JP2008151235A - Rolling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling device which hardly causes damage to a raceway surface and enables a long service life. <P>SOLUTION: Raceway surfaces 1a, 2a of a ball bearing are subjected to superfinishing and two types of shot peening. The shot peening in which substantially spherical ceramic particles having an average particle diameter of 200 μm or smaller are projected is applied to the raceway surfaces 1a, 2a subjected to superfinishing. Subsequently, the shot peening in which substantially spherical rubber particles having an average particle diameter of 1.5 mm or smaller are projected is applied to the raceway surfaces 1a, 2a. The rubber particle is formed of rubber on which an abrasive having an average particle diameter of 3 μm or smaller is dispersed. The surface roughnesses Ra of the raceway surfaces 1a, 2a subjected to these treatment are between 0.01 μm and 0.07 μm. The surface residual stress of the raceway surfaces 1a, 2a is between -1,400 MPa or larger and -900 MPa or smaller. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rolling device such as a rolling bearing, a linear guide device, a ball screw, a linear motion bearing and the like.

Generally, in a rolling device such as a rolling bearing, a rolling motion is performed between an inner member, an outer member, and a rolling element constituting the rolling device, and the inner member, the raceway surface of the outer member, and the rolling member. The rolling surface of the moving body is repeatedly subjected to shear stress under high surface pressure. Therefore, the materials constituting the inner member, the outer member, and the rolling element are required to have properties such as being hard and having a long rolling fatigue life.
Therefore, high carbon chrome bearing steel such as SUJ2 and case-hardened steel such as SCr420, SCM420, and SAE4320H are often used as materials constituting these members. In order to obtain the required properties such as rolling fatigue life, these materials are hardened and tempered if they are bearing steel, and the hardness is set to HRC 58 or more and 64 or less. In case of case-hardened steel, quenching and tempering are performed after carburizing or carbonitriding, and the surface hardness is HRC 58 or more and 64 or less, and the core hardness is HRC 30 or more and 48 or less.

  However, in recent years, there has been a demand for maintenance-free rolling devices and reduction in fuel consumption of automobiles equipped with rolling devices, and the use conditions of the rolling devices have become severe. For this reason, the foreign matter mixed in the lubricant for lubricating the rolling device and the damage and peeling of the raceway surface and the rolling surface due to poor lubrication of the rolling device have become a problem. There is an increasing demand for extending the life of rolling devices.

In response to such demands, Patent Documents 1 to 3 propose methods for extending the life of a rolling device by paying attention to compressive residual stress effective in improving rolling fatigue life.
Patent Document 1 describes a rolling component in which a number of minute depressions that become oil pools are formed on the rolling surface by barrel finishing after shot blasting. And the minimum value of the compressive residual stress in the surface layer part from the surface of this rolling surface to the depth of 100 μm is 90 MPa or more.

Further, in Patent Document 2, by performing shot peening, the maximum compressive residual stress at the outermost surface portion of the raceway surface of the raceway is set to 100 kgf / mm ² or more, and the compressive residual stress at a position 300 μm below the surface is set to 40 kgf. A rolling bearing with a / mm ² or more is described.
Furthermore, Patent Document 3 describes a rolling sliding component in which the maximum compressive residual stress in the surface layer portion is set to 50 to 110 kgf / mm ² and the average wavelength of the surface roughness is set to 25 μm or less by performing shot peening. Has been.
Japanese Patent Application No. 7-43239 Japanese Patent No. 2949794 Japanese Patent No. 3125434

  However, in the rolling component described in Patent Document 1, the barrel finish is performed after shot blasting to finish the rolling surface. Therefore, due to the barrel finishing property of rotating the workpiece in the basket, the rolling component is a cam follower. There is a risk of being limited to a small diameter such as an outer ring. Therefore, for example, it is difficult to apply to a large-diameter rolling bearing having an inner diameter exceeding 80 mm. In addition, there is a problem that the workpieces collide with each other during barrel finishing, resulting in a dent, which is difficult to apply to the ball bearing race.

