Rolling bearing cage and rolling bearing

Abstract

Provided are a rolling bearing cage and a rolling bearing using the cage, the rolling bearing cage making it possible to: maintain an oil film on a contact surface even with a small amount of lubricant by defining the surface roughness of the cage by means of a plurality of three-dimensional surface roughness parameters; and stably maintain a low friction state even under severe lubrication conditions. The cage 5 is a resin-made cage for the rolling bearing, and has a plurality of pockets 6 that hold rolling elements. A value of A = (Sa / 10) + Str + (Spk / 10) obtained from an arithmetic average height Sa, an aspect ratio Str of surface properties, and a protruding peak height Spk on the surface 6a of the pockets 6 is equal to or greater than 1.20.

Description

Rolling bearing retainer and rolling bearing

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

[0002] In rolling bearings, plastic cages are widely used as cages that hold 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 by the shape of the cage.

[0005] Japanese Patent No. 7088286 Japanese Patent Application Laid-Open No. 2014-095469 Japanese Patent Application Laid-Open No. 2007-198469

[0006] The plateau structure surface (a surface formed by a smooth surface and recessed portions without 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 friction coefficient and generate heat. Therefore, it is desirable to keep the contact area with the rolling element as small as possible.

[0007] In addition, in Patent Documents 2 and 3, the surface roughness (arithmetic surface roughness Ra, maximum height Rt, etc.) of the inner surface of the pocket with which the rolling elements abut is specified so that the lubricant is retained in the recesses and a sufficient oil film is formed. However, the parameters used in these Patent Documents are parameters determined from a two-dimensional profile curve, and are insufficient to limit the area of ​​contact with the mating surface.

[0008] The present invention has been made in light of these circumstances, and aims to provide a retainer for a rolling bearing that can maintain a stable low-friction state even under severe lubrication conditions by specifying the surface roughness of the retainer using a plurality of roughness parameters, thereby enabling an oil film to be maintained on the contact surface with even a small amount of lubricant, and a rolling bearing that uses this retainer.

[0009] The present inventors have conducted extensive research focusing on three-dimensional surface roughness parameters on the surfaces of pockets of a cage for a rolling bearing as one form of cage for a rolling bearing, and have found that "(Sa / 10) + Str + (Spk / 10)", which is calculated from the arithmetic mean height Sa of the surface, the aspect ratio Str of the surface texture, and the protruding 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.

[0010] The cage for a rolling bearing of the present invention is a resin-made cage for a rolling bearing, characterized in that a plurality of pockets for holding rolling elements are formed in the cage, and the value of A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa of the pocket surface, the aspect ratio Str of the surface texture, and the protruding peak height Spk, is 1.20 or greater.

[0011] 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 contact surfaces 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 according to 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 values ​​of the contact surfaces or their average value.

[0012] Specifically, on the contact surfaces of any one or more (for example, all) pockets, one point where the rolling elements and the 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, is 1.20 or more for all measured values ​​of the contact surfaces or their average value.

[0013] 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.

[0014] The retainer for a rolling bearing of the present invention is a resin retainer for a rolling bearing, in which a plurality of pockets for holding rolling elements are formed, and the surfaces of the pockets have an arithmetic mean roughness Ra of 3.00 μm or more and 10.00 μm or less, an average element length RSm of 0.10 mm or more and 0.40 mm or less, and a kurtosis Rku of 1.0 or more and 5.0 or less.

[0015] 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 contact surfaces that come into sliding contact with the rolling elements are measured so that the measurement direction of the roughness curve is perpendicular to the rotation direction of the rolling elements, the roughness parameters calculated from the roughness curve in accordance with JIS B 0601 are such that the arithmetic mean roughness Ra is 3.00 μm or more and 10.00 μm or less, the mean element length RSm is 0.10 mm or more and 0.40 mm or less, and the kurtosis Rku is 1.0 or more and 5.0 or less for all the measured values ​​of the contact surfaces. Specifically, on the contact surfaces of any one or more (for example, all) pockets, one point where the rolling element and the contact surface can come into contact when the bearing rotates, 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 roughness parameters calculated from a roughness curve based on JIS B 0601 are characterized in that, for all contact surface values ​​or their average values, the arithmetic mean roughness Ra is 3.00 μm or more and 10.00 μm or less, the mean element length RSm is 0.10 mm or more and 0.40 mm or less, and the kurtosis Rku is 1.0 or more and 5.0 or less.

