WO2025028417A1 - Rolling bearing cage and rolling bearing - Google Patents

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

The present invention relates to a retainer for a rolling bearing and a rolling bearing using the retainer.

In rolling bearings, plastic cages are widely used as cages that hold 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 generally used as synthetic resins for plastic cages, and these are reinforced by adding fibrous reinforcing materials such as glass fiber as needed.

In recent years, there has been an increasing demand for rolling bearings used in high-speed environments, such as in electric vehicles and machine tools. Traditionally, air-oil lubrication has been used frequently under high-speed rotation, but the demand for grease lubrication is growing due to the high maintenance costs of the supply equipment. However, with grease lubrication, the grease is easily repelled from the contact surface during high-speed rotation, which can easily lead to insufficient lubrication between the rolling elements and the cage. Insufficient lubrication can lead to excessive heating and wear on the contact surface, shortening the lifespan of the bearing.

Measures to deal with such harsh lubrication conditions include, for example, forming grooves or holes on the inner circumferential 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 aim to retain the lubricant through the shape of the cage.

Patent No. 7088286 JP 2014-095469 A JP 2007-198469 A

A plateau structure surface (a surface formed of a smooth surface and recesses, without any protrusions) with recesses such as grooves or holes as described in Patent Document 1 can retain lubricant in the recesses and is known as a method for improving sliding characteristics. However, when the contact conditions become more severe, such as when two surfaces come into contact with each other, such as in boundary lubrication, the smooth surface of the plateau structure surface comes into contact with the mating surface, and even if lubricant is present in the recesses, it is removed from the smooth surface, making it more likely to cause an increase in the coefficient of friction and heat generation. For this reason, it is desirable for the area of contact with the rolling element to be as small as possible.

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 come into contact 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 to a small area.

The present invention was made in consideration of these circumstances, and aims to provide a retainer for rolling bearings that can maintain a stable low-friction state even under harsh lubrication conditions by defining the surface roughness of the retainer using multiple roughness parameters, allowing an oil film to be maintained on the contact surface even with a small amount of lubricant, and a rolling bearing that uses said retainer.

The inventors conducted extensive research focusing on the three-dimensional surface roughness parameters of the pocket surfaces of a rolling bearing retainer as one form of retainer for rolling bearings, and discovered that "(Sa/10) + Str + (Spk/10)" calculated from the arithmetic mean height Sa of the surface, the aspect ratio Str of the surface properties, and the protruding peak height Spk shows a high correlation with the coefficient of friction, and furthermore, that by specifying this value A, it is possible to manage a low-friction state. The present invention is based on such findings.

The roller bearing retainer of the present invention is a resin roller bearing retainer, in which a number of pockets are formed to hold the rolling elements, 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.

In one embodiment, the above-mentioned cage is characterized in that when the contact surface of any one or more (e.g. all) pockets in the contact surface that comes into sliding contact with the rolling element is measured so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling element, the surface roughness parameters calculated from ISO25178 have a value of A = (Sa/10) + Str + (Spk/10) calculated from the arithmetic mean height Sa, the aspect ratio Str of the surface characteristics, and the protruding peak height Spk, of 1.20 or more for all the measured contact surface values or their average values.

Specifically, on the contact surface of any one or multiple (e.g. all) pockets, a point where the rolling element and cage 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 value of A = (Sa/10) + Str + (Spk/10), calculated from the arithmetic mean height Sa calculated from ISO25178, the aspect ratio Str of the surface texture, and the protruding peak height Spk, for all the measured values of the contact surfaces or their average value, is characterized by being 1.20 or more.

The aspect ratio Str is 0.80 or more. Furthermore, 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.

The roller bearing retainer of the present invention is a resin roller bearing retainer, and is characterized in that a plurality of pockets for retaining rolling elements are formed in the retainer, and the arithmetic mean roughness Ra of the pocket surfaces 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.