  Further, in the rolling bearing described in Patent Document 2, the surface roughness of the raceway surface of the raceway ring is not specified, but in shot peening, a shot material having a large particle size (for example, having an average particle size of 0.72 mm) is used. Since steel balls are often used, the surface roughness after shot peening inevitably increases. Therefore, in order to make the surface roughness of the raceway surface at a level that can be used as a rolling bearing, it is necessary to finish the surface by performing polishing after shot peening. However, in particular, a rolling bearing with a large diameter and a large grinding allowance has a problem that a surface layer to which a compressive stress is applied is removed by the allowance, and is difficult to apply.

Furthermore, in the rolling and sliding component described in Patent Document 3, it is assumed that the mating surface to be slid is a relatively rough surface such as an outer ring of a cam follower, so that the so-called compatibility is improved. In addition, the surface roughness is defined in a wide range. For this reason, when the other surface to be slid is a mirror surface like the raceway of a ball bearing, there is a possibility that the other surface may be damaged, making it difficult to apply.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a rolling device that solves the above-described problems of the prior art and is less likely to damage the raceway surface and has a long life.

  In order to solve the above problems, the present invention has the following configuration. That is, the rolling device according to claim 1 of the present invention includes an inner member having a raceway surface on the outer surface, and a raceway surface facing the raceway surface of the inner member, and is disposed outward of the inner member. And a plurality of rolling elements arranged so as to be able to roll between the two raceway surfaces. At least one of the raceway surfaces has a substantially spherical shape with an average particle size of 200 μm or less. After the ceramic particles are projected, the finishing is performed by projecting the rubber particles having an average particle diameter of 1.5 mm or less composed of rubber containing an abrasive having an average particle diameter of 3 μm or less, and the surface roughness Ra is 0.01 μm or more and 0.07 μm or less, and the surface residual stress is −1400 MPa or more and −900 MPa or less. Since the surface residual stress of the raceway surface has a suitable value due to the projection of the ceramic particles, the rolling device has a long life. Further, since the finishing process is performed by the projection of the rubber particles, the raceway surface is finished extremely smoothly. Therefore, there is almost no possibility of damaging the mating surface even when the mating surface to be slid is a mirror surface, such as a ball bearing race. Furthermore, since it is a relatively simple process of projecting fine particles, the shape and size of the inner and outer members to be processed are not limited, and for almost all types of rolling devices. Thus, the present invention can be applied.

  If the average particle size of the ceramic particles exceeds 200 μm, the surface roughness of the raceway surface after projecting the ceramic particles becomes excessive, so that the surface roughness can be sufficiently reduced by the subsequent projection of the rubber particles. Therefore, the raceway surface is not sufficiently finished. Further, when the shape of the ceramic particles is not a spherical shape or a substantially spherical shape which is a smooth curved surface but a shape having corners, the surface roughness of the raceway surface after the ceramic particles are projected may be excessive. Furthermore, if the material of the projection material is soft, such as tin, the projection energy is expended on the deformation of the projection material itself, and the surface residual stress cannot be sufficiently applied to the raceway surface. Must be a good ceramic.

Furthermore, if the average particle size of the abrasive is more than 3 μm, the surface roughness of the raceway surface may not be sufficiently reduced. Furthermore, when the average particle diameter of the rubber particles is more than 1.5 mm, the polishing efficiency may be lowered.
Furthermore, in order not to impair the functions (for example, life and acoustic performance) required for the rolling device (particularly, a ball bearing that requires high accuracy), the surface roughness Ra of the raceway surface after finishing is performed. Needs to be 0.07 μm or less. However, in order to make it less than 0.01 μm, a long-time finishing process is required and it is not efficient. Therefore, the surface roughness Ra of the raceway surface needs to be 0.01 μm or more.

  Further, if the surface residual stress of the raceway surface is −900 MPa or less, that is, if the surface compressive residual stress is 900 MPa or more, the occurrence of cracks on the raceway surface is suppressed, and the rolling device has a long life. However, if the surface residual stress is less than −1400 MPa, that is, if the surface compressive residual stress is more than 1400 MPa, the raceway surface is overpeened, and on the contrary, it becomes a source of cracks and has a short life. There is a fear.

  The rolling device according to claim 2 of the present invention is the rolling device according to claim 1, wherein a portion from the surface of the raceway surface to which the finishing process has been performed to a depth of 20 μm contains residual austenite. The content is 13 mass% or more and 25 mass% or less. Ensuring residual austenite along with compressive residual stress on the raceway is important for extending the life of the rolling device. When the amount of retained austenite is less than 13% by mass, the life of the rolling device may be insufficient. However, since the residual austenite amount and the compressive residual stress are in a trade-off relationship, if the residual austenite amount exceeds 25% by mass, it becomes difficult to set the compressive residual stress to the above-described value.

