Resin cages and ball bearings for ball bearings

Abstract

This resin-made retainer (40) comprises: at least one annular section (41); and a plurality of pillar sections (42) which respectively extend in the axial direction from the annular section (41) and rotatably hold balls (11) in cylindrical or partially cylindrical pockets (P) provided between neighboring pillar sections, wherein the annular section (41) has a guide surface guided by an inner peripheral surface of an outer ring (20) or an outer peripheral surface of an inner ring (30). The roundness of the guide surface is 5μm or smaller, the differences between 360° / the number of pockets and angles between the centers of neighboring pockets P are all within ±0.1°, and as the directions of the centers C of all the pockets P head toward an inner diameter side from an outer diameter side, the directions head toward any one side in the circumferential direction, and any one side in the axial direction. Accordingly, vibration of the retainer is reduced during rotation of the bearing, and the lifetime of the bearing can be improved.

Description

Technical Field

[0001] The present invention relates to a resin cage for a ball bearing and a ball bearing, and more particularly to a resin cage for a ball bearing and a ball bearing used at high speed rotation, such as a dental air turbine, a cleaner, and a power tool.

Background Art

[0002] Generally, a resin cage applied to a ball bearing is manufactured by injection molding. Specifically, an annular cavity corresponding to the cage is formed in a mold, and a molten resin material (thermoplastic resin) is injected from a resin injection gate provided at the peripheral portion of the cavity and cooled and solidified to manufacture the cage.

[0003] In Patent Document 1, as a resin cage, a crowned cage having a spherical pocket and a double-ring cage having a cylindrical pocket are disclosed. Further, in the angular ball bearing described in Patent Document 2, a resin cage having a pocket combining a cylindrical portion and a reduced-diameter portion is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the resin cages as described in Patent Documents 1 and 2, although each pocket is generally shown to be equally arranged in the circumferential direction, in reality, the angles between the pockets vary and the equal arrangement is slightly disrupted. Furthermore, while it is generally stated that the center of each cylindrical pocket also points toward the center of the bearing, in reality, the centers of each pocket point toward the center of the bearing in varying directions.

[0006] Therefore, when a resin cage with variations in the arrangement angle and orientation of the pockets is used at high-speed rotations of, for example, dmn 1 million or more, the vibration of the cage increases, leading to a problem of shortened bearing life.

[0007] The present invention has been made in view of the aforementioned problems, and its purpose is to provide a resin cage for ball bearings and a ball bearing that can reduce cage vibration during bearing rotation and improve bearing life. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the following configuration. [1] A resin cage for a ball bearing comprising at least one annular portion and a plurality of columnar portions extending axially from the annular portion, wherein the balls of a ball bearing can be rotatably held in cylindrical or partially cylindrical pockets formed between adjacent columnar portions, and the annular portion has a guide surface that is guided by the inner circumferential surface of the outer ring or the outer circumferential surface of the inner ring of the ball bearing, The roundness of the guide surface is 5 μm or less. The difference between the angle between the centers of adjacent pockets and 360° / number of pockets is within ±0.1° in both cases. The orientation of the center of all the aforementioned pockets is such that, as you move from the outer diameter side to the inner diameter side, you move toward one side in the circumferential direction and one side in the axial direction. Resin cage for ball bearings. [2] For any given pocket, the sum of the difference between the angle between the centers of adjacent pockets on either side and 360° / number of pockets is within ±0.1°. [1] A resin cage for ball bearings as described above. [3] The resin cage for ball bearings according to [1] or [2], wherein the orientation of the centers of all the pockets is within 1°. [4] The ball bearing according to any one of [1] to [3], wherein the variation in the bottom thickness of each pocket is within 10 μm. [5] The resin cage is a crown-shaped cage or a double-ring cage having a pair of the aforementioned ring portions, the resin cage for a ball bearing according to any one of [1] to [4]. [6] An outer ring having an outer ring raceway groove formed on its inner surface, An inner ring having an inner ring raceway groove formed on its outer surface, A plurality of balls are arranged to roll freely between the outer ring raceway groove and the inner ring raceway groove, A resin cage for ball bearings as described in any of [1] to [5], A ball bearing equipped with [a specific feature]. [Effects of the Invention]

[0009] According to the resin cage and ball bearing for ball bearings of the present invention, the roundness of the guide surface is 5 μm or less, the difference between the angle between the centers of adjacent pockets and 360° / number of pockets is within ±0.1° in both cases, and the orientation of the centers of all pockets is such that they are directed toward one side in the circumferential direction and one side in the axial direction as they move from the outer diameter side to the inner diameter side, thereby reducing cage vibration during bearing rotation and improving bearing life. [Brief explanation of the drawing]