[0016] The skewness Rsk calculated from the roughness curve on the surface of the pocket is in the range of -1.00 to 1.00.

[0017] The kurtosis Rku is more than 3.0 and not more than 5.0.

[0018] The cage is characterized in that it is an injection-molded article made of a resin composition.

[0019] 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.

[0020] 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 / s or less.

[0021] The cage for a rolling bearing of the present invention has a roughened surface on the surface of the pocket, and this roughened surface is defined by a value A calculated from a plurality of three-dimensional surface roughness parameters determined from a roughness curve. Specifically, by setting 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, 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.

[0022] The cage for a rolling bearing of the present invention has a roughened surface on the surface of the pocket that comes into contact with the rolling elements, and the roughened surface is defined by a plurality of roughness parameters determined from a roughness curve. Specifically, by setting the arithmetic mean roughness Ra to be 3.00 μm or more and 10.00 μm or less, it becomes easier to retain lubricant and a film of oil can be maintained on the contact surface even when the amount of lubricant supplied is small. In addition, by setting the mean element length RSm to be 0.10 mm or more and 0.40 mm or less and the kurtosis Rku to be 1.0 or more and 5.0 or less, the contact area with the mating surface is reduced, and the coefficient of friction and temperature rise are suppressed, resulting in a cage that can stably maintain a low friction state even under harsher lubrication conditions.

[0023] Furthermore, since the skewness Rsk is between -1.00 and 1.00, deviations in height distribution are suppressed, and the contact area with the mating surface is easily maintained small, further contributing to suppression of the friction coefficient and temperature rise.

[0024] Furthermore, since the kurtosis Rku is greater than 3.0 and not greater than 5.0, the flat portions of the peaks and valleys of the roughness curve are reduced, and the contact area with the mating surface can be made smaller.

[0025] 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.

[0026] FIG. 1 is an axial sectional view showing an example of a rolling bearing of the present invention. FIG. 2 is a perspective view showing an example of a cage for a rolling bearing of the present invention. FIG. 3 is a diagram explaining an example of measurement locations for roughness parameters of a cage for a rolling bearing of the present invention. FIG. 4 is a diagram explaining arithmetic mean roughness Ra. FIG. 5 is a diagram explaining mean element length RSm. FIG. 6 is a diagram explaining kurtosis Rku. FIG. 7 is a diagram explaining skewness Rsk. FIG. 8 is a partially enlarged perspective view showing another example of a cage for a rolling bearing of the present invention. FIG. 9 is a diagram showing an outline of a Savin type friction and wear tester. FIG. 10 is a graph showing the friction coefficients of test examples A1 to A8. FIG. 11 is a graph showing the progression of the friction coefficients of test examples B1 to B3.

[0027] 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.

[0028] As shown in Figure 1, an angular contact ball bearing 1 comprises an inner ring 2, an outer ring 3, a plurality of balls (rolling elements) 4 interposed between the inner ring 2 and the outer ring 3, and a cage 5 that holds the balls 4 at regular intervals in the circumferential direction. The inner ring 2, the outer ring 3, and the balls 4 are in contact with each other at a predetermined angle θ (contact angle) relative to the radial centerline, allowing them to bear 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 enclosed at least around the balls 4. The inner ring 2, the outer ring 3, and the 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.

[0029] 1, the cage 5 is of an outer ring guide type, and a part of the outer peripheral surface of the cage has an outer ring guide portion that is guided by the outer ring 3. Note that the guide type of the cage is not limited to the outer ring guide type, and may be an inner ring guide type or a rolling element guide type.

