastomer in addition to the polyamide resin. Examples of such a thermoplastic elastomer include an acid-modified polyolefin thermoplastic elastomer.

[0017] <Other ingredients> The bearing cage of the present invention may contain various known additives in addition to the above-mentioned resin and fibrous reinforcing material (carbon fiber) as long as the effect of the present invention is not impaired.

[0018] The bearing cage can be manufactured by injection molding a resin mixture containing the above resin and the above fibrous reinforcing material. For example, the resin and the above fibrous reinforcing material (and various additives, if desired) are melt-kneaded using a twin-screw extruder to obtain a resin mixture, which is then injection-molded into a bearing cage of the desired shape and size. As another method for manufacturing a bearing cage, a bearing cage of the desired shape and size can be obtained by molding a molded body of a resin mixture containing the above-mentioned resin and the above-mentioned fibrous reinforcing material by machining such as cutting.

[0019] An example of the structure of a bearing cage according to the present invention is shown in Figs. 1 and 4, but the present invention is not limited to the following embodiment. As shown in FIG. 1, a crown-shaped cage 10, which is one embodiment of a bearing cage, has a cylindrical annular member 11 centered on the central axis (rotation axis) of a rolling bearing 20 (not shown) described later. The annular member 11 has an outer peripheral surface, an inner peripheral surface, and two end faces 11a connecting the outer peripheral surface and the outer peripheral surface. On one end face 11a of the annular member 11, a plurality of ball pockets (recesses) 12 for rotatably accommodating balls (rolling elements 23 in FIG. 2 described later, not shown) are formed at predetermined intervals along the circumferential direction. Furthermore, the annular member 11 has a pair of claws 13 (13a, 13b) extending from the one end face 11a at both ends of each ball pocket 12. The pair of claws 13 are curved to approach each other so as to follow the curved surface of the balls accommodated in each ball pocket 12, thereby preventing the balls accommodated in each ball pocket 12 from falling out. In addition, a grease pocket 14 is formed between the two ball pockets 12 due to the presence of the claws 13. The grease pocket 14 can contain a grease composition G (not shown), which contributes to lubrication between the ball pocket 12 and the balls (rolling elements 23 in FIG. 2 described below) contained therein. As shown in FIG. 4, a machined retainer 64, which is another embodiment of the bearing retainer, is a cylindrical molded body centered on the central axis (rotation axis) A of a rolling bearing 50 (not shown) described later, and has a plurality of pockets (ball retaining holes) 41 formed at predetermined intervals along the circumferential direction so as to penetrate radially therethrough for retaining balls (rolling elements (not shown)) so that they can roll freely.

[0020] [Rolling bearings] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the rolling bearing according to the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiments.

[0021] 2 is a radial cross-sectional view of a rolling bearing 20 according to a preferred embodiment of the present invention. The rolling bearing 20 has a basic structure similar to that of a rolling bearing of the prior art, and includes an annular inner ring 21, an outer ring 22, a plurality of rolling elements 23, a cage 24, and a seal member 25. The inner ring 21 is a cylindrical structure installed coaxially with the center axis of a shaft (not shown) on the outer periphery side of the shaft. The outer ring 22 is a cylindrical structure arranged coaxially with the inner ring 21 on the outer periphery side of the inner ring 21. Each of the multiple rolling elements 23 is a ball arranged in a raceway in an annular bearing space 26 formed between the inner ring 21 and the outer ring 22. That is, the rolling bearing 20 in this embodiment is a ball bearing.

[0022] In one embodiment of the rolling bearing of the present invention, a crown-shaped cage (see FIG. 1) containing the above-mentioned resin and fibrous reinforcing material is used as the cage 24. The cage 24 is disposed within the raceway and holds a plurality of rolling elements 23. As previously explained using FIG. 1, the cage 24 is an annular body installed coaxially with the central axis of the shaft, and is provided with a plurality of pockets (ball pockets 12 in FIG. 1) for holding the rolling elements 23 on one side in the direction of the central axis, with the rolling elements 23 housed in each pocket.