[0010] [Figure 1] This is a longitudinal cross-sectional view of the main part of a deep groove ball bearing incorporating two annular cages according to the first embodiment of the present invention. [Figure 2] Figure 1 is a perspective view of the double annular retainer shown. [Figure 3] This is a schematic diagram illustrating the orientation of the pockets in the double annular retainer. [Figure 4] (a) to (d) are schematic diagrams illustrating four different orientations of the pockets in the double annular retainers. [Figure 5]It is a schematic diagram of both annular cages showing the pocket equal-arrangement angular difference between each pocket and the direction of the pocket. [Figure 6] It is a graph showing the pocket equal-arrangement angular difference between each pocket for the three cages of this embodiment. [Figure 7] It is a developed view of both annular cages for explaining the variation in the bottom thickness of the pocket. [Figure 8] It is a schematic diagram of both annular cages of a comparative example showing the pocket equal-arrangement angular difference between each pocket and the direction of the pocket. [Figure 9] It is a graph showing the pocket equal-arrangement angular difference between each pocket for the three cages as a comparative example. [Figure 10] It is a graph showing the relationship between roundness and rotational life time. [Figure 11] It is a graph showing the relationship between the maximum value of the pocket equal-arrangement angular difference between each pocket, the number of pocket direction deviations, and the rotational life time. [Figure 12] It is a graph showing the relationship between the maximum value of the pocket direction angle and the rotational life time. [Figure 13] As a modified example, it is a perspective view of a crowned cage.

Mode for Carrying Out the Invention

[0011] Hereinafter, a resin cage for a ball bearing and a ball bearing incorporating the resin cage according to an embodiment of the present invention will be described in detail based on the drawings.

[0012] As shown in FIG. 1, the deep groove ball bearing 10 of this embodiment includes an outer ring 20 having an outer ring raceway groove 21 formed on its inner peripheral surface, an inner ring 30 having an inner ring raceway groove 31 formed on its outer peripheral surface, a plurality of balls 11 disposed rotatably between the outer ring raceway groove 21 and the inner ring raceway groove 31, and a both-annular cage 40 which is a resin cage having a plurality of cylindrical pockets P (see FIG. 2) for rotatably holding the balls 11 respectively.

[0013] As shown in Figure 2, the double annular retainer 40 comprises a pair of annular portions 41 arranged opposite each other in the axial direction, and a plurality of columnar portions 42 (seven in the embodiment shown in Figure 10) arranged at equal intervals in the circumferential direction, with the pair of annular portions 41 extending in the axial direction and connecting the pair of annular portions 41. The pocket P is formed by adjacent columnar portions 42 and the pair of annular portions 41. Furthermore, the double annular retainer 40 is an outer ring guide type, and the outer circumferential surfaces 46 of the pair of annular portions 41 are guided by the inner circumferential surfaces 22 of the shoulder portion of the outer ring 20. The double annular retainers 40 may be manufactured by machining or by injection molding.

[0014] As the resin material for the double-ring type retainer 40, for example, a resin composition is used which is obtained by adding 10 to 50 wt% of reinforcing fiber material (for example, glass fiber or carbon fiber) to a synthetic resin such as a polyamide resin such as nylon 46 or nylon 66, polybutylene terephthalate, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyether nitrile (PEN), or polyethylene terephthalate (PET).

[0015] Here, the double annular cage 40 of this embodiment is configured to satisfy all of the following conditions (i) to (iii), and preferably at least one of the following conditions (iv) to (vi), so as to reduce vibration of the cage 40 during bearing rotation and improve bearing life, even when used under high-speed rotation conditions of dmn 1 million or more.

[0016] (i) The roundness of the outer surface 46, which serves as the guide surface, is 5 μm or less. (ii) The difference between the angle between the centers C of adjacent pockets P and 360° / number of pockets (also referred to in this specification as the "equal pocket angle difference between each pocket P") is within ±0.1° in both cases. (iii) The orientation of the center C of all pockets P is such that, as you move from the outer diameter side to the inner diameter side, it is directed to one side in the circumferential direction and to one side in the axial direction. (iv) The orientation of the center C of all pockets P is within 1°. (v) For any pocket P, the sum of the difference between the angle between the centers C of the adjacent pockets P on both sides and 360° / number of pockets is within ±0.1°. (vi) The variation in the bottom thickness T of each pocket P (i.e., the minimum distance between each pocket P and the axial side surface of the retainer 40) is within 10 μm (see Figure 7).

