Rolling bearing retainer and rolling bearing

Abstract

The present invention provides a retainer for a rolling bearing that can stably maintain a low friction state even under severe lubrication conditions such as high-speed rotation by defining the surface roughness of the retainer using a plurality of three-dimensional surface roughness parameters, and a rolling bearing that uses the retainer. [Solution] The retainer 5 is a cylindrical resin retainer for a rolling bearing, and is formed with multiple pockets 6 that hold the rolling elements. The surfaces 6a that form the pockets 6 and at least one of the inner diameter surface 8 and outer diameter surface 9 of the retainer 5 have a value of A=(Sa / 10)+Str+(Spk / 10), which is calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding peak height Spk, of 1.20 or more.

Description

[Technical Field]

[0001] The present invention relates to a cage for a rolling bearing and a rolling bearing using the cage. [Background technology]

[0002] In rolling bearings, plastic cages are widely used as the cage that holds the rolling elements so that they can roll freely. Plastic cages are superior to steel cages in terms of self-lubrication, low friction characteristics, and light weight. Polyamide resins such as polyamide 66 (PA66) resin and polyamide 46 (PA46) resin are commonly used as synthetic resins for plastic cages, and these are reinforced as needed by adding fibrous reinforcing materials such as glass fiber.

[0003] In recent years, demand for rolling bearings used in high-speed environments, such as electric vehicles and machine tools, has been increasing. While air-oil lubrication has traditionally been used in high-speed rotation, the maintenance costs of supplying equipment have led to a rise in demand for grease lubrication. However, with grease lubrication, the grease tends to be repelled from the contact surfaces during high-speed rotation, leading to insufficient lubrication between the rolling elements and the cage. Insufficient lubrication can lead to excessive temperature rise and wear at the contact surfaces, shortening the bearing's lifespan.

[0004] Known countermeasures for such severe lubrication conditions include forming grooves or holes on the inner peripheral surface of pockets formed in the cage, as in Patent Document 1, and roughening the inner surface of pockets in the cage that come into contact with the rolling elements, as in Patent Documents 2 and 3. These are intended to retain the lubricant using the shape of the cage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7088286 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-198469 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-095469 Summary of the Invention [Problem to be solved by the invention]

[0006] The plateau structure surface (a surface formed by a smooth surface and recessed portions without any protrusions, such as grooves or holes) described in Patent Document 1 is known as a method for improving sliding characteristics by retaining lubricant in the recessed portions. However, under more severe contact conditions, such as boundary lubrication, where two surfaces come into contact, the smooth surface of the plateau structure surface comes into contact with the mating surface. Even if lubricant is present in the recessed portions, it is removed from the smooth surface, which can easily increase the coefficient of friction and generate heat. Therefore, it is desirable to keep the contact area with the rolling element as small as possible.

[0007] Furthermore, in Patent Document 2, the surface roughness (such as arithmetic surface roughness Ra) of the inner surface of the pocket against which the rolling elements abut is specified so that the lubricant is retained in the recesses and a sufficient oil film is formed. However, this is ineffective unless the lubricant is present on the inner surface of the pocket, and when the bearing rotates at higher speeds, it is expected that the lubricant will be expelled from the inner surface of the cage pocket due to centrifugal force, etc., making it insufficient.

[0008] Furthermore, in Patent Document 3, the surface roughness (arithmetic surface roughness Ra, maximum height Rt, etc.) of the guided surface guided by the inner or outer ring is specified in addition to the inner surface of the pocket with which the rolling elements abut, to ensure the formation of a sufficient oil film. However, the parameters used in these patent documents are determined from a two-dimensional profile curve, and are insufficient to limit the area of ​​contact with the mating surface.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a retainer for a rolling bearing that can stably maintain a low friction state even under harsh lubrication conditions such as high-speed rotation by defining the surface roughness of the retainer using a plurality of three-dimensional surface roughness parameters, and a rolling bearing that uses this retainer. [Means for solving the problem]

[0010] The inventors have conducted extensive research focusing on three-dimensional surface roughness parameters on the surfaces that form the pockets that come into contact with the rolling elements in a cage for a rolling bearing, as well as on the inner diameter surface and outer diameter surface, and have found that "(Sa / 10) + Str + (Spk / 10)", which is calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the peak height Spk, shows a high correlation with the coefficient of friction, and further that a low-friction state can be controlled by specifying this value A. The present invention is based on this finding.

