Holder and rolling bearing provided with same

Abstract

The present invention provides a resin bearing cage suitable for use environments in which high-speed rotation is expected, and a rolling bearing provided with the bearing cage. A bearing cage and a rolling bearing provided with the same, in which the bearing cage contains a resin and at least two different carbon fibers.

Description

TECHNICAL FIELD

[0001] The present application relates to a retainer provided to a rolling bearing, and a rolling bearing provided with the retainer. BACKGROUND

[0002] A retainer (holder) that plays a role of holding rolling elements (balls) inside a rolling bearing can be roughly classified into two types in terms of shape: one is a wave-shaped retainer composed of a member that is press-formed from a steel sheet; and the other is a crown-shaped or cut retainer that is manufactured by press-forming, cutting, or molding of a resin, or the like, of a steel sheet. A retainer made of resin is used for applications at high speed rotation and low noise, and has advantages of being lightweight, and being easy to mold into a complex shape and high in productivity as compared with a metal material, and thus the range of applications thereof is expanding.

[0003] In recent years, in various motors for driving, such as automobiles and vacuum cleaners, in order to achieve both downsizing / lightweight and high power, further high-speed rotation of the motor and even the bearing is required, and, for the retainer that constitutes the bearing, a product that can cope with higher-speed rotation, for example, a product that can cope with problems such as frictional wear and deformation that easily occur at high-speed rotation, is required.

[0004] A crown-shaped retainer has, as the name implies, an appearance shape in which a plurality of protruding "claws" are arranged in the axial direction on a ring-shaped base portion, and the claws are likely to be deformed by centrifugal force generated by rotation. For example, a crown-shaped retainer formed of a resin composition containing carbon fibers has been proposed as a crown-shaped retainer that is less likely to be deformed even at high-speed rotation of the bearing and in which the holding ability of the balls is improved (Patent Literature 1).

[0005] In addition, a cut retainer refers to a retainer obtained, for example, by forming a ball holding portion or the like by cutting processing or the like of a molded resin after molding, and is provided with ball holding holes formed through in the radial direction on a cylindrical resin molded body. Since the cut retainer having such a shape does not have "claws" like the crown-shaped retainer, it is less likely to be deformed in association with high-speed rotation. For example, in a proposal of a ball bearing in which the strength is reduced in a high-temperature high-humidity environment, a cut retainer formed of a resin composition containing carbon fibers is proposed (Patent Literature 2).

[0006] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: Japanese Patent Application Publication No. 2020-3070 Patent Literature 2: Japanese Patent No. 6776485 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION The present application has an object to provide a resin bearing retainer suitable for use in an environment in which high-speed rotation is anticipated, and a rolling bearing provided with the bearing retainer.

[0008] Solution to the problem One aspect of the present application relates to a bearing retainer comprising a resin and a fibrous reinforcing material, the fibrous reinforcing material comprising at least two different carbon fibers.

[0009] Further, the present application relates to a rolling bearing provided with the bearing retainer.

[0010] Furthermore, the present application relates to a motor provided with the rolling bearing, and a dental handpiece provided with the rolling bearing. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 A schematic view for explaining the structure of one example of the bearing retainer (crown-shaped retainer) of the present application.

[0012] Figure 2 A schematic view for explaining the structure of one example of the rolling bearing of the present application.

[0013] Figure 3 A schematic view for explaining the structure of one example of the motor of the present application.

[0014] Figure 4 A schematic view for explaining the structure of one example of the bearing retainer (cutting retainer) of the present application.

[0015] Figure 5 A schematic view for explaining the structure of one example of the rolling bearing of the present application.

[0016] Figure 6 A schematic view for explaining one example of the dental handpiece of the present application, Figure 6 (A) is an appearance view of the dental handpiece, Figure 6 (B) is an enlarged sectional view of the head periphery of the dental handpiece.

[0017] Figure 7 A graph showing the results of the proportion of carbon fiber 1A (PAN-based) [%] and the corresponding friction heat [°C] of Examples 1 to 5, Example 9, and Example 10, and the friction heat [°C] of Examples 11 to 13 in the test for frictional wear (load 9.8 N).

[0018] Figure 8A graph showing the proportion of carbon fiber 1A (PAN-based) [%] in the test for friction and wear and the results of the friction heat [°C] of Examples 1 to 5, Example 9, and Example 10, and the results of the friction heat [°C] of Examples 11 to 13.

[0019] Figure 9 A graph showing the proportion of carbon fiber 1A (PAN-based) [%] in the test for friction and wear and the results of the friction heat [°C] of Examples 6 to 8.

[0020] Figure 10 A graph showing the proportion of carbon fiber 1A (PAN-based) [%] in the test for friction and wear and the results of the wear scar width [mm] of Examples 1 to 5.