  The present invention can be applied to various rolling devices. For example, a rolling bearing, a ball screw, a linear guide device, a linear motion bearing, and the like. Further, the inner member in the present invention means an inner ring when the rolling device is a rolling bearing, a screw shaft when the ball screw is also used, a guide rail when the linear guide device is used, and a linear motion bearing. Means each axis. The outer member is the outer ring when the rolling device is a rolling bearing, the nut when it is a ball screw, the slider when it is a linear guide device, and the outer cylinder when it is also a linear bearing. Each means.

  The rolling device of the present invention has a long life with little damage to the raceway surface.

An embodiment of a rolling device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a structure of a ball bearing which is an embodiment of a rolling device according to the present invention.
This ball bearing includes an inner ring 1 (inner member) having a raceway surface 1a on the outer peripheral surface, an outer ring 2 (outer member) having a raceway surface 2a facing the raceway surface 1a of the inner ring 1 on the inner peripheral surface, A plurality of balls (rolling elements) 3 are provided between the raceway surfaces 1 a and 2 a so as to be freely rollable, and a cage 4 that holds the balls 3 between the inner ring 1 and the outer ring 2.

  The material of the inner ring 1, the outer ring 2, and the ball 3 is not particularly limited. For example, SUJ2 made of carbonitriding may be used, or SUJ2 made of quenching or induction hardening. Alternatively, it may be made of SCM420 or SCr420 and subjected to carbonitriding or carburizing. Further, the material of the cage 4 is not particularly limited, and examples thereof include plastic and steel. Further, a lubricant may be enclosed in a space formed between the inner ring 1 and the outer ring 2.

  Both raceway surfaces 1a and 2a of this ball bearing are subjected to super finishing and two types of shot peening. First, shot peening (hereinafter sometimes referred to as the first step) is performed on the raceway surfaces 1a and 2a that have been subjected to the superfinishing process to project substantially spherical ceramic particles having an average particle size of 200 μm or less. A general-purpose shot peening apparatus was used for the shot peening in the first step, the injection pressure was 0.196 to 0.588 MPa, and the injection time was 10 to 20 min. Moreover, the mass of the inner ring | wheel and outer ring | wheel used for 1 process was 1-20 kg, respectively.

  Subsequently, shot peening (hereinafter sometimes referred to as a second step) in which substantially spherical rubber particles having an average particle diameter of 1.5 mm or less are projected in a dry manner is applied to the raceway surfaces 1a and 2a. The rubber particles are made of rubber in which an abrasive having an average particle size of 3 μm or less is dispersed. An impeller-type shot peening apparatus was used for the shot peening in the second step, the injection speed was 30 m / s or more, and the injection time was 10 to 20 minutes. The shot peening apparatus is not limited to the impeller type but may be an air type.

  The surface roughness Ra of the raceway surfaces 1a and 2a subjected to these treatments is 0.01 μm or more and 0.07 μm or less. Moreover, the surface residual stress of the raceway surfaces 1a and 2a is -1400 MPa or more and -900 MPa or less. Furthermore, the part from the surface of the raceway surfaces 1a and 2a to the depth of 20 μm contains retained austenite, and the content thereof is 13% by mass or more and 25% by mass or less.

The ball bearing obtained by assembling the inner ring 1 and the outer ring 2 together with the ball 3 and the cage 4 has a long life because the raceway surfaces 1a and 2a are hardly damaged.
In the present embodiment, the deep groove ball bearing has been described as an example of the rolling device, but the type of the rolling bearing is not limited to the deep groove ball bearing, and the present invention is applicable to various types of rolling bearings. It can be applied to. For example, radial type rolling bearings such as angular contact ball bearings, self-aligning ball bearings, self-aligning roller bearings, needle roller bearings, cylindrical roller bearings, tapered roller bearings, and thrust types such as thrust ball bearings and thrust roller bearings This is a rolling bearing. Furthermore, the present invention can be applied not only to rolling bearings but also to various types of various rolling devices. For example, a ball screw, a linear guide device, a linear motion bearing, or the like.