[0023] The seal member 25 is fixed to the inner circumferential surface of the outer ring 22 and extends toward the inner ring 21, sealing the bearing space 26. The bearing space 26 sealed by the seal member 25 is usually filled with a grease composition G. That is, the grease composition G is held between the inner ring 21 and the outer ring 22. The amount of grease G filled inside the bearing space 26 can be, for example, 5 to 50% of its volume. The sealing member 25 is formed, for example, from a steel plate or rubber, and examples thereof include a steel plate shield that does not come into contact with the outer periphery of the inner ring 21, and a non-contact rubber seal that does not come into contact with the outer periphery of the inner ring 21. Either of the sealing members, the steel plate shield or the non-contact rubber seal, can be used in the present invention. Note that while the drawing shows an embodiment equipped with the sealing member 25, the rolling bearing of the present invention also covers an embodiment of a rolling bearing that does not have a sealing member.

[0024] Another embodiment of the rolling bearing of the present invention is shown in FIG. 5. FIG. 5 is a radial cross-sectional view of a rolling bearing 50 according to a preferred embodiment of the present invention. The rolling bearing 50 has the same basic structure as the rolling bearing of the prior art, as the rolling bearing 20 shown in FIG. 2 and the rolling bearing 20 described above, and includes an annular inner ring 51, an outer ring 52, a plurality of rolling elements 53, and a cage 54. An annular bearing space 56 is formed between the inner ring 51 and the outer ring 52. The inner ring 51, the outer ring 52, the rolling elements 53, and the bearing space 56 have the same configuration as the inner ring 21, the outer ring 22, the rolling elements 23, and the bearing space 26 in the rolling bearing 20 shown in FIG. 2. The embodiment of FIG. 5 does not include a seal member, but may include a seal member, as in the rolling bearing 20 shown in FIG. 2. In another embodiment of the rolling bearing of the present invention shown in Figure 5, a cylindrical machined cage containing the above-mentioned resin and fibrous reinforcing material (see Figure 4) is used as the cage 54. The cage 54 is placed in the raceway and holds a plurality of rolling elements 53. As previously explained using Figure 4, the cage 54 is an annular body installed coaxially with the central axis of the shaft, and has a plurality of pockets (pockets 41 in Figure 4) for rotatably holding the rolling elements 53 at intervals in the circumferential direction, with the rolling elements 53 housed in each pocket.

[0025] The rolling bearing equipped with the crown cage as one embodiment of the present invention, and the rolling bearing equipped with the machined cage as another embodiment, are not particularly limited in size, conditions of use, etc. The rolling bearing according to the present invention can be used as a rolling bearing for a bearing device used in motors (for example, fan motors, cleaner motors) used in automobiles, home appliances, information devices and the like, or in dental handpieces and the like.

[0026] As an example, FIG. 3 shows a detailed description of an embodiment of a motor equipped with a rolling bearing of this embodiment, and FIG. 6 shows a detailed description of an embodiment of a dental handpiece equipped with a rolling bearing of this embodiment, but the present invention is not limited to the following embodiments.

[0027] [Motor] 3 is a cross-sectional view in the shaft direction of a motor according to an embodiment of the present invention. Motor 30 has the same basic structure as motors of the prior art, and is composed of a housing 31, a stator 32, a coil 33, a rotor magnet 34, a shaft 35, and a rolling bearing 36 that supports shaft 35. The rolling bearing 36 used here can be a rolling bearing (FIG. 2) equipped with the above-mentioned crown cage (FIG. 1). In the motor 30, magnetic force is generated by passing current supplied from a power source (not shown) via a drive circuit through a coil 33 wound around a stator 32, which causes a rotor magnet 34 to rotate, and the rotation is transmitted to an external rotating body via a shaft 35.