[0021] Figure 11 A graph showing the proportion of carbon fiber 1A (PAN-based) [%] in the test for tension and the results of the tensile strength [MPa] of Examples 1 to 5 (●), and the results of the tensile strength [MPa] of Examples 6 to 8 (○).

[0022] Figure 12 A graph showing the proportion of carbon fiber 1A (PAN-based) [%] in the test for durability and the results of the durability [hrs] of Examples 1 to 5. DETAILED DESCRIPTION

[0023] As set forth in the above patent document 1, to date, in view of the problem of the ring-shaped retainer accompanying rotation of the bearing, such as deformation caused by centrifugal force, research has been conducted to seek a material and a shape of the retainer for suppressing the problem.

[0024] However, in recent years, as bearings are increasingly used in higher-speed rotation environments, heat generated by high-speed rotation and further increased centrifugal force place the retainer equipped in the bearing in an environment where friction and wear and deformation are increasingly likely to occur. In addition, the heat generated by high-speed rotation can also affect the performance of the lubricant. Due to the change in the performance of the lubricant, the bearing can become short-lived.

[0025] Note that, while the cut retainer is less likely to deform accompanying high-speed rotation than the crown-shaped retainer, the influence of centrifugal force is unavoidable when the rotational speed reaches a certain level, and, since the cut retainer is a sliding member, there are problems such as friction and wear, as with the crown-shaped retainer.

[0026] As described above, in either the crown-shaped retainer or the cut retainer, durability under high-speed rotation is required in the rolling bearing equipped with the retainer.

[0027] In the course of the development of the retainer suitable for high-speed rotation, the present inventors have focused on the fact that, in the case where the bearing generates heat due to high-speed rotation, deformation itself is inevitable regardless of the material that is less likely to deform due to heat. Furthermore, as described above, the heat is considered to also affect the lubricant. Therefore, the development of the retainer was conducted from the viewpoint of suppressing the heat itself, and as a result, it was first found that the scheme in which two kinds of carbon fibers, particularly two kinds of carbon fibers that differ in thickness and length, are present in the bearing retainer can significantly suppress the friction heat, and the adoption of the scheme to the rolling bearing retainer can also improve the durability life of the bearing.

[0028] Note that it is generally known that the reinforcing material such as carbon fiber can impart unique characteristics to the base resin depending on the kind and amount thereof. Therefore, it is expected that the heat generation of the bearing retainer can be more suppressed by adding the pitch-based carbon fiber having high thermal conductivity. However, as shown in the results of the examples described later, although the presence of the pitch-based carbon fiber does suppress the friction heat generation temperature, as a result, if the proportion of the pitch-based carbon fiber is increased, the pitch-based carbon fiber alone exhibits a high friction heat generation temperature. As a result, it is indicated that the effect of suppressing the heat generation cannot be obtained by simply incorporating the carbon fiber that is considered to impart the characteristics, and the present inventors have found that the heat generation can be suppressed by the presence of two different kinds of carbon fibers for the first time, and completed the present application.

[0029] Hereinafter, a detailed description will be given.

[0030] [Bearing retainer] The bearing retainer of the present application contains a resin and a fibrous reinforcing material. Hereinafter, each component constituting the bearing retainer will be described in detail.

[0031] <Fibrous reinforcing material> In the present application, the fibrous reinforcing material used contains at least two different kinds of carbon fibers, and as the carbon fibers, polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, and rayon-based carbon fibers can be listed as raw materials.

[0032] In the present application, as the at least two different kinds of carbon fibers, PAN-based carbon fibers using polyacrylonitrile as a raw material, and pitch-based carbon fibers using coal, a by-product of petroleum / coal tar (pitch) as a raw material can be used.

[0033] The pitch-based carbon fibers can be classified into isotropic pitch-based carbon fibers that exhibit optical isotropy (do not exhibit polarization) and anisotropic pitch-based carbon fibers that exhibit optical anisotropy depending on the modification and heat treatment process of the pitch as a raw material, and in the present application, the isotropic pitch-based carbon fibers can be used.

[0034] The ratio of the pitch-based carbon fiber to the PAN-based carbon fiber in the bearing retainer of the present invention, by mass ratio, can be set as pitch-based carbon fiber:PAN-based carbon fiber = 1:5 to 5:1, or for example, as pitch-based carbon fiber:PAN-based carbon fiber = 1:4 to 4:1, or as pitch-based carbon fiber:PAN-based carbon fiber = 1:3 to 3:1.

[0035] The average fiber diameter and average fiber length of the bearing retainer (product) of the present invention, particularly the pitch-based carbon fiber and the PAN-based carbon fiber, can be appropriately selected. In one embodiment, the average fiber diameter of the pitch-based carbon fiber can be larger (thicker) than that of the PAN-based carbon fiber; in another embodiment, the average fiber length of the pitch-based carbon fiber can be shorter than that of the PAN-based carbon fiber.