[0011] The retainer for a rolling bearing of the present invention is a cylindrical resin retainer for a rolling bearing, in which a plurality of pockets for holding rolling elements are formed, and the surfaces constituting the pockets and at least one of the inner diameter surface and outer diameter surface of the retainer are characterized in that the value of A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding peak height Spk, is 1.20 or greater.

[0012] In one form, the above-mentioned cage is characterized in that when the contact surfaces of any one or more (for example, all) pockets on the surface constituting the pocket that come into sliding contact with the rolling elements are measured so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling elements, the value of the surface roughness parameters calculated from ISO 25178, calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding peak height Spk, is 1.20 or more for all the measured contact surfaces or their average values.

[0013] Specifically, on the contact surfaces of any one or more (for example, all) pockets, one point where the rolling element and cage can come into contact when the bearing is rotating, and a point 180° away from that point are set as the center point (0°) of the measurement range, and when any location within a range of ±30° (measurement target area) is measured, the value of A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa calculated from ISO 25178, the aspect ratio Str of the surface texture, and the protruding peak height Spk, for all measured contact surface values ​​or their average value, is characterized by the following: A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa calculated from ISO 25178, the aspect ratio Str of the surface texture, and the protruding peak height Spk, is 1.20 or more.

[0014] The aspect ratio Str is 0.80 or more. The arithmetic mean height Sa is 2.00 μm or more and 10.00 μm or less, and the protruding peak height Spk is 5.0 μm or more.

[0015] The cage is characterized in that it is an injection-molded article made of a resin composition.

[0016] The rolling bearing of the present invention is a rolling bearing having an inner ring and an outer ring, a plurality of rolling elements interposed between the inner and outer rings, a retainer that holds the rolling elements, and grease sealed in the space within the bearing, wherein the retainer is the rolling bearing retainer of the present invention.

[0017] The grease contains a base oil and a urea-based thickener, and the kinematic viscosity of the base oil at 40°C is 10mm 2 / s or more 30mm 2 / s. [Effects of the Invention]

[0018] The cage for a rolling bearing of the present invention is made of resin and has a cylindrical shape, and has a rough surface on the surfaces that form the pockets and on at least one of the inner diameter surface and outer diameter surface of the cage, and the rough surface is defined by a value A calculated from a plurality of three-dimensional surface roughness parameters that are determined from a roughness curve. Specifically, by setting A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa, the aspect ratio of the surface texture Str, and the peak height Spk, to be 1.20 or greater, it becomes easier to retain lubricant, an oil film can be maintained on the contact surface even when the amount of lubricant supplied is small, the contact area with the mating surface is reduced, and the friction coefficient and temperature rise are suppressed, resulting in a cage that can stably maintain a low friction state even under harsher lubrication conditions.

[0019] Furthermore, the retainer has a roughened surface on its inner diameter surface facing the inner ring that can retain lubricant, thereby preventing the lubricant from migrating toward the outer ring due to centrifugal force during high-speed rotation and depleting the lubricant near the inner ring raceway surface. Retaining lubricant on the inner diameter surface of the retainer makes it easier for lubricant to be supplied to the surfaces of adjacent pockets, resulting in a retainer that can maintain a stable low-friction state even under harsher lubrication conditions.

[0020] Furthermore, the above-mentioned retainer has a rough surface that can retain lubricant on its outer diameter surface facing the outer ring, so that even if it comes into contact with the outer ring due to expansion of the retainer caused by centrifugal force or heat generation during high-speed rotation, the lubricant retained on the outer diameter surface of the retainer can maintain a good sliding condition, suppressing further heat generation.In addition, retaining lubricant on the outer diameter surface of the retainer makes it easier for lubricant to be supplied to the surfaces of adjacent pockets, resulting in a retainer that can maintain a stable low-friction condition even under harsher lubrication conditions.