[0028] [Dental handpiece] A dental handpiece (also called a dental handpiece) is an instrument used to cut teeth in dental treatment. The drill rotates at ultra-high speeds of 400,000 to 500,000 times per minute to smoothly cut through hard teeth. Fig. 6 is an external view (A) of a dental handpiece according to an embodiment of the present invention, and an enlarged cross-sectional view (B) of the head portion and its periphery of the dental handpiece. As shown in Fig. 6(A), the dental handpiece 60 has a head portion 61 having a rotation mechanism, and a tool 62 detachably attached to the head portion 61. When the dental handpiece 60 is used, the tool 62 is rotated at high speed (for example, 400,000 revolutions per minute or more) to cut teeth, etc. As shown in FIG. 6B, the head portion 61 of the dental handpiece 60 includes, in a housing 63, a shaft member 64, a pair of rolling bearings 65, a turbine impeller 66, and an air supply port 67, together with a tool 62. The tool 62 is attached to the shaft member 64, which is rotatably supported by the housing 63 via a pair of upper and lower rolling bearings 65 in the axial direction. Furthermore, the shaft member 64 is provided with a turbine impeller 66 between the pair of rolling bearings 65. When compressed air is supplied to the turbine impeller 66 from the air supply port 67, the turbine impeller 66 rotates at high speed. This allows the shaft member 64 and the tool 62 to rotate at high speed. The dental handpiece is not limited to a structure in which the turbine impeller 66 is rotated at high speed by compressed air, but may be a structure in which the shaft member 64 is rotated at high speed via an electric motor (similar to the structure of the motor described above). The rolling bearing 65 used here may be a rolling bearing (FIG. 5) equipped with the machined cage (FIG. 4). In the head portion 61 of the dental handpiece 60, the outer ring (62 in FIG. 5) of the rolling bearing 65 is fitted inside the housing 63, and the inner ring (61 in FIG. 5) is fitted outside the shaft member 64. In the rolling bearing 65, the inner ring and the outer ring are relatively rotatable around the rotation axis A (see FIG. 5). That is, when the dental handpiece 60 is used, the inner ring rotates at high speed relative to the outer ring.

[0029] The present invention is not limited to the embodiments and specific examples described in this specification, and various changes and modifications are possible within the scope of the technical ideas described in the claims. EXAMPLES

[0030] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0031] Details of the test materials evaluated in the examples below are as follows: <resin> PA9T: Genestar (registered trademark) N1001A-M41, manufactured by Kuraray Co., Ltd. PA46: Stanyl (registered trademark) TW341, manufactured by DSM Carbon Fiber Carbon fiber 1A (PAN-based carbon fiber): Tenax (registered trademark)-J HT C702 6MM, manufactured by Teijin Limited (fiber length: 6 mm) Carbon fiber 1B (PAN-based carbon fiber): Tenax (registered trademark)-J HT M100 (fiber length: 40 μm) Carbon fiber 2A (pitch-based isotropic carbon fiber): DonaCarbo (registered trademark) Milled S2404N, manufactured by Osaka Gas Chemicals Co., Ltd. (fiber length: 40 μm, fiber diameter: 13 μm) Carbon fiber 2B (pitch-based isotropic carbon fiber): DonaCarbo (registered trademark) Milled S-246, manufactured by Osaka Gas Chemicals Co., Ltd. (fiber length: 1 mm, fiber diameter: 13 μm) Note: The fiber length of the carbon fiber listed above is the average fiber length (nominal value from the manufacturer) of the test material itself (before mixing with resin), and does not indicate the fiber length after melt-kneading with resin and molding.

[0032] <Preparation of resin mixture (test material)> Resin mixtures of Examples 1 to 13 were prepared using the resin types and carbon fiber types, as well as the blending ratios (mass ratios) of carbon fiber shown in Table 1 below (Tables 1-1 to 1-3). In all cases, 20 parts by mass of carbon fiber (total amount) was mixed with 80 parts by mass of resin. In detail, the resin (pellets) and a predetermined amount of carbon fiber 2A or carbon fiber 1B shown in Table 1 were charged into a twin-screw kneading extruder and melt-kneaded, and then a predetermined amount of carbon fiber 1A or carbon fiber 2B was charged therein and further melt-kneaded to obtain a pellet-shaped resin mixture. Note that in Example 10, carbon fiber 2B was charged into the resin first and melt-kneaded, and then carbon fiber 1A was charged and melt-kneaded, and in Example 13, carbon fiber 1B was charged into the resin first and melt-kneaded, and then carbon fiber 2A was charged and melt-kneaded, to obtain a pellet-shaped resin mixture.