[0036] Furthermore, in the bearing retainer (product) of the present invention, the interquartile range (75% fiber length - 25% fiber length) of the PAN-based carbon fiber can be set to 90 μm or more, for example, it can be set to 90 μm or more and 200 μm or less, and the interquartile range (75% fiber length - 25% fiber length) of the pitch-based carbon fiber can be set to 40 μm or less, for example, it can be set to 10 μm or more and 40 μm or less.

[0037] The average fiber length of the aforementioned PAN-based carbon fibers can be set to, for example, 90μm to 180μm, or 100μm to 180μm, or even 110μm to 170μm. Furthermore, the fiber diameter of the PAN-based carbon fibers can be set to, for example, 5μm to 10μm, or 7μm to 8μm.

[0038] The average fiber length of the pitch-based carbon fiber can be set to, for example, 35 μm to 55 μm, or, for example, 40 μm to 50 μm. Furthermore, the average fiber diameter of the pitch-based carbon fiber can be set to, for example, 12 μm to 18 μm, or 14 μm to 16 μm.

[0039] In this 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 "75% fiber length" and "25% fiber length", are all the following values: values ​​obtained by analyzing a two-dimensional image of the residue (fibrous reinforcement material: carbon fiber) after removing the resin component in the bearing retainer by heat treatment (it should be noted that the heat treatment operation of the resin component has been confirmed to not cause modification of pitch-based carbon fiber and PAN-based carbon fiber).

[0040] The details are as follows: Image analysis is performed on the residue, and the fiber diameter is classified into intervals of 1 μm and a frequency distribution is plotted. The fiber length is also classified into intervals of 10 μm and a frequency distribution is plotted (see below). At this time, the fiber diameter of the carbon fiber can be considered to remain unchanged due to the melt mixing operation with the resin. In fact, in the embodiments described later, it was confirmed that the frequency distribution of the fiber diameter when the pitch-based carbon fiber and the PAN-based carbon fiber are mixed is equivalent to the result of superimposing the frequency distribution of the pitch-based carbon fiber alone and the frequency distribution of the PAN-based carbon fiber alone according to the mixing ratio (the frequency of each interval (fiber diameter) increases or decreases accordingly according to the mixing ratio). In the embodiments described later, the average values ​​of fiber diameter and fiber length are calculated according to the classification of each carbon fiber. In addition, the frequency distribution of fiber length is prepared according to the classification of each carbon fiber, thereby obtaining the quartiles, and the interquartile range (75% fiber length (third quartile) - 25% fiber length (first quartile)) is calculated.

[0041] In the bearing retainer of the present invention, the fibrous reinforcing material such as carbon fiber (pitch-based carbon fiber, PAN-based carbon fiber) can be contained in a proportion of 10 to 35 parts by mass when the mass of the bearing retainer is set to 100 parts by mass.

[0042] <Resin> As the resin constituting the bearing retainer of the present invention, a polyamide resin with excellent heat resistance can be selected.

[0043] Among them, semi-aromatic polyamides that improve heat resistance by partially introducing aromatic components and polyamide 46 (PA46) that improves heat resistance by increasing the concentration of amide groups can be used.

[0044] The semi-aromatic polyamide refers to a polyamide in which the dicarboxylic acid or diamine component that constitutes the polyamide contains an aromatic component. Examples include: polynonamethylene (nonylidene) terephthalamide (also known as polyamide 9T, PA9T) with nonamethylenediamine and terephthalic acid as the main components; polyhexamethylene terephthalamide (polyamide 6T, PA6T) with hexamethylene (hexamethylene)diamine and terephthalic acid as the main components; and polydecamethylene (decylidene) terephthalamide (polyamide 10T, PA10T) with decanediamine and terephthalic acid as the main components.

[0045] Furthermore, in addition to polyamide resins, the resin may also contain thermoplastic elastomers. Examples of such thermoplastic elastomers include acid-modified polyolefin thermoplastic elastomers.

[0046] <Other Ingredients> In addition to the resin and the fibrous reinforcing material (carbon fiber), the bearing retainer of the present invention may also contain various known additives without impairing the effects of the present invention.

[0047] Bearing retainers can be manufactured by injection molding a resin mixture comprising the resin and the fibrous reinforcing material. For example, the resin mixture can be obtained by melt-blending the resin and the fibrous reinforcing material (with various desired additives) using a twin-screw extruder and then injection molding it into a bearing retainer of the desired shape and size.

[0048] In addition, as another method of manufacturing bearing retainers, a bearing retainer of the desired shape and size can be obtained by molding a resin mixture containing the resin and the fibrous reinforcing material through machining such as cutting.