[0030] As shown in Figure 2, the cage 5 is a machined resin cage with a ring-shaped cage body having a plurality of pockets 6 for holding balls, spaced at regular intervals in the circumferential direction. Pillars 7 are formed between adjacent pockets 6 in the circumferential direction.

[0031] For example, the cage 5 is obtained by injection molding using a resin composition. The pockets 6 may be formed during the injection molding stage using a mold having a slide core, or may be formed by cutting after molding a base material.

[0032] [First embodiment] In a first embodiment of the present invention, the cage 5 has a pocket 6 surface (specifically, a contact surface that comes into contact with the ball) 6a that is a rough surface defined by a plurality of three-dimensional surface roughness parameters.

[0033] 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.

[0034] In the first embodiment, the value A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa of the surface 6a, the aspect ratio Str of the surface texture, and the protruding peak height Spk is 1.20 or more.

[0035] The surface 6a for which the above-mentioned value A is defined will be specifically described with reference to FIG. 3 . The 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 surface 6a is measured at the portion of the 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 element, the value A calculated using the surface roughness parameters calculated according to ISO 25178 will satisfy the above-mentioned range. More specifically, when the surface 6a is measured at 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 element, it is preferable that the value A calculated using the surface roughness parameters calculated according to ISO 25178 will satisfy the above-mentioned range. For example, it is preferable that the value A obtained using the values ​​of all the surfaces 6a or the average value thereof satisfies the above range.

[0036] Although the surface 6 a of one pocket has been described in FIG. 3 , it is sufficient that the value A obtained from the surface 6 a of at least one pocket in the cage satisfies the above range. For example, the value A obtained from the 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 surfaces of all pockets in the cage may satisfy the above range.

[0037] Each roughness parameter related to the value A will be described below.

[0038] [Arithmetic mean height Sa] The arithmetic mean height Sa is a parameter obtained by expanding 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 attached dirt, and is therefore generally used as an index of surface roughness. Since it evaluates a surface, it has less variation depending on the measurement position than Ra, making it preferable for evaluating surfaces.

[0039] Compared with a case where the arithmetic mean height Sa of the surface is small (for example, Sa 1.00 μm or less), by increasing the arithmetic mean height Sa of the surface (for example, Sa 2.00 μm or more), the lubricant is retained in the recesses, and a sufficient oil film is more likely to be formed. 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.

[0040] [Aspect Ratio Str of Surface Texture] The aspect ratio Str of surface texture is the ratio of the distance in the direction in which the surface autocorrelation decays to a specific value most rapidly to the distance in the direction in which it decays most slowly, and is a parameter that represents the isotropy or anisotropy of the surface texture. The aspect ratio Str of surface texture takes a value in the range of 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 the surface texture is 0.5 or more, the lubricant on the contact surface tends to wet and spread without being biased in a specific direction, making it easier to supply the lubricant over a wide area of ​​the contact surface.

[0041] The aspect ratio Str of the surface texture is preferably 0.50 or more, and more preferably 0.80 or more.

[0042] [Protruding Peak Height Spk] The protruding peak height Spk is determined from the load curve of the surface and is the average height of the protruding peaks that are higher than the core portion. More specifically, for the surface to be measured, the proportion of the load area at a certain height c (the area of ​​the region with a height of c or more) is defined as the load area ratio Smr(c), 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%, and the position where the slope of the secant line is the gentlest is defined as the center of the load curve, and the straight line where the sum of squares of the deviation in the vertical axis direction from this center portion is the smallest is defined as the equivalent line, and the surface obtained by removing the region 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 portion, and the portions protruding above this core portion are defined as protruding peaks, and their average height is determined. If the protruding ridge height Spk is small, the protruding ridge 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.

[0043] 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.