[0021] The rolling bearing of the present invention is equipped with the cage of the present invention, and therefore can achieve a longer life for the bearing even under more severe lubrication conditions. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an axial cross-sectional view showing an example of a rolling bearing of the present invention. [Figure 2]1 is a perspective view showing an example of a cage for a rolling bearing of the present invention. [Figure 3] FIG. 2 is a diagram illustrating an example of measurement locations for three-dimensional surface roughness parameters of the cage for a rolling bearing of the present invention. [Figure 4] FIG. 4 is a partially enlarged perspective view showing another example of the cage for a rolling bearing of the present invention. [Figure 5] FIG. 1 is a diagram showing an outline of a Savin friction and wear tester. [Figure 6] 1 is a graph showing the coefficients of friction of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0023] The cage for a rolling bearing and the rolling bearing of the present invention will be described with reference to Figures 1 and 2. Figure 1 is an axial cross-sectional view showing an outline of an angular contact ball bearing, which is an example of the rolling bearing of the present invention, and Figure 2 is a perspective view of a cage (machined type) for the rolling bearing of Figure 1.

[0024] As shown in Figure 1, angular contact ball bearing 1 comprises an inner ring 2, an outer ring 3, multiple balls (rolling elements) 4 interposed between the inner ring 2 and the outer ring 3, and a cage 5 that holds these balls 4 at regular intervals around the circumference. The inner ring 2, outer ring 3, and balls 4 are in contact with each other at a predetermined angle θ (contact angle) relative to the radial centerline, allowing them to withstand radial loads and unidirectional axial loads. Furthermore, openings at both axial ends of the inner and outer rings are sealed with sealing members (not shown), and grease G is packed around at least the balls 4. The inner ring 2, outer ring 3, and balls 4 are made of an iron-based metallic material, and grease G is interposed between the raceway surfaces of the balls 4 to lubricate them.

[0025] In Fig. 1, the cage 5 is of an outer ring guide type, and a part of the outer diameter surface of the cage has a guided surface that is guided by the outer ring 3. In Fig. 1, the outer diameter surface that becomes the guided surface is formed as a rough surface, which will be described later. Note that the guide type of the cage is not limited to an outer ring guide type, and it may also be an inner ring guide type or a rolling element guide type.

[0026] As shown in FIG. 2, the cage 5 is a machined cylindrical cage made of resin, with a plurality of pockets 6 for holding the balls provided at regular intervals in the circumferential direction in the annular cage body. The pockets 6 are spaces for accommodating the balls 4, and are circular holes (through holes) with a uniform cross-sectional shape along the radial direction. The pocket inner surface 6a is the surface that constitutes the space (pocket 6) provided for accommodating the balls 4, and is the surface that comes into contact with and slides against the balls 4. Pillar portions 7 are formed between adjacent pockets 6 in the circumferential direction.

[0027] For example, the cage 5 is obtained by injection molding using a resin composition. The pocket 6 may be formed during the injection molding stage, for example, using a mold with a slide core, or may be formed by cutting a preform after molding. In the cage 5, the pocket inner surface 6a (specifically, the abutment surface that contacts the balls) and the outer diameter surface 9 are roughened surfaces defined by multiple three-dimensional surface roughness parameters. In addition, the inner diameter surface 8 may also be roughened, which makes it easier to supply lubricant to the pocket inner surface 6a.

[0028] The rough surface may be formed, for example, by transferring from a mold, or may be formed after molding by machining such as shot blasting or filing. For example, shot blasting is preferred because it is easy to obtain a machined surface that exhibits isotropy.

[0029] In the present invention, the value A=(Sa / 10)+Str+(Spk / 10) calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding peak height Spk of the rough surface is 1.20 or more.

[0030] The pocket inner surface 6a for which the above-mentioned value A is defined will be specifically described with reference to FIG. 3. The pocket inner surface 6a is the portion that comes into contact with the balls 4, for example, the portion that comes into sliding contact with the balls 4. In this case, for example, when the pocket inner surface 6a is measured at the portion of the pocket inner surface 6a that comes into sliding contact with the balls 4 so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling elements, the value A calculated using the surface roughness parameters calculated from ISO 25178 will satisfy the above-mentioned range. More specifically, on the pocket inner surface 6a, one point where the balls 4 and the surface 6a can come into contact during bearing rotation (the direction of revolution of the balls 4 (X direction) in FIG. 3)) and a point 180° away from that point are defined as the center point (0°) of the measurement range, and any point within a ±30° range (region R in FIG. 3) is measured so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling elements. It is preferable that the value A calculated using the surface roughness parameters calculated from ISO 25178 will satisfy the above-mentioned range. For example, it is preferable that the value A obtained using the values ​​of all the pocket inner surfaces 6a or the average value thereof falls within the above range.