[0049] exist Figure 1 and Figure 4 An example of the structure of the bearing retainer of the present invention is shown, but the present invention is not limited to the following embodiments.

[0050] like Figure 1 As shown, the crown-shaped retainer 10, as one embodiment of the bearing retainer, has a cylindrical annular member 11 centered on the central axis (rotation axis) of the rolling bearing 20 (not shown), described later. The annular member 11 has two end faces 11a connecting the outer circumferential surface and the inner circumferential surface, as well as the outer circumferential surface and the inner circumferential surface. On one end face 11a of the annular member 11, balls (described later) are formed at predetermined intervals along the circumferential direction. Figure 2 The ball bearing 23 (not shown) is rotatably accommodated in a plurality of ball pockets (recesses) 12. Furthermore, the annular member 11 has a pair of claws 13 (13a, 13b) extending from one of the end faces 11a at both ends of each ball pocket 12. The pair of claws 13 are bent toward each other in a manner that approaches along the curved surface of the ball contained in each ball pocket 12, thereby preventing the ball contained in each ball pocket 12 from falling out. In addition, a grease pocket 14 is formed between two ball pockets 12 due to the presence of the claws 13. A grease composition G (not shown) can be accommodated in the grease pocket 14, which facilitates the interaction between the ball pocket 12 and the ball contained therein (described later). Figure 2 The middle part is for lubrication between the rolling elements 23).

[0051] In addition, such as Figure 4As shown, the cut retainer 64, as another embodiment of the bearing retainer, is a cylindrical molded body centered on the central axis (rotation axis) A of the rolling bearing 50 (not shown) described later. It has a plurality of pockets (ball retaining holes) 41 formed radially through and at predetermined intervals in the circumferential direction for retaining the balls (rolling elements (not shown)) to roll freely.

[0052] [Rolling bearings] The preferred embodiments of the rolling bearing of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiments.

[0053] Figure 2 This 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 the same basic structure as prior art rolling bearings, including an annular inner ring 21, an outer ring 22, a plurality of rolling elements 23, a retainer 24, and a sealing member 25.

[0054] The inner ring 21 is a cylindrical structure coaxially arranged on the outer periphery of the shaft (not shown in the figure) with its central axis. The outer ring 22 is a cylindrical structure coaxially arranged on the outer periphery of the inner ring 21 with the inner ring 21. Each of the plurality of rolling elements 23 is a ball in a raceway disposed within the 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.

[0055] In one embodiment of the rolling bearing of the present invention, a crown-shaped retainer comprising the resin and fibrous reinforcing material is used as the retainer 24 (see reference). Figure 1 The retainer 24 is disposed within the raceway and holds a plurality of rolling elements 23. (As previously used) Figure 1 As explained, the retainer 24 is an annular body coaxially disposed with the central axis of the shaft, and has a plurality of pockets on one side in the direction of the central axis for retaining the rolling element 23. Figure 1 The middle part is a ball pocket 12, which has a structure in which rolling elements 23 are housed in each pocket.

[0056] The sealing member 25 is fixed to the inner circumferential surface of the outer ring 22 and extends towards the inner ring 21 to seal the bearing space 26. A grease composition G is typically sealed into the bearing space 26, which is sealed by the sealing member 25. That is, the grease composition G is held between the inner ring 21 and the outer ring 22. It should be noted that the amount of grease G sealed into the bearing space 26 can be, for example, set to 5% to 50% of its volume.

[0057] The sealing member 25 is made of, for example, steel plate or rubber, and examples include a steel plate dust cover that does not contact the outer periphery of the inner ring 21, and a non-contact rubber seal that does not contact the outer periphery of the inner ring 21. In this invention, either the steel plate dust cover or the non-contact rubber seal can be used. It should be noted that... Figure 2 While the present invention provides a solution with a seal 25, the rolling bearing of the present invention also includes a rolling bearing without a seal.

[0058] In addition, Figure 5 Another embodiment of the rolling bearing of the present invention is shown in the figure. Figure 5 This is a radial cross-sectional view of a rolling bearing 50 according to a preferred embodiment of the present invention.

[0059] Rolling bearing 50 and Figure 2 The rolling bearing 20 shown also has the same basic structure as prior art rolling bearings, including an annular inner ring 51, an outer ring 52, a plurality of rolling elements 53, and a retainer 54, forming an annular bearing space 56 between the inner ring 51 and the outer ring 52. The inner ring 51, outer ring 52, rolling elements 53, and bearing space 56 have the same structure as the described... Figure 2 The inner ring 21, outer ring 22, rolling elements 23, and bearing space 26 in the shown rolling bearing 20 have the same structure. It should be noted that... Figure 5 The solution is one that lacks a seal, but it can still be like... Figure 2 The rolling bearing 20 shown is a design with a seal. Figure 5 In another embodiment of the rolling bearing of the present invention shown, a cylindrical cut retainer comprising the resin and fibrous reinforcing material is used as retainer 54 (see reference). Figure 4 The retainer 54 is disposed within the raceway and holds a plurality of rolling elements 53. (As previously used) Figure 4 As explained, the retainer 54 is an annular body coaxially arranged with the central axis of the shaft, and has a plurality of pockets for holding the rolling elements 53 circumferentially spaced and rotatable. Figure 4 The middle part is a pocket 41, which has a structure that accommodates rolling elements 53 in each pocket.