[0017] Regarding condition (iii), the center C of pocket P is designed to intersect the rotation axis center X of the ball bearing 10 (see Figure 1) from the outer diameter side to the inner diameter side, as shown by the dashed line in Figure 3, and its axial position does not change in the radial direction. In other words, on a plane that passes through the rotation axis center X and is perpendicular to the center C of the designed pocket P, if we define the rotation axis center X as the first axis L1 and the axis that passes through the axial position of the center C and is perpendicular to the rotation axis center X as the second axis L2, then when the designed pocket P is projected from the outer diameter side, the center C of pocket P is projected as pocket P' passing through the intersection XA of the first axis L1 and the second axis L2.

[0018] However, in a typical holder, the orientation of the center C of pocket P deviates from the intersection XA with the first axis L1 and the second axis L2 as you move from the outer diameter side to the inner diameter side, as shown by the dashed line in Figure 3. Pocket P is projected as pocket P', shown by the dotted line, on a plane containing the first axis L1 and the second axis L2. That is, as shown in Figures 4(a) to (d), with respect to the outer diameter opening of pocket P, the orientation of the center C of pocket P is formed to vary toward one of the four regions A1 to A4 separated by the first axis L1 and the second axis L2. On the other hand, in this embodiment, the pockets P are formed such that the orientation of the center C of all pockets P points toward one of the four regions A1 to A4.

[0019] Furthermore, condition (iv) indicates that the orientation of the center C of all pockets P intersects within 1° of the line connecting the intersection point XA of the first axis L1 and the second axis L2 and the center position C1 of the ball 11 (the position where the center C of pocket P and the pitch circle diameter of the ball 11 intersect). In other words, in Figure 3, in the plane containing the orientation of the center C of the design pocket P (axis of center C), shown by the dashed line, and the orientation of the center C of the pocket P (axis of center C), shown by the dashed line, the angle between these two axes of center C is within 1°.

[0020] For example, in the double-ring type retainer 40 having seven pockets P (P1 to P7) shown in Figure 2, in a typical retainer used as a comparative example, as shown in Figure 8, the orientation of the centers C of pockets P1, P3, and P7 is varied, with the orientation of the centers C of pockets P2, P5, and P6 pointing towards region A3 where the circumferential direction is negative and the axial direction is negative, the orientation of the centers C of pockets P2, P5, and P6 pointing towards region A1 where the circumferential direction is positive and the axial direction is positive, and the orientation of the center C of pocket P4 pointing towards region A2 where the circumferential direction is positive and the axial direction is negative. On the other hand, in the holder of this embodiment, as shown in Figure 5, pockets P1 to P7 are formed such that the orientation of the center C of all pockets P1 to P7 is in region A1 where the circumferential direction is positive and the axial direction is positive.

[0021] Furthermore, regarding condition (ii), in the comparative example, a typical retainer, as shown in the three examples in Figure 9, the equidistant angle difference between each pocket P7-P1 to P6-P7 exceeds the range of ±0.1 at one of the positions. On the other hand, in this embodiment, as shown in the three examples in Figure 6, the difference in equidistant pocket angles between each pocket P7-P1 to P6-P7 is formed to be within the range of ±0.1 at any position. In the graphs in Figures 6 and 9, the dashed lines correspond to the difference in equidistant pocket angles between pockets P7-P1 to P6-7 in the holder shown in Figures 5 and 8.

[0022] Next, regarding conditions (i) to (iv), the evaluation bearings were incorporated into the dental air turbine, and tests were conducted on the rotational life time under the following test conditions.

[0023] (Test conditions) • Bearing dimensions: Inner diameter φ3.175mm × Outer diameter φ6.35mm × Width 2.38mm • Rotation speed: 400,000 rpm • Bearing preload: 5N (±1N) • Lifespan determination criteria: The lifespan was defined as the point at which the initial 400,000 revolutions per minute (RPM) decreased to 360,000 revolutions per minute.

[0024] Figure 10 shows the test results when the roundness of the guide surface is changed with respect to condition (i) in cages that satisfy conditions (ii) to (vi). As can be seen from these results, if the roundness of the guide surface is 5 μm or less, any of the cages can be used without breaking up to the predetermined rotational life time (400 hours).