[0031] Although Figure 3 describes one pocket inner surface 6a, it is sufficient that the value A obtained from at least one pocket inner surface 6a in the cage satisfies the above range. For example, the value A obtained from the inner surfaces of at least four pockets (pockets located at positions of 0 degrees, 90 degrees, 180 degrees, and 270 degrees in the circumferential direction of the cage) may satisfy the above range, or the value A obtained from the inner surfaces of all pockets in the cage may satisfy the above range.

[0032] Each roughness parameter related to the value A will be explained below.

[0033] [Arithmetic mean height Sa] The arithmetic mean height Sa is a parameter that expands the arithmetic mean roughness Ra into three dimensions, and is the average value of the height difference from the average surface. Because it is an average value, it is not easily affected by local scratches on the surface or dust particles attached, so it is generally used as an index of surface roughness, and since it evaluates the surface, there is less variation depending on the measurement position than with Ra, making it preferable for evaluating surfaces.

[0034] Compared with a small arithmetic mean surface height Sa (e.g., Sa 1.00 μm or less), a large arithmetic mean surface height Sa (e.g., Sa 2.00 μm or more) allows the lubricant to be retained in the recesses, making it easier to form a sufficient oil film. The arithmetic mean height Sa is preferably 2.00 μm or more and 10.00 μm or less, and more preferably 4.00 μm or more. On the other hand, if the arithmetic mean height Sa is large, it may affect rotation accuracy, for example, during high-speed rotation, so Sa is preferably 8.00 μm or less, and may be less than 6.00 μm.

[0035] [Surface texture aspect ratio Str] The aspect ratio Str of a surface texture is the ratio of the distance in the direction where the surface autocorrelation decays to a specific value most quickly to the distance in the direction where it decays most slowly, and is a parameter that represents the isotropy or anisotropy of the surface texture. The aspect ratio Str of a surface texture ranges from 0 to 1, with Str > 0.5 indicating a strongly isotropic surface and Str < 0.3 indicating a strongly anisotropic surface. If the aspect ratio Str of a surface texture is 0.5 or greater, the lubricant on the contact surface will easily spread without being biased in a specific direction, making it easier to supply the lubricant over a wide area of ​​the contact surface.

[0036] The aspect ratio Str of the surface texture is preferably 0.50 or more, and more preferably 0.80 or more.

[0037] [Protruding peak height Spk] The protruding peak height Spk is calculated from the surface load curve and is the average height of the protruding peaks that are higher than the core. More specifically, for the surface being measured, the proportion of the load area (the area of ​​the region with height c or higher) at a certain height c is defined as the load area ratio Smr(c), and a curve (load curve) showing the heights at which the load area ratio ranges from 0% to 100% is graphed. A secant line is drawn along the load curve connecting two points where the difference in load area ratio is 40%, and the end of the secant line is moved from the point where the load area ratio is 0%. The position where the slope of the secant line is the gentlest is defined as the center of the load curve. The straight line where the sum of squares of the deviation in the vertical direction from this center is the smallest is defined as the equivalent line. The surface obtained by removing the area of ​​the equivalent line that is not included in the height range of the load area ratio from 0% to 100% is defined as the core, and the parts protruding above this core are defined as protruding peaks, and their average height is calculated. If the protruding peak height Spk is small, the protruding peaks will wear out in the early stages, flattening the contact surface and increasing the contact area, making it difficult for the lubricant to flow onto the contact surface.

[0038] The protruding peak height Spk is, for example, 2.00 μm or more, preferably 4.00 μm or more, and may be 5.00 μm or more. By setting it in this range, the contact area is reduced, resulting in a surface that allows the lubricant to easily flow in. Furthermore, the protruding peak height Spk is, for example, 15.00 μm or less, and may be 10.00 μm or less.

[0039] Generally, surface texture is often evaluated using a single roughness parameter. However, it is preferable to evaluate using multiple parameters. In this invention, the above-mentioned roughness parameters can be combined into a mathematical formula to evaluate a surface that can maintain low friction even under severe lubrication conditions where only a small amount of lubricant is present. Specifically, when the value A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the peak height Spk is 1.20 or greater, the surface will have low friction even under severe lubrication conditions where only a small amount of lubricant is present.