In one embodiment, the above-mentioned cage is characterized in that, when the contact surfaces of any one or more (for example, all) pockets in the contact surface that comes into sliding contact with the rolling element are measured so that the measurement direction of the roughness curve is perpendicular to the rotation direction of the rolling element, roughness parameters calculated from the roughness curve based on JIS B 0601 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 for all measured values of the contact surfaces.
Specifically, on the contact surfaces of any one or more (for example, all) pockets, a 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 any location within a range of ±30° (measurement target area) is measured.The roughness parameters obtained 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 average 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.

The skewness Rsk calculated from the roughness curve on the surface of the pocket is between -1.00 and 1.00.

Characterized by a kurtosis Rku greater than 3.0 and less than 5.0.

The retainer is an injection molded body of a resin composition.

The rolling bearing of the present invention is a rolling bearing having an inner ring, 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, characterized in that the retainer is the rolling bearing retainer of the present invention.

The grease contains a base oil and a urea-based thickener, and is characterized in that the kinematic viscosity of the base oil at 40° C. is 10 mm ² /s or more and less than 30 mm ² /s.

The cage for rolling bearings of the present invention has a rough surface on the surface of the pocket, and the rough surface is defined by a value A calculated from a plurality of three-dimensional surface roughness parameters obtained 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 protruding peak height Spk, to 1.20 or more, 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.

The cage for rolling bearings of the present invention has a rough surface on the surface of the pocket that comes into contact with the rolling elements, and the rough surface is defined by a plurality of roughness parameters obtained from a roughness curve. Specifically, by setting the arithmetic mean roughness Ra to 3.00 μm or more and 10.00 μm or less, it becomes easier to retain the lubricant, and an oil film can be maintained on the contact surface even when the amount of lubricant supplied is small. Furthermore, by setting the average length RSm of the elements to 0.10 mm or more and 0.40 mm or less, and the kurtosis Rku to 1.0 or more and 5.0 or less, 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.

Furthermore, since the skewness Rsk is between -1.00 and 1.00, it is possible to suppress the bias in the height distribution and to easily maintain a small contact area with the mating surface, which further contributes to suppressing the friction coefficient and temperature rise.

In addition, since the kurtosis Rku is greater than 3.0 and less than or equal to 5.0, the number of flat areas in the peaks and valleys of the roughness curve is reduced, making it possible to reduce the contact area with the opposing surface.

The rolling bearing of the present invention is equipped with the retainer of the present invention, so the bearing can achieve a longer life even under more severe lubrication conditions.

1 is an axial cross-sectional view showing an example of a rolling bearing of the present invention. 1 is a perspective view showing an example of a cage for a rolling bearing of the present invention. FIG. 2 is a diagram for explaining an example of measurement points of roughness parameters of the cage for a rolling bearing of the present invention. FIG. 2 is a diagram for explaining the arithmetic mean roughness Ra. FIG. 13 is a diagram for explaining the average length RSm of an element. FIG. 13 is a diagram for explaining kurtosis Rku. FIG. 11 is a diagram for explaining skewness Rsk. FIG. 4 is a partially enlarged perspective view showing another example of the cage for a rolling bearing of the present invention. FIG. 1 is a diagram showing an outline of a Savin type friction and wear tester. 1 is a graph showing the friction coefficients of Test Examples A1 to A8. 1 is a graph showing the change in friction coefficient in Test Examples B1 to B3.

The rolling bearing retainer and 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 a rolling bearing of the present invention, and Figure 2 is a perspective view of a retainer (machined type) for the rolling bearing of Figure 1.

As shown in FIG. 1, an angular ball bearing 1 comprises an inner ring 2, an outer ring 3, a number 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 specified angle θ (contact angle) relative to the radial centerline, and can bear radial loads and unidirectional axial loads. In addition, the 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.

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

As shown in FIG. 2, the cage 5 is a machined resin cage, with multiple pockets 6 for holding balls provided at regular intervals in the circumferential direction on the annular cage body. Pillar portions 7 are formed between adjacent pockets 6 in the circumferential direction.

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 having a slide core, or may be formed by cutting after molding the base material.

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

The rough surface may be formed, for example, by transferring from a mold, or may be formed after molding by mechanical processing such as shot blasting or filing. For example, shot blasting is preferred because it is easy to create a processed surface that exhibits isotropy.

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.