  The present invention will be described more specifically with reference to the following examples. In the bearing having substantially the same structure as the deep groove ball bearing shown in FIG. 1 described above, the surface residual stress and surface roughness of the raceways of the inner ring and the outer ring can be changed by variously changing the conditions of the shot peening in the first process and the second process. Test bearings with different amounts of retained austenite were prepared (see Tables 1 and 2), and their life was evaluated. That is, in the shot peening of the first step, the type (material, shape) and average particle size of the ceramic particles used were variously changed. In the case of glass ceramic particles, the shape is substantially spherical. In the case of silicon carbide (SiC) ceramic particles, the shape is a shape having corners. In the shot peening in the second step, the average particle diameter of the rubber particles and the average particle diameter of the abrasive dispersed in the rubber constituting the rubber particles were variously changed.

  This deep groove ball bearing is a bearing having a nominal number 6206, and has an inner diameter of 30 mm, an outer diameter of 62 mm, a width of 16 mm, and a ball diameter of 9.525 mm. Further, the amount of retained austenite in Tables 1 and 2 is the amount of retained austenite present in the portion from the surface of the raceway surface of the inner ring and outer ring to a depth of 20 μm. This amount of retained austenite is a measured value by X-ray, and is an average value of five measured values.

When such a test bearing was rotated under the following conditions and flaking occurred on the raceway surface, the number of rotations up to that time was regarded as the life. Then, the L ₁₀ life based on the Weibull distribution function was calculated. The results are shown in Tables 1 and 2. The numerical values of the L ₁₀ life of Tables 1 and 2 is shown as a relative value when the first and second steps of the shot peening of Comparative Example 1 not both subjected L ₁₀ life and 1.

Load: 6223N
Rotational speed: 3000min ^-1
Lubricating oil: Turbine oil whose ISO viscosity grade is ISO VG68 However, the lubricating oil contains 300 ppm of stainless steel powder as a foreign matter. The hardness of the stainless steel powder is HRC52, and the particle size is 74 to 147 μm.

Examples 1 to 10 in which the values of the surface residual stress are given by the shot peening of the first step and the second step are longer than those of Comparative Example 1, and are five times or more that of Comparative Example 1. Had a lifetime of.
Comparative Example 2 had a short life because the surface roughness was too large due to the influence of the shape of the ceramic particles used in the first step. Moreover, in Comparative Example 3, since the compressive residual stress was excessive due to the large average particle size of the ceramic particles used in the first step, minute cracks were generated and the life was shortened. Furthermore, Comparative Example 4 had a short life because the surface roughness was not sufficiently reduced due to the large average particle size of the abrasive used in the second step.

  Furthermore, Comparative Example 5 had a short life because the compressive residual stress was too small. Further, in Comparative Example 6, since the compressive residual stress was excessive, a minute crack was generated due to overpeening and the life was shortened. Furthermore, Comparative Example 7 had a short life because the surface roughness was excessive. Furthermore, since the shot peening of the second step was not performed in Comparative Example 8, the surface roughness was excessive and the life was shortened.

It is a longitudinal cross-sectional view which shows the structure of the deep groove ball bearing which is one Embodiment of the rolling device which concerns on this invention.

Explanation of symbols

1 inner ring 1a raceway surface 2 outer ring 2a raceway surface 3 balls

Claims (2)

An inner member having a raceway surface on the outer surface, an outer member having a raceway surface opposite to the raceway surface of the inner member, and arranged on the outer side of the inner member, and rolling between the both raceway surfaces In a rolling device comprising a plurality of freely arranged rolling elements,
At least one of the raceway surfaces is a rubber having an average particle size of 1.5 mm or less, which is made of rubber containing an abrasive having an average particle size of 3 μm or less after projecting substantially spherical ceramic particles having an average particle size of 200 μm or less. A rolling device characterized in that finishing is performed by projecting particles, surface roughness Ra is 0.01 μm or more and 0.07 μm or less, and surface residual stress is −1400 MPa or more and −900 MPa or less. .   The portion from the surface of the raceway surface to which the finishing process has been performed to a depth of 20 μm contains residual austenite, and the content thereof is 13% by mass or more and 25% by mass or less. The rolling device described in 1.

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