[0040] The value A = (Sa / 10) + Str + (Spk / 10) is preferably 1.30 or more, more preferably 1.50 or more, and may be 1.70 or more. On the other hand, if the value A is too large, the surface tends to become rough, which may affect the rotation accuracy, etc., so the value A is, for example, 3.0 or less, and may be 2.5 or less.

[0041] The above-mentioned various roughness parameters (Sa, Str, Spk) are values ​​calculated in accordance with ISO25178, and are calculated from data measured by, for example, a non-contact surface roughness measuring instrument (for example, a laser microscope).

[0042] As described above, in the cage of the present invention, by combining and defining the arithmetic mean height Sa, Str indicating isotropy or anisotropy, and parameter Spk related to the shape of the contacting protruding ridge portion as a formula for the surfaces constituting the pocket and at least one of the inner diameter surface and outer diameter surface of the cage, it is possible to maintain a low friction state even under severe lubrication conditions, as will be shown in the examples described later.

[0043] In the pocket, at least the contact surface with which the rolling element comes into contact (see, for example, FIG. 3) may have the above-mentioned roughness, or the entire surface constituting the pocket may have the above-mentioned roughness.

[0044] Furthermore, when the cage is of an inner ring guide type, the inner diameter surface that serves as the guided surface may have the above-mentioned roughness. Furthermore, without being limited to the non-guiding surface, either the outer diameter surface or the inner diameter surface or both may be roughened as described above, and the entire surface of the cage may also be roughened as described above.

[0045] In the present invention, the cage may be made of resin, and the resin material is preferably injection moldable and has sufficient heat resistance and mechanical strength for a cage. For example, a resin composition can be used in which a PA resin such as polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin, thermoplastic polyimide resin, polyamide-imide resin, PA66, PA46 resin, PA6T resin, or PA9T resin is used as the resin matrix, and reinforcing fibers such as carbon fiber and glass fiber and other additives are blended.

[0046] Returning to FIG. 1, in angular contact ball bearing 1, both inner ring 2 and outer ring 3 are made of steel. Any material commonly used as a bearing material can be used for the steel. For example, high-carbon chromium bearing steel (SUJ1, SUJ2, SUJ3, SUJ4, SUJ5, etc.; JIS G 4805), carburized steel (SCr420, SCM420, etc.; JIS G 4053), stainless steel (SUS440C, etc.; JIS G 4303), cold-rolled steel, etc. can be used. Furthermore, the above-mentioned steel or ceramic material can be used for ball 4. The surface roughness of ball 4 is, for example, Ra 0.1 μm or less.

[0047] The rolling bearing of the present invention is lubricated with grease. The grease is sealed in the space within the bearing and lubricates the raceway surfaces and the contact surfaces between the balls and the cage. The base oil constituting the grease can be any oil typically used in rolling bearings, such as mineral oil or synthetic oil, without any particular limitation. The thickener constituting the grease can also be any oil typically used in rolling bearings, such as metal soaps or urea compounds, without any particular limitation.

[0048] The grease is preferably a grease containing a base oil and a urea-based thickener. In this case, the base oil is preferably a synthetic oil such as ether oil or ester oil. The kinematic viscosity of the base oil at 40°C is not particularly limited, but a base oil with a relatively low viscosity is preferred in terms of the roughness of the cage. 2 / s or more 50mm 2 / s and less than 10 mm2 / s or more 30mm 2 / s or less is preferred.

[0049] In FIG. 1, an angular contact ball bearing is used as an example of the rolling bearing of the present invention, but the bearing type to which the present invention can be applied is not limited to this, and the present invention can also be applied to other ball bearings, tapered roller bearings, cylindrical roller bearings, self-aligning roller bearings, needle roller bearings, etc.

[0050] As another example of a rolling bearing cage according to the present invention, a crown-type cage will be described with reference to Fig. 4. Fig. 4 is a partially enlarged perspective view of the crown-type cage. As shown in Fig. 4, the cage 10 is cylindrical and has a pair of opposing retaining claws 11 formed at a constant circumferential pitch on the upper surface of an annular cage body. The opposing retaining claws 11 are curved toward each other, and pockets 12 for holding balls as rolling elements are formed between the retaining claws 11. A flat portion 13 serving as a rising reference surface for the retaining claws 11 is formed between the back surfaces of adjacent retaining claws 11 in adjacent pockets 12. In the crown-type cage 10, the pocket inner surface 12a and at least one of the inner diameter surface and the outer diameter surface 14 have a value A = (Sa / 10) + Str + (Spk / 10) calculated from the respective three-dimensional surface roughness parameters of 1.20 or more.