The surface 6a for which the above value A is defined will be specifically described with reference to FIG. 3. The surface 6a is a portion that comes into contact with the ball 4, for example, a portion that comes into sliding contact with the ball 4. In this case, for example, when the surface 6a is measured so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling element at the portion of the surface 6a that comes into sliding contact with the ball 4, the value A obtained using the surface roughness parameters obtained from ISO25178 satisfies the above range. More specifically, on the surface 6a, when one point where the ball 4 and the surface 6a can come into contact during the bearing rotation (the revolution direction (X direction) of the ball 4 in FIG. 3) and a point 180° away from the one point are set as the center point (0°) of the measurement range, and any point in the range of ±30° (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 obtained using the surface roughness parameters obtained from ISO25178 satisfies the above range. For example, it is preferable that the value A calculated using the values of all surfaces 6a or the average value thereof falls within the above range.

Note that while FIG. 3 describes the surface 6a of one pocket, it is sufficient that the value A obtained from the surface 6a of at least one pocket in the retainer 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 retainer) may satisfy the above range, or the value A obtained from the surfaces of all pockets in the retainer may satisfy the above range.

The following describes each roughness parameter related to value A.

[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 attached thereto, and is therefore generally used as an index of surface roughness. Since it evaluates the surface, it has less variation depending on the measurement position compared to Ra, and is therefore preferable for evaluating the surface.

Compared to when the arithmetic mean height Sa of the surface is small (e.g., Sa 1.00 μm or less), by increasing the arithmetic mean height Sa of the surface (e.g., Sa 2.00 μm or more), the lubricant is 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 the 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.

[Surface texture aspect ratio Str]
The aspect ratio Str of the surface texture is the ratio of the distance in the direction in which the autocorrelation of the surface decays to a specific value the fastest to the distance in the direction in which it decays the slowest, and is a parameter that represents the isotropy or anisotropy of the surface texture. The aspect ratio Str of the 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 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.

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

[Protruding peak height Spk]
The protruding peak height Spk is obtained from the load curve of the surface, and is the average height of the protruding peaks that are higher than the core. More specifically, for the surface to be measured, the ratio of the load area (area of the area with height c or more) at a certain height c is defined as the load area ratio Smr(c), a curve (load curve) showing the height at which the load area ratio becomes 0% to 100% is graphed, a secant line is drawn along the load curve connecting two points where the difference between the load area ratios 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 is the smallest is defined as the equivalent straight line, and the surface obtained by removing the area not included in the height range of the load area ratio of 0% to 100% of the equivalent straight line is defined as the core, and the part protruding above this core is defined as the protruding peak, and its average height is determined. If the protruding peak height Spk is small, the protruding peak will wear away at an early stage, causing the contact surface to become flattened, increasing the contact area, and making it difficult for the lubricant to flow to the contact surface.

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 such a range, the contact area is reduced, resulting in a surface into which the lubricant can easily flow. Furthermore, the protruding peak height Spk is, for example, 15.00 μm or less, and may be 10.00 μm or less.

In general, surface properties are often evaluated using a single roughness parameter. However, it is preferable to evaluate using multiple parameters, and in the first embodiment, the above-mentioned roughness parameters are particularly combined into a formula to evaluate a surface that can maintain a low friction state even under harsh 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 properties, and the protruding peak height Spk is 1.20 or greater, the surface will have low friction even under harsh lubrication conditions where only a small amount of lubricant is present.

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.

The various roughness parameters (Sa, Str, Spk) mentioned above are numerical values calculated in accordance with ISO 25178, and are calculated from data measured, for example, by a non-contact surface roughness measuring device (e.g., a laser microscope).

As described above, in the cage of the first embodiment, 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 are combined and defined as a formula, so that a low friction state can be maintained even under harsh lubrication conditions, as shown in the test example described below.

[Second embodiment]
In the 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, for example, or may be formed by machining such as shot blasting after molding.