[0044] Generally, surface texture is often evaluated using a single roughness parameter. However, it is preferable to evaluate using multiple parameters. In the first embodiment, the above-mentioned roughness parameters are combined into a mathematical formula to evaluate a surface that can maintain a low friction state even under severe lubrication conditions with only a small amount of lubricant. 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 with only a small amount of lubricant.

[0045] 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.

[0046] The various roughness parameters (Sa, Str, Spk) described above are numerical values ​​calculated in accordance with ISO 25178, and are calculated from data measured using, for example, a non-contact surface roughness measuring instrument (for example, a laser microscope).

[0047] As described above, in the retainer of the first embodiment, by combining and defining the arithmetic mean height Sa of the roughness of the pocket surface, Str indicating isotropy or anisotropy, and the parameter Spk related to the shape of the contacting protruding ridge portion as a formula, it is possible to maintain a low friction state even under harsh lubrication conditions, as will be shown in the test examples described below.

[0048] [Second embodiment] In a second embodiment of the present invention, the cage 5 (see FIG. 2) has a pocket 6 surface (specifically, a contact surface that comes into contact with the balls) 6a that is a rough surface defined by a plurality of roughness parameters. Note that this rough surface may be formed by transferring from a mold, or may be formed by machining such as shot blasting after molding, for example.

[0049] In the second embodiment, the roughness parameters of the surface 6a are an arithmetic mean roughness Ra of 3.00 μm or more and 10.00 μm or less, an average element length RSm of 0.10 mm or more and 0.40 mm or less, and a kurtosis Rku of 1.0 or more and 5.0 or less.

[0050] The surface 6a for which the above-mentioned roughness parameters are defined will be specifically described with reference to FIG. 3 . The surface 6a is the portion that contacts the ball 4, for example, the portion that is in sliding contact with the ball 4. In this case, for example, when the surface 6a is measured at the portion of the surface 6a that is in sliding contact with the ball 4 so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling element, the roughness parameters calculated from the roughness curve based on JIS B 0601 will satisfy the above-mentioned range. More specifically, when the surface 6a is measured at any point within a ±30° range (region R in FIG. 3 ) of the measurement range, with one point on the surface 6a where the ball 4 and the surface 6a can come into contact during bearing rotation (the revolution direction (X direction) of the ball 4 in FIG. 3 ) and a point 180° away from that point as the center point (0°), the roughness parameters calculated from the roughness curve based on JIS B 0601 preferably satisfy the above-mentioned range. For example, it is preferable that the roughness parameters be satisfied for all values ​​of the surface 6a or their average values.

[0051] Although Figure 3 illustrates the surface 6a of one pocket, it is sufficient that the surface 6a of at least one pocket in the cage has the above-mentioned roughness parameters. For example, the 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 have the above-mentioned roughness parameters, or the surfaces of all pockets in the cage may have the above-mentioned roughness parameters.

[0052] Each roughness parameter will be explained below.

[0053] [Arithmetic mean roughness Ra] When a roughness curve is represented by Z(x), the arithmetic mean roughness Ra is the average value of the absolute values ​​of Z(x) over a reference length. Because Ra is an average value, it is less susceptible to the influence of local scratches on the surface or adhering dirt, and is therefore commonly used as an index of surface roughness.

[0054] As shown in Figure 4, compared to a case where the surface Ra is small (e.g., Ra 1.00 μm or less), by increasing the surface Ra (e.g., Ra 3.00 μm or more), the lubricant is retained in the recesses and a sufficient oil film is more likely to be formed. The arithmetic mean roughness Ra is 3.00 μm or more and 10.00 μm or less, preferably 4.00 μm or more, and more preferably 5.00 μm or more. On the other hand, if the Ra is large, it may affect the rotation accuracy, for example, during high-speed rotation, so Ra is preferably 8.00 μm or less, and may be less than 6.00 μm.