[0025] Furthermore, Figure 11 shows the test results for a cage that satisfies conditions (i), (iv), and (vi), where the maximum value of the equidistant angle difference between pockets is changed for condition (ii), and the number of pocket orientation deviations is changed for condition (iii). As can be seen from these results, if the roundness of the guide surface is 5 μm or less, the maximum value of the equidistant angle difference between pockets is ±0.1° or less, and the orientation of all pockets is directed to one side in the circumferential direction and one side in the axial direction, the cage can be used without breaking up to a predetermined rotational life time (1000 hours).

[0026] Furthermore, Figure 12 shows the test results when conditions (i) to (iii), (v), and (vi) are satisfied, and the maximum value of the orientation of the center C of all pockets P is changed with respect to condition (iv). As can be seen from these results, if the maximum value of the orientation of the center C of all pockets P is within 1°, a rotational life of 1000 hours or more can be obtained.

[0027] Furthermore, regarding condition (v), if the sum of the difference between the angle between the centers of adjacent pockets P and any pocket P, and 360° / number of pockets, is within ±0.1°, the retainer will not break and its rotational life can be further extended.

[0028] Similarly, with respect to condition (vi), if the variation in the bottom thickness T of each pocket P is within 10 μm, the retainer will not break, its rotational life can be further extended, and good acoustic performance can be ensured.

[0029] As described above, the deep groove ball bearing 10 of this embodiment has a roundness of 5 μm or less, the difference between the angle between the centers of adjacent pockets and 360° / number of pockets is within ±0.1° in both cases, and the orientation of the centers of all pockets is such that they are directed toward one side in the circumferential direction and one side in the axial direction as they move from the outer diameter side toward the inner diameter side, thereby reducing cage vibration during bearing rotation and improving bearing life.

[0030] Furthermore, the present invention is not limited to the embodiments described above, and can be modified, improved, etc., as appropriate. In the above embodiment, a deep groove ball bearing was described as the ball bearing, but the ball bearing of the present invention may also be an angular contact ball bearing. Furthermore, the applicant confirmed that substantially similar test results could be obtained when conducting the tests shown in Figures 10 to 12 above using angular contact ball bearings incorporating both of the above-mentioned annular cages.

[0031] Furthermore, although the two annular retainers in the above embodiment use an outer ring guide system, an inner ring guide system using the inner circumferential surface of the annular portion as the guide surface may also be used. Furthermore, although the above embodiment described a double-ring type retainer, the retainer of the present invention may be a crown-type retainer 40A having a partially cylindrical pocket P, as shown in Figure 13.

[0032] This application is based on Japanese Patent Application No. 2022-020600 filed on February 14, 2022, and its contents are incorporated herein by reference. [Explanation of symbols]

[0033] 10. Deep groove ball bearings (ball bearings) 11 balls 40. Double-ring type retainer (resin retainer) 40A Crown-type retainer (resin retainer) 41 Annular section 42 Column section 46 Outer surface (guide surface) A1~A4 area P, P1~P7 Pocket

Claims

1. A resin cage for a ball bearing, comprising at least one annular portion and a plurality of columnar portions extending axially from the annular portion, wherein the balls of a ball bearing can be rotatably held in cylindrical or partially cylindrical pockets formed between adjacent columnar portions, and the annular portion has a guide surface that is guided by the inner circumferential surface of the outer ring or the outer circumferential surface of the inner ring of the ball bearing, The roundness of the guide surface is 5 μm or less. The difference between the angle between the centers of adjacent pockets and 360° / number of pockets is within ±0.1° in both cases. The orientation of the center of all the aforementioned pockets is such that, as you move from the outer diameter side to the inner diameter side, you move toward one side in the circumferential direction and one side in the axial direction. Resin cage for ball bearings.

2. For any given pocket, the sum of the difference between the angle between the centers of the adjacent pockets on either side and 360° / number of pockets is within ±0.1°. A resin cage for a ball bearing according to claim 1.

3. The resin cage for a ball bearing according to claim 1, wherein the orientation of the centers of all the aforementioned pockets is within 1°.

4. The resin cage for a ball bearing according to claim 1, wherein the variation in the bottom thickness of each of the aforementioned pockets is within 10 μm.

5. The resin cage for a ball bearing according to claim 1, wherein the resin cage is a crown-shaped cage or a double-ring type cage having a pair of the aforementioned ring portions.

6. An outer ring with an outer ring raceway groove formed on its inner circumferential surface, An inner ring having an inner ring raceway groove formed on its outer surface, A plurality of balls are arranged to roll freely between the outer ring raceway groove and the inner ring raceway groove, A resin cage for a ball bearing according to any one of claims 1 to 5, A ball bearing equipped with [a specific feature].

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