[0060] There are no particular limitations on the size, usage conditions, etc., of the rolling bearing equipped with the crown retainer as one embodiment of the present invention, and the rolling bearing equipped with the cutting retainer as another embodiment.

[0061] The rolling bearing of the present invention can be used as a rolling bearing in bearing devices used in motors (e.g., fan motors, vacuum cleaner motors), dental handpieces, etc., in automobiles, home appliances, information equipment, etc.

[0062] As an example, in Figure 3 In this document, an embodiment of a motor equipped with the rolling bearing of this embodiment will be described in detail. Furthermore, in... Figure 6 (A) Figure 6 In (B), an embodiment of a dental handpiece equipped with the rolling bearing of this embodiment will be described in detail, but the present invention is not limited to the following embodiments.

[0063] [motor] Figure 3 This is a cross-sectional view along the axial direction of a motor according to one embodiment of the present invention. The motor 30 has the same basic structure as prior art motors, including a housing 31, a stator 32, coils 33, a rotor magnet 34, a shaft 35, and a rolling bearing 36 supporting the shaft 35. As the rolling bearing 36 used herein, a bearing equipped with the aforementioned crown retainer (…) Figure 1 Rolling bearings ( Figure 2 ).

[0064] The motor 30 generates magnetic force by causing current supplied from a power source (not shown above) to flow through the coil 33 wound on the stator 32 via a drive circuit, thereby rotating the rotor magnet 34 and transmitting the rotation to an external rotating body via the shaft 35.

[0065] [Dental Handpiece] A dental drill bit (also known as a dental instrument) is an instrument used to cut teeth during dental treatment so that hard teeth can be easily shaved off. Its drill bit is said to rotate at an ultra-high speed of 400,000 to 500,000 revolutions per minute.

[0066] Figure 6 (A) is an external view of a dental handpiece according to one embodiment of the present invention, and Figure 6 (B) is an enlarged sectional view of the periphery of the dental instrument head. For example... Figure 6 As shown in (A), the dental instrument head 60 includes a head 61 having a rotating mechanism and a tool 62 detachably mounted on the head 61. When using the dental instrument head 60, the tool 62 is rotated at a high speed (e.g., more than 400,000 revolutions per minute) to perform tooth cutting, etc.

[0067] like Figure 6As shown in (B), the head 61 of the dental instrument head 60, together with the tool 62, has a shaft member 64, a pair of rolling bearings 65, a turbine blade 66, and an air supply port 67 within the housing 63. The tool 62 is mounted on the shaft member 64, which is supported in a freely rolling manner by means of a pair of upper and lower rolling bearings 65 arranged axially. Furthermore, a turbine blade 66 is assembled between the pair of rolling bearings 65 on the shaft member 64. If compressed air is supplied to the turbine blade 66 from the air supply port 67, the turbine blade 66 rotates at high speed. Thus, the shaft member 64 and the tool 62 can also rotate at high speed. It should be noted that the dental instrument head is not limited to a structure that uses compressed air to rotate the turbine blade 66 at high speed; it can also be a structure that rotates the shaft member 64 at high speed via an electric motor (the same structure as the motor).

[0068] As the rolling bearing 65 used herein, a bearing equipped with the aforementioned cut retainer can be used. Figure 4 Rolling bearings ( Figure 5 In the head 61 of the dental instrument head 60, the outer ring of the rolling bearing 65 ( Figure 5 The middle part (62) is embedded in the shell 63, and the inner ring ( Figure 5 The inner and outer rings (61) are externally embedded in the shaft member 64. In the rolling bearing 65, the inner and outer rings can rotate around the axis A (see...). Figure 5 It can rotate relatively freely. That is, when using the dental instrument head 60, the inner ring rotates at high speed relative to the outer ring.

[0069] This invention is not limited to the embodiments or specific examples described in this specification, and various changes and modifications can be made within the scope of the technical concept described in the claims.

[0070] [Example] The present invention will now be described in more detail through embodiments. However, the present invention is not limited thereto.

[0071] The details of the test materials evaluated in the following examples are as follows.

[0072] <Resin> PA9T: Genestar (registered trademark) N1001A-M41, manufactured by Kuraray.

[0073] PA46: Stanyl (registered trademark) TW341, manufactured by DSM.