[0055] Here, the arithmetic mean roughness Ra is a parameter in the height direction of the roughness curved surface. Other parameters such as the maximum peak height Rp, the maximum valley depth Rv, and the maximum height Rt are also parameters in the height direction. These parameters in the height direction cannot determine the period of peaks and valleys, which is considered important for retaining lubricant. In order to retain lubricant on the contact surface, it is preferable for there to be many peaks and valleys on the contact surface. In this regard, in the second embodiment, the average length RSm of the elements is defined as a parameter related to the lateral direction.

[0056] [Average element length RSm] The average element length RSm represents the average value of the element length in the reference length. As shown in Figure 5, the element length is the length of one set of peaks and valleys. Compared to when the surface RSm is large (e.g., RSm 0.50 mm or more), by reducing the surface RSm (e.g., RSm 0.40 mm or less), the roughness period becomes shorter, and as a result, the contact area with the mating surface can be reduced.

[0057] The average length RSm of the elements is 0.10 mm or more and 0.40 mm or less, preferably 0.30 mm or less, and may be 0.20 mm or less.

[0058] Furthermore, in the second embodiment, from the viewpoint of contact with the mating surface, the shape of the contacting convex portion (mountain portion) is considered to be important, and kurtosis Rku is defined as a parameter thereof.

[0059] [Kurtosis Rku] Kurtosis Rku is a value indicating the degree of sharpness of the probability density function of the roughness curve. As shown in FIG. 6, when the kurtosis Rku value is 3, the probability density function is a normal distribution. When the kurtosis Rku is greater than 3, the probability density function is sharp, and the roughness curve has sharp peaks and valleys. When the kurtosis Rku is less than 3, the probability density function is flat, and the peaks and valleys of the roughness curve are flattened. Here, if the kurtosis Rku is too small, the peaks that come into contact with the mating surface are flat, resulting in a contact surface where lubricant is less likely to be present, and the friction coefficient and temperature are more likely to increase. Conversely, if the kurtosis Rku is too large, the contact area with the mating surface becomes too small, which may cause early wear and flattening due to stress concentration.

[0060] The kurtosis Rku is 1.0 or more and 5.0 or less, and the closer the kurtosis Rku is to 3, the better the balance is, and the more easily the lubricant will be interposed between the surfaces. Preferably, the kurtosis Rku is more than 3.0 and 5.0 or less. This increases the sharpness of the peaks, thereby making it possible to further reduce the contact area with the mating surface.

[0061] Furthermore, other roughness parameters may be set for the roughness of the pocket surface. For example, skewness Rsk may be adopted from the viewpoint of controlling the shape of the contacting convex portion (ridge portion).

[0062] [Skewness Rsk] Skewness Rsk is a value that indicates the degree of asymmetry of the probability density function of the roughness curve. As shown in FIG. 7, when the skewness Rsk value is 0, the height distribution is symmetrical vertically. As the skewness Rsk is smaller than 0, the roughness curve is biased upward relative to the mean line, resulting in a shape with many valleys. Note that a shape with many valleys tends to have a higher proportion of flat portions that come into contact with the mating surface, making it difficult for lubricant to be interposed in the flat portions. Therefore, skewness Rsk is preferably -1.0 or greater. In this case, increases in the friction coefficient and temperature are more easily suppressed. A more preferable range for skewness Rsk is -1.0 or greater and 1.0 or less, and may be -1.0 or greater and less than 0.

[0063] The above-mentioned various roughness parameters (Ra, RSm, Rku, Rsk) are values ​​calculated in accordance with JIS B 0601, and are calculated from data measured, for example, by a contact surface roughness measuring instrument. Specific measurement conditions for Ra are a measurement length of 12.5 mm and a cutoff of 2.5 mm.

[0064] As described above, in the cage of the second embodiment, the roughness of the pocket surface is specified by combining the arithmetic mean roughness Ra, a parameter related to the lateral direction (RSm), and a parameter related to the shape of the contacting ridge portion (Rku), making it possible to maintain a low friction state even under severe lubrication conditions, as will be shown in the test examples described below.