[0051] The cage for a rolling bearing of the present invention can maintain a stable low-friction state even with a small amount of lubricant, and therefore can be used particularly for rolling bearings that rotate at high speeds. Specifically, it can be used for bearings used in spindle devices for machine tool main shafts and rolling bearings used in motors. For example, a bearing for high-speed rotation with a dm·n value of 80×10 4 ~300×10 4 It is used in the rotation range.

[0052] The present invention is based on the fact that "(Sa / 10) + Str + (Spk / 10)," which is calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the peak height Spk of the surfaces constituting the pockets and at least one of the inner and outer diameter surfaces of the cage for a rolling bearing, shows a high correlation with the coefficient of friction. Therefore, by using this as an index, the friction characteristics of the cage for a rolling bearing can be evaluated. Here, "evaluating the friction characteristics" means determining the degree of friction (e.g., the coefficient of friction) when sliding against the rolling elements.

[0053] Specifically, the evaluation method is a method for evaluating the frictional characteristics with rolling elements in a cylindrical resin rolling bearing cage having multiple pockets formed therein for holding the rolling elements, and is characterized in that the frictional characteristics are evaluated on the surface constituting the pocket and at least one of the inner diameter surface and the outer diameter surface based on the value A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding peak height Spk of the surface constituting the pocket and at least one of the inner diameter surface and the outer diameter surface.

[0054] The value A exhibits a high correlation with the coefficient of friction, as will be shown in the examples described later (see FIG. 6). Specifically, the larger the value A, the smaller the coefficient of friction tends to be. Therefore, in the above evaluation method, the friction characteristics can be evaluated based on the magnitude of the calculated value A. For example, by comparing the value A with a predetermined threshold, if the value A is equal to or greater than the predetermined threshold, the cage can be determined to have low friction, and if the value A is less than the predetermined threshold, the cage can be determined not to have low friction. The predetermined threshold is not particularly limited, but can be set to, for example, 1.20.

[0055] Furthermore, by comparing the magnitude of the value A obtained from each of a plurality of cages, it is possible to select the cage with the lowest friction. [Example]

[0056] Examples of the present invention will be described below. Using a Savin abrasion tester shown in Fig. 5, the coefficients of friction of test pieces with different surface roughnesses were evaluated.

[0057] (1) Preparation of test specimens An injection-molded body (composition: glass fiber reinforced polyamide 66) was cut into a size of 10 mm x 15 mm and a thickness of 4 mm to prepare test specimens. The sliding surfaces of the test specimens were roughened isotropically by shot blasting and anisotropically by filing to obtain test specimens for Examples 1 to 6. Note that the test specimens for Comparative Examples 1 and 2 were not roughened, and the sliding surfaces were left as injection-molded surfaces.

[0058] (2) Measurement of roughness parameters The roughness parameters (Sa, Str, Spk) of the sliding surface of each test piece obtained above were measured using a laser microscope OPTELICS HYBRID manufactured by Lasertec Corporation under the measurement conditions shown below. Measurement range: 870μm x 870μm Lens magnification: 50x

[0059] The measurement results are shown in the following Table 1. The surface roughness of Comparative Examples 1 and 2 is equivalent to the roughness of a cage obtained by general injection molding.

[0060] When measuring the roughness of a cage, at least four pockets out of all pockets (e.g., pockets located at 0, 90, 180, and 270 degrees around the cage) are targeted, and within one pocket, one point where the rolling element and the abutting surface of the cage pocket can come into contact when the bearing is rotating, and a point 180 degrees away from that point are set as the center point (0°) of the measurement range, and any point within a range of ±30° is measured.