[0074] (Carbon fiber) Carbon fiber 1A (PAN-based carbon fiber): Tenax (registered trademark) - J HT C702 6MM, manufactured by Teijin Co., Ltd. (fiber length: 6mm).

[0075] Carbon fiber 1B (PAN-based carbon fiber): Tenax (registered trademark) - J HT M100 (fiber length: 40μm).

[0076] Carbon fiber 2A (pitch-based isotropic carbon fiber): Donacarb Milled S2404N, manufactured by Osaka Gas Chemical Co., Ltd. (fiber length: 40μm, fiber diameter: 13μm).

[0077] Carbon fiber 2B (pitch-based isotropic carbon fiber): Donacarb (registered trademark) Milled S-246, manufactured by Osaka Gas Chemical Co., Ltd. (fiber length: 1 mm, fiber diameter: 13 μm).

[0078] Note: It should be noted that the fiber length of the carbon fiber described is the average fiber length of the test material itself (before resin mixing) (manufacturer's nominal value), and does not represent the fiber length after melt mixing / molding with resin.

[0079] <Preparation of Resin Mixtures (Experimental Materials)> Resin mixtures of Examples 1 to 13 were prepared according to the types of resin and carbon fibers and the mixing ratio (mass ratio) of carbon fibers shown in Table 1 (Tables 1-1 to 1-3) below. It should be noted that, in all cases, the mixture was prepared in such a manner that 80 parts by mass of resin and 20 parts by mass of carbon fibers (total weight) were present.

[0080] In detail, after melt-blending the resin (granules) shown in Table 1 and a specified amount of carbon fiber 2A or carbon fiber 1B in a twin-screw extruder, a specified amount of carbon fiber 1A or carbon fiber 2B is added to further melt-blend the resin to obtain a granular resin mixture. It should be noted that in Example 10, carbon fiber 2B is added to the resin first for melt-blending, followed by carbon fiber 1A for melt-blending; conversely, in Example 13, carbon fiber 1B is added to the resin first for melt-blending, followed by carbon fiber 2A for melt-blending, resulting in granular resin mixtures.

[0081] [Table 1] [Table 1-1] [Table 1-2] [Table 1-3] The resin mixtures (test materials) of each example are molded into shapes suitable for various tests described later (disc, dumbbell, crown retainer) for various evaluations.

[0082] In the following description, the example numbers of the resin mixtures shown in Table 1 will also be used as example numbers for each test sample (disc, dumbbell test piece, crown retainer) and the example numbers for each test evaluation.

[0083] <Analysis of carbon fibers in crown retainers> The resin components of the crown retainers in Examples 1 to 8 were removed by heat treatment (600°C for 1 hour under a nitrogen atmosphere). Image analysis was performed on the carbon fibers as residue after heat treatment. Fiber diameter was classified into 1μm intervals, and fiber length was classified into 10μm intervals, and frequency distributions were generated for each. It should be noted that in the combination of carbon fiber 1A and carbon fiber 2A, fibers with a diameter of 10μm or more (coarse fibers) were assigned to carbon fiber 2A (pitch-based carbon fiber), and fibers with a diameter less than 10μm (fine fibers) were assigned to carbon fiber 1A (PAN-based carbon fiber). The average value of the fiber diameter or fiber length was obtained based on their respective assignments.

[0084] The results obtained for Examples 1 to 5 are shown in Tables 2 to 4.

[0085] [Table 2] [Table 3] [Table 4] <Various Reviews> (1) Friction and wear test Friction and wear testing was conducted using a friction and wear testing machine (UMT TriboLab, manufactured by Bruker) with a ball-and-disc type to evaluate the frictional heat generation and friction and wear of the samples.

[0086] The test was conducted using a test plate (30 mm in length, 10 mm in width, and 4 mm in thickness) made from the resin compositions of Examples 1 to 13, and a ball (material: SUJ2, diameter: 24 mm) as a disk. The test conditions were set as follows: load: 9.8 N or 49 N; measurement temperature: room temperature (25 °C ± 5 °C); stroke distance: 12.5 mm (25 mm per cycle); frequency: 20 Hz (sliding speed: 0.5 m / s); test time: 2 minutes (total sliding distance: 60 m).

[0087] After the test, the length (mm) of the wear mark width on the disc side of Examples 1 to 5 was measured (average value of N=3). In addition, during the test, the ball temperature of Examples 1 to 13 was measured using thermocouples attached to the test apparatus, and the temperature at which the highest value was reached was evaluated as frictional heat generation (°C).