[0065] In the pocket surfaces of the first and second embodiments, the contact surfaces with which the rolling elements come into contact (see, for example, FIG. 3) may have the above-described roughness, or the entire surfaces may have the above-described roughness. In addition to the pocket surfaces, the guide surfaces that come into contact with the races may also have the above-described roughness.

[0066] Furthermore, the elements relating to the three-dimensional surface roughness parameters of the first embodiment and the elements relating to the roughness parameters of the second embodiment may be appropriately combined. For example, in the cage, the value A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa of the pocket surface, the aspect ratio Str of the surface texture, and the protruding peak height Spk may be 1.20 or more, the arithmetic mean roughness Ra may be 3.00 μm or more and 10.00 μm or less, the mean element length RSm may be 0.10 mm or more and 0.40 mm or less, and the kurtosis Rku may be 1.0 or more and 5.0 or less. Furthermore, preferred configurations may be appropriately combined.

[0067] In the present invention, the cage may be made of a resin, and the resin material is preferably one that can be injection molded and has sufficient heat resistance and mechanical strength for use as a cage material. For example, a resin composition can be used that uses a PA resin such as polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin, thermoplastic polyimide resin, polyamide-imide resin, PA66 resin, PA46 resin, PA6T resin, or PA9T resin as a resin matrix, and is blended with reinforcing fibers such as carbon fiber and glass fiber, and other additives.

[0068] Returning to FIG. 1 , in the angular contact ball bearing 1, both the inner ring 2 and the 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 the ball 4. The surface roughness of the ball 4 is, for example, Ra of 0.1 μm or less.

[0069] 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.

[0070] 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 is less than 10 mm ２ / s or more 30mm ２ / s or less is preferred.

[0071] In FIG. 1, an angular contact ball bearing has been described 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.

[0072] As another example of a cage for a rolling bearing according to the present invention, a crown-type cage will be described with reference to FIG. 8 . FIG. 8 is a partially enlarged perspective view of the crown-type cage. As shown in FIG. 8 , the cage 8 has a pair of opposing retaining claws 9 formed at a constant circumferential pitch on the upper surface of an annular cage body. The opposing retaining claws 9 are curved toward each other, and pockets 10 for holding balls as rolling elements are formed between the retaining claws 9. Furthermore, a flat portion 11 serving as a rising reference surface for the retaining claws 9 is formed between the back surfaces of adjacent retaining claws 9 in adjacent pockets 10. In the crown-type cage 8 according to the first embodiment, the value A = (Sa / 10) + Str + (Spk / 10) calculated from the three-dimensional surface roughness parameters of the surface 10a of the pocket 10 is 1.20 or greater. In the second embodiment, the surface roughness of the pocket 10a of the pocket 10 satisfies the above-described plurality of roughness parameters. The description using FIG. 3 can also be applied to this cage 8.

[0073] 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 can be used for a rolling bearing having a dm·n value of 80×10 ４ ~300 x 10 ４ It is used in the rotation range.

[0074] One aspect of the present invention is based on the fact that "(Sa / 10) + Str + (Spk / 10)," which is calculated from the arithmetic mean height Sa of the surface of a pocket of a rolling bearing cage, the aspect ratio Str of the surface texture, and the peak height Spk, shows a high correlation with the coefficient of friction. Therefore, by using this as an index, the friction characteristics of the pocket surface of a rolling bearing cage can be evaluated. Here, "evaluating the friction characteristics" means determining the degree of friction (e.g., the coefficient of friction) when sliding against a rolling element.

[0075] Specifically, the evaluation method is a method for evaluating the friction characteristics with rolling elements in a resin rolling bearing cage having multiple pockets formed therein for holding the rolling elements, and is characterized in that the friction characteristics on the surface of the pocket are evaluated based on the value A = (Sa / 10) + Str + (Spk / 10) calculated from the arithmetic mean height Sa on the surface of the pocket, the aspect ratio Str of the surface texture, and the protruding peak height Spk.