[0033] [Table 1]

[0034] The resin mixture (test material) of each example was molded into a shape (disc-shaped, dumbbell-shaped, crown-shaped cage) suitable for the various tests described below, and used for various evaluations. In the following description, the example numbers of the resin mixtures shown in Table 1 will also be treated as the example numbers of each test sample (disk, dumbbell test piece, crown cage) and the example numbers of each test evaluation.

[0035] <Analysis of carbon fiber in crown cage> The resin components of the crown cages of Examples 1 to 8 were removed by heat treatment (under nitrogen atmosphere at 600°C for 1 hour). The carbon fibers remaining after the heat treatment were image-analyzed, and the fiber diameters were classified into intervals with 1 μm intervals, and the fiber lengths were classified into intervals with 10 μm intervals, and a frequency distribution was created for each. In the combination of carbon fiber 1A and carbon fiber 2A, those with a fiber diameter of 10 μm or more (thick ones) were assigned to carbon fiber 2A (pitch-based carbon fiber), and those with a fiber diameter of less than 10 μm (thin ones) were assigned to carbon fiber 1A (PAN-based carbon fiber), and the average values ​​of the fiber diameters and fiber lengths were obtained based on the respective assignments. The results obtained for Examples 1 to 5 are shown in Tables 2 to 4.

[0036] [Table 2]

[0037] [Table 3]

[0038] [Table 4]

[0039] <Various evaluations> (1) Friction and wear test A ball-on-disk type friction and wear test was performed using a friction and wear tester (UMT TriboLab, manufactured by Bruker) to evaluate the frictional heat generation and frictional wear of the samples. The tests were carried out using a test plate (length 30 mm, width 10 mm, thickness 4 mm) processed from the resin mixture of Examples 1 to 13 as a disk, and a ball (material: SUJ2, φ24 mm). The test conditions were: load: 9.8 N or 49 N, measurement temperature: room temperature (25°C ± 5°C), stroke distance: 12.5 mm (one cycle 25 mm), vibration frequency: 20 Hz (sliding speed: 0.5 m / s), test time: 2 minutes (total sliding distance: 60 m). After the test, the wear scar width (mm) on the disk side was measured for Examples 1 to 5 (average value of N=3). During the test, the ball temperature for Examples 1 to 13 was measured with a thermocouple attached to the test device, and the highest temperature was evaluated as frictional heat (°C).

[0040] Fig. 7 shows the results of frictional heat generation [°C] for Examples 1 to 5, 9 and 10 (resin: PA9T, load 9.8N) versus the proportion [%] of carbon fiber 1A (PAN-based), and Fig. 8 shows the results of frictional heat generation [°C] for Examples 1 to 5, 9 and 10 (resin: PA9T, load 49N) versus the proportion [%] of carbon fiber 1A (PAN-based). The results of frictional heat generation for Examples 11 to 13, which do not contain carbon fiber 1A (PAN-based), are also shown on the horizontal axis (load 9.8N) and the horizontal axis (load 49N) of the carbon fiber 1A (PAN-based) proportion of 50%, as control examples such as Example 3, which contains two types of carbon fibers in a mass ratio of 50 / 50. In addition, in Figures 7 and 8, the results of Examples 1 to 5 are shown with white circles (○), the results of Example 9 are shown with an asterisk (*), the results of Example 10 are shown with a white triangle (△), the results of Example 11 are shown with a cross (+), the results of Example 12 are shown with a white square (□), and the results of Example 13 are shown with a white diamond (◇). 9 shows the results of frictional heat generation [°C] for Examples 6 to 8 (resin: PA46) versus the proportion [%] of carbon fiber 1A (PAN-based). In FIG. 9, the results for a load of 9.8 N in Examples 6 to 8 are shown with black circles (●) and the results for a load of 49 N are shown with white circles (◯). Furthermore, the wear scar width [mm] for Examples 1 to 5 (resin: PA9T) versus the proportion [%] of carbon fiber 1A (PAN-based) is shown in Figure 10. In Figure 10, the results for Examples 1 to 5 at a load of 9.8 N are shown with black circles (●) and the results at a load of 49 N are shown with white circles (○). 7, 8, and 10 show the results of Examples 5 to 1 in ascending order of the proportion of carbon fiber 1A (PAN-based), and the results in FIG. 9 show the results of Examples 8 to 6 in ascending order of the proportion of carbon fiber 1A (PAN-based).