[0088] Figure 7 The results of frictional heat generation [°C] for Examples 1-5, 9, and 10 (resin: PA9T, load 9.8N) corresponding to the proportion [%] of carbon fiber 1A (PAN-based) are shown. Figure 8 The results of frictional heat generation [°C] for Examples 1-5, 9, and 10 (resin: PA9T, load 49N) corresponding to the proportion [%] of carbon fiber 1A (PAN-based) are shown. It should be noted that the results of frictional heat generation for Examples 11-13, which do not contain carbon fiber 1A (PAN-based), are compared with those for Example 3, etc., which contain both types of carbon fiber in a 50 / 50 mass ratio, as control examples. Figure 7 (Load 9.8N) and Figure 8 (Load 49N) is shown along the horizontal axis where the proportion of carbon fiber 1A (PAN-based) is 50%. Furthermore, in Figure 7 and Figure 8 In the diagram, white circles (○) represent the results of Examples 1 to 5, asterisks (*) represent the result of Example 9, white triangles (△) represent the result of Example 10, crosses (+) represent the result of Example 11, white squares (□) represent the result of Example 12, and white rhombuses (◇) represent the result of Example 13.

[0089] also, Figure 9 The results of frictional heat generation [°C] for Examples 6-8 (resin: PA46) corresponding to the proportion [%] of carbon fiber 1A (PAN-based) are shown. Figure 9 In the diagram, black circles (●) represent the results of a load of 9.8 N in Examples 6 to 8, and white circles (○) represent the results of a load of 49 N.

[0090] Furthermore, in Figure 10 The results of wear mark widths [mm] for Examples 1 to 5 (resin: PA9T) corresponding to the percentage [%] of carbon fiber 1A (PAN-based) are shown respectively. Figure 10 In the diagram, black circles (●) represent the results of a load of 9.8 N in Examples 1 to 5, and white circles (○) represent the results of a load of 49 N.

[0091] In addition, Figure 7 and Figure 8 ,as well as Figure 10 In the table, the results of Examples 5 to 1 are shown in order of decreasing proportion of carbon fiber 1A (PAN-based). Figure 9 The results are shown in Examples 8 to 6, starting with the lowest proportion of carbon fiber 1A (PAN system).

[0092] (2) Tensile test Tensile tests were conducted using a tensile compression testing machine (TG-10kN Minebea Mitsukoshi Co., Ltd.) to evaluate the tensile strength (tensile fracture stress) of the samples.

[0093] The resin compositions of Examples 1 to 8 were processed according to the specifications of dumbbell-shaped tensile test piece 1A of JIS K7139 to produce dumbbell test pieces for each example.

[0094] According to JIS K7161, at a test temperature of room temperature (25℃±5℃), dumbbell test pieces were stretched using a clamping distance of 115mm and a tensile speed of 5mm / min, and the tensile strength (tensile breaking stress) (MPa) (average value of N=3) was measured.

[0095] Figure 11 In the figures, black circles (●) indicate the tensile strength [MPa] of Examples 1-5 (resin: PA9T) corresponding to the percentage [%] of carbon fiber 1A (PAN-based), and white circles (○) indicate the results of Examples 6-8 (resin: PA46). Furthermore, Figure 11 The results are shown in the order of the lowest proportion of carbon fiber 1A (PAN system), from Example 5 to Example 1 (●) and Example 8 to Example 6 (○).

[0096] (3) Durability life test A ball bearing (inner diameter 5 mm, outer diameter 13 mm, width 4 mm) with a crown-shaped retainer made of the resin composition of Examples 1 to 5 is placed in a housing. After applying a preload of 2.5 N axially to the outer ring of the ball bearing, a shaft is inserted into the inner diameter of the ball bearing, and the shaft is connected to the rotating shaft of the test motor to make the inner ring of the ball bearing rotate.

[0097] Next, at the test temperature of room temperature (25℃±5℃), the ball bearing was rotated at a speed of 170,000 rpm, and the time until the ball bearing stopped was measured.

[0098] The stopping condition is defined as the point at which the torque increases and the rotational speed decreases by 10% from the specified value. The test time up to the point of stopping is defined as the durability life (hrs). Three tests were performed on each ball bearing with a crown retainer, and the durability life was calculated from the average value.

[0099] Figure 12 The results of the durability [hrs] of Examples 1 to 5 (resin: PA9T) corresponding to the proportion [%] of carbon fiber 1A (PAN-based) are shown. Furthermore, Figure 12 The results are shown in Example 5 to Example 1, starting from the lowest proportion of carbon fiber 1A (PAN system).