[0076] The value A exhibits a high correlation with the coefficient of friction, as shown in a test example (see FIG. 10 ) described later. Specifically, the larger the value A, the smaller the coefficient of friction tends to be. Therefore, in the evaluation method described above, 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.

[0077] 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.

[0078] Examples of the present invention will be described below. Using a Savin abrasion tester shown in Figure 9, the coefficients of friction of test pieces with different surface roughnesses were evaluated.

[0079] [Test Examples A1 to A8] (1) Preparation of Test Specimens Test specimens were prepared by cutting an injection-molded molded body (composition: glass fiber reinforced polyamide 66) into a size of 10 mm x 15 mm and a thickness of 4 mm. The sliding surfaces of the test specimens were roughened by shot blasting and filing to obtain test specimens for Test Examples A1 to A6, respectively. Note that the test specimens for Test Examples A7 to A8 were not roughened, and the sliding surfaces were left as injection-molded surfaces.

[0080] (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 following measurement conditions: Measurement range: 870 μm × 870 μm Lens magnification: 50x

[0081] The measurement results are shown in the following Table 1. The surface roughness of test samples A7 and A8 is equivalent to the roughness of a cage obtained by general injection molding.

[0082] When measuring the roughness of the cage, for example, at least four pockets out of all pockets (e.g., pockets located at 0, 90, 180, and 270 degrees in the circumferential direction of the cage) are targeted, and in one pocket, one point where the abutment surface of the rolling element and 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 measurements are taken at any point within a range of ±30°. The same applies to Test Example B, which will be described later.

[0083]

[0084] (3) Savin Abrasion Test A Savin abrasion tester 21 shown in Figure 9 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 of insufficient lubricant supply during high-speed rotation of a bearing. 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> Mating member: SUJ2 cylinder, Φ40 mm x 10 mm, arithmetic mean roughness Ra 0.01 μm Grease: base oil (ester oil; kinematic viscosity at 40°C 22 mm ２ / s, thickener (urea-based) Relative speed: 4.2 m / s Load: 15 N (surface pressure 60 MPa)

[0085] The friction coefficients obtained by the Savin abrasion test for each test example are shown in Figure 10. Figure 10 is a graph plotting the relationship between the value A and the friction coefficient for each test example. As shown in Figure 10, 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. On the other hand, a correlation as strong as that between each three-dimensional surface roughness parameter (Sa, Str, Spk) and the friction coefficient was not observed.

[0086] As shown in Figure 10, Test Examples A1 to A6 had lower coefficients of friction than Test Examples A7 and A8, which had injection-molded surfaces. Specifically, the coefficients of friction for Test Examples A1 to A6 were less than 0.20, while the coefficients of friction for Test Examples A7 to A8 were 0.20 or greater. Furthermore, compared to Test Examples A5 to A6 (file-processed), Test Examples A1 to A4 (shot-blasted) had coefficients of friction less than 0.15, demonstrating lower friction. Test Examples A5 to A6 had aspect ratios less than 0.3, while Test Examples A1 to A4 had aspect ratios of 0.80 or greater, demonstrating high isotropy. This difference is thought to have influenced the low friction.

[0087] In this way, when the value A defined by the surface roughness defined 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.

[0088] [Test Examples B1 to B3] (1) Preparation of Test Specimens Test specimens were prepared by cutting an injection-molded body (composition: glass fiber reinforced polyamide 66) into a size of 10 mm x 15 mm and a thickness of 4 mm. The sliding surfaces of the test specimens were roughened by filing to obtain test specimens for Test Examples B1 to B2 and Test Example B3, respectively.

[0089] (2) Measurement of Roughness Parameters The roughness parameters (Ra, RSm, Rku, Rsk) of the sliding surfaces of each test piece obtained above were measured using a stylus surface roughness tester. Each roughness parameter was calculated in accordance with JIS B 0601 and measured using a contact or non-contact surface roughness meter. Specific measurement conditions were a cutoff value λc = 0.8 mm or λc = 2.5 mm, and the average value of five intervals was taken as the measurement value, with a reference length equal to the cutoff value as one interval. The cutoff value varies depending on the surface roughness and is a value determined in accordance with JIS B 0601. The measurement results are shown in Table 1 below. The surface roughness of Test Sample B3 is equivalent to the roughness of a cage obtained by general injection molding.