[0061] [Table 1]

[0062] (3) Savin abrasion test A Savin wear tester 21 shown in Figure 5 was used. A cylindrical mating member 25 was attached to the rotating shaft, and a test piece 24 was fixed to it. A small amount of grease (0.02 g) was applied to the contact area between the test piece 24 and the cylindrical mating member 25, and no more grease was supplied thereafter, simulating a state in which the lubricant supply is insufficient when the bearing rotates at high speed. The cylindrical mating member 25 was brought into rotating contact with the test piece 24 while a load was applied from above in the figure by a weight 23. The friction force generated when the cylindrical mating member 25 was rotated was detected by a load cell 22. The friction coefficient was measured 60 minutes after the start of the test. <Test conditions> Counterpart material: SUJ2 cylinder Φ40mm x 10mm, arithmetic mean roughness Ra0.01μm Grease: Base oil (ester oil; kinematic viscosity at 40°C 22mm 2 / s), thickener (urea-based) Relative velocity: 4.2 m / s Load: 15N (surface pressure 60MPa)

[0063] The friction coefficients obtained by the Savin abrasion test for each test example are shown in Figure 6. Figure 6 is a graph plotting the relationship between the value A and the friction coefficient for each test example. As shown in Figure 6, a high correlation was observed between the value A and the friction coefficient (correlation coefficient -0.91), and the larger the value A = (Sa / 10) + Str + (Spk / 10), the lower the friction coefficient. However, a correlation as strong as that between each three-dimensional surface roughness parameter (Sa, Str, Spk) and the friction coefficient was not observed.

[0064] As shown in Figure 6, Examples 1 to 6 had lower coefficients of friction than Comparative Examples 1 and 2, which had injection-molded surfaces. Specifically, the coefficients of friction for Examples 1 to 6 were less than 0.20, while the coefficients of friction for Comparative Examples 1 and 2 were 0.20 or greater. Furthermore, compared to Examples 5 and 6 (file processing), the coefficients of friction for Examples 1 to 4 (shot blast processing) were less than 0.15, indicating lower friction. Examples 5 and 6 had aspect ratios Str of less than 0.3, while Examples 1 to 4 had aspect ratios Str of 0.80 or greater, indicating high isotropy, and it is believed that this difference affected the low friction.

[0065] In this way, when the value A defined by the surface roughness determined in the present invention of the surface that slides against another member is large, it is possible to reduce the coefficient of friction during sliding. [Industrial Applicability]

[0066] The rolling bearing cage of the present invention defines the surfaces that make up the pocket and at least one of the inner diameter surface and outer diameter surface by a value A determined from multiple three-dimensional surface roughness parameters, thereby enabling an oil film to be maintained on the contact surfaces even with a small amount of lubricant, and enabling a stable low-friction state to be maintained even under severe lubrication conditions, making it particularly suitable for use in the field of rolling bearings that rotate at high speeds. [Explanation of symbols]

[0067] 1. Angular contact ball bearings (rolling bearings) 2. Inner circle 3 outer ring 4 balls (rolling elements) 5 Cage 6 pockets 6a Pocket inner surface (surface that makes up the pocket) 7 Pillar part 8 Inner diameter surface 9 Outer diameter surface 10 Cage 11 Holding claw 12 pockets 12a Pocket inner surface (surface that makes up the pocket) 13 Flat area 14 Outer diameter surface 21 Saban type abrasion tester 22 load cells 23 Weight 24 test specimens 25 Cylindrical mating member

Claims

1. A cylindrical resin rolling bearing retainer, A retainer for a rolling bearing, characterized in that a plurality of pockets for holding rolling elements are formed in the retainer, and the surfaces constituting the pockets and at least one of the inner diameter surface and outer diameter surface of the retainer have a value of A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface texture, and the protruding ridge height Spk, of 1.20 or more.

2. 2. The cage for a rolling bearing according to claim 1, wherein the aspect ratio Str is 0.80 or more.

3. 3. The cage for a rolling bearing according to claim 2, wherein the arithmetic mean height Sa is 2.00 μm or more and 10.00 μm or less, and the protruding ridge height Spk is 5.0 μm or more.

4. 3. The cage for a rolling bearing according to claim 1, wherein the cage is an injection-molded article made of a resin composition.

5. A rolling bearing having an inner ring, an outer ring, a plurality of rolling elements interposed between the inner and outer rings, a cage that holds the rolling elements, and grease sealed in a space within the bearing, 3. A rolling bearing, wherein the cage is the cage for a rolling bearing according to claim 1 or 2.

6. The grease contains a base oil and a urea-based thickener, and the kinematic viscosity of the base oil at 40°C is 10 mm ２ / s or more 30mm ２ 6. The rolling bearing according to claim 5, wherein the rolling bearing has a rolling resistance of less than 1 / s.

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