[0100] <Evaluation Results> like Figures 7-10 As shown, frictional heating was achieved by combining thin and long carbon fiber 1A (PAN-based) with thick and short carbon fiber 2A (pitch-based). Figures 7-9) and friction and wear ( Figure 10 The result of suppression (Examples 2-4, Example 7). It should be noted that, as... Figure 7 and Figure 8 As shown, in Example 9, which combines fine and long carbon fiber 1A (PAN system) with fine and short carbon fiber 1B (PAN system), Example 10, which combines fine and long carbon fiber 1A (PAN system) with coarse and long carbon fiber 2B (pitch system), Example 11, which combines fine and short carbon fiber 1B (PAN system) with coarse and long carbon fiber 2B (pitch system), Example 12, which combines coarse and short carbon fiber 2A (pitch system) with coarse and long carbon fiber 2B (pitch system), and Example 13, which combines fine and short carbon fiber 1B (PAN system) with coarse and short carbon fiber 2A (pitch system), the result of suppressing frictional heat generation seen in the above-mentioned combination of fine and long carbon fiber 1A (PAN system) with coarse and short carbon fiber 2A (pitch system) (Examples 2 to 4) was not achieved.

[0101] On the other hand, such as Figure 11 As shown, the tensile strength (tensile fracture stress) tends to increase with the increase of the proportion of fine and long carbon fiber 1A (PAN system).

[0102] In addition, such as Figure 12 As shown, regarding the bearing's durability, similar to frictional heating and frictional wear, the lifespan is extended by combining fine and long carbon fiber 1A (PAN-based) with coarse and short carbon fiber 2A (asphalt-based).

[0103] In summary, no correlation was observed between the increase in tensile strength and the suppression of heat generation. Furthermore, as mentioned above, pitch-based carbon fibers, which are considered to have high thermal conductivity, alone cannot achieve the effect of suppressing heat generation. It is confirmed that the presence of two types of carbon fibers is necessary to suppress tribothermia, tribothermia, and improve bearing durability for the first time.

[0104] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described above. Various modifications and improvements are included in the present invention within the scope of achieving the purpose of the present invention.

[0105] Explanation of reference numerals in the attached figures 10: Crown retainer; 11: Annular member; 11a: End face; 12: Ball pocket (recess); 13 (13a, 13b): Claw; 14: Grease pocket; 20: Rolling bearing; 21: Inner ring; 22: Outer ring; 23: Rolling element; 24: Retainer; 25: Sealing member; 26: Bearing space; 30: Motor; 31: Housing; 32: Stator; 33: Coil; 34: Rotor magnet; 35: Shaft; 36: Rolling bearing; 40: Cutting retainer; 41: Pocket (ball retainer hole); 50: Rolling bearing; 51: Inner ring; 52: Outer ring; 53: Rolling element; 54: Retainer; 56: Bearing space; 60: Dental instrument head; 61: Head; 62: Tool; 63: Housing; 64: Shaft member; 65: Rolling bearing; 66: Turbine blade; 67: Air supply port.

Claims

1. A bearing holder comprising a resin and a fibrous reinforcing material, the fibrous reinforcing material comprising at least two different carbon fibers.

2. The bearing holder according to claim 1, wherein the at least two different carbon fibers comprise a PAN-based carbon fiber and a pitch-based carbon fiber.

3. The bearing holder according to claim 2, wherein the average fiber diameter of the pitch-based carbon fiber contained in the bearing holder is larger than the average fiber diameter of the PAN-based carbon fiber contained in the bearing holder.

4. The bearing holder according to claim 2, wherein the average fiber length of the pitch-based carbon fiber contained in the bearing holder is shorter than the average fiber length of the PAN-based carbon fiber contained in the bearing holder.

5. The bearing holder according to claim 2, wherein the pitch-based carbon fiber is an isotropic pitch-based carbon fiber.

6. The bearing holder according to claim 2, wherein the interquartile range of the fiber length of the PAN-based carbon fiber contained in the bearing holder, i.e., 75% fiber length - 25% fiber length, is 90 μm or more, the interquartile range of the fiber length of the pitch-based carbon fiber contained in the bearing holder, i.e., 75% fiber length - 25% fiber length, is 40 μm or less.

7. The bearing holder according to claim 2, wherein the contained proportion of the pitch-based carbon fiber to the PAN-based carbon fiber contained in the bearing holder, pitch-based carbon fiber : PAN-based carbon fiber = 1 : 5 to 5 : 1 in terms of mass ratio.

8. The bearing holder according to claim 2, wherein the PAN-based carbon fiber contained in the bearing holder and the pitch-based carbon fiber contained in the bearing holder are contained in a proportion of 10 to 35 parts by mass in total with respect to 100 parts by mass of the bearing holder 100.

9. The bearing holder according to claim 1, wherein the resin comprises a polyamide-based resin.

10. The bearing holder according to claim 9, wherein the polyamide-based resin is a semi-aromatic polyamide.

11. The bearing holder according to claim 9, wherein the polyamide-based resin is polyazanonyl terephthalamide PA9T or polyamide 46 PA46.

12. A rolling bearing provided with the bearing holder according to any one of claims 1 to 11.

13. A motor provided with the rolling bearing according to claim 12.

14. A dental handpiece provided with the rolling bearing according to claim 12.

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