[0041] (2) Tensile test A tensile test was carried out using a tension / compression tester (TG-10kN, manufactured by MinebeaMitsumi Inc.) to evaluate the tensile strength (tensile breaking stress) of the sample. The resin mixtures of Examples 1 to 8 were processed in accordance with the standard for dumbbell-shaped tensile test pieces 1A of JIS K 7139 to prepare dumbbell test pieces for each example. In accordance with JIS K 7161, the dumbbell test pieces of each example were stretched at room temperature (25°C ± 5°C), with a gripping distance of 115 mm, and a tensile speed of 5 mm / min, and the tensile strength (tensile breaking stress) (MPa) was measured (average value of N=3).

[0042] In Fig. 11, the results of the tensile strength [MPa] of Examples 1 to 5 (resin: PA9T) versus the proportion [%] of carbon fiber 1A (PAN-based) are shown with black circles (●), and the results of Examples 6 to 8 (resin: PAN46) are shown with white circles (○). The results in Fig. 11 are shown in order of decreasing proportion of carbon fiber 1A (PAN-based) for Examples 5 to 1 (●) and Examples 8 to 6 (○).

[0043] (3) Durability test A ball bearing (inner diameter 5 mm, outer diameter 13 mm, width 4 mm) equipped with a crown-shaped cage made of the resin mixture of Examples 1 to 5 was set in a housing, and a preload of 2.5 N was applied in the axial direction to the outer ring of the ball bearing.A shaft was then inserted into the inner diameter of the ball bearing and connected to the rotating shaft of a test motor so that the ball bearing rotated on the inner ring. Next, the ball bearing was rotated at a rotation speed of 170,000 rpm at a test temperature of room temperature (25° C.±5° C.), and the time until the ball bearing stopped was measured. The stopping condition was the point at which the torque increased and the rotational speed dropped 10% below the specified value, and the test time until the stopping was taken as the endurance life (hrs). For each example of ball bearing equipped with a crown cage, the test was carried out three times, and the endurance life was calculated as the average value.

[0044] Fig. 12 shows the results of durability life [hrs] for Examples 1 to 5 (resin: PA9T) versus the ratio [%] of carbon fiber 1A (PAN-based). The results in Fig. 12 are shown for Examples 5 to 1 in order of decreasing ratio of carbon fiber 1A (PAN-based).