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

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 a portion that comes into contact with the ball 4, for example, a portion that comes into sliding contact with the ball 4. In this case, for example, when the surface 6a is measured so that the measurement direction of the roughness curve is perpendicular to the direction of rotation of the rolling element at the portion of the surface 6a that comes into sliding contact with the ball 4, the roughness parameters obtained from the roughness curve based on JIS B 0601 satisfy the above-mentioned range. More specifically, when the surface 6a is measured at any point within a range of ±30° (region R in FIG. 3) with one point at which 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 the one point as the center point (0°) of the measurement range, it is preferable that the roughness parameters obtained from the roughness curve based on JIS B 0601 satisfy the above-mentioned range. For example, it is preferable that the values of all the surfaces 6a or their average values satisfy the above-mentioned roughness parameters.

Note that in FIG. 3, the surface 6a of one pocket is described, but 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.

The roughness parameters are explained below.

[Arithmetic mean roughness Ra]
The arithmetic mean roughness Ra is the average of the absolute values of Z(x) over a reference length when the roughness curve is represented by Z(x). Because Ra is an average value, it is not easily affected by local scratches on the surface or dirt adhering thereto, and is therefore commonly used as an index of surface roughness.

As shown in Figure 4, 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 than when the surface Ra is small (e.g., Ra 1.00 μm or less). 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.

Here, the arithmetic mean roughness Ra is a parameter in the height direction of the roughness curved surface. Other parameters such as maximum peak height Rp, maximum valley depth Rv, and 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 of the elements RSm is defined as a parameter related to the horizontal direction.

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

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.

Furthermore, in the second embodiment, the shape of the contacting convex portion (ridge portion) is considered important from the viewpoint of contact with the opposing surface, and kurtosis Rku is defined as the parameter.

[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 value of kurtosis Rku 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 tips of peaks and valleys. When the kurtosis Rku is less than 3, the probability density function is flat, and the tips of peaks and valleys are flattened, and the roughness curve has flat tips. Here, when the kurtosis Rku is too small, the tips of the peaks that contact the mating surface are flat, resulting in a contact surface that is difficult for lubricant to intervene, and the friction coefficient and temperature are likely to increase. On the other hand, when the kurtosis Rku is too large, the area of contact with the mating surface becomes too small, and there is a risk of early wear and flattening due to stress concentration.

Kurtosis Rku is between 1.0 and 5.0, and the closer to 3 the kurtosis Rku is, the better the balance is, and the easier it is for the lubricant to penetrate the surface. Preferably, kurtosis Rku is between 3.0 and 5.0. This increases the sharpness of the peaks, making it possible to reduce the contact area with the opposing surface.

Furthermore, other roughness parameters may be set regarding 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).

[Skewness Rsk]
The skewness Rsk is a value indicating the degree of asymmetry of the probability density function of the roughness curve. As shown in FIG. 7, when the value of the skewness Rsk is 0, the height distribution is symmetrical up and down. The smaller the skewness Rsk is than 0, the more the roughness curve is biased upward with respect to the average line, resulting in a shape with many valleys. In addition, in a shape with many valleys, the proportion of flat parts that come into contact with the counter surface tends to increase, and as a result, it becomes difficult for the lubricant to be interposed in the flat parts. Therefore, the skewness Rsk is preferably -1.0 or more. In this case, it is easier to suppress the increase in the friction coefficient and temperature. As a more preferable range, the skewness Rsk is -1.0 or more and 1.0 or less, and may be -1.0 or more and less than 0.

The above-mentioned 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.

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 ridges (Rku), making it possible to maintain a low friction state even under severe lubrication conditions, as shown in the test example described below.

In the pocket surfaces of the first and second embodiments, the contact surface with which the rolling elements come into contact (see, for example, FIG. 3) may have the above-mentioned roughness, or the entire surface may have the above-mentioned roughness. In addition to the pocket surface, the guide surface that comes into contact with the raceway may have the above-mentioned roughness.

Furthermore, the elements related to the three-dimensional surface roughness parameters of the first embodiment and the elements related 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, and the arithmetic mean roughness Ra may be 3.00 μm or more and 10.00 μm or less, the average length RSm of the elements 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.

In the present invention, the material of the retainer may be resin, and it is preferable that the resin material be injection moldable and have sufficient heat resistance and mechanical strength as a retainer material. 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 base material, and reinforcing fibers such as carbon fiber or glass fiber and other additives are blended.