[0090]

[0091] (3) Savin Abrasion Test Using a Savin abrasion tester 21 shown in FIG. 9, tests were carried out under the same test conditions as those of the above-mentioned Test Examples A1 to A8.

[0092] The change in the coefficient of friction over time in the Savin wear test is shown in Figure 11. As shown in Figure 11, compared to Test Example B3, Test Examples B1 and B2 had lower coefficients of friction during the test, and the variation in the coefficients of friction was also smaller. Specifically, the coefficients of friction for Test Examples B1 and B2 remained below 0.3 until 20 hours had elapsed from the start of the test. As such, when the contact surface has the surface roughness specified in one embodiment of the present invention, it is possible to reduce the coefficient of friction during sliding.

[0093] Furthermore, compared to Test Example B1, Test Example B2 had a smaller friction coefficient, and the friction coefficient of Test Example B2 was less than 0.2 until 20 hours had elapsed from the start of the test. For example, Test Example B2 had a larger arithmetic mean roughness Ra than Test Example B1, and this difference is thought to have affected the experimental results. For example, by setting Ra to 5.00 μm or more, lower friction can be expected.

[0094] The cage for a rolling bearing of the present invention defines the surface of the pocket face by, for example, a value A determined from a plurality of three-dimensional surface roughness parameters, so that an oil film can be maintained on the contact surface even with a small amount of lubricant, and a stable low-friction state can be maintained even under severe lubrication conditions, making it particularly suitable for use in the field of rolling bearings that rotate at high speeds.

[0095] REFERENCE SIGNS LIST 1 Angular contact ball bearing (rolling bearing) 2 Inner ring 3 Outer ring 4 Ball (rolling element) 5 Cage 6 Pocket 6a surface 7 Column portion 8 Cage 9 Retaining claw 10 Pocket 10a surface 11 Flat portion 21 Savin type wear tester 22 Load cell 23 Weight 24 Test piece 25 Cylindrical mating member

Claims

1. A plastic rolling bearing retainer, comprising a plurality of pockets formed in the retainer for retaining rolling elements, and wherein the value of A = (Sa / 10) + Str + (Spk / 10), calculated from the arithmetic mean height Sa of the pocket surface, the aspect ratio Str of the surface texture, and the protruding peak height Spk, is 1.20 or greater.

2. A cage for a rolling bearing according to claim 1, characterized in that the aspect ratio Str is 0.80 or more.

3. A cage for a rolling bearing according to claim 2, characterized in that 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. A cage for a rolling bearing as recited in claim 1, characterized in that the arithmetic mean roughness Ra on the surface of the pocket is 3.00 μm or more and 10.00 μm or less, the average length RSm of the elements is 0.10 mm or more and 0.40 mm or less, and the kurtosis Rku is 1.0 or more and 5.0 or less.

5. A cage for a rolling bearing according to claim 4, wherein the skewness Rsk obtained from the roughness curve of the pocket surface is in the range of -1.00 to 1.

00.

6. A cage for a rolling bearing according to claim 1, characterized in that the cage is an injection-molded body of a resin composition.

7. A rolling bearing having an inner ring, an outer ring, a number of rolling elements interposed between the inner and outer rings, a retainer for retaining the rolling elements, and grease sealed in the space within the bearing, wherein the retainer is the rolling bearing retainer described in claim 1.

8. The grease contains a base oil and a urea-based thickener, and the kinetic viscosity of the base oil at 40°C is 10 mm ２ / s or more 30mm ２ 8. The rolling bearing according to claim 7, characterized in that the rolling bearing has a rolling resistance of less than 1 / s.

9. A rolling bearing according to claim 8, which is a bearing used in a spindle device for a main shaft of a machine tool.

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