[0045] <Evaluation Results> As shown in Figures 7 to 10, by combining long and thin carbon fibers 1A (PAN-based) with thick and short carbon fibers 2A (pitch-based), frictional heat generation (Figures 7 to 9) and frictional wear (Figure 10) were suppressed (Examples 2 to 4, Example 7). As shown in Figures 7 and 8, in Example 9, in which elongated carbon fiber 1A (PAN-based) was blended with thin and short carbon fiber 1B (PAN-based), Example 10, in which elongated carbon fiber 1A (PAN-based) was blended with thick and long carbon fiber 2B (pitch-based), Example 11, in which thin and short carbon fiber 1B (PAN-based) was blended with thick and long carbon fiber 2B (pitch-based), Example 12, in which thick and short carbon fiber 2A (pitch-based) was blended with thick and long carbon fiber 2B (pitch-based), and Example 13, in which thin and short carbon fiber 1B (PAN-based) was blended with thick and short carbon fiber 2A (pitch-based), the results showed that the frictional heat generation was not suppressed as observed in the combination of elongated carbon fiber 1A (PAN-based) and thick and short carbon fiber 2A (pitch-based) (Examples 2 to 4). On the other hand, as shown in FIG. 11, the tensile strength (tensile breaking stress) showed a tendency to increase as the proportion of the elongated carbon fiber 1A (PAN type) increased. As shown in Figure 12, the durability life of the bearings was extended by combining long and thin carbon fiber 1A (PAN-based) with thick and short carbon fiber 2A (pitch-based), just as it was for frictional heat generation and abrasive wear. As can be seen from the above, no correlation was found between increased tensile strength and heat generation suppression, and as mentioned above, pitch-based carbon fiber alone, which is said to have high heat transfer performance, is not able to achieve the effect of heat generation suppression. It was confirmed that the presence of these two types of carbon fiber is the first to suppress frictional heat generation and abrasive wear, and also improves the durability and life of the bearings.

[0046] Although the best embodiment has been described in detail above, the present invention is not limited to the above embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention. [Explanation of symbols]

[0047] 10...crown-shaped cage, 11...annular member, 11a...end face, 12...ball pocket (recess), 13 (13a, 13b)...claws, 14...grease pocket, 20... rolling bearing, 21... inner ring, 22... outer ring, 23... rolling element, 24... cage, 25... sealing member, 26... bearing space, 30...motor, 31...housing, 32...stator, 33...coil, 34...rotor magnet, 35...shaft, 36...rolling bearing, 40...machined retainer, 41...pocket (ball retaining hole) 50... rolling bearing, 51... inner ring, 52... outer ring, 53... rolling element, 54... cage, 56... bearing space, 60: dental handpiece, 61: head portion, 62: tool, 63: housing, 64: shaft member, 65: rolling bearing, 66: turbine blade, 67: air supply port

Claims

1. A bearing cage comprising a resin and a fibrous reinforcing material, The fibrous reinforcing material includes PAN-based carbon fiber and pitch-based carbon fiber, The bearing cage includes: The pitch-based carbon fibers have a larger average fiber diameter than the PAN-based carbon fibers. Bearing retainer.

2. A bearing cage comprising a resin and a fibrous reinforcing material, The fibrous reinforcing material includes PAN-based carbon fiber and pitch-based carbon fiber, The bearing cage includes: The pitch-based carbon fibers have a shorter average fiber length than the PAN-based carbon fibers. Bearing retainer.

3. The pitch-based carbon fiber is an isotropic pitch-based carbon fiber. The bearing cage according to claim 1 .

4. A bearing cage comprising a resin and a fibrous reinforcement material, The fibrous reinforcing material includes PAN-based carbon fiber and pitch-based carbon fiber, The bearing cage includes: The PAN-based carbon fiber has a fiber length interquartile range of 90 μm or more; The interquartile range of the fiber length of the pitch-based carbon fiber is 40 μm or less. Bearing retainer.

5. The bearing cage includes: The content ratio of the pitch-based carbon fiber and the PAN-based carbon fiber is, in mass ratio, pitch-based carbon fiber:PAN-based carbon fiber=1:5 to 5:

1. The bearing cage according to claim 1 .

6. The bearing cage includes: The PAN-based carbon fiber and the pitch-based carbon fiber are contained in a total amount of 10 to 35 parts by mass when the mass of the bearing cage is 100 parts by mass. The bearing cage according to claim 1 .

7. The resin includes a polyamide resin. The bearing cage according to claim 1 .

8. The polyamide resin is a semi-aromatic polyamide.

8. The bearing cage according to claim 7.

9. The polyamide resin is polynonamethylene terephthalamide (PA9T) or polyamide 46 (PA46).

8. The bearing cage according to claim 7.

10. A rolling bearing comprising the bearing cage according to any one of claims 1 to 9.

11. A motor comprising the rolling bearing according to claim 10.

12. A dental handpiece comprising the rolling bearing according to claim 10.

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