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 steel materials or ceramic materials can be used for the balls 4. The surface roughness of the balls 4 is, for example, Ra of 0.1 μm or less.

The rolling bearing of the present invention is lubricated with grease. The grease is sealed in the space inside the bearing and lubricates the raceway surfaces and the contact surfaces between the balls and the cage. The base oil that constitutes the grease can be any oil that is normally used in rolling bearings, such as mineral oil or synthetic oil, without any particular restrictions. The thickener that constitutes the grease can also be any oil that is normally used in rolling bearings, such as metal soap or urea compound, without any particular restrictions.

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 preferable in terms of the roughness of the cage, for example, 10 ^mm2 /s or more and less than 50 ^mm2 /s, and preferably 10 ^mm2 /s or more and less than 30 ^mm2 /s.

In Figure 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, spherical roller bearings, needle roller bearings, etc.

As another example of the cage for rolling bearings of 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 pitch in the circumferential direction on the upper surface of the annular cage body, and the opposing retaining claws 9 are curved in a direction approaching each other, and a pocket 10 for holding balls as rolling elements is formed between the retaining claws 9. In addition, a flat portion 11 that serves as a rising reference surface for the retaining claws 9 is formed between the back faces of the retaining claws 9 adjacent to each other in the adjacent pockets 10. In 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 in the crown-type cage 8 is 1.20 or more. In the second embodiment, the surface roughness of the 10a of the pocket 10 has the above-mentioned multiple roughness parameters, and the contents described using FIG. 3 can also be applied to this cage 8.

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. As a bearing for high speed rotation, it is used in a rotation range where the dm·n value is, for example, 80×10 ⁴ to 300×10 ⁴ .

One aspect of the present invention is based on the fact that "(Sa/10) + Str + (Spk/10)", calculated from the arithmetic mean height Sa of the surface of the pocket of the cage for rolling bearings, the aspect ratio Str of the surface texture, and the protruding peak height Spk, shows a high correlation with the coefficient of friction. Therefore, by using this as an index, it is possible to evaluate the friction characteristics of the surface of the pocket of the cage for rolling bearings. Here, "evaluating the friction characteristics" means judging the degree of friction (for example, the coefficient of friction) when sliding against the rolling element.

Specifically, the evaluation method is a method for evaluating the frictional characteristics between rolling elements and a resin rolling bearing cage having multiple pockets formed therein for holding the rolling elements, and is characterized in that the frictional 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 quality, and the protruding peak height Spk.

The value A shows a high correlation with the coefficient of friction, as shown in the test example described later (see Figure 10). 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.

In addition, by comparing the magnitude of the value A obtained from multiple cages, it is possible to select the cage with the lowest friction.

The following describes examples of the present invention. The friction coefficients of test pieces with different surface roughnesses were evaluated using a Saban abrasion tester as shown in Figure 9.

[Test Examples A1 to A8]
(1) Preparation of test specimens Test specimens were prepared by cutting out 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 shot blasting and filing to obtain test specimens for Test Examples A1 to A6. Note that the test specimens for Test Examples A7 to A8 were not roughened, and the sliding surfaces were left as injection-molded surfaces.

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

The measurement results are shown in Table 1 below. Note that the surface roughness of test examples A7 and A8 is equivalent to the roughness of retainers obtained by general injection molding.

When measuring the roughness of the cage, for example, at least four pockets out of all pockets (e.g. pockets located at 0 degrees, 90 degrees, 180 degrees, and 270 degrees in the cage circumferential direction) are targeted, and in one pocket, one point where the abutting surface of the rolling element and cage pocket can come into contact when the bearing rotates, 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. The same applies to test example B described below.

(3) Savant wear test A Savant wear tester 21 shown in FIG. 9 was used. A cylindrical mating member 25 was attached to the rotating shaft, and a test piece 24 was fixed. A small amount of grease (0.02 g) was applied to the contact portion between the test piece 24 and the cylindrical mating member 25, and no grease was supplied thereafter to simulate a state of insufficient supply of lubricant during high-speed rotation of the 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 drawing by a weight 23. The frictional 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 Ra 0.01μm
Grease: Base oil (ester oil; kinematic viscosity at 40°C: 22 ^mm2 /s, thickener (urea-based)
Relative speed: 4.2 m/s
Load: 15N (surface pressure 60MPa)

The friction coefficient for each test example, measured by the Savin abrasion test, is shown in Figure 10. Figure 10 is a graph plotting the relationship between value A and the friction coefficient for each test example. As shown in Figure 10, a high correlation was observed between 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, no correlation as strong as that with value A was observed between each three-dimensional surface roughness parameter (Sa, Str, Spk) and the friction coefficient.

As shown in Figure 10, test examples A1 to A6 had a lower coefficient of friction compared to test examples A7 and A8, which have injection molded surfaces. Specifically, the coefficient of friction for test examples A1 to A6 was less than 0.20, while the coefficient of friction for test examples A7 to A8 was 0.20 or more. Furthermore, compared to test examples A5 to A6 (file processing), the coefficient of friction for test examples A1 to A4 (shot blast processing) was less than 0.15, indicating lower friction. Test examples A5 to A6 had an aspect ratio Str of less than 0.3, while test examples A1 to A4 had an aspect ratio Str of 0.80 or more, indicating high isotropy, and it is believed that this difference affected the low friction.

In this way, when the value A defined by the surface roughness defined in this invention for the surface that slides against another member is large, it is possible to reduce the coefficient of friction during sliding.

[Test Examples B1 to B3]
(1) Preparation of test specimens Test specimens were prepared by cutting out 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 file processing to obtain test specimens for Test Examples B1 to B2 and Test Example B3.

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

(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.

The change in friction coefficient 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 friction coefficients during the test, and the variation in friction coefficient was also smaller. Specifically, the friction coefficients of test examples B1 and B2 remained below 0.3 until 20 hours had passed from the start of the test. In this way, when the contact surface has the surface roughness defined in one embodiment of the present invention, it is possible to reduce the friction coefficient during sliding.

Furthermore, compared to Test Example B1, Test Example B2 had a smaller friction coefficient value, and the friction coefficient of Test Example B2 was less than 0.2 until 20 hours had passed 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 influenced the experimental results. For example, by setting Ra to 5.00 μm or more, it is expected that friction will be reduced even further.

The rolling bearing retainer of the present invention allows an oil film to be maintained on the contact surface even with a small amount of lubricant by defining the surface of the pocket face with a value A determined, for example, from multiple three-dimensional surface roughness parameters, and is able to maintain a stable low-friction state even under harsh lubrication conditions, making it particularly suitable for use in the field of rolling bearings that rotate at high speeds.

1. Angular ball bearing (rolling bearing)
2 Inner ring 3 Outer ring 4 Ball (rolling element)
Reference Signs List 5: retainer 6: pocket 6a surface 7: column portion 8: retainer 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 (9)

A resin-made rolling bearing retainer,
a retainer for a rolling bearing, characterized in that a plurality of pockets for retaining rolling elements are formed in the retainer, and a value of A=(Sa/10)+Str+(Spk/10) calculated from an arithmetic mean height Sa of the pocket surface, an aspect ratio Str of the surface texture, and a protruding ridge height Spk is 1.20 or more. The rolling bearing retainer according to claim 1, characterized in that the aspect ratio Str is 0.80 or more. The rolling bearing retainer 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 peak height Spk is 5.0 μm or more. The cage for a rolling bearing according to claim 1, characterized in that the arithmetic mean roughness Ra of the pocket surface 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. The cage for a rolling bearing according to claim 4, characterized in that the skewness Rsk calculated from the roughness curve of the pocket surface is between -1.00 and 1.00. The cage for a rolling bearing according to claim 1, characterized in that the cage is an injection molded body of a resin composition. 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,
2. A rolling bearing, wherein the cage is the cage for a rolling bearing according to claim 1. 8. The rolling bearing according to claim 7, wherein the grease contains a base oil and a urea-based thickener, and the kinetic viscosity of the base oil at 40° C. is equal to or greater than 10 mm ² /s and less than 30 mm ² /s. The rolling bearing according to claim 8, characterized in that the rolling bearing is a bearing used in a spindle device for a machine tool main shaft.

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